Peroxisome proliferator-activated receptors gamma and alpha agonists stimulate cardiac glucose uptake via activation of AMP-activated protein kinase

The potential of herbal drugs to treat heart failure: The roles of Sirt1/AMPK

Heart failure (HF) is a highly morbid syndrome that seriously affects the physical and mental health of patients and generates an enormous socio-economic burden. In addition to cardiac myocyte oxidative stress and apoptosis, which are considered mechanisms for the development of HF, alterations in cardiac energy metabolism and pathological autophagy also contribute to cardiac abnormalities and ultimately HF. Silent information regulator 1 (Sirt1) and adenosine monophosphate-activated protein kinase (AMPK) are nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases and phosphorylated kinases, respectively. They play similar roles in regulating some pathological processes of the heart through regulating targets such as peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), protein 38 mitogen-activated protein kinase (p38 MAPK), peroxisome proliferator-activated receptors (PPARs), and mammalian target of rapamycin (mTOR). We summarized the synergistic effects of Sirt1 and AMPK in the heart, and listed the traditional Chinese medicine (TCM) that exhibit cardioprotective properties by modulating the Sirt1/AMPK pathway, to provide a basis for the development of Sirt1/AMPK activators or inhibitors for the treatment of HF and other cardiovascular diseases (CVDs).

Nrf2 prevents diabetic cardiomyopathy via antioxidant effect and normalization of glucose and lipid metabolism in the heart

Metabolic disorders and oxidative stress are the main causes of diabetic cardiomyopathy. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) exerts a powerful antioxidant effect and prevents the progression of diabetic cardiomyopathy. However, the mechanism of its cardiac protection and direct action on cardiomyocytes are not well understood. Here, we investigated in a cardiomyocyte-restricted Nrf2 transgenic mice (Nrf2-TG) the direct effect of Nrf2 on cardiomyocytes in DCM and its mechanism. In this study, cardiomyocyte-restricted Nrf2 transgenic mice (Nrf2-TG) were used to directly observe whether cardiomyocyte-specific overexpression of Nrf2 can prevent diabetic cardiomyopathy and correct glucose and lipid metabolism disorders in the heart. Compared to wild-type mice, Nrf2-TG mice showed resistance to diabetic cardiomyopathy in a streptozotocin-induced type 1 diabetes mouse model. This was primarily manifested as improved echocardiography results as well as reduced myocardial fibrosis, cardiac inflammation, and oxidative stress. These results showed that Nrf2 can directly act on cardiomyocytes to exert a cardioprotective role. Mechanistically, the cardioprotective effects of Nrf2 depend on its antioxidation activity, partially through improving glucose and lipid metabolism by directly targeting lipid metabolic pathway of AMPK/Sirt1/PGC-1α activation via upstream genes of sestrin2 and LKB1, and indirectly enabling AKT/GSK-3β/HK-Ⅱ activity via AMPK mediated p70S6K inhibition.

A glimpse of the connection between PPARγ and macrophage

Nuclear receptors are ligand-regulated transcription factors that regulate vast cellular activities and serve as an important class of drug targets. Among them, peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family and have been extensively studied for their roles in metabolism, differentiation, development, and cancer, among others. Recently, there has been considerable interest in understanding and defining the function of PPARs and their agonists in regulating innate and adaptive immune responses and their pharmacological potential in combating chronic inflammatory diseases. In this review, we focus on emerging evidence for the potential role of PPARγ in macrophage biology, which is the prior innate immune executive in metabolic and tissue homeostasis. We also discuss the role of PPARγ as a regulator of macrophage function in inflammatory diseases. Lastly, we discuss the possible application of PPARγ antagonists in metabolic pathologies.

SGLT2 inhibitors: role in protective reprogramming of cardiac nutrient transport and metabolism

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce heart failure events by direct action on the failing heart that is independent of changes in renal tubular function. In the failing heart, nutrient transport into cardiomyocytes is increased, but nutrient utilization is impaired, leading to deficient ATP production and the cytosolic accumulation of deleterious glucose and lipid by-products. These by-products trigger downregulation of cytoprotective nutrient-deprivation pathways, thereby promoting cellular stress and undermining cellular survival. SGLT2 inhibitors restore cellular homeostasis through three complementary mechanisms: they might bind directly to nutrient-deprivation and nutrient-surplus sensors to promote their cytoprotective actions; they can increase the synthesis of ATP by promoting mitochondrial health (mediated by increasing autophagic flux) and potentially by alleviating the cytosolic deficiency in ferrous iron; and they might directly inhibit glucose transporter type 1, thereby diminishing the cytosolic accumulation of toxic metabolic by-products and promoting the oxidation of long-chain fatty acids. The increase in autophagic flux mediated by SGLT2 inhibitors also promotes the clearance of harmful glucose and lipid by-products and the disposal of dysfunctional mitochondria, allowing for mitochondrial renewal through mitochondrial biogenesis. This Review describes the orchestrated interplay between nutrient transport and metabolism and nutrient-deprivation and nutrient-surplus signalling, to explain how SGLT2 inhibitors reverse the profound nutrient, metabolic and cellular abnormalities observed in heart failure, thereby restoring the myocardium to a healthy molecular and cellular phenotype.

