An approach for evaluating and increasing the informational content of mutagenicity and clastogenicity data bases

A method is described for using the fragments identified by the CASE structure-activity relational expert system to identify the type of chemicals that require further testing in mutagenicity and clastogenicity assays. Inclusion of such chemicals will increase the informational content of databases with respect to structural features that are under-represented in currently available data bases. The method is applied to existing databases (mutagenicity in Salmonella, chromosomal aberrations in Chinese hamster ovary cells, unscheduled DNA synthesis in rat hepatocytes, in vivo induction of micronuclei, somatic mutations in Drosophila melanogaster) to identify structural determinants that are absent.

Modulation of O6-methylguanine-DNA methyltransferase-mediated 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea resistance by O6-benzylguanine in vitro and in vivo

Our previous studies have indicated that O6-methyl-guanine-DNA methyltransferase (MGMT) is a key factor determining tumor cellular resistance to 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU). This study describes the modulation of MGMT-mediated ACNU resistance by O6-benzylguanine pretreatment. The ACNU sensitivity of MGMT proficient human tumor HeLa S3, SMMC-7721, and Cc801 cells in tissue culture was markly enhanced by 10 mm O6-benzylguanine, and a correlation between the extent of enhancement and the level of MGMT activities was observed. A single i.p. injection of 100 mg/kg of O6-benzylguanine caused a complete inhibition of MGMT activities in HeLa S3 tumor xenografts and combination of O6-benzylguanine with ACNU (7.5 mg/kg) significantly inhibited HeLa S3 tumor growth. The results demonstrated that O6-benzylguanine could be used as a potential adjuvant in combination chemotherapy with ACNU to treat MGMT proficient tumors.

Depletion of O6-methylguanine-DNA methyltransferase and potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea antitumor activity by O6-benzylguanine in vitro

The overcoming effect of O6-benzylguanine on O6-methylguanine-DNA methyltransferase (MGMT)-mediated 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resistance in vitro was evaluated. Depletion of MGMT activity in Mer+ HeLa S3 cells by O6-benzylguanine was dose-dependent and a complete loss of MGMT activity was achieved at a concentration of 0.5 microM. The cytotoxic potential of BCNU on MGMT proficient HeLa S3 (1.10 pmol/mg of protein), SMMC-7721 (0.72 pmol/mg of protein) and Cc801 (0.39 pmol/mg of protein) was greatly enhanced when cells were exposed to 10 microM O6-benzylguanine for 1 h, but there was a lack of potentiation of BCNU sensitivity in Mer- HeLa MR cells due to its nearly undetectable level of MGMT. There existed a correlation between the extent of enhancement and the amount of MGMT activity. The intensity of enhancement expressed as dose modifying factor = IC50 (BCNU alone)/IC50 (10 microM O6-benzylguanine + BCNU) was 4.56, 3.89, 3.67 and 0.97 in HeLa S3, SMMC-7721, Cc801 and HeLa MR cells respectively. The results further demonstrated that O6-benzylguanine may have potential utility as an adjuvant in combination chemotherapy with chloroethylnitrosourea agents.

O6-methylguanine-DNA methyltransferase and human cancer chemotherapy

Two kinds of human tumor cell strains having different activity of O6-methylguanine-DNA methyltransferase (O6-MT) were transplanted into nude mice. Mice were then injected intraperitoneally (i.p.) with the bifunctional agent 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride(ACNU). The tumors with low O6-MT activity were quickly suppressed or cured. This result suggests that some tumors, if determined to have low O6-MT activity, might be cured if the host is treated with ACNU. This observation may open a new approach to experimental cancer chemotherapy. Treatment with ACNU of experimental animals bearing HeLaMR tumors (which have low O6-MT activity and are Mer-), resulted in the regression of the tumors or their disappearance. In animals bearing HeLaS3 tumors (which have high O6-MT activity and are Mer+) the tumors were hyperplastic.

