October 21, 2008; doi:10.1152/ajpendo.90634.2008.-A link between altered levels of various gangliosides and the development of insulin resistance was described in transgenic mice. Naturally occurring glycosphingolipids were shown to exert immunomodulatory effects in a natural killer T (NKT) cell-dependent manner. This study examined whether glycosphingolipid-induced modulation of the immune system may reduce pancreatic and liver steatosis and stimulate insulin secretion in the Cohen diabetes-sensitive (CDS) rat, a lean model of non-insulin-resistant, nutritionally induced diabetes. Four groups of CDS rats fed a diabetogenic diet were treated with daily intraperitoneal injections of glycosphingolipids -glucosylceramide, -lactosylceramide, a combination of both (IGL), or vehicle (PBS) for up to 45 days. Immune modulation was assessed by fluorescence-activated cell sorting analysis of intrahepatic and intrasplenic lymphocytes. Steatosis was assessed by MRI imaging and histological examination of liver and pancreas, Blood glucose and plasma insulin concentrations were assessed during an oral glucose tolerance test. Administration of glycosphingolipids, particularly IGL, increased intrahepatic trapping of CD8 T and NKT lymphocytes. Pancreatic and liver histology were markedly improved and steatosis was reduced in all treated groups compared with vehicle-treated rats. Insulin secretion was restored after glycosphingolipid treatment, resulting in improved glucose tolerance. The immunomodulatory effect of -glycosphingolipids improved the -cell function of the hyperglycemic CDS rat. Thus our results suggest a role for the immune system in the pathogenesis of diabetes in this model. glycolipids; immune response; natural killer T cells; type 2 diabetes THE CHRONIC INCREASE in inflammatory mediators observed in type 2 diabetes (T2DM) has been shown to affect not only tissues and blood vessel walls but also pancreatic -cells (11). The hyperglycemic Cohen diabetes-sensitive (CDS) rat is a model of mild cytokine-mediated diabetes (34) The CDS rat develops postprandial hyperglycemia when fed a diabetogenic high-sucrose, copper-poor diet (HSD), characterized by elevated blood glucose and blunted insulin secretion in response to glucose loading (8,35,36). Glucose intolerance in these rats is associated with exocrine lesions, lipid deposition, and IL-1-positive macrophage infiltration in the exocrine pancreas (34). However, the way in which the immune system is involved in the development of diabetes in this model has not yet been elucidated. Natural killer T (NKT) cells, innate regulatory lymphocytes that express a conserved T-cell receptor, play important parts in diverse neoplastic, autoimmune, and infectious processes (3,22). NKT cells usually express an invariant T-cell receptor that recognizes glycolipids in the context of the major histocompatibility complex (MHC) class I-like molecule CD1d (13, 15). -Glucosylceramide (GC) and -lactosylceramide (LC) are naturally occurring glycosphingolipids that exert immunomodula...
