Calcium and protein kinase C mediate high-glucose-induced inhibition of inducible nitric oxide synthase in vascular smooth muscle cells

Evaluation of antihypertensive potential of Ficus carica fruit

CONTEXT

Ficus carica L. (Moraceae) fruit is said to possess cardiovascular activity and has been used empirically in traditional phytotherapies for the treatment of hypertension and various other cardiovascular diseases.

OBJECTIVE

This study investigated the antihypertensive and cardioinhibitory activity of the aqueous-methanol extract of F. carica fruit in rats.

MATERIALS AND METHODS

Extract in 250, 500 and 1000 mg/kg doses (p.o.) were administered to normotensive Sprague Dawley rats and blood pressure was measured using non-invasive technique. Hypertension was induced in rats by oral administration of 10% glucose for 3 weeks. Hypotensive effect of extract (1000 mg/kg p.o) was studied in normotensive and glucose-treated hypertensive rats. Langendorff's isolated heart technique was used to assess the effect of crude extract on force of contraction and heart rate. In addition, antioxidant potential, TPC, TFC were also assessed by DPPH free radical scavenging activity, Folin-Ciocalteu reagent and AlCl3 assay, respectively. Furthermore, phenolic compounds were analyzed using HPLC-DAD technique.

RESULTS AND DISCUSSION

The 1000 mg/kg dose decreased blood pressure significantly in normotensive and glucose-treated hypertensive rats. The isolated heart study showed that the extract produced negative inotropic and chronotropic effects but it failed to block the stimulatory effect of both adrenaline and CaCl2. HPLC studies on the F. carica extract indicated the presence of quercetin, gallic acid, caffeic acid, vanillic acid, syringic acid, coumaric acid and chromotropic acid.

CONCLUSIONS

This study demonstrated that aqueous methanol extract of F. carica fruit exerted hypotensive and antihypertensive effects in glucose-induced hypertensive rats.

The promise of inhibition of smooth muscle tone as a treatment for erectile dysfunction: where are we now?

Ten years ago, the inhibition of Rho kinase by intracavernosal injection of Y-27632 was found to induce an erectile response. This effect did not require activation of nitric oxide-mediated signaling, introducing a novel target pathway for the treatment of erectile dysfunction (ED), with potential added benefit in cases where nitric oxide bioavailability is attenuated (and thus phosphodiesterase type 5 (PDE5) inhibitors are less efficacious). Rho-kinase antagonists are currently being developed and tested for a wide range of potential uses. The inhibition of this calcium-sensitizing pathway results in blood vessel relaxation. It is also possible that blockade of additional smooth muscle contractile signaling mechanisms may have the same effect. In this review, we conducted an extensive search of pertinent literature using PUBMED. We have outlined the various pathways involved in the maintenance of penile smooth muscle tone and discussed the current potential benefit for the pharmacological inhibition of these targets for the treatment of ED.

Curcumin improves prostanoid ratio in diabetic mesenteric arteries associated with cyclooxygenase-2 and NF-κB suppression

BACKGROUND

Curcumin, the active ingredient from turmeric rhizomes, has been shown to have a wide range of pharmacological properties including antioxidant and anti-inflammatory effects. Curcumin has been reviewed for its multiple molecular action on inhibiting tumor angiogenesis via its mechanisms of cyclooxygenase (COX)-2, and vascular endothelial growth factor (VEGF) inhibition. In this present study, we aimed to assess the effects of curcumin on preventing diabetes-induced vascular dysfunction in association with COX-2, nuclear factor-κB (NF-κB) expression, and prostanoid production.

METHODS

Twelve-week-old male Wistar rats were separated into five groups: 1) diabetes with 0.9% normal saline (DM-NSS; n =10), 2) diabetes treated with curcumin 30 mg/kg (n =10), 3) diabetes treated with curcumin 300 mg/kg (n =10), 4) the control with 0.9% normal saline (n =10), and 5) the control treated with 300 mg/kg (n =10). Daily oral feeding of curcumin was started at 6 weeks after the streptozotocin injection. Levels of 6-keto prostaglandin (PG) F(1α)and thromboxane (TX) B(2) were determined from mesenteric perfusates using enzyme immunoassay kits. Protein kinase C (PKC)-β II and COX-2 with NF-κB levels were analyzed in the mesenteric arteries by immunofluorescent staining and immunohistochemistry, respectively.

RESULTS

The ratio of 6-keto-PGF(1α)and TXB(2) was significantly decreased in DM-NSS compared with the control (P < 0.05). Double-immunofluorescent staining with specific antibodies for PKC-βII and α-smooth muscle actins showed that the diabetic mesenteric arteries contained increased of PKC-βII within the vascular wall. Also, COX-2 expression and activated NF-κB in the small mesenteric artery of diabetes mellitus rats were markedly increased when compared with the control. Interestingly, curcumin could inhibit the upregulation of all of these biomarkers.

