Biomedical subjects
Publications and source records attributed to Chen-Zhong Li.
This communication reveals new and unique optical properties with respect to enhanced fluorescence of gold nanorods as they elongate; a novel strategy for DNA hybridization studies based on monitoring the fluorescence intensity of gold nanorods has been demonstrated.
Scanning electrochemical microscopy was used to examine electron transfer across a self-assembled monolayer of thiol-modified DNA duplexes on a gold electrode. The apparent rate constant for heterogeneous ET from a solution redox probe, Fe(CN)6(3-/4-), to the gold surface through ds-DNA was 4.6 (+/-0.2) x 10(-7) cm/s. With the addition of Zn2+, which resulted in the formation of a metalated DNA (M-DNA) monolayer, the rate constant increased to 5.0 (+/-0.3) x 10(-6) cm/s. Upon treating M-DNA with EDTA, the zinc ions were released from the monolayer and the original rate constant for the DNA duplexes was restored. The enhanced ET rate was also observed at a DNA monolayer treated with Ca2+ or Mg2+, which does not complex by the DNA bases to form M-DNA. The binding of these cations facilitated the monolayer penetration by the probe mediator Fe(CN)6(3-/4-) and accordingly caused an increased redox signal of the mediator at the ds-DNA-modified electrode. Cationic or neutral mediators were not blocked by the ds-DNA monolayer. These results suggest that although the increased electron transport through M-DNA could partially be ascribed to the intrinsic enhancement of electric conductivity of M-DNA, which has been confirmed by photochemical studies, the change in the surface charge of DNA monolayers on the electrode caused by the binding of metal ions to DNA molecules may play a more important role in the enhancement of current with M-DNA.
Interfacial interactions between immobilized DNA probes and DNA-specific sequence binding drugs were investigated using impedance spectroscopy toward the development of a novel biosensing scheme. The impedance measurements are based on the charge-transfer kinetics of the [Fe(CN)6]3-/4- redox couple. Compared to bare gold surfaces, the immobilization of DNA and then the DNA-drug interaction on electrode surfaces altered the capacitance and the interfacial electron resistance and thus diminished the charge-transfer kinetics by reducing the active area of the electrode or by preventing the redox species from approaching the electrode. Electrochemical deposition of gold nanoparticles on a gold electrode surface showed significant improvement in sensitivity. DNA-capped gold nanoparticles on electrodes act as selective sensing interfaces with tunable sensitivity due to higher amounts of DNA probes and the concentric orientation of the DNA self-assembled monolayer. The specificity of the interactions of two classical minor groove binders, mythramycin, a G-C specific-DNA binding anticancer drug, netropsin, an A-T specific-DNA binding drug and an intercalator, nogalamycin on AT-rich DNA-modified substrate and GC-rich DNA-modified substrate are compared. Using gold nanoparticle-deposited substrates, impedance spectroscopy resulted in a 20-40-fold increase in the detection limit. Arrays of deposited gold nanoparticles on gold electrodes offered a convenient tool to subtly control probe immobilization to ensure suitably adsorbed DNA orientation and accessibility of other binding molecules.
OBJECTIVE: To investigate the effects of Liuwei Dihuang Pills (LWDHP) on expressions of apoptosis-related genes bcl-2 and Bax in pancreas of OLETF rats. METHODS: Forty male OLETF rats were randomly divided into LWDHP-treated group and untreated group. Another ten male LETO rats were included in normal control group. OLETF rats in the LWDHP-treated group were given LWDHP (2.4 g.kg(-1).d(-1)) orally since the age of 8 weeks and the rats in the other two groups were given distilled water orally. Body weights of rats were recorded weekly and blood glucose concentration was determined by oral glucose tolerance test (OGTT). Pancreas weights were recorded after rats were killed and the expression levels of bcl-2 mRNA and Bax mRNA were detected by reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: In the LWDHP-treated group, the expression of bcl-2 mRNA in the pancreas of rats at the age of 40 weeks (1.25+/-0.07) was much higher than that in the untreated group (1.01+/-0.16), P<0.01. Bax mRNA level in the LWDHP-treated group (0.57+/-0.11) was obviously lower than that in the untreated group (1.18+/-0.28), P<0.01. There was no significant difference of pancreas-to-body weight ratios between the LWDHP-treated group and the untreated group. The ability of glucose tolerance was improved in the LWDHP-treated group. CONCLUSION: LWDHP can up-regulate the expression of bcl-2 and down-regulate the expression of Bax at transcription level, which maybe contribute to the anti-apoptosis effects of LWDHP.
