SLC22A2 gene 808 G/T variant is related to plasma lactate concentration in Chinese type 2 diabetics treated with metformin

Abstract

Aim: To investigate the potential relationship between the SLC22A2 gene polymorphism and blood lactate concentration in Shanghai Hans suffering from type 2 diabetes mellitus (T2DM).

Methods: The SLC22A2 single nucleotide polymorphism (SNP) 808G/T was genotyped in 400 T2DM patients, including a metformin-treated group (n=200) and a non-metformin-treated group (n=200). Fasting plasma lactic acid levels were measured with an enzyme-electrode assay. Biochemical indexes, including plasma alanine aminotransferase (ALT), creatinine (Cr), and glycolated hemoglobin (HbA1c), were also measured.

Results: The fasting plasma lactate concentration in the metformin-treated group was significantly higher than that in the non-metformin-treated group (1.29+/-0.45 mmol/L vs 1.18+/-0.44 mmol/L, P=0.015). Additionally, the ratio of patients with hyperlactacidemia was 8% (16/200) for the metformin-treated group and 5.5% (11/200) for the non-metformin-treated group, with no lactic acidosis found in either group. The frequency of the SLC22A2 808G/T T allele was 12.9%. Patients with the mutant genotype (TT) had a higher blood lactate concentration in the metformin-treated group than those in the non-metformin-treated group (t=2.492, P=0.013). This trend was not observed in the GG and GT genotypes when compared with metformin-treated and non-metformin-treated groups. Patients with the mutant genotype (TT) in the metformin-treated group also had a higher incidence of hyperlactacidemia compared with the GG genotype (40.0% vs 6.9%, P=0.050) in the metformin-treated group and the GG (6.0%, P=0.042) or GT (4.3%, P=0.043) genotypes in the non-metformin-treated group. In the metformin-treated group, there were significant gender differences in lactate concentrations in the TT (2.18+/-0.15 vs 1.04+/-0.27 mmol/L, P=0.008) and GG genotypes (1.40+/-0.51 vs 1.19+/-0.35 mmol/L, P=0.004). The lactate levels of women with the TT genotype were the highest in the metformin-treated group, but differences in lactate levels among the genotypes were not observed in the non-metformin-treated group.

Conclusion: There is an 808G/T polymorphism in the SLC22A2 gene in Chinese Hans with T2DM. The 808G>T variance in the SLC22A2 gene can affect the plasma lactate level and the incidence of hyperlactacidemia in T2DM patients undergoing metformin therapy. Additionally, the female patients carrying the TT genotype are prone to lactatemia.

Figure 1

Representative patterns of electrophoresis of allele specific primer-polymerase chain reaction (ASP-PCR) products with different primers for determination of 808G/T genotypes of the SLC22A2 gene. When the PCR products were observed in the lanes of 808G primers and no PCR products were observed in lanes for 808T primers (359 bp and 360 bp, respectively) , the strain was diagnosed as wild-type (wt) (A). When the PCR products were observed in the lanes of 808G and 808T primers (359 bp and 360 bp, respectively), the strain was considered as heterozygote (A). When the PCR products were observed in the lanes of 808T and no PCR products were observed in lanes for 808G primers, the strain was diagnosed as mutant homozygotes. (B) Applying the clear genotype of 8 samples as control for each test.

Figure 2

Direct sequence results of sense strands of SLC22A2 genotypes of (A) wildtype (wt), (B) 808T, (C) 808G/T strains. In the strains with wt, the sense base at position 808 was G (A). In the strain with 808T mutation, the sense base at position 808 was T (B). In the strain with 808G/T, the sense bases at position 808 were G and T, respectively.

Figure 3

The plasma lactate levels of three genotypes in two groups with and without metformin treatment. By the method of analysis of variance of factorial design, there was no significant difference in the blood lactate levels of GG and GT genotypes in two groups (P=0.053, P=0.344). The plasma lactate level of metformin group carried TT genotype was higher obviously than that of non-metformin group with TT (t=2.492, P=0.013). Each column represents as mean±SEM. ^bP=0.013, compared with non-metformin group with TT genotype.

Figure 4

The plasma lactate levels of three genotypes in different genders. In 400 subjects, the blood lactate concentration in women carried GG and TT genotype of SLC22A2 gene was higher significantly than that of men, and the difference of lactate concentration in GT genotype was no significance by the analysis of variance of factorial design. ^bP=0.025, ^cP=0.001, compared to lactate levels of males.

Figure 5

The plasma lactate levels of three genotypes between different genders in metformin group. The blood lactate concentration in women carried GG and TT genotype of SLC22A2 gene was higher significantly than that of men. The blood lactate concentration in women carried TT genotype of SLC22A2 gene was higher significantly than those with GG or GT genotypes. ^cP=0.004, ^fP=0.008, compared to lactate levels of males; ^hP<0.05 (P=0.045 for GG genotype, P=0.041 for GT genotype) compared to lactate levels of females with TT genotype.