Interpretation of the biological relevance of genotoxicity test results: the importance of thresholds

Despite recent improvements in genotoxicity protocols, we have observed an increase in the occurrence of positive results, particularly in chromosomal aberration tests in vitro, yet very few of these are accompanied by positive responses in vivo. Thus, the positive results may not be biologically relevant either for rodents or humans in vivo, but how should we determine "biological relevance"? Chemicals that produce thresholded dose-responses may well not pose a genotoxic risk at low (relevant to human) exposures, but thresholds should not just be "seen"; there must be an explanation and understanding of the underlying mechanism. In addition to extremes of pH, ionic strength and osmolality, as have been identified previously, such mechanisms include indirect genotoxicity resulting from interaction with non-DNA targets, chemicals/metabolites which are inherently genotoxic but which, at low concentrations, are effectively conjugated and unable to form adducts, and production of specific metabolites under in vitro conditions that are not formed in rodents or humans in vivo. If such thresholded mechanisms can be identified at exposures which are well in excess of expected human exposure, then there may be a strong argument that the positive results are not biologically relevant.

Considerations on photochemical genotoxicity: report of the International Workshop on Genotoxicity Test Procedures Working Group

Recent toxicological observations have caused concern regarding the need to test, for example, pharmaceuticals and cosmetic products for photochemical genotoxicity. The objective of this report is to give assistance on how to adapt existing test methods to investigate the potential of light-absorbing compounds to induce genotoxic effects on photoactivation. In general, the Organization for Economic Co-Operation & Economic Development (OECD) draft guideline on in vitro phototoxicity testing served as a basis for consideration. Concomitant exposure of the cells to the test compound and solar simulated light was considered appropriate as the initial, basic test condition. Optimization of the exposure scheme, e.g., a change of the irradiation spectrum, might be indicated depending on the initial test results. Selection of test compound concentrations should be based on results obtained with the dark version of the respective test system but might have to be modified if phototoxic effects are observed. Selection of the irradiation dose has to be performed individually for each test system based on dose-effect studies. The irradiation should induce per se a small, reproducible toxic or genotoxic effect. The report includes a specification of necessary controls, discusses factors that might have an impact on the irradiation characteristics, and gives a rationale for the omission of an external metabolic activation system. It also addresses the question that physicochemical and pharmacokinetic properties might trigger the need to test a chemical for photochemical genotoxicity. Relevant experimental observations are presented to back up the recommendations. The working group did not reach a consensus as to whether a single, adequately perfomed in vitro test for clastogenicity would be sufficient to exclude a photogenotoxic liability or whether a test battery including a gene mutation assay would be needed for product safety testing regarding photochemical genotoxicity.

Appropriate levels of cytotoxicity for genotoxicity tests using mammalian cells in vitro

Among standard battery genotoxicity assays, the in vitro chromosome aberration test and the mouse lymphoma tk assay (MLA) yield about fourfold higher incidences of positive test results than the bacterial reverse mutation test or in vivo bone marrow tests. This is a result of experience with submissions of 335 new pharmaceuticals to the German Federal Institute for Drugs and Medical Devices. While all of the standard systems have their value in detecting relevant genotoxins, there is no supportive evidence for DNA reactivity for a considerable number of in vitro clastogens and MLA positives. In particular the clastogenic response of such compounds is often associated with high cytotoxicity. This may invoke the need to change the approach to test for clastogenicity in vitro. A combination of measures such as (1) a change in the upper limits of cytotoxicity that are currently given in International Conference on Harmonisation (ICH) and Organization for Economic Co-Operation & Economic Development (OECD) guidelines, (2) the creation of a common ground of understanding for interpretation of in vitro (positive) test results, and (3) lowering the upper limits of test compound concentration irrespective of cytotoxicity may prove useful to ensure a sufficient reliability of genotoxicity testing with mammalian cells in vitro.

