Spontaneously hypertensive rats exhibit increased liver flavin monooxygenase expression and elevated plasma TMAO levels compared to normotensive and Ang II-dependent hypertensive rats

Background: Flavin monooxygenases (FMOs) are enzymes responsible for the oxidation of a broad spectrum of exogenous and endogenous amines. There is increasing evidence that trimethylamine (TMA), a compound produced by gut bacteria and also recognized as an industrial pollutant, contributes to cardiovascular diseases. FMOs convert TMA into trimethylamine oxide (TMAO), which is an emerging marker of cardiovascular risk. This study hypothesized that blood pressure phenotypes in rats might be associated with variations in the expression of FMOs. Methods: The expression of FMO1, FMO3, and FMO5 was evaluated in the kidneys, liver, lungs, small intestine, and large intestine of normotensive male Wistar-Kyoto rats (WKY) and two distinct hypertensive rat models: spontaneously hypertensive rats (SHRs) and WKY rats with angiotensin II-induced hypertension (WKY-ANG). Plasma concentrations of TMA and TMAO were measured at baseline and after intravenous administration of TMA using liquid chromatography-mass spectrometry (LC-MS). Results: We found that the expression of FMOs in WKY, SHR, and WKY-ANG rats was in the descending order of FMO3 > FMO1 >> FMO5. The highest expression of FMOs was observed in the liver. Notably, SHRs exhibited a significantly elevated expression of FMO3 in the liver compared to WKY and WKY-ANG rats. Additionally, the plasma TMAO/TMA ratio was significantly higher in SHRs than in WKY rats. Conclusion: SHRs demonstrate enhanced expression of FMO3 and a higher plasma TMAO/TMA ratio. The variability in the expression of FMOs and the metabolism of amines might contribute to the hypertensive phenotype observed in SHRs.

Trimethylamine, a gut bacteria metabolite and air pollutant, increases blood pressure and markers of kidney damage including proteinuria and KIM-1 in rats

Background

Trimethylamine oxide (TMAO) is a biomarker in cardiovascular and renal diseases. TMAO originates from the oxidation of trimethylamine (TMA), a product of gut microbiota and manufacturing industries-derived pollutant, by flavin monooxygenases (FMOs). The effect of chronic exposure to TMA on cardiovascular and renal systems is undetermined.

Methods

Metabolic, hemodynamic, echocardiographic, biochemical and histopathological evaluations were performed in 12-week-old male SPRD rats receiving water (controls) or TMA (200 or 500 µM/day) in water for 18 weeks. TMA and TMAO levels, the expression of FMOs and renin-angiotensin system (RAS) genes were evaluated in various tissues.

Results

In comparison to controls, rats receiving high dose of TMA had significantly increased arterial systolic blood pressure (126.3 ± 11.4 vs 151.2 ± 19.9 mmHg; P = 0.01), urine protein to creatinine ratio (1.6 (1.5; 2.8) vs 3.4 (3.3; 4.2); P = 0.01), urine KIM-1 levels (2338.3 ± 732.0 vs. 3519.0 ± 953.0 pg/mL; P = 0.01), and hypertrophy of the tunica media of arteries and arterioles (36.61 ± 0.15 vs 45.05 ± 2.90 µm, P = 0.001 and 18.44 ± 0.62 vs 23.79 ± 2.60 µm, P = 0.006; respectively). Mild degeneration of renal bodies with glomerulosclerosis was also observed. There was no significant difference between the three groups in body weight, water-electrolyte balance, echocardiographic parameters and RAS expression. TMA groups had marginally increased 24 h TMA urine excretion, whereas serum levels and 24 h TMAO urine excretion were increased up to 24-fold, and significantly increased TMAO levels in the liver, kidneys and heart. TMA groups had lower FMOs expression in the kidneys.

Conclusions

Chronic exposure to TMA increases blood pressure and increases markers of kidney damage, including proteinuria and KIM-1. TMA is rapidly oxidized to TMAO in rats, which may limit the toxic effects of TMA on other organs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03687-y.

Enalapril Diminishes the Diabetes-Induced Changes in Intestinal Morphology, Intestinal RAS and Blood SCFA Concentration in Rats

Evidence suggests that microbiota-derived metabolites, including short-chain fatty acids (SCFAs) and trimethylamine-oxide (TMAO), affect the course of diabetic multiorgan pathology. We hypothesized that diabetes activates the intestinal renin–angiotensin system (RAS), contributing to gut pathology. Twelve-week-old male rats were divided into three groups: controls, diabetic (streptozotocin-induced) and diabetic treated with enalapril. Histological examination and RT-qPCR were performed to evaluate morphology and RAS expression in the jejunum and the colon. SCFA and TMAO concentrations in stools, portal and systemic blood were evaluated. In comparison to the controls, the diabetic rats showed hyperplastic changes in jejunal and colonic mucosa, increased plasma SCFA, and slightly increased plasma TMAO. The size of the changes was smaller in enalapril-treated rats. Diabetic rats had a lower expression of Mas receptor (MasR) and angiotensinogen in the jejunum whereas, in the colon, the expression of MasR and renin was greater in diabetic rats. Enalapril-treated rats had a lower expression of MasR in the colon. The expression of AT1a, AT1b, and AT2 receptors was similar between groups. In conclusion, diabetes produces morphological changes in the intestines, increases plasma SCFA, and alters the expression of renin and MasR. These alterations were reduced in enalapril-treated rats. Future studies need to evaluate the clinical significance of intestinal pathology in diabetes.

