Alain Randoux

Non-enzymatic degradation of acid-soluble calf skin collagen by superoxide ion: Protective effect of flavonoids

Calf skin acid-soluble collagen in microfibrillar form was incubated with free oxygen radicals produced by the system xanthine oxidase + hypoxanthine. This incubation liberated peptides of a size smaller than that of alpha-chains, as demonstrated by SDS-PAGE and by evaluation of the 4-hydroxyproline contained in small peptides. The amount of liberated peptides was found to increase with time. The process was inhibited by addition of superoxide dismutase to the medium but not by addition of catalase. Two flavonoids extracted from bilberries and a third one from grapes were demonstrated to protect collagen against this non-enzymatic proteolytic activity. This work confirms that collagen may be degraded during the process of inflammation and that some flavonoids are endowed with protective properties.

Regulation of matrix metalloproteinase-2(gelatinase A, MMP-2), membrane-type matrixmetalloproteinase-1 (MT1-MMP) and tissue inhibitorof metalloproteinases-2 (TIMP-2) expression byelastin-derived peptides in human HT-1080 fibrosarcoma cell line

Soluble kappa-elastin peptides were shown to stimulate the expression of MMP-2 (but not MMP-9) byhuman fibrosarcoma HT-1080 cells, both at the protein and mRNA levels; maximal effect being observedat a concentration of 25 mg/ml of kappa-elastin. The stimulatory effect could be reproduced using Val-Gly-Val-Ala-Pro-Gly (VGVAPG) peptide, an elastin-derived hydrophobic hexapeptide which represented theelastin receptor binding sequence of tropoelastin. Furthermore, treatment of cells with lactose (30 mM),which dissociated 67-kDa elastin binding protein (EBP) from cell surfaces, completely abolished this effect,suggesting that the elastin receptor could mediate such a response. Using a specific monoclonal antibody,67-kDa EBP was detected in HT-1080 membrane preparations by Western immunoblotting. Following treat-mentwith 25 mg/ml kappa-elastin or 200 mg/ml VGVAPG, increased levels of the active 62-kDa form ofMMP-2 were found in HT-1080 cell extracts. Stimulation of MT1-MMP mRNA expression by treatmentwith elastin-derived peptides (EDPs) was shown by competitive polymerase chain reaction (PCR). A reversezymography analysis revealed that EDPs also stimulated TIMP-2 (but not TIMP-1) production by HT-1080cells. Competitive PCR confirmed increased TIMP-2 mRNA expression by such treatment. These resultssuggest that occupancy of the 67-kDa elastin receptor by elastin-derived peptides enhanced both expressionand activation of proMMP-2 and consequently, could promote the invasive/metastatic ability of tumor cellsexpressing this receptor. ©Kluwer Academic Publishers

Human Blood Monocytes Interact with Type I Collagen Through αxβ2 Integrin (CD11c-CD18, gp150-95)

Human blood monocytes are attracted into connective tissues during early steps of inflammation and wound healing, and locally interact with resident cells and extracellular matrix proteins. We studied the effects of type I collagen on monocyte adhesion and superoxide anion production, using human monocytes elutriated from peripheral blood and type I collagen obtained from rat tail tendon. Both acid-soluble and pepsin-digested type I collagens promoted the adhesion of monocytes, whereas only acid-soluble collagen with intact telopeptides induced the production of superoxide. Adhesion and activation of monocytes on acid-soluble type I collagen depended on the presence of divalent cations. mAbs directed against integrin subunits CD11c and CD18 specifically inhibited adhesion and activation of monocytes on type I collagen. Protein membrane extracts obtained from monocytes were submitted to affinity chromatography on collagen I-Sepharose 4B, and analyzed by Western blotting using specific anti-integrin subunit Abs. In the case of both acid-soluble and pepsin-digested collagens, two bands were revealed with mAbs against CD11c and CD18 integrin subunits. Our results demonstrate that monocytes interact with type I collagen through CD11c-CD18 (αxβ2) integrins, which promote their adhesion and activation. For monocyte activation, specific domains of the type I collagen telopeptides are necessary. Interactions between monocytes and collagen are most likely involved in the cascade of events that characterize the initial phases of inflammation.

Collagen degradation by superoxide anion in pulse and gamma radiolysis

Delipidated collagen fibrils reconstituted from acid-soluble calf skin collagen, suspended in 50 mM phosphate buffer, pH 7.4, containing 100 mM sodium formate, were submitted to pulse radiolysis in Febetron devices or to gamma radiolysis in a 60Co irradiator. A collagen degradation process was found. The kinetics of this degradation was followed by evaluation of the amount of 4-hydroxyproline present in the small peptides liberated during the irradiation period. The yield of 4-hydroxyproline small peptides was low (0.1 mol/100 eV for an initial collagen concentration 3.2 microM). It increased linearly with the dose of irradiation and the concentration of collagen in suspension. The kinetic competition between O2-. dismutation and O2-. reaction with collagen was studied by pulse radiolysis at several concentrations of collagen. A value of the kinetic constant of k(O2-. + collagen) = 4.8 . 10(6) mol-1.l.s-1 was determined.

