20722.qxd

Effects of polysulfated glycosaminoglycan and
hyaluronan on prostaglandin E2 production
by cultured equine synoviocytes
Stephen P. Frean, BVSc, PhD, and Peter Lees, PhD ly through inhibition of PGE2 production,9,11 although Objective-To investigate effects of the anti-arthritic
glucocorticoids possess other actions, such as inhibi- agents hyaluronan and polysulfated glycosaminogly- tion of induction of inducible nitric oxide synthase12,13 can (PSGAG) on inflammatory metabolism in cultured and the inducible isoform of cyclooxygenase (ie, cyclooxygenase 2 [COX-2]).14,15
Sample Population-Synoviocytes cultured from
Pharmacologic intervention also may be directed samples obtained from the metacarpophalangeal at limiting damage to, and stimulating repair of, artic- ular cartilage. To this end, glycosaminoglycan prepara- Procedure-Equine synoviocytes were grown in
tions such as polysulfated aminoglycan (PSGAG) and
monolayer culture. Synoviocytes were stimulated hyaluronan are administered intra-articularly or sys- with lipopolysaccharide (LPS) and simultaneously temically (IV administration in the case of hyaluronan treated with various concentrations of hyaluronan orPSGAG for 48 hours. Three hyaluronan preparations and IM administration in the case of PSGAG).
were compared. Prostaglandin E2 (PGE2) concentra- Although these compounds can directly stimulate tions in culture medium were measured, using neosynthesis of cartilage matrix,16,b it is possible that their chondroprotective effects may result indirectly Results-The highest concentrations of hyaluronan
from a diverse range of anti-inflammatory properties.
and PSGAG tested inhibited PGE2 production.
Included in these putative anti-inflammatory actions is Conclusions and Clinical Relevance-Clinically
achievable concentrations of hyaluronan and PSGAG Cultured equine synoviocytes synthesize large inhibited PGE2 synthesis by cultured equine synovio- amounts of PGE2 in vitro when treated with cytes. This anti-inflammatory action may be a mech- lipopolysaccharide (LPS).21 Using the in vitro system of
anism through which these agents exert anti-arthritic that study, we investigated the effects of various concen- effects. The effect was obtained at concentrations trations of hyaluronan and PSGAG on PGE2 production that can be achieved by use of intra-articular, but not by cultured equine synoviocytes. In light of claims by systemic, administration of hyaluronan or PSGAG.
pharmaceutic companies of benefit of 1 hyaluronan preparation, compared with other preparations,d,e it wasof interest to evaluate a therapeutic Streptococcus zooepi- Joint disease in horses commonly is characterized by demicus-derived hyaluronan preparation and a generic
inflammation of the synovium, producing the clas- laboratory-grade S zooepidemicus-derived preparation.
sic signs of swelling (joint effusion), heat, and pain,1,a Furthermore, claims have been made of greater thera- causing loss of normal function and manifesting as peutic effectiveness of bacterial-derived hyaluronan, lameness. Although synovitis often is characterized by compared with rooster comb-derived hyaluronan22; leukocytic infiltration of the synovial membrane,2 syn- thus, we believed it pertinent to evaluate a preparation oviocytes can produce pro-inflammatory cytokines,3,4 of hyaluronan from this latter source.
metalloproteinases,5 and eicosanoids.6-8 Of the latter, The purpose of the study reported here was to prostaglandin E
investigate possible anti-inflammatory properties of 2 (PGE2) has been suggested as an
important mediator of inflammation and hyperalgesia hyaluronan and PSGAG, which are used in the treat- through its enhancement of vascular permeability, ment of equine joint disease. Furthermore, the study vasodilatory properties, and sensitization of joint noci- was intended to reveal information about their mecha- ceptors.9,10 Pharmacologic treatment of joint disease nism of action, which remains poorly defined.
typically is directed at alleviating the signs of joint
inflammation; nonsteroidal anti-inflammatory drugs
Materials and Methods
(NSAID) and synthetic glucocorticoids are the most
Tissue specimens-Synovial membrane was obtained
commonly used compounds. These drugs act primari- from the cranial and palmar joint recesses of metacarpopha-langeal (fetlock) joints of euthanatized horses. Each experi-ment (1 therapeutic agent/experiment) used pooled tissue specimens obtained from both metacarpophalangeal joints of the same horse. Inter-individual variation was avoided as From the Department of Veterinary Basic Sciences, Royal Veterinary much as possible; tissue was obtained from horses < 10 years College, Hawkshead Ln, North Mymms, Herts AL9 7TA, UK.
old (as determined on the basis of examination of dentition).
