Two-order targeted brain tumor imaging by using an optical/paramagnetic nanoprobe across the blood brain barrier

Surgical resection is a mainstay of brain tumor treatments. However, the completed excision of malignant brain tumor is challenged by its infiltrative nature. Contrast enhanced magnetic resonance imaging is widely used for defining brain tumor in clinic. However its ability in tumor visualization is hindered by the transient circulation lifetime, nontargeting specificity, and poor blood brain barrier (BBB) permeability of the commercially available MR contrast agents. In this work, we developed a two-order targeted nanoprobe in which MR/optical imaging reporters, tumor vasculature targeted cyclic [RGDyK] peptides, and BBB-permeable Angiopep-2 peptides are labeled on the PAMAM-G5 dendrimer. This nanoprobe is supposed to first target the α(V)β(3) integrin on tumor vasculatures. Increased local concentration of nanoprobe facilitates the association between BBB-permeable peptides and the low-density lipoprotein receptor-related protein (LRP) receptors on the vascular endothelial cells, which further accelerates BBB transverse of the nanoprobe via LRP receptor-mediated endocytosis. The nanoprobes that have penetrated the BBB secondly target the brain tumor because both α(V)β(3) integrin and LRP receptor are highly expressed on the tumor cells. In vivo imaging studies demonstrated that this nanoprobe not only efficiently crossed intact BBB in normal mice, but also precisely delineated the boundary of the orthotropic U87MG human glioblastoma xenograft with high target to background signal ratio. Overall, this two-order targeted nanoprobe holds the promise to noninvasively visualize brain tumors with uncompromised BBB and provides the possibility for real-time optical-image-guided brain tumor resection during surgery.

Effects of interferon-gamma liposomes targeted to platelet-derived growth factor receptor-beta on hepatic fibrosis in rats

No drugs have been approved clinically for the therapy of hepatic fibrosis. Though interferon-γ (IFN-γ) is a highly effective anti-fibrotic agent in vitro and in some animal models in vivo, its anti-fibrotic potential in clinical trials has been disappointing, due to unwanted off-target effects and a short half-life period which results in poor efficacy. The aims of this study are to develop a new targeted drug delivery system to selectively deliver IFN-γ to hepatic stellate cells (HSCs) and to investigate whether it will improve the anti-fibrotic effect of IFN-γ and reduce its side effects in fibrotic livers. Sterically stable liposomes (SSLs) were modified by cyclic peptides (pPB) with a specific affinity for platelet-derived growth factor receptor-β (PDGFR-β), and then IFN-γ was encapsulated in the targeted liposomes (pPB-SSL-IFN-γ). In vitro, pPB-SSL was found to be taken up and internalized by cultured activated HSCs. The binding of FITC-labeled pPB-SSL to activated HSCs was in a time-dependent and concentration-dependent manner, which could be inhibited by excess unlabelled pPB-SSL, PDGF-BB, suramin or monensin. The inhibitory effect of pPB-SSL-IFN-γ on the proliferation of activated HSCs was respectively 7.24-fold and 2.95-fold higher than that of free IFN-γ and IFN-γ encapsulated in untargeted SSLs. In healthy rats, the tissue distribution, living-body tracing image analyses and pharmacokinetics study showed that pPB-SSL-IFN-γ accumulated mainly in the livers and had a longer half-life than free IFN-γ (3.98±0.52h vs. 0.21±0.03h). Furthermore, in rats with hepatic fibrosis induced by thioacetamide injection, FITC-labeled pPB-SSL was found to predominantly localize in activated HSCs by immunofluorescent double staining for FITC and albumin or α-smooth muscle actin (α-SMA). The enhanced anti-fibrotic effect of pPB-SSL-IFN-γ treatnment was indicated by significant decreases in the histologic Ishak stage, collagen I-staining positive areas, and α-SMA expression levels in fibrotic livers. In addition, pPB-SSL-IFN-γ treatment improved the leukopenia caused by low- and high-dosage free IFN-γ treatments. In conclusion, IFN-γ encapsulated in pPB-SSL had an extended circulation half-life and was selectively delivered to activated HSCs, which enhanced the anti-fibrotic effect of IFN-γ and reduced its side-effects in rats with hepatic fibrosis. Thus, pPB-SSL-IFN-γ may be an effective agent for the therapy of hepatic fibrosis.

