Circulating amino acids, amino acid metabolites, dipeptides, and other cationic metabolites and risk of breast cancer

Background: Breast cancer is the most common malignancy among women in the United States, with more than 250,000 cases diagnosed each year. Metabolomics, which reflect the aggregate effects of genetics and the environment on an individual's metabolic state, can shed light on biochemical pathways involved in susceptibility to breast cancer. We investigated associations between pre-diagnostic circulating amino acids-related metabolites and subsequent risk of breast cancer among predominantly premenopausal women. Methods: In 1996-1999, 29,611 women (average age, 44 years) in the Nurses' Health Study II donated blood samples. Between blood collection and June 2011, 1057 women were diagnosed with breast cancer (average of 8 years after blood collection). Women were predominately premenopausal at the time of blood collection. 207 amino acid and amino acid-related metabolites were profiled with LC-MS/MS. Conditional logistic regression (CLR) was used to estimate odds ratios (ORs) of breast cancer and 95% confidence intervals (CIs). Multivariable analyses evaluating the joint association of all metabolites with breast cancer risk were based on CLR with a lasso penalty (Lasso), CLR with an elastic net penalty (Elastic Net), and Random Forests. We used FDR to account for testing multiple hypotheses. Results: Eleven metabolites were associated with breast cancer risk in CLR models, after adjustment for multiple comparisons (p value < 0.05 and q value < 0.20; creatine had q value > 0.20), 6 of which remained significant after adjustment for breast cancer risk factors (p-value<0.05). Higher levels of six metabolites, including 2-aminohippuric acid, DMGV, kynurenic acid, N2, N2-dimethylguanosine, phenylacetyl glutamine and piperine, were associated with lower breast cancer risk (e.g., piperine: ORsimple (95%CI) = 0.85 (0.78-0.93); ORadjusted (95%CI)=0.84 (0.77-0.92)). Higher levels of asparagine, creatine and 3 lipids (C20:1 LPC, C34:3 PC plasmalogen, C40:7 PE plasmalogen) were associated with increased breast cancer risk (e.g., C40:7 PE plasmalogen ORsimple (95%CI) = 1.14 (1.05-1.25); ORadjusted (95%CI) = 1.11 (1.01-1.22)). Piperine, 2-aminohippuric acid, C40:7 PE plasmalogen and creatine were also selected in multivariable modeling approaches (Lasso, Elastic Net, and Random Forests). Conclusions: Two diet-related metabolites, piperine (responsible for the pungency of pepper) and 2-aminohippuric acid (the glycine conjugate of the tryptophan metabolite anthranilic acid) were inversely associated, while C40:7 PE plasmalogen (a highly unsaturated glycerophospholipid and key component of the lipid bilayer of cells) was positively associated with breast cancer risk among predominately premenopausal women, independent of established breast cancer risk factors. Further validation of the specific metabolite associations with breast cancer risk in independent cohorts is warranted.