Presented in part at the 42nd Annual Meeting of the Orthopaedic Synovium was only used when examination of the joints, lig- Research Society, Atlanta, Ga, Feb 22, 1996.
Support provided by the Home of Rest for Horses, Speen, UK, and aments, and tendons in the distal aspect of each limb did not Bayer Animal Health, Bury St Edmunds, UK.
reveal macroscopic signs of acute or chronic musculoskeletal disease. Criteria for selection were as follows: synovial mem- the following treatment conditions: unstimulated (medium brane did not have signs of acute or chronic inflammation; only), 10 µg of LPS/ml, l0 µg of LPS/ml and 10-6M articular cartilage did not have evidence of erosion or wear indomethacin, 10 µg of LPS/ml and various concentrations of lines; periarticular osteophytes were not observed; synovial PSGAG (2, 20, 200, 2,000, 10,000 and 20,000 µg/ml), PSGAG fluid appeared normal in quantity, viscosity, and color only (20,000 µg/ml), and 10 µg of LPS/ml and a volume of (ie, blood was not evident); and intra- or periarticular frac- PBS solution equivalent to that of 20,000 µg of PSGAG/ml.
Prostaglandin E2 assay-Radioimmunoassay for deter-
Cell culture-Synovial membrane was dissected from
mination of PGE2 concentration was conducted in accordance the underlying adipose subintima, transferred to a Dulbecco with the general methods described by Salmon,23 using com- modified Eagle mediumf containing 10% (vol:vol) heat-inac- mercially available antiserumv raised against PGE2-bovine tivated fetal calf serumg and 1% (vol:vol) 5,000 U of peni- serum albumin and tritiated PGE2 tracer.w Absolute PGE2 concentrations of specimens were calculated by comparison subjected to enzymatic digestion (type VIII collagenasei from with PGE2 standardsx of known concentration. Specimens Clostridium histolyticum, 300 U/ml, for 3 hours at 37 C).
were diluted to ensure that values could be extrapolated from Newly released synoviocytes were seeded in 25-cm3 flasks.j the standard curve and were subsequently corrected for the After incubation for 48 hours, medium was changed, remov- original dilution. Upper and lower limits of detection of the ing any cells not adhering to the culture flask. Flasks were assay were 10 ng/ml and 50 pg/ml, respectively.
maintained by changing medium at 48-hour intervals until Statistical analysis-Statistical analysis was conducted,
cell replication was observed; at that time, synoviocytes were using a proprietary statistical software program.y For each seeded in 24-well platesk and grown to confluence.
therapeutic agent, results represented the data of 1 experi- Procedures involving hyaluronan-The dose of
ment, with 4 replicates in each treatment group (ie, n = 4).
hyaluronan typically recommended for intra-articular admin- Values were expressed as mean ± SEM. Significant differences istration in horses is 20 mg/joint.l Typically, 5 to 6 ml of syn- in PGE2 synthesis in response to various treatments were ovial fluid can be aspirated from a fetlock joint of a clinical- determined by use of one-way ANOVA followed by use of the ly normal horse. Therefore, immediately subsequent to intra- Dunnett test. Significance was assigned at P < 0.05.
articular injection, it is possible to achieve a concentration of3 to 4 mg of hyaluronan/ml. An inflamed joint typically will be swollen as a result of synovial effusion; administration of Commercially available hyaluronan prepara-
20 mg of hyaluronan will result in concentrations in the syn- tion-Synoviocytes incubated with 10 µg of LPS/ml
ovial space that are < 4 mg/ml. The rate of decrease in con- produced concentrations of PGE2 significantly centration after intra-articular administration is not known; (P < 0.001) higher than the basal concentrations of therefore, hyaluronan was used at concentrations of 20, 200, unstimulated cells. The LPS-indomethacin positive- 500, 1,000 and 2,000 µg/ml. Because addition of the highest control treatment caused a significantly (P < 0.001) concentration of hyaluronan (ie, 2,000 µg/ml) resulted in dilution of culture medium to 80% of normal concentration, control treatments were incorporated into the experiment.
