Synergistic Effects Of Metformin Research Articles

Metformin: From Diabetes to Cancer-Unveiling Molecular Mechanisms and Therapeutic Strategies.

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin's role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Synergistic effects of Metformin and Forskolin on oxidative stress induced by diabetes and hepatocellular cancer: An animal study

AimThis study proposed to assess the synergistic effects of Forskolin and Metformin (alone and in combination) on glucose, hematological, liver serum, and oxidative stress parameters in diabetic, healthy, and hepatocellular carcinoma (HCC) induced rats. Materials and methodsEighty male Wistar rats were divided into 10 experimental groups (8 rats for each group), including 1) healthy group, 2) diabetic group, 3) HCC group, 4) diabet + Metformin (300 mg/kg), 5) diabet + Forskolin (100 mg/kg), 6) diabet + Metformin (300 mg/kg) & Forskolin (100 mg/kg), 7) HCC + Metformin (300 mg/kg), 8) HCC + Forskolin (100 mg/kg), 9) HCC + Metformin (300 mg/kg) & Forskolin (100 mg/kg), and 10) healthy group + Metformin (300 mg/kg) & Forskolin (100 mg/kg). The rats were administrated Forskolin/Metformin daily for 8 weeks. Glucose, hematological, and liver serum parameters were measured and compared among the groups. The levels of malondialdehyde (MDA), and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx), as well as 8-hydroxydeoxyguanosine (8 OHdG) levels, were also measured. ResultsThe average blood glucose reduction in diabetic rats with the Forskolin, Metformin, and Forskolin + Metformin treatments was 43.5%, 47.1%, and 53.9%, respectively. These reduction values for HCC rats after the treatments were 21.0%, 16.2%, and 23.7%, respectively. For all the diabetic and HCC rats treated with Forskolin/Metformin, the MDA, SOD, and GPx levels showed significant improvement compared with the diabetic and HCC groups (P < 0.05). Although the rats treated with Forskolin + Metformin experienced a higher reduction in oxidative stress of blood and urine samples compared to the Forskolin group, the differences between this group and rats treated with Metformin were not significant for all parameters. ConclusionMetformin and Forskolin reduced oxidative stress in diabetic and HCC-induced rats. The results indicated that the combination of agents (Metformin & Forskolin) had greater therapeutic effects than Forskolin alone in reducing glucose levels in diabetic rats. However, the ameliorative effects of combining Metformin and Forskolin on blood and urine oxidative stress were not statistically higher than those of Metformin alone.

Synergistic Effects of Metformin and Trastuzumab on HER2 Positive Gastroesophageal Adenocarcinoma Cells In Vitro and In Vivo.

The incidence of HER2 amplification in advanced gastroesophageal adenocarcinoma (GC) reportedly ranges between 10% and 20%, depending on the population studied and the geographical region. Trastuzumab (Tmab) is the standard treatment for GCs with HER2 amplification. Metformin, a widely used antidiabetic drug, is an activator of AMP kinase that can affect the mTOR signaling pathway. The following GC cells were evaluated: HER2+ NCI-N87, YCC-19, YCC-38, OE19, OE33, and HER2- AGS. The effects of Tmab and metformin on these cell lines were assessed as single agents and in combination using cell viability assays, Western blotting, and xenograft models. Metformin induced phosphorylation of AMP kinase in all tested GC cells and dephosphorylation of mTOR in Tmab-sensitive GC cells. We observed that treatment with Tmab in combination with metformin induced a significant decrease in the number of colonies formed on soft agar by N87, YCC-19, YCC-38, and OE19 cells (88%, 95%, 73%, and 98%, respectively), in comparison to the number formed by control cells or cells in the single-treatment groups. No growth inhibition was detected in OE33 cells treated with Tmab alone. Combination with metformin resulted in decreased phosphorylation of HER2 and its downstream targets, AKT and ERK, in Tmab-sensitive HER2+ cells. Phospho-receptor tyrosine kinase (RTK) arrays were used to profile the phospho-proteome, which demonstrated a synergistic decrease in phosphorylation of EGFR, HER2, and HER3. Furthermore, the combination of Tmab and metformin exhibited enhanced antitumor effects in a xenograft model. Collectively, these data suggest that Tmab and metformin act synergistically in HER2+ GC cells. Since metformin is widely used and relatively non-toxic, its addition to the therapeutic regimen along with Tmab could enhance the clinical efficacy in patients with HER2+ GC.

