INTRODUCTION: In provocative discography (PD), intervertebral discs are punctured with a spinal needle and pressurized in order to identify painful discs. Recently, Carragee et al (1) reported that PD accelerates progression of disc degeneration and suggested damage from the needle puncture as one possible mechanism. We suggest another source of damage might be exposure to iodinated contrast agent (ICA). In PD, discs are exposed to elemental iodine concentrations up to 350 mgI/ml and ICA may remain for days in the disc. No studies have been published that evaluate the effects of ICA on NP cells. In this study we assess the toxicity of iohexol (an ICA) on NP cells in vitro.
METHODS: Rabbit and sheep NP tissues and isolated NP cells were exposed for short (4, 18, 30, 50 and 72 hours) durations at 175 mgI/ml (high concentration) and for long (1 and 3 weeks) durations at 3.5 mgI/ml (low concentration) of iohexol. The effects of iohexol were assessed for: cell viability and proliferation, matrix production, and mechanism of cell death (e.g., apoptosis vs. necrosis).
RESULTS AND CONCLUSIONS: Viability of NP cells was significantly diminished by iohexol. Viability decreased with increasing concentration and time of exposure. For example, survival of isolated sheep NP cells exposed to 175 mgI/ml iohexol for 18 hours was 40% of control. Long term exposure (weeks) at low iohexol concentration (3.5 mgI/ml), however, did not significantly diminish NP cell viability or matrix production. Cell death was largely inhibited by apoptosis inhibitors. These results show that short‐term, in vitro exposure to iohexol at concentrations similar to that used in PD was toxic to NP cells. Iodinated contrast agents used in PD may impact the long‐term health of the disc.
1. Carragee et al., Spine 34; 21:2338-2345