Mukadder Yasa

Antioxidant Enzyme Activities and Total Nitrite/ Nitrate Levels in the Collar Model. Effect of Nicardipine

Abstract There is a large body of literature describing the causative role of oxidative stress mediated by increased levels of reactive oxygen species in the pathogenesis of cardiovascular disease such as atherosclerosis, hypertension, and restenosis after angioplasty. The positioning of a soft silicone collar around the rabbit carotid artery elicits intimal thickening. The findings from recent studies demonstrated that both intimal thickening and atherosclerosis lead to synthesis of inducible nitric oxide synthase, resulting in abundant amounts of nitric oxide. We investigated the effects of collaring and nicardipine treatment on the activities of antioxidant enzymes, superoxide dismutase and catalase, and total nitrite/nitrate levels, stable products of nitric oxide. Placing the collar increased the total nitrite/nitrate levels and decreased superoxide dismutase activity in collared arteries. Treatment with nicardipine (20 mg/kg/day, s.c.) prevented enhanced nitric oxide degradation without affecting superoxide dismutase and catalase activities. Our results suggest that enhanced nitric oxide production and superoxide anion are generated in response to the collaring, resulting in oxidative stress within the segment in this model.

Effect of verapamil on intimal thickening and vascular reactivity in the collared carotid artery of the rabbit.

1 . Intimal thickening is a common site for atherosclerosis. Therefore, we investigated whether the calcium entry blocker verapamil (10 mg kg−1 body weight day−1, s.c.) can retard intimal thickening and changes in vascular reactivity induced by a non‐occlusive, silicone collar positioned around the left carotid artery of rabbits. The contralateral carotid artery was sham‐operated and served as a control. 2 . Verapamil and placebo (saline 0.1 ml kg−1 day−1, s.c.) treatments were initiated 7 days before placing the collar and lasted 3 weeks. Thereafter, segments were cut from collared and sham‐treated arteries for histology and isometric tension recording. 3 . The intima/media (I/M) ratio increased after 14 days of collar treatment, but intimal thickening was not inhibited by verapamil (I/M ratio placebo 0.31 ± 0.07, verapamil 0.32 ± 0.09). 4 . The collar decreased the capacity to develop force, as indicated by the response to a supramaximal concentration of KC1, decreased the sensitivity (pD2) to acetylcholine (ACh) and phenylephrine (Phe), but increased the sensitivity to 5‐hydroxytryptamine (5‐HT). 5 . Although verapamil did not affect intimal thickening, it normalized the hypersensitivity to 5‐HT in collared arteries. 6 . The contraction to the supramaximal concentration of KC1 was not affected by verapamil. Verapamil decreased the Emax of ACh, but this was only seen in collar‐treated arteries. Verapamil also decreased the sensitivity to ACh and Phe, in both sham‐ and collar‐treated arteries. 7 . We conclude that verapamil, without preventing thickening of the intima, can modify collar‐induced changes in vascular reactivity.

Methylglyoxal causes endothelial dysfunction: the role of endothelial nitric oxide synthase and AMP-activated protein kinase α.

Abstract Background: Methylglyoxal is a major precursor in the formation of advanced glycation end products and is associated with the pathogenesis of diabetes-related vascular complications. The aim of this study was to evaluate whether methylglyoxal induces endothelial dysfunction and to determine the contributors involved in this process. Methods: Rat thoracic aortic rings were treated for 24 h with 100 μM methylglyoxal by using an organ culture method. A cumulative dose-response curve to acetylcholine was obtained to determine endothelium-dependent relaxation. The protein levels of endothelial nitric oxide synthase (eNOS) and its phosphorylated form at the serine 1177 site [p-eNOS (Ser1177)], heat shock protein 90 (Hsp90), AMP-activated protein kinase α (AMPKα) and its phosphorylated form at the threonine 172 site [p-AMPKα (Thr172)] were evaluated. Superoxide production was determined by lucigenin-chemiluminescence. Results: Treatment with 100 μM methylglyoxal for 24 h decreased acetylcholine-induced vascular relaxation. The levels of eNOS and p-eNOS (Ser1177) were reduced while no effect on Hsp90 was observed. Levels of p-AMPKα (Thr172) were significantly decreased without any change in total AMPKα protein levels. Superoxide level was not affected by methylglyoxal treatment. Conclusions: In rat aortic rings, methylglyoxal determines a reduction in endothelium-dependent relaxation. This effect seems to be mediated via a reduction in p-eNOS (Ser1177) and p-AMPKα (Thr172).

