Endocrine pancreas histology of congenic BB-rat strains with reduced diabetes incidence after genetic manipulation on chromosomes 4, 6 and X

Congenic BB.SHR rat strains were established by crossing of spontaneously diabetic BB/OK rats and diabetes-resistant SHR rats. Chromosomal regions on which the genes Iddm 4 (BB.6s), Iddm6 (BB.Xs) and Iddm 2 (BB.LL) are located were exchanged. As a result of genetic manipulation diabetes incidence was markedly reduced from 80% in BB/OK to 50% in BB.SHR (Chr. X), to 14% in BB.SHR (Chr. 6) and to 0% in BB.LL rats. Pancreata of these newly generated BB.SHR rats were investigated histologically. In newly diagnosed diabetic rats of congenic strains pancreatic insulin content (BB.6s: p < 0.05; BB.Xs p < 0.01) and relative volume of insulin-positive cells (BB.Xs: p < 0.001) were significantly higher than in BB/OK rats. The degree of insulitis was not different in 90-day-old and newly diagnosed diabetic animals. Surprisingly, in 30-day-old rats we observed an increase of the degree of insulitis with decreasing diabetes incidence. We suppose that by an earlier occurrence of the immunological beta-cell destruction, a part of the animals is able to develop a secondary diabetes resistance. The exchange of the BB-lymphopenia gene by that of SHR-rats prevented the development of hyperglycaemia without altering the auto-reactive immune response, which could be observed in all animals investigated.     

Phenotypical characterization of the cells invading pancreatic islets of diabetic BB/OK rats: effect of interleukin 2 receptor-targeted immunotherapy

We investigated immunohistochemically the phenotypes of mononucleated cells invading pancreatic islets of diabetic BB/OK rats in comparison to the diabetes-resistant parental strain, and 12 and 120 days after a temporary treatment (10 days) with a monoclonal antibody (1 mg/kg b.w.) directed against interleukin 2 receptor (IL 2R) combined with a subtherapeutic dose of cyclosporin A (1.5 mg/kg b.w.). Using a panel of monoclonal antibodies (OX-19, OX-8, W3/25, KI-M2R, OX-6, OX-17, ART-18) and the alkaline phosphatase anti-alkaline phosphatase system to visualize the bound primary antibodies, we observed an even distribution of mononucleated cells across the endocrine pancreas at a "background" level when obtained from diabetes-resistant parental rat strain. Diabetic BB/OK rats, characterized by a moderate hyperglycemia and a marked decrease of pancreatic insulin content, displayed a remarkable accumulation of mononucleated cells in the endocrine pancreas. Morphometric studies revealed an increase of all phenotypes investigated, nearly all mononucleated cells expressed class II histocompatibility antigens (OX-6+, OX-17+) and the number of cells expressing the IL 2R (ART-18+) was markedly enhanced. Sixty-seven percent of the immunotherapeutically treated BB/OK rats normalized plasma glucose and enhanced pancreatic insulin content. The successfully treated animals are characterized by a decrease of cells invading pancreatic islets (OX-19+, OX-8+, W3/25+, KI-M2R+), a decrease of class II histocompatibility antigen and IL 2R expression. The number of IL 2R cells is also diminished in the endocrine pancreas of unsuccessfully treated BB rats.     

Diabetes mellitus in the BB/W rat. Insulitis in pancreatic islet grafts after transplantation in diabetic recipients.

Spontaneous diabetes mellitus in the BioBreeding/Worcester (BB/W) rat is preceded by lymphocytic insulitis which destroys pancreatic beta cells. Cultured major histocompatibility complex identical pancreatic islets and adrenal cortex derived from diabetes-resistant BB/W donors were transplanted into diabetic recipients with hyperglycemia of variable duration. Islet grafts were the targets of BB/W immune attack and revealed lymphocytic insulitis after transplantation into diabetic recipients even in the absence of insulitis within endogenous pancreatic islets. These findings suggest that the BB/W immune attack on pancreatic beta cells can recur in islet grafts long after the onset of the diabetic syndrome.     

