Weight-bearing asymmetry and vertical activity differences in a rat model of post-traumatic knee osteoarthritis

OBJECTIVE

This study used a rat model of post-traumatic knee osteoarthritis (OA) created by anterior cruciate ligament transection with partial medial meniscectomy (ACLT + pMMx). In this model, mild to moderate structural changes that are typical of knee OA have been observed within 2 and 8 weeks post-surgery. We aimed to determine whether pain-related behaviours can distinguish between an ACLT + pMMx and a sham surgery group.

DESIGN

Three-month old male Sprague-Dawley rats underwent ACLT + pMMx on their right hindlimb within two groups of n = 6 each, and sham surgery within two groups of n = 5 each. Assessments evaluated percent ipsilateral weight-bearing for static weight-bearing and 18 different variables of exploratory motor behaviour at multiple time points between 1 and 8 weeks post-surgery. Histology was performed on the right hindlimbs at 4 and 8 weeks post-surgery.

RESULTS

Histology confirmed mild to moderate knee OA changes in the ACLT + pMMx group and the absence of knee OA changes in the sham group. Compared to the sham group, the ACLT + pMMx group had significantly lower percent ipsilateral weight-bearing from 1 through 8 weeks post-surgery. Compared to the sham group, the ACLT + pMMx group had significantly lower vertical activity (episode count, time, and count) values.

CONCLUSIONS

These findings suggest that ipsilateral weight-bearing deficit and vertical activity limitations resulted from the presence of knee OA-like changes in this model. When using the ACLT + pMMx-induced rat model of knee OA, percent ipsilateral weight-bearing and vertical activity distinguished between rats with and without knee OA changes. These variables may be useful outcome measures in preclinical research performed with this experimental post-traumatic knee OA model.

Study of subchondral bone adaptations in a rodent surgical model of OA using in vivo micro-computed tomography

OBJECTIVE

To non-invasively investigate the changes to epiphyseal bone occurring in a longitudinal pre-clinical model of osteoarthritis (OA) using in vivo micro-computed tomography (micro-CT).

DESIGN

In vivo micro-CT images were acquired using a bench-top micro-CT scanner, which produces three-dimensional data with isotropic voxel spacing of 0.046 mm. Male rodents were scanned prior to surgical destabilization, consisting of anterior cruciate ligament transection and partial medial menisectomy (ACLX). Subsequent scans were performed every 4 weeks post-ACLX, for up to 5 months. Volumetric bone mineral density (vBMD) was measured in specific, anatomically segmented regions within each image. The ACLX rodent data were compared with the contralateral non-operated hind limb of the same animal, as well as a sham-operated group (SHAM) of animals, for each time point. End-point histology compared changes to cartilage and bone between the ACLX and control animals.

RESULTS

The micro-CT protocol produced sufficient spatial resolution and signal-to-noise ratio (SNR=19) to quantify subchondral bone pathology, with an acceptable entrance exposure to radiation (0.36 Gy). Significantly lower vBMD was measured in the ACLX group, vs SHAM rodents, at 1, 4, and 5 months post-surgery (P<0.05). Qualitative observations of ACLX joints revealed significant loss of cartilage, subchondral bone cysts, and calcification of tendon similar to changes found in humans.

CONCLUSIONS

This study demonstrates in vivo micro-CT as an effective method for investigating the development of rodent knee OA longitudinally. This method can be applied, in future pre-clinical trials, to non-destructively monitor the efficacy of pharmacological interventions.

Global analyses of gene expression in early experimental osteoarthritis

OBJECTIVE

To analyze genome-wide changes in chondrocyte gene expression in a surgically induced model of early osteoarthritis (OA) in rats, to assess the similarity of this model to human OA, and to identify genes and mechanisms leading to OA pathogenesis.

METHODS

OA was surgically induced in 5 rats by anterior cruciate ligament transection and partial medial meniscectomy. Sham surgery was performed in 5 additional animals, which were used as controls. Both groups underwent 4 weeks of forced mobilization, 3 times per week. RNA was extracted directly from articular chondrocytes in the OA (operated), contralateral, and sham-operated knees. Affymetrix GeneChip expression arrays were used to assess genome-wide changes in gene expression. Expression patterns of selected dysregulated genes, including Col2a1, Mmp13, Adamts5, Ctsc, Ptges, and Cxcr4, were validated by real-time polymerase chain reaction, immunofluorescence, or immunohistochemistry 2, 4, and 8 weeks after surgery.

