Biomedical subjects

Jianxin Guo

Publications and source records attributed to Jianxin Guo.

15 recordsLinked to original sources

PubMed2006

Stability of helix-rich proteins at high concentrations.

A number of techniques, including circular dichroism, FTIR, front face fluorescence, and UV absorption spectrophotometries, dynamic light scattering, and DSC, were used to directly measure the colloidal and conformational stability of proteins in highly concentrated solutions. Using bovine serum albumin (BSA), chicken egg white lysozyme, human hemoglobin A0, and bovine fibrinogen as model proteins, the thermal transition temperatures of proteins in dilute and concentrated solutions were compared. At 10 degrees C, no significant differences in both secondary and tertiary structures were detected for proteins at different concentrations. When temperature was introduced as a variable, however, hemoglobin and fibrinogen demonstrated higher transition midpoints (T(m)s) in concentrated rather than in dilute solutions (deltaT(m) approximately 2-10 degrees C). In contrast, lysozyme and BSA in concentrated solutions exhibit a lower T(m) than in dilute solutions (deltaT(m) approximately 2-20 degrees C). From these studies, it appears that a variety of factors determine the effect of high concentrations on the colloidal and conformational stability of a particular protein. While the prediction of excluded volume theory is that high concentrations should conformationally stabilize proteins, other factors such as pH, kinetics, protein dynamics, and intermolecular charge-charge effects may affect the overall stability of proteins at high concentrations under certain conditions.

Animals↗

PubMed2006

Pharmacokinetics of lactone, carboxylate and total 9-nitrocamptothecin with different doses and administration routes in rats.

9-Nitrocamptothecin (9-NC) is a newly developed poorly soluble derivative of camptothecin and has a wide spectrum of anticancer activity in preclinical evaluation. The effects of the dose and administration route on pharmacokinetics and lactone/carboxylate equilibrium of 9-NC were studied in rats. A single intravenous dose of 1.5, 3 or 6 mg/kg of 9-NC solution was given to male rats (n = 6 per dose level). In another study, a single dose of 6 mg/kg 9-NC solution was given orally to rats (n = 6). Plasma samples were drawn at predetermined intervals and the concentrations of lactone, carboxylate and total 9-NC were determined by a validated HPLC method. Pharmacokinetic analysis was performed using non-compartmental analysis. Analysis of variance showed that the pharmacokinetic characteristics of lactone, carboxylate and total 9-NC were all independent of dose (p > 0.05). Based on the AUC measurements, the lactone 9-NC constituted 52% +/- 4%, 49% +/- 6% and 55% +/- 6% of the circulating total 9-NC in rats after intravenous administration of 1.5, 3, 6 mg/kg 9-NC solution, respectively. After oral administration of 6 mg/kg, the pharmacokinetics parameters were significantly different from those of intravenous administration at the same dose (p < 0.05). The lactone ratio was 60% +/- 14%. The absolute bioavailability of lactone and total 9-NC were calculated to be 23.4% and 22.7%, respectively. In conclusion, the pharmacokinetics of lactone, carboxylate and total 9-NC are not dose-dependent. Lactone, carboxylate and total 9-NC are poorly absorbed following oral administration. Both the dose and the route of administration have little effect on the lactone/carboxylate equilibrium of 9-NC in rats in vivo. But the route of administration plays an important part on the pharmacokinetics of 9-NC.

Administration, Oral↗

PubMed2006

Preparation and pharmacokinetics in rabbits of breviscapine unilamellar vesicles.

