Metabolism of the intervertebral disc: effects of low levels of oxygen, glucose, and pH on rates of energy metabolism of bovine nucleus pulposus cells.

STUDY DESIGN: In vitro measurements of metabolic rates of isolated bovine nucleus pulposus cells at varying levels of oxygen, glucose, and pH. OBJECTIVES: To obtain quantitative information on the interactions between oxygen and glucose concentrations and pH, and the rates of oxygen and glucose consumption and lactic acid production, for disc nucleus cells. SUMMARY OF BACKGROUND DATA: Disc cells depend on diffusion from blood vessels at the disc margins for supply of nutrients. Loss of supply is thought to lead to disc degeneration, but how loss of supply affects nutrient concentrations in the disc is not known; nutrient concentrations within discs can normally only be calculated, because concentration measurements are invasive. However, realistic predictions cannot be made until there are data from measurements of metabolic rates at conditions found in the disc in vivo, i.e., at low levels of oxygen, glucose, and pH. METHODS: A metabolism chamber was designed to allow simultaneous recording of oxygen and glucose concentrations and of pH. These concentrations were measured electrochemically with custom-built glucose and oxygen sensors; lactic acid was measured biochemically. Bovine nucleus pulposus cells were isolated and inserted into the chamber, and simultaneous rates of oxygen and glucose consumption and of lactic acid production were measured over a range of glucose, oxygen, and pH levels. RESULTS: There were strong interactions between rates of metabolism and oxygen consumption and pH. At atmospheric oxygen levels, oxygen consumption rate at pH 6.2 was 32% of that at pH 7.4. The rate fell by 60% as oxygen concentration was decreased from 21 to 5% at pH 7.4, but only by 20% at pH 6.2. Similar interactions were seen for lactic acid production and glucose consumption rates; we found that glycolysis rates fell at low oxygen and glucose concentrations and low pH. Equations were derived that satisfactorily predict the effect of nutrient and metabolite concentrations on rates of lactic acid production rate and oxygen consumption. CONCLUSIONS: Disc cell metabolism in air and at pH 7.4 differs markedly from that found in the disc nucleus in vivo, where low levels of oxygen, glucose, and pH all coexist.

Cell viability in scoliotic discs in relation to disc deformity and nutrient levels.

STUDY DESIGN: Intervertebral disc tissue was analyzed during or removed at routine surgery for correction of scoliosis. Tissue was analyzed for glucose, lactate, oxygen, glycosaminoglycan, collagen concentrations, and cell viability. OBJECTIVES: To investigate the cell viability of the scoliotic disc on the concave and convex sides and in relation to curve apex, and to relate cell viability to concentrations of nutrients, metabolites, and extracellular matrix components. SUMMARY OF BACKGROUND DATA: Compositional differences have been measured in relation to the deformation of scoliotic discs. However, the causes of these in relation to cellular activity or viability are unknown. METHODS: Oxygen concentration was measured at surgery using a microelectrode. A segment of disc then was removed and sections at defined locations measured for cell viability and glucose, lactate, glycosaminoglycan, and collagen concentrations. RESULTS Cell viability was lower toward the convex side of the curve, with the greatest difference between the sides in the apical disc. The apical disc had the lowest oxygen and highest lactate concentrations, and lowest total number of cells. Glucose concentration correlated with the number of live cells. Concentrations of glycosaminoglycans and collagen per dry weight of tissue were similar on both sides of the disc. CONCLUSIONS: Differences in cell viability correlated with changes in nutrient and metabolite levels, and also with disc deformity (convex concave and distance from curve apex). Thus asymmetrical loads, tissue deformation, and nutrient supply may work separately or in combination to cause cell death. A loss of matrix macromolecules was not seen, possibly because the period between cell death and surgery was too short, as compared with long matrix turnover times. Cell death is expected eventually to have a deleterious effect on cell matrix and disc function.