Mice lacking the poly(ADP-ribose) polymerase gene are resistant to pancreatic beta-cell destruction and diabetes development induced by streptozocin

Cell culture modeling to test therapies against hyperglycemia-mediated oxidative stress and injury

The concept that oxidative stress is a key mediator of nerve injury in diabetes has led us to design therapies that target oxidative stress mechanisms. Using an in vitro model of glucose-treated dorsal root ganglion (DRG) neurons in culture, we can examine both free radical generation, using fluorimetric probes for reactive oxygen species, and cell death via the TUNEL assay. The cell culture system is scaled down to a 96-well plate format, and so is well suited to high-throughput screening. In the present study, we test the ability of three drugs, nicotinamide, allopurinol, and alpha-lipoic acid, alone and in combination to prevent DRG neuron oxidative stress and cell death. This combination of drugs is currently in clinical trial in type 1 diabetic patients. We demonstrate independent effects on oxidative stress and neuronal survival for the three drugs, and neuronal protection using the three drugs in combination. The data strengthen the rationale for the current clinical trial. In addition, we describe an effective tool for rapid preclinical testing of novel therapies against diabetic neuropathy.

Aldose reductase deficiency prevents diabetes-induced blood-retinal barrier breakdown, apoptosis, and glial reactivation in the retina of db/db mice

In 15-month-old db/db mice, signs of diabetic retinopathy, including blood-retinal barrier breakdown, loss of pericytes, neuro-retinal apoptosis, glial reactivation, and proliferation of blood vessels, were evident. These changes in the diabetic retina were associated with increased expression of aldose reductase (AR). To further understand the role of AR in the pathogenesis of diabetic retinopathy, we generated db/db mice with an AR null mutation (AR-/- db/db). AR deficiency led to fewer retinal blood vessels with IgG leakage, suggesting that AR may contribute to blood-retinal barrier breakdown. AR deficiency also prevented diabetes-induced reduction of platelet/endothelial cell adhesion molecule-1 expression and increased expression of vascular endothelial growth factor, which may have contributed to blood-retinal barrier breakdown. In addition, long-term diabetes-induced neuro-retinal stress and apoptosis and proliferation of blood vessels were less prominent in AR-/- db/db mice. These findings indicate that AR is responsible for the early events in the pathogenesis of diabetic retinopathy, leading to a cascade of retinal lesions, including blood-retinal barrier breakdown, loss of pericytes, neuro-retinal apoptosis, glial reactivation, and neovascularization.

Determination of apoptosis, uracil incorporation, DNA strand breaks, and sister chromatid exchanges under conditions of thymidylate deprivation in a model of BER deficiency

Thymidylate synthase (TS) is an important target of several chemotherapeutic agents. During TS inhibition, dTTP levels decrease with a subsequent increase in dUTP. Uracil incorporated into the genome is removed by base excision repair (BER). BER has been hypothesized to play a role in the response to thymidylate deprivation, despite a lack of direct evidence. We previously found that beta-pol null murine fibroblasts were approximately six-fold more resistant than wild-type cells to raltitrexed, a folate-based inhibitor specific for TS. In this study, a number of endpoints were determined to understand the influence of BER and beta-pol during raltitrexed treatment. Raltitrexed induced apoptosis in wild-type cells to a greater extent than in beta-pol null cells. A PARP inhibitor decreased the sensitivity to raltitrexed, although the extent was not different between wild-type and beta-pol null cells. No evidence was seen for extensive strand break formation that preceded apoptosis, although raltitrexed induced more sister chromatid exchanges in wild-type cells. Increased levels of uracil in DNA were detected following treatment in wild-type and beta-pol null cells. However, uracil levels were only approximately two-fold higher in DNA from treated cells compared to untreated. Uracil DNA glycosylase activity was slightly higher in beta-pol null cells, although not sufficiently different to explain the difference in sensitivity to raltitrexed. Taken together, the data suggest that the sensitivity of the wild-type cells to raltitrexed is not associated with activation of PARP-1 dependent BER, extensive uracil incorporation into DNA and persistent strand breaks, but rather with changes suggestive of DNA recombination.

Roles of poly(ADP-ribose) polymerase activation in the pathogenesis of diabetes mellitus and its complications

Activation of poly(ADP-ribose) polymerase (PARP) plays a role in the pathogenesis of beta-cell necrosis that occurs in response to autoimmune disease associated with Type I diabetes. In addition, PARP activation also plays a role in the pathogenesis of endothelial injury that underlies the ethiology of various diabetic complications (vasculopathy, cardiomyopathy, retinopathy, neuropathy), which develop on the basis of chronically elevated circulating glucose levels in diabetes. Both during the pathogenesis of diabetes and during the pathogenesis of diabetic complications, free radical and oxidant production leads to DNA strand-breakage which activates the nuclear enzyme PARP and initiates an energy consuming, inefficient cellular metabolic cycle with transfer of the ADP-ribosyl moiety of NAD+ to protein acceptors. These processes lead to the functional impairment of the affected cells (beta-cells or vascular endothelial cells, respectively). PARP also promotes the activation of various pro-inflammatory signal transduction pathways. During the last two decades, a growing number of experimental studies demonstrated the beneficial effects PARP inhibition in various models of diabetes and diabetic complications. The current review provides an overview of the experimental evidence implicating PARP as a causative factor in the pathogenesis of diabetes and diabetic complications in vitro and in vivo.

Pivotal role of Akt activation in mitochondrial protection and cell survival by poly(ADP-ribose)polymerase-1 inhibition in oxidative stress

According to the classical view, the cytoprotective effect of inhibitors of poly(ADP-ribose)polymerase (PARP) in oxidative stress was based on the prevention of NAD+ and ATP depletion, thus the attenuation of necrosis. Our previous data on PARP inhibitors in an inflammatory model suggested that PARP-catalyzed ADP-ribosylations may affect signaling pathways, which can play a significant role in cell survival. To clarify the molecular mechanism of cytoprotection, PARP activity was inhibited pharmacologically by suppressing PARP-1 expression by a small interfering RNA (siRNA) technique or by transdominantly expressing the N-terminal DNA-binding domain of PARP-1 (PARP-DBD) in cultured cells. Cell survival, activation of the phosphatidylinositol 3-kinase (PI3-kinase)/Akt system, and the preservation of mitochondrial membrane potential were studied in hydrogen peroxide-treated WRL-68 cells. Our data showed that suppression of the single-stranded DNA break-induced PARP-1 activation by pharmacological inhibitor, siRNA, or by the transdominant expression of PARP-DBD protected cells from oxidative stress and induced the phosphorylation and activation of Akt. Furthermore, prevention of Akt activation by inhibiting PI3-kinase counteracted the cytoprotective effect of PARP inhibition. Microscopy data showed that PARP inhibition-induced Akt activation was responsible for protection of mitochondria in oxidative stress because PI3-kinase inhibitors diminished the protective effect of PARP inhibition. Similarly, Src kinase inhibitors, which decrease Akt phosphorylation, also counteracted the protection of mitochondrial membrane potential supporting the pivotal role of Akt in cytoprotection. These data together with the finding that PARP inhibition in the absence of oxidative stress induced the phosphorylation and activation of Akt indicate that PARP inhibition-induced Akt activation is dominantly responsible for the cytoprotection in oxidative stress.

