Biomarker for depression, method for measuring a biomarker for depression, computer program, and recording medium

This application is a U.S. national counterpart application of PCT International Application Serial No. PCT/JP2010/063713, filed Aug. 12, 2010, which claims priority to Japanese Patent Application Serial No. 2009-187521 having a filing date of 12 Aug. 2009 and Japanese Patent Application Serial No. 2009-291029 having a filing date of 22 Dec. 2009, all of which are incorporated herein in their entireties by this reference.

The present invention relates to biomarkers for diagnosing depression.

The depression is one type of mood disorders, and its predominant symptoms are the “depressed mood” and “loss of interest or pleasure”, but some patients complain other symptoms such as suppressed appetite, insomnia, fatigue, suicidal ideation etc. Its diagnosis is generally conducted based on the criterion under either ICD-10 (International Classification of Diseases) by WHO (World Health Organization) or “DSM-IV” by American Psychiatric Association.

However, the diagnosis of depression can be hardly objective because it depends on the impression by physician or psychologists, or impression by the patients or individuals complaining the symptom or stress. In fact, cases are often observed where symptoms are excessively reported either intentionally or unintentionally because of the disease gain in which a patient is somehow benefitted from the state of being sick, or otherwise symptoms are concealed for the purpose of avoiding prejudice or trouble from being known to be in depression. In such cases, accurate diagnosis of the disease is difficult, and determination of treatment method may become difficult, or even inappropriate treatment might be applied due to misdiagnosis.

Therefore, several methods have been tested to objectively assist the diagnosis by physician or psychologists. One example is the method in which the noise appearing in the symptom of a patient is excluded as much as possible by processing the results of diagnosis made by a physician or psychologist with a computer (WO2004/080312).

Several markers for depression are known, including macromolecular materials which have been reported in the method to measure the expression level of a gene (JP2008-253258) and the method to detect proteolytic products (JP2009-92550).

On the other hand, smaller compounds in living bodies are also tested as candidates for the depression marker, including those having been reported in the method to measure and analyze the contents of testosterone and cortisol (JP2007-24822) and the method to detect the degraded products of tryptophan in vivo (WO2006/105907), but none of them is brought into practice use so far.

Technical Problem

The present invention is aimed to provide biomarkers for diagnosing depression.

Solution to Problem

The present invention consists of the following Items.

(1) A biomarker for diagnosing depression, wherein the biomarker is selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA (symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine. (2) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine. (3) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of phosphoethanolamine, taurine, aspartic acid, methionine, tyrosine, aminoadipic acid, histidine and isoleucine. (4) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of hypotaurine, phosphorylcholine, arginine, 3-aminobutyric acid, β-alanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, tyramine, valine and ADMA. (5) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of asparagine, phenylalanine, glucaric acid, hydroxyproline and cystathionine. (6) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is cystathionine. (7) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of ADMA, hypotaurine, lysine, histidine, leucine, β-alanine, choline, threonine, glyceric acid, isocitric acid, serine, malic acid, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine, phenylalanine, alanine, 2-aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, betaine, phosphoethanolamine, taurine, ADP-RIBOSE, aspartic acid, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, isoleucine, SDMA, piperidine, pipecolic acid, creatine, nicotinamide, γ-butyrobetaine, uric acid, 3-methyl butyric acid, 3-aminobutyric acid, ornithine, carnitine, ethanolamine and methionine. (8) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of methionine, phosphoethanolamine, taurine, ADP-RIBOSE, aspartic acid, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, isoleucine, SDMA, piperidine, pipecolic acid, creatinine and nicotinamide. (9) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of ADMA, hypotaurine, lysine, histidine, leucine, β-alanine, choline, threonine, glyceric acid, isocitric acid, serine, malic acid, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine, isobutyric acid, γ-butyrobetaine, uric acid, 3-methyl butyric acid, 3-aminobutyric acid, ornithine, carnitine and ethanolamine. (10) The biomarker for diagnosing depression according to Item (1), wherein the biomarker is selected from the group consisting of phenylalanine, alanine, aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, sarcosine and betaine. (11) A method of measurement including the step of measuring a content of one or more compounds selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine in a collected blood sample. (12) The method of measurement according to Item (11), the method including the step of measuring a content of one or more compounds selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine in a collected blood sample. (13) The method of measurement according to Item (11), the method including the steps of:

measuring a content of a first compound selected from the group consisting of hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine in a collected blood sample, and measuring a content of a second compound selected from the group consisting of phosphoethanolamine and taurine in the blood sample.

