Curcumin prevents leptin raising glucose levels in hepatic stellate cells by blocking translocation of glucose transporter-4 and increasing glucokinase

A New Target for Hepatic Fibrosis Prevention and Treatment: The Warburg Effect

Hepatic fibrosis is a major public health problem that endangers human wellbeing. In recent years, a number of studies have revealed the important impact of metabolic reprogramming on the occurrence and development of hepatic fibrosis. Among them, the Warburg effect, as an intracellular glucose metabolism reprogramming, can promote the occurrence and development of hepatic fibrosis by promoting the activation of hepatic stellate cells (HSCs) and inducing the polarization of liver macrophages (KC). Understanding the Warburg effect and its important role in the progression of hepatic fibrosis will assist in developing new strategies for the prevention and treatment of hepatic fibrosis. This review focuses on the Warburg effect and the specific mechanism by which it affects the progression of hepatic fibrosis by regulating HSCs activation and KC polarization. In addition, we also summarize and discuss the related experimental drugs and their mechanisms that inhibit the Warburg effect by targeting key proteins of glycolysis in order to improve hepatic fibrosis in the hope of providing more effective strategies for the clinical treatment of hepatic fibrosis.

Antihypertensive Property of Celery: A Narrative Review on Current Knowledge

Background

The incidence of hypertension is increasing significantly on a global scale, and it is considered the leading cause of heart disease and death. Despite the availability of hypotensive drugs, they have many side effects that decrease adherence to treatments and lead to uncontrolled blood pressure. Studies have revealed that celery contains bioactive compounds that oppose hypotensive effect.

Methods

A thorough literature review was conducted using Scopus, PubMed, and Google Scholar databases. To identify relevant studies on the topic, our search strategy employed keywords such as "celery," "Apium gravenols L," "hypertension," "high blood pressure," "apigenin," "antihypertensive," and "hypotensive." The search was limited to articles published between January 2013 and December 2023. The inclusion criteria were original research articles that involved both animal and human subjects, published in English, and reported results applicable to the subject of this review. Review articles or articles in the form of theses or books were excluded.

Results

The available evidence revealed that celery enhances blood pressure parameters. Clinical trials clarified that celery possesses its effect through many bioactive compounds, specifically 3-n-butylphthalide and apigenin. Based on animal and human studies, celery seems to elicit blood pressure regulation mainly by the vasodilatory, diuretic, and calcium channel-blocking properties. Furthermore, celery seed extract seems to exert a bradycardia effect.

Conclusion

The current literature review showed a considerable number of studies on the hypertensive models, which confirmed that celery and its extracts are effective hypotensive agents. Some limitations in comparing published data should be considered, including differences in doses, extracts, species of celery, and administration form.

Curcumin as a hepatoprotective agent against chemotherapy-induced liver injury

Despite significant advances in cancer therapeutics, chemotherapy remains the cornerstone of treatment for many tumors. Importantly, however, chemotherapy-induced toxicity, including hepatotoxicity, can lead to the interruption or discontinuation of potentially effective therapy. In recent years, special attention has been paid to the search for complementary therapies to mitigate chemotherapy-induced toxicity. Although there is currently a lack of specific interventions to mitigate or prevent hepatotoxicity in chemotherapy-treated patients, the polyphenol compound curcumin has emerged as a potential strategy to overcome this adverse effect. Here we review, firstly, the molecular and physiological mechanisms and major risk factors of chemotherapy-induced hepatotoxicity. We then present an overview of how curcumin has the potential to mitigate hepatotoxicity by targeting specific molecular mechanisms. Hepatotoxicity is a well-described side effect of cytotoxic drugs that can limit their clinical application. Inflammation and oxidative stress are the most common mechanisms involved in hepatotoxicity. Several studies have shown that curcumin could prevent and/or palliate chemotherapy-induced liver injury, mainly due to its anti-inflammatory, antioxidant, antifibrotic and hypolipidemic properties. Further clinical investigation using bioavailable curcumin formulations is warranted to demonstrate its efficacy as an hepatoprotective agent in cancer patients.

Effects of turmeric (Curcuma longa) supplementation on glucose metabolism in diabetes mellitus and metabolic syndrome: An umbrella review and updated meta-analysis

AIMS

This study aims to comprehensively review the existing evidence and conduct analysis of updated randomized controlled trials (RCTs) of turmeric (Curcuma longa, CL) and its related bioactive compounds on glycemic and metabolic parameters in patients with type 2 diabetes (T2DM), prediabetes, and metabolic syndrome (MetS) together with a sub-group analysis of different CL preparation forms.

METHODS

An umbrella review (UR) and updated systematic reviews and meta-analyses (SRMAs) were conducted to evaluate the effects of CL compared with a placebo/standard treatment in adult T2DM, prediabetes, and MetS. The MEDLINE, Embase, The Cochrane Central Register of Control Trials, and Scopus databases were searched from inception to September 2022. The primary efficacy outcomes were hemoglobin A1C (HbA1C) and fasting blood glucose (FBG). The corrected covered area (CCA) was used to assess overlap. Mean differences were pooled across individual RCTs using a random-effects model. Subgroup and sensitivity analyses were performed for various CL preparation forms.

RESULTS

Fourteen SRMAs of 61 individual RCTs were included in the UR. The updated SRMA included 28 studies. The CCA was 11.54%, indicating high overlap across SRMAs. The updated SRMA revealed significant reduction in FBG and HbA1C with CL supplementation, obtaining a mean difference (95% confidence interval [CI]) of -8.129 (-12.175, -4.084) mg/dL and -0.134 (-0.304, -0.037) %, respectively. FBG and HbA1C levels decreased with all CL preparation forms as did other metabolic parameters levels. The results of the sensitivity and subgroup analyses were consistent with those of the main analysis.

CONCLUSION

CL supplementation can significantly reduce FBG and HbA1C levels and other metabolic parameters in T2DM and mitigate related conditions, including prediabetes and MetS.

TRIAL REGISTRATION

PROSPERO (CRD42016042131).

