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H Xia

Publications and source records attributed to H Xia.

At least 91 records · Page 5Linked to original sources
PubMed1997

Characterization of a BMS-181174-resistant human bladder cancer cell line.

This study was undertaken to elucidate the mechanism of cellular resistance to BMS-181174, a novel analogue of mitomycin C (MMC), in a human bladder cancer cell line. The BMS-181174-resistant variant (J82/BMS) was established by repeated continuous exposures of parental cells (J82) to increasing concentrations of BMS-181174 (9-40 nM) over a period of about 17 months. A 2.6-fold higher concentration of BMS-181174 was required to kill 50% of J82/BMS cell line compared with J82. The J82/BMS cell line exhibited collateral sensitivity to 5-fluorouracil (5-FU), but was significantly more cross-resistant to MMC, melphalan, taxol, doxorubicin and VP-16. NADPH cytochrome P450 reductase and DT-diaphorase activities, which have been implicated in bioreductive activation of MMC, were significantly lower in the J82/BMS cell line than in J82. The cytotoxicity of BMS-181174, however, was not affected in either cell line by pretreatment with dicoumarol, which is an inhibitor of DT-diaphorase activity. These results argue against a role of DT-diaphorase in cellular bioactivation of BMS-181174, a conclusion consistent with that of Rockwell et al (Biochem Pharmacol, 50: 1239-1243, 1995). BMS-181174-induced DNA interstrand cross-link (DNA-ISC) frequency was markedly lower in J82/BMS cell line than in J82 at every drug concentration tested. The results of the present study suggest that cellular resistance to BMS-181174 in J82/BMS cell line may be due to reduced DNA-ISC formation. However, the mechanism of relatively lower BMS-181174 induced DNA-ISC formation in J82/BMS cell line than in parental cells remains to be clarified.

Antineoplastic Agents, Alkylating↗
PubMed1997

Age might influence the frequency distribution of metoprolol hydroxylation polymorphism in a Chinese population.

The frequency distribution of the 8-hour urinary ratio of metoprolol/alpha-hydroxymetoprolol (MR) was investigated in 206 healthy rural Chinese volunteers. The frequency of the poor metabolizer phenotype of metoprolol alpha-hydroxylation was 0% in this Chinese population. When the 206 subjects were subgrouped into four groups by age, the excretion of alpha-hydroxymetoprolol was significantly lower in the subjects with age older than 41 years compared to two younger groups (16-30 years), and the metoprolol hydroxylation metabolic ratio(metoprolol/a-hydroxymetoprolol, MR) was higher in these middle-aged subjects, indicating that age may affect the frequency distribution of the 8-hour urinary MR or log MR, although multiple regression analysis did not show a significant correlation between age, urine volume and MR. Also, a significant correlation was found between age and the excretion (percentage of dose) of alpha-hydroxymetoprolol in 8-hour urine (r = 0.259, P < 0.001). On the other hand, both multiple regression analysis and nonparametric tests showed that the larger the amount of urine excreted, the more metoprolol was recovered, demonstrating that the urinary excretion of unchanged metoprolol is renal flow-limited.

Adolescent↗
PubMed1997

Regulation of neuronal nitric oxide synthase through alternative transcripts.

Nitric oxide (NO) participates in diverse physiological processes ranging from neurotransmission to muscle relaxation. Neuronal-derived NO can be either beneficial or detrimental depending on the cellular context. Neuronal NO synthase (nNOS) must therefore be tightly regulated. One level of regulation involves synthesis of numerous nNOS mRNA transcripts. At least six distinct molecular species of nNOS mRNA are expressed in a tissue and developmentally-regulated manner. Alternative splicing allows the creation of nNOS proteins differing in both enzymatic characteristics and structural features. As one example, we find that there are nNOS mRNAs lacking exon 2. One isoform, nNOS beta, retains full enzymatic activity but lacks a major protein-protein interaction domain (PDZ domain) responsible for targeting nNOS to synaptic membranes. This alternative splicing produces a mislocalized but fully active protein which may be relevant to certain pathologies. As evidence of this, we find that many human brain tumors express an alternatively spliced form of nNOS that co-migrates with nNOS beta, and lacks exon 2. Finally, we also find a 2.5-kb testis-specific nNOS mRNA corresponding to the C-terminal reductase domain of nNOS whose function is unclear.

