Rabbit aortic smooth muscle cell culture. A model for the pharmacological study of diabetes-induced alterations in cell proliferation

Possible involvement of enhanced arginase activity due to up-regulated arginases and decreased hydroxyarginine in accelerating intimal hyperplasia with hyperglycemia

The present study was designed to investigate the roles of enhanced arginase activity due to up-regulated arginases and the decreased hydroxyarginine for accelerating intimal hyperplasia with hyperglycemia. Thirteen weeks after injection of alloxan or physiological saline, endothelial denudation of the carotid artery was performed to induce intimal hyperplasia. The intimal hyperplasia occurred on 4 weeks following denudation was significantly accelerated by hyperglycemia. The method to measure L-arginine, endogenous NOS inhibitors such as monomethylarginine and asymmetric dimethylarginine, and hydroxyarginine as an intermediate of NO production simultaneously was established with the aid of high-performance liquid chromatography. In hyperglycemia group, the impaired cyclic GMP production as an indicator of NO production in endothelial cells was accompanied by the enhanced arginase activity together with increased expression of arginase I and II proteins, accumulated endogenous NOS inhibitors, reduced concentration of hydroxyarginine, and decreased DDAH activity in endothelial cells. However, NOS activity per se remained unchanged in the hyperglycemia group. Authentic hydroxyarginine inhibited arginase activity in a concentration-dependent manner. The inhibition of arginase with hydroxyarginine at a reduced concentration with hyperglycemia became significantly lower than that for the control. These results suggest that the accelerated intimal hyperplasia with hyperglycemia is closely related to the impaired NO production in endothelial cells, which results from accumulation of endogenous NOS inhibitors and accelerated arginase activity together with up-regulation of arginase I and II proteins. Decreased DDAH activity would bring about the accumulation of endogenous NOS inhibitors. Furthermore, reduced concentration of hydroxyarginine with hyperglycemia possibly results in an enhanced arginase activity in vivo, implicating partly in the impairment of NO production.

Possible involvement of facilitated polyol pathway in augmentation of intimal hyperplasia in rabbits with alloxan-induced hyperglycemia

Present experiments were designed to investigate whether the facilitated polyol pathway is involved in the augmentation of intimal hyperplasia with hyperglycemia. Twelve weeks after a single bolus intravenous injection of alloxan (100 mg/kg) or saline, rabbits underwent a unilateral endothelial denudation of the carotid artery. Intimal hyperplasia was evident 4 weeks after denudation and significantly augmented in hyperglycemic animals treated with alloxan. This effect was accompanied by the enhanced accumulation of endogenous NOS inhibitors (N(G)-monomethyl-l-arginine [l-NMMA] and asymmetric, N(G),N(G)-dimethyl-l-arginine [ADMA]) in regenerated endothelial cells, impairment of NO production and release, and enhanced accumulation of endothelin-1 (ET-1) within the vessel wall. Sorbitol levels in aortic endothelial cells and within the smooth muscle layer were significantly increased with hyperglycemia. All these changes associated with hyperglycemia were significantly reduced in animals treated with the selective aldose reductase inhibitor fidarestat (3 mg/kg/d). These findings suggest that the facilitated polyol pathway possibly plays an important role for the augmentation of intimal hyperplasia caused by the hyperglycemic state.

Cyclosporin effect on rat aorta alpha(1)-adrenoceptors and their transduction mechanisms

A possible explanation for cyclosporin-induced arterial hypertension may be its action on the adrenergic system. In spite of the controversial results reported in literature, it seems that cyclosporin changes the vascular response to noradrenaline. Therefore, after observation that two cyclosporin doses increase rat blood pressure and vascular reactivity in response to noradrenaline, the aim of this work was to study the cellular mechanisms beside the cyclosporin-induced changes in response to noradrenaline. Therefore, the cyclosporin influence on alpha(1)-adrenoceptors as well as on their transduction mechanism in smooth muscle cells was studied. Through Scatchard analysis of specific [(3)H]-prazosin binding, the alpha(1)-adrenoceptor number and related affinity were studied, before and after cyclosporin exposure. The cyclosporin influence on alpha1-adrenoceptor transduction mechanisms was also evaluated by the quantification of intracellular free calcium contents [Ca2+]i and inositol phosphate (InsP) turnover. All in vitro experiments were performed in rat aortic smooth muscle cells in culture. Results showed that both cyclosporin concentrations (10(-6) and 10(-7) M) changed alpha1-adrenoceptor number but only 10(-7) M cyclosporin increased its affinity for [(3)H]-prazosin. Compared with control cells, only 10(-7) M cyclosporin increased InsP levels. Stimulation by noradrenaline increased InsP in 10(-7) M cyclosporin-treated cells but decreased InsP in the presence of 10(-6) M cyclosporin. Both cyclosporin concentrations increased [Ca2+]i in basal conditions and after noradrenaline stimulation. The results suggest that after noradrenaline stimulation cyclosporin increases [Ca2+]i, probably through different mechanisms, depending on the cyclosporin concentration used. However, 10(-7) M cyclosporin increases alpha1-adrenoceptor affinity and their related transduction mechanisms. The higher cyclosporin concentration (10(-6) M) seems to induce downregulation of alpha1-adrenoceptors, probably by activation of protein kinase C.

