Diabetes-resistant BioBreeding Research Articles

A promising rat model of heart failure with preserved ejection fraction associated to multiple comorbidities

Abstract Background and aims Heart failure with preserved ejection fraction (HFpEF) is a complex clinical phenotype often associated to the presence of multiple non-cardiac interrelated comorbidities including diabetes, obesity, hypertension. A major challenge in the development of new therapies for HFpEF is the lack of animal models that truly recapitulate the complexities of the disease. One promising candidate is the Lund MetS rat, a congenic BBDR.cg-lepr.cp model generated by introgression of the Koletsky leptin receptor mutation into the BioBreeding Diabetes Resistant (BBDR) rat. Methods 14-week-old Lund MetS obese T2D rats were exposed to salt enriched diet (0.8% NaCl in diet) for 6 weeks. Age-matched lean rats (ctrl) were fed a normal chow diet. Cardiovascular phenotyping was assessed by echocardiography and blood pressure measurement. Vascular function of isolated thoracic aortas, as well as kidney and cardiac parameters were also evaluated at the end of the 6-week diet period. Results After 6-week enriched salt diet period, mean arterial pressure increased from 120mmHg to 160mmHg (vs 100mmHg in chow-fed lean rat). The hypertensive state also led to renal hypertrophy with up to a 2-fold higher kidney weights. Echocardiography showed a preserved systolic function with quite similar ejection fraction and fractional shortening in Lund MetS and lean rats. In contrast, high salt-fed Lund MetS rats developed cardiac hypertrophy confirmed by a large increase in heart, left ventricle, and left atria weights as compared to lean rats. Diastolic dysfunction was also highlighted with inverted E/A and E'/A' ratios along with a prolongation of the isovolumic relaxation time (IVRT). This was accompanied by an increase in circulating levels of soluble ST2 and NT- proBNP. Finally, aortic rings assays showed that both endothelium dependent and independent vasodilating properties were impaired in the high salt-fed Lund MetS rats. Conclusions The present data demonstrate that the Lund MetS rat fed a high salt diet developed a marked hypertension, pathological cardiac remodeling and diastolic dysfunction without modification of ejection fraction, along with obesity and type 2 diabetes. Thus, this could be a relevant model to bring forward effective new treatments for HFpEF patients. Funding Acknowledgement Type of funding sources: None.

MO615: The Lund Mets Rat, An Obese Type 2 Diabetic Preclinical Model, Develops Non-Alcoholic Steatohepatitis, Diabetic Nephropathy and Heart Failure with Preserved Ejection Fraction Under High Fat/Cholesterol/Fructose Diet

Abstract BACKGROUND AND AIMS Beyond the glucose control, anti-diabetic drugs need to demonstrate benefits on metabolic comorbidities. An animal model that recapitulates obesity and type 2 diabetes (T2D) comorbidities [i.e. non-alcoholic steato-hepatitis (NASH), nephropathy and heart failure with preserved ejection fraction (HFpEF)] is still needed for preclinical drug development. To overcome this limitation, we evaluated the effects of a high fat/cholesterol/fructose (HFCF) diet in the Lund MetS rat, a congenic BBDR.cg-lepr.cp model generated by introgression of the Koletsky leptin receptor mutation into the BioBreeding Diabetes Resistant (BBDR) rat. METHOD 17-week-old, male, lean control (ctrl) or Lund MetS obese T2D rats were fed a control chow (CC) diet or a HFCF diet, respectively for 8 weeks. Blood biochemistry was measured at 0, 4 and 8 weeks of diet. Kidney, heart and liver parameters were assessed at the end of the 8-week diet period. RESULTS Compared with ctrl, Lund MetS rats were obese (56% higher body weight) and diabetic with significantly higher %HbA1c (up to + 3%) and blood glucose levels (up to 3-fold higher) during the 8-week HFCF diet period. Significantly higher plasma insulin (up to 11-fold), total cholesterol (up to 5-fold), triglycerides (up to 8-fold), transaminases (up to 10-fold higher) levels were also observed in Lund MetS rats, as compared with ctrl. Hepatic total cholesterol, triglycerides and fatty acids levels were significantly higher in Lund Mets rats (14-, 7.3- and 6.7-fold higher as compared to ctrl, respectively). Liver histopathological scoring confirmed a NASH phenotype in Lund MetS rats fed the HFCF diet with strong liver steatosis, hepatic inflammation and portal to bridging fibrosis. Kidney function was substantially altered with a 60% decline in glomerular filtration rate and a 16-fold increase in urine albumin-to-creatinine ratio (both P < 0.0001 versus ctrl). Finally, echocardiography indicated diastolic dysfunction with significantly reduced E/A and greater E/e’ ratios, along with a preserved ejection fraction in Lund MetS rats, as compared with lean ctrl. CONCLUSION The present data demonstrate that the Lund MetS rat fed an HFCF diet that recapitulates the major metabolic comorbidities of obesity/T2D and may be a useful model for preclinical drug development.

