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Biomedical subjects

D S Howell

Publications and source records attributed to D S Howell.

At least 55 records · Page 3Linked to original sources
PubMed1990

Biochemical aspects of osteoarthritis.

The development of new technologies in the fields of cellular and molecular biology is contributing significantly to the understanding of the disease processes involved in the development and progression of human osteoarthritis (OA). In particular, the relationships between enzyme degradative pathways are becoming increasingly clear. Two prominent metalloenzymes and the specific tissue inhibitor of metalloproteinase have been studied in humans and animal models. Results indicate that such enzyme pathways may play a significant role in the degenerative tissue changes observed in OA.

Animals↗
PubMed1990

Morphological abnormalities in vitamin B6 deficient tarsometatarsal chick cartilage.

The aim of this study was to test the hypothesis that deficiency of vitamin B6 would produce morphological characteristics of osteochondral lathyrism. To accomplish this goal, morphological characteristics of chick cartilage in which lathyrism was produced by two separate dietary regimens was compared to morphological changes encountered in vitamin B6 deficiency. Vitamin B6 deficiency should reduce activity of lysyloxidase needed for producing intermolecular cross-links. The question to be addressed was: would this latter deficiency impair collagen morphological features and secondarily other structures indirectly by reducing collagen molecular assembly? Failure of cross-linking of collagen in the positive controls was related to a lack of functional aldehyde cross-link intermediates which are blocked by homocysteine and aminoacetonitrile. Day-old-male Lohmann chicks were fed adequate (6 mg/kg) or vitamin B6-deficient diets. Cross-link defects were induced by homocysteine-rich diets (0.6% w/w) or a diet containing aminoacetonitrile (0.1% w/w). Animals were sacrificed at 6 weeks of age and Ossa tarsalia articular cartilage specimens, as well as the proximal end of tarsometatarsus were dissected from the tibial metatarsal joint, a major weight-bearing site. Light microscopic observations revealed reduction of subarticular trabecular bone formation, concurrent with overexpansion of the hypertrophic cell zone. Ultrastructural electron microscopy observation of articular fibro-cartilage indicated significant thickening of collagen fibers in vitamin B6 deficient birds, as well as the positive controls in comparison to that of cage-matched control birds. It was concluded that vitamin B6 deficient cross-linking may be responsible for the observed delay in bone development and aforementioned cartilage histological alterations.

Aminoacetonitrile↗
PubMed1989

Prophylactic treatment of canine osteoarthritis with glycosaminoglycan polysulfuric acid ester.

The prophylactic effect of glycosaminoglycan polysulfuric acid ester (GAGPS) on cartilage lesions was studied using the Pond-Nuki model of canine osteoarthritis. Starting 2 days after anterior cruciate transection, GAGPS or saline was administered intraarticularly twice weekly for 4 weeks. After 4 weeks, gross and histologic medial femoral condylar lesions had developed to a lesser degree in GAGPS-treated dogs than in saline-treated dogs. The uronic acid and hydroxyproline levels in cartilage were significantly higher in the GAGPS-treated dogs than in the saline-treated dogs. Levels of active and latent collagenase in the cartilage of GAGPS-treated dogs were lower than in the cartilage of saline-treated dogs. With GAGPS treatment, swelling of the cartilage, an indicator of collagen network integrity, remained near control levels. Although increased synthesis of proteoglycan and collagen may account for some of these results, we propose that one mechanism of action of GAGPS is its ability to decrease collagen degradation, either by decreasing the synthesis of collagenase or by directly inhibiting the production of collagenase in cartilage.

Animals↗
PubMed1989

Therapeutic treatment of canine osteoarthritis with glycosaminoglycan polysulfuric acid ester.

