Biomedical subjects

P Zhong

Publications and source records attributed to P Zhong.

At least 19 recordsLinked to original sources

PubMed2001

Novel erythromycin derivatives with aryl groups tethered to the C-6 position are potent protein synthesis inhibitors and active against multidrug-resistant respiratory pathogens.

A novel series of erythromycin derivatives has been discovered with potent activity against key respiratory pathogens, including those resistant to erythromycin. These compounds are characterized by having an aryl group tethered to the C-6 position of the erythronolide skeleton. Extensive structural modification of the C-6 moiety led to the discovery of several promising compounds with potent activity against both mef- and erm-mediated resistant Streptoccoccus pneumoniae. Preliminary mechanistic studies indicated that the new macrolides are potent protein synthesis inhibitors, which interact with methylated ribosomes isolated from resistant organisms. In experimental animal models, these compounds exhibited excellent in vivo efficacy and balanced pharmacokinetic profiles.

Animals↗

PubMed2001

Dynamics of bubble oscillation in constrained media and mechanisms of vessel rupture in SWL.

Rupture of small blood vessels is a primary feature of the vascular injury associated with shock-wave lithotripsy (SWL) and cavitation has been implicated as a potential mechanism. To understand more precisely the underlying mechanical cause of the injury, the dynamics of SWL-induced bubble dynamics in constrained media were investigated. Silicone tubing and regenerated cellulose hollow fibers of various inner diameters (0.2 to 1.5 mm) were used to fabricate vessel phantoms, which were placed in a test chamber filled with castor oil so that cavitation outside the phantom could be suppressed. Degassed water seeded with 0.2% Albunex contrast agent was circulated inside the vessel phantom, and intraluminal bubble dynamics during SWL were examined by high-speed shadowgraph imaging and passive cavitation detection via a 20-MHz focused transducer. It was observed that, in contrast to the typical large and prolonged expansion and violent inertial collapse of SWL-induced bubbles in a free field, the expansion of the bubbles inside the vessel phantom was significantly constrained, leading to asymmetric elongation of the bubbles along the vessel axis and, presumably, much weakened collapse. The severity of the constraint is vessel-size dependent, and increases dramatically when the inner diameter of the vessel becomes smaller than 300 microm. Conversely, the rapid, large intraluminal expansion of the bubbles causes a significant dilation of the vessel wall, leading to consistent rupture of the hollow fibers (i.d. = 200 microm) after less than 20 pulses of shock wave exposure in a XL-1 lithotripter. The rupture is dose-dependent, and varies with the spatial location of the vessel phantom in the lithotripter field. Further, when the large intraluminal bubble expansion was suppressed by inversion of the lithotripter pressure waveform, rupture of the hollow fiber could be avoided even after 100 shocks. Theoretical calculation of SWL-induced bubble dynamics in blood confirms that the propensity of vascular injury due to intraluminal bubble expansion increases with the tensile pressure of the lithotripter shock wave, and with the reduction of the inner diameter of the vessel. It is suggested that selective truncation of the tensile pressure of the shock wave may reduce tissue injury without compromising the fragmentation capability of the lithotripter pulse.

Acoustics↗

PubMed2001

Dynamic photoelastic study of the transient stress field in solids during shock wave lithotripsy.

Photoelastic and shadowgraph imaging techniques were used to visualize the propagation and evolution of stress waves, and the resultant transient stress fields in solids during shock wave lithotripsy. In parallel, theoretical analysis of the wavefront evolution inside the solids was performed using a ray-tracing method. Excellent agreement between the theoretical prediction and experimental results was observed. Both the sample size and geometry were found to have a significant influence on the wave evolution and associated stress field produced inside the solid. In particular, characteristic patterns of spalling damage (i.e., transverse and longitudinal crack formation) were observed using plaster-of-Paris cylindrical phantoms of rectangular and circular cross sections. It was found that the leading tensile pulse of the reflected longitudinal wave is responsible for the initiation of microcracks in regions inside the phantom where high tensile stresses are produced. In addition, the transmitted shear wave was found to play a critical role in facilitating the extension and propagation of the microcrack.

High-Energy Shock Waves↗

PubMed2001

Binding site of macrolide antibiotics on the ribosome: new resistance mutation identifies a specific interaction of ketolides with rRNA.

