AMPK inhibits liver gluconeogenesis: fact or fiction?

Inhibition of hepatic gluconeogenesis in type 2 diabetes by metformin: complementary role of nitric oxide

Metformin is the first-line treatment for type 2 diabetes mellitus. Type 2 diabetes mellitus is associated with decreased nitric oxide bioavailability, which has significant metabolic implications, including enhanced insulin secretion and peripheral glucose utilization. Similar to metformin, nitric oxide also inhibits hepatic glucose production, mainly by suppressing gluconeogenesis. This review explores the combined effects of metformin and nitric oxide on hepatic gluconeogenesis and proposes the potential of a hybrid metformin-nitric oxide drug for managing type 2 diabetes mellitus. Both metformin and nitric oxide inhibit gluconeogenesis through overlapping and distinct mechanisms. In hepatic gluconeogenesis, mitochondrial oxaloacetate is exported to the cytoplasm via various pathways, including the malate, direct, aspartate, and fumarate pathways. The effects of nitric oxide and metformin on the exportation of oxaloacetate are complementary; nitric oxide primarily inhibits the malate pathway, while metformin strongly inhibits the fumarate and aspartate pathways. Furthermore, metformin effectively blocks gluconeogenesis from lactate, glycerol, and glutamine, whereas nitric oxide mainly inhibits alanine-induced gluconeogenesis. Additionally, nitric oxide contributes to the adenosine monophosphate-activated protein kinase-dependent inhibition of gluconeogenesis induced by metformin. The combined use of metformin and nitric oxide offers the potential to mitigate common side effects. For example, lactic acidosis, a known side effect of metformin, is linked to nitric oxide deficiency, while the oxidative and nitrosative stress caused by nitric oxide could be counterbalanced by metformin's enhancement of glutathione. Metformin also amplifies nitric oxide -induced activation of adenosine monophosphate-activated protein kinase. In conclusion, a metformin-nitric oxide hybrid drug can benefit patients with type 2 diabetes mellitus by enhancing the inhibition of hepatic gluconeogenesis, decreasing the required dose of metformin for maintaining optimal glycemia, and lowering the incidence of metformin-associated lactic acidosis.

Combined deletion of cytosolic 5'-nucleotidases IA and II lowers glycemia by improving skeletal muscle insulin action and lowering hepatic glucose production

Obesity and type 2 diabetes (T2D)-linked hyperglycemia, along with their associated complications, have reached pandemic proportions, constituting a major public health issue. Genetic deletion or pharmacological inhibition of purine nucleotide-metabolizing enzymes has emerged as a potential strategy for treating diseases. We previously showed that cytosolic 5'-nucleotidase II (NT5C2)-deficient mice were protected against high-fat diet (HFD)-induced insulin resistance. This study investigated the effects of dual deletion of cytosolic 5'-nucleotidases IA (NT5C1A) and II (NT5C2) in mice. We found that NT5C1A/NT5C2 double-knockout (NT5C-dKO) mice exhibited mild hypoglycemia, associated with enhanced skeletal muscle insulin action and reduced hepatic glucose production. This phenotype was accompanied by liver and skeletal muscle proteomic alterations notably related to amino acid metabolism, besides the potential involvement of adenosine monophosphate (AMP)-activated protein kinase (AMPK). Our findings support the development of novel anti-diabetic treatments using small-molecule cytosolic 5'-nucleotidase inhibitors.

A microscopy-based screen identifies cellular kinases modulating mitochondrial translation

Mitochondrial DNA encodes 13 subunits of the oxidative phosphorylation (OXPHOS) system, which are synthesized inside the organelle and essential for cellular energy supply. How mitochondrial gene expression is regulated and integrated into cellular physiology is little understood. Here, we perform a high-throughput screen combining fluorescent labeling of mitochondrial translation products with small interfering RNA (siRNA)-mediated knockdown to identify cellular kinases regulating translation. As proof of principle, the screen identifies known kinases that affect mitochondrial translation, and it also reveals several kinases not yet linked to this process. Among the latter, we focus on the primarily cytosolic kinase, fructosamine 3 kinase (FN3K), which localizes partially to the mitochondria to support translation. FN3K interacts with the mitochondrial ribosome and modulates its assembly, thereby affecting translation. Overall, our work provides a reliable approach to identify protein functions for mitochondrial gene expression in a high-throughput manner.

