Role of endothelin-1 and cyclic nucleotides in ischemia/reperfusion-mediated microvascular leak

Tubastatin A prevents hemorrhage-induced endothelial barrier dysfunction

BACKGROUND

Microvascular hyperpermeability resulting from endothelial barrier dysfunction (EBD) is associated with worse clinical outcomes in trauma-induced hemorrhagic shock. We have previously shown that treatment with Tubastatin A (TubA), a histone deacetylase 6 inhibitor, improves outcomes in animal models of shock. In this study, we investigate whether TubA treatment may prevent trauma-related EBD.

METHODS

Wistar-Kyoto rats subjected to 40% hemorrhage were treated with TubA or vehicle control. Acute lung injury (ALI) was assessed histologically from tissues harvested 6 hours posthemorrhage. In vitro, human umbilical vein endothelial cells (HUVECs) were cultured in EGM BulletKit medium. Medium was exchanged for glucose-free Dulbecco's Modified Eagle Medium (0.5% fetal bovine serum) with or without TubA, and cells were placed in an anoxic chamber (5% CO2, 95% N2, 20-48 hours). Expression of acetylated tubulin and hypoxia-inducible factor 1α was measured by Western blot. Soluble Intercellular Adhesion Molecule-1 concentration within the medium, a marker of endothelial integrity, was determined using enzyme-linked immunosorbent assay. Monolayers were assessed for permeability via transwell assays using fluorescein isothiocyanate-labeled albumin.

RESULTS

Rats treated with TubA had significantly reduced ALI relative to vehicle control. In vitro, TubA significantly attenuated anoxia-induced hyperpermeability, hypoxia-inducible factor 1α expression, and glycocalyx shedding.

CONCLUSIONS

Our findings demonstrate that TubA prevents hemorrhage-induced ALI in rats. Additionally, we have shown that TubA prevents anoxia-induced EBD in vitro. Taken together, these results suggest that TubA could attenuate microvascular hyperpermeability related to hemorrhagic shock.

Optimizing Transfusion Ratios in Massive Transfusion Protocols: An Argument Against the 1:1:1 Dogma and Approach to Trauma Resuscitation

We believe that the current practice of transfusing red blood cells (RBCs), plasma, and platelets in a 1:1:1 ratio is not optimal in massive transfusion protocols (MTPs) and is based on a simple yet profound misconception regarding the preparation of component blood products. This 1:1:1 approach ignores the additional fluids added for anticoagulation and preservation of the components and assumes that there is a one-size-fits-all ratio that must be used across all types of trauma. In this article, we explain the rationale behind our conclusion with supporting figures and suggest that although the 1:1:1 ratio might be within the range of hemostasis, it falls near the lower cusp of hemostasis, making it less than ideal. The patient in mind was one in whom transfusion was expected to exceed 10 units of packed RBCs (pRBCs) in a combat environment where the situation was too hectic for additional testing. The goal was to keep the patient within a hemostatic range until the crisis phase was averted and the transition could then be made to goal-directed therapy with point-of-care testing.

Endothelin-1 attenuates increases in hydraulic conductivity due to platelet-activating factor via prostacyclin release

We previously showed that endothelin-1 (ET-1) and prostacyclin (PGI(2)) similarly attenuate increases in microvascular permeability induced by platelet-activating factor (PAF). This led us to hypothesize that ET-1 attenuates trans-endothelial fluid flux during PAF through PGI(2) release. We tested this hypothesis in three phases. First, bovine pulmonary artery endothelial cells were exposed to 0.008-8 μM ET-1 and assayed for PGI(2) release. Second, to determine whether increased transmonolayer flux after PAF could be attenuated by ET-1 or PGI(2) and reversed by PGI(2) synthesis inhibition or PGI(2) receptor blockade, we measured endothelial cell transmonolayer flux after cells were exposed to 10 nM PAF plus 10 μM PGI(2) or 80 pM ET-1, with or without 500 μM tranylcypromine (PGI(2) synthase inhibitor) or 20 μM CAY-10441 (PGI(2) receptor blocker). Finally, hydraulic conductivity (L(p)) was measured in rat mesenteric venules in vivo after exposure to 10 nM PAF and 80 pM ET-1 with or without tranylcypromine (100 and 500 μM) or CAY-10441 (2 and 20 μM). We found that in vitro, ET-1 stimulated a dose-dependent increase in PGI(2) production (from 126 to 217 pg/ml, P < 0.01). Compared with PAF alone, PGI(2) plus PAF and ET-1 plus PAF decreased transmonolayer flux similarly by 52 and 46%, respectively (P < 0.01), while tranylcypromine and CAY-10441 reversed these effects by 92 and 47%, respectively (P < 0.05). In vivo, PAF increased L(p) fourfold (P < 0.01) and ET-1 attenuated this effect by 83% (P < 0.01). Tranylcypromine and CAY-10441 reversed the ET-1 attenuation in L(p) during PAF by 55 and 45%, respectively (P < 0.01). We conclude that ET-1 may stimulate endothelial cell PGI(2) release to attenuate the increases in transmonolayer flux and hydraulic conductivity secondary to PAF.

cGMP in the vasculature

Cyclic guanosine 3', 5'-monophosphate (cGMP) plays an integral role in the control of vascular function. Generated from guanylate cyclases in response to the endogenous ligands, nitric oxide (NO) and natriuretic peptides (NPs), cGMP influences a number of vascular cell types and regulates vasomotor tone, endothelial permeability, cell growth and differentiation, as well as platelet and blood cell interactions. Reciprocal regulation of the NO-cGMP and NP-cGMP pathways is evident in the vasculature such that one cGMP generating system may compensate for the dysfunction of the other. Indeed, aberrant cGMP production and/or signalling accompanies many vascular disorders such as hypertension, atherosclerosis, coronary artery disease and diabetic complications. This chapter highlights the main vascular functions of cGMP, its role in disease and the resulting current and potential therapeutic applications. With respect to pulmonary hypertension, heart failure and erectile dysfunction, as well as cGMP signal transduction, the reader is specifically referred to other dedicated chapters.

Effects of olprinone, a phosphodiesterase III inhibitor, on ischemic acute renal failure

OBJECTIVE

Renal ischemic reperfusion injury (IRI) is unavoidable and is still one of the major problems in renal transplantation. The aim of this study was to investigate the effects of olprinone, a phosphodiesterase III inhibitor, on renal IRI.

METHODS

After a right nephrectomy, renal IRI was induced in rats. Olprinone was given in two different ways: sustained systemic administration and transient local administration to the kidney. Control rats were treated with saline. Using a magnifying endoscope, the renal blood flow speed was measured at 23 h after reperfusion. Then, blood samples were collected, and kidney specimens were taken for histological study. In order to study the mechanism, we performed in vitro experiments, using human proximal renal tubular cells (HK-2) incubated with tumor necrosis factor (TNF)-alpha along with olprinone or saline, and interleukin (IL)-8 was measured in the culture supernatant.

RESULTS

In the saline group, the blood flow speed (BFS) was greatly reduced compared to that in normal kidneys. In both olprinone-treated groups, BFS of the renal microcirculation significantly increased, tubular damage and macrophage infiltration attenuated, and renal function greatly improved. Olprinone inhibited the increase in the IL-8 levels resulting from the incubation of HK-2 with TNF-alpha.

CONCLUSIONS

Our study successfully demonstrates that olprinone has renoprotective properties when applied locally as well as systemically. The results suggest that olprinone might be clinically useful in renal transplantation for the donor kidney, the recipient, and even in treating acute renal failure.