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Biomedical subjects

S Majumdar

Publications and source records attributed to S Majumdar.

At least 181 records · Page 10Linked to original sources
PubMed1997

A trace metal (zinc and iron) study on low dose x-radiation response in rat skin.

There is no reliable bio-dosimeter regarding low dose radiation effects in mammalian systems. In this study, chronic low dose (< 1 cGy) whole body x-irradiated rat skin have shown altered trace metal (zinc and iron) content which clearly indicated the redistribution of these metals in the integumentary system. The decreased zinc to iron ratios suggested enhanced oxidative stress of the tissue. Changes in trace metal content in irradiated rat skin, as a biological response to low dose radiation, were non-linear. Moreover, the lowered zinc content of E2, E3, E4 and E5 dose groups suggested a different steady state, compared to the control. The Zn: Fe ratio decreased with increasing radiation dose.

Animals↗
PubMed1997

Photooxidant injury to glucose-6-phosphate dehydrogenase-deficient erythrocytes with bilirubin as the sensitizer--an in vitro study.

To evaluate the hypothesis that glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes are more prone to photooxidant injury with bilirubin as the sensitizer, we compared the malonyl dialdehyde (MDA) levels and haematocrit values in 11 G6PD-deficient samples with a bilirubin: albumin molar ratio of 1:2 (10 mg% bilirubin, 2.5 g % albumin) photoexposed at 6 microW cm-2 nm-2 (420-460 nm), with 11 of control samples. Twelve hours after photoexposure the incremental changes in MDA levels (OD units) were higher in G6PD-deficient samples [mean (SE) = 0.230 (0.171) vs 0.075 (0.043), p < 0.01]. Antioxidant drugs may have a protective role while G6PD-deficient neonates undergo phototherapy.

Bilirubin↗
PubMed1997

Correlation of trabecular bone structure with age, bone mineral density, and osteoporotic status: in vivo studies in the distal radius using high resolution magnetic resonance imaging.

High resolution magnetic resonance (MR) images of the distal radius were obtained at 1.5 Tesla in premenopausal normal, postmenopausal normal, and postmenopausal osteoporotic women. The image resolution was 156 microm in plane and 700 microm in the slice direction; the total imaging time was approximately 16 minutes. An intensity-based thresholding technique was used to segment the images into trabecular bone and marrow, respectively. Extensions of standard stereological techniques were used to derive measures of trabecular bone structure from these segmented images. The parameters calculated included apparent measures of trabecular bone volume fraction, trabecular thickness, trabecular spacing, and trabecular number. Fractal-based texture parameters, such as the box-counting dimension, were also derived. Trabecular bone mineral density (BMD) and cortical bone mineral content (BMC) were measured in the distal radius using peripheral quantitative computed tomography (pQCT). In a subset of patients, spinal trabecular BMD was measured using quantitative computed tomography (QCT). Correlations between the indices of trabecular bone structure measured from these high-resolution MR images, age, BMD, and osteoporotic fracture status were examined. Cortical BMC and trabecular BMD at the distal radius, spinal BMD, trabecular bone volume fraction, trabecular thickness, trabecular number, and fractal dimension all decreased with age. Trabecular spacing showed the greatest percentage change and increased with age. In addition, significant differences were evident in spinal BMD, radial trabecular BMD, trabecular bone volume fraction, trabecular spacing, and trabecular number between the postmenopausal nonfracture and the postmenopausal osteoporotic subjects. Trabecular spacing and trabecular number showed moderate correlation with radial trabecular BMD but correlated poorly with radial cortical BMC. High resolution MR imaging, a potentially useful tool for quantifying trabecular structure in vivo, may have applications for understanding and evaluating skeletal changes related to age and osteoporosis.

Adult↗
PubMed1997

Image resolution and signal-to-noise ratio requirements for MR imaging of degenerative cartilage.

OBJECTIVE: The purpose of this study was to determine the MR image resolution and signal-to-noise ratio (SNR) required to reveal morphologic abnormalities in degenerative cartilage. MATERIALS AND METHODS: In vitro MR microscopy of healthy bovine and degenerative human patellar cartilage was performed and image resolution degraded to simulate resolution achievable in routine and optimized clinical MR images. Noise was then added to images as in-plane resolution was increased to simulate the MR imaging appearance of cartilage with improved resolution, which is possible using a standard magnetic field strength. MR images of patellar cartilage from a healthy volunteer were also obtained to determine optimal SNR and image resolution achievable at 1.5 T; these images were compared with in vitro images to determine those features of abnormal cartilage that can be identified using available clinical MR imaging techniques. RESULTS: In-plane resolution of 39 microns exquisitely defines degenerative changes in articular cartilage. As in-plane resolution decreases to 600 microns, only gross cartilage thinning and signal intensity alterations are seen. MR images simulating progressively improved resolution using higher field strength gradients with conventional field strengths and RF coils provided suboptimal information because of low SNR. CONCLUSION: Routine clinical MR images do not accurately reveal early degenerative changes in articular cartilage; only large defects and distorted changes in the signal intensity of cartilage are seen.

