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Biomedical subjects

C Zhao

Publications and source records attributed to C Zhao.

At least 145 records · Page 8Linked to original sources
PubMed1998

Discovery of ritonavir, a potent inhibitor of HIV protease with high oral bioavailability and clinical efficacy.

The structure-activity studies leading to the potent and clinically efficacious HIV protease inhibitor ritonavir are described. Beginning with the moderately potent and orally bioavailable inhibitor A-80987, systematic investigation of peripheral (P3 and P2') heterocyclic groups designed to decrease the rate of hepatic metabolism provided analogues with improved pharmacokinetic properties after oral dosing in rats. Replacement of pyridyl groups with thiazoles provided increased chemical stability toward oxidation while maintaining sufficient aqueous solubility for oral absorption. Optimization of hydrophobic interactions with the HIV protease active site produced ritonavir, with excellent in vitro potency (EC50 = 0.02 microM) and high and sustained plasma concentrations after oral administration in four species. Details of the discovery and preclinical development of ritonavir are described.

Administration, Oral↗
PubMed1998

Reversibility of omeprazole-evoked changes in the ultrastructure of ECL cells in the rat stomach.

The ECL cells are histamine- and peptide hormone-producing endocrine cells in the rat oxyntic mucosa. They are rich in secretory vesicles and also contain microvesicles and electron-dense granules. They operate under the control of circulating gastrin. In the present study, we examined the ECL-cell ultrastructure after long term treatment with omeprazole, which is known to induce hypergastrinemia, and after withdrawal of the drug. Rats received omeprazole (400 micromol/kg per day, orally) for 16 days and were killed 1, 5, 20, or 40 days after the last dose of the drug. Oxyntic mucosal specimens were processed for electron microscopy. Electron micrographs of ECL-cell profiles were analyzed planimetrically. The ECL-cell profile area increased promptly in response to omeprazole, the secretory vesicles and granules were reduced in number and volume density, the microvesicles were unchanged in number but reduced in volume density, and vacuoles appeared. Within a week after stopping the omeprazole treatment, the numbers and volume densities of secretory vesicles and microvesicles returned to pre-stimulation values. Also, the vacuoles disappeared promptly. The ECL-cell profile area decreased below the pre-stimulation level within five days after stopping treatment, while, in contrast, the granules increased in number and volume density. Somewhat surprisingly, the cell size and the granule compartment did not return to normal until 40 days after stopping treatment.

Animals↗
PubMed1998

Characterisation and partial purification of cellular factors interacting with a negative element on human papillomavirus type 1 late mRNAs.

We have previously identified and characterized an AU-rich inhibitory RNA element located in the 3' untranslated region on late human papillomavirus type 1 (HPV-1) mRNAs. This sequence is active in the absence of virus proteins and interacts specifically with cellular proteins, which presumably mediate the inhibitory activity. Here we have characterized and partially purified five proteins (80-, 52-, 46-, 44-, and 38-kDa) that interact independently and specifically with an AU-rich inhibitory sequence on HPV-1 late mRNAs. Dephosphorylation of the proteins resulted in loss of RNA binding activity. Proteins similar to the 38-, 44-, and 46-kDa proteins were detected also in murine epithelial cells, whereas proteins corresponding to the 80- and 52-kDa proteins were not. Since the inhibitory HPV-1 sequence is active in murine epithelial cells, the results suggested a role for the 38-, 41, and the 46-kDa proteins in the regulation of HPV-1 late gene expression.

Animals↗
PubMed1998

Synthesis and inhibitory action on HMG-CoA synthase of racemic and optically active oxetan-2-ones (beta-lactones).

A homologous series of both C3-unsubstituted and C3-methyl substituted oxetan-2-ones (beta-lactones) was investigated as potential inhibitors of yeast 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase. Several reported methods for racemic beta-lactone synthesis were studied for preparation of the target series. In addition, a novel aluminum-based Lewis acid obtained by combination of Et2AlCl with (1R,2R)-2-[(diphenyl)hydroxymethyl] cyclohexan-1-ol was studied for the asymmetric [2 + 2] cycloaddition of aldehydes and trimethylsilylketene. This Lewis acid exhibited good reactivity but variable enantioselectivity (22-85% ee). In in vitro assays using both native and recombinant HMG-CoA synthase from Saccharomyces cerevisiae, oxetan-2-ones mono-substituted at C4 with linear alkyl chains gave IC50s that decreased monotonically with chain length up to 10 carbons and then rose rapidly for longer chains. The trans isomers of 3-methyl-4-alkyl-oxetan-2-ones showed a similar trend but had 1.3- to 5.6-fold lower IC50s. The results imply a substantial hydrophobic pocket in this enzyme that interacts with both C-3 and C-4 substituents of oxetan-2-one inhibitors.

