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Biomedical subjects

S Majumdar

Publications and source records attributed to S Majumdar.

At least 253 records · Page 14Linked to original sources

Effect of indomethacin on serum lipids, lipoproteins, prostaglandins and the extent and severity of atherosclerosis in rhesus monkeys.

The present study evaluated indomethacin therapy--a nonsteroidal anti-inflammatory drug--on experimental hyperlipidemia and atherosclerosis in Rhesus monkeys. Twenty-four monkeys were divided randomly into four groups of six. Two groups received stock pellet diet and two were given an atherogenic diet for six months. After this period, one stock diet-fed group and one atherogenic diet-fed group were treated with oral indomethacin (2.5 mg) on alternate days for a further six months. Serum lipids and lipoproteins were markedly elevated in atherogenic diet-fed monkeys. Generally, indomethacin did not exert a hypocholesterolemic effect; however, liver cholesterol was decreased (P less than 0.05) in atherogenic diet-fed monkeys treated with indomethacin. High density lipoprotein cholesterol was increased in stock diet-fed, indomethacin-treated monkeys but not in atherogenic diet-fed, indomethacin-treated monkeys. Apoprotein A-I was not affected by indomethacin in either stock or atherogenic diet-fed monkeys; however, the drug produced a significant (P less than 0.01) reduction of serum thromboxane B2 in stock diet-fed monkeys, without restoring the 6-keto-prostaglandin F1 alpha to pretreatment levels. A protective role of the drug was noted on both the extent and severity of aortic and coronary atherosclerosis.

Animals↗

Chemiluminescence response of phagocytes in E. coli induced experimental ascending pyelonephritis.

The mechanism of tissue injury at the cellular level by following the chemiluminescence response of various phagocytes in E. coli induced experimental pyelonephritis in mice was investigated. There was a marked increase in the capacity of various phagocytic cells viz; renal neutrophils and macrophages peritoneal macrophages, blood monocytes and neutrophils to produce reactive oxygens species through the respiratory burst activity as monitored by the chemiluminescence response. The chemiluminescence response was observed to be increased significantly (p less than 0.001) with increasing days post infection in all phagocytic cells. However, the quantity of total reactive oxygen species produced per million cells was much more in the renal and peritoneal macrophages as compared to blood monocytes and neutrophils. The peak chemiluminescence response time was observed to be decreased from 4 to 2 minutes with the progression of the diseases. The implications of these findings have been discussed.

Animals↗

Aortic lysosomal hydrolases and pathological alterations in hypertensive and/or atherogenic diet fed rhesus monkeys.

Aortic lysosomal enzyme activities have been evaluated in relation to the extent and severity of aortic atherosclerosis in rhesus monkeys to see the biochemical and pathological effects of renal hypertension in experimental atherogenesis. The frequency and size of atherosclerotic plaques in aortas of atherogenic diet fed and/or hypertensive monkeys were calculated and an overall score of aortic atherosclerosis was computed on the basis of the gamut of pathological findings in relation to the biochemical alterations. This overall score of atherosclerosis was found to be significantly (p less than 0.01) greater in animals of all experimental groups as compared to the controls.

Animals↗

Protein kinase C isotypes and signaling in neutrophils. Differential substrate specificities of a translocatable calcium- and phospholipid-dependent beta-protein kinase C and a phospholipid-dependent protein kinase which is inhibited by long chain fatty acyl coenzyme A.

Neutrophils possess a classical Ca2+, phosphatidyl serine (PS) and diglyceride (DG)-dependent protein kinase C (beta-PKC) which was translocatable from cytosol to membrane in response to elevated Ca2+ in the physiologic range or to pretreatment with phorbol myristate acetate (PMA). The translocatable beta-PKC was purified from neutrophil membranes prepared in the presence of Ca2+, eluted with EGTA and subjected to hydroxyapatite chromatography. An 80-kDa protein possessing Ca/DG/PS-dependent histone phosphorylating activity was recognized by a monoclonal antibody to beta-PKC but not to alpha-PKC or gamma-PKC. A cytosolic kinase activity remaining after Ca(2+)-induced translocation of beta-PKC was dependent on PS and DG but did not require Ca2+. This novel Ca(2+)-independent, PS/DG-dependent kinase, termed nPKC, eluted from hydroxyapatite between alpha-PKC and beta-PKC, ran as a 76-kDa band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and was reactive to a polyclonal consensus antibody but not to monoclonal antibodies to alpha-PKC, beta-PKC, or gamma-PKC. Long chain fatty acyl-CoA, but not the corresponding free fatty acids, inhibited nPKC in the 1-10 microM range. The chemotactic peptide fMet-Leu-Phe triggered prompt but transient increases in neutrophil long chain fatty acid acyl-CoA, suggesting that nPKC is regulated by fatty acyl-CoA as well as DG during neutrophil activation. Purified beta-PKC phosphorylated a number of cytosolic proteins in a Ca(2+)-dependent manner, including a major 47-kDa cytosolic protein, which may be implicated in superoxide anion generation. In contrast, nPKC did not phosphorylate the 47-kDa protein, but phosphorylated numerous cytosolic proteins in a Ca(2+)-independent manner, including a 66-kDa protein which was not phosphorylated by beta-PKC. Differences in location, substrate specificity, and cofactor dependence between nPKC and beta-PKC suggest these kinases may play selective roles in the activation sequence of the neutrophil.

