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Biomedical subjects

M Saha

Publications and source records attributed to M Saha.

At least 19 recordsLinked to original sources
PubMed1997

Differential expression of Xenopus ribosomal protein gene XlrpS1c.

Components of the translational machinery of the cell, including ribosomal proteins, are generally considered to be clear examples of housekeeping genes with a spatially ubiquitous distribution of messenger RNA during embryonic development. Here we present data based upon in situ hybridization experiments as well as RNase protection assays, demonstrating that Xenopus ribosomal protein gene S1 is differentially expressed in a complex and spatially distinct pattern during embryogenesis. We observed dramatically high levels of expression in some tissues, such as the branchial arches, otic vesicles, optic vesicles and somites and virtually no expression in other tissues, such as the cement gland, epidermis and notochord. Moreover, ribosomal protein genes S22, L1, and L5 display expression patterns nearly identical to S1. Our data is consistent with a model of ribosomal gene expression according to which ribosomal protein genes (or perhaps a subset of ribosomal protein genes) may be expressed at low levels in all tissues, but are abundantly expressed in other cell types reflecting a dynamic and complex pattern of transcriptional control throughout embryonic development.

Amino Acid Sequence↗
PubMed1997

Retinoic acid can block differentiation of the myocardium after heart specification.

While a number of transcription factors that are likely to play a role in cardiac differentiation have recently been described, the signals that lead to the expression of these factors remains poorly understood. Here we report that exposure of Xenopus embryos to continuous low levels of all-trans retinoic acid (RA), starting at the time of neural fold closure, blocks expression of myocardial differentiation markers. The development of the remainder of the embryo is relatively normal, suggesting that retinoic acid can act rather specifically on myocardial precursors. Indeed, the pattern of endocardial gene expression appears to remain unaffected by RA treatment. Although RA blocks myocardial gene expression, a superficially normal heart tube forms. The heart tube, however, fails to loop during subsequent development and never forms beating tissue. The effect of RA treatment on expression of myocardial genes is developmental stage dependent, since no influence is observed after myocardial differentiation has commenced. These data indicate that a vital component of the myocardial determination pathway is sensitive to retinoid signaling.

Animals↗
PubMed1997

Ultrasonographic study of 793 foetuses: measurement of normal foetal kidney lengths in Bangladesh.

It is well known that, structurally, the people of Asia are shorter than Europeans. The size of different organs of the foetus may also vary accordingly. To assess this, 793 foetuses between 16 and 40 weeks' gestation were studied and 1175 kidneys were measured on ultrasonograms. Only normal pregnancies were included in the study. Our results show that, in the main, the mean length of foetal kidneys in the present study is either slightly higher or similar to that previously reported by many authors. In this study, the average kidney length at full term is 3.95 cm. An excellent correlation was seen between gestational age, biparietal diameter, femoral length and renal length measurement.

Bangladesh↗
PubMed1995

General method for determining ethylene oxide and related N7-guanine DNA adducts by gas chromatography-electron capture mass spectrometry.

A 112-micrograms sample of DNA was spiked with 103 pg of N7-(2'-hydroxyethyl)guanine and 100 pg of N7-(2'-hydroxyethyl-d4)guanine, the internal standard. The sample was subjected to the following sequence of steps: heating at 100 degrees C, precipitation of the DNA with HCl, reaction with nitrous acid to form the corresponding xanthines, reaction twice with pentafluorobenzyl bromide (first to derivatize NH, then OH), solid-phase extraction on silica and detection by gas chromatography-electron capture mass spectrometry. The absolute, overall yield of final product for both the analyte and internal standard was 9.7%. Conveniently, the three chemical reactions are conducted sequentially in the same vial and, aside from a washing step, are separated only by evaporations. Corresponding N7-guanine methyl, phenyl and styrene oxide adducts were detected at about the 50-ng level by the procedure, to indicate the generality of the method.

DNA↗
PubMed1995

Observations suggesting a high incidence of exercise-induced severe mitral regurgitation in patients with mild rheumatic mitral valve disease at rest.

OBJECTIVES: The aim of this study was to determine the hemodynamic effects of upright bicycle ergometry in symptomatic patients with mild, mixed mitral stenosis and regurgitation. BACKGROUND: Patients with seemingly mild rheumatic mitral valve disease often complain of exertional dyspnea or fatigue. These symptoms are usually ascribed to flow-dependent increases in the gradient across the stenotic mitral valve. Although catheterization studies in these patients may demonstrate an increase in mitral valve gradient proportional to an increase in cardiac output, this approach does not specifically address the underlying mechanism of any observed increases in mitral gradient or left atrial (i.e., pulmonary capillary wedge) pressure. Exercise echocardiography is uniquely suited to the dynamic assessment of exercise-induced hemodynamic changes. METHODS: Fourteen symptomatic patients with exertional dyspnea and mild mitral stenosis and regurgitation at rest performed symptom-limited upright bicycle ergometry with quantitative two-dimensional, Doppler and color Doppler echocardiographic analysis. RESULTS: Average pulmonary artery systolic pressure in the 13 patients with adequate spectral signals of tricuspid regurgitation increased from 36 +/- 5 mm Hg (mean +/- SD) at rest to 63 +/- 14 mm Hg at peak exercise (p < 0.001). The mean transmitral pressure gradient in all patients increased from 4.5 +/- 1.4 mm Hg at rest to 12.7 +/- 2.7 mm Hg at peak exercise (p < 0.001). Five patients developed severe mitral regurgitation during exercise. CONCLUSIONS: Patients with exertional dyspnea and mild mitral stenosis and regurgitation at rest demonstrate a marked increase in pulmonary artery systolic pressure and mean transmitral pressure gradient during dynamic exercise. In a subset of these patients, marked worsening of mitral regurgitation appears to be the underlying mechanism of this hemodynamic deterioration. Because of the small sample size, this novel observation must be considered preliminary with respect to the true prevalence of exercise-related development of severe mitral regurgitation. If additional studies confirm the importance of this phenomenon, it has important implications for the management of patients with rheumatic mitral valve disease.

