Urinary Orotic Acid Excretion Research Articles

Ion chromatographic method for the determination of orotic acid in urine

Excess urinary orotic acid excretion occurs in patients with some inborn errors of metabolic pathways such as pyrimidine synthesis and urea cycle. Thus, rapid diagnosis of orotic aciduria has a vital importance for patients. In this paper, a novel method for determination of orotic acid in urine samples by ion chromatography with suppressed conductivity detection was investigated. The separation of orotic acid from urine matrix was accomplished by using an anion exchange column with optimized isocratic eluent program which utilized 50 mM NaOH. The other chromatographic conditions were as follows: the suppressor current was 31 mA; the flow rate of mobile phase was 0.25 mL min−1; the column temperature was 30 °C; sample loop volume was 10 μL. Under optimized conditions, the limit of detection was 0.2 μmol L‾1. Dramatically elevated orotic acid concentration was observed on pathological urine samples comparing to healthy urines, as expected. There are a good many advantages of the proposed method, but using an environmentally friendly reagent free system, no organic solvent employment and its quick nature, and being a sensitive and reliable method are the most obvious ones. The proposed method, therefore, may be utilized as an alternative technique for clinical laboratories.

Mild orotic aciduria in UMPS heterozygotes: a metabolic finding without clinical consequences

BackgroundElevated urinary excretion of orotic acid is associated with treatable disorders of the urea cycle and pyrimidine metabolism. Establishing the correct and timely diagnosis in a patient with orotic aciduria is key to effective treatment. Uridine monophosphate synthase is involved in de novo pyrimidine synthesis. Uridine monophosphate synthase deficiency (or hereditary orotic aciduria), due to biallelic mutations in UMPS, is a rare condition presenting with megaloblastic anemia in the first months of life. If not treated with the pyrimidine precursor uridine, neutropenia, failure to thrive, growth retardation, developmental delay, and intellectual disability may ensue.Methods and resultsWe identified mild and isolated orotic aciduria in 11 unrelated individuals with diverse clinical signs and symptoms, the most common denominator being intellectual disability/developmental delay. Of note, none had blood count abnormalities, relevant hyperammonemia or altered plasma amino acid profile. All individuals were found to have heterozygous alterations in UMPS. Four of these variants were predicted to be null alleles with complete loss of function. The remaining variants were missense changes and predicted to be damaging to the normal encoded protein. Interestingly, family screening revealed heterozygous UMPS variants in combination with mild orotic aciduria in 19 clinically asymptomatic family members.ConclusionsWe therefore conclude that heterozygous UMPS-mutations can lead to mild and isolated orotic aciduria without clinical consequence. Partial UMPS-deficiency should be included in the differential diagnosis of mild orotic aciduria. The discovery of heterozygotes manifesting clinical symptoms such as hypotonia and developmental delay are likely due to ascertainment bias.

A Novel Description of Increased Urinary Orotic Acid Excretion in Pediatric Trauma

The diagnostic utility of orotic aciduria for suspected inborn errors of metabolism is well established. Orotic aciduria has been reported in traumatized adults, but not in children. A 2-year-old hyperammonemic girl with cardiac arrest and abdominal compartment syndrome secondary to non-accidental trauma with significant orotic aciduria is presented. To our knowledge, this is the first report highlighting the association of transiently elevated urinary orotic acid and mild uricosuria with severe trauma in children. Further investigations into the clinical use of orotic acid excretion as a biomarker of the catabolic state of pediatric trauma or other critical illness are warranted. J Endocrinol Metab. 2014;4(1-2):32-35 doi: http://dx.doi.org/10.14740/jem209w

A Novel Description of Increased Urinary Orotic Acid Excretion in Pediatric Trauma

The diagnostic utility of orotic aciduria for suspected inborn errors of metabolism is well established. Orotic aciduria has been reported in traumatized adults, but not in children. A 2-year-old hyperammonemic girl with cardiac arrest and abdominal compartment syndrome secondary to non-accidental trauma with significant orotic aciduria is presented. To our knowledge, this is the first report highlighting the association of transiently elevated urinary orotic acid and mild uricosuria with severe trauma in children. Further investigations into the clinical use of orotic acid excretion as a biomarker of the catabolic state of pediatric trauma or other critical illness are warranted. J Endocrinol Metab. 2014;4(1-2):32-35 doi: http://dx.doi.org/10.14740/jem209w

