Introduction

One typical urinary condition is kidney stones. The development of kidney stones is a complicated and multifactorial condition that involves the interaction of environmental and genetic factors [1]. More and more evidence shows that inflammation, oxidation–antioxidation imbalance, angiogenesis, and other factors may play a key role in the occurrence and development of renal stones [2]. Some views suggest that the origin of calcium oxalate stone is closely related to the excessive production of ROS mediated by oxidative stress [3]. This may be due to excessive reactive oxygen species that lead to the transformation of epithelial cells into osteoblasts and the remodeling of the extracellular matrix (ECM), which promotes the deposition of calcium phosphate [4] on the basement membrane of renal tubules or blood vessels. Continuous exposure of renal epithelial cells to high levels of oxalate and calcium oxalate crystals can lead to cell damage and oxidative stress, such as increased free radical production, increased lipid peroxidation, and decreased cellular antioxidant status [5]. Studies have shown that during the formation of calcium oxalate stone, 8-hydroxydeoxyguanosine (8-OHdG) and malondialdehyde (MDA) increased, while total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and glutathione (GSH) decreased, which confirmed the existence of DNA damage and lipid peroxidation caused by oxidative stress [6]. In addition, a number of studies have also confirmed that increasing antioxidants (SOD, GSH, and catalase) can effectively protect renal epithelial cells from calcium oxalate stones [5, 7, 8].

In particular, glutathione S-transferase (GSTs) helps maintain intracellular redox balance and protect DNA from damage by catalyzing the binding of reduced glutathione to ROS, carcinogens, and their metabolites. There are five known types of GSTs, including alpha, u, theta, pi, and zeta in humans [9]. The polymorphism of their alleles will result in differences in enzyme activity [9,10,11]. The GSTP1-I105V polymorphism is caused by the A-G substitution at the base binding site of the exon, resulting in the transformation of the 105th amino acid of the protein–peptide chain from ATC isoleucine (Ile) to GTC valine (Va1) [12]. This change will reduce the activity and thermal stability of the enzyme. Allele deletion is the main cause of GSTT1 and GSTM1 gene polymorphism, and the genetic deletion of this gene will lead to the loss of enzyme activity phenotype [13]. The DNA changes in these individuals are called single-nucleotide polymorphisms (SNPs). One of the reasons why SNPs are not uncommon in human individuals is the loss of gene methylation. In particular, GSTM1 is considered to be a potential candidate regulator of renal vascular injury in recent years, so it is defined as an important factor in the progression of renal disease [14]. Previous studies have shown that the absence of GSTM1 will lead to an increase in oxidative stress, inflammation, and injury in the kidney, suggesting that other GST pathways may lack the ability to combat oxidative stress in renal vessels [15]. Therefore, we speculate that GSTM1 may play an important role in the pathogenesis of renal calculi by regulating oxidative stress.

The current work aimed to determine whether GSTM1 gene polymorphism is associated with the occurrence of renal calculi.

Methods

Study subjects

A total of 159 patients with kidney stones were included in the case group, in accordance with the European Association of Urology (EAU) urolithiasis guidelines (updated 2022) (https://uroweb.org/guidelines/urolithiasis). All patients required PCNL therapy, and calcium oxalate was the main finding in the postoperative stone analysis. The control group included 200 healthy individuals with no history of urolithiasis and no family history of urolithiasis.

Exclusion standards such as 1. poor diet, excess weight, hyperuricemia, dyslipidemia, and parathyroid dysfunction; 2. metabolic syndrome, high blood pressure, diabetes, gout, severe respiratory conditions, chronic heart failure, chronic kidney illness, severe gastrointestinal conditions, and hyperthyroidism or hypothyroidism; and 3. patients who recently underwent blood transfusion therapy, have a history of urolithiasis, or have urolithiasis in their family should be properly watched.

Using a questionnaire, clinical information such as age, prior medical history, family history, height, weight, and blood pressure was gathered. Using computed tomography or ultrasonography, kidney stones were identified (CT). Creatinine (Cr), uric acid (UA), calcium (Ca), serum triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and fasting blood glucose were all measured in peripheral venous blood (FBG). For the urine creatinine (Ucr) test, urine was used. Statistics were examined for sex, age, blood creatinine, uric acid, calcium, and urine creatinine.

Detection of gene polymorphism

GSTM1 genotypes were detected by multiplex polymerase chain reaction (PCR) using primer sequences published by GENEWIZ (Suzhou) Biotechnology, as mentioned earlier [16]. The primers and products were summarized as follows.

The primer used was GSTM1 (positive, 5′-GAACTCCCTGAAAAGCTAAAGC-3′; reverse, 5′-GTTGGGCTCAAATATACGGTGG-3′), and the PCR product of the GSTM1 gene was a fragment of 215 bp. The marker used was DNA Ladder (Solarbio Science & Technology, Beijing).

NO, MDA, 8-OHdG, and TAC detection

Nitric oxide (NO), total antioxidant capacity (T-AOC), 8-OHdG, and malondialdehyde (MDA) levels in plasma were measured using colorimetric techniques and a spectrophotometer (BioMate 5, Thermo Electron Corporation, Rochester, NY, USA). The assays were carried out using the assay kits acquired from the Nanjing Jiancheng Institute of Bioengineering in accordance with the manufacturer’s instructions (Nanjing, China).

The statistical analysis was carried out using SPSS 22.0 (SPSS, Inc., Chicago, Illinois, USA). All data were expressed as mean ± standard deviation (mean ± SD), an independent-samples t-test was used to compare the two groups of data, the chi-square goodness-of-fit test was used to verify the Hardy–Weinberg balance, and multiple linear regression analysis was used to analyze the correlation. P < 0.05 was considered to be statistically significant.

