Downregulation of apoptosis in the target tissue prevents low-dose streptozotocin-induced autoimmune diabetes

A novel model of early type 1 diabetes mellitus: The chick embryo air sack model

Diabetes Mellitus (DM) is a metabolic disease characterized by hyperglycemia. Chronic hyperglycemia is associated with long-term dysfunction such as retinopathy, nephropathy, neuropathy and cardiovascular diseases. These complications increase rates of death and disability worldwide. Due to the negative effects of DM on the quality of life, the mechanism and treatments of the disease should be investigated in more detail. Most of the research in diabetes is performed in experimental animals. Experimental animal models contributed to the advancement of clinical research, the development of new therapeutic approaches, the discovery of insulin and the purification of insulin. There are many animal models of DM in the literature. But there are a few DM model studies created with chick embryos. In these studies, it was seen that there were differences in STZ doses and STZ administration techniques. The objective of this study was to create a more acceptable and easier DM model. 180 specific pathogen free (SPF) fertilized chicken eggs (White Leghorn chicken) were used in this study. STZ was administered to 160 SPF eggs for an induced DM model. The remaining 20 SPF eggs were separated as a control group. We used two different DM models (Air sack model (ASM) and Chorioallantoic membrane model (CAMM)) and blood sampling technique in our study. 160 SPF eggs were divided into two groups with 80 eggs in each group, according to the model in which STZ was administered. When the relationship between blood glucose and blood insulin levels were examined, it was determined that there was a significantly strong negative correlation in the control group and ASM 1 group; and a significantly very strong negative correlation was found in the ASM 2 group and ASM 3 group. Our data indicate that the optimal STZ dose to create a DM model was 0.45 mg/egg and the best DM model was ASM. The second technique to be the best blood sampling technique for determining blood glucose levels. We believe that ASM can be used in DM studies and anti-DM drug studies in terms of its easebly, applicability, reproducibility and low cost.

Immunoregulatory Effect of Acanthopanax trifoliatus (L.) Merr. Polysaccharide on T1DM Mice

Background

Acanthopanax trifoliatus (L.) Merr. is a medicinal plant found in Southeast Asia, and its young leaves and shoots are consumed as a vegetable. The main bioactive components of this herb are polysaccharides that have significant anti-diabetic effects. The aim of this study was to evaluate the immunoregulatory effect of A. trifoliatus (L.) Merr. polysaccharide (ATMP) on a mouse model of type 1 diabetes mellitus (T1DM).

Methods

The monosaccharide composition and mean molecular mass of ATMP were determined by HPLC and HPGPC. T1DM was induced in mice using STZ, and 35, 70 and 140mg/kg ATMP was administered daily via the intragastric route for six weeks. Untreated and metformin-treated positive control groups were also included. The body weight of the mice, food and water intake and fasting glucose levels were monitored throughout the 6-week regimen. Histological changes in the pancreas and spleen were analyzed by H&E staining. Oral glucose tolerance was evaluated with the appropriate test. Peroxisome proliferator-activated receptor γ (PPARγ) mRNA and protein levels in the spleen were measured by quantitative real time PCR and Western blotting. IL-10, IFN-γ and insulin levels in the sera were determined by ELISA. The CD4⁺ and CD8⁺T cells in spleen tissues were detected by immunohistochemistry (IHC).

Results

ATMP and metformin significantly decreased fasting blood glucose, and the food and water intake after 6 weeks of treatment. In contrast, serum insulin levels, glucose tolerance and body weight improved considerably in the high and medium-dose ATMP and metformin groups. T1DM was associated with pancreatic and splenic tissue damage. The high dose (140mg/kg) of ATMP reduced infiltration of inflammatory cells into the pancreas and restored the structure of islet β-cells in the diabetic mice. Consistent with this, 35, 70 and 140mg/kg ATMP increased IL-10 levels and decreased that of IFN-γ, thereby restoring the CD4⁺/CD8⁺ and Th1/Th2 cytokine ratio. At the molecular level, high-dose ATMP up-regulated PPARγ in the splenic cells.

Conclusion

ATMP exerts a hypoglycemic effect in diabetic mice by restoring the immune balance in the spleen.

