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Archives of Toxicology (v.71, #7)

Changes in protein and mRNA levels of growth factor/growth factor receptors in rat livers after administration of phenobarbitone or methylclofenapate by C. Garcia-Allan; J. Loughlin; T. Orton; P. Lord (pp. 409-415).

The effects of phenobarbitone and methylclofenapate were studied on the expression of growth factor and growth factor receptors in livers of male Wistar rats. The major findings were: (1) a significant reduction in epidermal growth factor receptor (EGFR) protein observed with both treatments, and (2) levels of EGFR transcripts were only slightly decreased with both compounds. The reduction in the receptor level therefore does not occur via regulation of transcription. Mannose-6-phosphate receptors (M6PR, also called insulin-like growth factor II receptor) and M6PR transcripts remained unchanged in both experimental groups. Hepatocyte growth factor receptor (HGFR) transcripts were also unchanged in both experimental groups. Transcript levels of transforming growth factor-beta 1 (TGF-β1) were lower in both treatment groups compared with the control; the reduction was significant in the methylclofenapate group. This may have relevance to the finding by others that nafenopin, another peroxisome proliferator, suppresses rat hepatocyte apoptosis. Another finding of general interest was that the three “housekeeping genes”, namely albumin, actin and glyceraldehyde-3-phosphate dehydrogenase, were influenced by both treatments thus limiting their use as controls for gel loading. The adaptation of a growth regulatory mechanism via EGFR and its ligands may provide conditions such that cells with aberrant growth control have a selective growth advantage over normal cells thus promoting tumorigenesis.

Keywords: Key words Liver enlargement ; Transforming growth factor alpha ; Transforming growth factor beta ; Epidermal growth factor receptor

Congener specific effects by polychlorinated biphenyls on catecholamine content and release in chromaffin cells by Maria Donata Messeri; Ulf Bickmeyer; Frank Weinsberg; Herbert Wiegand (pp. 416-421).

The effects of the non-planar polychlorinated biphenyl (PCB) congener 2,2′,4,4′-tetrachlorobiphenyl (2,4-TCB) and of the coplanar PCB congener 3,3′,4,4′-tetrachlorobiphenyl (3,4-TCB) were investigated on the catecholamine content and release from bovine adrenal chromaffin cells in culture. Each congener was tested at three concentrations (20, 50 and 100 μM) and two exposure periods (24 h and 5 days). Catecholamine release induced by K⁺-stimulation as well as catecholamine content of Triton X-100 treated cell cultures were examined using high-performance liquid chromatography (HPLC). 2,4-TCB showed dose- and time-dependent effects. 2,4-TCB at 100 μM reduced the K⁺-stimulated catecholamine release after 24 h of exposure. After 5 days of exposure, 2,4 TCB at 50 and 100 μM drastically reduced the K⁺-stimulated catecholamine release. 3,4-TCB even at a concentration of 100 μM over exposure of either 24 h or 5 days had no effects on the K⁺-stimulated secretion. When chromaffin cells, exposed to 2,4-TCB, were lysed with 0.5% Triton X-100, a dose- and time-dependent reduction of the catecholamine content appeared. The 3,4-TCB did not reduce the catecholamine content. Conversely there seemed to be a trend towards an increase in catecholamine content. Spontaneous release of catecholamines was strongly increased by the non-planar 2,4 TCB, while the coplanar 3,4 TCB showed no effects on this parameter. Furthermore, the effects of 2,4 TCB appeared to be reversible after replacing the highest concentration (100 μM) of the TCB-solution with culture-medium at the end of the 24-h exposure. Thus, K⁺-stimulated catecholamine release and the catecholamine content of bovine adrenal chromaffin cells was effectively reduced by the non-planar PCB congener whereas spontaneous catecholamine release was strongly increased. The coplanar PCB congener was ineffective at the same conditions.

Keywords: Key words Polychlorinated biphenyls ; Neurotoxicity ; Catecholamine release ; In vitro

The response of hepatocytes isolated from phenobarbitone treated mice to mitogenic growth factors by Karin Fletcher; Terry C. Orton; J. Kevin Chipman; Alastair J. Strain (pp. 422-428).

