Macro-and microvascular disease are the most common causes of morbidity and mortality in patients with diabetes mellitus. Diabetic cardiovascular dysfunction represents a problem of great clinical importance underlying the development of various severe complications including retinopathy, nephropathy, neuropathy and increase the risk of stroke, hypertension and myocardial infarction. Hyperglycemic episodes, which complicate even well-controlled cases of diabetes, are closely associated with increased oxidative and nitrosative stress, which can trigger the development of diabetic complications. Hyperglycemia stimulates the production of advanced glycosylated end products, activates protein kinase C, and enhances the polyol pathway leading to increased superoxide anion formation. Superoxide anion interacts with nitric oxide, forming the potent cytotoxin peroxynitrite, which attacks various biomolecules in the vascular endothelium, vascular smooth muscle and myocardium, leading to cardiovascular dysfunction. The pathogenetic role of nitrosative stress and peroxynitrite, and downstream mechanisms including poly(ADP-ribose) polymerase (PARP) activation, is not limited to the diabetes-induced cardiovascular dysfunction, but also contributes to the development and progression of diabetic nephropathy, retinopathy and neuropathy. Accordingly, neutralization of peroxynitrite or pharmacological inhibition of PARP is a promising new approach in the therapy and prevention of diabetic complications. This review focuses on the role of nitrosative stress and downstream mechanisms including activation of PARP in diabetic complications and on novel emerging therapeutical strategies offered by neutralization of peroxynitrite and inhibition of PARP.

Background-Increased oxidative stress and dysregulation of nitric oxide have been implicated in the cardiotoxicity of doxorubicin (DOX), a commonly used antitumor agent. Peroxynitrite is a reactive oxidant produced from nitric oxide and superoxide in various forms of cardiac injury. Using a novel metalloporphyrinic peroxynitrite decomposition catalyst, FP15, and nitric oxide synthase inhibitors or knockout mice, we now delineate the pathogenetic role of peroxynitrite in rodent models of DOX-induced cardiac dysfunction. Methods and Results-Mice received a single injection of DOX (25 mg/kg IP). Five days after DOX administration, left ventricular performance was significantly depressed, and high mortality was noted. Treatment with FP15 and an inducible nitric oxide synthase inhibitor, aminoguanidine, reduced DOX-induced mortality and improved cardiac function. Genetic deletion of the inducible nitric oxide synthase gene was also accompanied by better preservation of cardiac performance. In contrast, inhibition of the endothelial isoform of nitric oxide synthase with N-nitro-L-arginine methyl ester increased DOX-induced mortality. FP15 reduced the DOX-induced increase in serum LDH and creatine kinase activities. Furthermore, FP15 prevented the DOX-induced increase in lipid peroxidation, nitrotyrosine formation, and metalloproteinase activation in the heart but not NAD(P)H-driven superoxide generation. Peroxynitrite neutralization did not interfere with the antitumor effect of DOX. FP15 also decreased ischemic injury in rats and improved cardiac function and survival of mice in a chronic model of DOX-induced cardiotoxicity. Conclusions-Thus

Patients with diabetes exhibit a high incidence of diabetic cardiomyopathy and vascular complications, which underlie the development of retinopathy, nephropathy, and neuropathy and increase the risk of hypertension, stroke, and myocardial infarction. There is emerging evidence that the activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) importantly contributes to the development of endothelial dysfunction in a streptozotocin-induced model of diabetes. We investigated the role of PARP activation in the pathogenesis of cardiac dysfunction in streptozotocin-induced and genetic (nonobese diabetic) models of diabetes in rats and mice. Development of diabetes was accompanied by hyperglycemia, cardiac PARP activation, a selective loss of endothelium-dependent vasodilation in the thoracic aorta, and an early diastolic dysfunction of the heart. Treatment with a novel potent phenanthridinonebased PARP inhibitor, PJ34, starting 1 week after the onset of diabetes, restored normal vascular responsiveness and significantly improved cardiac dysfunction, despite the persistence of severe hyperglycemia. The beneficial effect of PARP inhibition persisted even after several weeks of discontinuation of the treatment. Thus, PARP activation plays a central role in the pathogenesis of diabetic cardiovascular (cardiac as well as endothelial) dysfunction. PARP inhibitors may exert beneficial effects against the development of cardiovascular complications in diabetes. Diabetes 51:514 -521, 2002 P oly(ADP ribose) polymerase (PARP), also known as poly(ADP ribose) synthetase (PARS), is an abundant nuclear enzyme of eukaryotic cells that participates in DNA repair in response to genotoxic stress. When activated by DNA single-strand breaks, PARP initiates an energy-consuming cycle by transferring ADP ribose units from NAD ϩ to nuclear proteins. This process results in rapid depletion of the intracellular NAD ϩ and ATP pools, slowing the rate of glycolysis and mitochondrial respiration, eventually leading to cellular dysfunction and death (1-7). Overactivation of PARP represents an important mechanism of tissue damage in various pathological conditions associated with oxidant stress, including myocardial reperfusion injury (4), stroke (3), shock (7,8), and autoimmune ␤-cell destruction (5,6). Recently, we reported that the activation of PARP importantly contributes to the development of endothelial dysfunction in a streptozotocin (STZ)-induced model of diabetes in mice (9,10).Cardiovascular complications are the most common cause of morbidity and mortality in diabetic patients. The presence of myocardial dysfunction independent of coronary artery disease in diabetes, known as "diabetic cardiomyopathy," has been well documented in both humans and animals (11-15). Diabetic cardiomyopathy is characterized by an early diastolic dysfunction and a late systolic one, with intracellular retention of calcium and sodium and loss of potassium. The mechanism of diastolic dysfunction remains unknown, but it does not appear to be due to cha...

