Interest of animal models in the preclinical screening of anti-osteoarthritic drugs

First in Vivo SPECT Imaging of Mouse Femorotibial Cartilage Using 99mTc-NTP 15-5

This study aimed to report the first single-photon emission computed tomographic (SPECT) imaging of articular cartilage in mice using 99mTc-NTP 15-5 radiotracer. Mice intravenously injected with 99mTc-NTP 15-5 were submitted to (1) dynamic planar imaging, (2) static planar imaging, (3) 1 mm pinhole SPECT acquisition, and (4) dissection. Tomographic reconstruction of SPECT data was performed with a three-dimensional ordered subset expectation maximization algorithm, and slices were reconstructed in three axes. 99mTc-NTP 15-5 rapidly accumulated in the joint, with a peak of radioactivity being reached from 5 minutes postinjection and maintained for at least 90 minutes. Given that bone and muscle did not show any accumulation of the tracer, highly contrasted joint imaging was obtained from 15 minutes postinjection. When 1 mm pinhole SPECT acquisition was focused on the knee, the medial and lateral compartments of both the femoral condyle and tibial plateau were highly delineated, allowing a separate quantitation of tracer accumulation within each component of the femorotibial joint. A good correlation was found between tracer uptake determined by region of interest analysis of both planar and SPECT scans and dissection. This new approach to imaging of cartilage in mice provides joint functionality assessment in vivo, giving a unique opportunity to achieve a greater understanding of cartilage physiology in health and disease.

Early detection and monitoring of cartilage alteration in the experimental meniscectomised guinea pig model of osteoarthritis by 99mTc-NTP 15-5 scintigraphy

PURPOSE

This study in the meniscectomised guinea pig aimed to demonstrate that the radiotracer (99m)Tc-NTP 15-5 would have pathophysiological validity for in vivo osteoarthritis imaging.

METHODS

The specificity of (99m)Tc-NTP 15-5 for cartilage was determined in healthy animals (n = 13), by tissue radioactivity counting, joint autoradiography and scintigraphy. (99m)Tc-NTP 15-5 scintigraphy was performed at 20, 50, 80, 115, 130, 150 and 180 days after medial meniscectomy (n = 10 MNX) or sham operation (n = 5), and scintigraphic ratios (operated/contralateral) were calculated for femoral (F) and tibial (T) areas. F and T ratios were compared with those of (99m)Tc-MDP bone scintigraphy. At the study end-point, autoradiographic analysis of joint (99m)Tc-NTP 15-5 distribution and macroscopic scoring of cartilage integrity were performed.

RESULTS

The high and specific accumulation of (99m)Tc-NTP 15-5 in normal cartilage (about 5.5 +/- 1.7 % of injected dose/g of tissue), which permitted joint imaging with high contrast, was affected by osteoarthritis. In the MNX group, (99m)Tc-NTP 15-5 accumulation in cartilage within the operated joint, relative to the contralateral joint, was observed to change in the same animals as pathology progressed. Although F and T ratios were significantly higher in MNX (F = 1.7 +/- 0.2; T = 1.6 +/- 0.1) than in shams (F = 1.0 +/- 0.1; T = 1.0 +/- 0.1) at day 50, they were significantly lower in MNX (F = 0.6 +/- 0.1; T = 0.7 +/- 0.1) than in shams (F = 1.0 +/- 0.1; T = 0.9 +/- 0.1) at day 180. No change in (99m)Tc-MDP uptake was observed over 6 months. Macroscopic analysis confirmed features of osteoarthritis only in MNX knees.

CONCLUSION

These results in MNX guinea pigs provide additional support for the use of (99m)Tc-NTP 15-5 for in vivo imaging of osteoarthritis.

Gene transfer with HSP 70 in rat chondrocytes confers cytoprotection in vitro and during experimental osteoarthritis