Visceral Adipose Tissue: A New Target Organ in Virus-Induced Type 1 Diabetes.

Type 1 diabetes (T1D) is a proinflammatory pathology that leads to the specific destruction of insulin producing β-cells and hyperglycaemia. Much of the knowledge about type 1 diabetes (T1D) has focused on mechanisms of disease progression such as adaptive immune cells and the cytokines that control their function, whereas mechanisms linked with the initiation of the disease remain unknown. It has been hypothesized that in addition to genetics, environmental factors play a pivotal role in triggering β-cell autoimmunity. The BioBreeding Diabetes Resistant (BBDR) and LEW1.WR1 rats have been used to decipher the mechanisms that lead to virus-induced T1D. Both animals develop β-cell inflammation and hyperglycemia upon infection with the parvovirus Kilham Rat Virus (KRV). Our earlier in vitro and in vivo studies indicated that KRV-induced innate immune upregulation early in the disease course plays a causal role in triggering β-cell inflammation and destruction. Furthermore, we recently found for the first time that infection with KRV induces inflammation in visceral adipose tissue (VAT) detectable as early as day 1 post-infection prior to insulitis and hyperglycemia. The proinflammatory response in VAT is associated with macrophage recruitment, proinflammatory cytokine and chemokine upregulation, endoplasmic reticulum (ER) and oxidative stress responses, apoptosis, and downregulation of adipokines and molecules that mediate insulin signaling. Downregulation of inflammation suppresses VAT inflammation and T1D development. These observations are strikingly reminiscent of data from obesity and type 2 diabetes (T2D) in which VAT inflammation is believed to play a causal role in disease mechanisms. We propose that VAT inflammation and dysfunction may be linked with the mechanism of T1D progression.

Impaired trophoblast invasion and increased numbers of immune cells at day 18 of pregnancy in the mesometrial triangle of type 1 diabetic rats

IntroductionType 1 diabetes (T1D) is associated with adverse pregnancy outcome, usually attributed to hyperglycemia. Recently, we showed that pregnancy outcome in normoglycemic T1D rats was characterized by decreased fetal and placental weight, suggesting impaired placental development. In the present study, we tested the hypothesis that trophoblast invasion and spiral artery (SA) remodeling is impaired in T1D rats ant that this is associated with aberrant local presence of NK cells and macrophages in the mesometrial triangle (MT). MethodsPlacentae with MT from pregnant biobreeding diabetes-prone (BBDP; T1D model) rats, control biobreeding diabetes-resistant (BBDR) and Wistar-rats were dissected at day 18 of gestation and stained for trophoblast invasion, SA remodeling, uNK cells and macrophages. ResultsInterstitial trophoblast invasion and SA remodeling was impaired in BBDP-rats vs. control rats, coinciding with increased presence of NK cells and an increased iNOS+/CD206+ ratio of macrophages. DiscussionDecreased fetal and placental weight in BBDP-rats was associated with diminished interstitial trophoblast invasion and less optimal SA remodeling, increased numbers of NK cells and increased iNOS+/CD206+ macrophage ratio in the MT of BBDP-rats. ConclusionsThe impaired trophoblast invasion and SA remodeling may be due to an aberrant local immune-response and may result in damage to the fetal placenta and insufficient supply of nutrients towards the fetus with eventually decreased fetal weight as a consequence.

