Metformin activates a duodenal Ampk-dependent pathway to lower hepatic glucose production in rats

Determination of metformin bio-distribution by LC-MS/MS in mice treated with a clinically relevant paradigm

Metformin, an anti-diabetes drug, has been recently emerging as a potential “anti-aging” intervention based on its reported beneficial actions against aging in preclinical studies. Nonetheless, very few metformin studies using mice have determined metformin concentrations and many effects of metformin have been observed in preclinical studies using doses/concentrations that were not relevant to therapeutic levels in human. We developed a liquid chromatography-tandem mass spectrometry protocol for metformin measurement in plasma, liver, brain, kidney, and muscle of mice. Young adult male and female C57BL/6 mice were voluntarily treated with metformin of 4 mg/ml in drinking water which translated to the maximum dose of 2.5 g/day in humans. A clinically relevant steady-state plasma metformin concentrations were achieved at 7 and 30 days after treatment in male and female mice. Metformin concentrations were slightly higher in muscle than in plasma, while, ~3 and 6-fold higher in the liver and kidney than in plasma, respectively. Low metformin concentration was found in the brain at ~20% of the plasma level. Furthermore, gender difference in steady-state metformin bio-distribution was observed. Our study established steady-state metformin levels in plasma, liver, muscle, kidney, and brain of normoglycemic mice treated with a clinically relevant dose, providing insight into future metformin preclinical studies for potential clinical translation.

Metformin monotherapy for adults with type 2 diabetes mellitus

BACKGROUND

Worldwide, there is an increasing incidence of type 2 diabetes mellitus (T2DM). Metformin is still the recommended first-line glucose-lowering drug for people with T2DM. Despite this, the effects of metformin on patient-important outcomes are still not clarified.

OBJECTIVES

To assess the effects of metformin monotherapy in adults with T2DM.

SEARCH METHODS

We based our search on a systematic report from the Agency for Healthcare Research and Quality, and topped-up the search in CENTRAL, MEDLINE, Embase, WHO ICTRP, and ClinicalTrials.gov. Additionally, we searched the reference lists of included trials and systematic reviews, as well as health technology assessment reports and medical agencies. The date of the last search for all databases was 2 December 2019, except Embase (searched up 28 April 2017).

SELECTION CRITERIA

We included randomised controlled trials (RCTs) with at least one year's duration comparing metformin monotherapy with no intervention, behaviour changing interventions or other glucose-lowering drugs in adults with T2DM.

DATA COLLECTION AND ANALYSIS

Two review authors read all abstracts and full-text articles/records, assessed risk of bias, and extracted outcome data independently. We resolved discrepancies by involvement of a third review author. For meta-analyses we used a random-effects model with investigation of risk ratios (RRs) for dichotomous outcomes and mean differences (MDs) for continuous outcomes, using 95% confidence intervals (CIs) for effect estimates. We assessed the overall certainty of the evidence by using the GRADE instrument.

MAIN RESULTS

We included 18 RCTs with multiple study arms (N = 10,680). The percentage of participants finishing the trials was approximately 58% in all groups. Treatment duration ranged from one to 10.7 years. We judged no trials to be at low risk of bias on all 'Risk of bias' domains. The main outcomes of interest were all-cause mortality, serious adverse events (SAEs), health-related quality of life (HRQoL), cardiovascular mortality (CVM), non-fatal myocardial infarction (NFMI), non-fatal stroke (NFS), and end-stage renal disease (ESRD). Two trials compared metformin (N = 370) with insulin (N = 454). Neither trial reported on all-cause mortality, SAE, CVM, NFMI, NFS or ESRD. One trial provided information on HRQoL but did not show a substantial difference between the interventions. Seven trials compared metformin with sulphonylureas. Four trials reported on all-cause mortality: in three trials no participant died, and in the remaining trial 31/1454 participants (2.1%) in the metformin group died compared with 31/1441 participants (2.2%) in the sulphonylurea group (very low-certainty evidence). Three trials reported on SAE: in two trials no SAE occurred (186 participants); in the other trial 331/1454 participants (22.8%) in the metformin group experienced a SAE compared with 308/1441 participants (21.4%) in the sulphonylurea group (very low-certainty evidence). Two trials reported on CVM: in one trial no CVM was observed and in the other trial 4/1441 participants (0.3%) in the metformin group died of cardiovascular reasons compared with 8/1447 participants (0.6%) in the sulphonylurea group (very low-certainty evidence). Three trials reported on NFMI: in two trials no NFMI occurred, and in the other trial 21/1454 participants (1.4%) in the metformin group experienced a NFMI compared with 15/1441 participants (1.0%) in the sulphonylurea group (very low-certainty evidence). One trial reported no NFS occurred (very low-certainty evidence). No trial reported on HRQoL or ESRD. Seven trials compared metformin with thiazolidinediones (very low-certainty evidence for all outcomes). Five trials reported on all-cause mortality: in two trials no participant died; the overall RR was 0.88, 95% CI 0.55 to 1.39; P = 0.57; 5 trials; 4402 participants). Four trials reported on SAE, the RR was 0,95, 95% CI 0.84 to 1.09; P = 0.49; 3208 participants. Four trials reported on CVM, the RR was 0.71, 95% CI 0.21 to 2.39; P = 0.58; 3211 participants. Three trial reported on NFMI: in two trials no NFMI occurred and in one trial 21/1454 participants (1.4%) in the metformin group experienced a NFMI compared with 25/1456 participants (1.7%) in the thiazolidinedione group. One trial reported no NFS occurred. No trial reported on HRQoL or ESRD. Three trials compared metformin with dipeptidyl peptidase-4 inhibitors (one trial each with saxagliptin, sitagliptin, vildagliptin with altogether 1977 participants). There was no substantial difference between the interventions for all-cause mortality, SAE, CVM, NFMI and NFS (very low-certainty evidence for all outcomes). One trial compared metformin with a glucagon-like peptide-1 analogue (very low-certainty evidence for all reported outcomes). There was no substantial difference between the interventions for all-cause mortality, CVM, NFMI and NFS. One or more SAEs were reported in 16/268 (6.0%) of the participants allocated to metformin compared with 35/539 (6.5%) of the participants allocated to a glucagon-like peptide-1 analogue. HRQoL or ESRD were not reported. One trial compared metformin with meglitinide and two trials compared metformin with no intervention. No deaths or SAEs occurred (very low-certainty evidence) no other patient-important outcomes were reported. No trial compared metformin with placebo or a behaviour changing interventions. Four ongoing trials with 5824 participants are likely to report one or more of our outcomes of interest and are estimated to be completed between 2018 and 2024. Furthermore, 24 trials with 2369 participants are awaiting assessment.

AUTHORS' CONCLUSIONS

There is no clear evidence whether metformin monotherapy compared with no intervention, behaviour changing interventions or other glucose-lowering drugs influences patient-important outcomes.

Metformin, an AMPK Activator, Inhibits Activation of FLSs but Promotes HAPLN1 Secretion

AMP-activated protein kinase (AMPK) is essential for maintaining energy balance and has a crucial role in various inflammatory pathways. In this study, AMPK levels positively correlated with many inflammatory indexes in rheumatoid arthritis (RA) patients, especially in the affected synovium. In RA sera, a positive correlation between phosphorylated (p-)AMPK-α1 levels and DAS28 (disease activity score 28) activity (r = 0.270, p < 0.0001) was found. Similarly, a positive correlation was observed between AMPK-α1 and tumor necrosis factor α (TNF-α) levels (r = 0.460, p = 0.0002). Differentially expressed genes between osteoarthritis (OA) and RA synovium from NCBI GEO profiles and our RNA sequencing data suggested activation of metabolic pathways specific to RA-fibroblast-like synoviocytes (FLSs). AMPK-α1 was highly expressed in the synovium of RA but not OA patients. An AMPK activator, metformin, inhibited FLS proliferation at higher but not lower concentrations, whereas the inhibitor dorsomorphin promoted the proliferation of RA-FLSs. Interestingly, both metformin and dorsomorphin inhibited the migration of RA-FLSs. After metformin treatment, expression of interleukin 6 (IL-6), TNF-α, and IL-1β were significantly downregulated in RA-FLSs; however, increased expression of p-AMPK-α1, protein kinase A (PKA)-α1, and HAPLN1 (hyaluronan and proteoglycan link protein 1) was observed. Increased levels of HAPLN1 in RA-FLSs by an AMPK activator could potentially be beneficial in protecting the joints. Hence, our results demonstrate the potential of an AMPK activator as a therapeutic for RA.

