Increased H2O2, vascular endothelial growth factor and receptors in the retina of the BBZ/Wor diabetic rat.

Hyperglycemia in diabetes induces increased levels of hydrogen peroxide (H2O2), a reactive oxygen species generated by reduced nicotinamide adenine dinucleotide (NADH) oxidase. Nontoxic levels of H2O2 increase endothelial cell permeability. Using a model of non-insulin-dependent diabetes, the BBZ/Wor rat, we investigated retinal levels of H2O2, vascular endothelial growth factor (VEGF) and its receptors, VEGF-R1 and VEGF-R2 by transmission electron microscopy at sites of the blood-retinal barrier (BRB). H2O2 localization was done by the cerium NADH oxidase method, and extravasation of endogenous serum albumin was used to document disruption of the BRB. Higher levels of H2O2 were detected in blood vessels of diabetic (78.7 +/- 4.84%) as compared with vessels from nondiabetic rats (39.0 +/- 4.47%). VEGF immunoreactivity was statistically higher in the inner BRB (24.67 +/- 0.33 colloidal gold particles/63 microm2 vs. 21.52 +/- 0.43 colloidal gold particles/63 microm2, p = .0001) and outer BRB (42.56 +/- 0.45 colloidal gold particles/63 microm2 vs. 15.51 +/- 0.51 colloidal gold particles/63 microm2, p = .0001) of diabetic rats as compared with age matched nondiabetic control rats. VEGF-R1 immunoreactivity was significantly higher in diabetic retinas in both the inner BRB (21.66 +/- 0.75 colloidal gold particles/63 microm2 vs. 12.69 +/- 0.61 colloidal gold particles/63 microm2, p = .0001) and outer BRB (22.76 +/- 2.36 colloidal gold particles/63 microm2 vs. 8.53 +/- 2.67 colloidal gold particles/63 microm2, p = .0013). VEGF-R2 was statistically higher in the inner BRB (8.97 +/- 0.57 colloidal gold particles/63 microm2 versus 7.03 +/- 0.65 colloidal gold particles/63 microm2, p = .0419) but not in the outer BRB (29.42 +/- 1.25 colloidal gold particles/63 microm2 vs. 28.07 +/- 1.42 colloidal gold particles/63 microm2, p = .4889). H2O2 levels correlated with increased VEGF (correlation coefficient = 0.82, p = .001) in this model of nonproliferative diabetic retinopathy. These results support that hyperglycemia is one factor that induces retinal endothelial cells in vivo to increase H2O2 via NADH oxidase and stimulates increases in VEGF resulting in disruption of the BRB.

Increased NADH oxidase activity in the retina of the BBZ/Wor diabetic rat.

This morphological study demonstrates a role for endothelial cells in generating reactive oxygen species in early stages of retinopathy in the BBZ/Wor rat, an obese, noninsulin dependent model of diabetes. Hyperglycemia induced pseudohypoxia results in an imbalance in cytosolic NADH/NAD+. In the oxygen-rich environment of the retina, NADH oxidase generates superoxide radical which is dismutated to hydrogen peroxide. Localization of hydrogen peroxide by the cerium NADH oxidase enzyme activity cytochemical localization technique shows a statistically significant increase of peroxide localization in the central retina of diabetic rats as compared to age-matched, nondiabetic controls. Endothelial cell dysfunction, indicated by leakage of endogenous serum albumin, coincided with areas of NADH oxidase activity localization. In diabetic rats there are increased levels of fibronectin in areas of hydrogen peroxide localization. This in vivo, morphological study is the first demonstration of oxidative injury and endothelial cell dysfunction in the retina of a spontaneous, noninsulin dependent model of diabetes.

Kilham rat triggers T-cell-dependent autoimmune diabetes in multiple strains of rat.

