Age-related macular degeneration and genetic polymorphisms of glutathione S-transferases M1 (GSTM1) and T1 (GSTT1)

The Role of Glutathione in Age-Related Macular Degeneration (AMD)

Age-related macular degeneration (AMD) is a chronic disease that usually develops in older people. Pathogenetic changes in this disease include anatomical and functional complexes. Harmful factors damage the retina and macula. These changes may lead to partial or total loss of vision. The disease can occur in two clinical forms: dry (the progression is slow and gentle) and exudative (wet-progression is acute and severe), which usually starts in the dry form; however, the coexistence of both forms is possible. The etiology of AMD is not fully understood, and the precise mechanisms of the development of this illness are still unknown. Extensive genetic studies have shown that AMD is a multi-factorial disease and that genetic determinants, along with external and internal environmental and metabolic-functional factors, are important risk factors. This article reviews the role of glutathione (GSH) enzymes engaged in maintaining the reduced form and polymorphism in glutathione S-transferase theta-1 (GSTT1) and glutathione S-transferase mu-1 (GSTM1) in the development of AMD. We only chose papers that confirmed the influence of the parameters on the development of AMD. Because GSH is the most important antioxidant in the eye, it is important to know the influence of the enzymes and genetic background to ensure an optimal level of glutathione concentration. Numerous studies have been conducted on how the glutathione system works till today. This paper presents the current state of knowledge about the changes in GSH, GST, GR, and GPx in AMD. GST studies clearly show increased activity in ill people, but for GPx, the results relating to activity are not so clear. Depending on the research, the results also suggest higher and lower GPx activity in patients with AMD. The analysis of polymorphisms in GST genes confirmed that mutations lead to weaker antioxidant barriers and may contribute to the development of AMD; unfortunately, a meta-analysis and some research did not confirm that connection. Unspecific results of many of the parameters that make up the glutathione system show many unknowns. It is so important to conduct further research to understand the exact mechanism of defense functions of glutathione against oxidative stress in the human eye.

Association of GSTM1, GSTT1, and GSTP1 Ile105Val polymorphisms with risk of age-related macular degeneration: a meta-analysis

BACKGROUND

This study determined to evaluate the association between glutathione S-transferase (GST) polymorphisms, namely, GSTM1 (rs1183423000, presence/absence), GSTT1 (rs1601993659, presence/absence), and GSTP1 Ile105Val (rs1695, A>G) polymorphisms, and AMD risk.

METHODS

We searched PubMed, Embase, and Web of Science databases from January 2000 to June 2021. The odds ratio (OR) and 95% confidence interval (95% CI) were used as effect sizes. Heterogeneity was assessed using the heterogeneity metric I².

RESULTS

Five relevant studies involving 875 patients with AMD and 966 healthy controls were included in this meta-analysis, four studies concerning GSTM1 null polymorphism, four studies regarding GSTT1 null polymorphism, and four studies on GSTP1 Ile105Val polymorphism. The GSTM1 null polymorphism, GSTT1 null polymorphism and GSTP1 Ile105Val polymorphism were not significantly associated with AMD risk (OR 1.13, 95% CI 0.73-1.75, p = 0.59; OR 1.05, 95% CI 0.81-1.36, p = 0.69; OR 1.20, 95% CI 0.97-1.47, p = 0.09, respectively). There was no association between the combined GSTM1 null genotype and GSTT1 null genotype and AMD risk (OR 1.16, 95% CI 0.42-3.17, p = 0.77). Subgroup analyses revealed that the GSTM1 null genotype was associated with an increased risk of AMD in the Turkish population (OR 1.67, 95% CI 1.13-2.47, p = 0.01) and the GSTM1 null genotype was associated with a decreased incidence of non-exudative AMD (OR 0.72, 95% CI 0.52-0.99, p = 0.01). There was no obvious risk of publication bias found.

CONCLUSIONS

This meta-analysis indicated that there were no significant associations between GSTM1, GSTT1, and GSTP1 Ile105Val polymorphisms and AMD risk.

