PubMed Health⌕ Search

Biomedical subjects

N Rajan

Publications and source records attributed to N Rajan.

At least 19 recordsLinked to original sources
PubMed2001

Host pathogenesis in urinary tract infections.

Urinary tract infections (UTIs) are the result of an interaction between bacterial virulence and host defense factors that compete to invade or protect the host, respectively. Research over the past 30 years has demonstrated that vaginal colonization with uropathogens precedes most UTIs. Receptivity of the vaginal mucosa for uropathogens is an essential initial step in vaginal mucosa colonization. When vaginal and buccal epithelial cells were collected from patients susceptible to reinfection and compared with such cells obtained from controls resistant to UTIs, the strains that caused cystitis adhered much more avidly to the epithelial cells from susceptible women. These genotypic traits for epithelial cell receptivity may be a major susceptibility factor in UTIs. The presence or absence of blood group determinants on the surface of uroepithelial cells may influence an individual's susceptibility to UTIs. The protective effect in women with the secretor phenotype may be due to fucosylated structures at the cell surface which decrease the availability of putative receptors for Escherichia coli. Susceptibility among women who do not secrete blood group antigens may be due to specific E. coli-binding glycolipids that are absent in women who secrete blood group antigens. Recent studies have shown that the vaginal fluid, which forms an interface between uropathogens and epithelial cells, also influences vaginal colonizations.

Bacterial Adhesion↗
PubMed2000

Characterization of an immortalized human vaginal epithelial cell line.

PURPOSE: Adherence of type 1 piliated Escherichia coli to vaginal mucosa plays a major role in the pathogenesis of ascending urinary tract infections (UTIs) in women. Progress in understanding the mechanism of adherence to the vaginal surface could be enhanced by the utilization of well-characterized vaginal epithelial cells. The objective of this study was to immortalize vaginal epithelial cells and study their bacterial adherence properties. MATERIALS AND METHODS: Primary vaginal cells were obtained from a normal post-menopausal woman, immortalized by infection with E6/E7 genes from human papillomavirus 16 (HPV 16) and cultured in serum free keratinocyte growth factor medium. RESULTS: Positive immunostaining with a pool of antibodies to cytokeratins 1, 5, 10 and 14 (K1, K5, K10 and K14) and to K13 confirmed the epithelial origin of these cells. The immortalized cells showed binding of type 1 piliated E. coli in a pili specific and mannose sensitive manner. CONCLUSION: This model system should facilitate studies on the interaction of pathogens with vaginal mucosal cells, an essential step in the progression of ascending UTIs in women.

Bacterial Adhesion↗
PubMed1999

Histidine-193 of rat glucosylceramide synthase resides in a UDP-glucose- and inhibitor (D-threo-1-phenyl-2-decanoylamino-3-morpholinopropan-1-ol)-binding region: a biochemical and mutational study.

Glucosylceramide synthase (GCS) catalyses the transfer of glucose from UDP-glucose (UDP-Glc) to ceramide to form glucosylceramide, the common precursor of most higher-order glycosphingolipids. Inhibition of GCS activity has been proposed as a possible target of chemotherapeutic agents for a number of diseases, including cancer. Design of new GCS inhibitors with desirable pharmaceutical properties is hampered by lack of knowledge of the secondary structure or catalytic mechanism of the GCS protein. Thus we cloned the rat homologue of GCS to begin studies to identify its catalytic regions. The histidine-modifying agent diethyl pyrocarbonate (DEPC) inhibited recombinant rat GCS expressed in bacteria; this inhibition was rapidly reversible by hydroxylamine and could be diminished by preincubation of GCS with UDP-Glc. These data suggest that DEPC acts on histidine residues within or near the UDP-Glc-binding site of GCS. Mutant proteins were expressed in which the eight histidine residues in GCS were individually replaced by other amino acids. H193A (His193-->Ala) and H193N (His193-->Asn) mutants were unaffected by 0.1 mM DEPC, a concentration that inhibited other histidine mutants and the wild-type enzyme by at least 60%. These results indicate that His193 is the primary target of DEPC and is at, or near, the UDP-Glc-binding site of GCS. His193 mutants were also insensitive to the GCS inhibitor d-threo-1-phenyl-2- decanoylamino-3-morpholinopropan-1-ol, at concentrations which inhibited the wild-type enzyme by >80%. These results have significance for both an understanding of the GCS active site and also for the possible design of new and specific inhibitors of GCS.