Overview of Curcumin and Piperine Effects on Glucose Metabolism: The Case of an Insulinoma Patient’s Loss of Consciousness

The hypoglycemic properties of curcumin supplements in therapeutic doses are well-known and may represent a useful tool for the treatment of chronic diseases such as metabolic syndrome, insulin resistance and type 2 diabetes. The poor bioavailability of curcumin can be improved with the concomitant administration of piperine, with no severe adverse effects on glycemia reported so far in the literature. In this article, we further discuss a previously reported case of a helicopter pilot, affected by grade I obesity who, under curcumin and piperine treatment, experienced a transient loss of consciousness (TLOC), during a low-altitude flight. This episode led to a diagnosis of insulinoma, previously asymptomatic. We hypothesized that the combined effects of curcumin and piperine might have caused a severe hypoglycemic episode and subsequent TLOC. Therefore, further studies should be conducted to evaluate the safety of curcumin and piperine supplementation in subjects with impaired glucose metabolism and insulin secretion.

AMPK/PGC-1α/GLUT4-Mediated Effect of Icariin on Hyperlipidemia-Induced Non-Alcoholic Fatty Liver Disease and Lipid Metabolism Disorder in Mice

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. Therapeutic activity of icariin, a major bioactive component of Epimedii Herba, in NAFLD is still unknown. Herein, the C57BL/6J mice were fed with a high-fat diet for 16 weeks to establish a NAFLD model. Mice were assigned to five groups: control group, NAFLD group, and icariin treatment groups. Effects of icariin on blood indices, glucose tolerance, insulin sensitivity, histopathological morphology, cell apoptosis, lipid accumulation, and AMPK signaling were analyzed. In addition, another cohort of mice were assigned to five groups: control group, NAFLD group, dorsomorphin treatment group, icariin treatment group, and dorsomorphin + icariin treatment group. Expression of proteins in liver tissues associated with AMPK signaling, and levels of ALT and AST were evaluated. Icariin attenuated the NAFLD-induced increase of the TG, TC, LDL-C, ALT, AST levels. HDL-C levels were affected neither by NAFLD nor by icariin. Furthermore, icariin treatment (100-200 mg/kg) counteracted the NAFLD-reduced glucose tolerance and insulin sensitivity and modulated histopathological changes, cell apoptosis, and lipid accumulation in liver tissues. Additionally, icariin mitigated the NAFLD-induced up-regulation of the cleaved caspase 3/9, SREBP-1c, and DGAT-2 levels, and enhanced the expression level of CPT-1, p-ACC/ACC, AMPKα1, PGC-1α, and GLUT4. Effects of icariin on the AMPK signaling and levels of AST and ALT could be reversed by AMPK inhibitor, dorsomorphin. This paper investigates the glucose-reducing and lipid-lowering effects of icariin in NAFLD. Moreover, icariin might function through activating the AMPKα1/PGC-1α/GLTU4 pathway.

Curcumin Affects Leptin-Induced Expression of Methionine Adenosyltransferase 2A in Hepatic Stellate Cells by Inhibition of JNK Signaling

INTRODUCTION

Obese patients are often accompanied by hyperleptinemia and prone to develop liver fibrosis. Accumulating data including those obtained from human studies suggested the promotion role of leptin in liver fibrosis. The remodeling of the DNA methylation is an epigenetic mechanism for regulating gene expression and is essential for hepatic stellate cell (HSC) activation, a key step in liver fibrogenesis. Leptin increases the expression of methionine adenosyltransferase 2A (MAT2A) which is associated with DNA methylation and HSC activation. Curcumin, an active polyphenol of the golden spice turmeric, inhibits leptin-induced HSC activation and liver fibrogenesis. Thus, the present research aimed to investigate the influence of curcumin on the roles of leptin in MAT2A expression in HSCs.

METHODS

The in vivo experiments were conducted by using leptin-deficient obese mice. The gene expressions were examined by Western blot, real-time PCR, promoter activity assay, and immunostaining analysis.

RESULTS

Curcumin reduced leptin-induced MAT2A expression. JNK signaling contributed to leptin-induced increase in MAT2A level, which could be interrupted by curcumin treatment. Curcumin inhibited leptin-induced MAT2A promoter activity by influencing MAT2A promoter fragments between -2,847 bp and - 2,752 bp and between -2,752 bp and +49 bp. The effect of curcumin on leptin-induced MAT2A expression paralleled the reductions in leptin-induced activated HSCs and liver fibrosis.

CONCLUSION

These results might have implications for curcumin inhibition of the liver fibrogenesis in obese patients with hyperleptinemia.

Turmeric and its bioactive constituents trigger cell signaling mechanisms that protect against diabetes and cardiovascular diseases

Turmeric, the rhizome of Curcuma longa plant belonging to the ginger family Zingiberaceae, has a history in Ayurvedic and traditional Chinese medicine for treatment of chronic diseases, including metabolic and cardiovascular diseases (CVD). This parallels a prevalence of age- and lifestyle-related diseases, especially CVD and type 2 diabetes (T2D), and associated mortality which has occurred in recent decades. While the chemical composition of turmeric is complex, curcuminoids and essential oils are known as two major groups that display bioactive properties. Curcumin, the most predominant curcuminoid, can modulate several cell signaling pathways involved in the etiology and pathogenesis of CVD, T2D, and related morbidities. Lesser bioactivities have been reported from other curcuminoids and essential oils. This review examines the chemical compositions of turmeric, and related bioactive constituents. A focus was placed on the cellular and molecular mechanisms that underlie the protective effects of turmeric and turmeric-derived compounds against diabetes and CVD, compiled from the findings obtained with cell-based and animal models. Evidence from clinical trials is also presented to identify potential preventative and therapeutic efficacies. Clinical studies with longer intervention durations and specific endpoints for assessing health outcomes are warranted in order to fully evaluate the long-term protective efficacy of turmeric.

