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Biomedical subjects

P Mehta

Publications and source records attributed to P Mehta.

At least 109 records · Page 6Linked to original sources
PubMed1994

The expression and processing of human beta-amyloid peptide precursors in Saccharomyces cerevisiae: evidence for a novel endopeptidase in the yeast secretory system.

In mammalian cells, the transmembrane beta-amyloid peptide precursor (beta-APP) undergoes a complex series of alternative proteolytic processing steps that result in the secretion of varying proportions of its extra-cellular domain (protease nexin II) and beta-amyloid peptide. The protein is also reinternalized and degraded in the endosomal-lysosomal system. The relative efficiencies of these competing processes determine the yield of beta-amyloid peptide. Several proteases have been implicated in this complex processing pathway, although none has been identified to date. The yeast secretory system contains proteases homologous to mammalian pro-hormone convertases and is susceptible to genetic manipulation. We therefore investigated the expression and processing of the beta-amyloid peptide precursors (beta-APP-695 and beta-APP-751) in Saccharomyces cerevisiae transformed with human beta-APP cDNA's. beta-APP (695 or 751) cDNA either with its authentic signal sequence or the yeast-derived prepro-alpha-factor leader, was inserted into a glucose-regulated expression vector and transfected into a protease-deficient yeast strain. In all instances, expression of beta-APP was about 1% of total protein. Protease protection studies indicated that either the natural human signal sequence or the alpha-factor leader sequence targetted beta-APP to the endoplasmic reticulum and inserted it with the amino-terminal domain in the lumen. All of the beta-APP fused to the alpha-factor leader proceeded to the trans-Golgi, where Kex2 endopeptidase removed the leader and released the normal amino-terminus of beta-APP. About one-half of the beta-APP was also cleaved at the "alpha-secretase" site in the middle of the beta-peptide sequence, 12 residues before the membrane-spanning sequence. A fraction of the alpha-secretase-cleaved beta-APP appeared in the culture medium; however, most of it associated with the exterior of the cells. The carboxyl-terminal fragments formed by cleavage at the alpha-secretase site accumulated in the membranes. Other proteolytic processes generated membrane-associated carboxyl-terminal fragments that also resembled those found in mammalian cells. These results indicate that the secretory system of S. cerevisiae possesses proteases with specificities similar to the mammalian enzymes that process beta-APP.

Amino Acid Sequence↗
PubMed1993

Groove- and sequence-selective alkylation of DNA by sulfonate esters tethered to lexitropsins.

A series of sulfonate esters that are attached to a noncationic minor-groove-binding N-methylpyrrole dipeptide (Lex) related to netrospin have been synthesized. The compounds prepared differ in two respects: (1) the length [(CH2)2 vs (CH2)8] of the tether between the DNA affinity binding portion of the molecule and the sulfonate ester and (2) whether a methyl group [MeOSO2(CH2)n-Lex] or the dipeptide including the aliphatic tether [MeSO2O(CH2)n-Lex] is covalently transferred to the DNA. The DNA-cleavage patterns of these bimolecular alkylating compounds have been mapped in 32P-end-labeled restriction fragments using neutral thermal hydrolysis and alkali treatment to expose single-strand breaks at bases with thermally labile modifications. In contrast to the alkylation of DNA by simple alkyl alkanesulfonate esters, that predominantly yield major-groove alkylation at N7-guanine, the modification of DNA by MeOSO2(CH2)n-Lex and MeSO2O(CH2)n-Lex occurs primarily at N3-adenine residues associated with previously footprinted Lex DNA affinity binding regions. The ratio for the formation of N3-methyladenine (minor groove) to N7-methylguanine (major groove) in calf thymus DNA is 1:7 for dimethyl sulfate, while only the former adenine product is observed with MeSO2O(CH2)n-Lex indicating the change in groove specificity. DNA cleavage by MeOSO2(CH2)n-Lex and MeSO2O(CH2)n-Lex is efficiently inhibited by the coaddition of distamycin; however, only the DNA damage generated by the latter is blocked by NaCl. As expected, increasing the length of the (CH2)n tether from n = 2 to n = 8 moves the alkylation site by 1-2 base pairs further from the affinity binding domain. Finally, a comparison of the methylation patterns of MeOSO2(CH2)n-Lex as a function of tether length provides an insight into Lex sequence and orientational preferences.

