Studies of early hepatocellular proliferation and peroxisomal proliferation in Wistar rats treated with herbicide diclofop.

A study was performed to determine whether diclofop (2-(4-(2,4-dichlorophenoxy) phenoxy)propionic acid), introduced as a herbicide, exhibits the properties of peroxisome proliferators (PPs). Diclofop was administered orally at 7-56 mg/kg body weight per day to male Wistar rats for 2, 4, 7 or 14 consecutive days and some effects regarded as early hepatic markers of PPs were studied. The early changes in rat liver, produced by short-term treatment with diclofop consisted of mitogenesis and, time- and dose-related increase in liver weight. Hepatomegaly was typically associated with proliferation of smooth endoplasmic reticulum (SER) and peroxisomes. The parallel biochemical measurements showed that there was a dose-dependent increase in peroxisomal palmitoyl-CoA oxidation and catalase activity in treated rats. Markers of hepatocellular proliferation (S- and M-phase) indicated that mitogenesis was transient and declined despite continuation of diclofop treatment. The threshold exposure level for the palmitoyl-CoA oxidation (one of the peroxisome proliferation markers) was approximately the same (14 mg/kg body weightxper day) as for the stimulation of mitogenesis in Wistar rats. However, for hepatomegaly and catalase activity the threshold exposure level was 7 mg/kg body weightxper day. The results presented here demonstrate clearly that diclofop belongs to a class of rodent PPs.

Early hepatic changes in rats induced by permethrin in comparison with DDT.

In this study permethrin [(3-phenoxyphenyl)-methyl-3-(2,2-dichloroethenyl)-2,2-dim ethylcyclopropanecarboxylate] and DDT [1,1-(2,2,2 trichloroethylidene)-bis-(4-chlorobenzene)] were compared in rats for their effects on early hepatic changes, proposed in the literature to be useful endpoints in screening for non-genotoxic hepatocarcinogenesis and/or liver tumour promotion. We compared the effects of both insecticides on the following endpoints: hepatomegaly, mitogenesis (DNA synthesis, mitotic activity, percentage of binuclear cells) and liver pathology. Male Wistar rats received permethrin (PERM) or DDT in one, three, five and 14 daily oral doses (at 24-h intervals) equivalent to 1/10 LD50. Distinct differences in early liver response between PERM and DDT were observed. DDT stimulated the early effect consisting of hepatomegaly accompanied by an increase in hepatocellular proliferation with signs of cell necrosis. Thus, it might be concluded, that the mitogenic effect of DDT was at least partly related to a regenerative liver response. Although PERM significantly affected DNA synthesis and increased binuclear hepatocytes, this compound did not increase the number of mitotic figures. These results suggest that PERM may inhibit of phase G2 in the cell cycle and consequently it may suppress the cell entering into the stage of mitosis (M-phase). In addition, the present findings provide evidence for the occurrence of abnormal mitoses in the hepatocytes of rats treated with DDT.

[Molecular mechanisms of chemically induced carcinogenesis]. / Molekularne mechanizmy chemicznej kancerogenezy.

In this review recent point of view concerning the molecular mechanisms of chemically induced carcinogenesis is presented. The new and promising trends of neoplasia investigations are based on discovery of protooncogenes and tumor suppressor genes, which maintain tissue homeostasis by controlling cellular proliferation and differentiation. It is generally recognised, that mutations induced by genotoxic carcinogens, particularly those resulting in activation of protooncogenes and inactivation of suppressor genes, play a crucial role in the initiation step of multistage process of tumorigenesis. Tumor promotion is recognized as a process whereby initiated cells are stimulated to selective growth and then, to develop into the cancer during progression step. Tumor promotion can be affected by many nongenotoxic carcinogens. In this review the attention is given to the mutational activation of the c-ras oncogenes and inactivation of p53 suppressor gene in rodent and human cancers by genotoxic carcinogens. Moreover, the significance of nongenotoxic carcinogens and the mechanisms by which these compounds may accelerate tumorigenesis are discussed.