CONCLUSION

These findings show that curcumin can attenuate diabetes-induced vascular dysfunction in association with its potential for COX-2 and NF-κB suppression, PKC inhibition, and improving the ratio of prostanoid products PGI(2)/TXA(2).

Glucose downregulation of PKG-I protein mediates increased thrombospondin1-dependent TGF-{beta} activity in vascular smooth muscle cells

Diabetes is a major predictor of in-stent restenosis, which is associated with fibroproliferative remodeling of the vascular wall due to increased transforming growth factor-beta (TGF-beta) action. It is well established that thrombospondin1 (TSP1) is a major regulator of TGF-beta activation in renal and cardiac complications of diabetes. However, the role of the TSP1-TGF-beta pathway in macrovascular diabetic complications, including restenosis, has not been addressed. In mesangial cells, high glucose concentrations depress protein kinase G (PKG) activity, but not PKG-I protein, thereby downregulating transcriptional repression of TSP1. Previously, we showed that high glucose downregulates PKG-I protein expression by vascular smooth muscle cells (VSMCs) through altered NADPH oxidase signaling. In the present study, we investigated whether high glucose regulation of PKG protein and activity in VSMCs similarly regulates TSP1 expression and downstream TGF-beta activity. These studies showed that high glucose stimulates both TSP1 expression and TGF-beta bioactivity in primary murine aortic smooth muscle cells (VSMCs). TSP1 is responsible for the increased TGF-beta bioactivity under high glucose conditions, because treatment with anti-TSP1 antibody, small interfering RNA-TSP1, or an inhibitory peptide blocked glucose-mediated increases in TGF-beta activity and extracellular matrix protein (fibronectin) expression. Overexpression of constitutively active PKG, but not the PKG-I protein, inhibited glucose-induced TSP1 expression and TGF-beta bioactivity, suggesting that PKG protein expression is insufficient to regulate TSP1 expression. Together, these data establish that glucose-mediated downregulation of PKG levels stimulates TSP1 expression and enhances TGF-beta activity and matrix protein expression, which can contribute to vascular remodeling in diabetes.

The deleterious effect of high concentrations of D-glucose requires pro-inflammatory preconditioning

OBJECTIVES

The present study investigated whether high concentrations of D-glucose can trigger pro-inflammatory mechanisms in human aortic smooth muscle cells.

METHODS

The expression and/or the activity of inducible nitric oxide synthase (iNOS), the extracellular signal-regulated kinase (ERK) 1/2 and nuclear factor (NF)-kappaB were studied in cultured human aortic smooth muscle cells (HASMC) in response to increasing concentrations of D-glucose and/or the inflammatory cytokine interleukin (IL)-1beta.

RESULTS

Increasing D-glucose in the medium from 5.5 to 22 mmol/l had no effect on any of these parameters. However, the high concentration of D-glucose did increase iNOS expression in response to low concentrations of IL-1beta (2.5 and 5 ng/ml), as well as the IL-1beta-induced activation of both ERK 1/2 and NF-kappaB. D-glucose also enhanced, concentration-dependently, the expression and activity of iNOS induced by co-incubation with IL-1beta (10 ng/ml). Pretreatment with IL-1beta sensitized the cells to the subsequent effects of high D-glucose.

CONCLUSIONS

The results indicate that high concentrations of D-glucose exacerbate the pro-inflammatory effects of IL-1beta. We suggest that the observed association between inflammation and diabetes is the result of elevated D-glucose enhancing a pre-existing inflammatory condition, rather than a direct effect of D-glucose on the production of inflammatory mediators.

Regulation of the inducible nitric oxide synthase and sodium pump in type 1 diabetes

Insulin-like growth factor-1 (IGF-1) is a hormone and growth factor closely related to insulin. The autocrine/paracrine actions of IGF-1 involve activation of inducible nitric oxide synthase (iNOS) and the Na(+), K(+)-ATPase sodium pump in cardiovascular tissues. Data from literature indicate that iNOS is expressed in vascular smooth muscle cells (VSMC) and that IGF-1-induced release of NO is both rapid and delayed. We hypothesize that impaired IGF-1-induced sodium pump activity/expression in rats with type 1 diabetes is related to activation of phosphatidylinositol 3 kinase (PI3K)/cytosolic phospholipase 2 (cPLA(2))/protein kinase B (Akt) signaling, and that IGF-1 prevents acute and chronic dysfunction of iNOS and sodium pump activity in a chemically induced model of type 1 diabetes, the streptozotocin-treated rat heart (STZ). Understanding how iNOS and sodium pump activity are regulated by IGF-1 activation of the PI3K/cPLA(2)/Akt cascade should provide novel and fundamental knowledge regarding the regulatory actions of IGF-1 in promoting vasodilation. Since insulin resistance is currently a major focus of research, the use of IGF-1 to improve insulin resistance and glucose metabolism has opened a new arena for treatment of comorbid conditions. Future investigations should now focus on mechanisms of action of IGF-1 and its clinical applicability.

