Mechanisms of nicotinamide and thymidine protection from alloxan and streptozocin toxicity

Hypoglycemic and Antihyperglycemic Activities of 80% Methanol Root Extract of Acanthus polystachyus Delile (Acanthaceae) in Type 2 Diabetic Rats

Background

The morbidity and mortality rate from diabetic mellitus are increasing in the world especially in low- and middle-income countries; hence, it is necessary to evaluate the efficacy and safety of medicinal plants to support existing drugs in treating diabetes mellitus. Therefore, the aim of this study was to evaluate the hypoglycemic effect of 80% methanol root extract of Acanthus polystachyus in normoglycemic, hyperglycemic, and streptozotocin–nicotinamide induced diabetic rats.

Methods

Male albino Wistar rats were divided into five groups (n=6) in all three models. In all models, group one rats served as a negative control and were received vehicle (10mL/kg distilled water), whereas group two (APRE100), three (APRE200), and four (APRE400) were treated with 100, 200, and 400mg/kg of extract, respectively, and group five were treated with glibenclamide (5mg/kg) and served as a positive control. Blood glucose levels were measured at different time points by taking blood from their tails. Data were analyzed using one-way ANOVA followed by Tukey’s post hoc test to carry out comparisons between and within-group and P < 0.05 was considered as statistically significant.

Results

The root of Acanthus polystachyus reduces peak blood sugar levels significantly after the loading of oral glucose at all tested doses. In streptozotocin–nicotinamide-induced type 2 diabetic rats, the daily oral administration of the crude extracts showed a significant reduction of blood glucose level at all tested doses compared to the negative control group. However, the extract did not reduce blood glucose levels in normoglycemic rats at all tested doses compared to both negative and positive control.

Conclusion

From this study, it can be concluded that the root extract of Acanthus polystachyus showed an antihyperglycemic effect in hyperglycemic and diabetic rats but lack hypoglycemic effect in normoglycemic rats. Hence, the plant root may be a good candidate for the development of new antidiabetic drugs.

Embedded-Culture of Pancreatic β-Cells Derived from Transgenic Mouse Insulinoma as a Potential Source for Xenotransplantation using a Diffusion Chamber

Embedded-culture of pancreatic β-cells derived from a transgenic mouse insulinoma (MIN6 cells) was studied in vitro and in vivo. The MIN6 cells were enmeshed in an agarose-PVMA-collagen matrix for long-term maintenance. The cells formed islet-like cell clusters (ICCs) in the mixed matrix. When 10 mmol/L nicotinamide was added to these cultures the cells secreted insulin in response to various concentrations of glucose, whereas the untreated control cells were unresponsive. Both control and nicotinamide-treated MIN6 cells exhibited normal β-cell function for up to 35 days in the mixed matrix, and the cells were much better preserved with nicotinamide than without it. MIN6 cells were suspended in the mixed matrix with nicotinamide and transferred into diffusion chambers to create a bio-artificial endocrine pancreas (Bio-AEP). In streptozotocine-induced diabetic rats with implanted Bio-AEP but without any immunosuppressants, a return to normoglycaemia was observed for up to 12 wk or more after transplantation. Our results indicate that nicotinamide-treated MIN6 cells embedded in a mixed matrix should be useful for the study of xenotransplantation and the development of a bioartificial endocrine pancreas.

Arachidonic acid and lipoxinA4 attenuate streptozotocin-induced cytotoxicity to RIN5 F cells in vitro and type 1 and type 2 diabetes mellitus in vivo

OBJECTIVE

The aim of this study was to observe whether polyunsaturated fatty acids (PUFAs) can protect rat insulinoma (RIN5 F) cells against streptozotocin (STZ)-induced apoptosis in vitro and type 1 diabetes mellitus (T1DM) and type 2 DM (T2DM) in vivo and if so, what would be the mechanism of this action.

METHODS

RIN5 F cells were used for the in vitro study, whereas the in vivo study was performed in Wistar rats. STZ was used to induce apoptosis of RIN5 F cells in vitro and T1- and T2DM in vivo. The effect of PUFAs: γ-linolenic acid (GLA), arachidonic acid (AA) of ω-6 series, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) of ω-3 series; cyclooxygenase (COX) and lipoxygenase (LOX) inhibitors and antiinflammatory metabolite of AA and DHA, lipoxin A4 (LXA4), and resolvin D2 and protectin, respectively against STZ-induced cytotoxicity to RIN5 F cells in vitro and LXA4 against T1- and T2DM in vivo was studied. Changes in the antioxidant content, lipid peroxides, nitric oxide, and expression of PDX1, P65, nuclear factor-κb (NF-κb), and IKB genes in STZ-treated RIN5 F cells in vitro and Nrf2, GLUT2, COX2, iNOS protein levels in the pancreatic tissue of T1- and T2DM and LPCLN2 (lipocalin 2), NF-κb, IKB I in adipose tissue of T2DM after LXA4 treatment were studied. Plasma glucose, insulin, and tumor necrosis factor (TNF)-α levels also were measured in STZ-induced T1- and T2DM Wistar rats.

RESULTS

Among all PUFAs tested, AA and EPA are the most effective against STZ-induced cytotoxicity to RIN5 F cells in vitro. Neither COX nor LOX inhibitors blocked the cytoprotective action of AA in vitro and T1- and T2DM by STZ. LXA4 production by RIN5 F cells in vitro and plasma LXA4 levels in STZ-induced T1- and T2DM animals were decreased by STZ that reverted to normal after AA treatment. AA prevented both T1- and T2DM induced by STZ. Antiinflammatory metabolite of AA and LXA4 prevented both T1- and T2DM induced by STZ. The expression of Pdx1, NF-κb, IKB genes in the pancreas and plasma TNF-α levels in T1- and T2DM; Nrf2, Glut2, COX2, and iNOS proteins in pancreatic tissue of T1DM and LPCLN2, NF-κb, IKB I in adipose tissue of T2DM reverted to normal in LXA4-treated animals.

CONCLUSION

Both AA and LXA4 prevented STZ-induced cytotoxicity to RIN5 F cells in vitro and T1- and T2DM in vivo, suggesting that these two bioactive lipids may function as antidiabetic molecules. AA is beneficial against STZ-induced cytotoxicity and T1- and T2DM by enhancing the production of LXA4.

