Biomedical subjects

A Das

Publications and source records attributed to A Das.

At least 127 records · Page 7Linked to original sources

PubMed2000

Histological subtypes of symptomatic central nervous system tumours in Singapore.

The objective was to identify the different subtypes of symptomatic CNS tumours that are encountered in Singapore. Our hospital pathology and operative records from 1994 to 1998 were reviewed and information regarding all patients who underwent biopsy or resection as part of their diagnostic and therapeutic evaluation was extracted. Only histologically confirmed tumours were included in this analysis. Meningiomas made up the largest subgroup of tumours, accounting for 35.1% of all tumours. In order of decreasing frequency, the remaining most often reported histologies were pituitary adenomas (11.8%), secondary neoplasms (10%), tumours of nerve sheath (9.4%), glioblastoma multiforme (9.3%), astrocytomas including anaplastic, diffuse and pilocytic (9.2%), primary CNS lymphomas (2.9%), oligodendrogliomas (2.2%), hemangioblastomas (2. 2%), craniopharyngiomas (1.7%), and embryonal tumours (1.2%). Genetic and environmental factors may be responsible for the proportionately higher than expected percentage of meningiomas seen and further study is required to identify these factors.

Adolescent↗

PubMed2000

Micropropagation of sweet orange, Citrus sinensis Osbeck. for the development of nucellar seedlings.

Protocol for micropropagation of elite plants of sweet orange (Citrus sinensis) through nucellar embryo culture has been standardized. Three to four nucellar embryos and a zygotic embryo could be excised from a single mature seed and successfully generated as healthy plants in basal MS medium. MS medium supplemented with NAA (1 mg/L) or 2, 4.D (1 mg/L) promoted callus development in both nucellar and zygotic embryos. GA3 (1 mg/L) enriched medium induced plantlets initiation but their growth was very poor. No significant differences were observed between initial growth patterns of nucellar and zygotic seedlings developing from the same ovule. Five to six shoots were obtained from collar region of both category of embryos in MS medium supplemented with BAP (1 mg/L) within 60 days of inoculation. The number of plantlets were almost doubled after their transfer in the same medium and culture for another 30 days. Higher doses of BAP resulted in initiation of callus directly from the embryos. The regenerated shoots (2-3 cm) could be rooted in MS medium supplemented with either only NAA (0.75 mg/L) or NAA (0.50 mg/L) and IBA (2.0 mg/L). A number of plantlets could be obtained from a nucellar embryo grown shoot within a limited time period.

Botany↗

PubMed1999

Inhibition of herpes simplex virus type 1 and adenovirus type 5 by heterocyclic Schiff bases of aminohydroxyguanidine tosylate.

Eleven heterocyclic Schiff bases of aminohydroxyguanidine tosylate (SB-AHGs), compounds I-XI, were tested for antiviral activity against herpes simplex virus type 1 (HSV-1) and adenovirus type 5 (Ad 5) via plaque reduction and virus yield reduction assays. This work was undertaken to test the hypothesis that low molecular weight SB-AHGs (MW < 235 for the free SB) make better antiviral agents than high MW SB-AHGs (MW > 300). The plaque reduction assay method demonstrated that three compounds, I, VII and IX, had moderate activity against HSV-1, with 50% inhibitory concentration (IC50) values of 38.0, 23.5 and 52.1 microM, respectively. Against Ad 5, compounds I, VIII and XI exhibited moderate activity, with IC50 values of 52.7, 19.3 and 5.1 microM, respectively. Among the compounds screened, compound I (1-[(3'-hydroxy-6'-methyl-2'-pyridyl)methylene]amino-3-hydroxyguanidi ne tosylate) was the most promising antiviral candidate, with selectivity indices (SI) of 10.2 (HSV-1) and 7.6 (Ad 5), respectively. Virus yield reduction assays indicated that compound I had less antiviral potency against HSV-1 than against Ad 5. The antiviral effects of compound I at a high input virus multiplicity of infection (MOI > 5) indicated that compound I had effective anti-adenoviral activity at 24 h post infection. This work demonstrated that some of SB-AHGs only have moderate antiviral activities against Ad 5 and HSV-1 viruses. In general, low MW SB-AHGs have low cytotoxicities to the host cells.

Adenoviridae↗

PubMed1999

Topography of contextual modulations mediated by short-range interactions in primary visual cortex.

