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N Chen

Publications and source records attributed to N Chen.

At least 199 records · Page 11Linked to original sources
PubMed1993

Polyclonal amanitin-specific antibodies: production and cytoprotective properties in vitro.

The amanitins found in several mushroom species are responsible for many deaths every year. Based on its successful application to cardiac glycoside overdose, immunotherapy could be applicable to amanitin toxicity. Therefore, we produced polyclonal amanitin antibodies by immunizing rabbits with a novel conjugate of alpha-amanitin. Purified antibodies had an average association constant for alpha-amanitin of 1.3 x 10(9) M-1. A partially protective effect of the antibodies against amanitin toxicity in vitro in Chang cells was evident at a molar ratio of antibody binding sites to alpha-amanitin of 4:1. Together with reported studies in vivo, these investigations indicate the potential of immunotherapy for amanitin poisoning.

Amanitins↗
PubMed1993

Phototoxicity of lumidoxycycline.

Doxycycline (DOTC) is a photosensitizing drug whose mechanism of phototoxicity is complicated by the large variety of stable photoproducts formed. To assess the role of a DOTC photoproduct, lumidoxycycline (LuDOTC), in the photosensitization mechanism of DOTC, MGH-U1 human bladder carcinoma cells were treated in vitro with either DOTC or LuDOTC, and irradiated with the 351-nm emission of an argon-ion laser. Both DOTC and LuDOTC were phototoxic and caused radiant-exposure-dependent inhibition of cellular incorporation of tritiated thymidine. On an absorbed-photon basis, DOTC was about five times as phototoxic as LuDOTC. Cellular uptake of DOTC was about five times as great as that of LuDOTC. Epifluorescence microscopy showed localization of LuDOTC predominantly within cellular membranes, particularly of mitochondria, as well as a low level of LuDOTC fluorescence diffusely within the cytoplasm. Epifluorescence microscopy of cells labeled with the mitochondrial probe, rhodamine 123, showed mitochondrial fragmentation and altered mitochondrial membrane integrity after LuDOTC photosensitization; these effects depended on radiant exposure and were partially reversible by 24 h after irradiation. For both DOTC and LuDOTC, phototoxicity was increased by irradiation in the presence of deuterium oxide and decreased in the presence of sodium azide, effects consistent with an important mechanistic role for singlet oxygen, O2(1 delta g), in the injury. In solution, LuDOTC and DOTC had similar quantum yields for generation of O2(1 delta g) as measured by time-resolved spectroscopy and by O2(1 delta g) trapping. LuDOTC was photostable in solution, but DOTC underwent significant photodegradation. These data demonstrate that DOTC photo-products such as LuDOTC have significant photobiologic activity and may play an important role in the phototoxicity mechanism of DOTC.

Doxycycline↗
PubMed1993

How frequent are hepatitis B virus markers in adult patients with glomerular diseases in a low endemic country? A French study from Paris and Saint-Brieuc.

In order to appreciate the frequency of hepatitis B virus (HBV) infection in patients with glomerular diseases in France, a low endemic country, we reviewed the series of patients biopsied in the years 1983-1989 in 2 departments of nephrology differing by the characteristics of the population. In Saint-Brieuc, where the population is almost exclusively Caucasian, with nearly no immigrant, HBsAg was not detected in any of the 86 patients. In Paris, a large number of patients come from highly or intermediately endemic regions. HBsAg was detected in 3 of 209 patients, 2 of the 75 patients with membranous nephropathy and 1 of the 32 patients with minimal-change nephrotic syndrome. These patients came from Africa and Asia. Therefore, in low endemic countries, the role of HBV infection in the etiology of glomerulonephritis is minimal. But, because of the late severity of the disease, screening remains essential in patients belonging to the high-risk groups.

Adolescent↗
PubMed1992

Competition between paraquat and putrescine for uptake by suspensions of rat alveolar type II cells.

