Heparin suppresses endothelin-1 peptide and mRNA expression in cultured endothelial cells of spontaneously hypertensive rats

Alteration of endothelial proteoglycan and heparanase gene expression by high glucose, insulin and heparin

Heparan sulfate proteoglycans (HSPGs) contain a core protein with glycosaminoglycans attached. Reduced glycosaminoglycan, in endothelial HSPGs syndecan and perlecan, is associated with diabetic cardiovascular complications but changes in core protein remain controversial. Since heparanase degrades heparan sulfate, we wished to determine if changes in endothelial heparanase mRNA, by high glucose (HG), correlate with changes in syndecan and perlecan core proteins, and to observe effects of heparin or insulin. RNA was isolated from cultured human aortic endothelial cells treated with HG (30mM), insulin (0.01 units/mL), heparin (0.5μg/mL), HG plus heparin and/or insulin for 24h. Real time PCR revealed that HG alone significantly increased heparanase, decreased syndecan with no effect on perlecan mRNA. Heparin or insulin significantly prevented the increase in heparanase but decreased perlecan mRNA while heparin, but not insulin, prevented the decrease in syndecan mRNA in HG treated cells. HG plus heparin and insulin increased heparanase and syndecan mRNA compared to all other treatments and decreased perlecan mRNA compared to control and HG alone. Heparin may protect endothelium from HG injury by reducing heparanase and increasing syndecan while insulin inhibits heparanase expression. Effects with insulin plus heparin suggest interference in transcriptional regulation of heparanase and syndecan genes.

Changes in cultured endothelial cell glycosaminoglycans under hyperglycemic conditions and the effect of insulin and heparin

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) contain glycosaminoglycan (GAG) chains made primarily of heparan sulfate (HS). Hyperglycemia in diabetes leads to endothelial injury and nephropathy, retinopathy and atherosclerosis. Decreased HSPG may contribute to diabetic endothelial injury. Decreased tissue HS in diabetes has been reported, however, endothelial HS changes are poorly studied.

OBJECTIVE

To determine total GAGs, including HS, in endothelium under hyperglycemic conditions and the protective effect of insulin and heparin.

METHODS

Confluent primary porcine aortic endothelial cells (PAECs) were divided into control, glucose (30 mM), insulin (0.01 unit/ml) and glucose plus insulin treatment groups for 24, 48 and 72 hours. Additionally, PAECs were treated with glucose, heparin (0.5 microg/ml) and glucose plus heparin for 72 hours. GAGs were isolated from cells and medium. GAG concentrations were determined by the carbazole assay and agarose gel electrophoresis.

RESULTS

GAGs were significantly increased only in control and glucose plus insulin groups at 72 versus 24 hours. Glucose decreased cell GAGs and increased medium GAGs, and insulin alone decreased cell GAGs at all times compared to control. In the glucose plus insulin group, cell GAGs were less than control at 24 hours, and greater than glucose or insulin alone at 48 and 72 hours while GAGs in medium were greater than control at all times and glucose at 72 hours. Heparin increased GAGs in glucose treated cells and medium.

CONCLUSION

High glucose and insulin alone reduces endothelial GAGs. In hyperglycemic conditions, heparin or insulin preserves GAGs which may protect cells from injury. Insulin is an effective diabetic therapy since it not only lowers blood glucose, but also protects endothelium.

Microalbuminuria as a target to improve cardiovascular and renal outcomes in diabetic patients

Microalbuminuria has been shown to be a risk factor for adverse renal and cardiovascular outcomes in patients with diabetes mellitus. This risk appears to increase with higher levels of albuminuria. There is also evidence that reducing the level of albuminuria improves these outcomes. This review focuses on the most recent advances in this area and reviews literature over the past year on this topic.

Heparin Regulates Transcription of Endothelin-1 Gene in Endothelial Cells

Heparin, which is widely used as an anticoagulant, has been shown to have antiatherosclerotic and antihypertensive effects in animals and humans. These effects are mediated by the inhibition of endothelin-1 (ET-1) production in endothelial cells. To clarify the mechanism of this inhibition, we investigated the effect of heparin on transcriptional regulation of the ET-1 gene in bovine aortic endothelial cells (BAEC) cultured in fetal calf serum. ET-1 mRNA expression was significantly suppressed by heparin in a dose-dependent manner. Promoter analysis revealed that the minimum ET-1 promoter containing only the GATA and AP-1 sequences as positive cis-acting sites in the ET-1 promoter is sufficient for this suppression. Gel mobility shift assays using oligonucleotides encoding the ET-1 AP-1 and ET-1 GATA sites confirmed that both AP-1 and GATA binding activities in BAEC nuclear extract were markedly inhibited by heparin. Western blot analyses indicated that heparin completely blocked extracellular signal-regulated kinase (ERK) activation, and inhibiting ERK activity resulted in loss of heparin-dependent inhibition of the ET-1 gene. These data indicate that the ET-1 mRNA level is negatively regulated by heparin at the transcription level, through modification of AP-1 and GATA protein binding activities, which direct the ET-1 promoter in BAEC. This effect may be mediated, at least in part, through inhibition of ERK activity.

