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Biomedical subjects

A Sen

Publications and source records attributed to A Sen.

At least 109 records · Page 6Linked to original sources
PubMed1996

Quantitative assessment of beam perturbations caused by silicon diodes used for in vivo dosimetry.

PURPOSE: To measure the effect of silicon diode detectors used for in vivo dosimetry on beam characteristics and determine whether this effect is clinically significant. METHODS AND MATERIALS: Commercially available photon and electron diodes were placed on the central axis of photon and electron beams. The beam characteristics were measured for 6- and 10-MV photon and 6-20-MeV electron energies from a Varian Clinac 1800 medical linear accelerator. Water was used for the medium, and measurements were made for various clinically common field sizes and depths. RESULTS: Beam attenuations along the central axis were 10 and 7.5% for 6- and 10-MV photons, respectively. Electron beam dose reductions were between 13 and 25% for 20-6-MeV electrons. Photon beam flatness varied up to 7% at different depths, but the symmetry was not affected much. Electron beam flatness and symmetry were significantly changed to as much as 18 and 6%, respectively. CONCLUSION: Use of diode detectors on central axis of photon and electron beams for in vivo dosimetry causes significant attenuation and alteration of the beam characteristics. The percentage of the volume affected is significant (e.g., 23% of the volume in a 4 x 4 field gets 10% less dose for a 6-MV photon beam), especially if these diodes are used for in vivo dosimetry on the central axis every day for every treatment, as is done in some clinics. Other beam parameters such as penumbra and skin dose are also affected. It is therefore recommended that the diodes be used only as needed.

Humans↗
PubMed1996

Thermodynamics of the interactions of sanguinarine with DNA: influence of ionic strength and base composition.

Using a combination of spectrophotometric and spectrofluorimetric techniques, we report the first thermodynamic characterization of sanguinarine binding to a series of natural and synthetic host DNA duplexes over a wide range of temperature and sodium concentration. The binding isotherms fit reasonably well to the neighbour exclusion model. The salt and temperature dependence of the binding constants is used to estimate the thermodynamic parameters involved in the interaction of the alkaloid with DNA. The resulting binding data are found to be sensitive to the ionic strength of the medium, base composition and sequence of base pairs. When the sodium ion concentration is increased from 0.005 M to 0.5 M, the binding free energy changes vary in a range from -8.47 to -7.1 kcal mol-1, which corresponds to a binding constant range from 1.85 x 10(6) to 1.8 x 10(5) M-1 at 20 degrees C. More distinct is the spread in the binding enthalpy changes which range from -6.35 to -2.62 kcal mol-1 corresponding to binding entropy changes from +7.22 to +15.3 cal K-1 mol-1 at 20 degrees C. On the other hand when the GC content of the host DNA duplexes is increased, the binding free energy varies in a range from -7.28 to -8.58 kcal mol-1 with the binding enthalpy changes ranging from -0.46 to -14.31 kcal mol-1, while corresponding binding entropy changes range from +23.3 to -19.56 cal K-1 mol-1 at 20 degrees C. Sanguinarine binding to natural DNAs and homo- and heteropolymers of AT is characterized by negative enthalpy changes and positive entropy changes, while binding to homo- and heteropolymers of GC is reflected by both negative enthalpy changes and entropy changes. Possible molecular contributions towards sign and magnitude of the thermodynamic parameters and their dependence on ionic strength, base composition and sequences, are discussed.

Alkaloids↗
PubMed1996

Structural study of the interaction between the SIV fusion peptide and model membranes.

It has been shown that there is a correlation between the fusogenecity of synthetic peptides corresponding to the N-terminal segment of wild-type and mutant forms of simian immunodeficiency virus gp32 (SIV) and their mode of insertion into lipid bilayers. Fusogenic activity is only observed when the peptide inserts into the bilayer with an oblique orientation. Since bilayer destabilization is a necessary step in membrane fusion, we investigate how fusion peptides, which insert at different orientations into lipid bilayers, structurally affect model membranes. We use X-ray diffraction to investigate the structural effects of two synthetic peptides on three different lipid systems. One peptide corresponds to the wild-type sequence (SIVwt), which inserts into the membrane at an oblique angle and is fusogenic. The other peptide has a rearranged sequence (SIVmutV), inserts into the membrane along the bilayer normal, and is nonfusogenic. Our results are expressed through different structural effects, which depend on the lipid system: for example, (i) disordering of the L alpha phase as evidenced by the broadening of the diffraction peaks, (ii) morphological convertion of multilamellar vesicles into unilamellar vesicles, (iii) decrease of the hexagonal phase cell parameter when SIVwt is added, and (iv) change in the conditions for the formation of cubic phases as well as its kinetic stability over a range of temperatures. Some of these observations are explicable based on the fact that the SIVwt destabilizes bilayers by inducing a negative monolayer curvature, while the SIVmutV destabilizes bilayers by inducing a positive monolayer curvature. Finally, we present a model which describes how these findings correlate with fusogenic activity and fusion inhibitory activity, respectively.

Amino Acid Sequence↗
PubMed1996

Serum cortisol and prolactin levels in childhood paroxysmal disorders.

Postictal serum prolactin and cortisol levels were measured in 37 children having either epilepsy, febrile seizure or syncopal attack and in 37 normal controls. Blood samples were obtained within 1.5 h following the seizure episode. All serum levels were compared between each group and the control groups. Significantly higher (P < 0.005) prolactin levels (56.64 +/- 34.78 ng/mL) were found in the epileptic group, compared to the levels in children with febrile seizures (21.72 +/- 12.92 ng/mL), syncope attacks (13.88 +/- 5.27 ng/mL) and the control group (14.32 +/- 5.05 ng/mL). In contrast, serum cortisol levels were non-specifically elevated in children with epilepsy, febrile seizures and syncopal attacks. Cortisol secretion appears to be non-specifically elevated in all stressful events. Elevated prolactin levels may be helpful in differentiating epilepsy from febrile seizures and syncope.