Ephedra Herb extract ameliorates adriamycin-induced nephrotic syndrome in rats via the CAMKK2/AMPK/mTOR signaling pathway

This study aimed to investigate the effect and mechanisms of Ephedra Herb (EH) extract on adriamycin-induced nephrotic syndrome (NS), providing an experimental basis for the clinical treatment of NS. Hematoxylin and eosin staining, creatinine, urea nitrogen, and kidn injury molecule-1 were used to evaluate the activities of EH extract on renal function. The levels of inflammatory factors and oxidative stress were detected by kits. The levels of reactive oxygen species, immune cells, and apoptosis were measured by flow cytometry. A network pharmacological approach was used to predict the potential targets and mechanisms of EH extract in the treatment of NS. The protein levels of apoptosis-related proteins and CAMKK2, p-CAMKK2, AMPK, p-AMPK, mTOR and p-mTOR in the kidneys were detected by Western blot. The effective material basis of EH extract was screened by MTT assay. The AMPK pathway inhibitor (compound C, CC) was added to investigate the effect of the potent material basis on adriamycin-induced cell injury. EH extract significantly improved renal injury and relieve inflammation, oxidative stress, and apoptosis in rats. Network pharmacology and Western blot results showed that the effect of EH extract on NS may be associated with the CAMKK2/AMPK/mTOR signaling pathway. Moreover, methylephedrine significantly ameliorated adriamycin-induced NRK-52e cell injury. Methylephedrine also significantly improved the phosphorylation of AMPK and mTOR, which were blocked by CC. In sum, EH extract may ameliorate renal injury via the CAMKK2/AMPK/mTOR signaling pathway. Moreover, methylephedrine may be one of the material bases of EH extract.

Soyasapogenol C from Fermented Soybean (Glycine Max) Acting as a Novel AMPK/PPARα Dual Activator Ameliorates Hepatic Steatosis: A Novel SANDA Methodology

(1) Background: Soyasapogenol C (SSC), a derivative of soyasapogenol B (SSB), is specifically found high in many fermented soybean (Glycine max) products, including Cheonggukjang (in Korean). However, the biological activities for preventing and treating hepatic steatosis, and the precise underlying mechanisms of SSC, remain to be explored. (2) Methods: A novel SANDA (structural screening, ADMET prediction, network pharmacology, docking validation, and activity evaluation) methodology was used to examine whether SSC exerts hepatoprotective effects in silico and in vitro. (3) Results: SSC had better ADMET characteristics and a higher binding affinity with predicted targets chosen from network pathway analysis than SSB. SSC induced the phosphorylation of AMP-activated protein kinase (AMPK) and stimulated the nuclear translocation of peroxisome proliferator-activated receptor alpha (PPARα), further enhancing PPAR response element (PPRE) binding activity in HepG2 cells. Concurrently, SSC significantly inhibited triglyceride accumulation, which was associated with the suppression of lipogenesis genes and the enhancement of fatty acid oxidation gene expression in HepG2 cells. (4) Conclusions: Soyasapogenol C, discovered using a novel SANDA methodology from fermented soybean, is a novel AMPK/PPARα dual activator that is effective against hepatic steatosis. Dietary supplementation with soyasapogenol C may prevent the development of hepatic steatosis and other diseases associated with fat accumulation in the liver.

A Novel Multidrug Combination Mitigates Rat Liver Steatosis Through Activating AMPK Pathway During Normothermic Machine Perfusion

BACKGROUND

Hepatic steatosis is now the leading cause of liver discards in deceased donors. Previous studies [Yarmush formula (Y) defatting] have successfully reduced the fat content by treating rat steatotic livers on extracorporeal normothermic machine perfusion (NMP) with a multidrug combination including the GW compounds that were linked to an increased risk of carcinogenesis.

METHODS

We developed a novel multidrug combination by replacing the GW compounds with 2 polyphenols, epigallocatechin-3-gallate (E) and resveratrol (R). Sixteen rat livers were placed on NMP and assigned to control, Y defatting, Y + E + R defatting, or Y'-GW + E + R defatting groups (Y'-GW = 90% dose-reduced Y defatting, n = 4/group).

