Low-density lipoproteins and vasomotor responses in the rabbit aorta

The relationship between elevated plasma levels of low- density lipoproteins and the development of atherosclerosis is well established and recent evidence suggests that oxidation of LDL is a key process in atherogenesis. Clinical and experimental studies have shown that, in isolated blood vessels from hypercholesterolemic and atherosclerotic animals and humans endothelium-dependent relaxations (EDR) are inhibited whereas contractile responses to some agonists are potentiated. This study investigated the effects of human LDL and oxidized LDL (OXLDL) on EDR and contractile responses in isolated rabbit aortic rings. LDL (2 mg protein/ml) caused an immediate, reversible attenuation of EDR elicited by acetylcholine (ACh) and A23187 in tissues pre-contracted with noradrenaline (NA) and serotonin (5-HT) but not in aortic rings contracted to PE. The inhibition was abolished by the addition of the anti-oxidants probucol and ascorbic acid, indicating that an oxidative interaction between LDL and NA or 5-HT may play a role. Relaxations to nitric oxide (NO), the proposed mediator of EDR, were also attenuated in the presence of LDL, but endothelium-independent relaxations evoked by glyceryl trinitrate were unaffected indicating that LDL may directly inactivate NO but does not inhibit activation of vascular smooth muscle soluble guanylate cyclase. OXLDL also inhibits EDR but the extent and reversibility of the inhibition is dependent on the donor of the plasma from which the LDL was prepared. The inhibition of EDR by OXLDL requires 30 mins pre-incubation and is independent of the agonist used to pre-contract the tissues. High-density lipoproteins (HDL) and serum albumin decreased the inhibition of EDR by OXLDL, indicating that the transfer of lipid components from the OXLDL may be involved. All preparations of OXLDL reversibly attenuated NO evoked relaxations and caused a reversible decrease in sensitivity to GTN. LDL and OXLDL can also modulate contractile responses and in the presence of all preparations of LDL and OXLDL contractile responses to NA were reversibly attenuated whereas contractions to 5 HT were potentiated. In conclusion, both LDL and OXLDL can modulate EDR and contractile responses and thus, may contribute to the alterations in vascular reactivity observed in hypercholesterolemia and atherosclerosis

ارزيابی فعاليت آنزيم نيتريک اکسيد سنتتاز در سلول‌های آندوتليال آئورت موش‌های صحرايی سالم و ديابتی به روش هيستوشيميايی NADPH ديافورزيز

اختلالات عروقی يکی از عوارض شايع بيماری ديابت است. مطالعات انجام شده نشان داده‌اند که اتساع وابسته به آندوتليوم عروق در اين بيماری دچار اختلال می‌شود. اگر چه عقايد مختلفی در مورد علل وقوع اين اختلال عمل‌کرد وجود دارد اما علت(يا علل) ايجاد اين عارضه هنوز مشخص نيست. در اين مطالعه علاوه بر ارزيابی اتساع وابسته به آندوتليوم در حيوان ديابتی از راه فارماکولوژيک(با به دست آوردن منحنی غلظت ـ پاسخ استيل کولين روی آئورت مجزای سينه‌ای موش صحرايی ديابتی شده با استرپتوزوتوسين) و مقايسه آن با حيوان سالم، فعاليت آنزيم نيتريک اکسيد سنتتاز(NOS) در سلول‌های آندوتليال آئورت سينه‌ای موش‌های ديابتی و سالم با استفاده از روش رنگ‌آميزی هيستوشيميايی NADPH ديافورزيز مورد بررسی قرار گرفت. نتايج آزمايش‌ها از يک سو نشان‌دهنده کاهش معنی‌دار در اتساع وابسته به آندوتليوم در پاسخ به استيل‌کولين(نه اتساع غير وابسته به آندوتليوم در پاسخ به يک متسع کننده عروقی نيترو) بود و از سوی ديگر در مطالعه هيستوشيميايی، شدت رنگ در رنگ‌آميزی NADPH ديافورزيز در سلول‌های آندوتليال آئورت موش‌های ديابتی به طور قابل توجهی کم‌تر از سلول‌های آندوتليال آئورت موش‌های سالم بود. با توجه به اين که رنگ‌آميزی NADPH ديافورزيز به عنوان شاخصی از فعاليت NOS مورد استفاده قرار می‌گيرد، می‌توان نتيجه گرفت که فعاليتNOS در موش‌های صحرايی ديابتی شده با استرپتوزوتوسين کاهش می‌يابد و بخشی از اختلال عمل‌کرد در اتساع وابسته به آندوتليوم، ناشی از اين امر می‌باشد. علاوه بر کاهش فعاليت آنزيم NOS در مقاطع به دست آمده از آئورت موش‌های ديابتی، غشای سلول‌های آندوتليال به طور شايعی دچار پارگی شده بود که اين عدم سلامت آندوتليوم در ديابت، خود می‌تواند يکی از علل اختلال در اتساع وابسته به آندوتليوم باشد

