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

Protective effect of cirsimaritin against streptozotocin-induced apoptosis in pancreatic beta cells

Objectives

Maintaining glucose homoeostasis is essential for the survival of cells. Despite the various health benefits of Korean thistle (Cirsium japonicum var. maackii), their effects on pancreatic β-cell apoptosis in type 1 diabetes mellitus and the underlying mechanisms remain unclear, and experimentally investigated in this study.

Methods

The effects of C. japonicum var. maackii and its active component cirsimaritin against streptozotocin (STZ)-induced cytotoxicity were assessed in INS-1 cells. By Western blotting analysis, protein expressions related to apoptosis were evaluated. The involvement of apoptosis was also confirmed with image-based cytometric assay and caspase activity tests.

Key findings

Cirsium japonicum var. maackii extract and cirsimaritin in non-toxic concentrations improved cell viability to near normal levels and protected INS-1 cells against STZ-induced damage. In addition, cirsimaritin reduced the intracellular oxidative stress induced by STZ. Cirsimaritin effectively suppressed apoptosis in pancreatic β cells by decreasing the activation of caspase-8 and caspase-3, BID and the DNA repair protein poly (ADP-ribose) polymerase (PARP) and increasing anti-apoptotic BCL-2 protein expression.

Conclusions

This study demonstrates the therapeutic potential and action mechanism of cirsimaritin for the prevention and treatment of type 1 diabetes mellitus.

PARP inhibition ameliorates nephropathy in an animal model of type 2 diabetes: focus on oxidative stress, inflammation, and fibrosis

Poly(ADP-ribose) polymerase (PARP) enzyme contributes to nephropathy, a serious diabetic complication which may lead to end-stage renal disease. The study aims to investigate the effect of PARP over-activation on kidney functions in a type 2 diabetic rat model. The study also tests the therapeutic use of PARP inhibitors in diabetic nephropathy. Type 2 diabetes was induced in adult male rats by high-fructose/high-fat diet and low streptozotocin dose. Then, the PARP inhibitor 4-aminobenzamide (4-AB) was administered daily for 10 weeks. At the end, urine samples were collected to measure urine creatinine, albumin, and total proteins. PARP activity, superoxide dismutase (SOD) activity, and nitrite content were measured in kidney tissue homogenate. Glucose, fructosamine, insulin, and tumor necrosis factor-alpha (TNF-α) were measured in serum. Furthermore, histological studies, collagen deposition, and immunofluorescence of nuclear factor kappa B (NFκB) and transforming growth factor beta1 (TGF-β1) were carried out. PARP enzyme activity was significantly higher in the diabetic group and was significantly reduced by 4-AB administration. Diabetic animals had clear nephropathy indicated by proteinuria and increased albumin excretion rate (AER) which were significantly decreased by PARP inhibition. In addition, PARP inhibition increased creatinine clearance in diabetic animals and reduced renal TGF-β1 and glomerular fibrosis. Moreover, PARP inhibition alleviated the elevated serum TNF-α level, renal NFκB, nitrite, and the decrease in SOD activity in diabetic animals. However, PARP inhibition did not significantly affect neither hyperglycemia nor insulin sensitivity. PARP enzyme inhibition alleviates diabetic nephropathy through decreasing inflammation, oxidative stress, and renal fibrosis.

Photodynamic therapy combined to cisplatin potentiates cell death responses of cervical cancer cells

BACKGROUND

Photodynamic therapy (PDT) has proven to be a promising alternative to current cancer treatments, especially if combined with conventional approaches. The technique is based on the administration of a non-toxic photosensitizing agent to the patient with subsequent localized exposure to a light source of a specific wavelength, resulting in a cytotoxic response to oxidative damage. The present study intended to evaluate in vitro the type of induced death and the genotoxic and mutagenic effects of PDT alone and associated with cisplatin.

METHODS

We used the cell lines SiHa (ATCC® HTB35™), C-33 A (ATCC® HTB31™) and HaCaT cells, all available at Dr. Christiane Soares' Lab. Photosensitizers were Photogem (PGPDT) and methylene blue (MBPDT), alone or combined with cisplatin. Cell death was accessed through Hoechst and Propidium iodide staining and caspase-3 activity. Genotoxicity and mutagenicity were accessed via flow cytometry with anti-gama-H2AX and micronuclei assay, respectively. Data were analyzed by one-way ANOVA with Tukey's posthoc test.

RESULTS

Both MBPDT and PGPDT induced caspase-independent death, but MBPDT induced the morphology of typical necrosis, while PGPDT induced morphological alterations most similar to apoptosis. Cisplatin predominantly induced apoptosis, and the combined therapy induced variable rates of apoptosis- or necrosis-like phenotypes according to the cell line, but the percentage of dead cells was always higher than with monotherapies. MBPDT, either as monotherapy or in combination with cisplatin, was the unique therapy to induce significant damage to DNA (double strand breaks) in the three cell lines evaluated. However, there was no mutagenic potential observed for the damage induced by MBPDT, since the few cells that survived the treatment have lost their clonogenic capacity.

CONCLUSIONS

Our results elicit the potential of combined therapy in diminishing the toxicity of antineoplastic drugs. Ultimately, photodynamic therapy mediated by either methylene blue or Photogem as monotherapy or in combination with cisplatin has low mutagenic potential, which supports its safe use in clinical practice for the treatment of cervical cancer.

PARP inhibition and postinfarction myocardial remodeling

Coronary artery disease accounts for the greatest proportion of cardiovascular diseases therefore it is the major cause of death worldwide. Its therapeutic importance is indicated by still high mortality of myocardial infarction, which is one of the most severe forms of CVDs. Moreover, the risk of developing heart failure is very high among survivors. Heart failure is accompanied by high morbidity and mortality rate, therefore this topic is in the focus of researchers' interest. After a myocardial infarct, at first ventricular hypertrophy develops as a compensatory mechanism to decrease wall stress but finally leads to left ventricular dilation. This phenomenon is termed as myocardial remodeling. The main characteristics of underlying mechanisms involve cardiomyocyte growth, vessel changes and increased collagen production, in all of which several mechanical stress induced neurohumoral agents, oxidative stress and signal transduction pathways are involved. The long term activation of these processes ultimately leads to left ventricular dilation and heart failure with decreased systolic function. Oxidative stress causes DNA breaks producing the activation of nuclear poly(ADP-ribose) polymerase-1 (PARP-1) enzyme that leads to energy depletion and unfavorable modulation of different kinase cascades (Akt-1/GSK-3β, MAPKs, various PKC isoforms) and thus it promotes the development of heart failure. Therefore inhibition of PARP enzyme could offer a promising new therapeutical approach to prevent the onset of heart failure among postinfarction patients. The purpose of this review is to give a comprehensive summary about the most significant experimental results and mechanisms in postinfarction remodeling.

Mitochondria mediates caspase-dependent and independent retinal cell death in Staphylococcus aureus endophthalmitis

Bacterial endophthalmitis, a vision-threatening complication of ocular surgery or trauma, is characterized by increased intraocular inflammation and retinal tissue damage. Although significant vision loss in endophthalmitis has been linked to retinal cell death, the underlying mechanisms of cell death remain elusive. In this study, using a mouse model of Staphylococcus aureus endophthalmitis and cultured human retinal Müller glia (MIO-M1 cell line), we demonstrate that S. aureus caused significant apoptotic cell death in the mouse retina and Müller glia, as evidenced by increased number of terminal dUTP nick end labeling and Annexin V and propidium iodide-positive cells. Immunohistochemistry and western blot studies revealed the reduction in mitochondrial membrane potential (JC-1 staining), release of cytochrome c into the cytosol, translocation of Bax to the mitochondria and the activation of caspase-9 and -3 in S. aureus-infected retina/retinal cells. In addition, the activation of PARP-1 and the release of apoptosis inducing factor from mitochondria was also observed in S. aureus-infected retinal cells. Inhibition studies using pan-caspase (Q-VD-OPH) and PARP-1 (DPQ) inhibitors showed significant reduction in S. aureus-induced retinal cell death both in vivo and in vitro. Together, our findings demonstrate that in bacterial endophthalmitis, retinal cells undergo apoptosis in the both caspase-dependent and independent manners, and mitochondria have a central role in this process. Hence, targeting the identified signaling pathways may provide the rationale to design therapeutic interventions to prevent bystander retinal tissue damage in bacterial endophthalmitis.