Glucokinase activation as antidiabetic therapy: effect of nutraceuticals and phytochemicals on glucokinase gene expression and enzymatic activity

Diabetes represents an important public health problem. Recently, new molecular targets have been identified and exploited to treat this disease. Due to its pivotal role in glucose homeostasis, glucokinase (GCK) is a promising target for the development of novel antidiabetic drugs; however, pharmacological agents that modulate GCK activity have been linked to undesirable side-effects, limiting its use. Interestingly, plants might be a valuable source of new therapeutic compounds with GCK-activating properties and presumably no adverse effects. In this review, we describe biochemical characteristics related to the physiological and pathological importance of GCK, as well as the mechanisms involved in its regulation at different molecular levels. Posteriorly, we present a compendium of findings supporting the potential use of nutraceuticals and phytochemicals in the management of diabetes through modulation of GCK expression and activity. Finally, we propose critical aspects to keep in mind when designing experiments to evaluate GCK modulation properly.

Curcumin reduces methionine adenosyltransferase 2B expression by interrupting phosphorylation of p38 MAPK in hepatic stellate cells

The active polyphenol curcumin demonstrates therapeutic effects against various different diseases. Researches revealed the inhibitory roles of curcumin in hepatic stellate cell (HSC) activation and fibrogenesis. HSC activation, a key step in liver fibrogenesis, requires the remodeling of DNA methylation, which is associated with methionine adenosyltransferase II (MATII) composed of catalytic subunit MAT2A and regulatory subunit MAT2B. MATII is essential for HSC activation in vitro. The present researches aimed to investigate the effect of curcumin on MAT2B expression in HSCs in vivo and in vitro. Results demonstrated that curcumin could reduce MAT2B expression in HSCs at multiple levels. The activation of p38 MAPK pathway promoted MAT2B expression in HSCs. The effect of curcumin on MAT2B was through its interruption of p38 MAPK signaling pathway. Knockdown of MAT2B inhibited HSC activation and reduced collagen level in the model of liver fibrosis. Curcumin down-regulation of MAT2B contributed to the inhibitory role of curcumin on HSC activation and collagen expression in mouse livers. This study provided evidences for the effect of curcumin on the expression of MAT2B, an enzyme for the biosynthesis of methyl donor S-adenosylmethionine, in HSCs and demonstrated the function significance of curcumin-induced downregulation of MAT2B in curcumin inhibition of liver fibrosis.

Antidiabetic Properties of Curcumin I: Evidence from In Vitro Studies

Type 2 diabetes mellitus (T2DM) is a growing metabolic disease characterized by insulin resistance and hyperglycemia. Current preventative and treatment strategies for T2DM and insulin resistance lack in efficacy resulting in the need for new approaches to prevent and manage/treat the disease better. In recent years, epidemiological studies have suggested that diets rich in fruits and vegetables have beneficial health effects including protection against insulin resistance and T2DM. Curcumin, a polyphenol found in turmeric, and curcuminoids have been reported to have antioxidant, anti-inflammatory, hepatoprotective, nephroprotective, neuroprotective, immunomodulatory and antidiabetic properties. The current review (I of II) summarizes the existing in vitro studies examining the antidiabetic effects of curcumin, while a second (II of II) review summarizes evidence from existing in vivo animal studies and clinical trials focusing on curcumin’s antidiabetic properties.

Metabolic control of gene transcription in non-alcoholic fatty liver disease: the role of the epigenome

Non-alcoholic fatty liver disease (NAFLD) is estimated to affect 24% of the global adult population. NAFLD is a major risk factor for the development of cirrhosis and hepatocellular carcinoma, as well as being strongly associated with type 2 diabetes and cardiovascular disease. It has been proposed that up to 88% of obese adults have NAFLD, and with global obesity rates increasing, this disease is set to become even more prevalent. Despite intense research in this field, the molecular processes underlying the pathology of NAFLD remain poorly understood. Hepatic intracellular lipid accumulation may lead to dysregulated tricarboxylic acid (TCA) cycle activity and associated alterations in metabolite levels. The TCA cycle metabolites alpha-ketoglutarate, succinate and fumarate are allosteric regulators of the alpha-ketoglutarate-dependent dioxygenase family of enzymes. The enzymes within this family have multiple targets, including DNA and chromatin, and thus may be capable of modulating gene transcription in response to intracellular lipid accumulation through alteration of the epigenome. In this review, we discuss what is currently understood in the field and suggest areas for future research which may lead to the development of novel preventative or therapeutic interventions for NAFLD.

Increased butyrate priming in the gut stalls microbiome associated-gastrointestinal inflammation and hepatic metabolic reprogramming in a mouse model of Gulf War Illness

Most of the associated pathologies in Gulf War Illness (GWI) have been ascribed to chemical and pharmaceutical exposures during the war. Since an increased number of veterans complain of gastrointestinal (GI), neuroinflammatory and metabolic complications as they age and there are limited options for a cure, the present study was focused to assess the role of butyrate, a short chain fatty acid for attenuating GWI-associated GI and metabolic complications. Results in a GWI-mouse model of permethrin and pyridostigmine bromide (PB) exposure showed that oral butyrate restored gut homeostasis and increased GPR109A receptor copies in the small intestine (SI). Claudin-2, a protein shown to be upregulated in conditions of leaky gut was significantly decreased following butyrate administration. Butyrate decreased TLR4 and TLR5 expressions in the liver concomitant to a decrease in TLR4 activation. GW-chemical exposure showed no clinical signs of liver disease but a significant alteration of metabolic markers such as SREBP1c, PPAR-α, and PFK was evident. Liver markers for lipogenesis and carbohydrate metabolism that were significantly upregulated following GW chemical exposure were attenuated by butyrate priming in vivo and in human primary hepatocytes. Further, Glucose transporter Glut-4 that was shown to be elevated following liver complications were significantly decreased in these mice after butyrate administration. Finally, use of TLR4 KO mice completely attenuated the liver metabolic changes suggesting the central role of these receptors in the GWI pathology. In conclusion, we report a butyrate specific mechanistic approach to identify and treat increased metabolic abnormalities in GWI veterans with systemic inflammation, chronic fatigue, GI disturbances, metabolic complications and weight gain.

