Peroxynitrite induces arteriolar smooth muscle cells membrane hyperpolarization with arteriolar hyporeactivity in rats

Effects of ω-3 PUFA-Rich Oil Supplementation on Cardiovascular Morphology and Aortic Vascular Reactivity of Adult Male Rats Submitted to an Hypercholesterolemic Diet

Simple Summary

Currently, processed and ultraprocessed foods represent a significant component of the diet of modern societies, increasing the risk of developing obesity, diabetes and atherosclerosis. Therefore, replacing saturated fats with mono- and polyunsaturated fats, such as omega-3 polyunsaturated fatty acids (ω-3 PUFAs), has been considered as a dietary strategy to reduce clinical events related to atherosclerosis. In the present study, the effects of 56-day ω-3 PUFA-rich oil supplementation on liver function, lipid profile, and oxidative stress in hypercholesterolemic rats were investigated, as well as its impact on cardiovascular health. Interestingly, we observed a positive effect in reducing hepatic markers, preserving cardiovascular morphology, and increasing vasodilator responsiveness. These findings contribute to the generation of consistent recommendations for the therapeutic use of ω-3 PUFAs in the treatment of atherosclerosis, leading to a consequent reduction in related morbidity and mortality.

Abstract

Atherosclerosis is a cardiovascular disease associated with abnormalities of vascular functions. The consumption of mono- and polyunsaturated fatty acids can be considered a strategy to reduce clinical events related to atherosclerosis. In the present study, we investigated the effects of supplementation with 310 mg of ω-3 PUFAs (2:1 eicosapentaenoic/docosahexaenoic acids) for 56 days on rats with hypercholesterolemia induced by a diet containing cholesterol (0.1%), cholic acid (0.5%), and egg yolk. Serum biochemical parameters were determined by the enzymatic colorimetric method. Assessment of vascular effects was performed by analysis of histological sections of the heart and aortic arch stained with hematoxylin and eosin and vascular reactivity of the aorta artery. We observed that treatment with ω-3 PUFAs did not promote alterations in lipid profile. On the other hand, we documented a favorable reduction in liver biomarkers, as well as contributions to the preservation of heart and aortic arch morphologies. Interestingly, the vascular reactivity of rat thoracic aortic preparations was improved after treatment with ω-3 PUFAs, with a decrease in hyperreactivity to phenylephrine and increased vasorelaxation promoted by acetylcholine. Our findings suggest that the supplementation of hypercholesterolemic rats with ω-3 PUFAs promoted improvement in liver and vascular endothelial function as well as preserving heart and aortic tissue, reinforcing the early health benefits of ω-3 PUFAs in the development of atherosclerotic plaque and further related events.

Pathophysiological roles of peroxynitrite in circulatory shock

Peroxynitrite is a reactive oxidant produced from nitric oxide and superoxide, which reacts with proteins, lipids, and DNA, and promotes cytotoxic and proinflammatory responses. Here, we overview the role of peroxynitrite in various forms of circulatory shock. Immunohistochemical and biochemical evidences demonstrate the production of peroxynitrite in various experimental models of endotoxic and hemorrhagic shock both in rodents and in large animals. In addition, biological markers of peroxynitrite have been identified in human tissues after circulatory shock. Peroxynitrite can initiate toxic oxidative reactions in vitro and in vivo. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na+/K+ ATPase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of peroxynitrite. In addition, peroxynitrite is a potent trigger of DNA strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) polymerase, which promotes cellular energetic collapse and cellular necrosis. Additional actions of peroxynitrite that contribute to the pathogenesis of shock include inactivation of catecholamines and catecholamine receptors (leading to vascular failure) and endothelial and epithelial injury (leading to endothelial and epithelial hyperpermeability and barrier dysfunction), as well as myocyte injury (contributing to loss of cardiac contractile function). Neutralization of peroxynitrite with potent peroxynitrite decomposition catalysts provides cytoprotective and beneficial effects in rodent and large-animal models of circulatory shock.

Inhibition of L-type calcium channels in arteriolar smooth muscle cells is involved in the pathogenesis of vascular hyporeactivity in severe shock

The objective was to investigate the changes in the function of L-type calcium (L-Ca2+) channels of arteriolar smooth muscle cells (ASMCs) in the genesis of vascular hyporeactivity during severe shock. A hemorrhagic shock (HS) model was reproduced in rats, and the responsiveness of arterioles in the cremaster muscle to norepinephrine (NE) was measured. The inward currents of L-Ca2+ channel and intracellular concentration of Ca2+ ([Ca2+]i) level in isolated ASMCs were measured using patch clamp and fluorescent probe techniques. The arteriolar vasoreactivity was significantly reduced with a 12.5-fold increase of NE threshold level 2 h post-HS. Meanwhile, the inward currents through L-Ca2+ channels of ASMCs were significantly decreased at different holding potentials, and the maximal inward current was only 26.7% of control value in the shock group. The increased intracellular concentration of Ca2+ level of ASMCs stimulated by NE was reduced to 32.0% of control value 2 h post-HS. Administration of the L-Ca2+ channel stimulator, Bay K8644, partially restored the NE threshold level and transiently increased the mean arterial pressure during HS, lending further support to the importance of ASMC L-Ca2+ channel inhibition in the genesis of low vasoreactivity in vivo during severe shock. Our results suggest that stimulation of L-Ca2+ channels of ASMCs might be a potential therapeutic approach for treatment of refractory hypotension in severe shock.