[The role of apoptosis in cell physiology and pathology]. / Rola apoptozy w fizjologii i patologii komórki.

The cell death is a natural physiological process that occurs in every living organism. It is clear that programmed cell death--apoptosis--is an important mechanism maintaining cell number in a multicellular organism. This review summarises recent progress in the field of apoptosis. Extracellular signals, such as various growth factors and antigen Fas ligand can trigger apoptosis via cell surface receptors. Within the cell the tumor suppressor gene p53 and oncogenes c-myc, c-fos and c-jun tend to activate apoptosis, while other genes such as most members of the bcl-2 family, tend to suppress it. Many of these signals regulate a family of cysteine proteases--related to interleukin 1 beta converting enzyme (ICE)--caspases--which play a crucial role in apoptosis. Many factors that affect apoptosis also affect the cell cycle. For example, p53 appears to be an important mediator of both apoptosis and cycle arrest. If DNA damage is repaired during cycle arrest, the cell survives. Special attention is paid to the abnormalities in the regulation of apoptosis that may contribute to different pathogenic processes.

[The evaluation of urine and hair total mercury content in occupationally exposed and non-exposed people]. / Ocena calkowitej zawartosci rteci w moczu i wlosach ludzi narazonych i nienarazonych zawodowo.

The study aimed at the evaluation of total mercury content in hair and urine of the workers occupationally exposed to various levels of mercury vapours. The hair and urine were taken from the workers employed in Chemical Plant Oswiecim and from thermometer factory in Warsaw. The urine and hair of non-exposed Warsaw inhabitants served as a reference. Mercury levels in hair and urine were determined with atomic absorption spectrometry. The highest mercury concentration in hair (range 1.13-325.16 micrograms/g) and urine (range 15.7-800 ng/mg of creatinine) of workers employed in processing chloroalkali in Chemical Plant Oswiecim. The results also suggest that the average mercury concentration in hair (0.17 and 1.0 microgram/g) and urine (0.4 and 2.36 ng/mg of creatinine) of non-occupationally exposed inhabitants from Warsaw and Oswiecim does not endanger human population. Nevertheless a positive correlation between distance from chloroalkali plant in Oswiecim and mercury content in the specimens from inhabitants has been observed.

The effect of fenarimol on marker enzymes in rat liver in two-stages model of hepatocarcinogenesis.

The two-stage model for the development of early markers of hepatocarcinogenesis was applied to assess the potential of fungicide fenarimol (alpha-(2-chlorophenyl)-alpha-(4-chlorophenyl)-5-pirimidinemethanol++ +) as a possible promoter in this process. In this experiment the rats were subjected to partial hepatectomy (to induce proliferation), followed by the single (50 mg/kg bw) dose of diethylnitrosamine (DEN) (initiator) and then, followed by the 26 weeks exposure to fenarimol administered in the olive oil suspension (250 mg/kg daily). The activities of gamma-glutamyltransferase (GGTase), glucose-6-phosphatase (G-6-Pase) and alkaline phosphatase (APase) regarded as markers of early stages of hepatocarcinogenesis were measured biochemically and histochemically in the livers of exposed rats as well as in the respective positive and negative controls. Rats exposed to 2-acetylaminofluorene (2-AAF), instead of fenarimol, served as positive controls. It was found that in the full initiation/promotion regimen both 2-AAF and fenarimol induced the increase of GGTase activity in the liver and formation of GGTase-positive hepatocytes. However the exposure to fenarimol alone also increased GGTase activity, although this response was not observed in rats exposed to 2-AAF alone. The possible mechanisms and explanation for such types of responses were discussed, and conclusion has been drawn that fenarimol did not affect the rat hepatocarcinogenesis induced by PH and DEN.

[Proliferation of peroxisomes and the hepatocarcinogenic process]. / Proliferacja peroksysomów a proces hepatokancerogenezy.

