Osteogenesis imperfecta: morphological, histochemical and biochemical aspects. Modifications induced by (+)-catechin

An in vitro model to evaluate the properties of matrices produced by fibroblasts from osteogenesis imperfecta and Ehlers-Danlos Syndrome patients

AIM OF THE STUDY

Osteogenesis imperfecta and Ehlers Danlos syndrome are hereditary disorders caused primarily by defective collagen regulation. Osteogenesis imperfecta patients were divided to haploinsufficient and dominant negative depending on the effect of COL1A1 and COL1A2 mutations whereas Ehlers Danlos syndrome patients had a mutation in PLOD1. Although collagen abnormalities have been extensively studied in monolayer cultures, there are no reports about 3D in vitro models which may reflect more accurately the dynamic cell environment. This is the first study presenting the structural and mechanical characterization of a 3D cell-secreted model using primary patient fibroblasts.

MATERIALS AND METHODS

Fibroblasts from patients with osteogenesis imperfecta and Ehlers Danlos syndrome were cultured with ascorbic acid for 5 weeks. The effect of mutations on cytosolic and secreted collagen was tested by electrophoresis following incubation with radiolabeled ¹⁴C proline. Extracellular matrix was studied in terms of collagen fiber orientation, stiffness, as well as glycosaminoglycan and collagen content.

RESULTS AND CONCLUSIONS

Osteogenesis imperfecta patients with haploinsufficient mutations had higher percentage of anisotropic collagen fibers alignment compared to other patient groups; all patients had a lower percentage of anisotropic samples compared to healthy controls. This correlated with higher average stiffness in the control group. Glycosaminoglycan content was lower in the control and haploinsufficient groups. In cells with PLOD1 mutations, there were no differences in PLOD2 expression. This proof of concept study was able to show differences in collagen fiber orientation between different patient groups which can potentially pave the way towards the development of 3D models aiming at improved investigation of disease mechanisms.

Amine oxidase-like activity of polyphenols. Mechanism and properties

Polyphenols in several oxidation systems gained amine oxidase-like activity, probably due to the formation of the corresponding quinones. In the presence of Cu(II), o- and p-phenolic compounds exhibited amine oxidase-like activity, whereas only the o-phenolic compounds showed the activity in the presence of 1,1-diphenyl-2-picrylhydrazyl radical. The activity was determined by measuring the conversion of benzylamine to benzaldehyde by HPLC. Moreover, gallic acid, chlorogenic acid, and caffeic acid, which are plant polyphenols, converted the lysine residue of bovine serum albumin to alpha-amino-adipic semialdehyde residue, indicating lysyl oxidase-like activity. We also characterized the activity of pyrocatechol, hydroquinone, and pyrogallol in the presence of Cu(II). The oxidative deamination was accelerated at a higher pH, and required O2 and transition metal ions. Furthermore, EDTA markedly inhibited the reaction but not beta-aminopropionitrile, which is a specific inhibitor of lysyl oxidase. Catalase significantly inhibited the oxidation, implying the participation of hydroxyl radical in the reaction, but superoxide dismutase stimulated the oxidation, probably due to its radical formation activity. We discussed the mechanism of the oxidative deamination by polyphenols and the possible significance of the activity for biological systems.

A morphological and ultrastructural study of bone in osteogenesis imperfecta

A morphological and electron microscopic study of bone from patients with osteogenesis imperfecta (OI) has been performed. Bone from OI patients from various anatomical sites has been compared with that from normal, age-, site-, and sex-matched controls. The morphology of OI bone appeared variable among patients and sites of bone examined. Immature woven bone and a poor lamellar pattern were the significant morphological features and demonstrated that OI could not be characterized on the basis of a single histological pattern. At the ultrastructural level, a number of previously unreported features were evident. Abnormal collagen fibers and an altered mineral composition were found in many OI patients, however, the panoramic heterogeneity between clinical types and indeed within a single clinical type made it difficult to classify OI in this manner. The presence of intermitochondrial inclusions containing calcium and phosphorus and the presence of a stromal calcification in the bone in some OI patients suggested an abnormal mineral formation. Qualitatively, no obvious difference in the number of osteoblasts or osteoclasts was observed. The morphology and ultrastructure of OI bone were good indicators of the disease and serve a role in assessing the progress of a patient through diagnosis and treatment. This report presents new ultrastructural findings in collagen and in mineral formation in OI compared with normal human bone.

