Biomedical subjects

R Parthasarathy

Publications and source records attributed to R Parthasarathy.

At least 19 recordsLinked to original sources

PubMed2006

Developmental and hormonal regulation of midgut remodeling in a lepidopteran insect, Heliothis virescens.

Midgut tissue undergoes remodeling during metamorphosis in insects belonging to orders Lepidoptera and Diptera. We investigated the developmental and hormonal regulation of these remodeling events in lepidopteran insect, Heliothis virescens. In H. virescens, programmed cell death (PCD) of larval midgut cells as well as proliferation and differentiation of imaginal cells began at 108 h after ecdysis to the final larval instar (AEFL) and proceeded through the pupal stages. Expression patterns of pro- cell death factors (caspase-1 and ICE) and anti-cell death factor, Inhibitor of Apoptosis (IAP) were studied in midguts during last larval and pupal stages. IAP, Caspase-1 and ICE mRNAs showed peaks at 48 h AEFL, 96 h AEFL and in newly formed pupae, respectively. Immunohistochemical analysis substantiated high caspase-3 activity in midgut at 108 h AEFL. Application of methoprene, a juvenile hormone analog (JHA) blocked PCD by maintaining high levels of IAP, downregulating the expression of caspase-1, ICE and inhibiting an increase in caspase-3 protein levels in midgut tissue. Also, the differentiation of imaginal cells was impaired by methoprene treatment. These studies demonstrate that presence of JHA during final instar larvae affects both midgut remodeling and larval-pupal metamorphosis leading to larval/pupal deformities in lepidopteran insects, a mechanism that is different from that in mosquito, Ae. aegypti where JHA uncouples midgut remodeling from metamorphosis.

Animals↗

PubMed2006

Stage- and cell-specific expression of ecdysone receptors and ecdysone-induced transcription factors during midgut remodeling in the yellow fever mosquito, Aedes aegypti.

In insects, especially in mosquitoes that are adult blood feeders, midgut remodeling is an important event during metamorphosis. It involves two processes viz., programmed cell death (PCD) of larval cells, and proliferation and differentiation of imaginal cells to form pupal/adult midgut. These processes are regulated by 20-hydroxyecdysone (20E) and juvenile hormone (JH), but the signaling mechanisms, which trigger specific changes remain poorly understood. Here, we report stage- and cell-specific expression of ecydone receptor (EcR), ultraspiracle (USP), broad (Br), E75B and hormone receptor 3 (HR3) during midgut remodeling in Aedes aegypti. In Ae. aegypti both EcR and USP genes code for two isoforms each and the expression of mRNA for these isoforms showed both stage- and cell-specific regulation. In general, EcR-B and USP-A mRNAs were detected during larval stages in larval cells, and EcR-A and USP-B mRNAs were detected during pupal stages in imaginal cells. These data suggest that EcR-B/USP-A heterodimer is important for PCD of larval cells and EcR-A/USP-B heterodimer is important for formation of pupal/adult midgut. Broad Z1 mRNA was detected only in the larval cells suggesting its primary role in PCD. It is likely that E75B and HR3 are probably involved in both PCD and imaginal cell proliferation and differentiation as their mRNAs were expressed in the larval as well as in imaginal cells. Application of JH analog, methoprene, lowered or delayed the expression of all the genes studied. These data suggest that 20E plays a major role in midgut remodeling and coordinates this process through stage- and cell-specific expression of different isoforms of nuclear receptors and transcription factors in the target larval and imaginal cells.

Aedes↗

PubMed2006

Mechanisms of midgut remodeling: juvenile hormone analog methoprene blocks midgut metamorphosis by modulating ecdysone action.

