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Biomedical subjects

J Fink-Gremmels

Publications and source records attributed to J Fink-Gremmels.

At least 37 records · Page 2Linked to original sources
PubMed2004

Benzimidazole drugs and modulation of biotransformation enzymes.

Benzimidazole drugs (e.g., anthelmintics albendazole, fenbendazole, oxfenbendazole, thiabendazole, mebendazole; inhibitors of proton pump omeprazole, lansoprasole, pantoprasole) represent substances used in both human and veterinary medicine; however, from the point of view of induction and inhibition of biotransformation enzymes, research has been carried out mainly due to the initiative of human pharmacologists. The purpose of the present review is to inform about inductive and inhibitive effects of benzimidazole drugs in man, animals and cell cultures. Pharmacological and toxicological consequences of modulation of biotransformation enzymes are discussed and the significance of studies in the field of modulation of biotransformation enzymes in food-producing animals is explained. Since the modulating effect of benzimidazoles strongly varies depending on structure of the individual substances, the particular attention is paid to structure-modulation relationships.

Animals↗
PubMed2004

Metabolism-mediated cytotoxicity of ochratoxin A.

Ochratoxin A (OTA) is produced by various strains of Aspergillus and Penicillium and is a common contaminant of food commodities. OTA is metabolised by cytochrome P450 (CYP450) enzymes resulting in hydroxylated metabolites, 4R-OH-OTA and 4S-OH-OTA, and possibly in other minor metabolites including OTA-quinones. However, until now conflicting data have been presented regarding the role of biotransformation products in the adverse effects of OTA. Hence, the aim of this study was to further assess the metabolism-mediated cytotoxicity of OTA in an in vitro model encompassing NIH/3T3 cells, stably expressing the human CYP450 enzymes CYP2C9 and CYP3A4, respectively. In addition, modulation of the cellular glutathione (GSH) content was used to identify a role of GSH in OTA-induced cytotoxicity. Following exposure to OTA, cells expressing CYP2C9 showed a significant reduction in neutral red (NR) uptake but not in Alamar blue (AB) reduction, as compared to the control LNCX cells which do not express CYP450 enzymes. CYP3A4-expressing cells showed no difference in viability from control LNCX cells. When pre-treated with l-buthionine S,R-sulphoximine (BSO) to deplete GSH, CYP2C9-expressing cells showed also a loss of cell viability as compared to LNCX cells, although to a lesser extent as compared to non-depleted CYP2C9-expressing cells. Data presented in this study support previous findings, indicating that different biotransformation pathways contribute to the cytotoxicity induced by OTA.

Animals↗
PubMed2004

Metabolism of bromhexine in pig hepatocyte cultures.

The metabolism of bromhexine [N-cyclohexyl-N-methyl-2-(2-amino-3,5-di-bromo-benzyl)-amine] was studied using pig hepatocyte cultures and LC/MS/MS techniques. Phase I 'single-step' reactions, i.e. hydroxylation and demethylation occurred the fastest whereas the formation of hydroxylated/demethylated and aminal hydroxylated metabolites, which can be considered as multiple-step reactions, occurred more slowly. Phase II conjugates were detected for all hydroxylated metabolites. The glucuronides of the hydroxylated/demethylated components tended to accumulate. In addition to metabolites known to be formed in vivo, three unknown components related to bromhexine were detected. Two of these metabolites accumulated during incubation. Based on the fragmentation patterns, a possible molecular structure is proposed for these components.

Animals↗
PubMed2003

The effects of benzimidazole anthelmintics on P4501A in rat hepatocytes and HepG2 cells.

Benzimidazole anthelmintics including albendazole, fenbendazole, and mebendazole are widely used in veterinary medicine. The effects of these benzimidazoles on cytochrome P4501A were investigated in primary cultures of rat hepatocytes and in the HepG2 cell line. After incubation of rat hepatocytes and HepG2 for 24-, 48-, and 72-h cells with drugs at various concentrations (0.1-50 microM), the enzyme activities associated with P4501A1/2 (7-ethoxyresorufin O-deethylation and 7-methoxyresorufin O-demethylation) were measured. The P4501A1/2 protein levels in both model systems were determined by Western blotting. Although all benzimidazoles provoked a significant increase of P4501A1/2 protein levels and P4501A activities, large differences in the induction response were found which was dependent on drug structure, concentration, and model system used. Based on the results, relationships between induction potency and structure of drug were demonstrated, as well as differences between the in vitro systems used. Therefore, pharmacological and toxicological consequences of cytochrome P4501A induction by benzimidazole drugs should be taken into account in veterinary therapy.

