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Biomedical subjects

A K Tyagi

Publications and source records attributed to A K Tyagi.

At least 19 recordsLinked to original sources
PubMed2006

Cytomegalovirus retinitis in chronic lymphocytic leukaemia.

PURPOSE: To describe a rare association of cytomegalovirus (CMV) retinitis. PATIENTS AND METHODS: Report of three patients with chronic lymphocytic leukaemia (CLL) who developed CMV retinitis. RESULTS: The diagnosis was established by the detection of CMV DNA by polymerase chain reaction analysis of aqueous and/or vitreous humour. CD4+ T-lymphocyte count was reduced in two patients and normal in the third one. There was bilateral involvement in two of the three patients. There was delay of 8-10 months in diagnosis. The visual outcome was poor in four out of the five eyes involved owing to optic atrophy or total retinal detachment with proliferative vitreoretinopathy. CONCLUSION: Increased awareness of CMV retinitis in patients who have received immunosuppression for haematological malignancies, such as CLL, could lead to earlier diagnosis and possibly better visual outcome.

Aged↗
PubMed2006

Dilated examination of patients referred with minor lid complaints--is it necessary?

OBJECTIVE: To evaluate whether dilated fundus examination is necessary on patients presenting to clinic with lid complaints and normal vision. METHODS: Patients with lid complaints were recruited from general and emergency clinics. Patients with visual symptoms or previous ophthalmic history were excluded. Subjects were examined by a junior ophthalmologist with slit-lamp biomicroscopy and Goldmann tonometry. Dilated posterior segment examination was performed with a Volk lens and the peripheral retina was examined with a three-mirror contact lens. RESULTS: A total of 100 patients (200 eyes) were recruited, 63 females and 37 males with an average age of 45 years (SD of 19 years). The majority of lid abnormalities were chalazia (66) and papilloma (21). Posterior segment findings were early cataracts in five cases (eight eyes), macular drusen in three cases (five eyes), peripheral retinal lattice degeneration in two cases (three eyes), retinal pigment epithelial changes in one case (two eyes), a choroidal naevus in one eye, choroidal atrophy in one eye, and one case with asymmetric disc cupping. Six patients were seen by senior ophthalmologists and all were discharged after the first visit. CONCLUSIONS: In our sample of 100 patients presenting with lid complaints and normal visual acuity, dilated examination revealed no sight-threatening conditions that required further treatment or regular follow-up. Therefore, a single episode of screening for nonspecified retinal disease in a group with no particular risk factors is an inefficient screening method.

Adult↗
PubMed2006

Correlation of phase transition with the change in TL characteristics in CaSO4:Dy phosphor--effect of thermal treatment.

The study is aimed at optimising the glow curve structure of CaSO4:Dy phosphor for dosimetric purpose and also to understand the observed changes owing to thermal treatment in the thermoluminescence (TL) sensitivity and glow curve structure. The reversible changes in the intensities of the lower temperature satellite peak and the main dosimetric glow peak with temperature of thermal treatment in the temperature range 400-700 degrees C indicates the interconversion of defect complexes responsible for the glow peaks in CaSO4:Dy. Phosphor samples subjected to thermal treatment in temperature range beyond 800 degrees C, showed irreversible changes in the intensities of the lower temperature and dosimetric peaks. The changes in TL characteristics of the phosphor for thermal treatments >800 degrees C are attributed to the partial phase transition in the phosphor as confirmed by the XRD and TG/DTA analysis of the phosphor.

Calcium Sulfate↗
PubMed2006

Nanocrystalline ceria powders through citrate-nitrate combustion.

Nanocrystalline ceria powders have been synthesized by combustion technique using citric acid as a fuel and nitrate as an oxidizer. The auto-ignition of the gels containing cerium nitrate and citric acid resulted in ceria powders. A theory based on adiabatic flame temperature for different citric acid-to-cerium nitrate molar ratios has been proposed to explain the nature of combustion reaction and its correlation with the powder characteristics. Specific surface area and primary particle size of the ceria powder obtained through fuel-deficient precursor was found to be approximately = 127 m2/g and 2.5-10 nm, respectively. The combustion synthesized ceria powder when cold pressed and sintered in air at 1250 degrees C for 1 hour resulted in approximately = 96% of its theoretical density with sub-micron grains.

Cerium↗
PubMed2006

Synthesis of nanocrystalline La(Ca)CrO3 through a novel gel combustion process and its characterization.

