Far-Infrared-Emitting Sericite Board Upregulates Endothelial Nitric Oxide Synthase Activity through Increasing Biosynthesis of Tetrahydrobiopterin in Endothelial Cells

Abstract

Far-infrared ray (FIR) therapy has been reported to exert beneficial effects on cardiovascular function by elevating endothelial nitric oxide synthesis (eNOS) activity and nitric oxide (NO) production. Tetrahydrobiopterin (BH₄) is a key determinant of eNOS-dependent NO synthesis in vascular endothelial cells. However, whether BH₄ synthesis is associated with the effects of FIR on eNOS/NO production has not yet been investigated. In this study, we investigated the effects of FIR on BH₄-dependent eNOS/NO production and vascular function. We used FIR-emitting sericite boards as an experimental material and placed human umbilical vein endothelial cells (HUVECs) and Sprague-Dawley rats on the boards with or without FIR irradiation and then evaluated vascular relaxation by detecting NO generation, BH₄ synthesis, and Akt/eNOS activation. Our results showed that FIR radiation significantly enhanced Akt/eNOS phosphorylation and NO production in human endothelial cells and aorta tissues. FIR can also induce BH₄ storage by elevating levels of enzymes (e.g., guanosine triphosphate cyclohydrolase-1, 6-pyruvoyl tetrahydrobiopterin synthase, sepiapterin reductase, and dihydrofolate reductase), which ultimately results in NO production. These results indicate that FIR upregulated eNOS-dependent NO generation via BH₄ synthesis and Akt phosphorylation, which contributes to the regulation of vascular function. This might develop potential clinical application of FIR to treat vascular diseases by augmenting the BH₄/NO pathway.

Figure 1

FIR radiation stimulates Akt/eNOS phosphorylation and NO production in HUVECs. (a) Cellular NO levels were measured with FIR emitting sericite board for 0, 24, 48, and 72 hours. (b) Phosphorylation of Akt and eNOS was determined after 48 hours of cultivation with FIR radiation. β-actin is shown as a loading control. Data are shown as the mean ± SEM of three independent experiments. ^∗P < 0.01 compared with control cells. ^#P < 0.05 compared with control cells.

Figure 2

FIR radiation induces BH₄ synthesis in HUVECs. HUVECs were cultured with or without FIR-emitting sericite board for 48 hours. (a) Schematic model summarizing the mechanism of FIR-induced improvement of vascular function. (b) Intracellular levels of total biopterin and BH₄. (c) The protein expression of GCH1, PTS, SPR, and DHFR. β-actin is shown as a loading control. (d) Protein levels were quantified by densitometric analysis. Data are shown as the mean ± SEM of three independent experiments. ^∗P < 0.05 compared with control cells.

Figure 3

FIR radiation stimulates Akt/eNOS phosphorylation and NO production in vivo. Rats were exposed with or without FIR-emitting sericite board for 7 days. (a) NO production level was measured in the plasma of SD rats. (b) Concentration-response curves to phenylephrine in isolated aortic rings. (c) Phosphorylation of eNOS. (d) Phosphorylation of Akt protein levels from the aortic rings. β-actin is shown as a loading control. Data are shown as the mean ± SEM of three independent experiments. ^∗P < 0.05 compared with control cells.

Figure 4

FIR radiation induces tetrahydrobiopterin (BH₄) synthesis in vivo. Rats were exposed with or without FIR-emitting sericite board for 7 days. (a) Lung endothelial cells were isolated from control and FIR group rats using CD31 and CD45 beads. Endothelial biopterin and BH₄ levels were quantified by HPLC analysis. (b) GCH1, PTS, SPR, and DHFR protein expression in aorta tissues. β-actin is shown as a loading control. Protein levels were quantified by densitometric analysis. Data are shown as the mean ± SEM of three independent experiments. ^∗P < 0.05 compared with control cells.