Carnosic Acid (CA) Induces a Brown Fat-like Phenotype, Increases Mitochondrial Biogenesis, and Activates AMPK in 3T3-L1 Adipocytes

Adipose tissue plays a crucial role in regulating metabolic homeostasis, and its dysfunction in obesity leads to insulin resistance and type 2 diabetes (T2D). White adipose tissue (WAT) primarily stores energy as lipids, while brown adipose tissue (BAT) regulates thermogenesis by dissipating energy as heat. The process of browning involves the transdifferentiation of WAT into brown-like or beige adipocytes, which exhibit a similar phenotype as BAT. The browning of WAT is an attractive approach against obesity and T2D, and the activation of the energy sensor AMP-activated protein kinase (AMPK) has been shown to play a role in browning. Carnosic acid (CA), a polyphenolic diterpene, found in many plants including rosemary, is reported to possess potent antioxidant, anti-inflammatory, and anti-hyperglycemic properties. The limited evidence available indicates that CA activates AMPK and may have anti-obesity and antidiabetic potential; however, the effects in adipocyte browning remain largely unexplored. This study aimed to examine the effects of CA on the markers of adipocyte browning. The treatment of 3T3L1 adipocytes with CA activated AMPK, reduced lipid accumulation, and increased the expression of browning protein markers (UCP-1, PGC-1α, PRDM16, and TFAM) and mitochondrial biogenesis. The use of compound C, an AMPK inhibitor, significantly attenuated the effects of CA, indicating AMPK involvement. These studies demonstrate that CA can activate AMPK and stimulate the browning of white adipocytes. Future animal and human studies are required to examine the effects of CA in vivo.

Natural activators of AMPK signaling: potential role in the management of type-2 diabetes

Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an evolutionarily conserved serine/threonine kinase involved in the homeostasis of cellular energy. AMPK has developed as an appealing clinical target for the diagnosis of multiple metabolic diseases such as diabetes mellitus, obesity, inflammation, and cancer. Genetic and pharmacological studies indicate that AMPK is needed in response to glucose deficiency, dietary restriction, and increased physical activity for preserving glucose homeostasis. After activation, AMPK influences metabolic mechanisms contributing to enhanced ATP production, thus growing processes that absorb ATP simultaneously. In this review, several natural products have been discussed which enhance the sensitivity of AMPK and alleviate sub complications or different pathways by which such AMPK triggers can be addressed. AMPK Natural products as potential AMPK activators can be developed as alternate pharmacological intervention to reverse metabolic disorders including type 2 diabetes.

Muscle Cell Insulin Resistance Is Attenuated by Rosmarinic Acid: Elucidating the Mechanisms Involved

Obesity and elevated blood free fatty acid (FFA) levels lead to impaired insulin action causing insulin resistance in skeletal muscle, and contributing to the development of type 2 diabetes mellitus (T2DM). Mechanistically, insulin resistance is associated with increased serine phosphorylation of the insulin receptor substrate (IRS) mediated by serine/threonine kinases including mTOR and p70S6K. Evidence demonstrated that activation of the energy sensor AMP-activated protein kinase (AMPK) may be an attractive target to counteract insulin resistance. We reported previously that rosemary extract (RE) and the RE polyphenol carnosic acid (CA) activated AMPK and counteracted the FFA-induced insulin resistance in muscle cells. The effect of rosmarinic acid (RA), another polyphenolic constituent of RE, on FFA-induced muscle insulin resistance has never been examined and is the focus of the current study. Muscle cell (L6) exposure to FFA palmitate resulted in increased serine phosphorylation of IRS-1 and reduced insulin-mediated (i) Akt activation, (ii) GLUT4 glucose transporter translocation, and (iii) glucose uptake. Notably, RA treatment abolished these effects, and restored the insulin-stimulated glucose uptake. Palmitate treatment increased the phosphorylation/activation of mTOR and p70S6K, kinases known to be involved in insulin resistance and RA significantly reduced these effects. RA increased the phosphorylation of AMPK, even in the presence of palmitate. Our data indicate that RA has the potential to counteract the palmitate-induced insulin resistance in muscle cells, and further studies are required to explore its antidiabetic properties.

Assessment of Effects of Rosemary Essential Oil on the Kidney Pathology of Diabetic Adult Male Albino Rats

