Autoactivation of proteolytic activity in human whole saliva

Proteolytic activity is reportedly present in saliva and seems to play a role in oral diseases such as periodontitis and dental caries. The present study aimed to investigate the autoactivation of proteolytic activity in whole saliva and its influence on salivary proteins. Whole saliva obtained from 10 healthy volunteers (mean age, 27.3±1.5 yr) by chewing paraffin displayed both gelatinolytic (1.21±0.52 unit/mL) and collagenolytic (0.05±0.02 unit/mL) activities using fluorescentlabeled substrates. These activities were partly inhibited by EDTA. Gelatinolytic and collagenolytic activities were significantly increased (p<0.01) in whole saliva by incubation at 37°C, and reached 5.6- and 8.8-times the original activities at 12 h,respectively. However, gelatinolytic activities in the supernatant or sediment of whole saliva showed no or low autoactivation. Gelatin zymography suggested that proteases in whole saliva mainly consisted of high-molecular-weight complex forms (>300 and 120 kDa) and a latent form (92 k Da) of matrix metalloproteinase -9 (MMP-9), and that these species were autoactivated at 37°C and truncated to a 42-kDa protein through 100-, 67-, and 50-kDa proteins. Moreover, SDS-PAGE analysis indicated that salivary proteins in whole saliva were gradually degraded and completely disappeared over 12 h. The present study revealed that whole saliva exhibits mainly gelatinolytic activity, which can be autoactivated in whole saliva and degrade salivary proteins.