Excessive stimulation of poly(ADP-ribosyl)ation contributes to endothelial dysfunction in pre-eclampsia

1. Pre-eclampsia is a serious pregnancy disorder associated with widespread activation of the maternal vascular endothelium. Recent evidence implicates a role for oxidative stress in the aetiology of this condition. 2. Reactive oxygen species, particularly superoxide anions, invokes endothelial cell activation through many pathways. Oxidant-induced cell injury triggers the activation of nuclear enzyme poly(ADP-ribose) polymerase (PARP) leading to endothelial dysfunction in various pathophysiological conditions (reperfusion, shock, diabetes). 3. We have studied whether the loss of endothelial function in pre-eclampsia is dependent on PARP activity. Endothelium-dependent responses of myometrial arteries were tested following exposure to either plasma from women with pre-eclampsia or normal pregnant women in the presence and absence of a novel potent inhibitor of PARP, PJ34. Additional effects of plasma and PJ34 inhibition were identified in microvascular endothelial cell cultures. 4. In myometrial arteries, PARP inhibition blocked the attenuation of endothelium-dependent responses following exposure to plasma from women with pre-eclampsia. In endothelial cell cultures, plasma from pre-eclamptics induced measurable oxidative stress and a concomitant increase in PARP activity and reduction in cellular ATP. Again, these biochemical changes were reversed by PJ34. 5. These results suggest that PARP activity plays a pathogenic role in the development of endothelial dysfunction in pre-eclampsia and promotes PARP inhibition as a potential therapy in this condition.

Synthesis and in vivo evaluation of [11C]PJ34, a potential radiotracer for imaging the role of PARP-1 in necrosis

Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear enzyme of eukaryotic cells that has been implicated in response to DNA injury. PARP-1 detects single-strand DNA breaks induced by a variety of genotoxic insults. A hyperactivation of PARP-1 is believed to play a critical role in tissues undergoing cellular death by necrosis. Therefore, a radiotracer that could image PARP-1 levels with PET could provide a useful tool in measuring necrosis in a variety of pathological conditions. The phenanthridinone derivative, 2-(dimethylamino)-N-(5,6-dihydro-6-oxophenanthridin-2-yl)acetamide (PJ34), has a high affinity for PARP-1 (IC(50) = 20 nM) and is a suitable lead compound for PET radiotracer development. The synthesis of [(11)C]PJ34 was accomplished by base-catalyzed reaction of the corresponding des-methyl precursor, N-(5,6-dihydro-6-oxophenanthridin-2-yl)-2-(methylamino)acetamide with [(11)C]methyl iodide in DMF. The radiolabeling yield was 60% and the specific activity was approximately 2000 mCi/micromol (decay corrected to E.O.B.). The total radiosynthesis time was approximately 50 min. Preliminary in vivo biodistribution studies in a rodent model of diabetes indicate that [(11)C]PJ34 displays a high uptake in tissues where PARP-1 is hyperactivated. These data indicate that [(11)C]PJ34 may be a useful radiotracer for imaging tissues undergoing cellular death via necrosis.

The pathogenesis of diabetic complications: the role of DNA injury and poly(ADP-ribose) polymerase activation in peroxynitrite-mediated cytotoxicity

Recent work has demonstrated that hyperglycemia-induced overproduction of superoxide by the mitochondrial electron-transport chain triggers several pathways of injury [(protein kinase C (PKC), hexosamine and polyol pathway fluxes, advanced glycation end product formation (AGE)] involved in the pathogenesis of diabetic complications by inhibiting glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity. Increased oxidative and nitrosative stress activates the nuclear enzyme, poly(ADP-ribose) polymerase-1 (PARP). PARP activation, on one hand, depletes its substrate, NAD+, slowing the rate of glycolysis, electron transport and ATP formation. On the other hand, PARP activation results in inhibition of GAPDH by poly-ADP-ribosylation. These processes result in acute endothelial dysfunction in diabetic blood vessels, which importantly contributes to the development of various diabetic complications. Accordingly, hyperglycemia-induced activation of PKC and AGE formation are prevented by inhibition of PARP activity. Furthermore, inhibition of PARP protects against diabetic cardiovascular dysfunction in rodent models of cardiomyopathy, nephropathy, neuropathy, and retinopathy. PARP activation is also present in microvasculature of human diabetic subjects. The present review focuses on the role of PARP in diabetic complications and emphasizes the therapeutic potential of PARP inhibition in the prevention or reversal of diabetic complications.

Inhibition of TRPM2 function by PARP inhibitors protects cells from oxidative stress-induced death

TRPM2 is a member of the transient receptor potential (TRP) protein superfamily of calcium-permeable, voltage-independent ion channels expressed in nonexcitable cells. Activation of TRPM2 by oxidative stress results in calcium influx and susceptibility to cell death, whereas inhibition of TRPM2 function enhances cell survival. In the present edition of this journal, Fonfria et al. demonstrate a role for poly(ADP ribose) polymerase (PARP) as a mediator between oxidative stress and TRPM2 activation. They present evidence that inhibition of either PARP or TRPM2 protects cells from plasma membrane damage and cell death. The therapeutic implications of this important observation are discussed.

O-GlcNAcase uses substrate-assisted catalysis: kinetic analysis and development of highly selective mechanism-inspired inhibitors

The post-translational modification of serine and threonine residues of nucleocytoplasmic proteins with 2-acetamido-2-deoxy-d-glucopyranose (GlcNAc) is a reversible process implicated in multiple cellular processes. The enzyme O-GlcNAcase catalyzes the cleavage of beta-O-linked GlcNAc (O-GlcNAc) from modified proteins and is a member of the family 84 glycoside hydrolases. The family 20 beta-hexosaminidases bear no apparent sequence similarity yet are functionally related to O-GlcNAcase because both enzymes cleave terminal GlcNAc residues from glycoconjugates. Lysosomal beta-hexosaminidase is known to use substrate-assisted catalysis involving the 2-acetamido group of the substrate; however, the catalytic mechanism of human O-GlcNAcase is unknown. By using a series of 4-methylumbelliferyl 2-deoxy-2-N-fluoroacetyl-beta-D-glucopyranoside substrates, Taft-like linear free energy analyses of these enzymes indicates that O-GlcNAcase uses a catalytic mechanism involving anchimeric assistance. Consistent with this proposal, 1,2-dideoxy-2'-methyl-alpha-D-glucopyranoso-[2,1-d]-Delta2'-thiazoline, an inhibitor that mimics the oxazoline intermediate proposed in the catalytic mechanism of family 20 glycoside hydrolases, is shown to act as a potent competitive inhibitor of both O-GlcNAcase (K(I) = 0.070 microm) and beta-hexosaminidase (K = 0.070 microm). A series of 1,2-dideoxy-2'-methyl-alpha-D-glucopyranoso-[2,1-d]-Delta2'-thiazoline analogues were prepared, and one inhibitor demonstrated a remarkable 1500-fold selectivity for O-GlcNAcase (K(I) = 0.230 microm) over beta-hexosaminidase (K(I) = 340 microm). These inhibitors are cell permeable and modulate the activity of O-GlcNAcase in tissue culture. Because both enzymes have vital roles in organismal health, these potent and selective inhibitors of O-GlcNAcase should prove useful in studying the role of this enzyme at the organismal level without generating a complex chemical phenotype stemming from concomitant inhibition of beta-hexosaminidase.

Experimental diabetic neuropathy with spontaneous recovery: is there irreparable damage?

Progressive diabetic neuropathy has hitherto been irreversible in humans. New approaches raise the question of whether islet cell reconstitution rendering euglycemia can reverse specific features of neuropathy. We evaluated physiological and structural features of experimental neuropathy in a long-term murine model of diabetes induced by streptozotocin. By serendipity, a subset of these diabetic mice spontaneously regained islet function and attained near-euglycemia. Our hypotheses were that this model might better reflect axon loss observed in human disease and that spontaneous recovery from diabetes might identify the features of neuropathy that are reversible. In this model, experimental neuropathy closely modeled that in humans in most critical aspects: declines in motor conduction velocities, attenuation of compound muscle (M waves) and nerve action potentials, axon atrophy, myelin thinning, loss of epidermal axons, and loss of sweat gland innervation. Overt sensory neuron loss in dorsal root ganglia was a feature of this model. In mice with recovery, there was robust electrophysiological improvement, less myelin thinning, and remarkable epidermal and sweat gland reinnervation. There was, however, no recovery of populations of lost sensory neurons. Our findings identify a robust model of human diabetic neuropathy and indicate that overt, irretrievable loss of sensory neurons is one of its features, despite collateral reinnervation of target organs. Sensory neurons deserve unique protective strategies irrespective of islet cell reconstitution.