Can pentoxifylline and similar xanthine derivatives find a niche in COVID-19 therapeutic strategies? A ray of hope in the midst of the pandemic

COVID-19 pandemic presents an unprecedented challenge to identify effective drugs for treatment. Despite multiple clinical trials using different agents, there is still a lack of specific treatment for COVID-19. Having the potential role in suppressing inflammation, immune modulation, antiviral and improving respiratory symptoms, this review discusses the potential role of methylxanthine drugs like pentoxifylline and caffeine in the management of COVID-19 patients. COVID-19 pathogenesis for clinical features like severe pneumonia, acute lung injury (ALI) / acute respiratory distress syndrome (ARDS), and multi-organ failures are excessive inflammation, oxidation, and cytokine storm by the exaggerated immune response. Drugs like pentoxifylline have already shown improvement of the symptoms of ARDS and caffeine has been in clinical use for decades to treat apnea of prematurity (AOP) in preterm infants and improve respiratory function. Pentoxifylline is well-known anti-inflammatory and anti-oxidative molecules that have already shown to suppress Tumor Necrosis Factor (TNF-α) as well as other inflammatory cytokines in pulmonary diseases, and this may be beneficial for better clinical outcomes in COVID-19 patients. Pentoxifylline enhances blood flow, improves microcirculation and tissue oxygenation, and caffeine also efficiently improves tissue oxygenation, asthma, decreases pulmonary hypertension and an effective analgesic. There are significant shreds of evidence that proved the properties of pentoxifylline and caffeine against virus-related diseases as well. Along with the aforementioned evidences and high safety profiles, both pentoxifylline and caffeine offer a glimpse of considerations for future use as a potential adjuvant to COVID-19 treatment. However, additional clinical studies are required to confirm this speculation.

Experimental models and methods for cutaneous wound healing assessment

Wound healing studies are intricate, mainly because of the multifaceted nature of the wound environment and the complexity of the healing process, which integrates a variety of cells and repair phases, including inflammation, proliferation, reepithelialization and remodelling. There are a variety of possible preclinical models, such as in mice, rabbits and pigs, which can be used to mimic acute or impaired for example, diabetic and nutrition-related wounds. These can be induced by many different techniques, with excision or incision being the most common. After determining a suitable model for a study, investigators need to select appropriate and reproducible methods that will allow the monitoring of the wound progression over time. The assessment can be performed by non-invasive protocols such as wound tracing, photographic documentation (including image analysis), biophysical techniques and/or by invasive protocols that will require wound biopsies. In this article, we provide an overview of some of the most often needed and used: (a) preclinical/animal models including incisional, excisional, burn and impaired wounds; (b) methods to evaluate the healing progression such as wound healing rate, wound analysis by image, biophysical assessment, histopathological, immunological and biochemical assays. The aim is to help researchers during the design and execution of their wound healing studies.

Synergistic effect of PEGylation and pentoxifylline addition on immunoprotection of pancreatic islets

In this study, a method is proposed to reduce immunological response of immune system against Langerhans islets by PEGylation of islets combined with adjuvant therapy. For this purpose, the best composition for a mixture of succinimidyl valeric acid activated mPEG (mPEG-SVA) with different molecular weights (MWs) and for a mixture of succinimidyl carbonate activated mPEG (mPEG-SC) with different MWs was determined separately. Then, the effect of pentoxifylline (PTX) as an adjuvant drug on immunological response against PEGylated islets at best mPEG composition was studied. The extent of mPEGs reaction, the amount of interlukin-2 (IL-2) and perforin secretion, and the viability of lymphocytes and islets in homo and co-cultures in the presence of PTX at different concentrations were considered for the in vitro evaluation of the proposed method. It was found, that a mixture of mPEG-SVA with MWs of 10 and 5 kDa at a composition of 75 and 25%, respectively, was the best formulation. Also, the addition of PTX drug to co-culture medium increased the protection of PEGylated islets against immune system and a concentration of 75 μg mL^-1 of PTX was suitable for islet protection with no adverse effect on immune cells.