Macrolides represent a clinically important class of antibiotics that block protein synthesis by interacting with the large ribosomal subunit. The macrolide binding site is composed primarily of rRNA. However, the mode of interaction of macrolides with rRNA and the exact location of the drug binding site have yet to be described. A new class of macrolide antibiotics, known as ketolides, show improved activity against organisms that have developed resistance to previously used macrolides. The biochemical reasons for increased potency of ketolides remain unknown. Here we describe the first mutation that confers resistance to ketolide antibiotics while leaving cells sensitive to other types of macrolides. A transition of U to C at position 2609 of 23S rRNA rendered E. coli cells resistant to two different types of ketolides, telithromycin and ABT-773, but increased slightly the sensitivity to erythromycin, azithromycin, and a cladinose-containing derivative of telithromycin. Ribosomes isolated from the mutant cells had reduced affinity for ketolides, while their affinity for erythromycin was not diminished. Possible direct interaction of ketolides with position 2609 in 23S rRNA was further confirmed by RNA footprinting. The newly isolated ketolide-resistance mutation, as well as 23S rRNA positions shown previously to be involved in interaction with macrolide antibiotics, have been modeled in the crystallographic structure of the large ribosomal subunit. The location of the macrolide binding site in the nascent peptide exit tunnel at some distance from the peptidyl transferase center agrees with the proposed model of macrolide inhibitory action and explains the dominant nature of macrolide resistance mutations. Spatial separation of the rRNA residues involved in universal contacts with macrolides from those believed to participate in structure-specific interactions with ketolides provides the structural basis for the improved activity of the broader spectrum group of macrolide antibiotics.

Anti-Bacterial Agents↗

PubMed2001

[Effect of simulated weightlessness on the apoptosis of thymus cells in tail-suspended mice].

OBJECTIVE: To investigate the effect of simulated weightlessness on apoptosis of thymus cells in mice. METHOD: Tail-suspended mice were used as an animal model of simulated weightlessness; chromosome breakage was measured by PI staining, and changes of cell membrane were determined by Annexin-V analysis. RESULT: As compared with the control, there was no obvious chromosome breakage; the total number of apoptotic cells and number of early apoptotic cells increased in 1 d suspended group; the number of early apoptotic cells increased significantly and the total number of apoptotic cells increased very significantly in 2d suspended groups. CONCLUSION: These results suggested that simulated weightlessness could promote apoptosis of thymus cells.

Animals↗

PubMed2000

Molecular determinants of the functional interaction between syntaxin and N-type Ca2+ channel gating.

Syntaxin is a key presynaptic protein that binds to N- and P/Q-type Ca(2+) channels in biochemical studies and affects gating of these Ca(2+) channels in expression systems and in synaptosomes. The present study was aimed at understanding the molecular basis of syntaxin modulation of N-type channel gating. Mutagenesis of either syntaxin 1A or the pore-forming alpha(1B) subunit of N-type Ca(2+) channels was combined with functional assays of N-type channel gating in a Xenopus oocyte coexpression system and in biochemical binding experiments in vitro. Our analysis showed that the transmembrane region of syntaxin and a short region within the H3 helical cytoplasmic domain of syntaxin, containing residues Ala-240 and Val-244, appeared critical for the channel modulation but not for biochemical association with the "synprint site" in the II/III loop of alpha(1B). These results suggest that syntaxin and the alpha(1B) subunit engage in two kinds of interactions: an anchoring interaction via the II/III loop synprint site and a modulatory interaction via another site located elsewhere in the channel sequence. The segment of syntaxin H3 found to be involved in the modulatory interaction would lie hidden within the four-helix structure of the SNARE complex, supporting the hypothesis that syntaxin's ability to regulate N-type Ca(2+) channels would be enabled after SNARE complex disassembly after synaptic vesicle exocytosis.

Amino Acid Sequence↗

PubMed2000

Microdialysis assessment of shock wave lithotripsy-induced renal injury.