Adult↗
PubMed1997

Assessment of trabecular structure using high resolution magnetic resonance imaging.

Although bone mineral density is one of the most important contributing factors to bone strength and risk of fracture, studies have shown that changes in bone quality and structure independent of bone mineral density, influence both bone strength and individual risk of fracture. The influence of these other factors is thought to explain at least partially the observed overlap in bone mineral measurements between patients with and without osteoporotic fractures, irrespective of measurement site or technique. Thus, several new emerging techniques have been aimed at quantifying trabecular bone structure in addition to bone density. With recent hardware and software advances magnetic resonance (MR) images with spatial resolutions of 80-150 microns and slice thickness of 300-700 microns which resolve the trabecular structure have been obtained both in vitro and in vivo. Both modified spin-echo and gradient echo based imaging sequences have been used to obtain these images, and although the technical parameters and the sequence specific mechanisms affect the depiction of trabecular bone. In conjunction with three dimensional image processing and an understanding of the mechanisms of image formation, these high resolution images may be used to quantify trabecular bone architecture. In addition to obtaining standard stereological measures such as trabecular bone volume, mean trabecular width, mean trabecular spacing, mean intercept length as a function of angle, parameters such as three dimensional connectivity as measured by the Euler number, fabric tensor in three dimensions and texture related parameters such as fractal dimension may be derived from such images. Quantitative measures of trabecular architecture derived from such images have been compared with those obtained from higher resolution 18 microns images, and with biomechanical properties. In vivo studies in the radius and calcaneus have been performed and differences between osteoporotic and normal subjects are distinguishable. Thus, MR imaging techniques coupled with computerized image analysis may potentially be very useful for studying osteoporosis and quantifying trabecular bone architecture and may provide information in addition to bone density.

Biomechanical Phenomena↗
PubMed1997

Ticlopidine-associated pancytopenia: implications of an acetylsalicylic acid alternative.

Ticlopidine is an antiplatelet agent that has been proven efficacious in preventing vascular events in patients with a history of vasculopathy. Neutropenia is a significant adverse effect and pancytopenia is rarely reported. A fatal case of pancytopenia associated with unmonitored use of ticlopidine is presented. A 59-year-old woman presented with severe pneumonia and profound neutropenia (absolute neutrophil count 0%). She deteriorated with development of acute respiratory distress syndrome and a marked reduction in trilineage hematopoiesis. Despite prompt marrow response to granulocyte macrophage colony-stimulating factor (GM-CSF) and cessation of ticlopidine, appropriate antibiotics and other supportive therapy, she died 17 days after admission. Hematological monitoring is imperative to identify potential complications: if discovered late, there may be a role for GM-CSF for marrow support. Ticlopidine is indicated for patients intolerant of or nonresponsive to acetylsalicylic acid therapy. As the use of ticlopidine increases, clinicians must be aware of potential life-threatening complications associated with its use and monitor appropriately.

Aspirin↗
PubMed1996

Selective constraints on the activation domain of transcription factor Pit-1.

The POU transcription factor Pit-1 activates members of the prolactin/growth hormone gene family in specific endocrine cell types of the pituitary gland. Although Pit-1 is structurally conserved among vertebrate species, evolutionary changes in the pattern of Pit-1 RNA splicing have led to a notable "contraction" of the transactivation domain in the mammalian lineage, relative to Pit-1 in salmonid fish. By site-directed mutagenesis we demonstrate that two splice insertions in salmon Pit-1, called beta (29 aa) and gamma (33 aa), are critical for cooperative activation of the salmon prolactin gene. Paradoxically, Pit-1-dependent activation of the prolactin gene in rat is enhanced in the absence of the homologous beta-insert sequence. This apparent divergence in the mechanism of activation of prolactin genes by Pit-1 is target gene specific, as activation of rat and salmon growth hormone genes by Pit-1 splice variants is entirely conserved. Our data suggest that efficient activation of the prolactin gene in the vertebrate pituitary has significantly constrained the pattern of splicing within the Pit-1 transactivation domain. Rapid evolutionary divergence of prolactin gene function may have demanded changes in Pit-1/protein interactions to accommodate new patterns of transcriptional control by developmental or physiological factors.

