Accuracy of three techniques to determine cell viability in 3D tissues or scaffolds.

Several different assays are commonly used to evaluate survival of cells inside tissues or three-dimensional carriers, but their accuracy and reliability have not been evaluated. Here, we compare three methods for cell viability (CV) determination: (i) lactate dehydrogenase (LDH) staining on cryosections, (ii) calcein AM/ethidium homodimer-1 (CaAM/EthH) staining, and (iii) carrier digestion and trypan blue (TB) assay. Living and dead cell populations were generated from bovine chondrocytes and combined to produce approximately 0%, 25%, 50%, 75%, and 100% CV mixtures. CV ratios were measured with TB assay (MIX) before seeding cells into fibrin carriers. CV was then determined using the three methods (n = 5/method). Custom-written macros were used to process LDH- and CaAM/EthH-stained images, and hand counting with hemocytometer was used for the TB method. Absolute error and intraclass correlation (ICC) were used for accuracy and reliability evaluation. All methods estimated CV values close to MIX values. TB method was the most accurate (ICC = 0.99) followed by CaAM/EthH (ICC = 0.98) and LDH (ICC = 0.97). As for absolute quantification of living and dead cells, TB and LDH methods performed well (ICC = 0.75-0.96), whereas CaAM/EthH largely overestimated cell numbers (living, ICC = 0.30; dead, ICC = 0.30). Although TB was the most accurate, LDH and CaAM/EthH provide valuable information on cell shape and spatial distribution of cells in tissue or a scaffold.

Inhibition of vertebral endplate perfusion results in decreased intervertebral disc intranuclear diffusive transport.

Impaired nutrition of the intervertebral disc has been hypothesized to be one of the causes of disc degeneration. However, no causal relationship between decreased endplate perfusion and limited nutrient transport has been demonstrated to support this pathogenic mechanism. To determine the importance of endplate perfusion on solute diffusion into the nucleus pulposus and to show causality of endplate perfusion on intranuclear diffusion in large animal lumbar intervertebral discs, diffusive transport into ovine lumbar intervertebral discs was evaluated after inhibiting adjacent vertebral endplate perfusion. Partial perfusion blocks were created in vertebrae close and parallel to both endplates of lumbar discs of anaesthetized sheep. To assess diffusivity of small molecules through the endplate, N2O was introduced into the inhalation gas mixture and concentrations of intranuclear N2O were measured for 35 min thereafter. Post mortem, procion red was infused through the spinal vasculature and perfusion through the endplate was assessed by quantifying the density of dye-perfused endplate vascular buds in histology sections. Perfusion of the endplates overlying the nucleus pulposus was inhibited by almost 50% in the partially blocked discs relative to the control discs. There was also a nine-fold decreased transport rate of intranuclear N2O in partially blocked discs compared with control discs. The density of perfused endplate vascular buds correlated significantly to the amount of transported intranuclear N2O (r2 = 0.52, P = 0.008). The vertebral endplate was demonstrated to be the main route of intravascular solute transport into the nucleus pulposus of intervertebral discs, and inhibition of endplate perfusion can cause inhibited solute transport into the disc intranuclear tissue.