Abstract
BackgroundThe interaction between ionizing radiation and substances in cells will induce the production of free radicals. These free radicals inflict damage to important biomolecules such as chromosomes, proteins and lipids which consequently trigger the expression of genes which are involved in protecting the cells or repair the oxidative damages. Honey has been known for its antioxidant properties and was used in medical and cosmetic products. Currently, research on honey is ongoing and diversifying. The aim of this study was to elucidate the role of Gelam honey as a radioprotector in human diploid fibroblast (HDFs) which were exposed to gamma-rays by determining the expression of genes and proteins involved in cell cycle regulation and cell death.MethodsSix groups of HDFs were studied viz. untreated control, irradiated HDFs, Gelam honey-treated HDFs and HDF treated with Gelam honey pre-, during- and post-irradiation. HDFs were treated with 6 mg/ml of sterilized Gelam honey (w/v) for 24 h and exposed to 1 Gray (Gy) of gamma-rays at the dose rate of 0.25 Gy/min.ResultsOur findings showed that, gamma-irradiation at 1 Gy up-regulated ATM, p53, p16ink4a and cyclin D1 genes and subsequently initiated cell cycle arrest at G0/G1 phase and induced apoptosis (p < 0.05). Pre-treatment with Gelam honey however caused down regulation of these genes in irradiated HDFs while no significant changes was observed on the expression of GADD45 and PAK genes. The expression of ATM and p16 proteins was increased in irradiated HDFs but the p53 gene was translated into p73 protein which was also increased in irradiated HDFs. Gelam honey treatment however significantly decreased the expression of ATM, p73, and p16 proteins (p < 0.05) while the expression of cyclin D1 remained unchanged. Analysis on cell cycle profile showed that cells progressed to S phase with less percentage of cells in G0/G1 phase with Gelam honey treatment while apoptosis was inhibited.ConclusionGelam honey acts a radioprotector against gamma-irradiation by attenuating radiation-induced cell death.
Highlights
The interaction between ionizing radiation and substances in cells will induce the production of free radicals
Cell cycle progression Analysis on cell cycle profile showed that human diploid fibroblast (HDFs) population in Go/G1 phase was significantly decreased while S phase and G2/M phase cells increased in irradiated and Gelam honey-treated HDFs as compared to untreated control HDFs (Figure 1A, 1B) (p < 0.05)
Irradiated HDFs pre-treated with Gelam honey or treated with Gelam honey during irradiation showed decreased percentage of cells in G0/G1 phase with significant increased in S phase cells as compared to irradiated HDFs (p < 0.05) without Gelam honey treatment
Summary
The interaction between ionizing radiation and substances in cells will induce the production of free radicals These free radicals inflict damage to important biomolecules such as chromosomes, proteins and lipids which trigger the expression of genes which are involved in protecting the cells or repair the oxidative damages. Ionizing radiation is known to cause DNA damage which leads to cell cycle arrest at G0/G1 phase. The G1 phase is critical for cells to get ready for DNA synthesis at S phase [1], while at G2 phase cells make final preparation before division during mitosis [2] Defects in both phases may allow cells with damaged DNA to enter mitosis phase. Two discrete cell cycle checkpoints are present at G1/S or G2/M phases Upon radiation exposure, these checkpoints will be activated which provides time for DNA repair and thereby promote genomic stability [3]. The DNA damage is irreparable and cells will either enter a permanent growth arrest at G0 phase [4] or undergo apoptosis [5]
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