Endocrine Pancreas Histology of Congenic BB-Rat Strains with Reduced Diabetes Incidence After Genetic Manipulation on Chromosomes 4, 6 and X

Congenic BB.SHR rat strains were established by crossing of spontaneously diabetic BB/OK rats and diabetes-resistant SHR rats. Chromosomal regions on which the genes Iddm 4 (BB.6s), Iddm6 (BB.Xs) and Iddm 2 (BB.LL) are located were exchanged. As a result of genetic manipulation diabetes incidence was markedly reduced from 80% in BB/OK to 50% in BB.SHR (Chr. X), to 14% in BB.SHR (Chr. 6) and to 0% in BB.LL rats. Pancreata of these newly generated BB.SHR rats were investigated histologically. In newly diagnosed diabetic rats of congenic strains pancreatic insulin content (BB.6s: p<0.05; BB.Xs p<0.01) and relative volume of insulin-positive cells (BB.Xs: p<0.001) were significantly higher than in BB/OK rats. The degree of insulitis was not different in 90-day-old and newly diagnosed diabetic animals. Surprisingly, in 30-day-old rats we observed an increase of the degree of insulitis with decreasing diabetes incidence. We suppose that by an earlier occurrence of the immunological β-cell destruction, a part of the animals is able to develop a secondary diabetes resistance. The exchange of the BB-lymphopenia gene by that of SHR-rats prevented the development of hyperglycaemia without altering the auto-reactive immune response, which could be observed in all animals investigated.     

Prevention of autoimmune but not allogeneic destruction of grafted islets by different therapeutic strategies

Grafting autoimmune-diabetic recipients with allogeneic islets, graft rejection and disease recurrence as major problems of reaching indefinite survival and tolerance induction have to be solved. Anti-CD25 and anti-CD4 monoclonal antibodies were successfully used after allogeneic islet transplantation in experimentally diabetic rats. A temporary anti-CD25 therapy also prevented disease recurrence in autoimmune-diabetic BB rats, while this was not yet reported for an anti-CD4 treatment. In autoimmune-diabetic NOD mice disease recurrence can be successfully treated using an anti-CD4 monoclonal antibody. We, therefore, compared the efficacy of a short-term anti-CD25 and anti-CD4 treatment regarding the prevention of allograft rejection and disease recurrence in autoimmune-diabetic BB/OK rats. Both monoclonal antibodies were combined with low doses of Cyclosporin A. Untreated BB/OK rats relapsed into hyperglycaemia within 3 weeks independent of the islet donor, LEW.1A, LEW.1BB/OK or BB/OK rats. However, after grafting MHC-identical allogeneic (LEW.1BB/OK) or syngeneic (BB/OK) islets we observed about 30% spontaneous acceptance. Both the anti-CD25 and anti-CD4 therapy significantly prolonged the survival of allogeneic grafted islets. After MHC-identical allogeneic and syngeneic islet transplantation the temporary immunotherapy increased the proportion of permanent acceptors to 63% and 75%, respectively. The efficacy of both treatment strategies in prolonging allograft survival and prevention of disease recurrence was identical. In summary, anti-CD25 as well as anti-CD4 therapy prevented autoimmune but not allogeneic islet destruction in autoimmune-diabetic BB/OK rats. In conclusion, targeting different immune cells by monoclonal antibodies with different specificities can lead to very similar results with respect to an interruption of allograft rejection and autoimmune reaction.     

Prophylactic insulin treatment of diabetes-prone BB/OK rats by application of a sustained release insulin implant