Alkanesulfonates↗
PubMed1993

Prognostic significance of immunohistochemical analysis of cathepsin D in low-stage breast cancer.

BACKGROUND: Cathepsin D is an estrogen-regulated lysosomal protease that may be overexpressed in breast cancer. Several studies based on biochemical analysis of tumor cytosol have shown that high levels of cathepsin D are associated with poor outcome in patients with breast cancer. In contrast, a few immunohistochemical studies have shown that cathepsin D positivity in breast cancer cells indicates a favorable prognostic outcome or is of no prognostic significance. METHODS: Because of the current controversy, the authors studied, using immunohistochemistry, the distribution (0 to 3) and intensity (0 to 3) of cathepsin D in Stage I and II infiltrating ductal carcinoma of the breast from 245 patients treated at the City of Hope National Medical Center, Duarte, California, from 1970 to 1986. A commercially available rabbit antiserum to purified human cathepsin D and the standard avidin-biotin complex method were used. Statistical analysis was based on a combined low (0 or 2) or high (3 to 6) score. RESULTS: A high cathepsin D score was associated with Stage II disease (P = 0.007), positive lymph nodes (P = 0.019), high nuclear grade (P = 0.005), and c-erbB-2 oncogene amplification (P = 0.013). Cathepsin D positivity was not an independent prognostic indicator of disease-free survival (DFS) or overall survival (OS). In a subgroup analysis, the presence of cathepsin D had only a modest association with predicting a shorter DFS in patients with negative lymph nodes (P = 0.072) or positive progesterone receptors (PR) (P = 0.086). CONCLUSIONS: Immunohistochemical analysis of cathepsin D, with the antiserum used in this study, is not an independent predictor of outcome in patients with breast cancer because of its strong associations with several well-established prognostic indicators.

Adult↗
PubMed1993

Codeine disposition in sickle cell patients compared with healthy volunteers.

The pharmacokinetics of codeine were determined after oral administration of codeine sulfate (60 mg) with sickle cell patients (SCPs) and healthy controls (HCs). Plasma concentrations of codeine were measured by reversed-phase high-pressure liquid chromatography with fluorescence detection. Pharmacokinetic parameters were calculated using both compartmental and noncompartmental analysis. No significant differences were observed in time to reach maximum peak plasma concentration (tmax) (1.0 +/- 0.4 versus 1.4 +/- 1.0 hours), maximum peak plasma concentration (Cmax) (172 +/- 25 versus 225 +/- 97 ng/mL), area under the curve (AUC infinity) (590 +/- 96 versus 779 +/- 234 ng*h/mL), and Cl/F (104 +/- 17 versus 89 +/- 27 L/h) between SCPs and HCs. Conversely, significant differences were observed in mean residence time (MRT) (3.7 +/- 0.3 versus 4.7 +/- 0.3 hours) and half-life (t1/2) (1.7 +/- 0.2 versus 2.8 +/- 0.3 hours). In a separate study, significant differences were observed in the in vitro plasma protein binding of codeine in SCPs (66.0 +/- 8.6%) and HCs (30.5 +/- 2.7%) as well as in vivo binding (68.4 +/- 11.1% for SCPs versus 29.2 +/- 3.4% for HCs). Codeine is a relatively high-extraction drug that is primarily eliminated by metabolism in the liver. Generally, the clearance of such drugs is approximately equal to hepatic blood flow and is not affected by changes in protein binding. Therefore, the change in t1/2 observed in SCPs can be attributed to changes in volume of distribution rather than clearance.