The application of the micronucleus test in Chinese hamster V79 cells to detect drug-induced photogenotoxicity

Recent reports on the photochemical carcinogenicity and photochemical genotoxicity of fluoroquinolone antibacterials led to an increasing awareness for the need of a standard approach to test for photochemical genotoxicity. In this study the micronucleus test using V79 cells was adapted to photogenotoxicity testing. Results of using different UVA/UVB relationships enabled us to identify a suitable irradiation regimen for the activation of different kinds of photosensitizers. Using this regimen, 8-methoxypsoralen and the fluoroquinolones lomefloxacin, grepafloxacin and Bay Y 3118 were identified to cause micronuclei and toxicity upon photochemical activation. Among the phenothiazines tested, chlorpromazine and 2-chlorophenothiazine, were positive for both endpoints, whereas triflupromazine was only slightly photoclastogenic in the presence of strong phototoxicity. Among the other potential human photosensitizers tested (oxytetracycline, doxycycline, metronidazole, emodin, hypericin, griseofulvin), only hypericin was slightly photogenotoxic. Photochemical toxicity in the absence of photochemical genotoxicity was noted for doxycycline and emodin. With the assay system described, it is possible to determine photochemical toxicity and photochemical genotoxicity concomitantly with sufficient reliability.

[Health effects of weight reduction]

Although weight loss is routinely recommended for obese person, the observational literature is controversial in respect of prolongation of life longevity after body weight loss. The positive long-term outcome has been found only in intentional weight loss in obese people with obesity-related comorbidities. The main task in obesity treatment strategy is "primum non nocere". The authors analysed the short-term effect and acceptability of low calorie diet (5 MJ) on health state of 150 obese people (BMI x = 35.9 kg/m2). The acceptability of this diet was 60% only, when the rest of patients has broken this regime mostly after second appointment with their physician. The successful patients achieved 10% weight loss from initial body weight during in average 5 months (95% CI for BMI reduction = (-4.55; -3.01), as well as reduction of percentage of body fat (95% CI = -7.7; -3). During this period has been observed in consistency with experimental evidence of other authors a decrease of plasma values of triacylglycerol, LDL cholesterol in hyperlipidemic patients, but not significant increase of HDL cholesterol. During this period obese persons have taken up more physical activities and felt themselves more psychologically comfortable.

[Energy expenditure at rest and obesity]

Adult human body has to have, because of every day fluctuating energy intake and energy needs, very precious adaptive mechanisms for maintenance of heat homeostasis in the body and nearly stable body weight and body composition, which are optimal for life and reproduction. These short term functioning adaptive mechanisms are called "empty biochemical mechanisms", where chemically bound energy is transformed to heat without work performance. These mechanisms are present on the cellular level (substrates cycles, uncoupling of respiration chain), on the interorgan metabolic level (glycolysis and gluconeogenesis between liver and adipose tissue-glucose-lactate cycle). Central nervous system controls them via many factors; the most important are catecholamines, leptin, insulin, thyroid hormones, cortisol, growth and sex hormones. Neurotransmitters and neuronal net influence energy intake and other behavior. Obesity seems to be associated with the amelioration or overcoming of possibilities of function short-term effective adaptive mechanisms.

ICH-harmonised guidances on genotoxicity testing of pharmaceuticals: evolution, reasoning and impact

The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) has convened an expert working group which consisted of the authors of this paper and their respective committees, consulting groups and task forces. Two ICH guidances regarding genotoxicity testing have been issued: S2A, 'Guidance on Specific Aspects of Regulatory Genotoxicity Tests' and S2B, 'Genotoxicity: A Standard Battery for Genotoxicity Testing of Pharmaceuticals.' Together, these guidance documents now form the regulatory backbone for genotoxicity testing and assessment of pharmaceuticals in the European Union, Japan, and the USA. These guidances do not constitute a revolutionary new approach to genotoxicity testing and assessment, instead they are an evolution from preexisting regional guidelines, guidances and technical approaches. Both guidances describe a number of specific criteria as well as a general test philosophy in genotoxicity testing. Although these guidances were previously released within the participating regions in their respective regulatory communiqués, to ensure their wider distribution and better understanding, the texts of the guidances are reproduced here in their entirety (see Appendix A) and the background for the recommendations are described. The establishment of a standard battery for genotoxicity testing of pharmaceuticals was one of the most important issues of the harmonisation effort. This battery currently consists of: (i) a test for gene mutation in bacteria, (ii) an in vitro test with cytogenetic evaluation of chromosomal damage with mammalian cells or an in vitro mouse lymphoma tk assay, (iii) an in vivo test for chromosomal damage using rodent hematopoietic cells. A major change in testing philosophy is the acceptance of the interchangeability of testing for chromosomal aberrations in mammalian cells and the mouse lymphoma tk assay. This agreement was reached on the basis of the extensive review of databases and newly generated experimental data which are in part described in this publication. The authors are fully aware of the fact that some of the recommendations given in these ICH guidances are transient in nature and that the dynamic qualities and ongoing evolution of genetic toxicology makes necessary a continuous maintenance process that would serve to update the guidance as necessary.