OBJECTIVES: Shock wave lithotripsy (SWL) is the primary treatment modality for managing the majority of symptomatic renal calculi. However, the fundamental mechanisms for stone fragmentation and the resultant morphologic changes that occur are not fully understood. Furthermore, a thorough understanding of the complex biologic pathways involved in SWL-induced renal injury does not exist at present. To elucidate the biologic processes involved in tissue injury after SWL, an animal model was designed to mimic the pathogenesis of high-energy SWL in humans. METHODS: Juvenile female swine were anesthetized, and a midline laparotomy incision was performed to expose the right kidney. Using an introducer apparatus, a microdialysis probe was placed into the renal parenchyma of the right kidney lower pole and a tunnel was generated to exit the distal ends of the inlet and outlet tubing outside the body. After a 72-hour postoperative recovery period, SWL was performed to the lower pole renal region of the kidney, as a microdialysis pump continuously infused dialysate through the inlet tubing. Microdialysis fluids were collected during SWL, and lipid peroxidation, as measured by conjugated diene concentrations, was monitored. RESULTS: All microdialysis probes remained patent for a total of 2000 shock waves. A significant elevation in conjugated diene levels was observed in the SWL versus untreated kidneys after 1000 shock waves were administered (P <0.02). CONCLUSIONS: This animal model is unique in that it represents the first system for the real-time collection of renal interstitial fluids during SWL. Analysis of this fluid may provide insight into the physiologic mechanisms responsible for shock wave-induced renal injury.

Animals↗

PubMed2000

Improvement of stone fragmentation during shock-wave lithotripsy using a combined EH/PEAA shock-wave generator-in vitro experiments.

To control the collapse of cavitation bubbles induced during shock-wave lithotripsy (SWL), a piezoelectric annular array (PEAA) shock-wave generator was fabricated and combined with an experimental electrohydraulic (EH) shock-wave lithotripter with a truncated HM-3 reflector. The PEAA generator consists of eight individual transducers of 200-kHz resonant frequency. At a discharge voltage of 15 kV, the PEAA generator produces a shock wave with a peak positive pressure of 8.2 MPa, a positive half cycle duration of 2.9 micros, and a -6-dB beam width of 5 mm. The trigger of the PEAA generator was controlled via fiberoptic link with reference to the spark discharge of the EH generator. Hence, the PEAA-generated shock wave could be used to interact with cavitation bubbles induced by the EH source at various stages of their oscillation. The duration of bubble oscillation during SWL was monitored by a 2.25-MHz focused hydrophone, and this information was used to control the release timing of the PEAA generator. Stone fragmentation tests in vitro were carried out, and demonstrated that stone comminution could be significantly enhanced when the shock wave-bubble interaction occurred during the collapsing phase of the bubbles. A maximum increment of 60% to 80% in stone fragmentation was achieved when the PEAA-generated shock wave arrives near the collapse of the bubbles. Under these conditions, much intensified collapse of the bubbles near the surface of the stone, with strong secondary shock-wave emission and increased stress concentration at the impact site of the solid boundary, was observed using high-speed shadowgraph and photoelastic imaging.

Calculi↗

PubMed2000

Studies of the novel ketolide ABT-773: transport, binding to ribosomes, and inhibition of protein synthesis in Streptococcus pneumoniae.

Macrolide resistance in Streptococcus pneumoniae has been associated with two main mechanisms: target modification by Erm methyltransferases and efflux by macrolide pumps. The ketolide ABT-773, which has a 3-keto group and no L-cladinose sugar, represents a new class of drugs with in vitro activity against a variety of resistant bacteria. Several approaches were undertaken to understand how ABT-773 was able to defeat resistance mechanisms. We demonstrated tighter ribosome binding of ABT-773 than erythromycin. We also showed that ABT-773 (i) accumulated in macrolide-sensitive S. pneumoniae at a higher rate than erythromycin, (ii) was able to bind with methylated ribosomes, though at lower affinities than with wild-type ribosomes, and (iii) accumulated in S. pneumoniae strains with the efflux-resistant phenotype.

Anti-Bacterial Agents↗

PubMed2000

The HIV-2 genotype and the HIV-1 syncytium-inducing phenotype are associated with a lower virus replication in dendritic cells.