The purpose of the study was to prepare the unilamellar liposomal vesicles of breviscapine (Breviscapine-LUVs) and investigate the pharmacokinetics of Breviscapine-LUVs in rabbits. Breviscapine-LUVs were prepared by the film dispersion method and treated further by extrusion. Its size distribution and zeta potential were determined by photon correlation spectroscopy. The encapsulation efficiency (EE) and cumulative release of Breviscapine-LUVs were assayed by the dialysis method. The crossover design (two periods) was used in six rabbits, which were administered Breviscapine-LUVs and reference preparation. Results showed that the particle size of Breviscapine-LUVs was 50.8 nm, and the polydispersity index was 0.287. The zeta potential was -24 mV +/- 9 mV (n = 3), and the EE% was 81.1 +/- 1.1% (n = 3). The cumulative release of vesicles in 0.9% NaCl was 17.2 +/- 0.78%, 26.1 +/- 0.68%, and 29.9 +/- 0.81% in 2, 8, and 24 h, respectively. The mean concentration-time curves of breviscapine liposomes and reference preparation were both fitted to a two-compartment model with the main pharmacokinetic parameters as follows: t(1/2beta) of Breviscapine-LUVs and reference preparation were (42.5 +/- 28.6) min and (6.01 +/- 4.64) min, respectively; CL((s)) were (15.3 +/- 9.03) mL x min(-1) and (84.6 +/- 40.6) mL x min(-1), respectively; AUC(0-300) were (1267 +/- 1083) microg x min x mL(-1) and (196 +/- 107) microg x min x mL(-1), respectively. Compared with the reference preparation, breviscapine liposomes had a much higher concentration in plasma and contained characteristic of sustained-release, which ameliorated the pharmacokinetic properties of scutellarin.

Animals↗

PubMed2005

Interactions of organophosphorus and related compounds with cholinesterases, a theoretical study.

Acetylcholinesterase (AChE) is an interesting research target not only because of its high enzyme catalytic rate but also because of the wide range of health effects resulting from its inhibition. This paper discusses results of a theoretical study of acetylcholinesterase inhibition using several simulation techniques. In the first technique, a novel method was developed and used for predicting the binding affinity of human AChE (huAChE) inhibitors. Results are also presented for classical molecular dynamics and quantum mechanical simulations. Theoretical proton NMR shift results are obtained and compared to experiment, and the importance of the Glu199 residue is discussed in the context of the model.

Binding Sites↗

PubMed2005

Distribution of liposomal breviscapine in brain following intravenous injection in rats.

AIM: To investigate distribution of breviscapine in brain after intravenous (i.v.) injection of liposomes. METHODS: Breviscapine liposomes were prepared by rotary evaporation-sonication method. Particle size, encapsulation efficiency and stability of liposomes were respectively examined. In vitro drug release was investigated in 0.9% sodium chloride at 37 degrees C. Rats were divided into two groups. Liposomes were given to one group and commercial injection (Injectio Breviscapine) was given to the other at a single dose of 28.1 mgkg(-1) i.v., respectively. Scutellarin in rat brain at different sampling time was determined by RP-HPLC. The brain concentration-time curves of breviscapine liposomes and commercial injection were constructed and pharmacokinetic parameters were calculated and compared by statistic analysis. RESULTS: The average liposome diameter was 735+/-59 nm and encapsulation efficiency was 85.1+/-2.3%. The average accumulative release percentage of breviscapine liposomes in 0.9% sodium chloride was less than 30% within 24h. The mean concentration-time curves of breviscapine liposomes and commercial injection were both fitted to one-compartment model. There are significant difference of parameter T(1/2) and AUC(0-360) between liposome and commercial injection (p<0.05). T(1/2) of breviscapine liposomes and commercial injection were 23.13+/-7.71 and 6.27+/-1.84min, respectively. The brain AUC ratio of breviscapine liposomes to commercial injection was 443.4+/-92.3%. CONCLUSION: Compared with the commercial injection, liposomes delivered more drugs into the brain and have longer elimination time.

Animals↗

PubMed2005

Differential interactions of G-proteins and adenylyl cyclase with nucleoside 5'-triphosphates, nucleoside 5'-[gamma-thio]triphosphates and nucleoside 5'-[beta,gamma-imido]triphosphates.

