Hypertension-Linked Pathophysiological Alterations in the Gut

RATIONALE

Sympathetic nervous system control of inflammation plays a central role in hypertension. The gut receives significant sympathetic innervation, is densely populated with a diverse microbial ecosystem, and contains immune cells that greatly impact overall inflammatory homeostasis. Despite this uniqueness, little is known about the involvement of the gut in hypertension.

OBJECTIVE

Test the hypothesis that increased sympathetic drive to the gut is associated with increased gut wall permeability, increased inflammatory status, and microbial dysbiosis and that these gut pathological changes are linked to hypertension.

METHODS AND RESULTS

Gut epithelial integrity and wall pathology were examined in spontaneously hypertensive rat and chronic angiotensin II infusion rat models. The increase in blood pressure in spontaneously hypertensive rat was associated with gut pathology that included increased intestinal permeability and decreased tight junction proteins. These changes in gut pathology in hypertension were associated with alterations in microbial communities relevant in blood pressure control. We also observed enhanced gut-neuronal communication in hypertension originating from paraventricular nucleus of the hypothalamus and presenting as increased sympathetic drive to the gut. Finally, angiotensin-converting enzyme inhibition (captopril) normalized blood pressure and was associated with reversal of gut pathology.

CONCLUSIONS

A dysfunctional sympathetic-gut communication is associated with gut pathology, dysbiosis, and inflammation and plays a key role in hypertension. Thus, targeting of gut microbiota by innovative probiotics, antibiotics, and fecal transplant, in combination with the current pharmacotherapy, may be a novel strategy for hypertension treatment.

Abstract P610: Hypertension Is Associated With Profound Pathological Changes In The Gut

Background and objective: Our previous studies have shown that gut microbial dysbiosis is linked to hypertension (HTN) in both animal models and patients with high blood pressure (BP) ( Hypertension 2015; 65:1331-40 ). The intestinal epithelial layer serves as a barrier against pathogens and is altered in paracellular permeability with bowel diseases. Accordingly, our objective in the present study was to test the hypothesis that HTN-linked gut dysbiosis is associated with changes in gut wall pathophysiology.

Methods and Results: Two rat models of were used: pre-hypertensive juvenile SHR (MAP 97 ± 5 mmHg) and adult SHR (MAP 160 ± 3 mmHg) with corresponding control WKY rats and chronic Angiotensin II (Ang II) infusion rat model of HTN (saline MAP 95 ± 2 mmHg vs. Ang II 150 ± 3 mmHg). A fluorescein isothiocyanate conjugated (FITC) dextran feeding protocol and a custom indentation system were used for permeability and stiffness assessments, respectively. Segments of small intestine were used for histology. We observed no significant differences in gut permeability and stiffness in pre-hypertensive juvenile SHR vs WKY controls. However, a 2-fold difference in gut permeability was observed in adult SHR (SHR 3514±563.4 vs WKY 1777±427.8, RFU, p<0.05). In addition, a 10-fold difference in gut wall stiffness (effective modulus) in adult SHR was observed (SHR 53.3±32.2 vs WKY 5.3±1.6, kPA, p<0.05). Histology revealed that adult SHR had 20% stunted villi length (SHR 580±54 vs WKY 718±6, μm, p<0.05) and a 60% increase in fibrotic area (SHR 13.8±1.3 vs WKY 8.5±0.8, p<0.05). Similar differences in gut permeability, elastic modulus, villi length and fibrotic area were observed in the Ang II HTN rat model. In contrast, pre-hypertensive, juvenile SHR did not show these differences.

Conclusions: These observations, for the first time, demonstrate that increased BP is associated with profound gut pathology. They suggest that gut wall integrity likely plays a critical role in regulation of BP hemostasis and host microbiota communications with blood vessels.

Abstract 027: Intestinal Permeability and Dysbiosis are Linked to Hypertension

Introduction: Emerging evidence implicates the involvement of intestinal microbiota in overall physiological homeostasis. Altered microbial composition is associated with metabolic, cardiovascular, and neurological diseases. However, the role of intestinal microbiota in blood pressure control and hypertension (HTN) remains unexplored. The present study was designed to evaluate the hypothesis that both intestinal dysbiosis and altered intestinal function are critical pathophysiological events in HTN.

Methods: 16S ribosomal DNA from fecal samples from SHR and chronic angiotensin II (Ang II, 200ng/kg/min) rat models was utilized to compare gut microbial communities between normotensive and hypertensive animals. Gut permeability was assessed by accumulation of FITC-dextran (44mg/100g BW) in the plasma 4 hours following oral feeding. Ex vivo atomic force microscopy was used to determine small intestine and colon stiffness (a measure of permeability). Tight junction gene expression was quantified by qPCR.