RESULTS

All livers in defatting groups had significant decreases in hepatic triglyceride content at the end of the experiment. However, livers treated with our novel Y'-GW + E + R combination had evidence of increased metabolism and less hepatocyte damage and carcinogenic potential. Our Y'-GW + E + R combination had increased phosphorylation of AMP-activated protein kinase (P = 0.019) and acetyl-CoA carboxylase (P = 0.023) compared with control; these were not increased in Y + E + R group and actually decreased in the Y group. Furthermore, the Y'-GW + E + R group had less evidence of carcinogenic potential with no increase in AKT phosphorylation compared with control (P = 0.089); the Y (P = 0.031) and Y + E + R (P = 0.035) groups had striking increases in AKT phosphorylation. Finally, our Y'-GW + E + R showed less evidence of hepatocyte damage with significantly lower perfusate alanine aminotransferase (P = 0.007) and aspartate aminotransferase (P = 0.014) levels.

CONCLUSIONS

We have developed a novel multidrug combination demonstrating promising defatting efficacy via activation of the AMP-activated protein kinase pathway with an optimized safety profile and reduced hepatotoxicity during ex vivo NMP.

Targeting Adrenergic Receptors in Metabolic Therapies for Heart Failure

The heart has a reduced capacity to generate sufficient energy when failing, resulting in an energy-starved condition with diminished functions. Studies have identified numerous changes in metabolic pathways in the failing heart that result in reduced oxidation of both glucose and fatty acid substrates, defects in mitochondrial functions and oxidative phosphorylation, and inefficient substrate utilization for the ATP that is produced. Recent early-phase clinical studies indicate that inhibitors of fatty acid oxidation and antioxidants that target the mitochondria may improve heart function during failure by increasing compensatory glucose oxidation. Adrenergic receptors (α₁ and β) are a key sympathetic nervous system regulator that controls cardiac function. β-AR blockers are an established treatment for heart failure and α_1A-AR agonists have potential therapeutic benefit. Besides regulating inotropy and chronotropy, α₁- and β-adrenergic receptors also regulate metabolic functions in the heart that underlie many cardiac benefits. This review will highlight recent studies that describe how adrenergic receptor-mediated metabolic pathways may be able to restore cardiac energetics to non-failing levels that may offer promising therapeutic strategies.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Systematic profiling of alternative splicing in Helicobacter pylori-negative gastric cancer and their clinical significance

Background

Alternative splicing (AS) may cause structural and functional variations in the protein to promote the proliferation of tumor cells. However, there is no comprehensive analysis of the clinical significance of AS in Helicobacter pylori-negative gastric cancer (HP⁻ GC).

Methods

The clinical, gene expression profile data and AS events of 138 HP⁻ GC patients were obtained from the database named the cancer genome atlas. Differently expressed AS (DEAS) events were determined by a comparison of the PSI values between HP⁻ GC samples and adjacent normal samples. Unsupervised clustering analysis, proportional regression and Kaplan–Meier analysis were used to explore the association between clinical data and immune features and to establish two nomograms about the prognosis of HP⁻ GC. Finally, splicing networks were constructed using Cytoscape.

Results

A total of 48141 AS events and 1041 DEAS events were found in HP⁻ GC. Various functions and pathways of DEAS events parent genes were enriched, such as cell-substrate junction, cell leading edge, focal adhension, and AMPK signaling. Seven overall survival (OS)-related and seven disease-free survival (DFS)-related AS events were used to construct the prognostic signatures. Based on the independent prognostic factors, two nomograms were established and showed excellent performance. Then, splicing regulatory networks among the correlations suggested that splicing factors were significantly associated with prognostic DEASs. Finally, the unsupervised clustering analysis revealed that DEAS-based clusters were associated with clinical characteristics, tumor microenvironment, tumor mutation burden, and immune features.

Conclusion

Seven OS-related and seven DFS-related AS events have been found to be correlated with the prognosis of HP⁻ GC and can be used as prognostic factors to establish an effective nomogram.

ROS/KRAS/AMPK Signaling Contributes to Gemcitabine-Induced Stem-like Cell Properties in Pancreatic Cancer

Poor prognosis in pancreatic cancer (PanCa) is partially due to chemoresistance to gemcitabine (GEM). Glucose metabolism has been revealed to contribute to the therapeutic resistance and pluripotent state of PanCa cells. However, few studies have focused on the effects of GEM on cancer cell metabolism, stemness of tumor cells, and molecular mechanisms that critically influence PanCa treatment. We demonstrate that GEM treatment induces metabolic reprogramming, reducing mitochondrial oxidation and upregulating aerobic glycolysis, and promotes stem-like behaviors in cancer cells. Inhibiting aerobic glycolysis suppresses cancer cell stemness and strengthens GEM's cytotoxicity. GEM-induced metabolic reprogramming is KRAS dependent, as knockdown of KRAS reverses the metabolic shift. GEM-induced metabolic reprogramming also activates AMP-activated protein kinase (AMPK), which promotes glycolytic flux and cancer stemness. In addition, GEM-induced reactive oxygen species (ROS) activate the KRAS/AMPK pathway. This effect was validated by introducing exogenous hydrogen peroxide (H₂O₂). Taken together, these findings reveal a counterproductive GEM effect during PanCa treatment. Regulating cellular redox, targeting KRAS/AMPK signaling, or reversing metabolic reprogramming might be effective approaches to eliminate cancer stem cells (CSCs) and enhance chemosensitivity to GEM to improve the prognosis of PanCa patients.