Characterisation of glucose transporters in the intact coronary artery endothelium in rats: GLUT-2 upregulated by long-term hyperglycaemia

AIMS/HYPOTHESIS

We have examined the effects of streptozotocin-induced type 1 diabetes on the expression and subcellular distribution of the classic sugar transporters (GLUT-1 to 5 and sodium-dependent glucose transporter-1 [SGLT-1]) in the endothelial cells of an en face preparation of septal coronary artery from Wistar rats.

METHODS

The presence of the GLUT isoforms and SGLT-1 in the endothelial cell layer was determined by immunohistochemistry using wide-field fluorescence microscopy coupled to deconvolution, and was quantified by digital image analysis.

RESULTS

We found that all of the transporters were expressed within these cells and that all except SGLT-1 were preferentially located on the abluminal side. The heaviest labelling was adjacent to the cell-to-cell junctions where the luminal and abluminal membranes are in close proximity, which may reflect a spatial organisation specialised for vectorial glucose transport across the thinnest part of the cytoplasm. Long-term hyperglycaemia, induced by streptozotocin, significantly downregulated GLUT-1, 3, 4 and 5 and dramatically upregulated GLUT-2, leaving SGLT-1 unchanged.

CONCLUSIONS/INTERPRETATION

We conclude that the high susceptibility of endothelial cells to glucose toxicity may be the result of the subcellular organisation of their GLUTs and the increased expression of GLUT-2.

Noncleavable poly(ADP-ribose) polymerase-1 regulates the inflammation response in mice

Poly(ADP-ribosyl)ation is rapidly formed in cells following DNA damage and is regulated by poly(ADP-ribose) polymerase-1 (PARP-1). PARP-1 is known to be involved in various cellular processes, such as DNA repair, genomic stability, transcription, and cell death. During apoptosis, PARP-1 is cleaved by caspases to generate 89-kDa and 24-kDa fragments, a hallmark of apoptosis. This cleavage is thought to be a regulatory event for cellular death. In order to understand the biological significance of PARP-1 cleavage, we generated a PARP-1 knockin (PARP-1(KI/KI)) mouse model, in which the caspase cleavage site of PARP-1, DEVD(214), was mutated to render the protein resistant to caspases during apoptosis. While PARP-1(KI/KI) mice developed normally, they were highly resistant to endotoxic shock and to intestinal and renal ischemia-reperfusions, which were associated with reduced inflammatory responses in the target tissues and cells due to the compromised production of specific inflammatory mediators. Despite normal binding of NF-kappaB to DNA, NF-kappaB-mediated transcription activity was impaired in the presence of caspase-resistant PARP-1. This study provides a novel insight into the function of PARP-1 in inflammation and ischemia-related pathophysiologies.

Apoptosis-inducing factor substitutes for caspase executioners in NMDA-triggered excitotoxic neuronal death

The profound neuroprotection observed in poly(ADP-ribose) polymerase-1 (PARP-1) null mice to ischemic and excitotoxic injury positions PARP-1 as a major mediator of neuronal cell death. We report here that apoptosis-inducing factor (AIF) mediates PARP-1-dependent glutamate excitotoxicity in a caspase-independent manner after translocation from the mitochondria to the nucleus. In primary murine cortical cultures, neurotoxic NMDA exposure triggers AIF translocation, mitochondrial membrane depolarization, and phosphatidyl serine exposure on the cell surface, which precedes cytochrome c release and caspase activation. NMDA neurotoxicity is not affected by broad-spectrum caspase inhibitors, but it is prevented by Bcl-2 overexpression and a neutralizing antibody to AIF. These results link PARP-1 activation with AIF translocation in NMDA-triggered excitotoxic neuronal death and provide a paradigm in which AIF can substitute for caspase executioners.

Association study of human MTH1 gene polymorphisms with type 1 diabetes mellitus

Reactive oxygen species are considered to play a role in the development of diabetes mellitus and its complications. Human MTH1 (mutT homologue 1) has 8-oxo-7,8-dihydrodeoxyguanosine triphosphatase activity, which repairs oxidized forms of dGTP. This enzyme is known to have a thermolabile Met83 variant. We examined whether Val83Met polymorphism of human MTH1 gene is associated with type 1 diabetes mellitus. We recruited 156 type 1 diabetic patients (59 males and 97 females). The polymorphism was analyzed by restriction fragment length polymorphism analysis with Nsi I. The Met/Met genotype at codon 83 was very rare in both control and patient groups. Val/Met genotype tended to be more frequent in the whole type 1 diabetic patients than in controls. When subjects were divided into subgroups according to gender, there were no differences in the genotype and allele frequencies between patients and controls in males. On the other hand, in female type 1 diabetic patients, the Val/Met genotype was more frequent than in female controls (corrected P = 0.102). The Met allele was significantly more frequent in female type 1 diabetic patients than in female controls (corrected P = 0.022). Our results suggested that the Met allele at codon 83 of MTH1 gene might be involved in the development of type 1 diabetes mellitus in the Japanese female population.

Increased expression of poly(ADP-ribose) polymerase-1 contributes to caspase-independent myocyte cell death during heart failure

Poly(ADP-ribose) polymerase-1 (PARP-1) plays a pivotal role in regulating genome stability, cell cycle progression, and cell survival. However, overactivation of PARP has been shown to contribute to cell death and organ failure in various stress-related disease conditions. In this study, we examined the role of PARP in the development and progression of cardiac hypertrophy. We measured the expression of PARP in mouse hearts with physiological (swimming exercise) and pathological (aortic banding) cardiac hypertrophy as well as in human heart samples taken at the time of transplantation. PARP levels were elevated both in swimming and banded mice hearts and demonstrated a linear positive correlation with the degree of cardiac hypertrophy. A dramatic increase (4-fold) of PARP occurred in 6-wk banded mice, accompanied by apparent signs of ventricular dilation and myocyte cell death. PARP levels were also elevated (2- to 3-fold) in human hearts with end-stage heart failure compared with controls. However, we found no evidence of caspase-mediated PARP cleavage in either mouse or human failing hearts. Overexpression of PARP in primary cultures of cardiac myocytes led to suppression of gene expression and robust myocyte cell death. Furthermore, data obtained from the analysis of PARP knockout mice revealed that these hearts produce an attenuated hypertrophic response to aortic banding compared with controls. Together, these results demonstrate a role for PARP in the onset and progression of cardiac hypertrophy and suggest that some events related to cardiac hypertrophy growth and progression to heart failure are mediated by a PARP-dependent mechanism.

Depletion of the 110-kilodalton isoform of poly(ADP-ribose) glycohydrolase increases sensitivity to genotoxic and endotoxic stress in mice

Poly(ADP-ribosylation) is rapidly stimulated in cells following DNA damage. This posttranslational modification is regulated by the synthesizing enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the degrading enzyme poly(ADP-ribose) glycohydrolase (PARG). Although the role of PARP-1 in response to DNA damage has been studied extensively, the function of PARG and the impact of poly(ADP-ribose) homeostasis in various cellular processes are largely unknown. Here we show that by gene targeting in embryonic stem cells and mice, we specifically deleted the 110-kDa PARG protein (PARG(110)) normally found in the nucleus and that depletion of PARG(110) severely compromised the automodification of PARP-1 in vivo. PARG(110)-deficient mice were viable and fertile, but these mice were hypersensitive to alkylating agents and ionizing radiation. In addition, these mice were susceptible to streptozotocin-induced diabetes and endotoxic shock. These data indicate that PARG(110) plays an important role in DNA damage responses and in pathological processes.