Dihydrofolate Reductase Deficiency Is Caused by a Homozygous DHFR Mutation and Leads to Congenital Megaloblastic Anemia and Cerebral Folate Deficiency

AbstractAbstract 1006Folate deficiency can be associated with megaloblastic anemia, neurological and mental disorders, cardiovascular disease, embryonic defects, in particular neural tube defects, and, possibly, malignancies. The importance of an intact intracellular folate metabolite cycle is illustrated by the severity of symptoms in rare inborn disorders of folate metabolism.Dihydrofolate reductase (DHFR) catalyzes the reduction of dihydrofolate (DHF) to tetrahydrofolate (THF) and at a lower rate of folic acid (FA) to DHF. DHFR plays a key role in maintaining intracellular folate homeostasis. A distinct genetic defect associated with DHFR deficiency has not been described.We examined three children of healthy distantly related parents presenting with megaloblastic anemia and neurological symptoms of varying severity. Total serum folate and cobalamin, homocysteine, urinary excretion of methylmalonic acid, orotic acid, formiminoglutamic acid, and cobalamin binding capacity were normal. Red blood cell (RBC) folate was below the normal range in all patients. Cerebrospinal fluid (CSF) analysis revealed very low 5-methyl-tetrahydrofolate (5MTHF) in one and the absence of detectable CSF 5MTHF in two siblings. Treatment with folinic acid (5-formyl-tetrahydrofolate; 5FTHF) increased RBC folate in all patients associated with a normalization of RBC indices and bone marrow morphology and led to CSF 5MTHF normalization.According to a recessive inheritance model, we conducted a screen for homozygous chromosomal regions using genome-wide analysis of single nucleotide polymorphisms. This analysis revealed a short overlap on the long arm of chromosome 2 and a second common region on the long arm of chromosome 5. This region included the DHFR gene locus. Genomic sequence analysis of DHFR exons and neighboring nucleotides revealed a homozygous mutation DHFR c.458A>T in exon 5 (RefSeq NM_000791) leading to the amino acid change DHFR p.Asp153Val (p.D153V) in all siblings.Assuming DHFR deficiency we analyzed folate metabolites in RBCs and plasma by liquid chromatography tandem mass spectrometry (LC-MS/MS). The folate profile in RBCs and plasma was compatible with DHFR deficiency. To examine DHFR function we studied the formation of THF out of DHF in EBV-immortalized lymphoblastoid cells from patients, their heterozygous mother and healthy control individuals. DHFR activity was severely reduced in all patient cells (12, 88, 51 pmol THF per hour and mg protein, respectively) as compared to controls (median 3741, range 1441–6828 pmol/h*mg) whereas cells of the heterozygous mother exhibited DHFR activity close to the lower limit of the control range (1156 pmol/h*mg). A fluorescent Methotrexate (MTX) binding assay showed a markedly reduced MTX binding capacity in EBV-immortalized lymphoblastoid cells of all three patients. Cells of the heterozygous mother presented an intermediate binding capacity. To assess whether the reduced DHFR activity was caused by an altered mRNA and protein expression due to the DHFR p.Asp153Val mutation we performed RT-PCR and western blot analyses. RT-PCR revealed a single ∼450bp cDNA fragment without significant quantitative differences between DHFR wildtype, DHFR p.Asp153Val heterozygous, or homozygous cells. In contrast, DHFR protein expression was reduced in EBV-immortalized lymphoblastoid cells carrying the DHFR mutation as compared to wildtype cells. Semiquantitative assessment revealed a reduction of the amount of intact DHFR protein in heterozygous lymphoblastoid cells to about 70 percent, in homozygous cells from one patient to 50 percent and from the other patients to 20–30 percent as compared to wildtype cells.In conclusion, the homozygous mutation DHFR p.Asp153Val causes DHFR deficiency and leads to a complex hematological and neurological disease which can successfully be treated with 5FTHF. Disclosures:No relevant conflicts of interest to declare.