Metformin combined with glucose starvation synergistically suppress triple-negative breast cancer by enhanced unfolded protein response

Metformin (MET) is a well-documented drug used in the treatment of type II diabetes. Recent studies have revealed its potential anti-tumor effects in various types of cancer. However, the dosage of MET required to exhibit anti-tumor activity is considerably higher than the clinically recommended dosage. In this study, we investigated the synergistical anti-tumor effect of glucose deprivation and MET in MDA-MB-231 cells, which represents a triple-negative breast cancer subtype (TNBC). Our findings demonstrate that glucose deprivation significantly enhances the anti-tumor activity of MET by reducing cell proliferation and increasing cell apoptosis. RNA-seq was performed to identify the key molecules involved in this process. Our results indicate that unfolded protein response of endoplasmic reticulum (UPRER) was significantly activated upon glucose starvation combining with MET compared to glucose starvation alone. Notably, the combined treatment significantly activated UPRER signaling pathway through ATF4/ATF3/CHOP axis, due to enhanced UPRER stress. In conclusion, our study suggests that the synergistic effects of MET and glucose deprivation suppress cell proliferation in TNBC by activating pro-apoptotic molecules through UPRER stress. These findings have potential implications for the anti-tumor application of MET in TNBC.

The Synergistic Glucose-lowering Effects of Metformin and Bavachinin on Type II Diabetic Rats

Background: Diabetes is one of the most prevalent endocrine disorders in humans, and its first-line medication is metformin. Peroxisome proliferator-activated receptor gamma (PPAR–γ) agonists are the adjuncts to metformin. Bavachinin is a PPAR pan-agonist with fewer side effects than metformin" into PPAR–γ agonists. In this study, the synergistic effects of metformin and Bavachinin were investigated on type II diabetic rats. Methods: After four weeks of a high fat and glucose diet, type II diabetes was induced in 28 male Wistar rats, using injection of streptozotocin and nicotinamide. The animals were distributed into five groups of seven each: 1) Normal control (N), 2) Diabetic control (D), 3) Diabetic rats receiving metformin (DM), 4) Bavachinin (DB), and 5) Metformin plus Bavachinin (DMB). Oral glucose tolerance test (OGTT), fasting blood glucose (FBG), fasting insulin (FINS), homeostasis model assessment of β-cell function (HOMA-β), homeostasis model assessment of insulin resistance (HOMA-IR), and insulin sensitivity index (ISI) were obtained. Results: The OGTT results in DM, DB, and DMB groups were significantly improved compared to that of D group. The FBG levels were significantly lower in DMB than in DB, DM, and D groups. The FINS levels of DMB were significantly less than those of DB, DM, and D groups. The HOMA-IR and HOMA-β were comparable between DMB and N groups. The ISI improved significantly in DMB compared to those in DM, DB, and D groups. Conclusion: Bavachinin may be used combined with metformin for the treatment of type II diabetes at lower doses of metformin, thus having fewer side effects.

