Diabetes is Associated with Increased Passage of Bacterial Metabolite TMA, a TMAO Precursor, Through the Intestinal Barrier
Authors: Jaworska Kinga , Gawryś-Kopczyńska Marta , Zaorska Ewelina , Hutsch Tomasz , Ufnal Marcin 
Published: April 2020

Trimethylamine N‐oxide (TMAO) is suggested to be a marker of cardiovascular outcome in diabetic patients. However, mechanism of the TMAO increase remains unclear. TMAO is a product of liver oxidation of trimethylamine (TMA), a metabolite of gut bacteria. Diabetes is associated with gut barrier disruption, which may result in increased passage of bacterial metabolites to the bloodstream. We hypothesized that higher gut barrier permeability to TMA is responsible for TMAO elevation in diabetic patients with increased cardiovascular risk. We assessed gut permeability to TMA and TMA liver clearance in animal model of diabetes. Additionally we studied therapeutic potential of ACE‐I (angiotensin‐converting enzyme inhibitor) in restoring proper gut barrier function.

12‐week‐old Sprague Dawley rats received either streptozotocin (65 mg/kg bw i.p.) (diabetic group, n=15, and ACE‐I group, n=12) or saline i.p. (control group, n=12). Fasting glucose level above 250mg/dl was considered a successful diabetes induction. Rats with ineffective diabetes induction were not included in the analysis. ACE‐I group was treated with enalapril (Polpharma, Poland), dissolved in drinking water 50mg/L (a dose of 6.5±0.3 mg/kg bw) for 4 weeks. Diabetic and control group were maintained on tap water. 4‐weeks after induction of diabetes, rats were anesthetized with urethane (1.5 g/kg bw i.p.) and blood samples from portal vein and inferior vena cava were collected. Rats were euthanized and tissues and colon content (stools) were harvested for histological and biochemical analysis, respectively. The concentration of TMA and TMAO in blood and stool samples were evaluated using liquid chromatography coupled with mass spectrometry. Gut permeability was estimated by the ratio of TMA stool concentration to TMA portal blood concentration. TMA liver clearance was calculated using the equation: 1−(systemic blood concentration/portal blood concentration).

Histological examination revealed pronounced changes in intestinal morphology in rats with induced diabetes. Diabetic group showed significantly increased concentration of TMA in portal blood and increased gut permeability to TMA in comparison to control group and ACE‐I group (diabetic rats treated with enalapril). Additionally, diabetic group demonstrated higher liver clearance of TMA in comparison to healthy rats, which was also reflected by a trend towards higher concentration of TMAO in diabetic rats.

Diabetes is associated with disruption of gut barrier, which results in increased permeability to TMA, and these changes are ameliorated by enalapril. Increased availability of TMA, a TMAO precursor, together with higher TMA liver clearance appear to be probable mechanisms of TMAO increase in diabetes. Given the potential harmful effects of TMA or TMAO our study indicates gut barrier as a therapeutic target with the promising use of ACE‐I.

Support or Funding Information

This work was supported by the Ministry of Science and Higher Education Republic of Poland, Diamond grant no: DI2017 009247.

Selected parameters in experimental groups: diabetic rats (diabetes), diabetic rats on enalapril (ACE‐I) and rats without diabetes on tap water (control). Gut permeability was assessed by the ratio: TMA stool concentration/TMA portal blood concentration; liver clearance was calculated: 1‐(systemic blood concentration/portal blood concentration). TMA ‐ trimethylamine, TMAO ‐ trimethylamine N‐oxide. Values are means ± SE, * ‐ p<0.05, by one‐way ANOVA followed by Duncan’s test.

Figure 1