Cultured mouse SR-1 cells exposed to low dose of gamma-rays become less susceptible to the induction of mutagenesis by radiation as well as bleomycin

The effect of pre-exposure of cultured mouse SR-1 cells to a low dose of gamma-rays on the induction of mutations at the hprt locus by subsequent high dose radiation or bleomycin was studied. When cells were pre-exposed to 0.01 Gy gamma-rays, the induction of mutations by a 3 Gy gamma-ray dose given 18 or 24 h later was significantly reduced as compared with those which did not receive the low dose pre-exposure. When cells were challenged with 5 or 10 micrograms/ml bleomycin for 12 h, which can produce double-strand breaks in DNA, instead of 3 Gy gamma-rays, a similar mutagenetic adaptive response was observed. We conclude that this resistance to radiation- or bleomycin-induced mutation is attributed to the induction of a DNA double-strand break repair mechanism.

Phylogenetic relationships of macaques as inferred from restriction endonuclease analysis of mitochondrial DNA

Mitochondrial DNAs (mtDNAs) purified from 25 samples of 6 species of macaques, Macaca mulatta, M. fascicularis, M. arctoides, M. nemestrina, M. assamensis and M. thibetana, were analyzed to study the phyletic relationships among the species. A total of 36-46 sites was observed in each sample. By combining the cleavage patterns for each of the endonucleases, the 25 samples were classified into 11 restriction types. When data on M. fuscata and M. cyclopis collected by other authors were added to our own, the resultant molecular phylogenetic trees indicated that the 8 species may be divided into 4 groups: (1) M. mulatta, M. fuscata, M. cyclopis and M. fascicularis; (2) M. arctoides; (3) M. nemestrina; (4) M. assamensis and M. thibetana. Our results suggest that within both the fascicularis and sinica groups genetic distances are small between members and that the status of the species within the groups may require further investigation.

Cariogenic potential of pooled plaque fluid from exposed root surfaces in humans

The composition of pooled plaque fluid from exposed root surfaces of five population samples was determined before and at selected times (3, 7 and 15 min) after a 5 and 10% sucrose rinse. Subjects were 45-65 yr old, had exposed, sound root surfaces, and were grouped according to root caries status [caries-free (CF), no root caries history; caries-positive (CP), recorded root caries experience]. Samples were obtained only from the sound surfaces of the CF and CP subjects after overnight fasting. Plaque samples from each subgroup were pooled under mineral oil and maintained on ice. Plaque fluid was then isolated by centrifugation and analysed for organic acids and inorganic ions (ion chromatography), and pH (microelectrodes). From these data, the degree of saturation [DS(TM)] in plaque fluid with respect to tooth mineral (TM) was calculated. Before exposure to sucrose, plaque fluids from the CF and the CP subgroups had similar ionic compositions. These fluids were also found to be supersaturated with respect to tooth mineral. After exposure to sucrose, a rapid decrease in plaque fluid pH was observed, which corresponded primarily to lactic acid production. For all times examined, mean pH and DS(TM) values were lower and lactic acid concentrations were higher in the CP than the CF samples. Lower values of DS(TM) suggest that plaque fluid from CP subjects had a measurably greater cariogenic potential. Calcium concentrations also increased significantly and to comparable levels in all plaque fluid samples after sucrose exposure, despite lower acid production in CF samples.(ABSTRACT TRUNCATED AT 250 WORDS)

[Esophageal cancer treated by intracavity radiotherapy with 131I combined with Chinese herbs]

106 patients with esophageal cancer were treated by intracavity radiotherapy with 131I combined with Chinese herbs. The ages ranged from 34-84 years with an average of 59.8 years. All cases were confirmed by cytology and/or pathology. According to the length of lesions the patients were divided into 4 groups: < 3 cm: 1 case; 3-5 cm: 30 cases; 5-7 cm: 37 cases and 7-9 cm: 38 cases. A special three-channel rubber tube were designed. The central tube linked up with a rubber balloon which contained Na131I solution (50 mCi/20 ml) for intracavity radiation. The radiation doses (19653 rads) were delivered continuously to esophageal lesions within 10 days. The Chinese herbs "203" powder and nutrient liquid meal were given separately through the feeding tube and herbs treatment tube. The results showed that 33 cases had complete response, 73 had partial response. The 1 year survival rate was 26/47 (55.3%). 131I combined with Chinese herbs therapy is a promising method for treatment of advanced esophageal cancer.

