The use of toxicokinetic data in preclinical safety assessment: a toxicologic pathologist perspective.

Collection of toxicokinetic data has become a routine practice during the last 15 years in most general toxicity studies on pharma. It enables the correlation of pathological changes with the plasma concentration of drugs and/or their metabolites. This overview summarizes the use of the toxicokinetic data from the perspective of the toxicologic pathologist.

Uniform procedure of (1)H NMR analysis of rat urine and toxicometabonomics Part II: comparison of NMR profiles for classification of hepatotoxicity.

A procedure of nuclear magnetic resonance (NMR) urinalysis using pattern recognition is proposed for early detection of toxicity of investigational compounds in rats. The method is applied to detect toxicity upon administration of 13 toxic reference compounds and one nontoxic control compound (mianserine) in rats. The toxic compounds are expected to induce necrosis (bromobenzene, paracetamol, carbon tetrachloride, iproniazid, isoniazid, thioacetamide), cholestasis (alpha-naphthylisothiocyanate (ANIT), chlorpromazine, ethinylestradiol, methyltestosterone, ibuprofen), or steatosis (phenobarbital, tetracycline). Animals were treated daily for 2 or 4 days except for paracetamol and bromobenzene (1 and 2 days) and carbon tetrachloride (1 day only). Urine was collected 24 h after the first and second treatment. The animals were sacrificed 24 h after the last treatment, and NMR data were compared with liver histopathology as well as blood and urine biochemistry. Pathology and biochemistry showed marked toxicity in the liver at high doses of bromobenzene, paracetamol, carbon tetrachloride, ANIT, and ibuprofen. Thioacetamide and chlorpromazine showed less extensive changes, while the influences of iproniazid, isoniazid, phenobarbital, ethinylestradiol, and tetracycline on the toxic parameters were marginal or for methyltestosterone and mianserine negligible. NMR spectroscopy revealed significant changes upon dosing in 88 NMR biomarker signals preselected with the Procrustus Rotation method on principal component discriminant analysis (PCDA) plots. Further evaluation of the specific changes led to the identification of biomarker patterns for the specific types of liver toxicity. Comparison of our rat NMR PCDA data with histopathological changes reported in humans and/or rats suggests that rat NMR urinalysis can be used to predict hepatotoxicity.

Sensitivity of (1)H NMR analysis of rat urine in relation to toxicometabonomics. Part I: dose-dependent toxic effects of bromobenzene and paracetamol.

(1)H nuclear magnetic resonance (NMR) spectroscopy of rat urine in combination with pattern recognition analysis was evaluated for early noninvasive detection of toxicity of investigational chemical entities. Bromobenzene (B) and paracetamol (P) were administered at five single oral dosages between 2 and 500 mg/kg and between 6 and 1800 mg/kg, respectively. The sensitivity of the proposed method to detect changes in the NMR spectra 24 and 48 h after single dosing was compared with histopathology and biochemical parameters in plasma and urine. Both B and P applied at the highest dosages induced liver necrosis and markedly increased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) plasma levels. At dosages of 125 mg/kg B and 450 mg/kg P, liver necrosis and changes in AST and ALT were less pronounced, while at lower dose levels these effects could not be detected. Changes in kidney pathology or standard urine biochemistry were not observed at any of these dosages. Evaluation of the total NMR dataset showed 80 signals to be sensitive for B and P dosing. Principal component analysis on the reduced dataset revealed that NMR spectra were significantly different at dosages above 8 mg/kg (B) and 110 mg/kg (P) at both sampling times. This implies a 4- to 16-fold increased sensitivity of NMR versus histopathology and clinical chemistry in recognizing early events of liver toxicity.

Use of physicochemical calculation of pKa and CLogP to predict phospholipidosis-inducing potential: a case study with structurally related piperazines.

