Isolation and characterization of a felinine-containing peptide from the blood of the domestic cat (Felis catus)

Amino Acids in the Nutrition, Metabolism, and Health of Domestic Cats

Domestic cats (carnivores) require high amounts of dietary amino acids (AAs) for normal growth, development, and reproduction. Amino acids had been traditionally categorised as nutritionally essential (EAAs) or nonessential (NEAAs), depending on whether they are synthesized de novo in the body. This review will focus on AA nutrition and metabolism in cats. Like other mammals, cats do not synthesize the carbon skeletons of twelve proteinogenic AAs: Arg, Cys, His, Ile, Leu, Lys, Met, Phe, Thr, Trp, Tyr, and Val. Like other feline carnivores but unlike many mammals, cats do not synthesize citrulline and have a very limited ability to produce taurine from Cys. Except for Leu and Lys that are strictly ketogenic AAs, most EAAs are both glucogenic and ketogenic AAs. All the EAAs (including taurine) must be provided in diets for cats. These animals are sensitive to dietary deficiencies of Arg and taurine, which rapidly result in life-threatening hyperammonemia and retinal damage, respectively. Although the National Research Council (NCR, Nutrient requirements of dogs and cats. National Academies Press, Washington, DC, 2006) does not recommend dietary requirements of cats for NEAAs, much attention should be directed to this critical issue of nutrition. Cats can synthesize de novo eight proteinogenic AAs: Ala, Asn, Asp, Gln, Glu, Gly, Pro, and Ser, as well as some nonproteinogenic AAs, such as γ-aminobutyrate, ornithine, and β-alanine with important physiological functions. Some of these AAs (e.g., Gln, Glu, Pro, and Gly) are crucial for intestinal integrity and health. Except for Gln, AAs in the arterial blood of cats may not be available to the mucosa of the small intestine. Plant-source foodstuffs lack taurine and generally contain inadequate Met and Cys and, therefore, should not be fed to cats in any age group. Besides meat, animal-source foodstuffs (including ruminant meat & bone meal, poultry by-product meal, porcine mucosal protein, and chicken visceral digest) are good sources of proteinogenic AAs and taurine for cats. Meeting dietary requirements for both EAAs and NEAAs in proper amounts and balances is crucial for improving the health, wellbeing, longevity, and reproduction of cats.

Simultaneous Chemical and Sensory Analysis of Domestic Cat Urine and Feces with Headspace Solid-Phase Microextraction and GC-MS-Olfactometry

The association between humans and cats (Felis catus) is well known. This domestic animal is also known for its malodorous urine and feces. The complexity of the odorous urine and feces impacts human life by triggering the human sensory organ in a negative way. The objective of this research was to identify the volatile organic chemicals (VOCs) and associated odors in cat urine and feces using gas chromatography–mass spectrometry and simultaneous sensory analysis of fresh and aged samples. The solid-phase microextraction (SPME) technique was used to preconcentrate the VOCs emitted from urine or feces samples. Twenty-one compounds were identified as emitted from fresh urine, whereas 64 compounds were emitted from fresh feces. A contrasting temporal impact was observed in the emission of VOCs for urine and feces. On aging, the emission increased to 34 detected chemicals for stale urine, whereas only 12 chemicals were detected in stale feces. Not all compounds were malodorous; some compounds had a pleasant hedonic smell to the human nose. Although trimethylamine, low-molecular-weight organic acids, and ketones were contributors to the odor to some extent, phenolic compounds and aromatic heterocyclic organic N compounds generated the most intense odors and substantially contributed to the overall malodor, as observed by this study. This work might be useful to formulate cat urine and feces odor remediation approaches to reduce odor impacts.