La(Ca)CrO3 (LCC) powders have been prepared through a novel gel combustion route using metal nitrates as oxidizers and ethylene diamine tetraacetic acid (EDTA) as a fuel. The process involves the combustion of a viscous gel obtained through mixed metal nitrate-EDTA solution. The effect of amount of EDTA used in the process on the nature of combustion reaction, phase formation, and densification has been studied. It was found that use of the fuel-rich precursor facile in controlling the reaction, which in turn helps in the scale up of the batch size. The calcination of the fuel-rich gel precursor at 650 degrees C resulted in the well-crystalline LCC along with a small amount of calcium chromate as a secondary phase. The HRSEM studies on the powder showed agglomerated nanoparticles. The average agglomerate size was found to be 0.54 microm. The cold pressing and sintering of the calcined powder at 1250 degrees C resulted in the mono-phasic La0.70Ca0.30CrO3 with 94% of its theoretical density. The sintered sample exhibited conductivity of 51 S/cm at 1000 degrees C. The average linear thermal expansion coefficient was found to be 10.3 x 10(-6) degrees C(-1).

Chromium Compounds↗
PubMed2005

Mapping of a major QTL for pre-harvest sprouting tolerance on chromosome 3A in bread wheat.

Quantitative trait loci (QTL) analysis was conducted for pre-harvest sprouting tolerance (PHST) in bread wheat for a solitary chromosome 3A, which was shown to be important for this trait in earlier studies. An inter-varietal mapping population in the form of recombinant inbred lines (RILs) developed from a cross between SPR8198 (a PHS tolerant genotype) and HD2329 (a PHS susceptible cultivar) was used for this purpose. The parents and the RIL population were grown in six different environments and the data on PHS were collected in each case. A framework linkage map of chromosome 3A with 13 markers was prepared and used for QTL analysis. A major QTL (QPhs.ccsu-3A.1) was detected on 3AL at a genetic distance of approximately 183 cM from centromere, the length of the map being 279.1 cM. The QTL explained 24.68% to 35.21% variation in individual environments and 78.03% of the variation across the environments (pooled data). The results of the present study are significant on two counts. Firstly, the detected QTL is a major QTL, explaining up to 78.03% of the variation and, secondly, the QTL showed up in all the six environments and also with the pooled data, which is rather rare in QTL analysis. The positive additive effects in the present study suggest that a superior allele of the QTL is available in the superior parent (SPR8198), which can be used for marker-aided selection for the transfer of this QTL allele to obtain PHS-tolerant progeny. It has also been shown that the red-coloured grain of PHS tolerant parent is not associated with the QTL for PHST identified during the present study, suggesting that PHS tolerant white-grained cultivars can be developed.

Chromosome Mapping↗
PubMed2005

Structural characterization, expression analysis and evolution of the red/far-red sensing photoreceptor gene, phytochrome C (PHYC), localized on the 'B' genome of hexaploid wheat (Triticum aestivum L.).

Phytochromes are a family of red/far-red light perceiving photoreceptors. The monocot phytochrome family is represented by three members, PHYA, PHYB and PHYC. We have isolated and characterized the first PHY gene member (TaPHYC) from common wheat, Triticum aestivum var. CPAN1676. It codes for a species of the photoreceptor, phyC, which is known to be light-stable in all plants analyzed so far. A sequence of 7.2 kb has been determined, which includes 3.42 kb of coding region. This is the second full-length PHYC gene sequenced from a monocot (first was from rice). TaPHYC gene shares structural similarities with the rice PHYC containing four exons and three introns in the coding region. The 5' UTR is 1.0-kb-long and harbors an upstream open reading frame (URF) encoding 28 aa. Southern blot analysis of TaPHYC indicates that it represents single locus in the wheat genome, although the possibility of additional loci cannot be completely ruled out. Chromosomal localization using nullisomic-tetrasomic lines of Triticum aestivum var. Chinese Spring places TaPHYC on chromosome 4B. PHYC represents a constitutively expressed gene in all the organs tested and under light/dark conditions. However, PHYC was found to be developmentally regulated showing maximal expression in 3-day-old dark-grown seedlings, which declined thereafter. In silico analysis has also been done to compare TaPHYC gene with the partial sequences known from other wheat species and cultivars. The presence of a topoisomerase gene immediately downstream of the PHYC gene, both in rice and wheat genomes, presents yet another example of synteny in cereals and its possible significance has been discussed.

Amino Acid Sequence↗
PubMed2005

Effectiveness of emergency argon laser retinopexy performed by trainee doctors.

