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Biomedical subjects

C Hou

Publications and source records attributed to C Hou.

At least 55 records · Page 3Linked to original sources
PubMed1999

Single-photon emission tomography imaging of serotonin transporters in the non-human primate brain with the selective radioligand [(123)I]IDAM.

A new radioligand, 5-iodo-2-[[2-2-[(dimethylamino)methyl]phenyl]thio]benzyl alcohol ([(123)I]IDAM), has been developed for selective single-photon emission tomography (SPET) imaging of SERT. In vitro binding studies suggest a high selectivity of IDAM for SERT (K(i)=0.097 nM), with considerably lower affinities for norepinephrine and dopamine transporters (NET K(i)= 234 nM and DAT K(i)>10 microM, respectively). In this study the biodistribution of SERT in the baboon brain was investigated in vivo using [(123)I]IDAM and SPET imaging. Dynamic sequences of SPET scans were performed on three female baboons (Papio anubis) after injection of 555 MBq of [(123)I]IDAM. Displacing doses (1 mg/kg) of the selective SERT ligand (+)McN5652 were administered 90-120 min after injection of [(123)I]IDAM. Similar studies were performed using a NET inhibitor, nisoxetine, and a DAT blocker, methylphenidate. After 60-120 min, the regional distribution of tracer within the brain reflected the characteristic distribution of SERT, with the highest uptake in the midbrain area (hypothalamus, raphe nucleus, substantia nigra), and the lowest uptake in the cerebellum (an area presumed free of SERT). Peak specific binding in the midbrain occurred at 120 min, with a ratio to the cerebellum of 1.80+/-0.13. At 30 min, 85% of the radioactivity in the blood was metabolite. Following injection of a competing SERT ligand, (+)McN5652, the tracer exhibited rapid washout from areas with high concentrations of SERT (dissociation rate constant in the midbrain, averaged over three baboons, k(off)=0. 025+/-0.002 min(-1)), while the cerebellar activity distribution was undisturbed (washout rate 0.0059+/- 0.0003 min(-1)). Calculation of tracer washout rate pixel-by-pixel enabled the generation of parametric images of the dissociation rate constant. Similar studies using nisoxetine and methylphenidate had no effect on the distribution of [(123)I]IDAM in the brain. These results suggest that [(123)I]IDAM is suitable for selective SPET imaging of SERT in the primate brain, with high contrast, favorable kinetics, and negligible binding to either NET or DAT.

Animals↗
PubMed1999

Single-photon emission tomography imaging of serotonin transporters in the nonhuman primate brain with [(123)I]ODAM.

We have described previously a selective serotonin transporter (SERT) radioligand, [(123)I]IDAM. We now report a similarly potent, but more stable IDAM derivative, 5-iodo-2-[2-[(dimethylamino)methyl]phenoxy]benzyl alcohol ([(123)I]ODAM). The imaging characteristics of this radioligand were studied and compared against [(123)I]IDAM. Dynamic sequences of single-photon emission tomography (SPET) scans were obtained on three female baboons after injection of 375 MBq of [(123)I]ODAM. Displacing doses (1 mg/kg) of the selective SERT ligand (+)McN5652 were administered 120 min after injection of [(123)I]ODAM. Total integrated brain uptake of [(123)I]ODAM was about 30% higher than [(123)I]IDAM. After 60-120 min, the regional distribution of tracer within the brain reflected the characteristic distribution of SERT. Peak specific binding in the midbrain occurred 120 min after injection, with an equilibrium midbrain to cerebellar ratio of 1. 50+/-0.08, which was slightly lower than the value for [(123)I]IDAM (1.80+/- 0.13). Both the binding kinetics and the metabolism of [(123)I]ODAM were slower than those of [(123)I]IDAM. Following injection of a competing SERT ligand, (+)McN5652, the tracer exhibited washout from areas with high concentrations of SERT, with a dissociation kinetic rate constant k(off)=0.0085+/-0.0028 min(-1) in the midbrain. Similar studies using nisoxetine and methylphenidate showed no displacement, consistent with its low binding affinity to norepinephrine and dopamine transporters, respectively. These results suggest that [(123)I]ODAM is suitable for selective SPET imaging of SERT in the primate brain, with higher uptake and slower kinetics and metabolism than [(123)I]IDAM, but also a slightly lower selectivity for SERT.

