Melatonin enhances cartilage matrix synthesis by porcine articular chondrocytes

Cytoprotective and anti-inflammatory effects of melatonin in hydrogen peroxide-stimulated CHON-001 human chondrocyte cell line and rabbit model of osteoarthritis via the SIRT1 pathway

Melatonin has potent antioxidant, analgesic, and antinociceptive properties. However, the effects of melatonin against oxidative stress-induced cytotoxicity and inflammatory mediators in human chondrocytes remain poorly understood. This study examined the effects and underlying mechanism of melatonin in hydrogen peroxide (H(2) O(2) )-stimulated human chondrocytes and rabbit osteoarthritis (OA) model. Melatonin markedly inhibited hydrogen peroxide (H(2) O(2) )-stimulated cytotoxicity, iNOS, and COX-2 protein and mRNA expression, as well as the downstream products, NO and PGE(2) . Incubation of cells with melatonin decreased H(2) O(2) -induced Sirtuin 1 (SIRT1) mRNA and protein expression. SIRT1 inhibition by sirtinol or Sirt1 siRNA reversed the effects of melatonin on H(2) O(2) -mediated induction of pro-inflammatory cytokines (NO, PGE(2) , TNF-α, IL-1β, and IL-8) and the expression of iNOS, COX-2, and cartilage destruction molecules. Melatonin blocked H(2) O(2) -induced phosphorylation of PI3K/Akt, p38, ERK, JNK, and MAPK, as well as activation of NF-κB, which was reversed by sirtinol and SIRT1 siRNA. In rabbit with OA, intra-articular injection of melatonin significantly reduced cartilage degradation, which was reversed by sirtinol. Taken together, this study shows that melatonin exerts cytoprotective and anti-inflammatory effects in an oxidative stress-stimulated chondrocyte model and rabbit OA model, and that the SIRT1 pathway is strongly involved in this effect.

Multiple enhancers associated with ACAN suggest highly redundant transcriptional regulation in cartilage

The chondroitin sulfate proteoglycan core protein aggrecan is the major protein constituent of cartilage aside from collagen, and is largely responsible for its distinctive mechanical properties. Aggrecan is required both for proper cartilage formation in development and maintenance of mature cartilage. Prominent ACAN transcription is a conserved feature of vertebrate cartilage, although little is known about its specific transcriptional regulation. We examined the genomic interval containing human ACAN for transcriptional enhancers directing expression to cartilage, using a functional assay in transgenic zebrafish. We tested 24 conserved non-coding sequences, representing ~6% of the total sequence in the interval, and identified eleven independently capable of regulating reporter gene expression in cartilage. These enhancers were widely spaced, from >100kb upstream of the gene to within the first intron. While the majority displayed broad cartilage expression in zebrafish larvae, several were restricted to a subset of cartilage cells in the craniofacial skeleton. In older fish, the enhancers displayed differential activity; some maintained expression, either in all cartilage or preferentially in articular cartilage at the joints, while others were not active. This remarkable degree of overlapping regulatory control has been highly conserved; we identified clear orthologues of six enhancers at the chicken ACAN locus, arranged in the same order relative to the gene. These were also functional in directing expression to cartilage in transgenic zebrafish. Several enhancers contain potential binding sites for Sox9, consistent with its described role as an upstream regulator of ACAN expression. However, others lacked Sox9 consensus binding sites, implicating additional pathways and transcription factors as regulators of ACAN expression in cartilage, either in development or adult tissue. Our identification of these enhancer sequences is the necessary first step in detailed examination of the upstream regulators of ACAN expression.

Extracellular matrix deposited by synovium-derived stem cells delays replicative senescent chondrocyte dedifferentiation and enhances redifferentiation

The aim of this study was to assess the effect of extracellular matrix (ECM) deposited by synovium-derived stem cells (SDSCs) on articular chondrocyte expansion and maintenance of differentiation status and redifferentiation capacity. Passage 0 (P0) pig articular chondrocytes were expanded for six passages on plastic flasks (Plastic), SDSC-derived ECM (ECM), or substrate switching from either Plastic to ECM (PtoE) or ECM to Plastic (EtoP). Cell morphology, gene expression profiles, and immunophenotypes at each passage were used to characterize differentiation status of expanded cells. Chondrocytes at P0, P2, and P6 were assessed for redifferentiation capacity in a pellet culture system treated with either TGF-β1- or serum-containing medium for 14 days, using histology, immunohistochemistry, biochemistry, Western blot, and real-time PCR. We found that ECM not only greatly enhanced chondrocyte expansion but also delayed dedifferentiation of expanded chondrocytes. Intriguingly, compared to a dramatic decrease in CD90+/CD105+ cells and CD90+ cells, CD105+ cells dramatically increased when chondrocytes were plated on Plastic; on the contrary, ECM expansion dramatically increased CD90+ cells and delayed the decrease of CD90+/CD105+ cells. Interestingly, expanded chondrocytes on ECM also acquired a strong redifferentiation capacity, particularly in the pellets treated with TGF-β1. In conclusion, the ratio of CD90 to CD105 may serve as a marker indicative of proliferation and redifferentiation capacity of dedifferentiated chondrocytes. ECM deposited by SDSCs provides a tissue-specific three-dimensional microenvironment for ex vivo expansion of articular chondrocytes while retaining redifferentiation capacity, suggesting that ECM may provide a novel approach for autologous chondrocyte-based cartilage repair.

Melatonin reduces the severity of experimental amoebiasis

BACKGROUND

Melatonin has immunomodulatory effects but very little is known about its influence in protozoan infections, such as Entamoeba histolytica, which causes amoebiasis, a disease with significant morbidity and mortality. In this study, we evaluated the effects of exogenous melatonin interference in experimental amoebiasis and on interactions between human blood cells and E. histolytica trophozoites.

METHODS

The effect of melatonin was investigated in models of experimental amoebiasis in hamsters and rats by evaluating the area of necrosis induced by E. histolytica. The activity of melatonin on the interactions between leukocytes and amoebae was determined by examining leukophagocytosis. For in vitro tests, polymorphonuclear and mononuclear human blood leucocytes were incubated with E. histolytica trophozoites.

RESULTS

The areas of amoebic necrosis were significantly reduced in animals treated with melatonin. Melatonin treatment increased leukophagocytosis but was associated with a greater number of dead amoebae.

CONCLUSIONS

These results suggest that melatonin may play a beneficial role in the control of amoebic lesions, raising the possibility that this drug may be used as an adjuvant in anti-amoebic therapy.