Biomedical subjects

Xianhua Zhang

Publications and source records attributed to Xianhua Zhang.

5 recordsLinked to original sources

PubMed2026

DNA hypermethylation of abscisic-acid-related genes helps enhance the cold tolerance of tetraploid rice.

Polyploid plants exhibit enhanced stress resistance and superior adaptability to extreme environments, but the underlying molecular mechanisms remain incompletely understood. Here we confirm that tetraploid rice exhibits stronger cold tolerance than diploid rice. This improved tolerance is mediated by reduced malondialdehyde accumulation, elevated antioxidant enzyme activity, and epigenetic regulation of genes involved in abscisic acid (ABA) biosynthesis and signaling. Under cold stress, tetraploid rice induces stress-responsive genes (especially in the ABA pathway) more rapidly and to higher levels than diploid rice. This enhanced gene expression coincides with increased endogenous ABA accumulation. Furthermore, polyploidization and cold stress synergistically induce high methylation at CG, CHG, and CHH sites in genes and transposons (TEs). Notably, the methylation level of class II TEs in tetraploid rice is significantly higher than in diploid rice under low temperatures. To suppress TE activation in gene promoter regions under cold stress, tetraploid rice enhances the methylation level of ABA pathway-related gene promoters, thereby silencing TEs and maintaining genome stability. Collectively, these results enrich the theoretical understanding of the strong stress tolerance in polyploid plants and provide theoretical support for breeding cold-tolerant polyploid rice varieties.

ABA↗

PubMed2006

Sensitive quantification of rifaximin in human plasma by liquid chromatography-tandem mass spectrometry.

A liquid chromatography-mass spectrometry method (LC-MS/MS) for the quantitative determination of rifaximin in human plasma was developed and validated. In the developed procedure, metoprolol was added to human plasma as an internal standard (IS) and acetonitrile was used to precipitate the plasma proteins before LC-MS/MS analysis. Chromatographic separation was obtained on a RESTEK Pinnacle C18 column (50 mm x 2.1mm, 5 microm) with a mobile phase consisted of ammonium acetate solution (15 mM, pH 4.32) as buffer A and methanol as mobile phase B. Quantification was performed in positive mode using multiple reaction monitoring (MRM) of the transitions m/z 786.1-->754.1 for rifaximin and m/z 268.3-->116.1 for the IS. The assay has been validated over the concentration range of 0.5-10 ng/ml (r=0.9992) based on the analysis of 0.2 ml of plasma. The assay accuracy was between 98.2% and 109%. The within-day and between-day precision was better than 3.9% and 8.9% at three concentration levels. The freeze-thaw stability was also investigated and it was found that both rifaximin and the IS were quite stable. This method provides a rapid, sensitive, specific and robust tool for the quantitative determination of rifaximin in human plasma, which is especially useful for the pharmacokinetic study of rifaximin.

Anti-Infective Agents↗

PubMed2003

Enantiomeric separation of beta-blockers by HPLC using (R)-1-naphthylglycine and 3,5-dinitrobenzoic acid as chiral stationary phase.

Direct liquid chromatographic separations of the enantiomers of metoprolol and bisoprolol have been developed, using (R)-1-naphthylglycine and 3,5-dinitrobenzoic acid as chiral stationary phase (CSP). The separations were achieved in a normal phase system employing a mobile phase containing n-hexane, 1,2-dichloroethane and methanol. Column efficiency was strongly dependent on the composition of the mobile phase. The eluent contents of methanol and of 1,2-dichloroethane were optimized, and so was flow-rate and column temperature. Under the optimal conditions, linear responses for (R)-metoprolol and (S)-metoprolol are obtained in the range of 0.079-1.38 and 0.015-5.80 mg/ml, with detection limits of 0.008 and 0.002 mg/ml, respectively. As for bisoprolol, the linear ranges of (R)-isomer and (S)-isomer are 0.05-1.31 and 0.02-1.00 mg/ml with detection limits of 0.001 and 0.008 mg/ml, respectively. The relative standard deviation (R.S.D.) of each enantiomer did not exceed 0.90%. The method has been successfully applied to the determination of enantiomers in pharmaceuticals.

Adrenergic beta-Antagonists↗

PubMed2003

[Distribution of 3 kinds of periodontal pathogens in subgingival plaques of patients with chronic periodontitis].

OBJECTIVE: To observe the prevalence of Porphyromonas gingivalis(Pg), Treponema denticola(Td) and Bacterides forsythus(Bf) subgingivally in diseased sites of chronic periodontitis (CP) patients. METHODS: Samples of subgingival plaque were detected by 3 kinds of oligonucleotide DNA probe from 60 sites of CP patients and 10 healthy sites of 10 healthy people. RESULTS: The positive rates of Pg, Bf and Td in patients were 91.67%, 90.00% and 95.67% respectively; Pg, Bf and Td were detected simultaneously in 83.33% patients and Pg, Bf and Td were found to be related with each other(P < 0.01). CONCLUSION: Pg, Bf and Td were prominent periodontopathic bacteria and related each other, might exist in complexes in subgingival plaque and coaggretate together.

Adult↗

PubMedDate not supplied

Flow-injection with enhanced chemiluminescence detection of ofloxacin in human plasma.

A simple, rapid and sensitive method for the determination of ofloxacin in plasma has been developed based on flow-injection analysis with enhanced chemiluminescence (CL) detection. This method employs the CL reaction of cerium(IV) and sulphite sensitized by a Tb(III)-ofloxacin complex. Plasma samples were deproteinized with acetonitrile before analysis. Under optimal conditions, the method allowed the quantitative analysis of ofloxacin in plasma over the range of 22.5-900 ng/mL with a detection limit of 7.5 ng/mL (3sigma). The intra-day and inter-day precision was < 3.0% (n = 11) and < 7.0% (n = 3), respectively. The method was a convenient tool, rapid (20 s/analysis) and well suited for pharmacokinetics studies in which thousands of samples must be analysed daily. It was applied to pharmacokinetics studies of ofloxacin.

Acids↗