(14) The method of measurement according to Item (11), the method including the step of measuring a content of aspartic acid and arginine in the blood sample. (15) The method of measurement according to Item (11), the method including the step of measuring a content of aspartic acid and tyrosine in the blood sample. (16) The method of measurement according to Item (11), the method including the step of measuring a content of tyrosine and glucaric acid in the blood sample. (17) The method of measurement according to Item (11), the method including the step of measuring a content of tyrosine and 3-aminobutyric acid in the blood sample. (18) The method of measurement according to Item (11), the method including the step of measuring a content of one or more compounds selected from the group consisting of ADMA, hypotaurine, lysine, histidine, leucine, β-alanine, choline, threonine, glyceric acid, isocitric acid, serine, malic acid, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine, phenylalanine, alanine, 2-aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, betaine, phosphoethanolamine, taurine, ADP-RIBOSE, aspartic acid, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, isoleucine, SDMA, piperidine, pipecolic acid, creatine, nicotinamide, γ-butyrobetaine, uric acid, 3-methyl butyric acid, 3-aminobutyric acid, ornithine, carnitine, ethanolamine and methionine in a collected blood sample. (19) A method for judging an effect of a drug for depression, the method including the steps of:

measuring a content of one or more compounds in blood samples collected from a patient afflicted with the depression before and after an administration of the drug to the patient, and

comparing the content of the compound between the blood samples before and after the administration,

wherein the compound is selected from the group consisting of ADP-RIBOSE, pairs of ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA (symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine.

(20) The method for judging an effect of a drug for depression according to Item (19), the method including the steps of:

measuring a content of one or more compounds in blood samples collected from a patient afflicted with the depression before and after an administration of the drug to the patient, and

comparing the content of the compound between the blood samples before and after the administration,

wherein the compound is selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine.

(21) A method for judging an effect of a drug for a depression, the method including the steps of:

measuring a content of one or more compounds in a blood sample drawn from a patient afflicted with the depression after an administration of the drug to the patient, and

comparing a threshold for a content of the compound in blood to distinguish a patient with depression from a healthy subject with the measured content of the compound,

wherein the compound is selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine.

(22) The method for judging an effect of a drug for a depression according to Item (21), the method including the steps of:

measuring a content of one or more compounds in a blood sample drawn from a patient afflicted with the depression after an administration of the drug to the patient, and

comparing a threshold for a content of the compound in blood to distinguish a patient with depression from a healthy subject with the measured content of the compound,

wherein the compound is selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine.

(23) A method for determining a threshold for a content of one or more compounds in blood to distinguish a patient with depression from a healthy subject, the method including the step of measuring a content of the compound in blood samples collected from plurality of patients diagnosed as being afflicted with depression and plurality of healthy subjects,

wherein the compound is selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine.

(24) The method for determining a threshold of a content of one or more compounds in blood to distinguish a patient with depression from a healthy subject according to Item (23), the method including the step of:

measuring a content of the compound in blood samples collected from plurality of patients diagnosed as being afflicted with depression and plurality of healthy subjects,

wherein the compound is selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine.

(25) A method for screening a model animal for depression, the method including the steps of:

collecting a blood sample from a candidate animal, and

measuring a content of one or more compounds selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine in the blood sample.

(26) A method for screening a therapeutic agent for patient with depression, the method including the steps of:

administering a candidate substance for the therapeutic agent to a model animal afflicted with the depression,

collecting blood samples before and after the administration of the candidate substance,

measuring a content of one or more compounds in the blood samples, and

comparing the content of the compound between the blood samples before and after the administration of the candidate substance,

wherein the compound is selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine.

(27) The method for screening a therapeutic agent for patient with depression according to Item (26), the method including the steps of:

administering a candidate substance for the therapeutic agent to a model animal afflicted with the depression,

collecting blood samples before and after the administration of the candidate substance,

measuring a content of one or more compounds in the blood samples, and

comparing the content of the compound between the blood samples before and after the administration of the candidate substance,

wherein the compound is selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine.

