Sodium Butyrate as Key Regulator of Mitochondrial Function and Barrier Integrity of Human Glomerular Endothelial Cells

The gut microbiota has emerged as an important modulator of cardiovascular and renal homeostasis. The composition of gut microbiota in patients suffering from chronic kidney disease (CKD) is altered, where a lower number of bacteria producing short chain fatty acids (SCFAs) is observed. It is known that SCFAs, such as butyrate and acetate, have protective effects against cardiovascular diseases and CKD but their mechanisms of action remain largely unexplored. In the present study, we investigated the effect of butyrate and acetate on glomerular endothelial cells. Human glomerular microvascular endothelial cells (hgMVECs) were cultured and exposed to butyrate and acetate and their effects on cellular proliferation, mitochondrial mass and metabolism, as well as monolayer integrity were studied. While acetate did not show any effects on hgMVECs, our results revealed that butyrate reduces the proliferation of hgMVECs, strengthens the endothelial barrier through increased expression of VE-cadherin and Claudin-5 and promotes mitochondrial biogenesis. Moreover, butyrate reduces the increase in oxygen consumption induced by lipopolysaccharides (LPS), revealing a protective effect of butyrate against the detrimental effects of LPS. Taken together, our data show that butyrate is a key player in endothelial integrity and metabolic homeostasis.

Acute attenuation of glycocalyx barrier properties increases coronary blood volume independently of coronary flow reserve

Vascular endothelium is covered with an extensive mesh of glycocalyx constituents, which acts like an effective barrier up to several micrometers thick that shields the luminal surface of the vasculature from direct exposure to flowing blood. Many studies report that various enzymatic and pharmaceutical challenges are able to increase glycocalyx porosity, resulting in farther permeation of plasma macromolecules and greater access of red blood cells into glycocalyx domain. Attenuation of glycocalyx barrier properties therefore potentially increases the amount of blood that effectively occupies available microvascular volume. We tested in the present study whether attenuation of coronary glycocalyx barrier properties actually increases coronary blood volume and whether such changes would be noticeable during measurements of coronary flow reserve using adenosine. In anesthetized goats ( n = 6) with cannulated left main coronary artery that were perfused under controlled pressure, coronary blood volume was measured via the indicator-dilution technique using high-molecular-weight (2,000 kDa) dextrans as plasma tracer and labeled red blood cells as red blood cell tracer. Coronary blood volume was determined at baseline and during intracoronary infusion of adenosine causing maximal vasodilation (0.2–0.6 mg·kg−1·h−1) before and after intracoronary hyaluronidase treatment (170,000 units) of the glycocalyx. With an intact glycocalyx, coronary blood volume was 18.9 ± 1.1 ml/100 g heart tissue at baseline, which increased to 26.3 ± 2.7 ml/100 g after hyaluronidase treatment of the coronary glycocalyx. Maximal vasodilation by administration of adenosine further increased coronary blood volume to 33.9 ± 6.8 ml/100 g, a value not different from the maximal coronary blood volume of 33.2 ± 5.3 ml/100 g obtained by administration of adenosine in the absence of hyaluronidase treatment. Adenosine-induced increases in coronary conductance were not affected by hyaluronidase treatment. We conclude that acute attenuation of glycocalyx barrier properties increases coronary blood volume by ∼40%, which is of similar magnitude as additional changes in coronary blood volume during subsequent maximal vasodilation with adenosine. Furthermore, maximal coronary blood volume following administration of adenosine was similar with and without prior hyaluronidase degradation of the glycocalyx, suggesting that adenosine and hyaluronidase potentially increase glycocalyx porosity to a similar extent. Hyaluronidase-mediated changes in coronary blood volume did not affect baseline and adenosine-induced increases in coronary conductance, demonstrating that measurements of coronary flow reserve are insufficient to detect impairment of coronary blood volume recruitment in conditions of damaged glycocalyx.