posted on 2020-03-17, 20:29authored byAllison
L. Phillips, Nicholas J. Herkert, Jake C. Ulrich, Jessica H. Hartman, Matthew T. Ruis, Ellen M. Cooper, P. Lee Ferguson, Heather M. Stapleton
Isopropylated
and tert-butylated triarylphosphate
esters (ITPs and TBPPs, respectively) are plasticizers and flame retardants
that are ubiquitous in indoor environments; however, no studies to
date have characterized their metabolism. Using human liver subcellular
S9 fractions, phase I and II in vitro metabolism
of triphenyl phosphate (TPHP), 4-tert-butylphenyl
diphenyl phosphate (4tBPDPP), 2-isopropylphenyl diphenyl phosphate
(2IPPDPP), and 4-isopropylphenyl diphenyl phosphate (4IPPDPP) was
investigated at 1 and 10 μM doses. Parent depletion and the
formation of known or suspected metabolites (e.g., likely hydrolysis
or hydroxylated products), including diphenyl phosphate (DPHP), hydroxyl-triphenyl
phosphate (OH-TPHP), isopropylphenyl phenyl phosphate (ip-PPP), and tert-butylphenyl phenyl phosphate (tb-PPP), were monitored
and quantified via GC/MS or LC-MS/MS. tb-PPP and its conjugates were
identified as the major in vitro metabolites of 4tBPDPP
and accounted for 71% and 49%, respectively, of the parent molecule
that was metabolized during the incubation. While the mass balance
between parents and metabolites was conserved for TPHP and 4tBPDPP,
approximately 20% of the initial parent mass was unaccounted for after
quantifying suspected metabolites of 2IPPDPP and 4IPPDPP that had
authentic standards available. Two novel ITP metabolites, mono-isopropenylphenyl
diphenyl phosphate and hydroxy-isopropylphenyl diphenyl phosphate,
were tentatively identified by high-resolution mass spectrometry and
screened for in recently collected human urine where mono-isopropenylphenyl
diphenyl phosphate was detected in one of nine samples analyzed. This
study provides insight into the biological fate of ITP and TBPP isomers
in human tissues and is useful in identifying appropriate biomarkers
of exposure to monitor, particularly in support of epidemiological
studies.