The therapeutic effect of glycosaminoglycan polysulfuric acid ester (GAGPS) was studied using the Pond-Nuki model of canine osteoarthritis. The clinical setting was simulated by permitting 4 weeks ambulation without treatment, following anterior cruciate transection. Animals were then injected with GAGPS, 4 mg/kg intramuscularly, twice weekly during weeks 4-8. Control animals received intramuscular saline. The study was terminated 4 weeks after completion of the GAGPS or saline regimen (i.e., 12 weeks postoperatively). Cartilage from the medial femoral condyle was analyzed for collagen integrity (swelling properties), hydroxyproline, uronic acid, active and total proteoglycan (PG)-degrading metalloproteinase, PG-degrading serine proteinase, and histopathology (Mankin score). Condylar cartilage from animals treated with GAGPS demonstrated less cartilage swelling, less total and active metalloproteinase, and lower histopathologic scores than were found in cartilage from saline-treated animals. GAGPS was able to suppress PG-degrading enzyme activity and maintain a more normal-appearing cartilage. It is proposed that GAGPS suppressed PG breakdown by decreasing synthesis of metalloproteinase or by directly inhibiting metalloproteinase in cartilage, rather than by increasing synthesis of PG by chondrocytes.

Animals↗
PubMed1989

Association of collagenase and tissue inhibitor of metalloproteinases (TIMP) with hypertrophic cell enlargement in the growth plate.

In the transition from proliferating to hypertrophic cell zones in the growth plate, there is an increased in chondrocyte cell volume and a corresponding decrease in collagen content to allow for cell enlargement. To substantiate our hypothesis that collagenase is responsible for these changes, growth plates from rats treated with bisphosphonate (HEBP) were compared histologically and biochemically with growth plates from normal and vitamin D and phosphate deficient (-VDP) rats. HEBP-treated rats developed an expanded hypertrophic cell zone (HCZ) characterized by the presence of two distinct populations of hypertrophic cells. The proximal hypertrophic cells were only 2-fold enlarged compared to the proliferating cells, whereas 1/6 of the distal hypertrophic cells were enlarged almost 5-fold and appeared morphologically identical with hypertrophic cells from normal and -VDP rats. The HEBP growth plates were divided into cross-sectional thirds and analyzed for active and latent collagenase. The juxta-metaphyseal (lower 1/3) cartilage contained 100% of the fully enlarged hypertrophic cells and appeared identical to those found in normal and -VDP growth plates, along with 81% of the active and 77% of the total collagenase. Collagenase and tissue inhibitor of metalloproteinases (TIMP) were measured in extracts of similarly divided tissues. The presence of true collagenas was confirmed by using [3H]-telopeptide-free collagen. TIMP levels were inversely related to the presence of active collagenase and cellular hypertrophy. Substantial levels of latent collagenase were found in the extracellular fluid at sites of active collagenolysis, but not in the fluid phase surrounding the 2-fold enlarged hypertrophic cells. It is postulated that increased amounts of active collagenase and insufficient levels of TIMP may account for the reduced collagen content seen in the lower HCZ of both -VDP and HEBP rickets. Unlike active collagenase, which remains localized by binding to collagen, latent enzyme is probably restricted in its mobility throughout the extracellular space by diffusion, itself, or the interstices of the extracellular matrix.

Animals↗
PubMed1989

Evidence for metalloproteinase and metalloproteinase inhibitor imbalance in human osteoarthritic cartilage.

Cartilage specimens from tibial plateaus, obtained from 13 osteoarthritic (OA) patients and seven controls, were selected from three regions: zone A, center of fibrillated area; zone B, area adjacent to fibrillation, and zone C, remote region of plateau. Acid and neutral metalloproteinases and tissue inhibitor of metalloproteinase (TIMP) were extracted with 2 M guanidine. Methods were developed to selectively destroy either proteinases or TIMP to prevent cross-reaction during assay. Acid and neutral proteinases were elevated approximately 150% in OA; TIMP was elevated approximately 50%. A positive correlation (r = 0.50) was found between acid and neutral proteinase activities in OA, but not in controls. Both proteinases were elevated two-to threefold in zones A, B, and C. However, the self-active form of the acid metalloproteinase was elevated only in zones A and B (200%); it correlated well with the Mankin scores, whereas the total activities did not. TIMP was elevated (50%) only in zones A and B. Both the proteinase levels and the Mankin score were elevated to a greater extent in the medial, than in the lateral, compartment. Titration of TIMP against the two metalloproteinases indicates that there is a small excess of inhibitor over enzymes in normal cartilage. In OA, TIMP does not increase to the same extent as the proteinases; the resultant excess of proteinases over TIMP may contribute to cartilage breakdown.