OBJECTIVE: To report the outcomes following treatment of retinal tears with argon laser photocoagulation by trainee doctors as an emergency procedure. METHODS: Retrospective, case note analysis of 100 consecutive patients treated between August 2000 and December 2002 at a tertiary referral hospital. RESULTS: The case notes of 100 consecutive patients (41 male, 59 female) with a mean age of 57.5 years were reviewed. Out of these 90 were symptomatic. The follow-up period ranged from 1 week to 8 months. All patients had argon laser retinopexy in the Emergency department. The on-call Registrar performed the procedure on 94 patients, and Senior House Officers performed the other six. A total of 98 procedures were performed on the slit lamp and two by laser indirect ophthalmoscope. In all, 24 patients needed further treatment with either indirect laser, cryotherapy, or surgery. At the last follow-up, all the patients had anatomically attached retinas. CONCLUSION: A significant proportion of patients (24%) undergoing laser retinopexy in the emergency department needed further treatment. The relative inexperience in using the indirect laser, together with its unavailability in the Emergency department, may be the contributory factors. There seems to be scope for supervised training in using the laser indirect ophthalmoscope for the trainees in the Ophthalmic Emergency department.

Adult↗
PubMed2005

Does vitreoretinal surgery under local anaesthesia result in missed fellow eye pathology?

PURPOSE: There has been a significant increase in the number of vitreoretinal procedures being performed under local anaesthesia over the past few years. This trend is expected to continue. This study was performed to investigate whether by undertaking retinal detachment surgery under local anaesthesia fellow eye examination was compromised. DESIGN: This was a prospective, consecutive, blind, observational study. METHODS SETTING: This study was performed at a tertiary referral vitreoretinal unit in a teaching hospital. STUDY POPULATION: In all, 108 consecutive patients undergoing retinal detachment surgery under general anaesthesia were included. OBSERVATION PROCEDURES: Patients were examined independently by different retinal surgeons pre- and intraoperatively. MAIN OUTCOME MEASURES: The findings of the two examiners were compared and differences were analysed. RESULTS: There were 108 patients in this study, 57 of these were males and 51 females. The mean age was 59.01 years (range 16-91). Of these 108 eyes, 48/108 (49.08%) the preoperative examination was regarded as unsatisfactory by the examiner. Over 34% of eyes had fellow eye pathology when examined preoperatively but there were nine (8.33%) eyes in which additional lesions were found intraoperatively. CONCLUSION: General anaesthesia should be considered for patients in whom preoperative fellow eye examination is unsatisfactory.

Adolescent↗
PubMed2005

Increased expression of Mycobacterium tuberculosis 19 kDa lipoprotein obliterates the protective efficacy of BCG by polarizing host immune responses to the Th2 subtype.

Mycobacterium tuberculosis can not only neutralize immune effector functions, but also has the ability to modulate host-signalling cascades involved in the development of these responses. The 19 kDa antigen (Rv3763), a lipoprotein of M. tuberculosis, elicits high levels of interleukin (IL)-12 from macrophages in addition to its powerful immunomodulatory properties, leading to suppression of antigen-presentation signalling cascades. The present study was aimed at analysing the effect of overexpression of this antigen on the immunostimulatory properties of M. bovis Bacille Calmette-Guerin (BCG). We have constructed a recombinant BCG strain (rBCG19N) producing higher levels of the 19 kDa antigen in both the cytoplasmic (approximately eightfold) and extracellular (approximately fivefold) fractions as compared to the wildtype BCG. Immunization of mice with rBCG19N elicited high levels of interferon-gamma (IFN-gamma) and relatively low levels of IL-10 against the purified 19 kDa antigen. However, in response to total BCG sonicate, mice immunized with rBCG19N produced significantly high levels of IL-10 with relatively very low levels of IFN-gamma. This polarization of the host immune responses towards T-helper 2 subtype resulted in complete abrogation of the protective efficacy of BCG, when rBCG19N was used as a live vaccine against M. tuberculosis challenge in guinea pigs.

Animals↗
PubMed2005

Utilization of composted sugar industry waste (pressmud) to improve properties of sodic soil for rice cultivation.