[A survey of nutrition knowledge-attitudes-practices of Sichuan urban and rural adults]

To provide a basis for designing nutrition education, two nutrition knowledge--attitudes--practices (KAP) surveys of adults aged 18 to 55 were conducted in 1989 in an urban (N = 1004) and a rural (N = 506) area of Sichuan. The results indicated that the nutrition levels in both sites were low, and an awareness of the relationship between nutrition and certain common diseases was lacking. However, both urban and rural adults possessed good attitudes toward nutrition and nutrition education. Large differences existed between urban and rural adults' food patterns, with the rural diet more monotonous than the urban one. The rural women will be a hard-to-reach audience requiring more intensive efforts. The findings suggest that nutrition education efforts for Sichuan urban and rural area adults will require different contents and emphases, different methods of delivery, and language suitable for each group, in order to obtain good results.

Effect of sucrose concentration on the cariogenic potential of pooled plaque fluid from caries-free and caries-positive individuals

Pooled plaque samples were obtained from (1) coronal surfaces of two groups of caries-free (CF) subjects, (2) coronal 'white-spot' surface areas of a group of caries-positive (CP) subjects, and (3) exposed, sound root surfaces of root caries-free (RCF) and root caries-positive (RCP) subjects. The plaque samples were obtained before and 3 min after a 1 min rinse with a 0.5, 1, 2, 5 and 10% sucrose solution. Plaque fluid was then isolated from each plaque sample by centrifugation and analyzed for inorganic ions, organic acids, and pH values. With increasing sucrose concentration: (1) plaque fluid pH and the degree of saturation (DS) with respect to tooth mineral decreased; (2) the pH and DS values of CP and RCP samples were consistently lower than those of CF and RCF samples, respectively; (3) plaque fluid lactic acid concentrations increased and were consistently higher in the CP and RCP samples than in the CF and RCF samples, respectively, and (4) plaque fluid lactic acid concentrations leveled off between 1 and 5% sucrose; this occurred at lower sucrose concentrations with CP and RCP samples than with CF and RCF samples, respectively. RCP samples contained consistently higher levels of mutants streptococci than RCF samples. The chemical composition of plaque fluids, following sucrose exposure, were found to correlate well with caries history. The observed differences in lactic acid concentrations in samples from CF and CP subjects are discussed with regard to differences in microbiological composition and possible differences in plaque permeability to sucrose.

Structural basis of the mutagenicity of heterocyclic amines formed during the cooking processes

A data base consisting of 61 heterocyclic amines formed during food preparation and their des-amino analogs were subjected to structure-activity analysis using the CASE method, a structural activity relational expert system. The program identified the major structural determinants associated with mutagenic activity or lack thereof. The structures identified as contributing to the probability of activity as well as those associated with mutagenic potency were highly predictive of molecules not in the learning set. The major structural determinant, the aromatic amino moiety, and quantum mechanical calculations revealed that the mutagenic potency associated with this functionality derived from their contribution to the energy of the Lowest Unoccupied Molecular Orbital (LUMO).

[Analysis of clinical effect and experimental study of 13 herbs anti-cough-dyspnea decoction in the treatment of chronic bronchitis]

In treating chronic bronchitis, the effect of 13 Herbs Anti-Cough-Dyspnea decoction was better than that of other traditional prescriptions such as Ephedria-almond decoction etc. The effective rate of this decoction in relieving cough, sputum, bronchial spasm and eliminating wheezing sound were 98.6%, 98.32%, 91.52% and 85.35% respectively. The total effective rate was 98%. The animal experiment revealed that the decoction was given to isolated trachea after medication for 30 min, the effective rate in easing bronchial spasm was 99.1 +/- 30.2%, which was two times than that of other prescriptions.

FTIR spectroscopic studies of the conformation and amide hydrogen exchange of a peptide model of the hydrophobic transmembrane alpha-helices of membrane proteins

