Apoptosis induced by NAD depletion is inhibited by KN-93 in a CaMKII-independent manner

Maintaining mitochondrial NAD+ homeostasis is key for heat-induced skeletal muscle injury prevention despite presence of intracellular cation alterations

Mitochondrial dysfunction is implicated in heat-induced skeletal muscle (SKM) injury and its underlying mechanisms remain unclear. Evidence suggests that cellular ions and molecules, including divalent cations and adenine nucleotides, are involved in the regulation of mitochondrial function. In this study, we examined Ca2+, Mg2+, and NAD+ levels in mouse C2C12 myoblasts and SKM in response to heat exposure. During heat exposure, mitochondrial Ca2+ levels increased significantly, whereas cytosolic Ca2+ levels remained unaltered. The mitochondrial Ca2+ levels in the SKM of heat-exposed mice were 28% higher compared to control mice. No changes in cytosolic Ca2+ were detected between the two groups. Following heat exposure, cytosolic and mitochondrial Mg2+ levels were reduced by 47% and 23% in C2C12 myoblasts, and by 51% and 44% in mouse SKMs, respectively. In addition, heat exposure decreased mitochondrial NAD+ levels by 32% and 26% in C2C12 myoblasts and mouse SKMs, respectively. Treatment with the NAD+ precursor nicotinamide riboside (NR) partially prevented heat-induced depletion of NAD+. Additionally, NR significantly reduced heat-increased mitochondrial fission, mitochondrial depolarization, and apoptosis in C2C12 myoblasts and mouse SKMs. No effects of NR on heat-induced changes in intracellular Ca2+ and Mg2+ levels were observed. This study provides in vitro and in vivo evidence that acute heat stress causes alterations in mitochondrial Ca2+, Mg2+, and NAD+ homeostasis. Our results suggest mitochondrial NAD+ homeostasis as a therapeutic target for the prevention of heat-induced SKM injury.

Quercetin alleviates zearalenone-induced apoptosis and necroptosis of porcine renal epithelial cells by inhibiting CaSR/CaMKII signaling pathway

Zearalenone (ZEA) is a mycotoxin that is highly contaminated in feed and can cause severe toxic effects on the kidneys and other organs of animals. Quercetin (QUE) is a plant-derived flavonoid with a variety of detoxification properties, but the mechanism by which QUE detoxifies the toxic effects induced by ZEA has not yet been fully elucidated. We treated porcine kidney cells (PK15) with 80 μM ZEA and/or 30 μM QUE. The results showed that ROS and MDA levels were increased, antioxidant system levels were down-regulated, anti-apoptotic factor expression levels were decreased, and apoptotic and necroptosis-related factors were up-regulated after ZAE exposure. In addition, the results of Ca2+ staining, mitochondrial membrane potential, and mitochondrial dynamics-related indicators showed that ZEA induced Ca2+ overload in PK15 cells and increased mitochondrial Ca2+ uptake (MCU expression increased). The accumulated ROS and free Ca2+ further aggravate mitochondrial damage and eventually lead to mitochondrial pathway apoptosis and necroptosis. Nevertheless, QUE targets CaSR to inhibit the CaSR/CaMKII pathway and regulate calcium homeostasis, thereby alleviating apoptosis and necroptosis mediated by mitochondrial dynamic disorder and dysfunction. The present study demonstrated the mechanism by which ZEA induces apoptosis and necroptosis in PK15 and the protective role of QUE in this process.

Evaluation of the synergistic effects of epigallocatechin-3-gallate-loaded PEGylated-PLGA nanoparticles with nimodipine against neuronal injury after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating subtype of stroke with high mortality and morbidity. Although serious side effects might occur, nimodipine, a second-generation 1,4-dihydropyridine calcium channel blocker, is clinically used to improve neurological outcomes after SAH. Recently, (-)-epigallocatechin-3-gallate (EGCG) has been reported to inhibit Ca²⁺ overloading-induced mitochondrial dysfunction, oxidative stress, and neuronal cell death after SAH; however, low bioavailability, instability, and cytotoxicity at a high dose limited the clinical application of EGCG. To overcome these limitations, PEGylated-PLGA EGCG nanoparticles (EGCG-NPs) were constructed to enhance the bioavailability by using the double-emulsion method. Antioxidative activity, cytotoxicity, behavioral, and immunohistochemistry studies were carried out to determine the neuroprotective effectiveness after cotreatment with EGCG-NPs (75 mg/kg/d preconditioning for 7 days before SAH) and nimodipine (10 mg/kg/d after 30 min of SAH) by using in vivo SAH models. The optimized EGCG-NPs with a Box-Behnken design showed a small particle size of 167 nm, a zeta potential value of -22.6 mV, an encapsulation efficiency of 86%, and a sustained-release profile up to 8 days in vitro. Furthermore, EGCG-NPs (75 mg/kg/d) had superior antioxidative activity to free EGCG (100 mg/kg/d). EGCG-NPs combined with nimodipine exhibited significant synergistic effects against neuronal cell death by suppressing oxidative stress, Ca²⁺ overloading, mitochondrial dysfunction, and autophagy after SAH. These results suggest that cotreatment with EGCG-NPs and nimodipine may serve as a promising novel strategy for the treatment of SAH.