Abstract-Oxygen-and nitrogen-derived free radicals and oxidants play an important role in the pathogenesis of diabetic endothelial dysfunction. Recently we proposed the importance of oxidant-induced DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) in the pathogenesis of diabetic endothelial dysfunction.In this study, we tested whether established diabetic endothelial dysfunction is reversible by PARP inhibition. The novel PARP inhibitor PJ34 (10 mg/kg per day PO) was given at various lengths (4 weeks or 3 days) for established streptozotocin-diabetic animals. In addition, we also tested whether incubation of the aortic rings with PJ34 (3 mol/L) or a variety of other PARP inhibitors for 1 hour affects the diabetic vascular changes. Both 4-week and 3-day PARP-inhibitor treatment of streptozotocin-diabetic mice with established endothelial dysfunction fully reversed the acetylcholine-induced endothelium-dependent relaxations in vitro. Furthermore, 1-hour in vitro incubation of aortae from streptozotocin-diabetic mice with various PARP inhibitors was able to reverse the endothelial dysfunction. ATP, NAD ϩ , and NADPH levels were markedly reduced in diabetic animals, and PARP-inhibitor treatment was able to restore these alterations. Unexpectedly, pharmacological inhibition of PARP not only prevents the development of the endothelial dysfunction but is also able to rapidly reverse it. Thus, PARP activation and the associated metabolic compromise represent an ongoing process in diabetic blood vessels. Pharmacological inhibition of this process is able to reverse diabetic endothelial dysfunction. Key Words: diabetes Ⅲ endothelium Ⅲ nitric oxide Ⅲ necrosis Ⅲ apoptosis P oly(ADP-ribose) polymerase (PARP) is an abundant nuclear enzyme that has been implicated in the cellular response to DNA injury. 1 We recently proposed a role for PARP activation in the pathogenesis of diabetic endothelial dysfunction. Endothelial cells and vascular rings from PARP ϩ/ϩ mice incubated in high glucose were found to exhibit metabolic suppression and loss of endotheliumdependent relaxant function, effects that did not develop in the vascular rings from PARP Ϫ/Ϫ mice and were prevented by pharmacological inhibition of PARP. 2 Ex vivo experiments, examining the immunohistochemical profile and the endothelium-dependent relaxant function of diabetic aortae, demonstrated intravascular production of reactive nitrogen species, the development of DNA strand breakage, and the activation of PARP. 2 Finally, in vivo treatment with PJ34, a novel potent phenanthridinone PARP inhibitor, was found to prevent the development of diabetic endothelial dysfunction in streptozotocin-diabetic mice. 2 In this study we report our recent, unexpected findings that demonstrate that pharmacological PARP inhibition not only prevents the development of diabetic vascular dysfunction but also rapidly restores the function of established diabetic blood vessels.

Recent studies demonstrated that activation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) by oxidant-mediated DNA damage is an important pathway of tissue injury in conditions associated with oxidative stress. Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the phenanthridinone PARP inhibitor PJ-34, we now demonstrate an essential role of PARP-1 in the development of pulmonary inflammation induced by lipopolysaccharide (LPS). PARP-1+/+ and PARP-1-/- mice received an intratracheal instillation of LPS (50 microg), followed after 24 h by bronchoalveolar lavage to measure the cytokines TNF-alpha, IL-1beta, and IL-6, the chemokines MIP-1alpha and MIP-2, leukocyte counts and myeloperoxidase activity (neutrophil accumulation), protein content (high permeability edema), and nitrite/ nitrate (nitric oxide production). Malondialdehyde (an index of lipid peroxidation) was measured in lung tissue. Similar experiments were conducted in BALB/c mice treated with PJ-34 or vehicle. The absence of functional PARP-1 reduced LPS-induced increases of cytokines and chemokines, alveolar neutrophil accumulation, lung hyperpermeability, NO production, and lipid peroxidation. Histological analysis revealed attenuated lung damage after PARP inhibition. Our findings support a mechanistic role of PARP-1 in the regulation of LPS-induced lung inflammation. Pharmacological inhibition of PARP may be useful in clinical conditions associated with overwhelming lung inflammation.

