Development and Validation of a Methodology for Establishing Obese Rat Models with Typical Fatty Pancreas

Obesity has emerged as a predominant global health epidemic, with nearly half of the world's population now classified as overweight or obese. A key pathological feature in obese individuals is ectopic lipid deposition in non-adipose tissues, including the pancreas-a condition termed pancreatic steatosis or fatty pancreas. In high-fat diet (HFD)-induced rodent models, pancreatic steatosis consistently precedes hepatic steatosis, underscoring the particular susceptibility of the pancreas to lipid accumulation. This early involvement positions the pancreas as a critical organ for understanding metabolic dysregulation in obesity. Although diet-induced obese (DIO) rats recapitulate core aspects of human disease progression, well-characterized animal models that reliably exhibit this pancreatic phenotype remain scarce in the literature. A significant methodological consideration in modeling human obesity is the timing of HFD introduction. Many existing models initiate HFD during the weaning period, which may introduce confounding developmental metabolic programming effects that do not fully reflect human obesity, which primarily develops post-developmentally. In contrast, the present study establishes a standardized protocol in which HFD is introduced post-weaning. This approach more accurately mimics the common human trajectory of obesity onset in adulthood, avoids early-life metabolic adaptations, and results in a more physiologically relevant progression toward pancreatic steatosis. This research provides a detailed and reproducible framework for generating a rat model of obesity characterized by prominent fatty pancreas pathology. The methodology includes a 1-week acclimatization phase, a 14-week HFD induction period starting after weaning, and systematic tissue harvesting. Two tissue processing pathways are described: snap-freezing for molecular analyses (e.g., Western blotting) and paraformaldehyde perfusion-fixation for morphological evaluations (e.g., IHC, H&E). This model offers a robust platform for mechanistic investigations into obesity-associated pancreatic metabolic dysfunction.