Biomedical subjects
Publications and source records attributed to K Zhao.
Morphological and histological characters of the roots of Euphorbia prolifera Buch.-Han., a traditional Chinese medicine, were described and illustrated with line drawings. TLC analysis of the above drug was also undertaken. These studies provide referencial informations for clinics, quality control, development and identification of this crude drug.
Lymphocyte activation is accompanied by visible changes in chromatin structure. We find that antigen receptor signaling induces the rapid association of the BAF complex with chromatin. PIP2, which is regulated by activation stimuli, is sufficient in vitro to target the BAF complex to chromatin, but it has no effect on related chromatin remodeling complexes containing SNF2L or hISWI. Purification and peptide sequencing of the subunits of the complex revealed beta-actin as well as a novel actin-related protein, BAF53. beta-actin and BAF53 are required for maximal ATPase activity of BRG1 and are also required with BRG1 for association of the complex with chromatin/matrix. This work indicates that membrane signals control the activity of the mammalian SWI/SNF or BAF complex and demonstrates a direct interface between signaling and chromatin regulation.
The effect of chemical penetration enhancers (e.g., eugenol, d-limonene and menthone in combination with 50% ethanol) on the in vitro percutaneous absorption of tamoxifen through porcine epidermis has been investigated. The above enhancers significantly increased (p<0.05) the permeability coefficient of tamoxifen in comparison with the control (50% ethanol). Fourier transform infrared spectroscopy (FT-IR) was employed to investigate the biophysical changes in the stratum corneum (SC) lipids by the enhancer(s). FT-IR results showed that the treatment of the SC with enhancers did not produce a blue shift in the asymmetric and symmetric C-H stretching peak positions. However, all of the above enhancers showed a decrease in peak heights and areas for both asymmetric and symmetric C-H stretching absorbances in comparison with the untreated SC. A decrease in peak heights and areas is a measure of lipid extraction. Partitioning of tamoxifen to powdered SC from control and enhancer solutions was also determined. FT-IR and partitioning studies reveal that the enhancement in the permeability coefficient of tamoxifen by eugenol and d-limonene is due to lipid extraction and improvement in the partitioning of the drug to the SC. However, menthone enhanced the permeability of tamoxifen by increasing extraction of the SC lipids and not by improving the partitioning of the drug to the SC.
The tumor suppressor protein p53 has been implicated in the response of cells to DNA damage. Studies to date have demonstrated a role for p53 in the transcriptional activation of target genes in the cellular response to DNA damage that results in either growth arrest or apoptosis. In contrast, here is demonstrated a role for p53 in regulating the basal level of expression of the cyclin-dependent kinase inhibitor p21 in the absence of treatment with DNA-damaging agents. Wild-type p53-expressing MCF10F cells had detectable levels of p21 mRNA and protein, whereas the p53-negative Saos-2 cells did not. Saos-2 cells were infected with recombinant retrovirus to establish a proliferating pool of cells with a comparable constitutive level of expression of wild-type p53 protein to that seen in untreated MCF10F cells. Restoration of wild-type but not mutant p53 expression recovered a basal level of expression of p21 in these cells. Constitutive expression of luciferase reporter constructs containing the p21 promoter was inhibited by co-transfection with the human MDM2 protein or a dominant-negative p53 protein and was dependent on the presence of p53 response elements in the reporter constructs. Furthermore, p53 in nuclear extracts of untreated cells was capable of binding to DNA in a sequence-specific manner. These results implicate a role for p53 in regulating constitutive levels of expression of p21 and demonstrate that the p53 protein is capable of sequence-specific DNA binding and transcriptional activation in untreated, proliferating cells.
CeReS-18 is a unique negative regulator of cell proliferation with a wide array of target cells. To elucidate the mechanism by which CeReS-18 mediates cell growth inhibition, the possibility that CeReS-18 alters the function of G1 cyclins and their respective cyclin-dependent kinases (cdks) has been examined in mouse fibroblasts (Swiss 3T3) synchronized by CeReS-18. We show here that cyclin D-associated cdk activity is significantly inhibited in the CeReS-18-treated cells. Corresponding to the inhibited cdk function, we demonstrate a low expression of cyclin D in mid G1 determined by Western blot analysis, and cyclin D was greatly reduced in the immunocomplex recovered with antibody to cdk4 and cdk6. Previously, we have shown that the retinoblastoma susceptibility gene product (pRb), a key substrate of cyclin D-cdk complex, was maintained in the hypophosphorylated state in the CeReS-18-inhibited cells. We conclude here that cyclin D/cdk4,6/pRb is the major pathway by which CeReS-18 mediates cell cycle arrest.
