Abstract
A prospective study was conducted in client-owned geriatric dogs to evaluate the short-term effects of a test food on serum symmetric dimethylarginine (SDMA) and creatinine (Cr) concentrations. Test food contained functional lipids (fish oil), antioxidants (lipoic acid, vitamins C and E), L-carnitine, botanicals (fruits and vegetables), controlled sodium concentration, and high quality protein sources (high bioavailability and an ideal amino acid composition). Dogs (n = 210) were fed either test food or owner’s-choice foods (non-nutritionally controlled cohort). Dogs were included based on age and body weight: small (6.8 to 11.4 kg) and medium dogs (11.5 to 22.7 kg) were ≥ 9 years, whereas dogs >22.7 kg were ≥ 7 years at baseline. At baseline, all dogs had to have serum Cr concentrations within the reference interval and be free of chronic disease. Renal function biomarkers and urinalysis results at baseline, and after consuming test food or owner’s-choice foods for 3 and 6 months, were evaluated. Only dogs consuming test food showed significant decreases in serum SDMA and Cr concentrations (both P ≤ 0.05) across time. At baseline or during the 6-month feeding trial, 18 dogs (8.6%) had increased serum SDMA, but normal serum Cr, consistent with IRIS Stage 1 chronic kidney disease. This included 9 dogs fed test food and 9 dogs fed owner’s-choice foods. Compared with baseline, after feeding 9 dogs test food for 6 months, serum SDMA decreased in 8 dogs and increased in 1 dog. After feeding 9 dogs owner’s-choice foods for 6 months, serum SDMA decreased in 4 dogs and increased in 4 dogs (remained stable in 1 dog). The decreases in serum SDMA and Cr concentrations were significant (both P = 0.03) only for dogs fed test food. These results suggest that nonazotemic dogs with elevated serum SDMA (early renal insufficiency) when fed a test food designed to promote healthy aging are more likely to demonstrate improved renal function compared with dogs fed owner’s-choice foods.
Highlights
Serum concentrations of symmetric dimethylarginine (SDMA) have been shown to detect chronic kidney disease (CKD) in cats on average 17.0 months before serum creatinine (Cr) concentration increased above the reference interval [1], and in dogs on average 9.8 months before serum Cr increased above the reference interval [2]
We have previously shown in dogs that serum SDMA concentrations are inversely related to glomerular filtration rate (GFR) [2], that serum SDMA concentrations can be used to detect renal dysfunction earlier in dogs with chronic renal disease compared with serum Cr concentrations [2], and that serum SDMA concentrations are not affected by lean body mass [7]
The upper reference interval for SDMA (< 14 μg/ dL) corresponds to a reduction in GFR of approximately 49% from mean GFR, whereas the upper reference interval for serum Cr corresponds to a reduction of approximately 75% from mean GFR in dogs [2]
Summary
Serum concentrations of symmetric dimethylarginine (SDMA) have been shown to detect chronic kidney disease (CKD) in cats on average 17.0 months before serum creatinine (Cr) concentration increased above the reference interval [1], and in dogs on average 9.8 months before serum Cr increased above the reference interval [2]. Serum SDMA is useful as a renal biomarker for identifying early compromise in renal function compared with serum Cr. Symmetric dimethylarginine is produced when nitrogen molecules of arginine-containing proteins are postranslationally modified by adding methyl groups. Symmetric dimethylarginine is produced when nitrogen molecules of arginine-containing proteins are postranslationally modified by adding methyl groups When these proteins are subsequently degraded, free methylarginines are released into the cytosol and enter the plasma. Because serum SDMA is filtered by the kidneys, plasma concentrations are correlated with changes in glomerular filtration rate (GFR). We have shown that serum SDMA correlates with GFR in cats [1, 6] as well as in dogs [2]
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