The conformation and amide hydrogen exchangeability of the hydrophobic peptide Lys2-Gly-Leu24-Lys2-Ala-amide were studied by Fourier transform infrared spectroscopy. In these studies information on the secondary structure of the peptide was obtained from an examination of the contours of both the amide I and amide II absorption bands. The conformationally sensitive amide I and amide II regions of the infrared spectra suggest that the peptide is predominantly alpha-helical and that it contains some non-alpha-helical structures which are probably in an extended conformation. Studies of the exchangeability of the amide protons of the peptide indicate that there are two populations of amide protons which differ markedly with respect to their exchangeability with the bulk solvent phase, whether the peptide is dissolved in methanol or dispersed in hydrated lipid bilayers. One population of amide protons is very readily exchangeable, and our data suggest that it arises primarily but not exclusively from the extended regions of the peptide. The other population exchanges very slowly with the bulk solvent and appears to originate entirely from the alpha-helical domain of the peptide. This latter population is virtually unexchangeable when the peptide is dispersed in hydrated phosphatidylcholine bilayers but can be largely exchanged when the peptide is solubilized with methanol. We suggest that this slowly exchanging population of amide protons arises from the central part of the hydrophobic polyleucine core which forms a very stable alpha-helix that would be deeply buried in the hydrophobic domain of hydrated lipid bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of a peptide model of a hydrophobic transmembrane alpha-helical segment of a membrane protein with phosphatidylcholine bilayers: differential scanning calorimetric and FTIR spectroscopic studies

High-sensitivity differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the interaction of a synthetic model hydrophobic peptide, Lys2-Gly-Leu24-Lys2-Ala-amide, and members of the homologous series of n-saturated diacylphosphatidylcholines. In the low range of peptide mole fractions, the DSC thermograms exhibited by the lipid/peptide mixtures are resolvable into two components. One of these components is fairly narrow, highly cooperative, and exhibits properties which are similar to but not identical with those of the pure lipid. In addition, the fractional contribution of this component to the total enthalpy change, the peak transition temperature, and cooperativity decrease with an increase in peptide concentration, more or less independently of acyl chain length. The other component is very broad and predominates in the high range of peptide concentration. These two components have been assigned to the chain-melting phase transitions of populations of bulk lipid and peptide-associated lipid, respectively. Moreover, when the mean hydrophobic thickness of the PC bilayer is less than the peptide hydrophobic length, the peptide-associated lipid melts at higher temperatures than does the bulk lipid and vice versa. In addition, the chain-melting enthalpy of the broad endotherm does not decrease to zero even at high peptide concentrations, suggesting that this peptide reduces but do not abolish the cooperative gel/liquid-crystalline phase transition of the lipids with which it is in contact. Our DSC results indicate that the width of the phase transition observed at high peptide concentration is inversely but discontinuously related to hydrocarbon chain length and that gel phase immiscibility occurs when the hydrophobic thickness of the bilayer greatly exceeds the hydrophobic length of the peptide. The FTIR spectroscopic data indicate that the peptide forms a very stable alpha-helix under all of our experimental conditions but that small distortions of its alpha-helical conformation are induced in response to any mismatch between peptide hydrophobic length and bilayer hydrophobic thickness. These results also indicate that the peptide alters the conformational disposition of the acyl chains in contact with it and that the resultant conformational changes in the lipid hydrocarbon chains tend to minimize the extent of mismatch of peptide hydrophobic length and bilayer hydrophobic thickness.

[Effect of injection of enkephalin and bestatin in caudate-putamen on operant conditioning in rats]

Female Wistar rats were trained in a Skinner-box, 30 trials per day in a dark room to establish operant defence conditioning. Training started with a light (15 s), then combined with footshock for further 8 s. When the rats learned to press the key to avoid footshock within 15 s, conditioned response was considered established. After the rats reached a conditioning rate (CR) above 80% for 5 days, cannulae were implanted into caudate-putamen. Two to three days later, Met-enkephalin (MEK) or bestatin (an aminopeptidase inhibitor) was injected bilaterally into caudate-putamen. 30 min, 2 h, 24 h and 48 h after injection, conditioning tests were conducted, with each session consisting of 30 trials. Control experiments were done when 0.9% NaCl (NS) was injected. After injection of NS, CR maintained above 80% in all 4 test sessions. MEK (60 ng/rat) or bestatin (10 micrograms/rat) significantly lowered the CR during the 30 min and 2 h test session. In the latter case, the latency (L) was also prolonged. However both CR and L returned to the control level in the 24 h and 48 h test sessions. Naloxone (2 mg/kg, i.p.) blocked the conditioning-depression effect of bestatin. No significant alteration was seen in locomotor activity after MEK or bestatin injection. The results suggest that enkephalin in caudate-putamen may be involved in the regulation of retrieval of conditioning. Bestatin mimics the effect of MEK on conditioning reflex probably by increasing production of endogenous enkephalin.