(28) A diagnostic method for diagnosing depression, the method including the step of measuring a content of one or more compounds in the blood sample of a subject to be tested,

wherein the compound is selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine.

(29) The diagnostic method according to Item (28), the method including the step of measuring a content of one or more compounds in the blood sample of the subject,

wherein the compound is selected from the group consisting of phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine.

(30) The diagnostic method according to Item (28), the method including the steps of:

measuring a content of a first compound selected from the group consisting of hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA, isoleucine, hydroxyproline and cystathionine in the blood sample of the subject, and

measuring a content of a second compound selected from the group consisting of phosphoethanolamine and taurine in the blood sample of the subject.

(31) The diagnostic method according to Item (28), the method including the step of measuring a content of aspartic acid and arginine in the blood sample of the subject. (32) The diagnostic method according to Item (28), the method including the step of measuring a content of aspartic acid and tyrosine in the blood sample of the subject. (33) The diagnostic method according to Item (28), the method including the step of measuring a content of tyrosine and glucaric acid in the blood sample of the subject. (34) The diagnostic method according to Item (28), the method including the step of measuring a content of tyrosine and 3-aminobutyric acid in the blood sample of the subject. (35) A diagnostic method for diagnosing severity of depression, the method including the step of measuring a content of cystathionine in blood sample of a patient. (36) The diagnostic method for diagnosing depression according to Item (28), the method including the step of measuring a content of one or more compounds in the blood sample of the subject to be tested,

wherein the compound is selected from the group consisting of ADMA (asymmetric dimethylarginine), hypotaurine, lysine, histidine, leucine, β-alanine, choline, threonine, glyceric acid, isocitric acid, serine, malic acid, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine, phenylalanine, alanine, aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, betaine, phosphoethanolamine, taurine, ADP-RIBOSE, aspartic acid, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, isoleucine, SDMA (symmetric dimethylarginine), piperidine, pipecolic acid, creatine and nicotinamide.

(37) The diagnostic method for diagnosing depression according to Item (28), the method including the step of measuring a content of one or more compounds in the blood sample of the subject,

wherein the compound is selected from the group consisting of phosphoethanolamine, taurine, ADP-RIBOSE, aspartic acid, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, isoleucine, SDMA, piperidine, pipecolic acid, creatinine and nicotinamide.

(38) The diagnostic method for diagnosing depression according to Item (28), the method including the step of measuring a content of one or more compounds in the blood sample of the subject,

wherein the compound is selected from the group consisting of ADMA, hypotaurine, lysine, histidine, leucine, β-alanine, choline, threonine, glyceric acid, isocitric acid, serine, malic acid, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine and isobutyric acid.

(39) The diagnostic method for diagnosing depression according to Item (28), the method including the step of measuring a content of one or more compounds in the blood sample of the subject,

wherein the compound is selected from the group consisting of phenylalanine, alanine, aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, sarcosine and betaine.

(40) A program to cause a computer to execute the steps of:

obtaining a content of a biomarker in a blood sample collected from a subject to be tested,

making a judgement based on the content as to whether the subject is either one or more of a healthy subject, not a healthy subject, a patient with depression and/or not a patient with depression, and

outputting the result of the judgement,

wherein the biomarker is selected from the group consisting of ADP-RIBOSE, ATP, ADP, AMP, serotonin, tryptophan, kynurenine, SDMA(symmetric dimethylarginine), threonine, glyceric acid, serine, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, 2-methyl serine, sphingosine, homovanillic acid, piperidine, sulfoxidated methionine, pipecolic acid, sphinganine, γ-butyrobetaine, guanidoacetic acid, isobutyric acid, creatinine, sarcosine, 3-methyl butyric acid, nicotinamide, betaine, ornithine, carnitine, ethanolamine, phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline and cystathionine.

(41) The program according to Item (40), further including the step of causing an apparatus for measuring biomarker to measure the content of the biomarker in the blood sample. (42) A recording medium readable by a computer, the medium storing the program according to Item (40) or (41). (43) The method according to any one of Items (19) to (22), wherein the depression is atypical depression. (44) The method according to Item (23) or (24), wherein the plurality of patients diagnosed as being afflicted with depression include a patient diagnosed as being afflicted with atypical depression. (45) The method according to Item (26) or (27), wherein the patient with depression is a patient afflicted with atypical depression.