The normoglycaemic biobreeding rat: a spontaneous model for impaired gastric accommodation

ObjectiveImpaired gastric accommodation is reported in patients with functional dyspepsia (FD). Previous findings in postinfectious patients with FD suggest that low-grade inflammation and dysfunction of nitrergic nerves play a role...

Cardiac hypertrophy and oxidative metabolism in novel congenic leptin receptor deficient BBDR.cg‐lepr.cp rats (1155.10)

Congenic BBDR.cg‐lepr.cp rats generated by introgression of the Koletsky leptin receptor mutation into the BioBreeding Diabetes Resistant (BBDR) rat develop obesity and diabetes mellitus, known risk factors for heart failure. Here we studied cardiac function and myocardial oxidative metabolism in these rats by non‐invasive imaging. Myocardial glucose utilization (18F‐fluorodeoxyglucose uptake) and oxygen consumption (washout constant for 11C‐acetate derived from monoexponential fitting) were measured by positron emission tomography (PET); left ventricle (LV) mass, systolic function and cardiac output by echocardiography. Compared with non‐diabetic littermates, diabetic rats were obese (body weight 463±36 vs. 706±65 g, p<0.01), hyperglycemic (6±1 vs. 22±10 mM, p<0.01), had elevated blood pressure (136±5 vs. 151±13 mmHg, p=0.02), comparable systolic function (fractional shortening 49 vs. 48%), but higher LV mass (0,6±0,1 vs. 0,9±0,1 g, p<0.01). Diabetic rats had lower fasting myocardial glucose uptake (p=0.04) and lower efficiency of myocardial forward work (LV work / oxygen consumption * myocardial mass; 69000±8000 vs. 54000±12000 mmHg L/min; p=0.03), despite having comparable resting myocardial oxygen consumption in fasting state. Results suggest that BBDR.cg‐lepr.cp rats should prove a useful new model to study the adverse effects of obesity and diabetes on cardiac metabolism.Grant Funding Source: Supported by: VR 2011‐3900; EFSD, SSMF, the SUMMIT consortium (IMI‐2008/115006).

Salicylate Prevents Virus-Induced Type 1 Diabetes in the BBDR Rat

Epidemiologic and clinical evidence suggests that virus infection plays an important role in human type 1 diabetes pathogenesis. We used the virus-inducible BioBreeding Diabetes Resistant (BBDR) rat to investigate the ability of sodium salicylate, a non-steroidal anti-inflammatory drug (NSAID), to modulate development of type 1 diabetes. BBDR rats treated with Kilham rat virus (KRV) and polyinosinic:polycytidylic acid (pIC, a TLR3 agonist) develop diabetes at nearly 100% incidence by ~2 weeks. We found distinct temporal profiles of the proinflammatory serum cytokines, IL-1β, IL-6, IFN-γ, IL-12, and haptoglobin (an acute phase protein) in KRV+pIC treated rats. Significant elevations of IL-1β and IL-12, coupled with sustained elevations of haptoglobin, were specific to KRV+pIC and not found in rats co-treated with pIC and H1, a non-diabetogenic virus. Salicylate administered concurrently with KRV+pIC inhibited the elevations in IL-1β, IL-6, IFN-γ and haptoglobin almost completely, and reduced IL-12 levels significantly. Salicylate prevented diabetes in a dose-dependent manner, and diabetes-free animals had no evidence of insulitis. Our data support an important role for innate immunity in virus-induced type 1 diabetes pathogenesis. The ability of salicylate to prevent diabetes in this robust animal model demonstrates its potential use to prevent or attenuate human autoimmune diabetes.

Susceptibility to Fatty Acid-Induced β-Cell Dysfunction Is Enhanced in Prediabetic Diabetes-Prone BioBreeding Rats: A Potential Link Between β-Cell Lipotoxicity and Islet Inflammation

