Search PubMed⌕ Search

Biomedical subjects

S Chowdhury

Publications and source records attributed to S Chowdhury.

At least 19 recordsLinked to original sources
PubMed2007

Preliminary work on the development of a novel detection method for osteoporosis.

Osteoporosis affects both the organic and mineral phases of bone resulting in a decrease in resistance to fracture. Dual x-ray absorptiometry (DEXA) scans are used for diagnosing osteoporosis, which is conventionally characterised by a decrease in mineral density. Unfortunately, some patients who suffer osteoporotic fractures have normal bone density, because both the organic and the mineral phase are affected. However, there are currently no methods of evaluating the health of the organic phase. Patients undergoing treatment for osteoporosis have reported hardening of their fingernails. As the properties of nail and bone may be linked in a comparable, measurable way, this work used both mechanical (nano-indentation) and chemical (Raman spectroscopy) methods to evaluate differences between fingernails sourced from osteoporotic and non-osteoporotic patients. The difference in mean modulus between the nails sourced from the groups was 1.1 GPa. The disulphide bond content of fingernail samples from each group was measured by Raman spectroscopy and disulphide bond content of fingernail was found to be significantly lower in the osteoporotic group. It can be concluded that a relationship between the mechanical and chemical properties of nail and bone may exist in a measurable way. This work has suggested that changes in the organic phase of bone are reflected in similar proteins, such as keratin, from which fingernails are composed. Collagen and keratin are two distinct structural proteins, but they share the need for protein sulphation and disulphide bond formation, via cysteine, for their structural integrity. A disorder of either process should lead to disordered collagen and keratin synthesis.

Bone Density↗
PubMed2007

Accelerating aging of zirconia femoral head implants: change of surface structure and mechanical properties.

Recently, alternations of zirconia ceramic femoral heads of total hip prostheses during in vivo conditions have caused concern in the medical disciplines regarding phase transformation of zirconia prosthetic components. In this paper, we have investigated the mechanical and structural properties of different laboratory aged zirconia femoral heads and correlated changes in mechanical properties with the phase compositions of the sample. From laser microscope observation, cross-sectional Scanning electron microscopy imaging, and X-ray diffraction analysis on the surface of the zirconia femoral heads, we found monoclinic to tetragonal phase transformation in zirconia prostheses over time during the aging process in the laboratory. Mechanical properties, mainly hardness (H) and Young's modulus (E) values, were measured by nanoindentation technique on the surface of these implants. The results showed that both H and E values decreased with increased monoclinic phase in zirconia, thus confirming a phase transformation over time during aging.

Biocompatible Materials↗
PubMed2006

Mesenchymal stem cell adhesion and spreading on microwave plasma-nitrided titanium alloy.

Improved methods to increase surface hardness of metallic biomedical implants are being developed in an effort to minimize the formation of wear debris particles that cause local pain and inflammation. However, for many implant surface treatments, there is a risk of film delamination due to the mismatch of mechanical properties between the hard surface and the softer underlying metal. In this article, we describe the surface modification of titanium alloy (Ti-6Al-4V), using microwave plasma chemical vapor deposition to induce titanium nitride formation by nitrogen diffusion. The result is a gradual transition from a titanium nitride surface to the bulk titanium alloy, without a sharp interface that could otherwise lead to delamination. We demonstrate that vitronectin adsorption, as well as the adhesion and spreading of human mesenchymal stem cells to plasma-nitrided titanium is equivalent to that of Ti-6Al-4V, while hardness is improved 3- to 4-fold. These in vitro results suggest that the plasma nitriding technique has the potential to reduce wear, and the resulting debris particle release, of biomedical implants without compromising osseointegration; thus, minimizing the possibility of implant loosening over time.

Cell Adhesion↗
PubMed2006

Mechano-morphological studies of aligned nanofibrous scaffolds of polycaprolactone fabricated by electrospinning.