Neurons in primary visual cortex (V1) respond differently to a simple visual element presented in isolation from when it is embedded within a complex image. This difference, a specific modulation by surrounding elements in the image, is mediated by short- and long-range connections within V1 and by feedback from other areas. Here we study the role of short-range connections in this process, and relate it to the layout of local inhomogeneities in the cortical maps of orientation and space. By measuring correlation between neuron pairs located in optically imaged maps of V1 orientation columns we show that the strength of local connections between cells is a graded function of lateral separation across cortex, largely radially symmetrical and relatively independent of orientation preferences. We then show the contextual influence of flanking visual elements on neuronal responses varies systematically with a neuron's position within the cortical orientation map. The strength of this contextual influence on a neuron can be predicted from a model of local connections based on simple overlap with particular features of the orientation map. This indicates that local intracortical circuitry could endow neurons with a graded specialization for processing angular visual features such as corners and T junctions, and this specialization could have its own functional cortical map, linked with the orientation map.

Animals↗

PubMed1999

Syringomyelia and complex regional pain syndrome as complications of multiple sclerosis.

OBJECTIVE: To describe a patient from Southeast Asia with the optic-spinal phenotype of multiple sclerosis who developed syringomyelia and resultant complex regional pain syndrome (formerly named reflex sympathetic dystrophy). DESIGN: Case report. SETTING: Department of neurology at a tertiary care hospital in the Republic of Singapore. PATIENT: A 53-year-old Chinese woman with a history of optic neuritis developed an episode of left hemiparesis leading to a diagnosis of multiple sclerosis. Serial neuroimaging studies revealed an active demyelinating plaque in the cervical area that later progressed into a syrinx. Over a period of 1 year she also developed signs of sympathetic dysfunction including Horner syndrome of the left eye and complex regional pain syndrome in the left hand. CONCLUSIONS: A case of the optic-spinal phenotype of multiple sclerosis that is commonly observed in Southeast Asia is described. This characteristically tissue-destructive form of multiple sclerosis resulted in syringomyelia complicated by a complex regional pain syndrome. Possible pathogenic mechanisms for these associations are discussed.

Cervical Vertebrae↗

PubMed1999

Retinal neovascularization is suppressed with a matrix metalloproteinase inhibitor.

OBJECTIVES: To determine the role of extracellular proteinases in ischemia-induced retinal neovascularization in an animal model and to examine the effect of proteinase inhibitors on retinal neovascularization. METHODS: Retinal neovascularization was induced in newborn mice exposed to 75% oxygen for 5 days, followed by room air. Retinal extracts underwent zymographic analysis to measure the activity of urokinase and matrix metalloproteinases (MMPs). Some animals under the same conditions also received intraperitoneal injections of an MMP inhibitor. Histological analysis was done to quantitate the neovascular response in these animals. RESULTS: Levels of urokinase and MMPs (MMP-2 and MMP-9) in retinas were significantly increased in animals with induced retinal neovascularization. Neovascularization was significantly inhibited with intraperitoneal administration of an MMP inhibitor. CONCLUSION: Systemic inhibition of MMPs may have therapeutic potential in preventing retinopathy associated with retinal neovascularization. CLINICAL RELEVANCE: Because up-regulation and activation of proteinases represents a final common pathway in the process of retinal neovascularization, pharmacological intervention of this pathway may be an alternative therapeutic approach to proliferative retinopathy.

Animals↗

PubMed1999

An economic analysis of different strategies of immunization against hepatitis A virus in developed countries.

Acute hepatitis A is a major public health problem in developed countries, and because a large proportion of patients with acute hepatitis A do not have any identifiable risk factors, current practice of targeting the high-risk groups for vaccination against hepatitis A virus (HAV) is unlikely to have a significant impact on the overall incidence of acute hepatitis A. No economic analysis of strategies of mass immunization against HAV is available. Three different strategies of immunization against HAV using commercially available inactivated vaccine were compared in a Markov model analysis of a cohort of 2-year-old healthy children in a developed country. In strategy I, universal vaccination was pursued. In strategy II, children were initially screened for antibody and, if susceptible, they were vaccinated. In strategy III, no vaccination was offered. Cost per person and quality adjusted life-years (QALY) gained in each strategy were the outcome measures compared. The baseline analysis showed that strategy II is more cost-effective than strategy I, with marginal cost-effectiveness ratios of $7,267. 67 and $12,833.34, respectively, compared with a strategy of no intervention. Sensitivity analysis showed that if the cost of the two-dose vaccine could be reduced to less than $57, the strategy of universal vaccination would be the preferred immunization strategy. Different strategies of mass immunization against HAV in the developed countries are cost-effective by current standards of health care interventions and should be considered for incorporation into current childhood immunization programs.