A new sensitive method for the quantitative evaluation of the hydroxyproline isomers

Abstract Proline, 4-hydroxyproline, and 3-hydroxyproline are combined with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and the fluorescent derivatives separated by thin-layer chromatography on silica gel prior to spectrofluorometric determination. The method is sensitive to 1 pmol, reproducible, and fast. It also permits the measurement of the specifie activities of proline and the hydroxyprolines.

Effects of preformed proline and proline amino acid precursors (including glutamine) on collagen synthesis in human fibroblast cultures

A technique of derivatizing proline and 4-hydroxyproline with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole was used to measure the radioactivities, concentrations and specific activities of proline and hydroxyproline. The technique was used to study the conditions of procollagen synthesis in cultured human foreskin fibroblasts. Procollagen synthesis appeared to be independent of the proline concentration in the medium, in the presence of glutamine, when monitored by the assay of non-dialyzable hydroxyproline, but not when monitored by [14C]proline incorporation. In the absence of unlabelled proline added to labelled proline in the medium, the specific activity of the secreted procollagen did not reach a plateau over a 24-h period. When the medium was supplemented with glutamine, glutamic acid, or aspartic acid, both the radioactivity and concentration of intracellular free proline decreased. Pyrrolidone-2-carboxylic acid and ornithine both induced a slight increase in concentration of the intracellular free proline. Glutamine competed with [14C]proline for incorporation into prolyl-tRNA and procollagen, independently of free intracellular proline, and it stimulated the biosynthesis of procollagen (expressed as non-dialyzable hydroxyproline) by a factor of 2.3.

Nonisotopic Evaluation of Collagen in Fibroblasts Cultures

A method for the evaluation of collagen concentrations in the medium of fibroblasts in culture was developed. Collagen was precipitated with other proteins by addition of ethanol and hydrolyzed by 6 M HCl. The primary amino acids of the hydrolyzate were reacted with o-phthalaldehyde (OPA) and secondary amino acids (Pro, Hyp) were derivatized with 9-fluorenylmethyl-chloroformate (FMOC-Cl). The mixture was separated by isocratic HPLC on a reverse-phase column. FMOC-derivatives were detected by fluorometry, whereas OPA-derivatives were not. This method is suitable for the monitoring of collagen metabolism in fibroblast cultures exposed to various effectors.

A Study of Collagen Metabolism in Cell Cultures by Fluorometric Determination of Proline and Hydroxyproline

A technique of derivatization of proline (Pro) and 4-hydroxyproline (Hyp) by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole permitted the measurement of Pro and Hyp radioactivities, concentrations, and specific activities in the main fractions separated from cultures of fibroblast cells (extracellular collagen and non-collagen proteins, intracellular free Pro and Hyp, Pro- and Hyp-containing peptides, procollagen, and non-collagen proteins). The evaluation of collagen in the medium was obtained from as few as 10(4) cells. The method might advantageously replace [14C] Pro or [3H] Pro incorporation studies. It permits measurement of the size of the Pro pool and the amount of peptides formed by intracellular catabolism of collagen. It demonstrates that the time necessary for a full equilibration of intracellular Pro and intracellular collagen is longer than is generally believed. It avoids the uncertainties of protein labelling, which may vary with uncontrolled variations of the intracellular Pro specific activity.

A parallel between two techniques of extraction of connective tissue macromolecules

A method of extraction of the collagen and noncollagen proteins from deep dermis of young adult rabbits using a 0.1 M tartaric acid solution was set up. The tartaric acid extraction, together with the preliminary neutral salt extraction, solubilized 95% of the total collagen and 98% of the noncollagen proteins, far more than the 6 M guanidinium Cl solution used for comparison. Elastin was not extracted. Studies on the fibrillation of the extracted collagen in neutral solution at 25 degrees C or on the results of pepsin digestion in acidic solution at +4 degrees C showed that the tartaric acid-extracted collagen was in a nondenatured form, whereas that extracted by guanidinium Cl was largely denatured. Polyacrylamide gel electrophoresis (PAGE) indicated that most of the collagen was of type I and that many noncollagen proteins were present, mostly in the molecular weight range of 40 kDa. Bidimensional PAGE gave a reproducible pattern of these noncollagen proteins, showing that several additional proteins were present in tartaric acid extracts and not in guanidinium chloride extracts.

A purified structural glycoprotein determines a strong inhibition of protein synthesis in fibroblast cultures

Abstract An homogeneous fraction of structural glycoproteins (SGP) purified from the connective matrix of rabbit skin, exerts a strong inhibitory influence on the protein syntheses that occur in cultured fibroblasts both from rabbit and human skin. The effect is dose dependent from 0.7 to 8.4 × 10 −6 M. The inhibition of collagen synthesis parallels that of the bulk of proteins.