PDGFbeta receptor blockade inhibits intimal hyperplasia in the baboon

BACKGROUND

We have evaluated the use of a mouse/human chimeric anti-platelet-derived growth factor-beta receptor antibody in combination with heparin to inhibit intimal hyperplasia in the saphenous artery of the baboon after balloon angioplasty.

METHODS AND RESULTS

The study evaluated lesion development in sequential injuries made 28 days apart. Each animal received control treatment after the first injury and antibody/heparin therapy after the second injury to the contralateral artery. The antibody was administered by bolus intravenous injections (10 mg/kg) on study days 1, 4, 8, 15, and 22 and heparin coadministered by continuous intravenous infusion at a dose of 0.13 mg/kg per hour. Morphometric analysis of tissue sections showed a 53% decrease in intimal area after antibody/heparin treatment (P=0.005), corresponding to a 40% decrease in the intima-to-media ratio (P=0.005). Smooth muscle cell proliferation in the injured wall, measured at both 4 and 29 days after balloon injury, were similar in the control and antibody/heparin-treated animals.

CONCLUSIONS

These data suggest that platelet-derived growth factor plays a key role in the development of intimal lesions at sites of acute vascular injury in the nonhuman primate.

Heparin inhibits the expression of tissue-type plasminogen activator by smooth muscle cells in injured rat carotid artery

Smooth muscle cells (SMCs) in balloon-injured rat carotid artery express tissue-type plasminogen activator (t-PA) at a time when they are migrating from the media to the intima. Since heparin inhibits SMC migration and intimal thickening, we have examined the possibility that heparin might also inhibit t-PA expression. Heparin (nonanticoagulant fraction; molecular weight, approximately 6,000) was administered by continuous intravenous infusion (1.0 mg/kg per hour) to Sprague-Dawley rats subjected to balloon injury of the left common carotid artery. At various times up to 14 days after injury, plasminogen activator expression was analyzed by zymography, plasmin generation, enzyme-linked immunosorbent assay, Northern blotting, and in situ hybridization. This dose of heparin inhibited SMC accumulation at 14 days by 60%. Both urokinase plasminogen activator (u-PA) and t-PA activity increased in injured arteries and reached a maximum at 7 days. Heparin treatment decreased t-PA, but not u-PA, activity. Total t-PA protein was decreased by treatment with heparin but not chondroitin sulfate, and the decrease in t-PA protein was associated with decreased t-PA mRNA in the media. These results in the injured rat carotid artery agree with our earlier observations that heparin inhibits t-PA gene expression in cultured baboon aortic SMCs. They also provide support for the hypothesis that heparin interferes with the expression of certain proteases required for SMC migration and proliferation.

Metabolism of low density lipoprotein by bovine endothelial cells as a function of cell density

The amount of low density lipoprotein (LDL) bound to the LDL receptor of bovine aortic endothelial cells at widely varying cell densities was measured by two methods: the commonly used dextran-sulfate-release method after LDL binding at 0-4 degrees C, and the method of assay of the LDL internalized in 30 minutes at 37 degrees C after LDL binding at 0-4 degrees C. Values obtained for LDL binding by the two methods were similar. At cell densities ranging from very sparse (6 X 10(3) to very dense (greater than 10(6) cells/cm2), both binding and degradation of 125I-LDL decreased in a nonlinear but parallel manner as cell density increased. This change began to occur at subconfluent densities and appeared to be not simply the result of establishment of a confluent cell layer. Thus, endothelial cells respond to changes in cell density with reciprocal changes in LDL metabolism in the same manner as reported for fibroblasts, so that at confluency both LDL receptor activity and LDL degradation are very low.

