2 research outputs found
Stereoselective Metabolism of α‑, β‑, and γ‑Hexabromocyclododecanes (HBCDs) by Human Liver Microsomes and CYP3A4
This
is the first study investigating the in vitro metabolism of
α-, β-, and γ-hexabromocyclododecane (HBCD) stereoisomers
in humans and providing semiquantitative metabolism data. Human liver
microsomes were incubated with individual racemic mixtures and with
individual stereoisomers of α-, β-, and γ-HBCDs,
the hydroxylated metabolites formed were analyzed by liquid chromatography–tandem
mass spectrometry, and the value of the intrinsic in vitro clearance
(Cl<sub>int,vitro</sub>) was calculated. Several mono- and dihydroxylated
metabolites of α-, β-, and γ-HBCDs were formed,
with mono-OH-HBCDs being the major metabolites. No stereoisomerization
of any of the six α-, β-, and γ-HBCD isomers catalyzed
by cytochrome P450 (CYP) enzymes occurred. The value of Cl<sub>int,vitro</sub> of α-HBCDs was significantly lower than that of β-HBCDs,
which, in turn, was significantly lower than that of γ-HBCDs
(<i>p</i> < 0.05). Such differences were explained by
the significantly lower values of Cl<sub>int,vitro</sub> of each α-HBCD
stereoisomer than those of the β- and γ-HBCD stereoisomers.
In addition, significantly lower values of Cl<sub>int,vitro</sub> of
the (−) over the (+)α- and β-HBCD stereoisomers,
but not γ-HBCDs, were obtained. Our data offer a possible explanation
of the enrichment of α-HBCDs over β- and γ-HBCDs
on the one hand and, on the other hand, of (−)α-HBCDs
over (+)α-HBCDs previously reported in human samples. It also
offers information about the mechanism resulting in such enrichments,
the stereoisomer-selective metabolism of α-, β-, and γ-HBCDs
catalyzed by CYPs with the lack of stereoisomerization
Case Study on Screening Emerging Pollutants in Urine and Nails
Alternative
plasticizers and flame retardants (FRs) have been introduced
as replacements for banned or restricted chemicals, but much is still
unknown about their metabolism and occurrence in humans. We identified
the metabolites formed in vitro for four alternative plasticizers
(acetyltributyl citrate (ATBC), bis(2-propylheptyl) phthalate (DPHP),
bis(2-ethylhexyl) terephthalate (DEHTP), bis(2-ethylhexyl) adipate
(DEHA)), and one FR (2,2-bis (chloromethyl)-propane-1,3-diyltetrakis(2-chloroethyl)
bisphosphate (V6)). Further, these compounds and their metabolites
were investigated by LC/ESI-Orbitrap-MS in urine and finger nails
collected from a Norwegian cohort. Primary and secondary ATBC metabolites
had detection frequencies (% DF) in finger nails ranging from 46 to
95%. V6 was identified for the first time in finger nails, suggesting
that this matrix may also indicate past exposure to FRs as well as
alternative plasticizers. Two isomeric forms of DEHTP primary metabolite
were highly detected in urine (97% DF) and identified in finger nails,
while no DPHP metabolites were detected in vivo. Primary and secondary
DEHA metabolites were identified in both matrices, and the relative
proportion of the secondary metabolites was higher in urine than in
finger nails; the opposite was observed for the primary metabolites.
As many of the metabolites present in in vitro extracts were further
identified in vivo in urine and finger nail samples, this suggests
that in vitro assays can reliably mimic the in vivo processes. Finger
nails may be a useful noninvasive matrix for human biomonitoring of
specific organic contaminants, but further validation is needed