Mohammed A. Azam

Arginase Promotes Neointima Formation in Rat Injured Carotid Arteries

Objective—Arginase stimulates the proliferation of cultured vascular smooth muscle cells (VSMCs); however, the influence of arginase on VSMC growth in vivo is not known. This study investigated the impact of arginase on cell cycle progression and neointima formation after experimental arterial injury. Methods and Results—Balloon injury of rat carotid arteries resulted in a sustained increase in arginase activity in the vessel wall and the induction of arginase I protein in both the media and neointima of injured vessels. Furthermore, local perivascular application of the potent and selective arginase inhibitors S-(2-boronoethyl)-l-cysteine (BEC) or NG-hydroxy-nor-l-arginine (L-OHNA) immediately after injury markedly attenuated medial and neointimal DNA synthesis and neointima formation. Substantial arginase I protein and arginase activity was also detected in rat cultured aortic VSMCs. Moreover, treatment of VSMCs with BEC or L-OHNA, or knockdown of arginase I protein, arrested cells in the G0/G1 phase of the cell cycle and induced the expression of the cyclin-dependent protein kinase inhibitor, p21. Conclusion—This study demonstrates that arginase is essential for VSMCs to enter the cell cycle and that arginase I contributes to the remodeling response after arterial injury. Arginase I represents a potentially new therapeutic target for the treatment of vasculoproliferative disorders.

Role of KATP Channels in the Maintenance of Ventricular Fibrillation in Cardiomyopathic Human Hearts

Rationale: Ventricular fibrillation (VF) leads to global ischemia. The modulation of ischemia-dependent pathways may alter the electrophysiological evolution of VF. Objective: We addressed the hypotheses that there is regional disease-related expression of KATP channels in human cardiomyopathic hearts and that KATP channel blockade promotes spontaneous VF termination by attenuating spatiotemporal dispersion of refractoriness. Methods and Results: In a human Langendorff model, electric mapping of 6 control and 9 treatment (10 &mgr;mol/L glibenclamide) isolated cardiomyopathic hearts was performed. Spontaneous defibrillation was studied and mean VF cycle length was compared regionally at VF onset and after 180 seconds between control and treatment groups. KATP subunit gene expression was compared between LV endocardium versus epicardium in myopathic hearts. Spontaneous VF termination occurred in 1 of 6 control hearts and 7 of 8 glibenclamide-treated hearts (P=0.026). After 180 seconds of ischemia, a transmural dispersion in VF cycle length was observed between epicardium and endocardium (P=0.001), which was attenuated by glibenclamide. There was greater gene expression of all KATP subunit on the endocardium compared with the epicardium (P<0.02). In an ischemic rat heart model, transmural dispersion of refractoriness (&Dgr;ERPTransmural=ERPEpicardium−ERPEndocardium) was verified with pacing protocols. &Dgr;ERPTransmural in control was 5±2 ms and increased to 36±5 ms with ischemia. This effect was greatly attenuated by glibenclamide (&Dgr;ERPTransmural for glibenclamide+ischemia=4.9±4 ms, P=0.019 versus control ischemia). Conclusions: KATP channel subunit gene expression is heterogeneously altered in the cardiomyopathic human heart. Blockade of KATP channels promotes spontaneous defibrillation in cardiomyopathic human hearts by attenuating the ischemia-dependent spatiotemporal heterogeneity of refractoriness during early VF.

Single Perivascular Delivery of Mitomycin C Stimulates p21 Expression and Inhibits Neointima Formation in Rat Arteries

Objective—Mitomycin C (MMc) is an antibiotic that exerts a potent antiproliferative effect in tumor cells. Because the proliferation of vascular smooth muscle cells (VSMCs) plays a prominent role in the development of restenosis after percutaneous coronary interventions, the present study examined the effect of MMc on VSMC proliferation and on neointima formation after arterial balloon injury. Methods and Results—Treatment of cultured rat aortic VSMCs with MMc (1 nmol to 30 &mgr;mol/L) inhibited VSMC proliferation in a concentration-dependent manner. Whereas high concentrations of MMc (1 to 30 &mgr;mol/L) induced VSMC apoptosis, as reflected by DNA laddering and caspase-3 activation, lower concentrations of MMc (1 to 300 nmol/L) directly inhibited VSMC growth by arresting cells in the G2/M phase of the cell cycle. The antiproliferative action of MMc was associated with a selective increase in the expression of the cyclin-dependent kinase inhibitor p21, and with a decrease in cyclin B1-cyclin-dependent kinase-1 complex activity. Finally, the local perivascular delivery of MMc immediately after balloon injury of rat carotid arteries induced p21 expression and markedly attenuated neointima formation. Conclusion—These studies demonstrate that MMc exerts a potent inhibitory effect on VSMC proliferation and neointima formation after arterial injury. MMc represents a potentially new therapeutic agent in treating and preventing vasculoproliferative disease.

Arginase promotes endothelial dysfunction and hypertension in obese rats

This study investigated whether arginase contributes to endothelial dysfunction and hypertension in obese rats.

Effects of Late Sodium Current Blockade on Ventricular Refibrillation in a Rabbit Model

Background— After defibrillation of initial ventricular fibrillation (VF), it is crucial to prevent refibrillation to ensure successful resuscitation outcomes. Inability of the late Na+ current to inactivate leads to intracellular Ca2+ dysregulation and arrhythmias. Our aim was to determine the effects of ranolazine and GS-967, inhibitors of the late Na+ current, on ventricular refibrillation. Methods and Results— Long-duration VF was induced electrically in Langendorff-perfused rabbit hearts (n=22) and terminated with a defibrillator after 6 minutes. Fibrillating hearts were randomized into 3 groups: treatment with ranolazine, GS-967, or nontreated controls. In the treated groups, hearts were perfused with ranolazine or GS-967 at 2 minutes of VF. In control experiments, perfusion solution was supplemented with isotonic saline in lieu of a drug. Inducibility of refibrillation was assessed after initial long-duration VF by attempting to reinduce VF. Sustained refibrillation was successful in fewer ranolazine-treated (29.17%; P=0.005) or GS-967–treated (45.83%, P=0.035) hearts compared with that in nontreated control hearts (84.85%). In GS-967–treated hearts, significantly more spontaneous termination of initial long-duration VF was observed (66.67%; P=0.01). Ca2+ transient duration was reduced in ranolazine-treated hearts compared with that in controls (P=0.05) and also Ca2+ alternans (P=0.03). Conclusions— Late Na+ current inhibition during long-duration VF reduces the susceptibility to subsequent refibrillation, partially by mitigating dysregulation of intracellular Ca2+. These results suggest the potential therapeutic use of ranolazine and GS-967 and call for further testing in cardiac arrest models.