Progressive damage of cultured pancreatic islets after single early exposure to streptozocin

High-resolution magnetic resonance imaging quantitatively detects individual pancreatic islets

OBJECTIVE

We studied whether manganese-enhanced high-field magnetic resonance (MR) imaging (MEHFMRI) could quantitatively detect individual islets in situ and in vivo and evaluate changes in a model of experimental diabetes.

RESEARCH DESIGN AND METHODS

Whole pancreata from untreated (n = 3), MnCl(2) and glucose-injected mice (n = 6), and mice injected with either streptozotocin (STZ; n = 4) or citrate buffer (n = 4) were imaged ex vivo for unambiguous evaluation of islets. Exteriorized pancreata of MnCl(2) and glucose-injected mice (n = 6) were imaged in vivo to directly visualize the gland and minimize movements. In all cases, MR images were acquired in a 14.1 Tesla scanner and correlated with the corresponding (immuno)histological sections.

RESULTS

In ex vivo experiments, MEHFMRI distinguished different pancreatic tissues and evaluated the relative abundance of islets in the pancreata of normoglycemic mice. MEHFMRI also detected a significant decrease in the numerical and volume density of islets in STZ-injected mice. However, in the latter measurements the loss of β-cells was undervalued under the conditions tested. The experiments on the externalized pancreata confirmed that MEHFMRI could visualize native individual islets in living, anesthetized mice.

CONCLUSIONS

Data show that MEHFMRI quantitatively visualizes individual islets in the intact mouse pancreas, both ex vivo and in vivo.

Pygeum africanum: effect on oxidative stress in early diabetes-induced bladder

OBJECTIVE

To evaluate the effect of Pygeum africanum on oxidative stress and functional changes of the bladder after diabetes induction.

MATERIALS AND METHODS

Thirty-two adult Wistar male rats were treated daily for 8 weeks and grouped as follows: Control group (n = 6), Streptozotocin-induced diabetic group (n = 10), diabetes plus P. africanum group (n = 10), and control plus P. africanum group (n = 6). After diabetes induction for 4 weeks, the diabetes plus P. africanum and control plus P. africanum groups were fed with P. africanum (100 mg/kg, orally) in peanut oil for another 4 weeks. The catalase, superoxide dismutase activity, and malondialdehyde levels were measured as a marker of lipid peroxidation. The levels of inducible nitric oxide synthase were also evaluated. Urodynamic studies were performed to evaluate the functional changes of diabetic bladders after P. africanum treatment.

RESULTS

The catalase and superoxide dismutase activities significantly increased (P < 0.05) and maleic dialdehyde levels significantly decreased from diabetic plus P. africanum group compared with diabetic group (P < 0.05). Immunohistochemical studies showed a significantly decreased number of inducible nitric oxide synthase-positive cells in diabetic plus P. africanum group compared with diabetic group (P < 0.05). In diabetic plus P. africanum group, maximal bladder volume significantly decreased, while bladder pressure and maximal bladder pressure significantly increased compared with diabetic group (P < 0.05).

CONCLUSIONS

Early treatment with P. africanum could effectively suppress the oxidative stress status in diabetic bladder and may slow down the process of diabetic cystopathy.

Novel role of curcumin in the prevention of cytokine-induced islet death in vitro and diabetogenesis in vivo

BACKGROUND AND PURPOSE

Oxidative stress caused by cytokine exposure is a major cause of pancreatic islet death in vitro and of diabetogenesis. Antioxidant compounds may prevent cytokine-induced damage to islet cells. Hence, we studied the potential of curcumin, an antioxidant and anti-inflammatory compound, in vitro to protect islets against pro-inflammatory cytokines and in vivo to prevent the progression of diabetes induced by multiple low doses of streptozotocin (MLD-STZ).

EXPERIMENTAL APPROACH

Pancreatic islets from C57/BL6J mice were pretreated with curcumin (10 microM) and then exposed to a combination of cytokines. Islet viability, reactive oxygen species (ROS), NO, inducible NO synthase and NF-kappaB translocation were studied. Curcumin pretreated (7.5 mg kg(-1) day(-1)) C57/BL6J mice were given MLD-STZ (40 mg kg(-1)), and various parameters of diabetes induction and progression were monitored.