Results: We observed a significant decrease in microbial richness (20%), diversity (12%), and evenness (10%) in SHR vs WKY. This was associated with an increased Firmicutes (F)/Bacteroidetes (B) ratio (4±1 vs 24±5), a hallmark of gut dysbiosis. Additionally, we observed a 95% increase in plasma FITC-dextran in SHRs (1777±428 vs 3514±563 ng/ml, p<0.05), which correlated with decreased mRNA of several tight junction genes throughout the intestine, including Ocln , Tjp1 , and Cldn4 . In addition, we found increased stiffness of both small intestine and colonic tissue, as evidenced by increased elastic modulus in SHR (small intestine: 21.2±3 vs 53.7±8 kPa, colon: 15.7±2 vs 53.4±14 kPa, p<0.05). Similar decreased microbial richness and increased F/B ratio (~2 fold) were observed in the Ang II rat model at 4 weeks. Plasma FITC-dextran began to rise by day 14 (SBP=160 mmHg), and reached maximal increase of 65% by day 21 (SBP=185 mmHg). Furthermore, colon wall stiffness was significantly increased by day 21 of Ang II infusion.

Conclusions: These observations show that increased gut permeability/leakiness and dysbiosis is associated with HTN. They are the first to demonstrate a profound intestinal pathophysiology and microbial dysbiosis in HTN.

Diminazene aceturate enhances angiotensin-converting enzyme 2 activity and attenuates ischemia-induced cardiac pathophysiology

Angiotensin-converting enzyme 2 (ACE2) plays a critical role against myocardial infarction (MI). We hypothesized that activation of intrinsic ACE2 would be protective against ischemia-induced cardiac pathophysiology. Diminazene aceturate (DIZE), a small molecule ACE2 activator, has been used to evaluate this hypothesis. DIZE (15 mg/kg per day, s.c.) was injected 2 days before MI surgery and continued throughout the study period. MI rats showed a 62% decrease in fractional shortening (%; control, 51.1±3.2; DIZE alone, 52.1±3.2; MI, 19.1±3.0), a 55% decrease in contractility (dP/dtmax mm Hg/s; control, 9480±425.3; DIZE alone, 9585±597.4; MI, 4251±657.7), and a 27% increase in ventricular hypertrophy (mg/mm; control, 26.5±1.5; DIZE alone, 26.9±1.4; MI, 33.4±1.1). DIZE attenuated the MI-induced decrease in fractional shortening by 89%, improved dP/dtmax by 92%, and reversed ventricular hypertrophy by 18%. MI also significantly increased ACE and angiotensin type 1 receptor levels but decreased ACE2 activity by 40% (control, 246.2±25.1; DIZE alone, 254.2±20.6; MI, 148.9±29.2; RFU/min), which was reversed by DIZE treatment. Thus, DIZE treatment decreased the infarct area, attenuated LV remodeling post-MI, and restored normal balance of the cardiac renin-angiotensin system. In addition, DIZE treatment increased circulating endothelial progenitor cells, increased engraftment of cardiac progenitor cells, and decreased inflammatory cells in peri-infarct cardiac regions. All of the beneficial effects associated with DIZE treatment were abolished by C-16, an ACE2 inhibitor. Collectively, DIZE and DIZE-like small molecules may represent promising new therapeutic agents for MI.

Progressive anatomical closure of foramen ovale in normal neonatal mouse hearts

In the prenatal heart, right-to-left atrial shunting of blood through the foramen ovale is essential for proper circulation. After birth, as the pulmonary circulation is established, the foramen ovale functionally closes as a result of changes in the relative pressure of the two atrial chambers, ensuring the separation of oxygen depleted venous blood in the right atrium from the oxygenated blood entering the left atrium. Little is known regarding the process of anatomical closure of the foramen ovale in the postnatal heart. Genetically engineered mouse models are powerful tools to study heart development and to reveal mechanisms underlying cardiac anomalies, including defects in atrioventricular septation. Using three-dimensional reconstructions of serial sectioned hearts at early postnatal Days 2-7, we show a progressive reduction in the size of the interatrial communication throughout this period and complete closure by postnatal Day 7. Furthermore we demonstrate that fusion of the septum primum and septum secundum occurs between 4 weeks and 3 months of age. This study provides a standard timeline for morphological closure of the right-left atrial communication and fusion between the atrial septa in normal mouse hearts.