Appraisal of the Possible Role of PPARγ Upregulation by CLA of Probiotic Pediococcus pentosaceus GS4 in Colon Cancer Mitigation

The prevalence of colon cancer (CC) is increasing at the endemic scale, which is accompanied by subsequent morbidity and mortality. Although there have been noteworthy achievements in the therapeutic strategies in recent years, the treatment of patients with CC remains a formidable task. The current study focused on to study role of biohydrogenation-derived conjugated linoleic acid (CLA) of probiotic Pediococcus pentosaceus GS4 (CLA_GS4) against CC, which induced peroxisome proliferator-activated receptor gamma (PPARγ) expression in human CC HCT-116 cells. Pre-treatment with PPARγ antagonist bisphenol A diglycidyl ether has significantly reduced the inhibitory efficacy of enhanced cell viability of HCT-116 cells, suggesting the PPARγ-dependent cell death. The cancer cells treated with CLA/CLA_GS4 demonstrated the reduced level of Prostaglandin E2 PGE₂ in association with reduced COX-2 and 5-LOX expressions. Moreover, these consequences were found to be associated with PPARγ-dependent. Furthermore, delineation of mitochondrial dependent apoptosis with the help of molecular docking LigPlot analysis showed that CLA can bind with hexokinase-II (hHK-II) (highly expressed in cancer cells) and that this association underlies voltage dependent anionic channel to open, thereby causing mitochondrial membrane depolarization, a condition that initiates intrinsic apoptotic events. Apoptosis was further confirmed by annexin V staining and elevation of caspase 1p10 expression. Taken all together, it is deduced that, mechanistically, the upregulation of PPARγ by CLA_GS4 of P. pentosaceus GS4 can alter cancer cell metabolism in association with triggering apoptosis in CC.

Sevoflurane exposure induces neurotoxicity by regulating mitochondrial function of microglia due to NAD insufficiency

Developmental neurons received with sevoflurane, the commonly used inhalational anesthetic agent in clinical surgery, several times tend to be destroyed. Microglia, the resident immune cells of the central nervous system (CNS), are activated after sevoflurane exposure, accompanied by releasing proinflammatory cytokines that damage developing neurons. The sevoflurane-induced neurotoxicity could be attributed to activated microglia presenting proinflammatory and anti-inflammatory functions. Proinflammatory microglia release cytokines to impair the CNS, while anti-inflammatory microglia engulf damaged neurons to maintain CNS homeostasis. Sevoflurane exposure promotes the secretion of proinflammatory cytokines by microglia, inhibiting the microglial phagocytic function. Microglia with poor phagocytic function cannot engulf damaged neurons, leading to the accumulation of damaged neurons. The mechanism underlying poor phagocytic function may be attributed to mitochondrial dysfunction of microglia induced by sevoflurane exposure, in which affected mitochondria cannot generate adequate ATP and NAD to satisfy the energy demand. We discovered that sevoflurane treatment impaired the mitochondrial metabolism of microglia, which resulted in NAD deficiency and couldn’t produce sufficient energy to clear damaged neurons to maintain CNS development. Our findings provide an explanation of a new mechanism underlying sevoflurane-induced neurotoxicity.

[Imeglimin: features of the mechanism of action and potential benefits]