We have previously reported that bone marrow B cell precursors from thymic-deprived nude and old mice express less recombination-activating gene-1 (RAG-1) mRNA than they do in young euthymic mice. We now report that both nude and old mice have decreased bone marrow pre-B cells and that fewer pre-B cells express RAG protein. This combination of events appears to be the basis for the lower level of bone marrow RAG mRNA in thymic-deprived mice. A link between thymic function and B cell development was suggested by the similar kinetics of thymic involution and of declining bone marrow RAG-1 gene expression during aging. Support for this hypothesis was obtained by demonstrating that injection of supernatant medium from activated CD8+ but not CD4+ young T cells from mice increases RAG mRNA, RAG protein, and the number of bone marrow pre-B cells in nude and old mice. Furthermore, in vivo CD8+ T cells also regulate bone marrow RAG gene expression. Thus, mice deficient in CD8+ T cells expressed levels of RAG-1 mRNA in their bone marrow that were only 10% of those observed in normal or CD4+ T cell-deficient mice. IL-16 was detected in the supernatant medium from activated T cell cultures, and injection of nanogram quantities of recombinant IL-16 (rIL-16) into nude or old mice increased the levels of RAG mRNA in bone marrow B cell precursors and the number of bone marrow pre-B cells. We conclude that the impaired development of B cells within the bone marrow of thymic-deprived nude and old mice can be reversed, at least in part, by the administration of rIL-16.
Cocaine addiction and overdose have long defied specific treatment. To provide a new approach, the high-activity catalytic antibody mAb 15A10 was elicited using a transition-state analog for the hydrolysis of cocaine to nontoxic, nonaddictive products. In a model of cocaine overdose, mAb 15A10 protected rats from cocaine-induced seizures and sudden death in a dose-dependent fashion; a noncatalytic anticocaine antibody did not reduce toxicity. Consistent with accelerated catalysis, the hydrolysis product ecgonine methyl ester was increased >10-fold in plasma of rats receiving mAb 15A10 and lethal amounts of cocaine. In a model of cocaine addiction, mAb 15A10 blocked completely the reinforcing effect of cocaine in rats. mAb 15A10 blocked cocaine specifically and did not affect behavior maintained by milk or by the dopamine reuptake inhibitor bupropion. This artificial cocaine esterase is a rationally designed cocaine antagonist and a catalytic antibody with potential for medicinal use.
There are two response elements for p53 in the promoter of the gene for the cyclin-dependent kinase inhibitor p21. The binding of p53 to the 5' site was enhanced by incubation with monoclonal antibody 421, whereas the binding of p53 to the 3' site was inhibited. Mutational analysis showed that a single-base change caused one element to behave like the other. A response element in the human cdc25C promoter is bound by p53 with properties similar to the 3' site. These results identify two classes of p53-binding sites and suggest a mechanism for target gene selectivity by p53.
The basic phospholipase A2 isolated from the venom of Agkistrodon halys Pallas (Agkistrodon blomhoffii Brevicaudus) is a hemolytic toxin and one of the few PLA2's capable of hydrolyzing the phospholipids of E. coli membranes in the presence of a bactericidal/permeability-increasing protein (BPI) of neutrophils. The crystal structure has been determined and refined at 2.13 A to an R factor of 16.5% (F > 3sigma) with excellent stereochemistry. A superposition of the two molecules in the asymmetric unit gives an r. m.s. deviation of 0.326 A for all Calpha atoms. The refined structure allowed a detailed comparison with other PLA2 species of known structures. The overall architecture is similar to those of other PLA2's with a few significant differences. One of which is in the region connecting the N-terminal helix and the Ca2+-binding loop. Unexpectedly, the conformation of the peptide plane Cys29-Gly30 in the Ca2+-binding loop is very different to that of other PLA2's. The amide NH of Gly30 does not point toward the proposed site for stabilization of the tetrahedral intermediate oxyanion of the substrate analogue. The structure includes four residues which occur less frequently in other PLA2's. His1, Arg6 and Trp70 located at the interfacial recognition site may play an important role in the interaction with aggregated substrates, while Trp77 contributes to the hydrophobic interactions between the beta-wing and the main body of the molecule. This structure analysis reveals that two clusters of basic residues are located at or near the interfacial recognition site, forming an asymmetric positively charge distribution. In contrast to the acidic isoform, the present enzyme is a dimer in the crystalline state. The special phospholipid hydrolysis behaviors are discussed in the light of the structure determined.