Antidiabetic potential of salvianolic acid B in multiple low-dose streptozotocin-induced diabetes

CONTEXT

Salvianolic acids are the most abundant water-soluble compounds extracted from the herb Salvia miltiorrhiza L. (Lamiaceae) with antioxidant and protective effects.

OBJECTIVE

This study evaluates the antidiabetic effect of salvianolic acid B (Sal B) in multiple low-dose streptozotocin (MLDS)-induced diabetes in rat.

MATERIALS AND METHODS

Rats were divided into control, Sal B40-treated control, diabetic, Sal B20-, and Sal B40-treated diabetic groups. Sal B was daily administered at doses of 20 or 40 mg/kg (i.p.), started on third day post-STZ injection for 3 weeks. Serum glucose and insulin level and some oxidative stress markers in pancreas were measured in addition to the oral glucose tolerance test (OGTT), histological assessment, and apoptosis determination.

RESULTS

After 3 weeks, treatment of diabetic rats with Sal B20 and Sal B40 caused a significant decrease of the serum glucose (p < 0.05-0.01) and improvement of OGTT. Meanwhile, serum insulin was significantly higher in Sal B20- and Sal B40-treated diabetics (p < 0.01) and treatment of diabetics with Sal B40 significantly lowered malondialdehyde (MDA) (p < 0.05), raised glutathione (GSH) (p < 0.05), and activity of catalase (p < 0.01) with no significant change of nitrite. Furthermore, the number of pancreatic islets (p < 0.05) and their area (p < 0.01) was significantly higher and apoptosis reactivity was significantly lower (p < 0.05) in the Sal B40-treated diabetic group versus diabetics.

DISCUSSION AND CONCLUSION

Three-week treatment of diabetic rats with Sal B exhibited antidiabetic activity which is partly exerted via attenuation of oxidative stress and apoptosis and augmentation of antioxidant system.

Mouse models of diabetic neuropathy

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes and is associated with significant morbidity and mortality. DPN is characterized by progressive, distal-to-proximal degeneration of peripheral nerves that leads to pain, weakness, and eventual loss of sensation. The mechanisms underlying DPN pathogenesis are uncertain, and other than tight glycemic control in type 1 patients, there is no effective treatment. Mouse models of type 1 (T1DM) and type 2 diabetes (T2DM) are critical to improving our understanding of DPN pathophysiology and developing novel treatment strategies. In this review, we discuss the most widely used T1DM and T2DM mouse models for DPN research, with emphasis on the main neurologic phenotype of each model. We also discuss important considerations for selecting appropriate models for T1DM and T2DM DPN studies and describe the promise of novel emerging diabetic mouse models for DPN research. The development, characterization, and comprehensive neurologic phenotyping of clinically relevant mouse models for T1DM and T2DM will provide valuable resources for future studies examining DPN pathogenesis and novel therapeutic strategies.

Description of the sphingolipid content and subspecies in the diabetic cornea

PURPOSE

Diabetes mellitus (DM) is characterized by high blood sugar levels over a prolonged period. Long term complications include but not limited heart disease, stroke, kidney failure, and ocular damage. An estimated 382 million people are diagnosed with Type 2 DM accounting for 90% of the cases. Common corneal dysfunctions associated with DM result in impaired vision due to decreased wound healing, corneal edema, and altered epithelial basement membrane. Lipids play a fundamental role in tissue metabolism and disease states. We attempt to determine the role of sphingolipids (SPL) in human Type I and Type II diabetic corneas.

MATERIALS AND METHODS

Cadaver corneas from healthy (non-diabetic/no ocular trauma), Type I (T1DM), and Type II diabetic (T2DM) donors were obtained and processed for lipidomics using LC-MS/MS.

RESULTS

Our data show significant differences in the SPL composition between control, T1DM and T2DM corneas. Both T1DM and T2DM showed a 10-folddownregulation of sphingomyelin(SM), 5-fold up regulation of Ceramides (Cer) and 2-fold upregulation of monohexosylceramides (MHC). Differences were also seen in total amounts of SPL where Cer was increased by approximately 3 fold in both T1DM and T2DM where SM decreased by 50% in both T1DM and T2DM when compared to healthy controls. No differences were seen in MHC amounts.

