Trends and Developments in Radioprotection: The Effect of Nicotinamide on DNA Repair

Abstract

Recent studies point to the naturally occurring molecules in expression of radiation damage and in protection. DNA repair was shown to be one of the parameters that can be modified to attain improved protection. The need for a natural compound that can enhance DNA repair in order to improve cellular protection focused our attention on nicotinamide (NA). The effects of addition of NA, a precursor for NAD+ synthesis, on the DNA repair capacity following gamma and ultraviolet irradiations were studied in several repair-proficient and repair-deficient cell lines. The addition of low concentrations of NA (less than 3 mM) resulted in increased repair synthesis in the repair-proficient cells. Addition to repair-deficient cells resulted in decreased repair synthesis. Cells which repair damage from one type of radiation, and not from another, responded accordingly to the presence of NA. However, addition of high concentrations of NA to repair-proficient cells resulted in decreased repair synthesis. Thus, nicotinamide can improve the repair capacity in a concentration-dependent manner, but it clearly requires the existence of functional repair processes.

Radioprotection byRhodiola imbricatain Mice Against Whole-Body Lethal Irradiation

“…It has often been observed that medicinal plants offer effective radioprotection at doses that are quite close to the MTD. 26,27 Contrary to this, RD-I or RD-II exhibited distinctly safe margins, which is revealed by the maximum therapeutic gain achieved in comparison with different plant extracts, investigated in our laboratory ( Table 2). This could have far-reaching implications from the point of view of development of a radioprotector for clinical applications.…”

Augmentation of Antioxidant Defense System by Tinospora cordifolia: Implications in Radiation Protection

“…2A). Our results counter earlier reports by Uma et al (1999) and Riklis et al (1990) that stated that a radioprotective agent renders its maximum effect when administered a little below the maximum tolerable dose. RTp treatment increased LD 50/30 value and the DRF was computed as 1.43 (Fig.…”

Role of Nicotinamide in DNA Damage, Mutagenesis, and DNA Repair

“…PARP-1 inhibition by nicotinamide in vitro has been reported to delay the rejoining of DNA strand breaks [95, 114, 115], induce UDS [95, 97, 116], and increase the frequency of spontaneous SCE [117, 118]. It has been suggested that high dose of nicotinamide (5 mM or more) inhibits DNA repair through PARP-1 inhibition while low dose nicotinamide enhances rejoining of DNA strand breaks through provision of NAD + [114]. However, it is argued that nicotinamide is unlikely to inhibit PARP in vivo [119].…”