Animals↗
PubMed2003

The short-term clinical efficacy of amitriptyline in the management of idiopathic feline lower urinary tract disease: a controlled clinical study.

In a controlled study, the effects of amitriptyline compared with that of a placebo in cats suffering from idiopathic Feline Lower Urinary Tract Disease (FLUTD) have been investigated. Thirty-six animals were selected by veterinary practitioners and treated with a placebo or 10mg amitriptyline once daily. All animals received concomitant antibiotic treatment. A total of 24 cats were included in the final assessment of the results. The severity of symptoms before and after treatment were compared between groups and showed no significant difference. Results indicated that the 7-day course of 10mg amitriptyline was not effective in the treatment of idiopathic FLUTD. Thus, it is considered not to be beneficial as a short-term therapy where the therapeutic results depend on peripheral effects of the drug. Long-term effects may be expected 4 or more weeks after the start of therapy and need to be further investigated.

Administration, Oral↗
PubMed2003

The effects of mebendazole on P4501A activity in rat hepatocytes and HepG2 cells. Comparison with tiabendazole and omeprazole.

Mebendazole is a benzimidazole anthelmintic widely used in veterinary and human therapy. Among benzimidazole derivatives, several drugs with inducing effect on cytochromes P450 can be found. However, the induction capacity of mebendazole on P450s has not been explored yet. In this study, the effects of mebendazole on P4501A activity was tested in primary cultures of rat hepatocytes and in human hepatoma HepG2 cell line. Two known P4501A inducers with benzimidazole structure, tiabendazole and omeprazole, were also included in the experiments with the aim of studying structure-induction relationships. After 24-, 48- and 72-h incubation of rat hepatocytes and HepG2 cells with drugs in various concentrations (0.1-100 microM), enzyme activity associated with P4501A1/2 (EROD, MROD) was measured. In addition, the P4501A1/2 protein levels in both in-vitro systems were determined by Western-blotting. Mebendazole provoked a significant increase in P4501A1/2 protein expression and P4501A activity in both in-vitro systems. Omeprazole caused a significant dose-dependent increase of P4501A activity only in HepG2 cells. Although tiabendazole treatment led to significant increase of P4501A protein level, no effect on P4501A activity was observed in either system. The results demonstrate that mebendazole possesses the ability to significantly induce P4501A. Thus, pharmacological and toxicological consequences of P4501A induction should be taken into account in human therapy. The structure-induction relationships and differences between in-vitro systems used are discussed.

Animals↗
PubMed2002

The role of oxidative stress in the ochratoxin A-mediated toxicity in proximal tubular cells.

Balkan endemic nephropathy (BEN), a disease characterized by progressive renal fibrosis in human patients, has been associated with exposure to ochratoxin A (OTA). This mycotoxin is a frequent contaminant of human and animal food products, and is toxic to all animal species tested. OTA predominantly affects the kidney and is known to accumulate in the proximal tubule (PT). The induction of oxidative stress is implicated in the toxicity of this mycotoxin. In the present study, primary rat PT cells and LLC-PK(1) cells, which express characteristics of the PT, were used to investigate the OTA-mediated oxidative stress response. OTA exposure of these cells resulted in a concentration-dependent elevation of reactive oxygen species (ROS) levels, depletion of cellular glutathione (GSH) levels and an increase in the formation of 8-oxoguanine. The OTA-induced ROS response was significantly reduced following treatment with alpha-tocopherol (TOCO). However, this chain-braking anti-oxidant did not reduce the cytotoxicity of OTA and was unable to prevent the depletion of total GSH levels in OTA-exposed cells. In contrast, pre-incubation of the cell with N-acetyl-L-cysteine (NAC) completely prevented the OTA-induced increase in ROS levels as well as the formation of 8-oxoguanine and completely protected against the cytotoxicity of OTA. In addition, NAC treatment also limited the GSH depletion in OTA-exposed PT- and LLC-PK(1) cells. From these data, we conclude that oxidative stress contributes to the tubular toxicity of OTA. Subsequently, cellular GSH levels play a pivotal role in limiting the short-term toxicity of this mycotoxin in renal tubular cells.

