Does the GSTP1 rs1695 A/G genotype cause intermediate GST activity and increased oxidative stress sensitivity?

The GSTP1 rs1695 polymorphism is a well-characterized genetic variant that significantly influences the body’s ability to detoxify environmental chemicals and neutralize oxidative stress. This variant involves an A-to-G transition (c.313A>G), which substitutes the amino acid isoleucine (Ile) with valine (Val) at position 105 of the enzyme, directly impacting its catalytic efficiency.

Enzymatic activity and gene-dosage effects

The GSTP1 rs1695 A/G (Ile/Val) genotype is associated with intermediate glutathione S-transferase activity, representing a midpoint between the high-activity A/A wild-type and the low-activity G/G variant.

• Structural mechanics: The substitution occurs at the substrate-binding site (H-site). Research indicates that GSTP1 functions as a dimer; in A/G heterozygotes, the formation of Ile/Val heterodimers disrupts subunit communication and reduces the catalytic rate (kcat) compared to wild-type homodimers.
• Catalytic efficiency: For most standard electrophilic substrates, the G (Val) allele results in a 50–70% reduction in catalytic efficiency. Clinical data consistently demonstrate a gene-dosage effect where the A/G genotype shows significantly lower activity than A/A but remains more functional than the G/G genotype.

Sensitivity to oxidative stress and toxicants

Carriers of the G allele, including those with the A/G genotype, exhibit a diminished capacity to handle oxidative challenges and toxicant exposure.

• Oxidative markers: Individuals with the G allele show significantly higher levels of oxidative damage markers, such as malondialdehyde (MDA) and F2-isoprostanes, particularly when the system is stressed by disease or environmental pollutants.
• Toxicant vulnerability: The A/G genotype is linked to increased sensitivity to external stressors. For example, research has identified higher rates of poisoning symptoms following pesticide exposure (p=0.025) and a higher risk of gastrointestinal and hematological toxicity during chemotherapy (Relative Risk: 1.61) compared to A/A carriers.
• Mechanistic pathway: GSTP1 is essential for conjugating glutathione (GSH) to toxic metabolites and reactive oxygen species (ROS). The reduced efficiency of the Val105 variant lowers the cellular threshold at which these harmful substances overwhelm antioxidant defenses, leading to increased cellular damage.

Bottom line

The GSTP1 rs1695 A/G genotype results in intermediate enzyme activity and heightened sensitivity to oxidative stress. For individuals with this genotype, exposure to environmental toxicants or high-oxidative-stress conditions may lead to greater cellular damage compared to those with the A/A wild-type.