RESULTS

After normalization, comparison of OA and sham-operated samples showed 1,619 differentially expressed probe sets with changes in their levels of expression > or = 1.5-fold, 722 with changes > or = 2-fold, 135 with changes > or = 4-fold, and 20 with changes of 8-fold. Dysregulated genes known to be involved in human OA included Mmp13, Adamts5, and Ptgs2, among others. Several dysregulated genes (e.g., Reln, Phex, and Ltbp2) had been identified in our earlier microarray study of hypertrophic chondrocyte differentiation. Other genes involved in cytokine and chemokine signaling, including Cxcr4 and Ccl2, were identified. Changes in gene expression were also observed in the contralateral knee, validating the sham operation as the appropriate control.

CONCLUSION

Our results demonstrate that the animal model mimics gene expression changes seen in human OA, supporting the relevance of newly identified genes and pathways to early human OA. We propose new avenues for OA pathogenesis research and potential targets for novel OA treatments, including cathepsins and cytokine, chemokine, and growth factor signaling pathways, in addition to factors controlling the progression of chondrocyte differentiation.

Nucleoside transporter subtype expression and function in rat skeletal muscle microvascular endothelial cells

1. Microvascular endothelial cells (MVECs) form a barrier between circulating metabolites, such as adenosine, and the surrounding tissue. We hypothesize that MVECs have a high capacity for the accumulation of nucleosides, such that inhibition of the endothelial nucleoside transporters (NT) would profoundly affect the actions of adenosine in the microvasculature. 2. We assessed the binding of [(3)H]nitrobenzylmercaptopurine riboside (NBMPR), a specific probe for the inhibitor-sensitive subtype of equilibrative NT (es), and the uptake of [(3)H]formycin B (FB), by MVECs isolated from rat skeletal muscle. The cellular expression of equilibrative (ENT1, ENT2, ENT3) and concentrative (CNT1, CNT2, CNT3) NT subtypes was also determined using both qualitative and quantitative polymerase chain reaction techniques. 3. In the absence of Na(+), MVECs accumulated [(3)H]FB with a V(max) of 21+/-1 pmol microl(-1) s(-1). This uptake was mediated equally by es (K(m) 260+/-70 microm) and ei (equilibrative inhibitor-insensitive; K(m) 130+/-20 microm) NTs. 4. A minor component of Na(+)-dependent cif (concentrative inhibitor-insensitive FB transporter)/CNT2-mediated [(3)H]FB uptake (V(i) 0.008+/-0.005 pmol microl(-1) s(-1) at 10 microm) was also observed at room temperature upon inhibition of ENTs with dipyridamole (2,6-bis(diethanolamino)-4,8-dipiperidinopyrimido-[5,4-d]pyrimidine)/NBMPR. 5. MVECs had 122,000 high-affinity (K(d) 0.10 nm) [(3)H]NBMPR binding sites (representing es transporters) per cell. A lower-affinity [(3)H]NBMPR binding component (K(d) 4.8 nm) was also observed that may be related to intracellular es-like proteins. 6. Rat skeletal muscle MVECs express es/ENT1, ei/ENT2, and cif/CNT2 transporters with characteristics typical of rat tissues. This primary cell culture model will enable future studies on factors influencing NT subtype expression, and the consequent effect on adenosine bioactivity, in the microvasculature.