Morin reduces inflammatory responses and alleviates lipid accumulation in hepatocytes

Morin (MO), a natural bioflavinoid, exists in many herbs. Previous studies have acclaimed MO's anti-inflammatory, antidiabetic, antioxidant, antifibrotic, anticancer, and antihyperglycemic biological effects. This study aimed to assess the molecular mechanism of MO involved in the oleic acid (OA)-induced inflammatory damage and lipid accumulation in HepG2 cell and tyloxapol (Ty)-induced hyperlipidemia in mice. We found that MO can efficaciously mitigate reactive tumor necrosis factor-α (TNF-α) level and triglyceride (TG) accumulation in OA-induced HepG2 cell and in tyloxapol-induced mice. Next, the study testified that MO apparently suppressed OA-excited nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinases (MAPKs) signaling pathways in HepG2 cell. In addition, MO distinctly upregulated the expression of peroxisome proliferator-activated receptor α (PPARα) and decreased the expression of sterol regulatory element-binding protein 1c (SREBP-1c) in OA-induced HepG2 cell and in tyloxapol-induced mice, both of which are dependent upon the phosphorylation of acetyl-CoA carboxylase (ACC), adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), and protein kinase B (AKT). In conclusion, these results suggest that MO has protective potential against hyperlipidemia and steatosis, and the potential mechanism may have a close relation with activation of PPARα and inhibition of SREBP-1c.

Metabolic reprogramming of macrophages during infections and cancer

In response to different microenvironmental stimuli, macrophages are polarized into two populations, M1 macrophages which are classically activated by interferon (IFN)-γ with lipopolysaccharides (LPSs) and M2 macrophages which are alternatively activated by interleukin-4 (IL-4), to perform specific roles in innate immune responses. Accordingly, macrophages occupy distinct metabolic profiles, regulated by orchestrated factors and signaling pathways, including the PI3K-AKT, HIF, c-Myc, AMPK, and PPARs pathways. These factors and pathways play pivotal roles not only in metabolic regulation but also in macrophage polarization. After activation, classically activated M1 macrophages and alternatively activated M2 macrophages display distinct patterns in glucose, lipid, amino acid and iron metabolism. Here, we summarized recently discovered metabolism-related inflammatory signaling factors, along with reprogrammed metabolism, after the activation of macrophages under conditions related to immunity and cancer. Additionally, macrophage regulatory roles in infectious diseases, cancer progression and anti-cancer immunotherapy are discussed in terms of metabolic profiles, providing insight into the prevention and treatment of immune-associated diseases.

AMPK is associated with the beneficial effects of antidiabetic agents on cardiovascular diseases

Diabetics have higher morbidity and mortality in cardiovascular disease (CVD). A variety of antidiabetic agents are available for clinical choice. Cardiovascular (CV) safety assessment of these agents is crucial in addition to hypoglycemic effect before clinical prescription. Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an important cell energy sensor, which plays an important role in regulating myocardial energy metabolism, reducing ischemia and ischemia/reperfusion (I/R) injury, improving heart failure (HF) and ventricular remodeling, ameliorating vascular endothelial dysfunction, antichronic inflammation, anti-apoptosis, and regulating autophagy. In this review, we summarized the effects of antidiabetic agents to CVD according to basic and clinical research evidence and put emphasis on whether these agents can play roles in CV system through AMPK-dependent signaling pathways. Metformin has displayed definite CV benefits related to AMPK. Sodium-glucose cotransporter 2 inhibitors also demonstrate sufficient clinical evidence for CV protection, but the mechanisms need further exploration. Glucagon-likepeptide1 analogs, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors and thiazolidinediones also show some AMPK-dependent CV benefits. Sulfonylureas and meglitinides may be unfavorable to CV system. AMPK is becoming a promising target for the treatment of diabetes, metabolic syndrome and CVD. But there are still some questions to be answered.

