Cellular and erythrocyte non-protein and protein thiols (NPSH and PSH)

Cellular and erythrocyte non-protein and protein thiols represent a collective pool of sulfur-containing compounds that serve as the primary defense mechanism against oxidative stress and electrophilic insult. The non-protein thiol (NPSH) fraction is predominantly composed of reduced glutathione (GSH), while the protein thiol (PSH) fraction consists of cysteine residues on various proteins, such as hemoglobin in erythrocytes and albumin in plasma. These thiols maintain the intracellular redox environment by scavenging reactive oxygen species (ROS) and facilitating the detoxification of xenobiotics through conjugation reactions. In clinical pharmacology, this thiol pool is rarely a direct therapeutic target but is frequently monitored as a biomarker of oxidative stress and drug-induced toxicity. For instance, the depletion of erythrocyte and hepatic glutathione is a hallmark of acetaminophen overdose, where the reactive metabolite NAPQI exhausts the thiol supply, leading to cell death. Conversely, drugs like N-acetylcysteine are administered to replenish these thiol stores. Because this term describes a broad chemical class and a physiological compartment rather than a specific protein or receptor, it is classified as an aggregate biomarker or a metabolic pool rather than a discrete molecular target.

Other names

Total thiolsSulfhydryl groupsThiol poolNon-protein sulfhydrylsProtein-bound thiolsErythrocyte glutathione and protein thiols

Drugs typically interact with this pool by either replenishing it (e.g., N-acetylcysteine providing cysteine for glutathione synthesis), depleting it through reactive metabolite conjugation (e.g., NAPQI from acetaminophen), or utilizing thiol groups for metal chelation and ROS scavenging.