The ability was investigated of epidermal growth factor (EGF) and hepatocyte growth factor (HGF) to stimulate DNA synthesis in hepatocytes isolated from C57Bl/6J mice following 1, 3, 7, 30 and 90 days pre-treatment with the hepatomegalic drug, phenobarbitone (PB). A 3-fold increase in S-phase labelled hepatocytes was observed in the absence of growth factors after 3 days treatment with PB, which was not seen at other investigated time points. This suggests that the proliferative influence present in vivo at this time interval is maintained in the ex vivo model. Maximum labelling indices of >5-fold the unstimulated control value were observed in hepatocytes isolated from control and 1 day PB pre-treated mice when cultured in the presence of 5 or 10 ng/ml EGF or HGF. Hepatocytes isolated from 3, 7, 30 or 90 day treated mice showed a considerably reduced responsiveness to growth factors; maximum labelling indices did not exceed by a factor of 2 the value obtained in the absence of growth factors. However, the apparent decrease in responsiveness to growth factors in hepatocytes isolated from 3 day pre-treated mice was due to an increased background level of proliferation and the attainment of a `ceiling level' of DNA synthesis at approx. 35%. DNA synthesis was not further enhanced by addition of both EGF and HGF. This maximal level of stimulation may indicate that only a specific hepatocyte sub-population is capable of responding to growth factors under the conditions employed. The loss in sensitivity to mitogenic stimuli after 7 days PB pre-treatment correlates with a reported decrease in receptor protein and mRNA levels in rats and coincides with the in vivo shift from hyperplasia to hypertrophy.

Keywords: Key words Phenobarbitone ; Epidermal growth factor ; Hepatocyte growth factor ; Proliferation ; Non-genotoxic

d-Amphetamine-induced hepatotoxicity: possible contribution of catecholamines and hyperthermia to the effect studied in isolated rat hepatocytes by Félix Carvalho; Fernando Remião; M. Elisa Soares; Rita Catarino; Glória Queiroz; M. Lourdes Bastos (pp. 429-436).

Amphetamines are indirect-acting sympathomimetic drugs widely abused due to their physical and psychostimulating effects. However, the use of these drugs has been associated with numerous reports of hepatotoxicity. While glutathione depletion induced by amphetamines contributes to the exposure of hepatocytes to oxidative damage, other indirect effects attributed to amphetamines may have a role in cell injury. To examine this possibility, Wistar rats were used for plasma measurements of d-amphetamine and catecholamines (noradrenaline, adrenaline and dopamine) (15 min) after i.p. injection of d-amphetamine (5, 20 and 80 mg/kg). Freshly isolated rat hepatocytes were put into contact for 2 h with concentrations of d-amphetamine and catecholamines similar to those found in vivo. Since hyperthermia is a common consequence of acute amphetamine intake, the study using isolated hepatocytes was conducted at 37 °C and also at 41 °C in order to simulate high temperature levels. We found that hyperthermia was an important cause of cell toxicity: in vitro, a rise in incubation temperature from 37 to 41 °C causes oxidative stress in freshly isolated rat hepatocytes, as shown by a depletion of reduced glutathione (GSH; 23%), an increase of oxidized glutathione (GSSG; 157%), the induction of lipid peroxidation with 77% increase of thiobarbituric acid substances TBARS) and the consequent loss of cell viability (≤ 44%). Single treatment of isolated hepatocytes with catecholamines at 37 °C induced lipid peroxidation (29% increase of TBARS) but had no effect on glutathione or cell viability. Conversely, a single treatment with d-amphetamine induced glutathione depletion (≤ 24% depletion of GSH) with no effect on lipid peroxidation or cell viability. Also, d-amphetamine potentiated the induction by catecholamines of lipid peroxidation at 37 °C (≤ 48% increase of TBARS), while concomitant treatment of d-amphetamine and catecholamines potentiated cell death at 41 °C (≤ 56% of cell death) although no effect on viability was seen at 37 °C. It is concluded that the aforementioned modifications induced by d-amphetamine in vivo are cytotoxic to freshly isolated rat hepatocytes.

Keywords: Key wordsd-Amphetamine ; Catecholamines ; Hyperthermia ; Freshly isolated rat hepatocytes ; Hepatotoxicity

Implication of CYP 3A in the toxicity of cyclosporin G (CsG), cyclosporin A (CsA) and FK506 on rat hepatocytes in primary culture by Sophie Ellouk-Achard; Chantal Martin; Chuong Pham-Huy; Huynh Thien Duc; Marc Thevenin; Hélène Dutertre-Catella; Jean-Michel Warnet; Jean-Roger Claude (pp. 437-442).