Metformin Facilitates Osteoblastic Differentiation and M2 Macrophage Polarization by PI3K/AKT/mTOR Pathway in Human Umbilical Cord Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are the most promising multipotent stem cells that can differentiate into osteoblasts, chondrocytes, and adipocytes. This cellular flexibility contributes to widespread clinical use of MSCs in tissue repair and regeneration. The immune system is a key player in regulating bone remodeling. In recent years, the association between the immune system and bone metabolism has become an increasing focus of interest. Metformin, a glucose-lowering drug, exerts powerful impact on metabolic signaling. However, whether metformin can modulate bone metabolism or whether metformin can influence immune milieu by regulation of macrophages has not been thoroughly elucidated. Herein, we specifically explored the complex interactions between macrophages and human umbilical cord mesenchymal stem cells (UC-MSCs) in the context of metformin. Our research demonstrated that metformin not only stimulated osteogenesis of UC-MSCs but also influenced the immune system via promoting M2 but reducing M1 macrophages. Mechanically, we found that metformin-treated M2 macrophages possessed more potent osteoinductive capacity in our coculture system. Molecularly, these metformin-stimulated M2 macrophages facilitated osteogenesis via activating the PI3K/AKT/mTOR pathway. As demonstrated by using PI3K-specific inhibitor LY294002, we found that the pathway inhibitor partly reversed osteoinductive activity which was activated by coculture of metformin-treated M2 macrophages. Overall, our novel research illuminated the cooperative and synergistic effects of metformin and M2 macrophages on the dynamic balance of bone metabolism.

Synergistic effects of metformin and curcumin on cytotoxicity of chemotherapy drugs using a gastric cancer cell line model.

Gastric cancer has a weak prognosis and its usual treatments depend on surgery and chemotherapy. These treatments suffer from some drawbacks such as high rates of local recurrence and metastasis, low survival rates, and significantly decreased life quality. Therefore, new therapeutic methods for improved gastric cancer care with minimal side effects seem necessary. Currently, combinatorial treatments for cancer are preferred and recently, metformin (Met) and curcumin (Cur) have been interesting options for this type of therapy. The aim of the present study was to investigate anticancer effects of metformin and curcumin in both single and combinatorial treatment forms on AGS gastric cancer cell line. In comparison to single treatments with each substance, the results of co-treatments with metformin and curcumin indicated synergistic inhibitory effects on cell viability, wound healing, cell migration and invasion, and primary tumor formation. To determine the selective effect of combination of “Met + Cur” on cancerous cells, very low doses of 8 anticancer drugs (cisplatin, carboplatin, oxaliplatin, epirubicin, doxorubicin, docetaxel, paclitaxel, and methotrexate) used in MTT assay were comparatively tested on AGS cancer cells and normal HDF cells for 48 and 72 hours. The results indicated that the combination of “Met + Cur” significantly increased cytotoxic effects of all anticancer drugs of AGS cells. It is while in normal HDF cells, combination of “Met + Cur” along with anticancer drugs had no effect. This can be inferred as selectively additive effect.

Inhibition of angiotensin-induced aortic aneurysm by metformin in apolipoprotein E–deficient mice

ObjectiveMetformin is associated with a reduced incidence and growth of abdominal aortic aneurysms (AAAs). The aim of the present study was to investigate the inhibitory effects of metformin on AAA development and possible underlying mechanisms in experimentally induced AAAs in mice, along with the possible synergistic effects of metformin and imatinib. MethodsAngiotensin II was used to induce AAAs in apolipoprotein E knockout (ApoE−/−) mice for 28 days. The mice were treated with metformin (n = 11), metformin combined with imatinib (n = 7), or vehicle (n = 12), starting 3 days before angiotensin II infusion. Ultrasound examination was used to analyze aneurysm formation. Cholesterol and blood pressure levels were measured at the start and end of the study. Gene array and quantitative polymerase chain reaction were used to analyze the changes in gene expression in the aorta. Wire myography was used to study vascular function. ResultsMetformin (n = 11) suppressed the formation and progression of AAAs by 50% compared with the vehicle controls (n = 12), with no further effects from imatinib (n = 7). Metformin reduced total cholesterol and mRNA expression of SPP1 (encoding osteopontin), MMP12, and the glycoprotein genes Gpnmb and Clec7a. Furthermore, metformin inhibited blood pressure increases and reduced vascular contractions, as determined by wire myography, and restored the anticontractile function of perivascular adipose tissue. ConclusionMetformin inhibited aneurysm formation and progression and normalized vascular function in ApoE−/− mice with no additional effect of imatinib. This might be mediated by the protective effects on vascular endothelial function and perivascular adipose tissue via reduced expression of genes promoting inflammation, including SPP1, MMP12, Gpnmb, and Clec7a. Clinical relevanceRetrospective studies of the effects of metformin in patients with aneurysm have so far only been performed of those with type 2 diabetes. The present study shows that metformin has effects on nondiabetic mice and revealed the mechanistic effects mediated by the drug that could also be important to study as outcomes in humans. Future clinical trials using metformin are warranted in patients without diabetes with abdominal aortic aneurysms.

