Opposite regulation of endothelial NO synthase by HSP90 and caveolin in liver and lungs of rats with hepatopulmonary syndrome

Mechanisms of decompensation and organ failure in cirrhosis: From peripheral arterial vasodilation to systemic inflammation hypothesis

The peripheral arterial vasodilation hypothesis has been most influential in the field of cirrhosis and its complications. It has given rise to hundreds of pathophysiological studies in experimental and human cirrhosis and is the theoretical basis of life-saving treatments. It is undisputed that splanchnic arterial vasodilation contributes to portal hypertension and is the basis for manifestations such as ascites and hepatorenal syndrome, but the body of research generated by the hypothesis has revealed gaps in the original pathophysiological interpretation of these complications. The expansion of our knowledge on the mechanisms regulating vascular tone, inflammation and the host-microbiota interaction require a broader approach to advanced cirrhosis encompassing the whole spectrum of its manifestations. Indeed, multiorgan dysfunction and failure likely result from a complex interplay where the systemic spread of bacterial products represents the primary event. The consequent activation of the host innate immune response triggers endothelial molecular mechanisms responsible for arterial vasodilation, and also jeopardizes organ integrity with a storm of pro-inflammatory cytokines and reactive oxygen and nitrogen species. Thus, the picture of advanced cirrhosis could be seen as the result of an inflammatory syndrome in contradiction with a simple hemodynamic disturbance.

Possible mechanisms involved in the discrepancy of hepatic and aortic endothelial nitric oxide synthases during the development of cirrhosis in rats

BACKGROUND/AIM

In cirrhosis, systemic nitric oxide (NO) overproduction and hepatic NO hypoproduction lead to arterial vasodilatation and portal hypertension. The mechanisms involved in these alterations in endothelial NO synthase (eNOS)-derived NO production in hepatic and systemic vasculature remain unknown. The aim of this study was to evaluate the regulation of eNOS and its major modulators in the liver and aorta during the development of cirrhosis in rats.

METHODS

Activated eNOS and Akt and expressions, and caveolin-1 (Cav-1) and scavenger receptor class B type I (SR-BI) expressions were measured before and 1, 2, 3 and 4 weeks after bile duct ligation. Plasma high-density lipoprotein (HDL) levels were measured.

RESULTS

Activated aortic eNOS increased at week 1, whereas it began to decrease at week 3 in the liver. Aortic expression of Cav-1 decreased at week 3 while hepatic expression increased by four-fold. Activated aortic Akt increased progressively while in the liver it gradually decreased during the development of cirrhosis. HDL levels decreased during the first week and decreased thereafter. The hepatic expression of SR-BI decreased.

CONCLUSION

This study shows that the modulation of Akt and Cav-1 is inverted in the liver and the aorta during the development of cirrhosis. In addition, decreased HDL levels may play a role in reduced hepatic eNOS activity.

Radicicol, a heat shock protein 90 inhibitor, reduces glomerular filtration rate

The heat shock protein subfamily of 90 kDa (HSP90) is composed of five isoforms. The more abundant proteins of this subfamily are cytosolic isoforms known as HSP90α and HSP90β. More than 100 client proteins have been found to be regulated by HSP90. Several studies have shown that HSP90 regulates nitric oxide synthesis that is dependent on endothelial nitric oxide synthase (eNOS). Because eNOS regulates renal vascular tone and glomerular filtration rate (GFR), the present study was designed to evaluate the effect of acute HSP90 inhibition with radicicol on GFR and the eNOS pathway. Twenty male Wistar rats were divided into two groups: control vehicle animals and radicicol-infused animals (25 μg·ml−1·min−1). Basal levels were taken before experimental measurements. Mean arterial pressure and renal blood flow (RBF) were recorded, as well as GFR, urinary nitrite and nitrate excretion (UNO2/NO3V). Additionally, we evaluated eNOS expression, Ser1177 and Thr495 eNOS phosphorylation levels, the eNOS dimer-to-monomer ratio, as well as oxidative stress by assessing renal lipoperoxidation and urinary isoprostane F2α and hydrogen peroxide. HSP90 inhibition with radicicol produced a fall in RBF and GFR that was associated with a significant reduction of UNO2/NO3V. The effects of radicicol were in part mediated by a significant decrease in eNOS phosphorylation and in the eNOS dimer-to-monomer ratio. Our findings suggest that GFR is in part maintained by HSP90-eNOS interaction.

Liver transplantation for pulmonary vascular complications of pediatric end-stage liver disease

PURPOSE

Hepatopulmonary syndrome (HPS) and portopulmonary hypertension (PPH) are poorly understood pulmonary complications of end-stage liver disease (ESLD). We present a case series of children with HPS and PPH.

METHODS

After institutional review board approval, query of our medical database identified children 0 to 18 years of age with ESLD diagnosed with HPS or PPH. Data were collected via chart review.

RESULTS

We identified 7 children with either HPS (n = 5) or PPH (n = 2). Patients with HPS presented with progressive dyspnea over a mean of 7 months (range, 4-12 months) at a mean of 13 years (range, 5-17 years) of age. Pulmonary shunting by albumin perfusion scan averaged 41% (range, 20%-66%) with an initial mean resting SpO(2) of 88% (range, 84%-94%) and mean SpO(2) during exertion of 79% (range, 60%-89%). Four patients required supplemental O(2) and, upon United Network for Organ Sharing (UNOS) appeal, received pediatric model for ESLD (or Child-Pugh) score exceptions, enabling them to undergo orthotopic liver transplant (OLT) within 1-2 months. The fifth patient was initially rejected by the UNOS regional review board, but 6 months of worsening hypoxemia led to OLT 2 months after successful UNOS appeal. All patients with HPS undergoing OLT experienced complete resolution of hypoxemia within 8 months. Both children with PPH were treated with intravenous epoprostenol, which lowered or stabilized mean pulmonary artery pressure and bridged them to OLT within 7 months of listing. Overall, there were no pulmonary complications; however, 1 patient with PPH expired shortly after OLT. The remaining patients are alive at a median follow-up of 27 months (range, 6-96 months).

CONCLUSION

Hepatopulmonary syndrome and PPH are uncommon complications of ESLD in children. Epoprostenol can bridge PPH patients to OLT. OLT leads to rapid resolution of HPS and PPH and currently represents the only successful treatment for these children.