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Biomedical subjects

A H Reddi

Publications and source records attributed to A H Reddi.

At least 163 records · Page 9Linked to original sources
PubMed1983

Changes in tissue concentration of prostaglandins during endochondral bone differentiation.

Prostaglandins are known to be involved in bone metabolism as evidenced by the ability of PGE2 to induce bone resorption. It was, therefore, of interest to determine if there was an association of specific prostaglandin metabolites with the various stages of developing bone by utilizing the matrix-induced endochondral bone formation system. During mesenchymal cell proliferation a peak of endogenous thromboxane B2 was detected. In the subsequent stages of chondrogenesis and chondrolysis PGF2 alpha was in high concentration, whereas during bone formation PGE2, 6-Keto-PGF1 alpha and thromboxane B2 were elevated. These changes in the peak levels of the various prostaglandin metabolites may reflect differences in the cell populations and function associated with various stages of endochondral bone formation.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Identification of a bone matrix-derived chemotactic factor.

When demineralized bone matrix powder is implanted subcutaneously in the rat, the early responses involve the appearance and proliferation of mesenchymal cells at the site of implantation, followed by cartilage and bone formation. The ability of cells to migrate to the implant suggests that chemotaxis may be a critical event in this process. Therefore, using the modified Boyden chamber assay, we tested extracts of demineralized bone matrix for chemotactic activity. We have identified and partially purified, on molecular sieve chromatography, a heat labile and trypsin-sensitive protein (Mr = 60,000-70,000) that is a potent chemoattractant for mouse calvaria, osteoblast-like cells (MMB-1), but not for monocytes (putative osteoclast precursors). These findings suggest that chemotactic protein(s) have a significant role in the recruitment of osteoprogenitor cells to a site of bone repair.

Bone Matrix↗
PubMed1983

Changes in lipids during matrix: induced endochondral bone formation.

The changes in lipids occurring during the process of endochondral ossification have been characterized by studying the discrete phases of matrix-induced endochondral bone formation in the rat. Calcium-acidic phospholipid-phosphate complexes were shown to increase in concentration during cartilage calcification (day 9) and to peak in content during early bone formation (days 11-13), the times during which the rate of mineral deposition, as indicated by the change in ash weight was greatest. These data support the hypothesis that the calcium-acidic phospholipid-phosphate complexes play a role in the in vivo initiation of hydroxyapatite deposition. The overall lipid composition of the induced matrix newly formed cartilage (days 7-9) was comparable to that of normal cartilage, with the phospholipid composition matching that of chondrocyte plasma membranes. Times of vascular invasion and formation of marrow cavities were marked by elevated total lipid and triglyceride contents.

Animals↗
PubMed1983

Influence of estrogen and progesterone on matrix-induced endochondral bone formation.

The influence of estradiol and progesterone, alone or in combination, on the discrete phases of matrix-induced endochondral bone formation was investigated. Administration of estradiol and progesterone in combination increased mesenchymal cell proliferation, as indicated by [3H] thymidine incorporation into acid precipitable material. However, ornithine decarboxylase (ODC) activity was significantly suppressed by the combination of estradiol and progesterone. Also, this treatment did not influence the 35SO4 incorporation into proteoglycans on day 7. Mineralization of newly induced bone was quantitated by alkaline phosphatase, 45Ca incorporation into bone mineral and calcium content, and was found to be significantly increased by progesterone alone and in combination with estradiol in both matrix-induced plaques and tibial metaphysis. These results demonstrated the stimulatory role of progesterone in combination with estradiol in bone formation and mineralization.

Acid Phosphatase↗
PubMed1983

Influence of vitamin A on matrix-induced endochondral bone formation.

The influence of retinoic acid on matrix-induced endochondral bone differentiation was determined. Retinoic acid was administered during discrete stages of endochondral bone formation, specifically, mesenchymal cell proliferation, chondrogenesis, bone formation, and mineralization. In retinoic acid-treated rats examined on day 3 following matrix implantation, biochemical markers for mesenchymal cell proliferation were about 50% of the controls. Chondrogenesis on day 7, assessed by 35 SO4 incorporation into proteoglycans, was 27% of the control. In addition, dissociative extraction of proteoglycans with 4.0 M guanidine-HCl and chromatography on Sepharose CL-2B revealed the synthesis of a smaller molecular weight proteoglycan when compared to controls which exhibited the cartilage-specific type. Osteogenesis and bone mineralization were monitored by alkaline phosphatase activity and 45Ca incorporation. On day 11 alkaline phosphatase activity was decreased by 40% and 45Ca incorporation was 48% of the control. These results revealed the multiple foci of the actions of excess vitamin A.

Alkaline Phosphatase↗
PubMed1983

An immunofluorescent study of the distribution of fibronectin and laminin during limb regeneration in the adult newt.