The road ahead for health and lifespan interventions

Aging is a modifiable risk factor for most chronic diseases and an inevitable process in humans. The development of pharmacological interventions aimed at delaying or preventing the onset of chronic conditions and other age-related diseases has been at the forefront of the aging field. Preclinical findings have demonstrated that species, sex and strain confer significant heterogeneity on reaching the desired health- and lifespan-promoting pharmacological responses in model organisms. Translating the safety and efficacy of these interventions to humans and the lack of reliable biomarkers that serve as predictors of health outcomes remain a challenge. Here, we will survey current pharmacological interventions that promote lifespan extension and/or increased healthspan in animals and humans, and review the various anti-aging interventions selected for inclusion in the NIA's Interventions Testing Program as well as the ClinicalTrials.gov database that target aging or age-related diseases in humans.

Oleoylethanolamide Increases Glycogen Synthesis and Inhibits Hepatic Gluconeogenesis via the LKB1/AMPK Pathway in Type 2 Diabetic Model

Oleoylethanolamide (OEA) is an endogenous peroxisome proliferator-activated receptor α (PPARα) agonist that acts on the peripheral control of energy metabolism. However, its therapeutic potential and related mechanisms in hepatic glucose metabolism under type 2 diabetes mellitus (T2DM) are not clear. Here, OEA treatment markedly improved glucose homeostasis in a PPARα-independent manner. OEA efficiently promoted glycogen synthesis and suppressed gluconeogenesis in mouse primary hepatocytes and liver tissue. OEA enhanced hepatic glycogen synthesis and inhibited gluconeogenesis via liver kinase B1 (LKB1)/5' AMP-activated protein kinase (AMPK) signaling pathways. PPARα was not involved in the roles of OEA in the LKB1/AMPK pathways. We found that OEA exerts its antidiabetic effect by increasing glycogenesis and decreasing gluconeogenesis via the LKB1/AMPK pathway. The ability of OEA to control hepatic LKB1/AMPK pathways may serve as a novel therapeutic approach for the treatment of T2DM. SIGNIFICANCE STATEMENT: Oleoylethanolamide (OEA) exerted a potent antihyperglycemic effect in a peroxisome proliferator-activated receptor α-independent manner. OEA played an antihyperglycemic role primarily via regulation of hepatic glycogen synthesis and gluconeogenesis. The main molecular mechanism of OEA in regulating liver glycometabolism is activating the liver kinase B1/5' AMP-activated protein kinase signaling pathways.

Type 2 diabetes mellitus does not increase the risk of multiple myeloma: a systematic review and meta-analysis

Background

Epidemiological studies have shown that patients with type 2 diabetes mellitus (T2DM) are at a higher risk of secondary tumors. However, no consensus has been made about whether T2DM can increase the risk of multiple myeloma (MM).

Methods

We searched the databases of PubMed, Cochrane Library and EMBASE and cross-checked the bibliography. Data quality was assessed using the Newcastle-Ottawa scale (NOS). Heterogeneity was calculated as the odds ratio (OR) using a random-effects model. Data were analyzed using Stata version 12.0 software.

Results

A total of 13 articles were selected into this meta-analysis. Initially, we found that diabetic patients had a higher risk of myeloma than non-diabetic patients (OR =1.60, 95% CI: 1.13–2.26, I²=98%, P=0.000). But the data in these articles were highly heterogeneous (I²>75%). Therefore, eight of the included articles showed a moderate heterogeneity (I²=71.6%). We used Galbraith heterogeneity map to analyze the causes of heterogeneity. Two articles with high heterogeneity were excluded. Then, we found the heterogeneity of the left six articles was reduced from moderate to mild (I²=45.9%, P=0.100). The final results of this meta-analysis showed that T2DM was not a risk factor for increased incidence of MM (OR =1.05, 95% CI: 0.83–1.33, I²=45.9%, P=0.100). Also, the subgroup analysis (case-control studies vs. cohort studies) showed no statistical difference (OR =1.19, 95% CI: 0.76–1.85, I²=1%, P=0.364; OR =1.00, 95% CI: 0.75–1.33, I²=71.2%, P=0.031; respectively).

Conclusions

T2DM is not a risk factor for the increased incidence of MM, a finding that should be validated with more strictly designed randomized controlled trials (RCTs).

Sperm Proteomics Analysis of Diabetic Induced Male Rats as Influenced by Ficus carica Leaf Extract

Diabetes mellitus is shown to bring negative effects on male reproductive health due to long-term effects of insulin deficiency or resistance and increased oxidative stress. Ficus carica (FC), an herbal plant, known to have high antioxidant activity and antidiabetic properties, has been used traditionally to treat diabetes. The objective of this study is to determine the potential of the FC leaf extract in improving sperm quality of streptozotocin (STZ) induced diabetic male rats from proteomics perspective. A total of 20 male rats were divided into four groups; normal (nondiabetic rats), negative control (diabetic rats without treatment), positive control (diabetic rats treated with 300 mg/kg metformin), and FC group (diabetic rats treated with 400 mg/kg FC extract). The treatments were given via oral gavage for 21 consecutive days. The fasting blood glucose (FBG) level of FC treated group demonstrated a significant (p < 0.05) decrease compared to negative group after 21 days of treatment, as well as a significant (p < 0.05) increase in the sperm quality parameters compared to negative group. Sperm proteomics analysis on FC treated group also exhibited the increase of total protein expression especially the proteins related to fertility compared to negative group. In conclusion, this study clearly justified that FC extract has good potential as antihyperglycemic and profertility agent that may be beneficial for male diabetic patients who have fertility problems.

Sodium butyrate ameliorates insulin resistance and renal failure in CKD rats by modulating intestinal permeability and mucin expression

Background

The associated increase in the lipopolysaccharide (LPS) levels and uremic toxins in chronic kidney disease (CKD) has shifted the way we focus on intestinal microbiota. This study shows that a disruption of the intestinal barrier in CKD promotes leakage of LPS from the gut, subsequently decreasing insulin sensitivity. Butyrate treatment improved the intestinal barrier function by increasing colonic mucin and tight junction (TJ) proteins. This modulation further ameliorated metabolic functions such as insulin intolerance and improved renal function.

Methods

Renal failure was induced by 5/6th nephrectomy (Nx) in rats. A group of Nx and control rats received sodium butyrate in drinking water. The Nx groups were compared with sham-operated controls.

Results

The Nx rats had significant increases in serum creatinine, urea and proteinuria. These animals had impaired glucose and insulin tolerance and increased gluconeogenesis, which corresponded with decreased glucagon-like peptide-1 (GLP-1) secretion. The Nx animals suffered significant loss of intestinal TJ proteins, colonic mucin and mucin 2 protein. This was associated with a significant increase in circulating LPS, suggesting a leaky gut phenomenon. 5′adenosine monophosphate-activated protein kinase (AMPK) phosphorylation, known to modulate epithelial TJs and glucose metabolism, was significantly reduced in the intestine of the Nx group. Anti-inflammatory cytokine, interleukin 10, anti-bacterial peptide and cathelicidin-related antimicrobial peptide were also lowered in the Nx cohort. Butyrate treatment increased AMPK phosphorylation, improved renal function and controlled hyperglycemia.

Conclusions

Butyrate improves AMPK phosphorylation, increases GLP-1 secretion and promotes colonic mucin and TJ proteins, which strengthen the gut wall. This decreases LPS leakage and inflammation. Taken together, butyrate improves metabolic parameters such as insulin resistance and markers of renal failure in CKD animals.

Why the endothelium? The endothelium as a target to reduce diabetes-associated vascular disease

Over the past 66 years, our knowledge of the role of the endothelium in the regulation of cardiovascular function and dysfunction has advanced from the assumption that it is a single layer of cells that serves as a barrier between the blood stream and vascular smooth muscle to an understanding of its role as an essential endocrine-like organ. In terms of historical contributions, we pay particular credit to (1) the Canadian scientist Dr. Rudolf Altschul who, based on pathological changes in the appearance of the endothelium, advanced the argument in 1954 that "one is only as old as one's endothelium" and (2) the American scientist Dr. Robert Furchgott, a 1998 Nobel Prize winner in Physiology or Medicine, who identified the importance of the endothelium in the regulation of blood flow. This review provides a brief history of how our knowledge of endothelial function has advanced and now recognize that the endothelium produces a plethora of signaling molecules possessing paracrine, autocrine, and, arguably, systemic hormone functions. In addition, the endothelium is a therapeutic target for the anti-diabetic drugs metformin, glucagon-like peptide I (GLP-1) receptor agonists, and inhibitors of the sodium-glucose cotransporter 2 (SGLT2) that offset the vascular disease associated with diabetes.