Mechanical and morphological studies of aligned nanofibrous meshes of poly(epsilon-caprolactone) (PCL) fabricated by electrospinning at different collector rotation speeds (0, 3000 and 6000 rpm) for application as bone tissue scaffolds are reported. SEM, XRD and DSC analyses were used for the morphological characterization of the nanofibers. Scaffolds have a nanofibrous morphology with fibers (majority) having a diameter in the range of 550-350 nm (depending on fiber uptake rates) and an interconnected pore structure. With the increase of collector rotation speed, the nanofibers become more aligned and oriented perpendicular to the axis of rotation. Deposition of fibers at higher fiber collection speeds has a profound effect on the morphology and mechanical properties of individual fibers and also the bulk fibrous meshes. Nanoindentation was used for the measurement of nanoscopic mechanical properties of individual fibers of the scaffolds. The hardness and Young's modulus of aligned fibers measured by nanoindentation decreased with collector rotation speeds. This reveals the difference in the local microscopic structure of the fibers deposited at higher speeds. The sequence of nanoscopic mechanical properties (hardness and modulus) of three fibers is PCL at 0 rpm > PCL at 3000 rpm > PCL at 6000 rpm. This may be explained due to the decrease in crystallinity of fibers at higher uptake rates. However, uni-axial tensile properties of (bulk) scaffolds (tensile strength and modulus) increased with increasing collector rotation speed. The average ultimate tensile strength of scaffolds (along the fiber alignment) increased from 2.21 +/- 0.23 MPa for PCL at uptake rate of zero rpm, to a value of 4.21 +/- 0.35 MPa for PCL at uptake rate of 3000 rpm and finally to 9.58 +/- 0.71 MPa for PCL at 6000 rpm. Similarly, the tensile modulus increased gradually from 6.12 +/- 0.8 MPa for PCL at uptake rate of zero rpm, to 11.93 +/- 1.22 MPa for PCL at uptake rate of 3000 rpm and to 33.20 +/- 1.98 MPa for PCL at 6000 rpm. The sequence of macroscopic mechanical properties (tensile strength and modulus) of three fibers, from highest to lowest, is PCL at 0 rpm < PCL at 3000 rpm < PCL at 6000 rpm. This is attributed to the increased fiber alignment and packing and decrease in inter-fiber pore size at higher uptake rates.

Biocompatible Materials↗
PubMed2005

The prevalence and associated features of posterior embryotoxon in the general ophthalmic clinic.

PURPOSE: To estimate the prevalence of posterior embryotoxon (PE) in the general ophthalmic clinic and to identify any features of PE that suggest that it is pathological rather than physiological. METHODS: Over 700 consecutive patients of all ages were examined with the slit lamp during their routine eye clinic appointment. Patients with posterior embryotoxon were invited to return for full ocular examination including keratometry, corneal topography, and gonioscopy. RESULTS: In all, 49 out of 723 patients were found to have PE. This gives a prevalence of 6.8% with an age range of 18 months to 95 years. There was a higher prevalence in the younger age group of 22.5% (age range 18 months to 20 years) compared to 5.9% in the older age range (21-95 years). A total of 29 patients with PE returned for further examination. Six patients had glaucoma (two with Axenfeld's syndrome and one with aniridia), and one had ocular hypertension. In all, 20 patients had bilateral PE on slit-lamp examination, which increased to 24 with gonioscopy. The majority of the PE was seen temporally (97.9%) and limited to a few clock hours. Gonioscopy showed that eight patients with PE had associated inferior pigmentation of schwalbes line. CONCLUSION: This large series found the prevalence of PE the general ophthalmic clinic to be 6.8%. Its presence should prompt careful anterior segment examination, including gonioscopy, to identify any associated abnormalities that may carry a risk of glaucoma. Children should also be assessed for any associated systemic or genetic abnormality.

Abnormalities, Multiple↗
PubMed2005

Metabolism and excretion of loratadine in male and female mice, rats and monkeys.

