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Biomedical subjects

V Ramachandran

Publications and source records attributed to V Ramachandran.

At least 37 records · Page 2Linked to original sources
PubMed2000

The role of conjugation in hepatotoxicity of troglitazone in human and porcine hepatocyte cultures.

In primary human and porcine hepatocyte cultures, we investigated the relationship between metabolism and cytotoxicity of troglitazone. Treatment of human hepatocytes for 2 h with 10, 20, 25, 35, and 50 microM troglitazone in protein-free medium resulted in concentration-dependent decreases in total protein synthesis. Decreases at 10 and 20 microM were reversible by 24 h, however protein synthesis did not recover at concentrations >/=25 microM. Troglitazone at 50 microM caused cellular death. In porcine hepatocytes, 100 microM troglitazone was lethal, whereas at 50 microM, protein synthesis completely recovered by 24 h. Recovery in protein synthesis was associated with metabolism of parent drug, whereas toxicity correlated (r(2) = 0.82) with accumulation of unmetabolized troglitazone. By 1 h, in human hepatocytes, troglitazone was metabolized to similar amounts of sulfate and quinone metabolites with little glucuronide detected. In contrast, porcine hepatocytes metabolized troglitazone to the similar amounts of glucuronide and the quinone metabolites with little sulfate detected. Exposure of human hepatocytes to a combination of 10 microM troglitazone and 10 microM 2,4-dichloro-4-nitrophenol resulted in a 70% decrease in protein synthesis, associated with 90% inhibition in the formation of troglitazone sulfate, a 4-fold increase in unmetabolized troglitazone, and no effect on formation of the quinone metabolite. Treatment with a combination of acetaminophen or phenobarbital with 20 microM troglitazone resulted in sustained decrease in protein synthesis associated with inhibition of sulfation and accumulation of troglitazone. These results suggest that inhibition of troglitazone sulfation may result in increased hepatotoxicity due to exposure to parent drug, or increased metabolism by alternate pathways.

Acetaminophen↗
PubMed2000

Milk thistle, a herbal supplement, decreases the activity of CYP3A4 and uridine diphosphoglucuronosyl transferase in human hepatocyte cultures.

Milk thistle extract is one of the most commonly used nontraditional therapies, particularly in Germany. Milk thistle is known to contain a number of flavonolignans. We evaluated the effect of silymarin, on the activity of various hepatic drug-metabolizing enzymes in human hepatocyte cultures. Treatment with silymarin (0.1 and 0.25 mM) significantly reduced the activity of CYP3A4 enzyme (by 50 and 100%, respectively) as determined by the formation of 6-beta-hydroxy testosterone and the activity of uridine diphosphoglucuronosyl transferase (UGT1A6/9) (by 65 and 100%, respectively) as measured by the formation of 4-methylumbelliferone glucuronide. Silymarin (0.5 mM) also significantly decreased mitochondrial respiration as determined by MTT reduction in human hepatocytes. These observations point to the potential of silymarin to impair hepatic metabolism of certain coadministered drugs in humans. Indiscriminate use of herbal products may lead to altered pharmacokinetics of certain drugs and may result in increased toxicity of certain drugs.

Cells, Cultured↗
PubMed1999

Tyrosine replacement in P-selectin glycoprotein ligand-1 affects distinct kinetic and mechanical properties of bonds with P- and L-selectin.

Selectins are adhesion molecules that initiate tethering and rolling of leukocytes on the vessel wall. Rolling requires rapid formation and breakage of selectin-ligand bonds that must have mechanical strength to resist premature dissociation by the forces applied in shear flow. P- and L-selectin bind to the N-terminal region of P-selectin glycoprotein ligand-1 (PSGL-1), a mucin on leukocytes. To define determinants on PSGL-1 that contribute to the kinetic and mechanical properties of bonds with selectins, we compared rolling of transfected preB cells expressing P- or L-selectin on transfected cell monolayers expressing wild-type PSGL-1 or PSGL-1 constructs with substitutions in targeted N-terminal residues. Rolling through P- or L-selectin required a Thr or Ser at a specific position on PSGL-1, the attachment site for an essential O-glycan, but required only one of three nearby Tyr residues, which are sites for Tyr-SO(3) formation. The adhesive strengths and numbers of cells rolling through P- or L-selectin were similar on wild-type PSGL-1 and on each of the three PSGL-1 constructs containing only a single Tyr. However, the cells rolled more irregularly on the single-Tyr forms of PSGL-1. Analysis of the lifetimes of transient tethers on limiting densities of PSGL-1 revealed that L-selectin dissociated faster from single-Tyr than wild-type PSGL-1 at all shears examined. In sharp contrast, P-selectin dissociated faster from single-Tyr than wild-type PSGL-1 at higher shear but not at lower shear. Thus, tyrosine replacements in PSGL-1 affect distinct kinetic and mechanical properties of bonds with P- and L-selectin.