Amino Acid Sequence↗
PubMed1999

Roles of glycoproteins and oligosaccharides found in human vaginal fluid in bacterial adherence.

Adherence of type 1-piliated Escherichia coli to carbohydrate structures of vaginal mucosa plays a major role in the pathogenesis of ascending urinary tract infections in women. Colonization of the vaginal introitus is influenced by interactions between pathogens, vaginal fluid, and vaginal epithelium. In this study, the type and amount of carbohydrates and glycoproteins present in vaginal fluid were determined. Free and protein-bound oligosaccharides in vaginal fluid specimens were analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE) and high-pressure liquid chromatography (HPLC). Two-dimensional electrophoretic separations of vaginal fluid glycoproteins were performed together with bacterial overlay assays. The results of FACE showed that the majority of the oligosaccharides are in the free state and the bound oligosaccharides are undetectable. HPLC analysis of free sugars revealed glucose as the major sugar (3.3 +/- 0.3 mM), and the concentrations of mannose and glucosamine were 0.065 +/- 0.04 and 0.02 +/- 0.001 mM, respectively. Radiolabeled E. coli bound three vaginal fluid glycoproteins with the following molecular masses and pIs: 82 kDa and pI 5.5, 55 kDa and pI 4.5, and 55 kDa and pI 6.5. The binding was inhibited by mannose and by deglycosylation of the proteins prior to the overlay assay. One of these putative receptors was identified to be the heavy chain of secretory IgA (S-IgA). These data suggest that the free mannose in the fluid is less than that required to affect E. coli-epithelial cell binding interactions and that S-IgA may bind E. coli in the vaginal introitus.

Adult↗
PubMed1999

Hyperbaric oxygen therapy for radiation induced hemorrhagic cystitis.

PURPOSE: Radiation therapy has been used successfully to treat pelvic malignancy but morbidity from hemorrhagic cystitis remains a major long-term sequela in 1 to 2% of patients. Obliterative endarteritis secondary to ionizing radiation leads to tissue hypoxia and poor healing. Hyperbaric oxygen therapy has been demonstrated to improve angiogenesis and promote healing in radiation injured tissue, including the bladder. We describe the treatment and long-term followup of a cohort of patients treated with hyperbaric oxygen for hemorrhagic cystitis. MATERIALS AND METHODS: A total of 17 patients (mean age 62 years) with hemorrhagic cystitis received hyperbaric oxygen following failure of standard treatment modalities. Hyperbaric oxygen was administered on a once daily schedule (mean number of treatments 14) until hematuria resolved. Followup ranged from 9 to 60 months (mean 21). RESULTS: Hematuria resolved completely in 11 of 17 patients (64%), 2 had only residual microscopic hematuria, 2 had improvement but died of complications relating to cancer shortly after completion of treatment and 2 had recurrence of gross hematuria. Early application of hyperbaric oxygen was associated with earlier resolution of hemorrhagic cystitis. CONCLUSIONS: Radiation induced hemorrhagic cystitis that does not respond to standard regimens can be successfully treated with hyperbaric oxygen. This modality is well tolerated even in patients debilitated by advanced cancer and blood loss. Long-term remission can be achieved in the majority of patients.

Aged↗
PubMed1998

Nicotine abstinence syndrome precipitated by the competitive nicotinic antagonist dihydro-beta-erythroidine.

Rats infused subcutaneously with 9 mg/kg/day nicotine tartrate for 7 days exhibit behavioral abstinence signs following either termination of nicotine infusion or injection of the noncompetitive nicotinic antagonists mecamylamine (s.c.) or hexamethonium (ic.c.v.). This study examined the abstinence precipitating effects of dihydro-beta-erythroidine (DHbetaE), a competitive nicotinic antagonist. Twenty-four nicotine-dependent rats were injected in the third ventricle with 10, 18, or 25 microg DHbetaE in 20 microl saline or with saline alone and observed for abstinence signs over a 20-min period. There was a significant positive linear trend of overall abstinence signs as a function of dose, p < 0.01. In 12 nondependent rats, the high dose of DHbetaE did not induce more abstinence-like signs than saline alone. In a second experiment, 18 nicotine-dependent rats were injected s.c. with 1 or 6 mg/kg of the muscarinic antagonist scopolamine or with saline alone. Few abstinence signs were observed in any group: there was no significant drug effect. The results suggest that nicotine abstinence signs observed in the rat are specific to reduced stimulation of previously overstimulated nicotinic receptors.

