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Organophosphate sensitive and insensitive carboxylesterases in human skin

E Heymann1, W Hoppe, A Krüsselmann

  • 1Arbeitsgruppe Gesundheitswissenschaften, University of Osnabrück, Germany.

Chemico-Biological Interactions
|June 1, 1993
PubMed

Insights

Human skin contains at least four distinct carboxylesterases that metabolize aromatic esters. Organophosphate inhibitors like paraoxon reveal functional heterogeneity among these skin enzymes.

Area of Science:

  • Biochemistry
  • Dermatology
  • Enzymology

Background:

  • Carboxylesterases are crucial enzymes involved in metabolizing various xenobiotics and endogenous compounds.
  • Organophosphates, such as paraoxon and bis(4-nitrophenyl)phosphate (BNPP), are known inhibitors of B-esterase type carboxylesterases.
  • Understanding the specific carboxylesterases in human skin is important for assessing dermal exposure and metabolism of ester-containing compounds.

Purpose of the Study:

  • To investigate the influence of paraoxon and BNPP on human skin carboxylesterases.
  • To characterize the different carboxylesterase activities present in human skin homogenates.
  • To determine the sensitivity of various skin carboxylesterase isoenzymes to organophosphate inhibition.

Main Methods:

  • Human skin homogenates were prepared and assayed for carboxylesterase activity.
  • Isoelectric focusing (IEF) was used to separate and visualize different carboxylesterase isoenzyme bands.
  • Organophosphate inhibitors (paraoxon and BNPP) were applied to assess enzyme inhibition kinetics.
  • Anion exchange chromatography and Fast Protein Liquid Chromatography (FPLC) were employed for enzyme enrichment.

Main Results:

  • Human skin homogenates exhibited minimal paraoxon-cleaving or phosphodiesterase activity with BNPP.
  • IEF revealed three distinct zones of carboxylesterase activity, with varying sensitivities to organophosphates.
  • A major zone with carboxylesterase activity (pI 5.7-6.2) was rapidly and completely inhibited by paraoxon.
  • Another zone (pI 4.9) and a zone with 5 bands (pI 6.7-7.0) were insensitive to organophosphate inhibition, indicating functional heterogeneity.

Conclusions:

  • Human skin possesses at least four distinct carboxylesterases capable of hydrolyzing simple aromatic esters.
  • The identified carboxylesterases exhibit differential sensitivity to organophosphate inhibition, suggesting functional heterogeneity.
  • Specific carboxylesterase isoenzymes, particularly those in the pI range of 5.7-6.2 and at pI 4.9, can be enriched via chromatographic techniques.

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