Kilham rat virus (KRV) infection of BB/Wor diabetes-resistant (DR) RT1(u) rats induces autoimmune diabetes without direct cytolytic infection of pancreatic beta-cells and is a new model of virus-induced IDDM. To investigate genetic susceptibility to KRV-induced diabetes, major histocompatibility complex congenic and other inbred rats were infected with the virus and studied for the appearance of diabetes and insulitis. KRV infection alone induced insulitis, selective beta-cell necrosis, and diabetes in BB/Wor DR and LEW1.WR1 (RT1 A(u) B/D(u) C(a)) but not other rats. Thus, KRV, an environmentally ubiquitous rat parvovirus, can precipitate autoimmune diabetes in rats that are not susceptible to spontaneous diabetes. If rats are injected with poly(I.C) immediately before KRV infection, diabetes frequency increases to >90% in BB/Wor DR and LEW1.WR1 rats, and PVG.RT1(u) rats are converted from KRV-resistant to KRV-susceptible status. Susceptibility to KRV-induced diabetes thus requires the presence of class I A(u) and class II B/D(u) gene products, which are shared by DR, LEW1.WR1, and PVG.RT1(u) rats. The RT1(u) haplotype is not sufficient for susceptibility, however, because while WF rats are RT1(u), they resist KRV-induced diabetes. If rats are depleted of RT6.1+ regulatory T-cells before KRV infection, the frequency of diabetes is dramatically increased in DR and LEW1.WR1, but not PVG.RT1(u) or other rats. These data confirm a regulatory role of RT6.1+ T-cells in diabetes induction, but indicate that they may not operate as such in all rat strains. KRV-induced diabetes is T-cell-mediated: DR and LEW1.WR1 rats are protected from diabetes by treatment with monoclonal antibodies directed against alpha beta T-cell receptor (TCR)+, CD5+, and CD8+ T-cells. Concanavalin A-activated spleen cells from KRV-infected DR rats adoptively transfer diabetes and insulitis into class II(u) compatible rats, suggesting that KRV infection of susceptible rats leads to the activation of diabetogenic class II(u) restricted T-cells. The ability of a common rat virus to initiate IDDM in multiple strains of rats strengthens the possibility that viruses may also initiate IDDM in human populations.

Genetics of the BB rat: association of autoimmune disorders (diabetes, insulitis, and thyroiditis) with lymphopenia and major histocompatibility complex class II.

The BB/Wor rat develops spontaneous autoimmune diabetes mellitus and also frequently develops lymphocytic thyroiditis. To clarify the role of T cell lymphopenia and the major histocompatibility complex (MHC) in the development of these autoimmune disorders, we studied back-cross animals between the inbred thyroiditis and diabetes-prone BBNB/Wor subline (MHC RT1.AuBuDuCu) and three nonlymphopenic MHC-congenic rat strains: PVG.RT.1u (RT1.AuBuDuCu), PVG.R8 (RT1.AaBuDuCu), and PVG.R23 (RT1.AuBaDaCav1). We observed that 1) lymphopenia is absolutely required for the development of spontaneous diabetes and insulitis, and is usually associated with the development of thyroiditis; 2) the MHC region to the right of the class I RT1.A locus is strongly correlated with diabetes and insulitis; and 3) this region is also significantly associated with the development of thyroiditis, but the susceptibility of certain MHC class II alleles (u and a) for disease development is distinct for insulitis and thyroiditis. Furthermore, no recombination was observed between lymphopenia (lyp) and the neuropeptide Y (Npy) gene polymorphism, which confirmed that lyp maps very close to Npy. The present data suggest that spontaneous insulitis and thyroiditis in the BB/Wor rat develop through common immune defects involving T cell lymphopenia, but do not always segregate together due to disease-specific interactions with the MHC class II-linked genes.

Preservation of GLUT 2 expression in islet beta cells of Kilham rat virus (KRV)-infected diabetes-resistant BB/Wor rats.

Loss of GLUT 2, the glucose transporter isoform of pancreatic beta cells, has been reported to accompany the onset and perhaps contribute to the pathogenesis, of insulin-dependent and non-insulin-dependent diabetes mellitus in BB/Wor and Zucker fatty rats. In this study we investigated the effect of Kilham Rat Virus infection on GLUT2 expression in diabetes-resistant BB/Wor rats. Viral antibody-free diabetes-resistant rats do not develop spontaneous diabetes, but inoculation with Kilham Rat Virus induces autoimmune beta-cell destruction and hyperglycaemia. Pancreas sections from normoglycaemic diabetes-resistant BB/Wor rats were obtained 5, 7 and 25 days after inoculation with Kilham Rat Virus and stained for GLUT2 using a rabbit polyclonal antibody. At all time points, beta cells displayed GLUT2 expression comparable to uninfected diabetes-resistant controls. Immunostained insulin content of the beta cells also remained unchanged. Sections were also examined from Kilham Rat Virus inoculated diabetes-resistant rats with lymphocytic insulitis or diabetes. GLUT2 and insulin immunostaining were unchanged in non-diabetic rats with early insulitis. GLUT2 beta-cell staining was variably reduced in diabetic rats with established insulitis and reduced beta-cell insulin immunostaining. Hence, the initial stages of Kilham Rat Virus-induced diabetes in diabetes-resistant rats are not accompanied by a significant reduction in GLUT2 expression. These results suggest that the loss of GLUT2 does not play a significant role in the aetiology of diabetes in the Kilham Rat Virus-infected diabetes-resistant BB/Wor rat.

