PubMed Health⌕ Search

Biomedical subjects

Zhi Su

Publications and source records attributed to Zhi Su.

At least 19 recordsLinked to original sources
PubMed2006

The development and regulation of occupational exposure limits in China.

Of the 700 million workers in China, approximately 200 million workers are potentially exposed to industrial hazards. Although the promulgation and implementation of occupational exposure limits (OELs) in China began in the mid-1950, a systematic approach was not formalized until the formation of the Subcommittee of Occupational Health Standards Setting (SOHSS) in 1981. More recently, the 2002 Occupational Disease Prevention and Control Act of the People's Republic of China created the legislative framework for the development and enforcement of OELs. The SOHSS, whose members are primarily health professionals, is the organization responsible for the development of recommended standards, under the auspices of the Ministry of Health. The philosophy of OEL development of the SOHSS consists of a two-step approach: (1) an initial health-based recommended standard is established based on scientific data, and (2) a final law-based standard takes into consideration both socioeconomic and technological feasibility. Governmental agencies such as the Centers for Diseases Control and Prevention and the Institutes of Public Health Supervision at the state, provincial or municipal levels are charged with the responsibilities of the enforcement of OELs. The process and challenges in the enforcement of OELs are discussed. A comparison is made between selected Chinese OELs and those in other countries. The OELs for benzene and industrial dusts (including silica) are discussed in some detail.

Carcinogens, Environmental↗
PubMed2006

Utility of hERG assays as surrogate markers of delayed cardiac repolarization and QT safety.

HERG (human-ether-a-go-go-related gene) encodes for a cardiac potassium channel that plays a critical role in defining ventricular repolarization. Noncardiovascular drugs associated with a rare but potentially lethal ventricular arrhythmia (Torsades de Pointes) have been linked to delayed cardiac repolarization and block of hERG current. This brief overview will discuss the role of hERG current in cardiac electrophysiology, its involvement in drug-induced delayed repolarization, and approaches used to define drug effects on hERG current. In addition, examples of hERG blocking drugs acting differently (i.e., overt and covert hERG blockade due to multichannel block) together with the utility and limitations of hERG assays as tools to predict the risk of delayed repolarization and proarrhythmia are discussed.

Animals↗
PubMed2006

In vitro preclinical cardiac assessment of tolterodine and terodiline: multiple factors predict the clinical experience.

Terodiline and tolterodine are drugs used to treat urinary incontinence. Terodiline was removed from the market in 1991 for proarrhythmia, whereas tolterodine has a generally benign clinical cardiac profile. To assess differences in the electrophysiologic actions of these drugs, we evaluated their effects on hERG current (HEK cells) and cardiac Purkinje fiber repolarization. The IC50 for hERG block (37 degrees C) by tolterodine was 9.6 nM and by terodiline was 375 nM, values near or below clinical concentrations. Tolterodine elicited concentration-dependent prolongation of the action potential duration (APD90). In contrast, terodiline depressed the action potential plateau and induced triangulation without affecting APD90. The triangulation ratios (normalized ratio of APD50 over APD90) for terodiline were 0.94 and 0.59 for 1.0 and 10 microM and for tolterodine, were 0.99 and 0.97 at 7 and 70 nM. In summary, tolterodine, a potent hERG blocker, has a benign clinical cardiac profile at therapeutic concentrations that may be due to its lack of triangulation, as well as extensive plasma protein binding. However, at supratherapeutic concentrations, preclinical data predict risk of QT prolongation. These data suggest that hERG block and triangulation are among multiple factors that must be considered in preclinical cardiac safety assessments.

Action Potentials↗
PubMed2006

Altering extracellular potassium concentration does not modulate drug block of human ether-a-go-go-related gene (hERG) channels.

