Aims: To examine the cytoprotective effects and mechanisms of a royal jelly extract in protecting the human umbilical vein endothelial cells (HUVECs) from nicotine toxicity.

Study Design: Laboratory experimental tests.

Place and Duration of Study: Department of Physiology and Department of Surgery, Faculty of Medicine, Srinakharinwirot University, Bangkok 10110, Thailand, between June 2011 and February 2012.

Methodology: Cytotoxic assay of royal jelly to HUVECs was performed by using the 3-(4,5-dimethylthiazol,2-yl)-2,5-diphenyltetrazolium bromide (MTT) reagent. The cytoprotective effect was then investigated by examining the presence of vacuole-like structures in HUVECs exposed to nicotine 5 or 7.5 mM with and without royal jelly. Cells were stained with crystal violet and photographed under phase contrast microscope. mRNA levels of genes involved in intracellular antioxidant system, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GSR) were confirmed by reverse transcription-polymerase chain reaction (RT-PCR). Catalase activity was also determined by examining peroxidative function.

Results: Vacuole-like structures were found in the cytoplasm of HUVECs exposed to 5 mM nicotine and higher. Royal jelly alone at the concentrations lower than 2 mg/ml did not affect the structure or the survival rate of HUVECs after 1, 4, and 7 days of treatment. For cytoprotective effect, royal jelly 1-4 mg/ml mixed with 5 mM nicotine could obviously decrease the numbers of cells containing vacuole-like structures in the cytoplasm of HUVECs with the dose- and time-dependent fashion. The catalase mRNA levels and catalase activity in HUVECs exposed to 5 mM nicotine decreased significantly, but recovered when the cells were treated with royal jelly.

Conclusion: Royal jelly can be safety applied to endothelial cells even at high doses. Royal jelly is able to attenuate the abnormal vacuole-like structures induced in endothelial cell cytoplasm when exposed to nicotine. Further investigation of antioxidant gene expression showed that the mechanism possibly involves a reduction of oxidative stress via an up-regulation of catalase. Besides the supplementary food, royal jelly could be useful for endothelial cell protection from nicotine toxicity found in smoking or nicotine addiction.