Adult↗
PubMed1989

Changes in the sedimentation profile of proteoglycan aggregates in early experimental canine osteoarthritis.

Osteoarthritis was induced in 12 normal dogs by severing of the anterior cruciate ligament of the right knees, the left knees serving as sham operated controls. The animals were killed at 7 and 14 weeks postsurgery. The total hexuronate, and thus proteoglycan, content of the articular cartilage of operated knees remained unaltered during the period of study. After pretreatment with a highly purified collagenase and in the presence of selected protease inhibitors, a higher proportion of the tissue hexuronate could be extracted from the different topographical areas of osteoarthritic joints under non dissociative conditions (70-75% versus 55-65% for control knees). The nondissociatively recovered osteoarthritic proteoglycans (a-A1 preparations) displayed progressive and consistent changes in their sedimentation profile. First, the size of the fast sedimenting or more saturated aggregates appeared to be reduced in the different regions of osteoarthritic joints at 7 weeks postoperatively. The disappearance of the faster sedimenting mode as well as a dramatic increase in the proportion of monomers were only detected in the topographical zones exhibiting the most severe surface damage and histologic abnormalities at 14 weeks postsurgery. The proteoglycan molecules present as "free" or "nonaggregated" monomers in a-A1 preparations recovered from normal and osteoarthritic cartilage at different time periods after surgery were separated from their corresponding aggregates by rate zonal centrifugation in isokinetic cesium sulfate gradient. Although they were severely depleted in keratan sulfate, the purified "free" and "aggregated" osteoarthritic monomers appeared to be normal in terms of aggregating capacity and size distribution, and were therefore not degraded. This progressive changes in size distribution of proteoglycan aggregates in the early stages of experimental canine osteoarthritis could contribute significantly to the biochemical and biomechanical alterations of osteoarthritic cartilage.

Animals↗
PubMed1989

Hypertrophic chondrocytes produce immunoreactive collagenase in vivo.

A monospecific, polyclonal antibody to neutral collagenase purified from rat myometrial cells was used to examine decalcified sections of normal and rachitic rat long bones, including epiphyses, for presence of immunoreactive collagenase in situ. Reactive antigen was uniformly present in hypertrophic chondrocytes of articular and epiphyseal plate cartilage. Preincubation of antibody with excess homogeneously purified antigen blocked the staining, indicating specificity of the staining for the antigen. Reaction was present in the borders of the enlarging lacunae, suggesting functional importance of this enzyme in the process of lacunar enlargement prior to mineralization. No detectable enzyme was observed in osteoblasts, osteocytes, or osteoclasts. No difference between expression of collagenase by bone cells in rachitic or normal bone was seen. Thus, at the level of sensitivity of this procedure, neutral collagenase appears to function in mature rat bone only in enlarging chondrocyte lacunae.

Animals↗
PubMed1989

The research arena of this symposium and an outlook for future treatment of osteoarthritis.

Attention of researchers in the field of cartilage degradation in osteoarthritis is being focused on pathways of enzymic degradation and their control. Whereas, it is unlikely that a precise cascade as in the complement and clotting systems will be found, a more loosely knit cascade is evolving in terms of mediators, activators, and inhibitors of enzymes, which degradate matrix stroma. Structural changes in the proteoglycans are becoming clearly obvious with newer technologies, which can be visualized with extended path ultracentrifugation techniques.

Animals↗
PubMed1988

Superficial and deeper layers of dog normal articular cartilage. Role of hyaluronate and link protein in determining the sedimentation coefficients distribution of the nondissociatively extracted proteoglycans.

