Alan H. Singer

Antiatherogenic effects of L-arginine in the hypercholesterolemic rabbit.

The purpose of this study was to determine if chronic administration of L-arginine, the precursor of endothelium-derived relaxing factor (EDRF), normalizes endothelium-dependent relaxation and decreases atherosclerosis in hypercholesterolemic animals. Male rabbits were fed (a) normal rabbit chow; (b) 1% cholesterol diet; or (c) 1% cholesterol diet supplemented by 2.25% L-arginine HCl in drinking water. Arginine supplementation doubled plasma arginine levels without affecting serum cholesterol values. After 10 wk, the thoracic aorta was harvested for studies of vascular reactivity and histomorphometry. Endothelium-dependent relaxations (to acetylcholine and calcium ionophore A23187) were significantly impaired in thoracic aortae from animals fed a 1% cholesterol diet. By contrast, vessels from hypercholesterolemic animals receiving L-arginine supplementation exhibited significantly improved endothelium-dependent relaxations. Responses to norepinephrine or nitroglycerin were not affected by either dietary intervention. Histomorphometric analysis revealed a reduction in lesion surface area and intimal thickness in thoracic aortae from arginine-supplemented animals compared to those from untreated hypercholesterolemic rabbits. This is the first study to demonstrate that supplementation of dietary L-arginine, the EDRF precursor, improves endothelium-dependent vasorelaxation. More importantly, we have shown that this improvement in EDRF activity is associated with a reduction in atherogenesis.

L-arginine attenuates platelet reactivity in hypercholesterolemic rabbits.

Platelets are capable of producing nitric oxide (NO) through the L-arginine-NO synthase pathway. Acute exposure to supraphysiological concentrations of L-arginine in vitro increases the production of NO by platelets and is associated with an increase in platelet cyclic GMP (cGMP) levels and a reduction in platelet aggregation. The purpose of this study was to determine if chronic oral administration of L-arginine decreases platelet aggregation in hypercholesterolemic animals and to determine if this effect is mediated by the metabolism of L-arginine to NO. Male New Zealand White rabbits were fed normal chow (Con), a 1% cholesterol diet (Chol), or a 1% cholesterol diet supplemented with a sixfold enrichment of dietary L-arginine (Arg) or L-methionine (Met). After 10 weeks, cholesterol levels were equally increased in Chol and Arg animals, whereas plasma arginine levels were doubled in the Arg group. There was no difference in maximum aggregation initiated by ADP (100 mumol/L) between washed platelets from Con, Met, and Chol animals, but aggregation of platelets from Arg animals was significantly decreased (P < .05). In aggregating platelets from Arg animals, cGMP levels were significantly higher than the other groups (P < .05). When platelets were incubated ex vivo with the NO synthase inhibitor NG-monomethyl-L-arginine, the effects of dietary L-arginine were reversed. Chronic dietary supplementation of L-arginine decreases platelet aggregation in hypercholesterolemic rabbits. This effect appears to be due to the metabolism of L-arginine to NO.

Dietary arginine prevents atherogenesis in the coronary artery of the hypercholesterolemic rabbit.

OBJECTIVES This study was designed to test the hypothesis that long-term oral supplementation of dietary L-arginine (to provide a sustained elevation of nitric oxide activity) would inhibit atherogenesis in hypercholesterolemic rabbits, as assessed by histomorphometric measurements. BACKGROUND Endothelium-derived nitric oxide inhibits a number of processes that are critical in atherogenesis. Hypercholesterolemia reduces endothelial nitric oxide activity, and we postulate that this may promote atherogenesis. This reduction in nitric oxide activity can be reversed acutely by intravenous infusion of L-arginine, the precursor of nitric oxide. We show that dietary supplementation of L-arginine abrogates the development of coronary atheroma in hypercholesterolemic rabbits. METHODS Male New Zealand White rabbits were fed normal rabbit chow, 1% cholesterol chow or 1% cholesterol chow with dietary arginine or methionine supplementation to increase their intake of these amino acids sixfold. After 1 or 10 weeks of dietary intervention, the left main and left anterior descending coronary arteries were harvested for histologic study. Plasma cholesterol measurements were elevated to the same degree in all groups of rabbits receiving the 1% cholesterol diet, whereas plasma arginine levels were doubled in the arginine-treated group. High density lipoprotein (HDL) cholesterol values were not affected by arginine treatment. RESULTS In rabbits receiving the 1% cholesterol diet, with or without methionine supplementation, light and electron microscopy revealed a marked increase from 1 to 10 weeks in the intimal accumulation of macrophages, associated with an increase in the intimal area of the left main coronary artery. By contrast, in arginine-treated hypercholesterolemic rabbits, there was a near absence of adherent monocytes and tissue macrophages and no progression of intimal thickness from 1 to 10 weeks. CONCLUSIONS Dietary supplements of L-arginine prevent intimal thickening in the coronary arteries of hypercholesterolemic rabbits. This antiatherogenic effect is not due to an alteration in plasma total cholesterol, HDL cholesterol or caloric or nitrogen balance. The data are consistent with the hypothesis that nitric oxide has antiatherogenic properties.

