Polycyclic aromatic hydrocarbons xenobiotics

Although these issues have already been briefly noted, they deserve a few additional comments. For freely water-soluble substrates that have low volatility, there are few difficulties in carrying out the appropriate experiments described above. There is, however, increasing interest in xenobiotics such as polycyclic aromatic hydrocarbons (PAHs) and highly chlorinated compounds including, for example, PCBs, which have only low water solubility. In addition, attention has been focused on volatile chlorinated aliphatic compounds such as the chloroethenes, dichloromethane, and carbon tetrachloride. All of these substrates present experimental difficulties of greater or lesser severity. 

A wide variety of xenobiotics, such as polycyclic aromatic hydrocarbons or dioxins, are analyzed in human body fluids for the investigation of environmental and occupational exposure. 

Polycyclic aromatic hydrocarbons together with other xenobiotics are a major source of contamination in soil, and their correct degradation is of great environment importance. 

As observed in mammalian models, the immune system of fishes is a sensitive target organ system to evaluate toxicity. For a more thorough review of environmental immunotoxicology in fishes, with reference to specific classes of xenobiotics, readers are referred to several reviews that deal with the subject over a span of nearly three decades [45-47, 54-57], While fish in the environment may be exposed to a variety of xenobiotics, the most frequently investigated xenobiotics are the polycyclic aromatic hydrocarbons (PAHs) and halogenated aromatic hydrocarbons (HAHs) due to the presence and activation of the aryl hydrocarbon receptor (AhR) in fish, and heavy metals due to their ubiquitous environmental distribution. 

Such xenobiotics as aliphatic hydrocarbons and derivatives, chlorinated ahphatic compounds (methyl, ethyl, methylene, and ethylene chlorides), aromatic hydrocarbons and derivatives (benzene, toluene, phthalate, ethylbenzene, xylenes, and phenol), polycyclic aromatic hydrocarbons, halogenated aromatic compounds (chlorophenols, polychlorinated biphenyls, dioxins and relatives, DDT and relatives), AZO dyes, compounds with nitrogroups (explosive-contaminated waste and herbicides), and organophosphate wastes can be treated effectively by aerobic microorganisms. 

From these inventories and data, it is clear that society is facing an enormous problem of contamination. Many of the polluting compounds that are continuously dispersed are products of industrial activities such as phenols and halogenated phenols, polycyclic aromatic hydrocarbons (PAH s), endocrine disruptive chemicals (EDC), pesticides, dioxins, polychlorinated biphenyls (PCB s), industrial dyes, and other xenobiotics. In this chapter, we critically review the literature information on the enzymatic transformation of these polluting xenobiotics. This work is focused on peroxidases as enzymes able to transform a variety of pollutant compounds with the aim to reduce their toxicity and their environmental impact. 

SULT 2A and 2B sulfotransferase subfamily members sulfate the 3P-hydroxyl group of a variety of steroid hormones. Dehydroepiandrosterone (DHEA) is the prototypical substrate for the SULT 2 enzymes. However, other hydroxysteroids such as testosterone and its phase I hydroxylated derivatives are substrates for these enzymes. The SULT 2 sulfotransferases also are responsible for the sulfate conjugation of a variety of alcohols and xenobiotics that have undergone phase I hydro-xylation, including the polycyclic aromatic hydrocarbons (PAHs). The SULT 2 enzymes exhibit different patterns of tissue expression. SULT 2A1 is expressed primarily in the adrenal cortex, brain, liver, and intestine, while SULT 2B1 is expressed in the prostate, placenta, and trachea. 

Tannic acid is not consistently absorbed from intestinal mucosa or from the skin. Enhanced absorption rates can be seen in denuded skin and mucus membranes. Tannic acid can cause hardening of the gastrointestinal mucosa. This hardening can result in reduced gastrointestinal absorption of nutrients as well as of xenobiotics. Tannic acid has been experimentally shown to be able to reduce the carcinogenic potency of some amine derivatives and polycyclic aromatic hydrocarbons in laboratory animals. Tannic acid s anticarcinogenic properties appear to be mediated through the modulation of enzymes involved in xenobiotic metabolism. 

Shimada, T. (2006) Xenobiotic-metabolizing enzymes involved in activation and detoxification of carcinogenic polycyclic aromatic hydrocarbons. Drug Metab. Pharmacokinet. 21, 257-276. 

The PAS domain transcriptional factor AhR is a nonnuclear receptor xenobiotic receptor. In the early 1990s, the AhR and its partner Ah receptor nuclear translocator (Arnt) protein were identified as a transcriptional sensor mediating the induction of CYP1A and 1B1 genes by dioxin and related polycyclic aromatic hydrocarbons [62, 63],... 

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