Paraquat and the structurally similar polyamines, such as putrescine and spermidine, are accumulated actively and selectively by the alveolar type II cells via the polyamine uptake system. We report the uptake kinetics of paraquat and putrescine and their mutual inhibition in freshly isolated rat type II cell suspensions. The uptake of paraquat by type II cells exhibited saturation kinetics and could be inhibited in a concentration-dependent manner by putrescine. By applying enzyme kinetic analysis to our experimental data it was demonstrated that the uptake of paraquat or putrescine is inhibited in a partially competitive manner by the respective inhibitor. Thus, we postulate that the polyamine uptake pathway in type II cells for paraquat and putrescine has two separate sites, one for each substrate, and that binding of one leads to a conformational change in the other.

Animals↗
PubMed1992

Induction of the major integral membrane protein of mouse liver peroxisomes by peroxisome proliferators.

Peroxisome proliferators are known to increase the volume of the peroxisomal compartment in rodent liver. We have examined the induction of the major integral membrane protein of mouse liver peroxisomes (PMP68) by a number of these agents, and compared this with their effect on the peroxisomal bifunctional protein (PBP), an enzyme of the beta-oxidation pathway which is located in the peroxisome matrix. Dietary clofibrate, di-2-(ethylhexyl)phthalate and Wy-14,643, three structurally unrelated proliferators, all increased the mRNA and protein content of PMP68 approx. 2-fold, whereas PBP was induced 8-13-fold. The kinetics and sequence of induction of PMP68 and PBP following a single dose of Wy-14,643 were compared and shown to be similar, and the effects were reversible. Another proliferator, BM 15766, caused maximal induction of PMP68 but only a low induction of PBP; further PBP induction was achieved by the administration of BM 15766 in combination with Wy-14,643. Similarly, BM 15766 and Wy-14,643 increased transcription of the PMP68 gene in vitro, whereas PBP gene transcription was increased by Wy-14,643 but not by BM 15766. Thus peroxisome proliferators enhance the expression of the genes for both the membrane protein PMP68 and the matrix protein PBP, but the regulation of this expression appears to be mediated by different mechanisms.

Amino Acid Sequence↗
PubMed1992

Azidowarfarin photoaffinity probes of purified rat liver cytochrome P4501A1.

Substrate specificity differences between various forms of cytochrome P450 (P450) are governed by substrate binding site amino acid residue differences. To determine the identities of these residues, four analogs of warfarin, a thoroughly investigated anticoagulant drug which is regio- and stereoselectively metabolized by many P450s, have been synthesized as photoaffinity probes. The probes 4'-, 6-, 7-, and 8-azidowarfarin were readily photolyzed in neutral solution by 254-nm light, with half-lives of less than 15 s. When the azidowarfarins were photolyzed in the presence of beta-naphthoflavone-inducible P4501A1 (2.5 microM) at -196 degrees C and the P450 was subsequently reconstituted for warfarin metabolism, 50% inactivation was achieved with 160 microM 4'-azidowarfarin, 64 microM 6-azidowarfarin, 127 microM 7-azidowarfarin, and 29 microM 8-azidowarfarin. This inactivation is irreversible. When these concentrations of the azidowarfarins were photolyzed prior to addition to P4501A1, less inhibition of P450 activity was detected and the inhibition was reversible. The CO-ferrous P450 spectrum of P4501A1 at 448 nm was diminished when photoactivated azidowarfarins bound to and inactivated the enzyme, with essentially no formation of P420 except in the case of 4'-azidowarfarin. The inactivation of P4501A1 by photoactivated 4'-azidowarfarin was prevented by 50% by 1.2 mM R-warfarin or 0.3 mM 4'-nitrowarfarin, consistent with the latter being a better P4501A1 substrate than R-warfarin. The photoinactivation of P4501A1 by each of the azidowarfarins was prevented to variable extents by R-warfarin or by 4'-, 6-, 7-, or 8-nitrowarfarin. Taken together these results demonstrate that all four azidowarfarins are potentially useful photoaffinity probes of the substrate binding site amino acid residues of P450s.

Affinity Labels↗
PubMed1992

Significance of the 56th tyrosine on cytotoxic activity of tumor necrosis factor.