Long-term treatment with nicotinamide induces glucose intolerance and skeletal muscle lipotoxicity in normal chow-fed mice: compared to diet-induced obesity

Nicotinamide (NAM), or vitamin B3, is an essential coenzyme for ATP synthesis and an inhibitor of sirtuin 1. Recently, conflicting results were reported regarding the treatment of NAM in type 2 diabetes and obesity. The aim of this study was to determine whether and how long-term treatment with NAM at lower dose would affect insulin sensitivity in mice fed chow diet. We treated mice with NAM (100 mg/kg/day) and normal chow for 8 weeks. Strikingly, NAM induced glucose intolerance and skeletal muscle lipid accumulation in nonobese mice. NAM impaired mitochondrial respiration capacity and energy production in skeletal muscle, in combination with increased expression of the mediators for mitophagy (p62, PINK1, PARK2 and NIX) and autophagy (FOXO3, Bnip3, CTSL, Beclin1 and LC-3b). Next, we treated mice with high-fat diet (HFD) and resveratrol (RSV; 100 mg/kg/day) for 8 weeks. RSV protected against HFD-induced insulin resistance and obesity. HFD increased skeletal muscle lipid content as well as NAM, but this increase was attenuated by RSV. In contrast to NAM, HFD enhanced fatty acid oxidative capacity. Muscle transcript levels of genes for mitophagy and autophagy were largely suppressed by HFD, whereas RSV did not rescue these effects. These differences suggest that skeletal muscle autophagy may represent adaptive response to NAM-induced lipotoxicity, whereas reduced autophagy in skeletal muscle may promote HFD-induced lipotoxicity. Our results demonstrate that chronic NAM supplementation in healthy individuals, although at lower dose than previously reported, is still detrimental to glucose homeostasis and skeletal muscle lipid metabolism.

BDNF protects pancreatic β cells (RIN5F) against cytotoxic action of alloxan, streptozotocin, doxorubicin and benzo(a)pyrene in vitro

OBJECTIVE

The study was conducted to observe whether brain-derived neurotrophic factor (BDNF) has cytoprotective actions against alloxan (AL), streptozotocin (STZ), doxorubicin (DB) and benzo(a)pyrene (BP) compounds in vitro that may account for its beneficial action in diabetes mellitus.

MATERIALS AND METHODS

This in vitro study was performed using rat insulinoma (RIN5F) cells. Possible cytoprotective action of BDNF (using pre-treatment, simultaneous and post-treatment schedules of RIN5F cells with BDNF) against the four chemicals tested was evaluated using MTT and apoptosis assays. Possible mechanism of cytoprotective action of BDNF was assessed by measuring BCl2/IKB-β/Pdx mRNA transcripts and anti-oxidant levels in RIN5F cells. Effect of alloxan, STZ, doxorubicin and BP on the production of BDNF by RIN5F cells was also studied.

RESULTS

Results of the present study revealed that BDNF in the doses (100ng>50ng>10ng/ml) has significant cytoprotection (P<0.001, P<0.01) on cytotoxic action of AL, STZ, DB and BP against rat insulinoma RIN5F (5×10(4) cells/100μl) cells in vitro. It was observed that AL, STZ, DB and BP inhibited BDNF production significantly (P<0.001) in a dose-dependent manner by RIN5F cells (0.5×10(6) cells/500μl) in vitro, while BDNF not only prevented apoptosis induced by these four chemicals but also significantly increased (P<0.001) BCl2/IKB-β/Pdx mRNA transcripts and restored anti-oxidant levels (P<0.01) in RIN5F cells to normal.

DISCUSSION

These results suggest that BDNF has potent cytoprotective actions, restores anti-oxidant defenses to normal and thus, prevents apoptosis and preserves insulin secreting capacity of β cells. In addition, BDNF enhanced viability of RIN 5F in vitro. Thus, BDNF not only has anti-diabetic actions but also preserves pancreatic β cells integrity and enhances their viability. These results imply that BDNF functions as an endogenous cytoprotective molecule that may explain its beneficial actions in some neurological conditions as well.

Ameliorative effect of naringenin on hyperglycemia-mediated inflammation in hepatic and pancreatic tissues of Wistar rats with streptozotocin- nicotinamide-induced experimental diabetes mellitus

In diabetes mellitus (DM), sustained hyperglycemia results in the generation of reactive oxygen species, ultimately leading to increased oxidative stress and inflammation in vital tissues. In the present study, possible ameliorative effects of naringenin on hyperglycemia-mediated inflammation in experimental streptozocin (STZ)-nicotinamide-induced DM were sought. DM was induced experimentally in overnight-fasted Wistar rats (150-180 g) by intra-peritoneal injection of STZ (50 mg/kg.b.w) and of nicotinamide (110 mg/kg.b.w); control rats (n = 6) received only vehicle (0.5 ml of 0.1 M of cold citrate buffer; pH 4.5). One group of diabetic rats (n = 6) was left untreated while another group of diabetic rats (n = 6) received naringenin (50 mg/kg b.w./day) orally for 21 days. At this time, hemotological indices (erythrocyte sedimentation rate [ESR], total white blood cell [WBC] count, differential WBC percentage, and platelet count) were measured. Significant alterations in expression of gene and protein biomarkers of inflammation in hepatic and pancreatic tissues were determined by measuring mRNA levels and the level of protein expressed, respectively, as was the total nitric oxide level in these tissues. Diabetic rats showed significantly higher mean ESR values, total WBC counts, differential WBC percentages, and platelet counts than those in control rats; similarly, mean mRNA levels of C-reactive protein, pro-inflammatory cytokine, nuclear factor-κB and inducible nitric oxide synthase genes and mean intensities of expression of the corresponding proteins in the hepatic and pancreatic tissue samples from diabetic rats significantly exceeded those in control rats. However, in diabetic rats treated with naringenin, the values of hematological, mRNA transcript and protein indices of inflammation were all lower than those in diabetic rats. These results suggest that naringenin possibly alleviates hyperglycemia-mediated inflammation in experimental STZ-nicotinamide-induced DM in Wistar rats.