OBJECTIVE: To investigate the prevalence of microalbuminuria in type 2 diabetic patients with hypertension. METHOD: Urinary albumin excretion was measured in 55 diabetic patients with hypertension by colorimetric methods using commercially available test strips of Nephur 7 and Micro-II, the latter test strips employed only when the former yielded negative results for proteinuria. The height, body weight, waist circumference and blood pressure were measured for all the patients with also biochemical examination for serum total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, blood glucose and creatinine. HbA1c was determined by Bio-STAT. RESULTS: The rates of normal urinary albumin, micro- and macroalbuminuria were 66.67%, 22.22% and 11.11% in these patients, respectively. In patients with a history of diabetes for more than 10 years, the rates were 58.33%, 8.33% and 33.33%, respectively. CONCLUSION: Nearly 1/3 of type 2 diabetic patients with hypertension have microalbuminuria and proteinuria, and screening for microalbuminuria and proper interventions in these patients might prove beneficial.
The detection of a single-nucleotide mismatch in unlabeled duplex DNA by electrochemical methods is presented. Impedance spectroscopy is used to characterize a perfect duplex monolayer and three DNA monolayers differing in the position of the mismatch. The monolayers were studied as B-DNA (normal duplex DNA) and after conversion to M-DNA (a metalated duplex). Modeling of the impedance data to an equivalent circuit provides parameters that are useful in discriminating the four monolayer configurations. The resistance to charge transfer, R(CT), was lower for all duplexes after conversion to M-DNA. Contrary to expectations, R(CT) was also found to decrease for duplexes containing a mismatch. However, R(CT) was found to be diagnostic for mismatch detection. In particular, the difference in R(CT) between B- and M-DNA (deltaR(CT)) decreased from 190(22) omega.cm(2) for a perfectly matched duplex to 95(20), 30(20), and 85(20) omega.cm(2) for a mismatch at the top (distal), middle, and bottom (proximal) positions of the monolayer with respect to the gold surface. Further, a method to form loosely packed single-stranded (ss)-DNA monolayers by duplex dehybridization that is able to rehybridize to target strands is presented. Rehybridization efficiencies were in the range of 40-70%. Under incomplete hybridization conditions, the R(CT) was the same for matched and mismatched duplexes under B-DNA conditions. However, deltaR(CT) between B- and M-DNA, under incomplete hybridization, still provided a distinction. The deltaR(CT) for a perfect duplex was 76(12) omega.cm(2), whereas a mismatch in the middle of the sequence yielded a deltaR(CT) value of 30(15) omega.cm(2). The detection limit was measured and the impedance methodology reliably detected single DNA base pair mismatches at concentrations as low as 100 pM.
MutS binding to a double-stranded DNA containing a single nucleotide mismatch can be conveniently monitored by impedance spectroscopy and represents the first step in developing an electrochemical binding essay for single nucleotide mismatch detection.
Electron transfer (ET) through two configurations of double-stranded (ds)-DNA was investigated by the attachment of a ferrocenoyl (Fc)-labeled and thiol-labeled DNA to Au electrodes. The first configuration positions the Fc moiety on the same strand as the thiolate, whereas the second configuration positions the Fc group on the complementary strand. The subtle difference in structure leads to a difference in E0' values (29 mV) and in ET rate constants (25 vs 115 s-1). The results have led to a further understanding of electron transfer in ds-DNA, and several models of ET are proposed.