Normoglycemic diabetes-prone BB/OK rats aged 33, 45 or 75 days were subjected to prophylactic insulin treatment by means of a single subcutaneous application of a sustained release insulin implant. The single application of a sustained release insulin implant decreased the incidence of diabetes or delayed the onset of the disease in BB/OK rats of all treatment groups. Prophylactic insulin administration caused a transient hypoglycemic period accompanied by an inhibition of glucose stimulated insulin secretion and a decrease of the insulin content of Langerhans' islets as detectable in vitro. Compared to islets of normoglycemic controls pancreatic islets isolated from hypoglycemic BB/OK rats within 7-21 days after the insulin application at 45 days of age displayed a decreased susceptibility of the cells to complement-dependent cytotoxicity of the monoclonal islet cell surface antibody (ICSA) K14D10 but not to the cytotoxic effect of the ICSA M3aG8. The appearance of complement-dependent antibody-mediated cytotoxicity to islet cells and pancreatic exocrine cells in serum regarded as a sign of immune dysregulation in BB/OK rats seems not to be affected by insulin prophylaxis and was detectable during hypoglycemia as well as in the subsequent normoglycemic state. In conclusion, BB/OK rats of different age can be protected from diabetes by a single application of a sustained release insulin implant. Insulin and/or hypoglycemia seem to influence the expression of cell surface antigens, thus render the islets of Langerhans less vulnerable to immune cytolysis, whereas the appearance of humoral immunological abnormalites is not affected.     

Prophylactic Insulin Treatment of Diabetes-prone BB/OK Rats by Application of a Sustained Release Insulin Implant

Normoglycemic diabetes-prone BB/OK rats aged 33, 45 or 75 days were subjected to prophylactic insulin treatment by means of a single subcutaneous application of a sustained release insulin implant. The single application of a sustained release insulin implant decreased the incidence of diabetes or delayed the onset of the disease in BB/OK rats of all treatment groups. Prophylactic insulin administration caused a transient hypoglycemic period accompanied by an inhibition of glucose stimulated insulin secretion and a decrease of the insulin content of Langerhans' islets as detectable in vitro . Compared to islets of normoglycemic controls pancreatic islets isolated from hypoglycemic BB/OK rats within 7-21 days after the insulin application at 45 days of age displayed a decreased susceptibility of the cells to complement-dependent cytotoxicity of the monoclonal islet cell surface antibody (ICSA) K14D10 but not to the cytotoxic effect of the ICSA M3aG8. The appearance of complement-dependent antibody-mediated cytotoxicity to islet cells and pancreatic exocrine cells in serum regarded as a sign of immune dysregulation in BB/OK rats seems not to be affected by insulin prophylaxis and was detectable during hypoglycemia as well as in the subsequent normoglycemic state. In conclusion, BB/OK rats of different age can be protected from diabetes by a single application of a sustained release insulin implant. Insulin and/or hypoglycemia seem to influence the expression of cell surface antigens, thus render the islets of Langerhans less vulnerable to immune cytolysis, whereas the appearance of humoral immunological abnormalites is not affected.     

Brain-reactive autoantibodies in BB/d rats do not recognize glutamic acid decarboxylase.

The BB rat spontaneously develops insulin-dependent diabetes mellitus (IDDM) similar to that in humans. The most practical markers of beta cell autoimmunity are circulating antibodies to islet cell components. In particular autoantibodies to the enzyme glutamic acid decarboxylase (GAD) are a common feature of IDDM development in humans. This study aims at investigating the prevalence and levels of autoantibodies in BB rats to antigens in a semipurified, GAD-enriched preparation from rat brain. Eighteen diabetes-prone BB/d rats (10 male and eight female) were tail bled weekly from age 28 days to 113 days and antibodies detected on the rat brain preparation by ELISA. Antibody levels were expressed as arbitrary units relative to a standard positive serum. Individual rats varied in the time and order of antibody appearance and IDDM onset, with the earliest occurrence being 42 days and 69 days, respectively. In some rats antibody production was maintained but declined in others. By 113 days 85% of diabetic rats had at some time been positive for autoantibodies to brain components, compared with 25% of non-diabetics (P = 0.09 by Fisher's exact test). Immunoabsorption studies using recombinant rat GAD-65 or recombinant human GAD-67 failed to inhibit the binding of BB rat sera to the original rat brain preparation. A capture ELISA using GAD-6 MoAb to capture GAD-65 from rat brain preparation or from a preparation of recombinant rat GAD-65, failed to detect anti-GAD antibodies in BB rats. Immunofluorescent staining of tissue sections showed the autoantibodies to be brain-specific, but having distinct staining patterns to the anti-GAD antibodies of Stiff Man Syndrome serum. In conclusion, BB rats possess autoantibodies reactive with rat brain antigens which may be associated with IDDM. However, these are not directed against GAD.     

