Safety of intradiscal delivery of triamcinolone acetonide by a poly(esteramide) microsphere platform in a large animal model of intervertebral disc degeneration

Abstract

Background context: Local corticosteroids have been used to relieve symptoms of chronic low back pain, although treatment effects have been shown to wear off relatively fast. Prolonging corticosteroid presence by controlled release from biomaterials may allow for longer pain relief while circumventing adverse effects such as high bolus dosages.

Purpose: The purpose of this study was to evaluate the safety and efficacy of intradiscal controlled release of triamcinolone acetonide (TAA) by poly(esteramide) microspheres in a canine degenerated intervertebral disc (IVD) model.

Study design: In a preclinical experimental large animal model, the effect of prolonged glucocorticoid exposure on disc degeneration was evaluated.

Methods: Degeneration was accelerated by nucleotomy of lumbar IVDs of Beagle dogs. After 4 weeks, microspheres loaded with 8.4 µg TAA, and 0.84mg TAA were administered to the degenerated IVDs by intradiscal injection (n=6 per group). Empty microspheres (n=6) and all adjacent non-nucleotomized noninjected IVDs were included as controls (n=24). Immediately prior to TAA administration and after 12 weeks, magnetic resonance imaging was performed. Degenerative changes were evaluated by disc height index, Pfirrmann grading, T1ρ and T2 mapping values, postmortem CT scans, macroscopic and microscopic grading, and biochemical/immunohistochemical analysis of inflammation and extracellular matrix content. In addition, nerve growth factor (NGF) protein expression, a biomarker for pain, was scored in nucleus pulposus (NP) tissues. The study was funded by a research grant from Health Holland (1.3million euros = 1.5million US dollars).

Results: Macroscopic evaluation and CT images postmortem were consistent with mild disc degeneration. Other abnormalities were not observed. Nucleotomy-induced degeneration and inflammation was mild, reflected by moderate Pfirrmann grades and PGE₂ levels. Regardless of TAA dosage, local sustained delivery did not affect disc height index nor Pfirrmann grading, T1ρ and T2 mapping values, PGE₂ tissue levels, collagen, GAG, and DNA content. However, the low dosage of TAA microspheres significantly reduced NGF immunopositivity in degenerated NP tissue.

Conclusions: This is the first in vivo application in a preclinical large animal model of a controlled release formulation of corticosteroids in mild IVD degeneration. Sustained release of TAA locally in the IVD appeared safe and reduced NGF expression, suggesting its potential applicability for pain relief, although beneficial effects were absent on tissue degeneration.

Clinical significance: The present platform seems to be promising in extending the local controlled delivery of TAA with the potency to provide long-standing analgesia in the subset of LBP patients suffering from discogenic pain.

Keywords: chronic low back pain; controlled release; corticosteroid; intervertebral disc degeneration; intradiscal injection; poly(esteramide) microspheres; preclinical animal model; triamcinolone acetonide.