Influence of fenofibrate on cellular and subcellular liver structure in hyperlipidemic patients.

The administration of lipid-lowering drugs to rodents, notably those related to clofibrate, rapidly provokes a hepatic response characterized by hepatomegaly, proliferation of smooth endoplasmic reticulum and proliferation of peroxisomes in hepatocytes. In some studies hepatocellular carcinoma has been found in rats or mice exposed for their entire life-span to high dose levels of various fibrates. In the present study liver biopsy samples were obtained from 38 hyperlipidemic patients, 28 of whom had been receiving fenofibrate for between 2 months and approximately 3 years (mean values: males 1.79, females 1.98 years). The remaining 10 patients had never been treated with a lipid-lowering drug. Examination of the biopsy samples by a variety of optical techniques and by electron microscopy failed to reveal any difference between the groups. Peroxisomes were relatively rare, there being no evidence of the clear proliferation seen in rodent studies. Other microscopic features of interest were some variation of nuclear size, mitochondria containing paracrystalline inclusions, dilated endoplasmic reticulum associated with reduced amounts of rough endoplasmic reticulum, and the presence of lipid droplets in the liver cells. However, these variations from normal were in general not much more apparent in samples from the fenofibrate-treated patients than in the untreated group. Light- and electron-microscopic observations did not suggest liver intoxication or a carcinogenic pattern.

Chronic relapsing experimental allergic encephalomyelitis in the Lewis rat.

Chronic relapsing experimental allergic encephalomyelitis (CR-EAE) was induced in rats with an emulsion of guinea-pig spinal cord tissue (GPSC) in complete Freund's adjuvant (CFA) enriched with Mycobacterium tuberculosis H37RA (Tbc). 78% of the sensitized rats developed a CR-EAE showing 2 to 3 clinical relapses during the first 40 days. After 60-80 days, approximately half of the rats with CR-EAE had a further relapse which was followed by complete recovery in only 35% of the cases. The remaining 65% of these animals showed a progressive state of the disease, characterized by paralysis or severe motor deficit, eventually leading to death. CR-EAE in rats showed some similarities to multiple sclerosis in man (MS) and it may be a useful model for the study of this disease.

Aspects of the immunotoxicity of chronic tobacco smoke exposure of the rat.

One hundred and eighty Wistar-strain rats were exposed to differing concentrations of tobacco smoke, for periods of up to 20 months, in order to examine the response of the pulmonary immune system. The amount of bronchus-associated lymphoid tissue (BALT) in the lungs of exposed rats increased initially over the first 5 weeks of exposure, subsequently falling to below control levels by the fourteenth week and eventually increasing again to a level slightly higher than that of the controls by the twelfth month, at which level it was maintained until the twentieth month. Quantitative immunohistochemical assay of bronchial immunoglobulin levels (only assessed over the initial 14 weeks of exposure) revealed a transitory enhancement of levels followed by a depression, the speed of response being apparently dose-related. Alveolar macrophage activity, indicated by lysosomal enzyme activity, increased relative to the control animals over the same 14-week exposure period. The significance of these observations is discussed and a tentative explanatory hypothesis is advanced.

The toxicity of 1-amino-3-chloro-2-propanol hydrochloride (CL88,236) in the rhesus monkey.

The toxicity of 1-amino-3-chloro-2-propanol is associated with acute histopathological change in the medulla oblongata, characterised lesions of focal oedema. Continued administration results in neurological scars. Lesions can be induced at dose levels of 50 mg . kg-1 day-1. Clinical manifestations of neurological involvement are periods of slight incoordination and loss of balance in a few animals only.

Serum bile acid concentration in some experimental liver lesions of rat.

The usefulness of measuring serum bile acid concentrations by RIA in a number of acute experimental liver injuries of rats was assessed by comparing the concentrations with the results of some of the routinely employed methods of examining hepatotoxic changes. Centrilobular liver cell injury produced by CCl4 revealed leakage of GPT and GDH and to a lesser extent AP; along with minimal increase in serum bile acid levels. Serum bilirubin concentration remained unchanged. Surgical bile duct ligation resulted in marked rises in AP, GPT and GDH and total bilirubin levels and levels of serum bile acids. Intravenous injection of MnSO4 induced focal necrosis of liver and bile canalivular dilation associated with elevated GDH and GPT concentrations. AP and bilirubin levels were unchanged. Bile acid levels were raised among female rats. 2,4-Xylidine induced hepatotoxicity revealed bile duct hyperplasia, liver cell enlargement, liver cell necrosis, biliary canalicular dilation and proliferation of endoplasmic reticulum. GDH and GPT levels were raised along with bile acid concentrations. This study suggested that assay of bile acid concentration is a sensitive indicator of several acute hepatic injuries.

Clioquinol toxicity in the dog.

