Effects of physicochemical factors on the growth of mandibular condyles in vitro

Abstract

Cartilage growth and remodeling are known to be influenced by the biochemical and mechanical environment of the tissue. Previous investigators have shown that chemical factors that are relevant to mechanical loading, such as osmotic pressure and pH, induce changes in cartilage metabolism in vitro. Using a neonatal rat mandibular condyle culture system, the objectives of the work reported here were to determine (1) how the growth is influenced by osmotically applied mechanical loads; and (2) whether changes in intratissue osmotic pressure or pH cause metabolic changes in the cartilage which are then reflected by altered growth behavior. High molecular weight (MW) uncharged macromolecules polyvinylpyrrolidone (PVP) and Ficoll (presumed unable to penetrate the tissue matrix) were used to examine the effect of osmotic loading on tissue growth; concentrations corresponding to osmotic pressures of up to 100 kPa resulted in a dose-dependent depression in growth and matrix accumulation. Raffinose (which can penetrate the matrix but not the cells) had no significant effect on growth for osmotic pressures of up to 87 kPa, suggesting that compression-induced changes in intratissue osmotic pressure are unlikely to provide a signal by which cells sense and respond to mechanical compression. By contrast, changes in medium pH resulted in dose-dependent changes in growth behavior. Specifically, slight alkalinity (acidity) greatly enhanced (diminished) growth and matrix accumulation; the sensitivity to pH suggests that intratissue pH could provide a mechanism for cells to sense local glycosaminoglycan concentration and mechanical compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of matrix synthesis in isolated bovine chondrocytes by extracellular and intracellular pH

“…The marked inhibition of synthesis by high levels of acidity using lactate or HCl reported here in isolated chondrocytes has been described previously in cartilage explants (Gray et al, 1988;Ohshimet and Urban, 1992;Sah et al, 1989Sah et al, , 1992Garcia et al, 1994;Boustany et al (1995). This monotonic depression contrasts to the bimodal relationship described here possibly because in the previous studies extracellular pH values of sufficient alkalinity were not studied; it is also conceivable that the optimal pH values for synthesis may differ between the tissues studied and their culture conditions.…”

“…Previous work using intact cartilage explants has suffered from the complexities of the extracellular matrix and the difficulty of determining the pH, of cells in situ, but, despite this, there are clear parallels with the results presented here. A bimodal response to changes in extracellular pH (using lactate or HC1) has been observed in studies on intervertebral disc (Ohshima and , calf epiphyseal cartilage (Sah et al, 19921, and rat mandibular chondyles (Garcia et al, 1994). Of interest is the pH at which optimal synthesis rates are recorded, showing that only small changes in pH, within the physiological range (in either the acidic or basic direction) quickly and significantly (by up to 50%) inhibit synthesis rates.…”

Physical and Biological Regulation of Proteoglycan Turnover around Chondrocytes in Cartilage Explants: Implications for Tissue Degradation and Repair

“…45 However, PG and collagen synthesis were upregulated by low-amplitude, sinusoidal, dynamic thickness perturbations at frequencies between ∼ 0.01 Hz and 1 Hz. 42 The mechanisms by which such normal levels of applied mechanical compression influence ECM macromolecule synthesis, assembly, degradation, and release are not well understood, and may involve a confluence of physicochemical [51][52][53] and biomechanical 54,65 factors, including interactions with cytokine/biochemical factor-mediated regulatory pathways. 27,41,43 Applied mechanical stresses that exceed the normal amplitude and/or frequency ranges may give rise to significant tissue injury in vitro , 46,56 providing reasonable models for in vivo cartilage mechanical trauma.…”

“…44 Low frequency (∼ 0.001 Hz) alternation between levels of static compression, or “cyclic” compression, has been observed to significantly decrease the half‐lives of PGs and collagen in the ECM. 45 However, PG and collagen synthesis were upregulated by low‐amplitude, sinusoidal, dynamic thickness perturbations at frequencies between ∼ 0.01 Hz and 1 Hz.42 The mechanisms by which such normal levels of applied mechanical compression influence ECM macromolecule synthesis, assembly, degradation, and release are not well understood, and may involve a confluence of physicochemical 51–53 and biomechanical 54,65 factors, including interactions with cytokine/biochemical factor‐mediated regulatory pathways. 27,41,43…”

Combination of automated high throughput platforms, flow cytometry, and hierarchical clustering to detect cell state

“…Thus the in vivo microenvironment can not be fully captured in vitro, resulting in poor correlation between in vitro and in vivo experiments. For example, in vivo, cells are targeted with multiple stimuli that occur either in combination or sequentially and include soluble and insoluble factors (50,51), mechanical and electrical signals (50), osmotic pressure (52), hydrophobicity (53), and oxygen tension (52). In these experiments, the experimental design included both multiparameter inputs and multiparameter outputs.…”