Jacinthe Lemay

Metabolic and Additional Vascular Effects of Thiazolidinediones

Several cardiovascular risk factors (dyslipidaemia, hypertension, glucose intolerance, hypercoagulability, obesity, hyperinsulinaemia and low-grade inflammation) cluster in the insulin resistance syndrome. Treatment of these individual risk factors reduces cardiovascular complications. However, targeting the underlying pathophysiological mechanisms of the insulin resistance syndrome is a more rational treatment strategy to further improve cardiovascular outcome.Our understanding of the so-called cardiovascular dysmetabolic syndrome has been improved by the discovery of nuclear peroxisome proliferator-activated receptors (PPARs). PPARs are ligand-activated transcription factors belonging to the nuclear receptor superfamily. As transcription factors, PPARs regulate the expression of numerous genes and affect glycaemic control, lipid metabolism, vascular tone and inflammation. Activation of the subtype PPAR-γ improves insulin sensitivity. Expression of PPAR-γ is present in several cell types involved in the process of atherosclerosis. Thus, modulation of PPAR-γ activity is an interesting therapeutic approach to reduce cardiovascular events.Thiazolidinediones are PPAR-γ agonists and constitute a new class of pharmacological agents for the treatment of type 2 (non-insulin-dependent) diabetes mellitus. Two such compounds are currently available for clinical use: rosiglitazone and pioglitazone. Thiazolidinediones improve insulin sensitivity and glycaemic control in patients with type 2 diabetes. In addition, improvement in endothelial function, a decrease in inflammatory conditions, a decrease in plasma levels of free fatty acids and lower blood pressure have been observed, which may have important beneficial effects on the vasculature.Several questions remain to be answered about PPAR-γ agonists, particularly with respect to the role of PPAR-γ in vascular pathophysiology. More needs to be known about the adverse effects of thiazolidinediones, such as hepatotoxicity, increased low-density lipoprotein cholesterol levels and increased oedema. The paradox of adipocyte differentiation with weight gain concurring with the insulin-sensitising effect of thiazolidinediones is not completely understood. The decrease in blood pressure induced by thiazolidinedione treatment seems incompatible with an increase in the plasma volume, and the discrepancy between the stimulation of the expression of CD36 and the antiatherogenic effects of the thiazolidinediones also needs further explanation. Long-term clinical trials of thiazolidinediones with cardiovascular endpoints are currently in progress.In conclusion, studying the effects of thiazolidinediones may shed more light on the mechanisms involved in the insulin resistance syndrome. Furthermore, thiazolidinediones could have specific, direct effects on processes involved in the development of vascular abnormalities.

Norepinephrine-induced aortic hyperplasia and extracellular matrix deposition are endothelin-dependent.

Background Sympathetic hyperactivity is observed in several disease states and may contribute to cardiovascular hypertrophic remodeling. Endothelin has been suggested to be a mediator of hypertrophy. Objective To examine the involvement of endothelin in maintaining the growth response induced by exogenous norepinephrine. Design and methods Rats were treated with norepinephrine (2.5 μg/Kg per min subcutaneously) for 2 and 4 weeks, alone or in association with the selective endothelin-A (ETA) receptor antagonist, darusentan (LU135252, 30 mg/Kg per day orally) for weeks 3 and 4. Results Increases in medial cell number and accumulation of collagen and elastin characterized norepinephrine-induced aortic remodeling. These effects occurred without marked changes of mean arterial pressure, but may be related to enhanced pressure variability in addition to direct effects of norepinephrine. Inhibition of ETA receptors by darusentan reversed aortic alterations produced by infusion of norepinephrine. Evaluation of medial apoptosis did not reveal any significant change in any group at 4 weeks. Conclusions Antagonism of ETA receptors effectively and rapidly reversed norepinephrine-induced aortic structural and compositional changes, suggesting a central role of endothelin in mediating this response. Thus, ETA receptor antagonists may help to regress large artery remodeling in conditions of increased circulating catecholamine concentrations.

Pregabalin for peripheral neuropathic pain: a multicenter, enriched enrollment randomized withdrawal placebo-controlled trial.

