Protective Effects of Imeglimin and Metformin Combination Therapy on β-Cells in db/db Male Mice

Imeglimin modulates mitochondria biology and facilitates mitokine secretion in 3T3-L1 adipocytes

AIMS

Imeglimin, a novel antidiabetic drug, has recently been reported to affect pancreatic β-cells and hepatocytes. Adipose tissue plays a crucial role in systemic metabolism. However, its effect on adipocytes remains unexplored. Herein, we investigated the effects of imeglimin on adipocytes, particularly in the mitochondria.

MAIN METHODS

The 3T3-L1 adipocytes were treated with imeglimin. Mitochondrial respiratory complex I activity and NAD+, NADH, and AMP levels were measured. Protein expression levels were determined by western blotting, mitochondrial DNA and mRNA expression levels were determined using quantitative polymerase chain reaction, and secreted adipocytokine and mitokine levels were determined using adipokine array and enzyme-linked immunosorbent assay.

KEY FINDINGS

Imeglimin inhibited complex I activity, decreased the NAD+/NADH ratio, and increased AMP levels, which were associated with the enhanced phosphorylation of AMP-activated protein kinase. In addition, imeglimin increased the mitochondrial DNA content and levels of mitochondrial transcription factor A and peroxisome proliferator-activated receptor-γ coactivator 1-α mRNA, which were abolished by Ly294002, a phosphoinositide 3-kinase inhibitor. Furthermore, imeglimin facilitated the expression levels of markers of the mitochondrial unfolded protein response, and the gene expression and secretion of two mitokines, fibroblast growth factor 21 and growth differentiation factor 15. The production of both mitokines was transcriptionally regulated and abolished by phosphoinositide 3-kinase and Akt inhibitors.

SIGNIFICANCE

Imeglimin modulates mitochondrial biology in adipocytes and may exert a mitohormetic effect through mitokine secretion.

Protective effects of imeglimin on the development of atherosclerosis in ApoE KO mice treated with STZ

BACKGROUND

Imeglimin is a new anti-diabetic drug which promotes insulin secretion from pancreatic β-cells and reduces insulin resistance in insulin target tissues. However, there have been no reports examining the possible anti-atherosclerotic effects of imeglimin. In this study, we investigated the possible anti-atherosclerotic effects of imeglimin using atherosclerosis model ApoE KO mice treated with streptozotocin (STZ).

METHODS

ApoE KO mice were divided into three groups: the first group was a normoglycemic group without injecting STZ (non-DM group, n = 10). In the second group, mice were injected with STZ and treated with 0.5% carboxymethyl cellulose (CMC) (control group, n = 12). In the third group, mice were injected with STZ and treated with imeglimin (200 mg/kg, twice daily oral gavage, n = 12). We observed the mice in the three groups from 10 to 18 weeks of age. Plaque formation in aortic arch and expression levels of various vascular factors in abdominal aorta were evaluated for each group.

RESULTS

Imeglimin showed favorable effects on the development of plaque formation in the aortic arch in STZ-induced hyperglycemic ApoE KO mice which was independent of glycemic and lipid control. Migration and proliferation of vascular smooth muscle cells and infiltration of macrophage were observed in atherosclerotic lesions in STZ-induced hyperglycemic ApoE KO mice, however, which were markedly reduced by imeglimin treatment. In addition, imeglimin reduced oxidative stress, inflammation and inflammasome in hyperglycemic ApoE KO mice. Expression levels of macrophage makers were also significantly reduced by imeglimin treatment.

CONCLUSIONS

Imeglimin exerts favorable effects on the development of plaque formation and progression of atherosclerosis.