Delayed-nonmatching-to-sample performance is impaired by extensive, but not by limited, lesions of the thalamus in the rat

Two experiments were conducted to determine whether lesions affecting limited areas of the thalamus can impair the performance of rats on a spatial delayed-nonmatching-to-sample (DNMTS) task trained before surgery. In Experiment 1, DNMTS was not affected by lesions produced by injecting 5 microliters of 1 mM N-methyl-D-aspartate into either the midline thalamus (n = 16) or bilaterally 1.0 mm from the midline (n = 16). In experiment 2, radio-frequency lesions were made 1.0 mm lateral to the midline at 3 anterior-posterior locations that destroyed the full rostral-caudal extent of the lateral internal medullary lamina (L-IML; n = 8), or at single anterior-posterior locations that destroyed either the anterior (n = 8) or posterior (n = 8) portions of the L-IML site. Although complete L-IML lesions disrupted DNMTS performance to an extent comparable to that of another study (Mair & Lacourse, 1992), lesions that were restricted to either the anterior or posterior portion of the L-IML site had no significant effect on this task.

O6-methylguanine-DNA methyltransferase activity in human tumors

The distribution of O6-methylguanine-DNA methyltransferase (MGMT) activity in extracts of tumors from 74 patients was measured. The results demonstrated that there was considerable variation of MGMT activity in different human tumor tissues as well as in different individuals. The mean values (X +/- SD, pmol/mg of protein) in breast cancer, stomach cancer, small cell lung cancer, non-small cell lung cancer, renal cell carcinoma, esophageal carcinoma, brain tumors, colon carcinoma and malignant melanoma were 1.071 +/- 0.374 (9), 0.515 +/- 0.107 (5), 0.509 +/- 0.251 (5), 0.461 +/- 0.227 (24), 0.329 +/- 0.246 (5), 0.273 +/- 0.376 (5), 0.244 +/- 0.175 (14), 0.242 +/- 0.308 (5) and 0.201 +/- 0.161 (2) respectively. It was notable that six samples (1/24 non-small cell lung cancer, 3/5 esophageal carcinoma, 1/14 brain tumors and 1/5 colon carcinoma) did not have any detectable level of MGMT activity. Activity of glutamine pyruvic transaminase (GPT) was also measured in the same extracts used for the assay of MGMT activity. The activity of GPT in these samples with undetectable level of MGMT activity was similar to those with significant MGMT activity. These results further strengthen the assumption that a certain fraction of human tumors are Mer-.

LEU2 gene homolog in Kluyveromyces lactis

A DNA fragment that can complement the leu2 mutation of Saccharomyces cerevisiae was cloned from the genomic library of Kluyveromyces lactis. The nucleotide sequence revealed an open reading frame of 362 codons, 75% homologous to S. cerevisiae LEU2 gene. The upstream region contained a CCGGAACCGG sequence identical to the site of leucine-specific control of LEU2. Further upstream, there is a partial open reading frame homologous to rat ribosomal protein L7.

Transformation of the gram-positive bacterium Clavibacter xyli subsp. cynodontis by electroporation with plasmids from the IncP incompatibility group

We report the transformation of a gram-positive bacterium, Clavibacter xyli subsp. cynodontis, with several plasmids in the IncP incompatibility group from gram-negative bacteria. Our results suggest that IncP plasmids may be transferable to other gram-positive organisms. After optimizing electroporation parameters, we obtained a maximum of 2 x 10(5) transformants per microgram of DNA. The availability of a transformation system for this bacteria will facilitate its use in indirectly expressing beneficial traits in plants.