Enzyme Inhibitors↗
PubMed1998

Targeted disruption of the biglycan gene leads to an osteoporosis-like phenotype in mice.

The resilience and strength of bone is due to the orderly mineralization of a specialized extracellular matrix (ECM) composed of type I collagen (90%) and a host of non-collagenous proteins that are, in general, also found in other tissues. Biglycan (encoded by the gene Bgn) is an ECM proteoglycan that is enriched in bone and other non-skeletal connective tissues. In vitro studies indicate that Bgn may function in connective tissue metabolism by binding to collagen fibrils and TGF-beta (refs 5,6), and may promote neuronal survival. To study the role of Bgn in vivo, we generated Bgn-deficient mice. Although apparently normal at birth, these mice display a phenotype characterized by a reduced growth rate and decreased bone mass due to the absence of Bgn. To our knowledge, this is the first report in which deficiency of a non-collagenous ECM protein leads to a skeletal phenotype that is marked by low bone mass that becomes more obvious with age. These mice may serve as an animal model to study the role of ECM proteins in osteoporosis.

Age Factors↗
PubMed1998

Plant homologue of human excision repair gene ERCC1 points to conservation of DNA repair mechanisms.

Nucleotide excision repair (NER), a highly versatile DNA repair mechanism, is capable of removing various types of DNA damage including those induced by UV radiation and chemical mutagens. NER has been well characterized in yeast and mammalian systems but its presence in plants has not been reported. Here it is reported that a plant gene isolated from male germline cells of lily (Lilium longiflorum) shows a striking amino acid sequence similarity to the DNA excision repair proteins human ERCC1 and yeast RAD10. Homologous genes are also shown to be present in a number of taxonomically diverse plant genera tested, suggesting that this gene may have a conserved function in plants. The protein encoded by this gene is able to correct significantly the sensitivity to the cross-linking agent mitomycin C in ERCC1-deficient Chinese hamster ovary (CHO) cells. These findings suggest that the NER mechanism is conserved in yeast, animals and higher plants.

Amino Acid Sequence↗
PubMed1998

Prevention of acetaminophen-induced cataract by a combination of diallyl disulfide and N-acetylcysteine.

Injection of acetaminophen (APAP) (350 mg/kg body weight) into C57BL/6 mice in which cytochrome P450 (CYP) 1A1/1A2 had been induced produced acute cataract and other ocular tissue damage. Treatment of APAP-injected mice with one of the major organosulfides in garlic oil, diallyl disulfide (DADS) (200 mg/kg body weight), prevented cataract development and prolonged survival time. N-acetyl L-cysteine (NAC) (500 mg/kg body weight), a prodrug that stimulates glutathione synthesis, also prolonged survival time but was effective only weakly to prevent cataract formation. A combination of DADS and NAC completely prevented cataractogenesis, and all of the treated animals survived APAP toxicity. Neither DADS nor NAC inhibited CYP 1A1/1A2 induction as determined by their effect on the induction of hepatic microsomal ethoxyresorufin O-dealkylase (ERD) activity. However, in the in vitro enzyme assay, DADS, but not NAC, was a potent inhibitor of ERD activity (IC50 = 3.5 mM). Treatment with DADS or NAC slowed but did not stop the decrease of hepatic glutathione (GSH) content. At 4 hours after APAP injection, hepatic GSH began to increase only when DADS and NAC were administered together. These results suggest that the protective effect of DADS is due to its inhibition of biotransformation of APAP to the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI) by CYP 1A1/1A2 enzymes and that NAC provides protection by increasing cellular cysteine level and GSH synthesis, thus facilitating detoxification of NAPQI by glutathione conjugation. Assay of plasma glutamate-pyruvate transaminase activity, an indicator of liver necrosis, showed that treatment with DADS and NAC together effectively protected the liver. Therefore, the decrease of GSH as much as 30% of normal concentration, by itself, is not responsible for liver damage. The primary cause of hepatic necrosis is rapid accumulation of NAPQI.

