Ann E. Black

Inhibition of acyl-CoA cholesterol O-acyltransferase reduces the cholesteryl ester enrichment of atherosclerotic lesions in the Yucatan micropig.

Atherosclerotic lesion development may be altered indirectly by regulating plasma cholesterol or directly by inhibition of acyl-CoA cholesterol O-acyltransferase (ACAT) within cells of the artery. Yucatan micropigs were meal-fed a 2% cholesterol, 8% peanut oil, 8% coconut oil purified diet for 1 month prior to administration of the potent, bioavailable ACAT inhibitor CI-976, and induction of atherosclerotic lesions by chronic endothelial damage. After 84-108 days of therapy, CI-976 decreased mean plasma VLDL-cholesterol 85-91% and cumulative VLDL-exposure (area under VLDL-time curve) by 65%. However, overall plasma total, LDL and HDL cholesterol and triglyceride levels were unchanged. CI-976 decreased liver cholesteryl ester (CE) content 65% without significantly affecting adrenal CE content. The CE content of the injured left femoral, left iliac and abdominal aorta and uninjured right femoral and iliac arteries and thoracic aorta was reduced 62-78% by CI-976. Systemic plasma CI-976 levels measured 24 h post-dose ranged from 2.26 to 4.05 micrograms/ml and significantly correlated with the reduction in both VLDL and vessel CE content. Thus, we conclude that inhibition of ACAT can blunt the cholesteryl ester enrichment of developing atherosclerotic lesions by preventing reesterification and storage of lipoprotein cholesterol within vascular cells and by reducing the plasma level and delivery to the arterial wall of such atherogenic lipoproteins as VLDL.

Disposition kinetics of cobalt mesoporphyrin in mouse, rat, monkey and dog

1. Radiometric and UV analyses indicated > 95% unchanged cobalt mesoporphyrin (CoMP) in plasma after i.v. or i.m. administration. Blood clearance of CoMP is < 2% of hepatic blood flow in mouse and rat, and < 0.5% of hepatic blood flow in monkey and dog. CoMP elimination t1/2 ranged from 3.1 to 9.9 days in animals after i.v. administration. 2. CoMP is highly (> 99.5%) bound to plasma proteins, but has low affinity for blood cells (Kp < 0.15). The volume of CoMP distribution (Vss < 0.91/kg) is reflective of a distribution to total body water following i.v. administration to mouse, rat, monkey and dog. 3. [14C]CoMP reached highest levels in rat tissue between 1 and 4 days following i.m. injection. Liver, kidney cortex, lymph node, adrenal and spleen demonstrated greatest uptake of radiolabel. Concentration in tissues was readily detectable at 60 days post-dose. 4. CoMP was slowly absorbed after i.m. administration showing dose-dependent pharmacokinetics. The major route of radiolabel elimination was faecal excretion (54% of dose) in rat after an i.m. dose of [14C]CoMP. Approximately 1% of the 14C dose was recovered in the urine over 7 days post-dose. 5. As a polar metalloporphyrin, CoMP has low clearance, restricted tissue distribution and long elimination t1/2 in the laboratory animals.

Metabolic disposition of the non-steroidal anti-inflammatory agent isoxicam in man

SummaryThe metabolic fate of isoxicam, a long half-life non-steroidal anti-inflammatory agent, in human subjects was investigated using isoxicam labelled with14C in the N-methyl position. Three healthy male subjects were each administered a single oral 200 mg dose (90.7 μCi) with plasma and urine collected. Total plasma radioactivity peaked between 8 and 24 h postdose with mean14C plasma radioactivity half-life of 36.1 h. Low levels of plasma radioactivity precluded plasma metabolic profiling. In urine, 37% of the administered radioactivity was recovered through 168 h. Metabolic profiling of urine confirmed the major oxidative excretion product as the hydroxymethlyisoxazole metabolite. Identified and confirmed as minor urinary metabolites were radiolabelled open-ring sulfonamide and N-methylsaccharin. Non-labelled saccharin formed by oxidative loss of the14C N-methyl group from N-methylsaccharin, was also observed. The role of this ‘saccharin pathway’ in the overall human disposition of isoxicam remains to be elucidated.

In vitro metabolism of isoxicam by horseradish peroxidase

1. Disposition studies in vivo in animals and man indicate that hydroxylation of the isoxazole methyl group of isoxicam is the major route of metabolism. 2. Recently, N-methylsaccharin, saccharin, and an open-ring sulphonamide have been identified as additional isoxicam metabolites. 3. Attempts to form these metabolites in vitro with hepatic microsomal incubations were unsuccessful. However, incubations of isoxicam with purified horseradish peroxidase resulted in the formation of N-methylsaccharin and the open-ring sulphonamide in good overall yield (28% in 1 h). 4. A possible mechanism for HP-catalysed conversion of isoxicam to N-methylsaccharin and open-ring sulphonamide is presented.

Determination of 2,2-dimethyl-N-(2,4,6-trimethoxyphenyl) dodecanamide, CI-976, in rat plasma by reversed-phase high-performance liquid chromatography

A quantitative reversed-phase high-performance liquid chromatographic procedure was developed to facilitate the preclinical development of a new Acyl-CoA:cholesterol acyltransferase inhibitor, CI-976 (I). This procedure has a lower quantitation limit of 0.06 micrograms/ml and a quantitation range of 0.06 to 8.0 micrograms/ml of I in rat plasma. The method was applied to pharmacokinetic and toxicokinetic studies of I in rat. With minor modifications, it has also been employed for analysis of I in human, monkey, and rabbit plasma.