A number of instances have been reported in the scientific literature in which acute intoxication with halogenated oxyquinolines has led in some species to convlusions, often followed by death. The toxicity of repeated doses of clioquinol has been investigated extensively in the dog. The clinical syndrome induced in this species is characterized by anorexia, weight loss, extremem muscle weakness and emaciation. In some animals surviving this impairment of condition for several weeks, neuropathy of the central nervous system, but not of the peripheral nerves ensued. It is suggested that these toxicological manifestations are less dependent on the dose-level than on the degree of absorption. Some suggestions regarding the aetiology of the lesions are made.

Unexpected tumour findings in lifetime rodent bioassay studies--what to do?

Currently, the majority of substances tested in lifetime bioassays in rodents are not mutagenic and, therefore, at the most weakly carcinogenic, generally by epigenetic mechanisms. It thus appears obvious that only marginal increases of tumour incidences can be expected in lifetime bioassays and that, therefore, every aspect of a potential carcinogenic effect must be thoroughly evaluated. This paper describes a series of key factors, which should be looked at in order to exclude that the lifetime bioassay in question is flawed for design, technical or qualification reasons. It also provides some hints whether there is indeed a real effect and not just a variation of the spontaneous tumour incidences. Tumour findings must be seen in the context of the animal model, the pharmcokinetics and pharmcodynamics of the test substance, as well as any other observation in the present or other studies with the test substance, including non-tumour findings and--in particular--potential precursor lesions and effects on feed intake and survival. The possibility that the observed carcinogenic effects may be species-specific and not relevant for man is discussed. It is also important to check what findings are reported with similar substances or substances with the same pharmacological effect. Data from additional investigations on material of the same study and/or mechanistic studies are often needed to support the final risk assessment.

Sub-acute toxicity studies on a new piperidine derivative (HSR-902) in dogs.

The administration of a new piperidine antispasmodic agent (HSR-902) to the dog by the oral and intravenous routes, induced clinical signs attributable to parasympathetic blockage. The only significant toxicological finding was rarefied appearance and enlargement of the hepatocytes at the high dose level (50 mg/kg/day); this was shown to be reversible.

A quantitative ultrastructural comparison of macrophages from rats exposed to smoke derived from conventional tobacco and a tobacco substitute.

Using an image analysing computer a variety of ultrastructural features from micrographs of alveolar macrophages have been quantified. Macrophages from rats exposed to smoke from conventional tobacco cigarettes, for 6 months, revealed statistically significant changes when compared to controls. The macrophages were larger, rounded with fewer pseudopodia and contained increased numbers of inclusions. There were no statistically significant changes in macrophages from rats exposed to smoke from a tobacco substitute.

The intravenous toxicity of lentinan to the beagle dog.

The i.v administration of lentinan to the Beagle dog induced changes in the cytoplasm of macrophagic cells in the liver, spleen, kidney, lungs, lymph nodes, small intestine. Electron-lucent or filamentous inclusions were demonstrated in the liver, kidney and spleen. A dose level of 0.5 mg/kg/day was without adverse effect.

The toxicology of a ganglioside extract (Cronassial).

The accepted animal toxicity studies indicate that the ganglioside mixture extracted and purified from the bovine brain cortex (Cronassial) is without detectable toxicity. It did not induce any adverse effects on any of the characteristics of reproduction and it is not antigenic.

The effect of dose and vehicle on early tissue damage and regenerative activity after chloroform administration to mice.

The relationship between the acute toxicity of orally-administered chloroform and its long-term tumorigenic potential was studied in male mice of the CFLP outbred Swiss albino mouse strain. A single dose of approximately 18 mg CHCl3/kg had no detectable acute toxic effect on the liver or kidneys and did not stimulate regenerative activity, whereas both toxicity and subsequent tissue regeneration were observed with single doses of about 60 mg/kg or higher. The severity of the toxic effects and regenerative changes was greater when corn oil was used as a vehicle for chloroform than when the vehicle was a toothpaste base. In earlier long-term studies in mice of the same strain, kidney tumours occurred in males given 60 mg/kg/day throughout life but not in mice given 17 mg/kg/day. The tumour response was greater when the 60-mg/kg/day dose was given in an oily vehicle than when it was given in toothpaste. The findings are consistent with the hypothesis that early acute toxic change and subsequent repair are a sine qua non for tumorigenesis in the kidney and liver in response to chloroform.

Proliferating cell nuclear antigen expression in Wistar rat livers. A retrospective immunohistochemical study of normal and neoplastic livers.