1. Drug-induced block of the rapidly activating delayed rectifier K+ current (I(Kr)), encoded by human ether-a-go-go-related gene (hERG), has been linked to acquired long QT syndrome (aLQTS). Hypokalaemia is a recognized risk factor in aLQTS. To further understand why hypokalaemia is a risk factor in aLQTS, we examined the effect of [K+]o on drug block of the hERG potassium channel stably expressed in human embryonic kidney (HEK-293) cells using whole-cell voltage-clamp techniques. 2. The effects of selected [K+]o (1-20 mmol/L) on hERG block with four structurally diverse compounds (dofetilide, mesoridazine, quinidine and terfenadine) from different therapeutic classes were evaluated. Reducing [K+]o from 20 to 1 mmol/L had little effect on IC50 values for hERG current block for all four compounds. For example, evaluating quinidine in external potassium concentrations of 20, 10, 5 and 1 mmol/L resulted in IC50 values of 1.82 +/- 0.33, 2.04 +/- 0.28, 1.57 +/- 0.52 and 1.14 +/- 0.21 mmol/L, respectively. No statistically significant difference (P > 0.35, anova) was observed between drug block of hERG in different external potassium concentrations. These data are in contrast with previously reported results examining hERG channel modulation expressed in AT-1 cells under similar experimental conditions. 3. These results demonstrate that [K+]o does not directly modulate drug block of hERG channels expressed in an HEK-293 cell line. The enhanced risk of Torsades de Pointes associated with hypokalaemia in aLQTS may be due to reduction of other (non-hERG) potassium currents, further reducing the repolarization reserve, and not due to direct modulation of hERG block by [K+]o.

Cell Line↗
PubMed2006

[Recombinant adenovirus vectors carrying antisense matrix metalloproteinase-2 inhibits hepatocellular carcinoma growth in vivo].

OBJECTIVE: To investigate the inhibitory effect of a recombinant adenoviral vector carrying antisense matrix metalloproteinase-2(MMP2) on the growth of hepatocellular carcinoma(HCC) in vivo. METHODS: The recombinant adenoviral vector carrying antisense MMP2(Ad-MMP2(AS))which had been constructed by us in readiness was used to infect the human HCC cell line (Bel-7402). Then the invasiveness of the Bel-7402 cells was assayed in Matrigel, and the production of MMP2 in the Bel-7402 cells was detected with Western blot analysis and Gelatin zymography. After the Ad-MMP2(AS)-infected Bel-7402 cells being subcutaneously inoculated in nude mice, the production of tumors was under observation, and then Ad-MMP2(AS) was injected intratumorally into the pre-existing tumors. RESULTS: Compared with PBS or Ad-CMV-infected cells, infection of Bel-7402 cells with Ad-MMP2(AS) significantly reduced MMP2 enzyme activity, the invasiveness resulted in 52% reduction in Matrigel assays, and the tumor volume displayed a 4.3-fold reduction in nude mice. In addition, direct intratumoral injection of Ad-MMP2(AS) into pre-existing tumors significantly impaired the further expansion of the tumor mass and resulted in a 63% reduction in tumor cell growth. CONCLUSION: The recombinant adenovirus with antisense MMP2 can effectively inhibit the invasiveness and growth of Bel-7402 cells in vitro and in vivo, and has a therapeutic potential for HCC.

Adenoviridae↗
PubMed2005

Block of hERG channel by ziprasidone: biophysical properties and molecular determinants.

