TY - JOUR
T1 - In vitro metabolism of acitretin by human liver microsomes
T2 - Evidence of an acitretinoyl-coenzyme A thioester conjugate in the transesterification to etretinate
AU - Knights, Kathleen M.
AU - Gasser, Rodolfo
AU - Klemisch, Wolfgang
PY - 2000/8/15
Y1 - 2000/8/15
N2 - The aromatic retinoid acitretin is the primary active metabolite of etretinate, and in this study we investigated the ethyl esterification of acitretin to etretinate using [14C]acitretin and human liver microsomes. Samples were analysed by TLC, HPLC, and LC-MS. Essential requirements for the transesterification reaction were identified and included viable microsomal protein, ATP, CoASH, and ethanol. Human liver microsomes catalysed formation of acitretinoyl-CoA at the rate of 0.08 ± 0.02 nmol/min/mg (mean ± SD, N = 10). Acitretinoyl-CoA was pivotal for the transesterification to etretinate and in the presence of methanol, ethanol, n-propanol, n-butanol, and hexanol, the corresponding esters, namely methyl-, ethyl (etretinate)-, propyl-, butyl-, and hexyl-acitretinate, were formed. On average, 1.7% of the acitretin present in the incubation was converted to etretinate in the presence of ethanol. In the absence of ethanol, transesterification did not proceed. Inhibition of the ester hydrolysis of etretinate by bis-p-nitrophenylphosphate (BNPP, 1 mM) prevented futile cycling of etretinate via acitretinoyl-CoA. An additional finding was that acitretin (15-30 μM) activated significantly human liver microsomal long-chain fatty acid-CoA ligase (E.C.6.2.1.3, LCL), resulting in enhanced formation of palmitoyl-CoA. This study demonstrated that in the presence of ethanol the ethyl esterification of acitretin to etretinate proceeds via formation of acitretinoyl-CoA. Predicting clearance of acitretin in vivo via this unique metabolic pathway will be a challenge, as the intracellular concentration of ethanol could never be predicted with any degree of accuracy in humans. Copyright (C) 2000 Elsevier Science Inc.
AB - The aromatic retinoid acitretin is the primary active metabolite of etretinate, and in this study we investigated the ethyl esterification of acitretin to etretinate using [14C]acitretin and human liver microsomes. Samples were analysed by TLC, HPLC, and LC-MS. Essential requirements for the transesterification reaction were identified and included viable microsomal protein, ATP, CoASH, and ethanol. Human liver microsomes catalysed formation of acitretinoyl-CoA at the rate of 0.08 ± 0.02 nmol/min/mg (mean ± SD, N = 10). Acitretinoyl-CoA was pivotal for the transesterification to etretinate and in the presence of methanol, ethanol, n-propanol, n-butanol, and hexanol, the corresponding esters, namely methyl-, ethyl (etretinate)-, propyl-, butyl-, and hexyl-acitretinate, were formed. On average, 1.7% of the acitretin present in the incubation was converted to etretinate in the presence of ethanol. In the absence of ethanol, transesterification did not proceed. Inhibition of the ester hydrolysis of etretinate by bis-p-nitrophenylphosphate (BNPP, 1 mM) prevented futile cycling of etretinate via acitretinoyl-CoA. An additional finding was that acitretin (15-30 μM) activated significantly human liver microsomal long-chain fatty acid-CoA ligase (E.C.6.2.1.3, LCL), resulting in enhanced formation of palmitoyl-CoA. This study demonstrated that in the presence of ethanol the ethyl esterification of acitretin to etretinate proceeds via formation of acitretinoyl-CoA. Predicting clearance of acitretin in vivo via this unique metabolic pathway will be a challenge, as the intracellular concentration of ethanol could never be predicted with any degree of accuracy in humans. Copyright (C) 2000 Elsevier Science Inc.
KW - Acitretin
KW - Acitretinoyl-CoA
KW - Conjugation
KW - Etretinate
KW - Human liver microsomes
KW - Transesterification
UR - http://www.scopus.com/inward/record.url?scp=0034664222&partnerID=8YFLogxK
U2 - 10.1016/S0006-2952(00)00339-7
DO - 10.1016/S0006-2952(00)00339-7
M3 - Article
C2 - 10874125
AN - SCOPUS:0034664222
VL - 60
SP - 507
EP - 516
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
SN - 0006-2952
IS - 4
ER -