Amino Acid Nutrition for Optimum Growth, Development, Reproduction, and Health of Zoo Animals

Proteins are large polymers of amino acids (AAs) linked via peptide bonds, and major components for the growth and development of tissues in zoo animals (including mammals, birds, and fish). The proteinogenic AAs are alanine, arginine, aspartate, asparagine, cysteine, glutamate, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. Except for glycine, they are all present in the L-isoform. Some carnivores may also need taurine (a nonproteinogenic AA) in their diet. Adequate dietary intakes of AAs are necessary for the growth, development, reproduction, health and longevity of zoo animals. Extensive research has established dietary nutrient requirements for humans, domestic livestock and companion animals. However, this is not true for many exotic or endangered species found in zoos due to the obstacles that accompany working with these species. Information on diets and nutrient profiles of free-ranging animals is needed. Even with adequate dietary intake of crude protein, dietary AAs may still be unbalanced, which can lead to nutrition-related diseases and disorders commonly observed in captive zoo species, such as dilated cardiomyopathy, urolithiasis, gut dysbiosis, and hormonal imbalances. There are differences in AA metabolism among carnivores, herbivores and omnivores. It is imperative to consider these idiosyncrasies when formulating diets based on established nutritional requirements of domestic species. With optimal health, populations of zoo animals will have a vastly greater chance of thriving in captivity. For endangered species especially, maintaining stable captive populations is crucial for conservation. Thus, adequate provision of AAs in diets plays a crucial role in the management, sustainability and expansion of healthy zoo animals.

Metabolic Profiling Reveals Effects of Age, Sexual Development and Neutering in Plasma of Young Male Cats

Neutering is a significant risk factor for obesity in cats. The mechanisms that promote neuter-associated weight gain are not well understood but following neutering, acute changes in energy expenditure and energy consumption have been observed. Metabolic profiling (GC-MS and UHPLC-MS-MS) was used in a longitudinal study to identify changes associated with age, sexual development and neutering in male cats fed a nutritionally-complete dry diet to maintain an ideal body condition score. At eight time points, between 19 and 52 weeks of age, fasted blood samples were taken from kittens neutered at either 19 weeks of age (Early Neuter (EN), n = 8) or at 31 weeks of age (Conventional Neuter (CN), n = 7). Univariate and multivariate analyses were used to compare plasma metabolites (n = 370) from EN and CN cats. Age was the primary driver of variance in the plasma metabolome, including a developmental change independent of neuter group between 19 and 21 weeks in lysolipids and fatty acid amides. Changes associated with sexual development and its subsequent loss were also observed, with differences at some time points observed between EN and CN cats for 45 metabolites (FDR p<0.05). Pathway Enrichment Analysis also identified significant effects in 20 pathways, dominated by amino acid, sterol and fatty acid metabolism. Most changes were interpretable within the context of male sexual development, and changed following neutering in the CN group. Felinine metabolism in CN cats was the most significantly altered pathway, increasing during sexual development and decreasing acutely following neutering. Felinine is a testosterone-regulated, felid-specific glutathione derivative secreted in urine. Alterations in tryptophan, histidine and tocopherol metabolism observed in peripubertal cats may be to support physiological functions of glutathione following diversion of S-amino acids for urinary felinine secretion.

Estimating energy losses with urine in the cat

Urinary energy losses in cats have to be determined in energy balance trials as well as for the calculation of the metabolizable energy (ME) content of cat food. The aim of the present study was: first, to assess whether the energy content of cat urine quantified by bomb calorimetry differs from that quantified using GE (kJ) urine = 33 kJ × g C urine + 9 kJ × g N urine and investigate whether this difference could be attributed to influences of diets. Second, to assess whether the subtraction of 3.1 kJ/g of protein intake used for estimation of metabolizable energy content of cat foods is confirmed as usable. Data from 27 energy and protein balance trials from different studies with complete sampling of urine and faeces (29 cats in part A and 35 cats in part B) were used. Gross energy, carbon and nitrogen were determined in food, faeces and urine. Gross energy values in urine tended to be higher when determined with the formula of Hoffman and Klein compared to bomb calorimetry. The average relative difference of gross energy values between the methods was 18.8%. The mean energy loss in kJ/g of protein intake resulted in 3.7 kJ/g protein intake, which was not statistically significantly different (p = 0.12) from the tested value of 3.1 kJ/g of protein intake. In conclusion, the formula of Hoffman and Klein is not appropriate for the estimation of energy in cat urine. In balance studies, it is advisable to quantify the urinary energy content by bomb calorimetry. In the second part of the study, the protein correction factor to determine ME of 3.1 kJ/g protein intake for urinary energy losses of Kienzle et al. could be confirmed.