After using site-specific mutagenesis a conserved amino acid residue, the 56th tyrosine in human tumor necrosis was substituted by glutamine. The expression level of the mutant protein in E. coli did not changed significantly, however, its specific activity of the cytotoxicity on L929 cultural cells was decreased to 1/583 of that of the unmutant tumor necrosis factor. The results show that the 56th tyrosine residue or the region where tyrosine 56th located is important for the cytotoxic activity of tumor necrosis factor.

Base Sequence↗
PubMed1991

Light-chain composition of serum IgA1 and in vitro IgA1 production in IgA nephropathy.

A predominant expression of IgA1 in mesangial deposits, serum, and bone marrow culture supernatants has been shown in IgA nephropathy (IgAN). Furthermore an excess of lambda light chains in both mesangial deposits and serum IgA has been observed. However, the origin of mesangial IgA remains controversial. In the present study, we have examined the IgA1 light chain type in IgAN. Total IgA1, IgA1 kappa and IgA1 lambda were measured by ELISA in serum and culture supernatants from spontaneous and pokeweed-mitogen (PWM)-stimulated peripheral blood mononuclear cells (PBMC). We observed an increase in IgA and IgA1 serum concentrations in IgA nephropathy patients, with a ratio of serum IgA1 to total serum IgA identical between patients and controls. The concentration of serum IgA kappa did not differ between patients and controls but patients had a significantly higher concentration of serum IgA lambda. The IgA1 kappa to IgA1 lambda ratio was 1.06 +/- 0.42 in IgAN patients versus 1.55 +/- 0.36 in controls (P less than 0.01). By contrast, the concentrations of IgA1 kappa and IgA1 lambda in PBMC culture supernatants, both spontaneous and PWM-stimulated, were identical in patients and controls. Therefore, there is a specific increase in IgA1 lambda in patients' sera. This contrasts with the normal IgA1 production by PBMC, which are derived from mucosal-associated lymphoid tissues. This suggests that IgA isotypic deregulation is confined to the bone marrow compartment and is not a generalised defect of the IgA system.

Adult↗
PubMed1991

Worldwide perspective of hepatitis B-associated glomerulonephritis in the 80s.

Chronic HBsAg carriers may develop glomerulonephritis (GN). Besides membranous GN (MGN), which seems a well established association, membranoproliferative GN (MPGN) or proliferative GN are also encountered in these patients. It is clear that the variations in the incidence of hepatitis B virus (HBV) GN may be real or related to a more or less vigorous search for HBV in the different nephrologic centers. However, the frequency of HBV GN in a country correlates with the underlying prevalence of HBV infection in the general population. Geographic patterns of HBV prevalence vary greatly from areas of low endemicity where less than 1% of adults are chronic carriers to areas of intermediate and high endemicity where between 2 and 15% of adults are chronic carriers. The most important factor affecting prevalence is age of HBV infection. The probability of becoming a chronic carrier is greater following infection during infancy and early childhood. The rarity of HBV GN in the U.S. and in western Europe probably reflects the rarity of HBV infection, especially in children. The frequency of HBV GN is high in Asian or Black children. It is possible to hope that, with the extensive immunization in countries of high endemicity, the frequency of HBV GN will diminish. In the U.S. and in Europe, patients with HBV GN frequently belong to high risk groups for HBV infection. In these countries, the increase in the percentage of HBV infection due to sexual transmission or linked with drug abuse may lead to an increase in the percentage of adult patients with HBV GN.

Africa↗
PubMed1990

Rhodamine 123 phototoxicity in laser-irradiated MGH-U1 human carcinoma cells studied in vitro by electron microscopy and confocal laser scanning microscopy.

