This study included 177 North Indian T2DM patients divided into two groups, responders (n = 127) and non-responders (n = 50). The responders were further subcategorized as T2DM patients on monotherapy (n = 55) and combination therapy (n = 72) of metformin. All included patients showed good knowledge and compliance to their therapy regimen and medication dosing. The groups did not differ significantly in age 49.64 ± 10.12; 49.89 ± 12.56 in the responder group (monotherapy and combination therapy respectively) and 50.66 ± 10.73 in the non-responder group (p = 0.891). Patient’s characteristics and demographics were all found to be statistically insignificant between the two groups. However, FBS, HbA1C and TG levels were significantly lower in the responders group compared to the non-responder group and nearly significant difference was observed in BMI too among the groups.
OCT1 (rs628031) polymorphism analysis
The frequencies of aa, AA and Aa genotypes were 10.91%, 72.73%, and 16.36% in monotherapy responders while they were 6%, 72% and 22% in non-responders (p = 0.369, 0.934 and 0.463 respectively). In responders on combination therapy, the frequencies of aa, AA and Aa genotypes were 4.17%; 70.83%; 25% respectively with no significant observed with frequencies observed in non-responders (p = 0.104, 0.889 and 0.702 respectively). The frequencies of a and A alleles in monotherapy responders and non-responders were 19.09%, 80.91 (p = 0.514) and 17%’ 83% (p = 0.395) respectively. Whereas, the frequencies of a and A alleles in combination therapy responders were 16.67% and 83.33% (p = 0.945) respectively.
The frequency of occurrence of mutant aa genotype and a allele was higher in monotherapy responders than non-responders but the difference was found to be non-significant (p > 0.05). On the other hand in case of combination therapy the prevalence of Aa genotype was marginally higher in responders than non-responders but again the difference was found to be non-significant (p > 0.05).
OCT3 (rs2292334) polymorphism analysis
The frequencies of AA, GG and AG genotypes were 40%, 34.55%, and 25.45% in monotherapy responders while they were 16%, 46% and 38% in non-responders (p = 0.007, 0.231 and 0.167 respectively). In responders on combination therapy, the frequencies of AA, GG and AG genotypes were 31.94%; 38.89%; 29.17% respectively with no significant observed with frequencies observed in non-responders (p = 0.047, 0.434 and 0.307 respectively). The frequencies of A and G alleles in monotherapy responders and non-responders were 52.73%, 35% (p = 0.01) and 47.27%’ 65% (p = 0.01) respectively. Whereas, the frequencies of A and G alleles in combination therapy responders were 46.53% and 53.47% (p = 0.073) respectively.
In case of patients on monotherapy, frequency of occurrence of AA genotype and A allele was significantly higher in responders than non-responders (p = 0.007 and p = 0.01 respectively). On the other hand frequency of occurrence of G allele was significantly lower in responders than non-responders (p = 0.01).
In case of patients on combination therapy, the prevalence of AA genotype was again significantly higher in responders than non-responders (p = 0.047) and the frequency of A and G allele were different between the two groups but the difference was found to be non-significant (p = 0.073).
Detailed results along with the genotype and allele frequencies for responders and non-responders are shown in Tables 4 and 5.
Table 4
Allele frequencies and genotype distribution of OCT1 (rs628031) and OCT3 (rs2292334) polymorphism in Metformin monotherapy responders and non-responders
Gene | Genotype/Alleles | Responders (n = 55) | Non-Responders (n = 50) | OR (CI) | P-Value |
Count | % | Count | % |
OCT1 (rs628031) | aa | 6 | 10.91 | 3 | 6 | 0.52 (0.12–2.21) | 0.369 |
| AA | 40 | 72.73 | 36 | 72 | 0.96 (0.41–2.27) | 0.934 |
| Aa | 9 | 16.36 | 11 | 22 | 1.44 (0.54–3.84) | 0.463 |
| a | 21 | 19.09 | 17 | 17 | 0.79 (0.39–1.61) | 0.514 |
| A | 89 | 80.91 | 83 | 83 | 0.71 (0.33–1.56) | 0.395 |
OCT3 (rs2292334) | AA | 22 | 40 | 8 | 16 | 0.29(0.11–0.72) | 0.007* |
| GG | 19 | 34.55 | 23 | 46 | 1.61 (0.74–3.54) | 0.231 |
| AG | 14 | 25.45 | 19 | 38 | 1.79(0.78–4.13) | 0.167 |
| A | 58 | 52.73 | 35 | 35 | 0.48(0.28–0.84) | 0.010* |
| G | 52 | 47.27 | 65 | 65 | 2.07(1.19–3.61) | 0.010* |
*Statistically significant |
Table 5
Allele frequencies and genotype distribution of OCT1 (rs628031) and OCT3 (rs2292334) polymorphism in Metformin combination therapy responders and non-responders
Gene | Genotype/Alleles | Responders (n = 72) | Non-Responders (n = 50) | OR (CI) | P-Value |
Count | % | Count | % |
OCT1 (rs628031) | aa | 3 | 4.17 | 3 | 6 | 3.14 (0.75–13.19) | 0.104 |
| AA | 51 | 70.83 | 36 | 72 | 1.06 (0.48–2.36) | 0.889 |
| Aa | 18 | 25 | 11 | 22 | 0.85 (0.36–1.99) | 0.702 |
| a | 24 | 16.67 | 17 | 17 | 1.02 (0.52–2.02) | 0.945 |
| A | 120 | 83.33 | 83 | 83 | 0.98(0.49–1.93) | 0.945 |
OCT3 (rs2292334) | AA | 23 | 31.94 | 8 | 16 | 0.41(0.16-1.0) | 0.047* |
| GG | 28 | 38.89 | 23 | 46 | 1.34(0.64–2.78) | 0.434 |
| AG | 21 | 29.17 | 19 | 38 | 1.49(0.69–3.2) | 0.307 |
| A | 67 | 46.53 | 35 | 35 | 0.62(0.37–1.05) | 0.073 |
| G | 77 | 53.47 | 65 | 65 | 1.62(0.96–2.73) | 0.073 |
*Statistically significant |