Animals↗
PubMed1997

Detection of mycoplasma infection of mammalian cells.

Mycoplasma infection was detected in cultures of COS cells with a novel, simple assay that detects the conversion of arginine to citrulline by the enzyme, arginine deiminase, specific to all species of mycoplasma. Transfection of COS cells was inhibited in mycoplasma-infected cells, a phenomenon that was readily reversed by treatment with a mycoplasma removal agent. Cultures of cells used for transfection should be regularly monitored for evidence of mycoplasma by assay of arginine deiminase activity or by other methods.

Animals↗
PubMed1997

CCD-3693: an orally bioavailable analog of the endogenous neuroactive steroid, pregnanolone, demonstrates potent sedative hypnotic actions in the rat.

An endogenous neuroactive steroid, pregnanolone, and an orally available synthetic analog, CCD-3693, were administered to rats at the middle of their circadian activity phase (6 hr after lights off). Electroencephalogram-defined sleep-wake states, locomotor activity and body temperature were concurrently measured 30 hr before and after treatment. Identical procedures were used to test triazolam and zolpidem. Triazolam (0.1-1.6 mg/kg), zolpidem (2.5-10 mg/kg) and the neuroactive steroids (10-30 mg/kg) produced dose-dependent increases in non-rapid eye movement (NREM) sleep. At this dose and time of day (in which the rats were predominantly awake during the 6 hr before treatment) the neuroactive steroids appeared more intrinsically efficacious in promoting NREM sleep than the benzodiazepine ligands. The neurosteroids did not, however, significantly interfere with rapid eye movement sleep and were more selective in reducing (EEG) wakefulness, with relatively less locomotor activity impairment during waking than triazolam and zolpidem. In addition, the benzodiazepine receptor ligands showed distinct "rebound" wakefulness after the NREM sleep-promoting effect subsided, although the neuroactive steroids did not. In addition, in vitro binding studies and in vivo pharmacological data confirmed that CCD-3693 was orally active in standard tests of anxiety, anticonvulsant, loss-of-righting and passive avoidance.

Administration, Oral↗
PubMed1997

[Analysis of the curative effect on ascites in liver cirrhosis by integrated traditional Chinese and Western medicine].

Eighty eight patients with cirrhosis ascites were treated with regular medicine and peritoneal cavity administration or with traditional Chinese medicine and western medicine. The results were as follows: The urine volume per day was markedly increased in the group treated with traditional Chinese medicine and western medicine, the abdominal circuit decreased, and the time of ascites disappearonce significantly shortened. There was a significant difference betwee the regular group and the peritoneal cavity administration group (P < 0.01); the serum albumin/globulin ratio was remarkably increased (P < 0.05). The curative effect on ascites disappearonce in the traditional Chinese medicine and western medicine group prevailed over the other two groups (P < 0.01).

Adult↗
PubMed1996

An alpha class mouse glutathione S-transferase with exceptional catalytic efficiency in the conjugation of glutathione with 7beta, 8alpha-dihydroxy-9alpha,10alpha-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene.

