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Biomedical subjects

S N Wickramasinghe

Publications and source records attributed to S N Wickramasinghe.

At least 109 records · Page 6Linked to original sources
PubMed1988

Haemoglobin synthesis in K562 erythroleukaemia cells is affected by intimate contact with monolayers of various human cell types.

The haemoglobin content of K562 erythroleukaemia cells was affected by co-culture over monolayers of various human cell types. Haemoglobin synthesis was increased after co-culture with umbilical-cord-derived endothelial cells and most monolayers of bone-marrow-derived macrophages, and inhibited after co-culture with two fibroblast lines, blood-monocyte-derived macrophages, a neuroglial cell line (U-251 MG) and most monolayers of bone-marrow-derived stromal cells. These effects were modified when a thin layer of agar was placed over the monolayers. Cell-free culture media conditioned by all but two of the seven types of monolayer studied inhibited haemoglobin synthesis by K562 cells; those conditioned by blood-monocyte-derived macrophages and two of 11 monolayers of bone-marrow-derived macrophages stimulated haemoglobin synthesis. Thus, the haemoglobin content of K562 cells appeared to be influenced both by intimate contact between K562 cells and the cells of the monolayers and by humoral factors released by the monolayers. The data support the concept that erythroid differentiation is partly dependent on intimate contact between erythroid progenitor cells and microenvironmental cells.

Amniotic Fluid↗
PubMed1988

Deoxyuridine suppression: biochemical basis and diagnostic applications.

The deoxyuridine (dU) suppression test evolved out of investigations into the biochemical basis of the megaloblastic changes seen in vitamin B12 and folate deficiency. Although the abnormality in dU suppression which occurs in vitamin B12- or folate-deficient states is assumed to reflect impaired methylation of deoxyuridylate, there is still no direct demonstration that this is so. Furthermore, there is evidence that reactions other than the methylation of deoxyuridylate are involved in the phenomenon of dU suppression. Nevertheless, in clinical practice abnormal dU suppression serves as a sensitive index of the presence of megaloblastosis due to vitamin B12 or folate deficiency. dU suppression is also abnormal in a number of conditions other than vitamin B12 or folate deficiency, but its overall specificity in detecting tissue dysfunction due to these two deficiency states is considerably higher than that of the serum vitamin B12 or red cell folate levels. Consequently, the test enables us simply and rapidly to define those patients in whom macrocytosis is unrelated to a deficiency of vitamin B12 or folate. For these reasons, the dU suppression test has been adopted by several laboratories across the world for investigating patients with (a) possible vitamin B12 or folate deficiency, (b) macrocytosis, and (c) megaloblastic erythropoiesis. Since the dU suppression test is abnormal in transcobalamin II deficiency and in some congenital disorders of vitamin B12 and folate metabolism, it is very useful in the investigation of obscure anaemias in infancy and childhood. In addition, it has contributed to our understanding of the mechanisms underlying the myelotoxicity of certain drugs, and particularly of nitrous oxide.

Deoxyuridine↗
PubMed1988

A study of erythroid progenitor cells in the bone marrow of Gambian children with falciparum malaria.

There was a wide variation in the number of BFUe and CFUe in the bone marrow of Gambian children with falciparum malaria and moderate or severe anaemia. However, such children were often not deficient in these erythroid progenitors. The number of BFUe in patients who had parasitaemias greater than 1% was significantly lower than that in patients with parasitaemias less than 1%. There was also a statistically significant negative correlation between the number of BFUe and CFUe in the entire group of children studied. When autologous serum (30%, v/v) was used in the culture system, CFUe growth was observed even in the absence of added erythropoietin (EPO), indicating the presence of high levels of EPO or an EPO-like substance in the anaemic sera. It is concluded that children with Plasmodium falciparum malaria show no major abnormality in their erythroid progenitor cells and that the perturbation of erythropoiesis in such children occurs mainly in the morphologically recognizable erythroid precursor cells. The wide variation observed in the number of CFUe and BFUe in different patients, and the correlations between the number of BFUe and parasitaemia and the number of BFUe and CFUe are all probably largely related to the changing clinicopathological situation in patients with malaria and anaemia.