Inhibition of rat vascular smooth muscle cell proliferation by taurine and taurine analogues

The growth of rat aorta vascular smooth muscle cells (VSMCs) was measured in the presence and absence of taurine. Concentrations of taurine as low as 0.3 mM in the culture medium inhibited the proliferation of the cells, as monitored by measuring cell count, and also inhibited the rate of DNA synthesis, as examined by measuring [3H]thymidine incorporation into DNA. However, even at the highest concentration of taurine (30 mM), the doubling time of the VSMCs was only increased by 38%. Protein content of the VSMCs was decreased by 30 mM taurine. [3H]Leucine incorporation into newly synthesized protein was not affected by the highest concentration of taurine tested (30 mM), indicating that taurine did not inhibit protein synthesis but rather decreased total protein content by inhibiting cellular proliferation. The effects of other amino acids such as alanine, glycine, and serine and of various taurine analogues such as beta-alanine, guanidinoethanesulfonic acid (GES), and isethionic acid also were tested at a concentration of 20 mM for their effects on the growth of the VSMCs. Alanine, glycine, and serine had only a minimal effect or no effect on cell count, quantity of protein, and incorporation of [3H]thymidine into DNA. GES, beta-alanine, and isethionic acid had a significant effect on cell count, protein content, and incorporation of [3H]thymidine into DNA. Beta-alanine was the only analogue tested that significantly depressed [3H]leucine incorporation into newly synthesized protein. It is concluded that taurine, GES, and isethionic acid inhibited proliferation of VSMCs but did not alter normal protein synthesis or survivability of VSMCs. In contrast, other amino acids, alanine, glycine and serine, had minimal effects on VSMC proliferation and protein synthesis, whereas beta-alanine appeared to be toxic, inhibiting both VSMC synthesis and de novo protein synthesis.

Accelerated intimal hyperplasia and increased endogenous inhibitors for NO synthesis in rabbits with alloxan-induced hyperglycaemia

1. We examined whether endogenous inhibitors of NO synthesis are involved in the augmentation of intimal hyperplasia in rabbits with hyperglycaemia induced by alloxan. 2. Four weeks after the endothelial denudation of carotid artery which had been performed 12 weeks after alloxan, the intimal hyperplasia was greatly augmented with hyperglycaemia. The degree of hyperplasia was assessed using three different parameters of histopathological findings as well as changes in luminal area and intima: media ratio. 3. There were positive and significant correlations between intima:media ratio, plasma glucose, and concentrations of N(G)-monomethyl-L-arginine (L-NMMA) and N(G), N(G)-dimethyl-L-arginine (ADMA) in endothelial cells, that is, the intima:media ratio became greater as plasma glucose and endothelial L-NMMA and ADMA were increased. Furthermore, endothelial L-NMMA and ADMA were increased in proportion to the increase in plasma glucose. 4. In contrast, there were inverse and significant correlations between cyclic GMP production by carotid artery strips with endothelium and plasma glucose, between cyclic GMP production and endothelial L-NMMA and ADMA, and between the intima:media ratio and cyclic GMP production. 5. Exogenously applied L-NMMA and ADMA inhibited cyclic GMP production in a concentration-dependent manner. IC50 values were determined to be 12.1 microM for the former and 26.2 microM for the latter. The cyclic GMP production was abolished after the deliberate removal of endothelium from the artery strips. 6. These results suggest that the augmentation of intimal hyperplasia with hyperglycaemia is closely related to increased accumulation of L-NMMA and ADMA with hyperglycaemia, which would result in an accelerated reduction in NO production/release by endothelial cells.

