Biomedical subjects
Publications and source records attributed to J M Papadimitriou.
In this report we demonstrate for the first time that differentiating myogenic cells, geographically located between the plasmalemma and external lamina of myofibres in the satellite cell position, can fuse directly with the plasmalemma of undamaged segments of mature myofibres.
Calcitonin is a direct inhibitor of osteoclastic activity. Osteoclast retraction is readily induced by calcitonin and it is possible that calcitonin-induced inhibition of bone resorption is in part due to this effect. However, little is known of the mechanisms of this action. In these studies, we have investigated the intracellular signalling pathway of calcitonin-induced osteoclast retraction using cultures of freshly isolated rat osteoclasts. The spread area occupied by single Giemsa-stained rat osteoclasts was measured in vitro by a computer imaging analysis system and used as a quantitative parameter for calculating the degree of osteoclast retraction in response to various agents. Our results show that cAMP may be an important second messenger in the reaction of osteoclasts to calcitonin. Moreover, both protein kinase-A and calcium/calmodulin-dependent protein kinase are involved in the osteoclast retraction induced by this hormone, while cytoskeletal proteins are required for the process to occur.
Myocardial ischemia is associated with accumulation of lyso-phospholipids, including lyso-platelet activating factor, the degradation product and precursor of platelet activating factor. These compounds produce cellular and microvascular damage and, in the myocardium, depression of contractility and arrhythmia. The potent platelet activating factor antagonist, WEB 2086, or placebo, was infused (IV) 10 min before constriction of the proximal left anterior descending coronary artery in open-chest dogs. Two protocols were followed: the dose of WEB 2086 was 0.5 mg/kg in those subjected to 20 min ischemia with 10 min reperfusion (n = 40) and 5 mg/kg preceding 60 min ischemia alone (n = 24). There was no significant difference in the number of ventricular premature complexes between WEB 2086 and placebo treated dogs during either period of ischemia. On reperfusion in those surviving 20 min of ischemia, 5 of the 18 WEB 2086 and 9 of the 18 placebo treated dogs developed ventricular fibrillation (NS). After 60 min of myocardial ischemia, there was no statistical difference in histological changes (nuclear swelling, aggregation of chromatin, myofibrillar separation) between groups. Hence, no substantial effect of relatively large doses of WEB 2086 on ischemia-induced histological change or arrhythmia was found in this preparation.
Recently published informed debate affords strong indication that in patients with the Acquired Immune Deficiency Syndrome, HIV cannot, directly or indirectly, be the cause of Kaposi's sarcoma. This paper provides reasons for disallowing a current alternative theory that Kaposi's sarcoma is due to an unidentified sexually transmitted infectious agent and proposes instead that Kaposi's sarcoma is the result of prolonged and repeated exposure to nitrites and/or semen. If this alternative hypothesis is strengthened by confirmation of its predictions then the relationship of HIV to Kaposi's sarcoma, one of the principal AIDS-associated diseases, becomes somewhat remote. This may facilitate a shift of emphasis and encourage the development of alternative therapies.
This review assesses recent data concerning the role of cytokines produced by a variety of cells in bone on osteoblast function. The following themes are presumed: (1) osteoblasts are mesenchymal cells which act as either the major cellular agents of bone formation or as modulators of bone resorption by osteoclasts. The regulation of osteoblast proliferation and differentiation may involve a negative feedback process resulting in phenotype suppression; (2) cytokines including platelet-derived growth factors (PDGF), parathyroid hormone-related proteins (PTHrP), bone morphogenic proteins (BMP), transforming growth factor beta (TGF beta), fibroblast growth factors (FGF), insulin-like growth factors (IGF), epidermal growth factors (EGF), interleukin-1 and 6, tumour necrosis factors (TNF), interferon and haematopoietic growth factors have effects on osteoblast differentiation and proliferation but their effectiveness may not be identical in vitro and in vivo; (3) finally, therapeutic strategies for cytokine use in clinical practice are considered.
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To investigate the role of proliferating local and emigrating circulatory leucocytes in skeletal muscle regeneration in mice, their bone marrow was ablated with whole body irradiation and compared with the effects of local irradiation. The results indicate that (1) the sealing of damaged myofibres is a function of local cells and is not dependent on the presence of infiltrating leucocytes; (2) the formation of sarcoplasmic projections at the ends of damaged myofibres is dependent on leucocyte infiltration; (3) nuclei in the sarcoplasmic projections are probably derived from fusion of muscle precursor cells; (4) most muscle precursor cells in vivo replicate at least once before fusion; and (5) both replication and fusion of muscle precursors can occur in the absence of infiltrating leucocytes. These results are discussed with respect to the interaction of various cell populations during regeneration of skeletal muscle, and are of clinical significance to pathological changes seen in many myopathies.
