Threshold effects in genetic toxicity: perspective of chemicals regulation in Germany.

In the regulation of chemical substances, it is generally agreed that there are no thresholds for genotoxic effects of chemicals, i.e. , that there are no doses without genotoxic effects. When classifying and labelling chemicals, dangerous properties of chemicals are to be identified. In this context, in general, the mode of action (threshold or not) is not considered for genotoxic substances. In the process of quantitative risk assessment, however, determination of the type of dose-effect relationships is decisive for the outcome and the type of risk management. The presence of a threshold must be justified specifically in each individual case. Inter alia, the following aspects may be discussed in this respect: aneugenic activity, indirect modes of action, extremely steep dose-effect relationships in combination with strong toxicity, specific toxicokinetic conditions which may lead to 'metabolic protection' prior to an attack of DNA. In the practice of the regulation of chemical substances with respect to their genotoxic effects, the discussion of thresholds has played a minor role. For notified new substances, there are, in general, no data available that would allow a reasonable discussion. Concerning substances out of the European programme on existing substances, so far 29 have been assessed in our institute with respect to genetic toxicity. Eight out of these have shown considerable evidence for genotoxicity. For two of them, a possible threshold is discussed: one substance is an aneugen, the other one is metabolised to an endogenic compound with genotoxic potential. In the practice of risk assessment of genotoxic substances, the discussion of the mode of action for genotoxicity is frequently associated with the evaluation of potential carcinogenic effects. Here, tissue-specific genotoxic effects in target organs for carcinogenicity are to be discussed. Moreover, the contribution of genotoxicity to the multifactorial process of tumour development should be assessed.

Genotoxicity tests for new chemicals in Germany: routine in vitro test systems.

According to regulations in the European Union, new chemical substances must be notified before they can be introduced onto the market. One of the prerequisites for notification is that toxicological properties, including mutagenicity, are examined. In this paper, a report on routine in vitro mutagenicity testing is given for 776 new substances notified in Germany between 1982 and 1997. In general, the methodological quality of testing was in line with internationally accepted guidelines. Bacterial gene mutation tests (Bact) were conducted for nearly all of the substances, 13.4% were positive. Of the Bact-positive substances, 36 were also tested in the in vitro chromosomal aberration test (CAbvit) and the mammalian cell gene mutation test (MCGM). Twenty-six of these (72. 2%) were negative in both mammalian cell tests indicating that the genotoxic potentials of the substances are not relevant for man. Of all new substances, 333 were tested in CAbvit, here the percentage of positive findings was 25.2%. More than 80% of the in vitro clastogens were negative in the Bact. With respect to a sensitive detection of genotoxic potentials of substances, the combination 'Bact+CAbvit' is appropriate for basic testing. In our database CHL cells were more sensitive to clastogenic effects than other cell types. Only very few clastogens were identified as 'high toxicity clastogens'. MCGM tests were performed for 118 substances, quite often as follow-up in case of positive Bact tests. In total, 12.7% of the substances were positive in the MCGM. However, there was a clear difference in the frequencies of positive findings in HPRT tests (5.5%) and mouse lymphoma assays (MLA; 37.0%). None of the MCGM-positive substances was a 'unique positive', i.e., negative in Bact and CAbvit.

[Nitrate and nitrite concentrations in gastric juice with regard to the physiologic condition of the gastric mucosa]. / Nitrat- und Nitritkonzentrationen im Magensaft unter Berücksichtigung des physiologischen Zustandes der Magenschleimhaut.

In a random sample comprising 101 test persons (35 without and 66 with gastric disorders) nitrate and nitrite concentrations in gastric juice were determined. It was shown that parameters like pH, physiological stage of gastric mucosa, concentrations of bacteria and fungi in gastric juice or nitrate and nitrite concentrations, fungi and bacteria in saliva do not sufficiently characterize the dynamics of nitrate and nitrite in human stomach.

[Results of clinical and epidemiologic studies of the nitrate problem]. / Ergebnisse klinischer und epidemiologischer Untersuchungen zum Nitratproblem.

Small differences in nitrate intake with the drinking water are not reflected in nitrate contents of saliva and urine of test persons. A correlation of nitrate concentration in body fluids and cancer incidence can be expected hardly. Inflammatory diseases of the gut are frequently accompanied by enhanced endogenous nitrate synthesis and have an essential influence on total nitrate load of the human organism. Nitrate contents in saliva and/or urine are not general indicators of inflammatory processes. As the role of the nitrate ion in humans is not yet understood, the claim remains for a nitrate intake being as low as possible.

[Nitrate and nitrite in the urine, saliva and blood of urologic patients]. / Nitrat und Nitrit in Urin, Speichel und Blut urologischer Patienten.

Nitrate and nitrite contents were determined in urine, saliva, and blood of 298 patients suffering from urological diseases. Crude values of nitrate and nitrite in morning urine without any correction due to density and creatinine are sufficient for epidemiological purposes. Significant correlations exist with vegetables intake and bacteriuria, but not with age, sex, disease, smoking, and medicaments. Neither nitrate nor nitrite may be considered to be general indicators of inflammatory processes in the urogenital tract. According to recent investigations nitrite formation during bacterial infections must be seen in connection with simultaneously occurring macrophage activation, as the latter one is catalyzing the formation of carcinogenic N-nitroso compounds from nitrite and secondary amines.

[Nitrate and nitrite content of the saliva, urine, blood and cerebrospinal fluid in patients at an infection clinic]. / Nitrat- und Nitritgehalt in Speichel, Urin, Blut und Liquor von Patienten einer Infektionsklinik.

In 254 patients of a ward for infectious diseases the authors demonstrated that inflammatory diseases are frequently accompanied by an increase in nitrate content of the blood, urine and saliva. This effect is especially evident in gastrointestinal disorders. Correlations of nitrate with indicators of the inflammatory process are, if at all, very weak. The endogenous synthesis of nitrate may be of importance for the total nitrate load to the organism especially in children or patients with long-lasting inflammatory disease.

[Pilot study of the nitrate, nitrite and bacterial content of human saliva as a function of environmental factors]. / Pilotstudie über den Nitrat-, Nitrit- und Bakteriengehalt des menschlichen Speichels in Abhängigkeit von Umweltfaktoren.

In a random sample comprising 160 test persons nitrate (12.4 +/- 7.6 mg/l) and nitrite (5.7 +/- 4.0 mg/l) concentrations as well as bacteria counts in saliva were determined. No dependence of the values from age and sex could be detected, whereas smokers have lower concentrations of both nitrate and nitrite. Persons suffering from inflammatory diseases did not have enhanced nitrate concentrations. Role of bacteria for nitrite production is confirmed. Patients, regularly taking nitro-remedies, showed enhanced NO3--(25.8 mg/l) and NO2--(8.4 mg/l)-values.

The utilization of nitrate and nitrite by Streptococcus salivarius in the saliva.

Streptococcus salivarius BU 104 utilizes nitrate and nitrite only under anaerobic conditions and thus adds to the nitrite exposure of the human organism.