The influence of cyclosporin A on the vascular permeability of the pancreatic islets and on diabetes induced by multiple low doses of streptozotocin in the mouse

An imazamox-based herbicide causes apoptotic changes in rat liver and pancreas

We studied the acute toxicity of an imazamox-based herbicide at 12, 24 and 36 mg/kg body (bw) weight imazamox equivalent dose on the liver and pancreatic tissue in Sprague Dawley rats. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, glucose, calcium as well as creatinine, were determined in blood samples, which were collected after 24, 48 and 72 h exposure. Caspase 3 and anti-insulin expression and immunopositivity were evaluated using in situ hybridization and immunohistochemistry, respectively. The imazamox-based herbicide evaluated in this study induced toxic effects even from the lowest dose tested (12 mg/kg bw). The two highest doses caused a statistically significant cytotoxicity on the Langerhans islet cells. Necrotic and degenerative changes were detected in hepatocytes at the two highest doses. Imazamox is considered to be poorly toxic to the liver. Nevertheless, the imazamox-based herbicide formulation tested here reduced the size of the β-islet cells, induced an elevation in serum glucose and calcium. Our data shows that commercial formulations of imazamox containing various co-formulants can have hepatic and pancreatic toxic effects.

An immunohistochemical study of the pancreatic endocrine cells of the ddN mouse

The regional distribution and frequency of the pancreatic endocrine cells in the ddN mouse were studied using specific antisera against insulin, glucagon, somatostatin and human pancreatic polypeptide (hPP). In the pancreatic islets, most of insulin-immunoreactive (IR) cells were located in the central region, and glucagon-, somatostatin and hPP-IR cells were located in the peripheral region regardless of the lobe. In the splenic part, glucagon-IR cells were also located in the central regions, and more numerous somatostatin-IR cells were detected in the central regions as compared with the duo-denal part. hPP-IR cells were restricted to the peripheral regions in both lobes but more numerous cells were detected in the duodenal portion. In the exocrine parenchyma of the splenic lobe, only insulin- and glucagon-IR cells were detected but all four kinds of IR cells were observed in the duodenal portion. In addition, insulin and hPP-IR cells were also demonstrated in the pancreatic duct regions. In conclusion, some strain-dependent characteristic distributional patterns of pancreatic endocrine cells were found in the ddN mouse with somewhat different distributional patterns between the two pancreatic lobes.

Aminoguanidine, an inhibitor of nitric oxide formation, fails to protect against insulitis and hyperglycemia induced by multiple low dose streptozotocin injections in mice

It has been suggested that pancreatic beta-cell destruction occurring during the process leading to insulin-dependent diabetes mellitus (IDDM) involves formation of nitric oxide (NO). We have presently studied the effect of aminoguanidine (AG), which has recently been reported to inhibit generation of NO induced by the cytokine interleukin-1 beta. AG currently counteracted IL-1 beta induced impairment of the glucose oxidation rate in rat pancreatic islets. Then we studied the effect of AG on the development of hyperglycemia and pancreatic insulitis in mice treated with multiple low dose injections of streptozotocin (40 mg/kg body-weight for five consecutive days). It was found that one daily intraperitoneal injection of AG (50 mg/kg body-weight) for 14 days failed to prevent the development of diabetes as well as insulitis following the streptozotocin injections. Furthermore, the mice treated with streptozotocin plus AG showed an increased mortality compared to mice treated with streptozotocin plus saline. Although the present data do not exclude a role for NO in IDDM, it raises concerns about the use of testing AG as therapeutic agent in IDDM.