Adult↗
PubMed1993

Microbial degradation of aquatic biomass by Trichoderma viride 992 and Aspergillus wentii 669 with reference to the physical structure.

There was a considerable change in the structural parameters of both the lignocellulosic substrates. This change was confirmed by infrared (IR) spectroscopy and X-ray diffraction data, which revealed the presence of phenolic groups in the peaks range 1310-1410 and 1200 cm-1 with large crystalline substrates. These were found to be reduced after treatment with alkali. Enzyme/s activity were found to be increased after pretreatment of hydrolysed substrates. The structural modifications in both the substrates were further evidenced by the results obtained after enzymatic hydrolysis of alkali-treated substrates.

Aspergillus↗
PubMed1993

Increased erythrocyte and protein binding of codeine in patients with sickle cell disease.

Erythrocyte binding and plasma protein binding of codeine in sickle cell patients and healthy controls were determined. A reversed-phase HPLC procedure was used for codeine analysis. Codeine was extracted from alkalinized plasma, separated on a CN column, and assayed by fluorescence detection. The erythrocyte-buffer partition coefficient was significantly higher in sickle cell patients (1.72 +/- 0.21) than in healthy controls (1.25 +/- 0.14). No time dependence of partitioning was observed. The fraction of codeine bound to plasma proteins, determined by ultrafiltration, was significantly higher in sickle cell patients (66.0% +/- 8.6%) than in healthy controls (30.5% +/- 2.7%). No concentration dependence of erythrocyte or protein binding was observed. Further studies were performed to elucidate the binding mechanisms. From a ghost cell binding study it was concluded that the major binding sites for codeine are in the cell membrane. A decrease in codeine binding was observed in the presence of bilirubin. Codeine binding to alpha 1-acid glycoprotein was found to be minimal. The levels of alpha 1-acid glycoprotein and other glycoproteins in sickle cell patients and healthy controls were measured by glycoprotein electrophoresis. The results showed no significant difference between the two groups. Plasma protein electrophoresis was performed for the two groups. The results showed a significant difference in gamma-globulin levels between sickle cell patients and healthy controls. Codeine is known to bind to gamma-globulin, a fact that may explain in part the observed increase in the plasma protein binding of codeine in sickle cell patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia, Sickle Cell↗
PubMed1993

Antibiotic inhibition of pectolytic and cellulolytic enzyme activity in two Fusarium species.

Among all antibiotics tested, amoxycillin (500 ppm) completely inhibited the polygalacturonase and pectinmethylgalacturonase enzyme activity in F. oxysporum; none of the antibiotics did so in F. moniliforme. No antibiotic completely inhibited the cellulase activity in both test organisms, however, amoxycillin was better than other antibiotics in inhibiting the cellulase activity in both the organisms.

Amoxicillin↗
PubMed1993

Sensitivity and specificity of Gold types 1 to 5 anti-carcinoembryonic antigen monoclonal antibodies: immunohistologic characterization in colorectal cancer and normal tissues.