Amino Acid Sequence↗
PubMed1999

Chemopreventive potential of neem (Azadirachta indica) on 7,12-dimethylbenz[a]anthracene (DMBA) induced hamster buccal pouch carcinogenesis.

The inhibitory effect of the aqueous extract of neem (Azadirachta indica A. Juss.) on 7,12-dimethylbenz[a]anthracene (DMBA) induced buccal pouch carcinogenesis was investigated in Syrian male hamsters. All hamsters painted on their buccal pouch with DMBA for 14 weeks developed squamous cell carcinoma. Administration of neem leaf extract effectively suppressed oral carcinogenesis initiated with DMBA as revealed by the reduced incidence of neoplasms. Lipid peroxidation, glutathione (GSH) content and the activities of glutathione peroxidase (GPx), glutathione S-transferase (GST) and gammaglutamyl transpeptidase (GGT) were used to biomonitor the chemopreventive potential of neem. Lipid peroxidation was found to be significantly decreased, whereas GSH, GPx, GST and GGT were elevated in the oral mucosa of tumour bearing animals. Our data suggest that neem may exert its chemopreventive effects in the oral mucosa by modulation of lipid peroxidation, antioxidants and detoxification systems.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1999

The use of human hepatocyte cultures to study the induction of cytochrome P-450.

We have previously reported that paclitaxel (Taxol) is a potent inducer of cytochrome P-450 (CYP) 3A protein and CYP3A mRNA in human hepatocyte cultures. Here we report that Taxol increased CYP3A-dependent testosterone 6beta-hydroxylation in intact hepatocytes. This effect was concentration-dependent, with maximal increase in enzyme activity being observed at 10 microM Taxol. Treatment of hepatocyte cultures with concentrations of Taxol higher than 10 microM caused a dose-dependent decrease in testosterone 6beta-hydroxylase activity, amount of CYP3A protein, and total protein synthesis. The maximal CYP3A activity detected after treatment with Taxol or rifampicin was similar in six separate human hepatocyte cultures, suggesting that the cultures have achieved a limit of maximally inducible CYP3A. The fold increase in enzyme activity, however, was different and was inversely related to the level of expression in untreated hepatocytes, with the greatest increases being observed in the hepatocytes that expressed the lowest basal level of CYP3A. Pretreatment of hepatocytes with triacetyloleandomycin resulted in a 90% inhibition of testosterone 6beta-hydroxylase activity. Our results demonstrate the use of human hepatocyte cultures to investigate the induction of cytochrome P-450 by xenobiotics in intact cells and stress the importance of large dose-response studies as well as the need to assess toxicity in these investigations. The response to inducers of CYP3A activity were very consistent among different hepatocyte donors. Absolute values of testosterone 6beta-hydroxylase activity did not vary more than 2- and 5-fold in induced and untreated hepatocytes, respectively.

Antibiotics, Antitubercular↗
PubMed1999

Troglitazone increases cytochrome P-450 3A protein and activity in primary cultures of human hepatocytes.

Troglitazone (TRO) is an insulin sensitizer used in the treatment of type II diabetes. TRO is known to increase the activity of cytochrome P-450 (CYP) 3A in vivo. We have investigated the effect of TRO on CYP3A protein content and the activity of CYP3A (as measured by the formation of 6beta-hydroxytestosterone formation) in primary cultures of human hepatocytes in comparison with rifampicin (RIF). Hepatocytes were isolated from four human livers by perfusion with collagenase, plated on collagen-coated plates, and maintained in William's E medium. After 48 h in culture, cells were exposed to RIF (10 microM) or TRO (0-50 microM) twice, each over a period of 24 h, and the activity of CYP3A was measured. TRO increased the activity of CYP3A in a concentration-dependent manner, reaching a maximal response at 5 microM. Pretreatment of the hepatocytes with 10 microM TRO or 10 microM RIF resulted in a 4- to 15-fold increase in the activity of CYP3A. Maximum increase in CYP3A protein was observed at 5 microM TRO. There was a significant correlation (R(2) = 0.89) between the content of immunoreactive CYP3A protein in the hepatocytes and the rate of formation of 6beta-hydroxytestosterone. These results indicate that TRO is a potent inducer of CYP3A and is similar to RIF in inducing CYP3A in human hepatocytes. At concentrations of 25 microM and above, TRO was toxic to the cells, as determined by a decrease in the activity of CYP3A, a reduction in the amount of immunoreactive protein, and changes in the morphology of the cells.

Aryl Hydrocarbon Hydroxylases↗
PubMed1998

Identification of N-terminal residues on P-selectin glycoprotein ligand-1 required for binding to P-selectin.