β-Cell lipotoxicity is thought to play an important role in the development of type 2 diabetes. However, no study has examined its role in type 1 diabetes, which could be clinically relevant for slow-onset type 1 diabetes. Reports of enhanced cytokine toxicity in fat-laden islets are consistent with the hypothesis that lipid and cytokine toxicity may be synergistic. Thus, β-cell lipotoxicity could be enhanced in models of autoimmune diabetes. To determine this, we examined the effects of prolonged free fatty acids elevation on β-cell secretory function in the prediabetic diabetes-prone BioBreeding (dp-BB) rat, its diabetes-resistant BioBreeding (dr-BB) control, and normal Wistar-Furth (WF) rats. Rats received a 48-h iv infusion of saline or Intralipid plus heparin (IH) (to elevate free fatty acid levels ~2-fold) followed by hyperglycemic clamp or islet secretion studies ex vivo. IH significantly decreased β-cell function, assessed both by the disposition index (insulin secretion corrected for IH-induced insulin resistance) and in isolated islets, in dp-BB, but not in dr-BB or WF, rats, and the effect of IH was inhibited by the antioxidant N-acetylcysteine. Furthermore, IH significantly increased islet cytokine mRNA and plasma cytokine levels (monocyte chemoattractant protein-1 and IL-10) in dp-BB, but not in dr-BB or WF, rats. All dp-BB rats had mononuclear infiltration of islets, which was absent in dr-BB and WF rats. In conclusion, the presence of insulitis was permissive for IH-induced β-cell dysfunction in the BB rat, which suggests a link between β-cell lipotoxicity and islet inflammation.

Haptoglobin as an early serum biomarker of virus-induced autoimmune type 1 diabetes in biobreeding diabetes resistant and LEW1.WR1 rats

Proteomic profiling of serum is a powerful technique to identify differentially expressed proteins that can serve as biomarkers predictive of disease onset. In this study, we utilized two-dimensional (2D) gel analysis followed by matrix-assisted-laser desorption/ionization time-of-flight mass spectrometry analysis to identify putative serum biomarkers for autoimmune type 1 diabetes (T1D) in biobreeding diabetes resistant (BBDR) rats induced to express the disease. Treatment with toll-like receptor 3 ligand, polyinosinic:polycytidilic acid (pIC), plus infection with Kilham rat virus (KRV), a rat parvovirus, results in nearly 100% of young BBDR rats becoming diabetic within 11-21 d. Sera collected from prediabetic rats at early time points following treatment with pIC + KRV were analyzed by 2D gel electrophoresis and compared with sera from control rats treated with phosphate-buffered saline, pIC alone or pIC + H1, a non-diabetogenic parvovirus. None of the latter three control treatments precipitates T1D. 2D gel analysis revealed that haptoglobin, an acute phase and hemoglobin scavenger protein, was differentially expressed in the sera of rats treated with pIC + KRV relative to control groups. These results were confirmed by Western blot and enzyme-linked immunosorbent assay studies, which further validated haptoglobin levels as being differentially increased in the sera of pIC + KRV-treated rats relative to controls during the first week following infection. Early elevations in serum haptoglobin were also observed in LEW1.WR1 rats that became diabetic following infection with rat cytomegalovirus. The identification and validation of haptoglobin as a putative serum biomarker for autoimmune T1D in rats now affords us the opportunity to test the validity of this protein as a biomarker for human T1D, particularly in those situations where viral infection is believed to precede the onset of disease.

Intracellular Ca2+ regulating proteins in vascular smooth muscle cells are altered with type 1 diabetes due to the direct effects of hyperglycemia

BackgroundDiminished calcium (Ca2+) transients in response to physiological agonists have been reported in vascular smooth muscle cells (VSMCs) from diabetic animals. However, the mechanism responsible was unclear.Methodology/Principal FindingsVSMCs from autoimmune type 1 Diabetes Resistant Bio-Breeding (DR-BB) rats and streptozotocin-induced rats were examined for levels and distribution of inositol trisphosphate receptors (IP3R) and the SR Ca2+ pumps (SERCA 2 and 3). Generally, a decrease in IP3R levels and dramatic increase in ryanodine receptor (RyR) levels were noted in the aortic samples from diabetic animals. Redistribution of the specific IP3R subtypes was dependent on the rat model. SERCA 2 was redistributed to a peri-nuclear pattern that was more prominent in the DR-BB diabetic rat aorta than the STZ diabetic rat. The free intracellular Ca2+ in freshly dispersed VSMCs from control and diabetic animals was monitored using ratiometric Ca2+ sensitive fluorophores viewed by confocal microscopy. In control VSMCs, basal fluorescence levels were significantly higher in the nucleus relative to the cytoplasm, while in diabetic VSMCs they were essentially the same. Vasopressin induced a predictable increase in free intracellular Ca2+ in the VSMCs from control rats with a prolonged and significantly blunted response in the diabetic VSMCs. A slow rise in free intracellular Ca2+ in response to thapsigargin, a specific blocker of SERCA was seen in the control VSMCs but was significantly delayed and prolonged in cells from diabetic rats. To determine whether the changes were due to the direct effects of hyperglycemica, experiments were repeated using cultured rat aortic smooth muscle cells (A7r5) grown in hyperglycemic and control conditions. In general, they demonstrated the same changes in protein levels and distribution as well as the blunted Ca2+ responses to vasopressin and thapsigargin as noted in the cells from diabetic animals.Conclusions/SignificanceThis work demonstrates that the previously-reported reduced Ca2+ signaling in VSMCs from diabetic animals is related to decreases and/or redistribution in the IP3R Ca2+ channels and SERCA proteins. These changes can be duplicated in culture with high glucose levels.

