Protective effect of Zingiber zerumbet Smith extract on thermotolerance
Background: Global warming causes severe heat conditions. Heat stress contributes to higher morbidity of heatstroke in human and mortality in livestock. To protect them from heat stress, thermotolerance mechanisms were widely studied, and some studies suggest relationship between heat shock proteins (HSPs) and thermotolerance. HSPs were not induced by only heat shock but also some stimulations including bioactive compounds from plants. Zingiber zerumbet is a perennial herb found in many tropical countries, including Thailand. The rhizome of Zingiber zerumbet contains zerumbone that is a bioactive compound to induce HSPs expression in animal cells.
Objective: To prevent higher morbidity of heatstroke in human and mortality in livestock by the heat stress, we investigated the effect of zerumbone, the extract of Zingiber zerumbet Smith, on thermotolerance, using a cell line and mice.
Methods: The murine liver hepatoma cell line, Hepa1c1c7 cells, were incubated in medium supplemented with extract from rhizome of Zingiber zerumbet Simith containing zerumbone, and then the expression of heat shock proteins (HSP) 40, 70 and 90 were investigated by western blotting. Furthermore, we established the evaluation system of thermotolerance using mice, and studied the effect of the extract on the growth rate of mice under the heat shock treatment. Briefly, 4 weeks old C57BL6 mice were fed that with the extract (or vehicle) for a week before the first heat shock treatment (38 °C for an hour). Before and after five days heat treatment, body weights were measured. The protein expressions of heat shock proteins in liver were measured by western blotting using HSPs antibodies.
Results: The extract of Zingiber zerumbet rhizome, equivalent to 50 μM zerumbone, significantly increased the expression of heat shock proteins (HSP40, HSP70, HSP90). The growth rate of the mice under the heat treatment were lower than control. The feeding with the extract containing 25 ppm zerumbone have significantly attenuated the decline of the growth rate led by the heat treatment, whereas there was little effect on mouse growth rate grown under normal conditions. The protein expression of HSP70 in the liver of zerumbone-fed mice was upregulated compared with control mice, equivalent to heat treatment without zerumbone. On the other hand, both treatments of zerumbone and heat resulted in highest HSP70 expression among four groups.
Conclusion: Our study demonstrated that oral administration of the extract of Zingiber zerumbet Smith led to the attenuation of decline of growth rate induced by heat treatment. HSP70 expression in murine liver was enhanced by either feeding the extract or heat treatment. More interestingly, HSP70 expression was further enhanced by both treatments of zerumbone and heat. These results suggested that zerumbone may contribute to thermotolerance via, at least, HSP70 expression.Keywords: Zingiber zerumbet, thermotolerance, heat shock protein
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