A Functional TGF-β/Smad Assay for Targeted Profiling of Demineralized Bone Matrix-Derived Allograft Bioactivity

Demineralized bone matrix (DBM)-derived allografts retain extracellular matrix (ECM)-associated factors involved in bone repair, but biochemical protein recovery alone may not predict functional pathway activation. We evaluated the HEK-Blue™ TGF-β Reporter Assay as a targeted method for assessing Smad-dependent reporter activity in DBM-derived materials. ECM proteins were extracted from cortical demineralized bone granules (DBG) using guanidine hydrochloride (GuHCl) or urea and quantified after extraction, dialysis, and sterile filtration. Reporter cells were stimulated with extracted ECM proteins or directly with processed cortical and cancellous products, including DBG, wet heat-treated DBG formulated as Putty (PHT), and gamma-irradiated PHT (PGI). Non-pooled DBM sponge samples were also tested. Secreted embryonic alkaline phosphatase (SEAP) activity served as the functional reporter readout. Material-only no-cell controls assessed material-derived background. PrestoBlue™ readouts served as exploratory quality controls. The urea-derived extract yielded a higher apparent BCA-detectable protein concentration than the GuHCl-derived extract. Only the GuHCl-derived extract induced increasing SEAP activity at matched protein input. Direct stimulation showed reporter activation above the TNF-α pathway-negative cytokine control for cortical DBG, PHT, PGI, and cancellous DBG. DBM sponges also induced detectable SEAP activity. These findings support targeted functional screening of Smad-dependent TGF-β reporter activation in DBM-derived materials, but not total osteoinductivity assessment.