Differences in collagen metabolism between normal and osteoarthritic human articular cartilage

Normal human articular cartilage synthesizes only one type of a chain, which exhibits the chromatographic behavior of the alpha(l)(II) chains described for chick and bovine cartilage. Osteoarthritic cartilage, on the other hand, synthesizes in addition a collagen containing alpha(2) chains and beta components. The different structural features of the two types of collagen may account for some of the functional defects of osteoarthritic cartilage.

Characterization of collagen and its precursors synthesized by rabbit-articular-cartilage cells in various culture systems

Rabbit articular cartilage synthesizes type II collagen, comprised of alpha1(II) chains, in vivo or in vitro. Chondrocytes from the same tissue have the ability to produce type I chollagen with the chain composition 2alpha(I)-alpha2 or type II collagen, depending upon the culture systems in which they are maintained. Type I collagen and its precursors have been identified in the medium of monolayer cultures. Upon transfer from monolayer to suspension cultures, the cells synthesize type II collagen in the medium devoid of CaCl2 and type I collagen and its precursors in the complete medium.

Synthesis of collagen by chondrocytes in suspension culture: modulation by calcium, 3':5'-cyclic AMP, and prostaglandins

Rabbit articular chondrocytes synthesize type II collagen [3alpha(1)(II)] in vivo and type I collagen [2alpha(1)(I).alpha(2)] in monolayer cultures. In suspension culture the nature of phenotype depends on extracellular Ca(2+). The relationship of Ca(2+) and 3':5'-cyclic AMP (cAMP) in regulation of collagen synthesis has been investigated. In suspension culture, cAMP levels of chondrocytes increase by 2- to 3-fold and then reach basal values regardless of the presence or absence of extracellular Ca(2+). The cells, however, synthesize primarily type II collagen in the absence of CaCl(2) in the medium and type I collagen in medium containing 1.8 mM CaCl(2). If CaCl(2) is added when intracellular cAMP levels are low, the phenotype is type I collagen. These observations minimize the role of cAMP as a second messenger in the chondrocyte culture system. Increasing endogenous cAMP with a phosphodiesterase inhibitor or adding exogenous dibutyryl-cAMP leads the cells to synthesize type I collagen, although this effect is significantly less pronounced if the medium contains ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA). Increased concentrations of cAMP may mobilize the intracellular calcium pools and activate the cells to switch their phenotypic expression. Prostaglandins E(2) and F(2)alpha, thought to be involved in rheumatoid arthritis and bone resorption, have no significant effect on cAMP content of chondrocytes and alter their collagen phenotype to a small extent.

Metabolic changes in rabbit articular cartilage due to inflammation

The effect of inflammation on the articular cartilage of rabbit knee joints were studied. The inflammation was induced by intraarticular injections of corton oil or rabbit peritoneal leukocyte lysates. An increase in the activities of various lysosomal enzymes was observed in the synovial fluid as well as in the cartilage of the inflamed joints. Loss of proteoglycans, increased rate of degradation of collagen and proteoglycans, and increased rate of their synthesis were evident in the treated cartilage. The rate of uptake of 3H-thymidine was also increased. A significant change was observed in the type of collagen synthesized by these explants in vitro. In addition to synthesizing their characteristics Type II collagen, the cartilage explants from the treated joints synthesized Type I collagen.

Chemical changes associated with aging of collagen in vivo and in vitro

Collagen extracted from rat skin by neutral-salt solutions contains less aldehydes than the more insoluble collagen fractions. The concentration of aldehydes in collagen is directly related to its capacity to form stable cross-linked gels, which do not redissolve on cooling and become more insoluble in a variety of reagents. Whereas the absorption spectrum of neutral-salt-soluble collagen treated with N-methylbenzothiazolone hydrazone resembles that of acetaldehyde, the more insoluble collagen fractions show increasing amounts of a component that behaves like an alphabeta-unsaturated aldehyde. The ratio between alpha- and beta-sub-units present in a particular fraction of soluble collagen seems to be constant and independent of the age of the animal. Neutral-salt-soluble collagen, which has a low concentration of beta-components, will generate intramolecular bonds if gelled at 37 degrees . These intramolecular bonds seem to precede the formation of stable intermolecular cross-links, since these gels can redissolve when cooled to yield a soluble collagen with a higher content of beta-components of intramolecular origin.

