Benzo(a)pyrene shows low toxicity to three species of terrestrial plants, two soil invertebrates, and soil-nitrifying bacteria

We examined the toxicity of benzo(a)pyrene (BaP) to several standard test organisms including the seed emergence and early life-stage growth of three terrestrial plants (Trifolium pratense, Lolium perenne, and Brassica alba), the survival and reproduction of enchytraeids (Enchytraeus crypticus), and the nitrifying ability of soil bacteria. To also have a look at possible food-chain effects, we included a two-species reproduction test with predatory mites (Hypoaspis aculeifer) and collembolan (Folsomia fimetaria) prey. No effect or only weak effects even at very high BaP concentrations were observed for all tests. None of the soil invertebrates were affected within the concentration range tested (up to 947 mg kg⁻¹). For soil-nitrifying bacteria, significant effects were recorded at 977 mg kg⁻¹, leaving a no observable effect concentration (NOEC) of 293 mg kg⁻¹. BaP did not affect seed emergence for any of the plants, but the growth of B. alba was significantly reduced at the highest concentration tested (375 mg kg⁻¹), leaving a NOEC of 69 mg kg⁻¹. Compared to a number of other polycyclic aromatic compounds previously tested in the same soil type, BaP is generally less toxic.     

Comparison of the metabolic profiles of benzo[alpha]pyrene obtained from primary cell cultures and subcellular fractions derived from normal and methylcholanthrene-induced rat liver

Hepatocyte primary cell (HPC) cultures derived from either (a) non-induced (normal) or (b) methylcholanthrene (MC)-induced rat liver actively metabolized the carcinogen benzol[alpha]pyrene (BaP) over a 24-h period. In both cases, the BaP metabolites generated were qualitatively similar to those seen in the metabolism of BaP by isolated rat liver microsomal fractions; in addition, unidentified compounds were evident in the chromatographic profile generated by the cultured cells. In cells derived from (a), levels of known metabolites (phenols and diols) increased over the time period studied. On the other hand, in cells derived from (b), levels of diols decreased markedly after 8 h. These results suggest that induction with MC enhances both activation and, to a greater extent, conjugative-detoxification pathways of BaP, so that in cells obtained from (b) the formation of water-soluble metabolites is enhanced and levels of organic soluble metabolites are lower than in cells obtained from (a). Metabolism of BaP in primary cell culture derived from rat liver is thus seen to be similar to in vivo metabolism of the carcinogen, but somewhat in contrast to the in vitro microsomal (subcellular) metabolism of BaP where conjugative-detoxification pathways are virtually inoperative.     

Quantitating exposure to chemical carcinogens: in vivo alkylation of hemoglobin by benzo[a]pyrene

Mild acid hydrolysis of globin preparations from erythrocytes of mice, previously exposed topically to benzo[a]pyrene (BaP), releases tetrols which are detectable by HPLC/fluorescence analysis. If the mouse is exposed to radiolabelled BaP, radioactivity can be found in the acid-releasable tetrols. Treatment of the globin preparations prior to acid hydrolysis with proteolytic enzymes, but not enzymes that degrade nucleic acids, followed by dialysis, reduces the amount of tetrols that can be detected. Because the procedure used for the isolation of globin preparations from mouse blood precludes the presence of non-covalently bound BaP or its cellular metabolites, it is concluded that prior to acid hydrolysis, the tetrols were covalently attached to the hemoglobin, most probably as a result of the metabolic conversion of the applied carcinogen to the chemically reactive anti-diol epoxide. There is a dose response relationship between the amount of BaP applied to the skin of the mouse and the occurrence, 24 h later, of BaP adducts to hemoglobin, while the adduct, once formed, disappears with a half-life of 6 days. The amount of anti-benzo[a]pyrene diol epoxide (anti-BaPDE) binding to DNA and hemoglobin at various doses of BaP appears to be qualitatively similar.     

Experimental and Numerical Smoke Carcinogen Deposition in a Multi-Generation Human Replica Tracheobronchial Model

A better understanding of submicron particle deposition in the respiratory tract is needed to study the health effects caused by carcinogenic particles. Recent studies indicate that random diffusion is not sufficient to describe the motion of these particles in complex geometries, rendering conventional models inaccurate. A solid replica of excised human lung segments was used to create digital and hollow models of the tracheobronchial region to investigate deposition of mainstream (MS) and sidestream (SS) cigarette smoke particles. Particle sizes for the carcinogen Benzo(a)pyrene (BaP) in SS smoke, and total particulate matter (UVPM) in SS and MS smoke were measured and used to compare the simulation to experimental data. Excellent agreement was found between predicted and measured results. Random diffusion was not found to be significant for submicron particles indicating that particles were instead transported to the airway wall by convective diffusion. BaP in SS smoke was an average 0.3 μm compared to 0.36 μm for UVPM in SS smoke. The trends in both experimental and numerical results indicated that the BaP in SS smoke deposits at a slightly higher efficiency than the UVPM, indicating that carcinogen-specific deposition, rather than total particulate matter should be considered when investigating health effects.     

