Effects of ethanol and sex on propionate metabolism evaluated via a faster (13)C-propionate breath test in rats

BACKGROUND: Alcoholism is regarded as a risk factor for vitamin B(12) (VB(12)) deficiency. Because VB(12) serves as a coenzyme of methylmalonyl-CoA mutase, a key enzyme in propionate metabolism, the (13)C-propionate breath test (PBT) has been studied as a non-invasive diagnostic modality for VB(12) deficiency. However, the conventional PBT requires 2 h, which is inconvenient in clinical practice. We hypothesized that a faster PBT can be used to evaluate propionate metabolism and is more easily adaptable for clinical practice. AIM: To evaluate a faster PBT for assessing the effects of long-term ethanol consumption on propionate metabolism in ethanol-fed rats (ERs). METHODS: ERs were obtained by replacing standard drinking water (for control rats, CRs) with 16% ethanol solution in descendants of F344/DuCrj rats. Faster PBT was performed by administering (13)C-propionate aqueous solution to male and female ERs and CRs by inserting a metal tubule from the mouth to the stomach; exhaled gas was collected in a bag to measure its (13)CO(2)/(12)CO(2) isotope ratio via infrared isotope spectrometry. Serum VB(12) and alanine transaminase (ALT) levels were measured via chemiluminescence immunoassay and the lactate dehydrogenase-ultraviolet method, respectively. We evaluated statistical differences in mean body weight, change in (13)CO(2) (Δ(13)CO(2)‰), peak Δ(13)CO(2)‰, and serum VB(12) and ALT, between males and females and between ERs and CRs using the t-test and Mann-Whitney U test for normally and non-normally distributed variables, respectively. RESULTS: Males weighed significantly more than females (P < 0.001); CRs weighed significantly more than ERs (P < 0.008). Δ(13)CO(2) reached a peak (C(max)) at 20 min and 30 min in females and males, respectively, decreasing after 20-30 min without rebound in all groups. Males had significantly higher C(max) and Δ(13)CO(2) at 15-45 min than females (P < 0.05; for all pairs). Propionate metabolism was enhanced in male ERs relative to male CRs, whereas metabolism did not differ markedly between ERs and CRs for females. Males had higher serum VB(12) levels than females, without prominent differences between the ER and CR groups. Male CRs had notably higher ALT levels than male ERs. Thus, chronic ethanol consumption may trigger fatty acid production via intestinal bacteria and changes in gut microbiome composition. CONCLUSION: Faster PBT shows that 16% ethanol consumption promotes propionate metabolism without inducing liver injury. This PBT may be used clinically to evaluate gut flora status.