Nicotinamide protects chronic hypoxic myocardial cells through regulating mTOR pathway and inducing autophagy

Effect of acute high-intensity exercise on myocardium metabolic profiles in rat and human study via metabolomics approach

Acute high-intensity exercise can affect cardiac health by altering substance metabolism. However, few metabolomics-based studies provide data on the effect of exercise along with myocardial metabolism. Our study aimed to identify metabolic signatures in rat myocardium during acute high-intensity exercise and evaluate their diagnostic potential for sports injuries. We collected rat myocardium samples and subjects’ serum samples before and after acute high-intensity exercise for metabolite profiling to explore metabolic alterations of exercise response in the myocardium. Multivariate analysis revealed myocardium metabolism differed before and after acute high-intensity exercise. Furthermore, 6 target metabolic pathways and 12 potential metabolic markers for acute high-intensity exercise were identified. Our findings provided an insight that myocardium metabolism during acute high-intensity exercise had distinct disorders in complex lipids and fatty acids. Moreover, an increase of purine degradation products, as well as signs of impaired glucose metabolism, were observed. Besides, amino acids were enhanced with a certain protective effect on the myocardium. In this study, we discovered how acute high-intensity exercise affected myocardial metabolism and exercise-related heart injury risks, which can provide references for pre-competition screening, risk prevention, and disease prognosis in competitive sports and effective formulation of exercise prescriptions for different people.

Exogenous spermine attenuates diabetic kidney injury in rats by inhibiting AMPK/mTOR signaling pathway

Diabetic nephropathy (DN) is the primary cause of end‑stage renal disease, which is closely associated with dysfunction of the podocytes, the main component of the glomerular filtration membrane; however, the exact underlying mechanism is unknown. Polyamines, including spermine, spermidine and putrescine, have antioxidant and anti‑aging properties that are involved in the progression of numerous diseases, but their role in DN has not yet been reported. The present study aimed to explore the role of polyamines in DN, particularly in podocyte injury, and to reveal the molecular mechanism underlying the protective effect of exogenous spermine. Streptozotocin intraperitoneal injection‑induced type 1 diabetic (T1D) rat models and high glucose (HG)‑stimulated podocyte injury models were established. It was found that in T1D rat kidneys and HG‑induced podocytes, ornithine decarboxylase (a key enzyme for polyamine synthesis) was downregulated, while spermidine/spermine N1‑acetyltransferase (a key enzyme for polyamines degradation) was upregulated, which suggested that reduction of the polyamine metabolic pool particularly decreased spermine content, is a major factor in DN progression. In addition, hyperglycemia can induce an increased rat kidney weight ratio, serum creatinine, urea, urinary albumin excretion and glomerular cell matrix levels, and promote mesangial thickening and loss or fusion of podocytes. The expression levels of podocyte marker proteins (nephrin, CD2‑associated protein and podocin) and autophagy‑related proteins [autophagy protein 5, microtube‑associated proteins 1A/1B light chain 3 (LC3)II/LC3I, Beclin 1 and phosphorylated (p)‑AMPK] were downregulated, while cleaved caspase‑3, P62 and p‑mTOR were increased. These changes could be improved by pretreatment with exogenous spermine or rapamycin (autophagic agonist). In conclusion, spermine may have the potential to prevent diabetic kidney injury in rats by promoting autophagy via regulating the AMPK/mTOR signaling pathway.

Nicotinamide as a Foundation for Treating Neurodegenerative Disease and Metabolic Disorders

Neurodegenerative disorders impact more than one billion individuals worldwide and are intimately tied to metabolic disease that can affect another nine hundred individuals throughout the globe. Nicotinamide is a critical agent that may offer fruitful prospects for neurodegenerative diseases and metabolic disorders, such as diabetes mellitus. Nicotinamide protects against multiple toxic environments that include reactive oxygen species exposure, anoxia, excitotoxicity, ethanolinduced neuronal injury, amyloid (Aß) toxicity, age-related vascular disease, mitochondrial dysfunction, insulin resistance, excess lactate production, and loss of glucose homeostasis with pancreatic β-cell dysfunction. However, nicotinamide offers cellular protection in a specific concentration range, with dosing outside of this range leading to detrimental effects. The underlying biological pathways of nicotinamide that involve the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), and mammalian forkhead transcription factors (FoxOs) may offer insight for the clinical translation of nicotinamide into a safe and efficacious therapy through the modulation of oxidative stress, apoptosis, and autophagy. Nicotinamide is a highly promising target for the development of innovative strategies for neurodegenerative disorders and metabolic disease, but the benefits of this foundation depend greatly on gaining a further understanding of nicotinamide's complex biology.