Culture-independent identification of gut bacteria correlated with the onset of diabetes in a rat model

Bacteria associated with the onset of type 1 diabetes in a rat model system were identified. In two experiments, stool samples were collected at three time points after birth from bio-breeding diabetes-prone (BB-DP) and bio-breeding diabetes-resistant (BB-DR) rats. DNA was isolated from these samples and the 16S rRNA gene was amplified using universal primer sets. In the first experiment, bands specific to BB-DP and BB-DR genotypes were identified by automated ribosomal intergenic spacer analysis at the time of diabetes onset in BB-DP. Lactobacillus and Bacteroides strains were identified in the BB-DR- and BB-DP-specific bands, respectively. Sanger sequencing showed that the BB-DP and BB-DR bacterial communities differed significantly but too few reads were available to identify significant differences at the genus or species levels. A second experiment confirmed these results using higher throughput pyrosequencing and quantitative PCR of 16S rRNA with more rats per genotype. An average of 4541 and 3381 16S rRNA bacterial reads were obtained from each of the 10 BB-DR and 10 BB-DP samples collected at time of diabetes onset. Nine genera were more abundant in BB-DP whereas another nine genera were more abundant in BB-DR. Thirteen and eleven species were more abundant in BB-DP and BB-DR, respectively. An average of 23% and 10% of all reads could be classified at the genus and species levels, respectively. Quantitative PCR verified the higher abundance of Lactobacillus and Bifidobacterium in the BB-DR samples. Whether these changes are caused by diabetes or are involved in the development of the disease is unknown.

The Role of Toll-Like Receptor Pathways in the Mechanism of Type 1 Diabetes

Toll-like receptors (TLRs) and the innate immune system play a key role in sensing and eliminating microbial infections. Interactions between TLRs and their ligands expressed by microbial pathogens induce a cascade of intracellular signaling events, culminating in the upregulation of proinflammatory pathways. Over the past two decades, numerous studies have established the role of the acquired immune system in the mechanism triggering type 1 diabetes (T1D). The recent discovery of TLRs has led to the recognition that the innate immune system may act, under some circumstances, as a double-edged sword. In addition to its beneficial role in host defense, it may lead to upregulation of proinflammatory autoimmune responses, islet destruction and diabetes. Indeed, recent observations are consistent with the hypothesis that altered innate functions exist in patients with T1D and could be part of the mechanism leading to disease onset, but the underlying mechanisms and the relevance of these alterations to early events triggering disease remain to be identified. Data obtained from mouse and rat models of T1D implicated TLR pathways in both disease induction and prevention. In both the NOD mouse and diabetes-prone BB (BBDP) rat, TLR upregulation can suppress disease. In the BioBreeding Diabetes Resistant (BBDR) rat, however, diabetes induced by virus infection involves the upregulation of TLR9 pathways, and generic TLR upregulation synergizes with virus infection on diabetes induction. Studies performed in mouse models of T1D with spontaneous or induced T1D implicate TLR1, TLR2, TLR3, and TLR7 in disease mechanisms. The finding that TLR pathways are involved in mediating islet inflammation holds great promise for identifying new molecules that could potentially be targeted to specifically suppress the autoimmune process in individuals at high risk for disease development. The potential link between TLR upregulation and autoimmunity emphasizes the need for caution in using new therapies involving TLR agonists as vaccine adjuvants.

