2:32 Effect of nutrient concentration and osteogenic protein–1 on the metabolism of intervertebral disc: in vitro organ culture study

Abstract

Purpose of study: Poor vascularity to the intervertebral discs (IVD) and sclerosis of the end plate may result in the decrease of nutrient diffusion and subsequent disc deterioration. The purpose of this study was to determine the effect of nutrition on disc metabolism using our recently developed in vitro organ culture model with end plate, and to see if osteogenic protein (OP)-1 can protect discs from a low-nutrient environment.Methods used: Twenty-four lumbar IVDs were obtained from adult New Zealand rabbits weighing 3 kg. Specimens were cultured over 21 days in DMEM/F12 with different concentrations of FBS (5%, 10% and 20%). Four of the specimens cultured in 5% FBS were injected with 0.2 mg OP-1 at 7 days. At 21 days, discs were dissected from end plate and annulus fibrosus (AF) and nucleus pulposus (NP) were separated. After measuring dry weight, the AF and NP tissue were analyzed for DNA content and proteoglycan content (PG) by Hoechst dye method and DMB, respectively. The results were statistically analyzed using analysis of variance with a Fisher's PLSD test as a post hoc test.of findings: The DNA content of the NP decreased as the concentration of FBS decreased (5%=1.28 ug/mg, 10%=2.67 ug/mg, 20%=3.92 ug/mg; p=.03). The PG content in NP showed a positive correlation with the concentration of FBS (5%=25.4 ug/mg, 10%=95.5 ug/mg, 20%=152.7 ug/mg; p=.02). The concentration of FBS did not, however, have an effect on the DNA or PG content in the AF. Discs cultured in 5% FBS plus OP-1 demonstrated increased DNA content in NP (1.52 ug/mg, p=.04) and PG content in NP (36.1 ug/mg, p=.05) when compared with discs cultured in 5% FBS without OP-1. The DNA content and PG content in the AF were not affected.Relationship between findings and existing knowledge: Numerous studies have demonstrated that decreased vascularity to the IVD is linked to disc degeneration. This is presumably because of decreased nutrition to the disc cells. However, no studies have been done on the direct relationship between nutrient supply and disc growth in an in vitro organ culture. Moreover, no studies are available on the effect of OP-1 on the IVD in the nutrient-poor environment.Overall significance of findings: In the in vitro organ culture system with end plate, the NP is very sensitive to nutrient supply. AF tissue was not dependent on the nutrition. These results suggest that the diminished vascularity and/or sclerotic end plate changes may contribute to the progress of disc degeneration. Administration of OP-1 appears to protect NP tissue from undergoing degeneration from poor disc nutrition.Disclosures: Device or drug: OP-1. Status: investigational.Conflict of interest: No conflicts.