GSTP1 Ile105Val

GSTP1 Ile105Val — Your Body's Chemical Defense Shield

Glutathione S-transferase Pi 1 (GSTP1) is one of the most important
Phase II detoxification enzymes | Phase II enzymes conjugate activated toxins with water-soluble molecules (like glutathione) so they can be excreted in urine or bile. Phase I enzymes activate toxins; Phase II neutralizes them.
in the human body. It catalyzes the conjugation of
glutathione | A tripeptide (glutamate-cysteine-glycine) that is the body's master antioxidant and primary substrate for Phase II detoxification reactions
to a broad range of electrophilic compounds -- carcinogens, chemotherapy drugs,
products of oxidative stress, and environmental pollutants including heavy metals.
GSTP1 provides the majority of GST activity in the lung and is widely expressed
in the liver, kidneys, and gastrointestinal tract.

The rs1695 variant causes an isoleucine-to-valine substitution at position 105
(Ile105Val), right in the
hydrophobic substrate-binding pocket (H-site) | The H-site is the region of the enzyme that physically contacts the electrophilic substrate. Position 105 sits on a helix alongside Tyr109, and together they define the shape and chemistry of the binding cleft.
of the enzyme. This single amino acid change reshapes the active site geometry,
fundamentally altering which substrates the enzyme handles efficiently -- and
which it does not.

The Mechanism

The Val105 substitution has a paradoxical effect on enzyme function that depends
on the substrate. For the general-purpose model substrate
CDNB | 1-chloro-2,4-dinitrobenzene, a standard laboratory substrate used to measure GST activity broadly,
the Val105 enzyme is approximately
three-fold less active | The essential role of GSTP1 I105V polymorphism in the prediction of CDNB metabolism and toxicity: In silico and in vitro insights. Toxicol In Vitro, 2023
than the Ile105 form. However, for the
diol epoxides of polycyclic aromatic hydrocarbons (PAHs) | Reactive metabolites of combustion products found in cigarette smoke, grilled meat, and vehicle exhaust; benzo[a]pyrene diol epoxide (BPDE) is the most studied,
the Val105 enzyme shows
seven-fold higher catalytic efficiency | Watson MA et al. Human glutathione S-transferase P1 polymorphisms: relationship to lung tissue enzyme activity and population frequency distribution. Carcinogenesis, 1998
compared to the Ile105 form. This substrate-dependent shift means carriers of the
Val105 allele process PAH carcinogens more efficiently but have reduced capacity
for many other electrophilic toxins and oxidative stress products.

The variant also affects the enzyme's thermal stability -- the Val105 protein is
less stable than the Ile105 form, which may reduce the total pool of functional
GSTP1 protein available for detoxification under physiological conditions.

Critically, GSTP1 also metabolizes
sulforaphane | The principal bioactive isothiocyanate from cruciferous vegetables (broccoli, kale, Brussels sprouts). Sulforaphane activates the Nrf2 pathway, which upregulates dozens of detoxification and antioxidant enzymes.,
the key compound from cruciferous vegetables that activates the
Nrf2/ARE pathway | Nuclear factor erythroid 2-related factor 2 / Antioxidant Response Element -- the master regulator of cellular antioxidant defense. When activated, Nrf2 drives expression of over 200 cytoprotective genes..
The Val105 variant has reduced specific activity toward sulforaphane, which
paradoxically may allow more sulforaphane to reach its target (Nrf2) rather
than being conjugated and eliminated. This creates a complex interplay between
genotype and dietary intervention.

The Evidence

Cancer risk. The most robust evidence comes from a
Shanghai Breast Cancer Study | Parl FF et al. Cruciferous vegetables, the GSTP1 Ile105Val genetic polymorphism, and breast cancer risk. Am J Clin Nutr, 2008
of 3,035 cases and 3,037 controls, which found that the Val/Val genotype was
associated with a 1.50-fold increased breast cancer risk (OR 1.50, 95% CI
1.12-1.99), with the effect strongest in premenopausal women (OR 2.08). A
meta-analysis of 51 studies | Wei B et al. Association between GSTP1 Ile105Val polymorphism and urinary system cancer risk. Onco Targets Ther, 2016
covering 11,762 cases and 15,150 controls found that Val allele carriers had
increased prostate cancer risk (OR 1.80, 95% CI 1.19-2.73) and elevated
bladder cancer risk across multiple genetic models (GG vs AA: OR 1.49,
95% CI 1.12-1.97).