In holometabolous insects such as mosquito, Aedes aegypti, midgut undergoes remodeling during metamorphosis. Insect metamorphosis is regulated by several hormones including juvenile hormone (JH) and 20-hydroxyecdysone (20E). The cellular and molecular events that occur during midgut remodeling were investigated by studying nuclear stained whole mounts and cross-sections of midguts and by monitoring the mRNA levels of genes involved in 20E action in methoprene-treated and untreated Ae. aegypti. We used JH analog, methoprene, to mimic JH action. In Ae. aegypti larvae, the programmed cell death (PCD) of larval midgut cells and the proliferation and differentiation of imaginal cells were initiated at about 36h after ecdysis to the 4th instar larval stage (AEFL) and were completed by 12h after ecdysis to the pupal stage (AEPS). In methoprene-treated larvae, the proliferation and differentiation of imaginal cells was initiated at 36h AEFL, but the PCD was initiated only after ecdysis to the pupal stage. However, the terminal events that occur for completion of PCD during pupal stage were blocked. As a result, the pupae developed from methoprene-treated larvae contained two midgut epithelial layers until they died during the pupal stage. Quantitative PCR analyses showed that methoprene affected midgut remodeling by modulating the expression of ecdysone receptor B, ultraspiracle A, broad complex, E93, ftz-f1, dronc and drice, the genes that are shown to play key roles in 20E action and PCD. Thus, JH analog, methoprene acts on Ae. aegypti by interfering with the expression of genes involved in 20E action resulting in a block in midgut remodeling and death during pupal stage.

Aedes↗

PubMed2005

Quantum phase transition of a magnet in a spin bath.

The excitation spectrum of a model magnetic system, LiHoF4, was studied with the use of neutron spectroscopy as the system was tuned to its quantum critical point by an applied magnetic field. The electronic mode softening expected for a quantum phase transition was forestalled by hyperfine coupling to the nuclear spins. We found that interactions with the nuclear spin bath controlled the length scale over which the excitations could be entangled. This generic result places a limit on our ability to observe intrinsic electronic quantum criticality.

Journal Article↗

PubMed2005

Rydberg electron transfer to C6H5NO2: lifetimes and characteristics of the product C6H5NO2- ions.

The nature of electron binding in C6H5NO2- ions produced by Rydberg electron transfer in K(np)C6H5NO2 collisions is investigated through measurements of the number and the lifetimes of the product ions and their dependence on Rydberg atom velocity and principal quantum number n in the range 12 <or approximately n <or approximately 30. The data are interpreted by comparison to results obtained using well-known dipole-bound and valence-bound anions. At high n direct capture into valence-bound states with a lifetime of approximately 1.6 ms is observed. At low n the data suggest that, while direct capture into valence-bound states is still possible, the majority of the observed C6H5NO2- ions result from the onset of a second reaction channel that involves the formation of a dipole-bound "doorway" state that rapidly evolves into a state with predominantly valence-bound character. These findings are discussed in the light of earlier work on electron binding to C6H5NO2.

Journal Article↗

PubMed2005

Comparative analysis of the development of the mandibular salivary glands and the labial silk glands in the mulberry silkworm, Bombyx mori.

The mulberry silkworm, Bombyx mori has a pair of salivary glands arising from the mandibular segment, in addition to the labial silk glands which are generally considered as modified salivary glands. Here we report the characterization of salivary glands and the comparative gene expression profiling of the silk and salivary glands. The two independent salivary glands made up by 330 cells, grow about 1000 fold during larval development. These individual glands extend up to the T(1) thoracic segment unlike silk glands with fused anterior ends and extending up to the caudal region. The salivary glands also undergo endomitosis resembling the silk glands. The B. mori homologue of the homeotic gene Deformed (BmDfd) was expressed in the mandibular and maxillary segments in stage 17 embryo and got localized to the centre of the mandibular segment at stage 18 to form the salivary gland placodes. The expression was also seen in the distal ends of the leg appendages after blastokinesis (stage 22). Only low variations in BmDfd expression ranging from 1.6 to 2.1 fold were apparent during embryonic development. BmDfd expression was observed in the salivary glands all through the larval instars but not in the silk glands. The transcription factor, Forkhead and the segment polarity gene, Wingless were expressed throughout the salivary glands, the latter confirming the absence of physiological compartmentation within these glands unlike the silk glands. The expression of Amylase and Fibrohexamerin was restricted to the salivary and silk glands, respectively and therefore, served as molecular markers for these tissues.

Amylases↗

PubMed2004

Dynamics of Rydberg electron transfer to CH3CN: velocity dependent studies.

