Clinical plausibility of eggshell membrane proteins for osteoarthritis: a study of solubility, digestibility, and...

Supplements are commonly used by osteoarthritis (OA) patients, and eggshell membrane (ESM) proteins are widely advertised as natural bioactive compounds for joint health. Here, we evaluated the solubility, digestibility, and immunomodulatory potential of commercial ESM supplements under physiologically relevant conditions to assess their plausibility as anti-inflammatory agents. We analyzed three commercial ESM formulations (NEM^®, Torolis^®, and Biova^®) using standardized extraction protocols. Protein solubility was assessed in physiological saline and under simulated gastric (pH 2) and intestinal (pH 5.8) conditions with controlled temperature, agitation, and digestive enzyme exposure. We examined the role of disulfide-crosslinked proteins in insolubility using dithiothreitol (DTT) and evaluated digestibility of proteins by SDS-PAGE after treatment with pepsin, pancrelipase (Creon^®), or sequential digestion. Released peptides were identified by MALDI-TOF mass spectrometry, and immunomodulatory effects were tested using human peripheral blood mononuclear cells (PBMC) by measuring cytokine release after stimulation with lipopolysaccharide or Phorbol 12-myristate 13-acetate/Ionomycin, in the presence or absence of Biova^®. NEM^® and Torolis^® showed extremely low solubility (< 0.3%) and remained insoluble under all conditions, including after DTT treatment. Although Biova^® was highly soluble (~ 90%), simulated gastrointestinal digestion produced minimal peptide generation. Only non-physiological extraction yielded sporadic trace peptides, most lacking known anti-inflammatory relevance. In PBMC assays, Biova^® increased IL-6 after lipopolysaccharide stimulation, showed a non-significant TNFα reduction, and had no effect on IL-17 A or granzyme B. Together, commercial ESM supplements are largely insoluble, resistant to digestion, and show no meaningful anti-inflammatory activity in human immune cells. These findings challenge the plausibility of orally administered ESM as a therapeutic intervention for osteoarthritis.