Reaction of nitric oxide and its derivatives with sulfites: A possible role in sulfite toxicity

AbstractThe reaction between sulfites and nitric oxide or proposed carriers of nitric oxide (nitrosylated bovine serum albumin and S-nitrosoglutathione) was investigated as a potential source of the adverse effects of sulfites on biological systems. Rapid reaction occurred between sulfites and all of these reagents. Also, the ability of nitric oxide and these carriers of nitric oxide to inhibit platelet aggregation was reversed by low concentrations of sulfites. Counteraction of nitric oxide's ability to function in cell signaling processes may be a major cause of sulfite toxicity

The impairment of endothelium-dependent relaxations in isolated rabbit aorta and coronary arteries by low-density lipoproteins and oxidised fatty acids

Vasodilation mediated by endothelium-derived relaxing factor (EDRF) is accounted for by the release of nitric oxide from the endothelium in response to acetylcholine and other agents. In isolated arteries from atherosclerotic and hypercholesterolaemic animals endothelium-dependent responses are attenuated. This dysfunction may result from the accumulation of oxidised low-density lipoproteins (OXLDL) within the vessel wall, a process known to contribute to the pathogenesis of atherosclerosis. Previous studies have shown that LDL oxidised by Cu2+ inhibits endothelium-dependent relaxation in isolated rabbit aorta and porcine coronary arteries. This study investigated the effects of Cu2+-oxidised LDL on relaxations in rabbit large coronary arteries and small resistance vessels which do not exhibit overt signs of atherosclerosis. The effects of lipoxygenase metabolites of linoleic and arachidonic acid, which are present in OXLDL, on vascular reactivity of rabbit aorta were also investigated. Oxidised, but not native, LDL caused a reversible inhibition of endothelium-dependent relaxations evoked by ACh in isolated rabbit coronary arteries precontracted with either PGF2α or KC1. Furthermore, the extent of the inhibitory effect was similar in both large and small coronary arteries. Relaxations evoked by the nitrovasodilator SNP were unaffected by the presence of OXLDL. Hydroperoxy and hydroxy derivatives of linoleic and arachidonic acid, which have been identified in OXLDL, caused an immediate and reversible attenuation of ACh-evoked relaxations in isolated rabbit aorta. The inhibition was prevented by the addition of the protein kinase C inhibitor chelerythrine chloride suggesting the inhibition is mediated through a mechanism involving the activation of protein kinase C. Metabolites of arachidonic but not linoleic acid inhibited endothelium-independent relaxations evoked by GTN. In addition, arachidonic acid oxidation products caused a direct contraction of rabbit aortic rings which was not altered by the presence of the endothelium. LDL modified by treatment with lipoxygenase (LO-LDL) also inhibited endothelium-dependent relaxations in rabbit aorta by a mechanism involving protein kinase C and not dependent on uptake via the scavenger receptor. Relaxations evoked by GTN were reversibly attenuated by the presence of LO-LDL. In conclusion, the inhibitory effect of OXLDL in coronary vessels suggests that the effects of atherosclerosis on vascular function may extend into the microcirculation. Products of fatty acid peroxidation may contribute, with other constituents of OXLDL, to the impairment of coronary vasodilation observed in atherosclerosis and hypercholesterolaemia. Arachidonic acid metabolites may also be involved in enhanced vasoconstrictor responses and vasospasm