Experimental diabetes induced by alloxan and streptozotocin: The current state of the art

Diabetes mellitus is a chronic metabolic disorder with a high prevalence worldwide. Animal models of diabetes represent an important tool in diabetes investigation that helps us to avoid unnecessary and ethically challenging studies in human subjects, as well as to obtain a comprehensive scientific viewpoint of this disease. Although there are several methods through which diabetes can be induced, chemical methods of alloxan- and streptozotocin-induced diabetes represent the most important and highly preferable experimental models for this pathological condition. Therefore, the aim of this article was to review the current knowledge related to quoted models of diabetes, including to this point available information about mechanism of action, particular time- and dose-dependent protocols, frequent problems, as well as major limitations linked to laboratory application of alloxan and sterptozotocin in inducing diabetes. Given that diabetes is known to be closely associated with serious health consequences it is of fundamental importance that current animal models for induction of diabetes should be continuously upgraded in order to improve overall prevention, diagnosis and treatment of this pathological condition.

Immuno-chemistry of hydroxyl radical modified GAD-65: A possible role in experimental and human diabetes mellitus

The repertoire of known auto-antigens is limited to a very small proportion of all human proteins, and the reason why only some proteins become auto-antigens is unclear. The 65 kDa isoform of the enzyme glutamic acid decarboxylase (GAD-65) is a major auto-antigen in type I diabetes, and in various neurological diseases. Most patients with type I diabetes (70-80%) have auto-antibodies against GAD-65, which often appear years before clinical onset of the autoimmune diabetes. Thus, the aim of the study is to focus on the immunogenicity of GAD65 and its reactive oxygen species (ROS) conformer in STZ-induced diabetic rats and on human diabetic patients. In the present study, GAD-65 was modified by hydroxyl radical following Fenton's reaction. The modifications in the structure of the GAD-65 are supported by UV-vis and fluorescence spectral studies. Immunogenicity of both native and hydroxyl radical modified GAD-65 (ROS-GAD-65) was studied in experimental rabbits and was confirmed by inducing type I diabetes in experimental male albino rats using streptozotocin (45 mg/kg). We found that ROS-GAD-65 was a better immunogen as compared to the native GAD-65. A considerable high binding to ROS-GAD-65 was observed as compared to native GAD-65 in both the serum antibodies from diabetes animal models and as well as in the serum samples of type I diabetes. Hydrogen peroxide under the exposure of UV light produces hydroxyl radical (·OH) which is most potent oxidant, and could cause protein damage (GAD-65) to the extent of generating neo-epitopes on the molecule, thus making it immunogenic.

PJ-34 inhibits PARP-1 expression and ERK phosphorylation in glioma-conditioned brain microvascular endothelial cells

Inhibitors of PARP-1(Poly(ADP-ribose) polymerase-1) act by competing with NAD(+), the enzyme physiological substrate, which play a protective role in many pathological conditions characterized by PARP-1 overactivation. It has been shown that PARP-1 also promotes tumor growth and progression through its DNA repair activity. Since angiogenesis is an essential requirement for these activities, we sought to determine whether PARP inhibition might affect rat brain microvascular endothelial cells (GP8.3) migration, stimulated by C6-glioma conditioned medium (CM). Through wound-healing experiments and MTT analysis, we demonstrated that PARP-1 inhibitor PJ-34 [N-(6-Oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide] abolishes the migratory response of GP8.3 cells and reduces their viability. PARP-1 also acts in a DNA independent way within the Extracellular-Regulated-Kinase (ERK) signaling cascade, which regulates cell proliferation and differentiation. By western analysis and confocal laser scanning microscopy (LSM), we analyzed the effects of PJ-34 on PARP-1 expression, phospho-ERK and phospho-Elk-1 activation. The effect of MEK (mitogen-activated-protein-kinase-kinase) inhibitor PD98059 (2-(2-Amino-3-methoxyphenyl)-4 H-1-benzopyran-4-one) on PARP-1 expression in unstimulated and in CM-stimulated GP8.3 cells was analyzed by RT-PCR. PARP-1 expression and phospho-ERK activation were significantly reduced by treatment of GP8.3 cells with PJ-34 or PD98059. By LSM, we further demonstrated that PARP-1 and phospho-ERK are coexpressed and share the same subcellular localization in GP8.3 cells, in the cytoplasm as well as in nucleoplasm. Based on these data, we propose that PARP-1 and phospho-ERK interact in the cytosol and then translocate to the nucleus, where they trigger a proliferative response. We also propose that PARP-1 inhibition blocks CM-induced endothelial migration by interfering with ERK signal-transduction pathway.

TRPM2-mediated intracellular Zn2+ release triggers pancreatic β-cell death

Reactive oxygen species (ROS) can cause pancreatic β-cell death by activating transient receptor potential (melastatin) 2 (TRPM2) channels. Cell death has been attributed to the ability of these channels to raise cytosolic Ca2+. Recent studies however revealed that TRPM2 channels can also conduct Zn2+, but the physiological relevance of this property is enigmatic. Given that Zn2+ is cytotoxic, we asked whether TRPM2 channels can permeate sufficient Zn2+ to affect cell viability. To address this, we used the insulin secreting (INS1) β-cell line, human embryonic kidney (HEK)-293 cells transfected with TRPM2 and pancreatic islets. H2O2 activation of TRPM2 channels increases the cytosolic levels of both Ca2+ and Zn2+ and causes apoptotic cell death. Interestingly, chelation of Zn2+ alone was sufficient to prevent β-cell death. The source of the cytotoxic Zn2+ is intracellular, found largely sequestered in lysosomes. Lysosomes express TRPM2 channels, providing a potential route for Zn2+ release. Zn2+ release is potentiated by extracellular Ca2+ entry, indicating that Ca2+-induced Zn2+ release leads to apoptosis. Knockout of TRPM2 channels protects mice from β-cell death and hyperglycaemia induced by multiple low-dose streptozotocin (STZ; MLDS) administration. These results argue that TRPM2-mediated, Ca2+-potentiated Zn2+ release underlies ROS-induced β-cell death and Zn2+, rather than Ca2+, plays a primary role in apoptosis.

The Role of Poly(ADP-ribose) Polymerase-1 in Rheumatoid Arthritis

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme with a crucial role in the maintenance of genomic stability. In addition to the role of PARP-1 in DNA repair, multiple studies have also demonstrated its involvement in several inflammatory diseases, such as septic shock, asthma, atherosclerosis, and stroke, as well as in cancer. In these diseases, the pharmacological inhibition of PARP-1 has shown a beneficial effect, suggesting that PARP-1 regulates their inflammatory processes. In recent years, we have studied the role of PARP-1 in rheumatoid arthritis, as have other researchers, and the results have shown that PARP-1 has an important function in the development of this disease. This review summarizes current knowledge on the effects of PARP-1 in rheumatoid arthritis.