The kinetics of the conjugation of glutathione (GSH) with anti-7beta, 8alpha-dihydroxy-9alpha,10alpha-oxy-7,8,9, 10-tetrahydrobenzo(a)pyrene (anti-BPDE) catalyzed by GSH S-transferase (GST) isoenzymes purified from the liver and forestomach of female A/J mouse has been investigated. The GST isoenzymes studied included an alpha class isoenzyme of forestomach (GST 9.5), alpha class hepatic isoenzymes mGSTA3-3 and mGSTA4-4, pi class hepatic isoenzyme mGSTP1-1, and mu class hepatic isoenzyme mGSTM1-1. When the concentration of (+)-anti-BPDE was varied (5-120 microM) at a fixed GSH concentration (2 mM), linear Lineweaver-Burk plots were observed for each isoenzyme. The kcat values for GST 9.5, mGSTA3-3, mGSTP1-1, mGSTM1-1, and mGSTA4-4 were 2.0, 0.02, 0.40, 0. 05, and 0.01 s-1, respectively, with corresponding Km values of 16, 12, 29, 27, and 49 microM. The catalytic efficiency (kcat/Km) of GST 9.5 in the conjugation of GSH with (+)-anti-BPDE, which is believed to be the ultimate carcinogenic metabolite of benzo(a)pyrene, was about 9-625-fold higher as compared with other mouse GST isoenzymes. These results indicate that GST 9.5 of forestomach is different among mammalian alpha class GSTs because (+)-anti-BPDE has been shown to be a poor substrate for alpha class rat or human GST isoenzymes. The catalytic efficiency of GST 9.5 was approximately 4.5-fold higher than that of pi class human isoenzyme (hGSTP1-1), which among human GSTs is reported to be most efficient in the detoxification of (+)-anti-BPDE. Unlike rat GST isoenzymes, linear Lineweaver-Burk plots were observed for mouse GSTs when GSH was used as a variable substrate. The catalytic efficiencies of the mouse GSTs toward (+)-anti-BPDE were about 2-20-fold higher as compared with the (-)-enantiomer of anti-BPDE. The results of the present study suggest that GST 9.5 may play an important role in the detoxification of (+)-anti-BPDE.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1996

Glutathione S-transferases of female A/J mouse liver and forestomach and their differential induction by anti-carcinogenic organosulfides from garlic.

This study characterizes glutathione (GSH) S-transferase (GST) isoenzymes of the liver and forestomach of the female A/J mouse and compares their specificities in catalyzing the conjugation of GSH with 7beta,8alpha-dihydroxy-9alpha,10alpha-oxy-7,8,9, 10-tetrahydrobenzo[a] pyrene (anti-BPDE), the ultimate carcinogenic metabolite of benzo[a]pyrene (BP). The GST activity in female A/J mouse liver was expressed by a minimum of seven isoenzymes which arose from different homo- or heterodimeric combinations of at least two alpha class (designated as alpha1 and alpha4), four micro class (micro1 to micro4), and one pi class GST subunit. The GST isoenzyme composition of A/J mouse forestomach appeared to be different from that of the liver. For example, while GST isoenzymes containing micro3 and micro4 type subunits were selectively expressed in the liver, an alpha class heterodimeric GST isoenzyme (containing alpha2 and alpha3 subunits) was expressed in the forestomach but could not be detected in the liver. The (+)-anti-BPDE appeared to be a better substrate than the (-)-enantiomer for all GSTs, except for isoenzymes containing the alpha4 type GST subunit. The murine pi class GST isoenzyme displayed relativey higher specific activity toward (+)-anti-BPDE compared to other GSTs. The specific activities of mouse GSTs toward (+)-anti-BPDE were in the order of pi > micro > alpha. These results suggest that the pi class GST isoenzyme may play an important role in providing protection against BP-induced cancer. Therefore, it seems logical to postulate that the ability of a chemoprotector to increase the expression of GST pi may be an important determinant of its effectiveness against BP-induced cancer. To test the validity of this contention, we have determined the effects on hepatic and forestomach GST isoenzyme/subunit expression of three naturally occurring organosulfides (OSCs) from garlic, which significantly differ in their effectiveness against BP-induced forestomach cancer. Treatment of mice with diallyl sulfide (DAS) and diallyl trisulfide (DATS), which are potent inhibitors of BP-induced fore- stomach cancer in mice, resulted in a significant increase in hepatic and forestomach GST activity toward anti-BPDE. On the contrary, this activity was not increased in either organ by dipropyl sulfide (DPS), which is ineffective against BP-induced forestomach cancer. The chemopreventive efficacy of these OSCs correlated with their ability to increase the expression of GST pi. For example, DAS treatment resulted in approximate increases of 1.7- and 2.2-fold in hepatic and forestomach GST pi expression, respectively, over the control. Treatment of mice with DATS, which is a relatively more potent inhibitor of BP-induced forestomach cancer than DAS, resulted in about 3.8- and 3.2-fold increases, respectively, in hepatic and forestomach GST pi expression over the control. On the contrary, the expression of hepatic and forestomach GST pi was increased only marginally (10-20%) upon DPS administration. In conclusion, the results of the present study suggest that induction of GST pi can be used as a bioassay for screening potential inhibitors of BP-induced cancer.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1996

Novel anti-carcinogenic activity of an organosulfide from garlic: inhibition of H-RAS oncogene transformed tumor growth in vivo by diallyl disulfide is associated with inhibition of p21H-ras processing.

