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Introduction and Aim: The use of aspirin is a potential protective factor against the development of hepatocellular carcinoma (HCC). Therefore, we conducted a meta-analysis to evaluate the contribution of aspirin to the risk of HCC. Methods:We searched for PubMed and EMBASE through September 2021.Results: Eighteen studies (16 cohort, 2 case-control) were included. Aspirin users were less likely to develop HCC than nonusers [adjusted odds ratio (OR), 0.54; 95% confidence interval (CI): 0.44-0.66]. Stratified analysis showed that aspirin reduced the risk of HCC in Asian and Western populations (OR, 0.59 vs. 0.67). Besides, aspirin has protective effects against HCC after hepatitis B virus (OR, 0.70; 95% CI: 0.52-0.93) and hepatitis C virus infections (OR, 0.41; 95% CI: 0.23-0.73). Aspirin has protective effects on people with chronic liver disease (OR, 0.46; 95% CI: 0.31-0.67) and on the general population (OR, 0.65; 95% CI: 0.54-0.79). In addition, confounding factors have an important impact on the results of aspirin prevention of liver cancer before (OR, 0.28; 95% CI: 0.06-1.27) and after (OR, 0.58; 95% CI: 0.47-0.71) adjustment. Further studies have shown that those in the long duration group do not experience better effects in preventing HCC (OR, 0.62 vs. 0.63). A further meta-analysis of 3 articles showed that the use of aspirin did not increase the risk of bleeding in patients with HCC (OR, 1.19; 95% CI: 0.87-1.64). Conclusion:Our meta-analysis shows that the use of aspirin is associated with a lower risk of liver cancer.

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The catalytic transformation of N 2 to NH 3 by transition metal complexes is of great interest and importance but has remained a challenge to date. Despite the essential role of vanadium in biological N 2 fixation, welldefined vanadium complexes that can catalyze the conversion of N 2 to NH 3 are scarce. In particular, a V(N x H y ) intermediate derived from proton/electron transfer reactions of coordinated N 2 remains unknown. Here, we report a dinitrogen-bridged divanadium complex bearing POCOP (2,6-( t Bu 2 PO) 2 -C 6 H 3 ) pincer and aryloxy ligands, which can serve as a catalyst for the reduction of N 2 to NH 3 and N 2 H 4 . Low-temperature protonation and reduction of the dinitrogen complex afforded the first structurally characterized neutral metal hydrazido(2−) species ([V]�NNH 2 ), which mediated 15 N 2 conversion to 15 NH 3 , indicating that it is a plausible intermediate of the catalysis. DFT calculations showed that the vanadium hydrazido complex [V]�NNH 2 possessed a N−H bond dissociation free energy (BDFE N−H ) of as high as 59.1 kcal/mol. The protonation of a vanadium amide complex ([V]−NH 2 ) with [Ph 2 NH 2 ][OTf] resulted in the release of NH 3 and the formation of a vanadium triflate complex, which upon reduction under N 2 afforded the vanadium dinitrogen complex. These transformations model the final steps of a vanadium-catalyzed N 2 reduction cycle. Both experimental and theoretical studies suggest that the catalytic reaction may proceed via a distal pathway to liberate NH 3 . These findings provide unprecedented insights into the mechanism of N 2 reduction related to FeV nitrogenase.

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