During sexual transmission, HIV infects the mucosal dendritic cells and is transferred to CD4 T cells. Whether HIV variants of a particular genetic (sub)type or phenotype selectively infect dendritic cells (DC) or are preferentially transferred to T cells remains highly controversial. To avoid the cumbersome use of primary dendritic cells, in vitro dendritic cell models were generated from precursors, either hematopoietic progenitor cells (HPC) or monocytes (MO). Productive infection in the dendritic cells and transfer of the virus to T cells was assessed for a range of HIV variants. HPC-derived dendritic cells (HPC-DC) were more susceptible to HIV-1 than to HIV-2 isolates. The HIV-1 group O strains were more productive in HPC-DC than group M, but amongst the latter, no subtype-related difference was observed. Both non-syncytium-inducing (NSI) and SI HIV isolates and lab strains could productively infect HPC-DC, albeit with a different efficiency. Adding blocking antibodies confirmed that both CCR-5 and CXCR-4 co-receptors were functional. Biological HIV-1 clones of the NSI/R5 phenotype infected more readily HPC-DC than SI/X4 clones. MO-derived dendritic cells were, however, more exclusive in their preference for NSI/R5 clones. Some HIV variants, that did not grow readily in HPC-DC alone, could be rescued by adding resting or pre-activated T cells. The present data show that HIV-2 isolates and SI clones replicate less in model-DC, but no preference for a particular HIV-1 subtype was evident. Co-culture with T cells could "correct" a limited growth in dendritic cells. Clearly, both intrinsic dendritic cell susceptibility and enhancement by T cells are explained only partly by HIV genotype and phenotype. The in vitro dendritic cell models seem useful tools to further unravel interactions between HIV, DC, and T cells.

CCR5 Receptor Antagonists↗

PubMed2000

Acoustic and mechanical properties of artificial stones in comparison to natural kidney stones.

PURPOSE: Standardized and reproducible artificial kidney stone models are important for performing comparative studies of different lithotripsy modalities. The acoustic and mechanical properties of renal calculi dictate the manner by which stones interact with the mechanical stresses produced by shock wave lithotripsy (SWL) or intracorporeal lithotripsy modalities. We have developed a novel artificial kidney stone model that is made of natural substances found in real kidney stones. These stone models appear to be much closer in physical properties to natural kidney stones than previously used stone models. MATERIALS AND METHODS: The acoustic and mechanical properties of six groups of artificial stone models were compared to corresponding natural stones of similar compositions. Moreover, three groups of artificial stone models made of plaster-of-Paris were compared to their natural counterparts. In terms of acoustic properties, stone density was measured using a pycnometer based on Archimedes' principle, whereas longitudinal and transverse (or shear) wave propagation speeds were measured using an ultrasound pulse transmission technique. These values were used to calculate wave impedance and dynamic mechanical properties (bulk modulus, Young's modulus, and shear modulus) of the stones. The microhardness of the stones was measured and the effect of composition on stone fragility was evaluated. RESULTS: Artificial stones, when compared to natural stones of similar composition, showed similar trends in longitudinal and transverse wave speeds, wave impedance, and dynamic elastic moduli. However, values for the artificial stones were uniformly low compared to those of natural stones, suggesting that these artificial stones may be more amenable to shock wave fragmentation. The results of SWL on stone fragmentation of artificial and natural stones also revealed similar trends with the exception of artificial cystine stones which were found to be the most resistant to shock wave fragmentation. CONCLUSIONS: The results indicate that the physical properties of artificial stones made of natural stone materials are comparable to renal calculi of the same chemical composition. The data suggests that these stone phantoms are suitable for performing standardized and reproducible in vitro investigations, especially with regards to fragility of kidney stones of different chemical compositions during SWL.

Acoustics↗

PubMed2000

Quantification of the tip movement of lithotripsy flexible pneumatic probes.

PURPOSE: We developed an optical system to quantify in vitro tip movement of the Lithoclastdouble dagger flexible probe, and correlated various physical parameters of the vibrating probe tip with resultant stone fragmentation. MATERIALS AND METHODS: A noncontact optical measurement system was developed to quantify in vitro tip movement of the Lithoclast flexible probe. This system and an in vitro fragmentation model were used to determine the tip displacement, velocity, impact momentum, impact energy and stone fragmentation of the flexible probe at 5 deflection angles between 0 and 48 degrees, and the 2 pneumatic pressure levels of 2.0 and 2.5 bar. RESULTS: An increase in maximum probe tip displacement, velocity, impact momentum and energy, and stone fragmentation was seen as the pneumatic pressure was increased from 2.0 to 2.5 bar. A progressive decrease in these parameters was demonstrated as the probe tip was deflected, especially at deflection angles greater than 24 degrees. Impact momentum appears to be the physical parameter most closely correlated with stone fragmentation efficiency. CONCLUSIONS: The optical measurement system and in vitro fragmentation model developed allow one to quickly and reliably assess the performance of flexible pneumatic probes in vitro. This system can be used for general bench testing and basic research that can provide critical information for the design of more effective and efficient flexible pneumatic lithotripsy probes.