Role of AMPK and PPARα in the anti-skin cancer effects of ursolic acid

The phytonutrient ursolic acid (UA), present in apples, rosemary, and other plant sources, has anti-cancer properties in a number of systems, including skin cancers. However, few reports have examined upstream mechanisms by which UA may prevent or treat cancer. Recent reports have indicated UA induces death of cancer cell lines via AMP-activated protein kinase (AMPK), an energy-sensing kinase which possesses both pro-metabolic and anti-cancer effects. Other studies have shown UA activates peroxisome proliferator activated receptor α (PPARα) and the glucocorticoid receptor (GR). Here, we found the cytotoxic effect of UA in skin carcinoma cells required AMPK activation. In addition, two inhibitors of PPARα partially reversed the cytotoxic effects of UA, suggesting its effects are at least partially mediated through this receptor. Finally, inhibition of the GR did not reverse the effects of UA nor did this compound bind the GR under the conditions of experiments performed. Overall, studies elucidating the anti-cancer effects of UA may allow for the development of more potent analogues utilizing similar mechanisms. These studies may also reveal the mediators of any possible side effects or resistance mechanisms to UA therapy.

Concerted redox modulation by sulforaphane alleviates diabetes and cardiometabolic syndrome

Diabetes and cardiometabolic disorders such as hypertension and obesity are major risk factors for the development of cardiovascular disease, with a wealth of evidence suggesting that oxidative stress is linked to the initiation and pathogenesis of these disease processes. With yearly increases in the global incidence of cardiovascular diseases (CVD) and diabetes, numerous studies have focused on characterizing whether upregulating antioxidant defenses through exogenous antioxidants (e.g. vitamin E, vitamin C) or activation of endogenous defenses (e.g. the Nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant defense pathway) may be of benefit. The dietary isothiocyanate sulforaphane (SFN) is currently the subject of several clinical trials for a variety of disease states, including the evaluation of its therapeutic potential to ameliorate diabetic and cardiometabolic complications. SFN is a well characterized and potent Nrf2 inducer, however recent studies suggest its protective actions may be in part mediated by its modulation of various pro-inflammatory (e.g. Nuclear factor-kappa B (NFκB)) and metabolic (e.g. Peroxisome Proliferator-Activator Receptor Gamma (PPARγ)) signaling pathways. The focus of this review is to provide a detailed analysis of the known mechanisms by which SFN modulates Nrf2, NFκB and PPARγ signaling and crosstalk and to provide a critical evaluation of the evidence linking these transcriptional pathways with diabetic and cardiometabolic complications and SFN mediated cytoprotection. To allow comparison between rodent and human studies, we discuss the published bioavailability of SFN metabolites achieved in rodents and man in the context of Nrf2, NFκB and PPARγ signaling. Furthermore, we provide an update on the functional outcomes and implicated signaling pathways reported in recent clinical trials with SFN in Type 2 diabetic patients.

Magnolol Alleviates Inflammatory Responses and Lipid Accumulation by AMP-Activated Protein Kinase-Dependent Peroxisome Proliferator-Activated Receptor α Activation

Magnolol (MG) is a kind of lignin isolated from Magnolia officinalis, which serves several different biological functions, such as antifungal, anticancer, antioxidant, and hepatoprotective functions. This study aimed to evaluate the protective effect of MG against oleic acid (OA)-induced hepatic steatosis and inflammatory damage in HepG2 cells and in a tyloxapol (Ty)-induced hyperlipidemia mouse model. Our findings indicated that MG can effectively inhibit OA-stimulated tumor necrosis factor α (TNF-α) secretion, reactive oxygen species generation, and triglyceride (TG) accumulation. Further study manifested that MG significantly suppressed OA-activated mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways and that these inflammatory responses can be negated by pretreatment with inhibitors of extracellular regulated protein kinase and c-Jun N-terminal kinase (U0126 and SP600125, respectively). In addition, MG dramatically upregulated peroxisome proliferator-activated receptor α (PPARα) translocation and reduced sterol regulatory element-binding protein 1c (SREBP-1c) protein synthesis and excretion, both of which are dependent upon the phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), acetyl-CoA carboxylase, and AKT kinase (AKT). However, MG suspended the activation of PPARα expression and was thus blocked by pretreatment with LY294002 and compound c (specific inhibitors of AKT and AMPK). Furthermore, MG clearly alleviated serum TG and total cholesterol release; upregulated AKT, AMPK, and PPARα expression; suppressed SREBP-1c generation; and alleviated hepatic steatosis and dyslipidemia in Ty-induced hyperlipidemia mice. Taken together, these results suggest that MG exerts protective effects against steatosis, hyperlipidemia, and the underlying mechanism, which may be closely associated with AKT/AMPK/PPARα activation and MAPK/NF-κB/SREBP-1c inhibition.