The major high affinity ligand for P-selectin on human leukocytes is P-selectin glycoprotein ligand-1 (PSGL-1). To bind P-selectin, PSGL-1 must be modified with tyrosine sulfate and sialylated, fucosylated, core-2 O-glycan(s). The required sites for these modifications on full-length PSGL-1 have not been defined. The N-terminal region of mature PSGL-1, which begins at residue 42, includes tyrosines at residues 46, 48, and 51, plus potential sites for Thr-linked O-glycans at residues 44 and 57. We expressed full-length PSGL-1 constructs with substitutions of these residues in transfected Chinese hamster ovary cells. The cells were co-transfected with cDNAs for the glycosyltransferases required to construct sialylated and fucosylated, core-2 O-glycans on PSGL-1. The transfected cells were assayed for their abilities to bind fluid-phase P-selectin and to support rolling adhesion of pre-B cells expressing P-selectin under hydrodynamic flow. In both assays, substitution of Thr-57 with alanine eliminated binding of PSGL-1 to P-selectin without affecting sulfation of PSGL-1, whereas substitution with serine, to which an O-glycan might also be attached, did not affect binding. Binding was not altered by substituting alanines for the two amino acids on either side of Thr-57, or by substituting alanine for Thr-44. Substitution of all three tyrosines with phenylalanines markedly reduced sulfation and prevented binding to P-selectin. However, all constructs in which one or two tyrosines were replaced with phenylalanines bound P-selectin. These results suggest that full-length PSGL-1 requires an O-glycan attached to Thr-57 plus sulfation of any one of its three clustered tyrosines to bind P-selectin.

Alanine↗
PubMed1997

Efficacy of partial wrap fundoplication for gastroesophageal reflux after repair of esophageal atresia.

Gastroesophageal reflux (GER) often develops in children who have undergone prior repair of esophageal atresia/tracheoesophageal fistula (EA/TEF). Fundoplication is necessary in many of these children. The complete wrap (Nissen) fundoplication is often used in this setting. However, poor results have been noted, with a mean failure rate of 30% reported in four recent studies. A partial wrap fundoplication for GER associated with EA/TEF is theoretically attractive, because the poor esophageal motility and diminished acid clearance (already physiologically present) is exacerbated by a complete wrap fundoplication. The authors reviewed their extensive experience with partial wrap (Thal) fundoplication in EA/TEF to determine if the failure rate was better than that reported for the Nissen fundoplication. In the past 18 years, the authors performed 1,467 fundoplication procedures. During the same period, 143 children underwent repair of EA/TEF. Fifty-nine children underwent fundoplication after a previous EA/TEF repair. Most of the fundoplications (58 of 59, 98%) were Thal procedures. Defining failure strictly as a need for reoperation, the failure rate in our series was 15% (9 of 59 children). Compared with the failure rate in the 1,408 non-EA/TEF patients (61 of 1408, 4.3%), results were significantly worse for the EA/TEF group (P > .001). The failure rate of Thal fundoplication performed for GER in the EA/TEF population is substantially higher than the non-EA/TEF patients. The same factors responsible for the development of reflux in these children (poor acid clearance, altered motility, esophageal shortening) may contribute to the higher failure rate. Although partial wrap fundoplication frequently failed (15%), the results were still substantially better than those reported for Nissen fundoplication in these children (30% failure rate).

Adolescent↗
PubMed1997

Detection of virulent Shigella and enteroinvasive Escherichia coli by induction of the 43 kDa invasion plasmid antigen, ipaC.

The invasion plasmid antigen, ipaC (43 kDa) of Shigella spp. and enteroinvasive Escherichia coli (EIEC) could be induced in vitro by growing them in the presence of Congo red. An enzyme-linked immunosorbent assay (ELISA) using antibodies to the 43 kDa protein of Shigella has been developed for specific detection of virulent Shigella spp and EIEC. The test is independent of initial isolation of individual colonies. As few as 10(2) CFU/ml of virulent Shigella present in mixed cultures could be detected and concurrently their susceptibility to antibiotics could be analysed after an initial growth of 8-16 h in Congo red-containing medium. The test may prove useful in the diagnosis and treatment of bacillary dysentery caused either by Shigella or EIEC through their rapid identification and proper antimicrobial therapy.

Antigens, Bacterial↗
PubMed1996

Thal fundoplication in neurologically impaired children.

Children with neurological impairment (NI) frequently require feeding gastrostomy, and this often aggravates or produces gastroesophageal reflux (GER). From 1976 to 1994, 141 children with severe NI underwent Thal fundoplication and gastrostomy (GT). GER was evident in 80%; in the rest, fundoplication was an adjunct to GT. Ph results were positive in 38 cases, and 57 children had reflux according to the barium studies. There were no major intraoperative complications. Disruption of the repair and/or recurrent GER was noted in 14 cases (10%); 8 were redone as Thals, and 6 were converted to Nissen procedures. Pyloroplasty was done later in 9 children (6%). Bowel obstruction was seen in 4 patients (3%). Clinical follow-up (mean, 54 months) showed improvement in 96%; only 5 of the 141 (3.2%) have residual symptoms. Of the patients with an intact Thal, 67% could burp or vomit. The ability to vomit may protect the Thal fundoplication and avoid disruption of the repair.