The regulatory G-proteins of adenylyl cyclase (AC), G(i) and G(s), are not only activated by GTP and the stable GTP analogs, guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) and guanosine 5'-[beta,gamma-imido]triphosphate (GppNHp), but also by hypoxanthine, xanthine, uracil and cytidine nucleotides. The latter nucleotides were previously used to analyze distinct active G-protein states. Surprisingly, recent studies have shown that inosine 5'-[gamma-thio]triphosphate and uridine 5'-[gamma-thio]triphosphate can also inhibit AC directly. Therefore, we systematically compared the interactions of nucleoside 5'-triphosphates (NTPs), nucleoside 5'-[gamma-thio]triphosphates (NTPgammaSs) and nucleoside 5'-[beta,gamma-imido]triphosphates (NppNHps) with G(i), G(s) and AC. NTPgammaSs exhibited up to 26,000-fold higher affinity for G-proteins than NTPs and NppNHps. NTPgammaSs were up to 150-fold more potent direct AC inhibitors than NTPs and NppNHps. G-proteins exhibited striking preference for guanine nucleotides compared to other purine and pyrimidine nucleotides, whereas base-selectivity of various ACs, particularly the purified catalytic subunits C1.C2, was rather poor. GTP, GTPgammaS and GppNHp exhibited much higher selectivity for G-proteins relative to AC than all other purine and pyrimidine nucleotides. We have energetically characterized the interactions of purine and pyrimidine nucleotides with AC in silico, constructing pharmacophore models that correlate well with experimental affinities and have elucidated specific amino acid residues with greatest influence on nucleotide binding. Collectively, both G-proteins and ACs bind purine and pyrimidine nucleotides, with G-proteins showing much higher base-selectivity than AC. Thus, direct inhibitory effects of nucleotides on AC should be understood and considered when probing distinct active G-protein states with non-guanine nucleotides.

Adenylyl Cyclases↗

PubMed2005

Albumin enhances the diffusion of lipophilic drugs into the membrane bilayer.

In earlier work, we reported on the manner with which lipophilic drug molecules interact with the cell membrane in order to (a) enter the bilayer and laterally diffuse to their respective protein sites of action, or (b) penetrate this biological barrier to reach the cell interior. A remaining uncertainty is how lipophilic molecules reach the hydrophobic membrane core after traversing the aqueous medium and membrane polar surface. Here we present preliminary data using deuterium NMR, demonstrating the role of bovine serum albumin in facilitating this process. Our observation allows us to postulate a mechanism by which the passive transport of lipophilic ligands across the membrane can be greatly enhanced through the assistance of carrier proteins.

Albumins↗

PubMed2005

The conformation, location, and dynamic properties of the endocannabinoid ligand anandamide in a membrane bilayer.

The endogenous cannabinoid ligand anandamide is biosynthesized from membrane phospholipid precursors and is believed to reach its sites of action on the CB1 and CB2 receptors through fast lateral diffusion within the cell membrane. To gain a better insight on the stereochemical features of its association with the cell membrane and its interaction with the cannabinoid receptors, we have studied its conformation, location, and dynamic properties in a dipalmitoylphosphatidylcholine multilamellar model membrane bilayer system. By exploiting the bilayer lattice as an internal three-dimensional reference grid, the conformation and location of anandamide were determined by measuring selected inter- and intramolecular distances between strategically introduced isotopic labels using the rotational echo double resonance (REDOR) NMR method. A molecular model was proposed to represent the structural features of our anandamide/lipid system and was subsequently used in calculating the multispin dephasing curves. Our results demonstrate that anandamide adopts an extended conformation within the membrane with its headgroup at the level of the phospholipid polar group and its terminal methyl group near the bilayer center. Parallel static (2)H NMR experiments further confirmed these findings and provided evidence that anandamide experiences dynamic properties similar to those of the membrane phospholipids and produces no perturbation to the bilayer. Our results are congruent with a hypothesis that anandamide approaches its binding site by laterally diffusing within one membrane leaflet in an extended conformation and interacts with a hydrophobic groove formed by helices 3 and 6 of CB1, where its terminal carbon is positioned close to a key cysteine residue in helix 6 leading to receptor activation.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2005

The conformation of the cytoplasmic helix 8 of the CB1 cannabinoid receptor using NMR and circular dichroism.