Genotoxicity testing of biotechnology-derived products. Report of a GUM task force. Gesellschaft für Umweltmutationsforschung

Various aspects of genotoxicity testing of biotechnology-derived products are discussed based on information gathered from a questionnaire which was sent to about 30 predominantly European companies. Feedback was received from 13 companies on 78 compounds, mostly recombinant proteins but also on a number of nonrecombinant proteins, which had been assessed for genotoxicity in a total of 177 tests. Four of the 78 compounds appeared to elicit reproducible genotoxic effects. For one of these compounds, the activity could be related to a nonpeptidic linker molecule. No scientifically convincing rationale for the other three compounds could be established, although, at least for two compounds, their activity may be connected with the enzymatic/hormonal activity. In addition to the survey, published reports on genotoxicity testing of biotechnology products were reviewed. The data are discussed relative to whether genotoxicity testing is a valuable exercise when assessing potentially toxic liabilities of biotechnology-derived compounds. It is concluded that genotoxicity testing is generally inappropriate and unnecessary, a position which is in accordance with the available guidelines addressing this area. For the 'average' protein, electrophilic reactions are difficult to envision. Indirect reactions via DNA metabolism and growth regulation seem possible for only very specific proteins such as nucleases, growth factors, cytokines. No information on testing of different types of biotechnology-derived products (e.g., ribozymes, antisense-oligonucleotides, DNA vaccines) has been received in the questionnaires. Discussion of their potential to cause genotoxic changes was based on literature reports. Even for those products for which concerns of genotoxic/tumourigenic potential cannot be completely ruled out, e.g., because of their interaction with DNA metabolism or proliferation control, the performance of standard genotoxicity assays generally appears to be of little value. All information, including also information on the occurrence of genotoxic impurities, has been utilized to formulate a decision tree approach for the genotoxicity testing of biotechnology-derived products.

Analgesic triterpenes from Sebastiania schottiana roots

The present study was conducted in order to isolate and identify the phytochemical constituents responsible for analgesic effects shown by a methanolic extract obtained from Sebastiania schottiana roots. Conventional chromatographic procedures led to the isolation of moretenone, glutinol, beta-sitosterol and stigmasterol. The structural elucidation of these compounds was done on the basis of spectral data (IR, 1H- and 13C-NMR) and comparison with authentic samples. Either glutinol or moretenone exhibited marked analgesic action against acetic acid induced abdominal constrictions in mice by intraperitoneal route, indicating 16 to 26-fold higher efficacy than aspirin and paracetamol. When analyzed in a formal-in test, both compounds and standard drugs inhibited only the second phase (inflammatory pain). Our results suggest that the roots of S. schottiana contain analgesic compounds which justify, at least partially, the popular use of this plant for the treatment of urinary problems.

Photochemical genotoxicity and photochemical carcinogenesis--two sides of a coin?