In this study, we report a novel anticarcinogenic activity of an organosulfur compound from garlic, diallyl disulfide (DADS). DADS treatment significantly inhibited the growth of H-ras oncogene transformed tumors in nude mice. As compared to controls, the appearance of tumors was also delayed markedly by oral administration of DADS. The inhibition of tumor growth by DADS treatment correlated with the inhibition of p21H-ras membrane association in the tumor tissue. The levels of membrane associated p21H-ras were markedly lower in the tumor tissues of DADS treated mice as compared to controls. An opposite trend, however, was evident for cytosolic p21H-ras. Furthermore, DADS treatment resulted in a significant inhibition of hepatic as well as tumoral 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. These results indicate that DADS suppresses the growth of H-ras oncogene transformed tumors in nude mice by inhibiting the membrane association of tumoral p21H-ras.

Allyl Compounds↗
PubMed1996

Lack of a role of glutathione in cellular nonenzymatic activation of BMS-181174, a novel analogue of mitomycin C.

Recent studies, using a cell-free system, have suggested that thiol-dependent nonenzymatic bioactivation may be responsible for the superior antitumor activity of the mitomycin C analogue BMS-181174 [N-7-[2-(4-nitrophenyldithio)ethyl]mitomycin C] when compared to the parent compound. If operational in tumor cells, this pathway could have enormous clinical implications since tumor cell resistance to a variety of anticancer agents is often associated with increased glutathione (GSH) levels and BMS-181174 may be used to reverse this mechanism of resistance. The present study was undertaken to determine the role of GSH in cellular activation of BMS-181174 using a pair of well-characterized human bladder cancer cells (J82 and SCaBER) as a model. A 20-h pretreatment of J82 and SCaBER cells with a nontoxic concentration of D,L-buthionine-S,R-sulfoximine (BSO) caused about 80-88% reduction in cellular GSH levels. Surprisingly, the sensitivity of both cells to BMS-181174 was increased, not reduced, by BSO-induced GSH depletion. On the other hand, the cytotoxicity of BMS-181174 was significantly reduced in both cells by a 4-h pretreatment with 1 mM GSH. Like BSO, a 4-h pretreatment with another thiol compound (cysteine) resulted in a statistically significant sensitization of both cells to BMS-181174. Cellular GSH levels were not affected in either of the cell lines by pretreatment with GSH or cysteine. In conclusion, the results or the present study argue against a role of GSH in cellular nonenzymatic activation of BMS-181174 in J82 and SCaBER cells.

Antineoplastic Agents, Alkylating↗
PubMed1996

Neuronal nitric-oxide synthase-mu, an alternatively spliced isoform expressed in differentiated skeletal muscle.

Nitric oxide (NO) functions as a molecular mediator in numerous processes in cellular development and physiology. Differential expression and regulation of a family of three NO synthase (NOS) gene products help achieve this diversity of action. Previous studies identify post-translational modification and interaction of NOS with specific protein targets as tissue-specific modes of regulation. Here, we show that alternative splicing specifically regulates neuronal NOS (nNOS, type I) in striated muscle. nNOS in skeletal muscle is slightly more massive than nNOS from brain owing to a 102-base pair (34-amino acid) alternatively spliced segment between exons 16 and 17. Following purification, this novel nNOS mu isoform has similar catalytic activity to that of nNOS expressed in cerebellum. nNOS mu appears to function exclusively in differentiated muscle as its expression occurs coincidentally with myotube fusion in culture. An isoform-specific antibody detects nNOS mu protein only in skeletal muscle and heart. This study identifies alternative splicing as a means for tissue-specific regulation of nNOS and reports the first additional protein sequence for a mammalian NOS since the original cloning of the gene family.