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

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 (P = 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 γ-glutamylfelinylglycine 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 (+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.

Testosterone increases urinary free felinine, N-acetylfelinine and methylbutanolglutathione excretion in cats (Felis catus)

Two days after castration, urinary free felinine plus N-acetylfelinine decreased 24% in male cats, but, by day 5, the concentration had not decreased to that routinely found in males that have been castrated for several months. In a second experiment, three groups of castrated adult male cats received different subcutaneous injections: control (carrier), testosterone, testosterone plus estradiol. A fourth group of intact adult female cats received a testosterone injection. Urine was collected and analysed for free felinine, N-acetylfelinine and 3-methylbutanolglutathione. Baseline blood testosterone and estradiol concentrations were low during the pre-period, but increased sharply after hormone injections. The concentration of all three urinary metabolites increased as a result of testosterone injections with estradiol not modulating the effect. The effect of testosterone was not gender dependent. The concentration of free felinine, N-acetylfelinine and 3-methylbutanolglutathione in the urine remained low in the placebo control group throughout the study. The relative molar contribution of free felinine to the total amount of felinine containing compounds increased due to testosterone treatment, while the contribution of 3-methylbutanolglutathione and N-acetylfelinine decreased. Testosterone increases free felinine, N-acetylfelinine and 3-methylbutanolglutathione excretion in castrated adult male and intact female cats, whereas estradiol does not modulate this effect.

Characterization of cauxin in the urine of domestic and big cats

Cauxin is an abundant protein in feline urine. We have used proteomics strategies to characterize cauxin from the urine of domestic cats and a number of big cat species. Proteins were resolved by gel-based electrophoretic purification and subjected to in-gel digestion with trypsin. The resultant tryptic peptides were mass-measured by matrix-assisted laser desorption ionization time of flight mass spectrometry. Peptides were also resolved by liquid chromatography and analyzed by electrospray ionization and tandem mass spectrometry to generate fragment ion data to infer the amino acid sequence. We identified cauxin polymorphisms and corrected a sequencing artifact in cauxin from the domestic cat. The proteomics data also provided positive evidence for the presence of a cauxin homolog in the urine of big cats (Pantherinae), including the Sumatran tiger, Asiatic lion, clouded leopard, Persian leopard, and jaguar. The levels of cauxin in the urine of all big cats were substantially lower than that in the urine of intact male domestic cats.

Application of Metabonomics in a Comparative Profiling Study Reveals N-Acetylfelinine Excretion as a Biomarker for Inhibition of the Farnesyl Pathway by Bisphosphonates

In this work, the results of metabolic profiling of urine from a preclinical comparative profiling study with the two biphosphonates ibandronate and zoledronate are reported. Toxicological assessment showed very different effects for the two compounds. Ibandronate did not cause major signs of toxicity, whereas zoledronate elicited hepatotoxicity and nephrotoxicity. Increased levels of urinary glucose and decreased levels of urinary creatinine detected by NMR also indicated drug-induced nephrotoxicity. Similarly, increased urinary levels of creatine and taurine indicated hepatotoxicity. Both organ toxicities were later confirmed by histopathology. In addition, the benefit of metabonomics as an open approach as compared to targeted methods was demonstrated by the identification of an unknown molecule in the urine of rats dosed with zoledronate. The structure elucidation revealed this molecule as N-acetylfelinine. Analysis of the pathways proposed for the biochemical synthesis of this molecule showed that the synthesis and excretion of N-acetylfelinine could easily be explained by drug-induced inhibition of farnesyl diphosphate synthase. This is the reported mode of action of bisphosphonates. Until now, N-acetylfelinine was exclusively observed in the urine of felidae species, where it is believed to be a precursor to a pheromone.