KEY RESULTS

Curcumin protected islets from cytokine-induced islet death in vitro by scavenging ROS and normalized cytokine-induced NF-kappaB translocation by inhibiting phosphorylation of inhibitor of kappa B alpha (IkappaBalpha). In vivo, curcumin also prevented MLD-STZ, as revealed by sustained normoglycaemia, normal glucose clearance and maintained pancreatic GLUT2 levels. Pro-inflammatory cytokine concentrations in the serum and pancreas were raised in STZ-treated animals, but not in animals pretreated with curcumin before STZ.

CONCLUSIONS AND IMPLICATIONS

Here, we have demonstrated for the first time that curcumin in vitro protects pancreatic islets against cytokine-induced death and dysfunction and in vivo prevents STZ-induced diabetes.

Blood-stage malaria infection in diabetic mice

Infection of mice with blood-stage Plasmodium yoelii and P. chabaudi malaria induced hypoglycaemia in normal mice and normalized the hyperglycaemia of mice made moderately diabetic with streptozotocin (STZ). Injection of parasite supernatants induced hypoglycaemia accompanied by hyperinsulinaemia in normal mice, and in STZ-diabetic mice induced a profound drop in blood glucose and restored insulin secretion; however, severely diabetic mice (two injections of STZ) remained hyperglycaemic with no change in insulin levels. We conclude that malaria infection and parasite-derived molecules lower blood glucose concentration, but only in the presence of some residual pancreatic function. Diabetic mice were less anaemic, exerted a significant control of parasitaemia, and showed enhanced phagocytic activity compared with normal mice.

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.

Modulation of low-dose streptozotocin-induced diabetes in mice by administration of antibodies to I-A, I-E and I-J determinants

In male mice of strains C3H and C57BL/6 an experimental immune-mediated diabetes can be induced by multiple low doses of streptozotocin. The delay and partial suppression of hyperglycaemia after anti-I-A monoclonal antibody administration was dose dependent. Even saturation levels of anti-I-A did not cause complete protection from diabetes development. Administration of anti-I-E monoclonal antibody also significantly delayed the onset of hyperglycaemia. Surprisingly, the combined treatment with anti-I-A and anti-I-E did not result in better protection from diabetes. Thus, there is an I-A and I-E independent component of the disease. Furthermore, there is no restriction to either I-A or I-E. Anti-I-A was only effective when given at the beginning of the experiment, which implies that I-A molecules have a primary function during the induction of diabetes. The contribution of I-J to the disease process is different. Administration of a polyspecific alloantiserum to I-J almost completely prevented hyperglycaemia. Injections of monospecific antibodies to I-J determinants enhanced hyperglycaemia, especially when given after the induction of diabetes. This indicates that I-J is involved in initial as well as in later stages of the disease process.

Functional restoration of cultured mouse pancreatic islets after in vitro exposure to alloxan

The molecular mechanisms behind the functional responses of the beta-cells after cytotoxic damage are still largely unknown. The aim of this study was to investigate to what extent the islet beta-cells are capable of repairing cellular injuries after acute treatment with increasing doses of alloxan. Isolated mouse pancreatic islets were exposed for 30 min. at 37 degrees to alloxan (1.0, 1.5 and 2.0 mM) or vehicle alone (controls). Immediately after alloxan exposure the islet glucose-stimulated insulin release was severely decreased, and there were morphological evidences of partial necrosis of the islets. After further six days in culture, there was a marked decrease in islet number in the groups of islets treated with 1.5 or 2.0 mM alloxan. However, the DNA and insulin contents of the remaining islets were similar to the values observed in cultured control islets. Furthermore, the insulin secretory response to glucose and the light microscopical appearance of these islets were largely restored on day 6. It is concluded that beta-cells surviving after an injury induced by alloxan may recover their functional capacity after an initial period of inhibited function.

Functional characteristics of cultured mouse pancreatic islets following exposure to different streptozotocin concentrations

The present study was undertaken to investigate the acute and long-term effects of streptozotocin (SZ) on pancreatic islet function and survival in vitro. Isolated mouse pancreatic islets, that had been cultured overnight, were exposed to SZ (0.55-4.4 mM) or critic acid buffer in the case of the control group. The islets were examined either immediately after SZ exposure or after one week in culture. There was a marked loss of islets treated with 2.2 and 4.4 mM SZ during the culture; however, the DNA content of the remaining islets was unaffected. The islet insulin content was reduced 7 days after treatment with 2.2 and 4.4 mM SZ. At 4.4 mM the glucagon and somatostatin content of the islet was also decreased but not to the same degree as the insulin content. SZ-induced inhibition of glucose-stimulated insulin release and (pro)insulin biosynthesis was more pronounced on day 7 as compared to day 0. A similar pattern of inhibitory action of SZ was observed on islet glucose oxidation rates. Islet ATP contents were depressed on day 7 in islets exposed 4.4 mM SZ, but were otherwise similar to the control group. Islet NAD + NADH contents were decreased by 50% after exposure to 2.2 mM SZ, compared to the control islets on day 0. This decrease in NAD + NADH contents was to a large extent restored during the one-week culture. The present study shows that islets failed to completely repair the acute damage caused by SZ, and that the impairment of the islet glucose-stimulated insulin release induced by SZ seemed to progress in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Streptozotocin toxicity to cultured pancreatic islets of the Syrian hamster