Hereinafter the embodiments of the present invention accomplished based on the abovementioned findings are described in detail with reference to Examples. Note that the objective, characteristics, and advantages of the present invention as well as the idea thereof will be apparent to those skilled in the art from the descriptions given herein, and the present invention can be easily worked by a person skilled in the art based on these descriptions. It is to be understood that the embodiments and specific examples of the invention described hereinbelow are to be taken as preferred examples of the present invention. These embodiments and examples are presented only for illustrative or explanatory purposes, and are not intended to restrict the present invention thereto. It is apparent to those skilled in the art that various changes and modifications may be made based on the descriptions given herein within the intent and scope of the present invention disclosed herein.

==Depression to be Diagnosed Using Biomarker==

As used herein, the “biomarkers for diagnosing depression” (hereinafter the term “biomarker for diagnosing” is also referred to as “diagnostic marker”) include the biomarkers that can identify patients with depression with high probability (disease markers), as well as the biomarkers that can exclude healthy subjects from the patients with depression with high probability (health markers).

==Method for Measuring Content of Diagnostic Marker==

The diagnostic marker according to the present invention may be phosphoethanolamine, taurine, hypotaurine, aspartic acid, methionine, tyrosine, phosphorylcholine, arginine, asparagine, 3-aminobutyric acid, β-alanine, phenylalanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, aminoadipic acid, tyramine, valine, glucaric acid, histidine, ADMA (asymmetric dimethylarginine), isoleucine, hydroxyproline or cystathionine. Whether or not a patient is afflicted with depression may be diagnosed by measuring a content of the diagnostic marker in a blood sample collected from the patient.

When the content of the diagnostic marker in the collected blood sample is to be measured, the blood sample may be preferably pretreated prior to the measurement. For example, a serum or plasma can be separated from the blood by incubation or centrifugation, and the separated serum or plasma may be preferably subjected to the measurement.

The content of a compound as the diagnostic marker in the collected blood sample may be measured by any known method. Examples of such method include, but not limited to, analysis of the mass of a target compound following isolation, such as high-performance liquid chromatography-mass spectrometer (LC-MS) and gas chromatography-mass spectrometer (GC-MS). When high-performance liquid chromatography is to be employed, any of those columns (ex. ion-exchange columns) capable of simultaneously analyzing multiple ionic metabolites may be preferably used.

Other methods for measuring the target compound include, but not limited to, those of measurement employing NMR analysis, those of measurement employing acid-base neutralization titration, those of measurement employing amino acid analyzer, those of measurement with enzymes, those of measurement using nucleic acid aptamars/peptide aptamers, those of measurement employing colorimetry, those of measurement only with high-performance liquid chromatography, those of measurement only with gas chromatography, and those of measurement only with mass spectrometer. When the high-performance liquid chromatography is to be employed, any of those columns (ex. ion-exchange columns) capable of simultaneously analyzing multiple ionic metabolites may be preferably used.

Use of capillary electrophoresis-time-of-flight mass spectrometer (CE-TOFMS) for the measurement is preferable in that it is capable of simultaneously analyzing the in-blood contents of all of the multiple compounds as the diagnostic markers. When CE-TOFMS is to be employed for the measurement, the pretreated serum or plasma may be further pretreated, preferably as follows.

The serum or plasma is mixed with an alcoholic solvent to terminate enzymatic reactions remaining in the serum or plasma. A preferable alcoholic solvent is methanol. The terminated serum or plasma is mixed with an organic solvent and water, and the mixture is subjected to phase separation and the organic phase containing liposoluble materials such as phospholipids etc. is removed. The organic solvent to be used may be of any type that can be separated from water by phase separation, and preferable examples are dichloromethane, chloroform, dichloroethane etc., and chloroform is particularly preferable. It is preferable that proteins are removed from the aqueous phase thus obtained. The method to remove proteins may be preferably ultrafiltration but not limited thereto. After removal of proteins, the alcoholic solvent remaining in the aqueous phase is preferably removed by distillation. The distillation methods for removal of the solvent include, but not limited to, natural drying, vacuum drying and centrifugal vacuum drying, but the centrifugal vacuum drying is preferable in that it can be conducted quickly and conveniently. Thus an aqueous solution can be prepared from the collected blood sample by removing insoluble materials, and this aqueous solution from which insoluble materials are removed may be preferably subjected to a measurement using CE-TOFMS.

