Mithramycin downregulates proinflammatory cytokine-induced matrix metalloproteinase gene expression in articular chondrocytes

Interleukin-1 (IL-1), IL-17 and tumor necrosis factor alpha (TNF-α) are the main proinflammatory cytokines implicated in cartilage breakdown by matrix metalloproteinase (MMPs) in arthritic joints. We studied the impact of an anti-neoplastic antibiotic, mithramycin, on the induction of MMPs in chondrocytes. MMP-3 and MMP-13 gene expression induced by IL-1β, TNF-α and IL-17 was downregulated by mithramycin in human chondrosarcoma SW1353 cells and in primary human and bovine femoral head chondrocytes. Constitutive and IL-1-stimulated MMP-13 levels in bovine and human cartilage explants were also suppressed. Mithramycin did not significantly affect the phosphorylation of the mitogen-activated protein kinases, extracellular signal-regulated kinase, p38 and c-Jun N-terminal kinase. Despite effective inhibition of MMP expression by mithramycin and its potential to reduce cartilage degeneration, the agent might work through multiple unidentified mechanisms.

Age-related changes in parathyroid hormone-related protein and vascular endothelial growth factor in human osteoblastic cells

Osteogenesis and angiogenesis occur in a coordinated manner in skeletal tissue, so that impaired angiogenesis is associated with decreased bone formation in aged subjects. However, the interaction between bone endothelium and osteoblastic cells is poorly understood. Parathyroid hormone-related protein (PTHrP), a bone factor which modulates osteoblastic cell growth and/or differentiation, stimulates vascular endothelial growth factor (VEGF), a potent angiogenic factor, in primary cultures of human osteoblastic (hOB) cells. In the present study, we examined the age-related changes of both factors in these cells. Human OB cells were isolated from trabecular bone samples from knee or hip explants obtained from 45 osteoarthritic patients: 12 <60 years (21-59 years), 5 women and 7 men, and 33 >60 years (61-82 years), 20 women and 13 men. Cell total RNA was isolated, and mRNA analysis was performed by reverse transcription-polymerase chain reaction. Relative ratios of amplified products with respect to glyceraldehyde-3-phosphate dehydrogenase were then calculated. PTHrP and VEGF were measured in the cell-conditioned medium, after stimulation with (or without) 10 nM 1,25(OH)(2)D(3) for 72 h, using specific immunoradiometric assay and a competitive immunoassay, respectively. A positive correlation was found between PTHrP and VEGF (both mRNA and secreted protein), and also between PTHrP mRNA and the secreted protein levels, in these cells. PTHrP, both mRNA and protein secretion levels, and VEGF secreted values were higher in knee hOB cells than in hip hOB cells only in the younger group. In addition, a decrease in the secreted levels of these factors occurs with aging only in hOB cells from knee. Treatment with 10 nM 1,25(OH)(2)D(3) induced a lower inhibitory response of PTHrP secretion, and a higher stimulatory response of secreted VEGF, in hOB cells with age. These findings indicate that age-related bone loss in humans is associated with a decrease in the osteoblastic secretion of both PTHrP and VEGF in the knee, a predominantly trabecular bone. These data might provide a rationale to explain the impaired angiogenesis associated with trabecular bone loss in aging.

Influence of proteoglycan contents and of tissue hydration on the frictional characteristics of articular cartilage

In this work, the hypothesis that water content and substances present on the articular surface play an important role in lubrication through the formation of a layer with a high content of water on the articular surface is analysed. The hydrophilic properties of proteoglycans exposed at the articular surface and hydration of tissue are the main responsible factors for the formation of this layer. The role of the articular surface in the frictional characteristics of articular cartilage was examined using specimens (femoral condyles of pigs) with intact and wiped surfaces tested in intermittent friction tests. Results indicated that the intact condition presented low friction in comparison with the wiped condition. The measured water loss of the articular cartilage after sliding and loading indicated a gradual decrease in the water content as the time evolved, and rehydration was observed after the submersion of unloaded specimens in the saline bath solution. Micrographic analyses indicated the presence of a layer covering the articular surface, and histological analyses indicated the presence of proteoglycans in this superficial layer. The hydration of the cartilage surface layer and proteoglycan in this layer influence lubrication.

The origin of osteoprogenitor cells responsible for heterotopic ossification following hip surgery: an animal model in the rabbit

PURPOSE

To investigate the source of osteoprogenitor cells responsible for heterotopic ossification (HO) following total hip arthroplasty in an animal model.