Background Diabetic nephropathy is a severe condition that causes persistent kidney problems and chronic renal failure. Rosemary (Rosmarinus officinalis L) is widely recognized for its antioxidant, antidiabetic, anti-inflammatory, antithrombotic, hepatoprotective, and anticancer activities. The current study evaluated rosemary essential oil (REO) effects on biochemical, histological, and immunohistochemical kidney alterations in streptozotocin (STZ)-induced diabetic rats and compared these effects with those of insulin and both combined. Methods We randomly distributed 36 adult albino rats into 6 groups: normal control (non-diabetic), diabetic (streptozotocin, 55 mg/kg, intraperitoneal), diabetic insulin-treated (Lantus insulin 2 units/day, SC), diabetic REO-treated (REO, 10 ml, nasogastric gavage), and diabetic insulin & REO-treated groups. Biochemical, histological, and immunohistochemical analyses were conducted. Results The diabetic group revealed a substantial increase in blood glucose, urea, creatinine, and uric acid, as well as malondialdehyde (MDA) and catalase (CAT) concentrations in kidney homogenates, high score of tubular injury, and increased glomerulosclerosis, along with marked reduction of total glutathione (GSH) and superoxide dismutase (SOD) when compared to control. Evident improvement was detected in rats treated with REO as it demonstrated antioxidant, anti-inflammatory, anti-apoptotic, pro-proliferative, and mild anti-hyperglycemic effects on diabetic rats, reducing the kidney damage caused by diabetes. Combined insulin and REO restored normal blood glucose, renal excretory function tests, antioxidant markers, and renal cortex histology. Conclusion The data presented in the current study's in vivo animal model suggests that REO supplementation has beneficial nephroprotective effects on the structural and, to a lesser extent, functional levels of diabetic rats. Furthermore, the detected nephroprotective effects of insulin and REO combined are superior to those of either administered alone. However, further studies are needed to evaluate these conclusions in humans further.

Anti-Inflammatory Therapeutic Mechanisms of Natural Products: Insight from Rosemary Diterpenes, Carnosic Acid and Carnosol

Carnosic acid (CA) and carnosol (CAR) are two major diterpenes of the rosemary plant (Rosmarinus officinalis). They possess a phenolic structural moiety and are endowed with the power to remove cellular reactive oxygen species (ROS) either through direct scavenging reaction or indirectly through upregulation of antioxidant defences. Hand in hand with these activities are their multiple biological effects and therapeutic potential orchestrated through modulating various signalling pathways of inflammation, including the NF-κB, MAPK, Nrf2, SIRT1, STAT3 and NLRP3 inflammasomes, among others. Consequently, they ameliorate the expression of pro-inflammatory cytokines (e.g., TNF-α, IL-1 and IL-6), adhesion molecules, chemokines and prostaglandins. These anti-inflammatory mechanisms of action as a therapeutic link to various effects of these compounds, as in many other natural products, are scrutinised.

The importance of AMPK in obesity and chronic diseases and the relationship of AMPK with nutrition: a literature review

This review will examine the role of 5'-adenosine monophosphate-activated protein kinase (AMPK) in the treatment of obesity, medical nutrition and chronic diseases, and its relationship with nutrition. In the literature, the number of studies examining the direct relationship of AMPK with nutrition is negligible. For this reason, information on the subject has been compiled from all the studies that can be accessed by searching the terms AMPK and disease, AMPK and health, AMPK and exercise, AMPK and nutrition. It can be stated that AMPK is inhibited in many pathological conditions such as inflammation, diabetes, aging and cancer, and AMPK activation has positive effects in many diseases such as insulin resistance, diabetes, obesity, cancer and Alzheimer's. When the relationship between nutrition and AMPK is examined, it is seen that food intake inhibits AMPK, but especially high-carbohydrate and fatty diets are more effective at this point. In addition, high fructose corn sirup and long chain saturated fatty acids increased by consumption of industrial foods and frequent meals appear to be an inactivator for AMPK. For AMPK activation in medical nutrition therapy, it is recommended to use methods such as evening fasting and intermittent fasting, taking into account the human circadian rhythm.

Carnosic Acid Attenuates the Free Fatty Acid-Induced Insulin Resistance in Muscle Cells and Adipocytes

Elevated blood free fatty acids (FFAs), as seen in obesity, impair insulin action leading to insulin resistance and Type 2 diabetes mellitus. Several serine/threonine kinases including JNK, mTOR, and p70 S6K cause serine phosphorylation of the insulin receptor substrate (IRS) and have been implicated in insulin resistance. Activation of AMP-activated protein kinase (AMPK) increases glucose uptake, and in recent years, AMPK has been viewed as an important target to counteract insulin resistance. We reported previously that carnosic acid (CA) found in rosemary extract (RE) and RE increased glucose uptake and activated AMPK in muscle cells. In the present study, we examined the effects of CA on palmitate-induced insulin-resistant L6 myotubes and 3T3L1 adipocytes. Exposure of cells to palmitate reduced the insulin-stimulated glucose uptake, GLUT4 transporter levels on the plasma membrane, and Akt activation. Importantly, CA attenuated the deleterious effect of palmitate and restored the insulin-stimulated glucose uptake, the activation of Akt, and GLUT4 levels. Additionally, CA markedly attenuated the palmitate-induced phosphorylation/activation of JNK, mTOR, and p70S6K and activated AMPK. Our data indicate that CA has the potential to counteract the palmitate-induced muscle and fat cell insulin resistance.