CONCLUSIONS

Overall, our data indicate major differences in SPL distribution in human diabetic corneas. Information on the sphingolipids role in cornea, corneal cell physiology, and diseases are very limitedwhich highlights the importance of these findings.

Induction of diabetes with signs of autoimmunity in primates by the injection of multiple-low-dose streptozotocin

AIM

To develop a preclinical large animal model of autoimmune diabetes to facilitate the translational research of autoimmune diabetes in human.

MATERIALS AND METHODS

Nine young rhesus monkeys received multiple-low-dose (MLD) intravenous injections of streptozotocin for five consecutive days, followed by two additional boosting injections of STZ given 1 week apart. The induction of autoimmune diabetes was evaluated by regular metabolic testing, serological assessment of islet-reactive autoantibodies and histological examination of pancreatic tissues.

RESULTS

Seven of nine treated animals became diabetic with moderate hyperglycemia initially and more severe hyperglycemia thereafter. All diabetic animals exhibited severely impaired glucose tolerance, limited islet function, and required insulin therapy to maintain relatively normal glucose metabolism and healthy status. Serological tests showed that all diabetic monkeys developed autoantibodies specifically against insulin and islet antigens. Furthermore, histological examination of the pancreata from diabetic animals revealed evidence of specific destruction of islet β cells and islets infiltrated with T lymphocytes. Overt and persistent diabetes can be induced in young rhesus monkeys by the injection of MLD-STZ, and autoimmune responses to pancreatic islet cells seem to be involved in the development of glucose intolerance and diabetes.

CONCLUSION

These data indicate for the first time that autoimmune diabetes can be induced in primates; this may serve as a valuable preclinical model for studying the pathogenesis of and potential therapies for autoimmune diabetes in humans.

Metabolic effects of various antidiabetic and hypolipidaemic agents on a high-fat diet and multiple low-dose streptozocin (MLDS) mouse model of diabetes

Insulin resistance and subsequent insulin secretory defect are two main features of type 2 diabetes and associated metabolic disorders. The animal models of type 2 diabetes are very complex and are as heterogeneous as the disease. We have evaluated the effect of various antidiabetic and lipid lowering agents (fenofibrate, rosiglitazone, glimepiride, metformin and simvastatin) on the metabolic abnormalities induced by combining a high-fat diet and multiple low-dose streptozocin (MLDS) in mice. Male Swiss albino mice were orally treated with the above agents and fed with a diet containing high fat for 28 days. On day 15 the animals were injected intraperitoneally with low-dose streptozocin (40 mg kg−1), which was administered for five consecutive days. At the end of the 28-day treatment plasma metabolic parameters (glucose, triglyceride and immunoreactive insulin) were estimated. The antidiabetic and hypolipidaemic agents exhibited differential effects on these metabolic parameters. With the exception of fenofibrate all these agents reduced the plasma glucose levels, and the effects of metformin and rosiglitazone on glucose were found to be statistically significant. Although the effect of the test drugs on cholesterol was modest, a significant decrease in triglyceride levels was observed with sub-chronic treatment with these agents. Interestingly, glimepiride mildly elevated the insulin levels while the other antidiabetics and hypolipidaemics reduced the insulin levels, with metformin and rosiglitazone exhibiting statistically significant effects on insulin. To our knowledge this is the first report on the effect of various peroxisome proliferator-activated receptor modulators and newer antidiabetics on the metabolic effects induced by the combined high-fat diet and MLDS model of type 2 diabetes in Swiss albino mice. The results suggested the complexity of the hyperglycaemia, hyperinsulinaemia and hypertriglyceridaemia induced by the high-fat diet and MLDS mouse model, and their correction by various antidiabetics and antihyperlipidaemics may have involved diverse mechanisms.