Animals↗
PubMed2002

Management of oxidative stress by heme oxygenase-1 in cisplatin-induced toxicity in renal tubular cells.

Induction of heme oxygenase-1 (HO-1) may serve as an immediate protective response during treatment with the cytostatic drug cisplatin (CDDP). Oxidative pathways participate in the characteristic nephrotoxicity of CDDP. In the present study, cultured tubular cells (LLC-PK1) were used to investigate whether induction of HO provided protection against CDDP by maintaining the cellular redox balance. The antioxidants, alpha-tocopherol (TOCO) and N-acetylcysteine (NAC), were used to demonstrate that elevation of ROS levels contribute to the development of CDDP-induced cytotoxicity. Chemical modulators of HO activity were used to investigate the role of HO herein. Hemin was used to specifically induce HO-1, while exposure of the cells to tin-protoporphyrin (SnPP) was shown to inhibit HO activity. Hemin treatment prior to CDDP-exposure significantly decreased the generation of ROS to control levels, while inhibition of HO increased the ROS levels beyond the levels measured in cells treated with CDDP alone. Furthermore, HO induction protected significantly against the cytotoxicity of CDDP, although this protection was limited. Similar results were obtained when the cells were preincubated with TOCO, suggesting that mechanisms other than impairment of the redox ratio are important in CDDP-induced loss of cell viability in vitro. In addition, SnPP treatment exacerbated the oxidative response and cytotoxicity of CDDP, especially at low CDDP concentrations. We therefore conclude that HO is able to directly limit the CDDP-induced oxidative stress response and thus serves as safeguard of the cellular redox balance.

Acetylcysteine↗
PubMed2001

Characterization of biotransformation enzyme activities in primary rat proximal tubular cells.

The proximal tubule is a frequent target for nephrotoxic compounds due to it's ability to transport and accumulate xenobiotics and their metabolites, as well as by the presence of an organ-selective set of biotransformation enzymes. The aim of the present study was to characterize the activities of different biotransformation enzymes during primary culturing of rat proximal tubular cells (PT cells). Specific marker substrates for determining cytochrome P450 (CYP450) activity of primary cultured PT cells include 7-ethoxyresorufin (CYP1A1), caffeine (CYP1A), testosterone (CY2B/C, CYP3A), tolbutamide (CYP2C) and dextromethorphan (CYP2D1). Activities of the CYP450 isoenzymes decreased considerably during culture with the greatest loss in activity within 24 h of culture. In addition, expression of CYP450 apoprotein, including CYP1A, CYP2C, CYP2D, CYP2E and CYP4A, was detected in microsomes from freshly isolated PT cells by immunoblotting using specific antibodies. CYP2B and CYP3A apoprotein could not be detected. Activity of the phase II biotransformation enzymes GST, GGT, beta-lyase and UGT was determined with 1-chloro-2,4-dinitrobenzene, L-glutamic acid gamma-(7-amido-4-methyl-coumarin), S-(1,1,2,2-tetrafluoroethyl)-L-cysteine and 1-naphthol, respectively, as marker substrates. Activity of the phase II enzymes remained more stable and, in contrast to CYP450 activity, significant activity was still expressed after 1 week of PT cell culture. Thus, despite the obvious advantages of PT cells as an in-vitro model for studies of biotransformation mediated toxicity, the strong time dependency of especially phase I and, to a lesser extent, phase II biotransformation activities confers limitations to their application.

Animals↗
PubMed2001

Direct cell-to-cell contact between Kupffer cells and hepatocytes augments endotoxin-induced hepatic injury.

This study focuses on the importance of direct contact between Kupffer cells (KCs) and hepatocytes (HCs) during the hepatic inflammatory response using an in vitro approach. The lipopolysaccharide (LPS)-induced inflammatory response in monocultures of porcine HCs and KCs were compared with cocultures prepared either with direct contact between KCs and HCs (DC cocultures) or without direct contact using cell culture membrane inserts. Our data show that DC cocultures exhibited the highest production of tumor necrosis factor (TNF)-alpha, interleukin-6, and nitric oxide (NO) compared with the other cultures. Immunohistochemical studies revealed that TNF-alpha was exclusively produced by KCs, whereas HCs were responsible for NO production after LPS stimulation. Biotransformation capacity, as determined by cytochrome P-450 and UDP glucuronosyl transferase enzyme activities, was most significantly decreased in DC cocultures. These results provide evidence that direct contact between KCs and HCs favors the extensive TNF-alpha production by KCs but in turn affects HC functionality and viability. These findings suggest that direct contact between KCs and HCs plays a key role in the development of a fulminating hepatic inflammatory response.