The effects of lysophospholipids and oxidised low-density lipoproteins on the L-arginine: Nitric oxide pathways in isolated rabbit and rat aorta

Elevated plasma levels of low-density lipoproteins (LDL) are a major risk factor for the development of atherosclerosis. Atherosclerotic vessels from humans and animals show impaired endothelium-dependent relaxations (EDR) and altered responses to contractile agonists. Recent evidence suggests that oxidation of LDL is a key process in atherogenesis and plays an important role in the alterations in vascular reactivity. This study investigated the effects of a major component of oxidised LDL (OXLDL), lysophosphatidylcholine (LPC), on vascular responses in isolated rabbit and rat aortic rings. In addition, the effects of OXLDL on EDR in rat aortic rings was also examined. Furthermore, the possibility that impaired EDR in atherosclerotic vessels could be restored by L-arginine was investigated. LPC caused immediate, dose dependent and partially reversible inhibition of EDR evoked by ACh, ATP and A23187 in rabbit aortic rings. This inhibition was decreased by serum albumin but not by L-arginine or indomethacin. Relaxations to exogenous NO and glyceryl trinitrate in endothelium-denuded tissues were unaffected by LPC, but responses were inhibited in endothelium-intact rings suggesting the release of an inhibitory factor from the endothelium. LPC also evokes EDR which are mediated by the release of NO. This dual effect of LPC can be demonstrated in the same tissue. Contractile responses to phenylephrine (PE) and 5-HT were unaffected in denuded tissues, but were inhibited in endothelium-intact tissues, again suggesting the release of a factor from the endothelium. Relaxations evoked by L-arginine in isolated rat aortic rings were mediated by an inducible nitric oxide synthase (NOS). At a concentration that inhibited relaxations elicited by ACh, OXLDL did not influence L-arginine-evoked relaxations, whereas LPC potentiated responses. NOS activity induced in vivo by endotoxin injection, was studied ex vivo by observation of PE-evoked contractions. Contractions were attenuated in rings from endotoxin-treated rats. However, the effect of this treatment was unaffected by the presence of OXLDL or LPC. Aortic rings from WHHL rabbits which spontaneously develop atherosclerosis, showed impaired EDR. This impairment was not influenced by incubation of the tissues with L-arginine. Furthermore, rabbits fed a diet supplemented with L-arginine did not show improved endothelium- dependent responses in vitro. In addition, L-arginine feeding did not influence contractile responses to PE. In conclusion, LPC can modulate EDR and contractile responses in isolated tissues although, these effects do not mimic those reported for OXLDL. In contrast, OXLDL and LPC do not inhibit the activity of an inducible form of NOS. Finally, the impairment of EDR observed in atherosclerotic vessels cannot be reversed by the administration of L-arginine

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G i (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G q (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients. © 2008 Scandinavian Physiological Society.postprin

Next generation sequencing discoveries of the nitrate-responsive oral microbiome and its effect on vascular responses

Cardiovascular disease is a worldwide human condition which has multiple underlying contributing factors: one of these is long-term increased blood pressure-hypertension. Nitric oxide (NO) is a small nitrogenous radical species that has a number of physiological functions including vasodilation. It can be produced enzymatically through host nitric oxide synthases and by an alternative nitrate-nitrite-NO pathway from ingested inorganic nitrate. It was discovered that this route relies on the ability of the oral microbiota to reduce nitrate to nitrite and NO. Next generation sequencing has been used over the past two decades to gain deeper insight into the microbes involved, their location and the effect of their removal from the oral cavity. This review article presents this research and comments briefly on future directions