Inhibition of Non-Small Cell Lung Cancer Proliferation and Survival by Rosemary Extract Is Associated with Activation of ERK and AMPK

Non-small cell lung cancer (NSCLC) represents an aggressive form of lung cancer which often develops resistance to chemo- and radiotherapy emphasizing a need to identify novel treatment agents to combat it. Many plants contain compounds with anti-inflammatory, antimicrobial, antidiabetic, and anticancer properties and some plant-derived chemicals are used in the treatment of cancer. A limited number of in vitro and in vivo animal studies provide evidence of anticancer effects of rosemary (Rosmarinus officinalis) extract (RE); however, no studies have explored its role in H1299 NSCLC cells, and its underlying mechanism(s) of action are not understood. The current study examined the effects of RE on H1299 cell proliferation, survival, and migration using specific assays. Additionally, immunoblotting was used to investigate the effects of RE treatment on signalling molecules implicated in cell growth and survival. Treatment with RE dose-dependently inhibited H1299 proliferation with an IC₅₀ value of 19 µg/mL. Similarly, RE dose-dependently reduced cell survival, and this reduction correlated with increased levels of cleaved poly (ADP-ribose) polymerase (PARP), a marker of apoptosis. RE was also able to inhibit cell migration as assessed with a wound healing assay. These cellular effects of RE were associated with an increase in phosphorylated levels of extracellular signal-regulated kinase (ERK), AMP-activated protein kinase (AMPK), and its downstream targets ACC, the mTORC1 protein raptor, and decreased p70S6K phosphorylation. More studies are required to fully examine the effects of RE against NSCLC.

Peptide Analogues of VPP and IPP with Improved Glucose Uptake Activity in L6 Myotubes can be Released from Cereal Proteins

VPP (Val-Pro-Pro) and IPP (Ile-Pro-Pro) are two famous antihypertensive peptides with possible benefits for type 2 diabetes mellitus (T2DM). The study was aimed to investigate the effect of peptide analogues of VPP and IPP on glucose uptake activity in L6 myotubes. The analogues were designed by replacing the N-terminal, middle, or C-terminal amino acid residues of VPP and IPP with one amino acid at a time from five amino acid groups (polar, nonpolar, basic, acidic, and aromatic amino acids). Among 26 tripeptides tested, IQP, IPQ, VPE, and VEP showed significantly higher glucose uptake activity than their parent peptides, and all were successfully released from rice proteins at the contents of 5415.82 ± 63.34, 1586.77 ± 14.94, 354.07 ± 6.56, and 596.10 ± 2.32 ng/mg dry basis, respectively, and quantified by liquid chromatography-mass spectrometry (MS)/MS using multiple reaction monitoring. All four peptides were shown to promote glucose uptake via the adenosine monophosphate-activated protein kinase pathway accompanied by glucose transporter type 4 (Glut4) translocation rather than the insulin signaling pathway.

Rosemary extract activates AMPK, inhibits mTOR and attenuates the high glucose and high insulin-induced muscle cell insulin resistance

Impaired action of insulin in skeletal muscle, termed insulin resistance, leads to increased blood glucose levels resulting in compensatory increase in insulin levels. The elevated blood glucose and insulin levels exacerbate insulin resistance and contribute to the pathogenesis of type 2 diabetes mellitus. In previous studies we found attenuation of free fatty acid-induced muscle cell insulin resistance by rosemary extract (RE). In the present study we investigated the effects of RE on high glucose (HG) and high insulin (HI)-induced muscle cell insulin resistance. Exposure of L6 myotubes to 25 mmol/L glucose and 100 nmol/L insulin for 24 h, to mimic hyperglycemia and hyperinsulinemia, abolished the acute insulin-stimulated glucose uptake, increased the serine phosphorylation of IRS-1 and the phosphorylation/activation of mTOR and p70S6K. Treatment with RE significantly improved the insulin-stimulated glucose uptake and increased the acute insulin-stimulated tyrosine phosphorylation while reducing the HG+HI-induced serine phosphorylation of IRS-1 and phosphorylation of mTOR and p70S6K. Additionally, treatment with RE significantly increased the phosphorylation of AMPK, its downstream effector ACC and the plasma membrane GLUT4 levels. Our data indicate a potential of RE to counteract muscle cell insulin resistance and more studies are required to investigate its effectiveness in vivo. Novelty: RE phosphorylated muscle cell AMPK and ACC under both normal and HG+HI conditions. The HG+HI-induced serine phosphorylation of IRS-1 and activation of mTOR and p70S6K were attenuated by RE. RE restored the insulin-stimulated glucose uptake by enhancing GLUT4 glucose transporter translocation to plasma membrane.