Schisandra sphenanthera extract modulates sweet taste receptor pathway, IRS/PI3K, AMPK/mTOR pathway and endogenous metabolites against T2DM

BACKGROUND

Southern Schisandra is the dried and matured fruit of Schisandra sphenanthera Rehd. et Wils. in the family of Magnoliaceae; Traditional medicine reports that Schisandra sphenanthera has astringent and astringent properties, benefiting qi and promoting the production of body fluid, tranquilising the heart and calming the mind; it is clinically utilized for prolonged cough, thirst due to injury of the body fluid, internal heat and thirst, palpitation and insomnia, etc., and thirst belongs to the category of diabetes mellitus; the literature reports and the preliminary study of our team showed that Schisandra sphenanthera can be used to prevent and control diabetes mellitus.

PURPOSE

In the research, we investigated the mechanism of action of SDP against T2DM by integrating pharmacodynamics, endogenous metabolite assays and signalling pathways.

MATERIALS AND METHODS

UPLC-MS/MS was used to identify the chemical constituents. HPLC was utilized to determine the content of eight lignan-like components in SDP. A T2DM rat model was established by the combined induction of high-fat and high-sugar feed and STZ, and the mechanism of action of SDP on T2DM was investigated by using biochemical indices, Western blot analysis of protein expression, mRNA expression, immunohistochemistry and endogenous metabolites.

RESULTS

The chemical components in SDP were determined by UPLC-MS/MS and HPLC, and biochemical indicators determined that SDP has the effects of lowering blood glucose, anti-glycolipid metabolism, and anti-oxidative stress, and is able to restore pathological damage in the liver and pancreas, activate the PI3K/AKT, AMPK/mTOR, and sweetness receptor signalling pathways, restore the sweetness receptor mRNAs, and modulate the urinary compounds such as malic acid, γ-aminobutyric acid, leucine, N-acetylaspartic acid and other compounds thereby achieving the therapeutic effect of T2DM.

CONCLUSION

SDP can ameliorate diabetes-induced symptoms related to elevated blood glucose, dyslipidaemia, elevated fasting insulin levels and impaired glucose tolerance in rats; the anti-T2DM of SDP may be through the regulation of the sweet taste receptor pathway, the PI3K/AKT/mTOR and the AMPK/mTOR signalling pathway, which leads to the development of a normal level and exerts an antidiabetic effect.

Insights into the Molecular Mechanisms of Purine Compounds Synergistically Inducing Larval Settlement in Mytilopsis sallei Using Multi-Group Comparative Transcriptomic Analysis

Most benthic marine invertebrates exhibit a characteristic biphasic life cycle, consisting of a planktonic larval stage followed by a benthic adult stage [...].

AMP kinase: A promising therapeutic drug target for post-COVID-19 complications

The COVID-19 pandemic, caused by SARS-CoV-2, has resulted in severe respiratory issues and persistent complications, particularly affecting glucose metabolism. Patients with or without pre-existing diabetes often experience worsened symptoms, highlighting the need for innovative therapeutic approaches. AMPK, a crucial regulator of cellular energy balance, plays a pivotal role in glucose metabolism, insulin sensitivity, and inflammatory responses. AMPK activation, through allosteric or kinase-dependent mechanisms, impacts cellular processes like glucose uptake, fatty acid oxidation, and autophagy. The tissue-specific distribution of AMPK emphasizes its role in maintaining metabolic homeostasis throughout the body. Intriguingly, SARS-CoV-2 infection inhibits AMPK, contributing to metabolic dysregulation and post-COVID-19 complications. AMPK activators like capsaicinoids, curcumin, phytoestrogens, cilostazol, and momordicosides have demonstrated the potential to regulate AMPK activity. Compounds from various sources improve fatty acid oxidation and insulin sensitivity, with metformin showing opposing effects on AMPK activation compared to the virus, suggesting potential therapeutic options. The diverse effects of AMPK activation extend to its role in countering viral infections, further highlighting its significance in COVID-19. This review explores AMPK activation mechanisms, its role in metabolic disorders, and the potential use of natural compounds to target AMPK for post-COVID-19 complications. Also, it aims to review the possible methods of activating AMPK to prevent post-COVID-19 diabetes and cardiovascular complications. It also explores the use of natural compounds for their therapeutic effects in targeting the AMPK pathways. Targeting AMPK activation emerges as a promising avenue to mitigate the long-term effects of COVID-19, offering hope for improved patient outcomes and a better quality of life.