Discordant effects of dietary L-arginine on vascular structure and reactivity in hypercholesterolemic rabbits

We investigated the effect of dietary supplementation of L-arginine (L-Arg), the precursor of endothelial nitric oxide (NO), on endothelium-dependent and endothelium-independent vascular responses, as well as vascular structure, in the abdominal aorta of hypercholesterolemic rabbits. Rabbits were fed (a) normal rabbit chow, (b) 1% cholesterol diet, or (c) 1% cholesterol diet supplemented with 2.25% L-Arg HCl in drinking water. After 10 weeks, the abdominal aorta was harvested for study of vascular reactivity and histomorphometry. L-Arg did not affect serum cholesterol levels. Histomorphometric analysis demonstrated an eightfold reduction in intimal thickening in the abdominal aorta of the arginine-supplemented hypercholesterolemic rabbits. By contrast, the effects on vascular reactivity were subtle. Contraction to norepinephrine (NE) was not altered by hypercholesterolemia or L-Arg. Contraction to acetylcholine (ACh) was increased in hypercholesterolemic animals; this was normalized by dietary arginine supplementation. Relaxation to nitroglycerin (NTG) was not altered by hypercholesterolemia but was attenuated in the arginine-supplemented rabbits. Endothelium-dependent relaxation to ACh was impaired in both hypercholesterolemic groups. Dietary L-Arg has a dramatic antiatherogenic effect in hypercholesterolemic rabbits. This effect is associated with rather slight changes in vascular reactivity that are suggestive of a slight increase in NO elaboration by the endothelium. The discordance between the effects of dietary arginine on vascular structure and reactivity suggests that the antiatherogenic effects of the NO precursor may not be mediated entirely by its effect on the endothelium.

Outcome of narrowing related side branches after high-speed rotational atherectomy

High-speed rotational atherectomy (HSRA) is advocated for calcified and diffusely narrowed coronary arteries. There are often side branches involving these kinds of lesions. The presence of significant lesion-related side branches has been considered a relative contraindication to rotational atherectomy. This study was performed to determine the rate, predictors, and outcome of side branch occlusion after HSRA. The angiograms of 418 patients were examined with 320 side branches in 240 target vessels of > or = 1 mm in diameter being identified. Vessels were scored as either perfused (Thrombolysis In Myocardial Infarction 2 or 3 flow) or occluded (Thrombolysis In Myocardial Infarction 0 or 1 flow before and after the procedure. A detailed quantitative angiographic analysis was performed on a total of 108 side branches including all cases of branch occlusion. Clinical outcomes were determined in all cases with side branch loss. There were 24 occlusions in 21 patients after the procedure, giving a rate of branch loss of 7.5%. Follow-up angiography of > or = 24 hours was available for 13 of the occluded branches and 12 were found to be patent. In the 21 patients with branch occlusion, 6 sustained a myocardial infarct (of which 5 were non-Q-wave), 2 underwent coronary artery bypass grafting, and 2 died. There are frequently lesion-associated side branches in the types of vessels to undergo HSRA. These branches remained patent 92.5% of the time, with occlusion occurring infrequently and usually being transient. When occlusion did occur, there was a 29% incidence of myocardial infarction.

