Hepatic demethylation of methoxy-bromodiphenyl ethers and conjugation of the resulting hydroxy-bromodiphenyl ethers in a marine fish, the red snapper, Lutjanus campechanus, and a freshwater fish, the channel catfish, Ictalurus punctatus.

Methoxylated bromodiphenyl ethers (MeO-BDEs), marine natural products, can be demethylated by cytochrome P450 to produce hydroxylated bromodiphenyl ethers (OH-BDEs), potentially toxic metabolites that are also formed by hydroxylation of BDE flame retardants. The OH-BDEs may be detoxified by glucuronidation and sulfonation. This study examined the demethylation of 6-MeO-BDE47, 2'-MeO-BDE68 and 4'-MeO-BDE68, in hepatic microsomes from the red snapper, Lutjanus campechanus, a marine fish likely to be exposed naturally to MeO-BDEs, and the channel catfish, Ictalurus punctatus, a freshwater fish in which pathways of xenobiotic biotransformation have been studied. We further studied the glucuronidation and sulfonation of the resulting OH-BDEs as well as of 6-OH-2'-MeO-BDE68 in hepatic microsomes and cytosol fractions of these fish. The three studied biotransformation pathways were active in both species, with high individual variability. The range of activities overlapped in the two species. Demethylation of MeO-BDEs, studied in the concentration range 10-500 µM, followed Michaelis-Menten kinetics in both fish species, however enzyme efficiencies were low, ranging from 0.024 to 0.334 µL min.mg protein. Conjugation of the studied OH-BDEs followed Michaelis-Menten kinetics in the concentration ranges 1-50 µM (glucuronidation) or 2.5-100 µM (sulfonation). These OH-BDEs were readily glucuronidated and sulfonated in the fish livers of both species, with enzyme efficiencies one to three orders of magnitude higher than for demethylation of the precursor MeO-BDEs. The relatively low efficiencies of demethylation of the MeO-BDEs, compared with higher efficiencies for OH-BDE conjugation, suggests that MeO-BDEs are more likely than OH-BDEs to bioaccumulate in tissues of exposed fish.

Sulfonation and glucuronidation of hydroxylated bromodiphenyl ethers in human liver.

Hydroxylated bromodiphenyl ethers (OH-BDEs) can arise from monooxygenation of anthropogenic BDEs or through natural biosynthetic processes in marine organisms, and several OH-BDEs have been shown to be toxic. OH-BDEs are expected to form sulfate and glucuronide conjugates that are readily excreted, however there is little information on these pathways. We examined the human hepatic glucuronidation and sulfonation of 6-OH-BDE47, 2-OH-BDE68, 4-OH-BDE68 and 2-OH-6'methoxy-BDE68. Human liver microsomes and cytosol were from de-identified female and male donors aged 31 to 75 under an exempt protocol. Recombinant human SULT1A1, 1B1, 1E1 and 2A1 enzymes were prepared from bacterial expression systems. Sulfonation and glucuronidation of each OH-BDE were studied using radiolabeled co-substrates, 3'phosphoadenosine-5'phospho-35S-sulfate or uridine diphospho-ß-D-14C-glucuronic acid in order to quantify the sulfated or glucuronidated products. The OH-BDEs studied were more efficiently glucuronidated than sulfonated. Of the compounds studied, 2-OH-BDE68 was the most readily conjugated, and exhibited an efficiency (Vmax/KM) of glucuronidation of 0.274 ±â€¯0.125 mL/min/mg protein, mean ±â€¯S.D., n = 3, while that for sulfonation was 0.179 ±â€¯0.030 mL/min/mg protein. For both pathways, all Km values were in the low µM range. Studies with human SULT enzymes showed that sulfonation of these four substrates was readily catalyzed by SULT1B1 and SULT1E1. Much lower activity was found with SULT1A1 and SULT2A1. Assuming that the glucuronide and sulfate conjugates are non-toxic and readily excreted, as is the case for most such conjugates, these studies suggest that OH-BDEs should not accumulate in people to the same extent as the parent BDEs.

Regulation of dichloroacetate biotransformation in rat liver and extrahepatic tissues by GSTZ1 expression and chloride concentration.

Biotransformation of dichloroacetate (DCA) to glyoxylate by hepatic glutathione transferase zeta 1 (GSTZ1) is considered the principal determinant of the rate of plasma clearance of the drug. However, several other organismal and subcellular factors are also known to influence DCA metabolism. We utilized a female rat model to study these poorly understood processes. Rats aged 4 weeks (young) and 42-52 weeks (adult) were used to model children and adults, respectively. Hepatic chloride concentrations, which influence the rate of GSTZ1 inactivation by DCA, were lower in rat than in human tissues and rats did not show the age dependence previously seen in humans. We found GSTZ1 expression and activity in rat brain, heart, and kidney cell-free homogenates that were age-dependent. GSTZ1 expression in brain was higher in young rats than adult rats, whereas cardiac and renal GSTZ1 expression levels were higher in adult than young rats. GSTZ1 activity with DCA could not be measured accurately in kidney cell-free homogenates due to rapid depletion of glutathione by γ-glutamyl transpeptidase. Following oral administration of DCA, 100 mg/kg, to rats, GSTZ1 expression and activity were reduced in all rat tissues, but chloride concentrations were not affected. Together, these data extend our understanding of factors that determine the in vivo kinetics of DCA.

Determination of antioxidant capacities, α-dicarbonyls, and phenolic phytochemicals in Florida varietal honeys using HPLC-DAD-ESI-MS(n.).

Honeys contain phenolic compounds and α-dicarbonyls with antioxidant and antimicrobial capacities, respectively. The type and concentration of these compounds vary depending on the floral source and geographical location where the honey is produced. Seventeen varietal honeys, including 12 monofloral and 5 multifloral honeys, were sampled from different regions of Florida. The monofloral honeys included those from citrus, tupelo, palmetto, and gallberry. These honeys were evaluated for their antioxidant capacity, total phenolic content, and free radical scavenging capacity and compared with three New Zealand Manuka honeys. Phenolic phytochemicals and α-dicarbonyls were identified and quantified using HPLC-DAD-MS(n). Several honey varieties from gallberry, Manuka, and multifloral displayed a total phenolic content >1000 µg GAE/g. A citrus honey had the lowest total phenolic content of 286 µg GAE/g. The oxygen radical absorbance capacity of the honeys ranged from 1.48 to 18.2 µmol TE/g. All honeys contained 3-deoxyglucosone at a higher concentration than methylglyoxal or glyoxal. Manuka honeys had higher concentrations of methylglyoxal than other varieties. Plant hormones 2-cis,4-trans-abscisic acid and 2-trans,4-trans-abscisic acid were the most abundant phytochemicals in all honeys. Coumaric acid, rutin, chrysin, pinocembrin, quercetin, luteolin, and kaempferol were also found in samples but at lower concentrations.