The metabolism of 3-phenoxybenzoic acid-containing xenobiotic triacylglycerols in vitro by pancreatic, hormone-sensitive and lipoprotein lipases

Incorporation of xenobiotic carboxylic acids into lipids by cultured 3T3-L1 adipocytes

The study was established to assess the potential for a variety of xenobiotic aromatic carboxylic acids to be incorporated into glycerolipids. The 14C-labelled xenobiotic acids were included in incubations of cultured 3T3-L1 adipocytes under defined conditions. Lipids were extracted and identified by TLC and radioscanning. Ibuprofen, 4-(2,4-dichlorophenoxy)-butanoic acid (2,4-DB), 4-(2-methyl-4-chlorophenoxy)-butanoic acid (MCPB) and 2-(2-methyl-4-chlorophenoxy)-propanoic acid (MCPP) (all 0.5 mM) were incorporated into lipid extracts at rates of 220, 227, 199 and 21 pmol microg(-1) phospholipid/h, respectively. 2,4-Dichlorophenoxyacetic acid (2,4-D), indomethacin, naproxen and fluroxypyr were incorporated at rates lower than MCPP or not at all. The incorporation of acids was first order to at least 1 mM acid (except MCPB: 300 microM). Triacylglycerol analogues were the major products with incorporation into diacylglycerol and phosphatidylcholine also observed. After digestion with pancreatic lipase, ibuprofen-containing triacylglycerol was unusual in that the main product was the monoacylglycerol analogue, suggesting that esterification had been at the sn-2 position. Incubation with cultured 3T3-L1 adipocytes is a useful and easy method to assess whether xenobiotic compounds can be incorporated into glycerolipids; of eight acids assessed, four (of which three have not previously been reported) were shown to form xenobiotic triacylglycerols.

Detoxification and transcriptome response in Arabidopsis seedlings exposed to the allelochemical benzoxazolin-2(3H)-one

Benzoxazolin-2(3H)-one (BOA) is an allelochemical most commonly associated with monocot species, formed from the O-glucoside of 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one by a two-step degradation process. The capacity of Arabidopsis to detoxify exogenously supplied BOA was analyzed by quantification of the major known metabolites BOA-6-OH, BOA-6-O-glucoside, and glucoside carbamate, revealing that detoxification occurs predominantly through O-glucosylation of the intermediate BOA-6-OH, most likely requiring the sequential action of as-yet-unidentified cytochrome P450 and UDP-glucosyltransferase activities. Transcriptional profiling experiments were also performed with Arabidopsis seedlings exposed to BOA concentrations, representing I(50) and I(80) levels based on root elongation inhibition assays. One of the largest functional categories observed for BOA-responsive genes corresponded to protein families known to participate in cell rescue and defense, with the majority of these genes potentially associated with chemical detoxification pathways. Further experiments using a subset of these genes revealed that many are also transcriptionally induced by a variety of structurally diverse xenobiotic compounds, suggesting they comprise components of a coordinately regulated, broad specificity xenobiotic defense response. The data significantly expand upon previous studies examining plant transcriptional responses to allelochemicals and other environmental toxins and provide novel insights into xenobiotic detoxification mechanisms in plants.

Rationale and applications of lipids as prodrug carriers

Lipidic prodrugs, also called drug-lipid conjugates, have the drug covalently bound to a lipid moiety, such as a fatty acid, a diglyceride or a phosphoglyceride. Drug-lipid conjugates have been prepared in order to take advantage of the metabolic pathways of lipid biochemistry, allowing organs to be targeted or delivery problems to be overcome. Endogenous proteins taking up fatty acids from the blood stream can be targeted to deliver the drug to the heart or liver. For glycerides, the major advantage is the modification of the pharmacokinetic behavior of the drug. In this case, one or two fatty acids of a triglyceride are replaced by a carboxylic drug. Lipid conjugates exhibit some physico-chemical and absorption characteristics similar to those of natural lipids. Non-steroidal, anti-inflammatory drugs such as acetylsalicylic acid, indomethacin, naproxen and ibuprofen were linked covalently to glycerides to reduce their ulcerogenicity. Mimicking the absorption process of dietary fats, lipid conjugates have also been used to target the lymphatic route (e.g., L-Dopa, melphalan, chlorambucil and GABA). Based on their lipophilicity and resemblance to lipids in biological membranes, lipid conjugates of phenytoin were prepared to increase intestinal absorption, whereas glycerides or modified glycerides of L-Dopa, glycine, GABA, thiorphan and N-benzyloxycarbonylglycine were designed to promote brain penetration. In phospholipid conjugates, antiviral and antineoplasic nucleosides were attached to the phosphate moiety. After presenting the biochemical pathways of lipids, the review discusses the advantages and drawbacks of lipidic prodrugs, keeping in mind the potential pharmacological activity of the fatty acid itself.

The metabolism of the xenobiotic triacylglycerols, rac-1- and sn-2- (3-phenoxybenzoyl)-dipalmitoylglycerol, following intravenous administration to the rat

The metabolism of 3-phenoxybenzoic acid (3PBA) in the form of triacylglycerol conjugates was compared with that of non-esterified 3PBA. Three radiolabeled triacylglycerols (rac-1-(3-phenoxy-[ring-14C]-benzoyl)-2,3-dipalmitoylglycerol (1(3PBA)DPG), sn-2-(3-phenoxy-[ring-14C]benzoyl)-1,3-dipalmitoylglycerol (2(3PBA)DPG) and the "natural" tri-[1-14C]oleoylglycerol) were incorporated into rat VLDL. Nonesterified 3PBA was prepared in rat serum albumin solution. Each preparation was administered i.v. to rats and serial blood samples were taken during the subsequent 6 hr. Urine and faeces were collected and tissue residues determined at 6 hr and 48 hr after administration. Biphasic elimination of 3PBA was observed with half-lives of 18 min and 2 hr. The triacylglycerols showed a rapid first phase and a longer second phase half-life: trioleoylglycerol 26 hr, 1(3PBA)DPG 7.6 hr and 2(3PBA)DPG 17.3 hr. The majority (63-76%) of 3PBA (whether esterified or not) was eliminated within 24 hr in urine, which contained similar profiles of metabolites. The triacylglycerols gave rise to higher tissue residues than did non-esterified 3PBA, particularly in adipose tissue which alone was not significantly depleted of radioactivity between 6 and 48 hr. The results accord with the rapid association of the VLDL-(3PBA)DPG complexes with lipoprotein lipase of the capillary epithelium, followed by hydrolysis to 3PBA, metabolism and elimination but with a proportion being redistributed into adipose tissue, re-esterified and then eliminated relatively slowly.