Mild gestational hyperglycemia in rat induces fetal overgrowth and modulates placental growth factors and nutrient transporters expression

Mild gestational hyperglycemia is often associated with fetal overgrowth that can predispose the offspring to metabolic diseases later in life. We hypothesized that unfavorable intrauterine environment may compromise the development of placenta and contribute to fetal overgrowth. Therefore, we developed a rat model and investigated the effects of maternal dysglycemia on fetal growth and placental gene expression. Female rats were treated with single injection of nicotinamide plus streptozotocin (N-STZ) 1-week before mating and were studied at gestational day 21. N-STZ pregnant females displayed impaired glucose tolerance that is associated with a lower insulin secretion. Moderate hyperglycemia induced fetal overgrowth in 40% of newborns, from pregnancies with 10 to 14 pups. The incidence of macrosomia was less than 5% in the N-STZ pregnancies when the litter size exceeds 15 newborns. We found that placental mass and the labyrinthine layer were increased in macrosomic placentas. The expression of genes involved in placental development and nutrient transfer was down regulated in the N-STZ placentas of macrosomic and normosomic pups from pregnancies with 10 to 14 ones. However, we observed that lipoprotein lipase 1 (LPL1) gene expression was significantly increased in the N-STZ placentas of macrosomic pups. In pregnancies with 15 pups or more, the expression of IGFs and glucose transporter genes was also modulated in the control placentas with no additional effect in the N-STZ ones. These data suggest that placental gene expression is modulated by gestational conditions that might disrupt the fetal growth. We described here a new model of maternal glucose intolerance that results in fetal overgrowth. We proposed that over-expression of LPL1 in the placenta may contribute to the increased fetal growth in the N-STZ pregnancies. N-STZ model offers the opportunity to determinate whether these neonatal outcomes may contribute to developmental programming of metabolic diseases in adulthood.

Antihyperglycemic and antioxidant effects of a flavanone, naringenin, in streptozotocin-nicotinamide-induced experimental diabetic rats

In the present study, the putative antihyperglycemic and antioxidant effects of a flavanone, naringenin, were evaluated in comparison with those of glyclazide, a standard drug for therapy of diabetes mellitus. Diabetes was induced experimentally in 12-h-fasted rats by intraperitoneal injections of first streptozotocin (50 mg/kg b.w.) and then of nicotinamide (110 mg/kg b.w.) after a 15-min interval. Untreated diabetic rats revealed the following in comparison with normal rats: significantly higher mean levels of blood glucose and glycosylated hemoglobin, significantly lower mean levels of serum insulin, significantly lower mean activities of pancreatic antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase), significantly lower mean levels of plasma non-enzymatic antioxidants (reduced glutathione, vitamin C , vitamin E), significantly elevated mean levels of pancreatic malondialdehyde (MDA) and significantly elevated mean activities of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH). Following oral administration of naringenin (50 mg/kg b.w./day) to diabetic rats for 21 days, the following observations were made in comparison with untreated diabetic rats: significantly lower mean levels of fasting blood glucose and glycosylated hemoglobin, significantly elevated serum insulin levels, significantly higher mean activities of pancreatic enzymatic antioxidants, significantly higher mean levels of plasma non-enzymatic antioxidants, lower mean pancreatic tissue levels of MDA and lower mean activities of ALT, AST, ALP and LDH in serum. The values obtained in the naringenin-treated animals approximated those observed in glyclazide-treated animals. Histopathological studies appeared to suggest a protective effect of naringenin on the pancreatic tissue in diabetic rats. These results suggest that naringenin exhibits antihyperglycemic and antioxidant effects in experimental diabetic rats.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Role of small bioorganic molecules in stem cell differentiation to insulin-producing cells

The use of small specific molecules has been instrumental in the modulation of stem cell proliferation and differentiation to obtain insulin-containing cells. Examples include nutrients (glucose, nicotinamide and retinoic acid), acids (butyrate), alkaloids (cyclopamine and conophylline) and pharmacological agents (LY294002 and wortmannin). These molecules, alone or in combination with specific growth factors and hormones, will likely provide key information to design specific culture media in order to obtain customized cells for implantation in diabetes. In addition, the study of such molecules will help to understand the mechanisms involved in stem cell biology as well as contribute to the design of specific drugs for islet repair and regeneration in diabetes.

Improved human islet isolation using nicotinamide

We investigated the effects of nicotinamide (NA) supplementation of the processing medium during islet isolation. One hundred and two human pancreata were processed for clinical transplantation after preservation either in the University of Wisconsin (UW) or using the two-layer method (TLM). Pancreata were then divided into four groups and retrospectively analyzed. Group I: UW preservation followed by processing without NA, Group II: UW preservation and processing with NA, Group III: TLM preservation without NA, Group IV: TLM preservation with NA. We observed a significant increase in islet yield in Group II (4343+/-348 IEQ/g) [mean+/-SEM], compared to Group I (2789+/-348 IEQ/g) (p=0.005). Similarly, a significant increase in islet yield was observed when NA was used in the processing of organs preserved with TLM (Group IV: 5538+/-413 vs. Group III: 3500+/-629; p=0.02). Furthermore islet yield was higher in Group IV than in Group II (p<0.05). The percentages of preparations that qualified for transplantation were 25, 47, 45, 69% in Groups I, II, III, IV, respectively. Addition of NA to the processing medium significantly improved islet yields in both the UW and TLM preservation protocols, allowing for a higher percentage of islet preparations to qualify for clinical transplantation.

Immunotherapeutic approaches to prevent, ameliorate, and cure type 1 diabetes

Type 1A diabetes (T1D) is caused by autoimmune islet beta cell destruction precipitated by environmental triggers in genetically predisposed individuals. Islet beta cells produce insulin and are the primary target of this autoimmune disorder. Insulin, glutamic acid decarboxylase, and insulinoma associated-2 autoantibodies (IAA, GAD65, and IA-2) are the autoantibodies that have been associated most clearly with the development of T1D. Despite our current ability to predict T1D using genetic markers and detecting islet autoantibodies, we have yet to find a safe way to prevent the disease. However, there are more than 100 different therapies that prevent T1D in the nonobese diabetic (NOD) mouse model or the BioBreeding (BB) rats. This paper reviews a few select therapeutic approaches that have been or are being evaluated as possibilities for the prevention, amelioration, or cure of T1D.

