Journal Article•
The mechanism of alloxan and streptozotocin action in B cells of the rat pancreas.
TL;DR: The cytotoxic action of both these diabetogenic agents is mediated by reactive oxygen species, however, the source of their generation is different in the case of alloxan and streptozotocin.
Abstract: Alloxan and streptozotocin are widely used to induce experimental diabetes in animals. The mechanism of their action in B cells of the pancreas has been intensively investigated and now is quite well understood. The cytotoxic action of both these diabetogenic agents is mediated by reactive oxygen species, however, the source of their generation is different in the case of alloxan and streptozotocin. Alloxan and the product of its reduction, dialuric acid, establish a redox cycle with the formation of superoxide radicals. These radicals undergo dismutation to hydrogen peroxide. Thereafter highly reactive hydroxyl radicals are formed by the Fenton reaction. The action of reactive oxygen species with a simultaneous massive increase in cytosolic calcium concentration causes rapid destruction of B cells. Streptozotocin enters the B cell via a glucose transporter (GLUT2) and causes alkylation of DNA. DNA damage induces activation of poly ADP-ribosylation, a process that is more important for the diabetogenicity of streptozotocin than DNA damage itself. Poly ADP-ribosylation leads to depletion of cellular NAD+ and ATP. Enhanced ATP dephosphorylation after streptozotocin treatment supplies a substrate for xanthine oxidase resulting in the formation of superoxide radicals. Consequently, hydrogen peroxide and hydroxyl radicals are also generated. Furthermore, streptozotocin liberates toxic amounts of nitric oxide that inhibits aconitase activity and participates in DNA damage. As a result of the streptozotocin action, B cells undergo the destruction by necrosis.
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TL;DR: The targeting of mitochondrial DNA, thereby impairing the signalling function of beta cell mitochondrial metabolism, also explains how streptozotocin is able to inhibit glucose-induced insulin secretion, causing a state of insulin-dependent ‘alloxan diabetes’.
Abstract: Alloxan and streptozotocin are toxic glucose analogues that preferentially accumulate in pancreatic beta cells via the GLUT2 glucose transporter. In the presence of intracellular thiols, especially glutathione, alloxan generates reactive oxygen species (ROS) in a cyclic redox reaction with its reduction product, dialuric acid. Autoxidation of dialuric acid generates superoxide radicals, hydrogen peroxide and, in a final iron-catalysed reaction step, hydroxyl radicals. These hydroxyl radicals are ultimately responsible for the death of the beta cells, which have a particularly low antioxidative defence capacity, and the ensuing state of insulin-dependent 'alloxan diabetes'. As a thiol reagent, alloxan also selectively inhibits glucose-induced insulin secretion through its ability to inhibit the beta cell glucose sensor glucokinase. Following its uptake into the beta cells, streptozotocin is split into its glucose and methylnitrosourea moiety. Owing to its alkylating properties, the latter modifies biological macromolecules, fragments DNA and destroys the beta cells, causing a state of insulin-dependent diabetes. The targeting of mitochondrial DNA, thereby impairing the signalling function of beta cell mitochondrial metabolism, also explains how streptozotocin is able to inhibit glucose-induced insulin secretion.
1,846 citations
Cites background from "The mechanism of alloxan and strept..."
...After decades of research a unifying explanation for the selective toxicity of these two most prominent diabetogenic agents [2, 17–22] can be provided....
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TL;DR: Some of the models currently used in diabetes research are outlined, including transgenic and knock‐out mouse models, which range from animals with spontaneously developing autoimmune diabetes to chemical ablation of the pancreatic beta cells.
Abstract: Diabetes is a disease characterized by a relative or absolute lack of insulin, leading to hyperglycaemia. There are two main types of diabetes: type 1 diabetes and type 2 diabetes. Type 1 diabetes is due to an autoimmune destruction of the insulin-producing pancreatic beta cells, and type 2 diabetes is caused by insulin resistance coupled by a failure of the beta cell to compensate. Animal models for type 1 diabetes range from animals with spontaneously developing autoimmune diabetes to chemical ablation of the pancreatic beta cells. Type 2 diabetes is modelled in both obese and non-obese animal models with varying degrees of insulin resistance and beta cell failure. This review outlines some of the models currently used in diabetes research. In addition, the use of transgenic and knock-out mouse models is discussed. Ideally, more than one animal model should be used to represent the diversity seen in human diabetic patients.
