Comparative ultrastructural study of rat hepatocytes after treatment with the hypolipidemic agents probucol, clofibrate, and fenofibrate

Experimental findings are reported for two similarly conducted studies. One was designed to compared rat liver cell ultrastructure during and after 91 d of dosing with probucol, a hypocholesterolemic agent, and clofibrate, a hypolipidemic drug known to elicit marked alteration of rat hepatocellular morphology. The second was designed to similarly assess male rats after 28 d of treatment with the hypolipidemic agent fenofibrate. Diet mixes for these studies were prepared to attain dosage levels of approximately 500 mg/kg . d for probucol, 250 mg/kg . d for clofibrate, and 100 mg/kg . d for fenofibrate. Control rats were given untreated basal ration. Weekly adjustments in dietary concentrations were made in accordance with group mean food consumption and body weight changes. Probucol and clofibrate treatments produced statistically significant reductions in mean serum cholesterol levels of both sexes after 28 and 91 d of dosing. Only male rats were given fenofibrate, and they exhibited statistically significant cholesterol reductions after 28 d. Clofibrate and fenofibrate administration resulted in marked increases in liver weight/body weight ratios. Probucol had no statistically significant effects on liver weight/body weight ratios after 28 and 91 consecutive days of treatment. Light microscopy of liver sections stained with hematoxylin and eosin revealed an abnormal amount of cytoplasmic granularity within hepatocytes from rats given clofibrate and fenofibrate. The granules were identified by electron microscopy and cytochemistry as enlarged, proliferated peroxisomes--a known rat hepatocellular response to treatment with many hypolipidemic drugs. In addition, ultrastructural cytochemistry suggested reduced amounts of catalase in individual peroxisomes after clofibrate and fenofibrate dosing. Liver tissue from rats given probucol showed no abnormal cytoplasmic granularity and, ultrastructurally, no peroxisomal changes. Liver tissues from probucol-treated rats revealed features similar to those encountered in tissues from untreated control animals. It was concluded that the hypocholesterolemic response elicited by probucol treatment does not involve significant changes in rat liver cell morphology.

Clofibrate and the development of rats

The peri- and postnatal effects of Clofibrate (CPIB) were studied in Wistar-H-Riop rats. 150 mg/kg/day of CPIB given to mothers from 16th gestational day to the 22nd day post partum decreased the birth-weight and increased the liver-weight of the young rats the and perinatal mortality. This effect was studied in the offspring of dams treated during the last week of pregnancy or in different periods of lactation. Increased liver weight was found in the newborn at the end of treatment period however, it disappeared after 1 week without treatment.

Tumors in male rats fed ethyl chlorophenoxyisobutyrate, a hypolipidemic drug

Clofibrate (ethyl chlorophenoxyisobutyrate, Atromid-S), because it contains a chlorinated phenoxy moiety and is the most commonly used hypolipidemic drug in the United States and Europe, was fed at a concentration of 0.5% in the diet of 25 male F344 rats for 72 to 97 weeks, and the animals were inspected for tumors up to a maximum of 129 weeks. Between 72 and 129 weeks, there were 10 rats with a total of 16 tumors. These included 4 hepatocellular carcinomas, an adenocarcinoma of the glandular stomach, papillary carcinoma of the urinary bladder, acinar cell carcinoma of the pancreas, lymphosarcoma involving pancreas, acinar cell adenomas of the pancreas, renal carcinoma, and sarcomas of the lung and parotid gland. Although the number of experimental animals was small, none of these tumors were present in 25 controls, and systematic examination of available literature dealing with spontaneous tumors in several thousand rats indicated that the tumors in clofibrate-fed rats were not spontaneous. A number of the tumors were transplanted through several generations. Clofibrate, like two other hypolipidemic drugs that are carcinogenic, causes peroxisome proliferation. It is speculated that some drugs that cause peroxisome proliferation may represent a new class of chemical carcinogens and that there may be a relationship between peroxisome proliferation and malignant transformation.

Tumorigenicity of the hypolipidaemic peroxisome proliferator ethyl-alpha-p-chlorophenoxyisobutyrate (clofibrate) in rats

Ethyl-alpha-p-chlorophenoxyisobutyrate), a hypolipidaemic drug which induces hepatomegaly and proliferation of peroxisomes in liver cells of rats and mice, was fed to 15 male F344 rats at a dietary concentration of 0.5% (v/w) for up to 28 months. Hepatocellular carcinomas developed in 10/11 (91%) rats killed between 24 and 28 months. Other tumours included carcinoma of the pancreas (2 rats), leiomyoma of the small intestine (1 rat) and a large dermatofibrosarcoma (1 rat). Clofibrate is the third hypolipidaemic peroxisome proliferator demonstrated to be hepatocarcinogenic in rats. These studies suggest that hypolipidaemic agents which are capable of producing a sustained hepatomegalic and peroxisome-proliferative effect also induce liver tumours.

Myotonia induced with clofibrate in rats

Myotonia was induced in rats with clofibrate given in daily subcutaneous injections of 0.4 g/kg. The first myotonic discharges were recorded electromyographically from the extensor digitorum longus, tibialis anterior, and gastrocnemius muscles after 4 days on clofibrate, but from the soleus not until after 11 days. Clofibrate induced myotonic activity in chronically denervated muscle also. During repetitive nerve stimulation the electrical response of the muscle was declining in all myotonic rats. It did so also when repetitive stimulation was applied directly to the muscle, which would seem to suggest a myotonic defect as the cause. Several drugs were tested and diphenylhydantoin proved to inhibit myotonia most effectively. Animals on an extended clofibrate schedule (12 weeks) had ECG abnormalities resembling those seen in patients with myotonic dystrophy.

Enhancement by Wy-14,643, a hepatic peroxisome proliferator, of diethylnitrosamine-initiated hepatic tumorigenesis in the rat

Diethylnitrosamine (DEN), at a concentration of 100 parts/10(6) in drinking water for 14 days, caused the development, by 48 weeks, of very few liver tumours in 5 of 18 (27%) male F=344 rats fed control diet. When the DEN treatment was followed one week later by continuous feeding of the hypolipidemic hepatic peroxisome proliferator, Wy-14,643, at 0.1% dietary level, all of 28 rats (100%) developed, between 38 and 48 weeks, a significantly higher number of liver tumours. Furthermore, laparotomy at 22 weeks revealed that several rats fed Wy-14,643 after DEN initiation had developed visible liver nodules, suggesting that Wy-14,643 also accelerates the appearance of these tumours. Administration of another peroxisome proliferator, clofibrate, at 0.5% level in the diet after DEN initiation, also caused a substantial enhancement of liver tumorigenesis. The enhancement of liver-tumour development by clofibrate, however, was less than that by Wy-14,643. The marked enhancing effect of Wy-14,643 may be due to its profound hepatomegalic and peroxisome proliferative properties.

Hypolipemic activity of clofibrate-related compounds. 2nd Communication

Clofibrate-related compounds were synthesized from substituted phenoxyacetic acids by esterification with salicylic acid derivatives, by amidation of thiazolidines or by reaction with cinnarizine. Lipid lowering effect was investigated in normolipemic and hyperlipemic rats. The long-term hyperlipemic model used permits differentiation of hypolipemic efficacy, i.e., from clofibrate or compounds of similar activity.