Nutritional risk predictors of beta cell autoimmunity and type 1 diabetes at a young age

Type 1 diabetes is an immune-mediated disease characterized by a preclinical prodrome during which beta cell autoimmunity proceeds at a variable rate. Large geographic differences and a conspicuous increase in incidence, especially among young children since the 1950s, and the relatively low concordance in identical twins are factors that favor a critical role of environmental factors in the etiology of this disease. Only approximately 5% or fewer subjects with HLA-conferred genetic susceptibility to type 1 diabetes actually develop the clinical disease. Breastfeeding, nicotinamide, zinc, and vitamins C, D, and E have been reported as possibly protecting against type 1 diabetes, whereas N-nitroso compounds, cow milk, increased linear growth, and obesity may increase the risk. Thus far, only the significance of infant feeding, cow milk, and vitamin D have been studied in both case-control and cohort settings. The major shortcoming of most studies done so far is that only single dietary exposures have been assessed at single time points. Putative nutritional and other confounding factors have received little attention as have the limitations of the dietary methods used. There is little firm evidence of the significance of nutritional factors in the etiology of type 1 diabetes. The availability of good markers of preclinical type 1 diabetes and of genetic risk have decreased the sample sizes needed and made longitudinal cohort studies of the assessment of children's diets feasible.

Nicotinamide increases systemic vascular resistance in ovine endotoxemia

OBJECTIVE

The nuclear enzyme Poly(ADP-Ribose)-Polymerase (PARP) has been hypothesized as playing a major role in various forms of inflammation. PARP activation is induced by DNA strand breakage and can result in intracellular energy depletion and, ultimately, cell death. Further, it is thought to influence cardiovascular function and organ failure in endotoxemia. Here, we investigated the effect of the PARP inhibitor nicotinamide on cardiovascular and liver function in healthy and chronically endotoxemic sheep.

DESIGN

Prospective controlled trial.

SETTING

University research laboratory.

SUBJECTS

12 female adult sheep.

INTERVENTIONS

Six healthy sheep, instrumented for chronic study, received nicotinamide intravenously as a bolus of 40 mg/kg followed by a continuous infusion of 10 mg.kg(-1).h(-1); six animals received the vehicle. One hour after bolus application, a continuous infusion of endotoxin ( Salmonella typhosa, 10 ng.kg(-1).min(-1)) was started. Hemodynamic parameters were determined before and during endotoxemia.

MEASUREMENTS AND RESULTS

Treatment with nicotinamide resulted in a significantly higher systemic vascular resistance index and lower cardiac index in endotoxemic animals, but not in controls. It also attenuated endotoxin-induced increase in gamma-glutamyl transferase.

CONCLUSIONS

The PARP inhibitor nicotinamide attenuates impairment of cardiovascular function during endotoxemia. In addition, PARP activation may be involved in endotoxin-induced liver injury.

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.

Dynamics of intracellular calcium and free radical production during ischemia in pyramidal neurons

Biochemical cascades initiated by oxidative stress and excitotoxic intracellular calcium rises are thought to converge on mitochondrial dysfunction. We investigated the contribution of mitochondrial dysfunction to free radical (FR) overproduction in rat CA1 pyramidal neurons of organotypic slices subjected to a hypoxic-hypoglycemic insult. Ischemia-induced FR generation was decreased by the mitochondrial complex I blocker, rotenone, indicating that mitochondria are the principal source of ischemic FR production. Measurements of mitochondrial calcium with the mitochondrial calcium probe dihydroRhod-2, revealed that FR production during and after the anoxic episode correlates with the accumulation of mitochondrial calcium. However, the mitochondrial calcium uptake inhibitor Ru360 did not prevent FR generation during ischemia and attenuated it to some degree during reoxygenation. On the other hand, the mitochondrial permeability transition blocker cyclosporinA (CsA) completely arrested both ischemic FR generation and mitochondrial calcium overload, and prevented deterioration of neuronal intrinsic membrane properties. CsA had no effect on the accumulation of intracellular calcium during ischemia-reperfusion. Nicotinamide, a blocker of NAD+ hydrolysis, reproduced the CsA effects on FR generation, mitochondrial calcium accumulation and cytoplasmic calcium increases. These observations suggest that a major determinant of ischemic FR generation in pyramidal neurons is the uncoupling of the mitochondrial respiratory chain, which may be associated with the mitochondrial permeability transition.

The NAD+ precursors, nicotinic acid and nicotinamide protect cells against apoptosis induced by a multiple stress inducer, deoxycholate

The bile salt, sodium deoxycholate (NaDOC), is a natural detergent that promotes digestion of fats. At high physiologic levels, NaDOC activates many stress-response pathways and induces apoptosis in various cell types. NaDOC induces DNA damage and activates poly(ADP-ribose) polymerase (PARP), an enzyme that utilizes NAD+ as a substrate to repair DNA. NaDOC also induces oxidative stress, endoplasmic reticulum (ER) stress and contributes to protein malfolding. The NAD+ precursors, nicotinic acid (NA) and nicotinamide (NAM) were found to protect cells against NaDOC-induced apoptosis. NA and NAM also decreased constitutive levels of both activated NF-kappaB and GRP78, two proteins that respond to oxidative stress. However, the mechanism by which NA and NAM protects cells against apoptosis does not involve a reduction in constitutive levels of oxidative stress. NA or NAM treatment increased the protein levels of glyceraldehyde-3-phosphate dehydrogense (GAPDH), a multi-functional enzyme, in the nucleus and cytoplasm, respectively. NAM did not activate the promoter/response elements of 13 stress response genes nor reduce intracellular non-protein thiols, suggesting that it is non-toxic to cells. NAM thus has promise as a dietary supplement to help prevent disorders involving excessive apoptosis.

Radicals and oxidative stress in diabetes

Recent evidence is reviewed indicating increased oxidative damage in Type 1 and Type 2 diabetes mellitus as well as deficits in antioxidant defence enzymes and vitamins. Mechanisms are considered whereby hyperglycaemia can increase oxidative stress, and change the redox potential of glutathione and whereby reactive oxygen species can cause hyperglycaemia. It is argued that oxygen, antioxidant defences, and cellular redox status should now be regarded as central players in diabetes and the metabolic syndrome.