[Amphetamine--induced rage reaction in mice and its mechanism]

Rage reaction was induced in mice by ip amphetamine sulfate (APT) 15 mg/kg. Mice appeared hyperreactive after 6 min and then squeaked and fought each other. These manifestations were most distinct in 15-30 min and subsided after 40-70 min. At 20 degrees C and 25 degrees C, the occurrence of rage reaction was 85.0% and 90.0% respectively. The ED50 of APT for eliciting rage reaction was 11.8 +/- 2.1 mg/kg ip. No significant difference in the induction of rage reaction was observed between male and female mice but ambient temperature affected the occurrence of this reaction. Neuroleptic drugs (chlorpromazine, haloperidol, tardan and clozapine), anxiolytic drugs (diazepam and meprobamate) and reserpine suppressed the rage reaction induced by APT in mice. Phenobarbital and pentobarbital (at sedative doses), atropine, scopolamine, phentolamine and propranolol exerted no influence on APT--induced rage reaction. Amantadine, levodopa and apomorphine at lower doses potentiated the rage inducing effect of APT. Moreover, at higher doses amantadine or levodopa alone also evoked rage reaction similar to that induced by APT. Therefore, it may be deduced that the APT-induced rage reaction results from increased release of dopamine in limbic system and has nothing to do with the simultaneous epinephrine release. The available data indicate that the APT--induced rage reaction in mice deserves to be recommended as an animal model for screening potential neuroleptic drugs. The merits and shortcomings of this new model are discussed.

Delayed-nonmatching-to-sample performance is impaired by extensive, but not by limited, lesions of the thalamus in the rat

Two experiments were conducted to determine whether lesions affecting limited areas of the thalamus can impair the performance of rats on a spatial delayed-nonmatching-to-sample (DNMTS) task trained before surgery. In Experiment 1, DNMTS was not affected by lesions produced by injecting 5 microliters of 1 mM N-methyl-D-aspartate into either the midline thalamus (n = 16) or bilaterally 1.0 mm from the midline (n = 16). In experiment 2, radio-frequency lesions were made 1.0 mm lateral to the midline at 3 anterior-posterior locations that destroyed the full rostral-caudal extent of the lateral internal medullary lamina (L-IML; n = 8), or at single anterior-posterior locations that destroyed either the anterior (n = 8) or posterior (n = 8) portions of the L-IML site. Although complete L-IML lesions disrupted DNMTS performance to an extent comparable to that of another study (Mair & Lacourse, 1992), lesions that were restricted to either the anterior or posterior portion of the L-IML site had no significant effect on this task.

A convenient method of measuring the thermal conductivity of biological tissue

The basic principle of the thermal conductivity probe is described. Thin probes were developed based on this principle, with a reproducibility of 5.3% and relative error less than 6.0%. Each measurement can be completed in 90 s and the temperature increase can be controlled within 2 degrees C. Using the probes, the thermal conductivities of pig fat, meat, liver, kidney and live and dead snake head were measured and it was found that water content plays an important role in influencing the magnitude of the thermal conductivity of biological tissues. The probe can be used over a temperature range from -40 to 150 degrees C.

Genetic diversity in the Chinese pangolin (Manis pentadactyla): inferred from restriction enzyme analysis of mitochondrial DNAs

Two different forms of Chinese pangolins can be recognized according to the color of their scales, i.e., brown and dusky. We analyzed mitochondrial DNA (mtDNA) purified from the livers of seven dusky and six brown Chinese pangolins from the same locality, using cleavage patterns from 19 restriction enzymes. From the 19 6-bp recognition enzymes used, 51-56 sites were observed. By combining the cleavage patterns for each enzyme, the 13 samples were classified into four restriction types: two in dusky and two in brown Chinese pangolins. The estimated number of nucleotide substitutions per site in dusky and brown types is 0.002, and that between dusky and brown types is 0.012. Divergence between brown and dusky forms began 0.6 Myr ago, provided the mean rate of sequence divergence is 0.02 per Myr in mtDNA. Our results suggest that there is considerable divergence in Chinese pangolins, and brown and dusky Chinese pangolins may be quite different forms or, at least, belong to different maternal groups.

Implications of newly recognized relationships between mutagenicity, genotoxicity and carcinogenicity of molecules

The CASE structure-activity relational method was used to predict the mutagenicity, cytogenotoxicity, carcinogenicity, sensory irritation, male rat-specific alpha 2 mu-nephrotoxicity and maximum tolerated dose of a population of molecules (N greater than or equal to 1300). These chemicals were then sorted out by their predicted responses to specific tests and sub-populations of molecules with different prevalence with respect to described endpoints were constructed, i.e. 0-100% prevalences of mutagens, rodent carcinogens and SCE inducers. The predicted properties of these populations were analyzed and the overlap among tests was determined. The method also permits the determination of the dependence among assays and the level of false-positive and false-negative predictions.