Les déficits du cycle de l’urée chez les patients adultes

Urea cycle disorders (UCD) usually present after 24 h to 48 h of life with failure to thrive, lethargy and coma leading to death, but milder forms may occur from infancy to adulthood. Survival of children with UCD has significantly improved and the need for transitional care to adulthood has emerged. Adult onset UCD present with chronic or acute neurological, psychiatric and digestive symptoms associated with protein avoidance. Ornithine transcarbamylase (OTC) deficiency, which is inherited as an X-linked disorder, is the most well-described UCD in adults. Acute decompensations associate the triad of encephalopathy, respiratory alkalosis and hyperammonemia. Acute encephalopathy is characterized by brain edema, which is life-threatening without treatment. Specific urea cycle enzyme deficiency can be suspected in the presence of abnormal plasma amino acids concentrations and urinary excretion of orotic acid. A measurement enzyme activity in appropriate tissue, or DNA analysis if available, is required for diagnosis. Treatment requires restriction of dietary protein intake and the use of alternative pathways of waste nitrogen excretion with sodium benzoate and sodium phenylbutyrate. Patients with acute forms may need hemodialysis or hemodiafiltration. Therapeutic goals for OTC deficiency are to maintain plasma ammonia<80 micromol/L, plasma glutamine<1,000 micromol/L, argininemia 80-150 micromol/L and branched chain amino acids within the normal range, in order to prevent episodes of potentially lethal acute hyperammonemia. Potentially fatal acute hyperammonemia may occur in male or female patients at any age. Ammonia should be measured promptly in case of acute neurological and psychiatric symptoms or coma.

Orotic Acid Excretion and Arginine Metabolism

The urinary excretion of orotic acid, an intermediate in the pyrimidine biosynthetic pathway, is markedly increased in many inborn errors of the urea cycle and in a number of other disorders involving arginine metabolism. Carbamoyl phosphate, which accumulates within hepatic mitochondria in patients with ornithine transcarbamoylase deficiency, can diffuse to the cytosol and enter the pyrimidine pathway, resulting in greatly increased orotic acid production and excretion. This orotic aciduria also occurs in inborn errors of the mitochondrial ornithine/citrulline transporter, arginase, argininosuccinate synthetase, and argininosuccinate lyase. Increased orotic acid excretion is also found in a number of hypoargininemic states, such as lysinuric protein intolerance. However, orotic aciduria should not be used uncritically as an index of arginine deficiency because it is found in patients with arginase deficiency who exhibit hyperargininemia. Increased orotic acid excretion can also arise as a result of impairments of pyrimidine synthesis, whether brought about by a genetic defect (e.g., in UMP synthase) or by drugs that inhibit the terminal part of the pathway (e.g., allopurinol or 6-azauridine). When used appropriately, measurement of urinary orotic acid is a valuable tool for the study of many derangements of arginine metabolism, including arginine depletion, and to assess the efficacy of therapies used to replete this amino acid.

Purine and pyrimidine metabolites in children's urine

Various enzyme defects in the metabolic pathways of purines and pyrimidines are known, which result in different diseases occurring in children. They mainly affect kidney function, central nervous system, immunological and blood system. For example, complete deficiency of HPRT (hypoxanthine-guanine-phosphoribosyl-transferase) causes the Lesch Nyhan syndrome, which is characterized by hyperuricemia, mental retardation, choreoathetosis and compulsive self-mutilation. XDH deficiency (xanthine-dehydrogenase) causes in arthropathia and myopathia. For screening for these and other enzyme defects, urinary purine and pyrimidine excretion is considered a simple diagnostic tool. The purpose of the present study was to establish a reverse phase HPLC screening method for urinary purines and pyrimidines and to establish age related reference ranges in children for the urinary excretion of orotic acid, uracile, pseudouridine, uric acid, hypoxanthine, xanthine, thymine, 7-methylguanine, inosine, guanosine and adenosine.