Animals↗
PubMed1999

Monitoring Inositol-Specific Phospholipase C Activity Using a Phospholipid FlashPlate(R).

Inositol-specific phospholipase Cs(PLCs) are a group of enzymes involved in the signal transduction pathway of many plasma membrane receptor mediated events. We developed a modified solid surface to capture [(3)H] PIP(2) onto the Basic FlashPlate(R) in order to monitor PLC activity. Our results clearly demonstrate the utility of [(3)H] PIP(2)-Coated Phospholipid FlashPlate(R) microtiter plates for assessing PLC activity for HTS of receptor-coupled functional assays. The results show that PLC activity can be measured easily from a variety of sources including purified recombinant enzyme preparations, crude HL60 cell lysates and permeabilized A431 human carcinoma cells. Moreover, this format provides a surface comparable to that used for classical solution based radiolabeled mixed phospholipid micelle studies and illustrates the feasibility of this assay for measuring PLC activation in a variety of different drug screening assays.

Journal Article↗
PubMed1999

Simultaneous SPECT studies of pre- and postsynaptic dopamine binding sites in baboons.

UNLABELLED: The central nervous system dopamine transporters (DATs) and dopamine D2/D3 receptors are implicated in a variety of neurological disorders. Both sites are also targets for drug treatment. With the successful development of [99mTc]TRODAT-1, single-isotope imaging studies using this ligand for DAT imaging can be complemented by additional use of 123I-labeled D2/D3 receptor ligand co-injected to assess both pre- and postsynaptic sites of the dopaminergic system simultaneously. METHODS: Twelve SPECT scans of the brain were obtained in two baboons after intravenous administration of 740 MBq (20 mCi) [99mTc]-TRODAT-1 (technetium, [2-[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo[3,2,1]oct-2-yl]methyl ](2-mercaptoethyl) amino]ethyl]-amino]ethanethiolato (3-)]- oxo-[1R-(exo-exo)]) and 185 MBq (5 mCi) [123I]iodobenzamide or [123I]iodobenzofuran. SPECT data were acquired by a triple-head gamma camera equipped with ultra-high-resolution fanbeam collimators (scan duration = 210 min). Two sets of SPECT data were obtained using energy windows of 15% centered on 140 keV for 99mTc and 10% asymmetric with a lower bound at 159 keV for 123I. After coregistration with MRI, region-of-interest analysis was performed using predefined templates from coregistered MRI. In blocking studies, baboons were pretreated with N-methyl-2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane (CFT, 14 mg) or raclopride (14 mg) to block DAT or D2/D3 binding site, respectively. RESULTS: Image quality of dual-isotope studies was similar to that obtained from single-isotope studies. When one site was blocked with CFT or raclopride, the binding of the respective ligand to the other site was not affected. CONCLUSION: This is the first example that clearly demonstrates the feasibility of simultaneous imaging of both pre- and postsynaptic sites of the dopaminergic system in baboons with dual-isotope SPECT studies. With or without corrections for cross-contamination of 123I into the 99mTc window, striatum-to-cerebellum ratios (target-to-nontarget) of dual-isotope experiments did not differ significantly from single-isotope experiments. This method may be a valuable and cost-effective tool for gaining comprehensive information about the dopaminergic system in one SPECT imaging session.

Animals↗
PubMed1999

Comparison of necrotic characteristics and benefits between 50% acetic acid and pure ethanol in local hepatic injection: a study in rats.