Exposure of tyrosine or DNA bases to acidic nitrite at low pH results in the nitration of tyrosine and the formation of base deamination products, respectively. At pH 1, hypoxanthine and xanthine are formed from the deamination of adenine and guanine, respectively, whereas under the same conditions, uracil is not detected. The yield of 3-nitrotyrosine derived from interaction of equimolar nitrite and tyrosine at pH 1 is approximately 50% of that obtained from equimolar peroxynitrite-tyrosine interactions at pH 7. 4. The ability of a range of plant phenolic constituents to prevent damage mediated by acidic nitrite was also examined in comparison with the activity of vitamin C. The epicatechin/gallate family of flavonols, constituents of green tea, red wine, etc., demonstrates the most extensive inhibitory properties against both tyrosine nitration and base deamination. The results also show that ascorbic acid is a poor inhibitor of nitration or deamination under acidic conditions such as those of the stomach. The ability of plant phenolics to scavenge reactive nitrogen species derived from acidic nitrite may contribute to the protective effects of tea polyphenols against gastric cancer.
The number of bone marrow pre-B cells is significantly lower in 18- than in 2-month-old BALB/c mice. The percentage of apoptotic pre-B cells, freshly isolated or cultured, from 18-month-old mice was significantly greater than from 2-month-old mice. The increased percentage of apoptotic pre-B cells from old mice was associated with a decreased level of bcl-xL mRNA, detected by RT-PCR, and of Bcl-xL protein, detected by intracellular staining. Consistent with an age-associated increase in apoptosis in pre-B cells was the fact that significantly fewer pre-B cells were generated after in vitro cultures of pro-B cells from old as compared to young mice. Furthermore, fewer pre-B cells survived and fewer sIg-expressing B cells were generated in cultures of pre-B cells from old as compared to young mice. In addition, there was no detectable difference in the secretion of IL-7 by bone marrow cells from 2- or 18-month-old mice. Thus, increased apoptosis of bone marrow pre-B cells in old mice appears to contribute to their decreased number.
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BACKGROUND: Variations in ablation profile may alter the stability of refraction and cause adverse effects in photorefractive keratectomy. We compared the benefits of multizone and transition zone ablation in the treatment of high and extreme myopia. METHODS: A scanning excimer laser system, Nidek EC-5000 was used with three-zone treatment and our results were compared retrospectively with results obtained in a group with a conventional ablation profile using a transition zone. RESULTS: Six-month follow-up data were available for 65 eyes with a transition zone and 46 eyes with three-zone treatment. Postoperative mean (+/- SD) healing time was 2.98 days (+/- 0.12) and 3.02 days (+/- 0.15) and night vision disturbances were 16% and 11.5% respectively, (p > 0.05). Refractive regression was also similar in the two groups; uncorrected visual acuity of 20/40 or better was 90.77% and 89.14%. At 6 months postoperatively, the mean (+/- SD) corneal clarity score was 0.61 (+/- 0.29) in the transition zone group, and 0.51 (+/- 0.07) in the multizone group (p < 0.05). CONCLUSION: No discernible differences between treatments were found in either epithelial healing or refractive outcome, such as regression, between the groups. Corneal haze was less in eyes treated with three-zone ablation.
The aim of this study was to prevent rejection after islet xenotransplantation. Islet obtained from Wistar Furth rats were macroencapsulated with agarose and collagen before transplanted into diabetic C57BL/6, B6AF1, and BALB/c mice. The results showed that the diabetic condition was reversed in 92.3% of recipients transplanted with macroencapsulated islets. The normoglycemic state of recipients was maintained 125.8 +/- 57.9 days without immunosuppression. The glucose tolerance curves in these mice were similar to those of normal mice. The macroencapsulated islets retrieved 103 days after transplantation showed no evidence of tissue reaction or fibrosis. These indicated that the macroencapsulated islets serve both to achieve and maintain normoglycemia of recipients, as well as to protect islet xenografts from rejection.