Plasma urea-cycle-related amino acids, ammonium levels, and urinary orotic acid excretion in short-bowel patients managed with an oral diet

Background and Aims: The small intestine contains several enzymes involved in arginine synthesis and converts glutamine to citrulline, the major compound for endogenous arginine synthesis. This study was conducted to assess the plasma status of urea-cycle intermediates and orotic urinary excretion in short-bowel patients. Methods:Thirteen stable short-bowel syndrome patients (7 men; 60.2±15.2 years) were studied. Patients were divided into moderately resected (Group A; n=6) and severely resected (Group B; n=7) according to their remnant bowel length (Group A: 61–150 cm; Group B: ≤60 cm). All subjects were consuming an oral diet plus dietetic supplements. Plasma urea-cycle amino acids, ammonium and urinary orotic acid were determined. Results: Plasma glutamine levels were significantly higher in both patient groups than in the control group ( P<0.001). Regarding citrulline, Group B levels were significantly lower vs. controls ( P<0.001). Comparisons between patient groups showed higher arginine in Group A ( P<0.05) and non-statistically lower citrulline in Group B. Blood ammonium and orotic urinary excretion were normal. Conclusions: Although plasma citrulline and glutamine alterations were found, patients showed no hyperammonemia or orotic aciduria, which suggests a certain degree of adaptation in arginine and related amino acid metabolism, when an adequate dietary supply of arginine is provided.

Effect of lysine infusion on urea cycle in lysinuric protein intolerance

Poor intestinal absorption and excessive renal loss of dibasic amino acids result in low plasma concentrations in patients with lysinuric protein intolerance (LPI). Arginine and ornithine deficiency impair the function of the urea cycle and cause hyperammonemia after protein intake, while chronic lysine deficiency may cause growth failure and lead to reduced bone density in such patients. Since high lysine concentrations inhibit several enzymes of the urea cycle in the liver, lysine supplementation may induce hyperammonemia in LPI. We thus studied how LPI patients tolerate high plasma lysine by intravenous (IV) infusion of 3.3 mmol/kg lysine hydrochloride over 90 minutes in 6 adult patients and 4 healthy controls. The plasma lysine concentration (mean +/- SD, range) peaked in the patients (9,114 +/- 1,864, 7,156 to 12,044 micromol/L) and controls (10,185 +/- 2,253, 7,714to 13,122 micromol/L) at 90 minutes. Urinary lysine excretion peaked in the second 2-hour urine collection in the patients (4,582 +/- 1,276, 3,018 to 6,315 micromol/m2 body surface area per hour) and in the first 2-hour collection in the controls (5,373 +/- 1,766, 3,551 to 7,286 micromol/m2/h). Two patients had mild nausea but no hyperammonemia and one patient had moderate hyperammonemia (peak, 112 micromol/L) at the end of the infusion. Orotic acid excretion increased in 2 subjects with a peak excretion rate of 33 and 251 micromol/m2/h in the third 2-hour collection after starting the load. All other subjects remained asymptomatic and showed no change in plasma ammonia or urinary orotic acid excretion. We thus conclude that an acute increase in plasma lysine caused minimal clinical or biochemical untoward effects in patients with LPI. Moderate increases in plasma lysine after low-dose oral supplementation with lysine or well-absorbed lysine derivatives are probably well tolerated in LPI.

Aberrations of ammonia metabolism in ornithine carbamoyltransferase-deficient spf-ash mice and their prevention by treatment with urea cycle intermediate amino acids and an ornithine aminotransferase inactivator

