Radioprotective effect of N-acetylcysteine in vitro using the induction of DNA breaks as end-point

N-acetylcysteine (NAC) in neurological disorders: mechanisms of action and therapeutic opportunities

BACKGROUND

There is an expanding field of research investigating the benefits of medicines with multiple mechanisms of action across neurological disorders. N-acetylcysteine (NAC), widely known as an antidote to acetaminophen overdose, is now emerging as treatment of vascular and nonvascular neurological disorders. NAC as a precursor to the antioxidant glutathione modulates glutamatergic, neurotrophic, and inflammatory pathways.

AIM AND DISCUSSION

Most NAC studies up to date have been carried out in animal models of various neurological disorders with only a few studies completed in humans. In psychiatry, NAC has been tested in over 20 clinical trials as an adjunctive treatment; however, this topic is beyond the scope of this review. Herein, we discuss NAC molecular, intracellular, and systemic effects, focusing on its potential applications in neurodegenerative diseases including spinocerebellar ataxia, Parkinson's disease, tardive dyskinesia, myoclonus epilepsy of the Unverricht-Lundbor type as well as multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease.

CONCLUSION

Finally, we review the potential applications of NAC to facilitate recovery after traumatic brain injury, cerebral ischemia, and in treatment of cerebrovascular vasospasm after subarachnoid hemorrhage.

N-acetylcysteine ameliorates γ-radiation-induced deterioration of bone quality in the rat femur

This animal study evaluated the radioprotective effects of N-acetylcysteine (NAC) and amifostine on the biomechanical properties of bone in Wistar albino rats of both genders. The rats were randomly divided into four groups of eight: a control group (C); a group given a single dose of 40 Gy of γ-irradiation (R); a group given γ-irradiation plus 200 mg/kg amifostine (R + amifostine); and a group given γ-irradiation plus 1000 mg/kg NAC (R + NAC). Extrinsic and intrinsic properties of bone, bone mineral density (BMD) and the cross-sectional area of the femoral shaft were determined. The cross-sectional area was significantly higher in the R + NAC and R + amifostine groups compared with the R and C groups. The BMD, maximum load and stiffness were also significantly higher in the R + NAC and R + amifostine groups than in the R group, and energy absorption capacity was higher in the R + NAC group than in the R group. These findings indicate that NAC and amifostine preserve bone quality in rats exposed to γ-irradiation.

Effect of N-acetylcysteine on radiation-induced genotoxicity and cytotoxicity in rat bone marrow

The aim of this study is to evaluate the potential radioprotective effects of N-acetylcysteine (NAC) against genotoxicity and cytotoxicity. The effect of WR-2721, as a representative of clinically used radioprotector, was compared with that of NAC, using the chromosomal aberration (CA) and micronucleus (MN) test systems in the irradiated rat's femoral bone marrow cells. We also investigated the mitotic index (MI), and the ratio of polychromatic erythrocytes (PCEs) to normochromatic erythrocytes (NCEs). The rats (n = 16) were divided randomly and equally into four groups: Control (C), Radiation (R), R+NAC (received irradiation and 1000 mg/kg NAC) and R+WR-2721 (received irradiation and 200 mg/kg WR-2721) rats. All the irradiated groups received whole-body gamma irradiation as a single dose of 6 Gy. Group R showed higher CA and MN formation when compared to C. Group R showed higher frequency of MN formation when compared to both R+NAC and R+WR-2721. The mean MI and PCE/NCE ratios were lower in Group R when compared to those of Group C. The mean MI and PCE/NCE ratios of both R+NAC and R+WR-2721 groups were lower when compared to those of Group C. The MI in Group R was lower when compared to that of both R+NAC and R+WR-2721 groups. In this study, the results give clues about the beneficial effects of NAC against radiation-induced genotoxicity and cytotoxicity in rat bone marrow and its effect may be comparable to that observed for WR-2721.

Influence of different radioprotective compounds on radiotolerance and cell cycle distribution of human progenitor cells of granulocytopoiesis in vitro