Alternative Splicing↗
PubMed1996

Isolation of type II epithelial cells from rabbit fetal lungs by adherence on an IgG-coated surface.

The lung is comprised of about 40 different cell types, of which only 15% are type II cells. These are the major, if not the sole, source of synthesis and secretion of lung surfactant. To date a large number of methods have been described for the isolation of pure populations of type II cells using a wide variety of techniques, but most of these have employed differential centrifugation methods and have used adult rodents. The present study reports the isolation of type II cells from fetal rabbit lungs by the immunoglobin G plating method. Pure populations of fetal type II cells in high yield and with good viability were obtained by the procedure for the first time from rabbit fetal tissue.

Animals↗
PubMed1996

Decay characteristics of bone marrow in the presence of a trabecular bone network: in vitro and in vivo studies showing a departure from monoexponential behavior.

In this study, we examine MRI T2' decay characteristics for bone marrow in trabecular bone networks, using an asymmetric spin-echo sequence to isolate the inhomogeneous decay due to susceptibility variations between bone and marrow or water. In in vitro measurements on trabecular bone specimens from human vertebral bodies, tibia, and radii, we find significant deviations from a monoexponential signal decay. The initial decay is seen to have a Gaussian decay character, switching to a primarily exponential decay at later decay times. A similar trend is observed in in vivo measurements in the distal radius. Unlike an exponential decay, which may be characterized by a single decay rate, this is indicative of a significant variation in the decay rate with time. The deviations from exponential decay are seen to be orientation dependent, being most significant when the primary trabecular orientation is perpendicular to the static magnetic field.

Bone Marrow↗
PubMed1996

Magnetic resonance imaging of trabecular bone structure in the distal radius: relationship with X-ray tomographic microscopy and biomechanics.

The contribution of trabecular bone structure to bone strength is of considerable interest in the study of osteoporosis and other disorders characterized by changes in the skeletal system. Magnetic resonance (MR) imaging of trabecular bone has emerged as a promising technique for assessing trabecular bone structure. In this in vitro study we compare the measures of trabecular structure obtained using MR imaging and higher-resolution X-ray tomographic microscopy (XTM) imaging of cubes from human distal radii. The XTM image resolution is similar to that obtained from histomorphometric sections (18 microns isotropic), while the MR images are obtained at a resolution comparable to that achievable in vivo (156 x 156 x 300 microns). Standard histomorphometric measures, such as trabecular bone area fraction (synonymous with BV/TV), trabecular width, trabecular spacing and trabecular number, texture-related measures and three-dimensional connectivity (first Betti number/volume) of the trabecular network have been derived from these images. The variation in these parameters as a function of resolution, and the relationship between the structural parameters, bone mineral density and the elastic modulus are also examined. In MR images, because the resolution is comparable to the trabecular dimensions, partial volume effects occur, which complicate the segmentation of the image into bone and marrow phases. Using a standardized thresholding criterion for all images we find that there is an overestimation of trabecular bone area fraction (approximately 3 times), trabecular width (approximately 3 times), fractal dimension (approximately 1.4 times) and first Betti number/ volume (approximately 10 times), and an underestimation of trabecular spacing (approximately 1.6 times) in the MR images compared with the 18-microns XTM images. However, even for a factor of 9 difference in spatial resolution, the differences in the morphological trabecular structure measures ranged from a factor of 1.4 to 3.0. We have found that trabecular width, area fraction, number, fractal dimension and Betti number/volume measured from the XTM and MR images increases, while trabecular spacing decreases, as the bone mineral density and elastic modulus increase. A preliminary bivariate analysis showed that in addition to bone mineral density alone, the Betti number, trabecular number and spacing contributed to the prediction of the elastic modulus. This preliminary study indicates that measures of trabecular bone structure using MR imaging may play a role in the study of osteoporosis.

Absorptiometry, Photon↗
PubMed1996

Effect of lung surfactant liposomes on the rabbit fetal lung type II cell antioxidant enzymes following prenatal dexamethasone treatment.

Prematurely born infants are at a high risk of developing neonatal respiratory distress syndrome (RDS), and it is believed that besides an insufficient surfactant (SF) system the initial breathing of O2-enriched air may in some way be responsible for this syndrome. Hyperventilation is a dominant stimulator for SF secretion but it may lead to oxidant-mediated cellular injury to type II cells. Since type II cells are the sole source of SF synthesis, the effect of ventilation support on these cells becomes important. In the present study, the changes in the antioxidant enzymes (AOEs) such as superoxide dismutase (SOD), catalase and glutathione peroxidase (GPX) in the type II cells of fetal rabbit lungs resulting from exogenous SF liposomes and steroid intervention have been investigated. The specific activities of the AOEs were found to be higher in the presence of SF liposomes in prematurely born pups whose mothers were not steroid treated (control), while such an increase was more pronounced in dexamethasone-treated groups. The results indicate that the exogenous surfactant and steroid intervention may favourably alter the AOE defences in the type II cells of fetal rabbits.