Anemia↗
PubMed1988

Ultrastructure and cell cycle distribution of bone marrow cells in protein-energy malnutrition.

Bone marrow aspirates from four children with kwashiorkor and three with marasmus were studied using the techniques of electron microscopy and combined Feulgen microspectrophotometry and 3H-thymidine autoradiography. The majority of the erythroblasts were ultrastructurally normal, the distribution of the early polychromatic erythroblasts between the various stages of the cell cycle was normal or almost normal, and the macrophages did not contain ingested erythroblasts. Since erythropoietin production has been shown to be normal in protein-energy malnutrition, these findings suggest that at least in some cases of PEM the impairment of erythropoiesis results primarily from an abnormality in the erythroid progenitor cell pool rather than from dyserythropoiesis and ineffective erythropoiesis. In one afebrile and apparently uninfected patient with marasmus, a substantial proportion of the neutrophil granulocytes and their more mature precursors contained electron-dense, myelin-containing intracytoplasmic structures which were presumed to be abnormal primary granules. In four of the patients, the 3H-thymidine labelling index of the neutrophil promyelocyte-myelocyte pool was increased. In addition, in all of the cases, neutrophils at various stages of degradation were readily found within the cytoplasm of some of the macrophages. Thus, whereas the techniques employed did not reveal a major disturbance in the morphologically recognizable precursor cells of the erythroid series in PEM, they demonstrated some abnormalities in such cells of the neutrophil series.

Autoradiography↗
PubMed1988

The deoxyuridine suppression test performed on phytohaemagglutinin-stimulated peripheral blood cells fails to reflect in vivo vitamin B12 or folate deficiency.

Because phytohaemagglutinin-stimulated lymphocytes acquire folate deficiency in vitro, we have re-examined the claim that the deoxyuridine suppression test (dU-test) based on such cells helps to diagnose megaloblastic states. dU-test results were obtained from the phytohaemagglutinin-stimulated blood cells of 77 patients at 6 concentrations of dU. 21 megaloblastic patients with cobalamin or folate deficiency did not have a mean blood dU-test result significantly higher than that of 21 normoblastic patients at any concentration of dU. Among all patients, however, there was a weak correlation between the blood and marrow dU-test results. Folic acid corrected the blood dU-test results more in the normoblastic than the megaloblastic patients, and a difference between the two groups appeared, but a large overlap persisted. Blood dU-test results tend to be higher in megaloblastic patients, but acquired folate deficiency obscures the distinction from normoblastic patients so that the test is not of diagnostic value.

Aged↗
PubMed1987

Circulating cytotoxic protein generated after ethanol consumption: identification and mechanism of reaction with cells.

Serum obtained from healthy volunteers 6-7 h after consumption of 60-95 g of ethanol contained cytotoxic activity against mouse A9 cells and all of six human cell lines tested. Affinity chromatography of such sera demonstrated that at least some of the cytotoxic molecules consisted of altered albumin. Complexes formed by the reaction of 14C-acetaldehyde with 125I-labelled human serum albumin in vitro were also cytotoxic. After treatment with a reducing agent, sodium borohydride, the cytotoxicity of both post-alcohol serum and the acetaldehyde-albumin complexes fell sharply, suggesting that the cytotoxic activity resided in the unstable Schiff bases formed during the first stage of reaction between the acetaldehyde and proteins. A detailed analysis of the reaction between the double-labelled acetaldehyde-albumin complexes and K562 cells revealed that the cytotoxic activity resulted from the release of acetaldehyde from such complexes and the preferential binding of the free acetaldehyde to the target cells.

Acetaldehyde↗
PubMed1987

The bone marrow in human cerebral malaria: parasite sequestration within sinusoids.