Nitric oxide is a mediator of the inhibitory effect of activated macrophages on production of androgen by the Leydig cell of the mouse

We hypothesized that macrophage activation results in nitric oxide (NO) production and that this NO acts directly on Leydig cells (LC) to alter androgen synthesis. Both peritoneal macrophages and a murine macrophage cell line (RAW 264.7) were activated in vitro by sequential exposure to interferon-gamma (50 U/ml) and then bacterial lipopolysaccharide (LPS; 100 ng/ml) for 24 h each. At various times after initiation of activation, selected wells were harvested for identification of messenger RNA for inducible NO synthase by RT-PCR. Amplicons of the predicted 651-bp product were isolated, cloned, and sequenced to validate the PCR procedure. Such amplicons first appeared between 2-4 h after exposure to LPS, and staining increased in intensity for the rest of the study. Nitrite accumulation followed a similar time course. Similarly treated wells were washed after 24-h activation and cocultured with purified LC for a final 24-h incubation in the absence of interferon-gamma and LPS. Basal and LH-stimulated production of androgen was estimated by RIA. In some experiments the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester or the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (C-PTIO) was added during activation and coculture. Coculture of LC with quiescent macrophages altered neither basal nor LH-stimulated androgen production. Coculture with either type of activated macrophage did not alter basal, but significantly reduced (by 50%) LH-stimulated, androgen production. N(omega)-Nitro-L-arginine methyl ester and C-PTIO blocked the inhibitory effect. The NO donor S-nitroso-N-acetyl penicillamine at concentrations greater than 10(-5) M significantly inhibited LH-stimulated androgen production by purified LC (P < 0.01). The inhibitory effect of S-nitroso-N-acetyl penicillamine was evident when exposure exceeded 4 h. Intermediates of steroidogenesis were added to elucidate the site of NO inhibition. The enzymatic inhibition occurred at least in part at 17alpha-hydroxylase/C(17/20) lyase (P450c17). Enzyme inhibition was reversed by C-PTIO. Northern blot analysis indicated that accumulation of messenger RNA for P450c17 was not significantly altered. Therefore, activation of macrophages results in decreased androgen production by cocultured LC. The inhibition is mediated in part by macrophage-derived NO acting directly on the LC via inhibition of at least one of the P450 steroidogenic enzymes.

Responses of luteinizing hormone (LH) and follicle-stimulating hormone levels to exogenous gonadotropin-releasing hormone during the estrogen-induced LH surge in the ovariectomized rhesus monkey

Experiments were performed to study the responsiveness of the pituitary to gonadotropin-releasing hormone (GnRH) during the dynamic changes in gonadotropin secretion associated with the estrogen-induced luteinizing hormone (LH) surge in the ovariectomized (OVX) rhesus monkey. Silastic capsules filled with estradiol-17-beta were implanted subcutaneously in ovariectomized rhesus monkeys, resulting in an initial lowering of circulating LH and follicle-stimulating hormone (FSH) concentrations followed by an LH-FSH surge. GnRH was injected intravenously just before estrogen implantation, during the negative feedback response and during the rising, the peak, and the declining phases of the LH surge. The LH and FSH responses during the negative feedback phase were as large as those before estrogen treatment (control responses). During the rising phase of the LH surge, the acute response to GnRH injection did not differ significantly from the control response, but the responses 60 and 120 min after injection were somewhat increased. During the declining phase of the LH surge, the pituitary was not responsive to exogenous GnRH, although LH probably continued to be secreted at this time since the LH surge decreased more slowly than predicted by the normal rate of disappearance of LH in the monkey. We conclude that an increased duration of response to GnRH may be an important part of the mechanism by which estrogen induces the LH surge, but we do not see evidence of increased sensitivity of the pituitary to GnRH as an acute releasing factor at that time.

Separate negative feedback effects of estrogen on the pituitary and the central nervous system in the ovariectomized rhesus monkey

The site(s) of the negative feedback action of estrogen on gonadotropin secretion were studied in the ovariectomized rhesus monkey by observing the serum LH and FSH responses to intravenous GnRH injections at various times after implantation of Silastic capsules filled with estrogen. Circulating estrogen concentrations produced by the capsules were within the normal midcycle range for this species. Four h after estrogen implantation, no LH or FSH response was seen to the GnRH injection, indicating a suppressive effect of the steroid directly on the pituitary. Twelve and 22 h after estrogen implantation, however, the LH and FSH responses were equal to or larger than control responses. Since preinjection LH and FSH levels were below control values at these times and the pituitary responded to exogenous GnRH, it appears that endogenous GnRH secretion was affected, indicating an inhibitory action of estrogen on the central nervous system. Thus these experiments suggest 2 separate negative feedback actions of estrogen: a transient one directly on the pituitary and a longer lasting effect on the central nervous system.