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U Sarma

Publications and source records attributed to U Sarma.

9 recordsLinked to original sources
PubMed2001

Investigation of ethnic neutropenia by assessment of bone marrow colony-forming cells.

Healthy individuals with African ancestry have lower neutrophil counts than Caucasians. It has previously been postulated that this was consequent on either a diminished bone marrow granulocyte reserve or an altered distribution of neutrophils between the circulating and marginated granulocyte pools. Recent indirect evidence supports the former hypothesis. In this study we have compared the number of granulocyte plus granulocyte-macrophage colony-forming units (CFUs) in the bone marrow of healthy African and Afro-Caribbean subjects with the number of CFUs in the bone marrow of healthy age and sex-matched Caucasians. We found the group with African ancestry to have significantly fewer CFUs than the Caucasian group. There was no evidence of any qualitative difference between the CFUs of the two ethnic groups: they showed similar sensitivity to granulocyte-monocyte colony stimulating factor and similar enhancement of growth when cultured with a larger range of cytokines. These observations suggest that ethnic neutropenia observed in those with African ancestry is likely to result from reduced numbers of bone marrow progenitor cells in comparison with numbers present in Caucasians.

Adolescent↗
PubMed2000

Study of the nonresorptive phenotype of osteoclast-like cells from patients with malignant osteopetrosis: a new approach to investigating pathogenesis.

Osteopetrosis manifests as failure of osteoclastic bone resorption. The cause of the disease lies either in the hematopoietic lineage or in the bone marrow stromal microenvironment. It has not been possible to define the cell type involved in the various forms of the human disease because of the inability to form human osteoclasts in vitro. Using the recently described method for generating human osteoclasts from peripheral blood in coculture with rat osteoblastic UMR 106 cells, we demonstrate that a defect lies in the mature osteoclast-like cells in four cases of this disease. Control and osteopetrotic cocultures generated large numbers of osteoclast-like cells (calcitonin and vitronectin receptor positive, and F-actin ring-positive cells) with similar morphology. Bone resorption did not occur in three of the four osteopetrotic cultures. In case 1, in which bone resorption was identified, the area of resorption was negligible compared with the number of osteoclast-like cells in the culture and was detected only by scanning electron microscopy. In contrast, up to 20% of the bone surface in controls was resorbed. The normal and osteopetrotic osteoclast-like cells had a similar phenotype except that two of the osteopetrotic cases did not express CD44 and two expressed CD44 weakly, whereas CD44 was strongly expressed in the controls. This study shows that it is possible to reproduce in vitro the pathological features of human osteopetrosis, and the assay provides a means of acquiring a greater understanding of the pathogenesis of human osteopetrosis.

Animals↗
PubMed1999

Macrophage colony stimulating-factor transcripts are differentially regulated in rat bone-marrow by gender hormones.

There are at least three forms of macrophage colony-stimulating factor (M-CSF), a cytokine that is critical for osteoclast formation; and evidence exists that the membrane-bound form is involved in this process. We wished to test the hypothesis that the expression of the membrane form of M-CSF is modulated by the presence of gender steroids. This was achieved by analyzing M-CSF messenger RNA and protein in the bone-marrow of estrogen- and androgen-replete, and -deficient female rats. We found that the 1.4-kb M-CSF transcript was not detected in sham-operated rats but that the 4.6-kb transcript was expressed in abundance. In contrast, these transcripts were differentially expressed in ovariectomized rats, and this effect was reversed by 17beta-estradiol treatment. Administration of androstenedione to ovariectomized rats, so that androstenedione plasma levels were restored to just below that in sham-operated rats, also suppressed the expression of the 1.4-kb M-CSF transcript. This effect was abrogated by antiandrogen treatment, indicating that this was an androgen-mediated effect. The membrane-bound protein was detected in the bone-marrow of sham-operated rats and was elevated post ovariectomy, whereas ovariectomy had no effect on the soluble isoform. Our data support the hypothesis that the membrane form of M-CSF is modulated by gender hormones and that this isoform is involved in the estrogen- and androgen-mediated effects on the skeleton.

Anastrozole↗
PubMed1998

Inhibition of bone resorption by 17beta-estradiol in human bone marrow cultures.

Estrogen deficiency puts individuals at risk of developing osteoporosis because it causes increased bone resorption. However, the mechanism by which this occurs is not known. We have shown, using a recently described two-phase human bone marrow culture system, that estradiol (17beta-E2) added to phase I results in inhibition of bone resorption by reducing the number of osteoclasts (identified as vitronectin receptor and/or calcitonin receptor-positive cells) formed in the cultures. The addition of 17beta-E2 in phase II was without effect, indicating that it does not interfere with the bone resorptive process. 17Beta-E2 down-regulated mRNA expression and protein synthesis of the membrane form of macrophage colony-stimulating factor (M-CSF). 17Beta-E2 did not the alter the expression of the 4.0 kb M-CSF transcript. However, it increased protein synthesis of the proteoglycan form of M-CSF, but not the 85 kDa soluble form in the same cultures. Finally, addition of M-CSF to the cultures reversed the 17beta-E2-induced inhibitory effect. These observations suggest that regulation of the synthesis of membrane-bound M-CSF plays a role in 17beta-E2-induced inhibition of bone resorption.