Synergistic Effects of Metformin and Cocoa Flavanol on Inflammatory and Oxidant Markers Induced by Carrageenan: Pathophysiological Approach

Background and Aim: The present study aims to evaluate the effects of metformin, cocoa flavanol and their combination as anti-inflammatory and antioxidant drugs. Methods: Forty adult male albino mice are divided into five groups: Control, Carrageenan (Cg), Cg Metformin (Met), Cg Cocoa and Cg Met Cocoa groups. Cg is used to induce the inflammation through injection of it in the paw of the hind leg and into the trunk of mice. Also, Met is applied intraperitoneally at the same time of Cg injection while Cocoa is received orally seven days before carrageenan injection. Biochemical estimation of inflammatory mediators (COX-2, PGE2, TNF-α, CRP) and selected oxidative stress markers (MDA, SOD, GSH) was performed. Results: This study elucidated the marvellous leverage of the metformin, cocoa flavanol and their combination as anti-inflammatory and antioxidant drugs, where metformin and Cocoa decreased all inflammatory mediators (COX-2, PGE2, TNF-α, CRP) with high significant (P<0.01) in comparing with Cg group. In addition, the level of MDA is decreased significantly (P<0.01), while the levels of SOD and GSH are increased significantly (P<0.01) in comparing with Cg group. Interestingly, their combination restored normal levels of the inflammatory mediators and the oxidative stress markers. Conclusion: I concluded that Met and cocoa are powerful anti-inflammatory substances and can ameliorate the oxidative stress that results from inflammation. Additionally, the mixture of them can retrieve the normal levels of all measured parameters.

The Role of SAPK/JNK Pathway in the Synergistic Effects of Metformin and Dacarbazine on Apoptosis in Raji and Ramos Lymphoma Cells.

Besides the first-line medication for the treatment of type 2 diabetes, the growth inhibitory activity of metformin alone or in combination with conventional chemotherapeutics has been addressed on a panel of cell lines. In this study, we investigated the cytotoxicity and apoptosis of the metformin alone and in combination with dacarbazine in Raji and Ramos lymphoma cell lines. Cell viability and apoptosis measured using resazurin assay, flow cytometry of PI stained cells and western blot analysis. Metformin showed synergistic cytotoxic effects in combination with dacarbazine, reduced cell viability, and increased apoptosis in Raji and Ramos lymphoma cells in comparison with the use of each drug alone. The activation of MAPK and SAPK/JNK (P-SAPK/JNK) were shown in both cells. Overall, the result verified the synergistic effect of the metformin-dacarbazine combination, which has the value in reducing the chemotherapeutic agent dose, adverse effect and the burden of treatment for the community and patients.

Synergistic effect of metformin on sorafenib in in vitro study using hepatocellular carcinoma cell lines.