Effects of Nicardipine on Collar-induced Intimal Thickening and Vascular Reactivity in the Rabbit

The effects of nicardipine treatment on collar‐induced intimal thickening and on accompanying reactivity changes in rabbit carotid artery have been investigated.

Different responses of fluvastatin to cholesterol-induced oxidative modifications in rabbits: evidence for preventive effect against DNA damage

Hypercholesterolemia is a major risk factor for atherosclerosis and related occlusive vascular diseases. We investigated the effect of low‐dose fluvastatin (2 mg kg−1 day−1) on antioxidant enzyme activities [superoxide dismutase (SOD), catalase], vascular reactivity changes and oxidatively induced DNA damage in early stage of atherosclerosis in hypercholesterolemic rabbits. The animals were divided into three groups each composed of 10 rabbits. The control group received a regular rabbit chow diet, and the cholesterol group had hypercholesterolemic diet (2%, 4 weeks). The fluvastatin group was given hypercholesterolemic diet plus fluvastatin. Dietary intake of cholesterol significantly increased total cholesterol levels in rabbits (control, 0.85 ± 0.29; cholesterol, 12.04 ± 4.61; fluvastatin, 8.07 ± 2.72 mmol l−1 ). Hypercholesterolemic diet revealed discernible fatty streaks in arcus aortae. Fluvastatin significantly reduced the areas of the lesions. The diet significantly increased SOD activities in both erythrocyte and tissue. Treatment with fluvastatin normalized the increased activity of SOD in both erythrocyte and aortic tissues from the cholesterol group. Cholesterol feeding decreased the sensitivity to acetylcholine, and treatment with fluvastatin significantly restored the diminished sensitivity to acetylcholine in thoracic aortae. Cholesterol feeding caused oxidatively induced DNA damage in liver tissues determined by the increased levels of 8‐hydroxyguanine (8‐OH‐Gua) and 2,6‐diamino‐4‐hydroxy‐5‐formamidopyrimidine (FapyGua). Fluvastatin decreased only FapyGua level in liver. In conclusion, our results may suggest that fluvastatin seems to play a protective role on high cholesterol‐induced oxidative stress and DNA damage. Copyright

Effects of treatment with FK409, a nitric oxide donor, on collar-induced intimal thickening and vascular reactivity.

Intimal thickening in arteries is considered a site of predilection for atherosclerosis. In a rabbit model of early atherosclerosis, a silastic collar was placed around the carotid artery, which resulted in the formation of intimal thickening. We investigated whether the oral application of FK409 ((+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide , 10 mg kg(-1) day(-1), p.o.), a nitric oxide donor, inhibited the collar-induced intimal thickening as well as accompanying reactivity changes in rabbit carotid artery. The intimal thickening was significantly inhibited by FK409. The collar treatment increased the pD2 value of 5-hydroxytryptamine (5-HT) whereas it decreased those of phenylephrine and acetylcholine and did not significantly alter that of nitroglycerine. Maximal contractile force development in response to potassium chloride (KCl), 5-HT and phenylephrine was decreased in collared arteries. The collar did not alter the maximal relaxant effects of acetylcholine and nitroglycerine. Despite the significant reduction of intimal thickening, FK409 treatment did not affect these collar-induced modifications in vascular reactivity.

The Effects of Calcium Channel Blockers are not Related to their Chemical Structure in the Collar Model of the Rabbit

Placing a silicone collar around the rabbit carotid artery induces intimal thickening, an early stage in atherosclerosis and restenosis. We investigated whether treatment with oral pranidipine, a new potent, long-lasting dihydropyridine calcium channel blocker (CCB), inhibited collar-induced intimal thickening in addition to the changes in vascular reactivity usually observed in this model. Pranidipine treatment did not inhibit collar-induced intimal thickening. Placing the collar around the carotid artery resulted in the characteristic changes in vascular reactivity, such as increased sensitivity to 5-hydroxytryptamine. Treatment with Nω-nitro-l-arginine (100 μM) and pranidipine, however, did not affect collar-induced changes in vascular reactivity. From results of this and previous studies, we conclude that pranidipine does not prevent collar-induced intimal thickening or collar-induced changes in vascular reactivity. Not all CCBs prevent collar-induced intimal thickening, suggesting that the effects of these agents are not related to their chemical structure and/or their calcium channel-blocking actions.