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

Human type 1 diabetes results from the selective destruction of insulin-producing pancreatic beta cells during islet inflammation. Cytokines and reactive radicals released during this process contribute to beta-cell death. Here we show that mice with a disrupted gene coding for poly (ADP-ribose) polymerase (PARP-/- mice) are completely resistant to the development of diabetes induced by the beta-cell toxin streptozocin. The mice remained normoglycemic and maintained normal levels of total pancreatic insulin content and normal islet ultrastructure. Cultivated PARP-/- islet cells resisted streptozocin-induced lysis and maintained intracellular NAD+ levels. Our results identify NAD+ depletion caused by PARP activation as the dominant metabolic event in islet-cell destruction, and provide information for the development of strategies to prevent the progression or manifestation of the disease in individuals at risk of developing type 1 diabetes.

Decreases in mouse brain NAD+ and ATP induced by 1-methyl-4-phenyl-1, 2,3,6-tetrahydropyridine (MPTP): prevention by the poly(ADP-ribose) polymerase inhibitor, benzamide

Inhibitors of poly(ADP-ribose) polymerase (PARP), including benzamide, protect against 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-induced dopamine neurotoxicity in vivo [Cosi et al., Brain Res. 729 (1996) 264-269]. In vitro, the activation of PARP by free radical damaged DNA has been shown to be correlated with rapid decreases in the cellular levels of its substrate nicotinamide adenine dinucleotide (NAD+), and ATP. Here, we investigated in vivo whether MPTP acutely caused region- and time-dependent changes in brain levels of NAD+, ATP, ADP and AMP in C57BL/6N mice killed by head-focused microwave irradiation, and whether such effects were modified by treatments with neuroprotective doses of benzamide. At 1 h after MPTP injections (4x20 mg/kg i.p.), NAD+ was reduced by 11-13% in the striatum and ventral midbrain, but not in the frontal cortex. The ATP/ADP ratio was reduced by 10% and 32% in the striatum and cortex, respectively, but was unchanged in the midbrain. All of these regional changes were prevented by co-treatment with benzamide (2x160 mg/kg i.p.), which by itself did not alter regional levels of NAD+, ATP, ADP or AMP in control mice. In a time-course study, a single dose of MPTP (30 mg/kg i.p.) resulted in maximal and transient increases in striatal levels of MPP+ and 3-methoxytyramine (+540%) at 0.5-2 h, followed by maximal and coincidental decreases in NAD+ (-10%), ATP (-11%) and dopamine content (-39%) at 3 h. Benzamide (1x640 mg/kg i. p., 30 min before MPTP) partially reduced MPP+ levels by 30% with little or no effect on MPTP or MPDP+ levels, did not affect or even slightly potentiated the increase in 3-methoxytyramine, and completely prevented the losses in striatal NAD+, ATP and dopamine content, without by itself causing any changes in these latter parameters in control mice. These results (1) confirm that MPTP reduces striatal ATP levels [Chan et al., J. Neurochem. 57 (1991) 348-351.]; (2) show that MPTP causes a regionally-dependent (striatal and midbrain) loss of NAD+; (3) indicate that the PARP inhibitor benzamide can prevent these losses without interfering with MPTP-induced striatal dopamine release; and (4) provide further evidence to suggest an involvement of PARP in MPTP-induced neurotoxicity in vivo.

Effect of beta-cell toxins on genetically engineered insulin-secreting cells

The betacyte is a genetically engineered insulin-secreting liver cell line that is glucose responsive. Whether this cell is affected by specific beta-cell toxins is unknown. To explore this possibility we exposed these cells and those from the NIT-1 beta-cell line (positive controls) to the toxins streptozotocin (STZ, 2.5-20 mM), alloxan (ALL, 2.5-20 mM), and pentamidine (PENT, 10(-6)-1 mM). STZ and ALL were added for 1 h and pentamidine for 24 h. Insulin secretion from betacytes during a period of 5 h after removal of the toxin was inhibited only by pentamidine; all agents were inhibitory to NIT-1 cells. Glucose metabolism, as determined by a colorimetric MTT reduction assay, was adversely affected in betacytes by ALL (20 mM) and PENT (1 mM), and in NIT-1 cells by STZ (20 mM) as well as by ALL (2.5 mM) and PENT (1 mM). The magnitude of inhibition was less for the betacytes-58 v. 99%. Confluence of cells in culture wells and cell viability as assessed by the fluorochromes propidium iodide and acridine orange was reduced to a lesser extent for the betacytes than for the NIT-1 cells. The metabolic and microscopic effects of the toxins were unchanged in the betacyte from those in the liver cell line, HEP G2, from which the betacyte was engineered. These results of general resistance of the betacyte to beta-cell toxins with differing modes of action offer hope that this cell, or cells created in a similar manner from primary hepatocytes, may be at least partly resistant to the adverse effect of beta-cell toxins involved in autoimmune destruction of the pancreas. This increases the potential of the use of these cells for reversal of diabetes.

Potential role of environmental genotoxic agents in diabetes mellitus and neurodegenerative diseases

Epidemiological data suggest that environmental genotoxins are risk factors for some forms of diabetes mellitus and neurodegenerative diseases. The present commentary focuses on mechanisms involved in genotoxin-induced pancreatic beta-cell and neuronal damage. These two cell types seem to share a similar vulnerability to different forms of DNA damage, and the long-term consequences of repeated genotoxic insults to post-mitotic neurons or slowly proliferating beta-cells remain to be clarified. One intriguing possibility is that genotoxins could act as "slow" toxins in these cells, triggering a cascade of cellular events, which culminates in progressive cell dysfunction and loss. Indeed, exposure to mutagenic nitroso agents such as streptozotocin and cycasin induces long-lasting damage to both beta -cells and neurons. These data on cycasin, a toxin obtained from the cycad plant (Cycas spp.), are of special interest, since this agent may be implicated in both amyotrophic lateral sclerosis/Parkinson dementia complex and diabetes mellitus in the western Pacific area. Future studies are required to sort out the interactions between different genotoxic agents, viral infections, and cellular repair mechanisms on cellular survival and function. Moreover, further epidemiological studies are needed to clarify the role of N-nitrosoureas in diabetes mellitus and neurodegenerative diseases in populations with different genetic backgrounds. Answers to these questions may provide useful information on the pathogenesis of these devastating diseases, and open the possibility for their primary prevention.