Imeglimin is the first drug in a new class of tetrahydrotriazine-containing oral hypoglycemic agents called «glimines». Its mechanism of action is aimed at achieving a double effect, firstly, to improve the function of beta cells of the pancreas, and secondly, to enhance the action of insulin in key tissues, including the liver and skeletal muscles. At the cellular level, imeglimin modulates mitochondrial function, which leads to an improvement in cellular energy metabolism, as well as to the protection of cells from death in conditions of excessive accumulation of reactive oxygen species. It is important to note that the mechanism of action of imeglimin differs from existing drugs used for the treatment of type 2 diabetes mellitus. Like glucagon-like peptide-1 receptor agonists, imeglimin enhances insulin secretion in an exclusively glucose-dependent manner, but their mechanism of action at the cellular level diverges. Sulfonylureas and glinides function by closing ATP-sensitive potassium channels to release insulin, which is also different from imeglimin. Compared with metformin, the effect of imeglimine is also significantly different. Other major classes of oral antihypertensive agents, such as sodium-glucose transporter-2 inhibitors, thiazolidinediones and α glucosidase inhibitors mediate their action through mechanisms that do not overlap with imeglimine. Given such differences in the mechanisms of action, imeglimin can be used as part of combination therapy, for example with sitagliptin and metformin. The imeglimine molecule is well absorbed (Tmax-4), and the half-life is 5-6 hours, is largely excreted through the kidneys, and also has no clinically significant interactions with either metformin or sitagliptin.

Comparative study on beneficial effects of vitamins B and D in attenuating doxorubicin induced cardiotoxicity in rats: Emphasis on calcium homeostasis

The use of doxorubicin (DOX) to treat various tumors is limited by its cardiotoxicity. This study aimed to investigate and compare the cardioprotective effects of nicotinamide (NAM) and alfacalcidol (1α(OH)D₃), against DOX-induced cardiotoxicity. Sprague Dawley male rats received DOX (5 mg/kg, i.p.) once/week for four consecutive weeks. Treated groups received either NAM (600 mg/kg, p.o.) for 28 consecutive days or 1α(OH)D₃ (0.5 ug/kg, i.p.) once/week for four consecutive weeks. DOX elicited marked cardiac tissue injury manifested by elevated serum cardiotoxicity indices, conduction and histopathological abnormalities. Both NAM and 1α(OH)D₃ successfully reversed all these changes. From the mechanistic point of view, DOX provoked intense cytosolic and mitochondrial calcium (Ca²⁺) overload hence switching on calpain1 (CPN1) and mitochondrial-mediated apoptotic cascades as confirmed by upregulating Bax and caspase-3 while downregulating Bcl-2 expression. DOX also disrupted cardiac bioenergetics as evidenced by adenosine triphosphate (ATP) depletion and a declined ATP/ADP ratio. Moreover, DOX upregulated the Ca²⁺ sensor; calmodulin kinase II gamma (CaMKII-δ) which further contributed to cardiac damage. Interestingly, co-treatment with either NAM or 1α(OH)D₃ reversed all DOX associated abnormalities by preserving Ca²⁺ homeostasis, replenishing ATP stores and obstructing apoptotic events. Additionally, DOX prompted nuclear factor kappa B (NF-κB) dependent inflammatory responses and subsequently upregulated interleukin-6 (IL-6) expression. Co-treatment with NAM or 1α(OH)D₃ effectively obstructed these inflammatory signals. Remarkably, NAM showed superior beneficial cardioprotective properties over 1α(OH)D₃. Both NAM and 1α(OH)D₃ efficiently attenuated DOX-cardiomyopathy mainly via preserving Ca²⁺ homeostasis and diminishing apoptotic and inflammatory pathways. NAM definitely exhibited effective cardioprotective capabilities over 1α(OH)D₃.

Imeglimin preserves islet β-cell mass in Type 2 diabetic ZDF rats

Objectives

Type 2 diabetes (T2D) is driven by progressive dysfunction and loss of pancreatic β-cell mass. Imeglimin is a first-in-class novel drug candidate that improves glycaemia and glucose-stimulated insulin secretion in preclinical models and patients. Given evidence that imeglimin can attenuate β-cell dysfunction and protect β cells in vitro, we postulated that imeglimin could also exert longer term effects to prevent pancreatic β-cell death and preserve functional β-cell mass in vivo.

Methods

Zucker diabetic fatty (ZDF) male rats were treated by oral gavage with imeglimin at a standard dose of 150 mg/kg or vehicle, twice daily for five weeks. At treatment completion, oral glucose tolerance tests were performed in fasted animals before a thorough histomorphometry and immunohistochemical analysis was conducted on pancreas tissue slices to assess cellular composition and disease status.

Results

Imeglimin treatment significantly improved glucose-stimulated insulin secretion (augmentation of the insulinogenic index) and improved glycaemia. Both basal insulinaemia and pancreatic insulin content were also increased by imeglimin. In ZDF control rats, islet structure was disordered with few β-cells; after imeglimin treatment, islets appeared healthier with more normal morphology in association with a significant increase in insulin-positive β-cells. The increase in β-cell mass was associated with a greater degree of β-cell proliferation in the presence of reduced apoptosis. Unexpectedly, a decrease in as a α-cell mass was also documented due to an apparent antiproliferative effect of imeglimin on this cell type.

