Prilocaine- and Lidocaine-Induced Methemoglobinemia Is Caused by Human Carboxylesterase-, CYP2E1-, and CYP3A4-Mediated Metabolic Activation

Abstract

Prilocaine and lidocaine are classified as amide-type local anesthetics for which serious adverse effects include methemoglobinemia. Although the hydrolyzed metabolites of prilocaine (o-toluidine) and lidocaine (2,6-xylidine) have been suspected to induce methemoglobinemia, the metabolic enzymes that are involved remain uncharacterized. In the present study, we aimed to identify the human enzymes that are responsible for prilocaine-and lidocaine-induced methemoglobinemia. Our experiments revealed that prilocaine was hydrolyzed by recombinant human carboxylesterase (CES) 1A and CES2, whereas lidocaine was hydrolyzed by only human CES1A. When the parent compounds (prilocaine and lidocaine) were incubated with human liver microsomes (HLM), methemoglobin (MetHb) formation was lower than when the hydrolyzed metabolites were incubated with HLM. In addition, Met-Hb formation when prilocaine and o-toluidine were incubated with HLM was higher than that when lidocaine and 2,6-xylidine were incubated with HLM. Incubation with diisopropyl fluorophosphate and bis-(4-nitrophenyl) phosphate, which are general inhibitors of CES, significantly decreased Met-Hb formation when prilocaine and lidocaine were incubated with HLM. An anti-CYP3A4 antibody further decreased the residual formation of Met-Hb. Met-Hb formation after the incubation of o-toluidine and 2,6-xylidine with HLM was only markedly decreased by incubation with an anti-CYP2E1 antibody. o-Toluidine and 2,6-xylidine were further metabolized by CYP2E1 to 4-and 6-hydroxy-o-toluidine and 4-hydroxy-2,6-xylidine, respectively, and these metabolites were shown to more efficiently induce Met-Hb formation than the parent compounds. Collectively, we found that the metabolites produced by human CES-, CYP2E1-, and CYP3A4-mediated metabolism were involved in prilocaine-and lidocaineinduced methemoglobinemia.

Accidental Ingestion of Local Anesthetic Solutions in Children

“…Cyanosis appears when Met-Hb reaches to 10-20%, while dyspnea and tachycardia are noted at 30-50%. Levels greater than 50% are accompanied by coma (8,9).…”

Screening of Specific Inhibitors for Human Carboxylesterases or Arylacetamide Deacetylase

“…The hydrolysis of lidocaine, CPT-11, and phenacetin was used to probe the activities of CES1, CES2, and AADAC, respectively, according to our previous studies Watanabe et al, 2010;Higuchi et al, 2013). A typical incubation mixture (at a final volume of 0.2 ml) contained 100 mM potassium phosphate buffer (pH 7.4), human liver microsomes (HLM) (pooled, n = 50, BD Gentest, Woburn, MA), or the homogenates of Sf21 cells expressing CES1, CES2, and AADAC (0.1 mg/ml).…”

Comparison of substrate specificity among human arylacetamide deacetylase and carboxylesterases

“…Flutamide is hydrolyzed by AADAC, but at low concentrations, flutamide is also efficiently hydrolyzed by CES2 (Watanabe et al, 2009;Kobayashi et al, 2012). Lidocaine is specifically hydrolyzed by CES1, whereas prilocaine is hydrolyzed by both CES1 and CES2 (Higuchi et al, 2013). p-Nitrophenyl acetate is hydrolyzed by all three esterases (Watanabe et al, 2009).…”

“…Chemical structures of the compounds hydrolyzed by human AADAC, CES1, and CES2. The esterases involved in the hydrolysis of flutamide, indiplon, lidocaine, p-nitrophenyl acetate, phenacetin, prilocaine, rifampicin, rifabutin, and rifapentine were analyzed in our previous studies (Watanabe et al, 2009(Watanabe et al, , 2010Nakajima et al, 2011;Kobayashi et al, 2012;Higuchi et al, 2013;Shimizu et al, 2014). An acyl moiety in each compound is indicated in red.…”