N-monomethyl-arginine and nicotinamide prevent streptozotocin-induced double strand DNA break formation in pancreatic rat islets

The impact of short term in vitro exposure to the diabetogenic drug streptozotocin on pancreatic islet glucose metabolism, insulin secretion, DNA fragmentation and cell viability, was studied. Streptozotocin impaired cell viability as well as insulin secretion and the oxidation of glucose. These effects were partially counteracted by inhibition of the inducible form of nitric oxide synthase with N-monomethyl-arginine and by scavenging oxygen free radicals with nicotinamide. Isolated islets underwent double strand DNA fragmentation after 24 h in culture. The degree of DNA breakdown was strongly enhanced by exposure of the islets to 0.55 mM streptozotocin for 30 min before culture. Prevention of streptozotocin-induced cleavage of islet DNA was obtained with N-monomethyl-arginine and nicotinamide. These data suggest that the generation of reactive oxygen and nitrogen species is involved in the deleterious action of streptozotocin on pancreatic islet tissue. A role for oxygen radicals generated during streptozotocin-induced islet cell damage as possible mediators of the expression of the inducible form of nitric oxide synthase and the scavenging action of nicotinamide on these radicals, is then proposed.

The development of mitochondrial medicine

I consider mitochondrial medicine a tentative designation for an area within clinical medicine still to be delineated. Its development extends over a period of 35 years, from its discovery in 1959 [1]. Progress had been gradual until recent years when it has become explosive in nature with extensions in many different directions. My presentation is an effort to illustrate this evolution with emphasis on especially important observations which by leaps advanced the area. We are fortunate to have here several of the distinguished investigators, who have contributed so much to those advances. They will share with us their deep knowledge in different aspects of mitochondrial medicine, what is known, what remains to be elucidated, and what the problems are to be encountered in that elucidation.

Fusidic acid suppresses nitric oxide toxicity in pancreatic islet cells

Earlier preclinical and clinical trials indicate that fusidic acid, a triterpenoid compound originally described as an antimicrobial drug may protect islet beta cells from destruction in type I (insulin-dependent) diabetes mellitus. Since nitric oxide appears to be an important mediator of inflammatory islet cell death we analyzed whether fusidic acid interferes with nitric oxide production or action. We report here that fusidic acid dose-dependently inhibits lysis of isolated islet cells by activated macrophages, a process mediated by nitric oxide. In the presence of 100 microM fusidic acid macrophage-mediated islet cell lysis was reduced from 52.5 to 1.7% (P < 0.001). Fusidic acid only slightly affected macrophage function and did not inhibit the release of nitric oxide. We therefore tested whether fusidic acid suppresses nitric oxide toxicity in target cells. Isolated islet cells were exposed to the nitric oxide donor nitroprusside which led to DNA strand breaks and plasma membrane lysis. DNA strand breaks were reduced from 54.6 to 34.9% (P < 0.001) in the presence of 100 microM fusidic acid and cell lysis was reduced from 60.1 to 27.5% with 100 microM (P < 0.001). In the presence of 500 microM fusidic acid DNA strand breaks and cell lysis were reduced further to 27.1 and 10.7%, respectively (P < 0.001). No protection by fusidic acid was observed when cells were exposed to oxygen radicals or the alkylating beta cell toxin streptozotocin. The suppression of nitric oxide toxicity by fusidic acid was not due to its known inhibitory action on protein biosynthesis and thus represents a hitherto unknown activity of this drug.

The development of mitochondrial medicine

Primary defects in mitochondrial function are implicated in over 100 diseases, and the list continues to grow. Yet the first mitochondrial defect--a myopathy--was demonstrated only 35 years ago. The field's dramatic expansion reflects growth of knowledge in three areas: (i) characterization of mitochondrial structure and function, (ii) elucidation of the steps involved in mitochondrial biosynthesis, and (iii) discovery of specific mitochondrial DNA. Many mitochondrial diseases are accompanied by mutations in this DNA. Inheritance is by maternal transmission. The metabolic defects encompass the electron transport complexes, intermediates of the tricarboxylic acid cycle, and substrate transport. The clinical manifestations are protean, most often involving skeletal muscle and the central nervous system. In addition to being a primary cause of disease, mitochondrial DNA mutations and impaired oxidation have now been found to occur as secondary phenomena in aging as well as in age-related degenerative diseases such as Parkinson, Alzheimer, and Huntington diseases, amyotrophic lateral sclerosis and cardiomyopathies, atherosclerosis, and diabetes mellitus. Manifestations of both the primary and secondary mitochondrial diseases are thought to result from the production of oxygen free radicals. With increased understanding of the mechanisms underlying the mitochondrial dysfunctions has come the beginnings of therapeutic strategies, based mostly on the administration of antioxidants, replacement of cofactors, and provision of nutrients. At the present accelerating pace of development of what may be called mitochondrial medicine, much more is likely to be achieved within the next few years.

Nitrate and nitrite intake and the risk for type 1 diabetes in Finnish children. Childhood Diabetes in Finland Study Group

The intakes of nitrate and nitrite of children and their parents from food and drinking water were estimated in a Finnish nation-wide case-control study on the epidemiology of Type 1 diabetes. The study population consisted of 684 case and 595 control children; 548 case-control pairs of fathers; and 620 case-control pairs of mothers. The consumption frequencies of foods which are important sources of nitrate and nitrite were assessed by structured questionnaire. Nitrate and nitrite concentration data were collected from Finnish water works. Diabetic children's and their mothers' daily dietary intake of nitrite was greater compared with that of control children and mothers (for case and control children 0.9 mg vs 0.8 mg, for case and control mothers 0.9 mg vs 0.8 mg, p < 0.001). Case mothers compared with control mothers received less (p < 0.05) nitrate from their diet. No differences were observed in the intake of nitrate or nitrite from drinking water. Dietary nitrite intake of children (odds ratios and 95% confidence intervals for the second, third, and fourth quartile 1.16, 0.82-1.65; 1.49, 1.06-2.10; 2.32, 1.67-3.24, respectively) and mothers (odds ratios and 95% confidence intervals for the second, third, and fourth quartile 1.15, 0.76-1.74; 1.29, 0.87-1.91; 1.98, 1.35-2.90, respectively) was positively associated with the risk for Type 1 diabetes independently from length of mother's education, child's or mother's age, place of residence or mother's smoking status.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA fragmentation is an early event in cytokine-induced islet beta-cell destruction