Monolayers of thiol-labeled DNA duplexes of 15, 20, and 30 basepairs were assembled on gold electrodes. Electron transfer was investigated by electrochemical impedance spectroscopy with Fe(CN)(6)(3-/4-) as a redox probe. The spectra, in the form of Nyquist plots, were analyzed with a modified Randles circuit which included an additional component in parallel, R(x), for the resistance through the DNA. For native B-DNA R(x) and R(ct), the charge transfer resistance, both increase with increasing length. M-DNA was formed by the addition of Zn(2+) at pH 8.6 and gave rise to characteristic changes in the Nyquist plots which were not observed upon addition of Mg(2+) or at pH 7.0. R(x) and R(ct) also increased with increasing duplex length for M-DNA but both were significantly lower compared to B-DNA. Therefore, electron transfer via the metal DNA film is faster than that of the native DNA film and certain metal ions can modulate the electrochemical properties of DNA monolayers. The results are consistent with an ion-assisted long-range polaron hopping mechanism for electron transfer.
M-DNA is a complex between divalent metal ions such as Zn2+ and duplex DNA which forms at pH 8.5. Unlike B-DNA, M-DNA does not bind ethidium so that M-DNA formation can be monitored conveniently by an ethidium fluorescence assay. M-DNA was shown to be a better conductor than B-DNA by fluorometric measurements of electron transport in donor-acceptor labelled duplexes; by direct conductivity measurements of M-DNA bound between gold electrodes and by cyclic voltammetric studies on ferrocene labelled duplexes attached to gold microelectrodes. As is the case with B-DNA, M-DNA can self-assemble into a variety of structures and is anticipated to find widespread use in nanoelectronics and biosensing.
OBJECTIVE: To investigate the relationship between insulin-degrading enzyme (IDE) activity and the onset and development of insulin resistance (IR). METHODS: Rat primary hepatocytes with IR induced by high concentration of human insulin were used in which the incorporation rates of 14C-2-deoxyglucose and 14C-acetate were determined to estimate the insulin sensitivity of the cells and IDE activity was assessed. The effects of IDE inhibitor, chloroquine, and IDE activator, iodoacetamide, on these indices were observed. RESULTS: IDE activity of IR cells was increased, and 14C-2-deoxyglucose and 14C-acetate incorporation rates were decreased as compared with the control cells. Significant inverse correlation was observed between IDE activity of IR cells and the incorporation rates of 14C-2-deoxyglucose and 14C-acetate. Iodoacetamide resulted in increase in IDE activity and decrease in the incorporation rates while chloroquine acted to the reverse effects. CONCLUSIONS: Increased IDE activity may be one of the mechanisms of IR genesis in rat primary hepatocytes cultured with high concentration of IDE, chloroquine, on the other hand, may ameliorate insulin sensitivity by inhibiting accelerated insulin degradation.
OBJECTIVE: To investigate the association of hyperuricemia with the incidence of stroke in type 2 diabetic patients. METHODS: Sixty type 2 diabetic patients with stroke, 75 patients with simple stoke and 67 simple type 2 diabetic patients were randomly selected from the hospitalized patients. The serum levels of uric acid (UA), total cholesterol (TC), triglyceride (TG), low-density lipoprotein-cholesterol(LDL), very-low-density lipoproteincholesterol (VLDL) and high-density lipoprotein- cholesterol (HDL) of all the patients were determined and comparison between the groups performed. RESULTS: Male type 2 diabetic patients with stroke had significantly higher mean levels of serum uric acid than simple diabetic patients, but such patients of both genders all had lower HDL levels. CONCLUSION: The decreased serum HDL level poses as an important risk factor for stroke in all type 2 diabetic patients, among whom the male patients in particular have hyperuricemia as another important risk factor for stroke.