Epidemiology of metabolite profile and prostate cancer risk
Keywords: Hexose
Sphingolipids
Amino acids
Prospective
European Prospective Investigation into Cancer and Nutrition
Glycerophospholipids
Cross-sectional
Acylcarnitines
Biogenic amines

Insulin-like growth factor-I (IGF-I) is the only known potentially modifiable risk factor for prostate cancer. Intake of dietary protein, especially from dairy products, might also be associated with risk and with circulating IGF-I, but it is not clear if amino acids play a role in these relationships. Moreover, investigations of circulating concentrations of metabolites might reveal novel risk factors for prostate cancer. This thesis investigates plasma concentrations of amino acids and other metabolites in relation to protein intake, IGF-I, and prostate cancer risk using data from the European Prospective Investigation into Cancer and Nutrition (EPIC).
To characterise plasma metabolite profile in men consuming markedly different amounts and types of animal products (meat-eaters, fish-eaters, vegetarians and vegans), cross-sectional analyses of 392 men in the EPIC-Oxford sub-cohort were conducted. Of 21 amino acids, six varied significantly by diet group, and the metabolite profile of vegans was different from those of other diet groups owing to lower concentrations of several glycerophospholipids and sphingolipids.
In a case-control study nested within EPIC, with a mean follow-up time of seven years, the relationship of plasma metabolites with risk of prostate cancer overall, by time to diagnosis, by tumour characteristics, and with risk of prostate cancer death, was investigated. Data from 1,077 matched sets suggested that seven metabolites, from various classes, were associated with risk of prostate cancer overall (p < 0.05). After correction for multiple testing, 12 glycerophospholipids were inversely associated with risk of advanced prostate cancer (the strongest OR1SD = 0.54; 95%CI: 0.40-0.72). In multivariate analyses, including data from 1,593 matched sets, principal component analysis (PCA) and treelet transform (TT) were used to identify patterns in metabolite profile, five of which were associated with risk of more aggressive tumour sub-types (high grade, advanced and aggressive disease) and/or prostate cancer death. There was a ≈ 50% lower risk of advanced and high grade prostate cancer in men with metabolite profiles characterised by high glycerophospholipids and sphingolipids (for advanced ORTT, top vs bottom third = 0:48; 95%CI: 0:31-0:74), with similar results for high grade and PCA).
To investigate if associations between protein intake and circulating IGF-I may be mediated by plasma amino acid concentrations, cross-sectional analyses of amino acid concentrations with protein intake and IGF-I concentrations were carried out in 1,697 and 1,142 control participants, respectively, from the nested case-control study. Dairy protein intake was positively associated with concentrations of branched-chain amino acids and several other essential amino acids, while plant protein intake was strongly associated only with histidine. Serum IGF-I was positively associated with arginine and inversely with ornithine and certain amino acid ratios.
In conclusion, men with different dietary habits with respect to the consumption of protein types have different amino acid and metabolite profiles, and metabolite concentrations may be associated with risk of more high-risk prostate cancer sub-types (high grade, advanced and aggressive disease) and prostate cancer death. Further large-scale studies are needed to determine if metabolites play a role in aetiology or are markers of sub-clinical prostate cancer.