E. M. O'Byrne

Magnetic resonance imaging reflects cartilage proteoglycan degradation in the rabbit knee

Cartilage degeneration in osteoarthritis is initiated by a loss of proteoglycan. Intra-articular injection of papain causes a reversible loss of proteoglycan in rabbit knees. Rabbits were scanned with magnetic resonance imaging (MRI), using a 1.5T Signa superconducting magnet with 3 inch surface coil. Spin echo sequences were performed in the coronal and sagittal planes at 0, 24, 48, and 72 h after intra-articular injection of papain to obtain T1, proton density, and T2-weighted images. Cartilage proteoglycan content was measured biochemically and histochemically. Reduced articular cartilage thickness in the MR images of papain-treated knees corresponded to changes in cartilage proteoglycan content.

In vivo qualitative assessments of articular cartilage in the rabbit knee with high-resolution MRI at 3 T.

Proteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high‐resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One‐millimeter thick coronal images were obtained at 3 T with a 97 × 97 μm2 pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an ∼2‐fold greater Gd(DTPA)2‐‐induced decrease in T1 relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two‐point method was tested as an alternative to the more time‐consuming multipoint method typically used to measure T1 changes. Kinetics of Gd(DTPA)2‐ uptake were observed with a 10‐min time resolution. The diffusive transport of Gd(DTPA)2‐ was characterized by a T1 decrease ∼2‐fold faster in papain‐treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T1 variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA)2‐‐MRI may help in identifying new active compounds during efficacy studies on cartilage protection. Magn Reson Med 50:541–549, 2003.

RELAXIN IN HUMAN SEMINAL PLASMA

While relaxin is known as a hormone of pregnant females, it has been identified in rooster l and boar testes.g A recent report described immunoreactive relaxin in human seminal p l a ~ m a . ~ Relaxin is a structural homologue of insulin and other growth factors.* Epidermal growth factor and nerve growth factor are found in secretions of male salivary glands and the genitourinary Seminal plasma is rich in proteins and contains other peptide hormones, including growth hormone,8 p ro la~ t in ,~ and insulin.10 In this report, we characterize the immunoreactive relaxin-like substance in seminal plasma as bioactive relaxin and determine its source of production.

In vivo assessment of macromolecular content in articular cartilage of the goat knee

Loss of proteoglycans (PGs) from the extracellular matrix of cartilage is an early event of osteoarthritis. The capability of Gd(DTPA)2–‐enhanced MRI to quantitatively assess PG content was explored in a goat model of cartilage degeneration. Partial to total PG depletion was induced by an intraarticular injection of papain 1 day prior to the MRI session. A close correlation was found between the extent of the PG loss and the Gd(DTPA)2–‐induced T1 decrease. Papain‐induced PG depletion was confirmed by post‐mortem histological and biochemical assessments. A 2‐hr delay after Gd(DTPA)2– injection was found to be optimal for an accurate quantitation of the cartilage defect. A series of knee flexions were performed post‐Gd(DTPA)2– injection to facilitate penetration of the contrast agent into cartilage. However, ΔT1s observed in cartilage of exercised goat knees were not affected by papain or IL1β pretreatment. Therefore, as long as a preinjection T1 map was obtained, the Gd(DTPA)2–‐enhanced MRI technique provided good sensitivity in detecting partial loss of PG in articular cartilage. This was true only when the animal was maintained in a resting state during diffusion of the Gd(DTPA)2–. This approach is of particular interest for long‐term evaluations of cartilage degeneration and regeneration. Magn Reson Med 49:1037–1046, 2003.

Oral administration of a matrix metalloproteinase inhibitor, CGS 27023A, protects the cartilage proteoglycan matrix in a partial meniscectomy model of osteoarthritis in rabbits.

Matrix metalloproteinases (MMP) are elevated in human osteoarthritic cartilage [1] and in cartilage from rabbits with experimental osteoarthritis (OA) following partial meniscectomy [2]. CGS 27023A is a M M P inhibitor that inhibits stromelysin, collagenase and gelatinase. CGS 27023A is an orally active inhibitor of stromelysin. CGS 27023A at 75 gmoles/kg p.o. inhibits release of proteoglycan into synovial fluid following intra-articular injection of stromelysin into rabbit knees. The purpose of these experiments was to determine whether CGS 27023A would inhibit cartilage proteoglycan loss in a partial meniscectomy model of osteoarthritis in rabbits [3]. Doxycycline was used as a reference drug [4].

Magnetic resonance imaging and morphometric quantitation of cartilage histology after chronic infusion of interleukin 1 in rabbit knees.

