Klaus E. Appel

Organotin Compounds: Toxicokinetic Aspects

Organotin compounds have a broad range of applications. While dialkyltin compounds are used primarily as stabilizers for plastics, trisubstituted organotins are mainly used as biocides e.g., as an active ingredient of marine antifouling paints for boats and ships. Since a number of organotin compounds have been demonstrated to be toxic, there is increasing concern that their widespread use may cause adverse effects within environmental and biological systems. Besides carcinogenic and neurotoxic effects, as well as effects on the reproductive system, the most obvious mammalian effects of both various di‐ and trisubstituted organotins were found on the immune system. Exposure of humans to organotin compounds can take place through consumption of contaminated fish and seafood. In human liver samples, mainly dibutyltin, the metabolite of tributyltin, could be detected indicating that organotin compounds are bioavailable after dietary exposure. The objective of this short review is to present various toxicokinetic aspects of organotin compounds in more detail. While several studies using in vitro systems investigated their metabolism especially by the monooxygenase system, various aspects of absorption, distribution, metabolism, and excretion (ADME) pathways of different organotin compounds were described by data obtained from several studies with laboratory animals. However, most of these studies were not conducted as full ADME studies but dealt only with some of these aspects. Therefore, for definitive conclusions in some cases, additional information is requested. By reviewing and updating the current literature consideration was given preferentially to those organotin compounds which have relevance with respect to human exposure and/or toxicological effects.

Risks and benefits of dietary isoflavones for cancer

A high intake of fruits and vegetables is associated with a lower risk of cancer. In this context, considerable attention is paid to Asian populations who consume high amounts of soy and soy-derived isoflavones, and have a lower risk for several cancer types such as breast and prostate cancers than populations in Western countries. Hence, interest focuses on soyfoods, soy products, and soy ingredients such as isoflavones with regard to their possible beneficial effects that were observed in numerous experiments and studies. The outcomes of the studies are not always conclusive, are often contradictory depending on the experimental conditions, and are, therefore, difficult to interpret. Isoflavone research revealed not only beneficial but also adverse effects, for instance, on the reproductive system. This is also the case with tumor-promoting effects on, for example, breast tissue. Isoflavone extracts and supplements are often used for the treatment of menopausal symptoms and for the prevention of age-associated conditions such as cardiovascular diseases and osteoporosis in postmenopausal women. In relation to this, questions about the effectiveness and safety of isoflavones have to be clarified. Moreover, there are concerns about the maternal consumption of isoflavones due to the development of leukemia in infants. In contrast, men may benefit from the intake of isoflavones with regard to reducing the risk of prostate cancer. Therefore, this review examines the risks but also the benefits of isoflavones with regard to various kinds of cancer, which can be derived from animal and human studies as well as from in vitro experiments.

Toxicological assessment of 3-chloropropane-1,2-diol and glycidol fatty acid esters in food.

Fatty acid esters of 3-chloropropane-1,2-diol (3-MCPD) and glycidol are a newly identified class of food process contaminants. They are widespread in refined vegetable oils and fats and have been detected in vegetable fat-containing products, including infant formulas. There are no toxicological data available yet on the 3-MCPD and glycidol esters, and the primary toxicological concern is based on the potential release of 3-MCPD or glycidol from the parent esters by lipase-catalyzed hydrolysis in the gastrointestinal tract. Although 3-MCPD is assessed as a nongenotoxic carcinogen with a tolerable daily intake (TDI) of 2 μg/kg body weight (bw), glycidol is a known genotoxic carcinogen, which induces tumors in numerous organs of rodents. The initial exposure estimates, conducted by Federal Institute for Risk Assessment (BfR) under the assumption that 100% of the 3-MPCD and glycidol are released from their esters, revealed especially that infants being fed commercial infant formula could ingest harmful amounts of 3-MCPD and glycidol. However, the real oral bioavailability may be lower. As this gives rise for toxicological concern, the currently available toxicological data of 3-MCPD and glycidol and their esters are summarized in this review and discussed with regard to data gaps and further research needs.

Toxicity and carcinogenicity of furan in human diet

Furan is formed during commercial or domestic thermal treatment of food. The initial surveys of furan concentrations in heat-treated foods, published by European and US authorities, revealed the presence of relatively high furan levels in coffee, sauces, and soups. Importantly, furan is consistently found in commercial ready-to-eat baby foods. Furan induces hepatocellular tumors in rats and mice and bile duct tumors in rats with a high incidence. Epidemiological studies are not available. It is assumed that cis-2-butene-1,4-dial, the reactive metabolite of furan, is the causative agent leading to toxicity and carcinogenicity. Based on this data, furan is classified as a possible human carcinogen. The initial exposure estimates revealed a relatively small margin (~2,000) between human exposure and those furan doses, which induce liver tumors in experimental animals. As this may give rise for concern, in this review, the currently available toxicological and mechanistic data of furan are summarized and discussed with regard to its applicability in assessing the risk of furan in human diet.