Ziprasidone, an antipsychotic agent, delays cardiac repolarization and, thus, prolongs the QT interval of the cardiac ECG. In this study, we examined the biophysical properties and the molecular determinants of the ziprasidone block of wild-type hERG potassium channels stably expressed in HEK-293 cells or wild-type and mutant hERG channels expressed in Xenopus oocytes. In stably transfected HEK-293 cells, ziprasidone blocked wild-type hERG current in a voltage- and concentration-dependent manner (IC(50)=120nM, 0mV, 37 degrees C). Ziprasidone showed minimal tonic block of hERG current estimated during a depolarizing voltage (-20 or +30mV) or evaluated by the envelope of tails test (+30mV). Rate of the block onset was rapid, but not significantly affected by test potentials ranging from -20 to +30mV (time constant (tau)=114+/-14ms at +30mV). The time constant of the slow component of hERG current deactivation (at -50mV) was significantly increased by ziprasidone (tau=1776+/-90 versus 1008+/-71ms, P<0.01). Time course of channel inactivation was slowed by ziprasidone in a voltage-dependent manner. The V(1/2) values for steady-state activation and inactivation of hERG channel in HEK-293 cells were not significantly altered by ziprasidone. In Xenopus oocytes, ziprasidone exhibited less potent block of wild-type hERG current (IC(50)=2.8microM, 0mV, 23 degrees C). Mutation of the aromatic residues (Tyr-652 or Phe-656) located in the S6 domain of hERG dramatically reduced the potency of channel block by ziprasidone (IC(50)>0.4 and 1mM at 0mV for Y652A and F656A, respectively). In conclusion, ziprasidone preferentially binds to and blocks open hERG channels. Tyr-652 and Phe-656 are two critical residues in the ziprasidone-binding site.

Animals↗
PubMed2005

Relative abundance of alpha2 Na(+) pump isoform influences Na(+)-Ca(2+) exchanger currents and Ca(2+) transients in mouse ventricular myocytes.

In the mouse, genetic reduction in the Na(+), K(+)-ATPase alpha1 or alpha2 isoforms results in different functional phenotypes: heterozygous alpha2 isolated hearts are hypercontractile, whereas heterozygous alpha1 hearts are hypocontractile. We examined Na(+)/Ca(2+) exchange (NCX) currents in voltage clamped myocytes (pipette [Na(+)]=15 mM) induced by abrupt removal of extracellular Na(+). In wild-type (WT) myocytes, peak exchanger currents were 0.59+/-0.04 pA/pF (mean+/-S.E.M., n=10). In alpha1(+/-) myocytes (alpha2 isoform increased by 54%), NCX current was reduced to 0.33+/-0.05 (n=9, P<0.001) indicating a lower subsarcolemmal [Na(+)]. In alpha2(+/-) myocytes (alpha2 isoform reduced by 54%), the NCX current was increased to 0.89+/-0.11 (n=8, P=0.03). The peak sarcolemmal Na(+) pump currents activated by abrupt increase in [K(+)](o) to 4 mM in voltage clamped myocytes in which the Na(+) pump had been completely inhibited for 5 min by exposure to 0 [K(+)](o) were similar in alpha1(+/-) (0.86+/-0.12, n=10) and alpha2(+/-) myocytes (0.94+/-0.08 pA/pF, n=16), and were slightly but insignificantly reduced relative to WT (1.03+/-0.05, n=24). The fluo-3 [Ca(2+)](i) transient (F/F(o)) in WT myocytes paced at 0.5 Hz was 2.18+/-0.09, n=34, was increased in alpha2(+/-) myocytes (F/F(o)=2.56+/-0.14, n=24, P=0.02), and was decreased in alpha1(+/-) myocytes (F/F(o)=1.93+/-0.08, n=28, P<0.05). Thus the alpha2 isoform rather than the alpha1 appears to influence Na(+)/Ca(2+) exchanger currents [Ca(2+)](i) transients, and contractility. This finding is consistent with the proposal that alpha2 isoform of the Na pump preferentially alters [Na(+)] in a subsarcolemmal micro-domain adjacent to Na(+)/Ca(2+) exchanger molecules and SR Ca(2+) release sites.

Animals↗
PubMed2005

[Recombinant adenovirus vectors carrying antisense MMP2 inhibit invasion of HCC cells in vitro].