Conclusion

In male ZDF rats, chronic imeglimin treatment corrects a paramount component of type 2 diabetes progression: progressive loss of functional β-cell mass. In addition, imeglimin may also moderate a-cell turnover to further ameliorate hyperglycaemia. Cumulatively, these cellular effects suggest that imeglimin may provide for disease modifying effects to preserve functional β-cell mass.

Mechanism of action of Imeglimin: A novel therapeutic agent for type 2 diabetes

Imeglimin is an investigational first-in-class novel oral agent for the treatment of type 2 diabetes (T2D). Several pivotal phase III trials have been completed with evidence of statistically significant glucose lowering and a generally favourable safety and tolerability profile, including the lack of severe hypoglycaemia. Imeglimin's mechanism of action involves dual effects: (a) amplification of glucose-stimulated insulin secretion (GSIS) and preservation of β-cell mass; and (b) enhanced insulin action, including the potential for inhibition of hepatic glucose output and improvement in insulin signalling in both liver and skeletal muscle. At a cellular and molecular level, Imeglimin's underlying mechanism may involve correction of mitochondrial dysfunction, a common underlying element of T2D pathogenesis. It has been observed to rebalance respiratory chain activity (partial inhibition of Complex I and correction of deficient Complex III activity), resulting in reduced reactive oxygen species formation (decreasing oxidative stress) and prevention of mitochondrial permeability transition pore opening (implicated in preventing cell death). In islets derived from diseased rodents with T2D, Imeglimin also enhances glucose-stimulated ATP generation and induces the synthesis of nicotinamide adenine dinucleotide (NAD+ ) via the 'salvage pathway'. In addition to playing a key role as a mitochondrial co-factor, NAD+ metabolites may contribute to the increase in GSIS (via enhanced Ca++ mobilization). Imeglimin has also been shown to preserve β-cell mass in rodents with T2D. Overall, Imeglimin appears to target a key root cause of T2D: defective cellular energy metabolism. This potential mode of action is unique and has been shown to differ from that of other major therapeutic classes, including biguanides, sulphonylureas and glucagon-like peptide-1 receptor agonists.

Minireview Exploring the Biological Cycle of Vitamin B3 and Its Influence on Oxidative Stress: Further Molecular and Clinical Aspects

Vitamin B3, or niacin, is one of the most important compounds of the B-vitamin complex. Recent reports have demonstrated the involvement of vitamin B3 in a number of pivotal functions which ensure that homeostasis is maintained. In addition, the intriguing nature of its synthesis and the underlying mechanism of action of vitamin B3 have encouraged further studies aimed at deepening our understanding of the close link between the exogenous supply of B3 and how it activates dependent enzymes. This crucial role can be attributed to the gut microflora and its ability to shape human behavior and development by mediating the bioavailability of metabolites. Recent studies have indicated a possible interconnection between the novel coronavirus and commensal bacteria. As such, we have attempted to explain how the gastrointestinal deficiencies displayed by SARS-CoV-2-infected patients arise. It seems that the stimulation of a proinflammatory cascade and the production of large amounts of reactive oxygen species culminates in the subsequent loss of host eubiosis. Studies of the relationhip between ROS, SARS-CoV-2, and gut flora are sparse in the current literature. As an integrated component, oxidative stress (OS) has been found to negatively influence host eubiosis, in vitro fertilization outcomes, and oocyte quality, but to act as a sentinel against infections. In conclusion, research suggests that in the future, a healthy diet may be considered a reliable tool for maintaining and optimizing our key internal parameters.

Pin1 Is Regulated by CaMKII Activation in Glutamate-Induced Retinal Neuronal Regulated Necrosis

In our previous study, we reported that peptidyl-prolyl isomerase 1 (Pin1)-modulated regulated necrosis (RN) occurred in cultured retinal neurons after glutamate injury. In the current study, we investigated the role of calcium/calmodulin-dependent protein kinase II (CaMKII) in Pin1-modulated RN in cultured rat retinal neurons, and in an animal in vivo model. We first demonstrated that glutamate might lead to calcium overloading mainly through ionotropic glutamate receptors activation. Furthermore, CaMKII activation induced by overloaded calcium leads to Pin1 activation and subsequent RN. Inactivation of CaMKII by KN-93 (KN, i.e., a specific CaMKII inhibitor) application can decrease the glutamate-induced retinal neuronal RN. Finally, by using an animal in vivo model, we also demonstrated the important role of CaMKII in glutamate-induced RN in rat retina. In addition, flash electroretinogram results provided evidence that the impaired visual function induced by glutamate can recover after CaMKII inhibition. In conclusion, CaMKII is an up-regulator of Pin1 and responsible for the RN induced by glutamate. This study provides further understanding of the regulatory pathway of RN and is a complementary mechanism for Pin1 activation mediated necrosis. This finding will provide a potential target to protect neurons from necrosis in neurodegenerative diseases, such as glaucoma, diabetic retinopathy, and even central nervous system diseases.