The cytoplasmic helix domain (fourth cytoplasmic loop, helix 8) of numerous GPCRs such as rhodopsin and the beta-adrenergic receptor exhibits unique structural and functional characteristics. Computational models also predict the existence of such a structural motif within the CB1 cannabinoid receptor, another member of the G-protein coupled receptor superfamily. To gain insights into the conformational properties of this GPCR component, a peptide corresponding to helix 8 of the CB1 receptor with a small contiguous segment from transmembrane helix 7 (TM7) was chemically synthesized and its secondary structure determined by circular dichroism (CD) and solution NMR spectroscopy. Our studies in DPC and SDS micelles revealed significant alpha-helical structure while in an aqueous medium, the peptide exhibited a random coil configuration. The relative orientation of helix 8 within the CB1 receptor was obtained from intermolecular 31P-1H and 1H-1H NOE measurements. Our results suggest that in the presence of an amphipathic membrane environment, helix 8 assumes an alpha helical structure with an orientation parallel to the phospholipid membrane surface and perpendicular to TM7. In this model, positively charged side chains interact with the lipid headgroups while the other polar side chains face the aqueous region. The above observations may be relevant to the activation/deactivation of the CB1 receptor.

Amino Acid Sequence↗

PubMed2005

How lipophilic cannabinergic ligands reach their receptor sites.

It is postulated that lipophilic ligands reach their sites of action on membrane-bound functional proteins through fast lateral diffusion across the membrane bilayer. We have shown using NMR experiments that such ligands when incorporated in a membrane system assume a preferred orientation and conformation. While occupying a specific location within the bilayer, these molecules undergo fast lateral diffusion which allows them to engage in productive interactions with their respective protein sites of action. The proposed model is discussed using a group of classical and non-classical cannabinoids as well as the endogenous cannabinoid ligand anandamide.

Animals↗

PubMed2005

The physicochemical characteristics of freeze-dried scutellarin-cyclodextrin tetracomponent complexes.

In an effort to improve the solubility of the insoluble drug scutellarin, a novel complexation of scutellarin with beta-cyclodextrin (beta-CD) was studied. Tetracomponent freeze-dried complex was prepared with scutellarin, beta-CD, Hydroxypropyl Methylcellulose (HPMC), and triethanolamine. To confirm complex formation, complex was characterized by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction, and differential scanning calorimetry (DSC). Phase-solubility analysis suggested the soluble complexes having 1:1 stoichiometry. The beta-CD solubilization of scutellarin could be improved significantly by combining water-soluble polymer and pH adjuster. Comparing the binary, ternary solid systems with tetrary systems, tetracomponent freeze-dried complex showed the best effect of solubilization. A maximal solubility of scutellarin (23.65 mg/ml) was achieved with tetracomponent freeze-dried complex, up to 148-fold increase over scutellarin solubility in water, and the solubility of scutellarin is 15.35 microg/ml (up to 6-fold) in simulated gastric fluid.

Apigenin↗

PubMed2004

A docking score function for estimating ligand-protein interactions: application to acetylcholinesterase inhibition.

Acetylcholinesterase (AChE) inhibition is an important research topic because of its wide range of associated health implications. A receptor-specific scoring function was developed herein for predicting binding affinities for human AChE (huAChE) inhibitors. This method entails a statistically trained weighted sum of electrostatic and van der Waals (VDW) interactions between ligands and the receptor residues. Within the 53 ligand training set, a strong correlation was found (R2 = 0.89) between computed and experimental inhibition constants. Leave-one-out cross-validation indicated high predictive power (Q2 = 0.72), and analysis of a separate 16-compound test set also produced very good correlation with experiment (R2 = 0.69). Scoring function analysis has permitted identification and characterization of important ligand-receptor interactions, producing a list of those residues making the most important electrostatic and VDW contributions within the main active site, gorge area, acyl binding pocket, and periferal site. These analyses are consistent with X-ray crystallographic and site-directed mutagenesis studies.

Acetylcholinesterase↗

PubMed2003

Conformational study of lipophilic ligands in phospholipid model membrane systems by solution NMR.