Strategies of Unloading the Failing Heart from Metabolic Stress

We propose a unifying perspective of heart failure in patients with type 2 diabetes mellitus. The reasoning is as follows: cellular responses to fuel overload include dysregulated insulin signaling, impaired mitochondrial respiration, reactive oxygen species formation, and the accumulation of certain metabolites, collectively termed glucolipotoxicity. As a consequence, cardiac function is impaired, with intracellular calcium cycling and diastolic dysfunction as an early manifestation. In this setting, increasing glucose uptake by insulin or insulin sensitizing agents only worsens the disrupted fuel homeostasis of the heart. Conversely, restricting fuel supply by means of caloric restriction, surgical intervention, or certain pharmacologic agents will improve cardiac function by restoring metabolic homeostasis. The concept is borne out by clinical interventions, all of which unload the heart from metabolic stress.

Metformin-Induced Stromal Depletion to Enhance the Penetration of Gemcitabine-Loaded Magnetic Nanoparticles for Pancreatic Cancer Targeted Therapy

Pancreatic ductal adenocarcinoma, as one of the most aggressive cancers, is characterized by rich desmoplastic stroma that forms a physical barrier for anticancer drugs. To address this issue, we herein report a two-step sequential delivery strategy for targeted therapy of pancreatic cancer with gemcitabine (GEM). In this sequential strategy, metformin (MET) was first administrated to disrupt the dense stroma, based on the fact that MET downregulated the expression of fibrogenic cytokine TGF-β to suppress the activity of pancreatic stellate cells (PSCs), through the 5'-adenosine monophosphate-activated protein kinase pathway of PANC-1 pancreatic cancer cells. In consequence, the PSC-mediated desmoplastic reactions generating α-smooth muscle actin and collagen were inhibited, which promoted the delivery of GEM and pH (low) insertion peptide (pHLIP) comodified magnetic nanoparticles (denoted as GEM-MNP-pHLIP). In addition, pHLIP largely increased the binding affinity of the nanodrug to PANC-1 cells. The targeted delivery and effective accumulation of MET/GEM-MNP-pHLIP in vivo were confirmed by magnetic resonance imaging enhanced by the underlying magnetic nanoparticles. The tumor growth inhibition of the sequential MET and GEM-MNP-pHLIP treatment were investigated on both subcutaneous and orthotopic tumor mice models. A remarkably improved therapeutic efficacy, for example, up to 91.2% growth inhibition ratio over 30 d of treatment, well-exemplified the novel cascade treatment for pancreatic cancer and the innovative use of MET.

Molecular Basis of the Beneficial Actions of Resveratrol

Resveratrol modulates the transcription factor NF-κB, cytochrome P450 isoenzyme CYP1A1, expression and activity of cyclooxygenase (COX) enzymes, Fas/Fas ligand mediated apoptosis, p53, mTOR and cyclins and various phospho-diesterases resulting in an increase in cytosolic cAMP levels. Cyclic AMP, in turn, activates Epac1/CaMKKβ/AMPK/SIRT1/PGC-1α pathway that facilitates increased oxidation of fatty acids, mitochondrial respiration and their biogenesis and gluconeogenesis. Resveratrol triggers apoptosis of activated T cells and suppresses tumor necrosis factor-α (TNF-α), interleukin-17 (IL-17) and other pro-inflammatory molecules and inhibits expression of hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) that may explain its anti-inflammatory actions. Polyunsaturated fatty acids (PUFAs) and their anti-inflammatory metabolites lipoxin A4, resolvins, protectins and maresins have a significant role in obesity, type 2 diabetes mellitus (T2DM), metabolic syndrome and cancer. We observed that PUFAs (especially arachidonic acid, AA) and BDNF (brain-derived neurotrophic factor) protect against the cytotoxic actions of alloxan, streptozotocin, benzo(a)pyrene (BP) and doxorubicin. Thus, there is an overlap in the beneficial actions of resveratrol, PUFAs and BDNF suggesting that these molecules may interact and augment synthesis and action of each other. This is supported by the observation that resveratrol and PUFAs modulate gut microbiota and influence stem cell proliferation and differentiation. Since resveratrol is not easily absorbed from the gut it is likely that it may act on endocannabinoid and light, odor, and taste receptors located in the gut, which, in turn, convey their messages to the various organs via vagus nerve.

Icariin treatment reduces blood glucose levels in type 2 diabetic rats and protects pancreatic function

Icariin, a flavonoid isolated from traditional oriental herbal medicines, has been demonstrated to exhibit several health benefits in animal models and in humans. The aim of the present study was to investigate the effect of Icariin on hyperglycemia in type 2 diabetes mellitus (T2DM) in rats. A model of diabetes was established in 50 Sprague Dawley rats using a high-sugar and high-fat diet and peritoneal injection of streptozotocin. Diabetic rats were divided into five groups: Diabetic control; metformin; and rats treated with three different doses of Icariin, 5, 10 and 20 mg/kg. Body weight and blood glucose levels were measured, and serum adiponectin levels, expression of phospho-AMP mediated protein kinase (p-AMPK) and glucose transporter isoform 4 (GLUT-4) were measured using ELISA, Realtime PCR and western blotting, respectively. Diabetic rats without drug treatment exhibited reduced body weight, increased blood glucose levels and decreased the number of islets. In T2DM rats treated with 10 or 20 mg/kg Icariin, the blood glucose levels were reduced, whereas serum adiponectin levels were not affected. Additionally, the mRNA and protein expression levels of p-AMPK and GLUT-4 protein were increased in the T2DM rats treated with Icariin. In conclusion, in the diabetes rat model, Icariin alleviated the severity of diabetes, and the effects may be associated with reduction of hyperglycemia by activating an AMPK/GLUT-4 pathway.

Mechanism of glucose-lowering by metformin in type 2 diabetes: Role of bile acids

Type 2 diabetes mellitus (T2DM) is an increasingly prevalent chronic condition, characterized by abnormally elevated blood glucose concentrations and, as a consequence, increased risk of micro- and macrovascular complications. Metformin is usually the first-line glucose-lowering medication in T2DM; however, despite being used for more than 60 years, the mechanism underlying the glucose-lowering action of metformin remains incompletely understood. Although metformin reduces hepatic glucose production, there is persuasive evidence that the gastrointestinal tract is crucial in mediating this effect, particularly via secretion of the incretin hormone glucagon-like peptide 1 (GLP-1). It is now well recognized that bile acids, in addition to their established function in fat digestion and absorption, are important regulators of glucose metabolism. Exposure of the small and large intestine to bile acids induces GLP-1 secretion, modulates the composition of the gut microbiota, and reduces postprandial blood glucose excursions in humans with and without T2DM. Metformin reduces intestinal bile acid resorption substantially, such that intraluminal bile acids may, at least in part, account for its glucose-lowering effect. The present review focuses on the conceptual shift in our understanding as to how metformin lowers blood glucose in T2DM, with a particular emphasis on the role of intestinal bile acids.

A new perspective on the biguanide, metformin therapy in type 2 diabetes and lactic acidosis

Recent topics about metformin mainly focus on clinical studies, briefly mentioning some new aspects on the mechanisms of metformin action.

Effects of a high concentration of hydrogen on neurological function after traumatic brain injury in diabetic rats

Reactive oxygen species, inflammation, and apoptosis are major contributors to secondary injuries that follow traumatic brain injury (TBI) in diabetic patients. Hydrogen (H₂) can selectively neutralize reactive oxygen species and downregulate inflammatory and apoptotic factors. Therefore, we investigated the effects of inhaled high and low concentrations of hydrogen on neurological function after TBI in diabetic rats and the potential mechanism. We found that the inhalation of high concentrations of H₂ significantly improved outcomes following TBI in diabetic rats. The inhalation of 42% H₂ for one hour per day for 48 h significantly reduced brain edema, decreased the extravasation of sodium fluorescein, and reduced oxidative stress markers (p < 0.05). In addition, the inhalation of a high concentration of H₂ (42% for one hour per day for 7 days) improved neurological deficits (p < 0.05) and reduced the expression of apoptotic protein markers (p < 0.05). However, the inhalation of 3% H₂ did not yield significant effects. These results showed that the inhalation of 42% H₂ can alleviate nerve damage and improve neurological function after TBI in diabetic rats. Therefore, the inhalation of a high concentration of H₂ may be associated with the treatment of traumatic brain injuries.