Bone marrow aspirates from patients with cerebral malaria were studied with the light and electron microscopes. Various abnormalities were found including: (1) an increase in plasma cells and macrophages, sometimes to a marked degree; (2) phagocytosis of parasitized red cells by macrophages and of merozoites by neutrophil metamyelocytes, neutrophil granulocytes and macrophages; (3) an increase in the proportion of eosinophil granulocytes and their precursors; (4) the presence of giant metamyelocytes; and (5) morphological abnormalities of erythroblasts, particularly irregularly-shaped nuclei and karyorrhexis. A high percentage of the red cells within marrow sinusoids were parasitized and the parasitized cells were attached to the endothelium. Some marrow sinusoids were packed with and completely obstructed by parasitized cells. Strands of electron-dense material were sometimes found connecting the knobs of parasitized red cells to endothelial cells or to the knobs of adjacent parasitized red cells. A striking finding was a complex interdigitation between cytoplasmic processes developed by some of the parasitized red cells and those developed by the endothelial cells to which they were attached. Occasionally, cytoplasmic processes arising from marginated parasitized red cells completely penetrated the endothelial cell and emerged extravascularly. Several parasitized red cells were also found extravascularly between haemopoietic cells. Sequestration of parasitized red cells within small blood vessels may play a part in the pathogenesis not only of the encephalopathy of cerebral malaria but also of the bone marrow dysfunction in severe malaria.

Adolescent↗
PubMed1987

Evidence of drug metabolism by macrophages: possible role of macrophages in the pathogenesis of drug-induced tissue damage and in the activation of environmental procarcinogens.

After interaction with human macrophages derived from blood, bone marrow or spleen, solutions of sodium phenobarbitone, phenytoin sodium and chlorpromazine hydrochloride showed reduced cytotoxicity towards K562 cells. The reduction in cytotoxicity was partially suppressed in the presence of tetrahydrofurane, an inhibitor of cytochrome P450. These data suggest that macrophages are capable of metabolizing certain drugs, probably via a cytochrome P450-dependent mechanism. The present findings raise the possibility that some drug-induced blood dyscrasias are caused by metabolism of the drug by bone marrow macrophages and the consequent release of relatively short-lived molecules which are toxic to adjacent haemopoietic cells. The generation of cytotoxic molecules during drug metabolism by macrophages may also be responsible for drug-induced damage to other macrophage-rich tissues. In addition, since cytochrome P450-dependent reactions seem to occur within macrophages, these cells may activate environmental procarcinogens and thus plays a role in carcinogenesis and leukaemogenesis.

Cells↗
PubMed1987

Neuroglial and neuroblastoma cell lines are capable of metabolizing ethanol via an alcohol-dehydrogenase-independent pathway.

Two neuroglial cell lines (U-251 MG and C6) had a substantial capacity to convert ethanol to acetate in vitro largely by an alcohol dehydrogenase (ADH)-independent mechanism and three neuroblastoma cell lines (IMR-32, NB41A3, and Neuro-2a) had a lesser but significant ethanol-metabolizing capacity which was also either partly or largely ADH-independent. The ADH-independent pathway of ethanol metabolism by neural cells appeared to be dependent on one or more isoenzymes of cytochrome P-450. The data emphasize the possibility that the neurotoxicity of ethanol may be related to a relatively high ethanol-metabolizing capability of neural tissue and particularly of neuroglial cells.

Acetates↗
PubMed1987

Ultrastructure of bone marrow in patients with visceral leishmaniasis.

Ultrastructural studies were performed on bone marrow aspirates from three patients with visceral leishmaniasis. The patients were moderately anaemic but showed a suboptimal increase in the absolute reticulocyte count. Serum and red cell folate concentrations and serum vitamin B12 concentrations were normal in all three cases, and serum ferritin concentrations were normal or increased. The bone marrows were hypercellular and showed erythroid hyperplasia; a high proportion of the erythroblasts showed dyserythropoietic changes. Amastigote forms of Leishmania donovani were found within bone marrow macrophages and within occasional neutrophil and eosinophil granulocytes. Electron microscopy showed the presence of many abnormal cells, which probably represented immature erythroblasts with giant lysosomes. These cells were often large, usually contained immature nuclei with relatively little condensed chromatin, had 1-20 electron dense cytoplasmic granules with an average diameter of 0.5 micron, and regularly displayed substantial rhopheocytotic activity. A few abnormal cells and intermediate and late erythroblasts appeared to have been phagocytosed by macrophages. The data indicate that dyserythropoiesis and ineffective erythropoiesis have a role in the pathogenesis of the anaemia of at least some cases of kala-azar.