Ellagic acid mitigates SNO-PDI induced aggregation of Parkinsonian biomarkers

Nitrosative stress mediated S-nitrosylation (SNO) of protein disulfide isomerase (PDI), a housekeeping oxidoreductase, has been implicated in the pathogenesis of sporadic Parkinson's (PD) and Alzheimer's (AD) diseases. Previous cell line studies have indicated that SNO-PDI formation provokes synphilin-1 aggregation, the minor Parkinsonian biomarker protein. Yet no work exists investigating whether SNO-PDI induces α-synuclein aggregation, the major Lewy body constituent associated with Parkinson's pathogenesis. Here, we report that SNO-PDI formation is linked to the aggregation of α-synuclein and also provokes α-synuclein:synphilin-1 deposits (Lewy-body-like debris) normally found in the PD brain. Furthermore, we have examined the ability of a small molecule, 2,3,7,8-tetrahydroxy-chromeno[5,4,3-cde]chromene-5,10-dione (ellagic acid; EA) to scavenge NOx radicals and to protect cells from SNO-PDI formation via rotenone insult both, cell-based and cell-independent in vitro experiments. Furthermore, EA not only mitigates nitrosative-stress-induced aggregation of synphilin-1 but also α-synuclein and α-synuclein:synphilin-1 composites (Lewy-like neurites) in PC12 cells. Mechanistic analyses of the neuroprotective phenomena revealed that EA lowered rotenone-instigated reactive oxygen species (ROS) and reactive nitrogen species (RNS) in PC12 cells, imparted antiapoptotic tributes, and directly interfered with SNO-PDI formation. Lastly, we demonstrate that EA can bind human serum albumin (HSA). These results collectively indicate that small molecules can provide a therapeutic foothold for overcoming Parkinson's through a prophylactic approach.

mPGES-2 deletion remarkably enhances liver injury in streptozotocin-treated mice via induction of GLUT2

BACKGROUND & AIMS

Microsomal prostaglandin E synthase-2 (mPGES-2) deletion does not influence in vivo PGE2 production and the function of this enzyme remains elusive. The present study was undertaken to investigate the role of mPGES-2 in streptozotocin (STZ)-induced type-1 diabetes and organ injuries.

METHODS

mPGES-2 wild type (WT) and knockout (KO) mice were treated by a single intraperitoneal injection of STZ at the dose of 120 mg/kg to induce type-1 diabetes. Subsequently, glycemic status and organ injuries were evaluated.

RESULTS

Following 4 days of STZ administration, mPGES-2 KO mice exhibited severe lethality in contrast to the normal phenotype observed in WT control mice. In a separate experiment, the analysis was performed at day 3 of the STZ treatment in order to avoid lethality. Blood glucose levels were similar between STZ-treated KO and WT mice. However, the livers of KO mice were yellowish with severe global hepatic steatosis, in parallel with markedly elevated liver enzymes and remarkable stomach expansion. However, the morphology of the other organs was largely normal. The STZ-treated KO mice displayed extensive hepatocyte apoptosis compared with WT mice in parallel with markedly enhanced inflammation and oxidative stress. More interestingly, a liver-specific 50% upregulation of GLUT2 was found in the KO mice accompanied with a markedly enhanced STZ accumulation and this induction of GLUT2 was likely to be associated with the insulin/SREBP-1c pathway. Primary cultured hepatocytes of KO mice exhibited an increased sensitivity to STZ-induced injury and higher cellular STZ content, which was markedly blunted by the selective GLUT2 inhibitor phloretin.

CONCLUSIONS

mPGES-2 deletion enhanced STZ-induced liver toxicity possibly via GLUT2-mediated STZ uptake, independently of diabetes mellitus.

Anti-diabetic effect of a preparation of vitamins, minerals and trace elements in diabetic rats: a gender difference

BACKGROUND

Although multivitamin products are widely used as dietary supplements to maintain health or as special medical food in certain diseases, the effects of these products were not investigated in diabetes mellitus, a major cardiovascular risk factor. Therefore, here we investigated if a preparation of different minerals, vitamins, and trace elements (MVT) for human use affects the severity of experimental diabetes.

METHODS

Two days old neonatal Wistar rats from both genders were injected with 100 mg/kg of streptozotocin or its vehicle to induce diabetes. At week 4, rats were fed with an MVT preparation or vehicle for 8 weeks. Well established diagnostic parameters of diabetes, i.e. fasting blood glucose and oral glucose tolerance test were performed at week 4, 8 and 12. Moreover, serum insulin and blood HbA1c were measured at week 12.

RESULTS

An impaired glucose tolerance has been found in streptozotocin-treated rats in both genders at week 4. In males, fasting blood glucose and HbA1c were significantly increased and glucose tolerance and serum insulin was decreased at week 12 in the vehicle-treated diabetic group as compared to the vehicle-treated non-diabetic group. All of the diagnostic parameters of diabetes were significantly improved by MVT treatment in male rats. In females, streptozotocin treatment resulted in a less severe prediabetic-like phenotype as only glucose tolerance and HbA1c were altered by the end of the study in the vehicle-treated diabetic group as compared to the vehicle-treated non-diabetic group. MVT treatment failed to improve the diagnostic parameters of diabetes in female streptozotocin-treated rats.

CONCLUSION

This is the first demonstration that MVT significantly attenuates the progression of diabetes in male rats with chronic experimental diabetes. Moreover, we have confirmed that females are less sensitive to STZ-induced diabetes and MVT preparation did not show protection against prediabetic state. This may suggest a gender difference in the pathogenesis of diabetes.

CXC chemokine ligand 12 protects pancreatic β-cells from necrosis through Akt kinase-mediated modulation of poly(ADP-ribose) polymerase-1 activity

The diabetes prevention paradigm envisages the application of strategies that support the maintenance of appropriate β-cell numbers. Herein we show that overexpression of CXC chemokine ligand12 (CXCL12) considerably improves the viability of isolated rat Langerhans islet cells and Rin-5F pancreatic β-cells after hydrogen peroxide treatment. In rat islets and wt cells hydrogen peroxide treatment induced necrotic cell death that was mediated by the rapid and extensive activation of poly(ADP-ribose) polymerase-1 (PARP-1). In contrast, CXCL12-overexpressing cells were protected from necrotic cell death as a result of significantly reduced PARP-1 activity. CXCL12 downstream signalling through Akt kinase was responsible for the reduction of PARP-1 activity which switched cell death from necrosis to apoptosis, providing increased protection to cells from oxidative stress. Our results offer a novel aspect of the CXCL12-mediated improvement of β-cell viability which is based on its antinecrotic action through modulation of PARP-1 activity.

Role of immune system in type 1 diabetes mellitus pathogenesis

The immune system is the body's natural defense system against invading pathogens. It protects the body from infection and works to communicate an individual's well-being through a complex network of interconnected cells and cytokines. This system is an associated host defense. An uncontrolled immune system has the potential to trigger negative complications in the host. Type 1 diabetes results from the destruction of pancreatic β-cells by a β-cell-specific autoimmune process. Examples of β-cell autoantigens are insulin, glutamic acid decarboxylase, tyrosine phosphatase, and insulinoma antigen. There are many autoimmune diseases, but type 1 diabetes mellitus is one of the well-characterized autoimmune diseases. The mechanisms involved in the β-cell destruction are still not clear; it is generally believed that β-cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T lymphocytes are involved in the β-cell-specific autoimmune process. It is necessary to determine what exact factors are causing the immune system to become unregulated in such a manner as to promote an autoimmune response.