Rhodamine 123 (R123) is a permeant, cationic, fluorescent dye that localizes preferentially within mitochondria of living carcinoma cells. MGH-U1 human bladder carcinoma cells incubated in vitro with 10 microM R123 for 30 min and then irradiated at 514.5 nm with an argon ion laser underwent selective, phototoxic injury to mitochondria. Ultrastructurally, treatment with R123 plus irradiation with 10 J/cm2 caused selective, progressive mitochondrial alterations consisting of disruption of cristae, vacuolization, swelling, increasing numbers of ring-shaped and angulated mitochondria at 4 to 8 h after irradiation, and obliteration of many mitochondria at 24 to 48 h. Confocal laser scanning microscopy after treatment with R123 plus irradiation with 10 to 30 J/cm2 demonstrated altered uptake and localization of subsequently administered R123, accompanied by striking mitochondrial fragmentation. Irradiation caused a dose-dependent depletion of extractable R123, due to a photosensitized efflux that began immediately and progressed by 4 h after irradiation with 10 to 30 J/cm2; further uptake after reincubation in the presence of R123 was also quantitatively impaired in cells previously irradiated with 30 J/cm2.

Carcinoma, Transitional Cell↗
PubMed1990

Effect of central obesity on regulation of carbohydrate metabolism in obese patients with varying degrees of glucose tolerance.

It has been proposed that central obesity, by virtue of the enhanced lipolytic activity of abdominal adipose tissue, leads to higher plasma FFA concentrations, which, in turn, decrease both hepatic removal of insulin and insulin-stimulated glucose uptake by peripheral tissues. In short, the predicted consequences of abdominal obesity are elevations in circulating FFA and insulin levels as well as insulin resistance. The goal of this study was to evaluate the relationships predicted by the overall hypothesis; this study was carried out in 31 obese females, defined as having normal glucose tolerance (n = 12), impaired glucose tolerance (n = 8), or noninsulin-dependent diabetes mellitus (n = 11). Abdominal obesity was estimated by determining the ratio of waist to hip girth, fasting and postprandial plasma FFA and insulin concentrations were measured at hourly intervals from 0800-1600 h, and insulin-stimulated glucose disposal was quantified by the euglycemic hyperinsulinemic clamp technique. The first step in the postulated sequence of events to be tested was that the greater the WHR, the higher the total integrated plasma FFA response. The correlation coefficient between these two variables was 0.29, indicating that the results did not support the prediction. Furthermore, we could not demonstrate any relationship between the magnitude of the plasma FFA and insulin responses (r = 0.20; P = NS). However, there was a modest inverse relationship between height of circulating plasma insulin concentration and a decrease in insulin-stimulated glucose uptake (r = -0.43; P less than 0.03) in the group as a whole. On the other hand, when the three groups were analyzed individually, a significant inverse relationship was only seen in the control group (r = -0.67), and a direct relationship was actually seen in patients with impaired glucose tolerance (r = 0.88). Furthermore, when the mean responses for the variables in each of the three groups were compared, it was apparent that the postulated relationships between abdominal obesity, plasma FFA concentration, and insulin secretion and action were not present. Thus, the data presented do not support the hypothesis that differences in the degree of central obesity play an important role in regulation of plasma concentrations of either FFA or insulin or in modulation of insulin-stimulated glucose uptake in the patients we studied.

Adipose Tissue↗
PubMed1990

[Effect of phospholipase A2 on pancreatic parenchymal necrosis in acute pancreatitis in rats].

The effect and mechanism of phospholipase A2 (PLA2) on pancreatic parenchymal necrosis in acute pancreatitis (AP) in rats were studied. Normal saline (NS), PLA2, phosphatidylcholine (PC), and PLA2 mixed PC were respectively injected into the biliopancreatic duct of the rat. The mixture of PLA2 and PC was found to result in necrotizing AP in the rat in 12 hours after injection of the reagent. The lysophosphatidylcholine (LPC) percentage in the amount of PC and LPC and the extent of pancreatic necrosis in this group increased much more significantly than those in other three groups (over about 4 and 15 times). There is evidently positive correlation (r = 0.9001, P less than 0.01) between LPC percentage and necrosis extent. The intraductal injection of PLA2, as well as NS or PC, failed to induce severe morphological changes in the pancreases. These results suggest that PC in bile is necessary in the pathogenesis of biliary pancreatitis and that LPC originated from bile PC by PLA2 may be the initiator in pancreatic parenchymal necrosis in AP.