Metformin and cognition from the perspectives of sex, age, and disease

Metformin is the safest and the most widely prescribed first-line therapy for managing hyperglycemia due to different underlying causes, primarily type 2 diabetes mellitus. In addition to its euglycemic properties, metformin has stimulated a wave of clinical trials to investigate benefits on aging-related diseases and longevity. Such an impact on the lifespan extension would undoubtedly expand the therapeutic utility of metformin regardless of glycemic status. However, there is a scarcity of studies evaluating whether metformin has differential cognitive effects across age, sex, glycemic status, metformin dose, and duration of metformin treatment and associated pathological conditions. By scrutinizing the available literature on animal and human studies for metformin and brain function, we expect to shed light on the potential impact of metformin on cognition across age, sex, and pathological conditions. This review aims to provide readers with a broader insight of (a) how metformin differentially affects cognition and (b) why there is a need for more translational and clinical studies examining multifactorial interactions. The outcomes of such comprehensive studies will streamline precision medicine practices, avoiding "fit for all" approach, and optimizing metformin use for longevity benefit irrespective of hyperglycemia.

Association Between Severity of Diabetic Neuropathy and Success in Weight Loss During Hospitalization Among Japanese Patients with Type 2 Diabetes: A Retrospective Observational Study

INTRODUCTION

This study aimed to examine the association between severity of diabetic neuropathy and weight loss during hospitalization in overweight participants with type 2 diabetes.

PATIENTS AND METHODS

Participants of this study comprised 193 patients who were hospitalized for type 2 diabetes treatment. The participants were divided into two groups in the study, based on whether or not reduction of bodyweight was at least 3% during hospitalization. Using Cox models, the association between severity of neuropathy and effectiveness of weight loss under a controlled diet was analyzed. Autonomic neuropathy was assessed on patient admission by R-R interval, as measured in an electrocardiogram (CVRR), and sensory neuropathy was assessed using both 128-Hz tuning-fork vibration and Achilles tendon reflex (ATR).

RESULTS

The adjusted hazard ratio for weight loss of at least 3% for CVRR was 1.17 (95% confidence interval 1.07-1.28, P=0.0006) and for vibration time 1.93 (1.01-3.68, P=0.045). After dividing CVRR and vibration time into tertiles based on participant number, the adjusted hazard ratio for the high tertile of CVRR was 2.17 (1.29-3.62, P=0.003), and for the long tertile of vibration time 1.84 (1.10-3.08, P=0.02), compared with the low and short tertiles, respectively. No association was detected between ATR category and weight loss.

CONCLUSION

Severity of diabetic neuropathy was found to be a determinant in weight loss under a caloric restriction regimen for patients with type 2 diabetes. The results of the study suggest that the peripheral nervous system is involved in responses to medical intervention for treatment for type 2 diabetes including bodyweight management.

Metformin and LW6 impairs pancreatic cancer cells and reduces nuclear localization of YAP1

The poor survival rate of pancreatic cancer is still a major challenge for the clinicians and their patients. In this study, we evaluated the efficacy of metformin, an inhibitor of oxidative phosphorylation, in combination with LW6, which impairs malate dehydrogenase 2 activities, in treating pancreatic cancer cells. We observed that this combinational therapy significantly reduced cell proliferation, migration, and significantly induced cell death when compared to cells treated by each monotherapy or Sham. In addition, we found that the combination of metformin and LW6 increased the phosphorylation of yes-associated protein 1 at serine 127 and attenuated the nuclear localization of this transcription factor. This combinatorial treatment also decreased the level of cellular yes-associated protein 1. This suggests that metformin in combination with LW6 impairs pancreatic cancer cells and reduces nuclear localization of yes-associated protein 1.

The Mechanism of Metabolic Influences on the Endogenous GLP-1 by Oral Antidiabetic Medications in Type 2 Diabetes Mellitus

Incretin-based therapy is now a prevalent treatment option for patients with type 2 diabetes mellitus (T2DM). It has been associated with considerably good results in the management of hyperglycemia with cardiac or nephron-benefits. For this reason, it is recommended for individuals with cardiovascular diseases in many clinical guidelines. As an incretin hormone, glucagon-like peptide-1 (GLP-1) possesses multiple metabolic benefits such as optimizing energy usage, maintaining body weight, β cell preservation, and suppressing neurodegeneration. However, recent studies indicate that oral antidiabetic medications interact with endogenous or exogenous GLP-1. Since these drugs are transported to distal intestine portions, there are concerns whether these oral drugs directly stimulate intestinal L cells which release GLP-1, or whether they do so via indirect inhibition of the activity of dipeptidyl peptidase-IV (DPP-IV). In this review, we discuss the metabolic relationships between oral antihyperglycemic drugs from the aspect of gut, microbiota, hormones, β cell function, central nervous system, and other cellular mechanisms.

Metformin for prevention or delay of type 2 diabetes mellitus and its associated complications in persons at increased risk for the development of type 2 diabetes mellitus

BACKGROUND

The projected rise in the incidence of type 2 diabetes mellitus (T2DM) could develop into a substantial health problem worldwide. Whether metformin can prevent or delay T2DM and its complications in people with increased risk of developing T2DM is unknown.

OBJECTIVES

To assess the effects of metformin for the prevention or delay of T2DM and its associated complications in persons at increased risk for the T2DM.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Scopus, ClinicalTrials.gov, the World Health Organization (WHO) International Clinical Trials Registry Platform and the reference lists of systematic reviews, articles and health technology assessment reports. We asked investigators of the included trials for information about additional trials. The date of the last search of all databases was March 2019.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) with a duration of one year or more comparing metformin with any pharmacological glucose-lowering intervention, behaviour-changing intervention, placebo or standard care in people with impaired glucose tolerance, impaired fasting glucose, moderately elevated glycosylated haemoglobin A1c (HbA1c) or combinations of these.

DATA COLLECTION AND ANALYSIS

Two review authors read all abstracts and full-text articles and records, assessed risk of bias and extracted outcome data independently. We used a random-effects model to perform meta-analysis and calculated risk ratios (RRs) for dichotomous outcomes and mean differences (MDs) for continuous outcomes, using 95% confidence intervals (CIs) for effect estimates. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

We included 20 RCTs randomising 6774 participants. One trial contributed 48% of all participants. The duration of intervention in the trials varied from one to five years. We judged none of the trials to be at low risk of bias in all 'Risk of bias' domains. Our main outcome measures were all-cause mortality, incidence of T2DM, serious adverse events (SAEs), cardiovascular mortality, non-fatal myocardial infarction or stroke, health-related quality of life and socioeconomic effects.The following comparisons mostly reported only a fraction of our main outcome set. Fifteen RCTs compared metformin with diet and exercise with or without placebo: all-cause mortality was 7/1353 versus 7/1480 (RR 1.11, 95% CI 0.41 to 3.01; P = 0.83; 2833 participants, 5 trials; very low-quality evidence); incidence of T2DM was 324/1751 versus 529/1881 participants (RR 0.50, 95% CI 0.38 to 0.65; P < 0.001; 3632 participants, 12 trials; moderate-quality evidence); the reporting of SAEs was insufficient and diverse and meta-analysis could not be performed (reported numbers were 4/118 versus 2/191; 309 participants; 4 trials; very low-quality evidence); cardiovascular mortality was 1/1073 versus 4/1082 (2416 participants; 2 trials; very low-quality evidence). One trial reported no clear difference in health-related quality of life after 3.2 years of follow-up (very low-quality evidence). Two trials estimated the direct medical costs (DMC) per participant for metformin varying from $220 to $1177 versus $61 to $184 in the comparator group (2416 participants; 2 trials; low-quality evidence). Eight RCTs compared metformin with intensive diet and exercise: all-cause mortality was 7/1278 versus 4/1272 (RR 1.61, 95% CI 0.50 to 5.23; P = 0.43; 2550 participants, 4 trials; very low-quality evidence); incidence of T2DM was 304/1455 versus 251/1505 (RR 0.80, 95% CI 0.47 to 1.37; P = 0.42; 2960 participants, 7 trials; moderate-quality evidence); the reporting of SAEs was sparse and meta-analysis could not be performed (one trial reported 1/44 in the metformin group versus 0/36 in the intensive exercise and diet group with SAEs). One trial reported that 1/1073 participants in the metformin group compared with 2/1079 participants in the comparator group died from cardiovascular causes. One trial reported that no participant died due to cardiovascular causes (very low-quality evidence). Two trials estimated the DMC per participant for metformin varying from $220 to $1177 versus $225 to $3628 in the comparator group (2400 participants; 2 trials; very low-quality evidence). Three RCTs compared metformin with acarbose: all-cause mortality was 1/44 versus 0/45 (89 participants; 1 trial; very low-quality evidence); incidence of T2DM was 12/147 versus 7/148 (RR 1.72, 95% CI 0.72 to 4.14; P = 0.22; 295 participants; 3 trials; low-quality evidence); SAEs were 1/51 versus 2/50 (101 participants; 1 trial; very low-quality evidence). Three RCTs compared metformin with thiazolidinediones: incidence of T2DM was 9/161 versus 9/159 (RR 0.99, 95% CI 0.41 to 2.40; P = 0.98; 320 participants; 3 trials; low-quality evidence). SAEs were 3/45 versus 0/41 (86 participants; 1 trial; very low-quality evidence). Three RCTs compared metformin plus intensive diet and exercise with identical intensive diet and exercise: all-cause mortality was 1/121 versus 1/120 participants (450 participants; 2 trials; very low-quality evidence); incidence of T2DM was 48/166 versus 53/166 (RR 0.55, 95% CI 0.10 to 2.92; P = 0.49; 332 participants; 2 trials; very low-quality evidence). One trial estimated the DMC of metformin plus intensive diet and exercise to be $270 per participant compared with $225 in the comparator group (94 participants; 1 trial; very-low quality evidence). One trial in 45 participants compared metformin with a sulphonylurea. The trial reported no patient-important outcomes. For all comparisons there were no data on non-fatal myocardial infarction, non-fatal stroke or microvascular complications. We identified 11 ongoing trials which potentially could provide data of interest for this review. These trials will add a total of 17,853 participants in future updates of this review.