Inhibition of Digestive Enzyme and Stimulation of Human Liver Cells (HepG2) Glucose Uptake by Date Seeds Extract

Type 2 diabetes mellitus is increasing worldwide, and the United Arab Emirates is presenting one of the world's highest prevalence rates. Dietary polyphenols exert an antidiabetic effect by modulating carbohydrates digestion and cellular glucose uptake. Due to their particularly high content in polyphenols, date seeds represent a potential antidiabetic agent. This study aims to determine if date seed polyphenols inhibit the activity of the enzymes (α-amylase and α-glucosidase), responsible for the digestion of carbohydrates and modulating the glucose uptake by human liver cells. In vitro activity of the intestinal α-glucosidase, pancreatic α-amylase, the glucose uptake by HepG2 cells, and the expression of GLUT4 and AMPK analyzed by western blotting (with and without date seeds extract). Our result showed that the maximum enzymes inhibition was obtained with 400 μg/mL and 900 μg/mL DSE for α-amylase and α-glucosidase, respectively. The HepG2 cell viability significantly decreased up to 80% at 4000 μg/mL DSE. The expression of GLUT4 was higher at 100 μg/mL DSE (with insulin and without insulin). However, the expressions of P-AMPK and AMPK were increased by DSE, mainly in a non-insulin-dependent manner. Therefore, DSE, by inhibiting carbohydrate digestion and stimulating glucose uptake by HepG2, can potentially demonstrate the therapeutic potential for diabetes management.

Fractions from Annona muricata attenuate oxidative stress in pancreatic tissues, inhibits key carbohydrate digesting enzymes and intestinal glucose absorption but enhances muscle glucose uptake

The ameliorating effect of different fractions of Anonna muricata ethanol leaves extract in oxidative pancreatic injury as well as their antihyperglycemic effect were investigated in vitro and ex vivo. Oxidative pancreatic injury was induced by incubating pancreatic tissue with ferrous sulphate (FeSO₄ )_. The antioxidative potentials of the fractions together with its ability to inhibit carbohydrate digesting enzymes, intestinal glucose absorption, and its ability to modulate muscle glucose uptake were determined. All the fractions significantly scavenge free radicals in dose-dependent manner and increase significantly increase the catalase and superoxide dimutase level thereby ameliorating lipid peroxidation. All the fractions also inihibited glucose digesting enzymes and absorption in dose-dependent manner. Glucose uptake was enhanced by the fractions in isolated psoas muscle of rats. The ethyl acetate fraction showed more potent amelioration and anti-hyperglycemic potentials among all the fractions. This could be further exploited as therapeutic strategy for the management of postprandial hyperglycemia as well as T2D. PRACTICAL APPLICATIONS: Annona muricata is among the edible fruits in the world with reported nutritional as well as medicinal values. The anticancer activity of the leaves and the fruits have been reported. Its ability to inhibit carbohydrate digesting enzymes and absorption and enhancing muscle glucose uptake as well as protection of pancreatic β-cell from oxidative damage further support its reported antidiabetic properties. A. muricata provided a cheap and alternative source of nutraceuticals, which could be further exploited as therapeutic strategy for the treatment of postprandial hyperglycemia in T2D.

The effect of BPA exposure on insulin resistance and type 2 diabetes - The impact of muscle contraction

Type 2 diabetes (T2D) is considered one of the leading causes of death worldwide. In addition to physical inactivity and obesity, established risk factors for T2D, chemical contaminants consumed in industrialized food such as BPA might also be a contributor to the development of T2D. Epidemiological studies have shown that BPA concentrations are higher in human specimens of T2D when compared to healthy subjects, while experimental studies suggested that bisphenol A (BPA) impairs the pathway by which insulin stimulates glucose uptake. In skeletal muscle and adipocytes, insulin resistance is developed by the impairment of the insulin pathway to stimulate the translocation of glucose transporter, GLUT4, to the cell membrane. Recent results demonstrated that BPA impairs several components of insulin-induced glucose uptake pathway and affect the expression of GLUT4. Regular physical exercise delays or inhibits the development of T2D due to the physiologic processes taking place during muscle contraction, and the fact that skeletal muscle is the site for almost 80% of the glucose transported under insulin stimulation. In fact, the mechanism by which contraction induces glucose uptake in skeletal muscle is partially independent of the insulin pathway, therefore, the effect of BPA on this mechanism is unknown. We hypothesize that during the development of insulin resistance, BPA contributes to the impairment of the molecular pathway by which insulin induces glucose uptake while contraction-induced glucose uptake is not impaired. At the late stages of T2D, BPA may affect GLUT4 expression that will decrease the ability of muscle contraction to induce glucose uptake.

Antidiabetic Effects and Mechanisms of Rosemary (Rosmarinus officinalis L.) and its Phenolic Components

Diabetes mellitus is a chronic endocrine disease result from absolute or relative insulin secretion deficiency, insulin resistance, or both, and has become a major and growing public healthy menace worldwide. Currently, clinical antidiabetic drugs still have some limitations in efficacy and safety such as gastrointestinal side effects, hypoglycemia, or weight gain. Rosmarinus officinalis is an aromatic evergreen shrub used as a food additive and medicine, which has been extensively used to treat hyperglycemia, atherosclerosis, hypertension, and diabetic wounds. A great deal of pharmacological research showed that rosemary extract and its phenolic constituents, especially carnosic acid, rosmarinic acid, and carnosol, could significantly improve diabetes mellitus by regulating glucose metabolism, lipid metabolism, anti-inflammation, and anti-oxidation, exhibiting extremely high research value. Therefore, this review summarizes the pharmacological effects and underlying mechanisms of rosemary extract and its primary phenolic constituents on diabetes and relative complications both in vitro and in vivo studies from 2000 to 2020, to provide some scientific evidence and research ideas for its clinical application.