Energy adaptive response during parthanatos is enhanced by PD98059 and involves mitochondrial function but not autophagy induction

Parthanatos is a programmed necrotic demise characteristic of ATP (adenosine triphosphate) consumption due to NAD+ (nicotinamide adenine dinucleotide) depletion by poly(ADP-ribose) polymerase 1 (PARP1)-dependent poly(ADP-ribosyl)ation on target proteins. However, how the bioenergetics is adaptively regulated during parthanatos, especially under the condition of macroautophagy deficiency, remains poorly characterized. Here, we demonstrated that the parthanatic inducer N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) triggered ATP depletion followed by recovery in mouse embryonic fibroblasts (MEFs). Notably, Atg5-/- MEFs showed great susceptibility to MNNG with disabled ATP-producing capacity. Moreover, the differential energy-adaptive responses in wild-type (WT) and Atg5-/- MEFs were unequivocally worsened by inhibition ofAMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), and mitochondrial activity. Importantly, Atg5-/- MEFs disclosed diminished SIRT1 and mitochondrial activity essential to the energy restoration during parthanatos. Strikingly, however, parthanatos cannot be exasperated by bafilomycin A1 and MNNG neither provokes microtubule-associated protein 1A/1B-light chain 3 (LC3) lipidation and p62 elimination, suggesting that parthanatos does not induce autophagic flux. Intriguingly, we reported unexpectedly that PD98059, even at low concentration insufficient to inhibit MEK, can promote mitochondrial activity and facilitate energy-restoring process during parthanatos, without modulating DNA damage responses as evidenced by PARP1 activity, p53 expression, and gammaH2AX (H2A histone family, member X (H2AX), phosphorylated on Serine 139) induction. Therefore, we propose that Atg5 deficiency confers an infirmity to overcome the energy crisis during parthanatos and further underscore the deficits in mitochondrial quality control, but not incapability of autophagy induction, that explain the vulnerability in Atg5-deficient cells. Collectively, our results provide a comprehensive energy perspective for an improved treatment to alleviate parthanatos-related tissue necrosis and disease progression and also provide a future direction for drug development on the basis of PD98059 as an efficacious compound against parthanatos.

PARP-1 hyperactivation and reciprocal elevations in intracellular Ca2+ during ROS-induced nonapoptotic cell death

The generation of reactive oxygen species (ROS) has been implicated in the pathogenesis of renal ischemia/reperfusion injury, and many other pathological conditions. DNA strand breaks caused by ROS lead to the activation of poly(ADP-ribose)polymerase-1 (PARP-1), the excessive activation of which can result in cell death. We have utilized a model in which 2,3,5-tris(glutathion-S-yl)hydroquinone (TGHQ), a nephrotoxic and nephrocarcinogenic metabolite of hydroquinone, causes ROS-dependent cell death in human renal proximal tubule epithelial cells (HK-2), to further elucidate the role of PARP-1 in ROS-dependent cell death. TGHQ-induced ROS generation, DNA strand breaks, hyperactivation of PARP-1, rapid depletion of nicotinamide adenine dinucleotide (NAD), elevations in intracellular Ca(2+) concentrations, and subsequent nonapoptotic cell death in both a PARP- and Ca(2+)-dependent manner. Thus, inhibition of PARP-1 with PJ34 completely blocked TGHQ-mediated accumulation of poly(ADP-ribose) polymers and NAD consumption, and delayed HK-2 cell death. In contrast, chelation of intracellular Ca(2+) with BAPTA completely abrogated TGHQ-induced cell death. Ca(2+) chelation also attenuated PARP-1 hyperactivation. Conversely, inhibition of PARP-1 modulated TGHQ-mediated changes in Ca(2+) homeostasis. Interestingly, PARP-1 hyperactivation was not accompanied by the translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus, a process usually associated with PARP-dependent cell death. Thus, pathways coupling PARP-1 hyperactivation to cell death are likely to be context-dependent, and therapeutic strategies designed to target PARP-1 need to recognize such variability. Our studies provide new insights into PARP-1-mediated nonapoptotic cell death, during which PARP-1 hyperactivation and elevations in intracellular Ca(2+) are reciprocally coupled to amplify ROS-induced nonapoptotic cell death.

Toll-like receptor 4 deficiency accelerates the development of insulin-deficient diabetes in non-obese diabetic mice

BACKGROUND/OBJECTIVE

Toll-like receptors (TLR) mediate the recognition of microbial constituents and stress-induced endogenous ligands by the immune system. They may also be involved in the maintenance or break down of tolerance against autologous antigens. The aim of our investigation was to study the consequence of TLR4 deficiency on the development of insulin-deficient diabetes in the NOD mouse.

METHODS

The TLR4 defect of the C57BL/10ScN mouse was backcrossed onto the NOD background and the effect of TLR4 deficiency on diabetes development was analysed by in vivo and in vitro studies.

RESULTS

Compared to animals with wildtype TLR4 expression (TLR4(+/+)), female NOD mice carrying a homozygous TLR4 defect (TLR4(-/-)), showed significant acceleration of diabetes development, with a younger age at diabetes onset (TLR4 (+/+) 177±22 d, TLR(-/-): 118±21 d; p<0.01). Pancreata of 120 d old TLR4(-/-) NOD mice revealed increased proportions of islets with advanced stages of immune cell infiltration compared to TLR4(+/+) mice (p<0.05). TLR4 deficiency did not affect the susceptibility of islet cells to the beta cell damaging mediators nitric oxide or the inflammatory cytokines tumor necrosis factor alpha, interleukin-1 beta and interferon gamma. The lack of TLR4 further had no effect on the frequency of regulatory T-cells but reduced their capacity to inhibit T-cell proliferation.

CONCLUSIONS

Our findings demonstrate that TLR4 deficiency results in an acceleration of diabetes development and immune cell infiltration of islets in NOD mice. We conclude that TLR4 is involved in the progression of the insulitis process thereby controlling the development of insulin-deficient diabetes in NOD mice.

Searching in mother nature for anti-cancer activity: anti-proliferative and pro-apoptotic effect elicited by green barley on leukemia/lymphoma cells

Green barley extract (GB) was investigated for possible anti-cancer activity by examining its anti-proliferative and pro-apoptotic properties on human leukemia/lymphoma cell lines. Our results indicate that GB exhibits selective anti-proliferative activity on a panel of leukemia/lymphoma cells in comparison to non-cancerous cells. Specifically, GB disrupted the cell-cycle progression within BJAB cells, as manifested by G2/M phase arrest and DNA fragmentation, and induced apoptosis, as evidenced by phosphatidylserine (PS) translocation to the outer cytoplasmic membrane in two B-lineage leukemia/lymphoma cell lines. The pro-apoptotic effect of GB was found to be independent of mitochondrial depolarization, thus implicating extrinsic cell death pathways to exert its cytotoxicity. Indeed, GB elicited an increase of TNF-α production, caspase-8 and caspase-3 activation, and PARP-1 cleavage within pre-B acute lymphoblastic leukemia Nalm-6 cells. Moreover, caspase-8 and caspase-3 activation and PARP-1 cleavage were strongly inhibited/blocked by the addition of the specific caspase inhibitors Z-VAD-FMK and Ac-DEVD-CHO. Furthermore, intracellular signaling analyses determined that GB treatment enhanced constitutive activation of Lck and Src tyrosine kinases in Nalm-6 cells. Taken together, these findings indicate that GB induced preferential anti-proliferative and pro-apoptotic signals within B-lineage leukemia/lymphoma cells, as determined by the following biochemical hallmarks of apoptosis: PS externalization, enhanced release of TNF-α, caspase-8 and caspase-3 activation, PARP-1 cleavage and DNA fragmentation Our observations reveal that GB has potential as an anti-leukemia/lymphoma agent alone or in combination with standard cancer therapies and thus warrants further evaluation in vivo to support these findings.

PARP-1 controls immunosuppressive function of regulatory T cells by destabilizing Foxp3

Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme and transcription factor that is involved in inflammatory response, but its role in T cell response remains largely unknown. We show here that PARP-1 regulates the suppressive function of CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs). Specifically, Tregs in mice with a null mutation of the PARP-1 gene (PARP-1^–/–) showed significantly stronger suppressive activity than did wild-type Tregs in culture. We elucidate that this enhanced suppressive function is attributed to sustained higher expression of Foxp3 and CD25 in PARP-1^−/− Tregs. Furthermore, in PARP-1^−/− Tregs, Foxp3 protein shows substantially higher levels of binding to the conserved non-coding DNA sequence 2 (CNS2) at the foxp3 gene, a region important in maintaining Foxp3 gene expression in Tregs. Thus, our data reveal a role for PARP-1 in controlling the function of Tregs through modulation of the stable expression of Foxp3.