Peroxisome proliferators are diverse group of chemicals which are regarded as rodent hepatocarcinogens and/or- liver tumor promoters. These compounds when administered to rats and mice produce a dramatic increase in the size and number of hepatic peroxisomes and increase in activities of enzymes involved in beta-oxidation of fatty acids. Peroxisome proliferation is accompanied by hepatocyte proliferation and liver growth. The steroid hormone receptors superfamily have been identified that can be activated by peroxisome proliferators and are called Peroxisome Proliferator Activated Receptors (PPARs). It is therefore suggests that PPARs mediate the pleiotropic effects of peroxisome proliferators including enzyme induction, peroxisome proliferation, cell proliferation and hepatocarcinogenesis. Although the correlation of peroxisome proliferation and hepatocarcinogenesis is striking, the mechanism(s) by which this class of chemicals induce tumor is still understood; however several other hypothesis have been advanced. One is based on knowledge that hydrogen peroxide is produced during the increase in peroxisomal fatty acid oxidation. An excess of hydrogen peroxide can lead to oxidative stress (generation of reactive oxyden species), DNA damage and possibly to tumor initiation. In rodents, an alternative mechanism is the promotion of spontaneously initiated lesions by sustained cell proliferation. Thirdly, it is conceivable that sustained growth stimulation may be sufficient for tumor formation. Marked species differences are apparent in response to peroxisome proliferators. Rats an mice are extremely responsive species, and hamsters show an intermediate response, while guinea pigs, monkeys and humans appear to be relatively non-responsive. In the light of these data it seems likely that risk to humans from peroxisome proliferators may be overestimated. However, peroxiome proliferators have shown to produce the other effects such as the suppression of hepatocyte apoptosis which could be an important factor in their hepatocarcinogenic response.

[The effect of permethrin and DDT on the activity of cytochrome P-450 1A and 2B molecular forms in rat liver]. / Wplyw permetryny i DDT na aktywnosc form molekularnych cytochromu P-4501A i 2B w watrobie szczura.

The effect of permethrin on relative liver weight (RLW) and the activity of hepatic monooxygenase system related to cytochrome P-4502B and 2A was studies. The effect of permethrin was compared with DDT used as phenobarbital-type of monooxygenase inducer (induces cyt. P-4502B). Male Wistar rats received permethrin and DDT for 4 days at 24 h intervals in daily oral doses of 1/10, 1/50 and 1/100 LD50. 3-methylocholantrene and phenobarbital which served as inducers of cytochrome P-4501A and 2B, respectively and were used as positive controls. The activities of cytochrome(s) P-450 were measured by 7-pentoxy- and 7-etoxyresofurin O-dealkylation by S-9 fraction of rat liver; these two compounds have been shown to be the substrates for reactions mediated by cytochrome P-4502B and 2A. Thus this biochemical procedure permits to determine whether tested compound belongs to one of two main types of inducers of the cytochrome P-450 monoxygenase system. Treatment of rats with both pesticides resulted in significant increase in RLW, to 30 and 15% of control, respectively. In animals treated with permethrin the metabolism of 7-pentoxyresofurin increased in a dose dependent manner. Phenobarbital and the highest dose of permethrin (620 mg/kg b.w. x day-1) induced similar (about 30-fold) increase in O-dealkylation of 7-pentoxyresofurin. DDT stimulated metabolism of 7-pentoxyresofurin to much higher degree as compared with phenobarbital. It should be noted that both pesticides induced only slight increase in O-dealkylation of 7-etoxyresofurin (cyt. P-4501A-mediated reaction). The present results indicate that permethrin as well as DDT shows the ability to induce the phenobarbital-type of cytochrome P-4502B.

Early hepatic changes induced in rats by two hepatocarcinogenic organohalogen pesticides: bromopropylate and DDT.