Acute Disease↗
PubMed1990

Effects of the heat-tonification method on the surface temperature of the body observed by infra-red thermography.

With the infra-red thermography, 73 tests of the effect of Heat-Tonification maneuvers on body surface temperature were made. The experiments showed that application of Heat-Tonification produced marked elevation of temperature at the site of puncture, over the face and the front of the neck. The differences between pre- and post-needling temperatures were statistically significant (P less than 0.02 and P less than 0.01). Furthermore, 44.8% of the tests showed elevation of temperature over the trunk and extremities, and the distribution of temperature elevation followed the course of the meridians mostly. The findings demonstrated that the Heat-Tonification method mobilized Qi and activated Blood through influence over the vegetative nervous system that led to readjustment of blood circulation.

Acupuncture Therapy↗
PubMed1989

Rhodamine dyes as potential agents for photochemotherapy of cancer in human bladder carcinoma cells.

The phototoxicity in vitro of rhodamine 123 and tetrabromo rhodamine 123 (TBR) was compared, in order to assess their photochemotherapeutic potential. Exposure to 514.5-nm radiation from an argon ion laser caused phototoxicity in MGH-U1 bladder carcinoma cells previously treated with either dye at 10 microM for 30 min. As assessed by colony formation and cellular morphology, TBR was markedly more phototoxic than rhodamine 123, reflecting increased intersystem crossing of TBR to the triplet manifold via spin-orbital coupling induced by the heavy bromine atoms. Photoreactions of TBR very efficiently generated singlet oxygen (1O2) in solution; furthermore, irradiation of TBR-treated cells was significantly more toxic when performed in the presence of deuterium oxide, an enhancer of damage caused by 1O2. Retention of fluorescence in TBR-treated cells was enhanced by irradiation, indicating that a stable photoproduct may be formed in reaction with cellular components.

Antineoplastic Agents↗
PubMed1989

Dynamic aspects of rhodamine dye photosensitization in vitro with an argon-ion laser.

Phototoxicity in cultured human bladder carcinoma cells treated by 514.5-nm argon-ion laser irradiation plus rhodamine-123 (R123) or tetrabromo-R123 (TBR) was assessed counting total cell number and percent viability at 1, 24, 48, 72, and 96 h after irradiation. TBR was markedly more efficient than R123 at causing both reversible and persistent phototoxic cytostasis. Furthermore, TBR photosensitization caused net cytocidal effects at 0.5 J/cm2, which were not seen with R123 photosensitization at up to 40 J/cm2. The reduced phototoxic efficiency of R123 as compared to TBR appears, in part, to reflect the presence of a fraction of cells refractory to R123 photosensitization.

Antineoplastic Agents↗
PubMed1989

Effect of age on glucose tolerance and glucose uptake in healthy individuals.

Plasma glucose and insulin responses and basal and insulin-stimulated glucose uptake were determined in 24 non-obese, healthy, physically active individuals, divided into two groups on the basis of age. The mean (+/- SEM) age of the younger group was 33 +/- 3 years, in contrast to an age of 64 +/- 2 years for the older group. Plasma glucose concentrations were significantly higher (two-way ANOVA, P less than .001) for three hours after a 75 g oral glucose challenge in the older group, as was the plasma insulin response (two-way ANOVA, P less than .001). Furthermore, there was a significant correlation between age and total plasma glucose (r = 0.63, P less than .001) and insulin (r = 0.44, P less than .01) during the glucose tolerance test. However, the magnitude of the decrease in glucose tolerance with age was relatively modest. For example, total plasma glucose response was only 11% higher in the older group, and the plasma glucose concentration 120 minutes after the oral glucose load only increased approximately 2 mg/dL per decade. Glucose uptake during euglycemic clamp studies was also reduced in the older group, and this was true if the clamps were performed at plasma insulin concentration of approximately 10 microU/mL (P less than .05) or 60 microU/mL (P less than .10). However the differences were relatively modest in magnitude, ie, 10-25%. The fact that the increase in glucose uptake when plasma insulin was raised six-fold was similar in both groups suggests that insulin sensitivity does not decline with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