Polyphenols targeting diabetes via the AMP-activated protein kinase pathway; future approach to drug discovery

Regarding the widespread progression of diabetes, its related complications and detrimental effects on human health, investigations on this subject seems compulsory. AMP-activated protein kinase (AMPK) is a serine/threonine kinase and a key player in energy metabolism regulation. AMPK is also considered as a prime target for pharmaceutical and therapeutic studies on disorders such as diabetes, metabolic syndrome and obesity, where the body energy homeostasis is imbalanced. Following the activation of AMPK (physiological or pharmacological), a cascade of metabolic events that improve metabolic health is triggered. While there are several publications on this subject, this is the first report that has focused solely on polyphenols targeting diabetes via AMPK pathway. The multiple characteristics of polyphenolic compounds and their favorable influence on diabetes pathogenesis, as well as their intersections with the AMPK signaling pathway, indicate that these compounds have a beneficial effect on the regulation of glucose homeostasis. PPs could potentially occupy a significant position in the future anti-diabetic drug market.

Attenuation of Free Fatty Acid-Induced Muscle Insulin Resistance by Rosemary Extract

Elevated blood free fatty acids (FFAs), as seen in obesity, impair muscle insulin action leading to insulin resistance and Type 2 diabetes mellitus. Serine phosphorylation of the insulin receptor substrate (IRS) is linked to insulin resistance and a number of serine/threonine kinases including JNK, mTOR and p70 S6K have been implicated in this process. Activation of the energy sensor AMP-activated protein kinase (AMPK) increases muscle glucose uptake, and in recent years AMPK has been viewed as an important target to counteract insulin resistance. We reported recently that rosemary extract (RE) increased muscle cell glucose uptake and activated AMPK. However, the effect of RE on FFA-induced muscle insulin resistance has never been examined. In the current study, we investigated the effect of RE in palmitate-induced insulin resistant L6 myotubes. Exposure of myotubes to palmitate reduced the insulin-stimulated glucose uptake, increased serine phosphorylation of IRS-1, and decreased the insulin-stimulated phosphorylation of Akt. Importantly, exposure to RE abolished these effects and the insulin-stimulated glucose uptake was restored. Treatment with palmitate increased the phosphorylation/activation of JNK, mTOR and p70 S6K whereas RE completely abolished these effects. RE increased the phosphorylation of AMPK even in the presence of palmitate. Our data indicate that rosemary extract has the potential to counteract the palmitate-induced muscle cell insulin resistance and further studies are required to explore its antidiabetic properties.

Glutamate increases glucose uptake in L6 myotubes in a concentration- and time-dependent manner that is mediated by AMPK

Various in vivo studies have investigated the insulin response that is elicited when glutamate is elevated in circulation or in a given tissue; fewer studies have investigated the effects of glutamate on glucose uptake and handling. Glutamate ingestion in humans can attenuate rises in blood glucose following a carbohydrate load in the absence of increases in serum insulin concentrations. However, the underlying mechanisms have yet to be investigated. To elucidate the effects of glutamate on glucose handling in skeletal muscle tissue, differentiated rat L6 myocytes were treated with glutamate, and glucose uptake was assessed with the use of 2-[³H]-deoxy-d-glucose ([³H]-2-DG). Cells treated with 2 mmol/L glutamate experienced the greatest increase in [³H]-2-DG uptake relative to the control condition (177% ± 2% of control, P < 0.001) and the uptake was similar to that of metformin (184% ± 4%, P < 0.001). In line with these findings, differentiated glucose transporter 4 (GLUT4)-overexpressing myotubes treated with 2 mmol/L glutamate displayed significantly increased GLUT4 translocation when compared with the control condition (159% ± 8% of control, P < 0.001) and to an extent similar to that of insulin and metformin (181% ± 7% and 159% ± 12%, respectively). An AMP-activated protein kinase (AMPK) inhibitor (Compound C) abolished the glutamate-stimulated glucose uptake (98% ± 12% of control), and Western blotting revealed significantly elevated AMPK phosphorylation (278% ± 17% of control, P < 0.001) by glutamate. Our findings suggest that when muscle cells are exposed to increased glutamate concentrations, glucose uptake into these cells is augmented through AMPK activation, through mechanisms distinct from those of insulin and leucine.