The direct tumorigenic effects of ultraviolet radiation (UVR) are well known. Specifically, the premutagenic lesions of UVB (290-320 nm), are known to be the most important molecular events in UVR tumorigenicity. The less carcinogenic UVA (320-400 nm) mainly generates oxidative damage in the DNA via photodynamic generation of active oxygen species involving endogenous or exogenous photosensitizers. Several pharmaceuticals are known to act as photosensitizers. Photoinstable phenothiazines, furocoumarins and fluoroquinolones were shown to be very efficient inducers of chromosomal damage in UV-irradiated mammalian cells. Testing for photochemical carcinogenesis in hairless mice of furocoumarins and several fluoroquinolones resulted in a higher incidence and a shorter latent period for skin tumors compared to UVR alone. Overall, the correlation of experimental data between photochemical carcinogens and photochemical genotoxins is quite convincing. Therefore, testing for photochemical genotoxicity preferably in mammalian cells in vitro may be an easy hazard identification approach for photochemical carcinogens. However, further factors such as immunosuppression, irritation and dedifferentiation are to be considered for risk assessment in photochemical carcinogenesis.

Molecular segments of protein Tpr that confer nuclear targeting and association with the nuclear pore complex

Tpr is a 267-kDa protein of unknown function recently identified as a constitutive component of the nuclear pore complex (NPC2)-attached intranuclear filaments. Secondary structure predictions suggest that the protein is divided into a large, coiled-coil forming aminoterminal domain and a shorter, highly acidic carboxyterminal domain. To identify which of Tpr's molecular segments determine its specific intranuclear localization, we have constructed expression vectors encoding various Tpr deletion mutants as well as chimeric combinations of Tpr sequences with the soluble cytoplasmic protein pyruvate kinase. Following transfection of cultured mammalian cells, we have identified a short region within Tpr's carboxyterminal domain that is essential and sufficient to mediate nuclear import of Tpr and which can also confer nuclear accumulation of pyruvate kinase. Tpr deletion mutants that contain this nuclear targeting segment, but lack the aminoterminal domain, appear evenly dispersed throughout the nucleus without any noticeable association to the NPC. In contrast, the aminoterminal domain lacking the carboxyterminal region remains located within the cytoplasm, forming aggregate-like structures not associated with the nuclear envelope. However, when tagged to Tpr's short nuclear targeting segment or to the nuclear localization signal of the SV40 large T protein, the aminoterminal domain is imported into the nucleus, where it then associates with the NPC. This association is mediated by shorter molecular segments within the aminoterminal domain which contain clusters of heptad repeats, whereas other regions are dispensable. This assignment of different topogenetic properties to distinct molecular segments of Tpr will now allow the design of future experiments to study the protein's structural properties further and determine its actual function.

[Reported malpractice after postoperative infection of the locomotor system. Analysis of 261 expert testimony evaluations]

Postoperative infection in the locomotor system may lead to malpractice suits. The aim of the study was to determine the success rate of these claims and the type of expert-confirmed medical negligence so that strategies for avoiding such negligence can be offered. A total of 261 degrees concerning suspected malpractice after postoperative infection in the locomotor system were retrospectively evaluated. Of these, 43.7% claims were successful. The most frequent type of negligence was late diagnosis (34.2%), followed by inconsistent treatment (27.2%) and insufficient surgical revision (5.3%). In 33.3%, combined types of negligence were found. Most frequently, negligence was suspected after infection following hand surgery and internal fixation of long bones. The highest success rate of claims was seen after puncture of joints (69.2%). Insufficient documentation was confirmed in 15.3%. The majority of negligence resulted from diagnostic and therapeutic doubts, which could be avoided, e.g., by a clear definition of infection, consultation of a second opinion, a 2nd-look operation, undelayed and radical surgical revision, painstaking follow-up and disciplined documentation.

Development of monoclonal antibodies specifically recognizing the cyst stage of Entamoeba histolytica

Protozoan cysts were isolated according to a two-step sucrose gradient procedure. Pure cysts of Entamoeba histolytica, in fixed and native states, were injected into BALB/c mice intraperitoneally for immunization. The spleens of these animals were used for fusion with AG8 mouse myeloma cells. Hybridomas were obtained and tested for the recognition of E. histolytica, E. dispar, E. coli, E. hartmanni, Endolimax nana, Jodamoeba biitschlii, and Giardia lamblia. Three monoclonal antibodies were identified that reacted only with cysts and trophozoites of E. histolytica. These can be used for differentiation and identification of E. histolytica in feces.