The BBZ/Wor rat: clinical characteristics of the diabetic syndrome.

The BBZ/Wor rat is a model of obesity and autoimmune diabetes mellitus developed by crossing the BB/Wor and Zucker rats. We studied circulating glucose and insulin levels, islet morphology and lymphocyte subsets in lean and obese BBZ/Wor rats before and after the onset of diabetes, and studied the clinical course of diabetes in animals after interruption of exogenous insulin therapy. Lean BBZ/Wor rats developed insulin-dependent diabetes and died in ketoacidosis within 1 week after cessation of insulin injections. Diabetes also developed in obese rats, but these animals were not insulin-dependent and survived for months without insulin therapy. The islets of the lean diabetic rats revealed complete destruction of pancreatic beta cells and plasma insulin levels were virtually undetectable. In contrast, the islets of the obese rats revealed insulitis and substantial beta-cell loss, however autoimmune beta-cell destruction was incomplete, and residual beta cells were presumably responsible for the presence of measurable levels of plasma insulin and the long-term survival of obese diabetics without insulin therapy. Obese rats were hyperinsulinaemic, developed diabetes significantly earlier, and with a greater incidence than lean rats, suggesting a possible relationship between enhanced beta-cell metabolic activity and immune destruction. Obese males became diabetic more frequently and at an earlier age than obese females and lean rats of both sexes, suggesting a role for gender in the pathogenesis of diabetes. We conclude that the BBZ/Wor rat is a unique animal model for investigating the interaction of obesity, beta-cell metabolism, autoimmune insulitis and genetic predisposition to diabetes.

Induction of type I diabetes by Kilham's rat virus in diabetes-resistant BB/Wor rats.

Type I diabetes mellitus is an autoimmune disease resulting from the interaction of genetic and environmental factors. A virus that was identified serologically as Kilham's rat virus (KRV) was isolated from a spontaneously diabetic rat and reproducibly induced diabetes in naive diabetes-resistant (DR) BB/Wor rats. Viral antigen was not identified in pancreatic islet cells, and beta cell cytolysis was not observed until after the appearance of lymphocytic insulitis. KRV did not induce diabetes in major histocompatibility complex-concordant and discordant non-BB rats and did not accelerate diabetes in diabetes-prone BB/Wor rats unless the rats had been reconstituted with DR spleen cells. This model of diabetes may provide insight regarding the interaction of viruses and autoimmune disease [corrected]

Influence of environmental viral agents on frequency and tempo of diabetes mellitus in BB/Wor rats.

Elimination of environmental viruses by cesarean derivation of the University of Massachusetts colony of BB/Wor rats increased the frequency and accelerated the tempo of spontaneous diabetes among diabetes-prone (DP) rats. In contrast, the viral-antibody-free (VAF) environment did not alter the resistance of pre-VAF diabetes-resistant (DR) rats to spontaneous and RT6+ T-lymphocyte-depletion-induced diabetes. Pre-VAF and VAF rats have essentially the same lymphocyte subsets, and VAF-DP rats are susceptible to the adoptive transfer of diabetes and to the diabetes-accelerating effects of polyinosinic-polycytidylic acid injections. These results suggest that the presence of environmental viral pathogens may act to inhibit effector cell function in lymphopenic DP rats while enhancing effector cell activity in nonlymphopenic DR rats.

Genetic studies in inbred BB/Wor rats. Analysis of progeny produced by crossing lymphopenic diabetes-prone rats with nonlymphopenic diabetic rats.