Animals↗
PubMed1998

Effectiveness and cost effectiveness of single bolus treatment with abciximab (Reo Pro) in preventing restenosis following percutaneous transluminal coronary angioplasty in high risk patients.

OBJECTIVE: To assess the clinical effectiveness and cost effectiveness of abciximab in preventing restenosis after percutaneous transluminal coronary angioplasty (PTCA). DESIGN: Data from a previous study, the EPIC trial, were used because only this trial was able to provide event data capable of constructing a cost effectiveness analysis over six months. All other study data reviewed supported the findings of the EPIC trial. To provide indicative results on long term health outcomes, survival and event-free survival were extrapolated using US epidemiological data in a Markov modelling process. SETTING AND PATIENTS: Patients who were at high risk for ischaemic complications after PTCA, treated in the standard manner. INTERVENTIONS: Abciximab was added to the regimen of intravenous heparin and aspirin. RESULTS: The EPIC study (n = 2099) indicated an 8.1% absolute reduction in serious cardiovascular events (95% confidence interval 3.1% to 12.7%) and a 23% relative risk reduction (p = 0.001). Based on the six month trial period, the additional cost per patient free from a serious event (Australian dollars) is $13,012 and for a special risk/benefit measure of outcome, the additional cost is $14,243. Epidemiological data support extended survival and ischaemic event-free survival with clinically successful PTCA. The results of the modelled analysis indicate a cost per additional life-year gained of $5547 and a cost per additional year event-free of $4285. CONCLUSIONS: At up to six months abciximab offers improvements in clinically important outcomes. A modelling exercise explores and highlights the likelihood of significant long term health benefits. The analysis provides information for decision makers and funders to consider the value for money of abciximab.

Abciximab↗
PubMed1998

Economic evaluation of insulin lispro versus neutral (regular) insulin therapy using a willingness-to-pay approach.

This willingness-to-pay (WTP) analysis is the first study of its kind undertaken in Australia to support an application for listing of a new drug on the Australian national formulary. The technique offers the advantage of being able to summarise diverse outcomes of therapy in a single unit of measure. Willingness to pay is used to value benefits in cost-benefit analysis (CBA), and CBA represents an absolute decision rule. An open-ended question with a bid-up approach was used to minimise bias and elicit the maximum amount patients would be willing to pay for insulin lispro. The WTP study incorporated scenarios describing the outcomes from insulin lispro and neutral (regular) insulin, the results from a formal metaanalysis and a description of the injection characteristics of the therapies. A sample of 83 patients with type I or II diabetes mellitus were surveyed using an open questionnaire to determine their maximum willingness to pay for the therapy they preferred. Overall, 92% of patients preferred insulin lispro (referred to as insulin A) and 8% preferred neutral insulin (referred to as insulin B). The incremental benefit per patient was calculated as 452.16 Australian dollars ($A) per year. Insulin lispro was listed on the Australian national formulary at a 36% premium over neutral insulin, so the additional cost per patient would be $A70.32 per year. Therefore, costs were exceeded by the benefits and insulin lispro was deemed to offer a net benefit. A multivariate analysis indicated that those patients who were middle-aged had the strongest preference for insulin lispro.

Australia↗
PubMed1997

Nicotine abstinence syndrome precipitated by central but not peripheral hexamethonium.