Effect of cyclosporin A on rat smooth-muscle cell proliferation

Cyclosporin A (CsA) is a potent immunosuppressive agent that has significantly improved graft survival in organ- and bone-marrow-transplant recipients. However, in the context of graft transplantation, CsA has been suggested to potentiate vascular disease by stimulating smooth-muscle cell (SMC) proliferation. As previous studies on the effect of CsA on smooth-muscle proliferation have afforded conflicting results, we conducted an in vitro study of the effect of two concentrations of CsA--10(-6) M (corresponding to the maximal concentration in patients) and 10(-7) M (corresponding to trough concentrations)--on cultured rat SMC proliferation, as assessed by [3H]thymidine incorporation into DNA and measuring cell number by a colorimetric method based on the quantitative staining of cell nuclei. In the presence of 0.5% fetal calf serum (FCS), 10(-6) M CsA induced an increase in [3H]thymidine incorporation into DNA (from 614.44 +/- 67.76 to 1,472.6 +/- 177.63 cpm/well; p < 0.05) with no increase in the number of cells. A cytotoxic effect for this dose was ruled out owing to the absence of significant levels of lactate dehydrogenase (LDH) activity in the supernatant. CsA, 10(-7) M, induced an increase in both [3H]thymidine incorporation into DNA (from 614.44 +/- 67.76 to 1,220.91 +/- 145.59 cpm/well) and cell number (82.49 +/- 6.16 to 165.79 +/- 10.48 cells x 10[3]; p < 0.05). In the presence of 10% FCS, the highest CsA concentration increased [3H]thymidine incorporation to 2,115.91 +/- 224.06 cpm/well, with no significant changes in cell number. However, the lowest CsA concentration increased both [3H]thymidine incorporation (to 3.752.58 +/- 525.06 cpm/well) and cell number (to 181.27 +/- 14.2 cells x 10[3]). These findings suggest that the proliferative effect of CsA on SMCs is variable and that it depends on the concentration of the drug, in support of the discordant results reported previously.

Effect of glycated collagen on proliferation of human smooth muscle cells in vitro

While non-enzymatic glycation of long-lived tissue proteins such as collagen has been implicated in chronic complications of diabetes mellitus, its role in the aetiology of diabetic macroangiopathy has not been elucidated. To test the hypothesis that glycation of collagen abolishes the inhibitory effect of native collagen on the proliferation of human smooth muscle cells, we obtained smooth muscle cells from human gastric arteries and cultured them on dishes coated with glycated or non-glycated collagen. The proliferation of human smooth muscle cells in the presence of 10% fetal calf serum or platelet derived growth factor-BB (10 ng/ml) was inhibited by type 1 collagen coated on the dishes. Glycation of collagen with glucose 6-phosphate for 7 days abolished the growth-inhibitory effect of native collagen. Succinylation of collagen, which like glycation blocked the lysyl residues in collagen, also abolished the growth-inhibitory effect. Adhesion of human smooth muscle cells to collagen-coated dishes was not affected by glycation of collagen. Addition of glycated albumin to the medium did not affect the growth of human smooth muscle cells on plastic dishes. The inhibition of human smooth muscle cell proliferation by collagen was not reversed by the glycation of collagen in the presence of aminoguanidine. Results suggest that early glycation abolishes the inhibitory effect of collagen on human smooth muscle cell proliferation and may thus participate in the progression of macro-angiopathy in diabetes.

Enhanced antiproliferative effect of nitric oxide in cultured smooth muscle cells from diabetic rats

We examined the influence of experimental diabetes on the proliferation of cultured vascular smooth muscle cells (VSMCs) in presence of a nitric oxide (NO)-generating agent, sodium nitroprusside (SNP), and 8-bromo-cGMP. VSMC cultures were prepared from aortas of control and streptozotocin-diabetic rats. SNP induced a time- and dose-dependent inhibition of control and diabetic VSMC proliferation, consistent with the data on [3H]thymidine incorporation, cell counts, and index of culture mass. However, the responses to SNP were significantly enhanced in VSMCs from diabetic rats. SNP induced an increased dose-dependent accumulation of intracellular cGMP in diabetic VSMCs. In contrast, growth-inhibitory responses to 8-bromo-cGMP were not significantly different between the two VSMC models. Moreover, basal cGMP content in VSMCs was lower in diabetic rats than in controls, a result that can explain the enhanced proliferation observed in VSMCs from diabetic rats. These results suggest an enhanced antiproliferative effect of NO in VSMCs from diabetic rats through increased cGMP production. Therefore, experimental diabetes may impair and up-regulate soluble guanylate cyclase activity in VSMCs.