TRPM2 channel opening in response to oxidative stress is dependent on activation of poly(ADP-ribose) polymerase

1. TRPM2 (melastatin-like transient receptor potential 2 channel) is a nonselective cation channel that is activated under conditions of oxidative stress leading to an increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)) and cell death. We investigated the role of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP) on hydrogen peroxide (H(2)O(2))-mediated TRPM2 activation using a tetracycline-inducible TRPM2-expressing cell line. 2. In whole-cell patch-clamp recordings, intracellular adenine 5'-diphosphoribose (ADP-ribose) triggered an inward current in tetracycline-induced TRPM2-human embryonic kidney (HEK293) cells, but not in uninduced cells. Similarly, H(2)O(2) stimulated an increase in [Ca(2+)](i) (pEC(50) 4.54+/-0.02) in Fluo-4-loaded TRPM2-expressing HEK293 cells, but not in uninduced cells. Induction of TRPM2 expression caused an increase in susceptibility to plasma membrane damage and mitochondrial dysfunction in response to H(2)O(2). These data demonstrate functional expression of TRPM2 following tetracycline induction in TRPM2-HEK293 cells. 3. PARP inhibitors SB750139-B (patent number DE10039610-A1 (Lubisch et al., 2001)), PJ34 (N-(6-oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylacetamide) and DPQ (3, 4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone) inhibited H(2)O(2)-mediated increases in [Ca(2+)](i) (pIC(50) vs 100 microm H(2)O(2): 7.64+/-0.38; 6.68+/-0.28; 4.78+/-0.05, respectively), increases in mitochondrial dysfunction (pIC(50) vs 300 microm H(2)O(2): 7.32+/-0.23; 6.69+/-0.22; 5.44+/-0.09, respectively) and decreases in plasma membrane integrity (pIC(50) vs 300 microm H(2)O(2): 7.45+/-0.27; 6.35+/-0.18; 5.29+/-0.12, respectively). The order of potency of the PARP inhibitors in these assays (SB750139>PJ34>DPQ) was the same as for inhibition of isolated PARP enzyme. 4. SB750139-B, PJ34 and DPQ had no effect on inward currents elicited by intracellular ADP-ribose in tetracycline-induced TRPM2-HEK293 cells, suggesting that PARP inhibitors are not interacting directly with the channel. 5. SB750139-B, PJ34 and DPQ inhibited increases in [Ca(2+)](i) in a rat insulinoma cell line (CRI-G1 cells) endogenously expressing TRPM2 (pIC(50) vs 100 microm H(2)O(2): 7.64+/-0.38; 6.68+/-0.28; 4.78+/-0.05, respectively). 6. These data suggest that oxidative stress causes TRPM2 channel opening in both recombinant and endogenously expressing cell systems via activation of PARP enzymes.

Poly(ADP-ribosyl)ation enhancement in brain cell nuclei is associated with diabetic neuropathy

The study has been undertaken to evaluate the effect of streptozotocin (STZ)-induced diabetes on rat brain poly(ADP-ribose)polymerase (Parp) activity and assess whether and how a Parp inhibitor, nicotinamide (NAm), may potentially regulate the diabetes-induced changes. Experiments were carried out after 4 weeks of diabetes duration in rats treated with or without NAm (100 or 200 mg kg(-1) day(-1), injected intraperitonally for 2 weeks). Assays were performed in purified brain cell nuclei to determine Parp activity by incorporation of radiolabeled ADP-ribose moieties from nicotinamide adenine dinucleotide (NAD+) into nuclear proteins. NAD+ and ATP levels were measured by enzymatic procedures. DNA damage was detected spectrophotometrically.

RESULTS

Parp activity but not NAD-glycohydrolase (NADase) was stimulated by 21% in diabetes vs. control while lowering effects of diabetes on NAD+ and ATP levels were observed. Increase in Parp activity was accompanied by accumulation of malondialdehyde (MDA) and increase in DNA breakage. Treatment with either 100 or 200 mg/kg NAm dose diminished both DNA damage and Parp activity and partially restored the NAD+ and ATP contents, which is probably associated with direct competitive inhibition of Parp as well as with NAm's ability to block diabetes induced oxidative stress.

CONCLUSION

Poly(ADP-ribosyl)polymerase overactivation is involved in the development of brain dysfunction in diabetic neuropathy. The mechanism of brain disorders seems to be at least partially connected with a decrease in cellular content and altered subcellular distribution of Parp substrate, NAD+, which, in turn, results in a reduction of ATP level that leads to a total failure of oxidative metabolism. NAm in both doses is effective for the inhibition of poly(ADP-ribosyl)ation.

A new, potent poly(ADP-ribose) polymerase inhibitor improves cardiac and vascular dysfunction associated with advanced aging

Increased production of reactive oxygen and nitrogen species has recently been implicated in the pathogenesis of cardiac and endothelial dysfunction associated with atherosclerosis, hypertension, and aging. Oxidant-induced cell injury triggers the activation of nuclear enzyme poly(ADP-ribose) polymerase (PARP), which in turn contributes to cardiac and vascular dysfunction in various pathophysiological conditions including diabetes, reperfusion injury, circulatory shock, and aging. Here, we investigated the effect of a new PARP inhibitor, INO-1001, on cardiac and endothelial dysfunction associated with advanced aging using Millar's new Aria pressure-volume conductance system and isolated aortic rings. Young adult (3 months old) and aging (24 months old) Fischer rats were treated for 2 months with vehicle, or the potent PARP inhibitor INO-1001. In the vehicle-treated aging animals, there was a marked reduction of both systolic and diastolic cardiac function and loss of endothelial relaxant responsiveness of aortic rings to acetylcholine. Treatment with INO-1001 improved cardiac performance in aging animals and also acetylcholine-induced, nitric oxide-mediated vascular relaxation. Thus, pharmacological inhibition of PARP may represent a novel approach to improve cardiac and vascular dysfunction associated with aging.

Alkylating DNA damage stimulates a regulated form of necrotic cell death

Necrosis has been considered a passive form of cell death in which the cell dies as a result of a bioenergetic catastrophe imposed by external conditions. However, in response to alkylating DNA damage, cells undergo necrosis as a self-determined cell fate. This form of death does not require the central apoptotic mediators p53, Bax/Bak, or caspases and actively induces an inflammatory response. Necrosis in response to DNA damage requires activation of the DNA repair protein poly(ADP-ribose) polymerase (PARP), but PARP activation is not sufficient to determine cell fate. Cell death is determined by the effect of PARP-mediated beta-nicotinamide adenine dinucleotide (NAD) consumption on cellular metabolism. Cells using aerobic glycolysis to support their bioenergetics undergo rapid ATP depletion and death in response to PARP activation. In contrast, cells catabolizing nonglucose substrates to maintain oxidative phosphorylation are resistant to ATP depletion and death in response to PARP activation. Because most cancer cells maintain their ATP production through aerobic glycolysis, these data may explain the molecular basis by which DNA-damaging agents can selectively induce tumor cell death independent of p53 or Bcl-2 family proteins.

Differential role of poly(ADP-ribose) polymerase-1in apoptotic and necrotic neuronal death induced by mild or intense NMDA exposure in vitro

Overactivation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) plays a key role in the mechanisms responsible for neuronal death. In the present study, we examined the effects of the PARP-1 inhibitor 3,4-dihydro-5-[4-1(1-piperidinyl)buthoxy]-1(2H)-isoquinolinone (DPQ) in two models of N-methyl-d-aspartate (NMDA)-induced neurotoxicity. The exposure of mixed cultured cortical cells to 300 microM NMDA for 10 min induced a caspase-dependent type of apoptotic neuronal death. Conversely, exposure to 2 mM NMDA for 10 min led to the appearance of morphological features of necrosis, with no increase in caspase-3 activity and depletion in adenosine triphosphate (ATP) levels. DPQ (10 microM) reduced the NMDA-induced PARP activation, restored ATP to near control levels and significantly attenuated neuronal injury only in the severe NMDA exposure model. Similar results were obtained when pure neuronal cortical cultures were used. PARP-1 activation thus appears to play a preferential role in necrotic than in caspase-dependent apoptotic neuronal death.