Animals↗
PubMed1996

Advances in the noninvasive assessment of bone density, quality, and structure.

Recent advances in the development of methods to assess the skeleton noninvasively have contributed to screening for risk of osteoporosis, early detection of the disease, and effective monitoring of its progression and response to therapy. The capability now exists to evaluate the peripheral, central, or entire skeleton as well as the trabecular bone or cortical bone envelopes accurately and precisely, with the capacity to determine bone strength and predict fracture risk. In this article we examine the current and future capabilities of quantitative computed tomography (QCT), quantitative ultrasound (QUS), and magnetic resonance microscopy (muMR) to assess architectural and densitometric properties of the skeleton to enhance the prediction of fracture risk.

Female↗
PubMed1996

Congenital hypoplasia of the extensor tendons of the hand.

An 18-year-old woman with congenital flexion contractures of the ulnar three digits bilaterally is presented. She had a three-generation family history of this disorder with autosomal dominant inheritance. Magnetic resonance imaging scan of the wrist and forearm was used to demonstrate a hypoplasia of the digital extensor muscles and tendons.

Adolescent↗
PubMed1996

Magnetic resonance imaging of the calcaneus: preliminary assessment of trabecular bone-dependent regional variations in marrow relaxation time compared with dual X-ray absorptiometry.

RATIONALE AND OBJECTIVES: Marrow transverse relaxation time (T2*) in magnetic resonance (MR) imaging may be related to the density and structure of the surrounding trabecular network. We investigated regional variations of T2* in the human calcaneus and compared the findings with bone mineral density (BMD), as measured by dual X-ray absorpiometry (DXA). Short- and long-term precisions were evaluated first to determine whether MR imaging would be useful for the clinical assessment of disease status and progression in osteoporosis. METHODS: Gradient-recalled echo MR images of the calcaneus were acquired at 1.5 T from six volunteers. Measurements of T2* were compared with BMD and (for one volunteer) conventional radiography. RESULTS: T2* values showed significant regional variation; they typically were shortest in the superior region of the calcaneus. There was a linear correlation between MR and DXA measurements (r = .66 for 1/T2* versus BMD). Differences in T2* attributable to variations in analysis region-of-interest placement were not significant for five of the six volunteers. Sagittal MR images had short- and long-term precision errors of 4.2% and 3.3%, respectively. For DXA, the precision was 1.3% (coefficient of variation). CONCLUSION: MR imaging may be useful for trabecular bone assessment in the calcaneus. However, given the large regional variations in bone density and structure, the choice of an ROI is likely to play a major role in the accuracy, precision, and overall clinical efficacy of T2* measurements.

Absorptiometry, Photon↗
PubMed1996

Zinc supplementation reduces the incidence of persistent diarrhea and dysentery among low socioeconomic children in India.

Persistent diarrhea (PD) and dysentery (DD) account for most diarrhea-associated deaths among children in developing countries. Zinc deficiency can cause stunting and impaired immune function, both of which are risk factors for these diarrheal illnesses. We investigated the effect of zinc supplementation on the incidence of PD and DD in a community-based, double-blind randomized trial in children 6-35 mo of age. Increase over baseline in plasma zinc concentrations in the supplemented group compared with a control group (3.61 vs. 0.009 mumol.L-1), indicated successful supplementation. The overall reductions in the zinc supplemented group of 21% in the incidence of PD (95% CI -6 to 42%) and 14% in the incidence of dysentery (95% CI -15 to 36%) were not significant. There was a significant interaction of treatment effect with baseline plasma zinc concentration and age for PD and with gender for DD. In the zinc-supplemented group compared with the control group, the incidence of PD was reduced by 73% (P < 0.05; 95% CI 34 to 91%) in children with a baseline zinc < 7.65 mumol.L-1 and by 49% (P < 0.05; 95%CI 24 to 66%) in children > 11 mo of age. Zinc supplementation resulted in a 38% (P < 0.05 95%CI 8 to 59%) reduction in the incidence of DD in boys. There was no effect on PD among children 6-11 mo old or on DD in girls. In conclusion, zinc supplementation had a significant impact on the incidence of persistent diarrhea in children > 1 y old and in children with low plasma zinc, as well as on dysentery in boys. These findings may have important implications for reducing diarrhea-related morbidity and mortality.

Child, Preschool↗