Backgrounds/AimsHepatocellular carcinoma (HCC) recurrence remains a great concern following hepatic resection and liver transplantation. We investigated the metformin-induced cytotoxic effects on sorafenib in an in vitro study using HCC cell lines.MethodsThis research was conducted through an in vitro study using one HepG2.2.15 liver tumor and two patient-derived graft HCC cell lines.ResultsAn in vitro study revealed noticeable cytotoxic effects of metformin as well as noticeable synergistic cytotoxic effects of metformin and sorafenib on cell viability. Assays for the mechanisms of action of antitumor effects revealed that alpha-fetoprotein expression was suppressed by both metformin and sorafenib, but no synergistic effect was observed. LC3-I and LC3-II assays revealed the synergistic upregulation of autophagy and assays for IL-1β, IL-6, p53, and TNF-α revealed the synergistic upregulation of cell damage and apoptosis. In contrast, metformin did not affect HBx expression, thus no noticeable synergistic effect was considered to be present.ConclusionsOur in vitro study demonstrated cytotoxic effects of metformin and synergistic antitumor effects of sorafenib. These results should be verified in further clinical studies with patients of advanced HCC.

Synergistic Effects of Metformin and Captopril on C. elegans

There are over 400 million patients suffering from type 2 diabetes and over 1 billion suffering from hypertension. Pharmaceuticals commonly used by these patients include Metformin for type 2 diabetes and Captopril for hypertension. Considering that the two diseases are interrelated, and can both be seen in an individual, Metformin and Captopril take part in combination therapies for many people. However, the synergistic effects of these active ingredients have not been previously documented. This study examines the effects of Metformin and Captopril using model organisms called Caenorhabditis elegans nematode worms. Concentrations of Metformin were 25mM, 50mM and 100mM, while those of Captopril were 2mM, 4mM, 6mM and 20mM. The combination group contained Metformin and Captopril synchronised as 25mM-2mM, 50mM-4mM, and 100mM-6mM, respectively. The independent variable is the concentration of active ingredients, whereas the dependent variable is the change in body length of C. elegans nematodes. The experiment involved the picking of the worms from the containing petri dishes under a stereomicroscope and measuring their body lengths with the software of a digital microscope. The results showed up to 25% decrease in average body lengths of the worms exposed to Metformin solely. Captopril caused 5% decrease in average body length of the worms. When Metformin and Captopril were combined, an increase of up to 11% in average body length was recorded. C. elegans body size is regulated by the TGF-β signal pathway, and the possible outcomes of the manipulation of body length by Metformin and Captopril are further discussed.

Synergistic effects of metformin with liraglutide against endothelial dysfunction through GLP-1 receptor and PKA signalling pathway

Metformin or glucagon-like peptide-1 (GLP-1) analogue liraglutide has cardiovascular benefits. However, it is not clear whether their combined treatment have additive or synergistic effects on the vasculature. In this study, human umbilical vein endothelial cells (HUVECs), exposed to palmitic acid (PA) to induce endothelial dysfunction, were incubated with metformin, liraglutide or their combination. High fat diet (HFD)-fed ApoE−/− mice were randomized into control, metformin, liraglutide, and combination treatment groups. Results showed that in PA-treated HUVECs and HFD-fed ApoE−/− mice, combination of metformin and liraglutide at lower dose significantly improved endothelial dysfunction compared with the single treatment. Metformin upregulated GLP-1 receptor (GLP-1R) level and protein kinase A (PKA) phosphorylation. However, PKA inhibition but not GLP-1R blockade eliminated the protective effects of metformin on endothelial function. Furthermore, AMPK inhibitor compound C abolished the metformin-mediated upregulation of GLP-1R level and PKA phosphorylation. In conclusion, combination of metformin and liraglutide has synergistic protective effects on endothelial function. Moreover, metformin stimulates GLP-1R and PKA signalling via AMPK-dependent pathway, which may account for its synergistic protective effects with liraglutide. Our findings provide new insights on the interaction between metformin and GLP-1, and provide important information for designing new GLP-1-based therapy strategies in treating type 2 diabetes.