Carnosol Increases Skeletal Muscle Cell Glucose Uptake via AMPK-Dependent GLUT4 Glucose Transporter Translocation

Skeletal muscle is a major insulin-target tissue and plays an important role in glucose homeostasis. Insulin action in muscle activates the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway causing the translocation of intracellularly stored GLUT4 glucose transporters to the plasma membrane and increased glucose uptake. Impaired insulin action in muscle results in insulin resistance and type 2 diabetes mellitus (T2DM). Activation of the energy sensor AMP-activated kinase (AMPK) increases muscle glucose uptake and the use of AMPK activators is viewed as an effective strategy to combat insulin resistance. Rosemary extract (RE) has been shown to stimulate muscle AMPK and glucose uptake, but the exact components responsible for these effects are unknown. In the current study, we investigated the effect of carnosol, a RE polyphenol, in L6 rat muscle cells. Carnosol stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner, did not affect Akt, increased AMPK phosphorylation and plasma membrane GLUT4 levels. The carnosol-stimulated glucose uptake and GLUT4 translocation was significantly reduced by the AMPK inhibitor compound C (CC). Our study is the first to show an AMPK-dependent increase in muscle glucose uptake by carnosol. Carnosol has potential as a glucose homeostasis regulating agent and deserves further study.

Metabolomics study of early metabolic changes in hepatic HepaRG cells in response to rosemary diterpenes exposure

Rosemary diterpenes have demonstrated diverse biological activities, such as anti-cancer, antiinflammatory, as well as other beneficial effects against neurological and metabolic disorders. In particular, carnosic acid (CA), carnosol (CS) and rosmanol (RS) diterpenes have shown interesting results on anti-cancer activity. However, little is known about the toxic effects of rosemary diterpenes at the concentrations needed to exert their antiproliferative effect on cancer cells. In our study, CA, CS and RS exhibited a concentration-dependent effect on cell viability of two human colon cancer cell lines (HT-29 and HCT116) after 24 h exposure. HT-29 cell line was more resistant to the inhibitory effect of the three diterpenes than HCT116 cell line. Among the three diterpenes, RS exerted the strongest effect in both cell lines. To investigate the hepatotoxicity of CA, CS and RS, undifferentiated and differentiated HepaRG cells were exposed to increasing concentrations of the diterpenes (from 10 to 100 μM). Differentiated cells were found to be more resistant to the toxic activity of the three diterpenes than undifferentiated HepaRG, probably related to a higher detoxifying function of differentiated HepaRG cells compared with the undifferentiated cells. The metabolic profiles of differentiated HepaRG cells in response to CA, CS and RS were examined to determine biochemical alterations and deepen the study of the effects of rosemary phenolic diterpenes at molecular level. A multiplatform metabolomics study based on liquid- and gas-chromatography hyphenated to high resolution mass spectrometry revealed that rosemary diterpenes exerted different effects when HepaRG cells were treated with the same concentration of each diterpene. RS revealed a greater metabolome alteration followed by CS and CA, in agreement with their observed cytotoxicity. Metabolomics provided valuable information about early events in the metabolic profiles after the treatment with the investigated diterpenes from rosemary.

Role of the AMPK pathway in promoting autophagic flux via modulating mitochondrial dynamics in neurodegenerative diseases: Insight into prion diseases

Neurons are highly energy demanding cells dependent on the mitochondrial oxidative phosphorylation system. Mitochondria generate energy via respiratory complexes that constitute the electron transport chain. Adenosine triphosphate depletion or glucose starvation act as a trigger for the activation of adenosine monophosphate-activated protein kinase (AMPK). AMPK is an evolutionarily conserved protein that plays an important role in cell survival and organismal longevity through modulation of energy homeostasis and autophagy. Several studies suggest that AMPK activation may improve energy metabolism and protein clearance in the brains of patients with vascular injury or neurodegenerative disease. Mild mitochondrial dysfunction leads to activated AMPK signaling, but severe endoplasmic reticulum stress and mitochondrial dysfunction may lead to a shift from autophagy towards apoptosis and perturbed AMPK signaling. Hence, controlling mitochondrial dynamics and autophagic flux via AMPK activation might be a useful therapeutic strategy in neurodegenerative diseases to reinstate energy homeostasis and degrade misfolded proteins. In this review article, we discuss briefly the role of AMPK signaling in energy homeostasis, the structure of AMPK, activation mechanisms of AMPK, regulation of AMPK, the role of AMPK in autophagy, the role of AMPK in neurodegenerative diseases, and finally the role of autophagic flux in prion diseases.

