Background This meta-analysis was performed to investigate the effects of nicotinamide adenine dinucleotide (NAD+) precursor supplementation on glucose and lipid metabolism in human body. Methods PubMed, Embase, CENTRAL, Web of Science, Scopus databases were searched to collect clinical studies related to the supplement of NAD+ precursor from inception to February 2021. Then the retrieved documents were screened, the content of the documents that met the requirements was extracted. Meta-analysis and quality evaluation was performed detection were performed using RevMan5.4 software. Stata16 software was used to detect publication bias, Egger and Begg methods were mainly used. The main research terms of NAD+ precursors were Nicotinamide Riboside (NR), Nicotinamide Mononucleotide (NMN), Nicotinic Acid (NA), Nicotinamide (NAM). The changes in the levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and fasting blood glucose were mainly concerned. Results A total of 40 articles were included in the meta-analysis, with a sample of 14,750 cases, including 7406 cases in the drug group and 7344 cases in the control group. The results of meta-analysis showed that: NAD+ precursor can significantly reduce TG level (SMD = − 0.35, 95% CI (− 0.52, − 0.18), P < 0.0001), and TC (SMD = − 0.33, 95% CI (− 0.51, − 0.14), P = 0.0005), and LDL (SMD = − 0.38, 95% CI (− 0.50, − 0.27), P < 0.00001), increase HDL level (SMD = 0.66, 95% CI (0.56, 0.76), P < 0.00001), and plasma glucose level in the patients (SMD = 0.27, 95% CI (0.12, 0.42), P = 0.0004). Subgroup analysis showed that supplementation of NA had the most significant effect on the levels of TG, TC, LDL, HDL and plasma glucose. Conclusions In this study, a meta-analysis based on currently published clinical trials with NAD+ precursors showed that supplementation with NAD+ precursors improved TG, TC, LDL, and HDL levels in humans, but resulted in hyperglycemia, compared with placebo or no treatment. Among them, NA has the most significant effect on improving lipid metabolism. In addition, although NR and NAM supplementation had no significant effect on improving human lipid metabolism, the role of NR and NAM could not be directly denied due to the few relevant studies at present. Based on subgroup analysis, we found that the supplement of NAD+ precursors seems to have little effect on healthy people, but it has a significant beneficial effect on patients with cardiovascular disease and dyslipidemia. Due to the limitation of the number and quality of included studies, the above conclusions need to be verified by more high-quality studies.

Antioxidants may provide a complementary treatment for patients with chronic diseases. Nevertheless, studies that have measured the effects of antioxidant on diabetes complications have provided conflicting results. This study aimed to elucidate the association between antioxidant and diabetic complications and to develop robust evidence for clinical decisions by systematic reviews and meta‐analysis. PubMed, Embase, The Cochrane Library, Web of Science, Scopus databases were searched to collect clinical studies related to the efficacy of antioxidants in the treatment of diabetes complications from inception to May 5, 2021. Statistical meta‐analyses were performed using the RevMan 5.4 software. Stata16 software was used to detect publication bias. The data of diabetic nephropathy (DN), diabetic nonalcoholic fatty liver disease (NAFLD), and diabetic periodontitis were collected to analyze the effect of antioxidant on diabetes and the above three complications. The meta‐analysis results showed that antioxidant treatment was associated with significantly changes in the fasting plasma glucose (FPG) (standardized mean difference [SMD]: − 0.21 [95% confidence interval [CI]: − 0.33, −0.10], p < 0.001), hemoglobin A1c (HbA1c) (MD: − 0.41 [95% CI: − 0.63, −0.18], p < 0.001), total antioxidant capacity (TAC) (SMD: 0.44 [95% CI: 0.24, 0.63], p < 0.001) and malondialdehyde (MDA) (SMD: − 0.82 [95% CI: − 1.24, −0.41], p < 0.001) than the control group. Antioxidant supplements have the potential to treat three complications of diabetes. In conclusion, the meta‐analysis results indicate that antioxidant treatment is effective clinically for diabetes mellitus and its complications.

Scope Obesity is a global threat for male infertility, which can cause spermatogenic dysfunction. However, there are no available drugs for the treatment of obesity‐induced spermatogenesis dysfunction. This study characterizes the protective effects of icariin (ICA) on spermatogenesis dysfunction in obese mice. Methods and results Obese mice are induced by a high‐fat diet to determine whether ICA has a protective effect. ICA treatment reduces body weight and the proportion of abnormal sperm, brings about a recovery of sperm count, and the number of spermatogenic cells. ICA treatment improves histopathological changes of the testes and inhibits testicular apoptosis, as evidenced by reduced the expression of Bax and increased the expression of Bcl‐2, PCNA, WT1, GATA‐4, vimentin, HK2, PKM2, and LDHA in the testes. In vitro, TM4 cells are treated with 0.4 mm palmitic acid (PA) to induce Sertoli cell injury, and are then utilized for ICA treatment. ICA improves PA‐induced decreased TM4 cells viability, reduces the levels of lactate, and increases the levels of pyruvate and the expression of HK2, PKM2, and LDHA and restores the glycolytic process in vitro. Conclusion ICA ameliorates spermatogenic dysfunction in obese mice by regulating glycolytic activity, providing effective strategies for obesity treatment.

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