The relationship between insulin autoantibodies and islet cell histology in the diabetes prone BB rat.

The relationship between insulin autoantibodies (IAA) and pancreatic islet cell histology was examined in 71 diabetes prone BB rats from the Toronto colony. Twenty-seven of the 71 became diabetic and of these, 18 (67%) were IAA positive by ELISA. IAA were also detected in 39/44 (89%) which did not develop diabetes, but in none of six control animals at 50-140 days of age. All 27 which became diabetic showed some evidence of lymphocytic infiltration scored + to ++++ histometrically and 26/27 evidence of beta cell degranulation. The frequency of diabetes increased with both intensity of insulitis and degree of beta cell degranulation, but there was no correlation between either and IAA. IAA are a marker for the BB strain of Wistar rat, but do not correlate with islet cell histology and do not predict clinical diabetes.     

Major histocompatibility complex gene product expression on pancreatic beta cells in acutely diabetic BB rats.

Type I diabetes mellitus was induced in young, diabetes-prone BB rats by the passive transfer of concanavalin A-activated T lymphocytes from the spleens of acutely diabetic BB rats. The pancreas of the recipients was examined 1-2 days after the onset of glycosuria by immunocytochemistry by means of monoclonal antibodies for determining whether 1) Class I and/or II major histocompatibility gene complex (MHC) products were expressed on beta cells and 2) the mononuclear cell infiltrates were represented by T cells. Marked expression of Class I MHC gene products was evident on beta cells. In contrast, Class II MHC gene products were not identified on normal-appearing beta cells. Dendritic cells dispersed throughout the acinar and interstitial pancreas were markedly increased in number. The mononuclear cell infiltrate contained few cells (1-15%) recognized by a pan-T cell marker. Although it is possible that this passive transfer model might differ considerably from the spontaneously occurring diabetic state in the rat, this study suggests that 1) Class I, rather than Class II, MHC gene expression may be pivotal to beta-cell injury in diabetic rats, and 2) non-T cells may constitute an effector cell population central to beta-cell necrosis in Type I diabetes mellitus.     

Antioxidant enzyme activity and mRNA expression in the islets of Langerhans from the BB/S rat model of type 1 diabetes and an insulin-producing cell line

It has been proposed that low activities of antioxidant enzymes in pancreatic beta cells may increase their susceptibility to autoimmune attack. We have therefore used the spontaneously diabetic BB/S rat model of type 1 diabetes to compare islet catalase and superoxide dismutase activities in diabetes-prone and diabetes-resistant animals. In parallel studies, we employed the RINm5F beta cell line as a model system (previously validated) to investigate whether regulation of antioxidant enzyme activity by inflammatory mediators (cytokines, nitric oxide) occurs at the gene or protein expression level. Diabetes-prone rat islets had high insulin content at the age used (58–65 days) but showed increased amounts of DNA damage when subjected to cytokine or hydrogen peroxide treatments. There was clear evidence of oxidative damage in freshly isolated rat islets from diabetes-prone animals and significantly lower catalase and superoxide dismutase activities than in islets from age-matched diabetes-resistant BB/S and control Wistar rats. The mRNA expression of antioxidant enzymes in islets from diabetes-prone and diabetes-resistant BB/S rats and in RINm5F cells, treated with a combination of cytokines or a nitric oxide donor, DETA-NO, was analysed semi-quantitatively by real time PCR. The mRNA expression of catalase was lower, whereas MnSOD expression was higher, in diabetes-prone compared to diabetes-resistant BB/S rat islets, suggesting regulation at the level of gene expression as well as of the activities of these enzymes in diabetes. The protein expression of catalase, CuZnSOD and MnSOD was assessed by Western blotting and found to be unchanged in DETA-NO treated cells. Protein expression of MnSOD was increased by cytokines in RINm5F cells whereas the expression of CuZnSOD was slightly decreased and the level of catalase protein was unchanged. We conclude that there are some changes, mostly upregulation, in protein expression but no decreases in the mRNA expression of catalase, CuZnSOD or MnSOD enzymes in beta cells treated with either cytokines or DETA-NO. The lower antioxidant enzyme activities observed in islets from diabetes-prone BB/S rats could be a factor in the development of disease and in susceptibility to DNA damage in vitro and could reflect islet alterations prior to immune attack or inherent differences in the islets of diabetes-prone animals, but are not likely to result from cytokine or nitric oxide exposure in vivo at that stage.     