New insights in endothelial and smooth muscle cell communication

Based on immunohistochemical techniques against connexins and the intercellular flux of staining molecules, it has previously been shown that electrotonic communication occurs among endothelial and vascular smooth muscle cells, this due to the presence of myoendothelial gap junctions. The aim of this study was to evaluate the density of myoendothelial contacts in the left coronary and internal mammary arteries as well as in the left saphenous vein by means of electron microscopy, the distance between both cells participating in an myoendothelial contact with a semi-automatic image analysis system and the presence of homocellular and heterocellular gap junctions between endothelial and smooth muscle cells by using the immunohistochemical technique and confocal microscopy in thoracic aorta were also analyzed. The results are that all blood vessels studied present myoendothelial contacts, while density studies show that they are more abundant in the saphenous vein. The myoendothelial contact distance is constant and in no case the cytoplasmic processes reach the plasma membrane of the partner cell toward which they are advanced. Homocellular gap junctions were found between smooth muscle cells and between endothelial cells. Heterocellular gap junctions were absent, evidencing the possibility that signaling molecules between endothelial and smooth muscle cells may be transferred through plasma membranes as was once thought and not necessarily by electrotonic communication.

Cross-talk between constitutive and inducible NO synthase: an update

Inducible nitric oxide synthase (iNOS) is expressed upon exposure of some cell types to bacterial lipopolysaccharides (LPS) and/or a variety of proinflammatory cytokines. The authors present an overview of some of the recent findings further supporting the notion that this response takes place after an early decline in constitutive nitric oxide (NO) levels (i.e., NO released by constitutive NOS, cNOS). This response is indeed critical for allowing activation of the transcription factor NF-kappaB. Thus, generation of NO by cNOS represents a limiting factor for iNOS expression. Some of the physiological and pathological implications of the cross-talk between these two NOS isoforms are discussed. In addition, the results of recent studies are summarized, suggesting possible mechanisms whereby LPS and/or proinflammatory cytokines may cause inhibition of cNOS.

High glucose enhances inducible nitric oxide synthase expression. Role of protein kinase C-betaII

The aim was to determine whether high glucose levels interfere with nitric oxide (NO) production and inducible NO synthase (iNOS) protein expression in interleukin-1beta-stimulated vascular smooth muscle cells from normotensive Wistar Kyoto and spontaneously hypertensive rats. Cells were incubated with either normal (5.5 mM) or high (22 mM) d-glucose for 72 h and with interleukin-1beta (10 ng/ml) for the last 24 h. High glucose increased nitrite levels, iNOS expression and protein kinase C activity in cells from normotensive rats and had no effect in cells from hypertensive rats. High glucose effects on nitrite production and iNOS expression was abolished by the selective inhibitor for the protein kinase C-betaII, 5,21:12,17-dimetheno-18H-dibenzo[i,o]pyrrolo[3,4-1] [1,8]diacyclohexadecine-18,20 (19H)-dione, 8-[(dimethylamino) methyl]-6,7,8,9,10,11-hexahydro-monomethanesulfonate (LY379196, 30 nM). Calphostin C (1 microM) and LY379196 (10 microM) reduced nitrite levels and iNOS expression only in cells from normotensive rats treated with both media. These results suggest that high glucose increases inducible nitric oxide synthase induction and subsequent NO production by activating the protein kinase C-betaII; this mechanism seems to be altered in hypertension.

Oxidative stress and diabetic cardiovascular complications

Diabetes diagnoses are increasing at an alarming rate worldwide. The majority of diabetes-related deaths arise from cardiovascular complications such as myocardial infarction, stroke, and peripheral vascular disease. Oxidative stress has been demonstrated to be present in animal models as well as in patients with diabetes and has been suggested as a possible contributor to the accelerated atherosclerosis seen in diabetics. The generation of reactive oxygen species in diabetes occurs via several mechanisms and is initiated not only by glucose, but also by other substances that are found at elevated levels in diabetic patients. The resulting oxidative stress leads to a number of proatherogenic events. The elucidation of the mechanisms of oxidative stress in diabetes and their relationship with atherosclerosis could potentially identify molecular targets of therapy for this condition and its cardiovascular consequences.