In search of an experimental model that would simulate the association between proteinuria and salt sensitivity in humans, we studied protein excretion in the Sabra rat model of salt susceptibility. Monthly measurements of urinary protein excretion in animals fed standard rat chow revealed that normotensive salt-sensitive SBH/y developed proteinuria that averaged 65 +/- 7 mg/day (n = 10) at 9 mo, whereas proteinuria in normotensive salt-resistant SBN/y was 39 +/- 4 mg/day (n = 10) (P < 0.01). Histopathological evaluation revealed focal and segmental glomerulosclerosis (FSGS) lesions grade 2 in SBH/y and normal histology in SBN/y. To amplify the differences between the strains, uninephrectomy was performed. At 9 mo, proteinuria in SBH/y with one kidney (SBH/y-1K) was 195 +/- 12 mg/day (n = 10) and in SBN/y was 128 +/- 10 mg/day (n = 10) (P < 0.001); histopathology revealed FSGS grade 3 in SBH/y-1K and grade 1-2 in SBN/y-1K. To determine the effect of salt loading, animals were provided with 8% NaCl in chow, causing hypertension in SBH/y but not in SBN/y. Proteinuria markedly increased in both SBH/y with two kidneys (SBH/y-2K) and SBH/y-1K, but not in SBN/y; histopathology revealed FSGS grade 1-2 in SBH/y-2K, grade 2 in SBH/y-1K, no lesions in SBN/y-2K, and grade 0-1 in SBN/y-1K. We concluded that the SBH/y strain is more susceptible to develop proteinuria and glomerulosclerosis than SBN/y. In search for the genetic basis of this phenomenon, we investigated the role of candidate proteinuric gene loci. Consomic strains were constructed by introgressing chromosome 1 (which harbors the rf-1 and rf-2 proteinuric loci) or chromosome 17 (which harbors rf-5) from SBH/y onto the SBN/y genomic background. The resulting consomic strains developed marked proteinuria that was severalfold higher than in SBN/y-1K; histopathological evaluation, however, revealed FSGS lesions grade 1-2, similar to those found in SBN/y-1K and less severe than in SBH/y-1K. These results suggest a functional role of gene systems located on chromosomes 1 and 17 in inducing proteinuria in the salt-susceptible Sabra rat strain. These genetic loci do not appear to harbor major genes for glomerulosclerosis.
The role of the antioxidant defense mechanism in diabetesinduced anomalies was studied in the Cohen diabetes-sensitive (CDs) and -resistant (CDr) rats, a genetic model of nutritionally induced type 2 diabetes mellitus. Embryos, 12.5-day-old, of CDs and CDr rats fed regular diet (RD) or a diabetogenic high-sucrose diet (HSD) were monitored for growth retardation and congenital anomalies. Activity of superoxide dismutase (SOD) and catalaselike enzymes and levels of ascorbic acid (AA), uric acid (UA), and dehydroascorbic acid (DHAA) were measured in embryonic homogenates. When fed RD, CDs rats had a decreased rate of pregnancy, and an increased embryonic resorption. CDs embryos were smaller than CDr embryos; 46% were maldeveloped and 7% exhibited neural tube defects (NTDs). When fed HSD, rate of pregnancy was reduced, resorption rate was greatly increased (56%; P < .001), 47.6% of the embryos were retrieved without heart beats, and 27% exhibited NTD. In contrast, all the CDr embryos were normal when fed RD or HSD. Activity of SOD and catalase was not different in embryos of CDs and CDr rats fed RD. When fed HSD, levels of AA were significantly reduced, the ratio DHAA/AA was significantly increased, and SOD activity was not sufficiently increased when compared to embryos of CDr. The reduced fertility of the CDs rats, the growth retardation, and NTD seem to be genetically determined. Maternal hyperglycemia seems to result in The increased rate of fetal malformations in diabetic pregnancy despite better glycemic control represents a clinical problem and a research challenge. The exact mechanism behind the elevated rate of malformations is presently unknown. It has, however, been suggested that both intrauterine (maternal) environment as well as genetic background may be important [1][2][3][4][5][6][7] in the teratogenic process. As of today, the literature describes 3 main pathways by which diabetes may affect the normal development of the embryos: disturbed inositol uptake, yielding lowered intracellular inositol concentration [8]; diminished flow in the arachidonic acid-prostaglandin pathway, yielding decreased PGE2 concentration [9]; and excess amount of reactive oxygen species, resulting in decreased amount of low-molecular-weight antioxidants, such as vitamin C, uric acid, glutathione, and vitamin E [5,6,10,11]. The reactive oxygen species pathway seems to be the most important pathway because antioxidants may protect against the disturbances of both the inositol and the arachidonic pathways. The proposed mechanisms for increased reactive oxygen species generation at higher glucose concentrations include nonenzymatic protein glycosylation [12][13][14], enhanced mitochondrial electron transport chain flow [15], autooxidation [16], and changes in the redox potential. The relative 247
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