Abstract Cartilage pathology in rabbit knees was monitored by noninvasive magnetic resonance imaging (MRI) and evaluated using morphometric histologic measurements. Infusion of rabbit knees with the cytokine interleukin 1 induces cartilage degradation and inflammation. A miniosmotic pump was implanted subcutaneously to deliver interleukin 1 through a polyethylene catheter inserted into the rabbit knee. Rabbit knees were imaged using MRI and prepared for histologic examination at 5 and 12 days after chronic infusion of interleukin 1. MRI obtained 0.7-mm sections for three-dimensional reconstruction of cartilage image. Cartilage deterioration near the site of infusion was visible on MRI. MRI measurements indicated a reduction in cartilage thickness. Histology revealed a loss of staining of cartilage matrix proteoglycan, synovial hypertrophy, and perichondral bone resorption. Morphometric analysis of cartilage histology indicated a reduction in both cellularity (chondrocytes/mμ2 area) and cell to matrix area ratio. These observations suggest that a loss of proteoglycan, an early event in cartilage degeneration, can be detected by MRI. [P.S.E.B.M. 1993, Vol 203]

Magnetic resonance imaging of the rabbit knee: Detection of cartilage proteoglycan degradation

Intra-articular (i.a.) injection of papain causes a reversible loss of proteoglycan in intact rabbit knees. Twelve rabbits were scanned with magnetic resonance imaging (MRI) at 0, 24, 48 and 72 hours after 5 units of papain i.a. in a 1.5 Tesla Signa with a three inch surface coil using spin echo sequence. Total cartilage thickness in proton density images was 1.08±0.09 mm prior to papain injection. The magnetic resonance images showed a reduction in articular cartilage thickness in papain-treated rabbit femurs at 24 hours to 0.69±0.18 mm and partial restoration by 72 hours to 0.77±0.21 mm.

Comparison of magnetic resonance imaging (MRI) and histopathology in rabbit models of osteoarthritis and immune arthritis

Osteoarthritis was surgically induced in mature male Dutch Belted rabbits by sectioning the fibular collateral and sesamoid ligaments and removal of the anterior horn of the lateral meniscus. The site of surgical intervention was detectable by MRI. Histopathologic analysis revealed severe focal cartilage lesions on opposing surfaces of the tibia and femur. Histology of cartilage adjacent to the osteoarthritic lesions appeared normal. In another animal model, arthritis was induced by immunization against ovalbumin followed by intra-articular injection of ovalbumin. MRI of immune arthritic rabbit knees showed accumulation of synovial fluid and cartilage degradation. Histopathology was characterized by vascular necrosis of the synovium and depletion of cartilage proteoglycan. MRI can be used to non-invasively follow the therapeutic effects of drug treatment on synovial inflammation and cartilage degradation in rabbit knees.

Synovial fluid levels of tumor necrosis factor-alpha in the inflamed rat knee: Modulation by dexamethasone and inhibitors of matrix metalloproteinase and phosphodiesterase

Tumor necrosis factora (TNF) is a pro-inflammatory cytokine that is elevated in the synovial fluid of rheumatoid arthritic (RA) patients [1]. TNF also plays a major role in the pathogenesis of septic shock induced by lipopolysaccharide (LPS) endotoxin injection [2]. Soluble TNF is released from a cell membrane bound precursor by proteolytic enzyme(s). Hydroxamine acid-based inhibitors of matrix metalloproteinases (MMP) have been shown to block TNF release into the blood following LPS injection [3–5]. Studies have also shown that glucocorticoids and phosphodiesterase (PDE) inhibitors can inhibit TNF production in a carrageenan-induced rat paw edema model [6]. In clinical trials involving RA patients, treatment with anti-TNF monoclonal antibodies had a beneficial effect [7]. Together, these studies indicate that lowering synovial fluid TNF levels may ameliorate RA. An acute inflammatory model of TNF release into rat synovial fluid [8] was standardized to evaluate test compounds for potency, oral activity and duration of action. The aim of this study was to determine if known TNF inhibitors of different types are active in blocking TNF release in the inflamed rat knee.

Catabolin/interleukin-1 regulation of cartilage and chondrocyte metabolism

Catabolin/interleukin-1 effects on metabolism were studied in bovine nasal cartilage organ culture and articular chondrocyte cell culture. Keratan sulfate (KS) and hyaluronic acid (HA) were determined by an ELISA; prostaglandin E2 by RIA, sulfated glycosaminoglycan using dimethylmethylene blue and proliferation by incorporation of tritiated thymidine. Gel filtration of untreated 4-day organ culture media indicated that large sulfated and KS-containing proteoglycans were released and eluted in the void volume. Catabolin/interleukin-1 increased release of sulfated glycosaminoglycans and these were of lower molecular weight with an altered distribution of KS. Catabolin/interleukin-1 treatment of chondrocytes caused a decrease in KS production and proliferation but an increase in HA and in prostaglanding E2 production. Alterations of the chondrocyte metabolism by catabolin/interleukin-1 causing proteoglycan matrix degradation and modulation of chondrocyte glycosaminoglycan biosynthesis and proliferation may play a role in cartilage erosion and failure to repair in arthritic diseases.