NMN partially rescues cuproptosis by upregulating sirt2 to increase intracellular NADPH.

Cuproptosis is characterized by lipoylated protein aggregation and loss of iron-sulfur (Fe-S) proteins, which are crucial for a wide range of important cellular functions, including DNA replication and damage repair. Sirt2 and sirt4 are lipoamidases that remove the lipoyl moiety from lipoylated proteins using nicotinamide adenine dinucleotide (NAD+) as a cofactor. However, to date, it is not clear whether nicotinamide mononucleotide (NMN), a precursor of NAD+, affects cellular sensitivity to cuproptosis. Therefore, in the current study, cuproptosis was induced by the copper (Cu) ionophore elesclomol (Es) in HeLa cells. It was also found that Es/Cu treatment increased cellular DNA damage level. On the other hand, NMN treatment partially rescued cuproptosis in a dose-dependent manner, as well as reduced cellular DNA damage level. In addition, NMN upregulated the expression of Fe-S protein POLD1, without affecting the aggregation of lipoylated proteins. Mechanistic study revealed that NMN increased the expression of sirt2 and cellular reduced nicotinamide adenine dinucleotide phosphate (NADPH) level. Overexpression of sirt2 and sirt4 did not change the aggregation of lipoylated proteins, however, sirt2, but not sirt4, increased cellular NADPH levels and partially rescued cuproptosis. Inhibition of NAD+ kinase (NADK), which is responsible for generating NADPH, abolished the rescuing function of NMN and sirt2 for Es/Cu induced cell death. Taken together, our results suggested that DNA damage is a characteristic feature of cuproptosis. NMN can partially rescue cuproptosis by upregulating sirt2, increase intracellular NADPH content and maintain the level of Fe-S proteins, independent of the lipoamidase activity of sirt2.

Protective effects of nicotinamide mononucleotide on ethanol-induced DNA damage in L02 cells / 预防医学

Objective@#To investigate protective effects of nicotinamide mononucleotide (NMN) on ethanol-induced DNA damage in L02 cells, so as to provide the evidence for adjuvant therapy of NMN on alcoholic liver diseases.@*Methods@#L02 cells were pretreated with different concentrations of NMN (0, 1, 2, 4 and 8 mmol/L) for 6 h, and then were exposed to 0.4% ethanol for 12 h. The treated cells were divided into the control group, 0.4% ethanol group and different concentrations of NMN groups. Cell viability was analyzed using trypan blue staining for determining the concentration of NMN as a protective agent. The effects of NMN on ethanol-induced DNA damage in L02 cells were evaluated using immunofluorescence detection and reactive oxygen species (ROS) assay. L02 cells were exposed to 0.4% ethanol for 12 h, cultured in a medium containing a protective concentration of NMN, and divided into PBS group and NMN group. Cell viability was detected at 0, 2, 4, 8, 16 and 32 h, and the effects of NMN on repairing ethanol-induced DNA damage were evaluated by alkaline comet assay.@*Results@#The cell viability was lower in 0.4% ethanol group than than in the control group, and was higher in different concentrations of NMN groups than in 0.4% ethanol group (all P<0.05), with no significant difference in the cells viability between 4 mmol/L and higher concentrations of NMN groups and the control group (all P>0.05). Therefore, 4 mmol/L NMN was selected as a protective agent. The cell tail moments, relative immunofluorescence intensities of γH2AX and relative levels of ROS were higher in 0.4% ethanol group than in the control group, and lower in 4 mmol/L and higher concentrations of NMN groups than in 0.4% ethanol group (all P<0.05). The cell viability was increased and the cell tail moment was shortened with the increase of 4 mmol/L NMN intervention time; and the cell viability in 4 h and more of NMN groups were higher, and the cell tail moment were lower than that in PBS group (all P<0.05).@*Conclusions@#NMN attenuates DNA damage in a dose-dependent manner and promotes the repair of DNA damage in a time-dependent manner. NMN has a protective effect on ethanol-induced DNA damage in hepatocytes.