METHODS

New Zealand White (NZW) rabbits (n = 20) received a radiation treatment 24 h preoperatively to the hip joint of one hindquarter and to the femoral shaft of the contralateral side. Subjects underwent bilateral hip surgery 24 h after treatment. Subjects were euthanized and radiographed 4 months postoperatively. Heterotopic ossification was graded according to a modified Brooker scale. Mean grade, intra-observer reliability, and statistical significance (p < 0.05) were evaluated to compare the severity of heterotopic ossification between hindquarters treated with hip irradiation versus those treated with femoral shaft irradiation.

RESULTS

The Fleiss Weighted Kappa Statistic indicated "almost perfect" (0.872) intra-rater reliability of radiographic heterotopic ossification grading. The average heterotopic ossification grade for the group receiving radiation to the hip was significantly greater than that for the group receiving radiation to the femoral shaft (2.575 versus 2.0, p < 0.02).

CONCLUSION

Although both have some beneficial effect, our results demonstrate that irradiation of the femoral canal is significantly more effective than irradiation of the hip joint and abductor musculature for heterotopic ossification prophylaxis. This suggests that osteoprogenitor cells responsible for heterotopic ossification originate from both the hip abductors and the femoral canal, but the data provide indirect evidence that the femoral canal may be a more dominant source of these cells in the rabbit model.

Patterns of osteocytic endothelial nitric oxide synthase expression in the femoral neck cortex: differences between cases of intracapsular hip fracture and controls

Evidence indicates that extensive amalgamation of adjacent resorbing osteons is responsible for destroying the microstructural integrity of the femoral neck's inferior cortex in osteoporotic hip fracture. Such osteonal amalgamation is likely to involve a failure to limit excessive resorption, but its mechanistic basis remains enigmatic. Nitric oxide (NO) inhibits osteoclastic bone destruction, and in normal bone cells its generation by endothelial nitric oxide synthase (eNOS, the predominant bone isoform) is enhanced by mechanical stimuli and estrogen, which both protect against fracture. To determine whether eNOS expression in osteocytes reflects their proposed role in regulating remodeling, we have examined patterns of osteocyte eNOS immunolabeling in the femoral neck cortex of seven cases of hip fracture and seven controls (females aged 68-96 years). The density of eNOS+ cells (mm(-2)) was 53% lower in the inferior cortex of the fracture cases (p < 0.0004), but was similar in the superior cortex. eNOS+ osteocytes were, on average, 22% further from their nearest blood supply, than osteocytes in general (p < 0.0001) and the nearest eNOS+ osteocyte was 57% further from its nearest canal surface (p < 0.0001). This differential distribution of eNOS+ osteocytes was significantly more pronounced in the cortices of fracture cases (p < 0.0001). We conclude that the normal regional and osteonal pattern of eNOS expression by osteocytes is disrupted in hip fracture, particularly at sites that are loaded most by physical activity. These results suggest that eNOS+ osteocytes may normally act as sentinels confining resorption within single osteons. A reduction in their number, coupled to an increase in their remoteness from canal surfaces, may thus permit the irreversible merging of resorbing osteons, and thus contribute to the marked increase in the fragility of osteoporotic bone.

Wear debris and cytokine production in the interface membrane of loosened prostheses

In this study, thirty-nine patients were examined. All of them suffered from hip joint prostheses loosening and underwent revision surgery. Bioptic samples were collected at the interface between bone and implant either at the stem or cotyle level. Immunohistochemistry was performed to detect IL-1alpha, IL-1beta, IL-6 and TNF, cytokines that directly cause bone resorption and indirectly induce synthesis of other bone resorbing cytokines. Quantitative analysis of the positive cells and correlation with clinical data was performed. It resulted that there is a great variability in positive cells for cytokines according to the harvest site; anyway, cytokines tend to be higher in patients carrying a joint prosthesis with polyethylene acetabular component and it is associated with plastic wear particles, even though there is no direct correlation between wear amount and cytokine levels. There is a statistically significant negative correlation between metal wear and a cytokine (IL-6); cytokines levels do not depend on the implant time to failure and do not correlate with pain score. As expected, cytokines levels tend to be lower in subjects being treated with non-steroidal antiinflammatory drugs. It can be concluded that plastic wear is the factor inducing the highest cytokine levels in the tissues around the prosthesis at the interface; cytokines that are an indicator of osteolysis risk.

