Novel non-invasive methods to evaluate glucose metabolism and beta cell function in cats
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Obesity is significant risk factor and strongly correlated with diabetes mellitus (DM) and insulin resistance in cats. The prevalence of feline obesity and feline DM has been drastically increased over the last two decades, and DM is one of the most common endocrinopathies in cats. However, their study has been hampered by the fact that thus far metabolism could not be evaluated easily in a non-invasive manner. However, without clear knowledge of disease processes, any treatment remains unfocused and non-specific. The purpose of this research was to study glucose metabolism and beta cell function and to determine possible dietary effects on glucose metabolism in lean and long-term obese cats. We used cutting-edge nuclear magnetic resonance technology in combination with indirect calorimetry to investigate key steps in glucose metabolism non-invasively and we developed a sensitive feline proinsulin (FPI) assay to evaluate the utility of proinsulin as a marker for beta cell function in lean and obese cats. Our results showed that cats are capable to adapt to different macronutrients and that dietary supplementation of n-3 polyunsaturated fatty acids (PUFAs) appear to have some beneficial metabolic effects whereas the supplementation of saturated fatty acids (SATs) seem to be less beneficial for cats. In addition we demonstrated that endogenous glucose production (EGP) is strongly negatively correlated to insulin concentration and obesity. We developed and validated an immunoradiometric and Enzyme-Linked ImmunoSorbent Assay for feline proinsulin for the assessment of beta cell function and demonstrated significantly differences in the proinsulin and insulin secretion pattern in response to glucose between lean and obese cats but similar pattern within their group. This novel assay will be useful to elucidate FPI secretion and can be used in a similar manner as the C-peptide assay in humans to evaluate residual beta cell function in cats.