Effects of long-term phenobarbital treatment on the liver in dogs.

Long-term administration of phenobarbital has been reported to cause hepatic injury in dogs. Phenobarbital induces hepatic enzymes, and it may be difficult to distinguish the effect of enzyme induction on serum liver enzyme activities from actual hepatic damage. The hepatotoxicity of phenobarbital and the impact of enzyme induction on serum liver enzyme activity were investigated prospectively in 12 normal dogs. Phenobarbital was administered for 29 weeks at 5 mg per kilogram of body weight (range, 4.8-6.6 mg/kg) PO q12h, resulting in therapeutic serum phenobarbital concentrations (20-40 microg/mL). Serum alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyltransferase (GGT), fasted bile acids (fBA), total bilirubin, and albumin were determined before and during treatment. Lateral abdominal radiographs, abdominal ultrasounds, and histopathologic examinations of liver tissue obtained by ultrasound-guided biopsy were performed before and during treatment. Radiographs revealed a moderate increase in liver size in most dogs. Ultrasonographic examination revealed no change in liver echogenicity or architecture. No evidence of morphologic liver damage was observed histopathologically. ALP and ALT increased significantly (P < .05), GGT increased transiently, and albumin decreased transiently during the study. There were no significant changes in AST, bilirubin, and fBA. These results suggest that increases in serum ALP, ALT, and GGT may reflect enzyme induction rather than hepatic injury during phenobarbital treatment in dogs. Serum AST, fBA, and bilirubin, and ultrasonographic evaluation of the liver are not affected by the enzyme-inducing effect of phenobarbital and can therefore be helpful to assess liver disease in dogs treated with the drug.

Identification of the 1-cyano-3,4-epithiobutane-derived urinary mercapturic acid N-acetyl-S-(4-cyano-2-thio-1-butyl)-cysteine in male Fischer 344 rats.

1-Cyano-3,4-epithiobutane (CEB), a naturally occurring nitrile derived from cruciferous plants, causes nephrotoxicity in male Fischer 344 rats. Nephrotoxicity induced by CEB is dependent on glutathione (GSH) conjugation and bioactivation. Conjugation with GSH and subsequent metabolism leads to the formation of specific urinary metabolites. The objectives of the present study were to identify CEB-derived urinary metabolites and quantify urinary non-protein thiols and thioethers in male Fischer 344 rats. Animals received 125 mg kg(-1) of CEB alone or following pretreatment with one of three selective inhibitors of GSH metabolism: acivicin, probenecid or aminooxyacetic acid. Total non-protein urinary thiol and urinary thioether concentrations were elevated in all treated groups at 12 and 24 h; however, elevations in non-protein thiols were not significantly greater in rats administered CEB alone as compared to negative controls. A single predominant urinary metabolite was identified as the CEB-derived mercapturic acid N-acetyl-S-(4-cyano-thio-1-butyl)-cysteine. Evidence for other CEB-derived metabolites was also demonstrated. These findings represent the identification of a unique compound and provide further evidence for the importance of GSH conjugation as a significant pathway in CEB metabolism.

Protection from 1-cyano-3,4-epithiobutane nephrotoxicity by aminooxyacetic acid and effect on xenobiotic-metabolizing enzymes in male Fischer 344 rats.

1-Cyano-3,4-epithiobutane (CEB), a naturally occurring nitrile derived from cruciferous plants, causes nephrotoxicity and increased renal glutathione (GSH) concentration in male F-344 rats. This CEB-induced nephrotoxicity is dependent on GSH conjugation and bioactivation. The objectives of the present study were to investigate the effect of CEB on several xenobiotic-metabolizing enzymes and to evaluate the effect of modulators of GSH transport and metabolism on CEB-induced nephrotoxicity and GSH concentration. Animals received 125 mg kg-1 CEB alone or following pretreatment with one of three selective inhibitors of GSH metabolism: acivicin, probenecid or aminooxyacetic acid. There were no significant alterations in epoxide hydrolase (EH), P-450, ethoxyresorufin O-deethylase (EROD) or pentoxyresorufin O-depentylase (PROD) enzyme activity, but renal glutamyl cysteine synthetase (GCS) activity was decreased at 12 and 24 h, as was renal glutathione S-transferase 4 h after CEB administration. Renal ECOD activity was also diminished at 24 h and at 12 and 24 h in liver. Aminooxyacetic acid (AOAA) abrogated the nephrotoxicity, the renal GSH-enhancing effect, and decreased GCS of CEB alone. These findings provide further evidence for the importance of GSH conjugation as a significant pathway in CEB metabolism and the role of a reactive thiol in nephrotoxicity and altered renal GSH.