AUTHORS' CONCLUSIONS

Metformin compared with placebo or diet and exercise reduced or delayed the risk of T2DM in people at increased risk for the development of T2DM (moderate-quality evidence). However, metformin compared to intensive diet and exercise did not reduce or delay the risk of T2DM (moderate-quality evidence). Likewise, the combination of metformin and intensive diet and exercise compared to intensive diet and exercise only neither showed an advantage or disadvantage regarding the development of T2DM (very low-quality evidence). Data on patient-important outcomes such as mortality, macrovascular and microvascular diabetic complications and health-related quality of life were sparse or missing.

Metformin-induced increases in GDF15 are important for suppressing appetite and promoting weight loss

Metformin is the most commonly prescribed medication for type 2 diabetes, owing to its glucose-lowering effects, which are mediated through the suppression of hepatic glucose production (reviewed in refs. ^1-3). However, in addition to its effects on the liver, metformin reduces appetite and in preclinical models exerts beneficial effects on ageing and a number of diverse diseases (for example, cognitive disorders, cancer, cardiovascular disease) through mechanisms that are not fully understood^1-3. Given the high concentration of metformin in the liver and its many beneficial effects beyond glycemic control, we reasoned that metformin may increase the secretion of a hepatocyte-derived endocrine factor that communicates with the central nervous system⁴. Here we show, using unbiased transcriptomics of mouse hepatocytes and analysis of proteins in human serum, that metformin induces expression and secretion of growth differentiating factor 15 (GDF15). In primary mouse hepatocytes, metformin stimulates the secretion of GDF15 by increasing the expression of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP; also known as DDIT3). In wild-type mice fed a high-fat diet, oral administration of metformin increases serum GDF15 and reduces food intake, body mass, fasting insulin and glucose intolerance; these effects are eliminated in GDF15 null mice. An increase in serum GDF15 is also associated with weight loss in patients with type 2 diabetes who take metformin. Although further studies will be required to determine the tissue source(s) of GDF15 produced in response to metformin in vivo, our data indicate that the therapeutic benefits of metformin on appetite, body mass and serum insulin depend on GDF15.

The Gastrointestinal Tract as Prime Site for Cardiometabolic Protection by Dietary Polyphenols

Substantial evidence from nutritional epidemiology links polyphenol-rich diets with reduced incidence of chronic disorders; however, biological mechanisms underlying polyphenol-disease relations remain enigmatic. Emerging evidence is beginning to unmask the contribution of the gastrointestinal tract on whole-body energy homeostasis, suggesting that the intestine may be a prime target for intervention and a fundamental site for the metabolic actions of polyphenols. During their transit through the gastrointestinal tract, polyphenols may activate enteric nutrient sensors ensuing appropriate responses from other peripheral organs to regulate metabolic homeostasis. Furthermore, polyphenols can modulate the absorption of glucose, attenuating exaggerated hormonal responses and metabolic imbalances. Polyphenols that escape absorption are metabolized by the gut microbiota and the resulting catabolites may act locally, activating nuclear receptors that control enteric functions such as intestinal permeability. Finally, polyphenols modulate gut microbial ecology, which can have profound effects on cardiometabolic health.

Metformin Alters Locomotor and Cognitive Function and Brain Metabolism in Normoglycemic Mice

Metformin is currently the most effective treatment for type-2 diabetes. The beneficial actions of metformin have been found even beyond diabetes management and it has been considered as one of the most promising drugs that could potentially slow down aging. Surprisingly, the effect of metformin on brain function and metabolism has been less explored given that brain almost exclusively uses glucose as substrate for energy metabolism. We determined the effect of metformin on locomotor and cognitive function in normoglycemic mice. Metformin enhanced locomotor and balance performance, while induced anxiolytic effect and impaired cognitive function upon chronic treatment. We conducted in vitro assays and metabolomics analysis in mice to evaluate metformin’s action on the brain metabolism. Metformin decreased ATP level and activated AMPK pathway in mouse hippocampus. Metformin inhibited oxidative phosphorylation and elevated glycolysis by inhibiting mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) in vitro at therapeutic doses. In summary, our study demonstrated that chronic metformin treatment affects brain bioenergetics with compound effects on locomotor and cognitive brain function in non-diabetic mice.

Understanding the glucoregulatory mechanisms of metformin in type 2 diabetes mellitus

Despite its position as the first-line drug for treatment of type 2 diabetes mellitus, the mechanisms underlying the plasma glucose level-lowering effects of metformin (1,1-dimethylbiguanide) still remain incompletely understood. Metformin is thought to exert its primary antidiabetic action through the suppression of hepatic glucose production. In addition, the discovery that metformin inhibits the mitochondrial respiratory chain complex 1 has placed energy metabolism and activation of AMP-activated protein kinase (AMPK) at the centre of its proposed mechanism of action. However, the role of AMPK has been challenged and might only account for indirect changes in hepatic insulin sensitivity. Various mechanisms involving alterations in cellular energy charge, AMP-mediated inhibition of adenylate cyclase or fructose-1,6-bisphosphatase 1 and modulation of the cellular redox state through direct inhibition of mitochondrial glycerol-3-phosphate dehydrogenase have been proposed for the acute inhibition of gluconeogenesis by metformin. Emerging evidence suggests that metformin could improve obesity-induced meta-inflammation via direct and indirect effects on tissue-resident immune cells in metabolic organs (that is, adipose tissue, the gastrointestinal tract and the liver). Furthermore, the gastrointestinal tract also has a major role in metformin action through modulation of glucose-lowering hormone glucagon-like peptide 1 and the intestinal bile acid pool and alterations in gut microbiota composition.

Three Structural Features of Functional Food Components and Herbal Medicine with Amyloid β42 Anti-Aggregation Properties

Aggregation of amyloid β42 (Aβ42) is one of the hallmarks of Alzheimer's disease (AD). There are numerous naturally occurring products that suppress the aggregation of Aβ42, but the underlying mechanisms remain to be elucidated. Based on NMR and MS spectroscopic analysis, we propose three structural characteristics found in natural products required for the suppressive activity against Aβ42 aggregation (i.e., oligomerization by targeting specific amino acid residues on this protein). These characteristics include (1) catechol-type flavonoids that can form Michael adducts with the side chains of Lys16 and 28 in monomeric Aβ42 through flavonoid autoxidation; (2) non-catechol-type flavonoids with planarity due to α,β-unsaturated carbonyl groups that can interact with the intermolecular β-sheet region in Aβ42 aggregates, especially aromatic rings such as those of Phe19 and 20; and (3) carboxy acid derivatives with triterpenoid or anthraquinoid that can generate a salt bridge with basic amino acid residues such as Lys16 and 28 in the Aβ42 dimer or trimer. Here, we summarize the recent body of knowledge concerning amyloidogenic inhibitors, particularly in functional food components and Kampo medicine, and discuss their application in the treatment and prevention of AD.

Metformin-induced changes of the gut microbiota in healthy young men: results of a non-blinded, one-armed intervention study

AIMS/HYPOTHESIS

Individuals with type 2 diabetes have an altered bacterial composition of their gut microbiota compared with non-diabetic individuals. However, these alterations may be confounded by medication, notably the blood-glucose-lowering biguanide, metformin. We undertook a clinical trial in healthy and previously drug-free men with the primary aim of investigating metformin-induced compositional changes in the non-diabetic state. A secondary aim was to examine whether the pre-treatment gut microbiota was related to gastrointestinal adverse effects during metformin treatment.