Identification of T cell subsets and class I and class II antigen expression in islet grafts and pancreatic islets of diabetic BioBreeding/Worcester rats

The BioBreeding/Worcester (BB/Wor) rat develops a spontaneous disorder that closely resembles human insulin-dependent (Type I) diabetes mellitus. The syndrome is preceded by lymphocytic insulitis that destroys pancreatic beta cells. The morphologic features of the spontaneous insulitis lesions are also observed within islets transplanted beneath the renal capsule of diabetes-prone and diabetic animals. This study reports the results of experiments in which immunohistochemical techniques were used to characterize the phenotype of the infiltrating mononuclear cells and detect the expression of class I and class II MHC antigens in native islets and islet transplants in diabetic and diabetes-prone BB/Wor rats. The infiltrates within native pancreatic islets and islet grafts were comprised predominantly of Ia+ cells (dendritic cells and macrophages) CD4+ cells (helper/inducer lymphocytes and macrophages), CD5+ (pan-T) cells and smaller numbers of CD8+ (cytotoxic/suppressor and NK) cells. Pancreatic and graft insulitis were accompanied by markedly enhanced class I antigen expression on islet and exocrine cells. Class II (Ia) antigens were not detected on normal islet cells, islets undergoing insulitis or on islet transplants subjected to immune attack. In islet grafts stained with polymorphic MAbs that distinguish Ia antigens of donor and host origin, Ia antigen expression was limited to infiltrating dendritic cells and macrophages of host origin. It is concluded that the phenotypes of infiltrating mononuclear cells that comprise the insulitis lesion in spontaneous BB/Wor diabetes, and the inflammatory attack on islets transplanted into diabetic BB/Wor rats are the same, that pancreatic islet and graft insulitis occur in the presence of enhanced class I antigen expression but in the absence of class II antigen expression, and that infiltrating Ia+ cells within islet grafts are exclusively of recipient (BB/Wor) origin and may explain the initiation of immune insulitis within grafts derived from donors of incompatible MHC.     

Effects of ginkgolide B, a platelet-activating factor inhibitor on insulitis in the spontaneously diabetic BB rat.

The BB rat spontaneously develops insulin-dependent diabetes mellitus (IDDM) in association with marked insulitis in the islet of Langerhans. Since platelet-activating factor (PAF-acether) is involved in allergic and inflammatory reactions, we tested a PAF antagonist, Ginkgolide B (BN 52021) for potential effects on islet inflammation and diabetes. Diabetes prone BB/Wor rats were treated daily from weaning at 25 days until 105 days of age with either saline (n = 30, controls), 10 (n = 25, low dose) or 20 (n = 30, high dose) mg/kg body weight of BN 52021. The overall incidence of IDDM was unaffected by treatment. Quantitative analysis of insulin area showed a dose-dependent protection of beta cells by Ginkgolide B, reflected in a 6- (low dose) to 8-fold (high dose) (P less than 0.01-0.005) increase in the insulin/glucagon cell ratio compared to the saline treated rats. Ginkgolide B reduced severe insulitis from 84% in the saline rats developing IDDM to 59% (n.s.) in the low and to 33% (P less than 0.001) in the high dose group. These data suggest that PAF inhibitors may prove useful in immunomodulator therapy of IDDM since beta cells are preserved.     

