An <em>In Vivo</em> Method for Evaluating the Gut-Blood Barrier and Liver Metabolism of Microbiota Products

The gut-blood barrier (GBB) controls the passage of nutrients, bacterial metabolites and drugs from intestinal lumen to the bloodstream. The GBB integrity ...

Medical University of Warsaw

Research suggests that hydrogen sulfide (HS) is an important biological mediator involved in various physiological processes including the regulation of arterial blood pressure (BP). Although HS is abundant in the colon, the effects of gut-derived HS on the circulatory system have not yet been investigated. We studied the effects of intracolonic administration of NaS, a HS donor, on systemic hemodynamics. Hemodynamics were recorded in anesthetized, normotensive Wistar Kyoto and spontaneously hypertensive rats at baseline and after intracolonic injection of either saline (controls) or NaS·9HO saline solution at a dose range of 10-300 mg/kg of BW. The HS donor produced a significant, dose-dependent decrease in mean arterial blood pressure (MABP), which lasted several times longer than previously reported after parenteral infusions (>90 min). The effect was more pronounced in hypertensive than in normotensive rats. The NaS-induced decrease in MABP was reduced by pretreatment with glibenclamide, an inhibitor of ATP-sensitive potassium-channels. NaS did not affect mesenteric vein blood flow. Rats treated with NaS showed increased portal blood levels of thiosulfate and sulfane sulfur, products of HS oxidation. In contrast, rats treated with neomycin, an antibiotic, showed significantly decreased levels of thiosulfate and sulfane sulfur, and a tendency for greater hypotensive response to NaS. The HS donor decreased heart rate but did not affect ECG morphology and QTc interval. In conclusion the gut-derived HS may contribute to the control of BP and may be one of the links between gut microbiota and hypertension. Furthermore, gut-derived HS may be a therapeutic target in hypertension.

Intracolonic hydrogen sulfide lowers blood pressure in rats.

The effect of renal denervation on the efficacy of antihypertensive drugs has not yet been elucidated. Twenty-week-old spontaneously hypertensive rats were treated with metoprolol, losartan, indapamide, or saline (controls) and assigned to renal denervation or a sham procedure. Acute hemodynamic measurements were performed ten days later. Series showing a significant interaction between renal denervation and the drugs were repeated with chronic telemetry measurements. In the saline series, denervated rats showed a significantly lower mean arterial blood pressure (blood pressure) than the sham-operated rats. In contrast, in the metoprolol series denervated rats showed a significantly higher blood pressure than sham rats. There were no differences in blood pressure between denervated and sham rats in the losartan and indapamide series. In chronic studies, a 4-week treatment with metoprolol caused a decrease in blood pressure. Renal denervation and sham denervation performed 10 days after the onset of metoprolol treatment did not affect blood pressure. Denervated rats showed markedly reduced renal nerve tyrosine hydroxylase levels. In conclusion, renal denervation decreases blood pressure in hypertensive rats. The hypotensive action of metoprolol, indapamide, and losartan is not augmented by renal denervation, suggesting the absence of synergy between renal denervation and the drugs investigated in this study.

Renal denervation decreases blood pressure and renal tyrosine hydroxylase but does not augment the effect of hypotensive drugs.

Hydrogen sulfide, a toxic gas, at low concentrations is also a biological mediator in animals. In the colon, hydrogen sulfide is produced by intestinal tissues and gut sulfur bacteria. Gut-derived molecules undergo liver metabolism. Portal hypertension is one of the most common complications contributing to the high mortality in liver cirrhosis. We hypothesized that the colon-derived hydrogen sulfide may affect portal blood pressure. Sprague-Dawley rats were maintained either on tap water (controls) or on water solution of thioacetamide to produce liver cirrhosis (CRH-R). Hemodynamics were measured after administration of either saline or NaS, a hydrogen sulfide donor, into (1) the colon, (2) the portal vein, or (3) the femoral vein. Expression of enzymes involved in hydrogen sulfide metabolism was measured by RT-PCR. CRH-R showed a significantly higher portal blood pressure but a lower arterial blood pressure than controls. Saline did not affect hemodynamic parameters. In controls, intracolonic hydrogen sulfide decreased arterial blood pressure and portal blood flow but increased portal blood pressure. Similarly, hydrogen sulfide administered into the portal vein decreased arterial blood pressure but increased portal blood pressure. In contrast, hydrogen sulfide administered into the systemic vein decreased both arterial and portal blood pressures. CRH-R showed significantly greater responses to hydrogen sulfide than controls. CRH-R had a significantly higher liver concentration of hydrogen sulfide but lower expression of rhodanese, an enzyme converting hydrogen sulfide to sulfate. In conclusion, colon-administered hydrogen sulfide increases portal blood pressure while decreasing the systemic arterial blood pressure. The response to hydrogen sulfide is more pronounced in cirrhotic rats which show reduced hydrogen sulfide liver metabolism. Therefore, colon-derived hydrogen sulfide may be involved in the regulation of portal blood pressure, and may contribute to portal hypertension. Impact statement Accumulating evidence suggests that gut-derived molecules affect the control of the circulatory system. Mechanisms controlling liver circulation have been profoundly studied; however, the effects of gut bacteria-derived molecules on portal blood pressure have not been established. In the colon, hydrogen sulfide is produced by intestinal tissues and gut sulfur bacteria. We found that colon-administered hydrogen sulfide increases portal blood pressure while decreasing the systemic arterial blood pressure. The hemodynamic response to hydrogen sulfide was more pronounced in cirrhotic rats which showed reduced hydrogen sulfide liver metabolism, i.e. lower expression of rhodanese, an enzyme converting hydrogen sulfide to sulfate. We propose that colon-derived hydrogen sulfide may affect the regulation of portal and arterial blood pressures and may be involved in portal hypertension.