Acyl Coenzyme A↗

Characterization of the human beta-thromboglobulin gene. Comparison with the gene for platelet factor 4.

beta-Thromboglobulin (beta TG) is a platelet alpha-granule protein that is released in large amounts following platelet activation. This protein has approximately 70% amino acid identity with another platelet alpha granule protein, platelet factor 4 (PF4), and approximately 30% identity with other members of a family of proteins encoded by the small inducible genes (SIG) that are involved in the overlapping processes of inflammation, wound repair, and coagulation. Thus, the isolated beta TG gene is of interest in that it may further increase our understanding of beta TG's biological role, the regulation of its megakaryocytic-specific nature of expression, and the evolution and divergence of the SIG family. Using a beta TG cDNA isolated from a DAMI cell cDNA library, we cloned the corresponding beta TG gene. The gene is 1,139 base pairs (bp) long, and, like other members of the SIG family, the beta TG gene is divided into 3 exons. Two major transcriptional start sites were defined by primer extension analysis of platelet RNA, and, based on the more commonly used start site, the 5'-untranslated region is 87 bp. A TATA box is present beginning 32 bp upstream to this site. The first exon contains the 5'-untranslated region as well as the signal peptide. The second exon begins 6 bp 3' to the homologous site in PF4, and the third exon begins at a position homologous to that in PF4. Interestingly, the beta TG and PF4 genes have little detectable homology in the flanking or intronic sequences. In particular, a pyrimidine tract 5' to both the rat and human PF4 genes is not present in the upstream region of the beta TG gene. Genomic Southern blot analysis suggests that, as with the PF4 gene, there are multiple copies of the beta TG gene in the human genome. Chromosomal localization using polymerase chain reaction analysis of human/hamster somatic cell hybrids demonstrated that the beta TG gene, like the PF4 gene, is located on chromosome 4. It is, therefore, possible that the beta TG and PF4 gene form a single genomic locus on chromosome 4 whose members become coordinately activated during megakaryocyte differentiation.

Amino Acid Sequence↗

NMR determination of myocardial pH in vivo: separation of tissue inorganic phosphate from blood 2,3-DPG.

Phosphorus NMR can measure myocardial tissue pH from the chemical shift of inorganic phosphate (Pi) in isolated buffer-perfused hearts, but in vivo the Pi peak originating from the myocardium is obscured by the resonance of 2,3-diphosphoglycerate (DPG) in the blood, making pH difficult to determine. Taking advantage of the fact that most of the interfering DPG is within the cardiac chambers and is rapidly flowing out of the sensitive volume of our coil, we developed a pulse sequence which would separate myocardial Pi signal from interfering DPG. We tested this method on a flow phantom and in living rat heart, using exogenous glycerol phosphate as a blood-pool marker. The results indicated that signal from moving and nonmoving substances could be separated, and derived values for myocardial pH and PCr/Pi ratio were consistent with previous estimates. This method should be useful for studying myocardial acid-base physiology with NMR.

2,3-Diphosphoglycerate↗

Quantitative study of the susceptibility difference between trabecular bone and bone marrow: computer simulations.