Innate Immune Pathways in Virus‐Induced Autoimmune Diabetes

We recently hypothesized that Toll-like receptor-induced innate upregulation by Kilham rat virus (KRV) in the BioBreeding diabetes-resistant (BBDR) rat model plays a key role in the mechanism of diabetes induction. To address this hypothesis, we analyzed innate immune signaling pathways upregulated by KRV in vitro and in vivo. We demonstrate that KRV activates the signal transducer and activator of transcription (STAT)-1 in spleen cells in vitro and that this activation can be blocked by TLR9 inhibition. We also show that KRV upregulates STAT-1 in pancreatic lymph nodes early after virus infection. Our data may implicate TLR9-induced STAT-1 signaling pathways in KRV-induced innate immune activation in the BBDR rat and raise the possibility that these pathways are involved in mediating autoimmune diabetes.

Prevention of diabetes: effect of mycophenolate mofetil and anti-CD25 on onset of diabetes in the DRBB rat

Anti-CD25 and mycophenolate mofetil (MMF) treatment of patients with new-onset diabetes is currently being tested as one of the trials in TrialNet. We tested the effectiveness of MMF and anti-CD25 in preventing autoimmune diabetes in the diabetes-resistant biobreeding (DRBB) rat. Autoimmune diabetes in the DRBB rat was induced with a Treg cell depletion regimen starting at 24-26 d of age. Treatment was started on the first day of the depletion regimen in the following groups: (i) control (vehicle); (ii) MMF 25 mg/kg/d intramuscularly daily for 8 wk; (iii) anti-CD25 0.8 mg/kg/d intraperitoneally 5 d/wk for 3 wk; and (iv) combination of MMF and anti-CD25. In a second set of experiments, treatments were started on day 5 of the depletion regimen (delayed treatment) with groups 1, 3, and 4. Rats that had diabetes-free survival for at least 30 d after the treatment was stopped underwent a second Treg depletion (redepletion). In each of the three treatment groups (n = 10/group), onset of diabetes was delayed or prevented in 20, 40 and 80% in groups 2, 3, and 4, respectively. After redepletion, diabetes-free survival was unchanged in group 2 and decreased to 10 and 30% in groups 3 and 4, respectively. With delayed treatment, groups 3 and 4 had 33 and 50% diabetes-free survival that decreased to 0 and 33% after redepletion. MMF and anti-CD25 alone or in combination are effective in delaying and preventing diabetes in the DRBB rat especially if treatment is started before stimulation and expansion of the autoreactive T cells.

TLR9-Signaling Pathways Are Involved in Kilham Rat Virus-Induced Autoimmune Diabetes in the Biobreeding Diabetes-Resistant Rat

Viral infections are associated epidemiologically with the expression of type 1 diabetes in humans, but the mechanisms underlying this putative association are unknown. To investigate the role of viruses in diabetes, we used a model of viral induction of autoimmune diabetes in genetically susceptible biobreeding diabetes-resistant (BBDR) rats. BBDR rats do not develop diabetes in viral-Ab-free environments, but approximately 25% of animals infected with the parvovirus Kilham rat virus (KRV) develop autoimmune diabetes via a mechanism that does not involve beta cell infection. Using this model, we recently documented that TLR agonists synergize with KRV infection and increase disease penetrance. We now report that KRV itself activates innate immunity through TLR ligation. We show that KRV infection strongly stimulates BBDR splenocytes to produce the proinflammatory cytokines IL-6 and IL-12p40 but not TNF-alpha. KRV infection induces high levels of IL-12p40 by splenic B cells and Flt-3-ligand-induced bone marrow-derived dendritic cells (DCs) but only low levels of IL-12p40 production by thioglycolate-elicited peritoneal macrophages or GM-CSF plus IL-4-induced bone marrow-derived DCs. KRV-induced cytokine production is blocked by pharmacological inhibitors of protein kinase R and NF-kappaB. Genomic KRV DNA also induces BBDR splenocytes and Flt-3L-induced DCs from wild-type but not TLR9-deficient mice to produce IL-12p40; KRV-induced up-regulation of B lymphocytes can be blocked by TLR9 antagonists including inhibitory CpG and chloroquine. Administration of chloroquine to virus-infected BBDR rats decreases the incidence of diabetes and decreases blood levels of IL-12p40. Our data implicate the TLR9-signaling pathway in KRV-induced innate immune activation and autoimmune diabetes in the BBDR rat.

