Hyaluronic acid-complement interactions—I. Reversible heat-induced anticomplementary activity

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The in vitro interaction of hyaluronic acid (HA) with complement (C) classical-pathway activity has been investigated. It was found that native HA, even at a high concn (>3 mg/ml), has a relatively weak anticomplementary activity. However, we report here that native HA can be reversibly altered by heat treatment such that C-inhibitory properties are manifested. We have determined in this study that a potent C-inhibitory activity can be obtained if HA solutions are thermally treated (100°C), and stabilized by prompt freezing with prompt thawing just prior to the interaction with human serum complement. Several investigators have proposed that the intermolecular-associated strands of HA undergo a reversible decoupling upon thermal treatment and this decoupled state of HA can be semi-stabilized by quickly cooling the sample. This heat-treated HA strongly inhibits Cl as well as classical-pathway-mediated C3 conversion. However, if heat-treated HA samples are not stabilized but, rather, slowly cooled after heating or if heated HA samples are snapfrozen and then slowly thawed, the anticomplementary activity is gradually lost. Interestingly, the activity for this same sample can be regenerated by retreatment of the same sample with heat followed by low-temp stabilization, indicating the reversibility of the physical state of HA responsible for the anticomplementary effect. Since no detectable molecular degradation of thermally-treated HA was found, it was assumed that a heat-induced physical transition of HA (decoupled state) was responsible for the C-inhibitory effect.