Zerumbone Ameliorates High Glucose-Induced Reduction in AMP-Activated Protein Kinase Phosphorylation in Tubular Kidney Cells

SIRT1/AMPK-mediated pathway: Ferulic acid from sugar beet pulp mitigating obesity-induced diabetes-linked complications and improving metabolic health

Obesity-induced type 2 diabetes (T2D) increases the risk of metabolic syndrome due to the high calorie intake. The role of sugar beet pulp (SBP) in T2D and the mechanism of its action remain unclear, though it is abundant in phenolics and has antioxidant activity. In this study, we isolated and purified ferulic acid from SBP, referred to as SBP-E, and studied the underlying molecular mechanisms in the regulation of glucose and lipid metabolism developing high glucose/high fat diet-induced diabetic models in vitro and in vivo. SBP-E showed no cytotoxicity and reduced the oxidative stress by increasing glutathione (GSH) in human liver (HepG2) and rat skeletal muscle (L6) cells. It also decreased body weight gain, food intake, fasting blood glucose levels (FBGL), glucose intolerance, hepatic steatosis, and lipid accumulation. Additionally, SBP-E decreased the oxidative stress and improved the antioxidant enzyme levels in high-fat diet (HFD)-induced T2D mice. Further, SBP-E reduced plasma and liver advanced glycation end products (AGEs), malondialdehyde (MDA), and pro-inflammatory cytokines, and increased anti-inflammatory cytokines in HFD-fed mice. Importantly, SBP-E significantly elevated AMPK, glucose transporter, SIRT1 activity, and Nrf2 expression and decreased ACC activity and SREBP1 levels in diabetic models. Collectively, our study results suggest that SBP-E treatment can improve obesity-induced T2D by regulating glucose and lipid metabolism via SIRT1/AMPK signalling and the AMPK/SREBP1/ACC1 pathway.

Role of Zerumbone, a Phytochemical Sesquiterpenoid from Zingiber zerumbet Smith, in Maintaining Macrophage Polarization and Redox Homeostasis

Macrophages and microglia are highly versatile cells that can be polarized into M1 and M2 phenotypes in response to diverse environmental stimuli, thus exhibiting different biological functions. In the central nervous system, activated resident macrophages and microglial cells trigger the production of proinflammatory mediators that contribute to neurodegenerative diseases and psychiatric disorders. Therefore, modulating the activation of macrophages and microglia by optimizing the inflammatory environment is beneficial for disease management. Several naturally occurring compounds have been reported to have anti-inflammatory and neuroprotective properties. Zerumbone is a phytochemical sesquiterpenoid and also a cyclic ketone isolated from Zingiber zerumbet Smith. In this study, we found that zerumbone effectively reduced the expression of lipocalin-2 in macrophages and microglial cell lines. Lipocalin-2, also known as neutrophil gelatinase-associated lipocalin (NGAL), has been characterized as an adipokine/cytokine implicated in inflammation. Moreover, supplement with zerumbone inhibited reactive oxygen species production. Phagocytic activity was decreased following the zerumbone supplement. In addition, the zerumbone supplement remarkably reduced the production of M1-polarization-associated chemokines CXC10 and CCL-2, as well as M1-polarization-associated cytokines interleukin (IL)-6, IL-1β, and tumor necrosis factor-α. Furthermore, the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 and the production of NO were attenuated in macrophages and microglial cells supplemented with zerumbone. Notably, we discovered that zerumbone effectively promoted the production of the endogenous antioxidants heme oxygenase-1, glutamate-cysteine ligase modifier subunit, glutamate-cysteine ligase catalytic subunit, and NAD(P)H quinone oxidoreductase-1 and remarkably enhanced IL-10, a marker of M2 macrophage polarization. Endogenous antioxidant production and M2 macrophage polarization were increased through activation of the AMPK/Akt and Akt/GSK3 signaling pathways. In summary, this study demonstrated the protective role of zerumbone in maintaining M1 and M2 polarization homeostasis by decreasing inflammatory responses and enhancing the production of endogenous antioxidants in both macrophages and microglia cells. This study suggests that zerumbone can be used as a potential therapeutic drug for the supplement of neuroinflammatory diseases.

Trans-ferulic acid attenuates hyperglycemia-induced oxidative stress and modulates glucose metabolism by activating AMPK signaling pathway in vitro

Adenosine monophosphate-activated protein kinase (AMPK) is a potent metabolic regulator and an attractive target for antidiabetic activators. Here we report for the first that, trans-ferulic acid (TFA) is a potent dietary bioactive molecule of hydroxycinnamic acid derivative for the activation of AMPK with a maximum increase in phosphorylation (2.71/2.67 ± 0.10; p < .001 vs. high glucose [HG] control) in hyperglycemia-induced human liver cells (HepG2) and rat skeletal muscle cells (L6), where HG suppresses the AMPK pathway. It was also observed that TFA increased activation of AMPK in a dose- and time-dependent manner and also increased the phosphorylation of acetyl-CoA carboxylase (ACC), suggesting that it may promotes fatty acid oxidation; however, pretreatment with compound C reversed the effect. In addition, TFA reduced the level of intracellular reactive oxygen species (ROS) and nitric oxide (NO) induced by hyperglycemia and subsequently increased the level of glutathione. Interestingly, TFA also upregulated the glucose transporters, GLUT2 and GLUT4, and inhibited c-Jun N-terminal protein kinase (JNK1/2) by decreasing the phosphorylation level in tested cells under HG condition. Our studies provide critical insights into the mechanism of action of TFA as a potential natural activator of AMPK under hyperglycemia. PRACTICAL APPLICATIONS: Hydroxycinnamic acid derivatives possess various pharmacological properties and are found to be one of the most ubiquitous groups of plant metabolites in almost all dietary sources. However, the tissue-specific role and its mechanism under hyperglycemic condition remain largely unknown. The present study showed that TFA is a potent activator of AMPK under HG condition and it could be used as a therapeutic agent against hyperglycemia in type 2 diabetes.

