Study Design: The effects of heat on porcine intertvertebral disc were studied experimentally.

Objective: To assess the effects of in-vitro heating of porcine nucleus pulposus on expression of inducible heat shock protein 70 and subsequent modification of biochemical responses to an inflammatory insult in the heated intervertebral disc tissue.

Subjects: Lumbar spines were harvested from six pigs. The nucleus pulposus was dissected from each intervertebral disc, divided into control (37°C) and heat shocked (42°C) groups then cultured in medium for one hour. All samples were then cultured at 37 C for a further two hours. After three hours tissue and supernatant were harvested from one third of the samples and the expression of inducible heat shock protein 70 (HSP70) was quantified via Western immunoblotting and enzyme linked immuno-sorbent assay (ELISA). The remaining samples were cultured either in normal medium or altered (pro-inflammatory) medium containing 5ug/ml bacterial lipopolysaccharide (LPS). At 24 hours the supernatant from these samples was analysed for both interleukin-8 (IL-8) and prostaglandin E2 (PGE2) secretion using ELISA.

Outcome Measures: Western immunoblotting and enzyme linked immuno-sorbent assay (ELISA) for heat shock protein 70. ELISA for interleukin-8 (IL-8) and prostaglandin E2 (PGE2).

Results: HSP70 expression was significantly increased in the heat shocked specimens. IL-8 and PGE2 secretion were significantly increased in nucleus pulposus exposed to LPS at both temperatures. The concentrations of IL-8 and PGE2 secreted in the heat shocked samples were significantly less than controls, particularly after exposure to LPS (p< 0.05, paired students t test).

Conclusions: In vitro heating of porcine nucleus pulposus causes overexpression of HSP70. This heat shock effect can alter aspects of the biochemical response of the intervertebral disc tissue to an inflammatory insult. Intradiscal electrothermal therapy (IDET) may, in theory, reduce discogenic pain at temperatures as low as 42°C by generating similar heat-induced changes in the nuclear biochemistry of degenerate intervertebral discs.