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1,023 citations
Cites background from "The mechanism of alloxan and strept..."
...Alloxan is reduced to dialuric acid and then re-oxidized back to alloxan, creating a redox cycle for the generation of superoxide radicals that undergo dismutation to form hydrogen peroxide and thereafter highly reactive hydroxyl radicals that cause fragmentation of beta cell DNA (Szkudelski, 2001)....
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...Doses in mice range from 50 to 200 mg·kg-1 and in rats from 40 to200 mg·kg-1, depending on the strain and the route of administration with i.p and s.c. administration requiring up to three times as high a dose as the i.v. route (Szkudelski, 2001)....
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...It should be noted that alloxan has a narrow diabetogenic dose, and even light overdosing can cause general toxicity, especially to the kidney (Szkudelski, 2001)....
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...administration, it enters the pancreatic beta cell through the Glut-2 transporter and causes alkylation of the DNA (Szkudelski, 2001)....
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...After i.p. or i.v. administration, it enters the pancreatic beta cell through the Glut-2 transporter and causes alkylation of the DNA (Szkudelski, 2001)....
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TL;DR: The term “type 3 diabetes” accurately reflects the fact that AD represents a form of diabetes that selectively involves the brain and has molecular and biochemical features that overlap with both type 1 diabetes mellitus and T2DM.
Abstract: Alzheimer's disease (AD) has characteristic histopathological, molecular, and biochemical abnormalities, including cell loss; abundant neurofibrillary tangles; dystrophic neurites; amyloid precursor protein, amyloid-β (APP-Aβ) deposits; increased activation of prodeath genes and signaling pathways; impaired energy metabolism; mitochondrial dysfunction; chronic oxidative stress; and DNA damage. Gaining a better understanding of AD pathogenesis will require a framework that mechanistically interlinks all these phenomena. Currently, there is a rapid growth in the literature pointing toward insulin deficiency and insulin resistance as mediators of AD-type neurodegeneration, but this surge of new information is riddled with conflicting and unresolved concepts regarding the potential contributions of type 2 diabetes mellitus (T2DM), metabolic syndrome, and obesity to AD pathogenesis. Herein, we review the evidence that (1) T2DM causes brain insulin resistance, oxidative stress, and cognitive impairment, but its aggregate effects fall far short of mimicking AD; (2) extensive disturbances in brain insulin and insulin-like growth factor (IGF) signaling mechanisms represent early and progressive abnormalities and could account for the majority of molecular, biochemical, and histopathological lesions in AD; (3) experimental brain diabetes produced by intracerebral administration of streptozotocin shares many features with AD, including cognitive impairment and disturbances in acetylcholine homeostasis; and (4) experimental brain diabetes is treatable with insulin sensitizer agents, i.e., drugs currently used to treat T2DM. We conclude that the term “type 3 diabetes” accurately reflects the fact that AD represents a form of diabetes that selectively involves the brain and has molecular and biochemical features that overlap with both type 1 diabetes mellitus and T2DM.
903 citations
TL;DR: It is suggested that QE treatment has protective effect in diabetes by decreasing oxidative stress and preservation of pancreatic beta-cell integrity.
782 citations
TL;DR: The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenousCardioprotection by pre- and postconditioning and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardiop Rotection conferred by preconditioning and post conditioning.