Sparse fur with abnormal skin and hair (spf-ash) mice are deficient in ornithine carbamoyltransferase (OCT) activity, but their OCT protein is kinetically normal. We administered ammonium chloride to spf-ash mice, in order to analyze ammonia metabolism and to find a rationale for the therapy of OCT deficiency. Ammonia concentration in the liver of spf-ash mice increased to a level much higher than in the control. Ammonium chloride injection caused an increase in ornithine (Orn) 5 min after injection and an increase in the sum of Orn, citrulline (Cit) and arginine (Arg) for at least 15 min in the liver of control mice, but no increase in Orn, Cit and Arg in the liver of spf-ash mice. Treatment of spf-ash mice with Arg 5–20 min prior to the injection of ammonium chloride kept the hepatic ammonia concentration at a level comparable to that without the load. A significant reciprocal relationship between ammonia and Orn concentrations in the liver of spf-ash mice 5 min after an ammonium chloride load with or without Arg strongly suggests that ammonia disposal is dependent on the supply of Orn. In spf-ash mice loaded with tryptone as a nitrogen source, Arg supplementation showed a dramatic decrease in urinary orotic acid excretion in a dose-dependent manner. Similar effects were observed with Cit and Orn at the same dose, and a long-lasting effect with an ornithine aminotransferase inactivator, 5-(fluoromethyl)ornithine, at a much lower dose. The rate of urea formation in liver perfused with ammonium chloride was lower in spf-ash mice than in controls, but with the addition of Orn to the medium it increased to a similar level in control and spf-ash mice. These results indicate that OCT is not saturated with Orn in vivo under physiological conditions and that the administration or enrichment of the urea cycle intermediate amino acids enhances the OCT reaction so that the ammonia metabolism of OCT-deficient spf-ash mice is at least partially normalized.

Effects of dietary supply of arginine on urinary orotic acid excretion, growth performance and blood parameters in growing mink (Mustela vison) kits fed low‐protein diets

Effects of dietary arginine levels of 1.2%, 1.7% and 2.2% of dry matter (DM) (4.8 g/16 g N, 6.4 g/16 g N and 8.0 g/16 g N, respectively) and excess dietary lysine (6.5% in DM, 22 g/16 g N) were investigated in male mink kits fed low‐protein diets supplemented with a mixture of amino acids in the growing period during 4 weeks in July‐August. Urinary excretion of orotic acid, growth performance, feed consumption, plasma concentrations of ammonia (NH3), orotic acid, urea and glucose were studied. The results showed that arginine is an essential nutrient for mink kits in the growing period and that excess dietary lysine antagonizes arginine. An arginine supply of 2.2% of DM (8.0 g/16 g N) resulted in minimum urinary excretion of orotic acid and a supply of 1.7% of DM (6.4 g/16 g N) prevented increased plasma concentrations of NH3. Growth performance was negatively affected by the low protein level in all diets. The plasma concentrations of orotic acid, urea and glucose were not affected by the dietary levels of arginine.

Cycloheximide sensitivity of orotic acid biosynthesis induced by ammonia and glycine administration.

Administration of either ammonia or glycine to both rats and mice results in an increased synthesis in the liver and urinary excretion of orotic acid. The two most relevant observations obtained are that carbamoyl phosphate synthesized inside the mitochondria is involved in the increased synthesis of orotic acid and that this latter process is almost completely abolished by cycloheximide and actinomycin D, inhibitors of protein and RNA synthesis. Orotic acid synthesis could be controlled by an induction-suppression mechanism. Inhibition of synthesis of excess orotic acid brought about by N-(phosphonacetyl)-L-aspartic acid but not by acivicin, suggests that glutamine-dependent cytosolic synthesis of carbamoyl phosphate, is not involved. Administration of ornithine together with glycine completely suppressed the synthesis of orotic acid, but promoted a twofold increase of urea excretion. The concentration of ornithine rather than that of carbamoyl phosphate or the activity of the enzymes involved, may represent a limiting factor controlling both the flux of ammonia in the urea cycle and the availability of mitochondrial carbamoyl phosphate for orotic acid synthesis. Two enzymes have been found to be induced by glycine: ornithine decarboxylase and aspartate transcarbamoylase (aspartate carbamoyltransferase). Both enzymes may contribute to the increase in orotic acid synthesis, aspartate transcarbamoylase more directly and ornithine decarboxylase by lowering the ornithine concentration. Ornithine decarboxylase activity was completely suppressed but that of aspartate transcarbamoylase was further increased by cycloheximide treatment. Inhibition of orotic acid biosynthesis by cycloheximide appears to be the result of a decreased availability in the cytosol of carbamoyl phosphate synthesized inside the mitochondria.