A Major Urinary Protein of the Domestic Cat Regulates the Production of Felinine, a Putative Pheromone Precursor

Domestic cats spray urine with species-specific odor for territorial marking. Felinine (2-amino-7-hydroxy-5,5-dimethyl-4-thiaheptanoic acid), a putative pheromone precursor, is excreted in cat urine. Here, we report that cauxin, a carboxylesterase excreted as a major urinary component, regulates felinine production. In vitro enzyme assays indicated that cauxin hydrolyzed the felinine precursor 3-methylbutanol-cysteinylglycine to felinine and glycine. Cauxin and felinine were excreted age dependently after 3 months of age. The age-dependent increases in cauxin and felinine excretion were significantly correlated. In mature cats, cauxin and felinine levels were sex-dependently correlated and were higher in males than in females. In headspace gas of cat urine, 3-mercapto-3-methyl-1-butanol, 3-mercapto-3-methylbutyl formate, 3-methyl-3-methylthio-1-butanol, and 3-methyl-3-(2-methyldisulfanyl)-1-butanol were identified as candidates for felinine derivatives. These findings demonstrate that cauxin-dependent felinine production is a cat-specific metabolic pathway, and they provide information for the biosynthetic mechanisms of species-specific molecules in mammals.

Species-, sex-, and age-dependent urinary excretion of cauxin, a mammalian carboxylesterase

Domestic cats exhibit physiological proteinuria due to the excretion of cauxin, a carboxylesterase, into the urine. In the present report, we demonstrate that cauxin is excreted in a species-, sex-, and age-dependent manner. Although the cauxin gene is conserved in mammals, including human, mouse, and dog, urinary cauxin was found only in member of the genus Felis and lynx (bobcat, and lynx) and not in other Felidae (genus: Panthera and puma) tested. In mature cats, cauxin excretion was higher in intact males than in castrated males or in intact or spayed females. Daily cauxin excretion decreased immediately after castration. Immunohistochemistry confirmed that cauxin expression in the kidney proximal straight tubules was higher in intact males than in castrated males. Urinary cauxin was detectable by Western blotting in cats older than about 3 months, and its excretion increased with age. In a zymographic esterase assay, urine contained a major cauxin band; by contrast, kidney homogenates contained three major bands, comprising two carboxylesterases and an unidentified esterase, and one minor cauxin band. These results suggest that 1. cauxin excretion is regulated by sex hormones, such as testosterone, 2. cauxin functions as an esterase in the urine rather than in kidney cells, and 3. the decomposition products by cauxin are excreted in a species-, sex-, and age-dependent manner, as is cauxin itself.

Isolation and characterisation of renal metabolites of γ-glutamylfelinylglycine in the urine of the domestic cat (Felis catus)

The renal metabolism of the tripeptide, gamma-glutamylfelinylglycine, which our group recently identified in the blood of domestic cats (Felis catus), was investigated. To test our hypothesis that this unique tripeptide is metabolised by the kidney in a similar manner to glutathione-S-conjugates in other animal species, [(35)S]cysteine was administered intraperitoneally to an entire male cat, and urine collected at 1, 4 and 8 h post-injection. Radiolabelled fractions were isolated from the urine following reversed-phase (RP) HPLC. Four [(35)S]radiolabelled fractions were identified and characterised by amino acid analysis, mass spectrometry and comparison of retention times with synthetic compounds (felinine, N-acetyl felinine, felinylglycine, gamma-glutamylfelinylglycine). In addition to the previously described presence of free felinine, we showed the presence of several felinine-containing metabolites, including N-acetyl felinine, felinylglycine and unaltered gamma-glutamylfelinylglycine in cat urine. The results show that renal metabolism of gamma-glutamylfelinylglycine in cats, generally occurs in a similar manner to glutathione S-conjugates in other animal species, although the detection of felinylglycine indicates that subtle differences may exist. Additionally, our research indicates that previously reported estimates of felinine excretion in male cats need to be increased by as much as 54% to account for other felinine containing metabolites in the urine.