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Biomedical subjects

M Saxena

Publications and source records attributed to M Saxena.

At least 19 recordsLinked to original sources
PubMed2006

Temporal expression of transforming growth factor-beta2 and myostatin mRNA during embryonic myogenesis in Indian broilers.

TGF-beta2 and myostatin, the members of TGF family, act through both autocrine and paracrine mechanisms to regulate the growth and differentiation at various developmental stages in chicken. The kinetics and expression profile of these two growth factors were investigated by semi-quantitative RT-PCR, during the myogenesis of Indian broiler chickens. Total RNA was isolated from whole embryos on each of embryonic days (E) 0-6 (n=3 per day) and from the biceps femoris muscle at E7-E18 (n=3 per day). The expression of TGF-beta2 was noticed on E2 that remained at the same level until E6. In biceps femoris muscle, higher level of TGF-beta2 expression was observed during E7-E12, which decreased gradually thereafter. These findings suggested that TGF-beta2 might be a regulatory factor participating in the myogenesis of chicken embryos. Initial myostatin expression was noticed on E1, even before the myogenic lineage is established in embryo. This finding suggested an additional role of myostatin in early chicken embryo development, other than myogenesis. Furthermore, myostatin expression was significantly higher on E3 as compared to earlier studies, where initial higher level was observed at E2, suggesting the differential expression of myostatin among breeds. Higher and almost static myostatin expression was noticed in biceps femoris muscle during the entire period of myogenesis (E7-E18). In the present study, the ontogeny of myostatin expression coincided with myogenesis of chicken. Therefore, it may be hypothesized that myostatin is not only a major determinant of muscle mass, but also involved in early embryogenesis in chickens.

Animals↗
PubMed2006

Development of pharmacophoric model of condensed pyridine and pyrimidine analogs as hydroxymethyl glutaryl coenzyme A reductase inhibitors.

Quantitative structure-activity relationship (QSAR) has been established on a series of thirty-eight compounds of four different sets of condensed pyridine and pyrimidine analogs, for their hydroxymethyl glutaryl coenzyme (HMG-CoA) reductase inhibitor activity, in order to understand the essential structural requirement for binding with receptor, in terms of common biophoric and secondary sites employing APEX-3D software. Among several 3D pharmacophoric models with different sizes and arrangements, one model was selected based on r2 = 0.8, chance<0.001, match equivalent to 0.38 and all the 38 compounds were considered. The results suggest that hydrophobicity, hydrogen acceptor and optimum steric refractivity play a dominant role in the inhibition of HMG-CoA reductase. The information obtained from the present study can be used to design and predict more potent molecules as HMG-CoA reductase inhibitors, prior to their synthesis.

Drug Design↗
PubMed2005

Differential expression of inducible nitric oxide synthase and cytokine mRNA in chicken lines divergent for cutaneous hypersensitivity response.

Phytohemagglutinin (PHA)-induced delayed-type hypersensitivity is an immunocompetent trait considered an indicator of cell-mediated immune or T-cell responses. Divergent selection was performed to generate high and low lines for response to PHA-P. Extreme-responder birds of the F2 generation in each line were used to study possible differences in macrophage activity and the associated functional genes. To evaluate macrophage activity, nitric oxide (NO) was estimated both systemically in serum and in in vitro monocyte culture. Semi-quantitative RT-PCR was used to detect the differential mRNA expression patterns of iNOS and MIP-1beta in monocyte culture, whereas T(H)1 cytokines (IL-2 and IFN-gamma) were studied in peripheral blood mononuclear cells (PBMC) at different time intervals after lipopolysaccharide (LPS) induction. The high line showed strong systemic, as well as in vitro NO production, compared to the low line, upon stimulation with NDV and LPS, similar to early and high iNOS mRNA expression. Following the pattern of iNOS gene expression, an early strong expression of cytokines with powerful iNOS-inducing action, such as IFN-gamma and the chemokine MIP-1beta, was observed in the high line. In contrast, for response to PHA-P, low expression of IL-2 was observed in the high compared to the low line. In conclusion, the study revealed that divergent selection for response to PHA-P resulted in a divergent effect on T(H)1 cell activity, resulting in altered macrophage function in chickens. Selection, based on response to PHA-P, could lead to more resistant birds or birds with an enhanced immune response.

Animals↗
PubMed2004

Difficult extubation: calming the sympathetic storm.

Tracheal extubation can evoke an equally strong haemodyamic stress response as tracheal intubation. We present a patient with myocardial infarction who repeatedly failed tracheal extubation. He developed acute pulmonary oedema following each attempt at tracheal extubation due to sympathetic overactivity. A change of approach with extubation under propofol sedation followed by continued sympatholysis with dexmedetomidine infusion allowed successful extubation.