The dynamics of free-ion production through electron transfer in K(np)/CH3CN collisions are examined through measurements using velocity-selected Rydberg atoms. The data show that Rydberg electron transfer leads to the creation of two groups of dipole-bound CH3CN- ions, one long lived (tau>85 micros), the other short lived (tau<1 micros). The velocity dependences associated with the production of both groups of ions are similar, the ion formation rate decreasing markedly with decreasing Rydberg atom velocity, principally as a consequence of postattachment electrostatic interactions between the product ions. The results are in reasonable accord with the predictions of a Monte Carlo collision model that considers the effect of crossings between the diabatic potential curves for the covalent K(np)/CH3CN system and the K+/CH3CN- ion pair. This model also accounts for the relatively small reaction rate constants, approximately 0.5-1.0 x 1.0(-8) cm(3) s(-1), associated with the formation of long-lived CH3CN- ions. No velocity dependence in the lifetime of the CH3CN- ions is observed.

Journal Article↗

PubMed2004

Beta-cell sparing in transplanted islets by vascular endothelial growth factor.

We have reported that vascular endothelial growth factor (VEGF) promotes the revascularization of transplanted islets, thereby reducing the initial number required to prevent diabetes. The present study was undertaken to assess other mechanisms of beta-cell sparing by VEGF. For in vitro studies, islets were cultured for 14 days with versus without 20 ng/mL VEGF. Viability, necrosis, and apoptosis were examined by specific staining (Alcein AM, propidium iodide, and annexin/phosphatidylserine). The effects of VEGF on islets were also examined in a proteomic study. In vivo streptozotocin-treated diabetic Lewis rats received 1000 Lewis or Sprague-Dawley islets beneath the renal capsule. Oxygen levels at the transplant site were monitored by a Clark-type oxygen electrode. Fasting blood glucose served as an indicator of islet survival and function. VEGF enhanced oxygen levels at the transplant site. Syngeneic recipients were euglycemic for over 6 months, whereas control islets failed within 30 to 60 days. VEGF prevented allograft rejection for over 14 days, whereas controls were rejected within 6 to 7 days. Immunostaining suggested that VEGF inhibited the presentation of MHC II antigen and promoted islet survival by the inhibition of necrosis and apoptosis. Our proteomic study suggested VEGF preserved systems required for cellular preservation (heat shock proteins) and insulin secretion. VEGF promotes the preservation of isolated and transplanted islets by a variety of mechanisms, including enhanced oxygenation and inhibition of immune rejection, necrosis, and apoptosis. The provision of exogenous VEGF may be a useful adjunct to islet transplantation.

Animals↗

PubMed2004

Biochemical and immunological properties of cytokines conjugated to dendritic polymers.

Here we describe a post-translational modification of SC-63032, a variant of the species restricted, multi-lineage hematopoeitic factor human interleukin-3 (hIL-3). We have made two new dendritic polymer (polyamidoamine or PAMAM dendrimers, generation 5)-SC-63032 bioconjugates. Using two distinct chemistries (one of which is novel to this work), we achieved site-specific conjugation with respect to the amino acid in the proteins ligated to the dendrimers. In both bioconjugates, conjugated cytokine maintains its ability to bind the hIL-3 alpha receptor subunit, but is significantly (about 10-fold) less potent in inducing hIL-3 dependent in vitro cell proliferation than is the free cytokine. In vivo data indicates that conjugation decreases the immunogenicity of the conjugated cytokine modestly. In the absence of pharmacokinetic or biodistribution effects associated with the bioconjugates that increase their potency in vivo (which can only be tested in a higher primate, due to the species restriction of hIL-3 and its derivatives), these immune mitigation effects may be too small to be therapeutically significant. Though unmodified PAMAM dendrimers fail to elicit an antibody response in mice, protein conjugation to dendrimers haptenizes them, and a dendrimer-specific antibody response is produced. In toto, the principal limitation of the dendrimer-cytokine bioconjugates herein is in their reduced receptor affinity and potency in vitro. Were the in vivo potency of the bioconjugates to parallel the in vitro potency of the conjugates reported here, it is likely that particular dendrimer bioconjugates could not justify their higher costs of goods relative to the parent SC-63032 molecule, though retention of SC-63032 biological activities in conjugates suggests that other cytokine-dendrimer bioconjugates may be bioactive. This is good news to the nanotechnology community, in as much as PAMAM dendrimers are among the monodisperse polymeric nanomaterials available, and these results show that they can be used successfully in conjugates to bioactive proteins.

Animals↗

PubMed2002

Coherent spin oscillations in a disordered magnet.