The samples to be subjected to measurement with CE-TOFMS may also include an internal standard to provide criteria for measurements of electrophoresis time, content, etc. of compounds as the diagnostic marker. The internal standard can be any compound that does not interfere with the efficiency of electrophoresis or mass spectroscopy, and preferable examples include methionine sulfone and 10-camphor sulfonate (10-camphorsulfonic acid, CSA).

The capillary to be used in the capillary electrophoresis is preferably made of fused-silica. The internal diameter of the capillary is preferably no more than 100 μm to ensure better separation, and is most preferably 50 μm. The length of the capillary is preferably in the range of 50 cm to 150 cm.

Fractions containing the compound as the target diagnostic marker among those obtained by the capillary electrophoresis may be identified by any method, and examples include a method in which the electrophoretic migration time of the target compound is measured using a sample of the compound in advance, as well as a method in which relative values of the migration time are compared with that of an internal standard.

As the content of the compound as the target diagnostic marker, the peak area at the m/z of the target compound in the fraction identified to contain the compound is then measured. Each peak area can be normalized by comparing it with the peak area of the internal standard. The absolute concentration of the compound as the diagnostic marker in the collected blood sample can be calculated from the measured peak area by making a calibration curve using a sample of the target compound. The calibration curve is made preferably by the standard addition method rather than the standard solution method.

==Use of Diagnostic Marker==

The diagnostic marker can be used in various embodiments of the present invention, including those illustrated below.

<Method for Diagnosing Depression>

First, a blood sample is collected from a human or non-human vertebrate. The collected blood sample may be used for diagnosing a disease by measuring the content of a diagnostic marker in the blood (hereinafter also referred to as a marker level). The in-blood content of a biomarker is preferably the absolute concentration of the biomarker, but may be any value that is correlated with the absolute concentration of the biomarker and can be used for comparison of the absolute concentrations among individuals, and examples include the relative concentration, the weight per unit volume, and the raw data from the measurement of absolute concentrations (for example, the value obtained by normalizing the peak area in a graph from CE-TOFMS measurement).

Prior to the diagnosis, measured are the ranges of the in-blood biomarker levels of individuals in a vertebrate species having been diagnosed as being afflicted with depression (hereinafter referred to as diseased individuals) and individuals in a vertebrate species having been diagnosed as not having depression (hereinafter referred to as healthy individuals). If a biomarker level in a blood sample of a subject vertebrate falls within the range of the in-blood biomarker level for the healthy vertebrate, then the probability that this vertebrate has not been afflicted with the disease is high, whereas if it falls within the range of the in-blood biomarker level for the diseased vertebrate, then the probability that the animal has been afflicted with disease is high. The diseased vertebrate may have had atypical depression. The diseased vertebrate as well as the subject vertebrate may also be complicated with another disease such as anxiety disorder, borderline personality disorder or panic disorder.

The range of in-blood biomarker level of the healthy vertebrate may be obtained by measuring in advance the range of in-blood biomarker levels of a subject of a vertebrate species at a time when the same vertebrate was healthy, and this range of biomarker level in the healthy state can be used when making diagnosis using the marker level at that time of the diagnosis.

The range of the in-blood biomarker level of the healthy vertebrate may be any range of values appropriate for diagnosing a disease by using a diagnostic marker, and it may be a range between an average plus a standard deviation and the average minus the standard deviation, or a range from the lower limit to the upper limit of the average, in which the average can be obtained from multiple measurements on each animal. The most preferable value or range for each diagnostic marker may be chosen for the diagnosis.