Aged↗
PubMed2001

Activation of the COOH-terminal Src kinase (Csk) by cAMP-dependent protein kinase inhibits signaling through the T cell receptor.

In T cells, cAMP-dependent protein kinase (PKA) type I colocalizes with the T cell receptor-CD3 complex (TCR/CD3) and inhibits T cell function via a previously unknown proximal target. Here we examine the mechanism for this PKA-mediated immunomodulation. cAMP treatment of Jurkat and normal T cells reduces Lck-mediated tyrosine phosphorylation of the TCR/CD3 zeta chain after T cell activation, and decreases Lck activity. Phosphorylation of residue Y505 in Lck by COOH-terminal Src kinase (Csk), which negatively regulates Lck, is essential for the inhibitory effect of cAMP on zeta chain phosphorylation. PKA phosphorylates Csk at S364 in vitro and in vivo leading to a two- to fourfold increase in Csk activity that is necessary for cAMP-mediated inhibition of TCR-induced interleukin 2 secretion. Both PKA type I and Csk are targeted to lipid rafts where proximal T cell activation occurs, and phosphorylation of raft-associated Lck by Csk is increased in cells treated with forskolin. We propose a mechanism whereby PKA through activation of Csk intersects signaling by Src kinases and inhibits T cell activation.

CSK Tyrosine-Protein Kinase↗
PubMed2001

Eyelid allergic contact dermatitis to black iron oxide.

Eye cosmetics are a common cause of eyelid dermatitis. These products contain pigments, fragrances, resins, preservatives and vehicles. Mascara might cause either irritant or allergic contact dermatitis (ACD) of the eyelids. We present the case of a 44-year-old woman with a 10-month history of periorbital and eyelid dermatitis. Epicutaneous patch testing using the TRUE Test, cosmetic series, steroid series, and her personal products yielded a strong reaction to her mascara. Subsequent patch testing to the mascara components provided by the manufacturer revealed a severe reaction only to 5% black iron oxide. This black iron oxide was further tested in 10 normal controls with no reactions produced. There is only one previous report of eyelid ACD secondary to iron oxide that represents a rare cause of eyelid ACD.

Adult↗
PubMed2000

Inhibitory role for dual specificity phosphatase VHR in T cell antigen receptor and CD28-induced Erk and Jnk activation.

The 21-kDa dual specific protein phosphatase VH1-related (VHR) is one of the smallest known phosphatases, and its function has remained obscure. We report that this enzyme is expressed in lymphoid cells and is not induced by T cell antigen receptor like other dual specificity phosphatases. Introduction of exogenous VHR into Jurkat T cells caused a marked decrease in the transcriptional activation of a nuclear factor of activated T cells and an activator protein-1-driven reporter gene in response to ligation of T cell antigen receptors. The inhibition was dose-dependent and was similar at different doses of anti-receptor antibody. Catalytically inactive VHR mutants caused an increase in gene activation, suggesting a role for endogenous VHR in this response. In contrast, the activation of a nuclear factor kappaB-driven reporter was not affected. The inhibitory effects of VHR were also seen at the level of the mitogen-activated kinases Erk1, Erk2, Jnk1, Jnk2, and on reporter genes that directly depend on these kinases, namely Elk, c-Jun, and activator protein-1. In contrast, p38 kinase activation was not affected by VHR, and p38-assisted gene activation was less sensitive. Our results suggest that VHR is a negative regulator of the Erk and Jnk pathways in T cells and, therefore, may play a role in aspects of T lymphocyte physiology that depend on these kinases.

CD28 Antigens↗
PubMed2000

The tumor suppressor PTEN regulates T cell survival and antigen receptor signaling by acting as a phosphatidylinositol 3-phosphatase.

The tumor suppressor gene PTEN encodes a 55-kDa enzyme that hydrolyzes both protein phosphotyrosyl and 3-phosphorylated inositol phospholipids in vitro. We have found that the latter activity is physiologically relevant in intact T cells. Expression of active PTEN lead to a 50% loss of transfected cells due to increased apoptosis, which was completely prevented by coexpression of a constitutively active, membrane-bound form of protein kinase B. A mutant of PTEN selectively lacking lipid phosphatase activity, but retaining protein phosphatase activity, had no effects on cell number. Active (but not mutant) PTEN also decreased TCR-induced activation of the mitogen-activated protein kinase ERK2 (extracellular signal-related kinase 2), as seen after inhibition of phosphatidylinositol 3-kinase. Our data indicate that PTEN is a phosphatidylinositol 3-phosphatase in T cells, and we suggest that PTEN may play a role in the regulation of T cell survival and TCR signaling by directly opposing phosphatidylinositol 3-kinase.

