Energy Expenditure, Protein and Water Turnover and Body Composition Assessment of Dogs with Chronic Kidney Disease

Abstract

Chronic kidney disease (CKD) in dogs may cause hyperphosphatemia, proteinuria, and water loss through urine. Inadequate calorie consumption can result in muscle protein catabolism (cachexia) as an energy source, and it is important to ensure an adequate intake of protein in the diet, avoiding excess to prevent uremia clinical signs. However, the energy and protein requirements of dogs with CKD remain unknown, so energy expenditure, body composition, protein and water turnover studies are necessary to establish precise nutritional treatment protocols for these patients. This study aims to compare healthy dogs and dogs with CKD's energy expenditure, protein and water turnover and body composition to better understand changes in energy expenditure and protein metabolism in dogs with this disease. The study will follow a completely randomized design, with 8 dogs with chronic kidney disease and 8 healthy adults. They will undergo standardization tests to better characterize health and stage CKD and will receive a renal diet for a period of 42 days, during which their energy expenditure will be assessed using the doubly labeled water (DLW) and ¹³C-bicarbonate methods, water turnover by DLW, body composition by DLW, and through ultrasound of the longissimus dorsi and gluteus medius muscles, and their protein metabolism by measuring free amino acids in plasma and urine, total amino acids in urine, and using the L-[¹³C] leucine method. For the DLW method, the animals will receive deuterium (2H) and oxygen-18 (18O) isotopes subcutaneously, and their concentration will be measured in plasma at baseline, after 2 hours (enrichment), and at 2, 4, and 6 days (decay). ¹³C-bicarbonate will be administered orally, and the concentration of ¹³C will be measured in exhaled air samples collected at baseline and 5, 10, 20, 30, 40, 60, 90, 120, 180, 360, and 540 minutes after isotope administration. As for the L-[¹³C] leucine method, this labeled amino acid will be administered intravenously, and its concentration will be measured in plasma and exhaled air samples at baseline and every 20 minutes after application for 180 minutes. Data will be subjected to analysis of variance, and values with temporal repetitions will be evaluated through repeated measures analysis of variance. The results of VCO2 and energy expenditure obtained by DLW and 13C-Bicarbonate will also be compared using Pearson correlation and with agreement limits established according to Bland and Altman. Muscle ultrasound and lean mass methods by DLW will be compared using Pearson correlation. P-values <0.05 will be considered significant.