Proteoglycans were extracted under nondissociative conditions from superficial and deeper layers of dog normal articular cartilage. The purified a-A1 preparations were characterized by velocity gradient centrifugation. Superficial specimens exhibited an abundant population of slow sedimenting aggregates whereas the aggregates of deeper preparations sedimented as two well-defined families of molecules. These dissimilarities in the size distribution of the aggregates observed between superficial and deeper a-A1 preparations derived most of all from differences in their content of hyaluronate and link proteins: (a) superficial preparations contained twice as much hyaluronate as deeper specimens; (b) superficial aggregates were link-free and unstable at pH 5.0 whereas deeper preparations contained link-proteins and their faster sedimenting aggregates were stabilized against dissociation at pH 5.0. In these proteoglycan preparations from different cartilage layers, the monomers exhibited an identical capacity for aggregation and the hyaluronate molecules displayed quite similar molecular weight (Mr = 5 x 10(5] and aggregating capacity. These observations as well as aggregating studies conducted with highly purified link protein and purified hyaluronate specimens of different molecular weights support the following conclusions: (a) link protein not only stabilizes proteoglycan aggregates but also enhances the aggregating capacity of hyaluronate; (b) for all practical purposes, the slow sedimenting aggregates represent a secondary complex of hyaluronate and proteoglycan monomers whereas the fast sedimenting aggregates may be considered as a ternary complex wherein link protein stabilizes the hyaluronate-proteoglycans interaction; (c) the distinctive heterogeneity of articular cartilage can be related to structurally different proteoglycan aggregates. The structural dissimilarities observed between superficial and deeper aggregates could reflect the different macromolecular organization of the proteoglycan molecules in the territorial and interterritorial matrices, respectively.

Animals↗
PubMed1988

EHDP-induced rachitic syndrome in rats is not reversed by vitamin D metabolites.

To examine whether either of the two known active vitamin D metabolites 1,25(OH)2D3 or 24,25(OH)2D3 could reverse the mineralization defect induced by 1-hydroxyethylidene-1,1-bis phosphonate (EHDP), a model of EHDP-induced rickets was used. Rats at the age of 31 days were injected for 10 consecutive days with EHDP (10 mg/kg). Other littermates were treated with a combination of EHDP and either 1,25(OH)2D3 or 24,25(OH)2D3 or were treated following 10 days of EHDP, with either of the vitamin D metabolites for an additional 72 hr. Samples of cartilage fluid (Cfl) and of blood were removed prior to sacrifice for biochemical studies of some parameters of calcification. These parameters were correlated with the results of light and electron microscope studies of growth plate cartilage and bone. EHDP-treated rats revealed signs of typical rickets, manifested by widened growth plates and impaired bone mineralization. Transmission electron microscope (TEM) examination revealed matrix vesicles distributed throughout the growth plate; however, there appeared to be an arrest of the spread of the crystals at the provisional zone of calcification. Treatment with either 1,25(OH)2D3 or 24,25(OH)2D3 failed to reverse the rachitic condition of the animals. Serum calcium blood levels were elevated in the 1,25(OH)2D3 and EHDP-treated group. 1,25(OH)2D3 and 24,25(OH)2/D3 further increased the already elevated serum alkaline phosphatase levels observed in EHDP rats, although the increase observed with 1,25(OH)2D3 was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Aspiration and characterization of predentin fluid in developing rat teeth by means of a micropuncture and micro-analytical technique.

A fluid phase was aspirated in vivo and in vitro from predentin or pulp of developing rat teeth by means of a micropuncture technique. Pooled aspirates (approx. 2 nL) were analyzed for P, Na, K, Ca, Mg, and S by electron probe microtechniques (Lechene and Warner, 1979). Compared with pulp fluid, currently and previously studied cartilage fluids, as well as serum, predentin fluid showed elevated K, depressed Na, Cl, and Ca, as well as increased P. Statistical analysis was possible for only a few groups of comparisons among the elemental profiles. Ultrastructural examination of the aspiration site and of the aspirates showed no evidence of contamination with cell organelles or other formed elements. The micropuncture technique used was a critically precise and laborious procedure; possible contamination with intracellular fluid could not be avoided. The consistently low Mg concentration found in the aspirates, however, supports our view that the samples were primarily extracellular.