The cytokines, interleukin 1, tumour necrosis factor, and interferon gamma are cytotoxic to islet beta cells, however, their mechanisms of beta-cell killing are not fully characterized. Since DNA damage is a mechanism of cytokine-induced cell death in some cell types, we sought evidence for cytotoxic effects of cytokines at a nuclear level in islet beta cells by measuring DNA fragmentation in rat islets and islet beta-cell lines. The individual cytokines, interleukin 1 (10 U/ml), tumour recrosis factor (10(3) U/ml) and interferon gamma (10(3) U/ml) inhibited insulin release from rat islets, but did not cause DNA fragmentation or destroy islet cells; by contrast, combination of the three cytokines induced DNA fragmentation and islet-cell death. Cytokine-induced DNA fragmentation preceded cell lysis in islet beta-cell lines (RINm5F, rat insulinoma cells; and NIT-1, NOD/Lt mouse transgenic beta cells), whereas in non-islet cell lines (GH-3, rat pituitary; and PC-12, rat adrenal) the cytokines induced cell lysis and no or late DNA fragmentation. Nicotinamide prevented both DNA fragmentation and destruction of RINm5F islet cells by the cytokines. These findings identify DNA as an early target of cytokine action in islet beta cells, and implicate DNA fragmentation as a mechanism of cytokine-induced beta-cell destruction.

The use of nicotinamide in the prevention of type 1 diabetes

Nicotinamide can protect the NOD mouse from diabetes if given early enough and in sufficient dose. The effect partly wanes with time. There is reduced islet inflammation. Similar protective effects can be demonstrated in quasi-experimental interventions in humans--both diabetes related and unrelated deemed at risk of developing diabetes by reason of having islet cell antibodies. Nicotinamide protects isolated islets in vitro from the toxicity of a number of agents, but only in doses that produce significant PARP inhibition, and increased intracellular levels of NAD. It is unlikely that the protective effect demonstrated in humans is due to significant PARP inhibition, as the levels of nicotinamide achieved with the doses used are too low. Other effects of the vitamin are more likely, e.g., increase in NAD pool size by de novo synthesis, or inhibition of free radical generation. The drug appears to be safe in the doses employed in humans.

Nicotinamide is a potent inducer of endocrine differentiation in cultured human fetal pancreatic cells

The effects of nicotinamide (NIC) on human fetal and adult endocrine pancreatic cells were studied in tissue culture. Treatment of the fetal cells with 10 mM NIC resulted in a twofold increase in DNA content and a threefold increase in insulin content. This was associated with the development of beta cell outgrowths from undifferentiated epithelial cell clusters and an increase in the expression of the insulin, glucagon, and somatostatin genes. DNA synthesis was stimulated only in the undifferentiated cells. Half-maximal doses for the insulinotropic and mitogenic effects of NIC were 5-10 and 1-2 mM, respectively. Islet-like cell clusters cultured with NIC responded to glucose stimulation with a biphasic increase in insulin release (fourfold peak), whereas control cells were unresponsive to glucose. Both control and NIC-treated cells developed into functional islet tissue after transplantation into athymic nude mice. As compared with adult islets, the insulinotropic action of NIC could only be demonstrated in the fetal cells. Our results indicate that NIC induces differentiation and maturation of human fetal pancreatic islet cells. This model should be useful for the study of molecular mechanisms involved in beta cell development.

Intervention therapies for insulin-dependent diabetes

Treatment of insulin-dependent diabetes remains problematic since there continues to be high rates of morbidity and mortality among affected patients. Good outcomes are most likely to be more common among patients who maintain endogenous insulin reserves for the longest time following diagnosis. The disease process can now be identified in its early, pre-symptomatic stages and thus, the time has come for the investigation of preventive therapies through multicenter clinical trials. A wide variety of strategies are available and their choice should be dependent on the pathogenic stage of disease at which treatment is initiated. This stage-specific approach to prevention is discussed with a particular focus on those therapies that will soon be tested in clinical trials.

Anti-free-radical and neutrophil-modulating properties of the nitrovasodilator, nicorandil

The nitrovasodilator, nicorandil, is a clinically effective antianginal agent. We tested whether nicorandil may also possess anti-free-radical characteristics, since the nicotinamide moiety of its molecular structure is a known hydroxyl radical scavenger. In vitro production of hydroxyl radicals by hypoxanthine plus xanthine oxidase in the presence of iron produced a marked degradation of deoxyribose. Nicorandil and the structural analogs, nicotinic acid and nicotinamide, produced significant inhibition of deoxyribose breakdown at concentrations equipotent to the classical hydroxyl radical scavenger, mannitol. Nicorandil also produced a concentration-dependent inhibition of superoxide anion production by canine neutrophils that were activated with either phorbol myristate acetate (PMA) or opsonized zymosan. This inhibition could not be mimicked by the analog, nicotinamide. While equimolar concentrations of nitroglycerin produced less inhibition of superoxide anion generation in opsonized zymosan-activated neutrophils than that observed with nicorandil, nitroglycerin did not alter free-radical production in PMA-stimulated neutrophils. Glyburide, the ATP-sensitive potassium-channel blocker, did not reverse the action of nicorandil on neutrophils. Thus, nicorandil is a uniquely different nitrovasodilator with anti-free-radical and neutrophil-modulating properties.

