Phenotypic classification of knee osteoarthritis according to pain mechanisms; a clinical observational study.

BACKGROUND: Pain in knee osteoarthritis is considered to be nociceptive. Recently, involvement of neuropathic pain and psychosocial factors in knee osteoarthritis has been reported. However, the following details are unclear: 1) How often are neuropathic pain and psychosocial factors involved? And 2) Which patients are associated with neuropathic pain and psychosocial factors? METHODS: In 104 patients with knee osteoarthritis, we evaluated neuropathic pain factor with a painDETECT questionnaire and catastrophic thinking using the pain catastrophizing scale. Pain intensity was assessed using the visual analog scale; patients with scores below the median were defined as low-pain group and others as high-pain group. Radiographic severity was categorized according to the Kellgren-Lawrence classification, with grades I-II and III-IV defined as low- and high-grades, respectively. We compared the painDETECT and pain catastrophizing scale scores between the low- and high-pain groups and low- and high-grade groups. Furthermore, the painDETECT and pain catastrophizing scale scores were compared among the following four groups: low-grade/low-pain, low-grade/high-pain, high-grade/low-pain, and high-grade/high-pain. RESULTS: Neuropathic pain factor and catastrophic thinking were found in 16% and 34% of patients, respectively. There were no significant differences in both painDETECT and pain catastrophizing scale scores between the two pain intensity groups. Between the two groups of radiographic severity, there was no significant difference in the painDETECT scores; however, the pain catastrophizing scale score was significantly high in the low-grade group. In addition, there was no significant difference in the painDETECT scores among the four groups; however, the pain catastrophizing scale scores were significantly higher in low-grade/high-pain than in high-grade/low-pain patients. CONCLUSIONS: Therefore, 64% had only nociceptive pain factor. Catastrophic thinking was strong in patients with low radiographic severity, especially in those with high pain intensity. Patients with neuropathic pain factor could not be identified from radiographic severity and pain intensity.

17ß-Oestradiol inhibits doxorubicin-induced apoptosis via block of the volume-sensitive Cl(-) current in rabbit articular chondrocytes.

BACKGROUND AND PURPOSE Chondrocyte apoptosis contributes to disruption of cartilage integrity in osteoarthritis. Recent evidence suggested that the volume-sensitive organic osmolyte/anion channel [volume-sensitive (outwardly rectifying) Cl(-) current (I(Cl,vol) )] plays a functional role in the development of cell shrinkage associated with apoptosis (apoptotic volume decrease) in several cell types. In this study, we investigated the cellular effects of 17ß-oestradiol on doxorubicin-induced apoptotic responses in rabbit articular chondrocytes. EXPERIMENTAL APPROACH Whole-cell membrane currents and cross-sectional area were measured from chondrocytes using a patch-clamp method and microscopic cell imaging, respectively. Caspase-3/7 activity was assayed as an index of apoptosis. KEY RESULTS Addition of doxorubicin (1 µM) to isosmotic bath solution rapidly activated the Cl(-) current with properties similar to those of I(Cl,vol) in chondrocytes. Doxorubicin also gradually decreased the cross-sectional area of chondrocytes, followed by enhanced caspase-3/7 activity; both of these responses were totally abolished by the I(Cl,vol) blocker DCPIB (20 µM). Pretreatment of chondrocytes with 17ß-oestradiol (1 nM) for short (approximately 10 min) and long (24 h) periods almost completely prevented the doxorubicin-induced activation of I(Cl,vol) and subsequent elevation of caspase-3/7 activity. These effects of 17ß-oestradiol were significantly attenuated by the oestrogen receptor blocker ICI 182780 (10 µM), as well as the phosphatidyl inositol-3-kinase (PI3K) inhibitors wortmannin (100 nM) and LY294002 (20 µM). Testosterone (10 nM) had no effect on the doxorubicin-induced Cl(-) current. CONCLUSIONS AND IMPLICATIONS 17ß-Oestradiol prevents the doxorubicin-induced cell shrinkage mediated through activation of I(Cl,vol) and subsequent induction of apoptosis signals, through a membrane receptor-dependent PI3K pathway in rabbit articular chondrocytes.

Effect of dynamic compressive loading and its combination with a growth factor on the chondrocytic phenotype of 3-dimensional scaffold-embedded chondrocytes.

BACKGROUND AND PURPOSE: Three-dimensionally (3D-) embedded chondrocytes have been suggested to maintain the chondrocytic phenotype. Furthermore, mechanical stress and growth factors have been found to be capable of enhancing cell proliferation and ECM synthesis. We investigated the effect of mechanical loading and growth factors on reactivation of the 3D-embedded chondrocytes. METHODS: Freshly isolated chondrocytes from rat articular cartilage were grown in monolayer cultures and then in collagen gel. Real-time RT-PCR and histological analysis for aggrecan and type II and type I collagen was performed to evaluate their chondrocytic activity. Then, the 3D-embedded chondrocytes were cultured under either mechanical loading alone or in combination with growth factor. The dynamic compression (5% compression, 0.33 Hz) was loaded for 4 durations: 0, 10, 60, and 120 min/day. The growth factor administered was either basic fibroblast growth factor (bFGF) or bone morphogenetic protein-2 (BMP-2). RESULTS: Mechanical loading statistically significantly reactivated the aggrecan and type II collagen expression with loading of 60 min/day as compared to the other durations. The presence of BMP-2 and bFGF clearly enhanced the aggrecan and type II collagen expression of 3D-embedded chondrocytes. Unlike previous reports using monolayer chondrocytes, however, BMP-2 or bFGF did not augment the chondrocytic phenotype when applied together with mechanical loading. INTERPRETATION: Dynamic compression effectively reactivated the dedifferentiated chondrocytes in 3D culture. However, the growth factors did not play any synergistic role when applied with dynamic compressive loading, suggesting that growth factors should be administered at different time points during regeneration of the transplantation-ready cartilage.

