Lack of effect of lysozymes on cartilage proteoglycans

Lactoferrin and lysozyme in arthritic exudates

Lactoferrin (LF) has been assayed by radioimmunoassay in plasma and arthritic exudates and compared with lysozyme (LZ) levels and leukocyte counts. The mean LF concentration in 38 rheumatoid arthritis (RA) exudates was 9.1 mg/l (range 0.02-39.2). In 30 non-RA exudates LF was 3.3 mg/l (range 0.01-14.6). The corresponding LZ levels were 7.4 mg/l (range 2.5-18.5) in RA and 4.7 (range 1.0-12.5) in non-RA fluids. Exudate/plasma ratios were much higher for LF than for LZ and higher in RA than in non-RA exudates, whereas leukocyte counts did not differ. The LF/leukocyte count ratio was significantly higher in RA than in the non-RA group. The data suggest a more prominent release of neutrophilic granulocyte components in RA than in non-RA arthritis.

Dependence of salt concentration on glycosaminoglycan-lysozyme interactions in cartilage

The cationic protein, lysozyme, has an extracellular distribution in cartilage but its precise role in this tissue has not yet been established. This study describes the dependence of salt concentration on the binding properties of lysozyme isoforms of different cationic charges, isolated from bovine cartilage, to the two major and structurally similar glycosaminoglycans of cartilage, i.e., chondroitin sulfate and hyaluronan. The binding of most cartilage lysozyme isoforms and hen egg-white lysozyme (control) to chondroitin sulfate and hyaluronan linked to agarose supports displayed optimal levels at approximately 20 and 5-10 mM salt, respectively, but decreased at both lower and higher salt concentrations indicating the electrostatic nature of the interactions. However, optimal binding of the most cationic lysozyme isoform to chondroitin sulfate occurred at 60 mM salt, with significant binding remaining at 150 mM. This isoform also showed binding to hyaluronan up to 60 mM salt, while for the other isoforms binding was observed only up to 150 and 40 mM salt for chondroitin sulfate and hyaluronan, respectively. The low salt concentrations at which these interactions occur are likely to exist in cartilage as shown from equilibrium dialysis studies performed using solutions of chondroitin sulfate (up to 10%, a concentration likely to occur in cartilage). From Scatchard analysis, the affinity of binding of all lysozymes to chondroitin sulfate was similar (Kd = 10(-6) M) and slightly lower than their binding to hyaluronan (Kd = 10(-7) M) of similar molecular mass.

Identification of a hyaluronic acid-binding protein that interferes with the preparation of high-buoyant-density proteoglycan aggregates from adult human articular cartilage

Adult human articular cartilage contains a hyaluronic acid-binding protein of Mr 60 000-75 000, which contains disulphide bonds essential for this interaction. The molecule can compete with proteoglycan subunits for binding sites on hyaluronic acid, and can also displace proteoglycan subunits from hyaluronic acid if their interaction is not stabilized by the presence of link proteins. The abundance of this protein in the adult accounts for the reported inability to prepare high-buoyant-density proteoglycan aggregates from extracts of adult human cartilage [Roughley, White, Poole & Mort (1984) Biochem. J. 221, 637-644], whereas the deficiency of the protein in newborn human cartilage allows the normal recovery of proteoglycan aggregates from this tissue. The protein shares many common features with a hyaluronic acid-binding region derived by proteolytic treatment of a proteoglycan aggregate preparation, and this may also represent its origin in the cartilage, with its production increasing during tissue maturation.

Correlation of lysozyme activity with proteoglycan biosynthesis in epiphyseal cartilage

Pig epiphyseal cartilage (proximal ulna epiphysis) previously incubated into vitro in the presence of sodium [35S]sulfate or [3H]thymidine was either analyzed by autoradiography or separated into 9 morphologically defined consecutive layers and investigated for 35S-incorporation into the guanidinium chloride-extractable proteoglycans and for lysozyme activity. The lowest 35S incorporation and lysozyme activity were determined in the zone of resting cells, but there is a consecutive increase in the rate of proteoglycan synthesis and lysozyme activity toward the diaphyseal cartilage-bone junction, with the maximum at the lower columnar cell zone and a sharp reduction of both parameters at the hypertrophic zone. The maxima of 35S incorporation and [3H]thymidine incorporation do not coincide. The guanidinium chloride-soluble proteoglycans exhibit macromolecular polydispersity. Fractions excluded from as well as retarded by Sepharose 2B gel could be separated and were detected in all zones. The results indicate a correlation of proteoglycan biosynthesis and lysozyme activity in epiphyseal cartilage.

Connective tissue lysozyme in health and disease

As the lysozyme story continues to unfold, rheumatic disease is one area where the study of this fascinating protein will be most important. The special biochemical features of lysozyme--its hexosaminidase function, its ability to bring about transglycosylation, its homology to alpha-lactalbumin, and its cationic nature--suggest that the connective tissues may prove to be the key to the understanding of the function of lysozyme. As methods for its accurate measurement become standardized, better data on the activity of the enzyme in various tissues and body fluids, in both health and disease, will be forthcoming. As additional studies are done to ascertain which of the hypothetical functions attributed to lysozyme are of significance in vivo, it will be the student of the connective tissues and the diseases thereof who can be expected to profit most from an udnerstanding of the role of lysozyme in mammalian biology.