Androgen receptor: a new player associated with apoptosis and proliferation of pancreatic beta-cell in type 1 diabetes mellitus

Androgen receptor (AR) mediates a wide range of cellular processes, such as proliferation, differentiation and apoptosis. Here we sought to identify whether AR was located in pancreatic beta-cells and investigate its functions in type 1 diabetes induced by multiple low doses of streptozotocin. Double/triple immunofluorescence, Western blot and semi-quantitative RT-PCR were carried out to determine variances of AR expression in beta-cells and correlation between AR and apoptosis/proliferation of beta-cells with progress of diabetes. In addition, in vitro primary beta-cells from control mice were cultured for 3 days or 6 days with compound stimulation in order to further identify effect of AR on beta-cell apoptosis and proliferation. AR expression in beta-cells peaked in control and 1-day diabetic mice, gradually and significantly decreased, even disappeared in diabetic mice with progress of diabetes. TUNEL-positive beta-cells were concomitant with overexpression of AR, and Ki67-positive beta-cells showed extremely weak, even negative AR staining. In vitro, AR could mediate beta-cell apoptosis, and AR antagonist flutamide contributed to beta-cell proliferation. In conclusion, AR is abundantly expressed in pancreatic beta-cell cytoplasm of control mice. With progress of type 1 diabetes, decrement of AR expression in diabetic mice contributes to prohibit beta-cells from apoptosis, and is strongly associated with beta-cell proliferation.

Protein-tyrosine phosphatase 1B expression is induced by inflammation in vivo

Protein-tyrosine phosphatase 1B (PTP1B) is a major negative regulator of insulin and leptin sensitivity. PTP1B overexpression in adipose tissue and skeletal muscle of humans and rodents may contribute to insulin resistance and obesity. The mechanisms mediating PTP1B overexpression in obese and diabetic states have been unclear. We find that adipose tissue inflammation and the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) regulate PTP1B expression in vivo. High fat feeding of mice increased PTP1B expression 1.5- to 7-fold in adipose tissue, liver, skeletal muscle, and arcuate nucleus of hypothalamus. PTP1B overexpression in high fat-fed mice coincided with increased adipose tissue expression of the macrophage marker CD68 and TNFalpha, which is implicated in causing obesity-induced insulin resistance. TNFalpha increased PTP1B mRNA and protein levels by 2- to 5-fold in a dose- and time-dependent manner in adipocyte and hepatocyte cell lines. TNFalpha administration in mice increased PTP1B mRNA 1.4- to 4-fold in adipose tissue, liver, skeletal muscle, and hypothalamic arcuate nucleus and PTP1B protein 2-fold in liver. Actinomycin D treatment blocked, and high dose salicylate treatment inhibited by 80%, TNFalpha-induced PTP1B expression in adipocyte cell lines, suggesting TNFalpha may induce PTP1B transcription via nuclear factor kappaB (NFkappaB) activation. Chromatin immunoprecipitation from adipocyte cell lines and liver of mice demonstrated TNFalpha-induced recruitment of NFkappaB subunit p65 to the PTP1B promoter in vitro and in vivo. In mice with diet-induced obesity, TNFalpha deficiency also partly blocked PTP1B overexpression in adipose tissue. Our data suggest that PTP1B overexpression in multiple tissues in obesity is regulated by inflammation and that PTP1B may be a target of anti-inflammatory therapies.

Immune tolerance induced by adoptive transfer of dendritic cells in an insulin-dependent diabetes mellitus murine model

AIM

To investigate the effect and underlying mechanisms of immune-tolerance induced by the adoptive transfer of bone marrow (BM)-derived dendritic cells (DC) in insulin-dependent diabetes mellitus (IDDM) mice.

METHODS

The IDDM model was established by a low dose of streptozotocin (STZ) in Balb/c mice. Two DC subpopulations were generated from the BM cells with granulocyte-macrophage colony-stimulating factor with or without interleukin-4. The purity and the T cell stimulatory capability of DC were identified. These cells were used to modulate autoimmune response in pre-diabetic mice. Blood glucose was examined weekly; pancreas tissues were taken for histopathological analysis, and CD4(+) T cells were isolated to detect lymphocyte proliferation by MTT assay and the ratio of CD4(+)CD25(+) T cells by fluorescence-activated cell sorting (FACS). The cytokine secretion was determined by ELISA analysis.

