Low-intensity pulsed ultrasound (LIPUS) treatment of cultured chondrocytes stimulates production of CCN family protein 2 (CCN2), a protein involved in the regeneration of articular cartilage: mechanism underlying this stimulation

OBJECTIVE

CCN family protein 2/connective tissue growth factor (CCN2/CTGF) promotes cartilage regeneration in experimental osteoarthritis (OA) models. However, CCN2 production is very low in articular cartilage. The aim of this study was to investigate whether or not CCN2 was promoted by cultured chondrocytes treated with low-intensity pulsed ultrasound (LIPUS) and to clarify its mechanism.

METHODS

Human chondrocytic cell line (HCS)-2/8, rat primary epiphyseal and articular cartilage cells, and Ccn2-deficient chondrocytes that impaired chondrocyte differentiation, were treated with LIPUS for 20 min at 3.0 MHz frequency and 60 mW/cm² power. Expressions of chondrocyte differentiation marker mRNAs were examined by real-time PCR (RT-PCR) analysis from HCS-2/8 cells and Ccn2-deficient chondrocytes at 30 min and 1 h after LIPUS treatment, respectively. CCN2 production was examined by Western blotting after 5 h of LIPUS treatment. Moreover, Ca²⁺ influx was measured by using a Fluo-4 probe.

RESULTS

The gene expression of chondrocyte differentiation markers and CCN2 production were increased in cultured chondrocytes treated with LIPUS. In addition, Ca²⁺ influx and phosphorylation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK)1/2 were increased by LIPUS treatment, and the stability of TRPV4 and BK_ca channel mRNAs was decreased by siRNA against CCN2. Consistent with those findings, the LIPUS-induced the gene expressions of type II collagen (COL2a1) and Aggrecan (ACAN) observed in wild-type cells were not observed in the Ccn2-deficient chondrocytes.

CONCLUSION

These data indicate that chondrocyte differentiation represented by CCN2 production was mediated via MAPK pathways activated by LIPUS-stimulated Ca²⁺ influx, which in turn was supported by the induced CCN2 molecules in articular chondrocytes.

Prevention of fatigue cracks in ultrahigh molecular weight polyethylene joint components by the addition of vitamin E

Flaking-type wear, so-called delamination, is often observed in polyethylene joint components. This is thought to occur partly due to crack formation and propagation at grain boundaries. This study examined the effect of vitamin E on the crack formation and/or propagation in UHMWPE by using 2-dimensional sliding fatigue testing and micro indenter testing. An in vitro sliding fatigue test was performed under two simplified articulating movements, and the cracks produced were observed by scanning acoustic tomography (SAT). Gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) specimens demonstrated a smaller area of accumulated cracks as compared to virgin specimens, when the loading movement was reciprocated on a single linear locus. However, four out of five gamma-irradiated UHMWPE specimens exhibited severe flaking-like destruction under the complicated sliding condition, suggesting that gamma irradiation accelerated crack propagation under multidirectional loading. All the gamma-irradiated vitamin-E-containing specimens demonstrated no subsurface crack formation and no flaking-like destruction. Results using micro indenter testing showed that the dynamic hardness at grain boundary was higher than that in grain, and was increased by gamma irradiation. This hardening at grain boundary was reduced by adding vitamin E. It is possible that the presence of vitamin E prevents crack propagation partly due to reduced hardness at grain boundaries. The gamma-irradiated vitamin-E-containing UHMWPE is a promising material to prevent flaking-like destruction of polyethylene joint components.

Improved flow injection analysis (FIA) method for determining selenium in biological samples, and the effect of captopril administration on selenium levels and glutathione peroxidase activity in rat

An improved flow injection analysis (FIA) method has been developed for the determination of trace selenium in biological samples, and this method has been applied to investigate the effect of captopril, an antihypertensive drug having a thiol group, on selenium concentrations in the rat blood, liver and urine. After oral administration of captopril, selenium levels in the blood decreased, while those in the liver increased significantly. However, no pronounced effect was observed on the urinary excretion rate. The glutathione peroxidase activities in the blood and the liver were comparable to the changes in the selenium levels.

Thiol exchange reactions involving selenotrisulfides

The occurrence of in vitro thiol exchange reactions involving selenotrisulfides has been documented by HPLC analyses of reaction solutions. Asymmetric selenotrisulfide (RSSeSR') (R,R' = penicillamine, cysteine, glutathione) was formed by the reactions between (i) a mixture of thiols and selenite, (ii) thiol (R'SH) and symmetric selenotrisulfide (RSSeSR), and (iii) symmetric selenotrisulfides (RSSeSR and R'SSeSR'). Further reaction of an asymmetric selenotrisulfide with thiol (R'SH) produced another symmetric selenotrisulfide (R'SSeSR'). These thiol exchange reactions may offer significant information to elucidate intake and metabolism of selenium in vivo.