Perilipin 5 and liver fatty acid binding protein function to restore quiescence in mouse hepatic stellate cells

Hepatic stellate cell (HSC) activation occurs along with decreased Perilipin5 (Plin5) and liver fatty acid-binding protein (L-Fabp) expression and coincident lipid droplet (LD) depletion. Conversely, the activated phenotype is reversible in WT HSCs upon forced expression of Plin5. Here, we asked if L-Fabp expression is required for Plin5-mediated rescue of the quiescent phenotype. Lentiviral Plin5 transduction of passaged L-Fabp^-/- HSCs failed to reverse activation markers or restore lipogenic gene expression and LD formation. However, adenoviral L-Fabp infection of lentiviral Plin5 transduced L-Fabp^-/- HSCs restored both the quiescent phenotype and LD formation, an effect also mediated by adenoviral intestine-Fabp or adipocyte-Fabp. Expression of exogenous Plin5 in activated WT HSCs induced a transcriptional program of lipogenic gene expression including endogenous L-Fabp, but none of the other FABPs. We further demonstrated that selective, small molecule inhibition of endogenous L-Fabp also eliminated the ability of exogenous Plin5 to rescue LD formation and reverse activation of WT HSCs. This functional coordination of L-Fabp with Plin5 was 5'-AMP-activated protein kinase (AMPK)-dependent and was eliminated by AMPK inhibition. Taken together, our results indicate that L-Fabp is required for Plin5 to activate a transcriptional program that restores LD formation and reverses HSC activation.

Curcumin and insulin resistance-Molecular targets and clinical evidences

Curcumin ((1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), the main component of the Indian spice turmeric, has been used in traditional medicine to improve diabetes and its comorbidities. Since the last two decades, scientific research has shown that in addition to its antioxidant properties, curcumin could also work as protein homeostasis regulator and it is able to modulate other intracellular pathways. Curcumin supplementation has been proposed to improve insulin resistance (IR) through the activation of the insulin receptor and its downstream pathways in several experimental models, pointing out that its clinical use may be a good and innocuous strategy to improve IR-related diseases. IR is associated with many diseases and syndromes like carbohydrate intolerance, diabetes, metabolic syndrome, and cardiovascular disease. Therefore, it is imperative to identify safe therapeutic interventions aimed to reduce side effects that could lead the patient to leave the treatment. To date, many clinical trials have been carried out using turmeric and curcumin to improve metabolic syndrome, carbohydrate intolerance, diabetes, and obesity in individuals with IR. Results so far are inconclusive because dose, time of treatment, and type of curcumin can change the study outcome significantly. However, there is some clinical evidence suggesting a beneficial effect of curcumin on IR. In this review, we discuss the factors that could influence curcumin effects in clinical trials aimed to improve IR and related diseases, and the conclusions that can be drawn from results obtained so far. © 2016 BioFactors, 42(6):561-580, 2016.

Perilipin 5 restores the formation of lipid droplets in activated hepatic stellate cells and inhibits their activation

Hepatic stellate cells (HSC) are major effectors during hepatic fibrogenesis. The activation of HSC is coupled to the loss of lipid droplets (LDs), which are specialized organelles composed of neutral lipids surrounded by perilipins. LDs have emerged as a focal point of interest in understanding the metabolic regulation of intrahepatic lipids during lipid-mediated liver fibrogenesis. Perilipin 5 (Plin5) is a newly identified LD protein in the perilipin family, which plays a key role in regulating aspects of intracellular trafficking, signaling, and cytoskeletal organization in hepatocytes. Recent work in Plin5 knockout mice suggests a role in high fat diet-induced hepatic lipotoxicity. The current report is to evaluate the impact of Plin5 on HSC activation and to elucidate the underlying mechanisms. We now show that high fat diet-induced liver fibrosis is accompanied by an approximate 75% reduction in Plin5 in HSC, and that spontaneous activation of primary HSC produces temporally coincident loss of Plin5 expression and LD depletion. As modulating lipid content in HSC is a suggested strategy for inhibition of HSC activation and treatment of hepatic fibrosis, we asked whether exogenous Plin5 expression in primary HSC would reverse the activation phenotype and promote LD formation. Recombinant lentiviral Plin5 expression in primary mouse HSC restored the formation of LDs, increased lipid content by inducing expression of pro-lipogenic genes and suppressing expression of pro-lipolytic genes, and suppressed HSC activation (~two fold reduction in expression of procollagen and α-smooth muscle actin, two unique biomarkers for activated HSC). In addition, the expression of exogenous Plin5 in HSC attenuated cellular oxidative stress by reducing cellular reactive oxygen species, elevating cellular glutathione, and inducing gene expression of glutamate-cysteine ligase. Taken together, our results indicate that expression of Plin5 plays a critical role in the formation of LDs, the elevation of lipid content in HSC, and the inhibition of the activation of HSC.

Curcumin directly inhibits the transport activity of GLUT1

Curcumin, a major ingredient in turmeric, has a long history of medicinal applications in a wide array of maladies including treatment for diabetes and cancer. Seemingly counterintuitive to the documented hypoglycemic effects of curcumin, however, a recent report indicates that curcumin directly inhibits glucose uptake in adipocytes. The major glucose transporter in adipocytes is GLUT4. Therefore, this study investigates the effects of curcumin in cell lines where the major transporter is GLUT1. We report that curcumin has an immediate inhibitory effect on basal glucose uptake in L929 fibroblast cells with a maximum inhibition of 80% achieved at 75 μM curcumin. Curcumin also blocks activation of glucose uptake by azide, glucose deprivation, hydroxylamine, or phenylarsine oxide. Inhibition does not increase with exposure time and the inhibitory effects reverse within an hour. Inhibition does not appear to involve a reaction between curcumin and the thiol side chain of a cysteine residue since neither prior treatment of cells with iodoacetamide nor curcumin with cysteine alters curcumin's inhibitory effects. Curcumin is a mixed inhibitor reducing the Vmax of 2DG transport by about half with little effect on the Km. The inhibitory effects of curcumin are not additive to the effects of cytochalasin B and 75 μM curcumin actually reduces specific cytochalasin B binding by 80%. Taken together, the data suggest that curcumin binds directly to GLUT1 at a site that overlaps with the cytochalasin B binding site and thereby inhibits glucose transport. A direct inhibition of GLUT proteins in intestinal epithelial cells would likely reduce absorption of dietary glucose and contribute to a hypoglycemic effect of curcumin. Also, inhibition of GLUT1 activity might compromise cancer cells that overexpress GLUT1 and be another possible mechanism for the documented anticancer effects of curcumin.