Carcinoembryonic antigen (CEA) is one of the better-studied oncodevelopmental antigens to which numerous monoclonal antibodies (MoAbs) have been generated. Many of these MoAbs have been recently grouped (Gold classification) according to their epitope recognition. The present study was designed to immunocharacterize various MoAbs, each representative of the five Gold groups, on colorectal cancers and normal tissues using semiquantitative immunohistochemistry. Sensitivity, based on the number of colorectal cancer cases (n = 100) with positive reaction (> 5% cells), was greater with Gold groups 1 and 2 (93% each) than with groups 3, 4, and 5 (78%, 83%, and 87%, respectively). The intensity of the strain also correlated with the Gold groups, with 24%, 20%, and 18% of cancer cases displaying weak or negative staining (0 or 1+) when reacted with MoAbs from groups 3, 4, and 5, respectively, versus 6% and 12% with Gold 1 and 2 antibodies. Cross-reactivity of the anti-CEA antibodies with CEA-related molecules was found to be significant with Gold 5 antibody, which stained most of the normal lung, liver, stomach, and intestinal tissues tested. Strong staining also was seen in granulocytes when they were reacted with Gold 4 and 5 antibodies. The other antibodies showed much less and variable cross-reactivity with normal tissues, with a not statistically significant advantage for Gold 1 antibodies. In addition to lower sensitivity in CEA detection, Gold 3 to 5 MoAbs were less specific due to cross-reaction with one or more of the CEA-related macromolecules expressed by normal tissues. Based on these results and given the broad clinical applications of anti-CEA MoAbs, it is essential to characterize each MoAb to be used for clinical purposes in order to avoid interpretation errors of potential relevance resulting from poor sensitivity/specificity. The use of antibodies that recognize the epitope of group 1 or 2 is recommended to maximize sensitivity and specificity for CEA detection.

Antibodies, Monoclonal↗
PubMed1993

Improvement of the quantification of estrogen and progesterone receptors in paraffin-embedded tumors by image analysis.

It has been shown previously that estrogen receptors (ER) detected by immunohistochemical examination of paraffin-embedded tissue sections could be quantified by computerized image analysis. Several factors were identified that were, in part, responsible for the modest correlation obtained with biochemical assay results. In the present study, 45 formalin-fixed, paraffin-embedded breast carcinomas from a previous study were reevaluated to determine if current methods could provide a better correlation and more consistent results. Sections of the tumors were made to react with estrogen and progesterone receptor antibodies (ER-ICA and PgR-ICA) and the intensity of the stain was quantified using an image analysis system. Vimentin immunostain was used to assess the degree of antigenic loss. Quantitation was performed only on the areas with nuclear staining. The correlation of the estrogen and progesterone receptor values obtained by the dextran charcoal-coated method with the percentages of stained areas and with the intensity of the stain was excellent. The agreement between both methods was 91.1% for estrogen and 86.7% for progesterone receptor values. These results represent a significant improvement compared with those found in a previous study (87% agreement for estrogen receptor). The current approach to estrogen and progesterone receptor quantitation is simplified and eliminates subjectiveness in the selection of the fields for evaluation. The studies are reproducible because discrepancies due to sampling techniques are excluded. Finally, the method validates the technique as a substitute for cytosol-based methods. The results of the two vastly dissimilar assays, the pitfalls of the "gold standard" dextran charcaol-coated assay, and the need for retrospective studies to acquire a range of quantified ER-ICA and PgR-ICA values with clinical significance are discussed.

Breast Neoplasms↗
PubMed1993

Effect of hyperkalemia on myocardial depression by verapamil in isolated hearts.

Verapamil can produce depression of left ventricular function, delayed atrioventricular conduction, and hypotension, which can be potentiated by hyperkalemia. We sought to investigate a direct cardiac interaction between verapamil and hyperkalemia. Studies utilized isolated guinea pig hearts (Langendorff) paced at 250 beats/min. Hearts were randomly assigned to perfusion (Krebs-Henseleit buffer) with potassium concentrations ([K]+) of 1.5, 3, 6 and 9 mmol/l. Infusion of verapamil at rates of 0.2 to 60 micrograms/min (approximately 3 x 10(-8) to 10(-5) mol/l) produced concentration-dependent reduction of isovolumic left ventricular developed pressure. As [K]+ increased, concentration response curves showed parallel shifts to the left. The ED50 for reduction of left ventricular developed pressure significantly decreased: 8.2 +/- 3.7, 2.9 +/- 1.4, 1.2 +/- 0.7, 0.6 +/- 0.2 micrograms/min (mean +/- SD), respectively. Nifedipine and diltiazem were also studied in hearts perfused with 3 and 9 nmol/l [K]+. Infusion of nifedipine 0.003-1 microgram/min (approximately 10(-9) to 3 x 10(-7) mol/l) produced concentration-dependent reduction of left ventricular developed pressure but the ED50 was not affected by [K]+: 0.06 +/- 0.03 and 0.05 +/- 0.04 microgram/min, respectively. Nifedipine vehicle was without effect at the infusion rates tested. Infusion of diltiazem 2-200 micrograms/min (approximately 3 x 10(-7) to 3 x 10(-5) mol/l) also produced concentration-dependent reduction of left ventricular developed pressure. The ED50 for diltiazem-induced reduction of left ventricular developed pressure was significantly reduced by elevated [K]+: 20.1 +/- 6.7 and 3.5 +/- 0.9 micrograms/min with 3 and 9 mmol/l [K]+, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Vimentin-negative epithelioid sarcoma. The value of an immunohistochemical panel that includes CD34.