The aim of the present studies was to describe the effect of two organohalogen pesticides: DDT and bromopropylate, on early changes in rat liver, proposed in the literature to be useful endpoints in screening of non-genotoxic hepatocarcinogens and/or liver tumor promoters. We investigated the effects on the following endpoints: hepatomegaly, mitogenesis (DNA synthesis, mitotic activity, percentage of binuclear cells) and cytochrome CYP2B1-dependent monooxygenase induction. The histological and cytochemical changes in the liver were also recorded. Male Wistar rats received bromopropylate in one, three or five daily oral doses of 125, 250, and 500 mg/kg body wt. day-1. DDT was applied as one, three, and five daily oral doses of 24 mg/kg body wt. day-1 (this dose is close to the mean hepatocarcinogenic dose in male Wistar rats: 34.1 mg/kg body wt. day-1). In the case of both pesticides the early effects observed consisted of hepatomegaly accompanied by an increase in the p-nitroanisole O-demethylase activity and hepatocyte proliferation. Hepatocyte proliferation was elevated during the total experimental period. Vacuolated cytoplasm and evident focal necrosis may suggest that the maximal increase in hepatocyte proliferation, preceding hepatomegaly, is at least partly related to a regenerative liver response to pesticides. In addition to the above-mentioned early changes, the present findings provide new evidence for the occurrence of dose-dependent abnormal mitoses (and c-mitoses) in the hepatocytes of the bromopropylate and DDT treated rats.

[The effect of selected polychlorinated hydrocarbon pesticides on proliferation of cells in rat liver (14 day experiment)]. / Wplyw wybranych pestycydów z grupy polichlorowanych weglowodorów na proliferacje komórkowa w watrobie szczurów (doswiadczenie 14 dniowe).

The aim of present studies was to describe the effect of two organochlorine pesticides: nuarimol and DDT on the changes in rat liver, proposed in the literature to be useful endpoints in screening of non-genotoxic hepatocarcinogens and/or liver tumor promoters. The effects on the following endpoints: mitogenesis (DNA synthesis and mitotic activity), hepatomegaly as well as histological changes in rat liver have been investigated. Male Wistar rats received nuarimol or DDT in one, five and fourteen daily oral administration of the doses of 125 and 12 mg/kg b.w. day-1 respectively. In the case of both pesticides the effects observed consisted of hepatomegaly and hepatocyte proliferation (DNA synthesis and mitotic activity), although our studies indicated several distinct differences in the hepatic response between nuarimol, on the one hand and DDT on the other. The differences were reflected in the character and the basal rate of hepatocyte proliferation. Nuarimol elicited rapid but transient wave of hepatocyte proliferation during the first day of exposure. As opposite to nuarimol, DDT induced sustained hepatocyte proliferation during experimental period (14 days). Moreover, DDT induced evident focal necrosis and abnormal mitoses whereas nuarimol caused only slight vacuolated cytoplasm. Thus it can be concluded that nuarimol induced in rat liver direct mitogenic effect. On the other hand, DDT which is well known hepatocarcinogen, was found to produce mitogenic effect appearing to be related to regenerative response, since histological signs of necrosis were apparent.

Early hepatic changes induced by nuarimol in rats.

It is commonly believed that in short-term tests hepatic cytochrome P-450b inducers stimulate liver enlargement and mitogenesis in the absence of overt hepatotoxic effects. In this investigation male Wistar rats received naurimol (an organochlorine pesticide) in one, three and five oral doses of 31.5, 62.5 and 125 mg kg-body wt. day-, whereupon the effects on liver were determined. The early effects were dose-dependent increases in p-nitroanisole metabolism, hepatocyte proliferation (DNA synthesis and mitotic activity) and liver weight. Five administrations of the lowest does (31.5 mg kg-1 body wt. day-1) did not change liver weight, despite increased p-nitroanisole metabolism and hepatocyte proliferation. In contrast to p-nitroanisole metabolism and hepatomegaly, proliferation was only transient and disappeared even when treatment continued. The increase in binuclear hepatocytes and signs of necrosis suggested that the hepatomitogenic effect of nuarimol reflected a regenerative response, which may simulate the proliferation caused by partial hepatectomy.

[Toxicity of aldehydes used as disinfectants]. / Toksycznosc aldehydów stosowanych jako srodki dezynfekcyjne.

The paper presents a review of current scientific literature on the toxicology of aldehydes used as cold disinfectants. A particular attention was paid towards the mutagenic, teratogenic and cancerogenic potential as well as occupational hazard and risk for patients exposed to aldehydes.