Human CYP2E1 mediates the formation of glycidamide from acrylamide

Regarding the cancer risk assessment of acrylamide (AA) it is of basic interest to know, as to what amount of the absorbed AA is metabolized to glycidamide (GA) in humans, compared to what has been observed in laboratory animals. GA is suspected of being the ultimate carcinogenic metabolite of AA. From experiments with CYP2E1-deficient mice it can be concluded that AA is metabolized to GA primarily by CYP2E1. We therefore examined whether CYP2E1 is involved in GA formation in non-rodent species with the focus on humans by using human CYP2E1 supersomes™, marmoset and human liver microsomes and in addition, genetically engineered V79 cells expressing human CYP2E1 (V79h2E1 cells). Special emphasis was placed on the analytical detection of GA, which was performed by gas chromatography/mass spectrometry. The results show that AA is metabolized to GA in human CYP2E1 supersomes™, in marmoset and human liver microsomes as well as in V79h2E1 cells. The activity of GA formation is highest in supersomes™; in human liver it is somewhat higher than in marmoset liver. A monoclonal CYP2E1 human selective antibody (MAB-2E1) and diethyldithiocarbamate (DDC) were used as specific inhibitors of CYP2E1. The generation of GA could be inhibited by MAB-2E1 to about 80% in V79h2E1 cells and to about 90% in human and marmoset liver microsomes. Also DDC led to an inhibition of about 95%. In conclusion, AA is metabolized to GA by human CYP2E1. Overall, the present work describes (1) the application and refinement of a sensitive methodology in order to determine low amounts of GA, (2) the applicability of genetically modified V79 cell lines in order to investigate specific questions concerning metabolism and (3) the involvement, for the first time, of human CYP2E1 in the formation of GA from AA. Further studies will compare the activities of GA formation in genetically engineered V79 cells expressing CYP2E1 from different species.

Toxicology and risk assessment of acrolein in food

Acrolein is an α,β-unsaturated aldehyde formed by thermal treatment of animal and vegetable fats, carbohydrates and amino acids. In addition it is generated endogenously. As an electrophile, acrolein forms adducts with gluthathione and other cellular components and is therefore cytotoxic. Mutagenicity was shown in some in vitro tests. Acrolein forms different DNA adducts in vivo, but mutagenic and cancerogenous effects have not been demonstrated for oral exposure. In subchronic oral studies, local lesions were detected in the stomach of rats. Systemic effects have not been reported from basic studies. A WHO working group established a tolerable oral acrolein intake of 7.5 μg/kg body weight/day. Acrolein exposure via food cannot be assessed due to analytical difficulties and the lack of reliable content measurements. Human biomonitoring of an acrolein urinary metabolite allows rough estimates of acrolein exposure in the range of a few μg/kg body weight/day. High exposure could be ten times higher after the consumption of certain foods. Although the estimation of the dietary acrolein exposure is associated with uncertainties, it is concluded that a health risk seems to be unlikely.

Risk assessment of Bundeswehr (German Federal Armed Forces) permethrin-impregnated battle dress uniforms (BDU)

In an age when vector-borne diseases are emerging worldwide, personal protective measures are essential for shielding soldiers and other exposed persons from arthropod attack. The development of permethrin-impregnated clothing has been one recent advance in protecting persons at-risk. However, to date risk assessment has not been performed related to wearing permethrin-impregnated clothing over longer time periods. Therefore, this paper describes relevant toxicological aspects of permethrin and estimates the extent of dermal permethrin uptake by soldiers wearing impregnated uniforms by determining urine metabolites of permethrin. The exposure monitoring conducted in wearers of untreated uniforms did not show any signs of increased permethrin uptake and was similar to that of the general population in Germany. By contrast, studies involving the soldiers wearing permethrin-impregnated uniforms identified far higher internal exposure, the amounts of urine metabolites clearly above the reference value for the background exposure of the German population at large. Comparing the median excretion values, an approximately 200 times higher exposure can be assumed. The excretion levels of the subject with the maximum amount of metabolites correspond to an internal exposure of around 5-6microg/kg body weight and day thereby considering that biomonitoring could not take all urine metabolites and other elimination routes into account. Based on an oral absorption rate of 50%, the internal dose of 5-6microg/kg body weight and day would correspond to an oral uptake of permethrin which is around 20% of the ADI value of 50microg/kg body weight and day. In addition, based on these data and using a dermal absorption rate of 2% the permethrin dose reaching the skin was estimated to be 250microg/kg body weight and day. Considering a standard body weight and the area covered by the uniform, an exposure level of about 1.25microg permethrin/cm(2) skin and day can be calculated. Clinical subjective symptoms were recorded by means of a self-reporting questionnaire which has been developed and used for this specific purpose in environmental outpatient departments in both groups (wearers of impregnated versus non-impregnated uniforms). Only minor sensory impairments were identified in one of the studies (Kabul/Afghanistan) which may represent skin paraesthesiae. Based on these results, it can be assumed that the normal use of permethrin-treated uniforms does not affect human health to a clinical relevant extent. We recommend that the release rate of permethrin from the textile material should be strictly monitored by means of a quality assurance method. It should comply with standards to which the results of this study may contribute.

