In type 2 diabetes, metformin treatment significantly decreased DNA methylation of metformin the transporter genes solute carrier family 22 member 1 (SLC22A1), solute carrier family 22 member 3 (SLC22A3), and solute carrier family 47 (multidrug and toxin extrusion), member 1 (MATE1) in the livers of patients; in the case of SLC22A1 and SLC22A3, reduced methylation was associated with less hyperglycemia and obesity [29]. This evidence concerns the gene SLC22A3 and type 2 diabetes mellitus.