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Biomedical subjects

D Kumar

Publications and source records attributed to D Kumar.

At least 19 recordsLinked to original sources
PubMed2000

Synthesis of spherical porous silicas in the micron and submicron size range: challenges and opportunities for miniaturized high-resolution chromatographic and electrokinetic separations.

Classical silica technology has reached its limit with respect to an ultimate minimum particle size of about 2 microm in diameter. Here, a novel process is presented which allows one to synthesize porous silica beads and control their particle diameter in situ, within the range of 0.2-2.0 microm. As a result, no sizing is required and losses of silica are avoided. Furthermore, the process enables one to control in situ the pore structural parameters and the surface chemistry of the silica beads. Even though surface funtionalized silicas made according to this process can principally be applied in fast HPLC the column pressure drop will be high even for short columns. In addition, the column efficiency, expressed in terms of the theoretical plate height is about H-2d(p) in the best case and limited by the A and C term of the Van Deemter equation. In other words the gain in total plate number when using 1-2 microm silica beads in short columns is minimal as compared to longer columns packed with 5 microm particles. Capillary electrochromatography (CEC) as a hybrid method enables the application of micron size as well as submicron size particles. This consequently enhances column efficiency by a factor of 5-10 when compared to HPLC. The use of short CEC columns packed with submicron size silicas provides the basis for fast and efficient miniaturized systems. The most significant feature of CEC as compared to HPLC is that the former allows one to resolve polar and ionic analytes in a single run. An alternative method for miniaturization is capillary electrophoresis (CE) which generates extremely high efficiencies combined with fast analysis. Its application, however, is limited to ionic substances.

Chromatography, Liquid↗
PubMed2000

Nitric oxide and salicylic acid signaling in plant defense.

Salicylic acid (SA) plays a critical signaling role in the activation of plant defense responses after pathogen attack. We have identified several potential components of the SA signaling pathway, including (i) the H(2)O(2)-scavenging enzymes catalase and ascorbate peroxidase, (ii) a high affinity SA-binding protein (SABP2), (iii) a SA-inducible protein kinase (SIPK), (iv) NPR1, an ankyrin repeat-containing protein that exhibits limited homology to IkappaBalpha and is required for SA signaling, and (v) members of the TGA/OBF family of bZIP transcription factors. These bZIP factors physically interact with NPR1 and bind the SA-responsive element in promoters of several defense genes, such as the pathogenesis-related 1 gene (PR-1). Recent studies have demonstrated that nitric oxide (NO) is another signal that activates defense responses after pathogen attack. NO has been shown to play a critical role in the activation of innate immune and inflammatory responses in animals. Increases in NO synthase (NOS)-like activity occurred in resistant but not susceptible tobacco after infection with tobacco mosaic virus. Here we demonstrate that this increase in activity participates in PR-1 gene induction. Two signaling molecules, cGMP and cyclic ADP ribose (cADPR), which function downstream of NO in animals, also appear to mediate plant defense gene activation (e.g., PR-1). Additionally, NO may activate PR-1 expression via an NO-dependent, cADPR-independent pathway. Several targets of NO in animals, including guanylate cyclase, aconitase, and mitogen-activated protein kinases (e.g., SIPK), are also modulated by NO in plants. Thus, at least portions of NO signaling pathways appear to be shared between plants and animals.

Adenosine Diphosphate Ribose↗
PubMed2000

A deficiency of interstitial cells of Cajal in Chagasic megacolon.

Disordered gut motor activity is a feature of patients with Chagas' disease: colonic involvement leads to the development of megacolon and symptoms of constipation. Interstitial cells of Cajal are thought to modulate gut motility. The aim of this study was to test the hypothesis that there is an abnormality of the density of distribution of interstitial cells of Cajal in Chagasic megacolon. Interstitial cells of Cajal were identified by immunohistochemistry using an anti-c-kit antibody. Six patients with Chagasic megacolon were compared with normal controls. The density of distribution of interstitial cells of Cajal was assessed in the longitudinal and circular muscle layers, and in the intermuscular plane of the Chagasic and normal colon. Statistical analysis was performed using Fisher's exact test. The interstitial cells of Cajal density in Chagasic megacolon was much reduced in comparison to normal colonic tissue in the longitudinal muscle layer (P=0.0084), intermuscular plane (P<0.0001), and circular muscle layer (P=0.0051). The lack of interstitial cells of Cajal may play a role in the pathophysiology of the disease, leading to the development of megacolon and symptoms of constipation.