Formalin-fixed, paraffin-embedded liver specimens from 27 2-year-old Wistar rats, including 10 normal livers, 11 hepatocellular adenomas, 2 hepatocellular carcinomas, and 4 cystic cholangiomas, were immunostained using the streptavidin/peroxidase method and the PC10 monoclonal antibody (Mab), which recognizes an epitope on the proliferating cell nuclear antigen (PCNA). The following PCNA labeling index (LI) mean values were found for the above four groups of liver specimens: normal livers, 0.43 +/- 0.31%; hepatocellular adenomas, 1.51 +/- 0.59%; hepatocellular carcinomas, 24.80% +/- 10.28%; and cystic cholangiomas, 0.61 +/- 0.21%. Our findings indicate that PCNA LI clearly separates liver malignancies from other benign liver tumors, as well as from normal, non-neoplastic, liver tissues. Although the mean PCNA LI values seemed to reflect histological grading (i. e. normal, neoplastic benign, neoplastic malignant), overlapping between normal livers and hepatocellular adenomas was observed in five cases (i. e. in 2 normal livers and 3 hepatocellular adenomas, where the PCNA LI values varied between 0.74% and 0.96%). It thus appears that PCNA immunohistochemistry represents a promising tool for investigating liver cell proliferation in laboratory rats, and permits distinguishing between benign and malignant liver parenchymal tumors.

Hypertrophic osteopathy in rats following chronic administration of SDZ MNS 949, an isoquinoline.

SDZ MNS 949, 6,7-dimethoxy-3-methyl-1-(3',5'-bis (methoxyethoxy) phenyl)-isoquinoline, a bronchodilating anti-inflammatory drug that inhibits phosphodiesterase, had been proposed for the treatment of bronchial asthma. Groups of 14 male and 14 female Wistar rats were administered doses of 12, 50, and 130 mg/kg/day in feed for 26 weeks. Periodic radiographic examinations were performed in addition to clinical observations, clinical chemistry measurements and urinalysis. At study termination full necropsy and histopathological examinations were performed on all animals. The principal clinical signs observed were unilateral edematous, red and painful swelling of the distal hindlimbs in 8 of 28 high dose animals, and abdominal swelling in 19 of 28 high dose animals. At radiographic examination periosteal new bone formation was predominantly along the tibia. Lesions at necropsy included dilated small and large intestines. Microscopically, enteritis was observed, and the periosteal new bone formation was confirmed. Hematological findings consisted of thrombocytosis and lymphocytosis, especially in high dose animals. The clinical, radiographical and histological findings in treated rats were consistent with the diagnosis of "hypertrophic osteopathy" or "Marie's Disease".

A review of drug-induced Leydig cell hyperplasia and neoplasia in the rat and some comparisons with man.

This paper describes control of normal Leydig cell function and testosterone production. The macroscopic and histopathological appearances of spontaneous Leydig cell hyperplasias and tumors (LCT) in the rat are reviewed together with their incidence and hormonal status. Drugs which induce LCTs in chronic studies are discussed and include busereline, carbamazepine, cimetidine, finasteride, flutamide, gemfibrozil, histrelin, hydralazine, indomethacin, isradipine, lactitol, leuprolide, metronidazole, mesulergine, nafarelin, norprolac and vidarabine. The known mechanisms of LCT induction in the rat are reviewed together with other possible etiological factors. The incidence, clinical picture and etiological factors of LCTs in man are also surveyed. Hormone production in Leydig cells and LCTs in rats and man are compared. Differences between the two species are considered, particularly with regard to Leydig cell control mechanisms. The paper concludes that drug-induced LCTs in rats are most probably not predictive for man and their occurrence has little relevance in human safety assessment.

Ultrastructure of rhesus monkey renomedullary interstitial cells.

The fine structure of rhesus monkey renomedullary interstitial cells was studied by electron microscopy. These stellate cells contained variable numbers of lipid droplets, moderate numbers of mitochondria, moderate amounts of rough endoplasmic reticulum, and prominent Golgi zones. In rare instances, apparent release of lipid droplets into the interstitium was observed. The most prominent feature of the interstitial cells was larger nuclear pseudoinclusions which were observed in a high proportion of the animals examined.

Postnatal development of bronchus-associated lymphoid tissue (BALT) in the rat, Rattus norvegicus.

The pattern of development of bronchus-associated lymphoid tissue (BALT) in specified-pathogen-free and conventional (non-barrier maintained) rats over the initial 4 weeks of life appeared to be similar. BALT first appeared around the 2nd week of life and increased in amount over the following 2 weeks. Overlying large nodules of BALT the bronchial epithelium becomes infiltrated by lymphocytes to form a lymphoepithelium. This transformation occurs earlier in conventional rats, possibly because of the differing antigen levels to which they are exposed.

Bronchus-associated lymphoid tissue (BALT) in the laboratory-bred and wild rat, Rattus norvegicus.

In juvenile wild rats, bronchus-associated lymphoid tissue (BALT) development was similar to that seen in adult specified-pathogen-free rats. In adult wild rats the BALT was widespread. In one animal infected with a mycoplasma-like organism, a region of bronchoepithelium overlying a large BALT nodule was seen, through which lymphocytes appeared able to pass to make direct contact with the bronchial lumen: the significance of this observation is discussed. There was no evidence of infection in lungs from any of the specified-pathogen-free animals, where small foci of BALT were seen.

Segmental aplasia of the vagina in the beagle bitch.

Segmental aplasia of the vaginal mucosa was discovered in 3 beagle bitches at the end of a routine toxicological experiment. Anomalies of Müllerian duct development in the bitch are discussed.