Sulphitation pressmud (SPM) and its composts were prepared by heap, pit, NADEP and vermicomposting methods and their effects were compared with soil properties and growth, yield and nutrient uptake by rice in a sodic soil under pot conditions. Application of 15 t ha(-1) SPM and its different composts significantly increased the plant height and dry matter accumulation at different intervals, grain and straw yields and N, P and K uptake by the crop over the control. NADEP compost of SPM alone recorded the maximum and significant plant height by 8.5 to 19.3% and plant dry matter by 14.6 to 32.8% over the raw SPM at different intervals. NADEP composts of SPM alone and SPM + rice straw were also found to be superior than raw SPM by recording 34.8 and 27.8% more grain yield respectively. The SPM composts prepared by NADEP and SPM by vermicomposting methods significantly accumulated higher N and K in rice grains and straw, while NADEP compost of SPM and SPM + rice straw recorded more P in grains and straw than raw SPM. Application of SPM and its composts reduced the pH, EC and bulk density of the soil after rice harvesting, though the reductions were not significant in comparison to the control. However, these treatments increased the soil organic C by 33.33 to 69.0%, available N by 41.4 to 74.8%, available P by 47.1 to 97.8%, available K by 11.8 to 59.2% and available S by 10.3 to 90.7% over the control. NADEP composts, in general, were found to be superior than the raw SPM and other composts in residual soil nutrient content after rice crop.

Agriculture↗
PubMed2004

Inhibition of Photosystem I and Photosystem II in Wheat Seedlings with their Root-shoot Transition Zones Exposed to Red Light.

The present study was conducted to observe the role of the root-shoot transition zone in the development of PS I and PS II in red light. The development of PS II and PS I was severely inhibited when root-shoot transition zones of wheat seedlings were exposed to red light (670 nm) of intensity 500 micromol m(-2) s(-1). Chlorophyll biosynthesis was also inhibited in these seedlings. Most of the PS I and PS II proteins (D1, LHCPII, CP47, OEC33) and their transcript levels were severely inhibited but cyt b6f complex proteins were only partially inhibited. Protein and transcript levels of Rubisco large subunit and protochlorophyllide (Pchlide) biosynthesis were also severely inhibited in these seedlings. When incubated in the dark with or without the precursor of chlorophyll biosynthesis ALA, these plants accumulated most of the Pchlide, as non-phototransformable Pchlide, suggesting low activity of NADPH:protochlorophyllide oxidoreductase (EC 1.6.99.1) in these plants. These effects were not observed when the seedlings were grown in red light with their root-shoot transition zones covered. These results suggest that the root-shoot transition zone plays an important role in the overall greening process involving transcription and translation of photosynthetic genes.

Journal Article↗
PubMed2004

Surgical treatment and outcome of patients with giant retinal tears.

OBJECTIVE: To report the management and outcome in retinal detachments associated with giant retinal tears (GRTs). METHODS: Retrospective, case note analysis of patients treated between November 1991 and June 2002 at a tertiary referral hospital. RESULTS: The case notes of 29 patients (24 males, 5 females) with a follow-up ranging from five months to 7 years were reviewed. In all, 25 eyes had retinal detachments with macular involvement and 10 patients had myopia more than 6 D. All patients underwent vitrectomy. A total of 23 patients had heavy liquid and 16 had scleral explants; 28 patients had silicone oil and one had C3F8 tamponade. Intraoperative complications included lens trauma and iatrogenic GRT. Six eyes had recurrent retinal detachment and needed multiple surgical procedures. At the last follow-up, 25 patients had anatomically attached retinas. In all, 18 fellow eyes were treated prophylactically. Three patients had total retinal detachment and marked PVR. The visual acuity improved in 20 eyes. CONCLUSION: GRTs are more common in patients with high myopia. With newer techniques of surgical treatment of GRTs, the anatomical and visual outcomes are more favourable.

Adolescent↗
PubMed2003

Studies on the immunogenic potential of plant-expressed cholera toxin B subunit.

Nicotiana tabacum var. Samsun was transformed via Agrobacterium-mediated transformation with a gene encoding the cholera toxin B subunit (CTB) of Vibrio cholerae, modified to contain a sequence coding for an endoplasmic reticulum retention signal (SEKDEL), under the control of the cauliflower mosaic virus 35S promoter. Total protein from the transgenic leaf tissue was isolated and an aliquot containing 5 microg recombinant CTB was injected intradermally into Balb/c (H2K(d)) mice. CTB-specific serum IgG was detected in animals that had been administered plant-expressed or native purified CTB. A T-cell proliferation study using splenocytes and cytokine estimations in supernatants generated by in vitro stimulation of macrophages isolated from the immuno-primed animals was carried out. Inhibition of proliferation of T lymphocytes was observed in splenic T lymphocytes isolated from animals injected with either native or plant-expressed CTB. Macrophages isolated from mice immunised with native or plant-expressed CTB showed enhanced secretion of interleukin-10 but secretion of lipopolysaccharide-induced interleukin-12 and tumor necrosis factor alpha was inhibited. These studies suggest that plant-expressed protein behaved like native CTB with regards to effects on T-cell proliferation and cytokine levels, indicating the suitability of plant expression systems for the production of bacterial antigens, which could be used as edible vaccine. The transgene was found to be inherited in the progeny and was expressed to yield a pentameric form of CTB as evident by its interaction with G(M1) ganglioside.