Alternatively, a threshold for the in-blood biomarker level may be determined to distinguish diseased individuals of a vertebrate species from healthy individuals of the vertebrate species. For example, in-blood biomarker levels of plurality of diseased individuals and plurality of healthy individuals may be measured to determine the threshold in advance. The threshold may be determined by any method known to those skilled in the art. For example, a threshold can be determined so that diseased individuals are included below the threshold (or above the threshold) at a first predetermined ratio and healthy individuals are included above the threshold (or below the threshold) at a second predetermined ratio. In an exemplary method, a statistical software such as JMP from SAS Inc. can be used to obtain a threshold value with which chi-square test yields the best result. A diagnostic marker is preferably provided with high values of both the first predetermined ratio and the second predetermined ratio; for example, the value may be no less than 70%, more preferably no less than 80%, even more preferably no less than 90%, and most preferably 100%. When both values are set high, specificity as well as sensitivity can be high. If it is impossible to set both of the first and second predetermined ratios high, the threshold may be determined so that either one of the specificity and the sensitivity becomes high. The values of both the specificity and sensitivity are high; for example, the value may be no less than 70%, more preferably no less than 80%, even more preferably no less than 90%, and most preferably 100%. As used herein, the specificity refers to a percentage value of (the number of healthy individuals above or below the threshold)/(the total number of healthy individuals), and the sensitivity refers to a percentage value of (the number of diseased individuals below or above the threshold)/(the total number of diseased individuals). Biomarkers having a high specificity can be suitably used as the biomarker for identifying a patient with depression (hereinafter referred to as a disease marker) because the probability of a patient being afflicted with depression is high if the level of such a biomarker of the patient is below (or above) the threshold. Biomarker having high sensitivity can be suitably used as the biomarker for excluding a healthy subject from patients with depression (hereinafter referred to as a health marker) because probability of a patient not being afflicted with depression is high if the level of such a biomarker is above (or below) the threshold.

The diagnostic markers according to the present invention may be used as a disease marker as well as a health marker. Among them, phosphoethanolamine, taurine, aspartic acid, methionine, tyrosine, aminoadipic acid, histidine, isoleucine, ADP-RIBOSE, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, SDMA (symmetric dimethylarginine), piperidine, pipecolic acid, creatinine, and nicotinamide are effective as both of the disease marker and the health marker, and their plasma concentration in a subject vertebrate may be measured to make a diagnosis that the probability of the subject being either afflicted with depression or healthy is high if the concentration falls in such a certain range as illustrated in Table 1 for human subjects. Among the biomarkers, asparagine, phenylalanine, glucaric acid, hydroxyproline, cystathionine, alanine, aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, sarcosine and betaine are suitably used as the disease markers, and their plasma concentration in a subject vertebrate may be measured to make a diagnosis that the probability of the subject being afflicted with depression is high if the concentration falls in such a certain range as illustrated in Table 1 for human subjects. Further, hypotaurine, phosphorylcholine, arginine, 3-aminobutyric acid, β-alanine, lysine, phosphocreatine, alanine, uric acid, choline, isocitric acid, leucine, malic acid, tyramine, valine, ADMA (asymmetric dimethylarginine), threonine, glyceric acid, serine, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine, isobutyric acid are suitably used as the health markers, and their plasma concentration in a subject vertebrate may be measured to make a diagnosis that the probability of the subject being healthy is high if the concentration falls in such a certain range as illustrated for human subjects in either Table 1 derived from Example 1 or Table 2 derived from Example 2. When phosphoethanolamine or taurine is to be used as the biomarker, the threshold may be preferably set to 2.41 or 50.54 (μM) respectively. The thresholds described herein are merely examples calculated from a particular population by a particular method, and they are likely to vary for different population.

These biomarkers may be used in combination to improve accuracy of diagnosis, and they may be combined in any combination. For example, when two kinds of disease markers are used, if only one of them is at a concentration indicating the probability of depression, then the subject may still be diagnosed as being afflicted with depression at a certain probability, but if both of the markers are at concentrations indicating the probability of depression, then the probability of depression would be higher than that in the case of the one marker. In a preferred embodiment, a health marker is used in combination with a disease marker. For example, a subject of an animal individual is diagnosed using a health marker, and if the health marker is at a concentration indicating a state of “not being healthy”, then the subject is further diagnosed by using a disease marker. If the disease marker is at a concentration indicating a state of “being afflicted”, then the probability of being afflicted with depression is judged to be high, whereas if the disease marker is not at a concentration indicating the state of “being afflicted”, then the probability of being healthy is judged to be high. In this way, the accuracy of diagnosis can be made higher than the case where only disease marker is used. When the health marker is at a concentration indicating a state of “being healthy”, the subject may be diagnosed as being probably healthy, but when another diagnosis is made using a disease marker and if it is at a concentration indicating a state of “not being afflicted”, then the probability of being healthy would be even higher. If the disease marker is at a concentration indicating a state of “being afflicted”, then further diagnosis may be made, for example, by analyzing the distance of the concentration of the biomarkers from their respective thresholds, or judgement by using a third biomarker.

