Nicotinamide reduces inflammation and oxidative stress via the cholinergic system in fructose-induced metabolic syndrome in rats
Introduction
Fructose overload generates metabolic syndrome (MetS) [1,2], which favors the production of reactive oxygen species and proinflammatory cytokines can generate type 2 diabetes (T2D). The acetylcholinesterase (AChE, E.C.3.1.1.7) and butyrylcholinesterase (BChE, E.C.3.1.1.8) enzymes regulate the neuromuscular cholinergic system, and recent research has shown their relationship to risk factors for MetS [3,4]. In addition, an increase in their activities maintains hydrolysis of the neurotransmitter acetylcholine (ACh), eliminating anti-inflammatory regulation mediated by the cholinergic system [5].
The presynaptic neurons of the vagus nerve secrete ACh, which is captured by muscarinic and nicotinic receptors; specifically, nicotinic α7 receptor (α7nAChR) regulates the translocation of nuclear factor kappa-beta (NFκ-β) to the nucleus and synthesis of proinflammatory cytokines, a mechanism called the cholinergic anti-inflammatory pathway [6].
Numerous studies have associated the elevated activity of both cholinesterases with body mass index (BMI), dyslipidemia, hypertension, increased triacylglycerols (TGs), low-density lipoprotein (LDL), C-reactive protein and proinflammatory cytokines [[7], [8], [9]]. In contrast, the activity of these cholinesterases is associated with decreased high-density lipoprotein (HDL).
For this reason, AChE and BChE have been proposed as early markers of MetS and as therapeutic targets to counteract low-level systemic inflammation, lipid synthesis and oxidative stress, factors associated with MetS development.
Nicotinamide (NAM) is an amide derived from nicotinic acid and the main precursor for nicotinamide adenine dinucleotide (NAD+) formation [10]. NAM supplementation could be beneficial due to the antioxidant, anti-inflammatory [11,12], immunoregulatory and antilipemic actions [13], which could be mediated by the synthesis of NAD+. Additionally, NAD+ and cofactors derived from NAD+, such as reduced/oxidized NAD (phosphate), are intimately involved in all essential bioenergetic, anabolic and catabolic pathways and contribute to posttranslational protein modification. NAM prevents pancreatic β-cell death by inhibiting poly-(ADP-ribose) polymerases and nitric oxide formation [14]. In addition, NAM inhibits NAD+-dependent deacetylase or sirtuins (SIRTs) in obese rats with T2D [15,16], preventing alterations in glucose metabolism and hepatic steatosis. The inhibition of SIRTs stops the activation of acetyl-CoA synthetase and therefore the production of acetyl-CoA, a precursor of fatty acids associated with steatosis. A study by our group showed that NAM supplementation decreased oxidative stress and lipid accumulation by modulating glucose 6-phosphate dehydrogenase (G6PD) activity in 3 T3-L1 adipocytes grown with high glucose [17]. Furthermore, NAM decreased lipid synthesis and improved antioxidant systems and steatosis in the livers of rats that consumed sucrose or fructose [12]. Recently, we reported that NAM improved nonalcoholic steatohepatitis, preventing lipid accumulation, the inflammatory response and oxidative stress in rats supplemented 40% fructose [18].
The purpose of this study was to evaluate whether NAM attenuates increases in AChE and BChE activities, improving anti-inflammatory cholinergic signaling and decreasing risk parameters for MetS.
Section snippets
Materials
The chemicals used in this study were purchased from Sigma (St. Louis, MO, USA). An RNeasy isolation kit (Qiagen, Valencia, California, USA), TriPure isolation reagent (Roche, Indianapolis, USA), a First Strand cDNA Synthesis Kit (Thermo Scientific, Massachusetts), Fast Start DNA Master SYBR Green Plus (Roche, Mannheim, Germany), polyvinylidene fluoride (PVDF) membranes (Merck Millipore, Bedford, MA, USA), protease inhibitor (GenDEPOT, Houston, Texas, USA), a rat insulin ELISA kit (ALPCO, New
Fructose induces MetS by altering some biochemical and anthropometric parameters
The sustained consumption of fructose produces caloric overload, leading to weight gain, increased TGs and VLDL levels and blood pressure, and decreased HDL levels; these changes can be used to confirm the presence of MetS.
Compared with the control group, the MetS group showed a 20% weight gain and the highest increases in TGs (20%), VLDL (24%) and systolic and diastolic pressure (15 and 18%, respectively) among treatment groups, which occurred in parallel with a decrease in HDL (30%).
Discussion
The present study shows that the excessive consumption of fructose triggers biochemical, anthropometric and hemodynamic alterations characteristic of MetS and the increased activity of serum and liver BChE and AChE. NAM was shown to prevent or mitigate these changes induced by MetS. Based on molecular modeling studies, we suggest that NAM interacts directly with cholinesterase to inhibit its activity.
Various characteristics of MetS, such as weight gain and increases in TGs, FFA and blood
Conclusion
Our in vivo analysis supports a model defining NAM as a modulator of both cholinesterases, contributing to improved anti-inflammatory and vasodilatory cholinergic pathways by attenuating ACh degradation in fructose-induced metabolic syndrome.
The following is the supplementary data related to this article.
Acknowledgments
The research was funded by Fondo de Investigación en Salud, Instituto Mexicano del Seguro Social (FIS/IMSS/PROT/GH-2/1738). And to CONACyT for granting me the scholarship with registration number 570363 and No. CVU 634838.
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