The metabolism and excretion of loratadine (LOR), a long-acting non-sedating antihistamine, have been evaluated in male and female mice, rats and monkeys. Following a single (8 mg kg-1) oral administration of [14C]LOR, radioactivity was predominantly eliminated in the faeces. Profiling and characterization of metabolites in plasma, bile, urine and faeces from male and female mice, rats and monkeys showed LOR to be extensively metabolized with quantitative species and gender differences in the observed metabolites. In all species investigated, the primary biotransformation of LOR involved decarboethoxylation to form desloratadine (DL), subsequent oxidation (hydroxylation and N-oxidation) and glucuronidation. More than 50 metabolites were profiled using liquid chromatography-mass spectrometry (LC-MS) with in-line flow scintillation analysis (FSA) and characterized using LC-MSn techniques. The major circulating metabolite in male rats is a DL derivative in which the piperidine ring was aromatized and oxidized to pyridine-N-oxide. Much lower levels of the pyridine-N-oxide metabolite were observed in female rat plasma. In contrast, the relative amount of DL was notably higher in female than in male rats. The major circulating metabolite in either gender of mouse and male monkey is a glucuronide conjugate of an aliphatic hydroxylated LOR; in the female monkey, the major circulating metabolite is formed through oxidation of the pyridine moiety and subsequent glucuronidation. Qualitatively similar metabolic profiles were observed in the mouse, rat and monkey urine and bile, and the metabolites characterized resulted from biotransformation of LOR to DL, hydroxylation of DL and subsequent glucuronide conjugation. 5-Hydroxy-desloratadine was the major faecal metabolite across all three species irrespective of gender.

Animals↗
PubMed2005

The use of fingernails as a means of assessing bone health: a pilot study.

BACKGROUND: Anecdotally, patients volunteer reports of increasing hardness of their fingernails within months of starting diverse treatments for osteoporosis. The properties of both nail and bone may be linked in a comparable, measurable way. METHODS: We examined the fingernails of two groups of patients, with (n = 9) and without (n = 13) osteoporosis at either the hip or lumbosacral spine. We performed nanoindentation to assess the degree of nail brittleness and Raman spectroscopy to assess the disulfide bond content of nail. RESULTS: The mean moduli of fingernails of patients with low bone mineral density (BMD) are lower than those of patients with normal BMD. The mean difference in mean modulus between the groups was found to be 0.996 (p = 0.15 between groups). The spectroscopy data also showed differences between the two sets of nails. The disulfide bond content of the nails sourced from osteoporotic patients was lower than that from healthy patients (p = 0.06 between groups). CONCLUSIONS: Bone collagen and nail keratin are two distinct structural proteins, and both require protein sulfation and disulfide bond formation, via cysteine, for structural integrity. A disorder of either process may lead to disordered collagen and keratin synthesis. This is reflected in the structural abnormalities seen in clinical syndromes in which there is either protein deficiency, disorders of sulfur metabolism, or cystathione beta-synthase deficiency. The relationship between nail and bone may exist in a measurable way. This pilot study should lead to further work to explore this relationship. Could nail prove to be a valuable adjunct to diagnosis or provide a means of more rapid follow-up after commencement of therapy?

Aged↗
PubMed2005

Nanoindentation on porous bioceramic scaffolds for bone tissue engineering.

We report nanoindentation mechanical properties measurements on porous ceramic scaffolds made for tissue engineering applications. The scaffolds have been made from tricalcium phosphate (TCP), hydroxyapatite (HA) nanopowder and mixed powders of HA (50 wt%) and TCP (50 wt%) using the polyurethane sponge method, which produces open porous ceramic scaffolds through replication of a porous polymer template. The scaffolds prepared by this method have a controllable pore size and interconnected pore structure. The crystal structures and morphology of porous scaffolds were determined by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. Nanoindentation measurements to a depth of 600 nm showed a Young's modulus value of 10.3 GPa for HA+TCP composite scaffolds and 1.5 GPa for TCP scaffolds. The hardness values were 240 MPa for HA+TCP composites and 21 MPa for TCP sample respectively. The results showed that the mechanical properties of the biodegradable scaffolds can be considerably enhanced with the addition of HA while maintaining the interconnected open pores and pore geometry desirable for bone tissue engineering.

Biocompatible Materials↗
PubMed2002

Sociocultural aspects of areca nut use.

This paper aims to describe the sociocultural context of areca nut use through exploring people's norms and values and the meaning underlying a wide range of different practices. A historical review is followed by an examination of more recent evidence, including quantitative and qualitative research conducted in the United Kingdom. It is concluded that some reports involving the various uses of areca nut and the conclusions drawn are confusing and that future studies need to be more explicit. While a sound scientific background is required, important sociocultural and religious issues around areca nut use must also be understood if health promotion initiatives are to be considered.