Cimetidine inhibits nitric oxide associated nitrate production in a soft-tissue inflammation model in the horse.

Cimetidine (CIM) is an H2-receptor antagonist that has been used in racehorses in an attempt to reduce the occurrence of stress-related gastric ulceration. It has also been shown to produce several useful effects other than its gastric acid suppression properties. Further, it is a well documented antagonist of cytochrome P-450 (CYP) mediated oxygenation reactions. Nitric oxide (NO), a recently discovered mediator or modifier of numerous physiological functions, is generated by several forms of nitric oxide synthase (NOS), one of which is inducible (iNOS). Inducible NOS, expressed in neutrophils and macrophages as part of the inflammatory response to noxious stimuli, contains both a CYP and a CYP reductase domain. Because of the similarity of structure of iNOS and CYP, it was decided to determine whether CIM could reduce NO production, using a carrageenan inflammation model in the horse. Two experiments were conducted. In Trial 1, six female Thoroughbred horses each had three tissue chambers inserted subcutaneously on the sides of the neck. The study was divided into three treatments: 0.9% NaCl (NaCI), CIM (3 mg/kg), and aminoguanidine (AG; 25 mg/kg), an inhibitor of iNOS. Each mare received three i.v. injections 12 h apart prior to instillation of 1 mL of carrageenan into the test chamber. Blood and tissue chamber fluid (TCF) were collected serially. Concentrations of NO3- (the major metabolite of NO), albumin, total protein, CIM and AG were measured and complete cell counts and differentials were conducted. Trial 2 also used six female Thoroughbred horses implanted with at least two tissue chambers inserted subcutaneously on the sides of the neck. The study was divided into two treatments: NaCl (0.9%) and CIM (6 mg/kg). Each mare received seven i.v. injections of either NaCl or CIM 8 h apart prior to instillation of 1 mL of carrageenan into the test chamber. Blood and TCF were collected serially as before, and analysed for NO3- and CIM content. Areas under the curve (AUC) of the different parameters were calculated for the periods of -1-1, -1-3 and -1-7 days (Trial 1) and -2-1 for Trial 2. Absolute values were also compared at 4, 8 and 12 h postcarrageenan. Saline treatment did not reduce the elevated concentrations of NO3- in either plasma or TCF. Plasma, test chamber and control chamber NO3-concentrations rose from 0 to 12 h, and were very similar in all three sampled fluids. Cimetidine significantly (P< or =0.05) decreased NO3- production in plasma over the periods of -1-1, -1-3, and -1-7 days post inflammation when compared to NaCl treatment in Trial 1. Aminoguanidine and CIM decreased NO3-production in TCF for the periods -1-1, 1-3, and -1-7 days post inflammation in Trial 1 and -2-1 for Trial 2. Both CIM and AG also significantly reduced NO3-concentrations in plasma and TCF at 12 h postinitiation (Trials 1 and 2). Thus CIM, at the doses studied, was capable of reducing NO3- concentrations in this model as effectively as AG, a relatively specific inhibitor of iNOS activity.

Effects of oral administration of orotic acid on hepatic morphologic characteristics and serum biochemical variables in cats.