Abstract: Therapeutic strategies to protect the ischemic myocardium have been studied extensively. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate lethal tissue injury, a process termed "reperfusion injury." Ischemia/reperfusion injury may lead to myocardial infarction, cardiac arrhythmias, and contractile dysfunction. Ischemic preconditioning of myocardium is a well described adaptive response in which brief exposure to ischemia/reperfusion before sustained ischemia markedly enhances the ability of the heart to withstand a subsequent ischemic insult. Additionally, the application of brief repetitive episodes of ischemia/reperfusion at the immediate onset of reperfusion, which has been termed "postconditioning," reduces the extent of reperfusion injury. Ischemic pre- and postconditioning share some but not all parts of the proposed signal transduction cascade, including the activation of survival protein kinase pathways. Most experimental studies on cardioprotection have been undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of other disease processes. However, ischemic heart disease in humans is a complex disorder caused by or associated with known cardiovascular risk factors including hypertension, hyperlipidemia, diabetes, insulin resistance, atherosclerosis, and heart failure; additionally, aging is an important modifying condition. In these diseases and aging, the pathological processes are associated with fundamental molecular alterations that can potentially affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Among many other possible mechanisms, for example, in hyperlipidemia and diabetes, the pathological increase in reactive oxygen and nitrogen species and the use of the ATP-sensitive potassium channel inhibitor insulin secretagogue antidiabetic drugs and, in aging, the reduced expression of connexin-43 and signal transducer and activator of transcription 3 may disrupt major cytoprotective signaling pathways thereby significantly interfering with the cardioprotective effect of pre- and postconditioning. The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenous cardioprotection by pre- and postconditioning (i.e., drug applied as trigger or to activate signaling pathways associated with endogenous cardioprotection) and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardioprotection conferred by preconditioning and postconditioning. We emphasize the critical need for more detailed and mechanistic preclinical studies that examine car-dioprotection specifically in relation to complicating disease states. These are now essential to maximize the likelihood of successful development of rational approaches to therapeutic protection for the majority of patients with ischemic heart disease who are aged and/or have modifying comorbid conditions.
737 citations
References
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TL;DR: Insulin-producing cells cannot adapt the low antioxidant enzyme activity levels to typical situations of cellular stress by an upregulation of gene expression, and inactiva-tion of hydrogen peroxide through catalase seems to be a step of critical importance for the removal of reactive oxygen species in insulin- producing cells.
Abstract: Antioxidant enzyme expression was determined in rat pancreatic islets and RINm5F insulin-producing cells on the level of mRNA, protein, and enzyme activity in comparison with 11 other rat tissues. Although superoxide dismutase expression was in the range of 30% of the liver values, the expression of the hydrogen peroxide-inactivating enzymes catalase and glutathione peroxidase was extremely low, in the range of 5% of the liver. Pancreatic islets but not RINm5F cells expressed an additional phospholipid hydroperoxide glutathione peroxidase that exerted protective effects against lipid peroxidation of the plasma membrane. Regression analysis for mRNA and protein expression and enzyme activities from 12 rat tissues revealed that the mRNA levels determine the enzyme activities of the tissues. The induction of cellular stress by high glucose, high oxygen, and heat shock treatment did not affect antioxidant enzyme expression in rat pancreatic islets or in RINm5F cells. Thus insulin-producing cells cannot adapt the low antioxidant enzyme activity levels to typical situations of cellular stress by an upregulation of gene expression. Through stable transfection, however, we were able to increase catalase and glutathione peroxidase gene expression in RINm5F cells, resulting in enzyme activities more than 100-fold higher than in nontransfected controls. Catalase-transfected RINm5F cells showed a 10-fold greater resistance toward hydrogen peroxide toxicity, whereas glutathione peroxidase overexpression was much less effective. Thus inactivation of hydrogen peroxide through catalase seems to be a step of critical importance for the removal of reactive oxygen species in insulin-producing cells. Overexpression of catalase may therefore be an effective means of preventing the toxic action of reactive oxygen species.
1,170 citations
"The mechanism of alloxan and strept..." refers background in this paper
...However, the liver and other tissues are more resistant to reactive oxygen species in comparison to pancreatic B cells and this resistance protects them against alloxan toxicity (Malaisse et al. 1982, Tiedge et al. 1997)....
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TL;DR: It is described that both Streptozotocin and alloxan cause DNA strand breaks which stimulate nuclear poly(ADP–ribose) synthetase, thereby depleting intracellular NAD and inhibiting proinsulin synthesis in isolated pancreatic islets of rats.
Abstract: Streptozotocin, which produces diabetes mellitus in experimental animals1–3, has been reported to reduce the level of NAD in pancreatic islets4,5 and to inhibit islet synthesis of proinsulin6. The decrease in NAD is due to increased NAD degradation mediated by islet nuclear poly(ADP–ribose) synthetase7,8. Evidence suggests that poly(ADP–ribose) synthetase is activated when DNA is fragmented9–17. Here we describe that both Streptozotocin and alloxan, which also produces experimental diabetes mellitus1,2, cause DNA strand breaks which stimulate nuclear poly(ADP–ribose) synthetase, thereby depleting intracellular NAD and inhibiting proinsulin synthesis in isolated pancreatic islets of rats.