Animals↗
PubMed2000

Effect of fumonisin B(1) on rat hepatic P450 system.

The effects of the mycotoxin fumonisin B(1) (FB(1)) on the hepatic cytochrome P450 system were investigated in male rats dosed daily by oral gavage with 3 mg FB(1) per kg body weight for 9 consecutive days. FB(1) treatment resulted in a reduced weight gain. At the same time, CYP2E activity was increased, which is considered to mark the metabolic changes inherent to growth retardation in young rats. Treatment with FB(1) also resulted in a selective inhibition of CYP2C11 and to a lesser extent, CYP1A2 in liver microsomes obtained from treated animals, whereas it did not affect significantly the activity of CYP2A1/2A2, CYP2B1/2B2, CYP3A1/3A2 and CYP4A. The significant inhibition of CYP2C11 is considered to reflect a suppressed activity of protein kinase activity resulting from the inhibition of sphingolipid biosynthesis caused by FB(1).

Journal Article↗
PubMed2000

Cytochrome P450-mediated metabolism and cytotoxicity of aflatoxin B(1) in bovine hepatocytes.

Aflatoxin B(1) (AFB(1)) biotransformation comprises cytochrome P450-mediated reactions resulting in hydroxylated and demethylated metabolites as well as AFB(1) epoxides. As the latter are highly nucleophilic, the species-specific rate of epoxidation and the ability for rapid conjugation to glutathione by glutathione S-transferase determines the individual susceptibility to AFB(1). Here we show the time- and dose-dependent rate of AFB(1)-metabolism in bovine hepatocytes. Aflatoxin M(1) (AFM(1)) is the most prominent metabolite formed within the first 2-8 hr of incubation, whereas AFB(1)-dhd is detectable in medium mainly after a prolonged incubation period. The delayed formation of AFB(1)-dhd corresponds to the cytotoxicity demonstrated by the MTT assay. alpha-Naphthoflavone and ketoconazole, inhibitors of CYP1A and CYP3A, respectively in humans, were used to evaluate the contribution of specific P450 isoenzymes in bovine biotransformation of AFB(1). Initial experiments confirmed that alpha-naphthoflavone and ketoconazole inhibited ethoxyresorufin O-deethylation and testosterone 6beta-hydroxylation also in bovine hepatocytes. Both inhibitors reduced AFM(1) and AFB(1)-dhd formation concentration dependently, suggesting that both enzyme groups contribute to the formation of these metabolites. However, the formation of AFM(1) was less inhibited by both compounds than the formation of AFB(1)-dhd.

Aflatoxin B1↗
PubMed2000

Cocultures of porcine hepatocytes and Kupffer cells as an improved in vitro model for the study of hepatotoxic compounds.

In this study primary hepatocyte cultures (HC cultures) and cocultures comprised of hepatocytes and Kupffer cells (HC/KC cocultures) were compared to investigate the inflammatory response induced by lipopolysaccharide (LPS). In addition both culture types were compared to study the hepatotoxic effects of two frequently used drugs: tiamulin and chlorpromazine. The inflammatory response in both culture types was determined by measurement of tumour necrosis factor-alpha (TNF-alpha), interleukin 6 (IL-6) and nitric oxide (NO). The drug-induced hepatotoxic effects were determined by measuring production of intracellular reactive oxygen species (ROS) and cytotoxicity. Exposure of both cultures to LPS resulted in a significantly increased production of TNF-alpha, IL-6 and NO. However, the production of TNF-alpha, IL-6 and NO was substantially increased in culture supernatant of cocultures, compared to single HC-cultures. Both tiamulin and chlorpromazine were potent inducers of intracellular ROS production at concentrations > or = 50 microM. High ROS production was paralleled by increased cytotoxicity as observed in both culture types. Incubation of cocultures with chlorpromazine resulted in a significant increased ROS production as compared to HC cultures. In contrast, no significant differences between HC-cultures and HC/KC cocultures were observed for tiamulin induced ROS production or cytotoxicity. The present study demonstrates that cocultures between Kupffer cells and hepatocytes provide an excellent model for the study of hepatotoxic compounds which exert (part) of their toxic effects via the activation of Kupffer cells. Furthermore they offer a valuable tool to study increased susceptibility to intoxication from xenobiotic agents in case of a concurrent or pre-existing inflammation.