Aged↗
PubMed2000

Identification of a novel tumor necrosis factor-alpha-inducible gene, SCC-S2, containing the consensus sequence of a death effector domain of fas-associated death domain-like interleukin- 1beta-converting enzyme-inhibitory protein.

We report here the isolation and characterization of a novel tumor necrosis factor-alpha (TNF-alpha)-inducible gene, SCC-S2. Based on the nucleotide sequence, the SCC-S2 open reading frame contains a sequence in the amino terminus that shows a significant homology to death effector domain II of cell death regulatory protein, Fas-associated death domain-like interleukin-1beta-converting enzyme-inhibitory protein (FLIP). Unlike FLIP, the SCC-S2 open reading frame contains only one death effector domain and lacks the carboxyl-terminal caspase-like homology domain, raising the possibility that SCC-S2 may be a novel member of the FLIP family. SCC-S2 mRNA expression is found in most normal tissues and malignant cells. The steady state level of SCC-S2 mRNA is significantly induced by TNF-alpha in different tumor cells (TNF-alpha at 20 ng/ml for 3 h: A549, approximately 2-9-fold; SKOV-3, approximately 3-fold; PCI-04A, approximately 3-6-fold). TNF-alpha treatment (100 ng/ml, 4 h) of HeLa cells transiently transfected with FLAG epitope-tagged SCC-S2 cDNA or expression vector alone led to an increase in the number of apoptotic cells as compared with the untreated counterpart. Interestingly, however, SCC-S2 transfectants revealed a significant decrease in the number of apoptotic cells as compared with the vector transfectants (p < 0.001). These data implicate a role of SCC-S2 as a negative mediator of apoptosis in certain cell types.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Clusters of new tuberculosis cases in North-west London: a survey from three hospitals based on IS6110 RFLP typing.

OBJECTIVES: The relative contributions of reactivation of latent infection and clusters of new infections to the overall incidence of tuberculosis in the U.K. is unknown. A study was carried out in North-West London to determine the feasibility of IS6110 RFLP strain typing as a tool to investigate the relative contributions of these two sources. METHODS: All available isolates of M. tuberculosis from specimens collected over a calendar year at three participating hospitals were typed by RFLP using an IS6110 probe. Isolates exhibiting a single band pattern were subject to further typing using an oligonucleotide direct repeat probe. Demographic and clinical information on cases was obtained from the National Survey of Tuberculosis Notifications in England and Wales and further information sought on clustered cases as identified by RFLP typing. RESULTS: Twenty-seven (23%) of the 118 cases had shared IS6110 RFLP patterns. Strains from nine cases had single band patterns, but these were all distinguishable from each other when subjected to further typing by direct repeat probe. The remaining 18 cases belonged to eight clusters. Epidemiological links were established between all the patients in each cluster. The likelihood of being in a cluster was increased in cases with pulmonary smear-positive disease. It was lower in cases of Indian Sub-continent ethnic origin. For 10 of the 18 clustered cases epidemiological links had not been established by conventional contact tracing. CONCLUSIONS: Investigation of the relative contributions of reactivation of latent infection and new infection is feasible in a UJK population, using IS6110 RFLP typing of M. tuberculosis isolates and epidemiological enquiries. This study in London identified clustered, presumably new cases, the majority of whom had not been linked epidemiologically. Comprehensive IS6110 RFLP typing of UK isolates would probably identify many clusters of incident tubercular infection.

Adolescent↗
PubMed2000

Effect of Kombucha tea on chromate(VI)-induced oxidative stress in albino rats.

The effect of Kombucha tea (KT) on oxidative stress induced changes in rats subjected to chromate treatment are reported. KT feeding alone did not show any significant change in malondialdehyde (MDA) and reduced glutathione (GSH) levels, but did enhance humoral response and delayed type of hypersensitivity (DTH) response appreciably over control animals. Chromate treatment significantly enhanced plasma and tissue MDA levels, decreased DTH response considerably, enhanced glutathione peroxidase and catalase activities; however, no change in GSH, superoxide dismutase and antibody titres was noticed. KT feeding completely reversed the chromate-induced changes. These results show that Kombucha tea has potent anti-oxidant and immunopotentiating activities.

Animals↗
PubMed2000

Adriamycin-induced heart failure: mechanism and modulation.