Increased hepatic gluconeogenesis and type 2 diabetes mellitus

Abnormally increased hepatic gluconeogenesis is a significant contributor to hyperglycemia in the fasting state in patients with type 2 diabetes mellitus (T2DM) due to insulin resistance. Metformin, the most prescribed drug for the treatment of T2DM, is believed to exert its effect mainly by reducing hepatic gluconeogenesis. Here, we discuss how increased hepatic gluconeogenesis contributes to T2DM and we review newly revealed mechanisms underlying the attenuation of gluconeogenesis by metformin. In addition, we analyze the recent findings on new determinants involved in the regulation of gluconeogenesis, which might ultimately lead to the identification of novel and targeted treatment strategies for T2DM.

How mass spectrometry can be exploited to study AMPK

AMP-activated protein kinase (AMPK) is a key regulator of metabolism and a recognised target for the treatment of metabolic diseases such as Type 2 diabetes (T2D). Here, we review how mass spectrometry (MS) can be used to study short-term control by AMPK via protein phosphorylation and long-term control due to changes in protein expression. We discuss how MS can quantify AMPK subunit levels in tissues from different species. We propose hydrogen-deuterium exchange (HDX)-MS to investigate molecular mechanisms of AMPK activation and thermoproteomic profiling (TPP) to assess off-target effects of pharmacological AMPK activators/inhibitors. Lastly, because large MS data sets are generated, we consider different approaches that can be used for their interpretation.

Targeting the autophagy-miRNA axis in prostate cancer: toward novel diagnostic and therapeutic strategies

Since prostate cancer is one of the leading causes of cancer-related death, a better understanding of the molecular pathways guiding its development is imperative. A key factor in prostate cancer is autophagy, a cellular mechanism that affects both cell survival and death. Autophagy is essential in maintaining cellular homeostasis. Autophagy is a physiological mechanism wherein redundant or malfunctioning cellular constituents are broken down and recycled. It is essential for preserving cellular homeostasis and is implicated in several physiological and pathological conditions, including cancer. Autophagy has been linked to metastasis, tumor development, and treatment resistance in prostate cancer. The deregulation of miRNAs related to autophagy appears to be a crucial element in the etiology of prostate cancer. These miRNAs influence the destiny of cancer cells by finely regulating autophagic mechanisms. Numerous investigations have emphasized the dual function of specific miRNAs in prostate cancer, which alter autophagy-related pathways to function as either tumor suppressors or oncogenes. Notably, miRNAs have been linked to the control of autophagy and the proliferation, apoptosis, and migration of prostate cancer cells. To create customized therapy approaches, it is imperative to comprehend the dynamic interplay between autophagy and miRNAs in prostate cancer. The identification of key miRNAs provides potential diagnostic and prognostic markers. Unraveling the complex network of lncRNAs, like PCA3, also expands the repertoire of molecular targets for therapeutic interventions. This review explores the intricate interplay between autophagy and miRNAs in prostate cancer, focusing on their regulatory roles in cellular processes ranging from survival to programmed cell death.

Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice

Regular exercise elicits adaptations in glucose and lipid metabolism that allow the body to meet energy demands of subsequent exercise bouts more effectively and mitigate metabolic diseases including fatty liver. Energy discharged during the acute exercise bouts that comprise exercise training may be a catalyst for liver adaptations. During acute exercise, liver glycogenolysis and gluconeogenesis are accelerated to supply glucose to working muscle. Lower liver energy state imposed by gluconeogenesis and related pathways activates AMP-activated protein kinase (AMPK), which conserves ATP partly by promoting lipid oxidation. This study tested the hypothesis that AMPK is necessary for liver glucose and lipid adaptations to training. Liver-specific AMPKα1α2 knockout (AMPKα1α2fl/fl+AlbCre) mice and littermate controls (AMPKα1α2fl/fl) completed sedentary and exercise training protocols. Liver nutrient fluxes were quantified at rest or during acute exercise following training. Liver metabolites and molecular regulators of metabolism were assessed. Training increased liver glycogen in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. The inability to increase glycogen led to lower glycogenolysis, glucose production, and circulating glucose during acute exercise in trained AMPKα1α2fl/fl+AlbCre mice. Deletion of AMPKα1α2 attenuated training-induced declines in liver diacylglycerides. In particular, training lowered the concentration of unsaturated and elongated fatty acids comprising diacylglycerides in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. Training increased liver triacylglycerides and the desaturation and elongation of fatty acids in triacylglycerides of AMPKα1α2fl/fl+AlbCre mice. These lipid responses were independent of differences in tricarboxylic acid cycle fluxes. In conclusion, AMPK is required for liver training adaptations that are critical to glucose and lipid metabolism.NEW & NOTEWORTHY This study shows that the energy sensor and transducer, AMP-activated protein kinase (AMPK), is necessary for an exercise training-induced: 1) increase in liver glycogen that is necessary for accelerated glycogenolysis during exercise, 2) decrease in liver glycerolipids independent of tricarboxylic acid (TCA) cycle flux, and 3) decline in the desaturation and elongation of fatty acids comprising liver diacylglycerides. The mechanisms defined in these studies have implications for use of regular exercise or AMPK-activators in patients with fatty liver.

Metabolic control by AMPK in white adipose tissue

White adipose tissue (WAT) plays an important role in the integration of whole-body metabolism by storing fat and mobilizing triacylglycerol when needed. The released free fatty acids can then be oxidized by other tissues to provide ATP. AMP-activated protein kinase (AMPK) is a key regulator of metabolic pathways, and can be targeted by a new generation of direct, small-molecule activators. AMPK activation in WAT inhibits insulin-stimulated lipogenesis and in some situations also inhibits insulin-stimulated glucose uptake, but AMPK-induced inhibition of β-adrenergic agonist-stimulated lipolysis might need to be re-evaluated in vivo. The lack of dramatic effects of AMPK activation on basal metabolism in WAT could be advantageous when treating type 2 diabetes with pharmacological pan-AMPK activators.

The Protective Effect of 11-Keto-β-Boswellic Acid against Diabetic Cardiomyopathy in Rats Entails Activation of AMPK

This study examined the protective effect of 11-keto-β-boswellic acid (AKBA) against streptozotocin (STZ)-induced diabetic cardiomyopathy (DC) in rats and examined the possible mechanisms of action. Male rats were divided into 5 groups (n = 8/each): (1) control, AKBA (10 mg/kg, orally), STZ (65 mg/kg, i.p.), STZ + AKBA (10 mg/kg, orally), and STZ + AKBA + compound C (CC/an AMPK inhibitor, 0.2 mg/kg, i.p.). AKBA improved the structure and the systolic and diastolic functions of the left ventricles (LVs) of STZ rats. It also attenuated the increase in plasma glucose, plasma insulin, and serum and hepatic levels of triglycerides (TGs), cholesterol (CHOL), and free fatty acids (FFAs) in these diabetic rats. AKBA stimulated the ventricular activities of phosphofructokinase (PFK), pyruvate dehydrogenase (PDH), and acetyl CoA carboxylase (ACC); increased levels of malonyl CoA; and reduced levels of carnitine palmitoyltransferase I (CPT1), indicating improvement in glucose and FA oxidation. It also reduced levels of malondialdehyde (MDA); increased mitochondria efficiency and ATP production; stimulated mRNA, total, and nuclear levels of Nrf2; increased levels of glutathione (GSH), heme oxygenase (HO-1), superoxide dismutase (SOD), and catalase (CAT); but reduced the expression and nuclear translocation of NF-κB and levels of tumor-necrosis factor-α (TNF-α) and interleukin-6 (IL-6). These effects were concomitant with increased activities of AMPK in the LVs of the control and STZ-diabetic rats. Treatment with CC abolished all these protective effects of AKBA. In conclusion, AKBA protects against DC in rats, mainly by activating the AMPK-dependent control of insulin release, cardiac metabolism, and antioxidant and anti-inflammatory effects.