Adolescent↗
PubMed1996

Esophageal duplication cyst with esophageal web and tracheoesophageal fistula.

The authors report the case of lower cervical/upper thoracic esophageal duplication associated with an obstructing esophageal web. This presented in the newborn period as an esophageal atresia. Initial resection of the web and closure of the fistula were performed. The duplication was excised electively at 2 months of age. Persistent symptomatic tracheomalacia required aortopexy, after which the child recovered uneventfully. There are only three other reports (four cases) in the literature of esophageal atresia (or variants) associated with esophageal duplication.

Aorta↗
PubMed1996

Genetic diversity of Neisseria gonorrhoeae IB-2 and IB-6 isolates revealed by whole-cell repetitive element sequence-based PCR.

Phenotypic characterization of 19 Neisseria gonorrhoeae serovar IB-2 and 8 serovar IB-6 isolates by the combined use of auxotypes, serological characterization, and penicillin susceptibility testing indicated intraserovar genetic diversity. In the present study, we applied whole-cell repetitive element sequence-based PCR (rep-PCR) analysis which allows a rapid assessment of the clonal relationships of IB-2 and IB-6 isolates. DNA templates were prepared by boiling cells harvested directly from plate cultures, eliminating the need for time-consuming phenol extraction. Six different rep-PCR profiles were established among the 19 IB-2 isolates. Rep-PCR typing results had a good correlation with pulsed-field gel electrophoresis patterns. It is slightly less discriminatory than BglII-generated macrorestriction pattern analysis by pulsed-field gel electrophoresis. It is capable of discriminating epidemiologically related from epidemiologically unrelated IB-2 isolates. It should serve as a rapid and useful subtyping tool for epidemiologic investigations in which there is a predominance of major serovar groups.

Bacterial Typing Techniques↗
PubMed1994

Characterization and partial purification of the human receptor for the heat-stable enterotoxin.

The receptor for the Escherichia coli heat-stable enterotoxin has been characterized and partially purified from the T84 human colonic cell line. Using a novel mutant heat-stable enterotoxin peptide as a radioligand (the C-terminal tyrosine residue is replaced by phenylalanine in the mutant), a single class of high-affinity receptor sites was detected in T84 cells, with a Kd of 0.1 nM, similar in affinity to the receptor described in human intestinal tissue. The receptor was solubilised from T84 cell membranes and affinity cross-linking of the solubilised preparation indicated that a single species of M(r) 160,000 served as the receptor. Freshly solubilised preparations of the receptor retained heat-stable enterotoxin-activable guanylyl cyclase activity. Purification of the receptor was achieved through sequential affinity chromatography on GTP--epoxy-Sepharose and wheat-germ-agglutinin columns resulting in purification of the receptor by 3000 fold. The heat-stable enterotoxin-binding characteristics of the receptor were unchanged during the purification and silver staining of the purified receptor preparation indicated a band of M(r) 160,000, which was specifically cross-linked to the 125I-labeled mutant peptide. The purified receptor retained guanylyl cyclase activity, but the activity was not stimulated on addition of human heat-stable enterotoxin, suggesting that accessory structural factors may be involved in the activation of the guanylyl cyclase/receptor.

Bacterial Toxins↗
PubMed1991

Effect of DDT on plant mineral nutrition.

DDT added to soil at a concentration of 50 microg g(-1) had no inhibitory effects on germination and plant growth of barley, mung and rice, but considerably inhibited the oilseed species tested in the laboratory. The uptake of one or other ions was affected in varying degrees, with plants grown in DDT-treated soils. Detailed field studies of a peanut crop further confirmed the inhibition of ion uptake with DDT, especially Ca(2+) and K(+). Reduced uptake of (86)Rb by germinated peanut seeds in the presence of DDT further supported the observations made with K(+). Cell number and length in plants were reduced in plants grown in DDT-treated soil and the role of calcium is discussed. It appears that growth inhibition in oil seed plants may arise from the low levels of Ca(2+) and K(+) in plants grown in DDT-treated soils.

Journal Article↗
PubMed1990

Jejunogastric intussusception as a technique for in situ resection.

A technique for resection of irreducible, gangrenous jejunogastric intussusception is presented. In comparison with previously described resection procedures involving division of the stoma, dismantling of the gastrojejunostomy or higher gastrectomy, in situ resection is simple and safe.

Anastomosis, Surgical↗