METHODS

Twenty-seven healthy young Danish men were included in an 18-week one-armed crossover trial consisting of a pre-intervention period, an intervention period and a post-intervention period, each period lasting 6 weeks. Inclusion criteria were men of age 18-35 years, BMI between 18.5 kg/m² and 27.5 kg/m², HbA_1c < 39 mmol/mol (5.7%) and plasma creatinine within the normal range. No prescribed medication, including antibiotics, for 2 months prior to recruitment were allowed and no previous gastrointestinal surgery, discounting appendectomy or chronic illness requiring medical treatment. During the intervention the participants were given metformin up to 1 g twice daily. Participants were examined five times in the fasting state with blood sampling and recording of gastrointestinal symptoms. Examinations took place at Frederiksberg Hospital, Denmark before and after the pre-intervention period, halfway through and immediately after the end of intervention and after the wash-out period. Faecal samples were collected at nine evenly distributed time points, and bacterial DNA was extracted and subjected to 16S rRNA gene amplicon sequencing in order to evaluate gut microbiota composition. Subjective gastrointestinal symptoms were reported at each visit.

RESULTS

Data from participants who completed visit 1 (n=23) are included in analyses. For the primary outcome the relative abundance of 11 bacterial genera significantly changed during the intervention but returned to baseline levels after treatment cessation. In line with previous reports, we observed a reduced abundance of Intestinibacter spp. and Clostridium spp., as well as an increased abundance of Escherichia/Shigella spp. and Bilophila wadsworthia. The relative abundance at baseline of 12 bacterial genera predicted self-reported gastrointestinal adverse effects.

CONCLUSIONS/INTERPRETATION

Intake of metformin changes the gut microbiota composition in normoglycaemic young men. The microbiota changes induced by metformin extend and validate previous reports in individuals with type 2 diabetes. Secondary analyses suggest that pre-treatment gut microbiota composition may be a determinant for development of gastrointestinal adverse effects following metformin intake. These results require further investigation and replication in larger prospective studies.

TRIAL REGISTRATION

Clinicaltrialsregister.eu 2015-000199-86 and ClinicalTrials.gov NCT02546050 FUNDING: This project was funded by Danish Diabetes Association and The Novo Nordisk Foundation.

Metformin and gut microbiota: their interactions and their impact on diabetes

The ratio of human to bacterial cells in the human body (microbiota) is around 1:1. As a result of co-evolution of the host mucosal immune system and the microbiota, both have developed multiple mechanisms to maintain homeostasis. However, dissociations between the composition of the gut microbiota and the human host may play a crucial role in the development of type 2 diabetes. Metformin, the most frequently administered medication to treat patients with type 2 diabetes, has only recently been suggested to alter gut microbiota composition through the increase in mucin-degrading Akkermansia muciniphila, as well as several SCFA-producing (short-chain fatty acid) microbiota. The gut microbiota of participants on metformin has exerted alterations in gut metabolomics with increased ability to produce butyrate and propionate, substances involved in glucose homeostasis. Thus, metformin appears to affect the microbiome, and an individual's metformin tolerance or intolerance may be influenced by their microbiome. In this review, we will focus on the effects of metformin in gut microbiota among patients with T2DM.

Metformin: Mechanisms in Human Obesity and Weight Loss

PURPOSE OF REVIEW

Metformin has multiple benefits for health beyond its anti-hyperglycemic properties. The purpose of this manuscript is to review the mechanisms that underlie metformin's effects on obesity.

RECENT FINDINGS

Metformin is a first-line therapy for type 2 diabetes. Large cohort studies have shown weight loss benefits associated with metformin therapy. Metabolic consequences were traditionally thought to underlie this effect, including reduction in hepatic gluconeogenesis and reduction in insulin production. Emerging evidence suggests that metformin-associated weight loss is due to modulation of hypothalamic appetite regulatory centers, alteration in the gut microbiome, and reversal of consequences of aging. Metformin is also being explored in the management of obesity's sequelae such as hepatic steatosis, obstructive sleep apnea, and osteoarthritis. Multiple mechanisms underlie the weight loss-inducing and health-promoting effects of metformin. Further exploration of these pathways may be important in identifying new pharmacologic targets for obesity and other aging-associated metabolic diseases.

Mitochondrial Regulation of Stem Cells in Bone Homeostasis

Mitochondria have emerged as key contributors to the organismal homeostasis, in which mitochondrial regulation of stem cells is becoming increasingly important. Originated from mesenchymal stem cell (MSC) and hematopoietic stem cell (HSC) lineage commitments and interactions, bone is a representative organ where the mitochondrial essentiality to stem cell function has most recently been discovered, underlying skeletal health, aging, and diseases. Furthermore, mitochondrial medications based on modulating stem cell specification are emerging to provide promising therapies to counteract bone aging and pathologies. Here we review the cutting-edge knowledge regarding mitochondrial regulation of stem cells in bone homeostasis, highlighting mechanistic insights as well as mitochondrial strategies for augmented bone healing and tissue regeneration.

Aerobic Exercise Training Decreases Hepatic Asprosin in Diabetic Rats

Asprosin, a novel hormone released from white adipose tissue, regulates hepatic glucose metabolism and is pathologically elevated in the presence of insulin resistance. It is unknown whether aerobic exercise training affects asprosin levels in type 1 diabetes mellitus (T1DM). The aim of this study was to determine whether (1) aerobic exercise training could decrease asprosin levels in the liver of streptozotocin (STZ)-induced diabetic rats and (2) the reduction in asprosin levels could induce asprosin-dependent downstream pathways. Five-week-old male Sprague–Dawley rats were randomly divided into control, STZ-induced diabetes (STZ), and STZ with aerobic exercise training groups (n = 6/group). T1DM was induced by a single dose of STZ (65 mg/kg intraperitoneally (i.p.)). The exercise group was made to run on a treadmill for 60 min at a speed of 20 m/min, 4 days per week for 8 weeks. Aerobic exercise training reduced the protein levels of asprosin, PKA, and TGF-β but increased those of AMPK, Akt, PGC-1β, and MnSOD. These results suggest that aerobic exercise training affects hepatic asprosin-dependent PKA/TGF-β and AMPK downstream pathways in T1DM.

Drug repurposing in oncology: Compounds, pathways, phenotypes and computational approaches for colorectal cancer

The strategy of using existing drugs originally developed for one disease to treat other indications has found success across medical fields. Such drug repurposing promises faster access of drugs to patients while reducing costs in the long and difficult process of drug development. However, the number of existing drugs and diseases, together with the heterogeneity of patients and diseases, notably including cancers, can make repurposing time consuming and inefficient. The key question we address is how to efficiently repurpose an existing drug to treat a given indication. As drug efficacy remains the main bottleneck for overall success, we discuss the need for machine-learning computational methods in combination with specific phenotypic studies along with mechanistic studies, chemical genetics and omics assays to successfully predict disease-drug pairs. Such a pipeline could be particularly important to cancer patients who face heterogeneous, recurrent and metastatic disease and need fast and personalized treatments. Here we focus on drug repurposing for colorectal cancer and describe selected therapeutics already repositioned for its prevention and/or treatment as well as potential candidates. We consider this review as a selective compilation of approaches and methodologies, and argue how, taken together, they could bring drug repurposing to the next level.

Metformin acutely lowers blood glucose levels by inhibition of intestinal glucose transport

Metformin is currently the most prescribed drug for treatment of type 2 diabetes mellitus in humans. It has been well established that long-term treatment with metformin improves glucose tolerance in mice by inhibiting hepatic gluconeogenesis. Interestingly, a single dose of orally administered metformin acutely lowers blood glucose levels, however, little is known about the mechanism involved in this effect. Glucose tolerance, as assessed by the glucose tolerance test, was improved in response to prior oral metformin administration when compared to vehicle-treated mice, irrespective of whether the animals were fed either the standard or high-fat diet. Blood glucose-lowering effects of acutely administered metformin were also observed in mice lacking functional AMP-activated protein kinase, and were independent of glucagon-like-peptide-1 or N-methyl-D-aspartate receptors signaling. [¹⁸F]-FDG/PET revealed a slower intestinal transit of labeled glucose after metformin as compared to vehicle administration. Finally, metformin in a dose-dependent but indirect manner decreased glucose transport from the intestinal lumen into the blood, which was observed ex vivo as well as in vivo. Our results support the view that the inhibition of transepithelial glucose transport in the intestine is responsible for lowering blood glucose levels during an early response to oral administration of metformin.