1,10-Phenanthroline stabilizes mRNA of the carcinogen-metabolizing enzyme,cytochrome P450 1a1

1,10-phenanthroline (phen), flufenamic acid, and indomethacin are inhibitors of aldo-keto reductases 1C1 (AKR1C1), but only phen decreased the benzo[a]pyrene (BaP)-induced cytochrome P450 1a1 (Cyp1a1) protein level. Therefore the decrease in the BaP-induced Cyp1a1 protein level was not due to inhibition of Akr1c1, but to phen itself. Phen decreased the BaP-induced Cyp1a1 promoter activity and protein expression, and in contrast, it increased Cyp1a1 mRNA, resulting from an increase in mRNA stability. Phen is also known as a transition metal ion-chelator. Along with the phen study, we also found that Zn²⁺, Fe²⁺ and Cu²⁺ increased Cyp1a1 mRNA and protein stability. Our results show that phen stabilized the mRNA of Cyp1a1, although it decreased cell viability. In addition, Zn²⁺ and Fe²⁺ highly neutralized phen's suppression of Cyp1a1 protein expression, but they only slightly neutralized phen's promotion of mRNA stability and suppression of cell viability, and had no effect on phen's suppression of promoter activity. Phen's effect on Cyp1a1 expression was reversible, which indicates that phen is non-covalently linked to its target. This report elucidates a new role for phen of stabilizing Cyp1a1 mRNA, and provides information for further studies on mRNA stabilization.     

Exposure of human skin to benzo[a]pyrene: Role of CYP1A1 and aryl hydrocarbon receptor in oxidative stress generation

Exposure to benzo[a]pyrene (BaP) can induce inflammatory skin diseases and skin cancer, which are both associated to oxidative stress. BaP is known to bind with high specificity to the aryl hydrocarbon receptor (AhR), modifying the expression of CYP1A1, involved both in cancer and inflammation.     

Determination of benzo[a]pyrene in charcoal grilled meat samples by HPLC with fluorescence detection

In this study, an HPLC procedure for the quantitative determination of benzo[a]pyrene (BaP) in charcoal grilled meat samples has been applied to the analysis of the Turkish meat samples. The grilled meat samples were first treated in alkaline medium, then BaP was extracted into n-hexane phase, purified on XAD-2 column and eluted with n-hexane/dichloromethane mixture (9:1,v/v). Separation and quantitative determination of BaP has been carried out by a C₁₈ reversed phase column mounted HPLC with a fluorescence detection of 254–355?nm (excitation–emission). The BaP levels determined in grilled and over-grilled lamb and beef meats were 43.80±1.80?µg/kg, 31.33±0.94?µg/kg and 62.60±3.72?µg/kg, 37.60±3.84?µg/kg, respectively.     

Topological aspects of oligomeric UDP-glucuronosyltransferases in endoplasmic reticulum membranes: Advances and open questions

UDP-glucuronosyltransferases (UGTs) represent major Phase II enzymes involved in detoxification of endo- and xenobiotics, including many drugs. The intraluminal orientation of the active site of UGTs in endoplasmic reticulum membranes necessitates a number of transporters in these membranes, for example, for UDP-glucuronic acid and glucuronides, the latter being insufficiently characterized. In addition, accumulating evidence suggests that UGTs are functional as homo- and heterodimers in monoglucuronide formation. They may form tetramers in diglucuronide formation. UGT oligomers probably serve to stabilize UGT monomers and fine-tune UGT activity. Glucuronide disposition may also be influenced by endoplasmic reticulum-localized β-glucuronidase, possibly involved in hydrolysis of hormone and drug glucuronides in target cells. The present commentary reviews recent advances and addresses open questions. Resolution of these questions may help to understand many problems of glucuronide synthesis and disposition in vivo, for example, under-prediction of the in vivo clearance of drugs mostly eliminated by glucuronidation by in vitro enzyme kinetic parameters of UGTs.     

The uptake and metabolism of benzo[a]pyrene from a sample food substrate in an in vitro model of digestion.

Food ingestion is the major route of exposure to many hydrophobic organic contaminants (HOCs) such as benzo[a]pyrene (BaP). It has been proposed that food-bound HOCs may become bioavailable after their mobilization by gastrointestinal fluids. The purpose of this research was to measure the uptake efficiency of [(14)C]-BaP bound to skim milk powder using an in vitro model of gastrointestinal digestion followed by sorption to human enterocytes (Caco-2 cells). Neutralization of intestinal fluids released [(14)C]-BaP into the soluble fraction. Ageing of benzo[a]pyrene onto skim milk for 6 months significantly decreased the mobilized fraction but did not affect the amount of benzo[a]pyrene taken up into Caco-2 cells. Hence, significant differences in aqueous phase concentrations may not always be reflected in significant differences in uptake. We obtained evidence that the digestion/uptake of skim milk lipids is accompanied by the diffusive uptake of BaP (the fat flush hypothesis) as trans-cellular transfer of BaP was favoured in the apical to basolateral direction. These data support the theory that non-polar substances including HOCs are preferentially transferred from the lumen into the bloodstream and provide indirect evidence that the uptake is related to the fugacity gradient created by the unidirectional uptake of dietary lipids.