Adolescent↗

PubMed1999

The preterm prediction study: failure of midtrimester cervical sialidase level elevation to predict subsequent spontaneous preterm birth.

OBJECTIVE: Our objective was to determine any associations among midtrimester cervical fluid sialidase activity, bacterial vaginosis, and subsequent spontaneous preterm birth. STUDY DESIGN: In this nested case-control study all patients (n = 126) with spontaneous preterm birth at <35 weeks' gestation and selected control subjects delivered at >/=37 weeks' gestation (n = 126, matched for race, parity, and center) were derived from women enrolled in the multicenter National Institute of Child Health and Human Development Preterm Prediction Study. Sialidase activity and presence of bacterial vaginosis according to Gram stain were determined in cervical swabs and vaginal smears, respectively, obtained at 22 weeks' to 24 weeks 6 days' gestation. RESULTS: The mean +/- SD sialidase activities were similar in case patients and control subjects (0.64 +/- 1.60 vs 0.41 +/- 0.94 nmol. mL-1. min-1, P =.21). Neither sialidase activity above the 90th percentile (10.3% vs 9.5%, P =.8) nor sialidase activity above the 95th percentile (7.9% vs 4. 8%, P =.3) of control specimens (>1.43 and >2.23 nmol. mL-1. min-1, respectively) was associated with spontaneous preterm birth. The frequency of combinations of bacterial vaginosis and elevated sialidase activity was similar (P >/=.63 with either cutoff) in case patients and control subjects. Sialidase activity was significantly higher among women with bacterial vaginosis than among those without bacterial vaginosis (1.35 +/- 1.87 vs 0.03 +/- 0.14 nmol. mL-1. min-1, P <.0001). CONCLUSIONS: Elevated cervical fluid sialidase activity at 22 to 24 weeks' gestation did not distinguish women at increased risk for spontaneous preterm birth, nor did it discriminate a subgroup of patients who had bacterial vaginosis associated with spontaneous preterm birth.

Case-Control Studies↗

PubMed1999

Reactivity of guanine at m5CpG steps in DNA: evidence for electronic effects transmitted through the base pairs.

BACKGROUND: Mitomycin C (MC), a DNA cross-linking and alkylating agent, targets guanines in the m5CpG sequence with 2-3-fold preference over guanines in unmethylated CpG. Benzo[a]pyrenediolepoxide (BPDE) and several other aromatic carcinogens form guanine adducts with an identical selectivity for m5CpG, and in certain cancers G to T transversion mutation 'hotspots' in the p53 tumor suppressor gene are more frequent at this sequence than at guanines in other sequences. MC appears suitable to probe the general mechanism of this selectivity. RESULTS: A 162-bp DNA fragment containing C, m5C or f5C (5-fluoro cytosine) at all cytosine positions was cross-linked by MC at guanines in CpG steps. The extent of cross-linking increased in the order f5C < C < m5C. Monoalkylation or cross-linking of duplex 12-mer oligonucleotides containing a single CpG, f5CpG or m5CpG step gave yields of adducts that increased in the same order. The rates showed a correlation with the Hammett sigma constant of the methyl and fluoro substituents of the cytosine. Only the base-pair cytosine substituent influenced reactivity of guanine. CONCLUSIONS: The 2-amino group of guanine in the m5CpG sequence of DNA has a greater nucleophilic reactivity with mitomycin than CpG. Evidence is presented for a novel mechanism: transmission of the electron-donating effect of the 5-methyl substituent of the cytosine to guanine through H-bonding of the m5C.G base pair. The results explain the enhanced reaction of BPDE at m5CpG in DNA and the origin of G-T mutational hotspots in the p53 gene in cancer.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed1999

Cleogynol, a novel dammarane triterpenoid from Cleome gynandra.

Chemical examination of Cleome gynandra (whole plant excluding seeds) led to the isolation and identification of a novel (20S, 24S)-epoxy-19,25-dihydroxydammarane-3-one hemiketal (1). The structure of the new compound, designated cleogynol, was determined using spectral and chemical methods.

Acetylation↗

PubMed1999

Glutaric aciduria type I: pathomechanisms of neurodegeneration.

In organotypic corticostriatal and hippocampal slice cultures from rat brain, 3-hydroxyglutaric acid but not glutaric and glutaconic acids induced neurodegeneration by activation of NMDA receptors. Electrophysiological investigations (Xenopus laevis oocytes expressing glutamate receptors; rat mixed cortex culture) revealed no direct interaction of 3-hydroxyglutaric acid with glutamate receptors. We speculate that 3-hydroxyglutaric acid induces a mild energy deprivation that interferes with the voltage-dependent Mg(2+)-block of NMDA receptors.

