Nonylphenol isomers differ in estrogenic activity.

Nonylphenol belongs to the most investigated xenohormones acting at the estrogen receptor. Technical nonylphenol contains approximately 20 para-substituted isomers. Because of limitations in testing and quantifying all 20 isomers in the mixture, the linear form, 4n-NP, is often used as a reference substance, even though it is not present in the technical mixture. Here, we report on the synthesis and estrogenic potency of six nonylphenol isomers that occur at different proportions in technical nonylphenol mixtures. The relative potency of each isomer was determined by use of the MVLN transcriptional activation cell assay. As well, a subset of isomers was tested in the E-screen assay. One isomer, p353-NP, exhibited the same relative potency as the nonylphenol mixture, whereas the other isomers were found to be less potent. Two isomers, p22-NP and p262 NP, and the linear 4n-NP were found to be weak ER agonists with responses near the detection limit in the MVLN assay. Two isomers, p262-NP and 4n-NP, exhibited measurable activity in the E-screen. Our results demonstrate that defined p-NP isomers are most suitable for reflecting the estrogenic potency of technical NP mixtures. Among other applications, they should be used in the future to explain differences in estrogenic potency due to NPs as detected by various in vitro assays.

Synthesis of branched para-nonylphenol isomers: occurrence and quantification in two commercial mixtures.

Eight tertiary nonanols were synthesized via Grignard reaction and coupled by Friedel-Crafts alkylation with phenol to the corresponding nonylphenols. Six branched para-nonylphenols (NP) were obtained: 4-(3'-methyl-3'-octyl)phenol (33NP), 4-(2'-methyl-2'-octyl)phenol (22NP), 4-(2',5'-dimethyl-2'-heptyl)phenol (252NP), 4-(2',5',5'-trimethyl-2'-hexyl)phenol (2552NP), 4-(2',4'-dimethyl-2'-heptyl)phenol (242NP) and 4-(4'-ethyl-2'-methyl-2'-hexyl)phenol (4E22NP). Their structures were confirmed by GC-MS and NMR spectroscopy. These six isomers as well as the earlier synthesized 4-(3',5'-dimethyl-3'-heptyl)phenol (353NP), 4-(3',6'-dimethyl-3'-heptyl)phenol (363NP) and 4-(2',6'-dimethyl-2'-heptyl)phenol (262NP) were compared with commercial NP mixtures purchased from Acros and Fluka by GC-MS (equipped with a 100 m polysiloxane column). The analyses revealed that all obtained isomers are occurring in different quantities in both commercial NP mixtures.

Metabolism of 4-n-nonylphenol by non-modified and CYP1A1- and CYP1A2-transgenic cell cultures of tobacco.

The metabolism of 14C-4-n-nonylphenol (l4C-4-n-NP), as a model for the xenoestrogen nonylphenol, was investigated in three types of tobacco cell suspension cultures: one genetically non-modified culture (NT) and two cultures constitutively expressing human cytochrome P450 CYP1A1 or CYP1A2. With 1 mg l(-1) of 14C-4-n-NP and 24 h of incubation, the xenobiotic was transformed almost completely to glycosides. After glycosidic cleavage, 14C-4-n-NP and several primary metabolites of 4C-4-n-NP were liberated. Portions of the primary metabolites were 29.3% (NT culture), 34.3% (CYP1A1 culture), and 50.7% of applied 14C (CYP1A2 culture). Thus, the endogenous capacity of the tobacco cells to form primary metabolites of 4-n-NP was noticeably higher than that of CYP1A1 or CYP1A2. The results however clearly suggest that 4-n-NP is - even though a poor - substrate of CYP1A1 and CYP1A2. In order to examine metabolic profiles of 4-n-NP in the NT, CYP1A1 and CYP1A2 cultures, the suspensions were exposed to 10 mg 1(-1) of 14C-4-n-NP using a two-liquid-phase system with carrier n-hexadecane and 192 h of incubation. Results obtained resembled those of the low concentration study. The oxidative metabolic profiles determined after hydrolytic cleavage using GC-EIMS were similar in the NT, CYP1A1 and CYP1A2 cultures. Main metabolites were side-chain mono-hydroxylated derivatives of 4-n-NP with 6'-, 7'- and 8'-OH-4-n-NP as prominent metabolites. In addition, olefinic side-chain hydroxy, ring methoxylated, keto and ring hydroxylated derivatives were observed. The lack of differences in metabolic profiles among the CYP1A1, CYP1A2 and NT cultures was referred to the low enzymatic activity of CYP1A1 and CYP1A2 as compared to the higher endogenous oxidative capacity of tobacco, as well as to similar metabolic profiles of 4-n-NP produced by CYP1A1 and CYP1A2 and tobacco itself.