Engineering an in-vitro model of rodent cartilage.

OBJECTIVES: The purpose of this study was to identify a cell source, scaffold substrate and culture environment suitable for use in engineering an in-vitro model of rodent cartilage. METHODS: The chondrogenic activity and stability of cells isolated at Day 18 of gestation was assessed under normoxia and hypoxia using a cytokine stimulation assay and gene expression analysis. The ability of the selected cells seeded in fibrous electrospun scaffolds to form cartilaginous tissue during longterm static and dynamic culture was assessed using immunocytochemistry and biochemical analysis. KEY FINDINGS: Rodent fetal chondrocytes appear to have enhanced phenotypic stability compared with other cell sources. Following 16 weeks under static culture, the engineered constructs were found to have greater cellularity and collagen content that native rodent cartilage. CONCLUSIONS: A cell source, scaffold and culture environment have been identified that support the generation of in-vitro rodent cartilage. In future work, cytokine treatment of the engineered tissues will take place to generate in-vitro osteoarthritis models.

Inhibition of inflammation and hyperalgesia in NK-1 receptor knock-out mice.

We sought to characterise the contribution of the neuropeptide substance P to the outcome of two models of footpad inflammation of differing severity. In an intense inflammatory model produced by intra-plantar Mycobacterium tuberculosus (10 mg/ml) substantial reductions in footpad swelling, histological outcome and mechanical hyperalgesia were observed from early time points in mice lacking the neurokin-1 receptor for substance P compared with wild-type controls. Conversely, in a less intense model (M. tuberculosus 1 mg/ml) no differences were observed other than for a reduction in mechanical hyperalgesia at later time points (day 9 onwards). The results point to a previously unrecognised influence of substance P on peripheral tissue injury and the maintenance of hyperalgesia during more severe or more chronic phases of inflammatory disease.

Enhancement of angiogenesis by endogenous substance P release and neurokinin-1 receptors during neurogenic inflammation.

Early angiogenesis is a key step in the transition from acute to persistent inflammation. The nervous system has long been known to play a role in inflammation, in part through the release of substance P from peripheral nerve terminals (neurogenic inflammation). Application of substance P can stimulate vessel growth in a variety of angiogenesis assays, although it was previously not known whether endogenous substance P released from sensory nerves could modulate angiogenesis. We hypothesized that endogenous substance P can initiate angiogenesis during acute neurogenic inflammation. Here we show that 10 nmol of substance P can stimulate angiogenesis within the rat knee synovium, as shown by increased endothelial cell proliferation index [PCNA index, 19% (95% confidence interval (CI), 17 to 20%)] compared with saline injected knees [6% (95% CI, 4% to 8%), p < 0.05]. Moreover, this was prevented by coadministration of an antagonist of the neurokinin-1 (NK1) subtype of neurokinin receptor SR140333 (nolpitantium), 1 micro mol [8% (95% CI, 5% to 11%)]. Capsaicin 0.5%, which stimulates release of endogenous substance P from sensory nerves, was also found to enhance synovial angiogenesis, [PCNA index 17% (95% CI, 14% to 19%)] compared with saline injected control knees [2% (95% CI, 1% to 3%), p < 0.05], and this also was inhibited by 1 micro mol of SR140333 [11% (95% CI, 8 to 16%)]. Inhibition of capsaicin-enhanced angiogenesis was incomplete, and this may indicate a contribution of other neuropeptides, in addition to substance P-NK1 receptor interactions, in capsaicin-enhanced angiogenesis. NK1 receptor antagonists could have therapeutic potential in conditions where neurogenic angiogenesis contributes to disease.