FK506, cyclosporin A (CsA), and its structural analog cyclosporin G (CsG) are immunosuppressant drugs mainly metabolized by hepatic cytochrome P-450 3A (CYP 3A) oxygenase. FK506 metabolites exhibit greater toxicity than the parent drug, while CsA metabolites are far less toxic than CsA itself. The aim of our study was to compare the toxicity of CsG with CsA and FK506 as a function of CYP 3A induction. Hepatocytes from Wistar rats with or without dexamethasone (DEX) induction (200 mg/kg per day, p.o for 4 days) were used in primary culture. The DEX-inductive effect on CYP 3A was assessed by SDS-PAGE. After 6 h incubation with CsG, CsA or FK506 (5 to 200 μM), cell viability (expressed as IC₅₀), intracellular calcium content and apoptosis were evaluated. Concerning cytotoxicity, IC₅₀ values for CsG, CsA and FK506 were 75, 50 and 180 μM respectively in non-induced cultures, and 150, 120 and 25 μM in induced cultures. For intracellular calcium content, a dose-dependent increase was observed in all cultures. However this increase is more important for CsG and CsA in non-induced cultures (150%) compared to induced cultures (110%) at 150 μM. Conversely for FK506, this increase is greater in induced cultures (150%) than in non-induced cultures (127%). Estimation of the percentage of apoptotic cells shows similar variations. Our results show that the toxicity of the three drugs in rat hepatocytes is dependent on CYP 3A induction: increased for FK506, decreased for CsA and CsG. Moreover, with regard to the three tests used, the toxic effects of CsG are close to those of CsA, indicating that CsG metabolites are also less toxic than the parent drug.

Keywords: Key words Cyclosporin G ; Cyclosporin A ; FK506 ; Cytotoxicity ; Cytochrome P-450 3A

Influence of subchronic administration of oestradiol, ethinyloestradiol and oestradiol sulphamate on bile flow, bile acid excretion, and liver and biliary glutathione status in rats by Astrid Barth; Walter Elger; Birgitt Schneider; Sigfrid Schwarz (pp. 443-449).

The cholestatic effect of the newly developed oestradiol sulphamate (J995) was compared with that of the natural oestrogen oestradiol (E) and of the cholestatic standard oestrogen ethinyloestradiol (EE). Female ovariectomized rats were orally treated for 7 days with oestrogen doses molar equivalent to 0.01, 0.1, 1, and 10 mg E/kg body wt. Bile flow, biliary bile acid and glutathione excretion as well as liver glutathione status were determined after bile duct cannulation under the influence of ketamine anaesthesia. For systemic oestrogen activity, the increase of uterine weight was measured. J995 showed the highest oestrogenic activity followed by EE and E. Impairment of bile flow and biliary glutathione excretion (GSH, GSSG) were found to be in the order E < J995 < EE. As all three oestrogens did not influence bile acid excretion, we postulate that mainly the bile acid-independent fraction of bile flow was inhibited, caused at least partly by impairment of canalicular glutathione transport. Based on the results of these studies, we conclude that a tenfold higher dose of J995 exhibited the same cholestatic effect as EE. Together with higher systemic oestrogenic activity, J995 may be used as a prodrug with reduced hepatic side-effects to replace EE in contraception strategies.

Keywords: Key words Oestrogens ; Bile flow ; Bile acids ; Glutathione ; Liver

DNA binding activity of the mammalian translation elongation complex: recognition of chromium- and transplatin-damaged DNA by Jian Fei Wang; Beatrice N. Engelsberg; Steven W. Johnson; Charlotte Witmer; William C. Merrick; Harry Rozmiarek; Paul C. Billings (pp. 450-454).

The elongation factor complex, EF-1H, serves an essential function in protein biosynthesis in eukaryotic cells, although the role of EF-1H in other physiological processes is unknown. In this report, we demonstrate that three components of EF-1H (EF-1β, EF-1δ, and EF-1γ) bind to DNA modified with chromium (Cr), a potent DNA-damaging agent and an established human carcinogen. The EF-1H complex also binds to transplatin modified DNA but not to cisplatin-modified DNA. These results demonstrate that the EF-1H complex has functional DNA binding activity and is capable of recognizing the distortions in DNA structure resulting from the covalent binding of Cr and transplatin to DNA.

Keywords: Key words DNA damage ; Elongation complex ; Chromium

Low levels of cadmium chloride damage the corneal endothelium by W. J. Weidner; A. J. Sillman (pp. 455-460).

The effect of cadmium chloride on the integrity of the endothelium of isolated bullfrog (Rana catesbeiana) corneas was examined by spectrophotometric analysis of corneal uptake of the vital stain Janus green and by scanning electron microscopy (SEM). The uptake of Janus green by the endothelium was dose related between 1.0 and 100.0 μM CdCl₂. The effect of cadmium was significantly attenuated by the calcium channel blocker SKF 96365 and was augmented by the calcium ionophore A23187, indicating that cadmium influx through calcium channels is an important determinant of its cellular effect. The effect of cadmium was not altered by changes in the external calcium concentration, indicating that the mechanism does not involve competitive inhibition by calcium. SEM demonstrated significant structural damage to the corneal endothelium exposed to cadmium chloride, including focal disruption and denuding of the apical endothelial membrane.