Evaluation of associations of GSTM1/GSTT1 null genotypes with the susceptibility to age-related macular degeneration: A meta-analysis

Background: The relationship between glutathione S-transferase M1 (GSTM1) and T1 (GSTT1) null genotypes (homozygotes for the null alleles) and the susceptibility to age-related macular degeneration (ARMD) have been reported and revealed inconsistent results. Therefore, the current meta-analysis was carried out. Methods: Eligible published articles (before December 2020) were found by searching 8 databases. The data was extracted from articles. The heterogeneity across studies was estimated using Q and I 2 statistics and the odds ratios (ORs) and its 95 % confidence intervals (95 % CI) were estimated. Results: In total, 6 independent studies including 1089 participants (634 controls and 455 patients) were used in the current study. There was no heterogeneity between studies for both polymorphisms. Statistical analysis showed that the null genotypes of the GSTM1 (OR = 1.18, 95 % CI: 0.91 - 1.53, p = 0.191) and GSTT1 (OR = 0.84, 95 % CI: 0.60 - 1.18, p = 0.328) loci were not correlated with the susceptibility to ARMD. Conclusion: The GSTT1 and GSTM1 genetic polymorphisms did not associated with the risk of ARMD in Caucasian populations.

Association of glutathione S-transferase M1 and T1 polymorphisms and temperament

Mizaj (Temperament) is one of the basic concepts of Iranian Traditional Medicine (ITM), which has great importance in diagnosis and treatment of diseases, as well as maintaining the ideal healthy state of an individual. However, very little is known about the biological mechanisms of mizaj dependence treatment in practical ITM. This study was aimed to evaluate any association between the mizaj and glutathione S-transferase M1 (GSTM1) and T1 (GSTT1) polymorphisms in healthy people. The samples included 247 healthy males from Fars province, southern Iran. The mizaj was determined using a self-reported mizaj identification scale. Subjects with equilibrium or any of four simple mizajes (warm, cold, moist, and dry) were included in the study. The GSTM1 and GSTT1 genotypes were determined using a polymerase chain reaction (PCR)-based method. No any differences in the frequency of GSTM1/T1 polymorphism between equilibrium and each of other mizaj groups were found. However, when equilibrium, moist, and dry groups were pooled and as a "medium warmness" group were compared to the warm group, the frequency of GSTT1-null in the warm group was significantly higher compare to that in the medium warmness group. Also, the combination genotypes of GSTM1 and GSTT1 was associated with the warmness; that is, individuals with combination of GSTM1 positive and GSTT1 null were more susceptible to have a warm temperament. This study indicated that the mizaj could be affected by GSTM1/T1 genes, although further research with larger samples is needed to reach full conclusions.

Is there association between Glutathione S Transferases polymorphisms and cataract risk: a meta-analysis?

Background

Glutathione S transferase (GST) polymorphisms have been considered as risk factors for age-related cataracts, but the results remain controversial. In this study, we have performed a meta-analysis to evaluate the association between polymorphisms of GSTM1 and GSTT1 and cataract risk.

Methods

Published literature from PubMed and other databases were retrieved. The case–control studies regarding the association between GSTM1 or GSTT1 polymorphism and cataract risk were included. Pooled odds ratio (OR) and 95 % confidence interval (CI) were calculated using random- or fixed-effects model.

Results

Fifteen studies on GSTM1 (3,065 patients and 2,105 controls), and nine studies on GSTT1 (2,374 patients and 1,544 controls) were included. By pooling all the studies, GSTM1 null polymorphism was not associated with cataract risk, and this negative association maintained in subgroup analyses. However, GSTT1 null polymorphism was significantly associated with increased risk of posterior subcapsular (OR, 1.42; 95 % CI, 1.04–1.94) but not other subtypes of cataract. Stratified analyses demonstrated an association of GSTT1 null genotype with increased risk of cataract in Asian (OR, 1.44; 95 % CI, 1.14–1.83) but not Caucasian populations. In addition, seven pooled studies showed no association of cataract risk with the combined GSTM1 and GSTT1 null genotypes.

Conclusions

This meta-analysis suggests that GSTT1 null polymorphism is associated with increased risk of posterior subcapsular cataract. Given the limited sample size, the association between GSTT1 null polymorphism and cataract risk in Asian awaits further investigation.

