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<p>Skin sensitization initiates with the covalent binding of sensitizers to nucleophilic thiol or amino residues in skin proteins. <i>N</i>-Acetyl-L-cysteine methyl ester (NACME) and glutathione selectively react with skin sensitizers, suggesting that simple thiol compounds can be used as nucleophiles to develop an in vitro identification method for chemical sensitizers. Herein, <i>N</i>-acetyl-L-cysteine (NAC) was evaluated as an electron donor to characterize its reactivity with sensitizers. The residual unreacted NAC was spectrophotometrically quantified using 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB). Tests of 64 standard chemicals showed 91.2% sensitivity, 85.2% specificity, and 88.5% accuracy using the cut-off of 4.45% NAC depletion with ACN, and 81.1% sensitivity, 92.6% specificity, and 85.9% accuracy using the cut-off of 3.75% with DMSO. These results were comparable to or exceeded those of OECD-approved methods. Overall, the NAC-based assay offers a practical and user-friendly approach for preliminary screening of skin-sensitizing potential to support decision-making during early-stage chemical safety assessment.</p>

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A spectrophotometry-based in chemico method for identifying skin-sensitizing chemicals by using N-acetyl-L-cysteine

  • 期刊论文

  • 发表日期：

    2026年5月11日

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  • Rahul Upadhyay Nepal,
  • Hye-Jin Eom,
  • Tae Cheon Jeong

摘要

Skin sensitization initiates with the covalent binding of sensitizers to nucleophilic thiol or amino residues in skin proteins. N-Acetyl-L-cysteine methyl ester (NACME) and glutathione selectively react with skin sensitizers, suggesting that simple thiol compounds can be used as nucleophiles to develop an in vitro identification method for chemical sensitizers. Herein, N-acetyl-L-cysteine (NAC) was evaluated as an electron donor to characterize its reactivity with sensitizers. The residual unreacted NAC was spectrophotometrically quantified using 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB). Tests of 64 standard chemicals showed 91.2% sensitivity, 85.2% specificity, and 88.5% accuracy using the cut-off of 4.45% NAC depletion with ACN, and 81.1% sensitivity, 92.6% specificity, and 85.9% accuracy using the cut-off of 3.75% with DMSO. These results were comparable to or exceeded those of OECD-approved methods. Overall, the NAC-based assay offers a practical and user-friendly approach for preliminary screening of skin-sensitizing potential to support decision-making during early-stage chemical safety assessment.