Effect of a low-frequency pulsed electromagnetic field on expression and secretion of IL-1β and TNF-α in nucleus pulposus cells

Abstract

Objective To investigate changes in nucleus pulposus cell expression and secretion of interleukin (IL)-1β and tumour necrosis factor (TNF)-α following stimulation with a low-frequency (LF) pulsed electromagnetic field (PEMF). Methods Primary rat nucleus pulposus cells were isolated and cultured in vitro, followed by stimulation with LF-PEMFs at a frequency of 2 Hz and different intensities, ranging from 0.5-3.0 A/m. Cells were observed for morphological changes, and proliferation rates were measured by cell viability counts. Expression of IL-1β and TNF-α within the nucleus pulposus cells was measured using western blotting, and levels of IL-1β and TNF-α secreted in the culture media were measured using enzyme-linked immunosorbent assay. Results Stimulation of nucleus pulposus cells with LF-PEMFs did not appear to affect cell morphology or nucleus pulposus cell IL-1β and TNF-α expression levels. LF-PEMFs did not significantly affect cell proliferation, however, levels of IL-1β and TNF-α secreted into the culture media were found to be significantly reduced in an intensity-dependent manner. Conclusion Low-frequency PEMF stimulation may inhibit secretion of IL-1β and TNF-α in cultured nucleus pulposus cells.

Keywords: Low-frequency pulsed electromagnetic field; interleukin-1β (IL-1β); nucleus pulposus cells; tumour necrosis factor-α (TNF-α).

Figure 1.

Representative phase-contrast photomicrographs showing morphology of primary rat nucleus pulposus cells (original magnification × 10) exposed to low-frequency pulsed electromagnetic fields at intensities of 0.5, 1.0, 2.0, and 3.0 A/m, and at a frequency of 2 Hz, compared with untreated control cells. Visual analyses showed that cell morphology appeared to be unaffected by exposure to low-frequency pulsed electromagnetic fields.

Figure 2.

Cell Counting Kit-8 analysis showing the effect of low-frequency (LF) pulsed electromagnetic field (PEMF) stimulation at intensities of 0, 0.5, 1.0, 2.0, and 3.0 A/m, and at a frequency of 2 Hz, on primary rat nucleus pulposus cell viability. There were no statistically significant differences in cell viability between the control group and experimental groups; data presented as mean ± SD (n = 3 replicates per group).

Figure 3.

Representative western blots showing the effect of low-frequency (LF) pulsed electromagnetic field (PEMF) stimulation at intensities of 0, 0.5, 1.0, 2.0, and 3.0 A/m, and at a frequency of 2 Hz, on expression of interleukin (IL)-1β and tumour necrosis factor (TNF)-α in primary rat nucleus pulposus cells (n = 3 replicates per group). IL-1β and TNF-α were expressed under all experimental conditions and there were no obvious visible changes in IL-1β and TNF-α levels between the experimental groups.

Figure 4.

Enzyme-linked immunosorbent assay showing the effect of low-frequency (LF) pulsed electromagnetic field (PEMF) stimulation at intensities of 0, 0.5, 1.0, 2.0, and 3.0 A/m, and at a frequency of 2 Hz, on secretion of interleukin (IL)-1β and tumour necrosis factor (TNF)-α by primary rat nucleus pulposus cells. LF-PEMF stimulation was associated with significantly decreased secretion of IL-1β and TNF-α into the cell culture supernatants. Data presented as mean ± SD (n = 3 replicates per group); *P < 0.05, versus other treatment groups (one way analysis of variance).