Does elevated urinary N-acetyl-S-(2-hydroxypropyl)-L-cysteine reflect glutathione-dependent processing of propylene oxide?

N-acetyl-S-(2-hydroxypropyl)-L-cysteine (2HPMA) is best understood as a urinary mercapturic-acid metabolite that records chemical biotransformation, not as a direct indicator of body glutathione stores.

Biochemical and clinical interpretation

• Propylene oxide undergoes glutathione conjugation—likely involving glutathione S-transferase—to form S-(2-hydroxy-1-propyl)glutathione. Sequential conversion to a cysteine conjugate and N-acetylation then produces 2HPMA, which is excreted in urine.
• Therefore, detectable or elevated urinary 2HPMA is compatible with engagement of the glutathione-conjugation/mercapturic-acid pathway. It does not measure circulating propylene oxide, tissue dose, or total metabolism, because propylene oxide can also be hydrolyzed by epoxide hydrolase to propylene glycol.

Interpreting an elevated result

• An elevated value provides plausible evidence of glutathione-dependent processing compatible with propylene oxide exposure, but cannot definitively establish active propylene oxide processing in an individual. Smoking, urine dilution, specimen timing, and interindividual metabolic variation affect results.
• Chemical specificity is limited: animal studies have also identified 2HPMA after exposure to 1,2-dibromopropane and 1,2-dichloropropane.
• In one cross-sectional occupational comparison, creatinine-adjusted median 2HPMA was 4.8 µg/g in workers versus 3.5 µg/g in controls, with overlapping distributions and no significant difference (p=0.293). This illustrates why a single result cannot reliably specify exposure source or magnitude.

Glutathione status

• Bottom line: High urinary 2HPMA does not prove glutathione deficiency. No validated diagnostic threshold, diagnostic-accuracy evidence, or demonstrated correlation links urinary 2HPMA to blood or tissue GSH, GSSG, total glutathione, or the GSH/GSSG ratio. If glutathione/redox status is clinically relevant, it requires separate, carefully handled and appropriately interpreted testing.