Metreleptin and generalized lipodystrophy and evolving therapeutic perspectives

INTRODUCTION

Metreleptin was recently approved by the Food and Drug Administration for the treatment of generalized lipodystrophy, a condition characterized by leptin deficiency. Its efficacy as hormone replacement therapy suggests broader applications in diseases also characterized by leptin abnormalities, such as familial partial lipodystrophy (FPLD), non-alcoholic fatty liver disease (NAFLD), and common obesity. Metreleptin, in conjunction with other pharmacologic interventions, has the potential to address one of the most widespread epidemics of our time, obesity.

AREAS COVERED

This review covers the physiology of leptin, the pharmacologic properties of recombinant methionyl human leptin (R-metHu-Leptin, metreleptin), evidence for metreleptin's efficacy in the treatment of generalized lipodystrophy from both completed and ongoing clinical trials, safety concerns, and future directions in metreleptin research.

EXPERT OPINION

Metreleptin's approval for generalized lipodystrophy is the first step in defining and expanding its role to other metabolic diseases. Clinical trials are underway to delineate its efficacy in FPLD, human immunodeficiency virus/highly active anti-retroviral therapy-associated acquired lipodystrophy (HAL), and NAFLD. Additionally, there is growing data that support a therapeutic role in obesity. One of the barriers to development, however, is metreleptin's safety and immunogenicity. Further advances in biologic compatibility are required before metreleptin can be approved for additional indications.

Purinergic receptor X7 mediates leptin induced GLUT4 function in stellate cells in nonalcoholic steatohepatitis

Metabolic oxidative stress via CYP2E1 can act as a second hit in NASH progression. Our previous studies have shown that oxidative stress in NASH causes higher leptin levels and induces purinergic receptor X7 (P2X7r). We tested the hypothesis that higher circulating leptin due to CYP2E1-mediated oxidative stress induces P2X7r. P2X7r in turn activates stellate cells and causes increased proliferation via modulating Glut4, the glucose transporter, and increased intracellular glucose. Using a high fat diet-fed NAFLD model where bromodichloromethane (BDCM) was administered to induce CYP2E1-mediated oxidative stress, we show that P2X7r expression and protein levels were leptin and CYP2E1 dependent. P2X7r KO mice had significantly decreased stellate cell proliferation. Human NASH livers showed marked increase in P2X7r, and Glut4 in α-SMA positive cells. NASH livers had significant increase in Glut4 protein and phosphorylated AKT, needed for Glut4 translocation while leptin KO and P2X7r KO mice showed marked decrease in Glut4 levels primarily in stellate cells. Mechanistically stellate cells showed increase in phosphorylated AKT, Glut4 protein and localization in the membrane following administration of P2X7r agonist or leptin+P2X7r agonist, while use of P2X7r antagonist or AKT inhibitor attenuated the response suggesting that leptin-P2X7r axis in concert but not leptin alone is responsible for the Glut4 induction and translocation. Finally P2X7r-agonist and leptin caused an increase in intracellular glucose and consumption by increasing the activity of hexokinase. In conclusion, the study shows a novel role of leptin-induced P2X7r in modulating Glut4 induction and translocation in hepatic stellate cells, that are key to NASH progression.

Curcumin targets multiple pathways to halt hepatic stellate cell activation: updated mechanisms in vitro and in vivo

Nonalcoholic steatohepatitis (NASH) is the advanced form of nonalcoholic fatty liver disease, which is often accompanied by obese and/or type II diabetes mellitus. Approximately one-third of NASH patients develop hepatic fibrosis. Hepatic stellate cells are the major effector cells during liver fibrogenesis. Advanced liver fibrosis usually proceeds to cirrhosis and even hepatocellular carcinoma, leading to liver failure, portal hypertension and even death. Currently, there are no approved agents for treatment and prevention of liver fibrosis in human beings. Curcumin, the principal curcuminoid of turmeric, has been reported to show antitumor, antioxidant, and anti-inflammatory properties both in in vitro and in vivo systems. Accumulating data shows that curcumin plays a critical role in combating liver fibrogenesis. This review will discuss the inhibitory roles of curcumin and update the underlying mechanisms by which curcumin targets in inhibiting hepatic stellate cell activation.

The good and bad of antioxidant foods: An immunological perspective

Maintenance of redox homeostasis plays a central role in health and disease prevention, and antioxidant foods are thought to exert protective effects by counteracting oxidative stress. The term "dietary antioxidant" implies a classical reducing or radical-scavenging capacity, but more data on the in vivo bioactivity of such compounds are needed. Indeed, several dietary antioxidants activate signaling cascades that lead to effects that extend beyond radical scavenging, such as the induction of endogenous cytoprotective mechanisms and detoxification. Currently, the overall uptake of antioxidants with diet exceeds actual needs, as food additives that include vitamins, colorants, flavoring agents, and preservatives are often also relatively strong antioxidants. Chronic antioxidative stress favors adverse effects, such as the suppression of T helper (Th) type 1 immune responses and consequent activation of Th2 reactions that support the development of asthma, allergies, and obesity. In this context, we discuss the immunoregulatory pathway of tryptophan breakdown by enzyme indoleamine 2,3-dioxygenase (IDO), which represents a central regulatory hub for immune, metabolic, and neuroendocrine processes. Activation of IDO-mediated tryptophan metabolism is strongly redox-sensitive and is therefore susceptible to modulation by dietary components, phytochemicals, preservatives, and drugs.