RESULTS

Two DC subsets were generated from BM, which have phenotypes of mature DC (mDC) and immature DC (iDC), respectively. The level of blood glucose decreased significantly by transferring iDC (P< 0.01) rather than mDC. Less lymphocyte infiltration was observed in the islets, and pancreatic structure was intact. In vitro, proliferation of lymphocytes decreased and the proportion of CD4(+)CD25(+) T cells increased remarkably, compared with the mDC-treated groups (P< 0.05), which were associated with increased level of the Th2 cytokine and reduced level of the Th1 cytokine after iDC transfer.

CONCLUSION

Our data showed that iDC transfer was able to confer protection to mice from STZ-induced IDDM. The immune-tolerance to IDDM may be associated with promoting the production of CD4(+)CD25(+) T cells and inducing regulatory Th2 responses in vivo.

The Immunotherapeutic Effects of Astragalus Polysaccharide in Type 1 Diabetic Mice

The present study investigated whether Astragalus polysaccharide (APS) possessed immunotherapeutic effects on type 1 diabetes mellitus. Diabetic mice induced by multiple low dose streptozotocin (MLD-STZ) were administered either APS (100, 200, 400 mg/kg body weight) or saline intraperitoneally daily, and sacrificed after 15 or 30 d of treatment. Meanwhile normal mice not treated with STZ nor with APS were offered into non-diabetic group. Blood glucose and serum insulin levels were measured, histologic and morphometric analyses of the pancreas were performed to determine the effect of APS on pancreatic islets. Further investigations on immune changes in spleens were tested by ELISA, semi-quantitative RT-PCR and Western blot. Downregulated blood glucose level, upregulated serum insulin concentration, increased beta cell mass, decreased apoptotic beta cell percentage, downregulation of Th1/Th2 cytokine ratio and upregulation of peroxisome proliferator-activated receptor gamma (PPARgamma) gene expression in spleens were significantly time- and dose-dependent on APS treatment, when compared to saline controls. These results show that APS seems to be helpful to attenuate insulitis and preserve beta cells from apoptosis, but it can't entirely rescue type 1 diabetes mellitus. APS ameliorates both the clinical and histological parameters of the MLD-STZ induced diabetic mice in a long-lasting fashion, most likely through immunoregulatory actions on Th1/Th2 cytokine ratio, strongly associated with PPARgamma gene expression in spleens.

Immune tolerance and its mechanism induced by adoptive transfer of bone marrow-derived dendritic cells in mice with insulin-dependent diabetes mellitus

AIM: To investigate immune tolerance induced by adoptive transfer of bone marrow-derived dendritic cells (DCs) in mice with type 1 diabetes, and to explore its underlying mechanism.

METHODS: Bone marrow cells from BALB/c mice were used to generate DCs by in vitro co-culturing with cytokines. After identifying the purity of DCs, We injected the cells into BALB/c mice intraperitoneally. The mouse model of type 1 diabetes was established by injecting low dose of streptozotocin (STZ) for 5 consecutive days. The blood glucose was examined once a week. At the end of the 4^th week, all the mice were killed and splenic lymphocytes were collected. After in vitro culturing, the proliferation of lymphocytes was detected by MTT assay, and the proportion of CD4⁺CD25⁺T cells was analyzed by fluorescence activated cell sorter (FACS). The serum levels of cytokines IL-2 and IL-4 were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS: The level of blood glucose was decreased significantly after adoptive transfer of DCs in comparison with that in the model controls (8.32 ± 1.05 mmol/L vs 18.36 ± 1.55 mmol/L, P < 0.01). In vitro, the proliferation of splenic lymphocytes was inhibited as compared with that of the model controls (0.264 ± 0.019 vs 0.489 ± 0.012, P < 0.05) while the proportion of CD4⁺CD25⁺ T cells was enhanced to 5.28% (1.56% in the model controls). Adoptive transfer of DCs effectively suppressed the secretion of IL-2 (121 ± 19 ng/L vs 195 ± 32 ng/L, P < 0.05) while elevated the content of IL-4 (187 ± 36 ng/L vs 76 ± 30 ng/L, P < 0.01).