Parp1 deficient mice are protected from streptozotocin-induced diabetes but not caerulein-induced pancreatitis, independent of the induction of Reg family genes

Poly(ADP-ribose) polymerase (Parp) 1 is a key regulator of cell death, its inhibition prevented streptozotocin-induced diabetes and attenuated caerulein-induced acute pancreatitis. Reg family proteins are significantly induced by Parp1 inhibitor, experimental diabetes and/or acute pancreatitis. We propose that Reg proteins are involved in the protection of pancreatic cells by Parp1 inhibition. To test this possibility, Parp1-/- and wild-type mice were injected with streptozotocin to induce diabetes. Separately, acute pancreatitis was induced with repeated injections of caerulein. Upon streptozotocin administration, Parp1-/- mice displayed much decreased hyperglycemia and preserved serum insulin level. The treatment induced similar levels of Reg1, -2, -3α and -3β genes in the pancreas of both wild-type and Parp1-/- mice, suggesting that the upregulation of Reg family genes during streptozotocin-induced diabetes was independent of Parp1 ablation. In caerulein-induced pancreatitis, unlike being reported, Parp1 knockout caused no relief on the severity of pancreatitis; the upregulation of pancreatic Reg1, -2, -3α and -3β genes upon caerulein was unaffected by Parp1 deletion. Our results reconfirmed the protective effect of Parp1 gene deletion on islet β-cells but questioned its effect on the acinar cells. In either case, the significant induction of Reg family genes seemed independent of Parp1-mediated cell death.

PARP-1 regulates expression of TGF-β receptors in T cells

Transforming growth factor-β (TGF-β) receptors (TβRs) are essential components for TGF-β signal transduction in T cells, yet the mechanisms by which the receptors are regulated remain poorly understood. We show here that Poly(ADP-ribose) polymerase-1 (PARP-1) regulates TGF-β receptor I (TβRI) and II (TβRII) expression in CD4(+) T cells and subsequently affects Smad2/3-mediated TGF-β signal transduction. Inhibition of PARP-1 led to the upregulation of both TβRI and TβRII, yet the underlying molecular mechanisms were distinct. PARP-1 selectively bound to the promoter of TβRII, whereas the enzymatic activity of PARP-1 was responsible for the inhibition of TβRI expression. Importantly, inhibition of PARP-1 also enhanced expression of TβRs in human CD4(+) T cells. Thus, PARP-1 regulates TβR expression and TGF-β signaling in T cells.

Minocycline influences the anti-inflammatory interleukins and enhances the effectiveness of morphine under mice diabetic neuropathy

A single streptozotocin (STZ) injection in mice can induce significant neuropathic pain along with an increase in plasma glucose levels and a decrease in body weight. Seven days after the administration of STZ, an upregulation of C1q-positive cells was observed. Additionally, interleukins (IL-1beta, IL-3, IL-4, IL-6, IL-9, IL12p70, IL-17); proteins of the tumor necrosis factor (TNF) family, e.g., IFNgamma and sTNF RII, were upregulated. Chronic administration of minocycline increases antinociceptive factors (IL-1alpha, IL-2, IL-10, sTNFRII) in diabetic mice. Minocycline also reduces the occurrence of neuropathic pain and significantly potentiates the antiallodynic and antihyperalgesic effects of morphine.

Deletion of CD73 promotes dyslipidemia and intramyocellular lipid accumulation in muscle of mice

CONTEXT

CD73 converts extracellular AMP to adenosine which is well known to inhibit lipolysis. It is unknown, however, whether adenosine formed directly by CD73 is functionally relevant in this process.

OBJECTIVE

We therefore explored the effect of CD73-derived adenosine on body fat of aged mice.

RESULTS

In lean mice, extracellular adenosine formation by adipocytes is dependent on CD73. High fat diet down-regulates the expression of CD73 in wildtype mice similar to ob/ob mice. Transgenic mice chronically lacking CD73 (CD73(-/-)) gain significantly less body weight and show decreased superficial white fat content as well as increased serum free fatty acids and triglycerides. In addition, intramyocellular lipid levels are significantly increased. This phenotype is accompanied by an increase in blood glucose and serum insulin levels although insulin secretion and the level of insulin degrading enzyme are unaltered. Additionally, insulin-induced Akt phosphorylation is reduced in skeletal muscle of CD73(-/-) mice.

CONCLUSION

CD73-derived adenosine is functionally involved in body fat homeostasis.

Protective effect of nicotinamide on high glucose/palmitate-induced glucolipotoxicity to INS-1 beta cells is attributed to its inhibitory activity to sirtuins

This study was initiated to determine whether the protective effect of nicotinamide (NAM) on high glucose/palmitate (HG/PA)-induced INS-1 beta cell death was due to its role as an anti-oxidant, nicotinamide dinucleotide (NAD+) precursor, or inhibitor of NAD+-consuming enzymes such as poly (ADP-ribose) polymerase (PARP) or sirtuins. All anti-oxidants tested were not protective against HG/PA-induced INS-1 cell death. Direct supplementation of NAD+ or indirect supplementation through NAD+ salvage or de novo pathway did not protect the death. Knockdown of the NAD+ salvage pathway enzymes such as nicotinamide phosphoribosyl transferase (NAMPT) or nicotinamide mononucleotide adenyltransferase (NMNAT) did not augment death. On the other hand, pharmacological inhibition or knockdown of PARP did not affect death. However, sirtinol as an inhibitor of NAD-dependant deacetylase or knockdown of SIRT3 or SIRT4 significantly reduced the HG/PA-induced death. These data suggest that protective effect of NAM on beta cell glucolipotoxicity is attributed to its inhibitory activity on sirtuins.

Crosstalk between poly(ADP-ribose) polymerase and sirtuin enzymes

Poly(ADP-ribose) polymerases (PARPs) are NAD(+) dependent enzymes that were identified as DNA repair proteins, however, today it seems clear that PARPs are responsible for a plethora of biological functions. Sirtuins (SIRTs) are NAD(+)-dependent deacetylase enzymes involved in the same biological processes as PARPs raising the question whether PARP and SIRT enzymes may interact with each other in physiological and pathophysiological conditions. Hereby we review the current understanding of the SIRT-PARP interplay in regard to the biochemical nature of the interaction (competition for the common NAD(+) substrate, mutual posttranslational modifications and direct transcriptional effects) and the physiological or pathophysiological consequences of the interactions (metabolic events, oxidative stress response, genomic stability and aging). Finally, we give an overview of the possibilities of pharmacological intervention to modulate PARP and SIRT enzymes either directly, or through modulating NAD(+) homeostasis.

Sirtuins and pyridine nucleotides

The silencer information regulator (Sir) family of proteins has attracted much attention during the past decade due to its prominent role in metabolic homeostasis in mammals. The Sir1-4 proteins were first discovered in yeast as nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylases, which through a gene silencing effect promoted longevity. The subsequent discovery of a homologous sirtuin (Sirt) family of proteins in the mammalian systems soon led to the realization that these molecules have beneficial effects in metabolism- and aging-related diseases. Through their concerted functions in the central nervous system, liver, pancreas, skeletal muscle, and adipose tissue, they regulate the body's metabolism. Sirt1, -6, and -7 exert their functions, predominantly, through a direct effect on nuclear transcription of genes involved in metabolism, whereas Sirt3-5 reside in the mitochondrial matrix and regulate various enzymes involved in the tricarboxylic acid and urea cycles, oxidative phosphorylation, as well as reactive oxygen species production. An interesting aspect of the functionality of sirtuin involves their regulation by the circadian rhythm, which affects their function via cyclically regulating systemic NAD(+) availability, further establishing the link of these proteins to metabolism. In this review, we will discuss the relation of sirtuins to NAD(+) metabolism, their mechanism of function, and their role in metabolism and mitochondrial functions. In addition, we will describe their effects in the cardiovascular and central nervous systems.