Acetaminophen↗
PubMed1998

Temperature-induced expression of yeast FKS2 is under the dual control of protein kinase C and calcineurin.

FKS1 and FKS2 are alternative subunits of the glucan synthase complex, which is responsible for synthesizing 1,3-beta-glucan chains, the major structural polymer of the Saccharomyces cerevisiae cell wall. Expression of FKS1 predominates during growth under optimal conditions. In contrast, FKS2 expression is induced by mating pheromone, high extracellular [Ca2+], growth on poor carbon sources, or in an fks1 mutant. Induction of FKS2 expression in response to pheromone, CaCl2, or loss of FKS1 function requires the Ca2+/calmodulin-dependent protein phosphatase calcineurin. Therefore, a double mutant in calcineurin (CNB1) and FKS1 is inviable due to a deficiency in FKS2 expression. To identify novel regulators of FKS2 expression, we isolated genes whose overexpression obviates the calcineurin requirement for viability of an fks1 mutant. Two components of the cell integrity signaling pathway controlled by the RHO1 G protein (MKK1 and RLM1) were identified through this screen. This signaling pathway is activated during growth at moderately high temperatures. We demonstrate that calcineurin and the cell integrity pathway function in parallel, through separable promoter elements, to induce FKS2 expression during growth at 39 degrees C. Because RHO1 also serves as a regulatory subunit of the glucan synthase, our results define a regulatory circuit through which RHO1 controls both the activity of this enzyme complex and the expression of at least one of its components. We show also that FKS2 induction during growth on poor carbon sources is a response to glucose depletion and is under the control of the SNF1 protein kinase and the MIG1 transcriptional repressor. Finally, we show that FKS2 expression is induced as cells enter stationary phase through a SNF1-, calcineurin-, and cell integrity signaling-independent pathway.

Calcineurin↗
PubMed1998

Encoded chemical synthesis coupled to screening: "Pot Assay".

A variety of screening methodologies is available to identify lead compounds. Screening methods that would permit the direct use of libraries made via the Radiofrequency Encoded Combinatorial chemistry paradigm (each individual small molecule in the library is presented separately on an individual encoded support) have the potential to diminish burdensome steps in this process. Here we report on our studies leading to such a direct method, which we have termed a Pot Assay. Pot Assay is a multiplex assay, which simultaneously measures specific binding of a number of ligands to at least one target. Pot Assay uses specific radiofrequency signals to decode compounds that are high affinity binders. We validated this approach by evaluating the interaction of biotin and its analogs with labeled streptavidin. This report introduces Pot Assay as a rapid, simple, sensitive and accurate format for identifying active members of libraries synthesized on solid supports. The success of this study demonstrates the power of coupling Radiofrequency Encoded Combinatorial chemistry and screening. This assay format may be applied to a wide range of screens that are based on binding events: ligand/receptor, inhibitor/enzyme, antigen/antibody, protein/protein, DNA/protein, and RNA/DNA.

Alkaline Phosphatase↗
PubMed1998

[Engineered glutamic acid decarboxylase fusion protein in diagnosis of type I diabetes mellitus].

OBJECTIVE: To get recombinant GAD 65 proteins which have immunogenicity by the method of gene engineering so that the recombinant protein can be used for early diagnosis in type I diabetes mellitus. METHOD: We amplified the complete fragment encoding GAD65 gene by PCR, and expressed its protein in E. coli. DH5 alpha after inserting it in the vector and determining its nucleotide sequence. Consequentially, we attempted to prove the immunogenicity of expresion products and construct a method for detecting antibodies against GAD65 in Diabetic serum. RESULT: The sequence analysis showed that the amplified fragments contained 1758 bp, encoded 585 amino acid, and had been correctly inserted into pGEX-3X vector. The recombinant proteins expressed in E. Coli. DH5 alpha had immunogenicity and could be used to detect agtibodies against GAD65 in diabetic serum. CONCLUSION: We have got recombinant GAD65 proteins which have immunogenicity and have used them to detect preliminarily antibodies against GAD65 in diabetic serum.