Osteoarthritis is characterized by a gradual degradation of extracellular matrix, resulting from an excess of chondrocyte cell death, mainly due to an increase in apoptotis. Recent studies have revealed the essential role of HSP70 in protecting cells from stressful stimuli. Therefore, overexpressing HSP70 in chondrocytes could represent a good strategy to prevent extracellular matrix destruction. To this end, we have developed a vector carrying HSP70/GFP, and transduced chondrocytes were thus more resistant to cell death induced by mono-iodoacetate (MIA). To overcome the barrier-effect of matrix, we investigated the efficacy of plasmid delivery by electroporation (EP) in rat patellar cartilage. Two days after EP, 50% of patellar chondrocytes were HSP/GFP+. After 3 months, long-term expression of transgene was only depicted in the deep layer (20-30% positive cells). HSP70 overexpression inhibited the natural endochondral ossification in the deep layer, thus leading to a lesser decrease in chondrocyte distribution. Moreover, overexpression of HSP70, after a preventive EP transfer in rat patella, was sufficient to decrease the severity of osteoarthritis-induced lesions, as demonstrated histologically and biochemically. In conclusion, intracellular overexpression of HSP70, through EP delivery, could protect chondrocytes from cellular injuries and thus might be a novel chondroprotective modality in rat OA.

Dose-response relationship for exercise on severity of experimental osteoarthritis in rats: a pilot study

OBJECTIVE

To investigate the influence of a calibrated exercise on the progression of structural lesions in an experimental model of osteoarthritis (OA) in the rat, and to explore the effect of exercise on the level of chondrocyte caspase-dependent apoptosis and of Hsp70.

METHODS

The OA model was induced by anterior cruciate ligament transection (ACLT). Rats were placed in 4 experimental groups: operated (ACLT) free moving rats, and 3 exercise groups (slight, moderate and intense) subjected to running training. Rats were killed 14 and 28 days after surgery.

RESULTS

On D14 histological assessment demonstrated a beneficial influence of a slight and a moderate exercise vs control ACLT group. Hsp70 increased significantly in the moderate group vs controls. On D28, histological lesions strongly decreased in the slight and moderate exercise groups vs ACLT group, while an intense effort abolished this beneficial trend. Interestingly, the concomitant course of apoptotic events (caspase 3-positive cells) and the co-expression of Hsp70 in the various groups varied, when significant, in an inverse manner. In the intense group this overexpression was not noted, as a "burn out" appeared, thus leading to a loss of this protective effect.

CONCLUSION

This study shows that a calibrated slight or moderate exercise exerts a beneficial influence on the severity of chondral lesions in ACLT rats. Conversely, a strong effort abolishes this chondroprotective effect. This effect could be related to a reduced level of chondrocyte apoptosis through anti-apoptotic capacities of stress-induced Hsp70 overexpression.

Site specific changes in gene expression and cartilage metabolism during early experimental osteoarthritis

OBJECTIVES

To characterize the molecular events underlying cartilage injury in the early phase of mono-iodoacetate-induced osteoarthritis (OA) in rats.

METHODS

Experimental osteoarthritis was induced by intra-articular injection of 0.03mg mono-iodoacetate (MIA) in Wistar rats. Animals were killed 2, 5, 10, 15 and 20 days post-injection. Synovial tissue and standardized biopsies from different areas of knee cartilage were examined. Proteoglycan synthesis ((35)S incorporation) and gelatinase activities (zymography), semi-quantitative RT-PCR and immunohistochemistry for IL1beta, iNOS, COX2 and PPARgamma, were performed on these samples.

RESULTS

Changes in proteoglycan synthesis and gelatinase activities were time and site-dependent. Proteoglycan synthesis inhibition was maximal by day 2 while the highest gelatinase activities were observed at day 5. Central part of patella and posterior plateaus and condyles, i.e. the weight-bearing cartilage areas, were the most affected. IL1beta and iNOS transcripts were induced early in cartilage at time of maximal proteoglycan synthesis inhibition, especially in weight-bearing areas. COX-2 was slightly up-regulated whereas PPARgamma gene expression remained unchanged. Gene expression profile in synovium paralleled that of cartilage, except for PPARgamma which was up-regulated at day 15 and 20. Immunostaining for IL1beta and iNOS showed that proteins were located in diseased cartilage areas at early stage of the experimental OA (day 2). At later time-points (day 20), IL1beta and iNOS were expressed in perilesional areas whereas immunostaining became below control level for COX-2 and PPARgamma.

CONCLUSIONS

Time-dependent degradation of cartilage after injection of low dose of MIA (0.03mg) into rat knee joint can be related to early loss of proteoglycan anabolism, increased gelatinase activities and expression of IL1beta and downstream inflammatory genes. Increased susceptibility to MIA in weight-bearing areas of cartilage further indicate that MIA-induced experimental OA is a relevant model to study not only metabolical but also biomechanical aspects of human OA.