Intermittent sub-ambient interstitial hydrostatic pressure as a potential mechanical stimulator for chondrocyte metabolism

Objective: Experimental findings have suggested that the metabolic activiti es of articular cartilage can be influenced by mechanical stimuli. Our math ematical analysis predicted that cyclic compressive loading may create peri ods of intermittent sub-ambient hydrostatic pressure within the cartilage e xtracellular matrix. Based on this mathematical analysis, the present study was aimed to investigate whether the intermittent sub-ambient hydrostatic pressure, created in the cartilage extracellular matrix during cyclic compr ession, has a stimulative effect on the biosynthesis of chondrocytes. Method: In order to test this hypothesis, the present study developed a cus tom-designed sub-ambient pressure generator to subject a monolayer culture of chondrocytes to an intermittent sub-ambient pressure. Using this pressur e generator, the monolayer chondrocyte culture system was analyzed for S-35 -sulfate and H-3-proline incorporation rates for biosynthesis of proteoglyc an and collagenous/noncollagenous protein molecules, respectively. Northern analyses for aggrecan and type II collagen mRNAs were also performed. Results: It was found that the intermittent sub-ambient pressure produced a 40% increase in proteoglycan and a 17% increase in non-collagenous protein synthesis during the pressurization period (P < 0.05). The collagenous pro tein synthesis was not affected by the intermittent sub-ambient pressure re gimen used in this study. After the intermittent sub-ambient pressurization , the metabolic activities of the chondrocytes returned to normal (control level). The intermittent sub-ambient pressure also produced an increase in the mRNA signals for aggrecan. Therefore, we conclude that intermittent sub -ambient pressure may be one of the potential mechanical stimulators of cho ndrocytes in articular cartilage during dynamic compression.