Effect of Metformin on Antipsychotic-Induced Metabolic Dysfunction: The Potential Role of Gut-Brain Axis

Antipsychotics are the first-line medications prescribed for patients with schizophrenia or other mental disorders. Cumulative evidence has revealed that metabolic dysfunctions frequently occur in patients receiving antipsychotics, especially second-generation antipsychotics, and these effects may decrease patient compliance and increase health costs. Metformin is an effective pharmaceutical adjuvant for ameliorating antipsychotic-induced metabolic dysfunction (AIMD) in clinical practice. However, the mechanism of the effects of metformin on AIMD remains unclear. The gut-brain axis is a bidirectional communication system between the gastrointestinal tract and the central nervous system and has been associated with many pathological and physiological conditions, such as those related to metabolism. Antipsychotics interact with and have affinity for dopamine receptors and other receptors in the brain, and treatment with these antipsychotics has been shown to influence gut microbiota metabolism and composition, as observed in both animal and human studies. Metformin exerts an antidiabetic effect that is correlated with activation of AMP-kinase in the hypothalamus, and metformin also influences gut flora. Therefore, the gut-brain axis may play a role in the effect of metformin on AIMD. Since no direct evidence is available, this perspective may provide a direction for further research.

Of mice and men: Is there a future for metformin in the treatment of hepatic steatosis?

Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver diseases, of which the first stage is steatosis. It is one of the most common liver diseases in developed countries and there is a clear association between type 2 diabetes (T2DM) and NAFLD. It is estimated that 70% of people with T2DM have NAFLD and yet there is currently no licensed pharmacological agent to treat it. Whilst lifestyle modification may ameliorate liver fat, it is often difficult to achieve or sustain; thus, there is great interest in pharmacological treatments for NAFLD. Metformin is the first-line medication in the management of T2DM and evidence from animal and human studies has suggested that it may be useful in reducing liver fat via inhibition of lipogenesis and increased fatty acid oxidation. Findings from the majority of studies undertaken in rodent models clearly suggest that metformin may be a powerful therapeutic agent specifically to reduce liver fat accumulation; data from human studies are less convincing. In the present review we discuss the evidence for the specific effects of metformin treatment on liver fat accumulation in animal and human studies, as well as the underlying proposed mechanisms, to try and understand and reconcile the difference in findings between rodent and human work in this area.

Caloric Restriction Mimetics against Age-Associated Disease: Targets, Mechanisms, and Therapeutic Potential

The increase in life expectancy has boosted the incidence of age-related pathologies beyond social and economic sustainability. Consequently, there is an urgent need for interventions that revert or at least prevent the pathogenic age-associated deterioration. The permanent or periodic reduction of calorie intake without malnutrition (caloric restriction and fasting) is the only strategy that reliably extends healthspan in mammals including non-human primates. However, the strict and life-long compliance with these regimens is difficult, which has promoted the emergence of caloric restriction mimetics (CRMs). We define CRMs as compounds that ignite the protective pathways of caloric restriction by promoting autophagy, a cytoplasmic recycling mechanism, via a reduction in protein acetylation. Here, we describe the current knowledge on molecular, cellular, and organismal effects of known and putative CRMs in mice and humans. We anticipate that CRMs will become part of the pharmacological armamentarium against aging and age-related cardiovascular, neurodegenerative, and malignant diseases.

Comparative effects of proximal and distal small intestinal administration of metformin on plasma glucose and glucagon-like peptide-1, and gastric emptying after oral glucose, in type 2 diabetes

AIMS

The gastrointestinal tract, particularly the lower gut, may be key to the anti-diabetic action of metformin. We evaluated whether administration of metformin into the distal, vs the proximal, small intestine would be more effective in lowering plasma glucose by stimulating glucagon-like pepetide-1 (GLP-1) and/or slowing gastric emptying (GE) in type 2 diabetes (T2DM).

MATERIALS AND METHODS

Ten diet-controlled T2DM patients were studied on three occasions. A transnasal catheter was positioned with proximal and distal infusion ports located 13 and 190 cm beyond the pylorus, respectively. Participants received infusions of (a) proximal + distal saline (control), (b) proximal metformin (1000 mg) + distal saline or (c) proximal saline + distal metformin (1000 mg) over 5 minutes, followed 60 minutes later by a glucose drink containing 50 g glucose and 150 mg ¹³ C-acetate. "Arterialized" venous blood and breath samples were collected over 3 hours for measurements of plasma glucose, GLP-1, insulin and glucagon, and GE, respectively.

RESULTS

Compared with control, both proximal and distal metformin reduced plasma glucose and augmented GLP-1 responses to oral glucose comparably (P < 0.05 each), without affecting plasma insulin or glucagon. GE was slower after proximal metformin than after control (P < 0.05) and tended to be slower after distal metformin, without any difference between proximal and distal metformin.

CONCLUSIONS

In diet-controlled T2DM patients, glucose-lowering via a single dose of metformin administered to the upper and lower gut was comparable and was associated with stimulation of GLP-1 and slowing of GE. These observations suggest that the site of gastrointestinal administration is not critical to the glucose-lowering capacity of metformin.

Amino acids at the intersection of nutrition and insulin sensitivity

A systems network that is coordinated in the sensing and management of nutrient signals is paramount to energy homeostasis, and its dysfunction induces metabolic stress and insulin resistance. Amino acids have recently emerged as a collection of signaling metabolites that underlie the metabolic impacts of different dietary patterns and life styles. This relationship is beginning to be understood from the close coupling of immune and metabolic systems, and serves to enrich our understanding of metabolic diseases, such as type 2 diabetes mellitus. In this review, we provide an overview of several amino acids or their metabolites that link nutrients with insulin sensitivity and discuss how they integrate into organ crosstalk pathways to influence physiological or pathological metabolic states.

Mulberry leaf active components alleviate type 2 diabetes and its liver and kidney injury in db/db mice through insulin receptor and TGF-β/Smads signaling pathway

Mulberry leaf is one of the commonly used traditional Chinese medicines, has been shown to exert hypoglycemic effects against diabetes. The aim of this study is to investigate the effects and mechanism of mulberry leaf flavonoids (MF), polysaccharides (MP) and alkaloids (MA) on diabetic and its liver and kidney injury. The db/db mice was adopted and the results showed that the FBG (fasting blood glucose) of model group continued to increase and associated liver and kidney injury. After the intervention of MP and MA, the value of FBG exhibited the most obvious hypoglycemic effect. MF and MP have obvious improved effect on kidney injury, which reduced the content of mALB/Cre (microalbumin/creatinine) in urine and improved the tubular epithelial cells edematous and renal cystic epithelial thickening. While the MF and MA possessed a significant effect on liver damage, manifested in reducing the levels of ALT (alanine aminotransferase) and AST (aspartate aminotransferase) and pathological changes of liver on db/db mice. Through metabolomics analysis, 13 endogenous potential biomarkers were identified in serum. The three effective components of mulberry can regulate the 13 potential biomarkers and the corresponding metabolic pathway. Collectively, the components of mulberry leaf have clear hypoglycemic effect and protective effect on liver and kidney injury and the effects are related to insulin receptor and TGF-β/Smads signaling pathway.

Inhibition of upper small intestinal mTOR lowers plasma glucose levels by inhibiting glucose production

Glucose homeostasis is partly controlled by the energy sensor mechanistic target of rapamycin (mTOR) in the muscle and liver. However, whether mTOR in the small intestine affects glucose homeostasis in vivo remains unknown. Here, we first report that delivery of rapamycin or an adenovirus encoding the dominant negative acting mTOR-mutated protein into the upper small intestine is sufficient to inhibit small intestinal mTOR signaling and lower glucose production in rodents with high fat diet-induced insulin resistance. Second, we found that molecular activation of small intestinal mTOR blunts the glucose-lowering effect of the oral anti-diabetic agent metformin, while inhibiting small intestinal mTOR alone lowers plasma glucose levels by inhibiting glucose production in rodents with diabetes as well. Thus, these findings illustrate that inhibiting upper small intestinal mTOR is sufficient and necessary to lower glucose production and enhance glucose homeostasis, and thereby unveil a previously unappreciated glucose-lowering effect of small intestinal mTOR.

The mechanistic target of rapamycin (TOR) functions as an energy sensor and contributes to the control of glucose homeostasis. Here, the authors show that mTOR in the upper small intestine regulates hepatic glucose production and is required for the glucose lowering effect of metformin.

Metformin attenuates renal medullary hypoxia in diabetic nephropathy through inhibition uncoupling protein-2

BACKGROUND

The purpose of the study is to examine the effect of metformin on oxygen metabolism and mitochondrial function in the kidney of an animal model of insulinopenic diabetes in order to isolate any renoprotective effect from any concomitant effect on blood glucose homeostasis.