Adult↗
PubMed1993

Chemical transformation/derivatization of O6-methyl- and O6-(hydroxyethyl)guanine for detection by GC-EC/MS.

In this project we set out to make an important class of DNA adducts, comprising O6-alkyl and O6-(hydroxyalkyl)guanines, susceptible to sensitive detection by GC-EC/MS. While existing literature indicated that pentafluorobenzylation would be useful for the ring NH site on these compounds, how to best overcome the polarity of the exocyclic NH2 and OH groups, without losing the O6-alkyl moiety, was less clear. Working with O6-methylguanine and O6-(2'-hydroxyethyl)guanine as representative analytes, we found that the NH2 group could be converted into fluoro without loss of the O6 substituent. For the OH group, a comparison of several derivatives (OR') led to R' = tert-butyl as the best choice at this stage. The latter work, especially via NMR, also allowed exact structural assignments to be made for the N7 and N9 pentafluorobenzyl isomeric derivatives that formed. Of these R' derivatives, the N7 isomers migrated slower on silica-TLC, had higher GC retention times, had lower responses by GC-EC/MS, and were preferentially destroyed as the GC column aged. However, the N9 isomer was slower on TLC when the OH was not derivatized. This behavior was rationalized using a concept of "polar footprint" for the derivatives. The concept also seemed to explain the puzzling GC-EC/MS behavior of some related compounds in our laboratory. Apparently the polar footprint should be minimized in designing derivatives for trace detection by GC-EC/MS.

Chromatography, Thin Layer↗
PubMed1993

4-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzyl bromide as a new electrophoric derivatizing reagent.

4-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzyl bromide (TTBB) was synthesized in a single step from alpha,alpha,alpha,2,3,5,6-heptafluoro-p-xylene. The purpose of TTBB is to function as an analogue of pentafluorobenzyl bromide (PFBB) in electrophoric derivatization reactions prior to detection by gas chromatography-electron-capture negative ion mass spectrometry (GC-ECNI-MS). In more detail, it was anticipated that TTBB could be used along with, or as a substitute for, PFBB to help control some interferences and confirm results. This is because a TTBB-product (of an analyte) would have different retention and sometimes m/z characteristics than a corresponding PFBB product in GC-ECNI-MS, while the two products should be similar in their ease of formation and yields. Results demonstrating these expectations were achieved by derivatizing and detecting two analytes with these reagents: N7-(2-hydroxyethyl)xanthine, and 2,3-pyrenedicarboxylic acid.

Fluorobenzenes↗
PubMed1993

Primary contribution of the injector to carryover of a trace analyte in high-performance liquid chromatography.

When a low-nanogram amount of N1,N3-bis-(pentafluorobenzyl)-N7-(2- [pentafluorobenzyloxy]ethyl)xanthine was subjected to HPLC, low-picogram amounts of the compound could be detected subsequently (off-line by gas chromatography-electron-capture negative-ion mass spectrometry) after injection of pure mobile phase. This was in spite of significant, intermediate washing of the injector and column. It was determined that essentially 99.9% of this analyte contamination came from the injector. Use of two injectors is a practical remedy for this problem.

Artifacts↗
PubMed1993

High-performance liquid chromatography versus solid-phase extraction for post-derivatization cleanup prior to gas chromatography-electron-capture negative-ion mass spectrometry of N1,N3-bis-(pentafluorobenzyl)-N7- (2-[pentafluorobenzyloxy]ethyl)xanthine, a product derived from an ethylene oxide DNA adduct.

N7-(2-Hydroxyethyl)xanthine (N7-HEX), as a standard, has been measured at the low picomole level by the following sequence of steps: (1) derivatization with pentafluorobenzyl bromide; (2) post-derivatization sample cleanup by reversed-phase high-performance liquid chromatography (HPLC) or silica solid-phase extraction; and (3) separation/detection by gas chromatography electron-capture negative-ion mass spectrometry (GC-ECNI-MS). The average yield of product from the two sample cleanup procedures applied to 95 pg (0.48 pmol) of N7-HEX was comparable: 60% for HPLC; 56% for solid-phase extraction. The reaction blanks (0 pg N7-HEX) showed an interfering GC-ECNI-MS peak after HPLC cleanup. This problem was not encountered with solid-phase extraction, which, along with its greater convenience, made it the preferred technique for post-derivatization sample cleanup.

Chromatography, High Pressure Liquid↗
PubMed1993

Footwear dermatitis.

We conducted a study to determine the prevalence and clinical patterns of footwear dermatitis, patch testing 50 patients with suspected footwear dermatitis and 30 controls with 22 allergens of a shoe series (Chemotechnique Diagnostics AB, Malmö, Sweden). The overall prevalence among contact dermatitis cases was 11.7%. The dorsa of the feet and toes were the commonest sites involved. 70% of patients showed sensitivity to footwear allergen(s), as opposed to 6.67% of controls. Potassium dichromate and colophony were the commonest sensitizers. Other sensitizers were the rubber accelerators 2-mercaptobenzothiazole (MBT) and diphenylguanidine (DPG) and a dye p-aminoazobenzene. Of the 23 patients patch tested with pieces or scrapings of footwear, only 3 showed positive reactions. We recommend that there should be primary and secondary footwear screening series to detect the responsible allergens, with the ultimate objective of providing correct nonallergenic footwear for our patients, with the help of manufacturers and research institutes.

Adolescent↗