Role of infiltrating T cells for impaired glucose metabolism in pancreatic islets isolated from non-obese diabetic mice

Pancreatic islets isolated from non-obese diabetic (NOD) mice, all of which have insulitis, exhibit an impaired glucose metabolism. In order to investigate the role of infiltrating lymphocytes for this altered metabolism, we injected 12- to 13-week-old female NOD mice with monoclonal antibodies directed against either the alpha beta-T cell receptor, CD4+ or CD8+ T cells. Control NOD mice were injected with normal rat IgG or with the vehicle (phosphate buffered saline) alone. Injection of the three different monoclonal antibodies markedly reduced the mononuclear cell infiltration. An intravenous glucose tolerance test showed no differences between the groups. Islet insulin release in response to glucose was similar in all groups. In contrast, islets isolated from the control NOD mice with insulitis showed a high basal (1.7 mmol/l glucose) glucose oxidation rate and a small increase in the glucose oxidation rate in response to a high glucose concentration (16.7 mmol/l glucose). The monoclonal antibodies counteracted the elevated basal glucose oxidation rate of the islets. Parallel studies of stimulated mononuclear cells suggested that the contribution of glucose oxidized by islet-infiltrating lymphocytes could only partially explain the observed alterations in NOD mouse islet metabolism. Culture of islets obtained from NOD mice in the presence of the cytokine interleukin-1 beta induced a similar pattern of glucose metabolism as seen earlier in IgG or phosphate-buffered saline treated control NOD mice. In conclusion, alterations in the glucose oxidation rates seem to be an early sign of disturbance in islets isolated from NOD mice. These early alterations in glucose metabolism can be reversed in vivo by monoclonal antibodies directed against effector lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection against hyperglycemia in female nonobese diabetic mice treated with 15-deoxyspergualin

The effects of 15-deoxyspergualin (15-DS), a newly described immunosuppressive agent, have been studied on the development of diabetes in female NOD mice. 15-DS treatment was started two weeks after weaning i.e. at five weeks of age. The mice received either one daily intraperitoneal injection of 15-DS (2.5 mg/kg body weight) or saline for two weeks. The mice were then injected every third day up to eight months of age for evaluation of the diabetes incidence. In another set of experiments the mice were treated up to three months of age, whereafter islet insulin release, islet insulin content and DNA content was measured together with an evaluation of spleen cell proliferation rates. Different spleen cell subsets were studied directly after the two weeks of daily injections. In the saline group 8 out of 9 mice developed diabetes, whereas only 4 out of 11 of the 15-DS treated mice became diabetic (p < 0.05). There was no difference between the groups in islet insulin release in response to glucose, however, the islet insulin release increased after one week in culture. The 15-DS treatment did not affect the insulin or DNA content of the isolated islets or the insulin concentration in the pancreas. No detectable changes in the relative number of CD4+ and CD8+ T-cell subsets in the spleen were seen and there were no obvious differences in splenocyte proliferation rates. The histological examinations of the pancreatic glands showed gradual increasing signs of islet inflammation with age and 15-DS could apparently not prevent this.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine-induced autoimmunity and immune hyperreactivity

Cyclosporine (CS) is a potent immunosuppressive agent which under some circumstances paradoxically augments DTH responses, aggravates some autoimmune diseases, and induces specific forms of autoimmunity. The enhancement of DTH and other immune responses is closely related to the timing of CS administration relative to immunization. CS inhibits IL-2 production (and several other lymphokines) at a pretranscriptional level, but does not usually prevent the antigen-specific priming of T cells, such that T cells may be poised to respond as soon as CS is withdrawn. Thus, accelerated GVHD and allograft rejection may occur after withdrawal of CS. CS has been shown to aggravate and/or induce relapse in several autoimmune diseases including collagen-induced arthritis, EAE, autoimmune thyroiditis, uveitis in SDA chickens, and an autoimmune form of myocarditis in mice. CS may enhance immune responses by inactivating suppressor cells, by altering Th1/Th2 antagonism (e.g., CS promotes a protective Th1-type response in BALB/c mice infected with Leishmania major), or by promoting T cell activation through a CS-resistant IL-2-independent T cell activation/differentiation pathway. At least three forms of CS-induced autoimmunity have been described: Syngeneic or autologous GVHD which occurs in CS-treated syngeneic or autologous bone marrow transplant recipients after CS is withdrawn in rats, mice, and humans; a systemic autoimmune disease with polyarthritis and glomerulonephritis which occurs in irradiated CBA/N mice treated with CS; and organ-specific autoimmune diseases which occur in mice treated with CS during the neonatal period. The precise mechanisms by which CS induces these autoimmune diseases are not clear, however, CS affects immune tolerance at three levels. CS induces thymic medullary involution with loss of medullary Ia+ cells, and appears to at least partially block the transition from double positive (CD4+CD8+) to single positive (mature type) thymocytes. In syngeneic bone marrow chimeras, CS appears to inhibit the intrathymic deletion of clones with relatively low affinity, but not those with high affinity, to self antigens. CS appears to inhibit the action of suppressor T cells which normally maintain an innate form of resistance to autoimmunity. Finally, CS has been shown to prevent the development of T cell clonal anergy. There is redundancy in immune tolerance mechanisms, i.e., clonal deletion, clonal anergy, and suppressor cells can each maintain tolerance to similar antigens, such that it is likely that CS must cripple more than one tolerance mechanism for autoimmunity to occur.