This study compares the characteristics of acetic acid and pure ethanol in local hepatic injection and identifies the possible benefits from acetic acid by an animal model. We injected 0.03 ml of pure ethanol and 0.01 ml of 50% acetic acid separately into different sites of the same liver. The shape and diameter of the lesions were recorded at 0 min, 5 min and 15 min, and 5 lesions were also reviewed one day later. The lesions induced by pure ethanol were irregular, whereas those induced by 50% acetic acid were round or oval. The diameter of lesions induced by 50% acetic acid was 2.62 +/- 0.58 mm initially and increased to 4.50 +/- 0.84 mm and 5.25 +/- 0.75 mm at 5 min and 15 min, (5 min compared with 0 min, p < 0.0001; 15 min compared with 5 min, p < 0.001) respectively. The diameters of lesions induced by pure ethanol did not increase. The diffusion diameter at 5 min and 15 min were 1.88 mm and 2.63 mm respectively. Furthermore, viable liver cells were occasionally found in two lesions induced by pure ethanol. Acetic acid had a more homogeneous distribution and better infiltrating ability than pure ethanol and may be superior to pure ethanol in local injection therapy of HCC. But more clinical trials in the treatment HCC should be carried out.

Acetic Acid↗
PubMed1999

[Low-tensioned and "b"-like ileocystoplasty].

OBJECTIVE: To perfectly solve the urine-kept and urinary problems of the vesical cancer patients after vesicoectomy. METHODS: We performed low-tensioned and "b"-like ileocystoplasty in 16 patients. RESULTS: After the operation, new vesica urinaria worked well in keeping and emptying urine-urine through the urethra. Residual urine test, chemical test and urography showed that there were no disturbance of body water and electrolyte metetabolism, no reterograde urine in the ureter, no uracratia, and no damage to renal function. CONCLUSIONS: Ileocystoplasty can be used clinically.

Aged↗
PubMed1998

Effect of truncation and mutation of the carboxyl-terminal region of the beta subunit on membrane assembly and activity of the pyridine nucleotide transhydrogenase of Escherichia coli.

The pyridine nucleotide transhydrogenase of Escherichia coli is a proton pump composed of two different subunits (alpha and beta) assembled as a tetramer (alpha 2 beta 2) in the cytoplasmic membrane. A series of mutants was generated in which the carboxyl-terminal region of the beta subunit was progressively truncated. Removal of the two carboxyl-terminal amino acid residues prevented incorporation of the enzyme into the cytoplasmic membrane. Deletion of the carboxyl-terminal amino acid allowed incorporation of the alpha subunit to near normal levels, but the amount of the beta subunit was much decreased. It is concluded that, although the alpha subunit can be incorporated into the cytoplasmic membrane without the beta subunit, the carboxyl-terminal region of the beta subunit is involved in determining the correct conformation of the alpha subunit for assembly. The carboxyl-terminal amino acid of the beta subunit, beta Leu462, and the penultimate residue, beta Ala461, were individually mutated and the effect on two transhydrogenase activities determined. The reduction of 3-acetylpyridine adenine dinucleotide (AcPyAD+) by NADPH, and by NADH in the presence of NADP+, was decreased maximally by about 60%. The reduction of AcPyAD+ by NADH in the absence of NADP+ was decreased to a greater extent. Most mutants of beta Leu462 showed at least an 80% reduction in activity as well as abnormal kinetics. The abnormal kinetics were explored in the beta A461P mutant and were attributed to tighter binding of the product AcPyADH. This compound competed with NADP+ at the NADP(H)-binding site. It is concluded that the carboxyl-terminal region of the beta subunit contributes to the NADP(H)-binding site on this subunit.

Amino Acid Sequence↗
PubMed1998

Comparison of biodegradable and metallic tension-band fixation for patella fractures. 38 patients followed for 2 years.