Ficoll-separated mononuclear cells (MNC) of cryopreserved human bone marrow were incubated with isotoxic doses of diltiazem, N-acetylcysteine (NAC), glycopolysaccharide extract of spirulina platensis (SPE), tempol, thiopental, WR2721 and WR1065. After irradiation with a single dose of 0.73 Gy, survival of granulocyte/macrophage colony-forming cells (GM-CFC) was determined at d 10-14, using an agar culture system. Diltiazem, NAC, tempol and WR1065 significantly improved radiotolerance with protection factors (PF) between 1.21 and 1.36 (n = 5, P < 0.05) at 0.73 Gy (PF-0.73 Gy). The survival curves of diltiazem (D0 = 0.88 Gy, n = 1.00), NAC (D0 = 0.92 Gy, n = 1.10), tempol (D0 = 0.99 Gy, n = 1.10), WR1065 (D0 = 0.89 Gy, n = 1.16) and control (D0 = 0.78 Gy, n = 1.00) over 0.36-2.91 Gy showed a significant radioprotective effect for D0 only for tempol (P = 0.018) and for the extrapolation number 'n' only in the case of NAC (P = 0.023). Cell cycle analysis of the CD34+ cell subpopulation (control-0 h: G1 = 82.7%, S = 13.7%, G2/M = 3.6%) revealed that all compounds with a significant PF-0.73 Gy also caused a significant increase in CD34+ cells in S phase up to 48 h. Within the first 24 h, only NAC (26.7 +/- 4.1%), tempol (14.3 +/- 1.0%) and possibly WR1065 (15.5 +/- 1.6%) had higher fractions of CD34+ S-phase cells compared with controls. This observation and the improvement of GM-CFC cloning efficiency indicated that only NAC was able to recruit progenitor cells in the cell cycle, whereas tempol and WR1065 possibly inhibited cell cycle progression by S and G2/M arrest. Of the radioprotectors tested, NAC, tempol and WR1065 may be suitable to support, alone or combined with cytokine therapy, accelerated haematopoietic recovery after irradiation.

The role of N-acetylcysteine as a putative radioprotective agent on X-ray-induced DNA damage as evaluated by alkaline single-cell gel electrophoresis

Samples of human whole blood from 8 different donors were incubated with physiological saline or N-acetyl-L-cysteine (NAC, 1 x 10(-3) M) before being irradiated in vitro with high-energy X-rays (0.7 or 2.0 Gy). Primary DNA damage was evaluated in isolated lymphocytes using alkaline single-cell gel electrophoresis. Whereas the lymphocytes from non-irradiated blood samples showed a similar 'background level' of damage, there was a difference in sensitivity towards the radiation-induced DNA damage, especially at 2.0 Gy. When the data were pooled there was a clear and dose-related increase (p < 0.001) in damage, both in the absence and presence of NAC. Using the two most sensitive 'comet parameters' for DNA damage, i.e., the tail inertia and tail moment, the radiation-induced damage was found to be significantly increased already at 0.7 Gy in the samples that had been irradiated without NAC. Overall, NAC was found to be without radioprotective effects. Instead, the incubation with NAC itself was found to be associated with a slightly increased level of DNA damage. If the present findings are relevant also in an in vivo situation using peripheral lymphocytes as a surrogate for non-malignant cells in the body, NAC seems to be of limited value as a radioprotective agent in the clinic, at least when it comes to the acute DNA-damaging effects of therapeutic doses of high-energy X-rays.

Catecholamines enhance dihydrolipoamide dehydrogenase inactivation by the copper Fenton system. Enzyme protection by copper chelators

Catecholamines (CAs: epinephrine, norepinephrine, dopamine, L-DOPA, 6-hydroxydopamine) and o-diphenols (DOPAC and catechol) enhanced dihydrolipoamide dehydrogenase (LADH) inactivation by Cu(II)/H2O2 (Cu-Fenton system). The inhibition of LADH activity correlated with Cu(II), H2O2 and CA concentrations. Similar inhibitions were obtained with the assayed CAs and o-diphenols. CAs enhanced HO. radical production by Cu(II)/H2O2, as demonstrated by benzoate hydroxylation and deoxyribose oxidation; LADH counteracted the pro-oxidant effect of CAs by scavenging hydroxyl radicals. Captopril, dihydrolipoamide, dihydrolipoic acid, DL-dithiothreitol, GSSG, trypanothione and histidine effectively preserved LADH from oxidative damage, whereas N-acetylcysteine, N-(2-mercaptopropionylglycine) and lipoamide were less effective protectors. Catalase (though neither bovine serum albumin nor superoxide dismutase) protected LADH against the Cu(II)/H2O2/CAs systems. Denatured catalase protected less than the native enzyme, its action possibly depending on Cu-binding. LADH increased and Captopril inhibited epinephrine oxidation by Cu(II)/H2O2 and Cu(II). The summarized evidence supports the following steps for LADH inactivation: (1) reduction of LADH linked-Cu(II) to Cu(I) by CAs; (2) production of HO. from H2O2 by LADH-linked Cu(I) (Haber-Weiss reaction) and (3) oxidation of aminoacid residues at the enzyme active site by site-specifically generated HO. radicals. Hydrogen peroxide formation from CAs autoxidation may contribute to LADH inactivation.