Keywords: Key words Cornea ; Cadmium chloride ; Calcium chloride ; Endothelium ; Frog

Effects of dose on the methylation of selenium to monomethylselenol and trimethylselenonium ion in rats by Makiko Itoh; Kazuo T. Suzuki (pp. 461-466).

Mechanisms and metabolic significance in rats of methylation to the reduced form of selenium (Se), i.e., selenide (Se²⁻), were studied by dose- and time-related experiments with injection of selenite. Urinary Se-metabolites were determined by HPLC using an inductively coupled argon plasma-mass spectrometer as an in-line detector (HPLC/ICP-MS method). Although only monomethylselenol (MMSe) has been detected in urine of normal rats even in those fed a Se-excess diet, the␣three types of Se-metabolites – MMSe, trimethylselenonium ion (TMSe), and inorganic Se, were detected in urine of Wistar rats injected with selenite (0, 0.1, 0.3, 0.5 and 1.0 mg Se/kg body weight) into the tail vein. The amount of the three Se-metabolites was plotted against the total urinary Se concentration and shown to change dose- and time-dependently. The monomethylated metabolite, i.e., MMSe, increased in urine rapidly at first and was slowly followed by linear dose-dependent excretion of the trimethylated metabolite, TMSe. The new methylation pathway of MMSe leading to TMSe was assumed to be induced or activated when the dose of Se exceeds the limit of the normal capacity for monomethylation. Progressive methylation reactions were suggested to be regulated enzymatically.

Keywords: Key words Selenium ; Monomethylselenol ; Trimethylselenonium ion ; HPLC/ICP-MS ; Methylation

Antidotal efficacy of quinuclidinium oximes against soman poisoning by A. Lucić; B. Radić; M. Peraica; M. Mesić; I. Primožič; Z. Binenfeld (pp. 467-470).

The efficiency of newly synthesized oxime derivatives of quinuclidinium were tested in vitro on soman inhibited acetylcholinesterase (AChE) of human erythrocytes and in vivo using soman poisoned mice. For this purpose, the inhibitory power of oximes (IC₅₀), acute toxicity (LD₅₀) as well as reactivating and protective capacities with respect to soman-inhibited AChE were determined for each of the oximes. All oximes tested were ineffective in vitro but protected mice very efficiently (BM-1 protects against 4LD₅₀ of soman). The results indicate that the in vivo effectiveness of quinuclidinium oximes against soman poisoning may not be related to reactivation or protection of AChE but rather to some other mechanism of the cholinergic system.

Keywords: Key wordsAcetylcholinesterase reactivators ; Oximes ; Quinuclidinium compounds ; Soman

In vitro evidence for a Donnan distribution of Mg 2+ and Ca2+ by chondroitin sulphate in cartilage by Theodor Günther; Marcus Rücker; Christian Förster; Jürgen Vormann; Ralf Stahlmann (pp. 471-475).

Fluoroquinolones are known for their ability to form chelate complexes with magnesium. Cartilage lesions observed in juvenile animals after quinolone treatment very probably are a consequence of the lack of functionally available magnesium. In cartilage, which contains high amounts of negatively charged proteoglycans, a Donnan distribution can be expected leading to an inhomogeneous distribution of ions (such as magnesium), which may support the toxic effects of magnesium deficiency or quinolone treatment of cartilage. We performed in vitro experiments using dialysis tubes to simulate the unequal distribution of proteoglycans in cartilage and measured the distribution of magnesium, calcium and ofloxacin. We found that the concentration of free magnesium is significantly reduced within the chondroitin sulphate-free solution due to a Donnan effect. For example, using a 3% chondroitin sulphate solution (outside the tubing) dialysed against a chondroitin sulphate-free solution (inside the tubing) the magnesium concentration decreased by 24% from 0.55 ± 0.02 to 0.42 ± 0.04 mmol/l inside the tubing during 48 h observation (P < 0.01). Under physiological conditions this unequal distribution of magnesium probably will be much more pronounced because chondroitin sulphate concentrations in cartilage are higher; nevertheless, magnesium concentration is sufficient for regular function of the tissue. During the sensitive phase of quinolone toxicity, magnesium in juvenile cartilage is lower than at other time points during postnatal development. Moreover, additional complexation by quinolones may further reduce the concentration of functionally available magnesium below the critical level.

Keywords: Key words Magnesium ; Calcium ; Fluoroquinolones ; Chondroitin sulphate ; Donnan distribution

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Archives of Toxicology (v.71, #7)