Fibronectin and laminin are two extracellular glycoproteins which are involved in various processes of cellular development and differentiation. The present investigation describes changes in their distribution during regeneration of the newt forelimb, as determined by indirect immunofluorescence. The distribution of fibronectin and laminin was similar in normal limb tissue components. These glycoproteins were localized in the pericellular region of the myofibers corresponding to its basement membrane; the perineurium and endoneurium of the nerves; and the basement membranes of blood vessels, skin epithelium, and dermal glands. The cytoplasm of myofibers, axons, skin epithelium, and bone matrix lacked fluorescence for both glycoproteins. After limb amputation in the regenerating blastema, extensive presence of fibronectin, but not laminin, was seen in and around the undifferentiated blastemal cells. Increased fluorescence for fibronectin was also seen during blastema growth, blastemal cell aggregation, and early stages of redifferentiation. As redifferentiation continued, staining for fibronectin slowly disappeared from the cartilage matrix and the myoblast fusion zone. Laminin was first observed around the regenerated myotubes; this was followed by the appearance of fibronectin suggesting a sequential formation of these two components of the new myotube basement membrane. In the regenerated limb, the distribution of laminin and fibronectin was similar to that seen in normal limb. Based on the distribution pattern of these glycoproteins, it is concluded that fibronectin may play an important role in blastemal cell aggregation, cell alignment, and initiation of redifferentiation. After redifferentiation, both laminin and fibronectin may be important in the determination of the architecture of the regenerated limb.

Animals↗
PubMed1983

Homology of bone-inductive proteins from human, monkey, bovine, and rat extracellular matrix.

Allogeneic implantation of rat extracellular demineralized diaphyseal bone matrix in subcutaneous sites induces a sequence of events resulting in the local differentiation of endochondral bone. However, xenogenic subcutaneous implantation of human, monkey, and bovine extracellular bone matrix into rat showed that bovine matrix had only a weak capacity to induce bone, whereas human and monkey matrix had none at all. This suggested that extracellular matrix-induced bone differentiation is apparently species-specific. We recently reported that the extraction of matrix with 4 M guanidine X HCl resulted in complete removal of the ability to induce endochondral bone differentiation, with the biological activity of the matrix being again restored when the extracted active matrix components (less than 50,000 daltons) were reconstituted with the inactive residue. To define the possible biochemical basis of species specificity, human, monkey, and bovine extracellular bone matrices were extracted with 4 M guanidine X HCl and the extracts were reconstituted with biologically inactive rat residue and bioassayed. The results were similar to those obtained with intact matrices and showed that total extracts of bovine matrix had a weak capacity to induce bone, whereas corresponding extracts of human and monkey matrix did not induce bone. However, partial purification by gel filtration of 4 M guanidine X HCl extracts from each species followed by reconstitution of the different fractions with inactive rat residue resulted in bone induction by all species from fractions containing proteins of less than 50,000 daltons. These observations demonstrate that species specificity of xenogenic extracellular bone matrix is due to immunogenic or inhibitory components (or both) in the guanidine X HCl residue and solubilized extracellular matrix components of greater than 50,000 daltons. These results imply that there is homology in the bone inductive proteins from human, monkey, bovine, and rat extracellular bone matrices.

Animals↗
PubMed1983

Changes in the basement membrane zone components during skeletal muscle fiber degeneration and regeneration.

The basement membrane of skeletal muscle fibers is believed to persist unchanged during myofiber degeneration and act as a tubular structure within which the regeneration of new myofibers occurs. In the present study we describe macromolecular changes in the basement membrane zone during muscle degeneration and regeneration, as monitored by immunofluorescence using specific antibodies against types IV and V collagen, laminin, and heparan sulfate proteoglycan and by the binding of concanavalin A (Con A). Skeletal muscle regeneration was induced by autotransplantation of the extensor digitorum longus muscle in rats. After this procedure, the myofibers degenerate; this is followed by myosatellite cell activation, proliferation, and fusion, resulting in the formation of new myotubes that mature into myofibers. In normal muscle, the distribution of types IV and V collagen, laminin, heparan sulfate proteoglycan, and Con A binding was seen in the pericellular basement membrane region. In autotransplanted muscle, the various components of the basement membrane zone disappeared, leaving behind some unidentifiable component that still bound Con A. Around the regenerated myotubes a new basement membrane (zone) reappeared, which persisted during maturation of the regenerating muscle. The distribution of various basement membrane components in the regenerated myofibers was similar to that seen in the normal muscle. Based on our present and previous study (Gulati, A.K., A.H. Reddi, and A.A. Zalewski, 1982, Anat. Rec. 204:175-183), it appears that some of the original basement membrane zone components disappear during myofiber degeneration and initial regeneration. As a new basement membrane develops, its components reappear and persist in the mature myofibers. We conclude that skeletal muscle fiber basement membrane (zone) is not a static structure as previously thought, but rather that its components change quite rapidly during myofiber degeneration and regeneration.

Animals↗
PubMed1983

Extracellular bone matrix dependent local induction of cartilage and bone.

Implantation of demineralized bone matrix in extraskeletal sites results in induction of new cartilage and bone formation locally. The sequence of events during this induction is reminiscent of embryonic development. Although the precise molecular mechanisms are unknown, several biochemical features of the bone induction are described. The extracellular bone matrix has components with chemotactic, mitogenic, and differentiative activities. It is likely that a matrix-dependent sequential cascade regulates bone induction.