Phospholipid bicelles were employed as a membrane bilayer model in the conformational studies of two lipophilic cannabinoids, delta(8)-THC and its O-methyl ether analogue, Me-Delta(8)-THC using conventional high-resolution NMR. A preparation of 8% (w/v) phospholipid concentration and a high DMPC/DHPC ratio (q = 2.0) was found to be optimal for not only effectively incorporating our ligands, but also providing a more bilayerlike environment suitable for conformational studies. While the conformational differences between the two cannabinoids could not be observed in chloroform and were barely detectable in SDS micelle solution, there is an increasing preference for the pentyl tail of Delta(8)-THC to bend toward the tricyclic ring system with increasing proportions of DMPC in the bicelle preparation. Our results highlight the advantages of exploring the conformational properties of cannabinoids using bicelle preparations as a medium that more closely resembles biological membrane bilayers and eliminates the need for isotopic labeling. This approach should also be of more general value for studying the interactions of other cannabinoids and biologically active, hydrophobic or amphipathic, small molecules with membranes.

Chloroform↗

PubMed2003

The absorption behavior of cyclosporin A lecithin vesicles in rat intestinal tissue.

The purpose of the study was to investigate the absorption behavior of lecithin vesicles of cyclosporin A (CsA-VES), prepared by the rotary evaporation method and treated further with sonication. The everted gut sac technique and in situ circulation method were used to examine: (1) relationship between the CsA-VES absorption velocity and the CsA-VES content; (2) the influence of the intestinal mucus, blank vesicles, concentration of Na(+), energy inhibitor and P-gp inhibitor on the absorption of CsA-VES; and (3) the respective accumulated content of CsA in the incubating medium and the sacs after incubation with Sandimmum Neoral((R))(CsA-NEO) and CsA-VES. Our results showed there was a saturated absorption of CsA. Most CsA-VES accumulated in the mucus before it reached the intestinal tissue. There was no significant difference in the accumulated absorption content in the incubating medium and the sacs of CsA-NEO and CsA-VES. The addition of blank vesicles and concentration of Na(+) had no significant influence on the accumulated absorption of CsA (P>0.05). The energy inhibitor and P-gp inhibitor influenced the accumulated absorption of CsA significantly (P<0.05). CsA-VES may be transported by phagocytosis. Mucus was a barrier blocking the diffusion of CsA-VES. CsA-NEO and CsA-VES showed equal absorption levels in the intestine.

Animals↗

PubMed2002

[Expression and role of placental vascular endothelial growth factor in patients with pregnancy induced hypertension].

OBJECTIVE: To investigate the expression of placental vascular endothelial growth factor (VEGF) and its relationship with construction of placental vascular network, placental weight and the newborns' weight in patients with pregnancy induced hypertension (PIH). METHODS: Twenty-five patients with PIH and twenty-five normal late pregnant (NLP) women in the third trimester were observed in this study. The expression of VEGF protein in placental, the placental vascular density were determined by Western blot and immunohistochemical F8 staining respectively. RESULTS: The VEGF values in patients with PIH and NLP were 24 793 +/- 6 579 and 41 903 +/- 11 009, and the vascular densities were (61 +/- 11) and (78 +/- 11) counts/400 x vision respectively. They were both significantly different in both groups and were closely related to the severity of PIH (P < 0.01). Placental weight and the newborns' weight in patients with PIH [(460 +/- 59) g, (3 176 +/- 503) g respectively] were also significantly decreased compared with NLP [(573 +/- 99) g, (3 468 +/- 493) g respectively], but the new newborns' length had no significant difference between the two groups (P > 0.05). In NLP group, placental vascular density, placental weight and the newborns' weight all had a significantly positive correlation with VEGF (P < 0.01, r = 0.823, 0.671, 0.888 respectively) and in PIH group, the situation was the same (P < 0.01, r = 0.905, 0.859, 0.732 respectively), but the new newborns' length had no correlation with VEGF (P > 0.05). CONCLUSION: It shows that the reduced expression of VEGF in placenta of patients with PIH may be one of the important factors responsible for decreased placental vascular density and fetal intrauterine growth restriction.

Adult↗