Pancreatic islets of the Syrian golden hamster were maintained in culture for extended periods of time. Toxicity of streptozotocin in these cultures was evaluated by measurement of insulin secretion. Exposure of islets to 1 or 2 mM streptozotocin immediately following isolation resulted in a permanent and dose-related inhibition of insulin secretion. This was accompanied by islet disruption as observed by phase-contrast microscopy. Culture of islets for 24 hours before streptozotocin exposure afforded protection from toxicity. For example, exposure of freshly isolated islets to 2 mM streptozotocin resulted in complete destruction of beta cells, whereas islets similarly exposed after a 24 hr culture period continued to secrete insulin for many months. Islets maintained in culture for one week before exposure to 0.1-0.5 mM streptozotocin, however, became more sensitive than freshly isolated islets. Repeated weekly exposure of cultured islets to a "non-toxic" concentration (0.1 mM) resulted in sustained suppression of insulin secretion after 11 weeks.

Culture of mouse pancreatic islets in different glucose concentrations modifies B cell sensitivity to streptozotocin

There have previously been divergent data published regarding the effects of glucose on the diabetogenic effects of streptozotocin. In order to further explore this issue, two separate sets of experiments were performed. In the first, mouse pancreatic islets were maintained in culture for 3 days at different glucose concentrations (5.6, 11.1 and 28 mmol/l) and then exposed to streptozotocin. After another 3 days in culture at 11.1 mmol/l glucose, the B cell function was evaluated by measurement of glucose-stimulated insulin release, the number of islets recovered after culture, and the islet DNA and insulin contents. In the second group of experiments islets were first maintained in culture at 11.1 mmol/l glucose, then treated with streptozotocin and subsequently cultured for 6 days at the different glucose concentrations given above. It was found that islets maintained in a medium containing 28 mmol/l glucose before or after streptozotocin exposure showed less signs of damage than islets cultured in 11.1 mmol/l glucose. A similar, but less pronounced, decreased sensitivity to streptozotocin was found in islets precultured in 5.6 mmol/l glucose, in comparison with those islets cultured in 11.1 mmol/l glucose. Culture at 5.6 mmol/l glucose just after streptozotocin treatment did not induce any improvement in islet survival or function. It is suggested that the increased damage induced by streptozotocin to islets precultured at 11.1 mmol/l glucose, in comparison with 5.6 mmol/l glucose, can be related to the fact that an increased metabolic activity of B cells render them more susceptible to the toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

The partial protective effect of branched chain amino acids against streptozotocin-induced cytotoxicity to mouse pancreatic islets in vitro

Recent experiments suggested that injections of branched chain amino acids (BCAA) immediately followed by streptozotocin (SZ), induced a partial protection against the diabetogenic action of SZ in vivo. In the present investigation, isolated mouse pancreatic islets were exposed in vitro to SZ (2.2-4.4 mM), with or without preincubation in a mixture of BCAA (15 mM leucine, 15 mM isoleucine and 15 mM valine). In order to evaluate the toxic action of SZ on the beta-cell, the islets were studies after culture for 3 days following SZ exposure. In control islets which had not been pretreated with BCAA, 4.4 mM SZ induced a 47% diminution in the islet number, while only 20% were lost after pretreatment with BCAA. There was also a greater total islet DNA content recovered in the islets pretreated with BCAA before SZ exposure. The BCAA islets furthermore maintained a slightly higher insulin release to the culture medium, insulin content and insulin response to an acute glucose stimulus. Preincubation with each of the amino acids alone did not protect against the SZ action. The present data are consistent with previous in vivo findings and suggest that a direct BCAA-induced decrease in the beta-cell sensitivity to SZ can explain the partial protective effect of these amino acids against the diabetogenic action of SZ.