[Compression of the ulnar nerve in Guyon's canal by a traumatic aneurysm. A case report]

A patient developed after an occupational trauma with fall on the ulnar edge of his right hand pain and swelling in the ulnar area with reduced sensation in the fourth and fifth finger. After examination performed by a neurologist, ulnar nerve-entrapment was diagnosed and operative treatment was indicated. The release of the ulnar tunnel showed a traumatic aneurysma of the ulnar artery compressing the superficial branch of the ulnar nerve. The tumor was removed and end-to-end anastomosis ensued. Four weeks after surgery, examination showed complete recovery. Various reasons of ulnar tunnel syndrome are discussed.

Temporal variation of PCDD/F concentrations in vegetation samples collected in the vicinity of a municipal waste incinerator (1996-1997)

In 1996, the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were determined by HRGC/HRMS in 24 vegetation samples collected in the vicinity of a municipal solid waste incinerator (Tarragona, Catalonia, Spain). In the present study 24 vegetation samples were again taken at the same sampling points and analyzed for the levels of PCDD/Fs. The results were compared with those obtained in the previous survey. While in the 1996 study, PCDD/F levels ranged from 0.15 to 62.09 ng I-TEQ/kg (dry matter) (median value, 0.33 ng I-TEQ/kg; mean value, 4.11 ng I-TEQ/kg), the concentrations of PCDD/Fs in the 1997 survey ranged between 0.11 and 0.50 ng I-TEQ/kg (dry matter) (median value, 0.20 ng I-TEQ/kg; mean value, 0.23 ng I-TEQ/kg). The individual comparison between PCDD/F levels in the samples collected in 1996 and 1997 showed a decrease in 15 of the 24 sampling points. When the comparison was carried out in relation to each of the four main wind directions in the area, the highest decrease in PCDD/F concentrations (64%) corresponded to samples in the SE direction, while those in the NE direction showed also a notable reduction in total I-TEQ (44%). In contrast, PCDD/F levels in vegetation samples from NW and SW directions were increased (37% and 6%, respectively). When the data were evaluated according to the distance of the sampling points to the plant, the highest decrease in total I-TEQ was found at 500 m from the stack. The results of this study seem to provide evidence for a decline in atmospheric emissions of PCDD/Fs in the area of Tarragona.

[Public health relevant levels of pollutants in soil. Considerations for preventive, environmental health protection]

A working document on nation-wide applicable health-related guiding levels of environmental pollutants in soil has been prepared. These levels are intended to be the base for the administrative regulation of soil contaminations in connection with the German "Bundesbodenschutzgesetz" (Federal law on the protection of soil). Legislation demands these base levels to be intensely related to protection against serious health effects (i.e. health hazards). Looking more closely at the toxicological deduction of these values and at some values extracted from that process some uncertainties become obvious with regard to a clearcut limit between dangerous and noxious levels in soil. Indeed there are some arguments which suggest a more conservative approach. Health-care based recommendations should be introduced also at lower contaminant levels in soil. Therefore, development of an internal administrative manual on basic noxious values of soil pollutants (e.g. values below the threshold of danger) is suggested which may be useful for health authorities to cope with special problems in individual cases.

Pattern generation by two coupled time-discrete neural networks with synaptic depression

Numerous animal behaviors, such as locomotion in vertebrates, are produced by rhythmic contractions that alternate between two muscle groups. The neuronal networks generating such alternate rhythmic activity are generally thought to rely on pacemaker cells or well-designed circuits consisting of inhibitory and excitatory neurons. However, experiments in organotypic cultures of embryonic rat spinal cord have shown that neuronal networks with purely excitatory and random connections may oscillate due to their synaptic depression, even without pacemaker cells. In this theoretical study, we investigate what happens if two such networks are symmetrically coupled by a small number of excitatory connections. We discuss a time-discrete mean-field model describing the average activity and the average synaptic depression of the two networks. Depending on the parameter values of the depression, the oscillations will be in phase, antiphase, quasiperiodic, or phase trapped. We put forward the hypothesis that pattern generators may rely on activity-dependent tuning of synaptic depression.