The influence of fenarimol on DNA synthesis and mitotic activity in rat liver.

Fenarimol administered in one single oral dose of 125 or 62.5 mg kg-1 body wt. day-1, respectively, stimulated rat liver enlargement at a dose-independent rate. Three single doses of fenarimol produced dose-dependent liver growth, whereas five single doses caused no further increase in liver weight. This increase was accompanied by an increase in hepatic DNA synthesis and mitotic activity, with a peak on the first day after the beginning of the experiments. The increase in binuclear hepatocytes and signs of necrosis suggested that the hepatomitogenic effect reflected a compensatory hyperplasia. After both three and five single doses the hepatomitogenic effect was suppressed, as a result of tolerance development.

[Changes in activity of G-6-pase, APase, and gamma-GTPase in liver and blood serum of rats exposed to nuarimol and NDEA]. / Zmiany aktywnosci G-6-Pazy, Apazy i gamma-GTPazy w watrobie i surowicy krwi szczurów narazonych na nuarimaol i NDEA.

The effect of simultaneous administration of N-diethylnitrosamine (NDEA) and Nuarimol on the activity of gamma-GTPase, G-6-Pase ans APase in the liver and serum of Wistar rats was investigated in the 2-weeks experiment. The two-stage hepato-cancerogenesis model was used with NDEA as initiating agent. The possible promoting potential of Nuarimol (DDT analogue) was checked in this experiment. gamma-GTPase and G-6-Pase activities were measured by biochemical and histochemical methods and AP-ase activity was measured by a biochemical method only. The occurrence of gamma-GTPase positive foci found by histochemical methods was partly confirmed by colorimetric methods. This suggest the need for further examination of this enzyme in conditions of prolonged exposure to Nuarimol.

Some biochemical changes associated with fenarimol-induced liver growth in the rat.

Fenarimol administered in one single or repeated oral doses of 250 or 125 mg/kg body weight per day, respectively, stimulated rat liver enlargement which was associated with a wave of DNA synthesis on the first day after start of treatment. Subsequently, even though fenarimol treatment was continued, the DNA synthesis was suppressed as soon as a new steady liver DNA level was reached. The early hyperplastic episode was evidently primary responsible for the liver growth that occurred within the first 3 days of administration of compound. Liver enlargement achieved maximum growth by 3 or 5 days from first administration of 125 and 250 mg fenarimol/kg body weight per day, respectively. This later stage of hepatomegaly was mainly due to cellular hypertrophy involving an increase in RLW accompanied by an increase in liver protein content. Hepatomegaly and DNA synthesis appeared to be threshold related.

Degenerative changes, DNA synthesis and mitotic activity in rat liver following single and repeated exposure to fenarimol.

Degenerative changes were observed in liver of rats treated with single and repeated doses of fenarimol (250 mg/kg body weight x day). Regenerative changes i.e. increase in: DNA synthesis, hepatic DNA, mitotic activity and number of binuclear hepatocytes, were also noted.

[Cytotoxic effect of fenarimol on peripheral blood cells and organs]. / Cytotoksyczne dzialanie fenarimolu na komórki krwi obwodowej i narzady.

The effect of fenarimol in blood cells and changes in liver and kidneys in rats were investigated. Fenarimol applied in doses 25 mg/ml intragastrically during 5 days, at 24h after the last doses caused functional and structural changes of blood cells and organs. The decreases of osmotic fragility of erythrocytes and phagocytic activity of neutrophils, and the increase of the percentage of lymphocytes without detectable lysosomes accompanied by the minor decrease of the number of blood cells was observed in the peripheral blood. The indistinctness of the structure of the hepatic lobules and of liver laminae and the vacuolized hepatic cells with pycnotic nuclei were visible in the liver. The abnormally enlarged cortical Malphighian++ glomeruli in kidney were found. The observed changes indicate the cytotoxic effect of fenarimol in strongly intoxicated rats. The impaired phagocytic activity of neutrophils may cause the growth of susceptibility to bacterial infection.