Urinary felinine excretion in intact male cats is increased by dietary cystine

Abstract

Felinine is a branched-chain sulfur amino acid present in the urine of certain Felidae, including domestic cats. The objective of the present study was to determine if additional cystine and/or dietary N would increase felinine and N-acetylfelinine excretion by intact male cats fed a low-protein (LP) diet. Feeding five adult intact male cats an LP diet (18·8 % of metabolisable energy (ME) as protein) v. a high-protein diet (38·6 % of ME as protein) resulted in a trend (P¼ 0·08) for decreased urinary felinine and no change in N-acetylfelinine excretion. In a 23 d study, when the LP diet was supplemented with L-cystine at 9·3 g/kg DM, urinary felinine:creatinine ratio showed a linear two-fold (121 %) increase (P,0·01) from 0·24 (SEM 0·05) to 0·53 (SEM 0·13) after 10 d. Subsequent feeding of the LP diet resulted in a decrease in felinine excretion to base levels. Plasma gglutamylfelinylglycine concentrations were consistent with the excretion of felinine. Supplementation of the LP diet with L-cystine (9·3 g/kg DM), dispensable amino acids and arginine to a second group (n 5) also resulted in a significant (P,0·01) but smaller (þ 72 %) increase in the daily felinine:creatinine ratio (0·25 (SEM 0·04) to 0·43 (SEM 0·05)). The degree of felinine N-acetylation within groups was unaffected by dietary addition and withdrawal of amino acids. The results indicate that felinine synthesis is regulated by cystine availability, and that arginine may be physiologically important in decreasing felinine biosynthesis in intact male cats. N-acetylfelinine: Arginine: Cats: Cysteine: FelinineFelinine is a unique amino acid excreted by certain species within the Felidae family, including the domestic cat. This sulfur-containing, branched-chain amino acid has been found in concentrations of 3·6 g/l in the urine of intact male cats (Felis catus), with castrated males excreting approximately one-quarter as much as intact males (1) . Synthesis of felinine is believed to occur from glutathione and isopentenylpyrophosphate, through a unique glutathione sulfur transferase enzyme which is under hormonal control (2,3) to form a felinine-containing tripeptide: g-glutamylfelinylglycine or methylbutanolglutathione (MBG). The g-glutamylfelinylglycine is transported in the blood (4) to the kidney where hydrolysis by g-glutamyltransferase present on the surface of the brushborder membrane of proximate tubular cells results in felinylglycine and glutamic acid. The dipeptide can be further hydrolysed to felinine and glycine by either dipeptidase activities or a recently discovered enzyme with carboxylesterase activity (5) . This 70 kDa enzyme (cauxin) has been found in relatively high concentrations in feline urine and has been shown to be able to hydrolyse felinylglycine but not MBG (5) . Following the hydrolysis of felinylglycine, N-acetylation of felinine can occur. This is an intracellular process catalysed by cysteine-S-conjugate N-acetyltransferase and yielding mercapturic acids via the addition of an acetyl group transferred from acetyl-CoA, whi...

Felinine excretion in domestic cat breeds: a preliminary investigation

“…However, impairment of renal function is normally seen in older cats (Burkholder, ), while the mean age of the cats used in present study was only 3.55 years. Also, as mentioned earlier, the observed Fel:Cr ratios here were comparable with ratios found in earlier studies on felinine excretion (Hendriks et al., ,b), which indicates that the results may be considered reliable.…”

“…The results of this study indicate that cat breeds indeed differ in felinine excretion when expressed as a ratio with urinary creatinine. The Fel:Cr ratios in this study are comparable with those published in earlier papers on this subject (Hendriks et al., ,b) and may thus be considered reliable. Expression of urinary components relative to the urinary creatinine concentration is commonly employed to compensate for possible variations in renal output.…”

“…Hendriks et al. () showed that felinine synthesis is regulated and can be influenced by cysteine availability.…”

Peculiarities of One-Carbon Metabolism in the Strict Carnivorous Cat and the Role in Feline Hepatic Lipidosis

“…Cysteine is an important component of proteins for their secondary structure [39] and is a major constituent of hair [44]. Cysteine also functions as an essential thiol donor for hepatocellular glutathione synthesis [39] and as a precursor for felinine [45,46] and taurine [39]. …”

The role of cysteine and cysteine–S conjugates as odour precursors in the flavour and fragrance industry

“…127 Further studies have also shown the presence in Felis catus urine of 78, 79 and 80. 128,129 The site of felinine synthesis in vivo remains unknown; the biosynthesis appears to occur through a condensation of isopentylpyrophosphate and glutathione by an uncharacterized glutathione sulphur transferase. A recent study confirmed the presence of a felinine precursor 79.…”