METHODS

Sprague-Dawley rats were injected with streptozotocin (STZ) (50 mg kg^-1 ) and when stable started on metformin treatment (250 mg kg^-1 ) in the drinking water. Rats were prepared for in vivo measurements 25 to 30 days after STZ injection, where renal function, including glomerular filtration rate and sodium transport, was estimated in anesthetized rats. Intrarenal oxygen tension was measured using oxygen sensors. Furthermore, mitochondrial function was assessed in mitochondria isolated from kidney cortex and medulla analysed by high-resolution respirometry, and superoxide production was evaluated using electron paramagnetic resonance.

RESULTS

Insulinopenic rats chronically treated with metformin for 4 weeks displayed improved medullary tissue oxygen tension despite of no effect of metformin on blood glucose homeostasis. Metformin reduced UCP2-dependent LEAK and differentially affected medullary mitochondrial superoxide radical production in control and diabetic rats.

CONCLUSIONS

Metformin attenuates diabetes-induced renal medullary tissue hypoxia in an animal model of insulinopenic type 1 diabetes. The results suggest that the mechanistic pathway to attenuate the diabetes-induced medullary hypoxia is independent of blood glucose homeostasis and includes reduced UCP2-mediated mitochondrial proton LEAK.

Metabolomics profiling of metformin-mediated metabolic reprogramming bypassing AMPKα

BACKGROUND

Metformin is a first-line drug for treating type 2 diabetes and has gained considerable interest as a potential anticancer agent. Increasing evidence suggests that metformin antagonizes diabetes and tumors through disrupting metabolic homeostasis and altering energy state. However, whether AMP activated protein kinase (AMPK) contributes to such effects of metformin remains controversial.

METHODS

We performed integrative metabolomics analyses to systematically examine the effects of metformin on metabolic pathways in Prkaa1 wild type (WT) and knock-out (KO) mouse embryonic fibroblast (MEF) cells as well as human cells based on gas chromatography-mass spectrometry and capillary electrophoresis-mass spectrometry (CE-MS).

RESULTS

Metformin treatment induced metabolic reprogramming and reduced the energy state of both Prkaa1 WT and KO MEF cells, as evidenced by suppressed tricarboxylic acid (TCA) cycle, elevated lactate production as well as decreased NAD⁺/NADH ratio. Additionally, metabolic flux analysis also showed that metformin Ampkα-independently increased metabolic flux from glucose to lactate and decreased metabolic flux from acetyl-CoA to TCA cycle as well as from pyruvate to malate. Moreover, metformin Ampkα-dependently upregulated P-Acc but Ampkα-independently inhibited the levels of P-mTor, P-S6, Lc3, Atgl and P-Erk in MEF cells. Similarly, we demonstrated that a commonly used AMPK agonist 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) and fetal bovine serum (FBS) starvation, as a common model for energy stress, both led to Ampkα-independent metabolism alterations in MEF cells. Furthermore, these effects of metformin were also confirmed in human hepatocellular carcinoma (HCC) cells as well as in MCF10A shControl and shPRKAA1 cells. Importantly, we found that metformin could obviously inhibit colony conformation of HCC cells in an Ampkα-independent manner.

CONCLUSIONS

Our data highlight a comprehensive view of metabolic reprogramming mediated by metformin as well as AICAR. These observations suggest that metformin could affect cellular metabolism largely bypassing Ampkα, and may provide a new insight for its clinical usage.

Gut ghrelin regulates hepatic glucose production and insulin signaling via a gut-brain-liver pathway

BACKGROUND

Ghrelin modulates many physiological processes. However, the effects of intestinal ghrelin on hepatic glucose production (HGP) are still unclear. The current study was to explore the roles of intestinal ghrelin on glucose homeostasis and insulin signaling in the liver.

METHODS

The system of intraduodenal infusion and intracerebral microinfusion into the nucleus of the solitary tract (NTS) in the normal chow-diet rats and pancreatic-euglycemic clamp procedure (PEC) combined with [3-³H] glucose as a tracer were used to analyze the effect of intestinal ghrelin. Intraduodenal co-infusion of ghrelin, tetracaine and Activated Protein Kinase (AMPK) activator (AICAR), or pharmacologic and molecular inhibitor of N-methyl-D-aspartate receptors within the dorsal vagal complex, or hepatic vagotomy in rats were used to explore the possible mechanism of the effect of intestinal ghrelin on HGP.

RESULTS

Our results demonstrated that gut infusion of ghrelin inhibited duodenal AMP-dependent protein kinase (AMPK) signal pathways, increased HGP and expression of gluconeogenic enzymes, and decreased insulin signaling in the liver of the rat. Intraduodenal co-infusion of ghrelin receptor antagonist [D-Lys³]-GHRP-6 and AMPK agonist with ghrelin diminished gut ghrelin-induced increase in HGP and decrease in glucose infusion rate (GIR) and hepatic insulin signaling. The effects of gut ghrelin were also negated by co-infusion with tetracaine, or MK801, an N-methyl-D-aspartate (NMDA) receptor inhibitor, and adenovirus expressing the shRNA of NR1 subunit of NMDA receptors (Ad-shNR1) within the dorsal vagal complex, and hepatic vagotomy in rats. When ghrelin and lipids were co-infused into the duodenum, the roles of gut lipids in increasing the rate of glucose infusion (GIR) and lowering HGP were reversed.

CONCLUSIONS

The current study provided evidence that intestinal ghrelin has an effect on HGP and identified a neural glucoregulatory function of gut ghrelin signaling.

Silibinin decreases hepatic glucose production through the activation of gut-brain-liver axis in diabetic rats

Silibinin, a flavonolignan derived from milk thistle (Silybum marianum), has been revealed to have a beneficial effect on improving diabetes-impaired glycemic control. However, the underlying mechanism is still unclear. In the present study, to evaluate whether the gut-brain-liver axis, an important neural pathway for the control of hepatic glucose production, is involved in silibinin-regulated glucose homeostasis, the expression of glucagon-like peptide-1 receptor (GLP1R) in the duodenum, activation of neurons in the nucleus of the solitary tract (NTS), as well as glycogen accumulation and expression of gluconeogenic enzymes in the livers of diabetic SHRSP·Z-Leprfa/IzmDmcr (SP·ZF) rats with 4-week oral administration of silibinin (100 and 300 mg kg-1 day-1) were evaluated. Common hepatic branch vagotomy was further conducted in high-fat diet/streptozotocin (HFD/STZ)-induced diabetic SD rats to confirm the role of the gut-brain-liver axis in silibinin-improved glycemic control. The results revealed a significant inhibition of fasting blood glucose after SP·ZF rats were administrated with silibinin for 4 weeks. The expression of GLP1R in the duodenum and the activation of neurons in the NTS increased, while hepatic glucose production decreased on silibinin administration. However, the hypoglycemic effect of silibinin was reversed by common hepatic branch vagotomy in diabetic SD rats. Our study suggested that silibinin may be useful as a potential functional food ingredient against diabetes by triggering the gut-brain-liver axis.

Glyoxalase 1 Modulation in Obesity and Diabetes

Significance: Obesity and type 2 diabetes mellitus are increasing globally. There is also increasing associated complications, such as non-alcoholic fatty liver disease (NAFLD) and vascular complications of diabetes. There is currently no licensed treatment for NAFLD and no recent treatments for diabetic complications. New approaches are required, particularly those addressing mechanism-based risk factors for health decline and disease progression. Recent Advances: Dicarbonyl stress is the abnormal accumulation of reactive dicarbonyl metabolites such as methylglyoxal (MG) leading to cell and tissue dysfunction. It is a potential driver of obesity, diabetes, and related complications that are unaddressed by current treatments. Increased formation of MG is linked to increased glyceroneogenesis and hyperglycemia in obesity and diabetes and also down-regulation of glyoxalase 1 (Glo1)-which provides the main enzymatic detoxification of MG. Glo1 functional genomics studies suggest that increasing Glo1 expression and activity alleviates dicarbonyl stress; slows development of obesity, related insulin resistance; and prevents development of diabetic nephropathy and other microvascular complications of diabetes. A new therapeutic approach constitutes small-molecule inducers of Glo1 expression-Glo1 inducers-exploiting a regulatory antioxidant response element in the GLO1 gene. A prototype Glo1 inducer, trans-resveratrol (tRES)-hesperetin (HESP) combination, in corrected insulin resistance, improved glycemic control and vascular inflammation in healthy overweight and obese subjects in clinical trial. Critical Issues: tRES and HESP synergize pharmacologically, and HESP likely overcomes the low bioavailability of tRES by inhibition of intestinal glucuronosyltransferases. Future Directions: Glo1 inducers may now be evaluated in Phase 2 clinical trials for treatment of NAFLD and vascular complications of diabetes.