Adriamycin (doxorubicin) is one of the most effective chemotherapeutic agents against a variety of cancers, but its usefulness is seriously curtailed by the risk of developing heart failure. Available laboratory evidence suggests that an increase in oxidative stress, brought about by increased free radical production and decreased myocardial endogenous antioxidants, plays an important role in the pathogenesis of heart failure. Adriamycin-induced apoptosis and hyperlipidemia may also be involved in the process. Probucol, a lipid-lowering drug and an antioxidant, completely prevents the occurrence of heart failure by reducing oxidative stress as well as by the modulation of apoptosis and high lipid concentrations. Thus, combined therapy with adriamycin and probucol has a high potential for optimizing the treatment of cancer patients.

Animals↗
PubMed2000

Reduction in cytokine production in colorectal cancer patients: association with stage and reversal by resection.

The aim of this study was to assess monocyte/macrophage function, as defined by lipopolysaccharide (LPS)-induced production of tumour necrosis factor (TNF)-alpha, interleukin (IL)-10 and interferon (IFN)-gamma by stimulated whole blood cultures in patients with colorectal carcinoma before and after surgical resection. Forty colorectal cancer patients prior to surgery and 31 healthy controls were studied. Heparinized venous blood was taken from colorectal cancer patients prior to surgery and from healthy controls. Serial samples were obtained at least 3-6 weeks post-operatively. Blood was stimulated with LPS for 24 h and supernatants were assayed for TNF-alpha, IFN-gamma and IL-10 by enzyme-linked immunosorbent assay. LPS-induced production of TNF-alpha and of IFN-gamma was reduced in patients with colorectal carcinoma compared to controls (TNF-alpha, 11,269 pg/ml(-1) ¿12,598¿; IFN-gamma, 0.00 pg/ml(-1) ¿226¿; median ¿IQR¿) (TNF-alpha, 20,576 pg/m(-1) ¿11,637¿, P < 0.0001; IFN-gamma, 1,048 ¿2,428¿, P = 0.0051, Mann-Whitney U-test). Production in patients after surgery had increased (TNF-alpha: 17,620 pg/ml(-1) ¿7,986¿; IFN-gamma. 410 pg/ml(-1) ¿2,696¿; mean ¿s.d.¿) and were no longer significantly reduced when compared to controls (TNF-alpha, P = 0.28; IFN-gamma, P = 0.76). Production of TNF-alpha and IFN-gamma prior to surgery were reduced to a greater extent in patients with Dukes' stage C tumours compared to those with Dukes' stage A and B stage. There was no difference in IL-10 production between any group. Monocytes/macrophages from patients with colorectal carcinoma are refractory to LPS stimulation as reflected by reduction in TNF-alpha and IFN-gamma production and this is more pronounced in patients with advanced stage tumours. This suppression is not mediated by IL-10 and disappears following surgical resection of the tumour. This provides evidence for tumour induced suppression of immune function in patients with colorectal cancer and identifies a potential therapeutic avenue.

Aged↗
PubMed2000

Further observations and characterization of monoclonal antibodies reacting with B cell alloantigens associated with rheumatic fever and rheumatic heart disease.

Elevated levels of B lymphocytes with a unique surface alloantigen have been reported to be characteristic of patients with acute rheumatic fever or rheumatic heart disease. Mouse monoclonal antibodies (mAbs) to this alloantigen have been proposed as being useful in identifying individuals at risk for the development of these sequelae of group A streptococcal infection. However, previous studies have suggested that the discriminating ability of the mAbs was highest when the mAbs were made by using lymphocytes from the same ethnic population. To confirm and extend this observation, additional mouse mAbs were developed and their properties defined. These three mAbs-PG-12A, PG-13A, and PG-20A-reacted with B cells from more than 90% of North Indian patients with acute rheumatic fever or rheumatic heart disease. Each of these three new mAbs identified the highest levels of reactive B cells in patients with active acute rheumatic fever. Lower levels of positive reacting lymphocytes were found in individuals with quiescent chronic rheumatic heart disease, and markedly reduced percentages of reactive cells were observed in normal control subjects. The proportion of reactive lymphocytes in individual patients varied according to which of the three was tested, suggesting the possibility of a spectrum of "rheumatic" epitopes in susceptible individuals. The data further suggested that enhanced discriminatory ability for identifying "at-risk" susceptible patients could be obtained by testing with a combination of mAbs. If reduction in the incidence of acute rheumatic fever can be facilitated by early identification of susceptible individuals, accurate and sensitive detection of a marker antigen would result in more cost-effective public health measures. Additional population studies are required to more precisely define and confirm these detection techniques.