Volumes of phosphate-buffered saline (PBS) solutionm
equivalent to volumes for the highest concentrations of
hyaluronan (ie, 1,000 and 2,000 µg/ml) were added with
LPSn (10 µg/ml) to culture wells. Indomethacin, a NSAID
that inhibits PGE2 synthesis, was used as a positive-control
Synoviocytes were incubated for 48 hours, using the fol- lowing treatment conditions: unstimulated (medium only),10 µg of LPS (Escherichia coli serotype B5:055)/ml, 10 µg ofLPS/ml and 10-6M indomethacin,o 10 µg of LPS/ml and vari-ous concentrations of hyaluronan (ie, 20, 200, 500, 1,000and 2,000 µg/ml), hyaluronan only (1,000 and 2,000 µg/ml),and 10 µg of LPS/ml and PBS solution equivalent in volumeto the volumes of 1,000 and 2,000 µg of hyaluronan/ml. In addition to a commercially available preparation of hyaluronan,p generic preparations of hyaluronan formulatedfrom S zooepidemicusq and rooster combr were tested. Theselatter hyaluronan preparations were obtained in solid form.
To simulate as closely as possible the preparation of the com-mercially available product, the generic products were dis-solved in PBS solution (initial concentration, 10,000 µg/ml).
Figure 1-Effect of a commercially available hyaluronan (HA)preparation on prostaglandin E2 (PGE2) synthesis by lipopolysac- Procedures involving polysulfated glycosamino-
charide (LPS)-stimulated synoviocytes obtained from the glycan-At the clinically recommended dose for horses of
metacarpophalangeal joints of clinically normal horses.
Synoviocytes were incubated for 48 hours at 37 C. Each treat- 250 mg of PSGAG/joint,s the highest concentration achievable ment group represents mean ± SEM PGE2 concentration of 4 by intra-articular injection of a fetlock joint is approximately replicate wells. Hyaluronan concentrations (in parentheses) are 50 mg/ml. The recommended dose for IM administration of expressed in µg/ml. The LPS concentration is 10 µg/ml.
PSGAG in horses is 500 mg/horse.t A theoretical maximum Indomethacin concentration is 10-6M. Values differ significantly plasma concentration of 0.025 mg/ml can be calculated for (n = P < 0.05, nn = P < 0.01, nnn = P < 0.001) from those forunstimulated synoviocytes (Dunnett test, 2-tailed). Values differ horses, assuming rapid and complete absorption from the significantly (o = P < 0.05, oo = P < 0.01, ooo = P < 0.001) from injection site. Therefore, various concentrations of PSGAGu those for synoviocytes incubated with LPS (Dunnett test, were tested. Synoviocytes were incubated for 48 hours, using 2-tailed). PBS = Phosphate-buffered saline solution.
Table 1-Effect of various concentrations of 3 hyaluronan prepa-rations on the percentage change in prostaglandin E2 synthesis by lipopolysaccharide (LPS)-stimulated synoviocytes obtainedfrom the metacarpophalangeal joints of clinically normal horses Hyaluronan preparation
Commercially Streptococcus
Treatment*
available
zooepidemicus
Positive values reflect increased PGE2 synthesis, negative values reflect decreased PGE2 synthesis, compared with values for synovio- *Concentration of LPS = 10 ␮g/ml, and hyaluronan concentrations a,bValues are significantly (a, P Ͻ 0.01; b, P Ͻ 0.001) different from Figure 2-Effect of a Streptococcus zooepidemicus HA prepa- those for synoviocytes incubated in LPS alone (Dunnett test, 2-tailed). ration on PGE2 synthesis by LPS-stimulated synoviocytes obtained from the metacarpophalangeal joints of clinically nor-mal horses. See Figure 1 for key.
Streptococcus zooepidemicus hyaluronan prepa-
ration-Incubation of ynoviocytes with LPS signifi-
cantly (P < 0.001) increased PGE2 concentrations,
compared with values for basal concentrations ofunstimulated cells. The LPS-indomethacin positive-control treatment significantly (P < 0.001) reducedPGE2 synthesis, compared with values for LPS alone.
Synoviocytes incubated with hyaluronan (1,000 and2,000 µg/ml) had slight, but not significant, decreas-es in PGE2 synthesis of 8 and 11%, respectively.