Inherent differences in tissue magnetic susceptibility produce inhomogeneities in the static magnetic field which give rise to an additional dephasing of the transverse magnetization in gradient-echo images. The enhanced dephasing of the signal results in an increase of the apparent relaxation rate 1/T2* and a corresponding decrease in signal intensity. These effects have been used to explain the regional loss of marrow signal intensity in the appendicular skeleton, where in the presence of trabecular bone in the proximal tibia there is an enhanced loss of signal compared to the tibial shaft where there is no trabeculation. It has been postulated that differences in tissue magnetic susceptibility arising due to the marrow--trabeculae interface give rise to magnetic field inhomogeneities and a reduced T2*. In this study computer simulations are used to determine whether susceptibility differences comparable to that between trabecular bone and tissue relate to the reduction of tissue T2* and whether the reduction in T2* is also related to the concentration and magnitude of susceptibility differences. In addition the effects of the spatial distribution of these particulate discontinuities in susceptibility on the measured relaxation time T2* are also estimated. This model demonstrates that 1/T2* increases as the number density and magnitude of such susceptibility differences increase. In a pixel of linear dimension L consisting of material simulating tissue water, the presence of circular point susceptibility differences of dimension 0.001 L with magnetic susceptibility equivalent to trabecular bone, 1/T2*, increases at a rate of 1.60 x 10(-2) s-1/N for N ranging from 25-2500. Differences in magnetic susceptibility that are less than that between soft tissue and trabecular bone are also modeled and the simulations demonstrate that differences in magnetic susceptibility, much lower than that between trabecular bone and tissue equivalent interfaces, also produce a relaxation rate enhancement in gradient-echo images.

Bone Marrow↗

Quantitation of the susceptibility difference between trabecular bone and bone marrow: experimental studies.

In this study we quantify the effects of different relaxation mechanisms on the signal intensity in gradient-echo images of tissue such as bone marrow in the presence of trabecular bone. The susceptibility difference between trabecular bone and soft tissue produces distortions in the magnetic lines of force which induce strong inhomogeneities in the static magnetic field. Diffusion of tissue protons in such magnetic field gradients produce a shortening of the transverse relaxation time T2, while the dephasing of the transverse magnetization due to susceptibility differences produces a shortening of the apparent relaxation time T2* as demonstrated in gradient-echo images. We have used specimens of dried human vertebrae with different bone densities immersed in either saline to simulate tissue water or an emulsion of oil and water to simulate bone marrow to quantify these relaxation mechanisms in vitro. We have measured the MR relaxation times T1, T2, and T2* of protons within the trabecular spaces and correlated their variations with trabecular bone density. We have found that in vitro, at 1.5 T, the relaxation times T1 and T2 do not show significant variations with bone density and there are no significant contributions to the transverse relaxation rate due to the diffusion of tissue water in the magnetic field gradients. However, the relaxation rate, 1/T2*, of saline in the presence of trabecular bone increases at a rate of 0.2 s-1/mg/cc due to the dephasing of the transverse magnetization in the magnetic field inhomogeneities. Similar bone density-related T2* variations were observed for fat protons within the trabeculae where the chemical-shift-induced modulations of signal intensity in an oil-water emulsion have been separated from the susceptibility-induced relaxation effects. In addition, we have verified these effects in vivo and quantified in vivo variations in fat and water relaxation rates of bone marrow in the epiphysis and diaphysis in the appendicular skeleton of normal volunteers and found that both fat and water T2* are shorter in the epiphysis compared to the diaphysis, which correlates well with previous observations.

Bone Marrow↗

Short-term and long-term effects of Norplant-2 on plasma lipoproteins and glucose tolerance.

Twenty-five women using the levonorgestrel-containing contraceptive implant, Norplant-2, were studied longitudinally, to see the effects on lipid profile, glucose tolerance and hepatic transaminases with short-term (12 weeks) and long-term (18 to 24 months) use of Norplant-2 [corrected]. Total lipids, cholesterol, phospholipids, triglycerides and their subfractions were evaluated. There was a significant increase in LDL-cholesterol after 12 weeks of use (p less than 0.05), which did not persist at 18-24 months follow-up. The HDL-cholesterol, HDL/LDL-cholesterol ratio, phospholipids, other lipid fractions, hepatic transaminases and glucose tolerance did not alter significantly following short-term or long-term use of Norplant-2.

Adult↗

Effects of a new compound (Zy 15850A) on cigarette smoke-induced bronchitis in the rat.