Polymorphism of the myogenic gene, Myo-D1, has been sought to examine genetic mechanisms which control skeletal muscle development. By Southern analysis, three restriction-fragment length polymorphisms (RFLPs) have been found in various mouse strains using the TaqI, SacI and BglII restriction endonucleases and a full-length cDNA Myo-D1 probe. Reference to the distribution of RFLPs in different mouse strains derived from Mus mus (M.m.) domesticus and M.m. musculus subspecies suggests that Myo-D1 rearrangements are subject to nonrandom association. The biological significance of RFLP of the Myo-D1 gene is yet to be determined.
Quantitative cytochemical, immunocytochemical, autoradiographic and electron cytochemical investigations have been used to compare osteoclasts with multinucleate giant cells that had been freshly obtained from the same animal. The levels of beta-acid galactosidase activity, the DNA in individual nuclei and the cellular protein content were similar in both cell types. However, osteoclasts generally possessed greater acid phosphatase and NADH dehydrogenase activity but lower levels of fluoride-inhibited non-specific esterase activity than multinucleate giant cells. The acid phosphatase activity in multinucleate giant cells was completely inhibited by 100 mM tartrate, but in osteoclasts only a 20% reduction in activity was observed. Formation of multinucleate giant cells in a "bone microenvironment" (thin bone slices) did not increase their content of tartrate-resistant acid phosphatase activity. Moreover, in osteoclasts, endogenous peroxidase activity was undetectable but present in several granules within the cytoplasm of multinucleate giant cells. Osteoclasts and multinucleate giant cells displayed a similar microtubules distribution, but calcitonin, which induced rearrangement of microtubules and cellular contraction in osteoclasts, had no effect on multinucleate giant cells. Thus, these investigations reveal both similarities and differences between these two syncytia and support the hypothesis that osteoclasts and multinucleate giant cells are related. Possibly osteoclasts arise from monocyte progenitors before commitment to a macrophage lineage has occurred.
During short term culture of murine resident peritoneal macrophages, increasing the temperature from 37 to 39 degrees C resulted in an increased activity of several surface receptors (FcR and receptor for gluteraldehyde-fixed sheep red blood cells), enhanced phagocytosis of yeast particles, improved spreading, and an accelerated reduction of nitroblue tetrazolium. At 41 degrees C, however, significant reduction of several functional properties (endocytosis of colloidal gold and horseradish peroxidase, phagocytosis of yeast particles) and a decrease in the reduction of nitroblue tetrazolium, the incorporation of tritiated uridine, and Fc and C3b surface receptor activity were observed. In addition morphological evidence of apoptosis, observed in a small number of cells cultured at 39 degrees C and in the majority of macrophages maintained at 41 degrees C, was confirmed by DNA electrophoresis. The data indicates that a reduction of several functional activities of macrophages occurs at 41 degrees C and apoptosis may largely account for these effects.
The metabolism of RNA has not been studied in the osteoclast (OC) because these bone-resorbing cells are only available in small numbers and cultures are always contaminated with other cells. Using two single-cell assay techniques, tritiated uridine (3H-UdR) autoradiography and gallocyanin quantitative cytophotometry, we have examined RNA synthesis in OCs isolated from neonatal rats. Oligo-nuclear OCs showed greater nuclear uptake of 3H-UdR than cells with many nuclei, and the variance of nuclear labeling within polykarya was greater in the latter, possibly because they contain nuclei of various ages. Salmon calcitonin (sCT) was a potent (ED50 approximately 5 x 10(-12) M) and rapid (40% reduction in 2 h, 75% reduction in 6 h) inhibitor of 3H-UdR uptake, and also reduced cytochemical total cellular RNA by 22% within 4 h. Forskolin (10(-5) M) inhibited nuclear uptake of 3H-UdR, suggesting that the sCT response may be mediated by cyclic AMP. Following a short (30 min) exposure to sCT, there was a progressive decline in labeling, followed by complete recovery by 4.5 h, a response possibly related to the phenomenon of calcitonin-induced persistent activation of adenylate cyclase. Inhibition of OC RNA synthesis may be an important component of its anti-resorptive action.
The osteoclast (OC) is a multinuclear bone-resorbing cell which shares several characteristics with cells of the mononuclear phagocyte system. Unlike terminally differentiated macrophages, OCs possess specialized characteristics such as tartrate resistant acid phosphatase activity and the presence of calcitonin receptors. It appears that myeloid progenitor cells, probably granulocyte-macrophage colony-forming units, generate OC precursors which then differentiate and fuse into OCs under the regulation of osteotropic hormones, cytokines and other local factors. Parathyroid hormone and 1,25 dihydroxy Vitamin D3 induce both the formation and fusion of OC precursors, while calcitonin inhibits fusion. Osteoblasts also produce factor(s) which regulate OC precursor differentiation and therefore bone resorption; the nature of these factor(s), however, is unknown. In addition, the OC surface interacts specifically with a range of cellular and extracellular matrix-associated ligands which influence OC differentiation. The precise regulation of OC formation, however, is complex and awaits further investigation.