Synergistic effects of metformin in combination with EGFR-TKI in the treatment of patients with advanced non-small cell lung cancer and type 2 diabetes

BackgroundAcquired resistance has become the bottleneck affecting the efficacy of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) treatment. Studies have shown that the antidiabetic drug metformin could effectively increase the sensitivity of TKI-resistant lung cancer cells to EGFR-TKI. This study aimed to evaluate the effect of metformin in combination with EGFR-TKI on the prognosis of non-small cell lung cancer (NSCLC) patients with diabetes mellitus type 2 (DM2). MethodsData of NSCLC patients with DM2 who received treatment in six hospitals in China between January 2006 and January 2014 were reviewed retrospectively. They were divided into two groups: Group A, where the patients (n = 44) received EGFR-TKI plus metformin; and Group B, where the patients (n = 46) received EGFR-TKI plus hypoglycemic agents other than metformin. Prognostic differences between the two groups were assessed. ResultsThe median progression-free survival (PFS) and median overall survival (OS) in Group A were significantly longer than those in Group B (19.0 months vs. 8.0 months, P = .005; 32.0 months vs. 23.0 months, P = .002). The objective response rate (ORR) and disease control rate (DCR) in Group A were significantly higher than those in Group B (70.5% vs. 45.7%, P = .017; 97.7% vs. 80.4%, P = .009). Secondary data analysis showed that metformin use significantly prolonged the median PFS in subgroups using either first-line EGFR-TKI or second-line EGFR-TKI. ConclusionsMetformin and EGFR-TKI have a synergistic effect in the treatment of DM2 NSCLC patients harboring EGFR-activating mutations. Metformin use is associated with improved survival and delayed onset of acquired resistance to EGFR-TKI.

Preclinical model for combined effects of metformin and vitamin D3 on colitis-associated colon neoplasia.

e14634 Background: Metformin and vitamin D each has been shown to have anti-colon carcinogenic effects in pre-clinical and epidemiologic studies. We tested the potential synergistic effects of Metformin and vitamin D3 against colorectal neoplasia in a DMH-DSS induced colitis-associated colon neoplasia mouse model. Methods: We randomized 182 5-week old ICR male mice into 7 groups: 1) normal controls; 2) DMH controls; 3) DSS controls; 4) DMH + DSS controls; 5) vitamin D3 (3 dosage groups), 6) metformin (3 dosage groups), and 7) vitamin D3 + metformin (3 dosage combinations). After 20 weeks of treatment, the mice were sacrificed and colon tissues were harvested and examined for multiplicity of adenoma/cancer, volume of each tumor, number and score of aberrant crypt foci (ACF). Results: Compared to the DMH + DDS controls, combination of vitamin D3 (200 IU/kg/day) and metformin (240 mg/kg/day) statistically significantly reduced the average number of adenoma/cancer per mouse formed (6.20 ± 3.68 vs. 2.20 ± 2.12, p&lt;0.01), volume (mm3 ) of tumor (115.46 ± 107.32 vs. 31.05 ± 38.26, p&lt; 0.05), number of ACF (0.46 ± 0.88 vs. 2.58 ± 1.93, p &lt;0.01), and ACF score (5.00 ± 3.26 vs. 1.23 ± 2.04, p &lt;0.01). Western blot and IHC show that vitamin D3 potentiates metformin in activating AMPK (phos-AMPK: 0.53 ± 0.01 vs. 0.70 ± 0.03, p &lt; 0.01), inhibiting AKT (phos-AKT: 0.39 ± 0.10 vs. 0.15 ± 0.04, p &lt; 0.01), S6P (phos-S6P: 0.36 ± 0.03 vs. 0.14 ± 0.04, p &lt;0.01), cyclin D1 (0.24 ± 0.02 vs. 0.06 ± 0.02, p &lt;0.01), ?-catenin (0.808 ± 0.142 vs. 0.010 ± 0.001, p &lt; 0.01), and VDR (0.182 ± 0.045 vs. 0.488 ± 0.081). Combination treatment also statistically significantly increases serum levels of IGFBP-3, with little effect on IGF-1, IGFBP-1 or IL-1?. Conclusions: Metformin and vitamin D3 synergistically inhibit the development of colorectal neoplasia in a colitis-associated mouse colon carcinogenesis model. Further study of the underlying mechanisms is warranted.