OBJECTIVES: To construct a recombinant adenoviral vector carrying antisense matrix metalloproteinase-2 (MMP2) and to study its inhibitory effects on the invasiveness and migratory capacity of hepatocellular carcinoma (HCC) cell line HepG2 in vitro. METHODS: Total RNA was extracted from HCC. Then a 500 bp fragment at the 5' end of the human MMP2 cDNA sequence was synthesized by polymerase chain reaction (PCR) and was reversely inserted into the multiclone site (MCS) of the shuttle plasmid pAdTrack-CMV. With the resultant plasmid and the backbone plasmid pAdEasy-1, the homologous recombination took place in the E.coli BJ5183 and the recombinant adenoviral plasmid carrying the antisense MMP2 gene was constructed. The adenovirus (Ad-MMP2AS) was packaged and amplified in the HEK 293 cells and the viral titer was checked by GFP. Using the Boyden chamber model, the influence of Ad-MMP2AS on the invasion ability of HepG2 cells was determined in vitro. RESULTS: The recombinant adenovirus vector carrying antisense MMP2 was constructed successfully and a strong green fluorescence was observed in HepG2 cells under a fluorescence microscope. The viral titer was 1 x 10(8); Ad-MMP2AS can effectively inhibit the penetrating capacity of HepG2 cells through Matrigel in vitro. CONCLUSION: The recombinant adenovirus with antisense MMP2 can effectively inhibit the invasiveness and migratory capacity of HepG2 in vitro and may have potential in treating HCC.

Adenoviridae↗
PubMed2005

[Inhibition of adenovirus-mediated gene transfer of antisense matrix metalloproteinase-2 on hepatocellular carcinoma growth in vivo].

OBJECTIVE: To investigate if a recombinant adenoviral vector carrying antisense matrix metalloproteinase-2 (MMP2) gene would inhibit the growth of hepatocellular carcinoma (HCC) in vivo. METHODS: Using the recombinant adenoviral vector carrying antisense MMP2 gene (Ad-MMP2AS) which was constructed by us previously, to infect the human HCC cell line (Bel-7402). Then the invasiveness of the Bel-7402 cells was assayed in Matrigel, and the production of MMP2 in the Bel-7402 cells was detected with Western blotting analysis and Gelatin zymography. Then the Ad-MMP2AS-infected cells were subcutaneously inoculated in nude mice. After tumors developed, Ad-MMP2AS was injected intratumorally into pre-existing tumors. The tumors were removed, sectioned, and stained with H E. RESULTS: Compared with PBS or Ad-CMV-infected cells, the infected Bel-7402 cells with Ad-MMP2AS injections significantly reduced their MMP2 enzyme activity and invasiveness about 52.05% in Matrigel assays, and the tumor volumes in nude mice resulted in a 3.3-fold reduction. In addition, direct intratumoral injection of Ad-MMP2AS into pre-existing tumors significantly prevented further expansion of the tumor masses and resulted in a 63.06% reduction in tumor cell growth. CONCLUSION: The recombinant adenovirus with antisense MMP2 can effectively inhibit the invasiveness and growth of Bel-7402 cells in vitro and in vivo, and it has a therapeutic potential for HCC.

Adenoviridae↗
PubMed2005

[Construction of recombinant adeno-associated virus vectors carrying double gene of antisense multidrug resistance-associated protein and antisense multidrug resistance].

OBJECTIVE: To construct a recombinant adeno-associated virus vectors carrying double gene of antisense multidrug resistance-associated protein (MRP) and antisense multidrug resistance (MDR1) for use in studying the gene therapy to reverse the multidrug resistance (MDR) in hepatocellular carcinoma (HCC). METHODS: The 500 bp fragment (mrp) of MRP cDNA 5' region and the 600 bp fragment (mdr1) of MDR1 cDNA 5' region were amplified through polymerase chain reaction (PCR), and then they were linked to a combined gene fragment (mrp+mdrl) by overlapping technique. The combined gene fragment(mrp+mdrl) was cloned reversely into the multiple cloning site (MCS) of the expression plasmid pAAV-IRES-hrGFP in AAV Helper-Free System to construct the recombinant expression plasmid pAAV-IRES-hrGFP-(mrp + mdr1)AS. The packaging cell line (HEK 293 cell) was co-transfected with the pAAV-IRES-hrGFP-(mrp+mdr1)AS together with the control plasmid pAAV-RC and pHelper in AAV Helper-Free System by means of lipofectamine. The recombinant adeno-associated virus vector : rAAV2-(mrp+mdr1)AS carrying the double gene of antisense multidrug resistance-associated protein (MRP)and antisense multidrug resistance (MDR1) was packaged. Then the viral titer was checked by GFP. RESULTS: The recombinant adeno-associated virus vector : rAAV2-(mrp + mdr1)AS carrying antisense MRP and antisense MDR1 was constructed successfully, the strong green fluorescence was observed in HEK 293 cells under a fluorescence microscope. The viral titer was 2.5 X 10(6) efu/ml. CONCLUSION: The rAAV2-(mrp+mdr1)AS thus constructed could introduce the antisense MRP and antisense MDR1 into the human drug-resistant hepatocellular cell line effectively, which might provide a sound basis for the mechanisms and reversal methods of the multidrug resistance in HCC.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Mesoridazine: an open-channel blocker of human ether-a-go-go-related gene K+ channel.