We compared the outcome of patella fractures fixed by biodegradable tension-band (B) with self-reinforced polyglycolide or self-reinforced poly-L-lactide plugs and polyester ligaments or by metallic tension-band (M) with Kirschner wires and metallic cerclage wire in a randomized study. 38 fractures (18 with B and 20 with M) were treated. The follow-up time was 24 (14-32) months. The fractures healed in all patients after a medium of 8 weeks. In the B group, the clinical outcome was good in 13, fair in 4, and poor in 1 patient. In the M group, the corresponding figures were 15, 3 and 2. There were no clinical or radiographic differences between the two methods. Patella fractures can be treated, successfully using biodegradable tension-band fixation with no need for a second operation to remove the implants after bone union.

Absorption↗
PubMed1998

[Experimental study of the effect on growth of Schwann cell from chitin and chitosan in vitro].

In order to study the effect of chitin and chitosan on the growth of Schwann cell (SC) of rats in vitro, the SC was isolated from sciatic nerve and brachial plexus of new-born rats. After the enzymatic and mechanical dissociation, the cell suspension was vaccinated on chitin membrane and chitosan fluid-coated glass coverslips. Then, the growth of SC was examined at 1, 3, 7 days after culture under light microscope and scanning electron microscope. The results showed that 94 percent of the cell grown from was SC and only 6% was fibroblast (FB), while that of the control SC 71% and FB 29% in population. The number of SC in chitosan suspension was more than that in chitin. Therefore, the conclusion was that the chitin and chitosan was histocompatible to SC, and chitosan suspension was superior to chitin, and both could inhibit the growth of fibroblast.

Animals↗
PubMed1998

[Clinical study of gentamycin-loaded chitosan drug delivery system].

An clinical and pharmacokinetic study for a drug delivery system (DDS) of gentamycin-loaded chitosan bar were carried out with the purpose to evaluate its efficacy and giving further data for its clinical applications. Eighteen cases of chronic osteomyelitis were treated by surgical necrectomy with implantation of gentamycin-load chitosan bar in the prepared bone cavity. After operation, the concentration of gentamycin in serum and wound drainage fluid were examined at different times and blood urea nitrogen (BUN) and serum creatinine (Cr) as well. The clinical results were evaluated by the conditions of wound healing and clinical and roentgenographic manifestations. The results showed that the serum gentamycin concentration reached its peak level (0.86 microgram/ml) at 24 hours after operation and lasted for 4 days. No increase in the concentrations of BUN and Cr were observed after implantation. The gentamycin concentration in wound drainage fluid was several hundred times higher than the minimum inhibitory concentration (MIC) for staphylococcus aureus. All of the 18 cases were followed up for 24.8 months (in an range of 6-34 months) 16 patients received initial cure and without any recurrence. So, it could be concluded that the gentamycin-loaded chitosan DDS was a simple and effective method for the treatment of chronic osteomylitis without the necessity to carry out a second operation to remove the drug carrier, and it was sound to popularize its clinical application.

Administration, Topical↗
PubMed1998

[A preliminary clinical observation of giant cell tumor of bone treated by adriamycin-loaded chitosan drug delivery system].

In order to observe the curative effect and general reaction of locally used adriamycin (ADM)-loaded chitosan drug delivery system on giant cell tumor of bone after curettage. The cavities of 4 cases of giant cell tumor after curettage were filled with ADM-loaded chitosan drug delivery system with 4 times the dosage usually used for intravenous application. After operation, the concentration of ADM in plasma on the 1st, 2nd and 5th day, and the functions of liver and kidney on the 1st week, 1st month and 6th month were all investigated. The results were that the concentration of ADM in plasma was (143.05 +/- 27.55) ng/ml, (52.17 +/- 11.28) ng/ml and (4.25 +/- 3.07) ng/ml respectively, and the functions of liver and kidney were all normal in 6 months. After a follow-up of 7-19 months, no local or general reactions were observed and X-ray showed no recurrence. Therefore, it was concluded that the locally used ADM-loaded chitosan delivery system was safe and effective in treatment of giant cell tumor of bone after curettage.

Adult↗
PubMed1998

[Distal clavicular fracture and dislocation of acromino-clavicular jiont treated with biopoly ligament].

