Characterization of Human Salivary Esterase in Enzymatic Hydrolysis of Phthalate Esters.

Abstract

tyl phthalate (DBP). 1)Some phthalate diesters induce testicular toxicity in the male reproductive tract. Jobling et al. showed that DBP binds to the estrogen receptor, displaces its natural ligand, and then acts as an estrogen antagonist.2) In addition, mono-n-butyl phthalate (MBuP) adversely affects development of the reproductive system in male rats.3) DEHP is a peroxisome proliferator that induces tumors in the rodent liver, and this effect is probably not exerted by DEHP itself but by one or more of its metabolites. 4)Phthalate diesters are metabolized to monoesters by hydrolases in many tissues, such as the pancreas, intestine, and blood.5-7) Generally orally ingested dialkyl phthalates are hydrolyzed by esterases in the wall of the small intestine and pancreatic lipases and not by gut flora. Absorption occurs almost entirely as the corresponding monoesters.5) Human saliva is a matrix of inorganic compounds, saliva proteins such as lingual lipase and α-amylase, oral flora, and cell debris. 8) However, to the best of our knowledge there are no reports concerning enzymatic hydrolysis of phthalate diesters in human saliva, except for our previous paper.9) The present work was therefore designed to characterize human salivary esterase in enzymatic hydrolysis of phthalate esters. These findings provide the information that will be required in considering the human health effects of phthalate esters. MATERIALS AND METHODSChemicals and Glassware ---Monoethyl phthalate (MEP), diethyl phthalate (DEP), and DEHP were purchased from Wako Pure Chemical Industries. (Osaka, Japan) and MBuP, mono-n-hexyl phthalate (MHxP), mono-2-ethylhexyl phthalate (MEHP), monobenzyl phthalate (MBeP), and di-n-hexyl phEnzymatic hydrolysis of phthalate esters in human saliva was investigated to characterize salivary esterase in the formation of monoesters from their diesters. The monoesters formed were analyzed by GC/ MS after incubation of phthalate diesters in the saliva. Hydrolytic activity in the supernatant obtained by centrifugation of the saliva at 1350 × g was equivalent to that in whole saliva, and the activity was inhibited by the addition of denaturing protein. The hydrolytic activity was dependent on the protein concentration in the supernatant. The optimum temperature and pH of the hydrolysis was 50°C and 8.2, respectively. In addition, the 80% acetone powder of the supernatant showed high substrate specificity for straight-chain alkyl group of phthalate diesters, especially the butyl group, whereas almost no specificity was seen for the 2-ethylhexyl and benzyl groups. These results indicate that not the oral flora but salivary esterase, such as lingual lipase, is involved in phthalate monoester formation from the diesters in human saliva, and do not act on the hydrolysis of monoester.

Organophosphate pesticide environmental exposure: analysis of salivary cholinesterase and carboxilesterase activities in preschool children and their mothers

“…They show greater promiscuity in substrates than ChE and therefore serve a protective and cleaning function for a large variety of foreign substrates (Satoh 2005). The characterization of a human saliva esterase that hydrolyzes phthalate esters was reported by Niino et al (2003). However, to our knowledge, there are no studies exploring salivary CE as potential indicator of environmental pesticide exposure.…”

A Mono-2-Ethylhexyl Phthalate Hydrolase from a Gordonia sp. That Is Able To Dissimilate Di-2-Ethylhexyl Phthalate

“…After this, microorganisms that could grow using PAEs as a sole carbon source were isolated from soils and enriched wastewater samples. The microorganisms were identified and were reported to be Rhodococcus erythropolis, Pseudomonas species, and members of the genus Corynebacterium (3, 21).It was reported previously that phthalate esters are hydrolyzed by specific and/or nonspecific esterases in many tissues of mammals and plants and in microorganisms (6,18,24,29,33). Phthalate diesters are metabolized to monoesters in many tissues of mice (18) and in human blood plasma (33).…”

“…It was reported previously that phthalate esters are hydrolyzed by specific and/or nonspecific esterases in many tissues of mammals and plants and in microorganisms (6,18,24,29,33). Phthalate diesters are metabolized to monoesters in many tissues of mice (18) and in human blood plasma (33).…”

“…Phthalate diesters are metabolized to monoesters in many tissues of mice (18) and in human blood plasma (33). The purified specific esterases from mouse hepatic microsomes and human saliva have activity that hydrolyzes phthalate diesters to the corresponding monoesters (18,29). Purified wheat plant esterase exhibits activity that hydrolyzes DEHP to mono-2-ethylhexyl phthalate (MEHP) (20).…”

Response to ‘Dr Raymond David, BASF Corporation’

“…The first and fast stage in the metabolism of DEHP is the hydrolytic cleavage to mono(2-ethylhexyl) phthalate (MEHP) and 2-ethylhexanol (2-EH). After oral uptake enzymatic hydrolysis occurs already in mouth (Niino et al 2003, Niino et al 2001) and especially in the gastrointestinal tract Thomas 1973). Thus it can be assumed that the majority of DEHP is rapidly absorbed as MEHP in gut following oral administration.…”