Date Published: January 23, 2012
Publisher: Public Library of Science
Author(s): Yung-Ho Hsu, Yen-Cheng Chen, Tso-Hsiao Chen, Yuh-Mou Sue, Tzu-Hurng Cheng, Jia-Rung Chen, Cheng-Hsien Chen, Carlo Gaetano. http://doi.org/10.1371/journal.pone.0030674
Many studies suggest that far-infrared (FIR) therapy can reduce the frequency of some vascular-related diseases. The non-thermal effect of FIR was recently found to play a role in the long-term protective effect on vascular function, but its molecular mechanism is still unknown. In the present study, we evaluated the biological effect of FIR on vascular endothelial growth factor (VEGF)-induced proliferation in human umbilical vein endothelial cells (HUVECs). We found that FIR ranging 3∼10 µm significantly inhibited VEGF-induced proliferation in HUVECs. According to intensity and time course analyses, the inhibitory effect of FIR peaked at an effective intensity of 0.13 mW/cm2 at 30 min. On the other hand, a thermal effect did not inhibit VEGF-induced proliferation in HUVECs. FIR exposure also inhibited the VEGF-induced phosphorylation of extracellular signal-regulated kinases in HUVECs. FIR exposure further induced the phosphorylation of endothelial nitric oxide (NO) synthase (eNOS) and NO generation in VEGF-treated HUVECs. Both VEGF-induced NO and reactive oxygen species generation was involved in the inhibitory effect of FIR. Nitrotyrosine formation significantly increased in HUVECs treated with VEGF and FIR together. Inhibition of phosphoinositide 3-kinase (PI3K) by wortmannin abolished the FIR-induced phosphorylation of eNOS and Akt in HUVECs. FIR exposure upregulated the expression of PI3K p85 at the transcriptional level. We further found that FIR exposure induced the nuclear translocation of promyelocytic leukemia zinc finger protein (PLZF) in HUVECs. This induction was independent of a thermal effect. The small interfering RNA transfection of PLZF blocked FIR-increased PI3K levels and the inhibitory effect of FIR. These data suggest that FIR induces the nuclear translocation of PLZF which inhibits VEGF-induced proliferation in HUVECs.
Infrared radiation is invisible electromagnetic radiation, the wavelength of which is longer than that of visible light. According to differences in wavelength, the International Commission on Illumination (CIE) recommends dividing infrared radiation into the following three bands: near-infrared radiation (IR-A: 0.7∼1.4 µm), middle-infrared radiation (IR-B: 1.4∼3 µm), and far-infrared (FIR) radiation (IR-C: 3∼1000 µm). FIR therapy has the potential to improve endothelial function and reduce the frequency of some vascular-related diseases –. Recently, a clinical study evaluated the effect of FIR therapy on 145 hemodialysis (HD) patients with a native arteriovenous fistula (AVF), and found that FIR therapy improved inadequate access flow and survival of the AVF in HD patients through both thermal and non-thermal effects . That study revealed that the non-thermal effects of FIR played a role in the long-term protective effect on vascular function.
Based on our results, the FIR exposure at 0.13 mW/cm2 for 30 min achieved the maximum inhibitory effect of FIR on VEGF-induced proliferation in HUVECs. A higher FIR intensity or longer exposure time was unable to increase the inhibitory effect of FIR. FIR exposure also reduced VEGF-induced ERK1/2 phosphorylation, and increased the phosphorylation of eNOS. Applications of the NOS inhibitor and ROS scavengers showed that the inhibition effect of FIR was associated with eNOS-mediated NO and VEGF-induced ROS. Although FIR exposure usually accompanies thermal transmission, we found thermal pretreatments slightly increased VEGF-induced proliferation in HUVECs. The thermal effect of 38 or 39°C did not influence phosphorylation levels of ERK1/2 or eNOS. Compared to the influence of FIR on the eNOS signaling pathway, these results show that the biological effects of FIR in HUVECs do not result from a thermal effect. Moreover, we found that FIR exposure induced the nuclear translocation of PLZF which increased PI3K expression. This PI3K increase activated Akt which phosphorylated eNOS to generate NO in HUVECs. Pretreatment at 38 or 39°C did not induce PLZF translocation. Therefore, a non-thermal effect of FIR inhibits VEGF-induced proliferation via PLZF activation.