Virtually all reported cases of epithelioid sarcoma have been vimentin rich, and the coexpression of vimentin and keratin is considered a characteristic immunophenotype in these tumors. We report three cases of soft tissue tumors with histologic and clinical features consistent with epithelioid sarcoma, all of which failed to immunoreact by standard immunohistochemistry for vimentin using two different monoclonal antibodies. Antigen retrieval demonstrated focal vimentin staining in one case, whereas the other two remained negative. An extensive panel of immunohistochemical stains revealed strong diffuse staining with keratin and epithelial membrane antigen in all three cases as well as patchy membrane staining with an antibody to CD34. CD34 positivity is commonly seen in epithelioid sarcoma, but it is very rarely found in carcinomas. We conclude that these cases represent a unique immunophenotypic variant of epithelioid sarcoma that can be immunohistochemically confirmed, despite the lack of identifiable vimentin, by their immunoreactivity for keratin and CD34.

Adult↗
PubMed1993

Effect of antiretroviral therapy on the cerebrospinal fluid of patients seropositive for the human immunodeficiency virus.

Elevated levels of beta 2-microglobulin and neopterin in cerebrospinal fluid (CSF) have been associated with neurologic complications of infection with the human immunodeficiency virus (HIV). The effect of zidovudine (ZDV) on these markers was assessed by studying the effect of ZDV treatment duration on CSF levels in a cohort of 145 HIV-positive men who were receiving ZDV. CSF beta 2-microglobulin and neopterin levels were significantly lower in those who had been taking ZDV for an intermediate period of time (46-365 days) than in those who had received ZDV either long term (> 365 days) or short term (1-45 days). CSF quinolinic acid levels were independent of duration of ZDV administration. A second CSF evaluation was available after 1 year for 54 HIV-positive men (19 of whom were also in the first cohort) and 11 HIV-negative controls. Patients who had started ZDV between lumbar punctures showed a significant decrease in CSF beta 2-microglobulin, but in those who had been receiving ZDV for > 1 year beta 2-microglobulin increased (p = 0.001). The effect was not observed with neopterin (p = 0.14). (Quinolinic acid levels were not studied longitudinally.) Finally, we observed that CSF levels of beta 2-microglobulin, neopterin, and quinolinic acid correlated strongly with each other in HIV-positive individuals (r = 0.7, p < 0.0001), even though ZDV might have different effects on these markers. In conclusion, we report that initiation of ZDV therapy is associated with a transient decrease in CSF levels of beta 2-microglobulin and neopterin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Co-purification of 130 kD nitric oxide synthase and a 22 kD link protein from human neutrophils.

The synthesis of nitric oxide (NO) from L-arginine has been demonstrated in several cell types. Both constitutive and inducible forms of NO synthase have been described in different cells. We purified the constitutive form of NO synthase enzyme in human neutrophils using a two-column procedure. Crude 100,000g supernatant of human neutrophils was passed through a 2'-5'-ADP-agarose column followed by a DEAE-Bio-Gel A anion exchange column. NO synthase enzyme migrated as a single band (MW approximately 130,000) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Its activity was dependent upon nicotinamide adenine dinucleotide phosphate (NADPH) and (6R)-tetrahydro-L-biopterin (BH4). In addition, flavin adenine dinucleotide (FAD) was also found to be essential for its maximal activity. A second NADPH, FAD-dependent component (MW approximately 22kD) was also found consistently on the SDS-PAGE gel. These observations suggest co-regulation between NO synthase enzyme and this NADPH, FAD-dependent component, which may be associated with the superoxide radical generating system.