Africa↗
PubMed2002

Distribution and pattern of water-soluble proteins of lens as revealed by gel filtration chromatography in fish (Catla catla) of different age groups.

The water soluble proteins of the lens collected from different age group of the fish Catla catla were subjected to Sephadex G 200 gel filtration to fractionate and to characterize the protein and further to determine the elution volume (Ve) of different fractions. The relative proportion of each fraction was also calculated. Total number of fractions F1 to F4 was discernible through gel filtration. The molecular weight of these varied from 35,000 Da to 640,000 Da. Three subfractions were also noted in F1 fraction. Interesting observations were, presence of alpha, betaH betaL crystallins in all age groups and LMW proteins in older age group. a-crystallin present in major amounts in comparison to betaH & betaL crystallins. Decrease of alpha-crystallins (except in age group II) with the increase of age, counter balanced by the increase of betaH crystallins. Increase of betaH crystallins was followed by the decrease of betaL crystallins. Results suggest that proportionate distribution of different classes of proteins determined by column chromatography is widely variable.

Animals↗
PubMed2002

Impact of lactational performance on bone mineral density in marginally-nourished Bangladeshi women.

This cross-sectional study, carried out during July 1997-June 1998, evaluated the effects of prolonged breast-feeding and lactational amenorrhoea on bone mineral density (BMD) in 400 marginally-nourished Bangladeshi women aged 20-81 years. A bone densitometer was used for measuring BMD in the distal and ultra-distal end of radius and ulna. The results showed that the women who breastfed for 60 months or less had a higher mean BMD compared to those who breastfed for 61-120 months and for over 120 months. There was a significantly higher BMD in the women who had a shorter duration of lactational amenorrhoea compared to those having a longer duration of lactational amenorrhoea. BMD was significantly and negatively correlated with total duration of lactational amenorrhoea (slope -0.024, p<0.05) after controlling for parity, physical workload, and total duration of breast-feeding. The study concluded that there was a negative correlation between longer duration of breast-feeding and BMD, but it was not found when other factors were controlled in multivariate analysis. The duration of lactational amenorrhoea, which is a proxy indicator of breast-feeding, showed a negative correlation with BMD. It is recommended that all lactating women be given diet with adequate calcium to support breast-feeding for maintaining good nutrition of their bones.

Adult↗
PubMed2002

Effect of vitamin A supplementation on childhood morbidity and mortality.

In a double blind design, 1520 children aged < 10 years were individually randomised in vitamin A and placebo group in slums of Chandigarh. Children > 12, 6-12 and < 6 months of age received 200,000, 100,000, 500,000 I.U. of vitamin A respectively every 4 to 6 months during 15 months trial period. The prevalence of vitamin A deficiency was significantly reduced in vitamin A compared to placebo group during the follow-up period. In vitamin A group, incidence of diarrhoea and measles was significantly reduced but incidence of acute respiratory infections was not significantly different compared to control group. Risk of death was also significantly less in vitamin A group. Therefore, promotion of vitamin A rich diet or supplementation with synthetic vitamin A at 4-6 month interval should be a priority in populations where risk of vitamin A deficiency is high.

Case-Control Studies↗
PubMed2001

First synthesis of lower-rim-substituted aryl ethers of p-tert-butylcalix[4]arene.

With the use of S(N)Ar or Ullmann reactions, the synthesis of the first lower-rim aryl ether derivatives of tert-butylcalix[4]arene is reported, as are some of their conformational properties, (1)H NMR spectra, and X-ray crystal structures. The lower-rim aryl pendants reported herein provide for new scaffolds upon which a host of other new molecular architectures can be constructed, thus extending the capability of the versatile calix[4]arenes even further.

Journal Article↗
PubMed2001

Functional neuroanatomy of biological motion perception in humans.