Results

Age and sex distribution between the case group and control group did not change (P > 0.05). The case group’s levels of Cr, Ucr, Ca, UA, UA/Cr, and Ca/Cr were considerably greater than those in the control group (P < 0.001), suggesting that the case group may have had a more pronounced kidney injury (Table 1).

Table 1 Clinical characteristics of the study subjects
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The results in Table 2 showed that GSTM1 was positively correlated with renal calcium oxalate. The susceptibility to stone in the GSTM1 null type increased by 2.213 times, and its distribution frequency in the case group and the control group was 60.31% and 40.78%, respectively. The patients in the study underwent the Hardy–Weinberg genetic equilibrium test of genotype distribution, and no differences were discovered between the case group and the control group (P = 0.23 and P = 0.09, respectively) (Table 3).

Table 2 Frequency distribution of genetic polymorphism of GSTM1 gene in the normal control group and the case group
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Table 3 Hardy–Weinberg genetic equilibrium test for the distribution of GSTM1 genotypes
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There were significant changes in 8-OHdG (P < 0.001), MDA (P < 0.001), NO (P < 0.001), and T-AOC (P < 0.001) between the control group and the case group. In the case group, oxidative stress appeared to be more severe. There were no significant changes in MDA (P = 0.12) or T-AOC (P = 0.053) when the GSTM1 genotypes of the case group were compared, although there were significant differences in 8-OHdG (P < 0.001) and NO (P < 0.05). According to this, the GSTM1 null group was more severely affected by oxidative stress (Table 4).

Table 4 Comparison of 8-OHdG, MDA, NO, and T-AOC
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The GSTM1 null genotype was favorably connected with 8-OHdG (P < 0.001) and NO (P < 0.001), according to multivariate regression analysis, but it was not significantly correlated with MDA (P = 0.102), T-AOC (P = 0.053), Cr (P = 0.31), Ucr (P = 0.882), UA (P = 0.926), or Ca (P = 0.709). It appeared that the GSTM1 null gene had no discernible impact on the level of antioxidants in general (Table 5).

Table 5 Multiple linear regression analysis of GSTM1 null genotype in the case group
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Discussion

The prevalence of kidney stones is significant and has been rising for several decades [11]. About 80% of kidney stones are calcium oxalate stones, and the mechanism involves the interaction of genes and the environment [17]. Oxidative stress enhances the adhesion and deposition of calcium oxalate on the surface of the renal nipple and causes inflammation and tissue damage, according to in vitro and animal model studies. They encourage one another and ultimately result in the production of kidney stones [18,19,20]. Overexposure to ROS triggers immune cell activation and damages renal tubular epithelial cells. More crystals remain in the kidney, resulting in stone formation, as a result of the injured cells’ increased expression of adhesion molecules. The mitogen-activated protein kinase (MAPK), c-Jun, and nuclear factor kappa B (NF-κB) signal pathways interact throughout this process [21,22,23]. By preventing the generation and activation of reactive oxygen species, the crystal deposition of inflammatory bodies can be decreased in the investigation of an animal model of calcium oxalate stones. Our analysis found the same pattern. Patients with kidney stones have higher NO and lower T-AOC compared with healthy individuals, as well as a higher overall oxidative stress burden, which may indicate more cell damage.

The enzyme glutathione S-transferase (GST) helps build the antioxidant defense system and keeps cells’ redox equilibrium in check [24, 25]. Previous research has demonstrated that the GST gene’s polymorphism affects the structure and activity of GST and alters the body’s ability to produce antioxidants and OS levels [26, 27]. It has been demonstrated that uric acid helps calcium oxalate crystals form while calcium oxalate stones are developing [28]. The free radicals OH-, ONOO, and others could interact with uric acid. The other radicals they creates, which has potent oxidizing capabilities, exacerbates cell oxidative damage [29]. OS damages the renal tubular epithelial cells and increases the likelihood of crystal adhesion [30]. In our investigation, patients in the case group who had the GSTM1 null genotype displayed a higher oxidative stress burden than those who had the GSTM1 genotype. 8-OHdG and NO were linked with the GSTM1 null genotype, indicating that patients who have this genotype may have more severe oxidative damage. We hypothesize that the GSTM1 null genotype may influence the resistance to oxidative stress of renal tubular epithelial cells. More crystals are formed as a result of the weak antioxidant capacity, which may be connected to the development of stones. Although T-AOC is lower in kidney stone patients than in healthy individuals, there is no distinction in T-AOC between the GSTM1 null and GSTM1 genotypes in the case group. Through correlation analysis, we discovered that the GSTM1 null genotype did not correlate with T-AOC. It might have something to do with the antioxidant system’s complicated makeup. SOD, GPX, GST, and other exogenous materials such as vitamin C and vitamin E are just a few of the enzymes that make up the human antioxidant system. The overall antioxidant effect may not be significantly impacted by the alteration of certain components. The GSTM1 null is only a small portion of the overall mechanism that results in the redox imbalance during stone formation. The entire mechanism of kidney stone production cannot be satisfactorily characterized because of the limitations of case–control research. Second, all of the case group participants in our study require surgical intervention. More mechanism investigations are required in future to prove that long-term stone stimulation cannot accurately reflect the small changes in oxidative stress at the early stage of stone formation.

Conclusion

The development of kidney calcium oxalate stones is closely tied to oxidative stress. Compared to healthy persons, patients with calcium oxalate stones displayed a higher load of oxidative stress. One of the major risk factors for kidney calcium oxalate stone development is oxidative stress, which renal tubular epithelial cells may be more susceptible to as a result of the reduction in GSTM1 enzyme activity brought on by GSTM1 null.