Ursolic Acid and Chronic Disease: An Overview of UA's Effects On Prevention and Treatment of Obesity and Cancer

Chronic diseases pose a worldwide problem and are only continuing to increase in incidence. Two major factors contributing to the increased incidence in chronic disease are a lack of physical activity and poor diet. As the link between diet and lifestyle and the increased incidence of chronic disease has been well established in the literature, novel preventive, and therapeutic methods should be aimed at naturally derived compounds such as ursolic acid (UA), the focus of this chapter. As chronic diseases, obesity and cancer share the common thread of inflammation and dysregulation of many related pathways, the focus here will be on these two chronic diseases. Significant evidence in the literature supports an important role for natural compounds such as UA in the prevention and treatment of chronic diseases like obesity and cancer, and here we have highlighted many of the ways UA has been shown to be a beneficial and versatile phytochemical.

The Role of Peroxisome Proliferator-Activated Receptor γ in Mediating Cardioprotection Against Ischemia/Reperfusion Injury

Myocardial infarction (MI) is a serious cardiovascular disease resulting in high rates of morbidity and mortality. Although advances have been made in restoring myocardial perfusion in ischemic areas, decreases in cardiomyocyte death and infarct size are still limited, attributing to myocardial ischemia/reperfusion (I/R) injury. It is necessary to develop therapies to restrict myocardial I/R injury and protect cardiomyocytes against further damage after MI. Many studies have suggested that peroxisome proliferator-activated receptor γ (PPARγ), a ligand-inducible nuclear receptor that predominantly regulates glucose and lipid metabolism, is a promising therapeutic target for ameliorating myocardial I/R injury. Thus, this review focuses on the role of PPARγ in cardioprotection during myocardial I/R. The cardioprotective effects of PPARγ, including attenuating oxidative stress, inhibiting inflammatory responses, improving glucose and lipid metabolism, and antagonizing apoptosis, are described. Additionally, the underlying mechanisms of cardioprotective effects of PPARγ, such as regulating the expression of target genes, influencing other transcription factors, and modulating kinase signaling pathways, are further discussed.

κ-opioid receptor is involved in the cardioprotection induced by exercise training

The present study was designed to test the hypothesis that exercise training elicited a cardioprotective effect against ischemia and reperfusion (I/R) via the κ-opioid receptor (κ-OR)-mediated signaling pathway. Rats were randomly divided into four groups: the control group, the moderate intensity exercise (ME) group, the high intensity exercise (HE) group, and the acute exercise (AE) group. For the exercise training protocols, the rats were subjected to one week of adaptive treadmill training, while from the second week, the ME and HE groups were subjected to eight weeks of exercise training, and the AE group was subjected to three days of adaptive treadmill training and one day of vigorous exercise. After these protocols, the three exercise training groups were divided into different treatment groups, and the rats were subjected to 30 min of ischemia and 120 min of reperfusion. Changes in infarct size and serum cTnT (cardiac troponin T) caused by I/R were reduced by exercise training. Moreover, cardiac dysfunction caused by I/R was also alleviated by exercise training. These effects of exercise training were reversed by nor-BNI (a selective κ-OR antagonist), Compound C (a selective AMPK inhibitor), Akt inhibitor and L-NAME (a non-selective eNOS inhibitor). Expression of κ-OR and phosphorylation of AMPK, Akt and eNOS were significantly increased in the ME, HE and AE groups. These findings demonstrated that the cardioprotective effect of exercise training is possibly mediated by the κ-OR-AMPK-Akt-eNOS signaling pathway.

Cardiac Fibrosis Alleviated by Exercise Training Is AMPK-Dependent

Regular exercise can protect the heart against external stimuli, but the mechanism is not well understood. We determined the role of adenosine monophosphate-activated protein kinase (AMPK) in regulating swimming exercise-mediated cardiac protection against β-adrenergic receptor overstimulation with isoproterenol (ISO) in mice. Ten-week-old AMPKα2^+/+ and AMPKα2-knockout (AMPKα2^-/-) littermates were subjected to 4 weeks of swimming training (50 min daily, 6 days a week) or housed under sedentary conditions. The mice received daily subcutaneous injection of ISO (5 mg/kg/d), a nonselective β-adrenergic receptor agonist, during the last 2 weeks of swimming training. Swimming training alleviated ISO-induced cardiac fibrosis in AMPKα2^+/+ mice but not AMPKα2^-/- mice. Swimming training activated cardiac AMPK in AMPKα2^+/+ mice. Furthermore, swimming training attenuated ISO-induced production of reactive oxygen species (ROS) and expression of NADPH oxidase and promoted the expression of antioxidant enzymes in AMPKα2^+/+ mice but not AMPKα2^-/- mice. In conclusion, swimming training attenuates ISO-induced cardiac fibrosis by inhibiting the NADPH oxidase–ROS pathway mediated by AMPK activation. Our findings provide a new mechanism for the cardioprotective effects of exercise.