Adult↗
PubMed2000

Differential induction of tobacco MAP kinases by the defense signals nitric oxide, salicylic acid, ethylene, and jasmonic acid.

In tobacco, two mitogen-activated protein (MAP) kinases, designated salicylic acid (SA)-induced protein kinase (SIPK) and wounding-induced protein kinase (WIPK) are activated in a disease resistance-specific manner following pathogen infection or elicitor treatment. To investigate whether nitric oxide (NO), SA, ethylene, or jasmonic acid (JA) are involved in this phenomenon, the ability of these defense signals to activate these kinases was assessed. Both NO and SA activated SIPK; however, they did not activate WIPK. Additional analyses with transgenic NahG tobacco revealed that SA is required for the NO-mediated induction of SIPK. Neither JA nor ethylene activated SIPK or WIPK. Thus, SIPK may function downstream of SA in the NO signaling pathway for defense responses, while the signals responsible for resistance-associated WIPK activation have yet to be determined.

Cyclopentanes↗
PubMed2000

Allergic colitis presenting in the first day of life: report of three cases.

Allergic colitis can occur within hours of birth and should be considered in the differential diagnosis of any newborn in whom hematochezia develops. This diagnosis should be considered after excluding infectious and anatomic disorders common to this age group. The diagnosis is supported by the healthy appearance of affected infants and specific proctosigmoidoscopic and histopathologic findings. Infants with allergic colitis usually respond to withdrawal of the offending antigen, by the use of hydrolyzed cow's milk protein formula or more elemental formulas, or if the infant has been breast fed, by the strict removal of the offending antigen from the breast-feeding mother's diet.

Biopsy↗
PubMed2000

Evidence for digenic inheritance in some cases of Antley-Bixler syndrome?

The Antley-Bixler syndrome has been thought to be caused by an autosomal recessive gene. However, patients with this phenotype have been reported with a new dominant mutation at the FGFR2 locus as well as in the offspring of mothers taking the antifungal agent fluconazole during early pregnancy. In addition to the craniosynostosis and joint ankylosis which are the clinical hallmarks of the condition, many patients, especially females, have genital abnormalities. We now report abnormalities of steroid biogenesis in seven of 16 patients with an Antley-Bixler phenotype. Additionally, we identify FGFR2 mutations in seven of these 16 patients, including one patient with abnormal steroidogenesis. These findings, suggesting that some cases of Antley-Bixler syndrome are the outcome of two distinct genetic events, allow a hypothesis to be formulated under which we may explain all the differing and seemingly contradictory circumstances in which the Antley-Bixler phenotype has been recognised.

Abnormalities, Drug-Induced↗
PubMed2000

Antidotal efficacy of pyridinium oximes and cholineacetyltransferase inhibitors against organophosphorus intoxication in rodents.

In an attempt to develop effective antidote against organophosphorus intoxication, some new imidazole-pyridinium mono-oximes, long chain pyridinium mono-oximes and cholineacetyltransferase inhibitors were synthesised. These compounds were evaluated for their in vivo therapeutic protection and neuromuscular function studies in rodents. The results indicate that SPK-series oximes may be useful against sarin poisoning without any beneficial effect against VX (O-Ethyl S-2-NN-diisopropylaminoethyl methylphosphonofluoridate) intoxication. The cholineacetyltransferase (ChAT) inhibitors may not be of any help against any of the OP compounds studied in this study.

Animals↗
PubMed1999

Sustained suppression of plasma HIV RNA is associated with an increase in the production of mitogen-induced MIP-1alpha and MIP-1beta.

The chemokine receptor CCR5 has been shown to be a major coreceptor for HIV-1. The chemokines that bind to this receptor (MIP-1alpha, MIP-1beta, and RANTES) are potent inhibitors of HIV replication and may play an important role in the pathophysiology of HIV disease. We investigated the effect of potent antiretroviral therapy (ritonavir and saquinavir) on the production of MIP-1alpha, MIP-1beta, and RANTES in 19 HIV-infected patients who had sustained decreases in plasma HIV RNA levels (<200 copies/ml). Chemokine concentrations were measured in serum, plasma, and PHA-stimulated PBMCs at baseline and 24 and 48 weeks after initiating therapy. MIP-1alpha, MIP-1beta, and RANTES levels in serum and plasma did not significantly change in the 48-week period. In contrast, MIP-1alpha and MIP-1beta secreted by PHA-stimulated PBMCs increased at 24 weeks, with this increase sustained at 48 weeks, whereas no significant change was observed in PHA-induced RANTES production. A significant positive correlation was found between the changes in PHA-induced chemokine production and baseline CD4+ T cell counts. These data demonstrate that sustained suppression of viral replication by potent antiretroviral therapy has a potentially beneficial effect on chemokine production and early initiation of this therapy appears to confer a more favorable chemokine profile.