Role of AIF in caspase-dependent and caspase-independent cell death

The major challenge in treating cancer is that many tumor cells carry mutations in key apoptotic genes such as p53, Bcl family proteins or those affecting caspase signaling. Such defects render treatment with traditional chemotherapeutic agents ineffective. Many studies have demonstrated the importance of caspase-independent cell death pathways in injury, degenerative diseases and tumor tissue. It is now recognized that in addition to their critical role in the production of cellular energy, mitochondria are also the source of key proapoptotic molecules involved in caspase activation. More recently, it has been discovered that in response to apoptotic stimuli, mitochondria can also release caspase-independent cell death effectors such as AIF and Endonuclease G. In this review, we examine the role of Bcl family proteins and poly(ADP-ribose) polymerase-1 signaling in the regulation of these apoptotic pathways and address the ongoing controversies in this field. Continued study of the mechanisms of apoptosis including caspase-independent death processes are likely to reveal novel therapeutic targets for the treatment of diverse human pathologies including cancer, neurodegenerative diseases and acute injuries such as stroke or myocardial infarction.

Poly(ADP-Ribose) Polymerase Contributes to the Development of Myocardial Infarction in Diabetic Rats and Regulates the Nuclear Translocation of Apoptosis-Inducing Factor

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP)-1 by oxidant-mediated DNA damage is an important pathway of cell dysfunction and tissue injury during myocardial infarction. Because diabetes mellitus can substantially alter cellular signal transduction pathways, we have now investigated whether the PARP pathway also contributes to myocardial ischemia/reperfusion (MI/R) injury in diabetes mellitus in rodents. Myocardial ischemia/reperfusion in control and streptozotocin-diabetic rats was induced by transient ligation of the left anterior descending coronary artery. PARP activation was inhibited by the isoindolinone derivative PARP inhibitor INO-1001. In diabetic rats, a more pronounced degree of myocardial contractile dysfunction developed, which also was associated with a larger infarct size, and significant mortality compared with nondiabetic rats. Inhibition of PARP provided a similar degree of myocardial protective effect in diabetic and nondiabetic animals and reduced infarct size and improved myocardial contractility. In diabetic rats, PARP inhibition reduced mortality during the reperfusion phase. There was marked activation of PARP in the ischemic/reperfused myocardium, which was blocked by INO-1001. In addition, there was a significant degree of mitochondrial-to-nuclear translocation of the cell death effector apoptosis-inducing factor (AIF) in myocardial infarction, which was blocked by pharmacological inhibition of PARP. The role of PARP in regulating AIF translocation in myocytes also was confirmed in an isolated perfused heart preparation. Overall, the current results demonstrate the importance of the PARP pathway in diabetic rats subjected to myocardial infarction and demonstrate the role of PARP in regulating AIF translocation in MI/R.

Defective transcription factor activation for proinflammatory gene expression in poly(ADP-ribose) polymerase 1-deficient glia

Poly(ADP-ribose) polymerase 1 (PARP-1) activity is detected in both neuronal and nonneuronal cells in the CNS, and excessive PARP-1 activity is known to be detrimental to tissue because of the cellular energy loss. Accordingly, PARP-1-deficient (PARP-1(-/-)) mice have been shown to be resistant to cerebral ischemia and several forms of inflammation. Recently, PARP-1 in glial cells has been shown to mediate the expression of proinflammatory genes in response to inflammatory stimuli by, in part, enhancing cognate DNA-binding capacities of transcription factors such as NF-kappaB and activator protein 1. Here, we demonstrate an additional mechanism whereby a significant reduction of proinflammatory gene expression such as IL-1beta, tumor necrosis factor alpha, and inducible nitricoxide synthase in PARP-1(-/-) glial cells is linked to defective inflammatory stimuli-induced p38MAPK-mediated phosphorylation of ATF-2 and cAMP-response element-binding protein and phosphorylation of NF-kappaB p65. Importantly, an inflammatory stimuli-induced p38MAPK activation is impaired in PARP-1(-/-) glial cells in a signaling pathway- and cell/tissue type-specific manner. These findings indicate that PARP-1 is an essential host factor among factors that actively mediate excessive production of proinflammatory molecules in glial cells, which may in turn contribute to the initiation of neuronal injuries.

Poly(ADP-ribose) polymerase-1 and apoptosis inducing factor in neurotoxicity

Poly(ADP-ribose) polymerase-1 (PARP-1) is the guardian of the genome acting as a sentinel for genomic damage. However, PARP-1 is also mediator of cell death after ischemia-reperfusion injury, glutamate excitotoxicity, and various inflammatory processes. The biochemistry underlying PARP-1-mediated cell death has remained elusive, although NAD(+) consumption and energy failure have been thought to be one of the possible molecular mechanisms. Recent observations link PARP-1 activation with translocation of apoptosis-inducing factor (AIF) to the nucleus and indicate that AIF is an essential downstream effector of PARP-1-mediated cell death. PARP-1 activation signals AIF release from the mitochondria, resulting in a novel, caspase-independent pathway of programmed cell death. These recent findings suggest that AIF maybe a target for development of future therapeutic treatment for many neurological disorders involving excitotoxicity.

Nitric oxide generation and poly(ADP ribose) polymerase activation precede beta-cell death in rats with a single high-dose injection of streptozotocin

Streptozotocin (STZ) is widely used for the induction of diabetes in animals by causing destruction of pancreatic beta cells. This experiment was designed to elucidate the sequential process of beta-cell destruction in rats with a single high-dose injection of STZ. At 0, 2, 5, 8 and 24 h after injection, rats were perfused with Krebs-Ringer buffer with dichlorofluorescein diacetate (DCF-DA), a marker for free radicals, and the pancreata were pathologically analyzed. Injection of STZ rapidly elicited an increase in fluorescence of DCF-DA in beta cells at 2 h after the injection. The fluorescence was diminished by carboxy-PTIO, a specific scavenger of nitric oxide (NO), but not by L-NAME, an inhibitor of NO synthase. During this process, an inducible form of NO synthase was not detected. Thereafter, upregulated expression of poly(ADP ribose) polymerase (PARP) and massive beta-cell death were detected at 5-8 h after injection. Migration of macrophages into the islet was conspicuous at 24 h, clearing up the debris of destroyed beta cells. Nicotinamide, a PARP inhibitor, significantly inhibited beta-cell death without apparent suppression of NO generation at 2 h. The current study documented serial processes of STZ-induced beta-cell death, starting with NO generation and PARP activation followed by a clearance with macrophages, where the activation of PARP plays a central role in beta-cell death.

Beta cell death and protection

Type 1 diabetes is an immune-mediated disease critically dependent upon the interaction between antigen-presenting cells and T cells. Clearly, both CD4+ and CD8+ T cells are required, but activated CD4+ T cells are both necessary and sufficient in causing disease. The mechanism of the Th1/Th2 immunoregulatory imbalance is unclear and needs to be further investigated. CD8+ T cells are not commonly sufficient in causing disease, but CD8 T cells are necessary in initiation (<14 weeks in the NOD mouse), but not in the later (>14 weeks) effector phase of the disease. It is still unclear whether the CD8+ T cell exerts its function as a classical effector cell or mainly as an immunomodulatory cell acting in synergy with the CD4+ T cell. The relative role of T cell effector mechanisms such as Fas/FasL, perforin/granzyme, and the TRAIL systems is unclear. Proinflammatory cytokines, reactive oxygen species, and other immune mediators seem to be involved in beta cell destruction, but much is to be learned about signaling, molecular mechanisms, and in vivo importance.