Following intranasal infection with murine cytomegalovirus (MCMV), the levels of viral replication in the lungs of susceptible BALB/c mice were enhanced by treatment with cyclophosphamide (CY), or to a greater extent cyclosporin A (CsA) or the Nu/Nu genotype. Focal inflammation was seen 2-4 days after infection in all groups. This was followed by diffuse interstitial pneumonitis which cleared 12-20 days later in the absence of immunosuppression. Although the initial foci of inflammation were less prominent in infected mice treated with CY or CsA, the most severe interstitial pneumonitis was seen 7 days p.i. in mice given CY, whilst CsA-treatment produced focal and disseminated pneumonitis 7-14 days p.i. and Nu/Nu mice exhibited only the focal response. MCMV-infected mice maintained from weaning on a low protein (4% casein) diet also retained higher titres of virus in their lungs than did normally-fed controls, and displayed more prominent focal pneumonitis.
Mice deficient in the fifth component of complement are known to be extremely susceptible to lethal challenge with Candida albicans. However, male mice, that have significantly higher concentrations of serum C5 than females, were markedly more susceptible to infection. This difference was observed in both susceptible (CBA/H) and resistant (BALB/c) mice. Levels of serum C3 likewise showed no correlation with susceptibility.
The yeast Candida albicans is a recognized, though uncommon, cause of osteomyelitis in humans. In a mouse model of systemic candidiasis, osteomyelitis has been found to occur in the vicinity of the inner ear, and to persist for at least 6 months after the initial infection.
The beige mutation in mice has a pervasive effect on mechanisms of host resistance to infectious agents. Best characterized are defects in granulocyte chemotaxis and phagocytosis, which are associated with increased susceptibility to bacteria, and a deficiency in the levels of natural killer (NK) cells, which has been linked to decreased resistance to both murine cytomegalovirus and the yeast Cryptococcus neoformans. The objective of the present experiments was to explore the cellular basis of the enhanced susceptibility of beige mice to systemic infection with the yeast Candida albicans. In contrast to murine cytomegalovirus and C. neoformans, infection with C. albicans did not induce any detectable NK cell activity in the spleen of bg/bg or bg/+ mice. Unfractionated bone marrow (BM) displayed some candidacidal activity, mediated by both phagocytic and nonphagocytic cells; however, there was no difference between homozygous and heterozygous mice in the effector function of normal BM cells or mononuclear cells derived from either short- or long-term BM cultures. On the other hand, peritoneal granulocytes from bg/bg mice were significantly more effective than those from bg/+ mice in killing Candida blastoconidia in vitro. A similar comparison of granulocytes from short-term BM cultures showed that the activities of cells from bg/bg and bg/+ mice were equivalent, indicating that the granulocytes derived from the peritoneal cavity of bg/bg mice had probably been exposed to some form of nonspecific stimulation in vivo. Somewhat surprisingly, long-term BM cultures did not support the continual growth of bg/bg granulocytes, and it is possible that the beige mutation may be associated with a lesion in the differentiation pathway that leads to the production of granulocytes. Taken together, the data indicate that, in beige mice, granulocytes rather than NK cells are a major determinant of natural resistance to C. albicans infections.
The hepatotoxicity of paracetamol in mice of 2, 3, 8-10, 24-26, 32-34, and 52-54 wk of age was determined by lethality data, histopathologic examination of the liver, and appearance of glutamate-pyruvate transaminase and glutamate-oxaloacetate transaminase activities in the plasma over an 8-h exposure period. At a dose of 300 mg/kg, there was evidence of hepatocytic necrosis and transaminase leakage in the 32- to 34- and 52- to 54-wk-old mice, but lethality was only recorded in the oldest age group. At 500 mg/kg, paracetamol produced 30% lethality in 3-wk-old mice and between 50 and 90% lethality in the adult age groups. There was histologic evidence of hepatocytic necrosis at all of these ages and its extent increased with age. Similarly, there were increases in plasma transaminases in each of these age groups. However, in 2-wk-old mice there was no lethality, no hepatocytic necrosis, and no increase in plasma transaminases. The lack of susceptibility of 2-wk-old mice to paracetamol toxicity was not due to immaturity of the cytochrome P-450 enzymes responsible for metabolism of paracetamol to its reactive metabolite (N-acetyl-p-benzoquinone imine). In fact, the activity of this enzyme pathway in 2-wk-old mice was greater than that in adults. The partial clearance of the glutathione-derived metabolites of paracetamol after a nontoxic (50 mg/kg) dose was 80% greater in 2-wk-old mice than in 8- to 10-wk-old mice.(ABSTRACT TRUNCATED AT 250 WORDS)