Axonal Protection by Nicotinamide Riboside via SIRT1-Autophagy Pathway in TNF-Induced Optic Nerve Degeneration

Nicotinamide adenine dinucleotide (NAD⁺) synthesis pathway has been involved in many biological functions. Nicotinamide riboside (NR) is widely used as an NAD⁺ precursor and known to increase NAD⁺ level in several tissues. The present study aimed to examine the effect of NR on tumor necrosis factor (TNF)-induced optic nerve degeneration and to investigate whether it alters SIRT1 expression and autophagic status in optic nerve. We also examined the localization of nicotinamide riboside kinase 1 (NRK1), which is a downstream enzyme for NR biosynthesis pathway in retina and optic nerve. Intravitreal injection of TNF or TNF plus NR was performed on rats. The p62 and LC3-II protein levels were examined to evaluate autophagic flux in optic nerve. Immunohistochemical analysis was performed to localize NRK1 expression. Morphometric analysis showed substantial axonal protection by NR against TNF-induced axon loss. TNF-induced increment of p62 protein level was significantly inhibited by NR administration. NR administration alone significantly increased the LC3-II levels and reduced p62 levels compared with the basal levels, and upregulated SIRT1 levels in optic nerve. Immunohistochemical analysis showed that NRK1 exists in retinal ganglion cells (RGCs) and nerve fibers in retina and optic nerve. NR administration apparently upregulated NRK1 levels in the TNF-treated eyes as well as the control eyes. Pre-injection of an SIRT1 inhibitor resulted in a significant increase of p62 levels in the NR plus TNF treatment group, implicating that SIRT1 regulates autophagy status. In conclusion, NRK1 exists in RGCs and optic nerve axons. NR exerted protection against axon loss induced by TNF with possible involvement of upregulated NRK1 and SIRT1-autophagy pathway.

New Insights for nicotinamide: Metabolic disease, autophagy, and mTOR

Metabolic disorders, such as diabetes mellitus (DM), are increasingly becoming significant risk factors for the health of the global population and consume substantial portions of the gross domestic product of all nations. Although conventional therapies that include early diagnosis, nutritional modification of diet, and pharmacological treatments may limit disease progression, tight serum glucose control cannot prevent the onset of future disease complications. With these concerns, novel strategies for the treatment of metabolic disorders that involve the vitamin nicotinamide, the mechanistic target of rapamycin (mTOR), mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP activated protein kinase (AMPK), and the cellular pathways of autophagy and apoptosis offer exceptional promise to provide new avenues of treatment. Oversight of these pathways can promote cellular energy homeostasis, maintain mitochondrial function, improve glucose utilization, and preserve pancreatic beta-cell function. Yet, the interplay among mTOR, AMPK, and autophagy pathways can be complex and affect desired clinical outcomes, necessitating further investigations to provide efficacious treatment strategies for metabolic dysfunction and DM.

Nicotinamide Increases Intracellular NAD+ Content to Enhance Autophagy-Mediated Group A Streptococcal Clearance in Endothelial Cells

Group A streptococcus (GAS) is a versatile pathogen that causes a wide spectrum of diseases in humans. Invading host cells is a known strategy for GAS to avoid antibiotic killing and immune recognition. However, the underlying mechanisms of GAS resistance to intracellular killing need to be explored. Endothelial HMEC-1 cells were infected with GAS, methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella Typhimurium under nicotinamide (NAM)-supplemented conditions. The intracellular NAD⁺ level and cell viability were respectively measured by NAD⁺ quantification kit and protease-based cytotoxicity assay. Moreover, the intracellular bacteria were analyzed by colony-forming assay, transmission electron microscopy, and confocal microscopy. We found that supplementation with exogenous nicotinamide during infection significantly inhibited the growth of intracellular GAS in endothelial cells. Moreover, the NAD⁺ content and NAD⁺/NADH ratio of GAS-infected endothelial cells were dramatically increased, whereas the cell cytotoxicity was decreased by exogenous nicotinamide treatment. After knockdown of the autophagy-related ATG9A, the intracellular bacterial load was increased in nicotinamide-treated endothelial cells. The results of Western blot and transmission electron microscopy also revealed that cells treated with nicotinamide can increase autophagy-associated LC3 conversion and double-membrane formation during GAS infection. Confocal microscopy images further showed that more GAS-containing vacuoles were colocalized with lysosome under nicotinamide-supplemented conditions than without nicotinamide treatment. In contrast to GAS, supplementation with exogenous nicotinamide did not effectively inhibit the growth of MRSA or S. Typhimurium in endothelial cells. These results indicate that intracellular NAD⁺ homeostasis is crucial for controlling intracellular GAS infection in endothelial cells. In addition, nicotinamide may be a potential new therapeutic agent to overcome persistent infections of GAS.

Nicotinamide: Oversight of Metabolic Dysfunction Through SIRT1, mTOR, and Clock Genes

Metabolic disorders that include diabetes mellitus present significant challenges for maintaining the welfare of the global population. Metabolic diseases impact all systems of the body and despite current therapies that offer some protection through tight serum glucose control, ultimately such treatments cannot block the progression of disability and death realized with metabolic disorders. As a result, novel therapeutic avenues are critical for further development to address these concerns. An innovative strategy involves the vitamin nicotinamide and the pathways associated with the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), the mechanistic target of rapamycin (mTOR), mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP activated protein kinase (AMPK), and clock genes. Nicotinamide maintains an intimate relationship with these pathways to oversee metabolic disease and improve glucose utilization, limit mitochondrial dysfunction, block oxidative stress, potentially function as antiviral therapy, and foster cellular survival through mechanisms involving autophagy. However, the pathways of nicotinamide, SIRT1, mTOR, AMPK, and clock genes are complex and involve feedback pathways as well as trophic factors such as erythropoietin that require a careful balance to ensure metabolic homeostasis. Future work is warranted to gain additional insight into these vital pathways that can oversee both normal metabolic physiology and metabolic disease.