Lower expression of Th1-related cytokines and inducible nitric oxide synthase in mice with streptozotocin-induced diabetes mellitus infected with Mycobacterium tuberculosis

Diabetes mellitus is an important predisposing factor for tuberculosis. The aim of this study was to investigate the mechanism underlying this association using a murine model. Mice with streptozotocin-induced diabetes mellitus were prone to Mycobacterium tuberculosis infection, as indicated by increased numbers of live bacteria in lung, liver and spleen. In diabetic mice, the levels of IL-12 and IFN-gamma in the lung, liver and spleen were lower than those in control animals on day 14 postinfection, while the opposite was true for IL-4 levels in the lung and liver. The expression pattern of inducible nitric oxide synthase (iNOS), in the two mice types was as for IL-12 and IFN-gamma. In addition, peritoneal exudate cells obtained from diabetic mice produced lower amounts of IL-12 and NO than those from control mice, when stimulated in vitro with M. bovis BCG. Spleen cells from diabetic mice infected with M. tuberculosis produced a significantly lower amount of IFN-gamma upon restimulation with purified protein derivatives (PPD) than those from infected nondiabetic mice. Interestingly, addition of high glucose levels (33 mM) to the cultures of PPD-restimulated spleen cells reduced the synthesis of IFN-gamma only in diabetic mice, and not in nondiabetic mice. Finally, control of blood glucose levels by insulin therapy resulted in improvement of the impaired host protection and Th1-related cytokine synthesis. Our results suggest that the reduced production of Th1-related cytokines and NO account for the hampered host defense against M. tuberculosis infection under diabetic conditions.

Nitric oxide-dependent synthesis of vascular endothelial growth factor is impaired by high glucose

Synthesis of vascular endothelial growth factor (VEGF), the major angiogenic molecule, is induced by nitric oxide (NO) in various cell types, including vascular smooth muscle cells (VSMC). Therefore, compounds which inhibit NO generation can also influence VEGF synthesis. Here we investigated the effect of increased glucose concentration (25 mM vs. 5.5 mM) on cytokine-induced VEGF synthesis in rat VSMC. The cells growing in the medium containing 5.5 mM glucose and exposed to IL-1-beta, TNF-alpha and IFN-gamma induced expression of an inducible isoform of nitric oxide synthase (NOS II). This is followed by generation of NO and the concomitant expression of VEGF gene and release of VEGF protein. In contrast, 25 mM glucose impaired induction of NOS II expression and thus NO synthesis was lower than in 5.5 mM glucose. Consequently, the VEGF promoter activation was attenuated, resulting in decreased mRNA synthesis and lower production of VEGF protein. The results indicate that abnormally high concentrations of glucose can impair generation of NO and the NO-dependent VEGF synthesis. This may play a role in the development and progression of vascular dysfunctions in cardiovascular diseases.

Early vitamin E supplementation attenuates diabetes-associated vascular dysfunction and the rise in protein kinase C-beta in mesenteric artery and ameliorates wall stiffness in femoral artery of Wistar rats

AIMS/HYPOTHESIS

The impact of early vitamin E supplementation on vascular function in diabetes remains unresolved. Therefore, we examined the effects of vitamin E on functional and structural parameters and on chemical markers that are disturbed in diabetes in mesenteric and femoral arteries.

METHODS

Segments of both arteries, taken from control and 8-week-old streptozotocin diabetic Wistar rats that were treated or not with vitamin E, were mounted on wire and pressure myographs, after which endothelium-dependent and -independent vasodilation was assessed. Passive mechanical wall properties and the localisation and levels of protein kinase C (PKC)-beta(2) and AGE were evaluated in these vessels.

RESULTS

Vitamin E supplementation was associated with improved endothelium-dependent and -independent vasodilatation in mesenteric arteries from diabetic rats. Impaired endothelium-dependent vasodilatation in diabetic mesenteric vessels was associated with PKC-beta(2) up-regulation and this was prevented by vitamin E supplementation. Increased AGE accumulation and plasma isoprostane levels in diabetic rats were not changed by vitamin E. In the femoral artery, vitamin E supplementation had no effect on endothelium-dependent or -independent vasodilatation, but did prevent the wall stiffening associated with diabetes.

CONCLUSIONS/INTERPRETATION

Early vitamin E supplementation has a beneficial effect on diabetes-induced endothelial dysfunction in resistance arteries. This benefit may arise from a direct effect on smooth muscle function, as a result of inhibition of the PKC-beta(2) isoform by vitamin E.