When identifying subjects with depression using plurality of biomarkers, the health marker may be used as a first biomarker with its threshold set at a higher level in order to increase the sensitivity, and subjects with high probability of being healthy may be excluded first. The threshold may be set at any high level, for example at about 90%, preferably at about 92%, and even more preferably at about 94%. According to this method, if the health marker at the first stage is proved to be at a concentration indicating a state of being “healthy”, then the subject may be diagnosed as being healthy with high probability. When the health marker is not at the concentration indicating the state of being “healthy”, the diagnostic marker may be used in the next step, and if the marker is at a concentration indicating the state of “being afflicted”, then the probability of being afflicted with depression is judged to be high, whereas if the marker is not at the concentration indicating the state of “being afflicted”, then the probability of being healthy is judged to be high. In this way, the accuracy of the judgement can be improved.

The diagnosis using these diagnostic markers may be combined with another conventional diagnostic method, such as an examination by interview or questionnaire.

The use of the diagnostic markers as described herein not only enables diagnosis with more easiness and higher accuracy at psychiatry, but also provides means for screening at the scenes such as health checkup where precise diagnosis cannot be conducted, clinical departments such as internal medicine and surgery other than psychiatry, and emergency conditions where verbal communication with a patient is not possible. In this way, it becomes possible to bring potential patients with depression who have been left off the psychiatric examination to the psychiatry department that should be the first place where they are to be treated.

By setting the threshold for the sensitivity of a marker at a very high level, the marker can be effectively used as a health marker. The threshold can be set at any high level, for example at about 90%, preferably at about 92%, and even more preferably at about 94%. At the scene of the health checkup where precise diagnosis cannot be conducted, a diagnosis using such a threshold may be employed as a first diagnosis. In this method, a subject who falls in the range which includes only small number of patients with depression but large number of healthy subjects is diagnosed as being healthy, whereas a patient who falls in the range which includes large number of patients with depression is diagnosed as being afflicted with depression at high probability, and then referred to a psychiatry department for specialized diagnosis. In this way, the ratio of patients with depression in the first diagnosis can be increased, thereby reducing the burden of second diagnosis at the psychiatry department.

The depression to be diagnosed herein may be of any type that can be diagnosed by a conventional diagnostic method, and preferable examples are depressions that can be judged according to SCID Interview method. Patients having adjustment disorder are preferably excluded in advance by a conventional diagnostic method such as an examination by interview or questionnaire. Patients having anxiety disorder, personality disorders such as borderline personality disorder and depressive personality disorder or dysthymic disorders can be diagnosed, in which case the use of ADMA, hypotaurine, lysine, histidine, leucine, β-alanine, choline, threonine, glyceric acid, isocitric acid, serine, malic acid, 2-methyl serine, sphingosine, homovanillic acid, sulfoxidated methionine, sphinganine, phenylalanine, alanine, aminoadipic acid, N-acetylaspartic acid, glutamic acid, trigonelline, creatine, guanidoacetic acid, sarcosine, betaine, phosphoethanolamine, taurine, ADP-RIBOSE, aspartic acid, tyrosine, ATP, ADP, asparagine, AMP, serotonin, valine, tryptophan, kynurenine, phosphorylcholine, isoleucine, SDMA, piperidine, pipecolic acid, isobutyric acid, creatinine, nicotinamide and the like are preferable, and the threshold for them are preferably taken from those shown in Table 2, or thresholds obtained by the same method as used for Table 2. Patients not having anxiety disorder, personality disorder such as borderline personality disorder and depressive personality disorder, nor dysthymic disorder can be diagnosed by any of the markers according to the present invention, and the thresholds to be used for them can be taken from both of Table 1 and Table 2, but the thresholds shown in Table 1 or thresholds obtained by the same method as used for Table 1 is more preferable.