The effect of 4H-4 phenylthieno-(3,2-C)-(1)-benzopyran-2-carboxylate (Zy 15850A) on mucous cell hyperplasia was examined in vivo using a well established rat model of cigarette smoke-induced bronchitis. Zy 15850A was given by gavage (25 mg/kg body weight) to male rats before and after sub-acute exposure (i.e. daily for 14 days) to an atmosphere of cigarette smoke (CS). CS significantly increased the thickness of the epithelium at three of the four sites studied in the trachea and in both of the intrapulmonary levels examined. CS increased the number of epithelial mucous cells in all intrapulmonary airways and also increased the mass of submucosal gland present in the larynx and upper trachea. Zy 15850A completely inhibited CS-induced increases in epithelial thickness in the upper trachea and the two intrapulmonary airway levels studied, and tended to inhibit CS-induced epithelial mucous cell hyperplasia in all the six intrapulmonary airway levels examined, with statistically significant inhibition in two. Zy 15850A had no inhibitory effect of the CS-induced enlargement of laryngo-tracheal submucosal glands. We conclude that, in the rat, the predominant inhibitory effect of Zy 15850A is on CS-induced epithelial thickening with weaker inhibitory effects on mucous cell hyperplasia and enlargement of submucosal glands. Zy 15850A is less effective than other mucoregulatory drugs or antiinflammatory agents we have tested in the same bronchitic model.

Animals↗

The effect of propane-diols on the intestinal uptake of nutrients and brush border membrane enzymes in the rat.

The effect on rats of oral doses (38.66 mM/kg body wt) of propane-1,2-diol (PD) administered daily for 10 (Group 1), 20 (Group 2), and 30 days (Group 3) was investigated. Weight gain was initially retarded (P less than 0.05) in Group 1, but was later reversed and elevated significantly (P less than 0.05) in Groups 2 and 3 as compared with their respective controls receiving an equal volume of saline. PD showed a tendency toward enhancing the activities of various enzymes involved in terminal digestion, with the significant effect exerted in few groups on sucrase (P less than 0.05), lactase (P less than 0.05), and gamma-glutamyl transpeptidase (P less than 0.05) when compared with the respective controls. Absorption of D-glucose, glycine, L-aspartic acid, L-lysine, and calcium was elevated and was especially significant in Groups 2 and 3 (P less than 0.001). The structural integrity of the jejunal surface was retained for the most part. A similar examination of the effects of PD was also carried out in vitro to ascertain whether PD itself or its metabolites are involved in its action. The in vitro effects of propane-1,2-diol were compared with those of the more toxic compound propane-1,3-diol. The former exerted greater inhibitory action on the activities of the disaccharidases. The degree of inhibition was in the order sucrase much greater than lactase greater than maltase. The kinetic data revealed that inhibition by 1,2-diol in native and detergent solubilized sucrase is noncompetitive, with Ki values in the range of 0.35-0.41 M. The two diols did not alter the nutrient transport in the brush border membrane vesicles. The present work on rats indicates that PD may influence the intestinal digestive and absorptive functions in vivo and that this in vivo effect of PD is different from that observed in vitro suggesting that the nutritional and toxicological effect of PD may be mediated by different mechanisms.

Administration, Oral↗

Killing of intracellular Mycobacterium tuberculosis by receptor-mediated drug delivery.

p-Aminosalicylic acid (PAS) conjugated to maleylated bovine serum albumin (MBSA) was taken up efficiently through high-affinity MBSA-binding sites on macrophages. Binding of the radiolabeled conjugate to cultured mouse peritoneal macrophages at 4 degrees C was competed for by MBSA but not by PAS. At 37 degrees C, the radiolabeled conjugate was rapidly degraded by the macrophages, leading to release of acid-soluble degradation products in the medium. The drug conjugate was nearly 100 times as effective as free PAS in killing the intracellular mycobacteria in mouse peritoneal macrophages infected in culture with Mycobacterium tuberculosis. The killing of intracellular mycobacteria mediated by the drug conjugate was effectively prevented by simultaneous addition of excess MBSA (100 micrograms/ml) or chloroquine (3 microM) to the medium, whereas these agents did not affect the microbicidal action of free PAS. These results suggest that (i) uptake of the PAS-MBSA conjugate was mediated by cell surface receptors on macrophages which recognize MBSA and (ii) lysosomal hydrolysis of the internalized conjugate resulted in intracellular release of a pharmacologically active form of the drug, which led to selective killing of the M. tuberculosis harbored by mouse macrophages infected in culture. This receptor-mediated modality of delivering drugs to macrophages could contribute to greater therapeutic efficacy and minimization of toxic side effects in the management of tuberculosis and other intracellular mycobacterial infections.

Albumins↗

Osteoarthritis of the knee: comparison of radiography, CT, and MR imaging to assess extent and severity.

