Protection with combinations of hydroxytryptophan and some thiol compounds against whole-body gamma irradiation

Safety evaluation of 5-hydroxytryptophan and S-(2-aminoethyl)isothiouronium bromide hydrobromide on rodent lungs

OBJECTIVES

During the past few decades, various compounds have been researched for their potential as radioprotectants, and many of them were found to be safe and effective in several preclinical models. However, many of these compounds were found to have serious adverse effects when evaluated in clinical settings, thereby making them unsuitable for human applications. 5-hydroxytryptophan (5-HTP) and S-(2-aminoethyl) isothiouronium bromide hydrobromide (AET) act in a synergistic fashion to promote radioprotection. The present study primarily emphasizes the safety of fixed dose of 5-HTP + AET in the lungs of C57BL/6 mice, a well-known model used in drug safety studies.

MATERIALS AND METHODS

Post-administration of the combination of HTP+AET at specific time points, blood and bronchoalveolar lavage fluid (BALF) were collected for the analysis of inflammatory and oxidative stress markers of the lungs. Thereafter, the mice were sacrificed and the lungs were dissected out, weighed, and fixed in formalin for histopathological studies.

RESULTS

The inflammatory biomarkers: tumor necrosis factor-alpha and interleukin-10 and oxidative stress biomarkers: 8-isoprostane and 8-hydroxy-2'-deoxyguanosine were found to have normal levels in blood and BALF in both control and treatment groups, which was further supported by normal histological findings. In addition, other endpoints such as food and water intake were found to be within normal limits.

CONCLUSION

The present safety study reflects that the combination has no adverse effects on the lungs of the experimental mouse. Further, evaluation in higher mammals including nonhuman primates is essential prior to validation of the safety of the combination in humans.

Radiation protection of male fertility in mouse and rat by a combination of 5-hydroxy-L-tryptophan and a thiol compound (AET)

Sperm abnormalities and fall in total sperm count following different doses (4 Gy, 5 Gy and 6 Gy) of whole body gamma irradiation (WBGR) were studied in adult male Swiss strain A mice. The protecting ability of a combination of 5-hydroxy-L-tryptophan (5-HTP, 100 mg/kg) and 2-aminoethyl isothiuronium bromide hydrobromide (AET, 20 mg/kg) was also investigated. Pretreatment with a 5-HTP+AET formulation i.p., 30 min before irradiation modified the fall in sperm counts significantly. Exposures to 4 Gy, 5 Gy and 6 Gy WBGR caused marked increase of sperm abnormalities which could be significantly reduced by pretreatment with 5-HTP-AET. WBGR with 4 Gy, 5 Gy and 6 Gy produced a short period of sterility associated with oligospermia but these abnormalities were corrected by pretreatment with 5-HTP+AET. This finding was supported by breeding experiments in pretreated adult male Sprague-Dawley rats which showed delivery of normal offsprings in drug-protected irradiated groups in contrast to irradiated controls.

Radioprotection of peripheral blood cells with a combination of hydroxytryptophan and a thiol compound in mice

Radiation induced changes in peripheral blood cells were studied in male Swiss albino mice after 4 Gy and 10 Gy whole body gamma irradiation with and without pretreatment with 2-amino-ethylisothiuronium bromide hydrobromide (AET) or with a combination of 5-hydroxy-L-tryptophan (5-HTP) and AET. Combination of 5-HTP with AET or AET alone in a high dose achieved excellent protection against both 4 Gy and 10 Gy whole body irradiation as regards peripheral blood cell counts.