NAMPT as a Dedifferentiation-Inducer Gene: NAD+ as Core Axis for Glioma Cancer Stem-Like Cells Maintenance

Glioma Cancer Stem-Like Cells (GSCs) are a small subset of CD133⁺ cells with self-renewal properties and capable of initiating new tumors contributing to Glioma progression, maintenance, hierarchy, and complexity. GSCs are highly resistant to chemo and radiotherapy. These cells are believed to be responsible for tumor relapses and patients' fatal outcome after developing a recurrent Glioblastoma (GBM) or High Grade Glioma (HGG). GSCs are cells under replicative stress with high demands on NAD⁺ supply to repair DNA, maintain self-renewal capacity and to induce tumor plasticity. NAD⁺ feeds Poly-ADP polymerases (PARP) and NAD⁺-dependent deacetylases (SIRTUINS) contributing to GSC phenotype. This energetic core axis is mainly controlled by the rate-limiting enzyme nicotinamide phosphoribosyltransferase (NAMPT), an important oncogene contributing to tumor dedifferentiation. Targeting GSCs depicts a new frontier in Glioma therapy; hence NAMPT could represent a key regulator for GSCs maintenance. Its inhibition may attenuate GSCs properties by decreasing NAD⁺ supply, consequently contributing to a better outcome together with current therapies for Glioma control.

EWS-FLI1 confers exquisite sensitivity to NAMPT inhibition in Ewing sarcoma cells

Ewing sarcoma (EwS) is the second most common bone cancer in children and adolescents with a high metastatic potential. EwS development is driven by a specific chromosomal translocation resulting in the generation of a chimeric EWS-ETS transcription factor, most frequently EWS-FLI1.

Nicotinamide adenine dinucleotide (NAD) is a key metabolite of energy metabolism involved in cellular redox reactions, DNA repair, and in the maintenance of genomic stability. This study describes targeting nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of NAD synthesis, by FK866 in EwS cells. Here we report that blocking NAMPT leads to exhaustive NAD depletion in EwS cells, followed by a metabolic collapse and cell death. Using conditional EWS-FLI1 knockdown by doxycycline-inducible shRNA revealed that EWS-FLI1 depletion significantly reduces the sensitivity of EwS cells to NAMPT inhibition. Consistent with this finding, a comparison of 7 EwS cell lines of different genotypes with 5 Non-EwS cell lines and mesenchymal stem cells revealed significantly higher FK866 sensitivity of EWS-ETS positive EwS cells, with IC₅₀ values mostly below 1nM.

Taken together, our data reveal evidence of an important role of the NAMPT-mediated NAD salvage pathway in the energy homeostasis of EwS cells and suggest NAMPT inhibition as a potential new treatment approach for Ewing sarcoma.

NAD+ salvage pathway in cancer metabolism and therapy

Nicotinamide adenine dinucleotide (NAD⁺) is an essential coenzyme for various physiological processes including energy metabolism, DNA repair, cell growth, and cell death. Many of these pathways are typically dysregulated in cancer cells, making NAD⁺ an intriguing target for cancer therapeutics. NAD⁺ is mainly synthesized by the NAD⁺ salvage pathway in cancer cells, and not surprisingly, the pharmacological targeting of the NAD⁺ salvage pathway causes cancer cell cytotoxicity in vitro and in vivo. Several studies have described the precise consequences of NAD⁺ depletion on cancer biology, and have demonstrated that NAD+ depletion results in depletion of energy levels through lowered rates of glycolysis, reduced citric acid cycle activity, and decreased oxidative phosphorylation. Additionally, depletion of NAD⁺ causes sensitization of cancer cells to oxidative damage by disruption of the anti-oxidant defense system, decreased cell proliferation, and initiation of cell death through manipulation of cell signaling pathways (e.g., SIRT1 and p53). Recently, studies have explored the effect of well-known cancer therapeutics in combination with pharmacological depletion of NAD⁺ levels, and found in many cases a synergistic effect on cancer cell cytotoxicity. In this context, we will discuss the effects of NAD⁺ salvage pathway inhibition on cancer cell biology and provide insight on this pathway as a novel anti-cancer therapeutic target.