MR angiography, MR imaging and proton MR spectroscopy in-vivo assessment of skeletal muscle ischemia in diabetic rats

To prospectively evaluate the feasibility of using magnetic resonance (MR) techniques for in-vivo assessing a rat diabetic model of limb ischemia. Unilateral hind limb ischemia was induced by ligation of the iliac-femoral artery in male streptozotocin-treated and non-diabetic control rats. Four weeks after ligation, rats underwent MR Angiography (MRA), T₁-weighted and Short Time Inversion Recovery (STIR) sequences and muscle Proton MR Spectroscopy (¹H-MRS) on both hind limbs. After MR examinations, immunoblotting and immunofluorescence analysis were performed. MRA showed a signal void due to flow discontinuation distal to the artery ligation. T₁-weighted and STIR images showed, respectively, the presence of tissue swelling (p = 0.018 for non-diabetic; p = 0.027 for diabetic rats) and signal hyperintensity in tissue affected by occlusion. Mean total creatine/water for the occluded limb was significantly lower than for the non-occluded limbs in both non-diabetic (5.46×10⁻⁴ vs 1.14×10⁻³, p = 0.028) and diabetic rats (1.37×10⁻⁴ vs 1.10×10⁻³; p = 0.018). MR Imaging and ¹H-MRS changes were more pronounced in diabetic than in non-diabetic occluded limbs (p = 0.032). MR findings were confirmed by using histological findings. Combined MR techniques can be used to demonstrate the presence of structural and metabolic changes produced by iliac-femoral artery occlusion in rat diabetic model of limb ischemia.

Pleiotropic cellular functions of PARP1 in longevity and aging: genome maintenance meets inflammation

Aging is a multifactorial process that depends on diverse molecular and cellular mechanisms, such as genome maintenance and inflammation. The nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1), which catalyzes the synthesis of the biopolymer poly(ADP-ribose), exhibits an essential role in both processes. On the one hand, PARP1 serves as a genomic caretaker as it participates in chromatin remodelling, DNA repair, telomere maintenance, resolution of replicative stress, and cell cycle control. On the other hand, PARP1 acts as a mediator of inflammation due to its function as a regulator of NF-κB and other transcription factors and its potential to induce cell death. Consequently, PARP1 represents an interesting player in several aging mechanisms and is discussed as a longevity assurance factor on the one hand and an aging-promoting factor on the other hand. Here, we review the molecular mechanisms underlying the various roles of PARP1 in longevity and aging with special emphasis on cellular studies and we briefly discuss the results in the context of in vivo studies in mice and humans.

The role of PARP-1 and PARP-2 enzymes in metabolic regulation and disease

While originally described as DNA damage repair agents, recent data suggest a role for poly(ADP-ribose) polymerase (PARP) enzymes in metabolic regulation by influencing mitochondrial function and oxidative metabolism. Here we review how PARP activity has a major metabolic impact and the role of PARP-1 and PARP-2 in diverse metabolic complications.

Pleiotropic neuroprotective and metabolic effects of Actovegin's mode of action

This article reviews the mechanisms of action of Actovegin in the context of its preclinical effects and new concepts in the pharmacological treatment of neurological disorders. Actovegin is an ultrafiltrate of calf blood, composed of more than 200 biological substances. The drug is used for a broad spectrum of diseases, including disturbances of peripheral and cerebral blood circulation, burns, impaired wound healing, radiation-induced damage and diabetic polyneuropathy. Actovegin is composed of small molecules present under normal physiological conditions, therefore pharmacokinetic and pharmacodynamic studies to determine its active substance are not feasible. Preclinical data have revealed that it improves metabolic balance by increasing glucose uptake and improving oxygen uptake under conditions of ischemia. Actovegin also resists the effects of gamma-irradiation and stimulates wound healing. More recent preclinical studies have suggested that anti-oxidative and anti-apoptotic mechanisms of action specifically underlie the neuroprotective properties of Actovegin. The drug has been found to exert these beneficial effects experimentally, in primary rat hippocampal neurons and in an STZ-rat model of diabetic polyneuropathy, while also providing evidence that it positively affects the functional recovery of neurons. Latest data suggest that Actovegin also has a positive influence on the NF-κB pathway, but many molecular and cellular pathways remain unexplored. In particular, Actovegin's influence on neuroplasticity, neurogenesis and neurotrophicity are questions that ideally should be answered by future research. Nevertheless, it is clear that the multifactorial and complex nature of Actovegin underlies its pleiotropic neuroprotective mechanisms of action and positive effect on clinical outcomes.

Cytokine-mediated β-cell damage in PARP-1-deficient islets

Poly(ADP)-ribose polymerase (PARP) is an abundant nuclear protein that is activated by DNA damage; once active, it modifies nuclear proteins through attachment of poly(ADP)-ribose units derived from β-nicotinamide adenine dinucleotide (NAD(+)). In mice, the deletion of PARP-1 attenuates tissue injury in a number of animal models of human disease, including streptozotocin-induced diabetes. Also, inflammatory cell signaling and inflammatory gene expression are attenuated in macrophages isolated from endotoxin-treated PARP-1-deficient mice. In this study, the effects of PARP-1 deletion on cytokine-mediated β-cell damage and macrophage activation were evaluated. There are no defects in inflammatory mediator signaling or inflammatory gene expression in macrophages and islets isolated from PARP-1-deficient mice. While PARP-1 deficiency protects islets against cytokine-induced islet cell death as measured by biochemical assays of membrane polarization, the genetic absence of PARP-1 does not effect cytokine-induced inhibition of insulin secretion or cytokine-induced DNA damage in islets. While PARP-1 deficiency appears to provide protection from cell death, it fails to provide protection against the inhibitory actions of cytokines on insulin secretion or the damaging actions on islet DNA integrity.

PTGS-2-PTGER2/4 signaling pathway partially protects from diabetogenic toxicity of streptozotocin in mice

Prostanoids are suggested to participate in diabetes pathology, but their roles are controversially discussed. The purpose of the current study was to examine the role of cyclooxygenase (prostaglandin synthase [PTGS]) enzymes and prostaglandin (PG) E(2) signaling pathways in streptozotocin (STZ)-induced type 1 diabetes. Blood glucose, insulin, and survival rate were studied in mice with targeted disruption of the genes for PTGS and PGE receptors (PTGERs). PGE(2) was found as the main prostanoid formed by the pancreas. Contrarily to PTGS-1, deficiency of PTGS-2 activity significantly amplified STZ effect, causing dramatic loss of insulin production and rise in blood glucose and death rate. STZ metabolism was unaffected by PTGS deficiency. Diabetogenicity of STZ in PTGER1(-/-), PTGER2(-/-), PTGER3(-/-), and PTGER4(-/-) mice was comparable to control mice. In striking contrast, combined knockout of PTGER2 and PTGER4 by blocking PTGER4 in PTGER2(-/-) mice strongly enhanced STZ pathology. Treatment of PTGS-2(-/-) and wild-type mice with PTGER2/PTGER4 agonists partially protected against STZ-induced diabetes and restored β-cell function. Our data uncover a previously unrecognized protective role of PTGS-2-derived PGE(2) in STZ-induced diabetes mediated by the receptor types PTGER2 and PTGER4. These findings offer the possibility to intervene in early progression of type 1 diabetes by using PTGER-selective agonists.

