Does the GSTP1 rs1695 variant increase risk of exercise-induced muscle damage?

The GSTP1 gene encodes glutathione S-transferase pi 1, a critical enzyme in the cellular detoxification system that conjugates glutathione to a variety of electrophilic compounds, including those generated during metabolic stress. The rs1695 polymorphism is one of the most studied genetic variations influencing antioxidant capacity and its subsequent impact on physical performance and recovery.

Impact on enzyme activity and stability

The GSTP1 rs1695 polymorphism (c.313A>G) results in a substitution of isoleucine with valine (Ile105Val) at the enzyme's substrate-binding pocket, known as the H-site. This structural change significantly alters the enzyme’s functional capacity:

• Reduced catalytic efficiency: The Val105 variant (G allele) exhibits a 20% to 40% reduction in catalytic efficiency ($k_{cat}/K_m$) for standard substrates compared to the ancestral Ile105 variant.
• Structural instability: Replacing isoleucine with the smaller valine residue reduces the thermodynamic stability of the GSTP1 homodimer. This makes the protein more susceptible to folding errors and rapid degradation, leading to lower overall enzyme concentrations in individuals carrying the G allele.
• Substrate binding: The mutation disrupts the precise hydrophobic interactions in the H-site and can interfere with glutathione (GSH) binding at the adjacent G-site, further impairing the detoxification pathway.

Oxidative stress during physical exertion

Reduced GSTP1 activity directly correlates with an impaired ability to neutralize reactive oxygen species (ROS) produced during intense physical activity.

• Lipid peroxidation: GSTP1 is essential for detoxifying secondary products of lipid peroxidation, such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). During high-intensity or anaerobic exercise, mitochondrial respiration increases ROS production; individuals with the "low-activity" Val/Val genotype often show significantly higher systemic markers of oxidative damage.
• Systemic antioxidant capacity: Clinical evidence suggests that while exercise normally triggers an adaptive rise in antioxidant enzymes, the structural deficit in the rs1695 variant limits this protective response, leaving cellular membranes more vulnerable to oxidative attack.

Exercise-induced muscle damage (EIMD)

The convergence of reduced enzymatic activity and increased oxidative stress places G-allele carriers at a higher risk for structural muscle damage following strenuous activity.

• Membrane permeability: Heightened lipid peroxidation weakens the sarcolemma (muscle cell membrane). This leads to increased leakage of intracellular proteins into the bloodstream.
• Clinical markers: Susceptibility to EIMD is typically measured via serum creatine kinase (CK) and lactate dehydrogenase (LDH) levels. Mechanistic models indicate that the impaired antioxidant defense of the Val105 variant contributes to significantly higher post-exercise CK elevations and prolonged recovery times, as the body struggles to clear the oxidative byproducts that drive myofibrillar disruption.

Bottom line

The GSTP1 rs1695 polymorphism is a functional variant that reduces enzyme activity by up to 40%, directly increasing oxidative stress and susceptibility to muscle damage during exercise. Individuals with the G allele (Val/Val or Ile/Val) may require more targeted recovery strategies or antioxidant support to mitigate the heightened risk of exercise-induced muscle injury.