Amino Acid Oxidoreductases↗
PubMed1992

Tumor-associated antigen 43-9F is of prognostic value in squamous cell carcinoma of the lung. A retrospective immunohistochemical study.

BACKGROUND: Squamous cell lung carcinoma (SLC), the most frequent type of lung cancer, generally is treated surgically and its prognosis is poor. The only current clinically useful prognostic criterion is lymph node staging (TNM classification). Expression of a novel tumor-associated carbohydrate epitope Gal beta 1-3[Fuc alpha 1-4]GlcNAc beta 1-4[Fuc alpha 1-3]GlcNAc beta 1-3 Gal beta 1-4Glc identified by the 43-9F monoclonal antibody (MoAb) is associated with the growth pattern of SLC cell lines in athymic mice and in vitro. This implies that the 43-9F epitope may be related to tumor progression in patients with SLC and that, as such, it could be of prognostic value. METHODS: Primary tumor specimens from 231 patients with lung carcinoma (130 with SLC, 64 with adenocarcinoma, 10 with small cell carcinoma, 16 with large cell carcinoma, and 11 with adenosquamous carcinoma) were examined by immunohistochemical studies on formalin-fixed, paraffin-embedded tissue samples for immunoreactivity with an MoAb to the 43-9F antigen. Univariate and step-wise Cox regression analyses were used to compare survival time by histopathologic diagnosis, smoker status, TNM classification, and type of surgical treatment. RESULTS AND CONCLUSIONS: Patients with 43-9F epitope-positive SLC tumors had a significantly (P less than 0.01) better prognosis than patients with epitope-negative tumors. In contrast, no association was seen between 43-9F epitope expression and survival time for patients with lung adenocarcinomas. Further, the prognostic value of 43-9F expression in SLC was found to be superior to the N-classification with the added advantage that it requires access only to primary tumor tissue and thus is available before therapy.

Adult↗
PubMed1992

A study of toxicity and comparative therapeutic efficacy of vindesine-prednisone vs. vincristine-prednisone in children with acute lymphoblastic leukemia in relapse. A Pediatric Oncology Group study.

Vindesine (des-acetyl Vinblastine) is a synthetic derivative of vinblastine, and was produced with the hope that it would have less neurotoxicity and hematopoietic toxicity than other vinca alkaloids. Phase I and II studies also demonstrated significant activity in lymphoid malignancies, especially Acute Lymphoblastic Leukemia (ALL). The present study was designed to compare therapeutic effectiveness of twice weekly vindesine (2 mg/M2/dose) plus Prednisone (60 mg/M2/dose) (Treatment 1) to weekly Vincristine (2 mg/M2/dose) plus Prednisone (60 mg/M2/day) (Treatment 2). All patients were less than 21 years of age, and had documented bone marrow relapse (blast count > 25%). In 39 patients presumed sensitive to vincristine, there were 11 complete responses out of 20 patients (55%) randomized to receive vindesine/prednisone and 7 complete responses out of 19 patients (37%) treated with Vincristine/Prednisone. In 37 patients resistant to vincristine, there were 7 complete responses (19%). Vindesine was more toxic than Vincristine. Major toxicities of vindesine included paraesthesias, peripheral neuropathy and ileus. Vindesine hematological toxicity appeared greater, but such toxicity is hard to assess in patients with bone marrow disease. In this study, vindesine and vincristine had similar efficacy, but vindesine use was associated with more toxicity.

Adolescent↗