Possible role of overglycosylation in the type I collagen triple helical domain in the molecular pathogenesis of osteogenesis imperfecta

The underlying defect in patients affected by a form of osteogenesis imperfecta (OI) clarified at the molecular level regards the amount or the structure of type I collagen synthesized. This leads to a decreased and/or abnormal mineral deposition in bone and affects bone mass and/or strength. Abnormal interactions between collagen molecules in the presence of mutant trimers could give rise to abnormal fibrils, which, in turn, can determine incorrect interactions with noncollagenous matrix macromolecules. The interactions can be disturbed or modulated by an abnormal distribution on the collagen fibril surface of electrically charged or hydrophobic groups, or by an increased presence of sugar moieties linked to hydroxylysyl residues due to chain post-translational overmodifications (lysyl overhydroxylation and hydroxylysyl overglycosylation) of the portion of the triple helical domain of abnormal type I collagen molecules N-terminal with respect to the defect localization.

Aortic elastin abnormalities in osteogenesis imperfecta type II

Skin and aortic samples from two patients who died by lethal perinatal Osteogenesis Imperfecta (O.I.) were studied by optical and electron microscopy and compared with similar samples from two normal human fetuses and one newborn child. No significant abnormalities were observed in the dermis of O.I. patients apart from small differences in the diameter of reticular collagen fibrils. On the contrary, in the aortas of both patients collagen fibrils were significantly smaller than in the controls; moreover, elastin lamellae were deeply altered and consisted of roundish aggregates of elastin, massively permeated by cytochemically recognizable glycosaminoglycans. As identical features were described in experimental lathyrism by using inhibitors of the enzyme lysyl oxidase (Pasquali Ronchetti et al., 1984), the conclusion is reached that in the two cases of lethal perinatal O.I. examined, a severe lysyl oxidase deficiency could account for the observed ultrastructural abnormalities of elastin and that, besides defects of collagen type I, additional alterations of cellular metabolism might be responsible for the clinical heterogeneity of the disease.

Proteoglycan histochemistry--a valuable tool for connective tissue biochemists

The histochemistry of connective tissue proteoglycans (PGs) poses two major requirements, 1. for the specific demonstration of a given PG and, 2. at the ultrastructural level, for the examination of the shape of the PG, and its interactions with other molecules and tissue elements. Techniques for the localisation and identification of PGs are discussed, according to the principles behind their application. The strengths and weaknesses of antibody stains are compared with those of mini-molecular reagents, based on resolution, sensitivity, stoichiometry and tissue penetration. The concept of specificity is analysed in this context. The polyanionic characteristics of PGs are exploited to allow very sensitive detection and localisation by cationic probes, both macro- and mini-molecular. Complex formation by heavy metal cations, basic dyestuffs and polycations with PGs is a simple ion-exchange process (basophilia), which can be manipulated to give considerable specificity, e.g. using the critical electrolyte concentration (CEC) concept. The fundamental physical chemical unity of the phenomena of basophilia, CEC and biochemical fractionations of tissue polyanions by anion-exchange is discussed. This unity allows direct quantitative and qualitative comparisons to be made between histochemical and biochemical results at all levels from the tissue sample to the single molecule of PG in situ. The great value of the partnership between microscopy and analytical biochemistry is emphasised. The expanded solution domain of PGs collapses during formation and processing of the 'stained' complex, obscuring molecular detail and possibly resulting in translocation of the PG. Approaches aimed at restoring the initial situation, and their application to electron microscopy of PGs in tissues are outlined. Complexes of PG with ambient polycations may form, either as artefacts during processing or as an integral part of in vivo ultrastructure. Uptake of stain may be partly or totally blocked, in consequence. Ways of investigating, avoiding, or making use of this phenomenon are described. Application of integrated approaches to the study of PG--collagen and PG--elastin interactions in tissues are discussed. Specific interactions and stoichiometric relationship, particularly of dermatan sulphate proteoglycans with type I collagen have been observed, in skin, tendon, and other non-calcifying tissue, but not in bone.

Structural changes of collagen fibrils in skeletal dysplasias. Ultrastructural findings in the iliac crest