Adolescent↗
PubMed1995

Technetium-99m-HMPAO SPECT cerebral blood flow study in children with craniosynostosis.

UNLABELLED: Premature closure of cranial sutures (primary craniosynostosis) in children leads to characteristic skull deformities and prevents the constricted brain from growing normally. Although the cause remains unknown, several etiological factors have been cited. Recently, hypovascularity has been reported as a possible cause of craniosynostosis. METHODS: In a prospective study regional cerebral blood flow studies were carried out with 99mTc-HMPAO SPECT in seven children with craniosynostoses. Five preoperative and six postoperative studies were conducted and the results correlated with radiological and surgical findings. RESULTS: Preoperative studies revealed regional hypovascularity in the underlying cerebral hemisphere, corresponding to the fused sutures. Postoperative studies revealed disappearance of these perfusion defects in most cases, indicating normalization of perfusion following surgical decompression. CONCLUSION: This study establishes the presence of cerebral hypovascularity in craniosynostoses and suggests that early surgery and release of craniostenosis is essential to achieve optimum perfusion and brain development.

Brain↗
PubMed1995

Tissue- and species-dependent expression of sheep lung microsomal cytochrome P4502B(LgM2).

Expression of sheep lung microsomal cytochrome P4502B(LgM2) isozyme was determined in lung and liver preparations from rabbits, rats, sheep, cows and humans. Several tissues of sheep such as lung, liver, adrenal, kidney, ovary, intestine, muscle, spleen, pancreas and brain were also examined. Tissue homogenates were analyzed by Western-blotting with an antibody raised against purified sheep lung P4502B(LgM2) isozyme in rabbits. This isozyme was detected in lung samples from every species examined. Homologues of cytochrome P4502B(LgM2) were expressed in livers of sheep and rabbits but not in those of humans and cows. Although homologous forms of P4502B(LgM2) were not expressed in sheep brain, ovary, pancreas, spleen and muscle tissues, they were expressed in sheep adrenal, intestine and kidney.

Animals↗
PubMed1994

Interaction of sanguinarine iminium and alkanolamine form with calf thymus DNA.

The interaction of sanguinarine iminium form (structure I) and sanguinarine alkanolamine form (structure II) with calf thymus DNA has been studied in buffer of pH 5.2 and pH 10.5, respectively, where the physicochemical properties of DNA remain unchanged. The binding of sanguinarine iminium form to DNA is characterized by hypochromism and bathochromism in the absorption band, quenching of fluorescence intensity, increase in fluorescence polarization anisotropy, increase in positive and negative ellipticity of DNA, sign and magnitude of the thermodynamic parameters and increase in contour length of sonicated rodlike duplex DNA indicating that it binds to DNA by a mechanism of intercalation. In contrast, sanguinarine alkanolamine form does not show (i) any significant change in fluorescence polarization anisotropy, (ii) alteration of B form structure of DNA and (iii) increase in contour length of DNA indicating that it does not bind to DNA. But at a very high concentration of DNA, the alkanolamine form is influenced to form an iminium-DNA complex.

Alkaloids↗
PubMed1994

In vivo effects of the anesthetic, benzocaine, on liver microsomal cytochrome P450 and mixed-function oxidase activities of gilthead seabream (Sparus aurata).

Gilthead seabreams were exposed to benzocaine, 4-aminobenzoic acid ethyl ester, 57 mg/l in sea water for 3 min, daily, for 2 or 3 consecutive days. The fish were killed 20 hr after the last treatment. Benzocaine treatment for 2 or 3 days resulted in 57% and 67% inhibition of liver microsomal aniline 4-hydroxylase and ethylmorphine N-demethylase activities, respectively. The total cytochrome P450 content of fish liver microsomes was unaltered following the 2-day benzocaine treatment. However, additional 3 min benzocaine treatment on day 3 reduced cytochrome P450 level by 50%. Benzocaine produced type II difference spectra with rabbit liver microsomes. Difference spectra of fish liver microsomes elicited by benzocaine were complex. The position of peak and intensity were greatly influenced by the concentration of benzocaine.

Animals↗
PubMed1994

Effects of in vivo benzo(a)pyrene treatment on liver microsomal mixed-function oxidase activities of gilthead seabream (Sparus aurata).

Benzo(a)pyrene [B(a)P] treatment of gilthead seabream, 25 mg/kg, i.p. for 5 consecutive days, did not cause any significant changes in ethylmorphine N-demethylase and aniline 4-hydroxylase activities of liver microsomes. The same treatment did not alter the liver microsomal cytochrome b5 content, NADH-cytochrome b5 reductase and NADPH-cytochrome P450 reductase activities. However, benzo(a)pyrene treatment caused a 2-3-fold increase in 7-ethoxyresorufin O-deethylase (7-EROD) activity of gilthead seabream liver microsomes. Although, upon treatment, total cytochrome P450 content of liver microsomes increased about 1.7-fold in 1990 fall, no such increase was observed in spring 1991. However, a new cytochrome P450 with an apparent M(r) of 58,000 was observed on SDS-PAGE of liver microsomes obtained from benzo(a)pyrene treated gilthead seabream. Besides, in vitro addition of 0.2 x 10(-6) M benzo(a)pyrene to the incubation mixture inhibited 7-ethoxyresorufin O-deethylase activity by 93%. Gilthead seabream liver microsomal 4-ethoxyresorufin O-deethylase activity was characterized with respect to substrate concentration, amount of enzyme, type of buffer used, incubation period and temperature.

Animals↗