Can GSTP1 rs1695 AG reduce antioxidant capacity and contribute to thyroid autoimmunity?

The synthesis of thyroid hormones inherently requires highly reactive chemical processes, establishing a delicate balance between physiological function and pathological oxidative stress.

Genetic and enzymatic mechanisms

• GSTP1 rs1695 AG variant: The heterozygous AG genotype (an A→G transition causing an Ile105Val substitution in the GSTP1 active site) produces an intermediate phenotype. It moderately reduces global glutathione S-transferase antioxidant and detoxification capacity compared to the wild-type AA genotype, particularly under conditions of elevated oxidative or chemical stress.

Thyroid physiology and redox balance

• Hydrogen peroxide chemistry: Thyroid hormone synthesis is fundamentally dependent on hydrogen peroxide ($\text{H}_2\text{O}_2$) generated by the DUOX2/DUOXA2 membrane-bound complex. Thyroid peroxidase (TPO) uses $\text{H}_2\text{O}_2$ as an essential, rate-limiting co-substrate to oxidize iodide and couple iodotyrosyl residues.
• Pathological transition: When cellular antioxidant defenses—such as glutathione-conjugating pathways—are compromised, the $\text{H}_2\text{O}_2$ physiologically required for hormone synthesis can overwhelm local defenses, shifting the tissue into a state of pathological oxidative stress.

Autoimmune implications

• Neoantigen formation: Excess reactive oxygen species oxidatively modify TPO and thyroglobulin into highly immunogenic neoantigens. This structural modification breaks immunological self-tolerance, leading to the production of anti-TPO and anti-Tg autoantibodies and driving a self-perpetuating cycle of thyroid autoimmunity.

Bottom line

• The GSTP1 rs1695 AG genotype moderately impairs glutathione S-transferase antioxidant capacity, which can compromise the thyroid's ability to detoxify excess $\text{H}_2\text{O}_2$ generated during hormone synthesis, thereby promoting localized oxidative stress and contributing to the development of thyroid autoimmunity.