The skeletal dysplasias are constitutional, generalized or localized disorders of the skeletal system involving a disturbance of growth and/or bone density; their genetic transmission varies. Pathomorphologically, a combined functional-structural disturbance of the cartilaginous and/or bone tissue is present. Clinically, the result is varying degrees of dwarfism. Within the framework of a systematic examination of skeletal dysplasias, a total of 84 iliac crest specimens/biopsies obtained from stillborn infants and patients varying in age from a few days to 40 years, were investigated in the electron microscope. The sections prepared extended from the perichondrium through the proximal resting zone to the primary mineralization zone. The structure of the collagen fibrils was studied in diastrophic dysplasia, pseudoachondroplasia, the WOLCOTT-RALLISON syndrome, osteogenesis imperfecta, and idiopathic juvenile osteoporosis. In diastrophic dysplasia, pseudoachondroplasia and idiopathic osteoporosis, the cartilaginous ground substance contains collagen fibrils that can vary considerably in length, structure and diameter. In one case of WOLCOTT-RALLISON syndrome, the lacunae of the chondrocytes are found to contain very wide amianthoid-like and inadequately aggregated collagen fibrils. In numerous cases, osteogenesis imperfecta reveals very fine and also irregularly structured collagen fibrils with scarcely discernible cross-striation in the region of the osteoid, which is of varying width. In some of the cases, catechin has a favourable effect on the formation of collagen fibrils, resulting in broader and more densely packed fibrils. In addition, the conditions are associated with considerable intracellular changes in the rough endoplasmic reticulum, the Golgi apparatus and the mitochondria. The varying collagen fibril findings in the cartilage and bone tissue also represent a morphological marker of the combined functional-structural disorder of chondrocytes and/or osteoblasts, and an expression of the differing aetiopathogenesis.

Evidence by in vivo and in vitro studies that binding of pycnogenols to elastin affects its rate of degradation by elastases

Procyanidol oligomers and (+) catechin bound to insoluble elastin markedly affect its rate of degradation by elastases. Insoluble elastin pretreated with procyanidol oligomers (PCO) was resistant to the hydrolysis induced by both porcine pancreatic and human leukocyte elastases. The quantitative adsorption of pancreatic elastase was similar on either untreated or PCO-treated elastin suggesting that the binding of this compound to elastin increases the non-productive catalytic sites of elastase molecules. (+) Catechin-insoluble elastin complexes were partially resistant to the degradation induced by human leukocyte elastase but were hydrolysed at the same rate as untreated samples by a constant amount of pancreatic elastase. In addition, the coacervation profile of kappa-elastin peptides as a function of temperature is greatly modified in presence of these flavonoids. We conclusively evidenced that PCOs bind to skin elastic fibres when injected intradermally into young rabbits. As a result, these elastic fibres were found more resistant to the hydrolytic action of porcine pancreatic elastase when injected to the same site. These in vivo studies further emphasized the potential effect of these compounds in preventing elastin degradation by elastase(s) as occurred in inflammatory processes.

Influence of age, sex and osteogenesis imperfecta on count, protein content, and monoamine oxidase activity of human thrombocytes

We determined the effect of count, age (2 to 24 year), sex, and osteogenesis imperfecta (OI) on the protein content and monoamine oxidase activity in human platelets. The reaction rate in presence of paramethoxybenzylamine was assessed in a sensitive and continuously recording spectrophotometric system. Platelets harvested from control subjects and OI patients displayed significant inverse linear correlations between count and protein content; there was near-constancy of the products of the two variables. The effects of age, sex, and osteogenesis imperfecta on protein content, count, and MAO activity were assessed by multivariate analysis of variance. It was found that, with increasing age, the count increased linearly and the protein content decreased. In patients with OI the protein content was depressed and monoamine oxidase activity elevated regardless of whether the latter was calculated on the basis of pellet protein or of count. The data suggest that, in osteogenesis imperfecta, thrombocytic monoamine and protein metabolism deviate from that of controls.

Altered glycosaminoglycan production in cultured osteogenesis-imperfecta skin fibroblasts

Collagen and glycosaminoglycan syntheses were studied in skin fibroblasts cultured from patients with osteogenesis imperfecta (OI) and from age-matched controls. Collagen synthesis (measured as protein-bound [3H]hydroxyproline) was decreased in all four OI cell lines studied in the present experiments, comprising 16-24% of total protein synthesis (40% in normal cells). Hyaluronic acid production in OI skin fibroblasts per cell was higher than in age-matched controls, but the production of sulphated glycosaminoglycans was at the normal level. Thus the ratio of the hyaluronic acid and sulphated-glycosaminoglycan radioactivities was markedly higher in OI cultures than in control cultures, especially at the exponential phase of growth where the synthesis of hyaluronic acid was highest. Hyaluronic acid in OI had a normal molecular weight when determined by gel filtration on Sepharose 2B. The removal of high-molecular-weight hyaluronic acid from the medium by hyaluronidase had no effect on the rate of collagen secretion in OI cell line 1 (A.T.C.C. 1262), in which the rate of collagen secretion was lowest.

Glycosaminoglycan synthesis in skin fibroblasts from patients with osteogenesis imperfecta

Glycosaminoglycans were analysed from skin fibroblasts with osteogenesis imperfecta (OI) IIA and IIB. The content of sulphated glycosaminoglycans was greatly increased over age-matched controls and to a lesser extent with respect to older age control. Dermatan sulphate in comparison with older control was unaltered in the cells of OI IIA and IIB. The concentration of heparan sulphate was higher in the cells than in the medium, whereas hyaluronic acid, chondroitin sulphate and dermatan sulphate content was higher in the medium. The level of hyaluronic acid was greatly elevated in the medium of OI IIB with respect to both controls.