Animals↗
PubMed2003

Modulation of host immune responses by overexpression of immunodominant antigens of Mycobacterium tuberculosis in bacille Calmette-Guérin.

Based on their immunodominant nature and ability to induce appropriate immune responses in the host, several antigens of Mycobacterium tuberculosis have shown promise of protection. However, most of the candidate vaccines developed by employing various strategies have afforded protection that is at best comparable with bacillus Calmette-Guérin (BCG) in animal models. Due to the inherent ability of BCG to prime cellular responses in the host, it has become an attractive vehicle for development of a vaccine against intracellular infections. In this study, we have cloned the genes of three immunodominant antigens of M. tuberculosis viz. the ESAT6 (Rv3875), the 19 kDa lipoprotein (Rv3763) and the 38 kDa antigen (Pst homolog) (Rv0934) in pSD5 under the transcriptional control of Trrn, a strong mycobacterial promoter, and expressed them in BCG. The19 kDa antigen and the 38 kDa antigen were expressed at levels that were approximately five and eightfolds higher in the cytosols of recombinant BCG strains rBCG19T and rBCG38T, respectively, as compared with their corresponding levels in M. bovis BCG. Both these antigens were also secreted into the extracellular medium at enhanced levels (19 kDa antigen fourfold and 38 kDa antigen twofold) by rBCG strains in comparison with the wild type BCG. ESAT6 antigen, which is absent in M. bovis BCG, was also expressed at a very high level in the cytosol of the rBCG strain (rBCGE6T). Evaluation of immune responses induced by these three rBCG strains in mice shows a markedly different pattern. The rBCG strain overexpressing the 38 kDa antigen exhibited a predominant T helper 1 (Th1) response with high levels of interferon-gamma (IFN-gamma) production, whereas overexpression of the 19 kDa antigen resulted in completely polarized Th2 responses against the BCG sonicate. The rBCG-expressing ESAT6 antigen induced a mixed Th1/Th2 response. Our observations suggest that the 38 kDa antigen may hold excellent promise in the rBCG approach for the development of a vaccine against tuberculosis.

Animals↗
PubMed2003

Raman scattering investigations of nanocrystalline thorium oxide.

Raman scattering investigations are carried out on nanocrystalline thorium oxide powders. Shift and broadening of the Raman peak associated with F2g phonons are observed for the nanocrystalline samples as compared with those of the bulk. The peak shift and broadening are found to increase further as the particle size decreases. A quantitative analysis of the Raman line shape is carried out with a Gaussian confinement model, and the estimated size is found to be consistent with that obtained from X-ray diffraction and transmission electron microscopy.

Crystallization↗
PubMed2003

Blood gases, hematology, and renal blood flow during prolonged mountain sojourns at 3500 and 5800 m.

BACKGROUND: This study mainly focused on renal blood flow, hematological parameters, blood gases, and blood pH, which are affected on exposure to moderate (3500 m) and extreme altitudes (5800 m) in sea level residents. HYPOTHESIS: Acute and prolonged exposure to high or extreme altitude may cause pathophysiological changes in kidney and renal plasma/blood flow, leading to retention of fluids in the tissues. Combined with the decreased availability of oxygen to the tissues, these may be responsible for high altitude maladies. METHOD: Fifteen male sea level (SL) volunteers, 22-25 yr old, were studied for blood gases, blood viscosity, hematocrit, hemoglobin concentration, and effective renal blood/plasma flow at Delhi (260 m), 3500 m (60 d stay), 5800 m (70 d stay), and 7 d after return to SL. RESULTS: Compared with SL, a significant increase from 7.34 to 7.43 (p < 0.01) in blood pH was observed at 3500 m that remained significantly increased at 5800 m. PO2 was about 39% less at 5800 m than at SL. PCO2 reduced significantly from 42.07 to 28.05 mm Hg on return from 5800 m to SL. The blood viscosity increased significantly (38%) at 5800 m and decreased significantly by 38% (p < 0.01) after return to SL. The effective renal plasma flow reduced significantly (p < 0.01) from 615.6 at SL to 381.5 ml x min(-1) x 1.73 m(-2) at 5800 m. CONCLUSION: The study suggests a crucial role of renal function in the acclimatization process; renal function also appears to be one factor by which the body protects itself against severe hypoxia.

Acclimatization↗