Calibration↗

PubMed2000

[Alteration of banked blood cholinesterase level and its significance in emergency treatment of acute organophosphorus pesticide poisoning].

OBJECTIVE: To observe the relationship between the preservation days of banked blood and the alteration level of plasma cholinesterase with the aim of making proper selection of banked blood in emergency treatment of acute organophosphorus pesticide poisoning (AOPP). METHODS: We selected at random the banked blood that has been stored for different length of time before blood transfusion so as to determine the plasma cholinesterase value. The normal plasma cholinesterase value was determined on blood samples in the Blood Center which served as a control group. The cholinesterase value was determined with a kit of the BM Company and the Cobes-Fara II automatic analysor of the Roch Company. RESULTS: It was found that there was no significant difference of plasma cholinesterase value between the one-day banked blood and the normal control group (P > 0.05), but the plasma cholinesterase values of the other experiment groups were all significantly lower than that of the control group (P < 0.05). As compared with the normal control group, the relative ratio with fixed base was about from 80 percent to 16 percent. It seems that the preservation days are in negative correlation with the cholinesterase value (r = -0.7929, P < 0.01). The curvilinear regression equation is Y = -1,823.3 Ln(X) +/- 6,229.4. CONCLUSION: With the increase of the banked blood preservation days after blood sampling, the plasma cholinesterase value decreased gradually. So in the emergency treatment of severe AOPP, it is essential to use the fresh blood collected within one day, so as to avoid missing the chance of first-aid treatment. This study provides the experimental basis for emphasizing transfusion of fresh blood and ensuring transfusion of highly active cholinesterase in treating AOPP.

Adolescent↗

PubMed1999

Novel inhibitors of Erm methyltransferases from NMR and parallel synthesis.

The Erm family of methyltransferases confers resistance to the macrolide-lincosamide-streptogramin type B (MLS) antibiotics through the methylation of 23S ribosomal RNA. Upon the methylation of RNA, the MLS antibiotics lose their ability to bind to the ribosome and exhibit their antibiotic activity. Using an NMR-based screen, we identified a series of triazine-containing compounds that bind weakly to ErmAM. These initial lead compounds were optimized by the parallel synthesis of a large number of analogues, resulting in compounds which inhibit the Erm-mediated methylation of rRNA in the low micromolar range. NMR and X-ray structures of enzyme/inhibitor complexes reveal that the inhibitors bind to the S-adenosylmethionine binding site on the Erm protein. These compounds represent novel methyltransferase inhibitors that serve as new leads for the reversal of Erm-mediated MLS antibiotic resistance.

Binding Sites↗

PubMed1999

The 2.2 A structure of the rRNA methyltransferase ErmC' and its complexes with cofactor and cofactor analogs: implications for the reaction mechanism.

The rRNA methyltransferase ErmC' transfers methyl groups from S -adenosyl-l-methionine to atom N6 of an adenine base within the peptidyltransferase loop of 23 S rRNA, thus conferring antibiotic resistance against a number of macrolide antibiotics. The crystal structures of ErmC' and of its complexes with the cofactor S -adenosyl-l-methionine, the reaction product S-adenosyl-l-homocysteine and the methyltransferase inhibitor Sinefungin, respectively, show that the enzyme undergoes small conformational changes upon ligand binding. Overall, the ligand molecules bind to the protein in a similar mode as observed for other methyltransferases. Small differences between the binding of the amino acid parts of the different ligands are correlated with differences in their chemical structure. A model for the transition-state based on the atomic details of the active site is consistent with a one-step methyl-transfer mechanism and might serve as a first step towards the design of potent Erm inhibitors.