Hypertension in diabetes: The role of the vasculature

This review is focused on the interplay between two major factors affecting the vascular tree in diabetes, insulin resistance, and hyperglycemia. The implications for vascular function, structure, and the interaction between vascular cells and other tissues by which they are affected under these conditions are reviewed.

Protein Kinase C Masks Nitric Oxide Synthase Activity in Vascular Smooth Muscle under Basal Conditions

Under basal conditions there is no observable nitric oxide synthase (NOS) activity in vascular smooth muscle (VSM). Pretreatment of endothelium-denuded aortic rings from Sprague-Dawley rats with 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), (0.1 micromol/L) significantly attenuated phenylephrine (PE)-induced contractile responses in a dose-dependent manner. In the presence of 10 micromol/L Nomega-nitro-L-arginine (L-NNA) or 0.1 mmol/L aminoguanidine (AG), the inhibition of contractions at 10 nmol/L PE by H-7 was blocked by 88% or 52%, respectively. The blockade by antagonists was completely reversed by l-arginine but not by d-arginine, and alone they did not significantly alter PE-induced contraction of endothelium-denuded aorta. Methylene blue (MB, 50 micromol/L) also inhibited the action of H-7. The inhibitory effect of H-7 occurred after 5 minutes and was reversible. PE-induced contraction was also inhibited by the selective protein kinase C inhibitors calphostin C (10 micromol/L), and bisindolylmaleimide IV (Bis-IV, 10 micromol/L), but not by the selective protein kinase A inhibitor H-89 (0.1 micromol/L). These results indicate protein kinase C inhibits NOS activity in VSM under basal conditions. Incubation of tissues with either H-7 or calphostin C stimulates NO production, and immunocytochemical studies reveal the presence of NOS in VSM under basal conditions.

High glucose inhibits apoptosis in human coronary artery smooth muscle cells by increasing bcl-xL and bfl-1/A1

Cardiovascular disease is a serious complication in diabetic patients. To elucidate the precise mechanisms of atherosclerosis in diabetic patients, the effects of high glucose concentration (25 mM) on apoptosis regulation and bcl-2 family protein expression in human coronary artery smooth muscle cells (CASMC) were examined. Treatment with a high level of glucose (25 mM) caused a significant decrease in apoptosis in CASMC compared with the same cells treated with a physiologically normal glucose concentration (5.5 mM) (23.9 +/- 2.4% vs. 16.5 +/- 1.8%; P < 0.01). With respect to apoptosis regulation, treatment of CASMC with high glucose concentration markedly increased mRNA expressions of bcl-xL and bfl-1/A1 compared with cells treated with normal glucose. High glucose induced phosphorylation of phosphatidylinositol 3-kinase (PI 3-K) and extracellular signal-regulated kinase (ERK)1/2 along with bcl-xL and bfl-1/A1 upregulation. These results suggest that high glucose suppresses apoptosis via upregulation of bcl-xL and bfl-1/A1 levels through PI 3-K and ERK1/2 pathways in CASMC. High glucose-induced increase in the expression of antiapoptotic proteins may be important in the development of atherosclerosis in diabetic patients.

Cardiovascular risk factors in diabetic patients with hypertension

Individuals with diabetes mellitus have cardiovascular disease (CVD) mortality comparable to nondiabetics who have suffered a myocardial infarction or stroke. Aggressive management of risk factors such as hypertension, dyslipidemia, and platelet dysfunction in persons with diabetes has been shown to reduce morbidity and mortality in prospective randomized controlled clinical trials. Accordingly, there are national mandates to lower blood pressure to less than 130/85 mm Hg, reduce low-density lipoprotein cholesterol to less than 100 mg/dL, and institute aspirin therapy in adult patients with diabetes. Although not definitively shown to reduce CVD, there are also recommendations to control the level of glycemia, as well. This article discusses CVD risk factors in the diabetic patient with hypertension.

Humic acid induces the generation of nitric oxide in human umbilical vein endothelial cells: stimulation of nitric oxide synthase during cell injury