Cardiac NO signalling in the metabolic syndrome

It is well documented that metabolic syndrome (i.e. a group of risk factors, such as abdominal obesity, elevated blood pressure, elevated fasting plasma glucose, high serum triglycerides and low cholesterol level in high-density lipoprotein), which raises the risk for heart disease and diabetes, is associated with increased reactive oxygen and nitrogen species (ROS/RNS) generation. ROS/RNS can modulate cardiac NO signalling and trigger various adaptive changes in NOS and antioxidant enzyme expressions/activities. While initially these changes may represent protective mechanisms in metabolic syndrome, later with more prolonged oxidative, nitrosative and nitrative stress, these are often exhausted, eventually favouring myocardial RNS generation and decreased NO bioavailability. The increased oxidative and nitrative stress also impairs the NO-soluble guanylate cyclase (sGC) signalling pathway, limiting the ability of NO to exert its fundamental signalling roles in the heart. Enhanced ROS/RNS generation in the presence of risk factors also facilitates activation of redox-dependent transcriptional factors such as NF-κB, promoting myocardial expression of various pro-inflammatory mediators, and eventually the development of cardiac dysfunction and remodelling. While the dysregulation of NO signalling may interfere with the therapeutic efficacy of conventional drugs used in the management of metabolic syndrome, the modulation of NO signalling may also be responsible for the therapeutic benefits of already proven or recently developed treatment approaches, such as ACE inhibitors, certain β-blockers, and sGC activators. Better understanding of the above-mentioned pathological processes may ultimately lead to more successful therapeutic approaches to overcome metabolic syndrome and its pathological consequences in cardiac NO signalling.

Glabridin induces glucose uptake via the AMP-activated protein kinase pathway in muscle cells

The present study demonstrates that glabridin, a prenylated isoflavone in licorice, stimulates glucose uptake through the adenosine monophosphate-activated protein kinase (AMPK) pathway in L6 myotubes. Treatment with glabridin for 4h induced glucose uptake in a dose-dependent manner accompanied by the translocation of glucose transporter type 4 (GLUT4) to the plasma membrane. Glabridin needed at least 4h to increase glucose uptake, while it significantly decreased glycogen and increased lactic acid within 15 min. Pharmacological inhibition of AMPK by Compound C suppressed the glabridin-induced glucose uptake, whereas phosphoinositide 3-kinase and Akt inhibition by LY294002 and Akt1/2 inhibitor, respectively, did not. Furthermore, glabridin induced AMPK phosphorylation, and siRNA for AMPK completely abolished glabridin-induced glucose uptake. We confirmed that glabridin-rich licorice extract prevent glucose intolerance accompanied by the AMPK-dependent GLUT4 translocation in the plasma membrane of mice skeletal muscle. These results indicate that glabridin may possess a therapeutic effect on metabolic disorders, such as diabetes and hyperglycemia, by modulating glucose metabolism through AMPK in skeletal muscle cells.

Compartment-specific activation of PPARγ governs breast cancer tumor growth, via metabolic reprogramming and symbiosis

The role of PPARγ in cancer therapy is controversial, with studies showing either pro-tumorigenic or antineoplastic effects. This debate is very clinically relevant, because PPARγ agonists are used as antidiabetic drugs. Here, we evaluated if the effects of PPARγ on tumorigenesis are determined by the cell type in which PPARγ is activated. Second, we examined if the metabolic changes induced by PPARγ, such as glycolysis and autophagy, play any role in the tumorigenic process. To this end, PPARγ was overexpressed in breast cancer cells or in stromal cells. PPARγ-overexpressing cells were examined with respect to (1) their tumorigenic potential, using xenograft models, and (2) regarding their metabolic features. In xenograft models, we show that when PPARγ is activated in cancer cells, tumor growth is inhibited by 40%. However, when PPARγ is activated in stromal cells, the growth of co-injected breast cancer cells is enhanced by 60%. Thus, the effect(s) of PPARγ on tumorigenesis are dependent on the cell compartment in which PPARγ is activated. Mechanistically, stromal cells with activated PPARγ display metabolic features of cancer-associated fibroblasts, with increased autophagy, glycolysis and senescence. Indeed, fibroblasts overexpressing PPARγ show increased expression of autophagic markers, increased numbers of acidic autophagic vacuoles, increased production of L-lactate, cell hypertrophy and mitochondrial dysfunction. In addition, PPARγ fibroblasts show increased expression of CDKs (p16/p21) and β-galactosidase, which are markers of cell cycle arrest and senescence. Finally, PPARγ induces the activation of the two major transcription factors that promote autophagy and glycolysis, i.e., HIF-1α and NFκB, in stromal cells. Thus, PPARγ activation in stromal cells results in the formation of a catabolic pro-inflammatory microenvironment that metabolically supports cancer growth. Interestingly, the tumor inhibition observed when PPARγ is expressed in epithelial cancer cells is also associated with increased autophagy, suggesting that activation of an autophagic program has both pro- or antitumorigenic effects depending on the cell compartment in which it occurs. Finally, when PPARγ is expressed in epithelial cancer cells, the suppression of tumor growth is associated with a modest inhibition of angiogenesis. In conclusion, these data support the "two-compartment tumor metabolism" model, which proposes that metabolic coupling exists between catabolic stromal cells and oxidative cancer cells. Cancer cells induce autophagy, glycolysis and senescence in stromal cells. In return, stromal cells generate onco-metabolites and mitochondrial fuels (L-lactate, ketones, glutamine/aminoacids and fatty acids) that are used by cancer cells to enhance their tumorigenic potential. Thus, as researchers design new therapies, they must be conscious that cancer is not a cell-autonomous disease, but rather a tumor is an ecosystem of many different cell types, which engage in metabolic symbiosis.