Anti-HIV Agents↗
PubMed1999

Isolation and characterisation of the cDNA encoding a glycosylated accessory protein of pea chloroplast DNA polymerase.

The cDNA encoding p43, a DNA binding protein from pea chloroplasts (ct) that binds to cognate DNA polymerase and stimulates the polymerase activity, has been cloned and characterised. The characteristic sequence motifs of hydroxyproline-rich glyco-proteins (HRGP) are present in the cDNA corres-ponding to the N-terminal domain of the mature p43. The protein was found to be highly O-arabinosylated. Chemically deglycosylated p43 (i.e. p29) retains its binding to both DNA and pea ct-DNA polymerase but fails to stimulate the DNA polymerase activity. The mature p43 is synthesised as a pre-p43 protein containing a 59 amino acid long transit peptide which undergoes stromal cleavage as evidenced from the post-translational in vitro import of the precursor protein into the isolated intact pea chloroplasts. Surprisingly, p43 is found only in pea chloroplasts. The unique features present in the cloned cDNA indicate that p43 is a novel member of the HRGP family of proteins. Besides p43, no other DNA-polymerase accessory protein with O-glycosylation has been reported yet.

Amino Acid Sequence↗
PubMed1999

Liposomes complexed to plasmids encoding angiostatin and endostatin inhibit breast cancer in nude mice.

Gene therapy transfer of angiostatin and endostatin represents an alternative method of delivering angiogenic polypeptide inhibitors. We examined whether liposomes complexed to plasmids encoding angiostatin or endostatin inhibited angiogenesis and the growth of MDA-MB-435 tumors implanted in the mammary fat pads of nude mice. We determined that plasmids expressing angiostatin (PCI-Angio) or endostatin (PCI-Endo) effectively reduced angiogenesis using an in vivo Matrigel assay. We then investigated the efficacy of these plasmids in reducing the size of tumors implanted in the mammary fat pad of nude mice. Both PCI-Angio and PCI-Endo significantly reduced tumor size when injected intratumorally (P < 0.05). Compared to the untreated control group, the mice treated with PCI-Angio and PCI-Endo exhibited a reduction in tumor size of 36% and 49%, respectively. In addition, we found that i.v. injections of liposomes complexed to PCI-Endo reduced tumor growth in the nude mice by nearly 40% when compared to either empty vector (PCI) or untreated controls (P < 0.05). These findings provide a basis for the further development of nonviral delivery of antiangiogenic genes.

Angiostatins↗
PubMed1999

Apoptosis in isolated adult cardiomyocytes exposed to adriamycin.

Adriamycin (doxorubicin) is a highly potent antineoplastic agent, but its use is limited by the risk of developing cardiomyopathy and congestive heart failure. Available evidence suggests that adriamycin-induced congestive heart failure is mediated by oxidative stress. We examined the possibility of adriamycin-induced apoptosis in isolated adult rat cardiomyocytes and its inhibition by trolox, a water-soluble antioxidant. Cardiomyocytes isolated from rat hearts were exposed to 20 microM adriamycin for 1 h and examined at different post-treatment durations (0-23 h). Adriamycin caused a significant decrease in rod-shaped cells and an increase in round cells. Both Hoechst 33258 staining and TUNEL assay revealed a significantly increased number of apoptotic myocytes and nucleosomal fragmentation upon exposure to adriamycin. In agarose gel electrophoresis, DNA laddering was found to be more intense in adriamycin-exposed myocytes. A bright smear at the leading edge of the gels suggested indiscriminate fragmentation of DNA and myocyte necrosis by adriamycin. Both types of DNA degradations due to adriamycin were significantly reduced by trolox. We suggest that adriamycin-induced cell death involves both apoptosis and necrosis and these may be mediated by oxidative stress.

Animals↗