Increased mitogenic response to heparin-binding epidermal growth factor-like growth factor in vascular smooth muscle cells of diabetic rats

We investigated the mitogenic effects of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in vascular smooth muscle cells (SMCs) obtained from rats with streptozotocin (STZ)-induced diabetes and evaluated the role of heparan sulfate proteoglycan (HSPG) in inducing these effects. HB-EGF significantly increased DNA synthesis in the SMCs of diabetic rats (STZ-SMCs) compared with control rats (control SMCs). However, the mitogenic effects of EGF, which shares EGF receptors with HB-EGF, and basic fibroblast growth factor, another heparin-binding growth factor, were similar in STZ-SMCs and control SMCs. The mitogenic response to HB-EGF in SMCs of insulin-treated diabetic rats was similar to the response in control SMCs. HB-EGF-induced autophosphorylation of EGF receptors was increased in STZ-SMCs compared with control SMCs, although the number of EGF receptors in STZ-SMCs was 40% of that in controls. This increased mitogenic response to HB-EGF in STZ-SMCs was completely inhibited by treatment with heparitinase, chlorate, and a synthetic peptide corresponding to the heparin-binding domain of HB-EGF. Compared with heparan sulfate isolated from control SMCs, heparan sulfate isolated from STZ-SMCs was of smaller molecular size and caused a greater mitogenic effect of HB-EGF. These findings suggest that the mitogenic response to HB-EGF is increased in SMCs of diabetic rats. Changes in cell-associated heparan sulfate in STZ-SMCs may be related to the increased mitogenic response to HB-EGF.

Responses of vascular smooth muscle cells to toxic insult: cellular and molecular perspectives for environmental toxicants

Over the past several decades emphasis has been given to the elucidation of mechanisms involved in the onset and progression of cardiovascular disorders. Stroke, hypertension, and atherosclerosis continue to rank as primary causes of death in the western world. In the case of atherosclerosis, the preferential localization of atheroma to large- and medium-sized blood vessels and the sequence of events leading to plaque development have been well defined. Damage to luminal endothelial and/or medial smooth muscle cells, migration of inflammatory cells, diffusion or local delivery of mediators within the vessel wall, proliferation of vascular smooth muscle cells, and cellular accumulation of lipids are now recognized as hallmarks of the pathologic process. Although these events have been established with a fair degree of certainty, the mechanisms responsible for initiation of the atherosclerotic process are not yet completely understood. Environmental chemicals have come under increasing scrutiny as evidence continues to accumulate suggesting that toxic insult plays an important role in the initiation and/or progression of atherosclerotic disorders. This review focuses on various aspects of xenobiotic-induced vascular injury with emphasis on the toxic effects of allylamine and benzo[a]pyrene in smooth muscle cells, the primary cellular component of atherosclerotic lesions. Both of these chemicals modulate growth and differentiation programs in aortic smooth muscle cells and have been implicated in the development of atherosclerotic-like lesions in laboratory animals. The major findings from recent studies examining the cellular and molecular basis of toxicant-induced phenotypic modulation of vascular smooth muscle cells to a proliferative state and the role of oxidative metabolism, phospholipid turnover, protein kinase C, ras-related signal transduction, and matrix interactions in the vasculotoxic response to allylamine and benzo[a]pyrene are discussed.

Diabetes mellitus induces accelerated growth of aortic smooth muscle cells: association with overexpression of PDGF beta-receptors

The mechanism of diabetic macroangiopathy was studied from the view point of phenotypic change of aortic smooth muscle cells (SMC). The growth rates of cultured SMC of diabetic rats or rabbits were higher than those of non-diabetic animals (controls). This difference of the growth responses was observed specifically with platelet-derived growth factor (PDGF). Of the three PDGF dimers, PDGF-AB heterodimer (PDGF-AB) and PDGF-BB homodimer (PDGF-BB) stimulated growth of diabetic SMC more than that of control SMC but PDGF-AA homodimer (PDGF-AA) did not. The binding of 125I-PDGF to the diabetic SMC was greater than that to control SMC. This was due to increase in the number of cell surface receptors for PDGF. On in vitro culture, SMC from diabetic rats expressed more PDGF beta-receptor mRNA than SMC from non-diabetic rats. Moreover, in vivo, the aortic media of diabetic rabbits expressed PDGF beta-receptor mRNA, but that from non-diabetic rabbits did not. Thus diabetic SMC over-react on PDGF stimulation through over-expression of the PDGF beta-receptor gene. The significance of this fact in development of diabetic macroangiopathy is discussed.