Incubation of LPS-stimulated cultures with PBS solu-tion equivalent in volume to 1,000 and 2,000 µg ofhyaluronan/ml significantly (P < 0.001) increasedPGE2 synthesis, compared with values for unstimu- lated cells; value for the cells incubated with LPS-
PBS solution was similar to that of cells treated with
LPS alone (Fig 2). Similar to the commercially avail-
able hyaluronan preparation, the S zooepidemicus
hyaluronan preparation at low concentrations did
Figure 3-Effect of a rooster comb HA preparation on PGE2 syn- not cause significant effects on LPS-enhanced PGE2 thesis by LPS-stimulated synoviocytes obtained from the synthesis (Table 1). Similar to the commercially metacarpophalangeal joints of clinically normal horses. See available hyaluronan preparation, however, the high- est concentration of S zooepidemicus hyaluronanpreparation (2,000 µg/ml) produced a significant with synoviocytes incubated with 10 µg of LPS/ml.
(P = 0.007) reduction (56%) in PGE Unstimulated synoviocytes incubated with the com- pared with that for cells incubated with LPS alone.
mercially available preparation at concentrations of1,000 and 2,000 µg/ml caused decreases in PGE2 syn- Rooster-comb hyaluronan preparation-Unstim-
thesis of 21 and 61%, respectively, but these values were ulated synoviocytes had a higher basal PGE2 synthesis not significantly different (Fig 1). The LPS-stimulated
than unstimulated synoviocytes in the other 2 experi- cultures incubated with PBS solution equivalent in vol- ments involving the use of hyaluronan. Incubation with ume to 1,000 and 2,000 µg of hyaluronan/ml had sig- LPS produced a comparatively weaker, nonsignificant nificantly (P < 0.001) increased PGE2 synthesis, com- increase in PGE2 concentration, although mean absolute pared with values for unstimulated cells. The LPS-stim- PGE2 concentration (724 ng/ml) was similar to that pro- ulated cells treated with hyaluronan (20, 200, 500 and duced by use of LPS in the other 2 experiments involv- 1,000 µg/ml) did not have significant changes in the ing hyaluronan (Fig 3). Incubation of LPS-stimulated
enhanced PGE2 synthesis, compared with values for cultures with PBS solution equivalent in volume to LPS-stimulated cells not treated with hyaluronan hyaluronan (1,000 and 2,000 µg/ml) enhanced PGE2 (Table 1). The highest concentration of the commer-
synthesis similar to that of cells treated with LPS alone.
cially available hyaluronan preparation (2,000 µg/ml) In contrast to the generic S zooepidemicus and commer- caused a significant (P < 0.001) decrease in PGE2 pro- cially available hyaluronan preparation, rooster comb duction, compared with PGE2 concentrations for cells hyaluronan (1,000 µg/ml) enhanced synthesis of PGE2 (increase of 83%) in unstimulated cells, which was not oviocytes; macrophage-like synovial cells cultured fromsynovium obtained from osteoarthritic humans had adecrease in interleukin-1α-induced PGE2 production when treated with hyaluronan at concentrations of 0.5and 1 mg/ml.20 This decrease in PGE2 synthesis also was dependent on hyaluronan molecular weight. Lapinechondrocytes stimulated with interleukin-1 similarlyhad a decrease in PGE2 synthesis when treated with hyaluronan at similar concentrations to those used onhuman cells17; in that study, hyaluronan had a concen-tration- (0.5, 1 and 2 mg/ml) and molecular weight-dependent (0.5, 1, and 2 kd) inhibition of PGE2 syn- thesis. The exact molecular weight of each hyaluronanpreparation used in the study reported here is notknown. However, the commercially available hyaluro-nan preparation used in our study is of lower viscositythan other commercially available hyaluronan prepara-tions licensed for intra-articular administration.22 Analysis of the data in the study reported here failed to confirm the findings of other investigators.17,20 None ofthe 3 hyaluronan preparations, at concentrations up to Figure 4-Effect of polysulfated glycosaminoglycan (PSGAG) on 1,000 µg/ml, exerted inhibitory actions on LPS-induced PGE2 synthesis by LPS-stimulated synoviocytes obtained from PGE2 synthesis. However, at the highest concentration the metacarpophalangeal joints of clinically normal horses. Eachtreatment group represents mean ± SEM PGE (2,000 µg/ml), 2 of the 3 preparations (commercially 4 replicate wells. The PSGAG concentrations (in parentheses) available preparation and S zooepidemicus preparation) are expressed in µg/ml. See Figure 1 for key.
significantly inhibited but, unlike indomethacin, did notabolish PGE significant (P = 0.08). This value compared favorably 2 production. The reason for the failure of the rooster comb hyaluronan preparation to inhibit PGE with the slight (7%) increase produced by 2,000 µg of synthesis at each concentration is not known. It may hyaluronan/ml, which also was not significant.