Felodipine Inhibits Intimal Lesion Formation in the Hypercholesterolemic Rabbit: Differential Effects on Endothelial and Monocyte Determinants of Atherogenesis

The purpose of this study was to determine if the calcium entry antagonist felodipine inhibited intimal lesion formation in hypercholesterolemic rabbits, and to determine if this was due to an effect upon monocyte and/or endothelial determinants of this interaction. Twenty-three male New Zealand White rabbits received the following treatment regimen for 10 weeks: normal chow (NP, n = 3); normal chow with felodipine infusion (NF, n=6); 0.5% cholesterol chow (CP, n = 7); or 0.5% cholesterol chow and felodipine infusion (CF, n=7). After 10 weeks blood was collected for biochemical measurements and mononuclear cell binding assays, and thoracic aortae were harvested for vascular reactivity studies and histomorphometry. In the animals receiving normal chow, felodipine did not significantly affect blood pressure, plasma cholesterol levels, binding studies, vascular reactivity, or structure; therefore these animals were analyzed as one group (N). Plasma cholesterol levels were significantly elevated in groups receiving the 0.5% cholesterol diet (N, 29±3 mg/dl; CP, 1221±73 mg/dl; CF, 979±108 mg/dl). High-density lipoprotein cholesterol was not different between the groups (25±4 vs 23±4 vs 27±4 mg/dl; N vs CF vs CP respectively; p=NS). Cholesterol feeding markedly augmented the adhesiveness of mononuclear cells, as demonstrated by a 250% increase in cell binding. Felodipine did not alter the adhesiveness of mononuclear cells in hypercholesterolemic animals. Cholesterol feeding significantly impaired endothelium-dependent relaxations. Endothelium-dependent relaxations were restored by felodipine treatment as reflected by the maximal responses to acetylcholine (40±7% vs 58±4% vs 67±5%; CP vs CF vs N respectively). The improvement in endothelium-dependent relaxation in the felodipine-treated animals was associated with a 2.2-fold reduction in lesion surface area of the thoracic aorta (8.2±6.3% vs 18.2±9.5%; CF vs CP; p<0.01). Moreover, the intima/media ratio reflecting lesion thickness was substantially reduced by felodipine treatment (0.05±0.02 vs 0.20±0.07; CF vs CP; p=0.006). Ex vivo studies revealed that felodipine inhibited the adhesiveness of vascular endothelium, but not mononuclear cells, derived from hypercholesterolemic animals. Low-dose felodipine appears to inhibit monocyte-endothelial interaction, as indicated by a reduction in the formation of lesions in hypercholesterolemic animals. This effect is not due to an alteration in adhesiveness of mononuclear cells. The salutary effect of felodipine is associated with an increase in vascular nitric oxide activity which may reduce endothelial adhesiveness.

High-speed rotational atherectomy: Six-month serial quantitative coronary angiographic follow-up

One hundred twenty-three patients treated with high-speed rotational atherectomy (HSRA) were restudied 6.9 +/- 1.2 months later. At the follow-up, the number of focal concentric lesions increased from 32.2 percent to 63.0 percent, p<0.01, with decrease of type C lesions from 54.8 percent to 30.8 percent, p<0.05. Comparison of the degree of the net gain (NG) showed more severe baseline lesions in the high-gain group (NG >20 percent) compared with the moderate-gain group (20 percent > NG > 0 percent) and to the loss group (minimal luminal diameter [MLD] 0.8 +/- 0.4 mm vs 1.0 +/ 0.4 mm, p<0.05; and 1.2 +/- 0.5 mm; p<0.01, respectively). Highest initial gain (36.5 percent +/- 26.2 percent vs 24.5 percent +/- 18.1 percent; p<0.015; and 19.0 percent +/- 23.2 percent; p<0.001) as well as lowest late loss (1.8 percent +/- 21.7 percent vs 14.0 percent +/-18.4 percent; p<0.01 and 28.1 percent +/- 25.0 percent; p<0.01) were found in the high NG group. A higher interaction between burr and atheroma resulted in the lowest restenosis rate of 6 percent.