Basic Study
Copyright ©The Author(s) 2023. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Jun 7, 2023; 29(21): 3269-3279
Published online Jun 7, 2023. doi: 10.3748/wjg.v29.i21.3269
Effects of ethanol and sex on propionate metabolism evaluated via a faster 13C-propionate breath test in rats
Yosuke Sasaki, Naoyuki Kawagoe, Tsunehiko Imai, Yoshihisa Urita
Yosuke Sasaki, Naoyuki Kawagoe, Tsunehiko Imai, Yoshihisa Urita, Department of General Medicine and Emergency Care, Toho University School of Medicine, Tokyo 143-8541, Japan
Author contributions: Sasaki Y and Urita Y coordinated the study; Sasaki Y, Kawagoe N, Imai T, and Urita Y performed the experiments; Sasaki Y and Urita Y acquired and analyzed the data; Sasaki Y and Urita Y interpreted the data; and Sasaki Y and Urita Y wrote the manuscript; All authors approved the final version of the article.
Supported by the Japan Society for the Promotion of Science KAKENHI Grant, No. JP21K18089.
Institutional review board statement: The study was reviewed and approved by the Toho University School of Medicine Institutional Review Board, No. 21-51-496.
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
Data sharing statement: Technical appendix, statistical code, and dataset available from the corresponding author at
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Corresponding author: Yosuke Sasaki, MD, PhD, Assistant Professor, Lecturer, Department of General Medicine and Emergency Care, Toho University School of Medicine, 6-11-1 Omori-Nishi, Ota-Ku, Tokyo 143-8541, Japan.
Received: February 2, 2023
Peer-review started: February 2, 2023
First decision: March 8, 2023
Revised: March 13, 2023
Accepted: May 6, 2023
Article in press: May 6, 2023
Published online: June 7, 2023
Research background

The 13C-propionate breath test (PBT) has been studied as a non-invasive diagnostic modality for vitamin B12 (VB12) deficiency by utilizing the role of VB12 as a coenzyme of methylmalonyl-CoA mutase in propionate metabolism. Although alcoholism has been regarded as a risk factor for deficiency, studies on propionate metabolism using the PBT in individuals with alcoholism is limited. Furthermore, conventional PBT requires up to 2 hours of breath collection time, which may undermine its clinical utility.

Research motivation

The scarcity of studies regarding the PBT in alcoholism, and the possibility of improving the clinical utility of the PBT by shortening the breath collection time, motivated us to perform this study.

Research objectives

The aim of this study was to evaluate the change in propionate metabolism due to long-term ethanol consumption in ethanol-fed rats (ERs) as an animal model of chronic alcoholism. We also aimed to evaluate the utility of a faster PBT that requires only 1 hour to collect breath.

Research methods

The ERs were 18th generation descendants of F344/DuCrj rats that had been bred by replacing standard drinking water with a 16% ethanol solution. A faster PBT was performed by injecting the 13C-propionate aqueous solution from the mouth to the stomach of ERs and control rats (CRs); we collected exhaled gas in bags, and measured the 13CO2/12CO2 isotope ratio using infrared isotope spectrometry. We measured serum VB12 and alanine transaminase (ALT) levels via chemiluminescence immunoassay and the lactate dehydrogenase-ultraviolet method, respectively. We evaluated statistical differences in mean body weight, change in 13CO213CO2‰), peak Δ13CO2‰, and serum VB12 and ALT, between ERs and CRs, and males and females, respectively.

Research results

Besides male dominance of body weight (P < 0.001), CRs weighed significantly more than ERs (P < 0.008). The Δ13CO2 reached a peak (Cmax) within 30 min in both sex groups, while males had a significantly higher Cmax and Δ13CO2 at 15-45 min than females (P < 0.05; for all pairs). Enhanced propionate metabolism was observed in male ERs relative to male CRs, and although males had higher serum VB12 levels than females, no prominent differences were observed between the ER and CR groups. Male CRs had notably higher ALT levels than male ERs. These results suggest that chronic ethanol consumption may trigger fatty acid production via intestinal bacteria and changes in gut microbiome composition.

Research conclusions

We believe that a faster (1-h) PBT could serve as a substitute for the conventional PBT, as the Δ13CO2 reached a peak (Cmax) within 30 min in both sex groups. We failed to evaluate the usefulness of the faster PBT as a diagnostic modality for VB12 deficiency in the chronic alcoholism rat model; however, our study suggests that instead of inducing alcoholism, chronic consumption of 16% ethanol changed the composition of fatty acids produced by the intestinal flora.

Research perspectives

Our study demonstrates the potential utility of the faster PBT as a non-invasive and more convenient modality to evaluate changes in the gut flora associated with ethanol consumption and various other conditions via changes in propionate metabolism.