have been attributable to a low molecular weight of that Treatment of LPS-stimulated cells with rooster comb preparation. Indeed, low concentrations of this prepara- hyaluronan increased production of PGE2; this tion failed to inhibit and actually increased PGE enhanced response was somewhat greater at lower con- sis beyond that caused by LPS alone.
centrations of hyaluronan (20 µg/ml = 76%, P < 0.001; A possible explanation for the increased PGE 200 µg/ml = 49%; 500 µg/ml = 40%; 1,000 µg/ml = 19%; concentrations measured in cultures treated with rooster comb hyaluronan is that there may be pro- Polysulfated glycosaminoglycan preparation-
inflammatory contaminants in the preparation, as has Incubation of synoviocytes with LPS caused PGE been suggested elsewhere.22 On the basis of this suppo- thesis that was significantly (P = 0.006) greater than the sition, it could be suggested that the enhanced PGE2 basal concentration of unstimulated cells. The LPS- synthesis obtained in our study may have been coun- indomethacin positive-control treatment significantly tered only by higher concentrations of hyaluronan ues for LPS alone. Incubation of synoviocytes with potential pro-inflammatory contaminants. However, it PSGAG (20,000 µg/ml) also profoundly decreased (82%) would appear that enhanced PGE2 synthesis was not an artifact resulting from contaminated PBS solvent, 2 synthesis. The LPS-stimulated cells treated with 2 µg of PSGAG/ml were unaffected, but treatment with 20 because the same stock of PBS solution was used µg of PSGAG/ml caused a significant (P = 0.035) increase throughout the study. Furthermore, LPS-stimulated of 44% above the concentrations for cells treated with cells incubated with a volume of PBS solution equiva- LPS alone (Fig 4). In contrast, 4 higher concentrations of
lent to that for hyaluronan concentrations of 1,000 and PSGAG (200, 2,000, 10,000, and 20,000 µg/ml) 2,000 µg/ml had similar PGE2 synthesis to those cells (decreases of 32, 58, 99, and 96%, respectively); howev- The reduction in PGE2 production in response to er, only the latter 2 decreases were significantly 2 hyaluronan preparations (commercially available and (P = 0.003) different from the value for cells stimulated S zooepidemicus preparations) at the highest concentra- by LPS alone. The control treatment (ie, incubation of tions used (2,000 µg/ml) as a result of mere dilution of cells with LPS and a volume of PBS solution equivalent the culture medium to 80% of its original concentra- to that for 20 µg of PSGAG/ml) produced a value for tion can be discounted. In control cells treated with LPS in medium diluted with a volume of PBS solution 2 synthesis similar to that of LPS alone.
equivalent to that for hyaluronan at 1,000 and 2,000 µg/ml, PGE2 concentrations were similar to Discussion
those obtained in LPS-stimulated cultures maintained Other investigators have documented that hyaluro- nan inhibits PGE2 synthesis by cultured human syn- Using unstimulated hamster kidney cells, Dietmar18 reported that PSGAG at concentrations of 0.03, 0.1, 0.3, hyaluronan inhibits the release of PGE2 into culture and 1% reduced PGE2 concentrations in culture super- medium, rather than inhibiting the synthesis of PGE2, natant in a concentration-dependent manner at 16 is worthy of consideration. Some investigators have hours (44 to 52%), and 48 hours (35 to 67%) after ini- suggested that the diverse actions of hyaluronan on tiation of incubation. The PSGAG used in that study is cellular metabolism may be a consequence of its high a preparation licensed for use in humans; that prepara- viscosity in solution; it has been suggested that tion, similar to the preparation licensed for use in hors- hyaluronan could physically retard the release of PGE2 es, contains 250 mg of PSGAG/ml. Conversion of units from cells, as opposed to inhibiting synthesis.17,20 of concentration used in our study (µg/ml) to those Similarly, it has been suggested that hyaluronan may used by Dietmar (percentage) indicates that reductions prevent mobilization of eicosanoid precursors. Release in LPS-induced PGE2 synthesis in cultures of equine of 14C-labeled arachidonic acid from human synovial synoviocytes were obtained at PSGAG concentrations fibroblasts in response to bradykinin and calcium of 0.02, 0.2, 1, and 2%, similar to those used with ham- ionophore is inhibited by hyaluronan in both a molec- ster kidney cells. The lower concentrations used in the ular weight- and concentration-dependent manner.24 study reported here (ie, 0.002 and 0.0002%) did not However, authors of that study concluded that inhibi- tion of arachidonic acid release was not associated with We were unable to account for the increase above viscosity, because methylcellulose, a liquid similarly baseline values of PGE2 synthesis by LPS-stimulated cells viscous to hyaluronan, did not inhibit arachidonic acid treated with 20 µg of PSGAG/ml. Results of experiments had little intra-experiment variation, and conditions Binding interactions of polysaccharide prepara- were standardized with regard to number of cells and tions, such as pentosan polysulfate and hyaluronan, population. Therefore, it is unlikely that these potential- with cell membrane molecules have received attention.