Curcumin Suppress Cardiac Fibroblasts Activities by Regulating Proliferation, Migration, and the Extracellular Matrix

BACKGROUND

Cardiac fibrosis plays a critical role in the pathophysiology of cardiovascular disease. It has been observed that curcumin has several cardiovascular effects. The purpose of this study was to evaluate whether curcumin can attenuate cardiac fibroblasts activity.

METHODS AND RESULTS

We evaluated the migration, proliferation, collagen production, and transcription signaling in rat cardiac fibroblasts isolated from Sprague-Dawley rats (males, weighing 300-350 g) that were or were not incubated with curcumin (25 μM) and the co-administration of transforming growth factor (TGF)- β1 (10 ng/ml) or angiotensin (Ang) II (100 nM) by a cell migration analysis, proliferation assay, and Western blot analysis. Compared to those without curcumin, curcumin-treated cardiac fibroblasts exhibited lower migratory, proliferative abilities and collagen production at the baseline and after the co-administration of TGF-β1 or Ang II. Curcumin-treated cardiac fibroblasts had increased matrix metalloproteinase (MMP)-2 activity in the presence of Ang II treatment. Curcumin-treated cardiac fibroblasts down-regulated phosphorylated protein kinase B (Akt) and phosphorylated Smad2/3 expression irrespective of TGF-β1 treatment. Curcumin also decreased phosphorylated extracellular signal-regulated kinase (ERK)1/2 levels in the presence of Ang II.

CONCLUSIONS

Curcumin attenuated Akt, Smad2/3, and ERK1/2 phosphorylation which were mediated by TGF-β1 and angiotensin II. This resulted in decreased cardiac fibroblast activation and supports the assertion that curcumin is an effective antifibrotic agent which can be used to treat heart failure.

KEY WORDS

Angiotensin; Curcumin; Fibroblasts; Heart failure; Transforming growth factor.

Exendin-4 Improves Nonalcoholic Fatty Liver Disease by Regulating Glucose Transporter 4 Expression in ob/ob Mice

Exendin-4 (Ex-4), a glucagon-like peptide-1 receptor (GLP-1R) agonist, has been known to reverse hepatic steatosis in ob/ob mice. Although many studies have evaluated molecular targets of Ex-4, its mechanism of action on hepatic steatosis and fibrosis has not fully been determined. In the liver, glucose transporter 4 (GLUT4) is mainly expressed in hepatocytes, endothelial cells and hepatic stellate cells (HSCs). In the present study, the effects of Ex-4 on GLUT4 expression were determined in the liver of ob/ob mice. Ob/ob mice were treated with Ex-4 for 10 weeks. Serum metabolic parameters, hepatic triglyceride levels, and liver tissues were evaluated for hepatic steatosis. The weights of the whole body and liver in ob/ob mice were reduced by long-term Ex-4 treatment. Serum metabolic parameters, hepatic steatosis, and hepatic fibrosis in ob/ob mice were reduced by Ex-4. Particularly, Ex-4 improved hepatic steatosis by enhancing GLUT4 via GLP-1R activation in ob/ob mice. Ex-4 treatment also inhibited hepatic fibrosis by decreasing expression of connective tissue growth factor in HSCs of ob/ob mice. Our data suggest that GLP-1 agonists exert a protective effect on hepatic steatosis and fibrosis in obesity and type 2 diabetes.

Curcumin eliminates the effect of advanced glycation end-products (AGEs) on the divergent regulation of gene expression of receptors of AGEs by interrupting leptin signaling

Non-alcoholic steatohepatitis (NASH) is a major risk factor for hepatic fibrogenesis. NASH is often found in diabetic patients with hyperglycemia. Hyperglycemia induces non-enzymatic glycation of proteins, yielding advanced glycation end-products (AGEs). Effects of AGEs are mainly mediated by two categories of cytoplasmic membrane receptors. Receptor for AGEs (RAGE) is associated with increased oxidative stress and inflammation, whereas AGE receptor-1 (AGE-R1) is involved in detoxification and clearance of AGEs. Activation of hepatic stellate cells (HSC) is crucial to the development of hepatic fibrosis. We recently reported that AGEs stimulated HSC activation likely by inhibiting gene expression of AGE-R1 and inducing gene expression of RAGE in HSC, which were eliminated by the antioxidant curcumin. This study is to test our hypothesis that curcumin eliminates the effects of AGEs on the divergent regulation of the two receptors of AGEs in HSC by interrupting the AGE-caused activation of leptin signaling, leading to the inhibition of HSC activation. We observed herein that AGEs activated leptin signaling by inducing gene expression of leptin and its receptor in HSC. Like AGEs, leptin differentially regulated gene expression of RAGE and AGE-R1. Curcumin eliminated the effects of AGEs in HSC by interrupting leptin signaling and activating transcription factor NF-E2 p45-related factor 2 (Nrf2), leading to the elevation of cellular glutathione and the attenuation of oxidative stress. In conclusions, curcumin eliminated the effects of AGEs on the divergent regulation of gene expression of RAGE and AGE-R1 in HSC by interrupting the AGE-caused activation of leptin signaling, leading to the inhibition of HSC activation.

Effects of curcumin on ion channels and transporters

Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione], a polyphenolic compound isolated from the rhizomes of Curcuma longa (turmeric), has been shown to exhibit a wide range of pharmacological activities including anti-inflammatory, anti-cancer, anti-oxidant, anti-atherosclerotic, anti-microbial, and wound healing effects. These activities of curcumin are based on its complex molecular structure and chemical features, as well as its ability to interact with multiple signaling molecules. The ability of curcumin to regulate ion channels and transporters was recognized a decade ago. The cystic fibrosis transmembrane conductance regulator (CFTR) is a well-studied ion channel target of curcumin. During the process of studying its anti-cancer properties, curcumin was found to inhibit ATP-binding cassette (ABC) family members including ABCA1, ABCB1, ABCC1, and ABCG2. Recent studies have revealed that many channels and transporters are modulated by curcumin, such as voltage-gated potassium (Kv) channels, high-voltage-gated Ca(2+) channels (HVGCC), volume-regulated anion channel (VRAC), Ca(2+) release-activated Ca(2+) channel (CRAC), aquaporin-4 (AQP-4), glucose transporters, etc., In this review, we aim to provide an overview of the interactions of curcumin with different types of ion channels and transporters and to help better understand and integrate the underlying molecular mechanisms of the multiple pharmacological activities of curcumin.