CONCLUSION: Adoptive transfer of bone marrow-derived DCs can induce the immune tolerance to type 1 diabetes in mice, and the mechanism may be related with the production of CD4⁺CD25⁺ T cells and balance between Th1 and Th2 cytokines.

Roles of dendritic cells and regulatory T cells in autoantigen-induced murine immune tolerance model

AIM: To investigate the important roles of dendritic cells (DC) and CD4⁺CD25⁺ regulatory T cells in immune prevention against insulin dependent diabetes (IDDM) by autoantigen insulin administration.

METHODS: The model of IDDM was established by intraperitoneal injection of low-dose streptozotocin (STZ) 40 mg/kg per day for 5 consecutive days in Balb/c mice. The bovine insulin (100 μg) in incomplete Freund's adjuvant (IFA, emulsified 1∶1) was given subcutaneously to the mice weekly for 4 wk. The blood glucose was examined once a week and all the mice were killed after 5 wk. Pancreas tissues were collected for histopathological examination. DC precursor cells from bone marrow and lymphocytes from spleen were isolated. The phenotype of DC and CD4⁺ CD25⁺ regulatory T cells were analyzed by fluorescence activated cell sorter (FACS). DC-stimulated proliferation of lymphacytes was determined by allo-mixed lymphocyte reaction (aMLR).

RESULTS: The level of blood glucose was decreased significantly after insulin injection in comparison with that in the model control group (13.79 ± 2.71 mmol/L vs 20.98 ± 1.43 mmol/L, P < 0.05). Fewer lymphocytes infiltration was observed and pancreatic histological structure was intact. The surface marker CD11c on DC from bone marrow was decreased markedly in IDDM mice (26.4%) than that in normal mice (47.5%). DC differentiated abnormally, and the capacity of stimulating proliferation of allogeneic T cell was weakened as compared with that of normal mice (1.47 ± 0.01 vs 2.93 ± 0.01, P < 0.01, and 1.32 ± 0.01 vs 2.94 ± 0.02, P < 0.01, at DC/T ratios of 1∶10 and 1∶20, respectively). The percentage of CD4⁺CD25⁺ T cells were decreased to 1.43%, while it was 5.09% in normal mice. In contrast, blood glucose in mice given insulin subcutaneously was well controlled, and the amount of DC with CD11c was increased (50% approximately); the expression of CD86 and MHC-Ⅱ was low (26.6% and 28.8%, respectively) and MLR showed that DC capacity in stimulating T cell proliferation was lower than those from the normal mice, but higher than those from IDDM model mice (2.30 ± 0.06 and 2.17 ± 0.02, at DC/T ratios of 1∶10 and 1∶20, respectively); the percentage of CD4⁺CD25⁺ T cells from spleen was enhanced to 7.15%.

CONCLUSION: Subcutaneous administration of insulin can confer protection to mice against IDDM induced by STZ. The immune protection of autoantigen may be associated with the establishment of immune tolerance by improving the function of abnormal DC and promoting the production of CD4⁺CD25⁺ T cells in vivo.

IL-23 leads to diabetes induction after subdiabetogenic treatment with multiple low doses of streptozotocin

IL-23, a proximal regulator of IL-17, may be a major driving force in the induction of autoimmune inflammation. We have used a model of subdiabetogenic treatment with multiple low doses of streptozotocin (MLD-STZ; 4 x 40 mg/kg body weight) in male C57BL/6 mice to study the effect of IL-23 on immune-mediated beta cell damage and the development of diabetes, as evaluated by blood glucose, quantitative histology, immunohistochemistry and expression of relevant cytokines in the islets. Ten daily injections of 400 ng IL-23, starting on the first day of MLD-STZ administration led to significant and sustained hyperglycemia along with weight loss compared with controls (no IL-23), and a significant increase in the number of infiltrating cells, a lower insulin content, enhanced apoptosis, expression of IFN-gamma and IL-17 (not seen in the controls) and a significant increase in the expression of TNF-alpha and IL-18 in the pancreatic islets. IL-23 treatment started 5 days prior to MLD-STZ administration had no effect on diabetogenesis or cytokines expression in the pancreatic islets. We provide the first evidence in an animal model that IL-23 is involved in the development of type-1 diabetes, by inducing IL-17 and possibly IFN-gamma production in the target tissue.

