Metformin: clinical topics and new mechanisms of action

Development of eco-friendly spectrophotometric methods for analysis of metformin hydrochloride and linagliptin in presence of metformin toxic impurity in their pure and dosage forms: Validation, practicality and greenness studies

Metformin is considered as type 2 diabetes first line treatment according to American Diabetes Association and European Association. But, in some cases, di- or tri - therapy should be prescribed for glycemic management, prevention of the maximum dose side effects and induced effectiveness. Co-administration of Linagliptin with metformin has many benefits on diabetic patients such as decrease the possibility of hypoglycemia. For the first time, novel and reliable techniques were developed and verified for the concurrent quantification of metformin hydrochloride and linagliptin, while accounting for the existence of metformin toxic impurity 1-cyanoguanidine in their pure and dosage forms. Method (A) utilizes the zero-order spectrophotometric approach to quantitatively determine the concentration of linagliptin. The measurements are performed at a wavelength of 295 nm. The double divisor derivative ratio spectrophotometric method is used in Method (B) to measure the amounts of metformin and cyanoguanidine at 252 nm and 219 nm wavelengths, respectively. The spectrophotometric method (C) for determining metformin and cyanoguanidine at 252 nm and 223 nm, respectively, is based on the single divisor derivative ratio-zero crossing technique. The obtained findings were subjected to statistical comparison with the reported method, revealing no statistically significant differences. The Green Analytical Procedure Index (GAPI) and Analytical GREEnness Metric approach (AGREE) determined that these approaches had a high degree of environmental friendliness. Additionally, the proposed strategy was deemed to be practical according to the Blue Applicability Grade Index (BAGI) assessment tool.

Mitigation of Insulin Resistance by Natural Products from a New Class of Molecules, Membrane-Active Immunomodulators

Insulin resistance (IR), accompanied by an impaired cellular glucose uptake, characterizes diverse pathologies that include, but are not limited to, metabolic disease, prediabetes and type 2 diabetes. Chronic inflammation associated with deranged cellular signaling is thought to contribute to IR. The key molecular players in IR are plasma membrane proteins, including the insulin receptor and glucose transporter 4. Certain natural products, such as lipids, phenols, terpenes, antibiotics and alkaloids have beneficial effects on IR, yet their mode of action remains obscured. We hypothesized that these products belong to a novel class of bioactive molecules that we have named membrane-active immunomodulators (MAIMs). A representative MAIM, the naturally occurring medium chain fatty acid ester diethyl azelate (DEA), has been shown to increase the fluidity of cell plasma membranes with subsequent downstream effects on cellular signaling. DEA has also been shown to improve markers of IR, including blood glucose, insulin and lipid levels, in humans. The literature supports the notion that DEA and other natural MAIMs share similar mechanisms of action in improving IR. These findings shed a new light on the mechanism of IR mitigation using natural products, and may facilitate the discovery of other compounds with similar activities.

Metformin Inhibits Autophagy, Mitophagy and Antagonizes Doxorubicin-Induced Cardiomyocyte Death

The antidiabetic drug metformin has been shown to reduce cardiac injury under various pathological conditions, including anticancer drug doxorubicin (DOX)-induced cardiotoxicity, which makes metformin a prime candidate for repurposing. However, the mechanisms that mediate the cardioprotective effects of metformin remain highly controversial. In this study, we tested a prevailing hypothesis that metformin activates autophagy/mitophagy to reduce DOX cardiotoxicity. FVB/N mice and H9C2 cardiac myoblasts were treated with metformin, respectively. Autophagy/mitophagy was determined by Western blot analysis of microtubule-associated protein light chain 3, form-II (LC3-II), a well-established marker of autophagic vesicles. Although metformin had minimal effects on basal LC3-II levels, it significantly inhibited the accumulation of LC3-II levels by the lysosomal protease inhibitors pepstatin A and E64d in both total cell lysates and mitochondrial fractions. Also, dual fluorescent autophagy/mitophagy reporters demonstrated that metformin slowed the degradation rate of autophagic cargos or mitochondrial fragments in the lysosomes. These surprising results suggest that metformin inhibits rather than stimulates autophagy/mitophagy, sharply contrasting the popular belief. In addition, metformin diminished DOX-induced autophagy/mitophagy as well as cardiomyocyte death. Together, these results suggest that the cardioprotective effects of metformin against DOX cardiotoxicity may be mediated by its ability to inhibit autophagy and mitophagy, although the underlying molecular mechanisms remain to be determined.

Demystifying the Relationship Between Metformin, AMPK, and Doxorubicin Cardiotoxicity

Doxorubicin (DOX) is an extremely effective and wide-spectrum anticancer drug, but its long-term use can lead to heart failure, which presents a serious problem to millions of cancer survivors who have been treated with DOX. Thus, identifying agents that can reduce DOX cardiotoxicity and concurrently enhance its antitumor efficacy would be of great clinical value. In this respect, the classical antidiabetic drug metformin (MET) has stood out, appearing to have both antitumor and cardioprotective properties. MET is proposed to achieve these beneficial effects through the activation of AMP-activated protein kinase (AMPK), an essential regulator of mitochondrial homeostasis and energy metabolism. AMPK itself has been shown to protect the heart and modulate tumor growth under certain conditions. However, the role and mechanism of the hypothesized MET-AMPK axis in DOX cardiotoxicity and antitumor efficacy remain to be firmly established by in vivo studies using tumor-bearing animal models and large-scale prospective clinical trials. This review summarizes currently available literature for or against a role of AMPK in MET-mediated protection against DOX cardiotoxicity. It also highlights the emerging evidence suggesting distinct roles of the AMPK subunit isoforms in mediating the functions of unique AMPK holoenzymes composed of different combinations of isoforms. Moreover, the review provides a perspective regarding future studies that may help fully elucidate the relationship between MET, AMPK and DOX cardiotoxicity.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

Oxidative stress is mainly caused by intracellular reactive oxygen species (ROS) production, which is highly associated with normal physiological homeostasis and the pathogenesis of diseases, particularly ocular diseases. Autophagy is a self-clearance pathway that removes oxidized cellular components and regulates cellular ROS levels. ROS can modulate autophagy activity through transcriptional and posttranslational mechanisms. Autophagy further triggers transcription factor activation and degrades impaired organelles and proteins to eliminate excessive ROS in cells. Thus, autophagy may play an antioxidant role in protecting ocular cells from oxidative stress. Nevertheless, excessive autophagy may cause autophagic cell death. In this review, we summarize the mechanisms of interaction between ROS and autophagy and their roles in the pathogenesis of several ocular diseases, including glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), and optic nerve atrophy, which are major causes of blindness. The autophagy modulators used to treat ocular diseases are further discussed. The findings of the studies reviewed here might shed light on the development and use of autophagy modulators for the future treatment of ocular diseases.