Colonic hydrogen sulfide produces portal hypertension and systemic hypotension in rats.

An increased blood trimethylamine N-oxide (TMAO) has emerged as a marker of cardiovascular mortality, however, the mechanisms of the increase are not clear. We evaluated if hypertension was associated with changes in the colon permeability to trimethylamine (TMA), a TMAO precursor. We did experiments on male, 24-26-week-old normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and SHR treated with enalapril, an antihypertensive drug (SHR-E). To check the colon permeability and liver TMA clearance, blood was collected from the portal vein and hepatic veins confluence, at baseline and after the intracolonic administration of TMA. Arterial blood pressure (BP) and intestinal blood flow (IBF) recordings and histological assessment of the colon were performed. SHR showed an increased gut-blood barrier permeability to TMA. Namely, at baseline SHR had a higher BP and portal blood TMA, but a lower IBF than WKY. After the intracolonic administration of TMA, SHR had a significantly higher portal blood TMA and higher TMA liver clearance than WKY. In SHR the arteriolar walls of the colon mucosa were significantly thicker than in WKY. Furthermore, SHR showed a significant decrease in the height of the mucosa. In contrast, SHR-E had lower portal blood TMA, lower BP and smaller thickness of arteriolar walls, but higher IBF than SHR, which indicates improved function of the gut-blood barrier in SHR-E. All groups had similar immunostaining of occludin and zonula occludens-1, markers of tight junctions. In conclusion, hypertensive rats show an increased permeability of the colon to TMA, which is accompanied by morphological and hemodynamic alterations in the colon. Therefore, cardiovascular diseases may be characterized by an increased permeability of the gut-blood barrier to bacterial metabolites such as TMA.

Hypertension in rats is associated with an increased permeability of the colon to TMA, a gut bacteria metabolite.

Arterial blood pressure (BP) is regulated by a complex network of peripheral and central (brain) mechanisms. Research suggests that gut bacteria-derived compounds may affect the circulatory system. We evaluated hemodynamic effects of indole, a gut bacteria-derived product of tryptophan, and indoxyl sulfate (indoxyl), a liver metabolite of indole. BP and heart rate (HR) were recorded in anesthetized, male, Wistar rats at baseline and after the administration of either a vehicle, indole, or indoxyl into the femoral vein (IV) or into the lateral ventricle of the brain (ICV). Besides, we evaluated the effect of pretreatment with flupentixol, a non-selective D, D, α and 5 HT receptor blocker; pizotifen, a non-selective 5-HT, 5-HT and 5HT receptor blocker; and ondansetron, a 5-HT blocker, on hemodynamic responses to indole and indoxyl. Vehicle infused IV and ICV did not affect hemodynamics. Indole administered IV produced a dose-dependent increase in BP but not HR. In contrast, the ICV infusion of indole produced a decrease in BP and HR. Indoxyl infused IV produced an increase in BP and HR, whereas indoxyl infused ICV did not affect BP and HR. The hemodynamic effects of indole and indoxyl were inhibited by pretreatment with ondansetron and pizotifen but not flupentixol. In conclusion, indole and indoxyl sulfate affect arterial blood pressure via peripheral and central mechanisms dependent on serotonin signalling. We propose that indole and indoxyl sulfate may be mediators in the interaction between gut bacteria and the circulatory system.

Indole and indoxyl sulfate, gut bacteria metabolites of tryptophan, change arterial blood pressure via peripheral and central mechanisms in rats.