Poly(ADP-ribose) and carcinogenesis

Poly(ADP-ribose) and poly(ADP-ribose) polymerase (PARP) were discovered about 40 years ago, but their significance was not well elucidated until recently. In the early stage of the history of PARP, the presence of antibodies in the sera of human patients with lupus erythematosus indicated its natural occurrence. PARP, as well as the degrading enzyme, poly(ADP-ribose) glycohydrolase (PARG), are present in most eukaryotes except for yeasts. Studies that used inhibitors of PARP indicated the involvement of PARP and poly(ADP-ribose) in DNA damage repair, and eventually PARP was purified and the gene was cloned. Molecular analysis then revealed various functional domains, such as the one for binding to strand breaks of DNA. Parp-1-deficient and Parg-deficient cells showed, in general, enhanced sensitivity to the lethal effects of ionizing radiation and alkylating agents. Parp-1 knockout mouse embryonic stem cells developed into teratocarcinoma-like tumors when injected subcutaneously into nude mice, these tumors featuring giant cells similar to syncytiotrophoblastic giant cells with hyperploidy. Parp-1 was also found in centrosomes, suggesting that poly(ADP-ribose) and PARP-1 are functionally involved in the maintenance of chromatin structure and the equal distribution of chromosomes into daughter cells. Intriguing findings on the real biological significance continue to be generated, with new light shed on mechanisms of carcinogenesis and pointing to novel cancer treatments. Highlights during the last four decades of studies by laboratories focusing on poly(ADP-ribose)/PARP, including our own, are condensed and summarized in this review.

Oxidative stress is a mediator of glucose toxicity in insulin-secreting pancreatic islet cell lines

Pancreatic beta cells secrete insulin in response to changes in the extracellular glucose. However, prolonged exposure to elevated glucose exerts toxic effects on beta cells and results in beta cell dysfunction and ultimately beta cell death (glucose toxicity). To investigate the mechanism of how increased extracellular glucose is toxic to beta cells, we used two model systems where glucose metabolism was increased in beta cell lines by enhancing glucokinase (GK) activity and exposing cells to physiologically relevant increases in extracellular glucose (3.3-20 mm). Exposure of cells with enhanced GK activity to 20 mm glucose accelerated glycolysis, but reduced cellular NAD(P)H and ATP, caused accumulation of intracellular reactive oxygen species (ROS) and oxidative damage to mitochondria and DNA, and promoted apoptotic cell death. These changes required both enhanced GK activity and exposure to elevated extracellular glucose. A ROS scavenger partially prevented the toxic effects of increased glucose metabolism. These results indicate that increased glucose metabolism in beta cells generates oxidative stress and impairs cell function and survival; this may be a mechanism of glucose toxicity in beta cells. The level of beta cell GK may also be critical in this process.

Mammalian DNA base excision repair proteins: their interactions and role in repair of oxidative DNA damage

The DNA base excision repair (BER) is a ubiquitous mechanism for removing damage from the genome induced by spontaneous chemical reaction, reactive oxygen species (ROS) and also DNA damage induced by a variety of environmental genotoxicants. DNA repair is essential for maintaining genomic integrity. As we learn more about BER, a more complex mechanism emerges which supersedes the classical, simple pathway requiring only four enzymatic reactions. The key to understand the complete BER process is to elucidate how multiple proteins interact with one another in a coordinated process under specific physiological conditions.

SAR analysis of adenosine diphosphate (hydroxymethyl)pyrrolidinediol inhibition of poly(ADP-ribose) glycohydrolase

Polyadenosine diphosphoribose glycohydrolase (PARG) catalyzes the intracellular hydrolysis of adenosine diphosphoribose polymers. Because structure-activity data are lacking for PARG, the specific inhibitor adenosine diphosphate (hydroxymethyl)pyrrolidinediol (ADP-HPD) was utilized to determine the effects of structure on inhibitor potency using PARG isolated from bovine thymus (bPARG) and recombinant bovine PARG catalytic fragment (rPARG-CF). Both enzymes were strongly inhibited by submicromolar levels of ADP-HPD, but ADP and the phosphorylated pyrrolidine displayed no activity. Utilizing ADP-HPD analogues containing 2-, N(6), or 8-adenosyl substituents or guanine instead of adenine, the importance of adenine ring recognition as well as a correlation between loss of PARG inhibition and the length and bulkiness of 8-adenosyl substituents was shown. Utilization of ADP-HPD analogues lacking one or both pyrrolidine cis-hydroxyls demonstrated their importance for inhibitor binding. Last, the similarity between naturally occurring bPARG and heterologously expressed rPARG-CF was demonstrated. Therefore, readily available rPARG-CF is suitable for use in future studies to determine the structural aspects of PARG.

Expression of Activated Notch3 in Transgenic Mice Enhances Generation of T Regulatory Cells and Protects against Experimental Autoimmune Diabetes

Thymic-derived dysregulated tolerance has been suggested to occur in type 1 diabetes via impaired generation of CD4(+)CD25(+) T regulatory cells, leading to autoimmune beta cell destruction. In this study, we demonstrate that Notch3 expression is a characteristic feature of CD4(+)CD25(+) cells. Furthermore, streptozotocin-induced autoimmune diabetes fails to develop in transgenic mice carrying the constitutively active intracellular domain of Notch3 in thymocytes and T cells. The failure to develop the disease is associated with an increase of CD4(+)CD25(+) T regulatory cells, accumulating in lymphoid organs, in pancreas infiltrates and paralleled by increased expression of IL-4 and IL-10. Accordingly, CD4(+) T cells from Notch3-transgenic mice inhibit the development of hyperglycemia and insulitis when injected into streptozotocin-treated wild-type mice and display in vitro suppressive activity. These observations, therefore, suggest that Notch3-mediated events regulate the expansion and function of T regulatory cells, leading to protection from experimental autoimmune diabetes and identify the Notch pathway as a potential target for therapeutic intervention in type 1 diabetes.

Little evidence of transdifferentiation of bone marrow-derived cells into pancreatic beta cells

AIMS/HYPOTHESIS

Bone marrow cells contain at least two distinct types of stem cells which are haematopoietic stem cells and mesenchymal stem cells. Both cells have the ability to differentiate into a variety of cell types derived from all three germ layers. Thus, bone marrow stem cells could possibly be used to generate new pancreatic beta cells for the treatment of diabetes. In this study, we investigated the feasibility of bone marrow-derived cells to differentiate into beta cells in pancreas.

METHODS

Using green fluorescent protein transgenic mice as donors, the distribution of haematogenous cells in the pancreas was studied after bone marrow transplantation.

RESULTS

In the pancreas of green fluorescent protein chimeric mice, green fluorescent protein-positive cells were found in the islets, but none of these cells expressed insulin. Previous data has suggested that tissue injury can recruit haematopoietic stem cells or their progeny to a non-haematopietic cell fate. Therefore, low-dose streptozotocin (30 or 50 mg/kg on five consecutive days) was injected into the mice 5 weeks after bone marrow transplantation, but no green fluorescent protein-positive cells expressing insulin were seen in the islets or around the ducts of the pancreas.

CONCLUSIONS/INTERPRETATION

Our data suggests that bone marrow-derived cells are a distinct cell population from islet cells and that transdifferentiation from bone marrow-derived cells to pancreatic beta cells is rarely observed.

Pyruvate inhibits zinc-mediated pancreatic islet cell death and diabetes

AIMS/HYPOTHESIS

We have shown that zinc ion (Zn2+) in secretory granules of pancreatic beta cells could act as a paracrine death effector in streptozotocin-induced diabetes. As Zn2+ has been reported to perturb glycolysis, we studied if pyruvate could inhibit Zn(2+)-mediated islet cell death in vitro and streptozotocin-induced diabetes in vivo by normalizing intracellular energy metabolism.

METHODS

Cell death was measured by quantitative viable cell staining and Hoechst/propidium iodide staining. ATP was measured by bioluminescence determination. Pyruvate was infused through the tail vein 1 h before streptozotocin administration. Beta-cell volume was measured by point counting of the insulin-containing cells.