Imeglimin mitigates the accumulation of dysfunctional mitochondria to restore insulin secretion and suppress apoptosis of pancreatic β-cells from db/db mice

Mitochondrial dysfunction in pancreatic β-cells leads to impaired glucose-stimulated insulin secretion (GSIS) and type 2 diabetes (T2D), highlighting the importance of autophagic elimination of dysfunctional mitochondria (mitophagy) in mitochondrial quality control (mQC). Imeglimin, a new oral anti-diabetic drug that improves hyperglycemia and GSIS, may enhance mitochondrial activity. However, chronic imeglimin treatment's effects on mQC in diabetic β-cells are unknown. Here, we compared imeglimin, structurally similar anti-diabetic drug metformin, and insulin for their effects on clearance of dysfunctional mitochondria through mitophagy in pancreatic β-cells from diabetic model db/db mice and mitophagy reporter (CMMR) mice. Pancreatic islets from db/db mice showed aberrant accumulation of dysfunctional mitochondria and excessive production of reactive oxygen species (ROS) along with markedly elevated mitophagy, suggesting that the generation of dysfunctional mitochondria overwhelmed the mitophagic capacity in db/db β-cells. Treatment with imeglimin or insulin, but not metformin, reduced ROS production and the numbers of dysfunctional mitochondria, and normalized mitophagic activity in db/db β-cells. Concomitantly, imeglimin and insulin, but not metformin, restored the secreted insulin level and reduced β-cell apoptosis in db/db mice. In conclusion, imeglimin mitigated accumulation of dysfunctional mitochondria through mitophagy in diabetic mice, and may contribute to preserving β-cell function and effective glycemic control in T2D.

Imeglimin: the New Kid on the Block

PURPOSE OF REVIEW

This review aims to collect all the data regarding imeglimin and present it as one of the options for managing diabetes.

RECENT FINDINGS

It is a new drug that has recently been approved as an oral anti-diabetic drug, either as monotherapy or in combination with other oral antidiabetic drugs including insulin, with modest HbA1c reduction, and a fairly safe profile. Imeglimin was first approved in 2021 in Japan and China and is available in India from October 2022. Imeglimin is the first compound in a new class of oral anti-diabetic medications known as "glimins" that include a tetrahydrotriazine ring. Glimins act by amplifying glucose-stimulated insulin secretion (GSIS) and preserving β-cell mass, leading to augmented insulin secretion. Furthermore, It also intensifies insulin action by inhibiting of hepatic glucose output and recovery of altered insulin signalling in both hepatocytes (liver) and myocytes (skeletal muscle). This is a unique mode of action than has been demonstrated to be distinct from other classes of drugs, as it targets both insulin secretion and insulin resistance by correcting the mitochondrial dysfunction. Imeglimin has been studied in various phase III trials which have equivocally shown it to be effective in lowering glucose levels and improving pancreatic function and its recommended dose set at 1000 mg bid.

Protective effects of metformin on pancreatic β-cell ferroptosis in type 2 diabetes in vivo

Metformin (Met) is the recommended first-line therapeutic drug for type 2 diabetes mellitus (T2DM) and exerts protective effects on β-cell damage. Ferroptosis, a new form of cell death, is associated with pancreatic islet injury in patients with T2DM. However, the protective effects of Met treatment against β-cell damage through ferroptosis modulation remain under-reported. This study investigated the in vivo effects of Met treatment on pancreatic β-cell ferroptosis using two different diabetic mouse models, namely, low-dose streptozotocin (STZ) and high-fat diet (HFD)-induced diabetic mice and db/db mice. Met treatment significantly restored insulin release, reduced cell mortality, and decreased the overproduction of lipid-related reactive oxygen species in the islets of both STZ/HFD-induced diabetic mice and db/db mice. Administration of the Ras-selective lethal 3 injection significantly attenuated the antiferroptosis effects of Met. Mechanistically, Met treatment alleviated β-cell ferroptosis in T2DM, which was associated with the regulation of the GPX4/ACSL4 axis in the islets. In conclusion, our findings highlight the significance of ferroptosis in T2DM β-cell damage and provide novel insights into the protective effects of Met against islet β cells.