OBJECTIVE: To evaluate orotic acid (OA) as a possible etiologic factor in cats with idiopathic hepatic lipidosis (HL). ANIMALS: 20 clinically normal adult female cats. PROCEDURE: Cats were fed a control diet or a diet containing less protein. On day 1 of the control period, blood, urine, and liver biopsy specimens were obtained. Each cat was given an oral dose of water daily. On days 8, 15, and 22, blood and urine specimens were collected as on day 1. On day 29, liver, blood, and urine samples were obtained as on day 1. After a resting period of 30 to 60 days, cats were treated with orotic acid. Serum biochemical analyses, urinary OA-to-creatinine ratios, and liver biopsy specimens were evaluated. Cats were given OA orally (suspension or capsules) for 29 days. Sample collection and data obtained were identical to those described for the control period. RESULTS: Urinary OA-to-creatinine ratios were significantly higher in all treated cats, but ratios were significantly higher in those receiving OA in capsules than in those receiving OA in suspension. Diet or treatment did not alter hepatic biochemical or histologic variables significantly. However, 7 cats given the highest dose of OA in capsules developed azotemia, urolithiasis, and renal changes. CONCLUSIONS: Most concentrations of OA used in this study did not induce HL in cats during a 29-day period, but the highest dosage used did result in renal disease. CLINICAL RELEVANCE: Orotic acid does not appear to be involved in the genesis of HL in cats.

Urinary orotic acid-to-creatinine ratios in cats with hepatic lipidosis.

OBJECTIVE: To determine urinary orotic acid (OA) concentration and evaluate the urinary OA-to-creatinine ratio (OACR) in cats with hepatic lipidosis (HL). ANIMALS: 20 cats with HL and 20 clinically normal cats. PROCEDURE: Hepatic lipidosis was diagnosed on the basis of clinical signs, results of serum biochemical analyses, exclusion of other concurrent illness, and cytologic or histologic evaluation of liver biopsy specimens. Urine samples were collected from each cat and frozen at -20 C until assayed. Urine creatinine concentrations were determined, using an alkaline picrate method followed by spectrophotometric assay. Urine OA concentration was determined, using high-performance liquid chromatography. Minimum amount of detectable OA in feline urine was 1 microg/ml. Because of small interfering peaks near the base of the OA peak, the minimum quantifiable concentration of OA was determined to be 5 microg/ml. Urinary OACR was compared in both groups of cats. RESULTS: Differences in urinary OACR were not detected between clinically normal cats and cats with HL. Peaks were not detected for urinary OA in any of the 20 clinically normal cats. Of the 20 HL cats, 14 did not have detectable peaks for urinary OA. Of the 6 HL cats that had detectable urinary OA peaks, 3 had values of <5 microg/ml. CONCLUSIONS: Apparently, OACR does not increase significantly in cats with HL. CLINICAL RELEVANCE: Urinary OACR is not a useful diagnostic test for HL in cats.

Cervical spinal cord compression caused by cryptococcosis in a dog: successful treatment with surgery and fluconazole.

A six-year-old, male Doberman pinscher was presented for acute onset of upper motor neuron tetraparesis. An extradural compressive lesion compatible with intervertebral disk rupture at the sixth to seventh cervical (C6-C7) disk space was evident on myelography. A large, gelatinous mass of pure cryptococcal organisms causing spinal cord compression was identified upon exploratory surgery. Removal of the mass caused relief of clinical signs. No evidence of involvement of other organ systems was found; however, serum and cerebrospinal fluid titers were positive for cryptococcal infection. The dog was treated with fluconazole (5.5 mg/kg body weight, per os sid) until serum titers for cryptococcal infection were negative at seven months postsurgery. To the authors' knowledge, this is the only report of a dog with cryptococcosis treated successfully using fluconazole as a sole agent.

Hemobartonella felis infection with atypical hematological abnormalities.

Two cases of clinical feline hemobartonellosis with dramatic hematological changes are reported. One cat succumbed to an acute, severe hemolytic anemia accompanied by markedly increased numbers of nucleated erythrocytes. The second cat presented with a remarkably elevated leukocyte count and responded well to treatment with tetracycline. In both instances, the initial hematological data was very unusual for feline hemobartonellosis. These cases further exemplify the greatly variable and sometimes misleading hematological changes seen with Hemobartonella felis infection.

The effect of glutathione depletion by buthionine sulphoximine on 1-cyano-3,4-epithiobutane toxicity.