Oxidative DNA lesions in V79 cells mediated by pentachlorophenol metabolites

Abstract Incubation of the pentachlorophenol (PCP) metabolites, tetrachloro-p-benzoquinone (chloranil, TCpBQ), tetrachloro-p-hydroquinone (TCpHQ) and tetrachloro-o-benzoquinone (TCoBQ) with V79 Chinese hamster cells led to a significant enhancement of the amount of 8-hydroxydeoxyguanosine (8-OH-dG) in DNA. With PCP itself and the metabolite tetrachloro-o-hydroquinone (TCoHQ) no distinct induction of this lesion could be observed. The average yields of 8-OH-dG were about 2–2.5 times above background levels. In addition, TCpBQ and TCpHQ were able to generate DNA single-strand breaks, while PCP, TCoHQ and TCoBQ failed to induce this lesion. All incubations were performed for 1 h without exogenous metabolic activation and concentrations were 25 μM of the respective agent. It is concluded that these metabolites may contribute to the carcinogenicity of PCP observed in mice, by generating reactive oxygen species (ROS) through their redox cycling properties.

Uptake of permethrin from impregnated clothing

In order to examine exposure and health risks which can arise from permethrin-impregnated clothing, a controlled trial was conducted. In a study group consisting of 187 volunteers in total, a subgroup of 86 persons was equipped with permethrin-impregnated battle dress uniforms (BDU) for 28 days. One hundred and one persons served as a control group, wearing non-impregnated BDUs throughout the entire study period of 56 days. Internal exposure of all participants was assessed by determination of urinary permethrin metabolites (cis-DCCA, trans-DCCA and 3-PBA) on day 0, 14 and 28 of the wearing period and 28 days after termination of wearing. Exposure levels in the control group ranged within background exposure of the general German population at all four dates of sampling (medians Sigma DCCA+3-PBA were 0.09, 0.13, 0.23 and 0.10mug/l, respectively). For the group equipped with impregnated BDUs this applied to day 0 (0.31mug/l) only, while the following measurements revealed considerably higher metabolite concentrations (31.39, 22.01 and 1.44mug/l, respectively), especially while wearing impregnated clothing. Due to these results a substantial uptake of permethrin from impregnated BDUs has to be assumed. However, since calculations reveal a maximum permethrin uptake clearly below the acceptable daily intake (ADI), health impairments are rather unlikely.

NO2-induced DNA single strand breaks are inhibited by antioxidative vitamins in V79 cells.

Recently, we were able to show that nitrogen dioxide (NO2), a strong oxidant, induced DNA single strand breaks (SSBs) in V79 cells. Possibly, special scavengers, e.g. antioxidative vitamins, may protect cells from NO2-induced damage. Therefore, the effect of various tocopherols, beta-carotene, retinol, and ascorbic acid on NO2-induced SSBs in V79 cells was investigated. Cells were preincubated with vitamins and treated for 10 min with 200 ppm NO2. The rate of SSBs was measured by the alkaline elution assay, the amount of DNA by a fluorimetric assay. Micromolar concentrations of d-gamma-tocopherol inhibited the rate of NO2-induced SSBs by 40%, beta-carotene and ascorbic acid by 25%. None of these vitamins had any effects on DNA or the viability of cells. When incubating the cells with retinol in a medium with pH 8.5, this vitamin inhibited NO2-induced SSBs, reducing them by 35%. However, in high concentrations, retinol itself induced SSBs and influenced cell viability. The results are discussed with regard to many toxic effects of NO2.