Endothelin-1 enhances nitric oxide-induced cytotoxicity in vascular smooth muscle

IGFBP-4 Proteolysis by PAPP-A in a Primary Culture of Rat Neonatal Cardiomyocytes under Normal and Hypertrophic Conditions

Cardiovascular diseases (CVD) are among the leading causes of death and disability worldwide. Pregnancy-associated plasma protein-A (PAPP-A) is a matrix metalloprotease localized on the cell surface. One of the substrates that PAPP-A cleaves is the insulin-like growth factor binding protein-4 (IGFBP-4), a member of the family of proteins that bind insulin-like growth factor (IGF). Proteolysis of IGFBP-4 by PAPP-A occurs at a specific site resulting in formation of two proteolytic fragments - N-terminal IGFBP-4 (NT-IGFBP-4) and C-terminal IGFBP-4 (CT-IGFBP-4), and leads to the release of IGF activating various cellular processes including migration, proliferation, and cell growth. Increased levels of the proteolytic IGFBP-4 fragments correlate with the development of CVD complications and increased risk of death in patients with the coronary heart disease, acute coronary syndrome, and heart failure. However, there is no direct evidence that PAPP-A specifically cleaves IGFBP-4 in the cardiac tissue under normal and pathological conditions. In the present study, using a primary culture of rat neonatal cardiomyocytes as a model, we have demonstrated that: 1) proteolysis of IGFBP-4 by PAPP-A occurs in the conditioned medium of cardiomyocytes, 2) PAPP-A-specific IGFBP-4 proteolysis is increased when cardiomyocytes are transformed to a hypertrophic state. Thus, it can be assumed that the enhancement of IGFBP-4 cleavage by PAPP-A and hypertrophic changes in cardiomyocytes accompanying CVD are interrelated, and PAPP-A appears to be one of the activators of the IGF-dependent processes in normal and hypertrophic-state cardiomyocytes.

α-Lipoic acid protected cardiomyoblasts from the injury induced by sodium nitroprusside through ROS-mediated Akt/Gsk-3β activation

It has been long noted that cardiac cell apoptosis provoked by excessive production of nitric oxide (NO) plays important roles in the pathogenesis of variant cardiac diseases. Attenuation of NO-induced injury would be an alternative therapeutic approach for the development of cardiac disorders. This study investigated the effects of α-lipoic acid (LA) on the injury induced by sodium nitroprusside (SNP), a widely used NO donor, in rat cardiomyoblast H9c2 cells. SNP challenge significantly decreased cell viability and increased apoptosis, as evidenced by morphological abnormalities, nuclear condensation and decline of mitochondrial potential (ΔΨm). These changes induced by SNP were significantly attenuated by LA pretreatment. Furthermore, LA pretreatment prevented the SNP-triggered suppression of Akt and Gsk-3β activation. Blockade of Akt activation with triciribin (API) completely abolished the cytoprotection of LA against SNP challenge. In addition, LA moderately increased intracellular ROS production. Interestingly, inhibition of ROS with N-acetylcysteine abrogated Akt/Gsk-3β activation and the LA-induced cytoprotection following SNP stimulation. Taken together, the results indicate that LA protected the SNP-induced injury in cardiac H9c2 cells through, at least in part, the activation of Akt/Gsk-3β signaling in a ROS-dependent mechanism.

Endothelin receptor blockade attenuates lipopolysaccharide-induced pulmonary nitric oxide production

Increased nitric oxide (NO) synthesis by the inducible nitric oxide synthase (iNOS) has been shown to contribute to the development of acute lung injury and delayed hypotension in animals injected with bacterial lipopolysaccharides (LPS). Recent evidence indicates that endothelin-1 (ET-1) is also elevated in septic humans and in animals. To assess the contribution of ETs to LPS-induced pulmonary NO production and iNOS expression, we used P1/fl, a 22 amino acid peptide, to selectively antagonize endothelin-A receptors. Anesthetized, mechanically ventilated rats were injected with either saline or LPS (E. coli endotoxin, 20 mg/kg) and studied for 5 h. Two other groups of rats were pretreated 15 min earlier with P1/fl peptide (20 microg/kg). Unlike saline-treated rats, rats injected with LPS showed a progressive decline in arterial pressure and a significant rise in plasma ET concentration and serum nitrite-nitrate level. In the lungs, LPS injection elicited a several-fold rise in lung iNOS activity and exhaled NO concentration and increased lung wet/dry ratio significantly. Pretreatment with P1/fl peptide eliminated the decline in arterial pressure, the rise in lung wet/dry ratio, lung NOS activity, and iNOS protein expression and significantly attenuated the increase in pulmonary exhaled NO production but had no effect on plasma ET concentration. We conclude that activation of ET-A receptors by rising ET-1 concentration enhances NO production and iNOS expression in the respiratory and vascular systems and contributes to both LPS-induced hypotension and acute lung injury.