OBJECTIVE: To probe into distal clavicular fracture and acromino-clavicular joint dislocation treatment. METHODS: 11 cases of distal clavicular fracture and 20 cases of acromino-clavicular joint dislocation were treated with biopoly ligament in recent 2 years. The follow-up period lasted from 3 to 24 months with an average of 16.7 months. RESULTS: Of 29 follow-up cases, 21 were excellent and 8 satisfactory. There was no redisplacement or refracture. CONCLUSION: Biopoly ligament is believed to be a good and safe material for this fracture or dislocation. This method is simple without needing a second operation for removal of implant.

Acromioclavicular Joint↗
PubMed1998

[The effect of chitosan in prevention of fibrous scar tissue formation after laminectomy].

OBJECTIVE: To study the effect of chitosan in the prevention of fibrous scar formation in the epidural space after laminectomy. METHOD: Fourty-eight SD rats were used as the animal model. Laminectomy was performed in lumber 1, and the exposed dura was covered with hyaluronate (group A), free fat (group B), chitosan (group C), and saline solution (group D) respectively. At 4, 8 and 12 weeks postoperation, scar formation was observed. RESULT: The results revealed that scar formed in the group D at the fourth week reached a peak at the eighth week and began to soften and constrict at the twelfth week. Sodium hyaluronate and chitosan had a significant efficacy in the prevention of scar formation, but the effect of chitosan was superior to that of sodium hyaluronate. CONCLUSION: The findings of this study indicate that chitosan has a preventive effect on scar tissue formation.

Animals↗
PubMed1997

Cross-linking and N-(1-pyrenyl)maleimide labeling of cysteine mutants of proton-pumping pyridine nucleotide transhydrogenase of Escherichia coli.

The pyridine nucleotide transhydrogenase of Escherichiacoli is a proton pump composed of two subunits (alpha and beta) organized as an alpha2beta2 tetramer. The enzyme contains seven cysteine residues, five in the alpha-subunit and two in the beta-subunit. The reaction of these residues with the cross-linking agent cupric 1, 10-phenanthrolinate and with the fluorescent thiol reagent N-(1-pyrenyl)maleimide was investigated in mutants in which one or more of these cysteine residues had been mutated to serine or threonine residues. Mutation of alphaCys395 and alphaCys397 prevented disulfide bond formation to give the cross-linked alpha2 dimer. We concluded that the two alpha-subunits of the holoenzyme interface in the region of these two cysteine residues. Pyrenylmaleimide reacted with detergent-washed cytoplasmic membrane vesicles containing high levels of transhydrogenase protein to show characteristic fluorescence emission bands at 378-379, 397-398, and 419-420 nm. At higher ratios of pyrenylmaleimide:transhydrogenase (>5:1) and longer times of reaction, an eximer band at 470 nm was formed. This was attributed to interaction between noncovalently bound molecules of pyrenylmaleimide. The cysteine residues of the beta-subunit (betaCys147 and betaCys260) were covalently modified by pyrenylmaleimide. betaCys147 reacted more strongly than betaCys260 with the fluorophore, and the pyrene derivative of betaCys147 was more accessible to quenching by 5-doxylstearate, suggesting a proximity to the surface of the membrane. Covalent modification of betaCys260 resulted in inhibition of enzyme activity. The inhibition was attributed to the introduction of the bulky pyrene group into the enzyme.

Amino Acid Sequence↗
PubMed1997

Properties of a cysteine-free proton-pumping nicotinamide nucleotide transhydrogenase.

