Amyloid deposition and reduced β-cell mass are pathological hallmarks of the pancreatic islet in type 2 diabetes; however, whether the extent of amyloid deposition is associated with decreased β-cell mass is debated. We investigated the possible relationship and, for the first time, determined whether increased islet amyloid and/or decreased β-cell area quantified on histological sections is correlated with increased β-cell apoptosis. Formalin-fixed, paraffin-embedded human pancreas sections from subjects with (n = 29) and without (n = 39) diabetes were obtained at autopsy (64 ± 2 and 70 ± 4 islets/subject, respectively). Amyloid and β cells were visualized by thioflavin S and insulin immunolabeling. Apoptotic β cells were detected by colabeling for insulin and by TUNEL. Diabetes was associated with increased amyloid deposition, decreased β-cell area, and increased β-cell apoptosis, as expected. There was a strong inverse correlation between β-cell area and amyloid deposition (r = -0.42, P < 0.001). β-Cell area was selectively reduced in individual amyloid-containing islets from diabetic subjects, compared with control subjects, but amyloid-free islets had β-cell area equivalent to islets from control subjects. Increased amyloid deposition was associated with β-cell apoptosis (r = 0.56, P < 0.01). Thus, islet amyloid is associated with decreased β-cell area and increased β-cell apoptosis, suggesting that islet amyloid deposition contributes to the decreased β-cell mass that characterizes type 2 diabetes.

Aims/hypothesis Islet amyloid in type 2 diabetes contributes to loss of beta cell mass and function. Since islets are susceptible to oxidative stress-induced toxicity, we sought to determine whether islet amyloid formation is associated with induction of oxidative stress. Methods Human islet amyloid polypeptide transgenic and non-transgenic mouse islets were cultured for 48 or 144 h with or without the antioxidant N-acetyl-L-cysteine (NAC) or the amyloid inhibitor Congo Red. Amyloid deposition, reactive oxygen species (ROS) production, beta cell apoptosis, and insulin secretion, content and mRNA were measured.Results After 48 h, amyloid deposition was associated with increased ROS levels and increased beta cell apoptosis, but no change in insulin secretion, content or mRNA levels. Antioxidant treatment prevented the rise in ROS, but did not prevent amyloid formation or beta cell apoptosis. In contrast, inhibition of amyloid formation prevented the induction of oxidative stress and beta cell apoptosis. After 144 h, amyloid deposition was further increased and was associated with increased ROS levels, increased beta cell apoptosis and decreased insulin content. At this time-point, antioxidant treatment and inhibition of amyloid formation were effective in reducing ROS levels, amyloid formation and beta cell apoptosis. Inhibition of amyloid formation also increased insulin content. Conclusions/interpretation Islet amyloid formation induces oxidative stress, which in the short term does not mediate beta cell apoptosis, but in the longer term may feed back to further exacerbate amyloid formation and contribute to beta cell apoptosis.

The increasing production of genetically-modified mouse models has necessitated studies to determine the inherent physiological characteristics of commonly used mouse strains. In this study we examined insulin secretory function in response to an intravenous bolus of glucose or glucose plus arginine in anesthetized C57BL/6, DBA/2 and 129T2 mice fed either a control or high fat diet for 6 weeks. The results show that 129T2 mice had higher fasting plasma glucose levels and lower fasting plasma insulin levels compared with C57BL/6 and DBA/2 mice regardless of diet. Furthermore, 129T2 mice were glucose intolerant and secreted significantly less insulin in response to glucose and glucose plus arginine irrespective of diet compared with the other two strains of mice. DBA/2 mice hypersecreted insulin in response to glucose and glucose plus arginine compared with C57BL/6 and 129T2 mice. Moreover while first phase insulin secretion was appropriately increased in response to the high fat diet in C57BL/6 and 129T2 mice, this was not the case for DBA/2 mice. Mean islet area was decreased in response to a high fat diet in DBA/2 mice, while there was no dietary effect on the other two strains. This study highlights the inherent genetic differences that exist among seemingly normal strains of mice that are commonly used to make transgenic and knockout mice. Understanding these differences will provide researchers with the information to choose the appropriate genetic background on which to express their particular genetic alteration.