Inflammation plays an important role in symptomatic
intervertebral disc degeneration and is associated with the production of
neurotrophins in sensitizing innervation into the disc. The use of high molecular weight (HMw)
hyaluronic acid (HA)
hydrogels offers a potential therapeutic
biomaterial for nucleus pulposus (NP) regeneration as it exerts an anti-inflammatory effect and provides a microenvironment that is more suitable for NP. Therefore, it was hypothesized that cross-linked HMw HA
hydrogels modulate the inflammatory receptor of IL-1R1, MyD88 and
neurotrophin expression of
nerve growth factor (
NGF) and
brain-derived neurotrophic factor (
BDNF) in an in vitro
inflammation model of NP. HA cross-linking was optimized using various concentrations of 4-arm PEG-
amine by determination of free carboxyl groups of HA and unreacted free
amine groups of PEG-
amine. The optimally cross-linked HA
hydrogels were characterized for hydrolytic stability, enzymatic degradation and cytotoxicity on NP cells. The
therapeutic effect of HA
hydrogels was further investigated in IL-1β induced
inflammation on NP cell cultures and the mechanism of HA by examining the expression of
cell surface receptor of CD44.
Hydrogel was optimally cross-linked at 75 mM PEG, stable in
phosphate buffered saline, and showed greater than 40% resistance to enzymatic degradation. No cytotoxic effect of NP cells was observed in the presence of
hydrogels for 1, 3, and 7 days. IL-1R1 and MyD88 were significantly suppressed. Additionally,
NGF and
BDNF mRNA were down-regulated
after treatment with cross-linked HA
hydrogel. Possible protective mechanism of HA is shown by high expression of CD44 receptor of NP cells after HA treatment in which suggest the binding of HA to CD44 receptor and prevent NP cells from further undergoing
inflammation. These results indicate that optimally stabilized cross-linked HMw HA
hydrogel has a
therapeutic effect in response to
inflammation-associated
pain and becomes an ideal matrices
hydrogel for NP regeneration.