Characterization of the IGF axis components in isolated rat hepatic stellate cells

The insulin-like growth factors I and II (IGF-I, -II) are circulating peptides known to participate in the regulation of metabolism, growth, and cellular differentiation. In the present study, "early cultured" (days 2-3 of culture) and "culture-activated" (days 6-7 of culture) rat hepatic stellate cells (HSCs) were analyzed for expression of individual components of the IGF axis. Northern blot analysis of IGF-I messenger RNA (mRNA) revealed transcripts of 7.5, 4, 2, and 1.0 to 1.5 kb in culture-activated HSCs, while early cultured HSCs did not express IGF-I mRNA. In culture-activated HSCs, an IGF-I secretion of 8.3+/-2.5 ng/10(6) cells per 24 hours was determined radioimmunologically. In media from early cultured HSCs, IGF-I was not detectable. The IGF-I receptor (IGF-I-R) mRNA expression was three-fold higher in early cultured HSCs than in culture-activated HSCs. By immunohistochemistry, a decrease of IGF-I-R expression of HSCs in vivo following CCl4-induced liver damage was noted as well. IGF binding proteins (IGFBPs) were detected in conditioned media from HSCs by 125I-IGF-I ligand blotting at apparent molecular masses of 24 and 41 to 45 kd that were immunologically identified as IGFBP-4 and -3, respectively. Synthesis of these IGFBPs increased with time of culture. At neutral pH, no IGFBP proteolysis was observed in conditioned media of early cultured and culture-activated HSCs, whereas at acidic pH, protease activities against IGFBP-3 and -4 were detectable. IGFBP protease activities were completely abolished by inhibitors of aspartyl and cysteine proteases. Addition of 100 nmol/L IGF-I stimulated cell proliferation of early cultured HSCs 5.6+/-1.1- and 4.6+/-0.2-fold as measured by [3H]thymidine and 5-bromo-2'-deoxyuridine incorporation, respectively. In culture-activated HSCs, proliferation was increased 1.2+/-0.1-fold in the presence of 100 nmol/L IGF-I in both proliferation assays. It can be concluded that due to a higher expression of the IGF-I-R and lower levels of IGFBPs, early cultured HSCs are more susceptible to the mitogenic actions of IGFs than the culture-activated HSCs. The present data suggest a role for the IGF axis components in the initiation rather than the perpetuation of HSC proliferation during hepatic fibrogenesis.

Industrial pollutants in ground waters from northern Milan

Ground water samples from an industrialised area near Milan were analysed by gas chromatography-mass spectrometry (GC-MS) to identify the main pollutants and to quantify two classes of chemicals: polychloro-1,3-butadienes (PCBD) and some aromatic amines. The water contained several halogenated aromatic and aliphatic compounds and heavy contamination due to PCBD, probably arising from contaminated land where a disused chemical plant is located. All the samples contained low levels of aromatic amines indicating a diffuse contamination probably arising from different sources.

Inter-laboratory validation of solid-phase microextraction for the determination of triazine herbicides and their degradation products at ng/l level in water samples

The accuracy and precision of solid-phase microextraction (SPME) were validated in an inter-laboratory study including ten laboratories for the analysis of triazine herbicides and their metabolites at ng/l level in aqueous samples. The SPME conditions were optimised in order to obtain maximum sensitivity. Especially, salt addition and choice of the SPME fibre coated with Carbowax-divinylbenzene increased the sensitivity. The average detection limits were in the range from 4 to 24 ng/l for the triazine herbicides, and 20 and 40 ng/l for desisopropylatrazine and desethylatrazine, respectively. The average r2 values of the calibration curves were above 0.99 for all of the analytes. The statistical data treatment was performed in accordance with the International Standardisation Organisation (ISO) standard 5725. Relative repeatability standard deviations between 6 and 14% and relative reproducibility standard deviations between 10 and 17% were found. The determined concentrations of the reference sample compared well to the "true" values, thus proving the good accuracy of the method. It is concluded that SPME is a reliable technique for the quantitative analysis of water samples containing triazine herbicides in concentrations around the European limit of 100 ng/l for individual pesticides in drinking water.