Although conventional radiography is the method most frequently used for monitoring progression of osteoarthritis, it may not show osteoarthritic changes of the knee until late in the disease, and it may show involvement of only one or two compartments in patients who have tricompartmental disease. We compared radiography, CT, and MR imaging for assessing the extent and severity of osteoarthritis of the knee in 20 patients. Radiography included posteroanterior weight-bearing, true lateral, and sunrise patellar projections. Axial CT scans were reformatted in sagittal and coronal planes. MR imaging consisted of spin-echo (600-800/20; 2000/60, 120 [TR/TE]), and gradient-echo (600/30, theta = 30 degrees) sequences. The severity of osteoarthritic changes was graded from 0 to 3. MR frequently showed tricompartmental cartilage loss when radiography and CT showed only bicompartmental involvement in the medial and patellofemoral compartments. In the lateral compartment, MR showed a higher prevalence of cartilage loss (60%) than radiography (35%) and CT (25%) did. In the medial compartment, CT and MR showed osteophytes in 100% of the knees, whereas radiography showed osteophytes in only 60%. Notably, radiography often failed to show osteophytes in the posterior medial femoral condyle. On MR images, meniscal degeneration or tears were found in all 20 knees studied. Partial and complete tears of the anterior cruciate ligament were found in three and seven patients, respectively. MR is more sensitive than radiography and CT for assessing the extent and severity of osteoarthritic changes and frequently shows tricompartmental disease in patients in whom radiography and CT show only bicompartmental involvement. MR imaging is unique for evaluating meniscal and ligamentous disease related to osteoarthritis.

Adult↗

Noninvasive measurements of bone mass, structure, and strength: current methods and experimental techniques.

Current methods for assessing osteoporotic fracture risk involve measuring the content and/or density of bone at a number of skeletal sites and relating the measurement to that in either age-matched or young control subjects measured at the same site with the same technique. These densitometric methods have been used to predict several types of fractures; however, engineering principles verify that the bone structure and loading conditions also affect skeletal strength. Many densitometric measurements inherently contain information about skeletal structure and bone distribution, yet this information is not clinically used. In this paper, the currently available techniques for assessing bone content and density, namely, single-photon absorptiometry, dual-photon absorptiometry, dual-energy X-ray absorptiometry, and quantitative CT, and their usefulness in assessing fracture risk and distinguishing between patients with and without osteoporosis are reviewed. Extensions of conventional densitometry that have been developed by several researchers to include information in addition to bone mass also are presented. Results from recent studies using new applications of ultrasound techniques and MR imaging are reviewed. Preliminary studies show the value of these new techniques in noninvasive measurement of bone structure in order to estimate bone strength and assess fracture risk more accurately. However, to become clinically useful, many of these methods require further investigation to increase their ease of use and decrease their cost.

Absorptiometry, Photon↗

Measurement of tissue blood flow using intravascular relaxation agents and magnetic resonance imaging.

Simple concepts of indicator-dilution techniques are described, and the theoretical basis of measuring regional blood flow via transit time measurements of a blood pool marker is discussed. Using very fast imaging of the effects of an appropriate and efficient relaxation agent, the concentration-time curve of the agent can be quantified. Preliminary measurements of the transit of superparamagnetic iron oxide through a rat brain at 2.0 T have been obtained. There are problems, however, in relating the NMR signal change to the tissue concentration of an intravascular relaxation agent when there is not fast exchange of the tissue water with the water in the vasculature, or when the precise efficacy of the agent varies with the geometrical arrangement of the capillaries. Studies of the effects of superparamagnetic iron oxide particles in different media confirm that the in vivo efficacy varies among different tissues, which complicates their use as blood flow markers.

Animals↗

Verapamil stimulates Ca(++)-uptake and Ca(++)-ATPase in plasma membrane vesicles of guinea pig spermatozoa.

Verapamil, a potent calcium channel blocker, was administered orally at three different doses to guinea pigs for both short- (4 weeks) and long-term (12 weeks) effects. The drug treatment stimulated Ca(++)-transport and Ca(++)-activated ATPase in isolated plasma membrane vesicles of guinea pig spermatozoa. Ca(++)-uptake studies exhibited partial to complete restoration of stimulated Ca(++)-transport during recovery period, whereas the CA(++)-activated ATPase system remained stimulated even after 4 and 6 weeks of withdrawal of the drug treatment. The lack of inhibitory effect of verapamil on Ca(++)-uptake ruled out the involvement of calcium channels in spermatozoal calcium uptake in guinea pigs. The stimulatory effect of the drug on CA(++)-uptake, on the other hand, might indicate the possible capability of this lipophilic compound to induce favourable changes in the lipid microenvironment of the membrane, wherein the integral membrane proteins operate.

Animals↗