Are SIRT1 activators another indirect method to increase AMPK for beneficial effects on aging and the metabolic syndrome?

Role of the AMPK/SIRT1 pathway in non‑alcoholic fatty liver disease (Review)

Non‑alcoholic fatty liver disease (NAFLD) is an increasingly prevalent ailment worldwide. Moreover, de novo lipogenesis (DNL) is considered a critical factor in the development of NAFLD; hence, its inhibition is a promising target for the prevention of fatty liver disease. There is evidence to indicate that AMP‑activated protein kinase (AMPK) and sirtuin 1 (SIRT1) may play a crucial role in DNL and are the regulatory proteins in type 2 diabetes mellitus, obesity and cardiovascular disease. Therefore, AMPK and SIRT1 may be promising targets for the treatment of NAFLD. The present review article thus aimed to summarize the findings of clinical studies published during the past decade that suggested the beneficial effects of AMPK and SIRT1, using their specific activators and their combined effects on fatty liver disease.

Emerging Role of cAMP/AMPK Signaling

The 5′-Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a natural energy sensor in mammalian cells that plays a key role in cellular and systemic energy homeostasis. At the cellular level, AMPK supports numerous processes required for energy and redox homeostasis, including mitochondrial biogenesis, autophagy, and glucose and lipid metabolism. Thus, understanding the pathways regulating AMPK activity is crucial for developing strategies to treat metabolic disorders. Mounting evidence suggests the presence of a link between cyclic AMP (cAMP) and AMPK signaling. cAMP signaling is known to be activated in circumstances of physiological and metabolic stress due to the release of stress hormones, such as adrenaline and glucagon, which is followed by activation of membrane-bound adenylyl cyclase and elevation of cellular cAMP. Because the majority of physiological stresses are associated with elevated energy consumption, it is not surprising that activation of cAMP signaling may promote AMPK activity. Aside from the physiological role of the cAMP/AMPK axis, numerous reports have suggested its role in several pathologies, including inflammation, ischemia, diabetes, obesity, and aging. Furthermore, novel reports have provided more mechanistic insight into the regulation of the cAMP/AMPK axis. In particular, the role of distinct cAMP microdomains generated by soluble adenylyl cyclase in regulating basal and induced AMPK activity has recently been demonstrated. In the present review, we discuss current advances in the understanding of the regulation of the cAMP/AMPK axis and its role in cellular homeostasis and explore some translational aspects.

Host NAD+ metabolism and infections: therapeutic implications

Nicotinamide adenine dinucleotide (NAD+) is both a crucial coenzyme and a cosubstrate for various metabolic reactions in all living cells. Maintenance of NAD+ levels is essential for cell energy homeostasis, survival, proliferation and function. Mounting evidence points to NAD+ as one of the major modulators of immuno-metabolic circuits, thus regulating immune responses and functions. Recent studies delineate impaired host NAD+ metabolism during chronic infections and inflammation, suggesting NAD+ replenishment as an avenue to ameliorate deleterious inflammatory responses. Here, we discuss aspects of NAD+ biosynthesis and consumption, NAD+ biology during infections and how NAD+ metabolism can be intervened with pharmacologically to enhance the host's immunological fitness against pathogens.

Effects of crocin and saffron aqueous extract on gene expression of SIRT1, AMPK, LOX1, NF-κB, and MCP-1 in patients with coronary artery disease: A randomized placebo-controlled clinical trial

This trial evaluated the potential impacts of saffron aqueous extract (SAE) and its main carotenoid on some of the atherosclerosis-related gene expression and serum levels of oxidized low-density cholesterol (ox-LDL) and Monocyte chemoattractant protein 1 (MCP-1) in patients with coronary artery disease (CAD). Participants of this randomized controlled trial included 84 CAD patients who categorized into three groups: Group 1 received crocin (30 mg/day), Group 2 SAE (30 mg/day), and Group 3 placebo for 8 weeks. Gene expression of Sirtuin 1 (SIRT1), 5'-adenosine monophosphate-activated protein kinase (AMPK), Lectin-like oxidized LDL receptor 1 (LOX1), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and MCP-1 in peripheral blood mononuclear cells assessed by real-time PCR. Furthermore, serum ox-LDL and MCP-1 levels measured at the beginning and end of the intervention. Compared with the placebo group, gene expression of SIRT1 and AMPK increased significantly in the crocin group (p = .001), and the expression of LOX1 and NF-κB decreased significantly (p = .016 and .004, respectively). Serum ox-LDL levels decreased significantly in the crocin group after the intervention (p = .002) while MCP-1 levels decreased both in crocin and SAE groups (p = .001). Crocin may have beneficial effects on CAD patients by increasing the gene expression of SIRT1 and AMPK and decreasing the expression of LOX1 and NF-κB.

The effect of crocetin supplementation on markers of atherogenic risk in patients with coronary artery disease: a pilot, randomized, double-blind, placebo-controlled clinical trial

BACKGROUND AND PURPOSE

Molecular mechanisms of atherogenesis are considered to be emerging therapeutic targets for atherosclerosis prevention. Cell and animal studies have shown that crocetin can decelerate atherogenesis. However, the anti-atherogenic properties of crocetin in humans are still ambiguous.