Hypersensitivity of BK Ca to Ca 2+ Sparks Underlies Hyporeactivity of Arterial Smooth Muscle in Shock

Large conductance Ca 2+ -activated K + channels (BK Ca ) play a critical role in blood pressure regulation by tuning the vascular smooth muscle tone, and hyposensitivity of BK Ca to Ca 2+ sparks resulting from its altered β1 subunit stoichiometry underlies vasoconstriction in animal models of hypertension. Here we demonstrate hypersensitivity of BK Ca to Ca 2+ sparks that contributes to hypotension and blunted vasoreactivity in acute hemorrhagic shock. In arterial smooth muscle cells under voltage-clamp conditions (0 mV), the amplitude and duration, but not the frequency, of spontaneous transient outward currents of BK Ca origin were markedly enhanced in hemorrhagic shock, resulting in a 265% greater hyperpolarizing current. Concomitantly, subsurface Ca 2+ spark frequency was either unaltered (at 0 mV) or decreased in hyperpolarized resting cells. Examining the relationship between spark and spontaneous transient outward current amplitudes revealed a hypersensitive BK Ca activity to Ca 2+ spark in hemorrhagic shock, whereas the spark–spontaneous transient outward current coupling fidelity was near unity in both groups. Importantly, we found an acute upregulation of the β1 subunit of the channel, and single-channel recording substantiated BK Ca hypersensitivity at micromolar Ca 2+ , which promotes the α and β1 subunit interaction. Treatment of shock animals with the BK Ca inhibitors iberiotoxin and charybdotoxin partially restored vascular membrane potential and vasoreactivity to norepinephrine and blood reinfusion. Thus, the results underscore a dynamic regulation of the BK Ca –Ca 2+ spark coupling and its therapeutic potential in hemorrhagic shock–associated vascular disorders.

Protective effect of green tea polyphenols on the SH-SY5Y cells against 6-OHDA induced apoptosis through ROS-NO pathway

Green tea polyphenols (GTP) are thought to help prevent oxidative stress-related diseases, such as cancer, cardiovascular disease, neurodegenerative disease, and aging. We here investigate the protective mechanisms of GTP on SH-SY5Y cells against apoptosis induced by the pro-parkinsonian neurotoxin 6-hydroxydopamine (6-OHDA). GTP rescued the changes in condensed nuclear and apoptotic bodies, attenuated 6-OHDA-induced early apoptosis, prevented the decrease in mitochondrial membrane potential, and suppressed accumulation of reactive oxygen species (ROS) and of intracellular free Ca(2+). GTP also counteracted the 6-OHDA-induced nitric oxide increase and overexpression of nNOS and iNOS, and decreased the level of protein-bound 3-nitrotyrosine (3-NT). In addition, GTP inhibited the autooxidation of 6-OHDA and scavenged oxygen free radicals in a dose- and time-dependent manner. Our results show that the protective effects of GTP on SH-SY5Y cells are mediated, at least in part, by controlling the ROS-NO pathway.

Calcium mobilization is required for peroxynitrite-mediated enhancement of spontaneous transient outward currents in arteriolar smooth muscle cells

Transiently local release of Ca(2+) from the sarcoplasmic reticulum (SR) activates nearby Ca(2+)-activated K(+) channels to produce spontaneous transient outward currents (STOCs) in smooth muscle cells. The purpose of the present study was to investigate the possible effect of peroxynitrite (ONOO(-)) on STOCs in mesenteric arteriolar smooth muscle cells (ASMCs) and decide whether Ca(2+) mobilization was involved in STOCs alteration by ONOO(-). STOCs were recorded and characterized using the perforated whole-cell patch-clamp configuration. The results demonstrated that STOCs activity was greatly suppressed by removal of extracellular Ca(2+); by addition of nifedipine, a specific inhibitor of L-type voltage-gated Ca(2+) channels (VGCCs); or by addition of ryanodine, a SR ryanodine receptors (RyRs) blocker. In contrast, both caffeine, a RyR activator, and 2-aminoethoxydiphenylborate (2-APB), a membrane-permeable inositol 1,4,5-trisphosphate receptors, (IP3R) antagonist, increased STOCs activity. 3-morpholinosydnonimine (SIN-1), an ONOO(-) donor, at concentrations of 20-200 microM, induced a dose-dependent enhancement of STOCs in ASMCs and led to conspicuous increases in STOCs frequency and amplitude, which were prevented by prior exposure to low external Ca(2+) (200 nM), ryanodine (10 microM), or nifedipine (10 microM). In contrast, caffeine (0.5 mM) did not further stimulate STOCs in ASMCs preincubated with SIN-1, and pretreatment with 2-APB (50 microM) had little effect on ONOO(-) -induced STOCs activation. These findings suggest that complex Ca(2+)-mobilizing pathways, including external Ca2+ influx through VGCCs activation and subsequent internal Ca(2+) release through RyRs but not IP3Rs, are involved in ONOO(-)mediated STOCs enhancement in ASMCs.