ly variable factors accounted for the increase in PGE2 Thrombospondin has been suggested as a receptor concentration. Thus, the implication is that the increase through which pentosan polysulfate may act as a in this treatment group may have been the result of a pos- matrix metalloproteinase inhibitor.25 Cellular receptors sible synergistic effect of LPS and PSGAG on PGE2 syn- for hyaluronan have been identified, and it has been thesis at that concentration of the compound. However, suggested that adhesion and migration of cells may be this is unlikely in view of the remainder of the data.
modulated through these hyaluronan receptors.26-29 Similar to our observations of decreased PGE2 syn- Also, the capacity of hyaluronan to form complexes thesis in response to hyaluronan, decreased PGE2 con- with phospholipids has been described recently,30,31,z,aa centrations were obtained in cultures treated with con- with the suggestion that administration of hyaluronan centrations of PSGAG similar to those estimated to be into the joint space may provide a source of binding obtainable by intra-articular injection, but not at con- sites for phospholipids and their metabolites (found in centrations that can be achieved after IM administration.
appreciable amounts in synovial fluid and synovial tis- Synoviocytes for each experiment were cultured sues of arthritic joints), which may stimulate chondro- from tissue of specific horses, which varied among cyte catabolism. Consequently, hyaluronan may exert a experiments. All other experimental conditions were chondroprotective effect by binding these pro-inflam- standardized, and batches of reagents and equipment matory (or pro-chondrodestructive) molecules. The were common to all experiments. Therefore, it is like- observation in the study reported here of reduced PGE2 ly that the differences in absolute baseline and LPS- synthesis after incubation with hyaluronan may be stimulated PGE2 concentrations measured in each explained by the binding capacity of hyaluronan, on experiment resulted from variation among horses, the basis that the production of eicosanoids such as despite efforts to standardize selection of synovium PGE2 results from metabolism of cell membrane phos- from nonarthritic joints in horses of similar age.
pholipids. Hyaluronan may bind these phospholipids In the study reported here, we measured reduc- in stable complexes, rendering them less susceptible to tions in the concentration of PGE2 in culture medium breakdown. This hypothesis has not been investigated.
obtained from monolayer cultures of equine synovial Using a model of osteoarthritis in which a carpal cells. However, these experiments did not address the chip was created surgically, Kawcak et al2 measured exact mechanism of action of hyaluronan and PSGAG PGE2 and protein concentrations in synovial fluid of at the cellular and molecular levels. Exposure of many horses treated by IV administration of hyaluronan.
cell types to LPS results in induction of COX-2, with Compared with concentrations for untreated control consequent synthesis of PGE2 by that inducible iso- horses, synovial fluid concentrations of PGE2 and pro- form of cyclooxygenase. Mechanisms of action of tein were decreased in hyaluronan-treated joints.
NSAID and corticosteroids in inhibiting inflammatory Furthermore, histologic examination of the synovial eicosanoid synthesis are established (inhibition of the membranes of surgically explored joints revealed actions of COX-2 and phospholipase A2 respectively, decreased synovial vascularity and cellular infiltration and, in the case of corticosteroids, inhibition of induc- in horses treated by use of IV administration of tion of the COX-2 isoenzyme as well). Given the dis- hyaluronan, compared with surgically explored joints similarity in molecular structure of hyaluronan and of untreated control horses.2 The authors of that study PSGAG to corticosteroids and NSAID, it may be con- concluded that IV administration of hyaluronan had a sidered unlikely that hyaluronan and PSGAG exert positive effect in ameliorating inflammatory synovitis, their PGE2 concentration-lowering effects through although the mechanism of action of hyaluronan inhibition of these enzymes. The possibility that remains unknown. The data from our in vitro study warrant discussion because of results of the aforemen- induces receptor shredding from synovial leukocytes (abstr). Br J tioned in vivo study. Our calculations of the plasma Rheumatol 1995;34(suppl 34):30.
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