ObjectivesTo date, published neuropathic pain randomized controlled trials of pregabalin have involved primarily diabetic peripheral neuropathy (DPN) and postherpetic neuralgia (PHN). This multicenter trial evaluated pregabalin in a broader range of neuropathic pain etiologies. MethodsIn this enriched enrollment randomized withdrawal trial, 256 patients received single blind, flexible dose pregabalin for 4 weeks; stable concomitant analgesics were allowed. One hundred sixty-five (65%) had a ≥30% pain improvement and 157 were randomized and treated, double blind, to either continue pregabalin (n=80) or to receive placebo (n=77) for 5 weeks. ResultsOf the single blind responders randomized, 81% on placebo and 86% on pregabalin completed the double-blind phase. At the double-blind endpoint, mean (SD) pain scores were 2.9 (1.9) in the pregabalin group and 3.5 (1.7) in the placebo group (P=0.002). These modest yet significant pregabalin-placebo differences were observed within each of the subgroups of patients with a diagnosis of either DPN or PHN (P=0.03), and with other diagnoses (P=0.02). Significant differences were also observed in sleep interference, Hospital Anxiety and Depression Scale Anxiety and Depression subscales, and other secondary measures. In total, 28 out of 80 (35.0%) in the pregabalin group and 28 out of 77 (36.4%) in the placebo group had either a meaningful increase in pain or discontinued the double-blind phase. Adverse events were consistent with the known tolerability profile of pregabalin and led to discontinuation of 9 during the single-blind phase, and 5 and 2 patients from the placebo and pregabalin groups, respectively. DiscussionThese results support previous evidence of pregabalin efficacy but further demonstrate efficacy and tolerability in a broader range of peripheral neuropathic pain conditions beyond just DPN and PHN.

Losartan-induced apoptosis as a novel mechanism for the prevention of vascular lesion formation after injury

Smooth muscle cell (SMC) apoptosis is transiently increased at the onset of the regression of aortic hypertrophy in spontaneously hypertensive rats (SHR) treated with the angiotensin II AT1 antagonist losartan. We postulated that losartan induction of SMC apoptosis contributes to suppression of neointimal hyperplasia after vascular injury. Losartan or placebo treatment was initiated two days before balloon injury in the SHR aorta. Compared with time-matched placebo, losartan decreased neointimal cross-sectional area at Days 5 and 10 after injury by 50% and 64% respectively, without affecting medial mass. At Day 10, losartan significantly decreased SMC number (by 56%) in the neointima, but not in the media. DNA synthesis was significantly inhibited at Day 5 but not at Day 10. Losartan significantly increased aortic DNA fragmentation by 2.6- and 4.1-fold, at Days 5 and 10, respectively. In situ labeling of SMC with terminal deoxynucleotidyltransferase revealed significant 61% and 68% increases in apoptotic SMC at Days 5 and 10 with losartan treatment, predominantly in the neointima. Thus, losartan suppressed neointima formation in part by the induction of SMC apoptosis, which may be dissociated from the inhibition of DNA synthesis. Therefore, losartan-induced SMC apoptosis may be a potential therapeutic approach to control occlusive vascular disorders.

Regression of Neointimal Lesions in the Carotid Artery of Nifedipine-Treated SHR and WKY Rats: Possible Role of Apoptosis

We previously observed that nifedipine reduces aortic hypertrophy in spontaneously hypertensive rats (SHR) partly by inducing smooth muscle cell (SMC) apoptosis. The present study examined nifedipine regulation of SMC apoptosis in carotids with or without a neointima. A neointima was produced by endothelial denudation of the left carotid of SHR and WKY rats. The contralateral carotid remained uninjured. Beginning at week 6 after injury, rats received nifedipine or placebo for 5 and 7 additional weeks. In situ terminal deoxynucleotidyl transferase (TdT)-mediated DNA labeling was used to mark apoptotic nuclei. Nifedipine reduced blood pressure in SHR but not WKY rats. Nifedipine had antihypertrophic effects in both SHR and WKY rats. In each strain, the greater reduction in cross-sectional area was seen in the neointima. In this tissue, nifedipine significantly increased TdT-positive SMC (4-fold at week 5 in SHR and 5-fold at week 7 in WKY rats) and reduced SMC number (70% in SHR and 29% in WKY rats) at week 7 compared to week 0. The effects were less pronounced in the injured and uninjured media. Thus, the antihypertrophic action of nifedipine is amplified in the neointima of SHR and WKY rat carotids, where histological evidence suggests SMC deletion via apoptosis.

