Impact of microwave irradiation on enzymatic activity at constant bulk temperature is enzyme-dependent

Anomalously Large Heat Generation of Hydration Water under Microwave Irradiation

Much attention has been paid to the biological effects of microwave irradiation. The hydration water surrounding a biomolecule is crucial in its biological reactions and functions. Therefore, it is important to know the response of hydration water to microwaves to understand their biological effects; however, the scarcity of studies about it often leads to speculations and debates about that effect. In this study, we have made real-time temperature measurements of reverse micellar solutions with their water droplet size from ∼2.3 to ∼9.5 nm using a waveguide system combined with a microwave generator at 2.45 GHz. The heat generated by water in reverse micelles has been observed to depend on their size. It is about 10 times larger than that of liquid water at their small sizes (<∼3.5 nm) and diminishes with further enlarging the size, approaching the water's value at their large sizes (∼10 nm). These results indicate that the heat generation behavior has an interfacial effect; specifically, the hydration water on the surfactant layer produces heat 10 times larger than bulk water. Moreover, the hydration number per surfactant molecule decreases in a core-shell model with increasing the reverse micelle size. These features are also reflected in the heat generation rate. Our findings may offer a new and fundamental perspective for studies on the biological effects of microwave irradiation.

Exposure to microwave irradiation at constant culture temperature slows the growth ofEscherichia coliDE3 cells, leading to modified proteomic profiles

E. coligrowth is slowed by exposure to non-lethal microwave irradiation, accompanied by changes in proteomic profiles.

Intervention of transglutaminase in surimi gel under microwave irradiation

Transglutaminase (TGase) was selected as model enzyme to investigate the effects of microwave (MW) heating on its activity and structure compared to water bath (WB) heating. MW heating can enhance the activity of TGase and reach the maximum at 20 min, whereas conduction heating has little effect on the activity of TGase. The difference of dielectric properties between MW heating and WB heating were not obvious, but MW heating had higher conductivity than WB heating. The results of ultraviolet and fluorescence spectra show that MW heating can change the enzyme activity by changing the conformation of TGase. The decrease of α-helix and an increase of β-sheet and β-turn investigated by circular dichroism (CD) indicated the secondary structures of TGase were changed when treated by MW heating. Further gel properties test confirmed that TGase treated by MW could improve the functional and mechanical properties of surimi gel.

Microwave-assisted delivery of an anticancer drug to cancer cells

Exposure of MCF-7 breast and PC-3 prostate cancer cells to 10 W microwaves at 2.45 GHz increased their uptake of the cancer drug doxorubicin from media by almost 100%, concomitantly increasing cell death, while microwave exposure alone had no cellular toxicity. Addition of inhibitors of endocytosis during the treatment of MCF-7 cells with doxorubicin and microwaves showed no impact on the uptake of the anticancer drug. Furthermore, the uptake of oligonucleotides by MCF-7 cells is not affected by the treatment with microwaves. These observations suggest that endocytosis is not involved in the uptake of doxorubicin while cells are exposed to microwave irradiation. Thus, targeted low power microwave irradiation could be a safe and effective means of promoting chemotoxin delivery to cancer cells, potentially reducing the dosages and side effects of anti-cancer drugs.

Exposure of MCF-7 breast and PC-3 prostate cancer cells to 10 W microwaves at 2.45 GHz increased their uptake of doxorubicin from media by almost 100%, concomitantly increasing cell death, while microwave exposure alone had no cellular toxicity.