Apoptosis↗
PubMed2000

Subcellular localization of intracellular protein tyrosine phosphatases in T cells.

A high protein tyrosine phosphatase (PTPase) activity is required to maintain circulating T lymphocytes in a resting phenotype, and to limit the initiation of T cell activation. We report that 15 of the currently known 24 intracellular PTPases are expressed in T cells, namely HePTP, TCPTP, SHP1, SHP2, PEP, PTP-PEST, PTP-MEG2, PTEN, PTPH1, PTP-MEG1, PTP36, PTP-BAS, LMPTP, PRL-1 and OV-1. Most were found in the cytosol and many were enriched at the plasma membrane. Only TCPTP and PTP-MEG2 had subcellular localizations that essentially excludes them from a direct role in early T cell antigen receptor signaling events. Overexpression of 6 of the PTPases reduced IL-2 gene activation, 3 of them thereby identified as novel candidates for negative regulators of TCR signaling. Our findings expand the repertoire of PTPases that should be considered for a regulatory role in T cell activation.

Cell Membrane↗
PubMed2000

Extracellular signals and scores of phosphatases: all roads lead to MAP kinase.

MAP kinases function as key signal integration points for a vast number of external stimuli that affect the life and death of cells and are therefore subject to rigorous regulation. Here we review the numerous protein phosphatases that directly counteract MAP kinase activation. To simplify the complexity, we attempt to integrate the information into a 'sequential phosphatase model' of MAP kinase regulation.

Animals↗
PubMed2000

Prognostic factors for persistent diarrhoea managed in a community setting.

Two hundred and five cases (mean age 13.4, SD 9.5) of persistent diarrhoea (PD) of 14-28 days duration, attending an urban slum clinic and treated according to standard WHO guidelines, were monitored at weekly intervals to obtain an estimate of treatment failure rates and to identify its clinical predictors. Vitamin and micronutrients (daily 2RDA) were additionally provided. Only 9 (8.2%) of 109 children with criteria for hospital care accepted in-patient care. Weight gain was considered inadequate if the daily increment between enrollment and day 7 of follow up was < 10 g at age 0-3 months, < 5 g at 4-6 months, and any weight loss for those older than 6 months. Recovery was considered delayed if diarrhoea ceased 7 days after enrollment. Overall, 28.3% cases had inadequate weight gain and 25.6% had delayed recovery. The non-breast milk calorie intake was 11.2% during infancy and 40.6% at later ages of the recommended intakes. In a logistic regression model, initial watery stool frequency greater than median (adjusted OR 2.30, p = 0.01), age < or = 6 months (adjusted OR 2.24, p = 0.04) and low consumption of micronutrient mixture (adjusted OR 2.62, p = 0.01) were associated with an increased risk of delayed recovery. In a Cox proportional hazards model for time to recovery from diarrhoea, low consumption of the micronutrient mixture and age < or = 6 months reduced the chances of recovery by 29% and 37% respectively. Low consumption of the prescribed micronutrient mixture (adjusted OR 2.21, p = 0.04), fever (adjusted OR 1.91, p = 0.05) and diarrhoea continuing beyond study day 7 (adjusted OR 2.29, p = 0.03) increased the risk of inadequate weight gain. Breast feeding status and animal milk consumption did not influence weight gain or recovery. Due to the low compliance for advised hospitalisation, approaches for care at community level itself need to be evolved. Focus should be on increasing the overall dietary intake and provision of generous but safe amount of micronutrients; our findings do not support need for routine elimination of animal milk. The efficacy of individual micronutrients needs evaluation in controlled trials.

Community Health Services↗
PubMed2000

Fourier transform infrared spectra and normal mode analysis of 1-[(3-methylphenyl)piperazin-1-yl]-3-[thio(4-acetamido-phenyl]pro pane: a potent 5-HT2 and D2 receptor ligand.

1-[(3-methylphenyl)piperazin-1-yl]-3-[thio(4-acetamidophenyl]propa ne and its analogs have shown good hypotensive activity and the title compound has shown a profile of centrally acting anti-hypertensive agent. It also binds with the 5-HT2 receptors. The conformation of the title compound was determined by X-ray diffraction but this is not possible for its analogs because of the difficulty in preparing their single crystals. A novel and easy approach is envisaged to determine the conformation in such cases by the application of semi-empirical molecular orbital calculations, Fourier transform infra red (FTIR) spectroscopy and normal mode analysis. As a first step in this direction the FTIR spectrum of the title compound has been recorded and its normal mode analysis carried out. The assignments of the frequencies are based on the concept of group frequencies and band intensities. The spectrally observed frequencies have been tabulated along with the theoretically calculated ones and their assignments. Good agreement has been obtained between them and a set of 101 force field constants is established.