Streptozotocin-nicotinamide-induced diabetes in the rat. Characteristics of the experimental model

Administration of both streptozotocin (STZ) and nicotinamide (NA) has been proposed to induce experimental diabetes in the rat. STZ is well known to cause pancreatic B-cell damage, whereas NA is administered to rats to partially protect insulin-secreting cells against STZ. STZ is transported into B-cells via the glucose transporter GLUT2 and causes DNA damage leading to increased activity of poly(ADP-ribose) polymerase (PARP-1) to repair DNA. However, exaggerated activity of this enzyme results in depletion of intracellular NAD(+) and ATP, and the insulin-secreting cells undergo necrosis. The protective action of NA is due to the inhibition of PARP-1 activity. NA inhibits this enzyme, preventing depletion of NAD(+) and ATP in cells exposed to STZ. Moreover, NA serves as a precursor of NAD(+) and thereby additionally increases intracellular NAD(+) levels. The severity of diabetes in experimental rats strongly depends on the doses of STZ and NA given to these animals. Therefore, in diabetic rats, blood glucose may be changed in a broad range--from slight hyperglycemia to substantial hyperglycemia compared with control animals. Similarly, blood insulin may be only slightly decreased or substantial hypoinsulinemia may be induced. In vitro studies demonstrated that the insulin-secretory response to glucose is attenuated in STZ-NA-induced diabetic rats compared with control animals. This is due to reduced B-cell mass as well as metabolic defects in the insulin-secreting cells. Results of numerous experiments have demonstrated that this model of diabetes is useful in studies of different aspects of diabetes.

Chronic treatment with a glucokinase activator delays the onset of hyperglycaemia and preserves beta cell mass in the Zucker diabetic fatty rat

AIMS/HYPOTHESIS

Glucokinase activators (GKAs) are currently being developed as new therapies for type 2 diabetes and have been shown to enhance beta cell survival and proliferation in vitro. Here, we report the effects of chronic GKA treatment on the development of hyperglycaemia and beta cell loss in the male Zucker diabetic fatty (ZDF) rat, a model of type 2 diabetes with severe obesity.

METHODS

Cell protection by GKA was studied in MIN6 and INS-1 cells exposed to hydrogen peroxide. Glucose homeostasis and beta cell mass were evaluated in ZDF rats dosed for 41 days with Cpd-C (a GKA) or glipizide (a sulfonylurea) as food admixtures at doses of approximately 3 and 10 mg kg(-1) day(-1).

RESULTS

Incubation of MIN6 and INS-1 832/3 insulinoma cell cultures with GKA significantly reduced cell death and impairment of intracellular NADH production caused by exposure to hydrogen peroxide. Progression from prediabetes (normoglycaemia and hyperinsulinaemia) to overt diabetes (hyperglycaemia and hypoinsulinaemia) was significantly delayed in male ZDF rats by in-feed treatment with Cpd-C, but not glipizide. Glucose tolerance, tested in the fifth week of treatment, was also significantly improved by Cpd-C, as was pancreatic insulin content and beta cell area. In a limited immunohistochemical analysis, Cpd-C modestly and significantly enhanced the rate of beta cell proliferation, but not rates of beta cell apoptosis relative to untreated ZDF rats.

CONCLUSIONS/INTERPRETATION

These findings suggest that chronic activation of glucokinase preserves beta cell mass and delays disease in the ZDF rat, a model of insulin resistance and progressive beta cell failure.

Poly(ADP-ribose) polymerase 1 inhibition improves coronary arteriole function in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is associated with microvascular dysfunction. We hypothesized that increased poly(ADP-ribose) polymerase 1 (PARP-1) activity contributes to microvascular dysfunction in T2DM. T2DM (db(-)/db(-)) and nondiabetic control (db(-)/db(+)) mice were treated with 2 different PARP-1 inhibitors (INO-1001, 5 mg/kg per day and ABT-888, 15 mg/kg per day) for 2 weeks. Isolated coronary arterioles were mounted in an arteriograph. Pressure-induced myogenic tone was significantly potentiated, whereas endothelium-dependent relaxation was significantly attenuated in diabetic mice compared with control mice. These results were associated with decreased endothelial NO synthase phosphorylation and cGMP level and increased PARP-1 activity in coronary arterioles from diabetic mice compared with control mice. Interestingly, PARP-1 inhibitors significantly reduced the potentiation of myogenic tone, improved endothelium-dependent relaxation, restored endothelial NO synthase phosphorylation and cGMP, and attenuated cleaved PARP-1. These results were supported by in vitro studies indicating that downregulation of PARP-1 in mesenteric resistance arteries using PARP-1 short hairpin RNA lentiviral particles significantly improved endothelium-dependent relaxation in mesenteric resistance arteries from diabetic mice compared with control mice. The inhibition of NO synthesis by N(G)-nitro-L-arginine methyl ester (L-NAME) significantly reduced the endothelium-dependent relaxation in coronary arterioles and mesenteric resistance arteries from control and diabetic mice treated with PARP-1 inhibitors and PARP-1 short hairpin RNA lentiviral particles. In addition, we demonstrated that enhanced cleaved PARP-1, its binding to DNA, and DNA damage were reduced after PARP-1 inhibition in cultured endothelial cells stimulated with high glucose. We provide evidence that T2DM impairs microvascular function by an enhanced PARP-1 activity-dependent mechanism. Therefore, PARP-1 could be a potential target for overcoming diabetic microvascular complications.

Altered REDD1, myostatin, and Akt/mTOR/FoxO/MAPK signaling in streptozotocin-induced diabetic muscle atrophy

Type 1 diabetes, if poorly controlled, leads to skeletal muscle atrophy, decreasing the quality of life. We aimed to search highly responsive genes in diabetic muscle atrophy in a common diabetes model and to further characterize associated signaling pathways. Mice were killed 1, 3, or 5 wk after streptozotocin or control. Gene expression of calf muscles was analyzed using microarray and protein signaling with Western blotting. We identified translational repressor protein REDD1 (regulated in development and DNA damage responses) that increased seven- to eightfold and was associated with muscle atrophy in diabetes. The diabetes-induced increase in REDD1 was confirmed at the protein level. This result was accompanied by the increased gene expression of DNA damage/repair pathways and decreased expression in ATP production pathways. Concomitantly, increased phosphorylation of AMPK and dephosphorylation of the Akt/mTOR/S6K1/FoxO pathway of proteins were observed together with increased protein ubiquitination. These changes were especially evident during the first 3 wk, along with the strong decrease in muscle mass. Diabetes also induced an increase in myostatin protein and decreased MAPK signaling. These, together with decreased serum insulin and increased serum glucose, remained altered throughout the 5-wk period. In conclusion, diabetic myopathy induced by streptozotocin led to alteration of multiple signaling pathways. Of those, increased REDD1 and myostatin together with decreased Akt/mTOR/FoxO signaling are associated with diabetic muscle atrophy. The increased REDD1 and decreased Akt/mTOR/FoxO signaling followed a similar time course and thus may be explained, in part, by increased expression of genes in DNA damage/repair and possibly also decrease in ATP-production pathways.

Antihyperglycemic potentials of a threatened plant, Helonias dioica: antioxidative stress responses and the signaling cascade

Helonias dioica (HD) is a threatened species of herb growing in North America. It is used as a traditional medicine for treating various ailments particularly related to reproductive issues. The root is reported to contain approximately 10% of a saponin (chamaelirin; C36H62O18) apart from certain other fatty acids. As saponins are known to have hypoglycemic effects, we suspected its possible antihyperglycemic potentials. We injected intraperitoneally alloxan (ALX) at the dose of 200 mg/kg body weight (bw) to induce hyperglycemia in mice and tested possible hypoglycemic effects of HD in vivo by deploying two doses (100 and 200 mg/kg bw, respectively). We also tested its effects on the isolated pancreatic islets cells in vitro. We used various standard protocols like reactive oxygen species (ROS) generation and DNA damage, activities of biomarkers like catalase (CAT), superoxide dismutase (SOD), lipid peroxidase (LPO), reduced glutathione (GSH) of the pancreas tissue and glucokinase and glycogen content of the liver of hyperglycemic mice. With a mechanistic approach, we also tracked down the possible signaling pathway involved. We found an elevated level of ROS generation, LPO and overexpression of inducible nitric oxide synthase (iNOS), tumor necrosis factor α (TNF- α), p38 Map kinase (p38 MAPK), nuclear factor (NF)- κβ, interferon gamma (IFN- γ), cytochrome c, caspase 3, poly [ADP ribose] polymerase (PARP) and cyclo oxygenase 2 (COX2) in ALX-induced diabetic mouse. Treatment of hyperglycemic mice with both the doses of HD showed a significant decrease with respect to all these parameters of study. Thus, our results suggest that HD prevents ALX-induced islet cell damage and possesses antihyperglycemic and antioxidative potentials.