Regulation of endothelin-1 and transforming growth factor-beta1 production in cultured proximal tubular cells by albumin and heparan sulphate glycosaminoglycans

BACKGROUND

Both endothelin-1 (ET-1) and transforming growth factor beta 1 (TGF-beta1) have been implicated in the progression of interstitial fibrosis. In the present study we enquired if albumin influences the production of these factors in cultured human proximal tubular epithelial cells (PTEC) and if heparan sulphate glycosaminoglycans (HS-GAG) can inhibit this production.

METHODS

ET-1 and TGF-beta1 production in supernatants of PTEC was measured by RIA and ELISA respectively. In addition semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed to study differences in ET-1 and TGF-beta1 mRNA expression. To demonstrate ET-1 or TGF-beta1 binding to heparin or HS-GAG, binding studies by means of dot blot analysis were carried out.

RESULTS

TGF-beta1 and ET-1 were both produced in different concentrations, depending on the PTEC culture tested. Human serum albumin (HSA) up-regulated the production of both factors in a time and dose dependent fashion. The production of these factors was inhibited by heparin under basal and stimulatory conditions. ET-1 production was only inhibited by HS-GAG with a high degree of sulphation. For the inhibition of TGF-beta1 production, the sulphation of HS-GAG was less critical. TGF-beta1, but not ET-1 mRNA expression was inhibited by HS-GAG. Inhibition of sulphation of cell surface HS-GAG resulted in the inhibition of ET-1 but not TGF-beta1 production. Both factors were able to bind to HS-GAG, although this required different amounts of HS-GAG sulphation for each factor.

CONCLUSIONS

Our data demonstrate that in PTEC the release of pro-fibrogenic factors can be inhibited by HS-GAG. This may explain to some extent the beneficial effect of heparin in the treatment of interstitial fibrosis.

Heparin attenuates norepinephrine-induced venoconstriction

Reversal by heparin of norepinephrine-induced constriction of normal hand veins was studied. Venous size was measured using a linear variable differential transformer (LVDT) during infusions of saline, norepinephrine, insulin and norepinephrine, and graded doses of heparin with norepinephrine. Heparin reduced the venoconstrictive effects of norepinephrine (p < 0.01), with the effects beginning at 18.5 nmol/min (0.05 U/min) and reaching a maximum between 185 nmol/min and 1.85 mumol/min (0.5 and 5 U/min). Maximal heparin-induced venorelaxation correlated with the maximal insulin effect within individuals (r = 0.8, p < 0.01) and was unchanged by the addition of insulin. Methylene blue, a non-specific inhibitor of the nitric oxide cGMP cascade, reduced heparin-induced venorelaxation. In conclusion, heparin in either physiologic or pharmacologic concentration attenuated norepinephrine-induced venoconstriction. A common mechanism of venorelaxation by heparin and insulin is not excluded given the correlation and lack of additivity of maximum effects and their inhibition by methylene blue.

Heparin-induced vasodilation in human hand veins

OBJECTIVE

To investigate whether heparin produces vasodilation in human veins and to explore the underlying mechanisms.

METHODS

Eleven healthy volunteers were studied with the dorsal hand vein compliance technique. Dose-response curves to heparin and enoxaparin were generated. Dose-response curves to heparin were also constructed before and after heparin was infused with the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine (L-NMMA) or combined histamine H1- and H2-receptor blockade.

RESULTS

Heparin but not enoxaparin caused significant dose-dependent relaxation with an average apparent maximal response (at an infusion rate of 20 IU/min) of 47% +/- 23%. L-NMMA attenuated heparin-induced relaxation (P < .001). The combination of H1-and H2-receptor antagonists attenuated heparin-induced relaxation to a lesser extent (P < .05). Heparin-induced relaxation decreased by 52%, 73%, and 35% in the presence of L-NMMA, indomethacin (INN, indometacin) plus L-NMMA, and combined H1- and H2-receptor blockade, respectively.

CONCLUSION

Heparin is an endothelium-dependent venodilator in humans. The mechanism of heparin-induced relaxation involves an increased availability of nitric oxide, possibly partially related to local release of histamine.