Endothelin-1 enhances nitric oxide-induced cell death in cultured vascular smooth-muscle cells

Increased expression of endothelin-1 (ET-1) immunoreactivity is demonstrated in the active atherosclerotic plaque. Here we show that both ETA and ETB receptors are expressed in rat vascular smooth-muscle cells (VSMCs). ET-1 binding to ETB receptors enhances nitric oxide-induced cell death in VSMCs. These findings suggest that ET-1 may participate in the mechanism of cell death (apoptosis) in the plaque through activation of ETB-mediated pathways and that a selective ETB receptor antagonist could be useful in preventing acute plaque alterations, such as plaque rupture.

Endothelial cell injury in cardiovascular surgery: the intimal hyperplastic response

Arteries and veins respond to injury by a healing process that includes the development of a neointima. This response to injury is implicated as the primary cause of failure after arterial reconstruction. Because it is an integrator and transmitter of blood flow variations, inflammation, and growth stimuli, the endothelium is a potent regulator of long-term arterial wall mass changes. The contribution of the endothelium to intimal development depends on the type of arterial conduit. In arteries, the growth of the intima stops when the endothelium has regrown. In synthetic grafts, the endothelium stabilizes intimal growth. Hence, the mere presence of endothelial cells can influence intimal changes in arterial conduits. Understanding endothelial biology should help us define methods to prevent cell proliferation, extracellular matrix accumulation, intimal hyperplasia, and vessel narrowing.

Effect of selective blockade of endothelin ETB receptors on the liver dysfunction and injury caused by endotoxaemia in the rat

1. We investigated the effects of the selective endothelin (ET)A receptor antagonist BQ-485 and the selective ETB receptor antagonist BQ-788 on circulatory failure, multiple organ dysfunction syndrome (MODS) and the alterations in acid base balance caused by endotoxaemia in the anaesthetized rat. 2. Male Wistar rats were anaesthetized (thiopentone sodium; 120 mg kg-1, i.p.) and received a continuous infusion of vehicle (saline, 0.6 ml kg-1h-1, i.v.), BQ-485 (10 nmol kg-1 min-1, i.v.) or BQ-788 (10 nmol kg-1 min-1, i.v.). Fifteen min later, animals received a bolus injection of either saline (0.9% NaCl, 1 ml kg-1, i.v.) or E. coli lipopolysaccharide (LPS, 10 mg kg-1, i.v.). 3. Injection of LPS resulted in a fall in blood pressure from 115 +/- 4 mmHg (time 0) to 82 +/- 4 mmHg at 360 min (n = 15) as well as a hyporeactivity to the pressor responses to noradrenaline (NA, 1 microgram kg-1, i.v.). Infusion of BQ-788 attenuated the delayed hypotension (at 360 min: 100 +/- 4 mmHg, n = 7; P < 0.05) and significantly enhanced the pressor responses elicited by NA (at 60 to 240 min). In contrast, treatment of LPS-rats with BQ-485 augmented the hypotension (at 360 min), but did not affect the vascular hyporeactivity elicited by endotoxaemia. 4. Endotoxaemia for 360 min resulted in rises in the serum levels of urea and creatinine (indicators of renal failure), glutamate-oxalate-transferase (GOT) and glutamate-pyruvate-transferase (GPT) (indicators of hepatocellular injury), and bilirubin and gamma-glutamyl transferase (gamma GT) (indicators of liver failure) as well as nitrite (indicator of the induction of nitric oxide synthase; iNOS). Treatment of LPS-rats with BQ-788, but not with BQ-485, attenuated the degree of liver injury and failure, while neither BQ-788 nor BQ-485 affected the acute renal failure or the induction of iNOS caused by endotoxin. 5. Endotoxaemia also caused (within 15 min) an acute metabolic acidosis (falls in pH, HCO3-and base excess) which was compensated by hyperventilation (fall in PaCO2). Treatment of LPS-rats with BQ-788 or BQ-485 did not affect the metabolic acidosis caused by LPS. 6. Thus, the selective ETB receptor antagonist BQ-788 attenuated (i) the delayed hypotension, (ii) the vascular hyporeactivity to NA as well as (iii) the degree of hepatocellular injury and dysfunction caused by endotoxin in the anaesthetized rat. In contrast, the selective ETA receptor antagonist did neither attenuate the circulatory failure nor the liver or renal dysfunction associated with endotoxaemia. We propose that the prevention of the hepatocellular dysfunction and injury caused BQ-788 in endotoxaemia is due to an improvement in oxygen delivery to the liver secondary to (i) inhibition of pre-sinusoidal constriction, (ii) inhibition of sinusoidal constriction, and (iii) improvement in perfusion pressure.