Adolescent↗
PubMed1998

Histochemical and immunohistochemical studies of distribution of acetylcholinesterase-positive fibers and peptidergic terminals in the nasal mucosa of rats.

OBJECTIVE: To further investigate the mechanism of nasal secretion closely related to the innervation patterns in nasal mucosa with emphasis on the acetylcholinesterase (AChE)-positive fibers and peptidergic terminals in nasal mucosa as well as trigeminal ganglion (TG) cells. METHODS: Histochemical demonstration of AChE-positive fibers, immunohistochemical study of the distribution patterns of multiple peptidergic terminals, double labelling of AChE and substance P (SP) and somatostatin (SOM) mRNA in situ hybridization were carried out in nasal mucosa and trigeminal ganglion (TG) in rats. RESULTS: AChE-positive terminals were mainly distributed in the mid to posterior one third of septal nasal mucosa, with greater staining density on the walls of small vessels and glands. There were fewer such terminals in turbinate mucosa. Tachykinins-ergic terminals, including substance P (SP)-, neurokinin A (NKA)-, neurokinin B (NKB)- and calcitonin gene-related peptide (CGRP)-ergic terminals, had an extensive localizations in nasal mucosa, involving the following areas: between epithelial cells, submucosa, the walls of small vessels, glands and venous sinusoids in both septal and turbinate nasal mucosa. Septal mucosa had the greater density. There were overlaps in the distribution of these peptidergic terminals. There were also vasoactive intestinal peptide (VIP)-, neuropeptide Y (NPY)- and galanin (GAL)-ergic terminals in nasal mucosa. But no neurotensin (NT)- and somatostatin (SOM)-ergic terminals were found. In situ hybridization revealed SOMmRNA expression in TG cells. AChE and nine neuropeptides existed in the cytoplasms of TG cells. Besides, AChE and SP could exist simultaneously in cytoplasms of TG cells. CONCLUSIONS: AChE-positive (corresponding to parasympathetic nerves) and peptidergic terminals have different distribution patterns in the nasal mucosa of rats, although an overlap does exist, indicative of their different physiological effects on the regulation of nasal secretion and other functions; AChE and multiple neuropeptides in the cytoplasm of TG cells might play a role in modulating the nasal secretion in response to stimuli in the nasal mucosa.

Acetylcholinesterase↗
PubMed1998

[Clinical analysis of Doppler waveform in arterial occlusive disease in the lower limbs].

OBJECTIVE: In order increase the diagnostic standard of Doppler ultrasound to arterial occlusive disease in the lower limbs. METHODS: 120 normal lower limbs and 66 lower limbs with arterial occlusive disease were measured by directional Doppler blood velocity detector in different segments. The peak forward velocity(PFV), peak reverse velocity(PRV), acceleration time(AT), and deceleration time(DT) were determined and compared. RESULTS: The blood flow velocity of the lower limb arteries was gradually slowed down from the proximal to the distal in the normal group. The ratio of distal to proximal PFA, PRV, AT and DT was less than 1.0. PFV and PRV in the disease group were slower than in the normal group(P < 0.01). AT and DT in the disease group were longer than in the normal group(P < 0.01). It was discovered that the ratio of distal to proximal DT was greater than 1.0 in arterial stenosis(> 50%) or occlusion (collateral artery development). CONCLUSION: The results were compared those of arteriography. The diagnostic coincidence ratio of Doppler ultrasound for localization was 91%(60/66).

Adult↗
PubMed1998

[Distribution of substance P receptors in rat nasal mucosa of allergic rhinitis].

OBJECTIVE: To explore the potential role of substance P receptor (SPR) in the initiation and development of allergic rhinitis (AR). METHODS: Twenty healthy rats were randomly divided into two groups. A model of allergic rhinitis in rat was established by using ovalbumin intraperitoneal immunization and nasal antigen challenge. The nasal mucosa obtained from seven out of ten AR models as well as ten normal controls were studied routinely by HE and immunohistochemical staining to observe the distribution and changes of SPR. RESULTS: The study showed that immunoreactivity to SPR was present both on the surface and in the cytoplasm of epithelial cells, eosinophils, glandular cells and its ducts, mast cells, plasmocyte and other monocytes. During nasal hypersensitiveness, the staining density and the positive staining cells increased significantly as compared with those in normal controls. CONCLUSION: The increase of SPR in nasal mucosa in rat AR model indicates that SPR might play a critical role in the development of AR.