Viruses Cause Type 1 Diabetes in Animals

More than 10 viruses have been reported to be associated with the development of type 1 diabetes-like symptoms in animals, with the best evidence coming from studies on the D variant of encephalomyocarditis (EMC-D) virus in mice and Kilham rat virus (KRV) in rats. A high titer of EMC-D viral infection results in the development of diabetes within 3 days, primarily due to the rapid destruction of beta cells by viral replication within the cells. A low titer of EMC-D viral infection results in the recruitment of macrophages to the islets. Soluble mediators produced by activated macrophages play a critical role in the destruction of residual beta cells. A single amino acid at position 776 of the EMC viral genome controls the diabetogenicity of the virus. In contrast, KRV causes autoimmune type 1 diabetes in diabetes-resistant BioBreeding (DR-BB) rats without direct infection of beta cells. Macrophages play an important role in the development of diabetes in KRV-infected DR-BB rats. As well, KRV infection preferentially activates effector T cells, such as Th1-like CD45RC(+)CD4(+) T cells and CD8(+) T cells, and downregulates regulatory T cells, such as Th2-like CD45RC(-)CD4(+) T cells. This results in the breakdown of the immune balance, contributing to the development of diabetes in KRV-infected DR-BB rats.

Diabetes-prone BioBreeding rats do not have a normal immune response when weaned to a diet containing fermentable fibre

Diet is known to modulate the development of diabetes in diabetes-prone BioBreeding (BBdp) rats. The objective of the present study was to determine the effect of fermentable fibre (FF) on immune function in BBdp and diabetes-resistant BioBreeding (BBdr) rats after weaning. Weanling BBdp (thirty-six to thirty-eight per diet) and BBdr rats (thirty to thirty-two per diet) were fed a nutritionally complete, semi-purified, casein-based diet containing either cellulose (control diet, 8 % w/w) or FF (3.2 % cellulose+4.8 % w/w inulin). At 35 d, the small intestine was excised and lymphocytes isolated from spleen, mesenteric lymph nodes and Peyer's patches. Feeding FF to both BBdr and BBdp rats affected the production of anti-inflammatory cytokines (P=0.02). In BBdr rats, feeding FF compared with cellulose resulted in an increased small intestinal length (P=0.0031), higher proliferative (stimulation) index from both splenocytes (P=0.001) and mesenteric lymph nodes (P=0.04), and an increased proportion of CD8+ T-cells in the Peyer's patches (P=0.003). We did not observe an effect of diet on the number of IgA-bearing cells in the jejunum from BBdr rats. Feeding FF to BBdp rats did not affect the same parameters. BBdp rats had both a higher proportion of B-cells in the Peyer's patches (P=0.01) and a higher number of IgA+ cells in the jejunum (P=0.0036) when fed a diet containing FF, a response not observed in BBdr rats. We demonstrate that several aspects of the BBdp immune system respond differently than that of BBdr rats when challenged at weaning with FF.

Unraveling the Pathogenesis of Type 1 Diabetes with Proteomics: Present And Future Directions