Chemoprevention of nonalcoholic fatty liver disease by dietary natural compounds

Nonalcoholic fatty liver disease (NAFLD) refers to a wide spectrum of liver disease that is not from excess alcohol consumption, but is often associated with obesity, type 2 diabetes, and metabolic syndrome. NAFLD pathogenesis is complicated and involves oxidative stress, lipotoxicity, mitochondrial damage, insulin resistance, inflammation, and excessive dietary fat intake, which increase hepatic lipid influx and de novo lipogenesis and impair insulin signaling, thus promoting hepatic triglyceride accumulation and ultimately NAFLD. Overproduction of proinflammatory adipokines from adipose tissue also affects hepatic metabolic function. Current NAFLD therapies are limited; thus, much attention has been focused on identification of potential dietary substances from fruits, vegetables, and edible plants to provide a new strategy for NAFLD treatment. Dietary natural compounds, such as carotenoids, omega-3-PUFAs, flavonoids, isothiocyanates, terpenoids, curcumin, and resveratrol, act through a variety of mechanisms to prevent and improve NAFLD. Here, we summarize and briefly discuss the currently known targets and signaling pathways as well as the role of dietary natural compounds that interfere with NAFLD pathogenesis.

Environmental toxin-linked nonalcoholic steatohepatitis and hepatic metabolic reprogramming in obese mice

Obesity is associated with strong risks of development of chronic inflammatory liver disease and metabolic syndrome following a second hit. This study tests the hypothesis that free radical metabolism of low chronic exposure to bromodichloromethane (BDCM), a disinfection byproduct of drinking water, causes nonalcoholic steatohepatitis (NASH), mediated by cytochrome P450 isoform CYP2E1 and adipokine leptin. Using diet-induced obese mice (DIO), mice deficient in CYP2E1, and mice with spontaneous knockout of the leptin gene, we show that BDCM caused increased lipid peroxidation and increased tyrosine nitration in DIO mice, events dependent on reductive metabolism by CYP2E1. DIO mice, exposed to BDCM, exhibited increased hepatic leptin levels and higher levels of proinflammatory gene expression and Kupffer cell activation. Obese mice exposed to BDCM also showed profound hepatic necrosis, Mallory body formation, collagen deposition, and higher alpha smooth muscle actin expression, events that are hallmarks of NASH. The absence of CYP2E1 gene in mice that were fed with a high-fat diet did not show NASH symptoms and were also protected from hepatic metabolic alterations in Glut-1, Glut-4, phosphofructokinase and phosphoenolpyruvate carboxykinase gene expressions (involved in carbohydrate metabolism), and UCP-1, PGC-1α, SREBP-1c, and PPAR-γ genes (involved in hepatic fat metabolism). Mice lacking the leptin gene were significantly protected from both NASH and metabolic alterations following BDCM exposure, suggesting that higher levels of leptin induction by BDCM in the liver contribute to the development of NASH and metabolic alterations in obesity. These results provide novel insights into BDCM-induced NASH and hepatic metabolic reprogramming and show the regulation of obesity-linked susceptibility to NASH by environmental factors, CYP2E1, and leptin.

Molecular understanding of curcumin in diabetic nephropathy

Diabetic nephropathy is characterized by a plethora of signaling abnormalities. Recent trials have suggested that intensive glucose-lowering treatment leads to hypoglycemic events, which can be dangerous. Curcumin is the active ingredient of turmeric, which has been widely used in many countries for centuries to treat numerous diseases. The preventive and therapeutic properties of curcumin are associated with its antioxidant and anti-inflammatory properties. Here, we highlight the renoprotective role of curcumin in diabetes mellitus (DM) with an emphasis on the molecular basis of this effect. We also briefly discuss the numerous approaches that have been undertaken to improve the pharmacokinetics of curcumin.

Why it is necessary to translate curcumin into clinical practice for the prevention and treatment of metabolic syndrome?

Curcumin (diferuloylmethane) is the yellow-orange pigment of dried Curcuma longa L. rhizomes (turmeric). During the past two decades, there has been a large volume of published studies describing the biological and pharmacological properties of this phytochemical including anticancer, anti-inflammatory, antioxidant, antithrombotic, antiatherosclerotic, cardioprotective, neuroprotective, memory enhancing, antiparkinsonism, antirheumatic, anti-infectious, antiaging, antipsoriatic, and anticonvulsant activities. In addition, curcumin has been shown to be extremely safe and interact with multiple molecular targets that are involved in the pathogenesis of metabolic syndrome. Curcumin could favorably affect all leading components of metabolic syndrome including insulin resistance, obesity, hypertriglyceridemia, decreased HDL-C and hypertension, and prevent the deleterious complications of MetS including diabetes and cardiovascular disease. Owing to its antioxidant and anti-inflammatory properties, curcumin can also exert several pleiotropic effects and improve endothelial dysfunction, adipokine imbalances, and hyperuricemia which usually accompany MetS. Despite the potential tremendous benefit of this multifaceted phytopharmaceutical, no trial result has yet been publicized on this issue. This review seeks to briefly summarize the ample scientific evidence that supports the therapeutic efficacy of curcumin, at least as an adjunctive treatment, in patients with MetS.

