Metformin suppresses pro-inflammatory cytokines in vitreous of diabetes patients and human retinal vascular endothelium

Abstract

Metformin is a traditional anti-hyperglycemic medication that has recently been shown to benefit vascular complications of diabetes via an anti-inflammatory mechanism other than glycemic control. This study aims to test the hypothesis that metformin suppresses diabetic retinopathy (DR) associated intraocular inflammation. Human vitreous from control and proliferative diabetic retinopathy (PDR) patients with or without long-term metformin treatment (> 5 years) were collected for multiple inflammatory cytokines measurements with a cytokine array kit. The vast majority of the measurable cytokines in PDR vitreous has a lower level in metformin group than non-metformin group. Although the p values are not significant due to a relatively small sample size and large deviations, the 95% confidence interval (CI) for the mean difference between the two groups shows some difference in the true values should not be neglected. Using quantitative ELISA, soluble intercellular adhesion molecule -1 (ICAM-1) and monocyte chemoattractant protein -1 (MCP-1) presented with significantly lower concentrations in metformin group versus non-metformin group. Metformin group also has significantly less up-regulated cytokines and diminished positive correlations among the cytokines when compared to non-metformin group. Possible role of AMP-activated protein kinase (AMPK) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in metformin’s anti-inflammatory effects were studied in human retinal vascular endothelial cells (hRVECs) cultured in normal glucose (NG) and high glucose (HG) conditions. Metformin inhibited HG-induced ICAM-1, IL-8, and MCP-1 via AMPK activation, whereas pharmacological AMPK inhibition had no effect on its inhibition of NF-κB p65, sICAM-1, and tumor necrosis factor-α (TNF-α). Metformin-induced suppression of the inflammatory cytokines could also be mediated through its direct inhibition of NF-κB, independent of AMPK pathway. This is a proof-of-concept study that found metformin treatment was associated with reduced inflammatory responses in vitreous of diabetes patients and retinal vascular endothelial cells, supporting the rationale for using metformin to treat DR at an early stage.

Diabetic retinopathy as the leading cause of blindness and early predictor of cascading complications—risks and mitigation

“…Among other effects, metformin is an AMPactivated protein kinase (AMPK) agonist, suggesting that AMPK-dependent signalling pathways are involved in the pathophysiology of DR [126]. Measurement of inflammatory cytokines in human vitreous from control individuals and patients with PDR with or without long-term metformin treatment (> 5 years) shows a decrease in PDR patients in metformin-treated compared to non-treated patients [127]. In the same study, metformin inhibited high glucose (HG)-induced ICAM-1, IL-8, and MCP-1 via AMPK activation in human retinal vascular endothelial cells (hRVECs) [127].…”

“…Measurement of inflammatory cytokines in human vitreous from control individuals and patients with PDR with or without long-term metformin treatment (> 5 years) shows a decrease in PDR patients in metformin-treated compared to non-treated patients [ 127 ]. In the same study, metformin inhibited high glucose (HG)–induced ICAM-1, IL-8, and MCP-1 via AMPK activation in human retinal vascular endothelial cells (hRVECs) [ 127 ]. On the other hand, inhibition of NF-κB p65, sICAM-1, and TNF-α by metformin was not dependent on the AMPK signalling pathway.…”

Association Between Oral Metformin Use and the Development of Age-Related Macular Degeneration in Diabetic Patients: A Systematic Review and Meta-Analysis

“…Apart from its antiglycemic effect, it was shown to possess antiaging properties. 4 In retinal tissues, metformin demonstrated antioxidative, 5 anti-inflammatory, 6 anti-angiogenic, 7 and pro-autophagic effects 8 mediated through activation of 5' adenosine monophosphate-activated protein kinase (AMPK). As the pathogenesis of AMD involves oxidative stress, 9 inflammation, 10 neovascularization, and autophagic dysfunction, 11 metformin may have potential in preventing or treating this sight-threatening disease.…”

Metformin therapy in pediatric type 2 diabetes mellitus and its comorbidities: A review

“…Metformin downregulates inflammation by inhibiting the NFϰB pathway and decreasing the secretion of inflammatory cytokines ( 93 , 94 ). It also affects the proportion of white blood cells by reducing the ratio of neutrophils to lymphocytes ( 93 ) and inhibits the differentiation of monocytes to macrophages ( 95 ).…”