Animal models of diabetes mellitus

Animal models have been used extensively in diabetes research. Early studies used pancreatectomised dogs to confirm the central role of the pancreas in glucose homeostasis, culminating in the discovery and purification of insulin. Today, animal experimentation is contentious and subject to legal and ethical restrictions that vary throughout the world. Most experiments are carried out on rodents, although some studies are still performed on larger animals. Several toxins, including streptozotocin and alloxan, induce hyperglycaemia in rats and mice. Selective inbreeding has produced several strains of animal that are considered reasonable models of Type 1 diabetes, Type 2 diabetes and related phenotypes such as obesity and insulin resistance. Apart from their use in studying the pathogenesis of the disease and its complications, all new treatments for diabetes, including islet cell transplantation and preventative strategies, are initially investigated in animals. In recent years, molecular biological techniques have produced a large number of new animal models for the study of diabetes, including knock-in, generalized knock-out and tissue-specific knockout mice.

Lack of the mediators of innate immunity attenuate the development of autoimmune diabetes in mice

Interleukin 15 (IL-15) and Interleukin 18 (IL-18) are key cytokines produced by macrophages during innate immune response. These cytokines can profoundly affect subsequent adaptive immune responses including autoimmunity. We have investigated the role of IL-15 and IL-18 in the development of autoimmune diabetes in mice induced by multiple low dose streptozotocin (MLD-STZ). To analyze the role of IL-15, we tested the effects of a soluble murine IL-15 receptor alpha-chain (smIL-15Ralpha), on the development of MLD-STZ in C57BL/6 mice. Animals were treated with 10 daily injections of 32 microg of smIL-15Ralpha starting on the first day of diabetes induction. This treatment significantly attenuated the development of diabetes as evaluated by significantly lower glycemia compared with control mice treated with an inactive mutant form of sIL-15Ra. To directly address the role of IL-18 in MLD-STZ we used IL-18 knockout (KO) mice on DBA/1 background. IL-18 deficient mice were significantly more resistant to the induction of diabetes compared with the wild-type controls and did not develop the typical mononuclear cell infiltrates in the islets. Taken together our data suggest that the innate mediators, IL-15 and IL-18, are essential for the development of diabetes and may be important targets in prevention and early treatment of autoimmune diabetes.

Epigallocatechin gallate prevents autoimmune diabetes induced by multiple low doses of streptozotocin in mice

Cytokines produced by immune cells infiltrating pancreatic islets have been incriminated as important mediators of beta-cell destruction in insulin-dependent diabetes mellitus. In non insulin-dependent diabetes, cytokines are also associated with impaired beta-cell function in high glucose condition. By the screening of various natural products blocking beta-cell destruction, we have recently found that epigallocatechin gallate (EGCG) can prevent the in vitro destruction of RINm5F cell, an insulinoma cell line, that is induced by cytokines. In that study we suggested that EGCG could prevent cytokine-induced beta-cell destruction by down-regulation of nitric oxide synthase (NOS) through inhibition of NF-kappaB activation. Here, to verify the in vivo antidiabetogenic effect of EGCG, we examined the possibility that EGCG could also prevent the experimental autoimmune diabetes induced by the treatment of multiple low doses of streptozotocin (MLD-STZ), which is recognized as an inducer of type I autoimmune diabetes. Administration of EGCG (100 mg/day/kg for 10 days) during the MLD-STZ induction of diabetes reduced the increase of blood glucose levels caused by MLD-STZ. Ex vivo analysis of beta-islets showed that EGCG downregulates the MLD-STZ-induced expression of inducible NOS (iNOS). In addition, morphological examination showed that EGCG treatment ameliorated the decrease of islet mass induced by MLD-STZ. In combination these results suggest that EGCG could prevent the onset of MLD-STZ-induced diabetes by protecting pancreatic islets. Our results therefore revealed the possible therapeutic value of EGCG for the prevention of diabetes mellitus progression.