Regulatory role of tyrosine phosphorylation in the swelling-activated chloride current in isolated rabbit articular chondrocytes.

Articular chondrocytes are exposed in vivo to the continually changing osmotic environment and thus require volume regulatory mechanisms. The present study was designed to investigate (i) the functional role of the swelling-activated Cl(-) current (I(Cl,swell)) in the regulatory volume decrease (RVD) and (ii) the regulatory role of tyrosine phosphorylation in I(Cl,swell), in isolated rabbit articular chondrocytes. Whole-cell membrane currents were recorded from chondrocytes in isosmotic, hyposmotic and hyperosmotic external solutions under conditions where Na(+), K(+) and Ca(2+) currents were minimized. The cell surface area was also measured using microscope images from a separate set of chondrocytes and was used as an index of cell volume. The isolated chondrocytes exhibited a RVD during sustained exposure to hyposmotic solution, which was mostly inhibited by the I(Cl,swell) blocker 4-(2-butyl-6,7-dichloro-2-cyclopentyl-indan-1-on-5-yl)oxobutyric acid (DCPIB) at 20 microM. Exposure to a hyposmotic solution activated I(Cl,swell), which was also largely inhibited by 20 microM DCPIB. I(Cl,swell) in rabbit articular chondrocytes had a relative taurine permeability (P(tau)/P(Cl)) of 0.21. Activation of I(Cl,swell) was significantly reduced by the protein tyrosine kinase (PTK) inhibitor genistein (30 microM) but was only weakly affected by its inactive analogue daidzein (30 microM). Intracellular application of protein tyrosine phosphatase (PTP) inhibitor sodium orthovanadate (250 and 500 microM) resulted in a gradual activation of a Cl(-) current even in isosmotic solutions. This Cl(-) current was almost completely inhibited by 4,4-diisothiocyanatostilbene-2,2-disulfonate (DIDS, 500 microM) and was also largely suppressed by exposure to hyperosmotic solution, thus indicating a close similarity to I(Cl,swell). Pretreatment of chondrocytes with genistein significantly prevented the activation of the Cl(-) current by sodium orthovanadate, suggesting that the basal activity of endogenous PTK is required for the activation of this Cl(-) current. Our results provide evidence to indicate that activation of I(Cl,swell) is involved in RVD in isolated rabbit articular chondrocytes and is facilitated by tyrosine phosphorylation.

Swelling-activated Cl(-) current in isolated rabbit articular chondrocytes: inhibition by arachidonic Acid.

Articular chondrocytes play an important role in maintaining the structure and function of the cartilage in synovial joints, which is closely influenced by mechanical or osmotic stress. In the present study, isolated rabbit articular chondrocytes were examined during hyposmotic stress using the whole-cell patch-clamp method. When exposed to hyposmotic external solutions (approximately 5% or 32% decrease in osmolarity), isolated rabbit articular chondrocytes exhibited hyposmotic cell swelling, accompanied by the activation of the swelling-activated Cl(-) current (I(Cl,swell)). I(Cl,swell) was practically time-independent at potentials negative to +50 mV but exhibited rapid inactivation at more positive potentials. I(Cl,swell) was potently inhibited by the Cl(-) channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid, glibenclamide, and tamoxifen, but was little affected by pimozide. I(Cl,swell) was also found to be acutely inhibited by arachidonic acid in a concentration-dependent manner with an IC50 of 0.81 microM. The maximal effect (approximately 100% block) was obtained with 10 microM arachidonic acid. The arachidonic acid metabolites prostaglandin E(2), leukotriene B(4), and leukotriene D(4) had no appreciable effect on IC(l,swell), suggesting that the inhibitory effect of arachidonic acid did not require its metabolism. The present study thus reveals the presence of I(Cl,swell) in rabbit articular chondrocytes that exhibits high sensitivity to direct inhibition by arachidonic acid.

Exogenous collagen-enhanced recruitment of mesenchymal stem cells during rabbit articular cartilage repair.

BACKGROUND: Despite the well-known effect of type-I collagen in promoting cartilage repair, the mechanism still remains unknown. In this study we investigated this mechanism using a rabbit model of cartilage defects. ANIMALS AND METHODS: 5-mm-diameter full-thickness defects were created on both patellar grooves of 53 Japanese white rabbits (approximately 13 weeks old). The left defect was filled with collagen gel and the right defect was left empty. The rabbits were killed and examined morphometrically until the twenty-fourth postoperative week, by (1) evaluation of matrix production, (2) enumeration of the total number of cells engaged in cartilage repair, (3) enumeration of the proliferating cells, (4) localization of mesenchymal stem cells, and (v) localization of apoptotic cells. RESULTS: We found that type-I collagen enhances cell recruitment, and thereby increases the number of proliferating cells. A considerable proportion of the proliferating cells were identified as bone marrow-derived mesenchymal stem cells. However, type-I collagen does not prevent the chondrocyte precursors from undergoing apoptotic disengagement from the chondrogenic lineage. INTERPRETATION: Type-I collagen promotes cartilage repair by enhancing recruitment of bone marrow-derived mesenchymal stem cells. Additional use of agent(s) that sustain mesenchymal stem cells along the chondrogenic path of differentiation may constitute an appropriate environment for cartilage repair.