Animals↗
PubMed1983

Hematopoiesis on cellulose ester membranes (CEM). V. Enrichment of CEM by demineralized mouse bone matrix powder.

Mouse bone matrix powder was implanted subcutaneously or put into folded tubular cellulose ester membranes (CEM) and implanted i.p. Calcification and new bone formation did not develop. Sinusoidal vascularization of the matrix developed by 3 to 4 wk. Stromal cells such as fat cells and fibroblasts were present by 4 wk. Hematopoiesis was absent except for rare foci of granulopoiesis on some of the CEM at 6 wk. Rat bone matrix implanted subcutaneously into mice and mouse bone matrix implanted subcutaneously into rats failed to induce new bone formation or hematopoiesis.

Animals↗
PubMed1982

Distribution of fibronectin in normal and regenerating skeletal muscle.

The distribution of fibronectin in normal and regenerating skeletal muscle (the latter caused by autotransplantation) was investigated by means of indirect immunofluorescent technique. Normal myofibers exhibited a thin, continuous pericellular (endomysium) fibronectin distribution; however, their sarcoplasm was devoid of fibronectin. After autotransplantation, the skeletal muscle fibers underwent a process of degeneration that was followed by regeneration from the premyogenic satellite cells. These cells multiplied, fused to form myotubes, and matured into new myofibers. A decrease and an eventual loss of endomysial fibronectin was seen in the degenerating myofibers. At the same time, fibronectin appeared in the sarcoplasm. No significant fibronectin was expressed in the myogenic zone until the formation of myotubes which possessed a complete, circular fibronectin ring. The sarcoplasm of the myotubes lacked fibronectin. Since fibronectin is a component of basement membrane of several tissues, its disappearance and reappearance can be used to follow the fate of basement membrane. We conclude that fibronectin may not be essential for early myogenesis and that regenerated myotubes form an entirely new or at least certain new molecular components of their basement membrane. The present muscle autotransplantation model can be used to further study the role of fibronectin during myogenesis and cell transformation in vivo.

Animals↗
PubMed1982

Reduction of hematopoietic stem cells and adaptive increase in cell cycle rate in rickets.

The close but complex physiological interactions between osteogenesis and hematopoiesis during differentiation, development, and function are unclear. As vitamin D has a major role in bone metabolism and function, we have investigated the effects of vitamin D deficiency on bone marrow cellular kinetics. Using rats in vitamin D-deficient status in utero as well as in postfetal life, we have investigated changes in hematopoiesis. Total cellularity, colony-forming unit (CFU) content, and the cycled rate were determined from the axial compartment of the femoral marrow. A marked reduction in the CFU content and a corresponding increase in the cycle fraction began at 30 days of age and stabilized by 45 days of age at 4.2 +/- 0.4 CFUs per 1 X 10(5) nucleated cells in the vitamin D-deficient animals as compared with 9.4 +/- 1.6 in the control group. During the same period of time the CFU generation time decreased from 61 +/- 5 h in the normal animals to 24 +/- 6 h in the vitamin D-deficient animals. Administration of either 1,25-dihydroxyvitamin D [1,25-(OH)2D3] or 24,25-(OH)2D3 at 45 days of age on a daily basis for 7-14 days failed to correct the defect although the serum calcium and phosphate were corrected. The data indicate that factors influencing the development of bones may affect bone marrow cells as well. Vitamin D metabolites may be needed for normal development and function of marrow-colony-forming cells in utero.

Acclimatization↗
PubMed1982

Regulation of local differentiation of cartilage and bone by extracellular matrix: a cascade type mechanism.

The regenerative potential of the vertebrate skeletal system is well known. Normal cartilage and bone development can be mimicked by implantation of demineralized bone matrix, which induces bone formation locally. The sequential stages of the matrix-induced bone development and recent advances in the underlying biochemical mechanisms are described. The extracellular matrix components have chemotactic, mitogenic and differentiative activities. It would appear that a cascade type mechanism is operative during local differentiation of endochondral bone.

Animals↗
PubMed1981

Isolation and characterization of rat plasma fibronectin.

Rat plasma fibronectin has been isolated and characterized and monospecific antibodies were prepared to it. Two components of fresh rat plasma (in the presence of proteinase inhibitors) bound to a gelatin-Sepharose affinity column. One protein was eluted with 4.0 M-urea and was identified as fibronectin. Another protein was eluted from the gelatin-Sepharose column with 8.0 M-urea and was identified as a 70 000-Mr collagen-binding molecule. This 70 000-Mr fragment was found to be a normal constituent of blood plasma, and its presence did not represent a proteolytic degradation product formed during isolation. The antibodies prepared against rat fibronectin only weakly cross-reacted with plasma fibronectins of chicken, horse and human. These studies shed light on the metabolic interrelationships between fibronectin and other collagen-binding molecules.

Amino Acids↗