Bioflavonoid-mediated stabilization of collagen in adjuvant-induced arthritis

In rats with adjuvant-induced arthritis, the effect of (+)-catechin (CA) and 0-(beta-hydroxyethyl) rutosides (HR) on the crosslinking of collagen was studied. Compared with controls the arthritic group showed an increase in the reversibility of neutral salt-soluble collagen gel, solubility of acid-insoluble collagen to denaturing agents and the ratio of alpha/beta subunits of neutral salt-soluble collagen. These results suggest an impaired maturation of collagen in arthritic animals. Administration of CA or HR to the arthritic animals caused a decrease in the reversibility of collagen gel and in the solubility of acid-insoluble collagen to denaturing agents and to pronase. In addition, the electrophoretic patterns of neutral salt-soluble collagen on SDS polyacrylamide gels also showed a decrease in the alpha/beta ratio. All these results may collectively indicate that both flavonoids promote the crosslinking of collagen in arthritic animals.

(+)-Cyanidanol-3 changes functional properties of collagen

About 6-7 (+)-cyanidanol-3 molecules are bound per collagen alpha-chain. The (+)-cyanidanol-3 treated collagen contains an increased number of pepsin-resistant cross-links, is less susceptible to attack by mammalian collagenase, has a higher shrinkage temp and forms unstructured aggregates. Cell and organ culture studies show that these biological systems produce less protein and collagen in the presence of (+)-cyanidanol-3 and that the newly synthesized collagen is less soluble.

Reduced secretion of structurally abnormal type I procollagen in a form of osteogenesis imperfecta

Osteogenesis imperfecta is a clinically and genetically heterogeneous group of inherited connective tissue disorders in which bone fragility is the predominant feature. Cultured dermal fibroblasts from one patient with the lethal perinatal form of osteogenesis imperfecta secrete type I procollagen at a rate half that of normal cells. Short-term labeling experiments and treatment with alpha,alpha'-dipyridyl (which prevents posttranslational prolyl and lysyl hydroxylation) demonstrated that these cells produce two distinct pro alpha 1(I) chains, which are synthesized at the same rate. Analysis of cyanogen bromide peptides indicated that the two chains differ in their primary structures. Thus, structural abnormalities in type I procollagen prevent this molecule from being secreted normally, resulting in an anomalously low ratio of type I procollagen to other extracellular matrix molecules. While the lethal perinatal form of osteogenesis imperfecta may be heterogeneous, we propose that the underlying pathogenesis of at least one form is decreased secretion of type I procollagen.

Effect of bioflavonoids on lysosomal acid hydrolases and lysosomal stability in adjuvant-induced arthritis

In rats with adjuvant-induced arthritis, the effect of (+)-catechin (CA) and 0-(beta-hydroxyethyl) rutosides (HR) on the activity of certain lysosomal acid hydrolases, viz., beta-glucuronidase, beta-N-acetyl glucosaminidase and cathepsin D in serum, liver, kidney and spleen and the stability of liver lysosomes was studied. The activity of these enzymes in arthritic tissues and serum increased significantly. The total activity of beta-glucuronidase in the lysosome-rich fraction from arthritic liver was appreciably decreased, while its release was significantly increased. These results demonstrate the fragility of lysosomes in arthritic tissues. Administration of CA or HR to the arthritic animals was found to have a prophylactic action by stabilizing liver lysosomes and reducing the free lysosomal enzyme activities in serum, liver, kidney and spleen. CA was more effective than HR.

In vitro sulfate turnover in osteogenesis imperfecta congenita and tarda

Sulfate (35SO4(-2)) uptake was studied in confluent skin fibroblasts from three patients with osteogenesis imperfecta "congenita," six patients with osteogenesis imperfecta "tarda," three clinically unaffected relatives of an osteogenesis imperfecta tarda patient, and four controls. Only two of the osteogenesis imperfecta congenita cell strains showed an increased uptake of sulfate, all other cell strains being comparable to the control group. The degradation rate of glycosaminolgycans in mutants as seen by the chase experimentas was comparable to that found in the normal control cell strains. Glucose oxidation was normal in the osteogenesis imperfecta cell strains having an abnormal sulfate uptake. This rules out the possibility of an hypermetabolic state of these cells. These findings do not warrant the use of 35SO4(-2) incorporation in cultured cells as a tool for prenatal diagnosis of osteogenesis imperfecta.