Animals↗

PubMed1999

A review of the therapy of paraneoplastic neurologic syndromes.

The therapy of paraneoplastic neurologic syndromes remains unclear and warrants a systematic review of the literature. Reports in English and foreign language literature were abstracted. Data were sorted by the primary paraneoplastic neurologic syndrome, the primary malignancy, and the methods of treatment. Neurologic improvement follows surgical, chemotherapeutic, and radiation treatments. Adjuvant immunosuppressive therapy with steroids, plasmapheresis, or immunoglobulin may help stabilize the progression of neurologic symptoms. Syndromes characterized by inflammation or neurotransmitter production without neuronal loss are most responsive to therapy. While treatment of the underlying cancer with appropriate surgery, chemotherapy, and radiation is recommended, the paraneoplastic syndrome should probably be managed with immunosuppressive therapy.

Humans↗

PubMed1999

A novel mutation in the KH domain of polynucleotide phosphorylase affects autoregulation and mRNA decay in Escherichia coli.

Polynucleotide phosphorylase (PNPase) is a key 3'-5' exonuclease for mRNA decay in bacteria. Here, we report the isolation of a novel mutant of Escherichia coli PNPase that affects autogenous control and mRNA decay. We show that the inactivation of PNPase by a transposon insertion increases the half-life of galactokinase mRNA encoded by a plasmid. When the bacteriophage lambda int gene retroregulator (sib/tI ) is placed between pgal and galK, it severely diminishes galactokinase expression because of transcription termination. The expression of galK from this construct is increased by a single base mutation, sib1, which causes a partial readthrough of transcription at tI. We have used this plasmid system with sib1 to select E. coli mutants that depress galK expression. Genetic and molecular analysis of one such mutant revealed that it contains a mutation in the pnp gene, which encodes the PNPase catalytic subunit alpha. The mutation responsible (pnp-71 ) has substituted a highly conserved glycine residue in the KH domain of PNPase with aspartate. We show that this G-570D substitution causes a higher accumulation of the alpha-subunit as a result of defective autoregulation, thereby increasing the PNPase activity in the cell. The purified mutant alpha-subunit shows the same electrophoretic mobility in denaturing gels as the wild-type subunit, as expected. However, the mutant protein present in crude extracts displays an altered electrophoretic mobility in non-denaturing gels that is indicative of a novel enzyme complex. We present a model for how the pnp-71 mutation might affect autoregulation and mRNA decay based on the postulated role of the KH domain in RNA-protein and protein-protein interactions.

Amino Acid Sequence↗

PubMed1999

Intestinal parasitic infections.

Our understanding of the biology of several intestinal parasites has progressed considerably in the past year, especially in the area of molecular biology. Information from molecular and genetic analyses has been used increasingly to improve understanding of pathogenesis, to apply improved diagnostic methods, and to seek new vaccination strategies. There were fewer relevant clinical studies than in previous years, but some are notable. Control of helminth infections by mass chemotherapy in school age children appears an achievable goal in many communities. Vaccine trials against some protozoan infections continue to show promise in animal models.

Journal Article↗

PubMed1999

Macular lesions in leprosy: a clinical, bacteriological and histopathological study.

Among 150 untreated patients of leprosy, 19 had only macular lesions; three were of the indeterminate type, and eight each were of the tuberculoid and the borderline types, according to the Indian Association of Leprologists (IAL, 1981) classification. The clinical, bacteriological, and histopathological parameters of these 19 patients were studied both before and after six months of WHO Multi Drug Therapy (MDT/1982). A single macule was present in seven (36.84%) patients. In twelve (63.16%), two or more were seen. In eighteen (94.74%), one or more peripheral nerves were enlarged. The size of the macules varied from 5 to 15 cm, and there were no changes seen even after treatment. In most (94.74%) of the patients, the macules were hypopigmented. The surfaces were rough and dry in seven (36.84%) but smooth in the other twelve (63.16%). The margins were well defined in the seven (36.84%) patients with single macules but ill defined in the other twelve (63.16%). After six months of antileprosy treatment, the single macules showed some resolution. Slit skin smear examination was negative in all cases before and after treatment. Clinico-histopathological correlations were seen in only six (31.58%) patients; the clinical diagnoses were indeterminate and tuberculoid leprosy in three (15.79%) patients each. In the indeterminate group, the clinico-histopathological correlation was 100%; it was 37.50% in the tuberculoid group. There were no correlations between the clinical and histopathological parameters in thirteen (68.42%) cases. After six months of treatment, the histopathology became nonspecific in all patients. The lepromin test was positive in six (31.58%) patients; four were of the tuberculoid group and one each from the indeterminate and borderline leprosy groups. Hence, although macular lesions can be seen throughout the leprosy spectrum, it is difficult to correlate their clinical, bacteriological and histopathological parameters.