RESULTS

Zn2+ induced classical necrosis on MIN6N8 insulinoma cells which was associated with a rapid decline of intracellular ATP levels. Pyruvate inhibited Zn(2+)-induced necrosis of insulinoma cells and depletion of intracellular ATP by Zn2+. Pyruvate did not inhibit other types of necrosis or apoptosis. Energy substrates such as oxaloacetate, alpha-ketoglutarate and succinic acid dimethylester also attenuated Zn(2+)-induced insulinoma cell death. Methylpyruvate that does not generate NAD+ in the cytoplasm or alpha-ketoisocaproate that stimulates ATP generation exclusively in mitochondria also protected insulinoma cells from Zn(2+)-induced necrosis. Pyruvate infusion inhibited the development of diabetes by protecting beta-cell mass after streptozotocin administration.

CONCLUSION/INTERPRETATION

These results indicate that pyruvate inhibits Zn(2+)-induced necrosis of beta cells in vitro by protecting intracellular ATP levels and also streptozotocin-induced diabetes in vivo where Zn2+ has been reported to act as a paracrine death effector.

Design and synthesis of poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors. Part 4: biological evaluation of imidazobenzodiazepines as potent PARP-1 inhibitors for treatment of ischemic injuries

A class of poly(ADP-ribose) polymerase (PARP-1) inhibitors, the imidazobenzodiazepines, are presented in this text. Several derivatives were designed and synthesized with ionizable groups (i.e., tertiary amines) in order to promote the desired pharmaceutical characteristics for administration in ischemic injury. Within this series, several compounds have excellent in vitro potency and our computational models accurately justify the structure-activity relationships (SARs) and highlight essential hydrogen bonding residues and hydrophobic pockets within the catalytic domain of PARP-1. Administration of these compounds (5q, 17a and 17e) in the mouse model of streptozotocin-induced diabetes results in maintainance of glucose levels. Furthermore, one such inhibitor (5g, IC(50)=26 nM) demonstrated significant reduction of infarct volume in the rat model of permanent focal cerebral ischemia.

Poly (ADP-ribose) polymerase inhibition prevents spontaneous and recurrent autoimmune diabetes in NOD mice by inducing apoptosis of islet-infiltrating leukocytes

Poly (ADP-ribose) polymerase (PARP) is a nuclear enzyme that consumes NAD in response to DNA strand breaks. The PARP inhibitor nicotinamide prevents NAD consumption and protects islet beta-cells from chemically induced necrosis but not cytokine-induced apoptosis. Therefore, it is unclear how nicotinamide protects NOD mice from autoimmune diabetes in which apoptosis is the mode of beta-cell death. To investigate the mechanism of diabetes prevention by PARP inhibition, we studied the effects of a novel, potent PARP inhibitor, PJ34, a phenanthridinone derivative, on diabetes development in NOD mice and on diabetes recurrence in diabetic NOD mice transplanted with syngeneic islets. PJ34 administration from age 5 or 15 weeks significantly decreased insulitis, beta-cell destruction and diabetes incidence, and protection from diabetes continued for 12 weeks after PJ34 therapy was stopped. Similarly, syngeneic islet graft survival was prolonged and outlasted therapy in PJ34-treated mice. Immunohistochemical studies revealed significantly fewer leukocytes in islet grafts of PJ34-treated mice, together with increased apoptosis of these cells and decreased expression of the T helper 1-type cytokine interferon (IFN)-gamma. These results suggest that PARP inhibition protects against autoimmune beta-cell destruction in NOD mice by inducing apoptosis of islet-infiltrating leukocytes and decreasing IFN-gamma expression in the islets.

Bone marrow-derived stem cells initiate pancreatic regeneration

We show that transplantation of adult bone marrow-derived cells expressing c-kit reduces hyperglycemia in mice with streptozotocin-induced pancreatic damage. Although quantitative analysis of the pancreas revealed a low frequency of donor insulin-positive cells, these cells were not present at the onset of blood glucose reduction. Instead, the majority of transplanted cells were localized to ductal and islet structures, and their presence was accompanied by a proliferation of recipient pancreatic cells that resulted in insulin production. The capacity of transplanted bone marrow-derived stem cells to initiate endogenous pancreatic tissue regeneration represents a previously unrecognized means by which these cells can contribute to the restoration of organ function.

Parp-1 deficiency implicated in colon and liver tumorigenesis induced by azoxymethane

Poly(ADP-ribose) polymerase-1 (Parp-1) is activated by DNA strand breaks and functions in the maintenance of genomic integrity and cell death control. On the other hand, Parp-1 is also involved in transcriptional regulation of various genes, and the relationship between Parp-1 deficiency and susceptibility to tumorigenesis has not been fully elucidated. In the present study, Parp-1(-/-) mice, harboring exon 1 disruption in Parp-1, and Parp-1(+/+) animals were administered azoxymethane (AOM) at a dose of 10 mg/kg body weight once a week for 6 weeks. At 30 weeks after the first carcinogen treatment, mice were sacrificed. The incidence of animals bearing either adenomas or adenocarcinomas in the colon and the average number of colon tumors per mouse were significantly higher in Parp-1(-/-) mice than in Parp-1(+/+) animals. beta-Catenin accumulation was observed in 43/44 of Parp-1 (-/-) tumors and 19/21 of the Parp-1(+/+) tumors and was not statistically different between the genotypes. This suggests that most tumors developed through a pathway involving the alteration of Wnt-beta-catenin signaling in both Parp-1(-/-) and Parp-1(+/+) mice. In the liver, where AOM is primarily activated, the incidence of animals bearing nodules and the average number of nodules per section were significantly increased in Parp-1(-/-) mice compared with Parp-1(+/+) mice. Therefore, the results indicate that susceptibility to AOM-induced tumorigenesis in the colon and also in the liver is enhanced in Parp-1(-/-) mice, and Parp-1 could have a substantial role in colon and liver tumorigenesis.

Poly(ADP-Ribose) polymerase-1 in acute neuronal death and inflammation: a strategy for neuroprotection

Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear enzyme that is activated primarily by DNA damage. Upon activation, the enzyme hydrolyzes NAD(+) to nicotinamide and transfers ADP ribose units to a variety of nuclear proteins, including histones and PARP-1 itself. This process is important in facilitating DNA repair. However, excessive activation of PARP-1 can lead to significant decrements in NAD(+), and ATP depletion, and cell death (suicide hypothesis). In response to cellular damage by oxygen radicals or excitotoxicity, a rapid and strong activation of PARP-1 occurs in neurons. Excessive PARP-1 activation is implicated in a variety of insults, including cerebral and cardiac ischemia, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism, traumatic spinal cord injury, and streptozotocin-induced diabetes. The use of PARP inhibitors has, therefore, been proposed as a protective therapy in decreasing excitotoxic neuronal cell death, as well as ischemic and other tissue damage. Excitotoxic brain lesions initially result in the primary destruction of brain parenchyma and subsequently in secondary damage of neighboring neurons hours after the insult. This secondary damage of initially surviving neurons accounts for most of the volume of the infarcted area and the loss of brain function after a stroke. One major component of secondary neuronal damage is the migration of macrophages and microglial cells toward the sites of injury, where they produce large quantities of toxic cytokines and oxygen radicals. Recent evidence indicates that this microglial migration is strongly controlled in living brain tissue by expression of the integrin CD11a, which is regulated in turn by PARP-1, proposing that PARP-1 downregulation may, therefore, be a promising strategy in protecting neurons from this secondary damage, as well. Studies demonstrating an important role for PARP-1 in the regulation of gene transcription have further increased the intricacy of poly(ADP-ribosyl)ation in the control of cell homeostasis and challenge the notion that energy collapse is the sole mechanism by which poly(ADP-ribose) formation contributes to cell death. The hypothesis that PARPs might regulate cell fate as essential modulators of death and survival transcriptional programs is discussed with relation to nuclear factor kappaB and p53.

