Increased metformin dosage suppresses pro-inflammatory cytokine levels in systemic circulation and might contribute to its beneficial effects.

Type 2 Diabetes Mellitus (T2DM) is a metabolic disorder, characterized by persistent elevation of blood glucose either due to insulin resistance or insulin insufficiency. Metformin is the recommended first choice of drug for the management of T2DM and is known to improve insulin sensitivity and prevents hyperglycemia by reducing chronic inflammation. T-helper type 1 (Th1) and type 17 (Th17) cells, are important pro-inflammatory CD4+ T cell subsets secreting TNF-α, and INF-γ (Th1), and interleukin 17 (Th17). These cytokines have been shown to play a crucial role in inflammation, insulin resistance, and the development of T2DM. Here, we explore the effect of different metformin dosages on pro-inflammatory cytokine (TNF-α, INF-γ, GM-CSF and IL-17) levels in systemic circulation among T2DM patients in Ghana, since inflammatory responses and cytokines play significant roles in the pathogenesis and progression of T2DM patients on metformin. Two hundred and nine (209) consenting T2DM patients receiving treatment at the Diabetic unit of the Komfo Anokye Teaching Hospital (KATH) in the Ashanti region of Ghana were recruited in a hospital-based cross-sectional study design. Blood samples were collected and serum obtained from each participant were analyzed for the concentrations of TNF-α, INF-γ, GM-CSF and IL-17 cytokine levels by solid-phase sandwich ELISA. We observed that participants on 3000 mg/day dose of metformin had significantly lower levels of TNF-α (p < .001) and IFN-γ (p = .014) compared to those on other dosages (1000 mg and 2000 mg/day). However, GM-CSF and IL-17 levels were not affected by increased metformin dosages. After adjusting for age, gender, dose and duration of metformin use, we observed that participants who took higher doses of metformin had significantly reduced levels of TNF-α (β = -0.0297, 95% CI = (-0.005 to -0.002) p < .001. Metformin dosage independently predicted reduced TNF-α levels with 14.4% variations in the metformin dosage levels. Increased metformin dosage suppresses TNF-α levels in systemic circulation and hence might contribute to its beneficial effects.