Type 1 diabetes (T1D) is the result of selective destruction of the insulin-producing beta-cells in the pancreatic islets of Langerhans. T1D is due to a complex interplay between the beta-cell, the immune system, and the environment in genetically susceptible individuals. The initiating mechanism(s) behind the development of T1D are largely unknown, and no genes or proteins are specific for most T1D cases. Different pro-apoptotic cytokines, IL-1 beta in particular, are present in the islets during beta-cell destruction and are able to modulate beta-cell function and induce beta-cell death. In beta-cells exposed to IL-1 beta, a race between destructive and protective events are initiated and in susceptible individuals the deleterious events prevail. Proteins are involved in most cellular processes, and it is thus expected that their cumulative expression profile reflects the specific activity of cells. Proteomics may be useful in describing the protein expression profile and thus the diabetic phenotype. Relatively few studies using proteomics technologies to investigate the T1D pathogenesis have been published to date despite the defined target organ, the beta-cell. Proteomics has been applied in studies of differentiating beta-cells, cytokine exposed islets, dietary manipulated islets, and in transplanted islets. Although that the studies have revealed a complex and detailed picture of the protein expression profiles many functional implications remain to be answered. In conclusion, a rather detailed picture of protein expression in beta-cell lines, islets, and transplanted islets both in vitro and in vivo have been described. The data indicate that the beta-cell is an active participant in its own destruction during diabetes development. No single protein alone seems to be responsible for the development of diabetes. Rather the cumulative pattern of changes seems to be what favors a transition from dynamic stability in the unperturbed beta-cell to dynamic instability and eventually to beta-cell destruction.

Immunoregulatory role of nitric oxide in Kilham rat virus-induced autoimmune diabetes in DR-BB rats.

Macrophages play a critical role in the pathogenesis of Kilham rat virus (KRV)-induced autoimmune diabetes in diabetes-resistant BioBreeding (DR-BB) rats. This investigation was initiated to determine the role of macrophage-derived soluble mediators, particularly NO, in the pathogenesis of KRV-induced diabetes in DR-BB rats. We found that the expression of inducible NO synthase (iNOS), an enzyme responsible for NO production, was significantly increased during the early phase of KRV infection. Inhibition of iNOS by aminoguanidine (AG) treatment resulted in the prevention of diabetes in KRV-infected animals. The expression of IL-1beta, TNF-alpha, and IL-12 was significantly decreased in the spleen of AG-treated, KRV-infected DR-BB rats compared with PBS-treated, KRV-infected control rats. Subsequent experiments revealed that AG treatment exerted its preventive effect in KRV-infected rats by maintaining the finely tuned immune balance normally disrupted by KRV, evidenced by a significant decrease in the expression of IFN-gamma, but not IL-4, and a decrease in Th1-type chemokine receptors CCR5, CXCR3, and CXCR4. We also found that iNOS inhibition by AG decreased the KRV-induced expression of MHC class II molecules and IL-2R alpha-chain, resulting in the suppression of T cell activation, evidenced by the decreased cytolytic activity of CD8(+) T cells. We conclude that NO plays a critical immunoregulatory role by up-regulating macrophage-derived proinflammatory cytokines, up-regulating the Th1 immune response, and activating T cells, leading to type 1 diabetes after KRV infection, whereas suppression of NO production by AG treatment prevents KRV-induced autoimmune diabetes in DR-BB rats.

The effect of immunomodulators on prevention of autoimmune diabetes is stage dependent: FTY720 prevents diabetes at three different stages in the diabetes-resistant biobreeding rat.

Autoimmune diabetes of the diabetes-resistant biobreeding (DRBB) rat shares similarities with diabetes in humans and has stages of diabetes that can be controlled and compared. FTY720 is an immunomodulator that has been efficacious in transplant and autoimmune models without inducing an immunosuppressed state. We determined the stages of diabetes that are affected by FTY720 in the DRBB rat. Autoimmune diabetes was induced with RT6.1 T-cell-depleting antibody and polyIC starting at 4 weeks of age. FTY720 (1 mg/kg/d) was started at day 0, 5, 7, and 14 following the start of depletion. The rats that did not develop diabetes were maintained for 60 d following the last dose of FTY720 before undergoing a second course of depletion. FTY720 starting at day 0, 5, 7, and 14 of depletion prevented diabetes in 100, 100, 50, and 20% of the DRBB rats compared to 0% of the control rats. The surviving rats in the 5-, 7-, and 14-d groups developed diabetes after FTY720 treatment was stopped. Histological examination indicated insulitis in the control rats between day 7 and 11 of depletion and end-stage insulitis by day 18 of depletion compared to negligible insulitis in rats without diabetes. Redepletion in the surviving day 0 rats resulted in development of diabetes in 25% of these rats compared to none of the age-matched controls. FTY720 can prevent autoimmune diabetes, if administered before and/or during stimulation and expansion of the autoreactive T cells or in the early stages of insulitis. The effectiveness diminishes with each successive stage of diabetes.