Adolescent↗

PubMed1999

Macular amyloidosis: etiological factors.

Macular amyloidosis is the commonest form of primary localized cutaneous amyloidosis; its etiology remains unclear. Various incriminating factors include genetics, sunlight, and friction. Seventy-five patients with a clinical diagnosis of macular amyloidosis (confirmed by at least two observers) were enrolled in the study. A detailed history was elicited in relation to the etiological factors and followed by cutaneous examination. Skin biopsy was performed in 44 patients. Amyloid deposits were demonstrated in 21 (48%) of the biopsies. The female to male ratio was over 3:1. Patients with skin type V had a more delayed onset than those with skin types III and IV. Two patients gave histories of regularly subjecting their skin to friction. There was no correlation between the sites affected and the sites subjected to friction, hair style of the patient, or the use of cosmetics. Family history was present in 7 (9.3%) patients. A majority, 44 (58.7%) of the patients, had involvement of both sun-exposed and sun-protected sites. To conclude, there was no direct correlation between macular amyloidosis and atopy, sunlight, or friction to the skin in our patients. Multiple factors may play a collective role in the genesis of macular amyloidosis to variable degrees. These include racial, familial, and environmental factors, atopy, sunlight, friction, and female gender.

Adolescent↗

PubMed1999

Presence of M. leprae in tissues in slit skin smear negative multibacillary (MB) patients after WHO-MBR.

This study looked for M. leprae in the lymph node, nerve and skin of multibacillary (MB) leprosy patients who become slit skin smear negative after the completion of WHO-MBR. Twenty-five WHO-MBR-treated multibacillary leprosy patients were studied; borderline lepromatous (BL) leprosy (n = 11) and lepromatous (LL) leprosy (n = 14)). Fifteen patients had reaction (erythema nodosum leprosum 11, upgrading reaction 4) either at presentation or during therapy. All patients attained slit skin smear negativity after WHO-MBR (range 24-39 months. Sixteen (64%) patients with multibacillary leprosy showed fragmented bacilli in skin and nerve biopsy or lymph node aspirates after WHO-MBR. Lymph node aspirates alone revealed M. leprae in seven patients, followed by nerve in two and skin in one patient. Four cases showed M. leprae at all sites followed by nerve and skin or lymph node in one case each. A pretreatment bacteriological index (BI) of 4+ or more was significantly associated with the presence of M. leprae at the end of treatment. Also, significantly more lymph node aspirates contained M. leprae in comparison with nerve or skin biopsies. All seven cases in whom treatment was extended beyond 24 months showed M. leprae in tissues even after attaining slit smear negativity. In conclusion, M. leprae persist in tissues after 2 years of WHO-MBR and patients with an initial BI of 4+ or more need to be closely followed up after stopping MDT.

Adolescent↗

PubMed1999

Human diabetic neovascular membranes contain high levels of urokinase and metalloproteinase enzymes.

PURPOSE: Retinal neovascularization is one of the leading causes of blindness. A crucial event in this process is the remodeling and penetration of the capillary basement membrane by migrating endothelial cells. This process requires proteolysis of basement membrane components by a variety of proteinases. The objective of the present study was to determine the expression of proteinases in human retinal tissues showing active neovascularization. METHODS: Epiretinal neovascular membranes surgically removed from patients with proliferative diabetic retinopathy were analyzed by zymography, and the types and amounts of proteinases present in the tissues were determined. Retinas from nondiabetic donor eyes served as control specimens. RESULTS: Both the high- (54 kDa) and low- (33 kDa) molecular-weight forms of urokinase were present at significantly higher levels in neovascular membranes than in normal retinas. The pro forms of the matrix metalloproteinases (MMP) MMP-2 and MMP-9 were significantly elevated in the neovascular membranes in comparison with levels in normal retinas. In addition, the active forms of these enzymes were present in the membranes, whereas there was no detectable level of the active forms in normal retinas. CONCLUSIONS: Human diabetic neovascular membranes contain high levels of urokinase and MMP. The increased activity of proteinases in the final common pathway of retinal neovascularization indicates that inhibition of these enzymes may be a useful therapeutic target as an alternative approach in the management of proliferative retinopathies.

Aged↗