Influence of skeletal site of origin and donor age on 1,25(OH)2D3-induced response of various osteoblastic markers in human osteoblastic cells

Age-related bone loss may be a consequence of a lack of osteoblastic formation and/or function. In vitro, the osteoblastic response to 1,25(OH)2D3, an important regulator of osteoblastic function, appears to depend on the stage of osteoblastic maturation. In this study, we examined the response to 1,25(OH)2D3 of C-terminal type I procollagen (PICP), alkaline phosphatase (ALP), and osteocalcin (OC) secretion in primary cultures of osteoblastic cells from human trabecular bone (hOB). Forty-four bone samples were obtained from subjects undergoing knee arthroplastia, 20 aged 50-70 (64 +/- 5), and 24 >70 (73 +/- 2) years. Another 33 bone samples were obtained from subjects undergoing hip arthroplastia, 21 were aged 50-70 (64 +/- 4) and 12 >70 (75 +/- 5) years. Pooling knee and hip hOB cell cultures, we found that PICP secretion decreased after 1,25(OH)2D3 in hOB cells from the older group (>70 years). Treatment with 1,25(OH)2D3 increased ALP secretion in these cells only in the younger group (50-70 years), whereas it increased OC secretion in hOB cells in both age groups. By pooling hOB cell cultures from both age groups we found that knee hOB cells increased OC secretion, and decreased PICP secretion, after 1,25(OH)2D3. This metabolite also increased OC secretion in hip hOB cells. Considering the influence of donor age at the same skeletal site, 1,25(OH)2D3 was found to stimulate ALP secretion only in knee hOB cells in the younger group. In contrast, this metabolite decreased ALP secretion in hip hOB cells in the older group. PICP secretion decreased after 1,25(OH)2D3 only in hOB cells in the older group, at both skeletal sites. In age-matched cultures, OC secretion was lower in hip hOB cells compared with those from the knee in the older group, but was similar in these cell cultures from both skeletal sites in the younger group. OC secretion after 1,25(OH)2D3 stimulation did not show age differences in knee hOB cells, but was lower in hip hOB in the older group. In summary, our results demonstrate that the response of various osteoblastic markers to 1,25(OH)2D3 in primary cultures of hOB cells depends on the donor age and skeletal site of origin.

Oxidative stress induced by humic acid solvent extraction fraction in cultured rabbit articular chondrocytes

Kashin-Beck disease (KBD), an endemic, chronic osteoarthritic disorder with necrosis of chondrocytes, commonly occurs in China. The humic substance present in the drinking water of endemic areas has been proposed as one of the causative factors. In this study an in vitro cell culture system was used to investigate the damaging effects of humic acid (HA), a constituent of humic substance, on cultured rabbit articular chondrocytes. The commercial Aldrich humic acid (AHA) was fractionated with a series of organic solvents including n-hexane, benzene, ethyl acetate, and methanol. Among the several fractions of AHA, the ethyl acetate fraction (AHA-[EA]) displayed the most potent inhibitory effect on the survival of chondrocytes in clonogenic assays. Cellular injury induced by AHA-[EA] was evaluated by measuring cell viability with methylthiazol tetrazolium (MTT) and by determining the release of intracellular lactate dehydrogenase (LDH). Incubation of chondrocytes with AHA-[EA] (100-500 microg/ml) for 12 h produced a concentration-dependent decrease in cell viability and increase in LDH release. In addition, AHA-[EA] triggered lipid peroxidation manifested by elevated malondialdehyde (MDA) formation. In chemiluminescence assay, AHA-[EA] at the concentrations of 150-600 microg/ml caused 6- to 15-fold increases of luminol-amplified chemiluminescence responses, which are considered to reflect the production of hydrogen peroxide (H2O2). Moreover, pretreating the cells with 500-750 U/ml of catalase significantly prevented the loss of cell viability, while superoxide dismutase (SOD) enhanced the adverse effect of 300 microg/ml AHA-[EA]. Data suggest that the injury to chondrocytes induced by AHA-[EA] may be first through O2.- production, which is then converted into H2O2, thus initiating lipid peroxidation and leading to chondronecrosis observed in KBD.