Impact of sodium arsenite on chromosomal aberrations with respect to polymorphisms of detoxification and DNA repair genes

Arsenic compounds can increase production of reactive oxygen species. Reactive oxygen species can induce double-strand breaks in DNA, which is a cause of chromosome aberrations (CAs). This study was conducted to determine the association between arsenic exposure and polymorphisms of genes involved in detoxification (glutathione S-transferase T1 [GSTT1], glutathione S-transferase M1 [GSTM1], glutathione S-transferase O2 [GSTO2], catalase [CAT], and NAD(P)H quinone oxidoreductase1 [NQO1]) as well as nonhomologous end joining DNA repair genes (XRCC4, XRCC5, and XRCC6) with induction of chromosomal aberrations. The participants consisted of 123 healthy males who were genotyped using polymerase chain reaction-based methods. Primary cultures of whole blood were treated with sodium arsenite (NaAsO(2); iAs(III); at final concentration 1 µmol/L), mitomycin C (at final concentration 60 ηg/mL; as positive control), or untreated. For each culture, mitotic index (MI), chromatid breaks (CBs), CAs, and total percentage of aberrant cells were determined. The levels of CB and percentage of aberrant cells were significantly higher in the TT genotype of CAT (C-262T polymorphism) than the CC genotype. The CB value in samples with GSTM1 active genotype was significantly higher than the null genotype. The MI in samples with TT genotype of NQO1 (C609T polymorphism) was significantly higher than MI in samples having CC and CT genotypes. There was no association between MI, CB, CA, and percentage of aberrant cells and polymorphisms of XRCC4, XRCC5, and XRCC6.

Are glutathione S-transferase polymorphisms (GSTM1, GSTT1) associated with primary open angle glaucoma? A meta-analysis

BACKGROUND

Glutathione S-transferase (GST) variants have been considered as risk factors for the pathogenesis of primary open angle glaucoma (POAG). However, the results have been inconsistent. In this study, we performed a meta-analysis to assess the association between GSTM1 and GSTT1 null genotypes and the risk for POAG.

METHODS

Published literature from PubMed and EMBASE databases was retrieved. All studies evaluating the association between GSTM1/GSTT1 variants and POAG were included. Pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using fixed- or random-effects model.

RESULTS

14 studies (1711 POAG cases and 1537 controls) were included in the meta-analysis of GSTM1 genotypes and 10 studies (1306 POAG cases and 1114 controls) were included in the meta-analysis of GSTT1 genotypes. The overall result showed that the association between GSTM1 and GSTT1 null genotypes and risk for POAG was not statistically significant (GSTM1: OR=1.19, 95% CI=0.82-1.73, p=0.361; GSTT1: OR=1.26, 95% CI=0.77-2.06, p=0.365). The results by ethnicity showed that the association between the GSTM1 null genotype and risk for POAG is statistically significant in East Asians (OR=1.41, 95% CI=1.04-1.90, p=0.026), but not in Caucasians (OR=1.13, 95% CI=0.69-1.84, p=0.638) and Latin-American (OR=1.09, 95% CI=0.62-1.92, p=0.767). In addition, there was no significant association of GSTT1 null genotype with risk for POAG in either ethnic population.

CONCLUSIONS

The present meta-analysis suggested that there might be a significant association of GSTM1 null genotype with POAG risk in East Asians.

Environmental light and endogenous antioxidants as the main determinants of non-cancer ocular diseases