Hepatic expression and cellular distribution of the glucose transporter family

Glucose and other carbohydrates are transported into cells using members of a family of integral membrane glucose transporter (GLUT) molecules. To date 14 members of this family, also called the solute carrier 2A proteins have been identified which are divided on the basis of transport characteristics and sequence similarities into several families (Classes 1 to 3). The expression of these different receptor subtypes varies between different species, tissues and cellular subtypes and each has differential sensitivities to stimuli such as insulin. The liver is a contributor to metabolic carbohydrate homeostasis and is a major site for synthesis, storage and redistribution of carbohydrates. Situations in which the balance of glucose homeostasis is upset such as diabetes or the metabolic syndrome can lead metabolic disturbances that drive chronic organ damage and failure, confirming the importance of understanding the molecular regulation of hepatic glucose homeostasis. There is a considerable literature describing the expression and function of receptors that regulate glucose uptake and release by hepatocytes, the most import cells in glucose regulation and glycogen storage. However there is less appreciation of the roles of GLUTs expressed by non parenchymal cell types within the liver, all of which require carbohydrate to function. A better understanding of the detailed cellular distribution of GLUTs in human liver tissue may shed light on mechanisms underlying disease pathogenesis. This review summarises the available literature on hepatocellular expression of GLUTs in health and disease and highlights areas where further investigation is required.

Curcumin ameliorates hepatic fibrosis in type 2 diabetes mellitus - insights into its mechanisms of action

A wide variety of beneficial effects have been attributed to curcumin, a major polyphenol from the golden spice Curcuma longa known as turmeric, including amelioration of severe complications of type 2 diabetes such as hepatic fibrosis, retinopathy, neuropathy and nephropathy. In the present issue of BJP, Lin and colleagues reveal new mechanisms by which curcumin inhibits the activation of hepatic stellate cells in vitro, a hallmark of non-alcoholic steatohepatitis and hepatic fibrogenesis associated with type 2 diabetes mellitus. They demonstrated that curcumin suppresses the advanced glycation end-products (AGEs)-mediated induction of the receptor for AGEs (RAGE) gene expression by increasing PPARγ activity and stimulating de novo synthesis of glutathione. As a result, downstream elements of RAGE-activated pathways are inhibited, which prevents oxidative stress, inflammation and hepatic stellate cell activation. This report suggests that curcumin may have potential as an anti-fibrotic agent in type 2 diabetes and opens the door to the evaluation of curcumin therapeutic effects in liver conditions of different aetiology and in other disorders linked to the impairment of PPARγ activity, such as obesity and atherosclerosis.

LINKED ARTICLE

This article is a commentary on Lin et al., pp. 2212-2227 of this issue. To view this paper visit http://dx.doi.org/10.1111/j.1476-5381.2012.01910.x.

Curcumin inhibits gene expression of receptor for advanced glycation end-products (RAGE) in hepatic stellate cells in vitro by elevating PPARγ activity and attenuating oxidative stress

BACKGROUND AND PURPOSE

Diabetes is characterized by hyperglycaemia, which facilitates the formation of advanced glycation end-products (AGEs). Type 2 diabetes mellitus is commonly accompanied by non-alcoholic steatohepatitis, which could lead to hepatic fibrosis. Receptor for AGEs (RAGE) mediates effects of AGEs and is associated with increased oxidative stress, cell growth and inflammation. The phytochemical curcumin inhibits the activation of hepatic stellate cells (HSCs), the major effectors during hepatic fibrogenesis. The aim of this study was to explore the underlying mechanisms of curcumin in the elimination of the stimulating effects of AGEs on the activation of HSCs. We hypothesize that curcumin eliminates the effects of AGEs by suppressing gene expression of RAGE.

EXPERIMENTAL APPROACH

Gene promoter activities were evaluated by transient transfection assays. The expression of rage was silenced by short hairpin RNA. Gene expression was analysed by real-time PCR and Western blots. Oxidative stress was evaluated.

KEY RESULTS

AGEs induced rage expression in cultured HSCs, which played a critical role in the AGEs-induced activation of HSCs. Curcumin at 20 µM eliminated the AGE effects, which required the activation of PPARγ. In addition, curcumin attenuated AGEs-induced oxidative stress in HSCs by elevating the activity of glutamate-cysteine ligase and by stimulating de novo synthesis of glutathione, leading to the suppression of gene expression of RAGE.

CONCLUSION AND IMPLICATIONS

Curcumin suppressed gene expression of RAGE by elevating the activity of PPARγ and attenuating oxidative stress, leading to the elimination of the AGE effects on the activation of HSCs.

LINKED ARTICLE

This article is commented on by Stefanska, pp. 2209-2211 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.01959.x.

Leptin regulates glutamate and glucose transporters in hypothalamic astrocytes

Glial cells perform critical functions that alter the metabolism and activity of neurons, and there is increasing interest in their role in appetite and energy balance. Leptin, a key regulator of appetite and metabolism, has previously been reported to influence glial structural proteins and morphology. Here, we demonstrate that metabolic status and leptin also modify astrocyte-specific glutamate and glucose transporters, indicating that metabolic signals influence synaptic efficacy and glucose uptake and, ultimately, neuronal function. We found that basal and glucose-stimulated electrical activity of hypothalamic proopiomelanocortin (POMC) neurons in mice were altered in the offspring of mothers fed a high-fat diet. In adulthood, increased body weight and fasting also altered the expression of glucose and glutamate transporters. These results demonstrate that whole-organism metabolism alters hypothalamic glial cell activity and suggest that these cells play an important role in the pathology of obesity.

Curcumin molecular targets in obesity and obesity-related cancers

Obesity is characterized as an increased BMI, which is associated with the increased risk of several common cancers, including colorectal, breast, endometrial, renal, esophageal, gallbladder, melanoma, multiple myeloma, leukemia, lymphoma and prostate cancer. The increased risk of obesity-related cancers could be mediated by insulin resistance, adipokines, obesity-related inflammatory cytokines, sex hormones, transcription factors and oxidative stress, which disrupt the balance between cell proliferation and apoptosis. The yellowish compound, curcumin (diferuloylmethane), is known to possess multifaceted pharmacological effects. The molecular mechanisms linking obesity to cancer risk, and how curcumin mediates anticancer and obesity activities, have not yet been publicized. Curcumin modulates multiple molecular targets and reverses insulin resistance as well as other symptoms that are associated with obesity-related cancers. In this study, we show that ample evidence exists to support recommendations that curcumin mediates multiple molecular pathways, and is considered to be of therapeutic value in the treatment and prevention of obesity-related cancers.