573 citations
TL;DR: It is concluded that expression of GLUT2 is required for efficient killing of neuroendocrine cells by STZ, and this effect is related to specific recognition of the drug as a transported substrate by GLut2 but not GLUT1.
Abstract: The glucose analog streptozotocin (STZ) has long been used as a tool for creating experimental diabetes because of its relatively specific β-cell cytotoxic effect, but the mechanism by which systemic injection of STZ causes β-cell destruction is not well understood. In the current study, we have used insulinoma (RIN) and AtT-20ins cell lines engineered for overexpression of GLUT2 or GLUT1 to investigate the role of glucose transporter isoforms in mediating STZ cytotoxicity. The in vivo effects of STZ were evaluated by implantation of RIN cells expressing or lacking GLUT2 into athymic nude rats. The drug had a potent cytotoxic effect on RIN cells expressing GLUT2, but had no effect on cells lacking GLUT2 expression, as indicated by histological analysis and measurement of the blood glucose levels of treated animals. The preferential cytotoxic effect of STZ on GLUT2-expressing cell lines was confirmed by in vitro analysis of GLUT2-expressing and untransfected RIN cells, as well as GLUT2- and GLUTl-overexpressing AtT-20ins cells. Consistent with these data, only GLUT2-expressing RIN or AtT-20ins cells transported STZ efficiently. We conclude that expression of GLUT2 is required for efficient killing of neuroendocrine cells by STZ, and this effect is related to specific recognition of the drug as a transported substrate by GLUT2 but not GLUT1
478 citations
TL;DR: The results are consistent with the central importance of selective uptake and alkylating activity in the mechanism of streptozotocin diabetogenicity.
Abstract: Aims/hypothesis. The role of selective uptake and alkylation in the diabetogenic action of streptozotocin was investigated in bioengineered RINm5F insulin-producing cells, with different expression levels of the glucose transporter GLUT2, by comparing the toxicity of streptozotocin with that of four chemically related alkylating compounds, N-methyl-N-nitrosourea (MNU), N-ethyl-N nitrosourea (ENU), methyl methanesulphonate (MMS) and ethyl methanesulphonate (EMS). Methods. GLUT2 expressing RINm5F cells were generated through stable transfection of the rat glucose transporter GLUT2 cDNA under the control of the cytomegalovirus promoter in the pcDNA3 vector. Viability of the cells was determined using a microtitre plate-based 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. Results. Cells expressing the glucose transporter GLUT2 were much more susceptible to streptozotocin toxicity than control cells due to the uptake of streptozotocin by this specific glucose transporter. In contrast, the GLUT2 expression had no effect upon the toxicity of MNU, ENU, MMS or EMS. Although the latter substances are, like streptozotocin, cytotoxic through their ability to cause DNA alkylation, they are not diabetogenic because they are not taken up through the glucose transporter GLUT2. Conclusion/interpretation. Our results are consistent with the central importance of selective uptake and alkylating activity in the mechanism of streptozotocin diabetogenicity. Alkylation of DNA leads to necrosis of pancreatic beta cells and thus to a state of insulin-dependent diabetes mellitus, well-known as streptozotocin diabetes in experimental diabetes research. [Diabetologia (2000) 43: 1528–1533]
354 citations
"The mechanism of alloxan and strept..." refers background in this paper
...Recent experiments have proved that the main reason for the STZ-induced B cell death is alkylation of DNA (Delaney et al. 1995, Elsner et al. 2000)....
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TL;DR: DNA damage and a major activation of PARP in pancreatic islets of STZ-treated mice are demonstrated and PARP activation may participate in the pathophysiology of type I diabetes, for which PARP inhibitors might afford therapeutic benefit.
Abstract: Streptozotocin (STZ) selectively destroys insulin-producing beta islet cells of the pancreas providing a model of type I diabetes. Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme whose overactivation by DNA strand breaks depletes its substrate NAD+ and then ATP, leading to cellular death from energy depletion. We demonstrate DNA damage and a major activation of PARP in pancreatic islets of STZ-treated mice. These mice display a 500% increase in blood glucose and major pancreatic islet damage. In mice with homozygous targeted deletion of PARP (PARP −/−), blood glucose and pancreatic islet structure are normal, indicating virtually total protection from STZ diabetes. Partial protection occurs in PARP +/− animals. Thus, PARP activation may participate in the pathophysiology of type I diabetes, for which PARP inhibitors might afford therapeutic benefit.
292 citations