Heparin inhibits human coronary artery smooth muscle cell migration

Heparin, an anticoagulant, has been shown to reduce neointimal proliferation and restenosis following vascular injury in experimental studies, but the clinical trials of heparin in coronary balloon angioplasty have been negative. The current study, therefore, examined the effect of heparin on basal or stimulated migration by serum and platelet-derived growth factor (PDGF)-BB in cultured human coronary artery smooth muscle cells (SMCs) by Boyden's chamber method. In addition, the reversibility of the heparin effect on human coronary artery SMC migration was examined. Fetal calf serum (FCS) and PDGF-BB stimulated SMC migration in a concentration-dependent manner. Heparin in moderate to high concentration (10 to 100 U/mL) exhibited concentration-related inhibition of FCS- and PDGF-BB-stimulated SMC migration; however, a low concentration (1 U/mL) of heparin had no inhibitory effects. Heparin also had weak inhibitory effects on nonstimulated SMC migration. The SMCs that were exposed to a high concentration (100 U/mL) of heparin for 6 hours were capable of migrating after a short lag period of removal of heparin from the culture medium. These SMCs also showed recovery of responses to FCS and PDGF-BB by migrating significantly greater than the nonstimulated level. Furthermore, heparin-containing medium did not contain detached cells. These results indicate that heparin inhibits human coronary artery SMC migration, especially when stimulated by FCS or PDGF-BB, and that this inhibitory effect of heparin is reversible and not simply a function of killing cells.

Heparin decreases blood pressure and response to exogenous endothelin but does not protect against chronic experimental cyclosporine nephropathy

Cyclosporine nephrotoxicity is caused by renal arteriolar vasoconstriction and tubulointerstitial fibrosis. Endothelin has been proposed as a major mediator of these phenomena. Heparin inhibits vascular smooth muscle cell proliferation and lowers blood pressure by regulating endogenous endothelin 1 production. In a model of chronic cyclosporine nephrotoxicity in the rat, animals were treated with cyclosporine alone, cyclosporine plus heparin, and heparin alone for 28 days. Independent experiments determined that these doses of heparin resulted in a marked decrease in responsivity to exogenous endothelin. Despite this, there were no beneficial effects on renal structure or function in this animal model of chronic cyclosporine nephrotoxicity. Thus, the role of endothelin in the pathogenesis of the chronic tubulointerstitial changes and arteriolopathy in this model is probably minor.

Heparin-induced endothelial cell cytoskeletal reorganization: a potential mechanism for vascular relaxation

We have previously shown that heparin given subcutaneously on a daily basis lowers blood pressure in hypertensive rat models, and that this blood pressure lowering effect is endothelium-dependent. The present study describes the effects of heparin on endothelial cell (EC) apical surface structures and cytoskeletal elements, namely, actin and vimentin as well as EC proliferative activity. The EC line (CRL 1998) was cultured, treated with different concentrations of heparin (0, 50, 100, 500 U/ml) for 4, 24 or 48 hours, and fixed for scanning electron microscopy (SEM), and immunofluorescence microscopy (IFM) studies. Enzyme-linked immunosorbent assays (ELISA) and flow cytometric analysis were performed on EC monolayers treated with different concentrations of heparin for quantitative detection of actin and vimentin. By SEM study the cell surface showed generalized smoothing as a result of blunting of surface microvilli with increasing time of exposure and dosage of heparin. By IFM study, the detectable actin signal within ECs became progressively reduced in both its cellular distribution and the apparent number of cells that remained reactive. By 48 hr/500 U heparin, the actin signal was almost undetectable. Vimentin showed a moderate reduction in the cellular distribution of labeling. Quantitatively, actin was significantly reduced after the 24 hour treatment with a higher dose of heparin (500 U/ml), from a baseline optical density (OD) of 1.12 +/- 0.060 to 0.866 +/- 0.008 (P < 0.0027). After 48 hours of treatment at both 100 U/ml and 500 U/ml heparin, actin was significantly reduced from a baseline OD of 1.347 +/- 0.063 to 1.090 +/- 0.039 (P < 0.0039) and 0.844 +/- 0.074 (P < 0.008), respectively. However, vimentin was significantly reduced only after 48 hours of treatment with a high dose of heparin (500 U/ml), from baseline OD 1.82 +/- 0.052 to 1.41 +/- 0.004 (P < 0.002). The flow cytometric findings were virtually identical to the ELISA data for actin and vimentin. These qualitative and quantitative changes in actin and vimentin are consistent with apparent smoothing and relaxation of the EC's apical surface. Labeling with the cell cycle marker MIB-1 (monoclonal antibody Ki-67), showed a progressive reduction in the observed intensity in heparin treated cells with substantially fewer cells being positive. After a 48 hour treatment with heparin (500 U/ml), most ECs displayed only dim labeling of the nucleolus. This finding is consistent with an antiproliferative effect. Overall, these findings are additive to our previous observations, and demonstrate that heparin causes EC cytoskeletal reorganization which is a potential mechanism for vascular relaxation.