We used whole brain functional MRI to investigate the neural network specifically engaged in the recognition of "biological motion" defined by point-lights attached to the major joints and head of a human walker. To examine the specificity of brain regions responsive to biological motion, brain activations obtained during a "walker vs. non-walker" discrimination task were compared with those elicited by two other tasks: (i) non-rigid motion (NRM), involving the discrimination of overall motion direction in the same "point-lights" display, and (ii) face-gender discrimination, involving the discrimination of gender in briefly presented photographs of men and women. Brain activity specific to "biological motion" recognition arose in the lateral cerebellum and in a region in the lateral occipital cortex presumably corresponding to the area KO previously shown to be particularly sensitive to kinetic contours. Additional areas significantly activated during the biological motion recognition task involved both, dorsal and ventral extrastriate cortical regions. In the ventral regions both face-gender discrimination and biological motion recognition elicited activation in the lingual and fusiform gyri and in the Brodmann areas 22 and 38 in superior temporal sulcus (STS). Along the dorsal pathway, both biological motion recognition and non-rigid direction discrimination gave rise to strong responses in several known motion sensitive areas. These included Brodmann areas 19/37, the inferior (Brodmann Area 39), and superior parietal lobule (Brodmann Area 7). Thus, we conjecture that, whereas face (and form) stimuli activate primarily the ventral system and motion stimuli primarily the dorsal system, recognition of biological motion stimuli may activate both systems as well as their confluence in STS. This hypothesis is consistent with our findings in stroke patients, with unilateral brain lesions involving at least one of these areas, who, although correctly reporting the direction of the point-light walker, fail on the biological motion task.

Adult↗
PubMed2001

CCAAT/enhancer-binding protein beta is required for activation of genes for ornithine cycle enzymes by glucocorticoids and glucagon in primary-cultured hepatocytes.

Transcription of genes for enzymes of the ornithine cycle is activated by hormones such as glucocorticoids and glucagon. Promoters and enhancers of several genes for the enzymes interact with the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors, and C/EBPbeta has been suggested to mediate glucocorticoid response of the gene for arginase, the last enzyme of the cycle. To determine the contribution of C/EBPbeta to hormonal regulation of genes for ornithine cycle enzymes, we examined mice with targeted disruption of the C/EBPbeta gene. Induction of genes for the enzymes by intraperitoneal injection of dexamethasone and glucagon was almost intact in the liver of C/EBPbeta-deficient mice. On the other hand, in primary-cultured hepatocytes derived from C/EBPbeta-deficient mice, induction of genes for the first enzyme carbamylphosphate synthetase, as well as for arginase, in response to dexamethasone and/or glucagon was severely impaired. Therefore, C/EBPbeta is required for hormonal induction of the genes for ornithine cycle enzymes in primary-cultured hepatocytes, while the deficiency of C/EBPbeta is compensated for in vivo.

Animals↗
PubMed2001

The coenzyme b12 analog 5'-deoxyadenosylcobinamide-gdp supports catalysis by methylmalonyl-coa mutase in the absence of trans-ligand coordination.

Methylmalonyl-CoA mutase is an 5'-adenosylcobalamin (AdoCbl)-dependent enzyme that catalyzes the rearrangement of methylmalonyl-CoA to succinyl-CoA. The crystal structure of this protein revealed that binding of the cofactor is accompanied by a significant conformational change in which dimethylbenzimidazole, the lower axial ligand to cobalt in solution, is replaced by His(610) donated by the active site. The role of the lower axial ligand in the trillion-fold labilization of the upper axial cobalt-carbon bond has been the subject of enduring debate in the model inorganic literature. In this study, we have used a cofactor analog, 5'deoxyadenosylcobinamide GDP (AdoCbi-GDP), which reconstitutes the enzyme in a "histidine-off" form and which allows us to evaluate the contribution of the lower axial ligand to catalysis. The k(cat) for the enzyme in the presence of AdoCbi-GDP is reduced by a factor of 4 compared with the native cofactor AdoCbl. The overall deuterium isotope effect in the presence of AdoCbi-GDP ((D)V = 7.2 +/- 0.8) is comparable with that observed in the presence of AdoCbl (5.0 +/- 0.6) and indicates that the hydrogen transfer steps in this reaction are not significantly affected by the change in coordination state of the bound cofactor. These surprising results are in marked contrast to the effects ascribed to the corresponding lower axial histidine ligands in the cobalamin-dependent enzymes glutamate mutase and methionine synthase.

Binding Sites↗