Cysteine protease inhibitory activity and levels of salivary cystatins in whole saliva of periodontally diseased patients

The 3 human salivary cystatins S, SA and SN are multifunctional proteins th at possess a cysteine protease inhibitory property, but their ability to ac t as such is very different (SN > SA >> S). One form, S, also appears to po ssess antibacterial properties towards the bacterium Porphyromonas gingival is, often associated with periodontal diseases. In this study we measured t he total cystatin inhibitory activity and the levels of each salivary cysta tin in the whole saliva of 8 periodontally diseased patients and 2 groups o f control subjects (n = 6 and n = 10). The total cystatin inhibitory activi ty and the total salivary cystatin concentration in the periodontally disea sed patients were found to be lower than the controls (p less than or equal to 0.005). The concentration of S was depleted to levels that would not al low it to be an effective antibacterial agent, and the concentration of SA, although depleted in some cases, was still present at sufficient levels to allow it to act as an effective physiological inhibitor of cathepsin L. Th e concentration of cystatin SN was also depleted in the periodontally disea sed patients, but was still present in sufficient quantities to act as an e ffective physiological cysteine protease inhibitor of cathepsins H and L. I n comparison, the concentration of all 3 salivary cystatins in the control subjects were sufficient to enable these proteins to be both effective phys iological cysteine protease inhibitors and antibacterial agents.