Regulation of low-density lipoprotein metabolism by cell density and proliferative state

Stimulation of the proliferation of human skin fibroblasts by platelet-derived growth factor increased the binding and degradation of low-density lipoproteins at cell densities of 2000-30,000 cells/cm2. Binding and degradation of low-density lipoprotein was an inverse function of cell density in both proliferating and quiescent cells, indicating that the effect of cell density on the LDL receptor has proliferation-dependent and proliferation-independent components. The effect of medium conditioned by confluent fibroblasts on LDL metabolism was tested to determine if the effects of cell density on LDL metabolism might be mediated by cellular secretion products. Fibroblast-conditioned medium increased LDL metabolism, suggesting secretion products do not mediate these effects of cell density. These data indicate that regulation of the low-density lipoprotein receptor is not a simple on/off response to growth stimulation, but is responsive to extracellular cues such as cell density.

Alterations of plasma HDL lipids and apolipoproteins in female rats treated with ethynyl estradiol

Female Sprague-Dawley rats (160-200 g body weight) were injected subcutaneously daily for 14 days with 1, 5, 15, 50 or 100 micrograms ethynyl estradiol in sesame oil/kg body weight, or with oil alone. Food consumption was restricted to 15 g/day, and animals were fasted overnight before exsanguination. Concentrations of plasma cholesteryl ester decreased with increasing dosage of ethynyl estradiol, as a result of decreases in HDL cholesteryl ester. Concentrations of plasma unesterified cholesterol were not altered by treatment; the tendency for a decrement in the HDL cholesterol was not statistically significant. Plasma and HDL phospholipid also tended to decrease with increasing dose of ethynyl estradiol. Plasma levels of apolipoprotein A-I increased on treatment with 5 micrograms ethynyl estradiol/kg but were diminished at a dose of 50 micrograms ethynyl estradiol/kg. The ultracentrifugally isolated high density lipoproteins were delipidated and the distribution of apolipoproteins was characterized by SDS-polyacrylamide gel electrophoresis and esoelectric focusing. The proportion of apolipoprotein E in HDL was depressed, while apolipoprotein A-I was increased and apolipoprotein C unchanged by treatment with ethynyl estradiol. Clearly, the alterations in plasma HDL lipid levels resulting from treatment with ethynyl estradiol were accompanied by distinct changes in composition of the apolipoproteins of HDL, and a biphasic response dependent on dose of the drug. A possible mechanism for the diminution in the proportion of HDL apolipoprotein E may be the enhanced removal of the apolipoprotein E-rich (HDL1) subfraction of the HDL from the circulation on treatment with ethynyl estradiol.

The effects of 17 beta-estradiol and progesterone on the metabolism of free fatty acid by perfused livers from normal female and ovariectomized rats

To determine whether any interaction occurs between progesterone and 17 beta-estradiol in the regulation of FFA metabolism by the liver, normal female rats were injected sc daily for 14 days with 7.5, 15, 50, or 100 microgram 17 beta-estradiol/kg, 25 mg progesterone/kg, 15 microgram 17 beta-estradiol plus 25 mg progesterone/kg, or vehicle (sesame oil) alone. To determine the effects of these hormones in the absence of endogenous estradiol and progesterone, ovariectomized rats were treated with the steroids. Livers were removed from the variously treated rats and perfused in vitro in a recycling system. An albumin-oleate complex was infused into the perfusate, providing a steady state concentration of 0.3--0.5 nM oleate. The uptake of FFA and output of ketone bodies and glucose by the livers were generally not altered by any of the steroid treatments. Neither these parameters nor triglyceride secretion was altered by ovariectomy. The administration of 15, 50, and 100 microgram estradiol/kg to normal, but not ovariectomized rats, increased triglyceride secretion. Progesterone alone had no effect on the secretion of triglyceride, but did antagonize the estradiol-mediated stimulation of triglyceride secretion in normal rats. The molar ratios of phospholipid to triglyceride and cholesterol to triglyceride of the very low density lipoprotein secreted by livers from normal females treated with estradiol were not altered, suggesting that the livers secreted more very low density lipoprotein particles of the same size. Based on the same criteria, livers from ovariectomized rats secreted smaller very low density lipoprotein particles compared to livers from control animals, an effect which was reversed by the administration of estradiol. We conclude that progesterone antagonizes the stimulation of hepatic triglyceride secretion by estradiol in normal female rats and that ovariectomy prevents this effect of progesterone.