Osteoarthritis (OA) is a degenerative joint disease characterized by loss of articular cartilage, subchondral bone remodeling, joint space narrowing, and bone spur formation, as well as synovial inflammation. There are several treatment modalities, including administration of nonsteroidal antiinflammatory drugs (1, 2) or steroids (3, 4), physical therapy (5), and surgery such as osteotomy and joint replacement as a last resort.
Although intraarticular corticosteroid injection has been recommended for the relief of pain and swelling, adverse effects (including possible infection) and concerns about the possible development of progressive cartilage damage through repeated injections, together with the short duration of action, have limited wider usage (6–9). Meanwhile, intraarticular injection of hyaluronan, which is one of the principal components of cartilage matrix, is now frequently performed for the palliation of joint pain and has been reported to have some positive effects on the maintenance of cartilage matrix integrity during the development of OA (10, 11). However, the mechanism of action of hyaluronan remains unclear, because the duration of benefit reported exceeds its synovial half-life.
Dehydroepiandrosterone (DHEA) is a 19-carbon steroid hormone classified as an adrenal androgen. DHEA is synthesized from pregnenolone (derived from cholesterol) and is rapidly sulfated to its ester form, DHEA-S, the predominant form found in circulating plasma (12). Because the plasma level of DHEA declines with age, numerous studies of DHEA in various disease conditions, such as atherosclerosis (13), cancer (14), diabetes (15), obesity (16), aging (17), and inflammatory arthritis, including rheumatoid arthritis (RA) (18–23), have been performed.
Although RA shares some aspects with OA, there is little information about the effects of DHEA on OA, as far as we know. In a previous in vitro study (24), we demonstrated that in OA, DHEA has an ability to modulate the imbalance between matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases 1 (TIMP-1) at the transcription level, which suggests that DHEA has a protective role against articular cartilage loss.
The aim of the present study was to investigate the in vivo effects of intraarticular injections of DHEA on the maintenance of the cartilage matrix and on the gene expression of various inflammatory mediators during the development of OA. The anterior cruciate ligament transection (ACLT) model of rabbit knee joints was used for this study.
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- MATERIALS AND METHODS
This study is the first to demonstrate the in vivo effects of DHEA on articular cartilage during experimentally induced OA. The gross morphologic osteoarthritic changes of the femoral condyles revealed that the extent and severity of articular cartilage damage were less in the DHEA-treated knees than in the control knees. Furthermore, quantitative histomorphometric analysis showed that cartilage thickness, area, and roughness in the DHEA-treated knees were all statistically superior compared with controls. Results of the gene expression analysis of articular cartilage support those of the gross morphologic and histomorphometric analyses. Gene expression of TIMP-1, an antagonist to the MMPs, was increased in the DHEA-treated knees, while gene expression of MMP-1 and MMP-3, which are important catabolic enzymes, and IL-1β, a proinflammatory cytokine, was decreased in the DHEA-treated knees more than in the control-treated knees. It has been suggested that DHEA is protective against age-related illnesses (13, 15, 17, 28, 29). We concentrated on the relationship between DHEA and OA development caused by ACLT in the rabbit. The findings of the present study are in accordance with those of our previous in vitro study (24), in which application of DHEA treatment to chondrocytes cultured in alginate beads increased the gene expression of TIMP-1 and decreased that of MMP-1 and MMP-3.
In this study, we injected DHEA at a concentration of 100 μM into the rabbit knee joint. The choice of that concentration was based on results of a previous in vitro study, in which use of a 100-μM concentration yielded the best results, with no toxic effects observed. However, we arbitrarily selected the number and sequence of the injections, because no work with DHEA has been performed in this experimental model. Because results of the present study are encouraging, further studies focusing on the dose, number, and sequence of injections are warranted.
Although ACLT for inducing OA was first introduced in the dog model (30), it has now also been popularized in the rabbit model, as evidenced by gradual and progressive changes in the morphology, histopathology, biochemistry, and the gene expression pattern of the articular cartilage of the operated knee (10, 26, 31–38). In the rabbit model of ACLT, the most extreme area of degeneration is known to occur along the posteromedial aspect of the medial femoral condyle (26), which is consistent with the results of this study. This is the reason we performed the histomorphometric assessment on the medial femoral condyles.
In the present study, we revealed the effects of DHEA quantitatively using histomorphometric parameters such as surface roughness, cartilage area, and thickness, which were first described by Yoshioka et al (26). However, we slightly modified the previous method to remove the selection bias in obtaining images of the region of greatest cartilage damage. Instead, we divided the sagittal contour of the medial femoral condyle into 3 regions (anterior, distal, and distal–posterior) and obtained 3 images. Because the length of the sagittal contour of the rabbit femoral condyle is ∼15–20 mm, the 3 images can include nearly all of the region of the femoral condyle. We believe that we could avoid the selection bias through this modification and subsequently obtain more objective measurements.
This study represents the first attempt to examine the effects of DHEA during the development of OA following ACLT. Using histomorphometric and gene expression analyses, we demonstrated quantitatively that exogenously administered DHEA has positive effects on the maintenance of articular cartilage matrix integrity. Despite the lack of understanding of the exact mechanism of DHEA action, the present study demonstrated protective effects of DHEA on articular cartilage during experimentally induced OA.