Necrosis is the predominant type of islet cell death during development of insulin-dependent diabetes mellitus in BB rats

Several reports propose that apoptosis of pancreatic beta cells may play a central role in the pathogenesis of both spontaneous and induced insulin-dependent diabetes mellitus (IDDM) in animal models. Whether apoptosis is a major cell death pathway during diabetes development, however, is highly controversial. The aim of this study was to examine the mode of islet cell death in prediabetic diabetes-prone (dp) BB rats, which spontaneously develop diabetes and serve as an animal model for human IDDM. In addition we investigated the cell death pathway of islet cells treated with the widely used diabetogenic compound streptozotocin or with nitric oxide (NO), which during IDDM development has been found to be present in inflamed islets in high concentrations because of the expression of inducible NO synthase. Islets of prediabetic BBdp rats were analyzed for DNA strand breaks and screened by electron microscopy. The mode of islet cell death in vitro after treatment with cytotoxic concentrations of streptozotocin or of NO was investigated using different methods including morphologic analysis by electron microscopy, detection of DNA strand breaks, poly(ADP-ribose) polymerase cleavage, and annexin V staining. Although cells with DNA stand breaks-often accepted as a proof for apoptosis-could be identified, we did not find apoptosis-specific features during islet cell death. Instead we observed massive necrosis as evidenced by disrupted plasma membranes and spilled-out cellular constituents in vitro as well as during disease manifestation in BBdp rats. These results may have serious consequences with regard to the treatment of humans to prevent the development of IDDM.

Intervening before the onset of Type 1 diabetes: baseline data from the European Nicotinamide Diabetes Intervention Trial (ENDIT)

AIMS/HYPOTHESIS

To set up a clinical trial to establish whether nicotinamide can prevent or delay clinical onset of Type 1 diabetes.

METHOD

The European Nicotinamide Diabetes Intervention Trial is a randomised, double-blind, placebo-controlled intervention trial undertaken in 18 European countries, Canada and the USA. Entry criteria were a first-degree family history of Type 1 diabetes, age 3-40 years, confirmed islet cell antibody (ICA) levels greater than or equal to 20 JDF units, and a non-diabetic OGTT; the study group was further characterised by intravenous glucose tolerance testing, measurement of antibodies to GAD, IA-2 and insulin and HLA class II genotyping.

RESULTS

ICA screening was carried out in approximately 30,000 first-degree relatives. A total of 1004 individuals fulfilled ICA criteria for eligibility, and 552 (288 male) were randomised to treatment. Of these, 331 were aged less than 20 years (87% siblings and 13% offspring of the proband with diabetes) and 221 were 20 years of age or more (76% parents, 21% siblings and 3% offspring). Oral glucose tolerance was normal in 500 and impaired in 52 (9.4%), and first phase insulin response in the IVGTT was below the 10(th) centile in 34%. Additional islet autoantibodies were identified in 354 trial entrants. Diabetes-associated HLA class II haplotypes were found in 84% of the younger age group and 80% of the older group. The protective haplotype HLA-DQA1*0102-DQB1*0602 was found in 10% overall.

CONCLUSIONS/INTERPRETATION

ENDIT has shown that a trial of an intervention designed to halt or delay progression to Type 1 diabetes can be carried out on a multinational collaborative basis, as and when potentially safe and effective forms of intervention become available. Primary screening with biochemically defined autoantibodies will substantially reduce the number of lower risk individuals to be included in future intervention trials

Long-chain polyunsaturated fatty acids and chemically induced diabetes mellitus. Effect of omega-3 fatty acids

In a previous study, we showed that prior oral feeding of oils rich in omega-3 eicosapentaenoic acid and docosahexaenoic acid and omega-6 gamma-linolenic acid and arachidonic acid prevent the development of alloxan-induced diabetes mellitus in experimental animals. We also observed that 99% pure omega-6 fatty acids gamma-linolenic acid and arachidonic acid protect against chemically induced diabetes mellitus. Here we report the results of our studies with omega-3 fatty acids. Alloxan-induced in vitro cytotoxicity and apoptosis in an insulin-secreting rat insulinoma cell line, RIN, was prevented by prior exposure of these cells to alpha-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid. Prior oral supplementation with alpha-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid prevented alloxan-induced diabetes mellitus. alpha-Linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid not only attenuated chemical-induced diabetes mellitus but also restored the anti-oxidant status to normal range in various tissues. These results suggested that omega-3 fatty acids can abrogate chemically induced diabetes in experimental animals and attenuate the oxidant stress that occurs in diabetes mellitus.

Long-chain polyunsaturated fatty acids and chemically induced diabetes mellitus: effect of omega-6 fatty acids

OBJECTIVE

We previously showed that prior oral supplementation of oils rich in omega-3, eicosapentaenoic acid and docosahexaenoic acid, and omega-6, gamma-linolenic acid and arachidonic acid, can prevent the development of alloxan-induced diabetes mellitus in experimental animals. But the effect of individual fatty acids on chemically induced diabetes mellitus is not known. We report the results of our studies with omega-6 fatty acids.

METHODS

Alloxan-induced in vitro cytotoxicity and apoptosis in an insulin-secreting rat insulinoma cell line, RIN, was prevented by prior exposure of these cells to linoleic acid, gamma-linolenic acid, and arachidonic acid (AA) but not to dihomo-gamma-linolenic acid. Cyclo-oxygenase and lipoxygenase inhibitors did not block this protective action of AA. Prior oral supplementation with gamma-linolenic acid and pre- and simultaneous treatments with AA prevented alloxan-induced diabetes mellitus.

RESULTS

Even though pretreatment with linoleic acid and dihomo-gamma-linolenic acid and simultaneous treatment with linoleic acid, gamma-linolenic acid, and dihomo-gamma-linolenic acid did not prevent the development of diabetes mellitus, the severity of diabetes was much less. The saturated fatty acid stearic acid and the monounsaturated fatty acid oleic acid were ineffective in preventing alloxan-induced diabetes mellitus. gamma-Linolenic acid and AA not only attenuated chemically induced diabetes mellitus but also restored the antioxidant status to normal range in various tissues. Changes in the concentrations of various fatty acids of the phospholipid fraction of plasma that occurred as a result of alloxan-induced diabetes mellitus also reverted to normal in the AA-treated animals.

CONCLUSIONS

These results suggest that polyunsaturated fatty acids can prevent chemically induced diabetes in experimental animals and attenuate the oxidant stress that occurs in diabetes mellitus.

Can perinatal supplementation of long-chain polyunsaturated fatty acids prevent diabetes mellitus?

It is suggested that the negative correlation between breast-feeding and insulin resistance and diabetes mellitus can be related to the presence of significant amounts of long-chain polyunsaturated fatty acids in the human breast milk. Based on this, it is proposed that provision of adequate amounts of long chain polyunsaturated fatty acids during the critical periods of brain growth and development can prevent or postpone the development diabetes mellitus.

Augmented lipopolysaccharide-induction of the histamine-forming enzyme in streptozotocin-induced diabetic mice

Disorders of the microcirculation and reduced resistance to infection are major complications in diabetes. Histamine enhances capillary permeability, and may also reduce cellular immunity. Here we demonstrate that streptozotocin (STZ)-induced diabetes in mice not only enhances the activity of the histamine-forming enzyme, histidine decarboxylase (HDC), but also augments the lipopolysaccharide (LPS)-induced elevation of HDC activity in various tissues, resulting in a production of histamine. The augmentation of HDC activity occurred as early as 2 days after STZ injection, but was not seen in nondiabetic mice. When given to STZ-treated mice, nicotinamide, an inhibitor of poly(ADP-ribose) synthetase, reduced both the elevation of blood glucose and the elevations of HDC activity and histamine production. These results suggest that hyperglycemia may initiate a sequence of events leading not only to an enhancement of basal HDC activity, but also to a sensitization of mice to the HDC-inducing action of LPS. We hypothesize that bacterial infections and diabetic complications may mutually exacerbate one another because both involved an induction of HDC.