Valeurs de référence de l'oroticurie dans une population tunisienne saine

Orotic acid (OA) is an intermediary metabolite of pyrimidine synthesis. An elevation of urinary orotic acid excretion has been described in congenital defect of the urea cycle enzymes and in primary orotic aciduria. Several techniques have been used to measure OA and many reference values are published without considering age and sex. The reference values of urinary OA excretion, expressed in mumol/mmol of creatinine, are reported in a healthy Tunisan population using a colorimetric method. The study included 20 men and 20 women (age = 31 +/- 11 years) and 30 children aged from 3 days to 8 years. There was a significant increase (P < 0.01) of urinary OA excretion in women (4.38 +/- 1.35) compared to men (3.26 +/- 0.80) and of children (5.03 +/- 1.14) compared to adults (3.82 +/- 1.24). Urinary OA excretion was significantly higher among children aged less than 1 year compared to older children. It is necessary for every laboratory practicing this kind of exploration to have its own norms which depend on both age and sex.

Increasing dispensable amino acids in diets of kittens fed essential amino acids at or below their requirement increases the requirement for arginine

Kittens fed diets containing 0.75 × the NRC (1986) essential amino acid requirement (EAArq) and 210 to 560g crude protein(CP)/kg diet exhibited, with increasing CP: 1) decreasing weight gain, 2) decreasing plasma arginine concentrations, 3) increasing urinary orotic acid excretion, 4) increasing plasma glutamic acid concentrations, and 5) plasma isoleucine concentrations at levels that suggest a marginal isoleucine deficiency. Kittens fed a control diet (CD) containing 1.5 × EAArq and 350 g CP/kg diet had maximal weight gains and no orotic aciduria. It was concluded that the decreased weight gain and adverse metabolic effects were caused by arginine deficiency and possibly glutamic acid toxicity induced by high dietary dispensable amino acids. Kittens fed the diets containing 1.0 × EAArq and 350 and 560 g CP/kg diet had depressed plasma arginine and elevated glutamic acid concentrations and orotic aciduria. These results indicate that 10 g arg/kg diet is not adequate at CP concentrations above 280 g/kg and the calculated requirement of arginine is (0.02 g arginine/g CP) × (Y g CP/kg diet) + (4.0 g arginine/kg diet) where Y is the dietary CP level.

Importance of ornithine transcarbamylase (OTC) deficiency in small intestine for urinary orotic acid excretion: Analysis of OTC-deficient spf-ash mice with OTC transgene

We report the effect of the ornithine transcarbamylase (OTC) transgene composed of 1.3 kb of the 5' flanking region of the rat OTC gene fused to rat OTC cDNA on urinary orotic acid excretion in OTC-deficient spf-ash (sparse-fur with abnormal skin and hair) mice during overnight-starvation and nitrogen loading. During starvation, spf-ash mice with about 6% and 2% of control levels of OTC activity in the liver and small intestine excreted a large amount of orotic acid in the urine. Transgenic spf-ash mice with about 10% and 30% of the control OTC activities in the liver and small intestine did not excrete more than the normal level of orotic acid. Accidental parasitization of transgenic spf-ash mice with ticks ( Myocoptes musculinus) resulted in decrease of the OTC activities in the liver and small intestine to the levels in spf-ash mice, and increased excretion of orotic acid. During extermination of the ticks, the mice showed varied levels of OTC activity and orotic acid excretion. On nitrogen loading, transgenic spf-ash mice as well as spf-ash mice excreted larger amounts of orotic acid, while control mice showed no increase in its excretion. The levels of urinary orotic acid were inversely correlated to the logarithms of the OTC activities in the liver and small intestine, the correlation being significantly higher with intestinal OTC than with hepatic OTC activity. These results suggest that the level of OTC activity in the small intestine is important for production of orotic acid.

Arginine becomes an essential amino acid after massive resection of rat small intestine.