Mesoridazine, a phenothiazine antipsychotic agent, prolongs the QT interval of the cardiac electrocardiogram and is associated with Torsade de pointes-type arrhythmias. In this study, we examined the effects of mesoridazine on human ether-a-go-go-related gene (HERG) K+ currents. HERG channels were stably expressed in human embryonic kidney 293 cells and studied using standard whole-cell patch-clamp technique (37 degrees C). Mesoridazine blocked HERG currents in a concentration-dependent manner (IC50 550 nM at 0 mV); block increased significantly over the voltage range where HERG activates and saturated at voltages eliciting maximal HERG channel activation. Tonic block of HERG current by mesoridazine (1.8 microM) was minimal (< 2-4%). The rate of the onset of HERG channel block was rapid and dose dependent (tau = 54 +/- 7 ms at 0 mV and 1.8 microM mesoridazine), but not significantly affected by test potentials ranging from -30 to +30 mV. The V1/2 for steady-state activation was shifted from -31.2 +/- 1.0 to -39.2 +/- 0.5 mV (P < 0.01). The apparent rate of HERG channel deactivation was significantly reduced (fast tau = 153 +/- 8 vs. 102 +/- 6 ms at -50 mV, P < 0.01; slow tau = 1113 +/- 63 vs. 508 +/- 27 ms, P < 0.01). The inactivation kinetics and voltage dependence of steady-state inactivation of the HERG channel were not significantly altered by mesoridazine. These findings demonstrate that mesoridazine is a potent and rapid open-channel blocker of HERG channels. This block would explain the QT prolongation seen clinically at therapeutic concentrations (0.3-3.6 microM).

Cell Line↗
PubMed2004

ABT-089: pharmacological properties of a neuronal nicotinic acetylcholine receptor agonist for the potential treatment of cognitive disorders.

ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine dihydrochloride salt] is a selective neuronal nicotinic receptor (NNR) modulator with cognitive enhancing properties in animal models of cognitive functioning. Amongst NNR subtypes, ABT-089 shows selectivity for the cytisine binding site on the alpha4beta2 receptor subtype as compared to the alpha-bungarotoxin (alpha-BgT) binding sites on the alpha7 and alpha1beta1deltagamma receptor subtypes. In functional in vitro electrophysiological and cation flux assays, ABT-089 displays differential activity including agonism, partial agonism and antagonism depending upon the NNR subtype and assay. ABT-089 is as potent and efficacious as (-)-nicotine at evoking acetylcholine (ACh) release from hippocampal synaptosomes. Furthermore, ABT-089 is neuroprotective against excitotoxic glutamate insults, with even greater potency seen after chronic treatment. Similarly, ABT-089 is effective in models of cognitive functioning, including enhancement of baseline functioning as well as improvement of impaired cognitive functioning seen following septal lesioning and natural aging. In neuroprotective assays the compound is most potent by chronic administration. In stark contrast to the positive effects in the cognitive models, ABT-089 shows little propensity to induce adverse effects such as ataxia, hypothermia, seizures, cardiovascular or gastrointestinal side effects. Together these data suggest that ABT-089 is a NNR modulator with the potential for treating cognitive disorders with markedly limited adverse cardiovascular and gastrointestinal side effects.