Exposure of pancreatic islets to different alkylating agents decreases mitochondrial DNA content but only streptozotocin induces long-lasting functional impairment of B-cells

Pancreatic B-cells exposed in vivo or in vitro to streptozotocin (SZ), the N-nitrosourea derivative of glucosamide, present a long-lasting impairment in the production and release of insulin while other cell functions are better preserved. This functional impairment is associated with a defective mitochondrial function. To further study the mechanisms behind SZ actions, mouse pancreatic islets were exposed in vitro to SZ (1.5 mM) or to different concentrations of methyl methanesulfonate (MMS; 2, 4 and 6 mM). The effect of the aglucone moiety of SZ, nitroso-N-methylurea (NMU; 2, 4 and 6 mM) was also tested. Islets were either studied immediately after exposure to the drugs (day 0) or after six days in culture following toxin treatment (day 6). On day 0 the islets showed a decrease in the NAD + NADH content, decreased glucose oxidation rates and an impaired insulin release in response to glucose. Six days after exposure to SZ there was still impaired glucose oxidation and insulin release, and decreased islet insulin mRNA and insulin content, but the NAD + NADH content was again similar to the control group. On the other hand, islets which survived for 6 days in culture following exposure to either MMS or NMU were able to regain normal B-cell function. The mouse islets exposed to SZ, NMU and MMS showed on day 6 a 30-40% decrease in the content of the mitochondrial DNA encoded cytochrome b mRNA and a 60-70% decrease in total mitochondrial DNA, as evaluated by dot and Southern blot analysis. Only SZ decreased the insulin mRNA content whereas both MMS and NMU decreased the glucagon mRNA content. As a whole, the data obtained indicate that SZ, NMU and MMS induce damage to the mitochondrial genome, and this may contribute to the B-cell dysfunction observed after SZ treatment. It is conceivable that the glucose moiety of SZ may direct the methylation to other intracellular sites besides the mitochondrial DNA, thus explaining the different functional responses of islets following exposure to SZ and NMU.

Prevention or delay of type 1 (insulin-dependent) diabetes mellitus in children using nicotinamide

A controlled trial of oral nicotinamide to prevent the onset of diabetes mellitus in high risk children was conducted in two centres. The selection criteria were age less than 16 years, islet cell antibody greater than or equal to 80 IUs, and first phase insulin release less than 5th percentile. All of eight untreated control subjects have developed diabetes, whereas only 1 of 14 treated children has diabetes to date. This data suggests that nicotinamide has an effect in preventing Type 1 (insulin-dependent) diabetes and that randomized controlled studies are now indicated.

Macrophage cytotoxicity towards isolated rat islet cells: neither lysis nor its protection by nicotinamide are beta-cell specific

In animal models of Type 1 (insulin-dependent) diabetes mellitus macrophages were shown to be the first immunocytes that infiltrate the pancreatic Langerhans islets in the autoimmune process. We now show direct macrophage cytotoxicity against isolated rat islet cells in an electron microscopical study, which permits investigation of the specificity of this process. Freshly isolated islet cells were co-incubated with syngeneic peritoneal macrophages at a target: effector-cell ratio of 1:2. After various time periods, the cells were directly fixed and embedded; the ratio of live and dead cells was evaluated by electron microscopy. Our results demonstrate that activated but not resident macrophages lyse islet cells in a time-dependent manner. After 15 h of co-incubation lysis of islet cells is complete. No islet cell-macrophage contacts and no differences between the lysis of Beta cells or non-Beta cells were observed during the observation period. Islet cells encapsulated in alginate were also lysed by macrophages as a direct proof for soluble mediator(s) of cytotoxicity. Nicotinamide protected islet cells from lysis in a dose-dependent manner. As a result of this electron microscopic study we conclude that even at very low target: effector ratios, activated macrophages lyse syngeneic islet cells regardless of islet cell type via secretion of humoral mediator(s).

Can insulin-dependent diabetes mellitus be cured or prevented? A status report on immunomodulatory strategies and pancreas transplantation

The past decade has brought advances in our undestanding of the etiology of beta cell destruction leading to insulin-dependent diabetes mellitus. Most patients have an autoimmune process that begins months or years prior to overt disease. There are now reliable techniques to monitor the inflammatory process, with increasingly accurate methods for predicting disease in susceptible individuals. This information should lead to new techniques that will cure or possibly prevent diabetes.

A trial of nicotinamide in newly diagnosed patients with type 1 (insulin-dependent) diabetes mellitus

Various agents have been tried in subjects with newly diagnosed Type 1 (insulin-dependent) diabetes mellitus in an attempt to preserve Beta-cell function. In this double-blind study, nicotinamide or placebo were given for one year to 35 children and adolescents with newly-diagnosed Type 1 diabetes. All subjects were within six weeks of diagnosis and were between the ages of 6 and 18 years. Nicotinamide, a poly-(ADP-ribose) synthetase inhibitor, was given in a dose of 100 mg/year of age up to a maximum of 1.5 g/day. There were no initial differences between the 17 control and the 18 test subjects in relation to mean age, sex distribution, or severity at onset. Mean insulin dosages and HbA1 values were similar for the two groups during the year of study. Fasting and glucagon-stimulated C-peptide levels were similar for the control and nicotinamide treated groups at the beginning and after 4 and 12 months. There were no differences in remission rates between the two groups. Nicotinamide, at this dosage, does not preserve residual insulin secretion in subjects with newly diagnosed Type 1 diabetes.

Oxygen free radical scavengers protect rat islet cells from damage by cytokines

A possible role for oxygen free radicals in mediating the cytotoxic effects of cytokines in islets was sought by the use of agents that scavenge free radicals. Rat islet cell monolayer cultures were incubated for 6 days with t-butylhydroperoxide, alloxan, streptozotocin, or the cytokines, interleukin 1, tumour necrosis factor, and interferon gamma, without and together with the oxygen free radical scavenger combination of dimethylthiourea and citiolone, and islet cell lysis was measured in a 51chromium cytotoxicity assay. The free radical scavengers significantly inhibited the islet cell cytotoxic effects of t-butylhydroperoxide and alloxan, but not streptozotocin. Similarly, the cytotoxic effects of the cytokine combinations of interleukin 1 plus tumour necrosis factor, interferon gamma plus tumour necrosis factor, and interferon gamma plus interleukin 1 were significantly inhibited by the free radical scavenger combination of dimethylthiourea and citiolone. These results suggest that the cytokine products of macrophages and lymphocytes infiltrating islets in Type 1 (insulin-dependent) diabetes may contribute to B-cell damage by inducing the production of oxygen free radicals in the islet cells.