Animals↗
PubMed1998

[The osteoinductivity and the dose-effect relationship with implantation of reconstituted bone xenograft: experimental study].

OBJECTIVE: To observe osteoinductivity and the dose-effect relationship with administration of reconstituted bone xenograft (RBX). METHOD: A posterior thigh muscle pouch model with RBX transplantation was established in BALB/C mice. Samples were treated at regular postoperative intervals for radiologic, histomorphologic and ALP examinations. RESULT: (1) In the groups that had been implanted with RBX, the osteoinductivity was positively correlated with the bBMP contents in RBX (r = 0.7204, P < 0.01), showing a dose-dependent relationship; (2) satisfactory osteogenesis was noted in the RBX I group, whereas no substantial bone formation was seen in the group implanted with bBMP alone apart from some evidence of osteogenic effect; (3) the alkaline phosphatase activity attained its peak on the 7th day postoperatively and kept still higher to the 42nd day. CONCLUSION: RBX is a highly osteoinductive grafting material with the treated homologous cancellous bone being a good slow-delivery carrier which can enhance the osteoinductive capacity of bBMP.

Alkaline Phosphatase↗
PubMed1998

[Study on a new type of endoscope based on micro motor].

The application of Micro Electro Mechanical System (MEMS) on the fields of biomedical engineering is a newly technological field. Applying a micro motor, whose diameter is only 2 mm, as driving device of this system, this paper presented a new type of medical endoscope whose front tip of diagnosing tube could work automatically.

Endoscopes↗
PubMed1997

AU-rich mRNA instability elements on human papillomavirus type 1 late mRNAs and c-fos mRNAs interact with the same cellular factors.

Expression levels of human papillomavirus type 1 late genes are determined in part by an AU-rich inhibitory sequence in the 3' untranslated region on the late mRNAs. Fine mapping of the AU rich inhibitory sequence revealed that it mapped to a 57 nucleotide sequence, consisting of an AU-rich region containing two AUUUA motifs and a U-rich region containing three UUUUU motifs. An internal deletion showed that the U-rich region was required for inhibition. Point mutations in the AUUUA- and UUUUU-motifs inactivated the inhibitory sequence. Analysis of the stability of mRNAs containing the AU-rich sequence in sense or anti-sense orientation showed that mRNAs containing the AU-rich sequence in sense orientation had reduced half life. Analysis of RNA-protein interactions revealed that binding to the inhibitory sequence of three poly(U) binding proteins (38, 44 and 46 kDa) correlated with inhibition and that the same proteins bind to the AU-rich mRNA instability element in the 3' untranslated region on the human c-fos mRNA. We speculate that the human papillomavirus late mRNAs, produced from several hundred copies of the virus genome present in infected cells, compete with the c-fos mRNAs for destabilizing cellular factors and that this may lead to elevated Fos protein levels in human papillomavirus infected cells.

Adenine↗
PubMed1997

Experimental antitumor activity of the Ce(IV)-mitoxantrone complex and its interaction with deoxyribonucleic acid.

The Ce(IV)-mitoxantrone complex exhibits a higher lethality to Ehrlich ascites tumor cells than that of the free drug and shows stronger inhibition ability on the DNA synthesis of the tumor cells. Thus the Ce(IV)-mitoxantrone complex may become a more potent antitumor drug than mitoxantrone. The different interaction model of mitoxantrone and its Ce(IV) complex with DNA were studied by the methods of spectroscopy, electrochemistry, and electrophoresis. Ce(IV) ions chelate with oxygens of the hydroxyl groups at the 1,4 position and the carbonyl function on C-9 and C-10, then intercalate into the base pairs of DNA together. The complexation of Ce(IV) gives rise to more compact binding of mitoxantrone with DNA, and leads to an additional change on the normal conformation and the double-helical structure of DNA; this may be related to the more stronger action of the complex on DNA synthesis and survival of cultured tumor cells.

Animals↗