The novel series of phenanthridinone PARS inhibitors have potent cytoprotective effects in vitro and significant protective effects in shock and reperfusion injury in rodent models in vivo.

Nitrosative stress, that is, enhanced peroxynitrite formation, has been documented in both experimental and clinical diabetic neuropathy (DN), but its pathogenetic role remains unexplored. This study evaluated the role for nitrosative stress in two animal models of type 1 diabetes: streptozotocin-diabetic mice and diabetic NOD mice. Control (C) and streptozotocin-diabetic (D) mice were treated with and without the potent peroxynitrite decomposition catalyst FP15 (5 mg kg(-1) d(-1)) for 1 wk after 8 wk without treatment. Sciatic nerve nitrotyrosine (a marker of peroxynitrite-induced injury) and poly(ADP-ribose) immunoreactivities were present in D and absent in C and D+FP15. FP15 treatment corrected sciatic motor and hind-limb digital sensory nerve conduction deficits and sciatic nerve energy state in D, without affecting those variables in C. Nerve glucose and sorbitol pathway intermediate concentrations were similarly elevated in D and D+FP15 vs C. In diabetic NOD mice, a 7-day treatment with either 1 or 3 mg kg(-1) d(-1) FP15 reversed increased tail-flick latency (a sign of reduced pain sensitivity); the effect of the higher dose was significant as early as 3 days after beginning of the treatment. In conclusion, nitrosative stress plays a major role in DN in, at least, type 1 diabetes. This provides the rationale for development of agents counteracting peroxynitrite formation and promoting peroxynitrite decomposition, and their evaluation in DN.

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) by oxidant-mediated DNA damage is an important pathway of cell dysfunction and tissue injury in conditions associated with oxidative stress. Increased oxidative stress is a major factor implicated in the cardiotoxicity of doxorubicin (DOX), a widely used antitumor anthracycline antibiotic. Thus, we hypothesized that the activation of PARP may contribute to the DOX-induced cardiotoxicity. Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the phenanthridinone PARP inhibitor PJ34, we now demonstrate the role of PARP in the development of cardiac dysfunction induced by DOX. PARP-1ϩ/ϩ and PARP-1Ϫ/Ϫ mice received a single injection of DOX (25 mg/kg i.p). Five days after DOX administration, left ventricular performance was significantly depressed in PARP-1ϩ/ϩ mice, but only to a smaller extent in PARP-1Ϫ/Ϫ ones. Similar experiments were conducted in BALB/c mice treated with PJ34 or vehicle. Treatment with a PJ34 significantly improved cardiac dysfunction and increased the survival of the animals. In addition PJ34 significantly reduced the DOX-induced increase in the serum lactate dehydrogenase and creatine kinase activities but not metalloproteinase activation in the heart. Thus, PARP activation contributes to the cardiotoxicity of DOX. PARP inhibitors may exert protective effects against the development of severe cardiac complications associated with the DOX treatment.Poly(ADP-ribose) polymerase (PARP), also known as poly-(ADP ribose) synthetase (PARS), is an abundant nuclear enzyme of eukaryotic cells. When activated by DNA singlestrand breaks, PARP initiates an energy-consuming cycle by transferring ADP ribose units from NAD ϩ to nuclear proteins. This process results in rapid depletion of the intracellular NAD ϩ and ATP pools, slowing the rate of glycolysis and mitochondrial respiration and eventually leading to cellular dysfunction and death (Eliasson et al., 1997;Szabó et al., 1997;Zingarelli et al., 1998;Burkart et al., 1999;Szabó, 2000). Overactivation of PARP represents an important mechanism of tissue damage in various pathological conditions associated with oxidant stress, including myocardial reperfusion injury (Zingarelli et al., 1998), stroke (Eliasson et al., 1997), circulatory shock Oliver et al., 1999;Liaudet et al., 2000), and autoimmune ␤-cell destruction (Burkart et al., 1999;Pieper et al., 1999). Activation of PARP also contributes to the development of cardiovascular dysfunction in diabetes (Soriano et al., 2001a,b;Pacher et al., 2002). Doxorubicin (DOX; Adriamycin; Pharmacia & Upjohn, Peapack, NJ) is a broad-spectrum antitumor anthracycline antibiotic that is commonly used to treat a variety of cancers, including severe leukemias, lymphomas, and solid tumors (Blum and Carter, 1974;Young et al., 1981;Singal et al., 1987;Hortobagyi, 1997;Singal and Iliskovic, 1998). However, the clinical use of DOX is limited because of its serious cardiotoxicity, which leads to irreversible...