A high-salt diet is considered a cardiovascular risk factor; however, the mechanisms are not clear. Research suggests that gut bacteria-derived metabolites such as trimethylamine N-oxide (TMAO) are markers of cardiovascular diseases. We evaluated the effect of high salt intake on gut bacteria and their metabolites plasma level.

High salt intake increases plasma trimethylamine N-oxide (TMAO) concentration and produces gut dysbiosis in rats.

Portal hypertension (PH) is a potentially life-threatening condition. We investigated the effects of indole and dietary tryptophan, a substrate for gut bacterial production of indole, on portal blood pressure (PBP), portal blood flow (PBF), and arterial blood pressure (ABP) in Sprague-Dawley rats (SD) and SD with PH induced by liver cirrhosis (SD-PH). Hemodynamics were recorded in anesthetized male 28-wk-old SD and SD-PH at baseline and after the administration of either a vehicle or indole into the colon. Blood levels of tryptophan and its bacterial metabolites were evaluated using chromatography coupled with mass spectrometry. Indole at lower doses increased PBP and PBF. Indole at higher doses produced a transient increase in PBP, which was accompanied by a decrease in ABP. Portal blood levels of indole, indole-3-propionic, indole-3-lactic, and indole-3-acetic acids were higher in SD-PH, suggesting an increased gut-blood barrier permeability. Rats on a tryptophan-rich diet showed a significantly higher PBP and portal blood level of indoles than rats on a tryptophan-free diet. In conclusion, a tryptophan-rich diet and intracolonic indole increase PBP and portal blood level of indole. Rats with PH show an increased penetration of indoles from the colon to the circulation. Intracolonic indole production may be of therapeutic importance in PH.

Colonic indole, gut bacteria metabolite of tryptophan, increases portal blood pressure in rats.

Several studies suggest negative effects of trimethylamine oxide (TMAO) on the circulatory system. However, a number of studies showed protective functions of TMAO, a piezolyte and osmolyte, in animals exposed to high hydrostatic and/or osmotic stress. We evaluated the effects of TMAO treatment on the development of hypertension and its complications in male, Spontaneously Hypertensive Rats maintained on water (SHR-WATER) and SHR drinking TMAO water solution from weaning (SHR-TMAO). Wistar-Kyoto rats (WKY) were used as normotensive controls to discriminate between age-dependent and hypertension-dependent changes. Telemetry measurements of blood pressure (BP) were performed in rats between 7 and 16 week of life. Anaesthetized rats underwent echocardiographic, electrocardiographic and direct left ventricular end-diastolic pressure (LVEDP) measurements. HE and van Gieson staining for histopathological evaluation were performed. Plasma TMAO measured by chromatography coupled with mass spectrometry was significantly higher in SHR-WATER than in WKY (≈20%). TMAO treatment increased plasma TMAO by 4-5-fold, and did not affect the development of hypertension in SHR. 16-week-old SHR-WATER and SHR-TMAO (12-week-TMAO-treatment) showed similar BP, angiopathy and cardiac hypertrophy. However, SHR-TMAO had lower plasma NT-proBNP, LVEDP, and cardiac fibrosis. In contrast to age-matched WKY, 60-week-old SHR showed hypertensive angiopathy and heart failure with preserved ejection fraction. In comparison to SHR-WATER, SHR-TMAO (56-week-TMAO-treatment) showed significantly lower plasma NT-proBNP and vasopressin, significantly lower LVEDP and cardiac fibrosis. In conclusion, 4-5-fold increase in plasma TMAO does not exert negative effects on the circulatory system. In contrast, increased dietary TMAO seems to reduce diastolic dysfunction in pressure-overloaded heart in rats.

Tomasz Huc

Department of Experimental Physiology and Pathophysiology,
Laboratory of Centre for Preclinical Research,
Department of Experimental Physiology and Pathophysiology, Laboratory of Centre for Preclinical Research

Medical University of Warsaw

An In Vivo Method for Evaluating the Gut-Blood Barrier and Liver Metabolism of Microbiota Products

Tomasz Huc

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Experimental Physiology and Pathophysiology,Laboratory of Centre for Preclinical Research,Department of Experimental Physiology and Pathophysiology, Laboratory of Centre for Preclinical Research

Medical University of Warsaw

An In Vivo Method for Evaluating the Gut-Blood Barrier and Liver Metabolism of Microbiota Products

Department of Experimental Physiology and Pathophysiology,
Laboratory of Centre for Preclinical Research,
Department of Experimental Physiology and Pathophysiology, Laboratory of Centre for Preclinical Research