The effect of glutathione (GSH) depletion by buthionine sulphoximine (BSO) on the nephrotoxicity and GSH-enhancing effect of the naturally occurring, crucifer-derived nitrile 1-cyano-3.4-epithiobutane (CEB), was investigated. Male Fischer 344 rats were administered 50 or 125 mg CEB/kg body weight by gavage with or without prior ip treatment with 550 mg/kg body weight L-BSO. One group of control animals was treated with water only by gavage, while another group was pretreated with BSO and then given water by gavage. Liver and kidney samples were taken 48 hr after CEB treatment for GSH determinations and histological examination. The high-dose CEB without BSO resulted in increased GSH in liver and kidney, marked karyomegaly in the pars recta of renal proximal tubules and tubular epithelial necrosis, which was limited to a few renal tubules. The low-dose CEB alone resulted in increased hepatic GSH and mild karyomegaly. Pretreatment with BSO abrogated the tubular necrosis and karyomegaly induced by either CEB dose. BSO pretreatment inhibited low-dose CEB-induced GSH enhancement in the liver. The combined BSO and high-dose CEB treatment still resulted in increased hepatic GSH, although the increase was less than that observed with high-dose CEB alone. In the kidney, BSO pretreatment abrogated the high-dose CEB-induced increase in GSH, but GSH content was not significantly different from that with high- or low-dose CEB alone. These results provide evidence that CEB conjugation may be a bioactivation reaction with the conjugate involved in nephrotoxicity. The conjugate may also be involved in increasing renal and hepatic GSH.

Sequential changes in hepatic and renal glutathione and development of renal karyomegaly in 1-cyano-3,4-epithiobutane toxicity in rats.

The effect of 1-cyano-3,4-epithiobutane (CEB) on glutathione (GSH) metabolism was investigated in rat liver, kidney and pancreas. Male Fischer 344 rats were gavaged with a single dose (125 mg/kg body weight or 50 mg/kg body weight) of CEB. Tissue samples were taken for histological examination, determination of GSH and oxidized glutathione (GSSG) concentrations and gamma-glutamyl transpeptidase (GGT) and glutathione S-transferase (GST) activities. Urine samples were analysed for non-protein thiol (NP-RSH) content. The high dose of CEB induced hepatic GSH depletion followed by increased GSH. The low dose of CEB induced elevated hepatic GSH by 12 hr without depletion. Renal GSH was increased with both doses without an observed depletion phase. Renal tubule epithelial cell death was observed only with the high dose of CEB, but both doses caused renal proximal tubule karyomegaly. Pancreatic GSH content was unaffected. No alterations of GSSG were observed. GST activity was unaffected in any tissue. Renal GGT activity was decreased at 12 hr with both doses and at 24 and 48 hr with the high dose. Urinary NP-RSH excretion was increased with both doses. Depletion of hepatic GSH concurrent with increased urinary NP-RSH excretion suggests that conjugation with GSH is a significant pathway in CEB metabolism.

Subcutaneous phaeohyphomycosis caused by Scolecobasidium humicola in a cat.

Scolecobasidium humicola was isolated from granulomatous lesions on the tail and foot of a cat. The paw lesion, of 2 years duration, had recurred after surgical debridement and antibiotic therapy. In tissue sections of the biopsy, S. humicola was observed in the form of broad, septate, dematiaceous hyphal elements and thick-walled, chlamydoconidium-like cells. The cat was successfully treated with ketoconazole and has since shown no signs of recurrence. This is the first record of S. humicola being an etiologic agent of phaeohyphomycosis in a mammalian host.

Free radicals: relation to tissue damage - a review.

Free radicals are any molecules having an odd number of electrons. These molecules are highly reactive and can be generated as byproducts of normal metabolism as well as by exposure to a number of environmental factors including drugs, radiation and air pollutants. Due to the ubiquity of molecular oxygen, the oxygen metabolites superoxide anion, hydrogen peroxide, and the hydroxyl radical are frequently involved in both beneficial and detrimental free radical reactions. Intracellular enzymes and radical scavengers help to protect against tissue damage by these reactive metabolites. The extent of free radical damage to tissue depends on the nature of the radical produced and its site of generation.

Atypical Histoplasma capsulatum infection in a dog.

Disseminated histoplasmosis was diagnosed in a 10-year-old dog suspected of having hepatic carcinoma. Clinical abnormalities included diffuse hepatomegaly, gastrointestinal bleeding, thoracic and abdominal effusion, anemia, leukocytosis, and thrombocytopenia. Histoplasmosis characteristically is a disease of the mononuclear phagocyte system, but in this case was diagnosed by finding Histoplasma capsulatum organisms in neutrophils on the blood smear.