Dynamic time course studies of the spontaneously diabetic BB Wistar rat. III. Light-microscopic and ultrastructural observations of pancreatic islets of Langerhans.

The pancreatic islet alterations were studied in spontaneously diabetic BB Wistar rats and in young (50 and 65 days old) normoglycemic BB rats with the use of light microscopy, immunohistochemistry, and electron microscopy. Three groups of diabetic rats were delineated: 1) early diabetes (1-3 days after detection of glycosuria), 2) stable diabetes (41-63 days after detection), and 3) unstable diabetes (7-22 days after detection). In early diabetes islets were extensively infiltrated by "activated" lymphocytes and macrophages, and B cells demonstrated marked degranulation, injury, and necrosis. Although no consistent changes were recorded in A cells, D cells appeared to be decreased in number. In stable and unstable diabetes, islets were small and markedly depleted of B cells, although more insulin-containing cells were identified in the stable group. The number of A and D cells appeared normal in the stable group, although some A cells appeared altered ultrastructurally. In the unstable group both A and D cells appeared decreased, and ultrastructurally altered A cells were again noted. These findings suggest that although B cells appear to be the principal islet target in this model, A and D cells also sustain cellular injury. Variable degrees of insulitis, B cell degranulation, and necrosis were documented in 65-day-old normoglycemic BB rats, suggesting that the destructive process in the islets is initiated well in advance of the onset of the clinical syndrome. The pancreases from many diabetic and normoglycemic BB rats also demonstrated mononuclear cell infiltrates distinct from insulitis in periductular and/or acinar locations. These infiltrates, not present in controls, appear to represent an additional morphologic expression of the process responsible for initiating the diabetic state.     

Curing BB rats of freshly manifested diabetes by short-term treatment with a combination of a monoclonal anti-interleukin 2 receptor antibody and a subtherapeutic dose of cyclosporin A

The BioBreeding (BB) rat develops spontaneously a syndrome resembling human type I diabetes mellitus. The short-term treatment of newly diagnosed diabetic BB rats with the anti-interleukin 2 receptor (IL 2R) monoclonal antibody ART-18 in combination with a subtherapeutic dose of cyclosporin A for 10 days, a treatment shown previously to eliminate specifically antigen-activated IL2R+ T lymphocytes by sparing suppressor cells, resulted in normoglycemia in 70% of the animals, the maintenance of B cell volume density and an increase in pancreatic insulin content. Moreover, the glucose tolerance of successfully treated animals was not significantly different from that of normoglycemic BB rats during the whole observation period (up to 120 days after the end of the therapy). This is the first report on successful treatment of a spontaneous autoimmune disease by a short-term and specific immunosuppressive regimen with limited side effects.     

Alleles of diabetes-resistant BN rats contribute to insulin-dependent type 1 diabetes mellitus

Diabetes in the biobreeding (BB) rat results from autoimmune destruction of pancreatic beta cells and thereby it is sharing many features with human type 1 diabetes. Independent crossing studies have demonstrated that diabetes in the BB rat is explained by at least three recessively acting genes termed Iddm1 (major histocompatibility complex), Iddm2 (lymphopenia), Iddm3 (unknown). About 50% of Iddm1 and Iddm2 homozygous first backcross hybrids (BC1) usually develop diabetes. However, 75% of these homozygotes become diabetic when using diabetic BB/HRI and diabetes-resistant BN/Mol rats. That prompted us to carry out a cross between BB/OK and BN/Crl rats in order to localise diabetogenic gene(s) of BB and/or BN rats.Fifty nine Iddm1 and Iddm2 homozygous [(BNxBB)F1xBB] BC1 hybrids (35 M, 24 F) were observed for diabetes occurrence up to an age of 30 weeks. All hybrids were used in a genome-wide scan carried out with 238 microsatellite markers covering about 92% of the genome.Significantly more Iddm1 and Iddm2 homozygous BC1 hybrids became diabetic (69 vs. 50%, p<0.003) with an age at onset of 91+/-31 days. Significant deviations from expected allele distribution between diabetic and non-diabetic BC1 hybrids were found at loci on chromosomes 1, 2, 3, 9, 10, 15, 16 and 19, with the strongest effect observed at locus D10Mgh2, where more heterozygous (91%) than homozygous diabetics (44%) were found. We conclude that BN rats possess more than one gene contributing to type 1 diabetes development.     