Diverse effects of calcium channel blockers in the collar model.

Objective — Calcium channel blockers (CCBs) are among the most frequently prescribed cardiovascular drugs. It has been shown that these drugs have antiatherosclerotic effects in both experimental and clinical settings. However, calcium channel blockers have markedly different chemical structures and different effects on the cardiovascular system.We investigated the effect of CD-832, a Ca+2 channel antagonist, on collar-induced intimal thickening, as well as accompanied reactivity changes in rabbit carotid artery. Methods and results — Rabbits received 5 mg/kg/day CD-832 or vehicle (polyethylene glycol, 0.5 ml/kg/day) intramuscularly for a week before and 2 weeks after the collar application. Histological and isometric force measurements were performed in segments from sham and collared carotid arteries. A three-week treatment with CD-832 did not inhibit the intimal thickening caused by perivascular application of a silicone collar. Potassium chloride (KCl), phenylephrine, 5-hydroxytryptamine (5-HT, serotonin) and histamine induced concentration-dependent contractions in both sham-operated (sham) and collared arteries. Collar-induced attenuations in maximum KCl, histamine, phenylephrine and 5-HT contractions were not affected by CD-832. Collaring caused an increase in pD2 values of 5-HT and a decrease in those of phenylephrine, histamine and acetylcholine. CD-832 did not affect the altered sensitivity to these agonists. Conclusions — These results demonstrate that, in rabbit carotid artery, CD-832 did not inhibit the collar-induced intimal thickening and did not affect the accompanying changes in vascular reactivity

Effects of levosimendan on isolated human internal mammary artery and saphenous vein: concurrent use with conventional vasodilators.

Graft spasm is a common problem in coronary artery bypass grafting (CABG). In this study, we aimed to investigate the interaction of levosimendan, a novel inodilator, with vasodilator agents that are clinically used for the treatment of graft spasm and with endogenous vasoconstrictors that are thought to play a role in graft vasospasm, in human internal mammary artery (IMA) and saphenous vein (SV). Isolated human IMA and SV segments derived from patients undergoing CABG were suspended in an organ bath. Responses to cumulative concentrations of noradrenaline (NA), serotonin (5‐HT), papaverine, nitroglycerin (NG), and diltiazem were recorded before and after 10−5 m levosimendan incubation (30 min). In addition, cumulative levosimendan responses were taken in vessels precontracted with NA or 5‐HT. 10−5 m levosimendan reduced NA Emax and sensitivity in IMA and SV, and 5‐HT Emax responses in IMA. Moreover, levosimendan caused concentration‐dependent relaxation in both grafts. Papaverine Emax or sensitivity was not altered by levosimendan neither in IMA nor in SV. Levosimendan diminished NG sensitivity in IMA and Emax responses in SV and decreased diltiazem Emax responses both in IMA and SV. Our results suggest that levosimendan may be used alone for prevention or treatment of graft spasm in IMA or in combination with papaverine in IMA and SV grafts. However, as concurrent administration with diltiazem or NG causes a reduction in relaxation in vitro, we suggest caution should be exercised when using levosimendan in combination with these agents.

Telomeric restriction analysis of vascular smooth muscle cells following balloon angioplasty in rabbits

Intimal hyperplasia due to smooth muscle cell proliferation and migration has been reported to be responsible for the pathogenesis of atherosclerosis and restenosis, manifested following balloon angioplasty. In this study, we employed the balloon angioplasty model to study telomere length regulation in proliferating vascular smooth muscle cells. Our results showed that balloon angioplasty in iliac arteries resulted in intimal hyperplasia due to proliferation of the smooth muscle cells and small size telomeric restrictional fragments were evident in injured arteries.