Several cationic amphiphilic compounds are known to induce phospholipidosis, a condition primarily characterized by excessive accumulation of phospholipids in different cell types, giving the affected cells a finely foamy appearance. Excessive storage of lamellar membranous intralysosomal inclusion bodies is the hallmark for phospholipidosis on the electron microscopic level. In case of alveolar phospholipidosis, foamy macrophages accumulate within the alveolar spaces of the lung. Based on such findings in a one-year toxicity study with gepirone in rats, we studied the molecular properties of this compound and compounds suspected of being phospholipidosis inducers by means of physicochemical calculations. Physicochemical molecular calculations of molecular weight, ClogP (partition coefficient octanol/water), logD at pH 7.4, and pKa were performed, for the cationic amphiphilic compounds chlorpromazine, amiodarone, imipramine, propranolol and fluoxetine, and for the structurally related compounds 1-phenylpiperazine (1-PHP), gepirone (and its major metabolites, 3-OH-gepirone and 1-pyrimidinylpiperazine [1-PP]), and buspirone. ClogP and calculated pKa cluster differently for the amphiphilic drugs compared to the chemical series of piperazines. In line with this analysis, lamellar inclusion bodies were found in an in vitro validation experiment in the human monoblastoid cell line U-937, incubated for 96 h at 10 microg/mL with cationic amphiphilic drugs (amiodarone, imipramine, or propranolol). No such lamellar inclusion bodies were seen for any of the compounds from the chemical series of piperazines including gepirone and its metabolites. The data presented support the use of simple physicochemical calculations of ClogP and pKa to discriminate rapidly between compounds suspected of being phospholipidosis inducers. Finally, the discriminative power of these physicochemical ClogP and pKa calculations to predict phospholipidosis-inducing potential was further validated by extension of the set of compounds.

The incidence of thymic B lymphoid follicles in healthy beagle dogs.

The incidence of thymic B cell lymphoid follicles was retrospectively studied in 62 male and 58 female healthy control beagle dogs (age 11.3 +/- 4.8, range 6 to 23 months). The animals were selected from toxicological studies performed in the period 1990-2001 at the Organon labs. The animals had received vehicle treatment. Thorough microscopic examination of the thymus in hematoxylin & eosin (H&E)-stained sections resulted in an unexpectedly high overall incidence of 70% of medullary lymphoid follicles. Occasionally, these lymphoid follicles contained germinal centers. With the use of a T- and B cell marker (respectively CD3 and CD79alpha) we confirmed that the lymphoid follicles exclusively contained large numbers of B lymphocytes. Moreover, with the use of the B cell marker, almost all animals (97%) prove to have B cell rich medullary areas. The study also confirmed that the dog thymus underwent progressive involution during the period from 6 to 23 months of age. As a consequence of the involution, B cell areas and lymphoid follicles may be obscured in some H&E sections. Results of this study indicated that dense B lymphocyte aggregates and/or B lymphoid follicles are a normal constituent of the canine thymus.

Intravenous tolerability of an acid vehicle in Sprague Dawley rats and beagle dogs after daily slow bolus injection and infusion for one hour during 14 days.

To assess the tolerability of an acid vehicle to be used in toxicology studies, a low pH aqueous solution containing 16.4 mg/ml of citric acid, 4.2 mg/ml of disodium phosphate, 25 mg/ml of mannitol, adjusted with phosphoric acid/NaOH 1 M to pH 3 was daily administered intravenously to rats and dogs for 14 consecutive days. The dosing regimen consisted of a slow intravenous bolus injection given over 30 s (0.75 and 0.625 ml/kg, for rats and dogs, respectively) followed by intravenous infusion for one hour (3.75 and 2.75 ml/kg/h, for rats and dogs, respectively). In rats, the dose was administered via the lateral tail vein. In dogs, the intravenous bolus dose was administered via the vena cephalica, vena saphena or vena jugularis, whilst the infusion dose was given into the vena cephalica or vena saphena. In rats, administration of the vehicle was associated with clinical signs (occasional mild vocalization and agitation) which were considered to be due to local irritation during the dosing procedure. Nevertheless, only mild histopathological changes at the injection site were found, while no relevant clinical chemistry changes were found in this species. However, the vehicle caused significant vascular damage with thrombus formation in the dog. It is therefore concluded that this vehicle is suitable for 2-week rat toxicity studies, if carefully applied. The vehicle with its present regimen should not be used in dogs, in view of the prohibitive findings.