Bone Marrow↗
PubMed1987

Hepatotoxicity of ethanol in mice.

Mice continuously exposed to ethanol vapour (for up to 19 days) developed fatty change in the liver (from 2 days onwards) and lesions resembling those of alcoholic hepatitis in man (from 5 days onwards). They also showed biochemical evidence of liver cell damage. Sera from ethanol-treated animals contained immunoglobulins that bound to the hepatocytes of ethanol-treated but not of control animals suggesting that exposure to ethanol was followed by an immunological response to a hepatocyte neo-antigen. In addition, such sera were cytotoxic in an in-vitro assay, and on Sephacryl S-300 gel filtration the cytotoxic activity eluted together with albumin molecules.

Administration, Inhalation↗
PubMed1987

Biochemically damaged erythroblasts bind natural serum antibodies and activate complement.

Friend leukaemia erythroblasts which had been damaged biochemically by treatment with inhibitors of cellular metabolism (sodium fluoride, sodium azide) or of protein synthesis (cycloheximide, puromycin) were incubated with heat-inactivated or fresh mouse serum and tested for surface-bound IgG and C3c, respectively, by reaction with FITC-immunoconjugates followed by flow-cytofluorometry. Erythroblasts exposed to sodium azide, cycloheximide or puromycin showed specific binding of IgG; the extent of binding was related to the concentration of the drugs and duration of treatment. Moreover, prolonged exposure of the cells to the inhibitors of protein synthesis lead to a dose-dependent activation of complement. The results suggest that the opsonization of biochemically-damaged Friend leukaemia erythroblasts with IgG and C3 may facilitate their interaction with macrophages.

Antibodies, Anti-Idiotypic↗
PubMed1987

The capacity of macrophages from different murine tissues to metabolise ethanol and generate an ethanol-dependent non-dialysable cytotoxic activity in vitro.

Tissue macrophages obtained from liver, bone marrow, spleen and thymus of C57 BL/6 mice closely resembled blood-monocyte-derived human macrophages in three characteristics. These were: the rate of metabolism of ethanol to acetate, the biochemical pathways involved in ethanol metabolism and the ability to generate an ethanol-dependent non-dialysable cytotoxic activity in vitro. The metabolism of ethanol by all four types of murine tissue macrophage was only slightly suppressed by pyrazole, 4-iodopyrazole and 3-amino-1,2,4-triazole, which are known to inhibit alcohol dehydrogenase (ADH), pi ADH and catalase respectively. By contrast, ethanol metabolism by these cells was strongly suppressed by three inhibitors of the cytochrome P-450-dependent microsomal ethanol-oxidising system--namely, carbon monoxide, metyrapone and tetrahydrofurane.

Acetates↗
PubMed1986

Cytotoxic protein molecules generated as a consequence of ethanol metabolism in vitro and in vivo.

A non-dialysable cytotoxic activity developed in the supernatants of human blood-monocyte-derived macrophages cultured in the presence of ethanol and in the serum of three healthy volunteers who drank 500-700 ml wine over 20-35 min. On 'Sephacryl S-300' gel filtration of the culture supernatants and the serum samples from the subjects who took alcohol, the cytotoxic activity eluted together with albumin molecules. Studies of human serum and of various commercially purchased human serum protein fractions treated with carbon-14-labelled acetaldehyde and non-radioactive acetaldehyde, respectively, provided strong circumstantial evidence that the cytotoxic proteins were albumin molecules that had become complexed with acetaldehyde generated by the metabolism of ethanol. The cytotoxic activity developing in vivo was greatest 6-10 h after the consumption of ethanol started, when blood alcohol levels were normal or only slightly high. The appearance of a circulating long-acting cytotoxic macromolecule after the ingestion of ethanol may be of considerable importance in clarifying the mechanisms underlying ethanol-induced tissue damage.

Acetaldehyde↗