Animals↗
PubMed1988

Future therapeutic trends in osteoarthritis.

Since cartilage contains no nerve endings, symptoms of osteoarthritis (OA) are indirect. Therapy of OA, to date, has been directed at the symptoms of pain, signs of inflammation and loss of function. A major advance has been surgical joint replacement. This benefit however, is often limited by the joint area involved and to the survival of the endoprosthesis. Orthopedic new approaches to therapy of OA include removal of abnormal tissue to stimulate repair (e.g., burring, abrasion) and grafting (e.g., osteochondral grafts, perichondrium, periosteum) to the subchondral bone. Controlled activity (e.g., passive motion) has been studied alone and with the above. Can a medication retard or reverse the degradative process of OA? Several medications are being examined for potential "chondroprotective" characteristics. Some of these agents are not new: oversulfated glycosaminoglycans (Arteparon) derived from cartilage and glycosaminoglycan peptides (Rumalon) derived from cartilage and bone marrow extracts may be prototypes of this approach to therapy. Other agents demonstrating potential benefit in retarding cartilage degradation may include non-steroidal anti-inflammatory agents, tiaprofenic acid, sodium pentosan sulfate and low dose corticosteroids. This concept of "chondroprotection" provides us a new approach to a disease in need of a new approach.

Animals↗
PubMed1987

Tensile properties of human knee joint cartilage. II. Correlations between weight bearing and tissue pathology and the kinetics of swelling.

The nonequilibrium or kinetic swelling behavior of normal, fibrillated, and osteoarthritic (OA) (removed from total knee joint replacements) human knee joint cartilage has been measured using our isometric tensile apparatus (ITA). We found that large local variations exist in the manner with which human knee joint cartilage swells, including anisotropic effects, inhomogeneities, and dependence on local biochemical composition and pathological condition. The ITA provides three convenient biomechanical parameters--peak stress (sigma p), stress relaxation (sigma R), and diffusion coefficient (D)--to quantify the kinetics of swelling. We used these parameters to quantify and differentiate the kinetic swelling behavior of normal, fibrillated, and osteoarthritic cartilage, as well as the swelling behavior of cartilage from high and low weight-bearing areas. Also, these kinetic swelling parameters correlated very well, though by varying degrees, with such biochemical measures as collagen/proteoglycan ratio, hexosamine content/wet weight, and hydroxyproline content/dry weight, providing important insight into the mechanisms and processes involved during the course of swelling. Hence, the kinetic swelling behavior of cartilage should be used to provide important information not obtainable from equilibrium swelling studies.

Body Water↗
PubMed1987

The effect of glycosaminoglycan polysulfuric acid ester on articular cartilage in experimental arthritis: effects on collagenolytic enzyme activity and cartilage swelling properties.

Some of the effects of the semi-synthetic glycosaminoglycan polysulfuric acid ester (GAGPE) were investigated on the osteoarthritis-like lesions in the Pond-Nuki dog model, in respect to histological grade of anatomical lesions, collagenolytic enzyme activity, and a parameter of collagen network integrity. Prophylactic treatment by intra-articular injections twice weekly for 4 weeks caused amelioration of canine cartilage erosions. Preliminary evidence for suppression of collagenolytic enzyme activity, as well as protection of a tight collagen network studied in the canine cartilage was obtained.

Animals↗
PubMed1987

Development of clinical criteria for osteoarthritis.

Clinical criteria for the classification of osteoarthritis (OA) in the knee have been developed and the use of algorithms has been proposed. Criteria for the classification of OA in the hand and hip are still being developed.

Hand↗
PubMed1986

Pathogenesis of osteoarthritis.

This article reviews the etiology and pathogenesis of osteoarthritis, particularly one of several current concepts concerning the possible central mechanisms regulating degradation of cartilage. According to this theory, degradation involves diffuse or focal exposure of the extracellular matrix to active neutral metalloproteinases, which then results in injury as well as initiation of repair processes. Diffuse matrix exposure is probably not a physiologic aberrancy but rather a pathologic result of either physical injury to local chondrocytes or inflammatory mediators.

Animals↗