Humic acid (HA) has been implicated as an etiological factor in the peripheral vasculopathy of blackfoot disease (BFD). In this study, we examined the effects of HA upon the generation of nitric oxide (NO) during the process of lethal cell injury in cultured human umbilical vein endothelial cells (HUVECs). NO production was measured by the formation of nitrite (NO(2)(-)), the stable end-metabolite of NO. Cell death was assessed by measuring the release of intracellular lactate dehydrogenase (LDH). Treatment HUVECs with HA at a concentration of 50, 100, and 200 microg/ml concentration-dependently increased nitrite levels, reaching a peak at 12 h subsequent to HA treatment, with a maximal response of approximately 400 pmole nitrite (from 1 x 10(4) cells). HA-induced nitrite formation was blocked completely by N(G)-nitro-L-arginine methyl ester (L-NAME) and also by N(G)-methyl-L-arginine (L-NMA), both being specific inhibitors of NO synthase. The LDH released from endothelial cells was evoked at from 24 h after the addition of HA (50, 100, 200 microg/ml) in a concentration- and time-dependent manner. The HA-induced LDH release was also reduced by the presence of both L-NAME and L-NMA. The addition of Ca(2+) chelator (BAPTA) inhibited both nitrite formation and LDH release by HA. Moreover, the antioxidants (superoxide dismutase, vitamin C, vitamin E) and protein kinase inhibitor (H7) effectively suppressed HA-induced nitrite formation. These results suggest that HA treatment of endothelial cells stimulates NO production, which can elicit cell injury via the stimulation of Ca(2+)-dependent NO synthase activity by increasing cytosolic Ca(2+) levels. Because the destruction of endothelial cells has been implicated in triggering the onset of BFD, the induction of excessive levels of NO and consequent endothelial-cell injury may be important to the etiology of HA-induced vascular disorders associated with BFD for humans.

Hypertension in L-NAME-treated diabetic rats depends on an intact sympathetic nervous system

We demonstrated previously that induction of diabetes in rats that were treated chronically with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) causes a severe, progressive increase in mean arterial pressure. This study tested the role of the sympathetic nervous system in that response. Rats were instrumented with chronic artery and vein catheters and assigned randomly to four diabetic groups pretreated with vehicle (D), L-NAME (D+L), the alpha(1)- and beta-adrenergic receptor antagonists terazosin and propranolol (D+B), or L-NAME, terazosin, and propranolol (D+LB). After baseline measurements were taken, rats were pretreated; 6 days later, streptozotocin was administered and 3 wk of diabetes ensued. D+L rats had a marked, progressive increase in arterial pressure that by day 20 was approximately 60 mmHg greater than in D rats. The pressor response to L-NAME was significantly attenuated in diabetic rats cotreated with adrenergic blockers. During week 1 of diabetes, plasma renin activity (PRA) increased and then returned to control levels in D rats. PRA increased progressively in D+L rats, and chronic adrenergic receptor blockade restored the biphasic renin response in D+LB rats. These results suggest that the sympathetic nervous system may be involved in the hypertensive response to onset of diabetes in L-NAME-treated rats, possibly through control of renin secretion.

Protein kinase C activation and its pharmacological inhibition in vascular disease

Vascular complications in diabetes mellitus are known to be associated with the activation of the protein kinase C (PKC) pathway through the de novo synthesis of diacylglycerol (DAG) from glycolytic intermediates. Specific PKC isoforms, mainly the beta- and delta-isoforms, have been shown to be persistently activated in diabetic mellitus. Multiple studies have reported that the activation of PKC leads to increased production of extracellular matrix and cytokines, enhances contractility, permeability and vascular cell proliferation, induces the activation of cytosolic phospholipase A2 and inhibits the activity of Na+-K+-ATPase. These events are not only frequently observed in diabetes mellitus but are also involved in the actions of vasoactive agents or oxidative stress. Inhibition of PKC by two different kinds of PKC inhibitors - LY333531, a selective PKC-beta-isoform inhibitor, and vitamin E, d-alpha-tocopheron - were able to prevent or reverse the various vascular dysfunctions in vitro and in vivo. Clinical studies using these compounds are now ongoing to evaluate the significance of DAG-PKC pathway activation in the development of vascular complications in diabetic patients.

Nitric oxide synthase activity and expression in experimental diabetic neuropathy

The changes of nitric oxide synthase (NOS) activity and expression in experimental diabetic neuropathy have not been examined. Increases in ganglia NOS might be similar to those that follow axotomy, whereas declines in endothelial NOS (eNOS) and immunological NOS (iNOS) might explain dysfunction of microvessels or macrophages. In this work, we studied NOS activity in lumbar dorsal root ganglia (DRG) of rats with both short- and long-term experimental streptozotocin-induced diabetes and correlated it with expression of each of the 3 NOS isoforms. NOS enzymatic activity in DRG increased after 12 months of diabetes. This increase, however, was not accompanied by an increase in neuronal NOS immunohistochemistry or mRNA. Immunohistochemical and RT-PCR studies did not identify changes of eNOS expression in 12-month sciatic nerves or DRG from diabetics. Two-month diabetic DRG had increased eNOS mRNA and there was novel eNOS labeling of capsular DRG and perineurial cells. iNOS mRNA levels were lower in diabetics at both time points in peripheral nerves but were unchanged in DRG. Diabetic ganglia showed an increase in NOS activity not explained by novel NOS isoform synthesis. The increases may compensate for NO "quenching" by endproducts of glycosylation. Declines in iNOS may indicate impaired macrophage function.