Effects of calcitonin and parathyroid hormone on the metabolism of chondrocytes in culture

Rabbit articular chondrocytes in suspension culture synthesize Type II collagen [3alpha1(II)] in the absence of extracellular Ca2+ and Type I collagen [2alpha1(I) - alpha2] in the complete medium. As a result of pre-treatment in monolayer culture with calcitonin or parathyroid hormone in the complete medium, an influx of Ca2+ into the cells occurs. These cells produce mainly Type I collagen when transferred to suspension cultures in the medium devoid of CaCl2. If added directly to the suspension culture medium containing no CaCl2, calcitonin stimulates an active efflux of Ca2+ from the cells into the medium and leads the cells to synthesize Type I collagen. Under similar conditions, parathyroid hormone does not change the collagen-phenotype.

Isolation and characterization of cyanogen bromide peptides from the collagen of bovine articular cartilage

Significant amounts of native collagen can be extracted from bovine articular cartilage after removal of the acid mucopolysaccharides by controlled proteolysis. The fraction thus solubilized upon denaturation gives rise to three identical alpha chains. Cleavage of these chains with CNBr generated nine peptides, all of which contain glycine as one-third of their total amino acid residues. Two of the smaller peptides CB-1 and CB-2 contain partially hydroxylated proline. A similar CNBr digest of intact cartilage also gives a series of peptides identical with those obtained from the soluble cartilage collagen. The absence of cross-linking peptides, the fact that only few beta components are seen in articular cartilage collagen and the similarity in peptide pattern between the two collagen fractions investigated, suggests that this collagen is stabilized by a different cross-linking mechanism, possibly involving an association with the tissue proteoglycans.

Have the COVID-19 pandemic and lockdown affected children's mental health in the long term? A repeated cross-sectional study

OBJECTIVE

The study aimed to evaluate the impact of the COVID-19 pandemic on levels of anxiety and depressive symptoms in children and adolescents.

DESIGN

Cross-sectional surveys were carried out on the mental health of children; one survey was conducted before the COVID-19 pandemic and one into the pandemic, 15 months after the school closures and implementation of lockdown and social distancing. Demographic data and COVID-19 pandemic-related data were collected from specific parent-report and self-report questionnaires.

PARTICIPANTS

Participants included children and adolescents between ages 6 and 16 years, attending a tertiary care hospital without any diagnosed major psychiatric or chronic disorder.

ANALYSIS

Data were collected at two points (before the COVID-19 pandemic and during it) and compared. Levels of anxiety and depressive symptoms were compared and tested for statistically significant differences between these two points using appropriate statistical tests. Regression models were constructed to predict the factors affecting increased anxiety levels and depressive symptoms in the COVID-19 period.

RESULTS

832 and 1255 children/adolescents were included in the study during the pre-COVID-19 and COVID-19 times, respectively. The median age of the participants was 10 years (IQR=4 years). The median (IQR) Spence Children's Anxiety Scale score was 24 (12) at the pre-COVID-19 point and 31 (13) during the COVID-19 pandemic (p<0.001, r=-0.27). 11% and 16% of children reported being depressed at these two-time points, respectively (p=0.004, φ_c=-0.063). Regression analysis showed that many factors, including the duration of smartphone use, female gender and only child status, were associated with increased anxiety or depression levels.

CONCLUSION

A large proportion of children had elevated anxiety and depressive symptoms during the pandemic relative to before the pandemic, suggesting a need for measures to engage children in healthy habits to protect children's mental health and continuous monitoring of children during such scenarios.