The human eye is constantly exposed to sunlight and artificial lighting. Exogenous sources of reactive oxygen species (ROS) such as UV light, visible light, ionizing radiation, chemotherapeutics, and environmental toxins contribute to oxidative damage in ocular tissues. Long-term exposure to these insults places the aging eye at considerable risk for pathological consequences of oxidative stress. Furthermore, in eye tissues, mitochondria are an important endogenous source of ROS. Over time, all ocular structures, from the tear film to the retina, undergo oxidative stress, and therefore, the antioxidant defenses of each tissue assume the role of a safeguard against degenerative ocular pathologies. The ocular surface and cornea protect the other ocular tissues and are significantly exposed to oxidative stress of environmental origin. Overwhelming of antioxidant defenses in these tissues clinically manifests as pathologies including pterygium, corneal dystrophies, and endothelial Fuch's dystrophy. The crystalline lens is highly susceptible to oxidative damage in aging because its cells and their intracellular proteins are not turned over or replaced, thus providing the basis for cataractogenesis. The trabecular meshwork, which is the anterior chamber tissue devoted to aqueous humor drainage, has a particular susceptibility to mitochondrial oxidative injury that affects its endothelium and leads to an intraocular pressure increase that marks the beginning of glaucoma. Photo-oxidative stress can cause acute or chronic retinal damage. The pathogenesis of age-related macular degeneration involves oxidative stress and death of the retinal pigment epithelium followed by death of the overlying photoreceptors. Accordingly, converging evidence indicates that mutagenic mechanisms of environmental and endogenous sources play a fundamental pathogenic role in degenerative eye diseases.

Association of glutathione S transferases polymorphisms with glaucoma: a meta-analysis

Background

Glutathione S transferase (GST) polymorphisms have been considered risk factors for the development of glaucoma, including primary open angle glaucoma (POAG) and other types of glaucoma. However, the results remain controversial. In this study, we have conducted a meta-analysis to assess the association between polymorphisms of GSTM1, GSTT1 and GSTP1 and glaucoma risk.

Methods

Published literature from PubMed and other databases were retrieved. All studies evaluating the association between GSTM1, GSTT1 and GSTP1 polymorphisms and glaucoma risk were included. Pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using random- or fixed-effects model.

Results

Twelve studies on GSTM1 (1109 cases and 844 controls), ten studies on GSTT1 (709 cases and 664 controls) and four studies on GSTP1 (543 cases and 511 controls) were included. By pooling all the studies, either GSTM1 or GSTT1 null polymorphism was not associated with a POAG risk, and this negative association maintained in Caucasian. The GSTP1 Ile 105 Val polymorphism was significantly correlated with increased POAG risk among Caucasian in a recessive model (Val/Val vs. Ile/Ile+Ile/Val: OR, 1.62, 95%CI: 1.00–2.61). Interestingly, increased glaucoma risk was associated with the combined GSTM1 and GSTT1 null genotypes (OR, 2.20; 95% CI, 1.47–3.31), and with the combined GSTM1 null and GSTP1 Val genotypes (OR, 1.86; 95% CI, 1.15–3.01).

Conclusions

This meta-analysis suggests that combinations of GST polymorphisms are associated with glaucoma risk. Given the limited sample size, the associations between single GST polymorphism and glaucoma risk await further investigation.

Association between exudative age-related macular degeneration and the G6721T polymorphism of XRCC7 in outdoor subjects

PURPOSE

To investigate whether the G6721T polymorphism (rs.7003908) of the non-homologous end-joining DNA repair XRCC7 gene contributes to the development of exudative age-related macular degeneration (ARMD).

METHODS

The present case-control study consisted of 111 patients with exudative ARMD and 112 sex frequency-matched healthy controls that were randomly selected from unrelated volunteers in the same clinic. Genotypes were determined by the Restriction Fragment Length Polymorphism (PCR-RFLP) based method. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for ARMD risk associated with polymorphism of XRCC7. In all analysis the GG genotype was considered to be the reference genotype.

RESULTS

There was no significant association between genotypes of XRCC7 and susceptibility to ARMD. Considering the significant difference in age distribution between cases and controls, age was used as a covariate in further analysis. After ORs were adjusted for age, the same result was observed. In the next step we stratified our subjects into outdoor and indoor groups according to their job titles. The outdoor and indoor patients were occupationally exposed to sunlight and not exposed to sunlight, respectively. Our present study showed that among indoor subjects there was no association between XRCC7 polymorphism and susceptibility to ARMD. However, among outdoor subjects, the GT + TT genotypes compared to the GG genotype increased the risk of ARMD (OR, 3.13; 95% CI, 1.04-9.39; p = 0.042).

CONCLUSIONS

Our study revealed that the T allele of the G6721T polymorphism of XRCC7 increased the risk of ARMD among outdoor subjects.