Reversal of beta-cell suppression in vitro in pancreatic islets isolated from nonobese diabetic mice during the phase preceding insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is characterized by a progressive autoimmune destruction of the pancreatic beta-cells. One of the best-suited animal models for IDDM is the nonobese diabetic (NOD) mouse. In this investigation pancreatic islets were isolated from female NOD mice aged 5-7, 8-11, and 12-13 wk and examined immediately (day 0) or after 7 d of culture (day 7). The mice showed a progressive disturbance in glucose tolerance with age, and a correspondingly increased frequency of pancreatic insulitis. Islets isolated from the oldest mice often contained inflammatory cells on day 0, which resulted in an elevated islet DNA content. During culture these islets became depleted of infiltrating cells and the DNA content of the islets decreased on day 7. Islets of the eldest mice failed to respond with insulin secretion to high glucose, whereas a response was observed in the other groups. After culture all groups of islets showed a markedly improved insulin secretion. Islets from the 12-13-wk-old mice displayed a lower glucose oxidation rate at 16.7 mM glucose on day 0 compared with day 7. Islet (pro)insulin and total protein biosynthesis was essentially unaffected. In conclusion, islets obtained from 12-13-wk-old NOD mice exhibit an impaired glucose metabolism, which may explain the suppressed insulin secretion observed immediately after isolation. This inhibition of beta-cell function can be reversed in vitro. Thus, there may be a stage during development of IDDM when beta-cell destruction can be counteracted and beta-cell function restored, provided the immune aggression is arrested.

Effects of (-)15-deoxyspergualin on pancreatic islet B-cell function in vitro and on the development of diabetes after multiple low dose streptozotocin administration

The effects of (-)15-deoxyspergualin (15-DS), a newly described immunosuppressive drug, have been investigated on diabetes induced in mice treated with multiple low-dose streptozotocin (multiple SZ). Male C3D2F1 mice were treated with either intraperitoneal injections of saline or 15-DS (2.5 mg/kg body weight) for a total of 10 days, starting during the first day of SZ administration (5 days; 40 mg/kg body weight). On day 14, 15-DS-treated animals were still normoglycaemic, whilst on day 21 there was only a partial reduction in the hyperglycaemia compared to that found in the saline treated animals receiving SZ. 15-DS did not prevent hyperglycaemia in the long run (day 35-63). Furthermore, morphological examinations of pancreatic glands suggested that the insulitis in the pancreatic islets was delayed in the 15-DS-treated animals. In control experiments mice were treated with 15-DS+ the vehicle for SZ. This regimen did not hamper the glucose homeostasis of the animals. In vitro effects of 15-DS were also examined. Isolated islets from C3D2F1 mice were cultured at different concentrations of 15-DS (0.1-10.0 mg/l). After one week in culture, islet insulin release, islet insulin and DNA content were measured. The islets looked fluffy after culture at the higher 15-DS concentrations (4.0-10.0 mg/l) and at 10 mM almost all of the islets disappeared. A dose-dependent reduction of glucose-stimulated insulin release could also be seen. In other experiments islets were exposed to SZ and subsequently cultured in the presence of 0.5 mM 15-DS, however, 15-DS could not prevent the reduction in insulin release due to SZ exposure. Since 15-DS influences macrophage functions, the presently observed protective effects against the multiple SZ-treatment could reflect a reduced local interleukin-1 production in the islet vicinity. Alternatively, a lowered interleukin-1 secretion could prevent the activation of other immune cells involved in the destruction of B-cells.