BB/Wor diabetes-prone (DP) rats are lymphopenic and frequently develop insulin-dependent diabetes. Diabetes-resistant (DR) BB/Wor rats are not lymphopenic and become diabetic rarely and at a significantly younger age. To examine the genetic basis for diabetes, lymphopenia, and age at onset of diabetes among inbred BB/Wor rats, we crossed nonlymphopenic diabetic rats with lymphopenic DP animals and studied F1, F2, and backcross progeny. F1 rats were neither diabetic nor lymphopenic. Diabetes (both types) and lymphopenia reappeared among F2 rats, confirming the permissive association of diabetes and lymphopenia and the recessive nature of both. The absence of diabetes in F1 rats also suggested that the combination of genes responsible for diabetes among lymphopenic and nonlymphopenic rats may be distinct. Nonlymphopenic parental, F1, and F2 rats revealed normal lymphocyte subsets, including CD8+ and RT6+ T-lymphocytes. Lymphopenic parental and F2 rats revealed the absence of CD8+ and RT6+ cells, indicating that these T-lymphocyte abnormalities of lymphopenic DP rats segregate with the lymphopenia gene. The distribution of the ages at onset of diabetes among F2 lymphopenic and F2 intercross rats was significantly earlier than among lymphopenic parental and backcross animals, suggesting that the age of diabetes onset is a heritable trait and that the gene(s) or genetic modifier(s) responsible for the earlier onset of F2 diabetes was acquired from the nonlymphopenic parents. Our genetic studies also confirmed the observations that the 2- and 7-kilobase Bam HI fragments of the MHC class I region do not correlate with diabetes or lymphopenia.

Glomerulopathy in spontaneously diabetic rat. Impact of glycemic control.

The spontaneously diabetic BioBreeding/Worcester (BB/W) rat was used to examine the role of glycemic control in the pathogenesis of diabetic glomerulopathy and proteinuria. Nondiabetic BB/W rats (group 1) were compared with moderately (group 2) and severely (group 3) hyperglycemic diabetic animals of similar age. Urinary protein excretion and morphometric measurements of glomerular basement membrane (GBM) width and mesangial area were performed after 4, 8, and 12 mo of study. At 4 mo, urinary protein excretion both in group 2 (9.3 +/- 0.7 mg/24 h) and group 3 (24.8 +/- 1.98 mg/24 h) exceeded that in group 1 (5.4 +/- 0.6 mg/24 h; P less than .05). Moreover, proteinuria in group 3 was significantly greater than in group 2 (P less than .05). In addition, proteinuria increased in group 3 animals between 4 and 12 mo of study but did not advance in groups 1 or 2. GBM width in both diabetic groups (168.8 +/- 2.4 and 165.7 +/- 2.2 nm, groups 2 and 3, respectively) exceeded that in group 1 (148.3 +/- 3.8 nm; P less than .01) by 4 mo. At 12 mo, severely hyperglycemic group 3 animals had significantly greater GBM thickening than group 2. GBM width increased in all three groups over the course of study, but the rate of growth did not differ between groups 1 and 2. However, the rate of growth in group 3 was greater than in either group 1 or group 2. Urinary protein excretion correlated significantly with GBM width in diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of diabetes in BioBreeding/Worcester rats with monoclonal antibodies that recognize T lymphocytes or natural killer cells.

Diabetes-prone BioBreeding/Worcester (BB/Wor) rats received thrice weekly injections of mAb against antigens expressed on the surface of all T cells (OX19), cytotoxic/suppressor, and NK cells (OX8), helper/inducer cells (W3/25, OX35, OX38), and Ia+ cells (OX6, 3JP, OX17). Treatment with OX8 or OX19 achieved stable reductions of splenic and peripheral blood NK cells and helper/inducer T lymphocytes, respectively, and protected against diabetes. OX19 injections also prevented lymphocytic insulitis, thyroiditis, and the synthesis of autoantibodies to thyroid colloid and smooth muscle antigens. OX8 injections reduced splenic NK-mediated YAC-1 cell lysis, but did not prevent insulitis, thyroiditis, or autoantibody synthesis. Injections of mAb specific for antigens on the surface of helper/inducer cells, and for cells expressing IaE antigens provided marginal protection against diabetes without reductions of phenotypic subsets. These findings suggest that pancreatic beta cell destruction in the spontaneously diabetic BB/Wor rat is mediated by the combined action of NK and helper/inducer cells.

Diabetic BioBreeding/Worcester (BB/Wor) rats need not be lymphopenic.

The BB/Wor rat is an animal model of spontaneous autoimmune type I diabetes mellitus. Previous reports have emphasized the presence of lymphopenia in all diabetic and diabetes-prone BB rats. This manuscript reports the appearance of diabetes among three family lines of BB/Wor animals that were previously free of diabetes. Diabetic W-line rats are not lymphopenic and possess normal percentages of phenotypic T cell subsets. Hence the presence of lymphopenia is not obligatory for the occurrence of diabetes in BB/Wor rats.

Prevention of diabetes mellitus in the BB/W rat with Cyclosporin-A.

