INDUCTION OF MICRONUCLEI AND SISTER-CHROMATID EXCHANGES BY POLYCYCLICAND N-HETEROCYCLIC AROMATIC-HYDROCARBONS IN CULTURED HUMAN-LYMPHOCYTES

Many natural environments are contaminated with carcinogenic polycycli c aromatic hydrocarbons (PAHs) and N-heterocyclic aromatic hydrocarbon s (NHAs) as complex mixtures of coal tar, petroleum, and shale oil. Th ese potentially hazardous substances are prevalent at many former tar production and coal gasification sites. Three polycyclic [benzo(a)pyre ne (BaP), benz(a)anthracene (BAA), and 7,12-dimethylbenz(a)anthracene (DMBA)] and two N-heterocyclic [7H-dibenzo(c,g)carbazole (DEC), and di benz(a,j)acridine (DBA)] aromatic hydrocarbons were analyzed for cytot oxic and genotoxic effects on human lymphocytes. All of these polyarom atic compounds are normally present in the environment, except for DMB A. lymphocytes from healthy donors were isolated from whole blood. The 5-ring polycyclic aromatic BaP consistently induced micronuclei in a linear dose-dependent manner with doses from 0.1-10.0 mu g/ml, whereas the 4-ring compounds (BAA and DMBA) had no effect on the induction of micronuclei above controls except at 5 and 10 mu g/ml. Of the two N-h eterocyclic compounds, DEC produced a significant increase in micronuc lei in lymphocytes, but the dose response tended to plateau above 0.1 mu g/ml. DBA showed on effect on the frequency of micronuclei above co ntrols only at high doses of 5 and 10 mu g/ml. The average background frequency of micronuclei for 7 lymphocyte donors averaged 3.1 per 1,00 0 stimulated cells, whereas the average frequency of micronuclei at 10 mu g/ml BaP was 36.8 per 1,000 stimulated cells. The lowest effective dose in 2 donors for BaP occurred at 0.1 mu g/ml. At a challenge dose of 1 mu g/ml (4 mu M) of BaP, considerable variation in micronuclei i nduction between 7 individuals was observed, ranging from 2-6-fold inc reases above spontaneous frequency. Over a dose range of 1-10.0 mu g/m l (4-40 mu M), BaP also induced sister chromatid exchanges (SCEs) in l ymphocytes, whereas BAA had no effect above controls. Parallel studies of both cytogenetic endpoints showed that the micronucleus assay is a more sensitive indicator of BaP exposure at equivalent doses. Mitotic and replication indices of BaP-exposed lymphocytes showed that cell p roliferation is only moderately inhibited even at the highest dose; th is shows that bulky DNA-adducts are generally compatible with cell sur vival. The cytogenetic data are consistent, firstoff, with reports tha t individuals in the population vary widely with respect to the induci bility of the CYP1A1 gene, which is known to be involved in polycyclic aromatic hydrocarbon metabolism, in particular, in BaP. Secondly, the data support the fact that polyaromatic compounds differ with regard to micronucleus induction within the some sample(s) of human lymphocyt es, indicating selective metabolism of polyaromatic compounds that may reflect carcinogen sensitivity of the individual. Thirdly, it would a ppear that the micronucleus induction in human lymphocytes by PAHs is an overall-sensitive endpoint for measuring PAH exposure. Lastly, this is the first report of the use of the micronucleus essay to assess a series of PAHs and NHAs For their ability to induce genetic damage in human lymphocytes. (C) 1995 Wiley-Liss, Inc.