Animals↗
PubMed2003

Saxitoxin blocks L-type ICa.

Saxitoxin (STX) and tetrodotoxin (TTX) are frequently used to selectively block sodium channels. In this study, we provide evidence that commercial STX also inhibits L-type Ca2+ currents (I(Ca,L)) in adult mouse ventricular myocytes (VMs) and tsA-201 cells that were transiently cotransfected with three calcium channel subunits. We measured inhibition of sodium currents (INa) in mouse VMs, of I(Ca,L) in mouse VM and tsA-201 cells, and intracellular calcium concentration ([Ca2+]i) transients in single mouse VMs. STX or TTX was abruptly applied before the test voltage pulse using a rapid solution switcher device. STX (10 microM; Calbiochem) and TTX (60 microM; Sigma-Aldrich) completely blocked INa in mouse VMs. However, STX at 10 microM also reduced I(Ca,L) in mouse VM by 39% (P < 0.0001; n = 14), whereas TTX at 60 microM had no effect on I(Ca,L). STX (10 microM; Calbiochem) reduced the amplitude of the [Ca2+]i transients in mouse VMs by 36% (P < 0.0001; n = 10). In contrast, TTX (60 microM; Sigma-Aldrich) only reduced the amplitude of the [Ca2+]i transients by 9% (P = 0.003; n = 5). STX (10 microM) obtained from Sigma-Aldrich showed a similar inhibitory effect on I(Ca,L) (33%) (P < 0.0001; n = 5) in mouse VMs. STX (Calbiochem) inhibited the calcium currents of tsA-201 cells in a dose-dependent manner. This inhibition was voltage-independent. The current-voltage relationship of calcium currents in tsA-201 cells was not altered by STX. These results indicate that STX partially blocks L-type Ca2+ channels and thus provide further evidence that its effects are not specific for Na+ channels.

Animals↗
PubMed2003

Comparison of sarcoplasmic reticulum Ca2+-ATPase function in human, dog, rabbit, and mouse ventricular myocytes.

It has been reported that sarcoplasmic reticulum (SR) Ca(2+) uptake is more rapid in rat than rabbit ventricular myocytes, but little information is available on the relative SR Ca(2+) uptake activity in others species, including humans. We induced Ca(2+) transients with a short caffeine pulse protocol (rapid solution switcher, 10 mM caffeine, 100 ms) in single ventricular myocytes voltage clamped (-80 mV) with pipettes containing 100 microM fluo-3 and nominal 0 Ca(2+), in 0 Na(+)(o)/0 Ca(2+)(o) solution to inhibit Na/Ca exchange. SR in non-paced human, dog, rabbit, and mouse ventricular myocytes could be readily loaded with Ca(2+) under our experimental conditions with a pipette [Ca(2+)] = 100 nM. Resting [Ca(2+)](i) was similar in four types of ventricular myocytes. Activation of the Ca(2+)-release channel with a 100-ms caffeine pulse produced a rise in [caffeine](i) to slightly above 2 mM, the threshold for caffeine activation of Ca(2+) release. This caused a similar initial rate of rise and peak [Ca(2+)](i) in the four types of ventricular myocytes. However, there were significant differences in the duration of the plateau (top 10%) [Ca(2+)](i) transients and the time constant of the [Ca(2+)](i) decline (reflecting activity of the SR Ca(2+)-ATPase), with values for human > dog > rabbit > mouse. In paced myocytes under physiologic conditions, SR Ca(2+) content was greater in mouse than in rabbit myocytes, while peak I(Ca,L) was smaller in mouse. These findings confirm substantial species difference in SR Ca(2+)-ATPase activity, and suggest that the smaller the animal and the more rapid the heart rate, greater the activity of the SR Ca(2+)-ATPase. In addition, it appears that substantial species differences exist in the degree of SR Ca(2+) loading and I(Ca,L) under physiologic conditions.

Animals↗