Autoimmune diabetes mellitus occurs spontaneously in 40-60% of a colony of BioBreeding/Worcester rats. Pretreatment of susceptible animals for 10-day intervals prior to 70 days of age with Cyclosporin-A (CSA) significantly reduced the frequency and delayed the onset of diabetes. The relatively narrow time frame of successful treatment suggests that effector cells responsible for beta cell destruction in this model of Type I diabetes may be activated during this period of time prior to the onset of overt hyperglycemia. CSA administration did not protect against the occurrence of lymphocytic thyroiditis or autoantibodies directed against smooth muscle or thyroid colloid, suggesting that these BB immunologic phenomena may be controlled by a distinct series of immunologic events.

The effect of inbreeding on the BB/W diabetic rat.

The Worcester colony of BB/W diabetic rats has been inbred by brother X sister matings for 12 generations. The litter size at both birth and weaning was dependent on whether the female was normal or diabetic. At the beginning of the inbreeding, the normal females produced 2.1 more young per litter than did the diabetic females, but the eleventh generation of inbreeding this difference had been reduced to 0.68 young. Diabetic males had little influence on litter size. At weaning, the normal mothers had raised litters that had 3.64 more young than the diabetics in the early generations, but this had dropped to 1.48 in later generations. After 11 generations of inbreeding, there was a 1.95 decrease in litter size from normal matings, but only a 0.86 decrease from diabetic matings. The average loss from birth to weaning was one pup for normal females and two pups for diabetic females. The time of onset (median 85 days) has not changed with inbreeding, nor is the onset pattern and severity different in any of the nine inbred lines. The penetrance in the D X D matings did change from 45% in the first five generations to 60% in the next six, but there has been no significant change in generations 6 through 11. Inbreeding changed the results obtained from outcrossing to nondiabetic lines. All crosses produced no diabetics in the F1, but noninbreds produced less than 2% in the F2 and 4% in the BC, whereas inbreds produced 18 to 32% in the BCs. These latter figures are consistent with the ratio of 7:3 expected with 60% penetrance.

Spontaneous diabetes mellitus in the BB/W rat. Effects of glucocorticoids, cyclosporin-A, and antiserum to rat lymphocytes.

Combination immunosuppression therapy with long-acting glucocorticoids, cyclosporin-A, and antiserum to rat lymphocytes (ALS) reduced the severity of spontaneous diabetes among BioBreeding/Worcester rats and decreased the frequency of diabetes in susceptible littermates. Combination therapy with glucocorticoids and three injections of ALS reversed hyperglycemia in a significant number of acutely diabetic animals. These results strengthen the hypothesis that autoimmunity plays a role in the pathogenesis of diabetes in these animals and increase our understanding of the requirements of treatment protocols for the prevention and cure of this spontaneous syndrome.

Genetic analysis of the BB/W diabetic rat.

A large colony of BB/W diabetic rats has been developed as a research model for insulin dependent, type 1 diabetes mellitus. The foundation stock had 8% diabetics which appeared in a sporadic manner. The Worcester (W) colony was inbred by brother X sister matings for 11 generations and the proportion of diabetics increased to over 50%. The age of detection varies from 46 to 250 days. For selection purposes, classification was made at 120 days, which means that 15 to 20% potential diabetics were classified as normal. Evidence from different analyses indicates that the inheritance of diabetes is by a recessive gene or gene cluster with 50% penetrance at 120 days. The selection of breeding stock from diabetic parents raised the proportion of diabetics produced by two normal parents from 12 to 43%. Diallel tests show that diabetic and normal offspring of two diabetic parents have the same diabetic genotype. Outcrosses to other strains of rat indicate that the trait is transferred as a recessive with only 3% diabetics recovered in the F2 where noninbred BB stock was used as the diabetic source, and 36% where partially inbred BB/W was used as the diabetic parent. Since the proportion of diabetics produced by all types of crosses has changed, and may continue to change with changes in the genetic background, we have used the operational term penetrance to describe the frequency of diabetes in individuals homozygous for the diabetes gene cluster. At present the penetrance at 120 days is 59% in the BB/W colony.

Spontaneous diabetes mellitus: reversal and prevention in the BB/W rat with antiserum to rat lymphocytes.

Injections of rabbit antiserum to rat lymphocytes reversed hyperglycemia in 36 percent of spontaneously diabetic rats (Bio Breeding/Worcester) and prevented diabetes in susceptible nondiabetic controls. These findings strengthen the hypothesis that cell-mediated autoimmunity plays a role in the pathogenesis of diabetes in this animal model that mimics many morpholigic and physiologic characteristics of human insulin-dependent diabetes mellitus.