Chemotherapy toxicity. GSTP1 directly metabolizes platinum-based
chemotherapy drugs. A
meta-analysis by Lv et al. | Lv F et al. Relationship between GSTP1 rs1695 gene polymorphism and myelosuppression induced by platinum-based drugs. J Int Med Res, 2018
found that G allele carriers had 1.7-fold higher hematological adverse events
and 2.6-fold higher neutropenia risk during platinum chemotherapy compared to
the AA genotype. The variant also predicts
cyclophosphamide-induced toxicity | Mokhtar GM et al. Evaluating the role of GSTP1 genetic polymorphism (rs1695, 313A>G) as a predictor in cyclophosphamide-induced toxicities. Genes Environ, 2021
including myelosuppression and gastrointestinal side effects.

Heavy metal detoxification. GSTP1 plays a direct role in conjugating
heavy metals with glutathione for elimination. A
study by Santos et al. | Santos A et al. The GSTP1 rs1695 polymorphism is associated with mercury levels and neurodevelopmental delay in indigenous Munduruku children. Toxics, 2024
found that the rs1695 polymorphism was associated with mercury levels and
neurodevelopmental outcomes, while in vitro studies show that
heavy metals can directly inhibit GST variants differently | Paiva L et al. Variants of glutathione S-transferase pi 1 exhibit differential enzymatic activity and inhibition by heavy metals. Toxicol In Vitro, 2012,
with the Val105 form showing altered sensitivity to mercury and cadmium
inhibition.

Oxidative stress and airway inflammation. The Val105 variant modulates
allergen-provoked airway inflammation in asthmatics. A
controlled allergen challenge study | Fryer AA et al. Glutathione S-transferase P1 Ile105Val polymorphism modulates allergen-induced airway inflammation in human atopic asthmatics in vivo. Clin Exp Allergy, 2013
found that Val105/Val105 asthmatics had greater generation of acute-phase
cytokines and inflammatory mediators after allergen challenge compared to
other genotypes, indicating reduced capacity to buffer oxidative stress in
the airways.

Practical Implications

The most actionable finding for everyday health is the interaction between
GSTP1 genotype and cruciferous vegetable intake. The Shanghai study showed
that women with Val/Val genotype and low cruciferous vegetable intake had
1.74-fold increased breast cancer risk, but high cruciferous intake
substantially ameliorated this risk. Since the Val105 enzyme is less efficient
at conjugating sulforaphane, more of this beneficial compound may actually
reach its Nrf2 target -- but only if you eat enough cruciferous vegetables
to begin with.

For individuals carrying one or two G alleles, supporting the body's
glutathione system becomes particularly important. This means ensuring
adequate intake of glutathione precursors (N-acetylcysteine, glycine,
glutamine), selenium (a cofactor for glutathione peroxidase), and
antioxidant-rich foods. Minimizing unnecessary exposures to environmental
toxins -- especially tobacco smoke, which contains PAHs -- is also relevant,
though the Val105 form is actually more efficient at clearing PAH metabolites
specifically.

For anyone undergoing platinum-based chemotherapy or cyclophosphamide
treatment, this variant should be discussed with the oncology team, as it
may affect drug metabolism and toxicity risk.

Interactions

The most direct interaction is with rs1138272 (GSTP1 Ala114Val), another
variant in the same enzyme. Together, these two SNPs define the GSTP1
haplotypes: GSTP1*A (Ile105/Ala114, wild-type), GSTP1*B (Val105/Ala114),
and GSTP1*C (Val105/Val114). The GSTP1*C haplotype, carrying both variant
alleles, has been associated with a 5.46-fold increased prostate cancer risk
compared to GSTP1*A. The two variants are separated by approximately 1 kb
with moderate linkage disequilibrium (D' approximately 0.48), so they
segregate partially independently.

GSTP1 also interacts with the other major glutathione S-transferase genes
-- GSTM1 and GSTT1 -- which can be completely deleted (null genotypes).
The combination of GSTM1 null, GSTT1 null, and GSTP1 Val105 creates a
severely compromised glutathione conjugation capacity. Studies have found
up to 6-8-fold increased risk for bladder cancer and other malignancies
when all three GST pathways are impaired simultaneously.