Platelets and platelet lysates can only degrade purified HA under acidic pH. (A-B) Platelets and platelet lysates were incubated with purified HA immobilized to wells of a 96-well plate for 18 hours at 37°C (3 × 108 platelets per well). At the end of the incubation, platelets and degraded HA were washed away, and hyaluronidase activity was measured by detecting residual HA colorimetrically. Maximum activity was achieved by HAase. (A) hyaluronidase activity of platelets and their lysates at different pHs. Platelets and their lysates demonstrated purified HA-degrading activity only under acidic pH (optimum pH, 3.5) with no detectable activity at neutral pH. (B) Purified HA-degrading activity of platelets compared with the activity of their lysates. Platelet lysates have significantly higher purified HA–degrading activity than intact platelets. n = 3; ***P < .001. (C) Purified HA (Select-HA, 1000 kDa) in RPMI medium (5 mg/mL) was incubated with platelets for 18 hours at 37°C. Platelets degraded purified HA only under acidic pH (pH 3.5) but not under neutral pH.