We compared effects of feeding arginine- and/or proline- deficient diets (-Arg, -Pro, and -Arg, Pro) with those of a complete diet (Complete) in rats whose small intestine had been massively resected. After 4 weeks, the rats fed -Arg and -Arg, Pro lost weight (a mean of 28 and 32 g, respectively), whereas those fed Complete and -Pro gained 80 and 58 g, respectively. The average nitrogen balance was about 117,100, -20 and -14 mg/day for Complete, -Pro, -Arg, and -Arg, Pro diets, respectively. The concentration of arginine in skeletal muscle was about 310, 330, 91, and 65 nmol/g for Complete, -Pro, -Arg, and -Arg, Pro, respectively; while plasma arginine concentration averaged 95, 107, 56, and 46 microM, respectively. The weight loss, the negative nitrogen balance, and the markedly reduced arginine concentration in the muscle observed in rats fed -Arg and -Arg, Pro clearly indicate that arginine becomes a strictly essential amino acid in the rats with massive resection of the small intestine. However, sufficient proline can be synthesized from arginine in tissues such as the liver and kidney in the absence of the small intestine. Plasma glutamine, citrulline in the muscle and plasma, urinary excretion of orotic acid and nitrate (to assess nitric oxide formation from arginine) were also measured, and the changes in these metabolites are discussed.

Long-Term Voluntary Fasting in Adult Obese Cats: Nitrogen Balance, Plasma Amino Acid Concentrations and Urinary Orotic Acid Excretion

Long-Term Voluntary Fasting in Adult Obese Cats: Nitrogen Balance, Plasma Amino Acid Concentrations and Urinary Orotic Acid Excretion

Nitrogen Balance, Plasma Free Amino Acid Concentrations and Urinary Orotic Acid Excretion during Long-Term Fasting in Cats1–4

The purpose of this study was to ascertain the changes in nitrogen balance, plasma free amino acid concentrations, urinary orotic acid excretion and body weight during long-term fasting in adult obese cats. Results from eight cats that fasted rather than eat an unpalatable diet are reported. After 5 to 6 wk of weight loss, six of the eight cats developed signs of hepatic lipidosis, and the livers of all cats were severely infiltrated with lipids. Cats lost (mean +/- SE) 33.2 +/- 1.4% of their pre-fasting body weight. Mean nitrogen balance (+/- SE) was -547 +/- 54 mg.d-1.kg-2/3 for the first week, and then the net nitrogen losses decreased to a plateau (-303 +/- 52 mg.d-1.kg-2/3) after 4 wk. Fasting was associated with a decrease in plasma concentration of essential amino acids. When plasma amino acid concentrations were considered individually, concentrations of alanine, methionine, taurine, citrulline, arginine and tryptophan decreased the most (> or = 50%), whereas concentrations of glutamine, glutamate and ornithine significantly increased. Orotic acid was not detected in the urine during the fast. After 1 wk of fasting, obese cats had reduced nitrogen excretion, but not to the same extent as has been shown in obese humans or obese rats. It is suggested that the availability of several amino acids may become limiting for liver protein synthesis during fasting and that these deficiencies may contribute to the development of hepatic lipidosis. Orotic acid was not linked to hepatic lipidosis caused by fasting in cats.

Normalization of hair growth in sparse fur-abnormal skin and hair (SPF-ASH) mice by introduction of the rat ornithine transcarbamylase (OTC) gene

The sparse fur-abnormal skin and hair (SPF-ASH) mouse is a model for the human X-linked hereditary disease, ornithine transcarbamylase (OTC) deficiency. This condition is characterized by abnormal skin and delayed hair growth, hyperammonemia, orotic aciduria and low levels of serum citrulline and arginine. Murakami et al. [1] established a line of transgenic mice, by introducing the recombinant rat OTC (rOTC) gene into fertilized C57BL mouse eggs. We introduced the rOTC gene into SPF-ASH mice by mating SPF-ASH heterozygotes and transgenic mice, which carried this gene. The hemizygous SPF-ASH mice bearing the rOTC gene showed normal hair growth without sparse fur, normal urinary orotic acid excretion and normal serum citrulline and arginine levels. These mice showed OTC activities 2 and 6 times higher in the liver and small intestine, respectively, than the SPF-ASH mice but about 12% and 27% those of the controls [2].