Inhibition of Rho protein stimulates iNOS expression in rat vascular smooth muscle cells

Inducible nitric oxide synthase (iNOS) in vascular smooth muscle cells (VSMCs) is upregulated in arterial injury and plays a role in regulating VSMC proliferation and restenosis. Inflammatory cytokines [e.g., interleukin-1beta (IL-1beta)] released during vascular injury induce iNOS. Small GTP-binding proteins of the Ras superfamily play a major role in IL-1beta-dependent signaling pathways. In this study, we examined the role of Rho GTPases in regulating iNOS expression in VSMCs. Treatment of VSMCs with mevastatin, which inhibits isoprenylation of Rho and other small GTP-binding proteins, produced significantly higher amounts of IL-1beta-evoked NO and iNOS protein compared with control. Similarly, bacterial toxins [Toxin B from Clostridium difficile and C3 ADP-ribosyl transferase (C3) toxin from Clostridium botulinium] that specifically inactivate Rho proteins increased NOS products (NO and citrulline) and iNOS expression. Toxin B increased the activity of iNOS promoter-reporter construct in VSMCs. Both toxins enhanced IL-1beta-stimulated iNOS expression and NO production. These data demonstrate for the first time that inhibition of Rho induces iNOS and suggest a role for Rho protein in IL-1beta-stimulated NO production in VSMCs.

The diabetic patient as paradigm for selective antihypertensive therapy

General recommendations from US and international organizations indicate that an ideal approach to the therapy of hypertension should begin with lifestyle modifications, such as decreased salt and fat intake and a careful aerobic exercise program, with the therapeutic goal of a blood pressure (BP) < 140/90 mm Hg. The most recent guidelines recommend more rigorous targets for BP lowering in high-risk populations, such as those with hypertension and concomitant diabetes and/or renal disease with proteinuria. This chapter addresses hypertension in patients with diabetes as an example of a group at especially high risk. It reviews recent clinical trials that support more rigorous BP goals in such patients to reduce cardiovascular morbidity and mortality and considers the importance of combination therapy in achieving these goals.

Glucose-induced changes in protein kinase C and nitric oxide are prevented by vitamin E

Changes in activity or expression of protein kinase C (PKC), reactive oxygen products, and nitric oxide (NO) may account for the alteration in cell behavior seen in diabetes. These changes have been proposed to be part of the pathophysiology of erectile dysfunction. We sought to ascertain if corpus cavernosal vascular smooth muscle cells (CCSMC) grown in a high glucose milieu exhibit changes in the activity and expression of PKC isoforms, NO, and reactive oxygen products and to find out if these changes are prevented by alpha-tocopherol. Rat CCSMC were grown in 5, 15, and 30 mM glucose concentrations for 3, 7, and 14 days. PKC isoform expression was assayed with isoform-specific antibodies. In CCSMCs grown in 30 mM glucose for 2-wk, PKC-beta(2)-isoform was upregulated (n = 4; P < 0.01), whereas the expression of alpha-, delta-, epsilon-, and beta(1)-isoforms was unchanged. NO as measured by nitrate-to-nitrite ratio was greatly diminished at 14 days in 30 mM (n = 4; P < 0.002) compared with 5 mM glucose. Reactive oxygen products were upregulated at 14 days when they were assayed by the fluorescent probe dichlorofluorescein diacetate bis(acetoxy-methyl) (DCFH-DA) (n = 5; P < 0.01). When these same cells were exposed to alpha-tocopherol for 14 days, there was a reduction of PKC-beta(2) (57.8%; P < 0.01; n = 4) and a reduction in reactive oxygen product formation (71.1%; P < 0.001; n = 4), along with an increase in nitrate-to-nitrite ratio (43.9%; P < 0.01, n = 4). These results suggest that there may be an interrelationship between PKC, NO, and reactive oxygen product formation in CCSMC exposed to a high glucose environment.

Genotyping and functional analysis of a polymorphic (CCTTT)(n) repeat of NOS2A in diabetic retinopathy

Accumulating evidence shows that the severity and rapidity of onset of diabetic retinopathy are influenced by genetic factors. Expression of the nitric oxide synthases is altered in the retinal vasculature in the early stages of diabetic retinopathy. We analyzed the allele distribution of a polymorphic pentanucleotide repeat within the 5' upstream promoter region of the NOS2A gene in samples of diabetic patients. In diabetic patients from Northern Ireland, the 14-repeat allele of the NOS2A marker was significantly associated with the absence of diabetic retinopathy. Carriers of this repeat had 0.21-fold the relative risk of developing diabetic retinopathy than noncarriers of this allele. They also had significantly fewer renal and cardiovascular complications. The ability of differing numbers of (CCTTT)(n) pentanucleotide repeats to induce transcription of the NOS2A gene was analyzed using a luciferase reporter gene assay in transfected colonic carcinoma cells. Interleukin 1beta (IL-1beta) induction was most effective in constructs carrying the 14-repeat allele. When cells were incubated in 25 mM glucose to mimic the diabetic state, IL-1beta induction was inhibited in all cases, but to a significantly lesser extent with the 14-repeat allele. These unique properties of the 14-repeat allele may confer selective advantages in diabetic individuals, which may delay or prevent microvascular complications of diabetes.

