Hydrolysed casein diet protects BB rats from developing diabetes by promoting islet neogenesis

Feeding diabetes-prone BioBreeding (BBdp) rats a hydrolysed-casein (HC)base d semi-purified diet results in two-to-three-fold fewer diabetes cases comp ared with feeding cereal-based diets such as NIH-07 (NIH). We showed previo usly that young NIH-fed BBdp rats had decreased islet area at a time when c lassic insulitis was minimal. Rats fed an HC diet maintained near normal is let area followed 3-4 weeks later by a deviation of the pancreas cytokine p attern from Th1 to Th2/Th3. This finding raised the possibility that BBdp r ats were more susceptible to diet-induced changes in islet homeostasis. To investigate this possibility further, BBdp rats were fed an NIH or HC diet from days 23 to 45. Bouin's fixed sections of pancreas were stained with H & E or antibodies for insulin and glucagon. Cell proliferation nuclear anti gen (PCNA) was used as a marker of cell proliferation and cells were staine d for putative markers of islet neogenesis, cytokeratin 20 (CK20) and Bcl-2 . Apoptotic bodies were recognized by morphological features and by TUNEL-p ositive staining. BBdp rats fed an HC diet had a significantly higher beta -cell fraction than rats fed NIH, whereas alpha -cell fraction and beta -ce ll size were not affected by diet or rat type. Apoptotic bodies of beta -ce lls were rare and unaffected by diet. The number of PCNA(+) beta -cells was not affected by diet. CK20 expression was localized in the ductular system and at the periphery of islets in rats aged 7 and 45 days. There were more CK20(+) islets in BBdp rats fed NIH than in those fed HC but the CK20 area fraction was unaffected by diet. Bcl-2 expression was scattered among duct s and central acinar cells. The number of extra-islet insulin(+) and glucag on(+) clusters (<four cells) was significantly higher in animals fed the HC diet compared with those fed NIH. Most of the insulin(+) clusters were als o homeodomain-containing transcription factor pancreas duodenum homeobox ge ne-1 (PDX-1) positive. Glucagon(+)/PDX-1(+) clusters were rarely found. The se data are consistent with a shift in pancreas homeostasis that maintains islet cell mass by increased islet neogenesis, a process that was enhanced in animals fed a diabetes-retardant diet. (C) 2000 Academic Press.