TAK-242 treatment and its effect on mechanical properties and gene expression associated with IVD degeneration in SPARC-null mice.

PURPOSE: Intervertebral disc (IVD) degeneration is accompanied by mechanical and gene expression changes to IVDs. SPARC-null mice display accelerated IVD degeneration, and treatment with (toll-like receptor 4 (TLR4) inhibitor) TAK-242 decreases proinflammatory cytokines and pain. This study examined if chronic TAK-242 treatment impacts mechanical properties and gene expression associated with IVD degeneration in SPARC-null mice. METHODS: Male and female SPARC-null and WT mice aged 7-9 months were given intraperitoneal injections with TAK-242 or an equivalent saline vehicle for 8 weeks (3x/per week, M-W-F). L2-L5 spinal segments were tested in cyclic axial tension and compression. Gene expression analysis (RT-qPCR) was performed on male IVD tissues using Qiagen RT2 PCR arrays. RESULTS: SPARC-null mice had decreased NZ length (p = 0.001) and increased NZ stiffness (p < 0.001) compared to WT mice. NZ length was not impacted by TAK-242 treatment (p = 0.967) despite increased hysteresis energy (p = 0.024). Tensile stiffness was greater in SPARC-null mice (p = 0.018), and compressive (p < 0.001) stiffness was reduced from TAK-242 treatment in WT but not SPARC-null mice (p = 0.391). Gene expression analysis found upregulation of 13 ECM and 5 inflammatory genes in SPARC-null mice, and downregulation of 2 inflammatory genes after TAK-242 treatment. CONCLUSIONS: TAK-242 had limited impacts on SPARC-null mechanical properties and did not attenuate NZ mechanical changes associated with IVD degeneration. Expression analysis revealed an increase in ECM and inflammatory gene expression in SPARCnull mice with a reduction in inflammatory expression due to TAK-242 treatment. This study provides insight into the role of TLR4 in SPARC-null mediated IVD degeneration.

A Novel Testing Method to Quantify Mechanical Properties of the Intact Annulus Fibrosus Ring From Rat-Tail Intervertebral Discs.

The annulus fibrosus is the ring-like exterior of the intervertebral disc, which is composed of concentrically organized layers of collagen fiber bundles. The mechanical properties of the annulus have been studied extensively; however, tests are typically performed on extracted fragments or multilayered samples of the annulus and not on the annulus as a whole. The purpose of this study was twofold: (1) to develop a novel testing technique to measure the mechanical properties of the intact, isolated annulus; and (2) to perform a preliminary analysis of the rate-dependency of these mechanical properties. Twenty-nine whole annulus ring samples were dissected from 11 skeletally mature Sprague Dawley rat tails and underwent a tensile failure test at either 2%/s (n = 16) or 20%/s (n = 13). Force and displacement were sampled at 100 Hz and were subsequently normalized to stress and strain. Various mechanical properties were derived from the stress-strain curves and statistically compared between the rates. All mechanical variables, with the exception of initial failure stress, were found to be unaffected by rate. Interestingly, initial failure stress was higher for samples tested at the slower rate compared to the higher rate which is atypical for viscoelastic tissues. Although in general rate did not appear to impact the annulus ring response to tensile loading, this novel, intact annular ring testing technique provides an alternative way to quantify mechanical properties of the annulus.