Resveratrol prevents streptozotocin-induced diabetes by inhibiting the apoptosis of pancreatic β-cell and the cleavage of poly (ADP-ribose) polymerase

Resveratrol (3,5,4'-trihydroxystilbene; RSV) is one kind of polyphenolic phytoalexin that has many effects on metabolic diseases. This study aimed to evaluate the protective effect of RSV pretreatment on β-cell. Male Sprague Dawley rats weighing 200-230 g were divided into 4 groups: (1) RSV; (2) streptozotocin (STZ, 70 mg/kg, intraperitoneally); (3) STZ after 7 days pretreatment with RSV; and (4) STZ pretreated with nicotinamide. Fasting glucose concentration was measured and an intraperitoneal glucose tolerance test was performed 72 h after STZ injection to determine the diabetic condition. The pancreas was removed 3, 6, 36, and 48 h after STZ injection. STZ induced diabetes in all rats not given RSV pretreatment, whereas none of the RSV-pretreated rats developed diabetes. Pretreatment with RSV inhibited apoptosis and reduced the activation of caspase-3 and poly(ADP-ribose) polymerase (PARP). However, expression of the total length PARP was not affected by pretreatment. Our findings suggest that RSV protects β-cells from STZ simultaneously with inhibiting the activation of PARP.

WldS enhances insulin transcription and secretion via a SIRT1-dependent pathway and improves glucose homeostasis

OBJECTIVE Wld(S) (Wallerian degeneration slow), a fusion protein from a spontaneous mutation containing full-length nicotinamide mononucleotide adenylyltransferase 1, has NAD biosynthesis activity and protects axon from degeneration robustly. NAD biosynthesis is also implicated in insulin secretion in β-cells. The aim of this study was to investigate the effect of Wld(S) on β-cells and glucose homeostasis.

RESEARCH DESIGN AND METHODS

Using the Wld(S) mice, we measured the expression of Wld(S) in pancreas and analyzed the effect of Wld(S) on glucose homeostasis. The direct effect of Wld(S) on insulin transcription and secretion and the related mechanisms was measured in isolated islets or β-cell lines. Silent information regulator 1 (SIRT1), an NAD-dependent protein deacetylase, is involved in insulin secretion. Thus, Wld(S) mice with SIRT1 deficiency were generated to study whether the SIRT1-dependent pathway is involved.

RESULTS

Wld(S) is highly expressed in the pancreas and improves glucose homeostasis. Wld(S) mice are resistant to high-fat diet-induced glucose intolerance and streptozotocin (STZ)-induced hyperglycemia. Wld(S) increases insulin transcription dependent on its NAD biosynthesis activity and enhances insulin secretion. SIRT1 is required for the improved insulin transcription, secretion, and resistance to STZ-induced hyperglycemia caused by Wld(S). Moreover, Wld(S) associates with SIRT1 and increases NAD levels in the pancreas, causing the enhanced SIRT1 activity to downregulate uncoupling protein 2 (UCP2) expression and upregulate ATP levels.

CONCLUSIONS

Our results demonstrate that Wld(S) combines an insulinotropic effect with protection against β-cell failure and suggest that enhancing NAD biosynthesis in β-cells to increase SIRT1 activity could be a potential therapeutic approach for diabetes.

The emerging role of autophagy in the pathophysiology of diabetes mellitus

An emerging body of evidence supports a role for autophagy in the pathophysiology of type 1 and type 2 diabetes mellitus. Persistent high concentrations of glucose lead to imbalances in the antioxidant capacity within the cell resulting in oxidative stress-mediated injury in both disorders. An anticipated consequence of impaired autophagy is the accumulation of dysfunctional organelles such as mitochondria within the cell. Mitochondria are the primary site of the production of reactive oxygen species (ROS), and an imbalance in ROS production relative to the cytoprotective action of autophagy may lead to the accumulation of ROS. Impaired mitochondrial function associated with increased ROS levels have been proposed as mechanisms contributing to insulin resistance. In this article we review and interpret the literature that implicates a role for autophagy in the pathophysiology of type 1 and type 2 diabetes mellitus as it applies to β-cell dysfunction, and more broadly to organ systems involved in complications of diabetes including the cardiovascular, renal and nervous systems.

Regulation of MKP-1 expression and MAPK activation by PARP-1 in oxidative stress: a new mechanism for the cytoplasmic effect of PARP-1 activation

Previously, it was suggested that the release of nuclearly formed ADP-ribose polymers or ADP-ribosylated proteins could be responsible for the cytosolic and mitochondrial effects of poly(ADP-ribose) polymerase (PARP)-1 activation in oxidative stress. In this report, we provide a novel alternative mechanism. We found that reactive oxygen species-activated PARP-1 regulated the activation of JNK and p38 mitogen-activated protein kinases (MAPKs) because inhibition of PARP-1 by pharmacons, small interfering RNA silencing of PARP-1 expression, or the transdominant expression of enzymatically inactive PARP-1 resulted in the inactivation of these MAPKs. This regulation was achieved by increased expression and enlarged cytoplasmic localization of MAPK phosphatase-1 (MKP-1) upon PARP-1 inhibition in oxidative stress because changes in MKP-1 expression were reflected in the phosphorylation states of JNK and p38. Furthermore, we found that in MKP-1-silenced cells, PARP inhibition was unable to exert its protective effect, indicating the pivotal roles of JNK and p38 in mediating the oxidative-stress-induced cell death as well as that of increased MKP-1 expression in mediating the protective effect of PARP inhibition. We suggest that regulation of a protein that can directly influence cytoplasmic signaling cascades at the expression level represents a novel mechanism for the cytoplasmic action of PARP-1 inhibition.

Increased poly(ADP-ribose) polymerase (PARP)-1 expression and activity are associated with inflammation but not goblet cell metaplasia in murine models of allergen-induced airway inflammation

Inflammation plays a key role in lung injury and in the pathogenesis of asthma. Two murine models of allergic airway inflammation-sensitization and challenge to ovalbumin (OVA) and intratracheal exposure to interleukin-13 (IL13)-were used to evaluate the expression of poly(ADP-ribose) polymerase-1 (PARP-1) in allergic airway inflammation. Inflammation is prominent in OVA-induced allergic asthma, but this inflammation is greatly reduced by a PARP-1 inhibitor and almost eliminated when PARP-1 knockout mice are subjected to the OVA model. The present study temporally evaluated PARP-1 protein expression, localization, and activity, as well as inflammation and goblet cell metaplasia (GCM), in murine lungs following a single OVA challenge or IL13 exposure. Following OVA challenge PARP-1 protein expression and activity were greatly increased, being maximal at 3 to 5 days following OVA exposure and beginning to decrease by day 8. These changes correlated with the timing and degree of inflammation and GCM. In contrast, PARP-1 protein or activity did not change following single IL13 exposure, though GCM was manifested without inflammation. This study demonstrates that both PARP-1 protein and activity are increased by allergen-activated inflammatory mediators, excluding IL13, and that PARP-1 increase does not appear necessary for GCM, one of the characteristic markers of allergic airway inflammation in murine models.