Most materials freeze when cooled to sufficiently low temperature. We find that magnetic dipoles randomly distributed in a solid matrix condense into a spin liquid with spectral properties on cooling that are the diametric opposite of those for conventional glasses. Measurements of the nonlinear magnetic dynamics in the low-temperature liquid reveal the presence of coherent spin oscillations composed of hundreds of spins with lifetimes of up to 10 seconds. These excitations can be labeled by frequency and manipulated by the magnetic fields from a loop of wire and can permit the encoding of information at multiple frequencies simultaneously.

Journal Article↗

PubMed2001

Suppression of matrix metalloproteinase-2 gene expression and invasion in human glioma cells by MMAC/PTEN.

Human gliomas are highly invasive, and remain to be a major obstacle for any effective therapeutic remedy. Among many other factors, gliomas express elevated levels of matrix metalloproteinases (MMPs), which have been implicated to play an important role in tumor invasion as well as neovascularization. The tumor suppressor gene mutated in multiple advanced cancers/phosphatase and tensin homologue (MMAC/PTEN) has been shown to inhibit cell migration, spreading, and focal adhesion. In this study, we determined whether MMAC/PTEN inhibits tumor invasion by modulating MMP-2 activity. Our results showed that reintroduction of the MMAC/PTEN gene into human glioma U251 and U87 cells modified their phenotype and growth characteristics. The ability of MMAC/PTEN to induce anoikis in U251 cells was accompanied by a significant inhibition of in vitro invasion (70%). Expression of MMAC/PTEN in U251 and U87 cells inhibited MMP-2 enzymatic activity as determined by zymography. Furthermore, MMAC/PTEN expression strongly decreased MMP-2 mRNA levels, which correlated well with the inhibition of invasion capacity in these cells. Concomitant with MMP-2 expression and activity, MMP-2 promoter activity was also reduced in MMAC/PTEN expressing cells. Our observations suggest that MMAC/PTEN inhibits tumor cell invasion in part by regulating MMP-2 gene transcription and thereby its enzymatic activity. Further characterization of this regulation will facilitate the development of MMAC/PTEN based gene therapy for gliomas.

Anoikis↗

PubMed2000

A generalized perceptual space.

Based upon experimental results on certain visual spatial discrimination tasks, we have developed a formalism for a non-Euclidian perceptual space. In this formalism, the transformation from real to perceptual space is given by a generalized covariant tensor. The concept of parallel transport of vectors in a curved space is used to prove that closed loops in real space imply closed loops with the same orientation in the perceptual space also.

Discrimination Learning↗

PubMed1999

Hammerhead ribozyme-mediated inactivation of mutant RET in medullary thyroid carcinoma.

Activating mutations of the RET proto-oncogene cause hereditary medullary thyroid carcinoma. To examine whether selective inactivation of mutant RET could prevent transformation, a hammerhead ribozyme was designed to cleave RET mRNA containing a transforming mutation of codon 634 TGC --> TAC (Cys634Tyr). In vitro RNA cleavage assay demonstrated that the ribozyme selectively cleaved RET RNA with a Cys634Tyr but not Cys634Arg or the normal sequence. Expression of ribozyme in NIH/3T3 cells prevented RET-mediated colony formation in soft agar. This inhibition required catalytically active ribozyme and was specific for the TAC mutation. Therefore, ribozymes designed to selectively target mutant RET RNA may provide an effective therapeutic in the treatment of this syndrome.

3T3 Cells↗

PubMed1999

Aerosol delivery of liposomal all-trans-retinoic acid to the lungs.

PURPOSE: To optimize the delivery of all-trans-retinoic acid (ATRA) to lung tissue, we determined the potential of vehiculating the drug in liposomes (L-ATRA) and delivering it via aerosol. Liposomes may provide a means to prevent local irritation of lung tissue and reduce pulmonary toxicity, prolong therapeutic levels and generate high drug concentrations at the tumor sites. Cumulatively, this would result in reduced systemic toxicity and enhanced drug efficacy. METHODS: Previous studies have shown that liposomes can serve as excellent carriers for otherwise poorly soluble ATRA. Delivery of ATRA to the lung tissue of mice was accomplished by nebulization of L-ATRA. The liposomes in the aerosol were relatively uniform (309 +/- 138 nm), stable, and retained the drug well. RESULTS: The drug was effectively delivered at high concentrations (10 +/- 2 microg/g of tissue) to the lungs of mice and was retained for at least up to 96 h after a single exposure to L-ATRA aerosol. No appreciable levels of ATRA were detected in the blood or the liver of treated mice. The aerosol-delivered ATRA was biologically active as demonstrated by its ability to induce the expression of tissue-type transglutaminase. CONCLUSION: Aerosol delivery of L-ATRA offers an effective way to deliver high levels of ATRA to the lung without apparent pulmonary toxic effects.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1999

Short-course chemotherapy for tuberculosis of the spine. A comparison between ambulant treatment and radical surgery--ten-year report.