Evidence that nitric oxide regulates AT1-receptor agonist and antagonist efficacy in rat injured carotid artery.

Vascular injury stimulates AT1-receptor expression and nitric oxide (NO) production in smooth muscle cells (SMCs). We examined the ability of AT1 agonists and antagonists to regulate vascular tone ex vivo in injured arteries and the possible modulation by SMC-derived NO. Rings of rat carotid arteries were isolated at day 7 after endothelial denudation and stimulated with angiotensin (Ang) II in the absence or presence of the AT1 antagonists losartan, L-158,809, or EXP-3174. Freshly denuded contralateral arteries were used as controls. AngII-induced contractions were similar in control and injured arteries. Losartan caused an insurmountable inhibition of AngII-induced contractions in injured but not control arteries. Enhanced inhibition of AngII in injured arteries also was observed in the presence of L-158,809 and EXP-3174. In the presence of the NO synthesis inhibitor nitromonomethyl-L-arginine (L-NMMA), maximal contractions to AngII were greater in injured than in control vessels, and AT1-receptor blockade with losartan was surmountable in all vessels. Mechanical removal of superficial neointimal SMCs attenuated NO production and normalized the efficacy of losartan in injured arteries. These results suggest a role for NO in reducing the biologic effects of AT1-receptor agonists and potentiating the efficacy of AT1 antagonists in vessels undergoing remodeling after injury.

Neointimal-specific induction of apoptosis by losartan results in regression of vascular lesion in rat aorta.

We previously reported that initiating treatment with the angiotensin II receptor antagonist losartan, prior to and immediately after balloon injury, attenuates neointimal hyperplasia via induction of smooth muscle cell (SMC) apoptosis in the aorta of spontaneously hypertensive rats (SHR). The present study examines whether losartan can induce regression of an established neointima. Balloon angioplasty was performed in the aorta of 1 1 week-old SHR. Five weeks were allowed for neointima formation before rats received placebo or losartan (30 mg/kg/day) for 1 to 4 weeks. Blood pressure was measured by tail cuff plethysmography. Losartan significantly reduced blood pressure (16%) versus placebo within 2 weeks of treatment. In situ labeling with terminal deoxynucleotidyl transferase among neointimal SMC was transiently increased with losartan (10-fold at 2 weeks; P=0.004) in correlation with internucleosomal fragmentation of vascular DNA. Accordingly, losartan reversed neointimal hyperplasia by 43% (P=0.002) and 61% (P=0.007) at weeks 2 and 4, respectively, and neointimal mass by 63% (P<0.001) and 75% (P<0.001) at weeks 2 and 4, respectively, as compared to pre-treatment values. No change in aortic medial hyperplasia or mass was observed during losartan treatment. Taken together, endothelial denudation rendered the underlying media resistant to drug-induced remodeling, while losartan treatment induced vascular lesion regression by inducing apoptosis selectively in neointimal SMC, an effect that may contribute to the reduction of cardiovascular complications in hypertension.

Angiotensin I-converting enzyme activity and vascular sensitivity to angiotensin I in rat injured carotid artery

We used a vasoreactivity assay to examine the functional significance of angiotensin I-converting enzyme overexpression in smooth muscle cells after vascular injury. Rat carotid arteries isolated at days 2 to 14 after in vivo endothelial denudation were compared with the contralateral freshly denuded (control) vessels. Arterial rings were constricted ex vivo with angiotensin I in the absence or presence of the angiotensin I-converting enzyme inhibitors captopril (300 nM and 3 microM) or perindoprilate (1 nM). Angiotensin I-converting enzyme activity was determined by cleavage of the chromogenic substrate Hip-His-Leu. Angiotensin I-converting enzyme activity in injured arteries was increased (2-fold) at day 7 only after vascular injury. Contractions to angiotensin I were unaffected after injury. Inhibition by captopril and perindoprilate of angiotensin I-induced contractions was significantly less potent in injured arteries at day 7 as compared to control vessels. Mechanical removal of neointimal smooth muscle cells normalized the inhibition by captopril in injured arteries at day 7. Captopril did not affect angiotensin II-induced contractions. Thus, upregulation of angiotensin I-converting enzyme after arterial injury confers resistance to angiotensin I-converting enzyme inhibitors.