Antihypertensive Agents↗
PubMed1999

Augmentation of an antitumor CTL response In vivo by inhibition of suppressor macrophage nitric oxide.

Evidence is provided that inhibition of macrophage NO production can augment in vivo CTL responses. Specifically, administration of NG-monomethyl-l -arginine (NGMMA) via osmotic pumps increases the tumor-specific CTL response against the P815 mastocytoma in the peritoneal cavity of preimmunized mice. Both the magnitude and duration of the CTL response were increased. That the augmented CTL response resulted from inhibition of the NO synthase pathway is supported by the finding that macrophage NO production from NGMMA-treated mice was reduced. Also, in vitro inhibition of NO production by peritoneal exudate cells from P815 tumor-challenged mice augmented the secondary CTL response observed. Cell proliferation was augmented by NGMMA in these cultures, suggesting that macrophage NO may suppress CTL by inhibiting clonal expansion. NO-mediated inhibition was observed in vivo in this experimental system, even though the CTL response is not suppressed, in that tumor rejection occurs. Therefore, the present results are consistent with the conclusion that macrophage NO-mediated inhibition of the CTL response is a side effect of activating macrophages rather than resulting from the action of a distinct subset of what have long been termed suppressor macrophages. Most important, the results indicate that NO-mediated suppressor macrophage activity can be an important CTL immunoregulatory element in vivo.

Animals↗
PubMed1999

Inhibition of T cell signaling by mitogen-activated protein kinase-targeted hematopoietic tyrosine phosphatase (HePTP).

Activation of T lymphocytes to produce cytokines is regulated by the counterbalance of protein-tyrosine kinases and protein-tyrosine phosphatases, many of which have a high degree of substrate specificity because of physical association with their targets. Overexpression of hematopoietic protein-tyrosine phosphatase (HePTP) results in suppression of T lymphocyte activation as measured by T cell antigen receptor-induced activation of transcription factors binding to the 5' promoter of the interleukin-2 gene. Efforts to pinpoint the exact site of action and specificity of HePTP in the signaling cascade revealed that HePTP acts directly on the mitogen-activated protein (MAP) kinases Erk1 and 2 and consequently reduces the magnitude and duration of their catalytic activation in intact T cells. In contrast, HePTP had no effects on N-terminal c-Jun kinase or on events upstream of the MAP kinases. The specificity of HePTP correlated with its physical association through its noncatalytic N terminus with Erk and another MAP kinase, p38, but not Jnk or other proteins. We propose that HePTP plays a negative role in antigen receptor signaling by specifically regulating MAP kinases in the cytosol and at early time points of T cell activation before the activation-induced expression of nuclear dual-specific MAP kinase phosphatases.

Enzyme Activation↗
PubMed1999

Characterization of TCR-induced receptor-proximal signaling events negatively regulated by the protein tyrosine phosphatase PEP.

The proline-, glutamic acid-, serine- and threonine-enriched protein tyrosine phosphatase PEP, which is expressed primarily in hematopoietic cells, was recently discovered to be physically associated with the 50-kDa cytosolic protein tyrosine kinase (PTK) Csk, an important suppressor of Src family PTK, including Lck and Fyn in T cells. We report that this phosphatase has an inhibitory effect on TCR-induced transcriptional activation of the c-fos proto-oncogene and elements from the IL-2 gene promoter. Catalytically inactive mutants of PEP had no effects in these assays. Expression of PEP also reduced activation of the N-terminal c-Jun kinase Jnk2 in response to receptor ligation, but not in response to UV light. In agreement with a more receptor-proximal site of action, we found that PEP reduced the TCR-induced increase in tyrosine phosphorylation of an Lck mutant, Lck-Y505F, which is only phosphorylated on tyrosine 394, the positive regulatory site. Finally, we observed that PEP reduced c-fos activation in a synergistic manner with Csk, supporting the notion that these two enzymes form a functional team acting on Src family kinases involved in TCR signaling.

Humans↗
PubMed1999

The next wave: protein tyrosine phosphatases enter T cell antigen receptor signalling.

Recent years have seen an exponentially increasing interest in the molecular mechanisms of signal transduction. Much of the focus has been on protein tyrosine kinase-mediated signalling, while the study of protein tyrosine phosphatases has lagged behind. We predict that the phosphatases will become a "hot topic" in the field within the next few years. This review summarizes the current state-of-the-art in our understanding of the structure, regulation and role of protein tyrosine phosphatases in T lymphocyte activation.

Animals↗