A rodent model of nicotine dependence has been developed based on continuous subcutaneous (s.c.) infusion of nicotine tartrate. Nicotine abstinence syndrome was precipitated by s.c. injection of the nicotinic antagonist mecamylamine, which freely crosses the blood-brain barrier. In contrast, the nicotinic antagonist hexamethonium crosses the blood-brain barrier very poorly. This study determined whether central or peripheral administration of hexamethonium could precipitate nicotine abstinence. In the first experiment, 26 nicotine-dependent rats were injected s.c. with 0.5, 5 or 10 mg/kg hexamethonium dichloride or saline alone and observed for 20 min. Few abstinence signs were observed in any group; there was no significant drug effect. In the second experiment, 18 rats were cannulated in the third ventricle and rendered nicotine dependent. One week later, rats were injected through the cannula with 12 or 18 ng hexamethonium or saline alone and observed for 20 min. Both dose groups differed significantly from the saline-injected group, and there was a significant positive linear trend of signs as a function of dose. The high dose had no significant effect in 14 nondependent rats. We conclude that hexamethonium is much more potent by the central route, and there is a major central nervous system component in nicotine dependence.

Animals↗
PubMed1996

Human interleukin 4 receptor complex: neutralization effect of two monoclonal antibodies.

The interaction of human interleukin 4 with the extracellular domain of its receptor alpha-subunit (shuIL-4R alpha) was characterized in studies utilizing chemical cross-linking, size exclusion chromatography, and Western blot analysis. A 1:1 stoichiometric complex could be demonstrated over a wide range (0.04-2.7) of ligand-receptor concentration ratios. It could also be cross-linked with bifunctional reagents containing a minimum chain length of eight methylene residues or the equivalent (11.4 angstroms). Using surface plasmon resonance, (SPR) technology, we established the high-affinity of human interleukin 4 (huIL-4) to shuIL-4R alpha which was immobilized on a BIAcore sensor chip (K(d) = 46 pM). The mechanisms of action of neutralizing monoclonal antibodies (Mab) 25D2 and 35F2 [Abrams et al. (1991) U.S. Patent 5,041,381; Ramanathan et al. (1990) in Advances in Gene Technology: The Molecular Biology of Immune Diseases and the Immune Response (Streilein, J. W., et al., Eds.) p 163, IRL Press, Oxford; DeKruyff et al. (1989) J. Exp. Med. 170, 1477-1493] were subsequently evaluated on the basis of their interaction with huIL-4 in the presence of shuIL-4R alpha. SPR studies showed that Mab 25D2 binds to huIL-4 and reduces its affinity for shuIL-4R alpha by 54-fold. Formation of a ternary complex between Mab 25D2 and the huIL-4/shuIL-4R alpha complex was demonstrated in size exclusion chromatography experiments. In contrast, Mab 35F2 which also binds huIL-4 failed to form a stable ternary complex with huIL-4 and shuIL-4 alpha during size exclusion chromatography. SPR studies supported this finding and showed that the interactions of Mab 35F2 and shuIL-4R alpha to huIL-4 are mutually exclusive. These data are consistent with results of previous epitope mapping studies showing that Mabs 25D2 and 35F2 bind to huIL-4 at two different sites [Ramanathan et al. (1993) Biochemistry 32, 3549-3556]. Together, the results suggest that Mab 25D2 binds to a domain in huIL-4 including helix D and exerts its inhibitory effect through a dual action. It decreases the affinity of huIL-4 for huIL-4R alpha and potentially blocks interaction with a secondary receptor subunit such as the IL-2R gamma [Reusch et al. (1994) Eur. J. Biochem. 222, 491-499]. Mab 35F2 operates through a direct and simpler mechanism, binding to helix C and inhibiting huIL-4 activity by sterically excluding all interaction with huIL-4R alpha.

Animals↗
PubMed1996

Stomach as a conduit for esophagus--a study of 105 cases.

BACKGROUND: The stomach is a well known esophageal substitute. To analyze the mortality and morbidity following total laryngopharyngoesophagectomy (TLPE) with pharyngogastric anastamosis done as a single-stage procedure. METHODS: The technique employed was esophageal extraction by stripping method followed by gastric pull up. In 104 patients transportation of the stomach was done through posterior mediastinum and in one patient through presternal route. RESULTS: Significant post-operative complications included pharyngocutaneous fistula in 15 patients (14.3%) and pneumonitis in 20 patients (19%), Fifteen patients (14.3%) died due to the causes related to surgery. All patients who survived were able to swallow solid and liquid food, on an average of 14 days post-operatively. CONCLUSION: The stomach as a conduit following TLPE is a procedure which has given satisfying results when done in carefully selected patients.

Adult↗