Actins↗
PubMed1998

Macrophage colony-stimulating factor increases bone resorption by osteoclasts disaggregated from human fetal long bones.

Macrophage colony-stimulating factor (M-CSF) is known to play an important role in human and murine osteoclast formation. Although M-CSF has been shown to inhibit isolated neonatal rat osteoclasts from resorbing bone, its action on the mature human osteoclast has not been described. We now report that M-CSF increases osteoclastic bone resorption in a dose-responsive manner. Bone resorption by mature human fetal osteoclasts, including pit area, depth, and volume, was increased in the presence of M-CSF compared with vehicle. The number of osteoclasts in the cultures was similar after 2 and 18 h in the presence of M-CSF, whereas there was a significant reduction in osteoclast number, whether assessed as the number of tartrate-resistant acid phosphatase (TRAP)-positive or vitronectin receptor-positive cells after 18 h in M-CSF-free cultures. The number of nuclei per osteoclast after 2 or 18 h in M-CSF was also similar and there was no difference in the number of vitronectin receptor-positive mononucleate cells at 2 and 18 h. This suggests that the increased bone resorption is likely to be accounted for by enhanced osteoclast survival in M-CSF compared with controls rather than by formation of new osteoclasts.

Acid Phosphatase↗
PubMed1998

Study of the cell biology and biochemistry of cherubism.

AIMS: To establish whether the multinucleate cells in lesions of patients with cherubism are also osteoclasts and if this is the case whether they were responsive to calcitonin; to carry out cytogenetic studies on two members of the same family affected by cherubism in an attempt to identify any major chromosomal defects; and to perform an in-depth modern biochemical study of four children in the same family. SUBJECTS AND METHODS: Four related children with cherubism were studied. Tissue taken from one of the children at elective decompression of an optic nerve was submitted to in vitro bone resorption studies. Cytogenetic studies were done on two of the children and biochemical studies on all four. RESULTS: The multinucleate cells in the cherubic lesions were shown to be osteoclasts since they synthesised tartrate resistant acid phosphatase, expressed the vitronectin receptor, and resorbed bone. Bone resorption by the cultured multinucleate cells was significantly inhibited by calcitonin. High resolution cytogenetic studies failed to detect any chromosomal abnormalities in two children with cherubism. The biochemistry profile of all four children with cherubism showed that serum calcium, parathyroid hormone, parathyroid related hormone, calcitonin, and alkaline phosphatase were within normal levels. Urine analysis of pyridinium and deoxypyridinium cross links, hydroxyproline, and calcium in relation to urine creatinine were measured to assess bone resorption in these children, and the values were at the upper end of the normal range in all four. CONCLUSIONS: Further studies are required to determine whether calcitonin treatment will control this grossly deforming disease until the time when the physiological changes that occur at puberty rectify the pathology. It is not recommended that biochemical markers of bone resorption are used in isolation to monitor the activity of cherubism in individuals because the results are based on a small number of children and because of reports of marked interindividual variation in the levels of these markers, particularly in children.

Bone Resorption↗
PubMed1996

Macrophage colony-stimulating factor induces substantial osteoclast generation and bone resorption in human bone marrow cultures.

Macrophage colony-stimulating factor (M-CSF) is essential for murine osteoclast formation and its role in human hematopoiesis in vitro is not fully defined. Therefore, we have investigated the effect of M-CSF on the formation of human osteoclasts in vitro. M-CSF was found to induce substantial bone resorption and osteoclast formation in a dose-responsive and time-dependent manner above that induced by 1,25 dihydroxyvitamin D3 (1,25 vitamin D3) in cultures of human bone marrow (BM) stromal cells sedimented onto devitalized bone. By day 14 there was a mean of approximately 50% of the surfaces of the bone slices resorbed compared with only 6% in cultures treated with 1,25 vitamin D3 alone. Osteoclasts were identified as 23c6+ cells (an antibody that recognizes the vitronectin receptor), 87.5% of which coexpressed the calcitonin receptor. The number of 23c6+ cells correlated strongly with bone resorption spatially, and in a dose-responsive and time-dependent manner; the correlation coefficient in cultures treated with 1,25 vitamin D3 alone was 0.856 and those treated with both M-CSF and 1,25 vitamin D3 was 0.880. Granulocyte-macrophage colony-stimulating factor, IL-1 beta, IL-3, IL-6, tumor necrosis factor-alpha, transforming growth factor-beta, leukemia inhibitory factor, and IL-11 did not increase bone resorption above that in 1,25 vitamin D3-treated cultures. We also found that 1,25 vitamin D3 increased, to a minor but significant degree, both bone resorption and the concentration of M-CSF in the culture supernatants above that in vehicle-treated cultures, indicating that M-CSF is present in our BM cultures, but that there is insufficient to induce substantial osteoclast formation. These results define a critical role for M-CSF in the formation of human osteoclasts.

Adult↗