1. Amyloidogenesis of feline amylin and plasma levels in cats with diabetes mellitus or pancreatitis
L Jotha-Mattos, A B Vieira, M da S M Castelo, A S de M Queiroz, H J M de Souza, N X de Alencar, L M T R Lima Domest Anim Endocrinol. 2021 Jan;74:106532. doi: 10.1016/j.domaniend.2020.106532. Epub 2020 Aug 1.
Amylin is a pancreatic hormone cosecreted along with insulin and involved in pancreatic amyloidosis and β-cell apoptosis in diabetic cats and humans. Amylin is usually elevated in early stages of type 2 diabetes but recently was found to be increased in acute and chronic pancreatitis in humans. Currently, there are little data about feline amylin propensity to fibrillate and no information on circulating levels of this hormone during feline pancreatitis. We compared 4 amylin analogues and found cat amylin to be more prone to amyloid fibrillation than human amylin, the triple-proline analogue pramlintide and rat amylin. We also measured plasma amylin levels in healthy lean cats, diabetic cats, and cats with pancreatitis. Plasma amylin was higher in diabetic cats compared with healthy lean cats (P < 0.001). Interestingly, amylin levels during pancreatitis were higher than those of both lean cats (P < 0.0001) and diabetic cats without pancreatitis (P < 0.005). These data support evidence of feline amylin being more prone to aggregation than human amylin in vitro, which may influence diabetes mellitus progression and β-cell failure in vivo. Furthermore, our data show an increase in amylin levels during feline pancreatitis and the need for future research on the role of this hormone in the pathogenesis of pancreatic inflammation associated to feline diabetes mellitus.
2. Islet amyloid polypeptide, islet amyloid, and diabetes mellitus
Per Westermark, Arne Andersson, Gunilla T Westermark Physiol Rev. 2011 Jul;91(3):795-826. doi: 10.1152/physrev.00042.2009.
Islet amyloid polypeptide (IAPP, or amylin) is one of the major secretory products of β-cells of the pancreatic islets of Langerhans. It is a regulatory peptide with putative function both locally in the islets, where it inhibits insulin and glucagon secretion, and at distant targets. It has binding sites in the brain, possibly contributing also to satiety regulation and inhibits gastric emptying. Effects on several other organs have also been described. IAPP was discovered through its ability to aggregate into pancreatic islet amyloid deposits, which are seen particularly in association with type 2 diabetes in humans and with diabetes in a few other mammalian species, especially monkeys and cats. Aggregated IAPP has cytotoxic properties and is believed to be of critical importance for the loss of β-cells in type 2 diabetes and also in pancreatic islets transplanted into individuals with type 1 diabetes. This review deals both with physiological aspects of IAPP and with the pathophysiological role of aggregated forms of IAPP, including mechanisms whereby human IAPP forms toxic aggregates and amyloid fibrils.
3. Pathogenesis of feline diabetes mellitus
T D O'Brien Mol Cell Endocrinol. 2002 Nov 29;197(1-2):213-9. doi: 10.1016/s0303-7207(02)00265-4.
The common form of spontaneous diabetes mellitus that occurs in domestic cats bears close resemblance clinically and pathologically to human type 2 diabetes mellitus (T2DM). For example, the typical diabetic cat is obese and middle-aged, and has low but detectable circulating insulin levels. However, the most striking similarity is the occurrence of islet amyloidosis (IA) in nearly all diabetic cats and in over 90% of humans with T2DM. IA in both humans and cats is derived from islet amyloid polypeptide (IAPP, or amylin) which is a hormone produced and secreted along with insulin by the pancreatic beta cells. Since all cats and humans normally produce IAPP, additional factors must be invoked in order to explain the development of IA. Several lines of evidence support the concept that IA is caused by chronically increased stimulus for beta cells to secrete IAPP (and insulin). For example, peripheral insulin resistance such as in chronic obesity results in increased IAPP and insulin secretion. A recent study, in which diabetes mellitus was induced in cats, demonstrated that IAPP hypersecretion was induced by treatment with a sulfonylurea drug and resulted in 4/4 cats in this group developing IA. In contrast, cats treated with insulin had low IAPP secretion and minimal IA developed in 1/4 cats. Several human-IAPP transgenic mouse models, in which there is IAPP overexpression, also support the notion that prolonged high expression of IAPP leads to IA. In vitro models of IAPP overexpression also support this mechanism for IA formation and by demonstrating an association between IA formation and beta cell toxicity, suggest a linkage between IA formation and loss of beta cells in T2DM. A recent study has indicated that intermediate-sized IAPP-derived amyloid fibrils can disrupt cell membranes and therefore, may be involved in the destruction of beta cells. Striking parallels between the pathogenesis of IA and beta-amyloid plaque formation in Alzheimer's disease suggest possible parallel pathogenetic mechanisms of cell death and provide potential avenues for future studies into the pathogenesis of IA.