Evaluation of thionolactones as a new type of hydrogen sulfide (H2S) donors for a blood pressure regulation

Hydrogen sulfide (H₂S) is a gaseous molecule that exhibits various biological effects. For example, H₂S has been recognized as a blood pressure-lowering agent. Presented in this report is a new modifiable platform for H₂S supply, its preparation and H₂S release kinetics from a series of structurally diversified thionolactones. Furthermore, the properties of the obtained H₂S donors were evaluated in both in vitro and in vivo studies. The kinetic parameters of H₂S release were determined and compared with NaHS and pyrrolidine-2-thione, a thiolactame analog, using a fluorescence detection method based on 7-azido-4-methyl-2H-chromen-2-one probe. We have shown that H₂S release rates from the developed compounds are controllable through structural modifications. This study shows that both the thiono-lactone ring's size and the presence of a methyl group in the thiono-lactone ring significantly influenced the rate of H₂S release. Finally, we have found a significant hypotensive response to intravenous administration of the developed donors in anesthetized rats.

Low-dose Bevacizumab Decreases Ocular Hypotensive Effect of Angiotensin II in Sprague Dawley Rats

PURPOSE

Although the effectiveness of anti-VEGF agents in ophthalmology has been thoroughly documented, we do not fully comprehend the epidemiology and mechanistic background of their side effects, including intraocular and systemic hypertension. Here, we investigate the interference of a low-dose bevacizumab with key neuronal and humoral mechanisms maintaining blood and intraocular pressure homeostasis.

MATERIALS AND METHODS

Intraocular pressure (IOP), blood pressure (BP), and heart rate (HR) were measured in SPRD rats pretreated with bevacizumab or 0.9% NaCl at baseline and after infusion of angiotensin II, a humoral mediator involved in BP and IOP regulation. Superior cervical gangliectomy was performed to assess the effect of sympathetic nervous system on the analyzed parameters. Additionally, we studied the expression of a subset of genes related to renin-angiotensin system in the anterior segment of the eye.

RESULTS

At baseline, there was no significant difference in IOP, BP, and HR between rats pretreated with 0.9% NaCl and bevacizumab. Infusion of angiotensin II lowered IOP in rats pretreated with 0.9% NaCl, but not in rats pretreated with bevacizumab (30 min: ∆4.22 ± 1.2 vs. baseline, p > .05; ∆0.83 ± 0.66 vs. baseline, p < .05) This effect was paralleled by an increased expression of angiotensin II type 1b and type 2 receptors in the anterior segment of the eye (AT1b: 1 ± 0.65 vs 7.35 ± 2.84, p < .05; AT2: 1 ± 0.05 vs. 12.8 ± 0.1, p < .05). Angiotensin II infusion increased BP in both groups (10 min: bevacizumab ∆44.6 ± 3.2, p < .05; 0.9%NaCl ∆37.1 ± 5.1, p < .05), whereas did not have any effect on HR. Sympathetic ocular denervation did not affect any of the analyzed parameters.

CONCLUSIONS

We found that low-dose bevacizumab interferes with IOP-lowering properties of angiotensin II. This effect might be related to increased expression of angiotensin II receptors in the anterior segment of the eye.

Hydrogen sulfide formation in experimental model of acute pancreatitis

Acute pancreatitis (AP) is a disease defined as acute or chronic inflammatory process of the pancreas characterized by premature activation of digestive enzymes within the pancreatic acinar cells and causing pancreatic auto-digestion. In mammalian tissues, H2S is synthesized endogenously from L-cysteine in regulated enzymatic pathways catalyzed by pyridoxal phosphate-dependent enzymes: cystathionine beta - synthase (CBS), gamma - cystathionase (CTH) and cysteine aminotransferase (CAT) coupled with 3-mercaptopyruvate sulfurtransferase (MPST). In the mitochondria, hydrogen sulfide is oxidized to sulfite, which is then converted to thiosulfate (sulfane sulfur-containing compound) by thiosulfate sulfurtransferase (rhodanese; TST). The activity and the expression of CBS, CTH, MPST, and TST have been determined in vivo in pancreas of control rats, rats with acute pancreatitis and sham group. Levels of low-molecular sulfur compounds such as reduced and oxidized glutathione, cysteine, cystine and cystathionine were also determined. The study showed the significant role of MPST in H2S metabolism in pancreas. Stress caused by the surgery (sham group) and AP cause a decrease in H2S production associated with a decrease of MPST activity and expression. Markedly higher level of cysteine in the AP pancreas may be caused by a reduced rate of cysteine consumption in reaction catalyzed by MPST but it can also be a sign of the processes of proteolysis occurring in the changed tissue.