Animals↗
PubMed2000

Inhibition of aflatoxin M1 production by bovine hepatocytes after intervention with oltipraz.

It is well known that cattle ingesting aflatoxin B1 contaminated feed commodities excrete aflatoxin M1 into their milk. As aflatoxin M1 originates from hepatic metabolism, measures to prevent aflatoxin M1 formation need to be directed to either the immobilization of aflatoxin B1 in the gastrointestinal tract or the modification of hepatic metabolism of aflatoxin B1. Here we studied the influence of oltipraz and a second dithiolthione, (1,2) dithiolo (4,3-c)-1,2-dithiole-3,6 dithione (DDD) on bovine hepatic aflatoxin B1 biotransformation. Oltipraz inhibited aflatoxin B1 metabolism as no aflatoxin M1 and no aflatoxin B1-dihydrodiol, the second metabolite found in bovine hepatocytes, was formed. DDD did not significantly inhibit aflatoxin B1 metabolism. It could be demonstrated that the inhibition of aflatoxin B1 metabolism was due to the inhibition of several cytochrome P450 enzyme activities by oltipraz. In contrast, DDD inhibited only ethoxyresorufin O-deethylation activity. These findings suggest a high efficacy of oltipraz in inhibiting aflatoxin M1 contamination of milk from dairy cows exposed to aflatoxin B1 contaminated feeds.

Aflatoxin M1↗
PubMed2000

Mutagenicity of mercury chloride and mechanisms of cellular defence: the role of metal-binding proteins.

The mechanisms of toxicity and, particularly, the potential carcinogenicity of inorganic mercury are still under debate. Results of mutagenicity and genotoxicity testing with mercury have been inconsistent: mercury induces DNA single-strand breaks at low concentrations in mammalian cells but has not proved mutagenic in several bacterial mutagenicity assays. We investigated the mutagenicity of subtoxic concentrations of inorganic mercury and the role of metal-binding proteins and free radicals in this process. A mutagenicity assay using NIH 3T3 cells, transfected with a vector containing lacZ' as a reporter for mutational events, was applied. In this model, inorganic mercury significantly increased the mutation frequency in the lacZ gene, even at the lowest concentration tested. The mutation frequency was greatest at an Hg(2+) concentration of 0.5 microM. To identify the mechanisms involved, different cellular responses to non-cytotoxic concentrations of HgCl(2) were measured. Hg(2+) increased the intracellular amount of reactive oxygen species. This induction of oxidative stress was observed, although the intracellular glutathione (GSH) and metallothionein (MT) concentrations were increased significantly. Mercury-induced MT expression was even more pronounced after GSH depletion. Correspondingly, radical formation was more evident in the presence of the GSH-depleting agent L-buthioneine-[S:,R:]-sulfoximine. These findings suggest that the observed mutations might be a consequence of oxidative processes, rather than due to a direct interaction of mercury with nuclear DNA. The results also indicate that the auto-induction of MT by Hg(2+) fails to prevent these mutational events.

3T3 Cells↗
PubMed1999

Mutagenicity of commercial Monascus fermentation products and the role of citrinin contamination.

Pigments produced as secondary metabolites by various isolates of moulds belonging to the genus Monascus have been used traditionally as colorants in Oriental food. Modern food industry has rediscovered these moulds as promising source for natural colorants. However, recent studies evidence that one of the secondary metabolites produced by Monascus is identical in structure to the mycotoxin citrinin. Thus, a sensitive HPLC method was developed to analyse these food colorants for contamination with citrinin. The mycotoxin could be detected in all the commercial Monascus samples at concentrations varying between 0.2 to 17.1 microg/g. In addition, the mutagenicity of commercial Monascus samples applying Salmonella-microsome assay and Salmonella-hepatocyte-assay was investigated and compared to the results obtained with citrinin. Citrinin and two Monascus extracts induced a positive dose depending mutagenic response in the Salmonella-hepatocyte-assay applying strain TA-98. However, no mutagenicity could be detected in the Salmonella-microsome assay, neither with nor without S9-mix, for citrinin and Monascus extracts, applying TA-98, TA-100, TA-1535, TA-1538 and TA-97. These findings provide further evidence that citrinin requires complex cellular biotransformation to exert mutagenicity.

Animals↗