Bioactive Compounds from Zingiber montanum and Their Pharmacological Activities with Focus on Zerumbone

The genus Zingiber consists of about 85 species and many of these species are used as food, spices, and medicines. One of the species, Zingiber montanum (J. Koenig) Link ex A. Dietr. is native to Southeast Asia and has been extensively used as traditional medicines and food. The aim of this review was to collect and critically analyze the scientific information about the bioactive compounds and pharmacological activities of Z. montanum with focus on one of the main components, zerumbone (ZER). Various studies have reported the analysis of volatile constituents of the essential oils from Z. montanum. Similarly, many phenylbutanoids, flavonoids and terpenes were also isolated from rhizomes. These essential oils, extracts and compounds showed potent antimicrobial, anti-inflammatory and antioxidant activities among others. Zerumbone has been studied widely for its anticancer, anti-inflammatory, and other pharmacological activities. Future studies should focus on the exploration of various pharmacological activities of other compounds including phenylbutanoids and flavonoids. Bioassay guided isolation may result in the separation of other active components from the extracts. Z. montanum could be a promising source for the development of pharmaceutical products and functional foods.

AMPK in microvascular complications of diabetes and the beneficial effects of AMPK activators from plants

BACKGROUND

Diabetes mellitus is a multifactorial disorder with the risk of micro- and macro-vascular complications. High glucose-induced derangements in metabolic pathways are primarily associated with the initiation and progression of secondary complications namely, diabetic nephropathy, neuropathy, and retinopathy. Adenosine monophosphate-activated protein kinase (AMPK) has emerged as an attractive therapeutic target to treat various metabolic disorders including diabetes mellitus. It is a master metabolic regulator that helps in maintaining cellular energy homeostasis by promoting ATP-generating catabolic pathways and inhibiting ATP-consuming anabolic pathways. Numerous pharmacological and plant-derived bioactive compounds that increase AMP-activated protein kinase activation has shown beneficial effects by mitigating secondary complications namely retinopathy, nephropathy, and neuropathy.

PURPOSE

The purpose of this review is to highlight current knowledge on the role of AMPK and its activators from plant origin in diabetic microvascular complications.

METHODS

Search engines such as Google Scholar, PubMed, Science Direct and Web of Science are used to extract papers using relevant key words. Papers mainly focusing on the role of AMPK and AMPK activators from plant origin in diabetic nephropathy, retinopathy, and neuropathy was chosen to be highlighted.

RESULTS

According to results, decrease in AMPK activation during diabetes play a causative role in the pathogenesis of diabetic microvascular complications. Some of the plant-derived bioactive compounds were beneficial in restoring AMPK activity and ameliorating diabetic microvascular complications.

CONCLUSION

AMPK activators from plant origin are beneficial in mitigating diabetic microvascular complications. These pieces of evidence will be helpful in the development of AMPK-centric therapies to mitigate diabetic microvascular complications.

Protective effects of (-)-epicatechin and the colonic metabolite 3,4-dihydroxyphenylacetic acid against glucotoxicity-induced insulin signalling blockade and altered glucose uptake and production in renal tubular NRK-52E cells

Glucotoxicity (high levels of glucose) is a major cause in the pathogenesis of diabetes. Evidences indicate that (-)-epicatechin (EC) and colonic metabolites derived from flavonoid intake could possess antidiabetic effects, but the mechanisms for their preventive activities related to glucose homeostasis and insulin signalling in the kidney remain largely unknown. This work is aimed to investigate the effect of EC and main colonic phenolic acids derived from flavonoid intake, i.e. 2,3-dihydroxybenzoic-acid, 3,4-dihydroxyphenylacetic-acid (DHPAA) and 3-hydroxyphenylpropionic-acid, on insulin signalling, and glucose production and uptake in renal tubular proximal NRK-52E cells treated with high glucose. Pre-treatment with EC or DHPAA prevented the decreased tyrosine-phosphorylated and total levels of IR caused by high glucose. EC and DHPAA pre-treatment also avoided the inactivation of the PI3K/AKT pathway and AMPK, and the elevation of PEPCK levels induced by high glucose. Additionally, EC and DHPAA pre-treatment alleviated the altered glucose uptake and production caused by high glucose, although this protective effect was abrogated when AKT and AMPK were inhibited. These results suggest EC and DHPAA prevent or delay a potential dysfunction of NRK-52E cells treated with high glucose through the attenuation of the insulin signalling blockade and the modulation of glucose homeostasis via AKT and AMPK.