Can protein kinase C inhibition and vitamin E prevent the development of diabetic vascular complications?

Hyperglycemia causes vascular complications of diabetes possible by the activation of protein kinase C (PKC). We have provided substantial evidence that activation of PKC can lead to a whole host of vascular dysfunction in diabetes. The activation of PKC induced by hyperglycemia appears to be due to an increase in diacylglycerol (DAG) levels, a physiological activator of PKC. Studies involving cultural cells, animal models of diabetes and patients have shown that inhibition of PKC by specific PKC inhibitor was able to reverse many of the vascular dysfunctions in the retina, kidney and cardiovascular systems induced by either hyperglycemia or diabetes. In addition high doses of vitamin E were shown to decrease the level of DAG and PKC induced by diabetes or hyperglycemia. Thus animal and clinical studies have shown that high doses of vitamin E treatment can apparently reverse some of the changes in the retinal and renal vessels.

Interleukin-1beta-induced nitric oxide production in rat aortic endothelial cells: inhibition by estradiol in normal and high glucose cultures

Expression of inducible nitric oxide synthase (iNOS) and the resultant increased nitric oxide (NO) production are associated with septic shock, atherosclerosis, and cytokine-induced vascular injury. Estrogen is known to impact vascular injury and vascular tone, in part through regulation of NO production. In the current study, we examined the effect of physiological concentrations of estradiol on interleukin-1beta (IL-1beta)-induced NO production in rat aortic endothelial cells (RAECs). 17Beta-estradiol significantly decreased IL-1beta-induced iNOS protein levels and reduced NO production in RAECs. High glucose (25 mM) elevated the increase in IL-1beta-induced iNOS protein and NO production. Nevertheless, estradiol still inhibited IL-1beta-induced iNOS and NO production even in the presence of high glucose. These data suggest that estradiol may exert its beneficial effects in part by inhibiting induction of endothelial iNOS, a possible mechanism for the protective effect of estradiol against diabetes-associated cardiovascular complications.

Autocrine function of inducible nitric oxide synthase and cyclooxygenase-2 in proliferation of human and rat pulmonary artery smooth-muscle cells: species variation

Pulmonary hypertension is characterized by hypertrophy and hyperplasia of vascular smooth muscle occurring via an unknown mechanism. Cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS) are expressed under inflammatory conditions and produce mediators that regulate growth in some tissues. We have therefore addressed the question of COX-2 and iNOS involvement in proliferation of human and rat pulmonary artery (PA) smooth-muscle cells (SMC). Interleukin (IL)-1beta suppressed proliferation of both human and rat PA SMC. Moreover, IL-1beta induced COX-2 expression in both cell types. By contrast, IL-1beta stimulated the expression of iNOS protein in rat cells only. COX-2 induced in human cells inhibited proliferation, whereas COX-2 products in rat cells were without affect. However, iNOS activity in rat cells suppressed their proliferation. We conclude that human and rat evolution has diverged such that COX-2 and iNOS, although induced by the same mediator, have different levels of activity and functions in the two species. In humans, induction of COX-2 during pulmonary hypertension may be beneficial for long-term treatment of this disease.

Special considerations in the therapy of diabetic hypertension

Patients with diabetes mellitus have an increased prevalence of hypertension and associated cardiovascular disease (CVD), including coronary and cerebrovascular disease. The risk of an individual of developing CVD is much greater when both diseases coexist and is further magnified by their frequent association with dyslipidemia, coagulation, platelet, and endothelial abnormalities. Metabolic abnormalities frequently associated with hypertension are insulin resistance, enhanced coagulation, and decreased fibrinolytic activity. Drug treatment of hypertension in diabetic subjects is fraught with potential difficulties, including altered efficacy of medications, possible side effects, worsening of glycemic control, and impairment of lipid metabolism. Because hypertension is a major contributor to morbidity and mortality in diabetes, it should be recognized and treated early and aggressively despite these difficulties. This article reviews the efficacy and side effects of the various classes of antihypertensive agents in patients with diabetes mellitus.