Synergistic effects of metformin, resveratrol, and hydroxymethylbutyrate on insulin sensitivity

BackgroundThe purpose of this study was to determine whether a mixture of the polyphenol, resveratrol, and the leucine metabolite, hydroxymethylbutyrate (HMB), acts synergistically with low doses of metformin to impact insulin sensitivity and AMP-activated protein kinase-dependent outcomes in cell culture and in diabetic mice.MethodsC2C12 skeletal myotubes and 3T3-L1 adipocytes were treated with resveratrol 0.2 μM, HMB 5 μM, and metformin 0.1 mM alone or in combination. db/db mice were treated for 2 weeks with high (1.5 g/kg diet), low (0.75 g/kg diet), or very low (0.25 g/kg diet) doses of metformin alone or in combination with a diet containing resveratrol 12.5 mg and CaHMB 2 g/kg.ResultsThe combination of metformin-resveratrol-HMB significantly increased fat oxidation, AMP-activated protein kinase, and Sirt1 activity in muscle cells compared with metformin or resveratrol-HMB alone. A similar trend was found in 3T3L1 adipocytes. In mice, the two lower doses of metformin exerted no independent effect but, when combined with resveratrol-HMB, both low-dose and very low-dose metformin improved insulin sensitivity (HOMAIR), plasma insulin levels, and insulin tolerance test response to a level comparable with that found for high-dose metformin. In addition, the metformin-resveratrol-HMB combination decreased visceral fat and liver weight in mice.ConclusionResveratrol-HMB combined with metformin may act synergistically on AMP-activated protein kinase-dependent pathways, leading to increased insulin sensitivity, which may reduce the therapeutic doses of metformin necessary in the treatment of diabetes.

Inverse relationship between peripheral insulin removal and action: studies with metformin

The interaction of insulin with metformin on muscle glucose metabolism was examined in the perfused rat hindquarter. Glucose, lactate, and insulin were measured at the inflow to and outflow from the hindquarter, which was perfused with human erythrocytes suspended in a Kreb's-Ringer albumin buffer for 120 min. Perfusions were performed with no additions (I) and with insulin infusions targeted to concentrations of 175 (II) and 350 pmol/l (III) as well as infusions targeted to levels of 0 (IV), 70 (V), and 175 pmol/l (VI) but in the presence of metformin (90 microg/ml). In the presence of metformin, identical infusion rates of insulin yielded higher insulin concentrations, namely 283 +/- 19 vs. 202 +/- 31 pmol/l for VI and II, respectively (P < 0.05). Glucose uptake (GU) increased correspondingly to 79.8 +/- 0.8 in VI from 60.8 +/- 2.1 for IV and 50.1 +/- 1.3 for II and 46.1 +/- 2.7 mg/120 min for I (P < 0.05). This enhanced GU was matched by increasing insulin levels using only a higher rate of its infusion (III): GU of 70.2 +/- 2.4 mg/120 min with insulin of 334 +/- 26 pmol/l (P > 0.05). The simple concurrent presence of metformin and insulin [matching insulin concentrations in II rather than infusion rates (IV)] demonstrated no additonal effect on GU above that of metformin. The synergistic effects of metformin and insulin could thus be explained by a metformin-mediated decrease in the extraction of insulin by the hindquarter (4.8 +/- 0.4% vs. 8.6 +/- 0.9%, P < 0.05). This increases interstitial insulin (and, in a closed system, perfusate insulin), which acts on cell surface receptors to increase glucose uptake. The results demonstrate that the extracellular insulin concentration, rather than insulin internalization and degradation, is the primary determinant of insulin action on GU in muscle and that changes in tissue insulin extraction may alter local concentrations and, therefore, systemic insulin sensitivity. This provides both a physiological mechanism and a possible therapeutic target for improving insulin sensitivity.