Adiponectin and PPARγ: cooperative and interdependent actions of two key regulators of metabolism

The recent advances in the understanding of adiponectin and other adipokines have highlighted the role of adipose tissue as an active endocrine organ. One of the central regulators of adipocyte biology is peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that induces the adipogenic gene expression program during development, promotes adipose remodeling, and regulates the functions of adipocytes in lipid storage, adipokine secretion, and energy homeostasis. Activation of PPARγ results in increased insulin sensitivity in skeletal muscle and liver and improves the secretory profile of adipose tissue, favoring release of insulin-sensitizing adipokines, such as adiponectin, and reducing inflammatory cytokines. Increased adiponectin production is likely a significant mediator of the systemic effects of PPARγ activation. This chapter will review the interplay between PPARγ and adiponectin in regulating metabolism, presenting evidence that PPARγ regulates adiponectin gene expression, processing, and secretion and that the two proteins have overlapping effects on downstream metabolic pathways.

Comparative analysis of telmisartan and olmesartan on cardiac function in the transgenic (mRen2)27 rat

Telmisartan, an angiotensin receptor blocker, may have unique benefits as it possesses partial peroxisome proliferator-activated receptor (PPAR)-γ agonist activity in addition to antihypertensive effects. In this study, we test whether treatment with telmisartan ameliorates cardiovascular abnormalities to a greater extent than olmesartan, which has little PPAR-γ activity. The hypertensive rodent model of tissue renin-angiotensin system activation, transgenic (mRen2)27 (Ren2) rats and their littermate Sprague-Dawley controls were used. Rats were treated with telmisartan (2 mg · kg(-1) · day(-1)), olmesartan (2.5 mg · kg(-1) · day(-1)), or vehicle via drinking water for 3 wk; these doses achieved similar blood pressure control, as measured by telemetry. Ren2 rats displayed impaired diastolic and systolic function using left ventricular (LV) pressure-volume (P-V) analysis. Load-independent diastolic indexes, including the time constant of isovolumic relaxation and the slope of the end-diastolic P-V relationship, as well as systolic indexes, including preload recruitable stroke work, the dP/dt(max)-end-diastolic volume (EDV) relationship, and the P-V area-EDV relationship, were elevated in Ren2 rats compared with Sprague-Dawley controls (P < 0.05). The Ren2 myocardium exhibited parallel increases in the oxidant markers NADPH oxidase and 3-nitrotyrosine. The increase in the prohypertrophic protein Jak2 in Ren2 rats was associated with cardiac structural abnormalities using light microscopic and ultrastructural analysis, which included interstitial fibrosis, cardiomyocyte and LV hypertrophy, and mitochondrial derangements. Both angiotensin receptor blockers attenuate these abnormalities to a similar extent. Our data suggest that the beneficial effect of telmisartan and olmesartan on cardiac structure and function may be predominantly pressor-related or angiotensin type 1 receptor dependent in this model of renin-angiotensin system activation.

Redox regulation of the AMP-activated protein kinase

Redox state is a critical determinant of cell function, and any major imbalances can cause severe damage or death.

AMPK-Dependent Metabolic Regulation by PPAR Agonists

Comprehensive studies support the notion that the peroxisome proliferator-activated receptors, (PPARs), PPARα, PPARβ/δ, and PPARγ, regulate cell growth, morphogenesis, differentiation, and homeostasis. Agonists of each PPAR subtype exert their effects similarly or distinctly in different tissues such as liver, muscle, fat, and vessels. It is noteworthy that PPARα or PPARγ agonists have pharmacological effects by modulating the activity of AMPK, which is a key cellular energy sensor. However, the role of AMPK in the metabolic effects of PPAR agonists has not been thoroughly focused. Moreover, AMPK activation by PPAR agonists seems to be independent of the receptor activation. This intriguing action of PPAR agonists may account in part for the mechanistic basis of the therapeutics in the treatment of metabolic disease. In this paper, the effects of PPAR agonists on metabolic functions were summarized with particular reference to their AMPK activity regulation.