We performed a randomised, controlled clinical trial to compare ambulant short-course chemotherapy with anterior spinal fusion plus short-course chemotherapy for spinal tuberculosis without paraplegia. Patients with active disease of vertebral bodies were randomly allocated to one of three regimens: a) radical anterior resection with bone grafting plus six months of daily isoniazid plus rifampicin (Rad6); b) ambulant chemotherapy for six months with daily isoniazid plus rifampicin (Amb6); or c) similar to b) but with chemotherapy for nine months (Amb9). Ten years from the onset of treatment, 90% of 78 Rad6, 94% of 78 Amb6 and 99% of 79 Amb9 patients had a favourable status. Ambulant chemotherapy for a period of six months with daily isoniazid plus rifampicin (Amb6) was an effective treatment for spinal tuberculosis except in patients aged less than 15 years with an initial angle of kyphosis of more than 30 degrees whose kyphosis increased substantially.

Adolescent↗

PubMed1998

Altered metabolism of all-trans-retinoic acid in liposome-encapsulated form.

Treatment with all-trans-retinoic acid (ATRA) induces complete remission in many acute promyelocytic leukemia patients. However, plasma drug levels progressively decrease following prolonged treatment with oral ATRA. This decrease is due, at least in part, to the induced cytochrome P-450-dependent metabolism of ATRA. To investigate if incorporation of ATRA in liposomes could alter its metabolism, we compared the cellular metabolism of liposomal-ATRA (L-ATRA) with free drug. Microsomes isolated from the rat liver metabolized L-ATRA to a significantly lower extent than they did free-ATRA. Similarly, in F9 cells, L-ATRA was metabolized at a slower rate than the free drug. These results suggest that L-ATRA may have important clinical implications in terms of slowing down the rate of ATRA metabolism and producing long-term remission in APL patients.

Animals↗

PubMed1998

Human chromosomal localization of a gene for inositol monophosphatase by fluorescence in situ hybridization.

Inhibition of the enzyme inositol monophosphatase (IMPase) (E.C. 3.1.3.25) has been linked to the therapeutic action of lithium in the treatment of manic-depression (bipolar) disorder. Because of the link between bipolar and IMPase, we felt it would be of considerable importance to determine the human chromosomal localization of the IMPase gene. Fluorescence in situ hybridization analysis using a human cDNA clone, which included the 5'-UTR and the complete coding region, mapped the human IMPase gene to chromosome 8q21.2-21.3. No gene locus for manic-depressive disorder has yet been identified. Further studies on this IMPase gene, and other potential gene variants and mutations, should help to determine if specific subgroups of patients with manic-depressive disorder can be determined on a molecular basis, with regard to the IMPase gene.

Brain↗

PubMed1998

Alzheimer's beta-amyloid peptide: affinity for metal chelates.

Alzheimer's amyloid peptide, A beta(1-42) and its fragments, A beta(1-28) and A beta(1-16), were chromatographed on IDA-M(II) columns (M: Cu2+, Ni2+ and Zn2+). The retention of A beta(1-42) and its fragments on IDA-Cu(II) could not be reversed in decreasing a gradient of pH, from 7.0 to 4.0. All A beta peptides were recovered from IDA-Ni(II) columns in a decreasing pH gradient from 7.0 to 4.0, within the pH range from 5.6 to 5.1. A beta(1-42) peptide was strongly retained on IDA-Zn(II) at pH 4.0, but its A beta(1-28) and A beta(1-16) were only transiently retained on IDA-Zn(II) columns when applied at pH 6.1. We submit that histidine clusters, residing both in the Alzheimer's beta-amyloid peptide and in most of the APP/APLP superfamily of proteins, constitute high-affinity binding sites for immobilized metal chelates.

Alzheimer Disease↗