METHODS AND RESULTS

Fifty clinically diagnosed CAD patients were randomly divided into two parallel groups, crocetin and placebo, who received one capsule of crocetin (10 mg) and placebo per day, respectively, for two months. Serum circulating homocysteine (Hcy) [-1.09 (-1.64 to -0.54) μM, P = 0.001], heart-type fatty acid binding protein (h-FABP) [-2.07 (-2.72 to -1.43) ng mL^-1, P = 0.001], intercellular adhesion molecule 1 [-14.92 (-21.92 to -7.92) ng mL^-1, P = 0.001], vascular cell adhesion molecule 1 [-18.61 (-29.73 to -7.49) ng mL^-1, P = 0.002], and monocyte chemoattractant protein 1 [-4.67 (-6.50 to -2.83) pg mL^-1, P = 0.001] decreased significantly after the trial in the crocetin group, while high-density lipoprotein (HDL) significantly increased [+4.21 (0.68 to 7.73) mg mL^-1, P = 0.021]. Also, systolic [-0.21 (-0.32 to -0.10) mmHg, P = 0.001] and diastolic [-0.20 (-0.34 to -0.07) mmHg, P = 0.004] blood pressures decreased significantly in the crocetin group. Nevertheless, clinically significant percentage changes were only observed in Hcy (-15.25 ± 3.15, μM), HDL (-10.70 ± 5.06, mg dL^-1), and h-FABP (-21.10 ± 3.09, ng mL^-1) in the crocetin group. Furthermore, the relative increase in the gene expressions of sirtuin1 and AMP-activated protein kinase and a decrease in the lectin-type oxidized LDL receptor 1 and nuclear factor-kappa B expression in isolated peripheral blood mononuclear cells in the crocetin group were significant at the end of the trial in comparison with the placebo.

CONCLUSION

As the first human study, we showed the ability of crocetin to alter the expression of atherogenic genes and endothelial cell adhesion molecules in CAD patients. It appears that crocetin could be considered as a promising anti-atherogenic candidate for future studies.

TRB3 stimulates SIRT1 degradation and induces insulin resistance by lipotoxicity via COP1

Fatty acid-induced lipotoxicity plays an important role in the pathogenesis of diabetes mellitus. Our previous studies have documented that lipotoxicity contributes to the onset and development of diabetes via insulin resistance and/or compromised function of the pancreatic β-cells. However, the underlying molecular mechanisms associating lipotoxicity with insulin resistance remain to be fully elucidated. In this study, we explored the role of TRB3-COP1-SIRT1 in lipotoxicity leading to insulin resistance in hepatocytes. High fat diet (HFD)-fed mice and hepG2 cells stimulated with palmitate were utilized as models of lipid metabolism disorders. We analyzed the interactions of SIRT1 and COP1 with each other and with TRB3 using co-immunoprecipitation, western blotting. SIRT1 ubiquitination was also explored. Animal and cell experiments showed that lipotoxicity induced SIRT1 down-regulation at the protein level without altering the mRNA level, whereas, lipotoxicity led to up-regulation of TRB3 and COP1 at both the gene and protein levels. Mechanistic analysis indicated that COP1 functioned as an E3 Ub-ligase of SIRT1, responsible for its proteasomal degradation under lipotoxic conditions. TRB3 recruited COP1 to SIRT1 to promote its ubiquitination. Our data indicated for the first time that TRB3-COP1-SIRT1 pathway played an important role in lipotoxicity leading to insulin resistance in hepatocytes, and suggested that COP1 could be a potential therapeutic choice for the treatment of diabetes mellitus, with lipotoxicity being the important pathomechanism.

Understanding mitochondrial biogenesis through energy sensing pathways and its translation in cardio-metabolic health

Mitochondria play a pivotal role in physiological energy governance. Mitochondrial biogenesis comprises growth and division of pre-existing mitochondria, triggered by environmental stressors such as endurance exercise, caloric restriction, cold exposure and oxidative stress. For normal physiology, balance between energy intake, storage and expenditure is of utmost important for the coordinated regulation of energy homeostasis. In contrast, abnormalities in these regulations render the individual susceptible to cardiometabolic disorders. This review provides a comprehensive coverage and understanding on mitochondrial biogenesis achieved through energy-sensing pathways. This includes the complex coordination of nuclear, cytosolic and mitochondrial events involving energy sensors, transcription factors, coactivators and regulators. It focuses on the importance of mitochondrial biogenesis in cardiometabolic health. Lastly, converging on the benefits of caloric restriction and endurance exercise in achieving cardiometabolic health.

Resveratrol's Hidden Hand: A Route to the Optical Detection of Biomolecular Binding

Resveratrol is a stilbenoid phytoalexin with promising myriad health benefits predominantly contributed by the trans ( E) diastereomeric form. A recent study has implicated the cis ( Z) diastereomer in human health. This stereoisomer binds with high affinity to human tyrosyl-tRNA synthetase, initiating a downstream cascade that promotes the expression of genes associated with the cellular stress response. We discovered that the nonplanar structure of the cis-resveratrol conformer possesses certain chiral signals in its simulated vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra. These features may be used for the optical detection of the binding event and in understanding the more diversified biological roles of trans-resveratrol over cis-resveratrol. We use a density functional theory model, which is validated against the known results for the E diastereomer. The Z diastereomer is significantly nonplanar and can exist in two helical atropisomeric forms. These forms exchange rapidly in solution, but only one is observed to bind with the synthetase. This suggests that the binding may generate an enantiomeric excess, leading to detectable changes in the vibrational optical activity spectra. We identify candidate features at 998, 1649, and 1677 cm^-1 in the ROA and at 1642 and 3834 cm^-1 in the VCD spectra of Z-resveratrol that may be useful for this purpose.