Adenosine↗

PubMed1999

How to improve lithotripsy and chemolitholysis of brushite-stones: an in vitro study.

Because of their resistance to fragmentation, treatment of brushite stones is a big problem. This study was performed to look for an improvement in therapeutic strategies by using artificial stones made of brushite (Bon(n)-stones), which are comparable to their natural counterparts. Using an ultrasound transmission technique, longitudinal wave propagation speeds were measured at different time intervals during treatment with hemiacidrin. From these and density measurements, transverse wave speed, wave impedance and dynamic mechanical properties of the artificial stones were calculated. Moreover, the microhardness of artificial stones was measured and investigations on shock wave lithotripsy (SWL) combined with initial chemolytic treatment of the stones were performed. The suggestion was confirmed that stone fragility and thus SWL can be improved by varying the physical properties of brushite stones through treatment with hemiacidrin. Additionally, we demonstrated the efficacy of Suby G in dissolving artificial brushite stones using an experimental arrangement simulating the physiological conditions in the upper urinary tract. Moreover, the efficacy of four different intracorporeal lithotripsy devices (electrohydraulic, pneumatic, laser and ultrasound) was tested and it was shown that electrohydraulic lithotripsy seems to be the best system for comminution of brushite stones.

Calcium Phosphates↗

PubMed1999

Recent developments in SWL physics research.

Two projects in our laboratory highlight some recent developments in shockwave lithotripsy (SWL) physics research. In the first project, we developed a prototype of a piezoelectric annular array (PEAA) shockwave generator that can be retrofitted on a Dornier HM-3 lithotripter for active control of cavitation during SWL. The PEAA generator, operating at 15 kV, produces a peak positive pressure of approximately 8 MPa with a -6-dB beam diameter of 5 mm. The shockwave generated by the PEAA was used to control and force the collapse of cavitation bubbles induced by a laboratory electrohydraulic shockwave lithotripter with a truncated HM-3 reflector. With optimal time delay between the lithotripter pulse and the PEAA-generated shockwave, the collapse of cavitation bubbles near the stone surface could be intensified, and the resultant stone fragmentation in vitro could be significantly improved. In the second project, high-speed shadowgraph imaging was used to visualize the dynamics of lithotripter-induced bubble oscillation in a vascular phantom. Compared with the free bubble oscillation in water, the expansion of cavitation bubble(s) produced in silicone tubes and a 200-microm cellulose hollow fiber by either a Nortech EHL or a Dornier XL-1 lithotripter was found to be significantly constrained. Rupture of the cellulose hollow fiber was observed consistently after about 20 shocks from the XL-1 lithotripter at an output voltage of 20 kV. These results confirm experimentally that SWL-induced cavitation in vivo can be significantly constrained by the surrounding tissue, and large intraluminal bubble expansions could cause rupture of capillaries and small blood vessels.

Humans↗

PubMed1999

Induction of ribosome methylation in MLS-resistant Streptococcus pneumoniae by macrolides and ketolides.

One major mechanism for resistance to macrolide antibiotics in Streptococcus pneumoniae is MLS (macrolide, lincosamide, and streptogramin B) resistance, manifested when the 23S rRNA is methylated by the product of an erm gene. This modification results in the decreased binding of all known macrolide, lincosamide, and streptogramin B antibiotics to the ribosome. More than 30 ermAM-containing clinical isolates of S. pneumoniae were examined in our lab and showed high-level resistance (MIC > or =128 microg/ml) to erythromycin, azithromycin, tylosin, clindamycin, and ketolide (macrolides that lack the cladinose sugar) TE-802. We found that the new generation of ketolides A965 and A088 displayed variable activity against the same group of resistant S. pneumoniae strains. To understand the basis of variability of the minimal inhibitory concentration (MIC) values of A965 and A088, we examined the effects of a series of macrolides and ketolides on the level of 23S rRNA methylation in five ermAM-containing resistant S. pneumoniae isolates. We show here that the basal levels of ribosomal methylation vary from strain to strain. The level of rRNA methylation can be strongly induced by erythromycin, azithromycin, and TE-802, resulting in high-level of resistance to these compounds. Ketolide A965 and A088, however, are weak inducers at sub-MIC drug concentrations, therefore showing variable activities in strains with differential methylation levels.

Anti-Bacterial Agents↗