<Method for Judging Severity of Depression>

The plasma concentration of cystathionine is inversely proportional to the scale by CESD as well as to the number of diagnostic match with SCID, and therefore cystathionine is useful as a biomarker for judging the severity of depression in a patient with depression.

First, whether or not a subject animal is in depression is judged by using either any of the biomarkers according to the present invention or any conventional diagnostic method such as the examination by interview or questionnaire. Then the plasma concentration of the patient with depression is examined, and if it is, for example, less than 18.36 μM, then a diagnosis of mild depression may be made, whereas if 18.36 μM or more, then diagnosis of severe depression may be made.

<Judgment of Drug Efficacy>

The effect of a therapeutic agent for certain disease often varies for different individuals. Therefore, knowing the efficacy of the therapeutic agent for a certain individual is quite beneficial, and it can be easily achieved by using the diagnostic marker according to the present invention. For example, blood samples are collected from a diseased vertebrate before and after administering a therapeutic agent for depression, and the content of a diagnostic marker in the collected blood samples is measured to make comparison of the content of the diagnostic marker between the blood samples before and after the administration of the therapeutic agent. A judgment for the therapeutic agent as being effective can be made if the content of the diagnostic marker comes closer to the range indicating the state as being healthy after the administration of the therapeutic agent. In this way, the diagnostic marker according to the present invention can be used to easily judge whether a therapeutic agent is effective.

<Method for Screening Model Animal for Depression>

By using the diagnostic marker according to the present invention, model animals with depression can be screened easily. For example, whether a candidate animal (excluding human) is indeed a model animal for depression may be judged by a diagnosis of the candidate animal, in which the content of the diagnostic marker in the blood of the animal is measured and compared with the content of the diagnostic marker in blood of a healthy animal of the same species.

<Method for Screening Drug with Effectiveness for Depression>

By using experimental animal of depression, a compound that has effectiveness for treatment of depression can be identified. For example, a compound as a candidate of a therapeutic agent for depression is administered to a model animal (excluding human) of depression, from which blood samples are collected before and after the administration, and the content of a diagnostic marker in the blood samples is measured to make comparison of the content of the diagnostic marker between the blood samples before and after the administration of the compound. A judgment for the administered compound as being effective for treatment of depression can be made if the content of the diagnostic marker comes closer to the range indicating the state as being healthy after the administration of the compound. In this way, the diagnostic marker according to the present invention can be used to easily screen compounds having effectiveness for treatment of a disease.

<Method for Screening Drug Most Effective for Diseased Animal>

In the case where drugs have different efficacy depending on different individuals, a drug that is most effective for a certain individual with depression can be screened by administering plurality of drugs to the individual and then conducting diagnosis using the diagnostic marker.

==Computer for Utilizing Biomarker==

After the content of a compound as the diagnostic marker in a blood sample collected from an individual of a vertebrate species is measured as described above, the result of the measurement may be transmitted to a computer, and the computer may utilize the results according to any of the methods described herein.

For example, a medical practitioner collects a blood sample from an individual of a vertebrate species and appropriately treats it, then loads the blood sample on an apparatus for measuring the biomarker. The computer causes an apparatus for measuring the biomarker to measure the content of the biomarker in the sample, and obtains the result of the measurement. Based on the plasma content of the marker thus obtained, the computer may then make a judgement as to whether the tested subject is either one or more selected from a group consisting of a healthy subject, not a healthy subject, a patient with depression and not a patient with depression. The computer may also make judgements regarding the severity of a depression, the efficacy of an antidepressant, and the like, similarly to the method described above. The computer may output the result of the judgements thus made, thereby enabling the medical practitioner to obtain information about the tested subject.

It should be noted that the program according to the present invention causes a computer to execute a method to utilize the plasma content of the marker thus obtained. It may also cause a computer to execute the step of causing the biomarker-measuring apparatus to measure the content of the biomarker in the sample.

The program may be recorded on a recording medium which is readable by a computer, and the recording medium may be any of a hard disk, CD, CD, DVD, USB memory, a floppy disk, and the like.

Embodiments of the present invention are hereinafter described by referring to examples, but the scope of the present invention is not to be limited to the examples described hereinbelow. In this example, it is demonstrated that patients with depression can be indeed distinguished from healthy subjects by using the marker according to the present invention on the patients who have been preliminary diagnosed as being depressed.