Rosmarinic Acid, a Rosemary Extract Polyphenol, Increases Skeletal Muscle Cell Glucose Uptake and Activates AMPK

Skeletal muscle is a major insulin-target tissue and plays an important role in glucose homeostasis. Impaired insulin action in muscles leads to insulin resistance and type 2 diabetes mellitus. 5' AMP-activated kinase (AMPK) is an energy sensor, its activation increases glucose uptake in skeletal muscle and AMPK activators have been viewed as a targeted approach in combating insulin resistance. We previously reported AMPK activation and increased muscle glucose uptake by rosemary extract (RE). In the present study, we examined the effects and the mechanism of action of rosmarinic acid (RA), a major RE constituent, in L6 rat muscle cells. RA (5.0 µM) increased glucose uptake (186 ± 4.17% of control, p < 0.001) to levels comparable to maximum insulin (204 ± 10.73% of control, p < 0.001) and metformin (202 ± 14.37% of control, p < 0.001). Akt phosphorylation was not affected by RA, while AMPK phosphorylation was increased. The RA-stimulated glucose uptake was inhibited by the AMPK inhibitor compound C and was not affected by wortmannin, an inhibitor of phosphoinositide 3-kinase (PI3K). The current study shows an effect of RA to increase muscle glucose uptake and AMPK phosphorylation. RA deserves further study as it shows potential to be used as an agent to regulate glucose homeostasis.

Carnosic acid as a component of rosemary extract stimulates skeletal muscle cell glucose uptake via AMPK activation

Compounds that increase the activity of the energy sensor AMP-activated kinase (AMPK) have the potential to regulate blood glucose levels. Although rosemary extract (RE) has been reported to activate AMPK and reduce blood glucose levels in vivo, the chemical components responsible for these effects are not known. In the present study, we measured the levels of the polyphenol carnosic acid (CA) in RE and examined the effects and the mechanism of action of CA on glucose transport system in muscle cells. High performance liquid chromatography (HPLC) was used to measure the levels of CA in RE. Parental and GLUT4myc or GLUT1myc overexpressing L6 rat myotubes were used. Glucose uptake was assessed using [³ H]-2-deoxy-d-glucose. Total and phosphorylated levels of Akt and AMPK were measured by immunoblotting. Plasma membrane GLUT4myc and GLUT1myc levels were examined using a GLUT translocation assay. Statistics included analysis of variance (ANOVA) followed by Tukey's post-hoc test. At concentrations found in rosemary extract, CA stimulated glucose uptake in L6 myotubes. At 2.0 μmol/L CA a response (226 ± 9.62% of control, P=.001), similar to maximum insulin (201 ± 7.86% of control, P=.001) and metformin (213 ± 10.74% of control, P=.001) was seen. Akt phosphorylation was not affected by CA while AMPK and ACC phosphorylation was increased and the CA-stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C. Plasma membrane GLUT4 or GLUT1 glucose transporter levels were not affected by CA. Our study shows increased muscle cell glucose uptake and AMPK activation by low CA concentrations, found in rosemary extract, indicating that CA may be responsible for the antihyperglycemic properties of rosemary extract seen in vivo.

Rosemary Extract as a Potential Anti-Hyperglycemic Agent: Current Evidence and Future Perspectives

Type 2 diabetes mellitus (T2DM), a disease on the rise and with huge economic burden to health care systems around the globe, results from defects in insulin action (termed insulin resistance) combined with impaired insulin secretion. Current methods of prevention and treatments for insulin resistance and T2DM are lacking in number and efficacy and, therefore, there is a need for new preventative measures and targeted therapies. In recent years, chemicals found in plants/herbs have attracted attention for their use as functional foods or nutraceuticals for preventing and treating insulin resistance and T2DM. Rosemary is an evergreen shrub indigenous to the Mediterranean region and South America, which contains various polyphenols. Rosemary extract and its polyphenolic constituents have been reported to have antioxidant, anti-inflammatory, anticancer, and anti-hyperglycemic properties. The current review summarizes the existing in vitro and in vivo studies examining the anti-diabetic effects of rosemary extract and its polyphenolic components and highlights the known mechanism of action.

Glucose Uptake Measurement and Response to Insulin Stimulation in In Vitro Cultured Human Primary Myotubes

Skeletal muscle is the largest glucose deposit in mammals and largely contributes to glucose homeostasis. Assessment of insulin sensitivity of muscle cells is of major relevance for all studies dedicated to exploring muscle glucose metabolism and characterizing metabolic alterations. In muscle cells, glucose transporter type 4 (GLUT4) proteins translocate to the plasma membrane in response to insulin, thus allowing massive entry of glucose into the cell. The ability of muscle cells to respond to insulin by increasing the rate of glucose uptake is one of the standard readouts to quantify muscle cell sensitivity to insulin. Human primary myotubes are a suitable in vitro model, as the cells maintain many features of the donor phenotype, including insulin sensitivity. This in vitro model is also suitable for the test of any compounds that could impact insulin responsiveness. Measurements of the glucose uptake rate in differentiated myotubes reflect insulin sensitivity. In this method, human primary muscle cells are cultured in vitro to obtain differentiated myotubes, and glucose uptake rates with and without insulin stimulation are measured. We provide a detailed protocol to quantify passive and active glucose transport rates using radiolabeled [³H] 2-deoxy-D-Glucose ([³H]2dG). Calculation methods are provided to quantify active basal and insulin-stimulated rates, as well as stimulation fold.