We measured mortality rates in a cohort of 20,508 aerospace workers who were followed up over the period 1950-1993. A total of 4,733 workers had occupational exposure to trichloroethylene. In addition, trichloroethylene was present in some of the washing and drinking water used at the work site. We developed a job-exposure matrix to classify all jobs by trichloroethylene exposure levels into four categories ranging from "none" to "high" exposure. We calculated standardized mortality ratios for the entire cohort and the trichloroethylene exposed subcohort. In the standardized mortality ratio analyses, we observed a consistent elevation for nonmalignant respiratory disease, which we attribute primarily to the higher background rates of respiratory disease in this region. We also compared trichloroethylene-exposed workers with workers in the "low" and "none" exposure categories. Mortality rate ratios for nonmalignant respiratory disease were near or less than 1.00 for trichloroethylene exposure groups. We observed elevated rare ratios for ovarian cancer among those with peak exposure at medium and high levels] relative risk (RR) = 2.74; 95% confidence interval (CI) = 0.84-8.99] and among women with high cumulative exposure (RR = 7.09; 95% CI = 2.14-23.54). Among those with peak exposures at medium and high levels, we observed slightly elevated rate ratios for cancers of the kidney (RR = 1.89; 95% CI = 0.85-4.23), bladder (RR = 1.41; 95% CI = 0.52-3.81), and prostate (RR = 1.47; 95% CI = 0.85-2.55). Our findings do not indicate an association between trichloroethylene exposure and respiratory cancer, liver cancer, leukemia or lymphoma, or all cancers combined.
Heterocyclic amines such as MeIQx and PhIP are potent genotoxic chemicals which are formed at part per billion levels when meat is cooked. Using assays based on gas chromatography/mass spectrometry with stable isotope labelled analogues as internal standards we have demonstrated MeIQx and PhIP, are efficiently absorbed into the systemic circulation after ingestion of fried beef. Using a potent and selective inhibitor of human CYP1A2, furafylline, we have shown that N-hydroxylation catalysed by this enzyme is the major pathway of metabolism of MeIQx and PhIP and is solely responsible for their oxidation to mutagenic species. This is in contrast to the situation in laboratory animals in which both activation by N-hydroxylation and deactivation by C-oxidation occurs. When furafylline was administered to human volunteers before ingestion of fried beef, we showed that > 90% of MeIQx and approximately 70% of PhIP elimination could be inhibited, demonstrating the extent to which activation occurred in man. MeIQx is a very powerful mutagen in bacterial assays whereas PhIP is a more potent mammalian cell mutagen. Using a mammalian cell target gene, hprt, we have shown that PhIP induces a characteristic mutational 'fingerprint' which is identical to that detected in the Apc gene of 5/8 colonic tumours induced by PhIP in rats. These studies support a biological association between HA exposure and diet-related tumours but emphasise that information obtained from animal studies does not always reflect the situation in humans.
A general equation relating the observed retention factor to the pH of the mobile phase, the dissociation constants, and the retention factors of the different ionic species has been derived. This equation is applicable to polyprotic weak acid and base dissociation events, that is, the secondary equilibria existing in the HPLC mobile phase. It is written as: [formula: see text] where the kr values are the retention factors of the dissociated species, and Ka(r), the product of the first r-dissociation constants, [formula: see text] is related to the pH of the mobile phase: x = 2.303.pH. The derived equation was used to calculate three dissociation constants of leukotriene E4. Also, a formula is established for calculating the range of pH values where an ionic species is most likely to be predominant in the mobile phase.
The contribution of peritoneal cells to lipopolysaccharide (LPS)-induced elevation of serum TNF-alpha and IL-6 levels and mortality has been studied. Peritoneal lavage performed before LPS administration reduced serum cytokine levels by approximately 50% and mortality from 50 to 100%. The effect of peritoneal lavage is due to the removal of peritoneal cells as reinjection of peritoneal cells eliminated the protective effect of lavage on LPS-induced mortality. A special role of peritoneal macrophages in the systemic response to LPS was suggested by the finding that LPS-induced an increase in intracellular TNF-alpha and IL-6 peritoneal macrophages but in neither splenic nor bone marrow macrophages. Intraperitoneal injection of thioglycollate broth 4 days prior to lavage increased the number of peritoneal cells removed by lavage and increased protection from LPS mortality. Peritoneal lavage performed 30 to 120 minutes after the LPS administration completely protected all mice from LPS-induced mortality, suggesting the possibility that such treatment may offer a novel therapeutic approach to septic shock.