Conjugation of organic pollutants in aquatic species.

Abstract

Aquatic organisms can take up organic pollutants from their environment and subsequently excrete the pollutant or its biotransformation products (metabolites). Phase II (conjugation) biotransformation products are almost always less toxic than the unmetabolized organic pollutant. For many organic pollutants, the extent to which conjugates are formed is extremely important in determining the rate of excretion of the pollutant. This is because most conjugates (glycosides, sulfates, amino acid conjugates, mercapturic acids) are organic anions which are readily water-soluble and are rapidly excreted by fish (and probably higher invertebrates) by a combination of glomerular filtration and tubular transport. In this paper, each major conjugation pathway is discussed with respect to what is known about its occurrence in fish and aquatic invertebrates, both from in vivo and in vitro data. Although limited data are available, this paper also considers what is known about how each conjugation reaction affects the toxicity and potential for renal and biliary excretion of organic xenobiotic substrates.

DNA adduct formation and 7-ethoxyresorufin O-deethylase induction in primary culture of rainbow trout hepatocytes exposed to benzo[a]pyrene

“…As implied by these results, the lack of association between EROD activity (P4501A level) and DNA adduct levels suggests a significant involvement of conjugating as well as DNA-repair enzymes in the regulation of DNA adduct formation and elimination, respectively, as discussed elsewhere (James, 1987;Klaunig, 1984;Zaleski et al, 1991). An increase in DNA adduct formation may require an induction threshold of P4501A that was not attained in our study (3.4-fold); thus, Monteith et al (1990) observed that an 1 I-fold preinduction in AHH activity was correlated with no more than a 1.7-fold increase in DNA-binding in a primary culture of human hepatocytes treated with radiolabelled B[a]P.…”

Characterization of phase-II conjugation reaction of polycyclic aromatic hydrocarbons in fish species: Unique pyrene metabolism and species specificity observed in fish species

“…In previous studies, it has been reported that fish can conjugate xenobiotics to sulfuric acid, glucuronic acid, and glutathione (GSH; Beyer et al, 2010;James, 1987). The conjugated metabolite of PAHs in fish is primarily glucuronic acid (Bayer et al, 2010;Hornung et al, 2007), and it is known that glucuronidation of xenobiotics is performed by the action of UGT (Leaver et al, 2007).…”

“…Several studies on metabolism of aryl-compounds show that fish can oxidize these compounds and further transform them into glucuronide conjugates, sulfate conjugates, and mercapturic acid. Glucoside conjugates can also be formed, although these are minor conjugates in aquatic species (James, 1987;Willett et al, 2000;Luthe et al, 2002). Oxidation by cytochrome P450 (CYP) and conjugation by enzymes such as UDP-glucuronosyltransferase (UGT), sulfotransferases (SULT), and glutathione S-transferase (GST) participate in the metabolism of aryl-compounds.…”

Freshwater Decapods and Pesticides: An Unavoidable Relation in the Modern World

“…The adverse effects of toxic products on crustaceans depend on its concentration and affinity, activity (intrinsic toxicity, which is function of molecular structure) and chemical biotransformations (James, 1987) and the acclimation responses of the individual (Klerks, 1999). For biocides, such as organophosphates and carbamate anticholinesterases (antiChEs), intrinsic toxicity can be judged by measuring the inhibition of cholinesterase and propagation of action potentials on synaptic transmission (see biomarkers section).…”

“…In this phase, several enzymes introduce a polar reactive group to the molecule, making it more water soluble while also increasing the possibility of further metabolism by Phase II enzymes. Two major groups of enzymes involved in Phase I metabolism include oxidoreductases and hydrolases that are located in the endoplasmic reticulum of the cell in many organs and tissues (James, 1987 (Tang et al, 2005). Metabolites formed by conjugation reactions are usually less toxic than the unconjugated compound, although there are notable exceptions to this rule (James, 1987).…”