Nicotinamide nucleotide transhydrogenase from Escherichia coli was investigated with respect to the roles of its cysteine residues. This enzyme contains seven cysteines, of which five are located in the alpha subunit and two are in the beta subunit. All cysteines were replaced by site-directed mutagenesis. The final construct (alphaC292T, alphaC339T, alphaC395S, alphaC397T, alphaC435S, betaC147S, betaC260S) was inserted normally in the membrane and underwent the normal NADPH-dependent conformational change of the beta subunit to a trypsin-sensitive state. Reduction of NADP+ by NADH driven by ATP hydrolysis or respiration was between 32% and 65% of the corresponding wild-type activities. Likewise, the catalytic and proton pumping activities of the purified cysteine-free enzyme were at least 30% of the purified wild-type enzyme activities. The H+/H- ratio for both enzymes was 0.5, although the cysteine-free enzyme appeared to be more stable than the wild-type enzyme in proteoliposomes. No bound NADP(H) was detected in the enzymes. Modification of transhydrogenase by diethyl pyrocarbonate and the subsequent inhibition of the enzyme were unaffected by removal of the cysteines, indicating a lack of involvement of cysteines in this process. Replacement of cysteine residues in the alpha subunit resulted in no or little change in activity, suggesting that the basis for the decreased activity was probably the modification of the conserved beta-subunit residue Cys-260 or (less likely) the non-conserved beta-subunit residue Cys-147. It is concluded that the cysteine-free transhydrogenase is structurally and mechanistically very similar to the wild-type enzyme, with minor modifications of the properties of the NADP(H) site, possibly mediated by the betaC260S mutation. The cysteine-free construct will be a valuable tool for studying structure-function relationships of transhydrogenases.

Bacterial Proteins↗
PubMed1997

Mutation of conserved residues in the NADP(H)-binding domain of the proton translocating pyridine nucleotide transhydrogenase of Escherichia coli.

Possible NADP(H)-binding sites of the beta subunit of the pyridine nucleotide transhydrogenase of Escherichia coli were examined by site-directed mutagenesis. The sequence of the beta subunit at positions 314-350 showed several features typical of NADP(H)-binding sites. Mutation of betaGly314, the first glycine residue of the GXGXXV motif, and of betaArg350, which probably interacts with the 2'-phosphate of the substrate NADP(H), resulted in drastic loss of enzyme activity. The loss of activity in the betaArg350 mutants was not due to loss of ability to bind NADP(H). Several residues (betaVal319, betaGly337, betaHis345, and betaArg350) were mutated to make the sequence more similar to that of a NAD(H)-binding site. The introduction of multiple mutations resulted in improper assembly of the enzyme and decreased incorporation into the membrane. The GXGXXG motif, typical of beta alphabeta nucleotide-binding folds, in the sequence of the beta subunit at positions 274-279 was mutated without causing major changes in transhydrogenase activities. It is unlikely to be part of a nucleotide-binding domain. Deletion of the carboxy-terminal 32 amino acids of the beta subunit, a possible nucleotide-binding site, prevented assembly and incorporation of the truncated enzyme into the cytoplasmic membrane of E. coli.

Amino Acid Sequence↗
PubMed1997

Modeling the G-protein-coupled neuropeptide Y Y1 receptor agonist and antagonist binding sites.

Neuropeptide Y (NPY) receptors belong to the G-protein-coupled receptor (GPCR) superfamily and mediate several physiological responses, such as blood pressure, food intake, sedation and memory retention. To understand the interactions between the NPY Y1 receptor subtype and its ligands, computer modeling was applied to the natural peptide agonist, NPY and a small molecule antagonist, BIBP3226. An agonist and antagonist binding domain was elucidated using mutagenesis data for the Y1 receptor as well as for other GPCR families. The agonist and antagonist ligands which were investigated appear to share common residues for their interaction within the transmembrane regions of the Y1 receptor structure, including Gln120, Asn283 and His306. This is in contrast to findings with tachykinin receptors where the binding domains of the non-peptide antagonists have very little in common with the binding domains of the agonist, substance-P. In addition, a hydrogen bond between the hydroxyl group of Tyr36 of NPY and the side chain of Gln219, an interaction that is absent in the model complex between Y1 and the antagonist BIBP3226, is proposed as one of the potential interactions necessary for receptor activation.

Amino Acid Sequence↗