acid-phosphatase and bis(4-nitrophenyl)phosphate

Dibasic esters (DBE) is a solvent mixture of dimethyl adipate, dimethyl glutarate, and dimethyl succinate which causes a selective degeneration of the nasal olfactory epithelium in rats following a 90-day inhalation exposure. In short-term cultures of rat nasal explants, it has been demonstrated that DBE cytotoxicity is due to a carboxylesterase-mediated activation. In the present study, the putative toxic metabolites of DBE, the monomethyl esters and the dicarboxylic acids, were evaluated in the nasal explant system at concentrations ranging from 10 to 50 mM. Monomethyl adipate (MMA), monomethyl glutarate (MMG), and monomethyl succinate (MMS) induced increases in nasal explant acid phosphatase release, a biochemical index of cytotoxicity. The nasal explant-mediated metabolism of MMA and MMG to their corresponding diacids paralleled the increases in acid phosphatase release. A carboxylesterase inhibitor, bis(p-nitrophenyl)phosphate (BNPP), inhibited both the cytotoxicity and the hydrolysis of MMA and MMG in the nasal explant system. The metabolism and cytotoxicity of MMS was not attenuated as effectively by BNPP pretreatment. Adipate, glutarate, and succinate induced concentration-related increases in cytotoxicity in the nasal explant system. These dicarboxylic acids were neither metabolized nor utilized significantly by the nasal explants. Diacid-induced cytotoxicity was not attenuated by BNPP pretreatment. This study further established the utility of the nasal explant system for evaluating cytotoxicity of organic esters in vitro. It was established that both the monomethyl ester and diacid metabolites are cytotoxic in rat nasal explants. Finally, it was concluded that although both the monomethyl esters and the diacids contribute to the cytotoxic potential of DBE in vitro, it is critical to establish if one or both of these are formed in vivo in order to identify the ultimate toxic metabolite of DBE.

Topics: Acid Phosphatase; Animals; Carboxylic Ester Hydrolases; Cell Survival; Dicarboxylic Acids; Dose-Response Relationship, Drug; Epithelium; Female; Methylation; Nitrophenols; Nose; Organ Culture Techniques; Rats; Rats, Inbred Strains; Turbinates

Dibasic esters (DBE) are a solvent mixture of dimethyl adipate (DMA), dimethyl glutarate (DMG), and dimethyl succinate (DMS) used in the paint and coating industry. Subchronic inhalation toxicity studies have demonstrated that DBE induce a mild degeneration of the olfactory, but not the respiratory, epithelium of the rat nasal cavity. Carboxylesterase-mediated hydrolysis of the individual dibasic esters is more efficient in olfactory than in respiratory mucosal homogenates. In the present study, an in vitro system of cultured rat nasal explants was utilized to determine if DBE toxicity is dependent on a metabolic activation by nonspecific carboxylesterase. Explants from both the olfactory and the respiratory regions of the female rat nasal cavity were incubated for 2 hr in Williams' medium E containing 10-100 mM DMA, DMG, or DMS. DBE caused a dose-related increase in nasal explant acid phosphatase release, a biochemical index of cytotoxicity. HPLC analysis demonstrated parallel increases in the carboxylesterase-mediated formation of monomethyl ester metabolites. Diacid metabolite production in the nasal explant system was not entirely concentration-dependent. Metabolite concentrations and acid phosphatase release were generally greater in olfactory than respiratory tissues. DBE-induced cytotoxicity and acid metabolite production were markedly attenuated in nasal tissue excised from rats which were pretreated with bis(p-nitrophenyl)phosphate, a carboxylesterase inhibitor. This study presents a viable in vitro method for assessing organic ester cytotoxicity in the rat nasal cavity. It was shown that DBE are weak nasal toxicants under the conditions of this system. It was further demonstrated that DBE toxicity is dependent on a carboxylesterase-mediated activation. A similar mechanism was proposed for the nasal toxicity induced by other organic esters following inhalation exposure.

Topics: Acid Phosphatase; Adipates; Administration, Inhalation; Animals; Carboxylic Ester Hydrolases; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; Female; Glutarates; Hydrolysis; Nasal Cavity; Nasal Mucosa; Nitrophenols; Olfactory Mucosa; Rats; Succinates; Time Factors

Topics: Acid Phosphatase; Chemical Phenomena; Chemistry; Fusarium; Hot Temperature; Hydrogen-Ion Concentration; Hydrolysis; Kinetics; Nitrophenols; Organophosphorus Compounds; Phosphates