Alternative Splicing↗
PubMed1996

Biochemical characterization of a mitomycin C-resistant human bladder cancer cell line.

This study describes characteristics of a mitomycin C (MMC)-resistant human bladder cancer cell line, J82/MMC-2, which was established by repeated in vitro exposures of a 6-fold MMC-resistant variant (J82/MMC) to 18 nM MMC. A 9.6-fold higher concentration of MMC was required to kill 50% of the J82/MMC-2 sub-line compared with parental cells (J82/WT). NADPH cytochrome P450 reductase and DT-diaphorase activities were significantly lower in J82/MMC-2 cells compared with J82/WT, suggesting that reduced sensitivity of J82/MMC-2 cells to MMC resulted from impaired drug activation. Consistent with this hypothesis, the formation of MMC-alkylating metabolites was significantly lower in J82/MMC-2 cells compared with J82/WT. Furthermore, DT-diaphorase activity in J82/MMC-2 cells was significantly lower compared with the 6-fold MMC-resistant variant. Glutathione (GSH) levels were comparable in all 3 cell lines. Although GSH transferase (GST) activity was significantly higher in the J82/MMC-2 cells compared with J82/WT, this enzyme activity did not differ between 6- and 9.6-fold MMC-resistant variants. Whereas DNA polymerase alpha mRNA expression was comparable in these cell lines, levels of DNA ligase I mRNA were slightly lower in both MMC-resistant variants relative to J82/WT. However, the DNA polymerase beta mRNA level was markedly higher in the J82/MMC-2 cell line compared with either J82/WT or J82/MMC. Thus, emergence of a higher level of resistance to MMC in J82/MMC-2 cells compared with J82/MMC may be attributed to (i) impaired drug activation through further reduction in DT-diaphorase activity and (ii) enhanced DNA repair through over-expression of DNA polymerase beta.

Antibiotics, Antineoplastic↗
PubMed1996

Interaction of nitric oxide synthase with the postsynaptic density protein PSD-95 and alpha1-syntrophin mediated by PDZ domains.

Neuronal nitric oxide synthase (nNOS) is concentrated at synaptic junctions in brain and motor endplates in skeletal muscle. Here, we show that the N-terminus of nNOS, which contains a PDZ protein motif, interacts with similar motifs in postsynaptic density-95 protein (PSD-95) and a related novel protein, PSD-93.nNOS and PSD-95 are coexpressed in numerous neuronal populations, and a PSD-95/nNOS complex occurs in cerebellum. PDZ domain interactions also mediate binding of nNOS to skeletal muscle syntrophin, a dystrophin-associated protein. nNOS isoforms lacking a PDZ domain, identified in nNOSdelta/delta mutant mice, do not associate with PSD-95 in brain or with skeletal muscle sarcolemma. Interaction of PDZ-containing domains therefore mediates synaptic association of nNOS and may play a more general role in formation of macromolecular signaling complexes.

Amino Acid Sequence↗
PubMed1996

Expression of neuronal-NOS in developing basal forebrain cholinergic neurons: regulation by NGF.

Nerve growth factor (NGF) acts through the receptor tyrosine kinase trkA to serve as a trophic factor for cholinergic neurons in the medial septal nucleus and vertical limb of the diagonal band. We have previously shown that the neuronal isoform of nitric oxide synthase (NOS) is selectively expressed in a large fraction of trkA-expressing cholinergic neurons in these brain regions in the adult rat, and that NGF induces the expression of neuronal-NOS in these cells. Herein, we show that: 1) neuronal-NOS is also localized to these neurons in the developing septum; 2) the expression of neuronal-NOS is regulated in the developing medial septal nucleus and vertical limb of the diagonal band; 3) neuronal-NOS regulation parallels that for other markers of basal forebrain cholinergic neuron differentiation, such as cholineacetyltransferase; and 4) NGF infusion in the postnatal period induces robust increases in neuronal-NOS mRNA and in NOS activity in the basal forebrain. Taken together with earlier findings, our results suggest that neuronal-NOS has a role in the differentiation and mature function of septal cholinergic neurons. Through enhancing neuronal-NOS synthesis, endogenous NGF is likely to regulate NO functions in vivo.

Acetylcholinesterase↗