Metabolic activation of 4H-cyclopenta[def]chrysene in human mammary carcinoma MCF-7 cell cultures

Major AhR-active chemicals in sediments of Lake Sihwa, South Korea: Application of effect-directed analysis combined with full-scan screening analysis

This study utilized effect-directed analysis (EDA) combined with full-scan screening analysis (FSA) to identify aryl hydrocarbon receptor (AhR)-active compounds in sediments of inland creeks flowing into Lake Sihwa, South Korea. The specific objectives were to (i) investigate the major AhR-active fractions of organic extracts of sediments by using H4IIE-luc in vitro bioassay (4 h and 72 h exposures), (ii) quantify known AhR agonists, such as polycyclic aromatic hydrocarbons (PAHs) and styrene oligomers (SOs), (iii) identify unknown AhR agonists by use of gas chromatography-quadrupole time-of-flight mass spectrometry (GC-QTOFMS), and (iv) determine contributions of AhR agonists to total potencies measured by use of the bioassay. FSA was conducted on fractions F2.6 and F2.7 (aromatics with log K_ow 5-7) in extracts of sediment from Siheung Creek (industrial area). Those fractions exhibited significant AhR-mediated potency as well as relatively great concentrations of PAHs and SOs. FSA detected 461 and 449 compounds in F2.6 and F2.7, respectively. Of these, five tentative candidates of AhR agonist were selected based on NIST library matching, aromatic structures and numbers of rings, and available standards. Benz[b]anthracene, 11H-benzo[a]fluorene, and 4,5-methanochrysene exhibited significant AhR-mediated potency in the H4IIE-luc bioassay, and relative potencies of these compounds were determined. Potency balance analysis demonstrated that these three newly identified AhR agonists explained 1.1% to 67% of total induced AhR-mediated potencies of samples, which were particularly great for industrial sediments. Follow-up studies on sources and ecotoxicological effects of these compounds in coastal environments would be required.

First Examples of Stable Arenium Ions from Large Methylene-Bridged Polycyclic Aromatic Hydrocarbons (PAHs). Directive Effects and Charge Delocalization Mode

In connection to a growing interest in developing structure/activity trends in nonalternant polyarenes, we report on the generation and NMR studies of the first series of persistent arenium ions from large methylene-bridged PAHs (mostly 22pi six-fused ring systems). Low-temperature protonation (FSO(3)H/SO(2)ClF) and model nitration (with HNO(3)/HOAc or NO(2)(+) BF(4)(-)) were used as mimic reactions for generation of biological electrophiles. The site(s) of protonation (and nitration) were determined as a function of PAH structure. Charge delocalization mode in the resulting arenium ions of protonation are assessed based on detailed low-temperature NMR studies at 500 MHz. Systems studied were 1-methylcyclopenta[def]phenanthrene 2, 11H-benz[bc]aceanthrylene 8, 5H-benzo[b]cyclopenta[def]chrysene 9, 13H-dibenzo-[bc,l]aceanthrylene 10, 13H-cyclopenta[rst]pentaphene 11, 4H-benzo[b]cyclopenta[mno]chrysene 12, 6H-cyclopenta[ghi]picene 13, 4H-cyclopenta[pqr]picene 14, 4H-cyclopenta[def]dibenz[a,c]anthracene 15. For comparison, dibenzo[a,c]anthracene 16 and dibenzo[a,h]anthracene 17 were also included (Figures 1 and 2). It is shown that the methano-bridge exerts a strong directive effect which diminishes as the bridge moves from the more central "inner" positions to more peripheral "outer" positions. Charge delocalization mode in the resulting carbocations are discussed based on the magnitude of Deltadelta (13)C values. Possible relationships with biological electrophiles formed by epoxide ring opening in the putative metabolites are also considered.