Phenolic Elderberry Extracts, Anthocyanins, Procyanidins, and Metabolites Influence Glucose and Fatty Acid Uptake in Human Skeletal Muscle Cells

Uptake of glucose and fatty acids in skeletal muscle is of interest for type 2 diabetes treatment. The aim was to study glucose and fatty acid uptake in skeletal muscle cells, antioxidant effects, and inhibition of carbohydrate-hydrolyzing enzymes by elderberries. Enhanced glucose and oleic acid uptake in human skeletal muscle cells were observed after treatment with phenolic elderberry extracts, anthocyanins, procyanidins, and their metabolites. The 96% EtOH and the acidified MeOH extracts were highly active. Of the isolated substances, cyanidin-3-glucoside and cyanidin-3-sambubioside showed highest stimulation of uptake. Phloroglucinol aldehyde was most active among the metabolites. Isolated anthocyanins and procyanidins are strong radical scavengers and are good inhibitors of 15-lipoxygenase and moderate inhibitors of xanthine oxidase. As α-amylase and α-glucosidase inhibitors, they are considerably better than the positive control acarbose. The antidiabetic property of elderberry phenolics increases the nutritional value of this plant and indicates potential as functional food against diabetes.

New insights into the anti-diabetic actions of metformin: from the liver to the gut

Metformin is established as the first-line therapy for type 2 diabetes (T2DM), but its mode of action remains elusive. Elucidation of the mechanisms underlying the anti-diabetic action of metformin may have the potential to optimise its glucose-lowering efficacy and lead to the development of agents acting on novel targets for the management of type 2 diabetes. Areas covered: This review highlights key pharmacokinetic features of metformin, summarises recent insights into its hepatic and gastrointestinal actions relevant to blood glucose homeostasis, and discusses the common gastrointestinal side effects of metformin. Literature concerning these areas was reviewed on PubMed. Expert commentary: The mechanisms by which metformin improves glycaemic control in type 2 diabetes are complex. Although novel hepatic pathways continue to be reported in preclinical studies, there is a lack of human evidence for most of these. Considering the fundamental role of the gastrointestinal tract in the regulation of blood glucose homeostasis and pleiotropic actions of metformin on several gastrointestinal targets relevant to glycaemic control, the gut is likely to represent at least as important a site of metformin action as the liver in the management of type 2 diabetes.

Rosemary (Rosmarinus officinalis) as a potential therapeutic plant in metabolic syndrome: a review

Metabolic syndrome is defined by a constellation of complex coexisting cardiometabolic risk factors such as hyperglycemia, dyslipidemia, inflammation, abdominal obesity, coagulopathies, and hypertension that raise the risk of diabetes mellitus and cardiovascular disease. Recently, there has been an increasing interest in the use of herbs and natural compounds in prevention and treatment of diseases and a large number of published articles have focused on this issue. Rosmarinus officinalis L. or rosemary (Lamiaceae) is a rich source of phenolic phytochemicals having significant anti-oxidant, anti-inflammatory, hypoglycemic, hypolipidemic, hypotensive, anti-atherosclerotic, anti-thrombotic, hepatoprotective, and hypocholesterolemic effects. The purpose of this review is to highlight the interesting pharmacological effects of rosemary, and its active compounds, and the related mechanisms in the management of metabolic syndrome that are documented in in vitro and in vivo studies.

Effect of a p38 MAPK inhibitor on FFA-induced hepatic insulin resistance in vivo

The mechanisms whereby prolonged plasma free fatty acids elevation, as found in obesity, causes hepatic insulin resistance are not fully clarified. We herein investigated whether inhibition of p38 mitogen-activated protein kinase (MAPK) prevented hepatic insulin resistance following prolonged lipid infusion. Chronically cannulated rats were subdivided into one of four intravenous (i.v.) treatments that lasted 48 h: Saline (5.5 μl min⁻¹), Intralipid plus heparin (IH, 20% Intralipid+20 U ml⁻¹ heparin; 5.5 μl min⁻¹), IH+p38 MAPK inhibitor (SB239063) and SB239063 alone. During the last 2 h of treatment, a hyperinsulinemic (5 mU kg⁻¹ min⁻¹) euglycemic clamp together with [3-³H] glucose methodology was carried out to distinguish hepatic from peripheral insulin sensitivity. We found that SB239063 prevented IH-induced hepatic insulin resistance, but not peripheral insulin resistance. SB239063 also prevented IH-induced phosphorylation of activating transcription factor 2 (ATF2), a marker of p38 MAPK activity, in the liver. Moreover, in another lipid infusion model in mice, SB239063 prevented hepatic but not peripheral insulin resistance caused by 48 h combined ethyloleate plus ethylpalmitate infusion. Our results suggest that inhibition of p38 MAPK may be a useful strategy in alleviating hepatic insulin resistance in obesity-associated disorders.