In vitro evaluation of stiffness graded artificial hip joint femur head in terms of joint stresses distributions and dimensions: finite element study

The aim of the present work is to evaluate the artificial hip joint femur head that is made of Stiffness Graded (SG) material in terms of joint stresses distributions and dimensions. In this study, 3D finite element models of femur head that is made of SG material and traditional femur heads made of Stainless Steel (SS), Cobalt Chromium alloy (Co Cr Mo) and Titanium alloy (Ti) have been developed using the ANSYS Code. The effects on the total artificial hip joint system stresses due to using the proposed SG material femur head (with low stiffness at the outer surface and high stiffness at its core) have been investigated. Also, the effects on the polymeric cup contact stresses due to the use of different sizes of femur heads, presence of metal backing shell and presence of radial clearance (gap) between cup and femur head have been investigated. The finite element results showed that using SG femur head resulted in a significant reduction in the cup contact stresses even for small femur heads compared with Ti alloy, SS and Co Cr Mo femur heads. The presence of radial clearance resulted in significant increase in the cup stresses especially for small femur heads. Finally, the presence of SS metal backing shell resulted in slight increase in the hip joint stresses especially for small femur head joints. This work analyzes successfully the usage of proposed SG material as femur head in order to reduce the predicted stresses at the total hip joint replacement due to the redistribution of strain energy in the hip prostheses. Therefore, the present results suggest that minor changes in design and geometrical parameters of the hip joint have significant consequences on the long term use of the joint and should be taken into consideration during the design of the hip joint.

Cartilaginous differentiation in the joint capsule

The proliferation and differentiation of cells are greatly influenced by their environment. Many growth factors and cytokines are reported to be environmental factors that affect the proliferation and differentiation of cells. Mechanical stress is also considered to influence these physiological reactions. The joint capsule, which is a part of the joint tissue, plays a very important role in the stability of the joint and in maintaining the intracapsular phenomenon. In patients with dislocated hip arthropathy, this capsule is involved in the weightbearing function by forming a sliding surface between the capsule and the femoral head articular cartilage. The surface of the tissue macroscopically shows cartilaginous change, which indicates cartilaginous differentiation caused by mechanical stress. We examined the cartilage-specific proteoglycan component, which is composed of cartilaginou matrix at the differentiation site. We investigated proteoglycan production, molecular size, and the gene expression of cartilaginous substrate. At the inner layer of the weightbearing area of the joint capsule, proteoglycan production was significantly higher than that of other noncartilaginous tissue. We also identified the gene expression of cartilaginous proteoglycan using the reverse transcription polymerase chain reaction (RT-PCR) method.

Biosynthetic response of cultured articular chondrocytes to mechanical vibration

The objective of this study was to determine the effects of mechanical vibration loading on DNA and proteoglycan syntheses in cultured rabbit articular chondrocytes. Chondrocyte culture plates were placed in a vibratory apparatus and subjected to a mechanical vibratory load at various frequencies and periods in culture. Mechanical vibration was applied at a sinusoidal waveform of 1.4 g acceleration with frequencies of 200, 300, 400, 800, and 1600 Hz. 3H-Thymidine and H2(35)SO4 incorporation were used to detect radiolabeled DNA and proteoglycan syntheses, respectively. A frequency of 300 Hz showed a time-dependent augmentation of DNA synthesis and gave a maximal increase at day 3 with periodic vibration (8 h per day) and at 72 h or longer with continuous vibration. It also promoted proteoglycan synthesis in long-term culture (from 3 to 15 days) by periodic vibration. However. frequencies above 400 Hz suppressed biosynthesis. These results suggest that mechanical vibration at certain frequencies may modulate biosynthetic response of articular chondrocytes.

Structural peculiarities of the tissue formed in modelling of the articular surface

A model of articular cavity with smooth cover was produced by influence of shape-forming element on regenerating bone tissue. Morphological, ultrastructural, histochemical, and biochemical peculiarities of the tissue of the formed articular surface are described.

Histologic, biochemical, and ion analysis of tissue and fluids retrieved during total hip arthroplasty

Large amounts of metal and polyethylene debris and high ion readings are found in capsule and fibrous membranes of both loose titanium and cobalt-chromium stems. Prostaglandin E2, interleukin-1, and collagenase levels are elevated when compared to control values with collagenase having the highest and most consistent elevations. Synovial fluid and blood ion readings were elevated in loose cemented and cementless stems made from both materials. Blood ion readings were not elevated in fixed stems. Fixed stems had much less particulate debris in soft tissues. The data showed that failure of most metal hip stems was initially due to a mechanical cause, with high debris and ion counts occurring secondarily in capsule and fibrous membranes. Particulate debris and high ion readings are primarily a focal problem contained by the periprosthetic fibrous connective-tissue encapsulation within the femoral canal and joint capsules. No systemic problems were manifest in any of the patients examined and followed in this study.