Diabetes-prone BB rats express the RT6 alloantigen on intestinal intraepithelial lymphocytes.

The RT6 alloantigen of the rat is expressed on most peripheral T cells but not on thymocytes and thus represents a marker for postthymic T lymphocyte maturation in this species. Diabetes-prone (DP) BB rats exhibit a genetically determined T cell lymphopenia associated with a deficiency of RT6+ T cells. In this study we have analyzed the expression of RT6 on lymph node (LN) cells and intestinal intraepithelial lymphocytes (IEL) in two DP BB strains (BB/OK and BB/Mol) and two control strains (non-lymphopenic BB/PhiK and LEW) by flow cytometry. In the DP BB rats the number of LN T cells was substantially reduced (less than 25% TcR2+ cells) and completely lacked RT6 expression. The IEL population was also reduced in number and in marked contrast to normal rats consisted predominantly of CD4+ cells. The majority of IEL, however clearly expressed RT6. Treatment with a phosphatidylinositol (PI)-specific phospholipase C markedly reduced the RT6 density showing that PI-mediated anchoring of RT6 in the cell membrane also applies to IEL of DP BB rats. The results demonstrate that the DP BB strains possess a functional RT6 gene and are also able to generate the PI anchor. The defect in RT6 expression is thus unlikely to be the primary cause of the T cell lymphopenia.     

Accelerated Loss of Islet β Cells in Sucrose-Fed Goto-Kakizaki Rats, a Genetic Model of Non-Insulin-Dependent Diabetes Mellitus

The Goto-Kakizaki (GK) rat is a spontaneously diabetic animal model of non-insulin-dependent diabetes mellitus, which is characterized by progressive loss of β cells in the pancreatic islets with fibrosis. In the present study, we examined the effects of sucrose feeding on the islet pathology in this model. Six-week-old GK rats were fed with 30% sucrose for 6 weeks to induce severe hyperglycemia, and their condition was compared with that of nontreated rats. Age-matched normal Wistar rats were also given sucrose for the same periods and used for comparison. The sucrose-treated GK rats showed elevated blood glucose levels on oral glucose tolerance tests at 60 minutes and 120 minutes, representing 123% and 127% of values in untreated GK rats, respectively. At the end of the study, the mean β-cell volume density in GK rats was 50% less than that in untreated Wistar rats. Sucrose feeding further reduced the volume densities of β cells to only 50% of the levels of age-matched GK rats. Apoptotic cells were found in islet β cells only in GK rats fed sucrose (mean 0.067%). There appeared to be more islets that immunohistochemically stained strongly positive with 8-hydroxy-deoxyguanosine as a marker of oxidative damage of DNA in GK rats fed sucrose compared with those not given sucrose. GK rats not fed sucrose showed significantly lower proliferative activity of β cells measured by 5-bromo-2′-deoxyuridine uptake and intensified expression of Bcl-2 immunoreactivities at 6 weeks of age compared with those in age-matched Wistar rats. These two indices were reduced in both GK and Wistar rats with increasing age and were not affected by sucrose feeding in either group. The present study thus indicated that sucrose feeding promoted the apoptosis of β cells in GK rats through increased oxidative stress without altering their proliferative activity.     

Immunological responses of the BB rat colony in Edinburgh.

Several immunological responses of the spontaneously diabetic BB rat colony in Edinburgh designated (BB/E) have been studied. The proliferative responses to Con A and LPS, ability to make IL-2 and to show NK activity have been studied using diabetic and non-diabetic BB/E rats and normal Wistar rats. Our data suggest that the diabetic animals in the BB/E colony do not have marked deficiencies in any of these parameters. Lymphopenia and depressed T-cell responses do not appear to be a prerequisite for the development of diabetes in the BB/E colony.