The use of myristic acid as a ligand of polyethylenimine/DNA nanoparticles for targeted gene therapy of glioblastoma

To establish a gene delivery system for brain targeting, a low molecular weight polyethylenimine (PEI(10 K)) was modified with myristic acid (MC), and complexed with DNA, yielding MC-PEI(10 K)/DNA nanoparticles successfully. The nanoparticles were observed to be successfully taken up by the brains of mice. The transfection efficiency of the nanoparticles was then investigated, and both the in vitro and in vivo gene expression of MC-PEI(10 K)/DNA nanoparticles is significantly higher than that of unmodified PEI(10 K)/DNA nanoparticles. The anti-glioblastoma effect of MC-PEI(10 K)/pORF-hTRAIL was demonstrated by the survival time of intracranial U87 glioblastoma-bearing mice. The median survival time of the MC-PEI(10 K)/pORF-hTRAIL group (28 days) was significantly longer than that of the PEI(10 K)/pORF-hTRAIL group (24 days), the MC-PEI(10 K)/pGL(3) group (21 days) and the saline group (22 days). Therefore, our results suggested that MC-PEI(10 K) could be potentially used for brain-targeted gene delivery and in the treatment of glioblastoma.

LyP-1-conjugated doxorubicin-loaded liposomes suppress lymphatic metastasis by inhibiting lymph node metastases and destroying tumor lymphatics

Lymphatic metastasis can be greatly promoted by metastases growth and lymphangiogenesis in lymph nodes (LNs). LyP-1, a cyclic peptide, is able to specifically bind with tumor cells and tumor lymphatics in metastatic LNs. This work aimed to use LyP-1-conjugated liposomes (L-LS) loaded with doxorubicin (DOX) (L-LS/DOX) to suppress lymphatic metastasis by inhibiting both metastases and tumor lymphatics in LNs. L-LS were prepared and exhibited sizes around 90 nm and spherical morphology as characterized by transmission electron microscopy. The in vitro cellular studies showed that LyP-1 modification obviously increased liposome uptake by MDA-MB-435 tumor cells and enhanced the cytotoxicity of liposomal DOX. A popliteal and iliac LN metastases model was successfully established by subcutaneous inoculation of tumor cells to nude mice. The immunofluorescence staining analysis indicated that LyP-1 modification enabled specific binding of liposome with tumor lymphatics and enhanced the destroying effect of liposomal DOX on tumor lymphatics. The in vivo fluorescence imaging and pharmacodynamic studies showed that LyP-1 modification increased liposome uptake by metastatic LNs and that L-LS/DOX significantly decreased metastatic LN growth and LN metastasis rate. These results suggested that L-LS/DOX were an effective delivery system for suppressing lymphatic metastasis by simultaneously inhibiting LN metastases and tumor lymphatics.

Molecular imaging of hepatic stellate cell activity by visualization of hepatic integrin αvβ3 expression with SPECT in rat

The key factors in the pathogenesis of liver fibrosis are the activation and proliferation of hepatic stellate cells (HSCs), which express integrin αvβ3 after activation. This study aimed to explore the potential of (99m)Tc-labeled cyclic arginine-glycine-aspartic acid pentapeptide (cRGD) as a single photon emission computed tomography (SPECT) radiotracer to image hepatic integrin αvβ3 expression to reflect HSC activity in fibrotic livers. Rat models of liver fibrosis caused by thioacetamide or carbon tetrachloride (CCl(4)) treatment were employed to examine the expression and distribution of integrin αvβ3 during fibrotic progression or regression. The binding activity of radiolabeled cRGD to integrin αvβ3 was assessed in liver sections. SPECT was performed to determine hepatic integrin αvβ3 expression in rats with different stages of liver fibrosis. Protein and messenger RNA (mRNA) levels of integrin αv and β3 subunits were increased with the progression of liver fibrosis and reduced with its regression. The cell type that expressed the majority of integrin αvβ3 in fibrotic livers was found to be activated HSCs. The cRGD binding to activated HSCs displayed a high receptor-coupling affinity and an abundant receptor capacity. Iodine-125 ((125)I)-labeled cRGD bound to fibrotic liver sections and the binding activity was the highest in advanced fibrosis. Intravenously administered carboxyfluorescein-labeled cRGD was accumulated in fibrotic liver, and the accumulation amount was increased with the progression and reduced with the regression of fibrosis. A SPECT imaging study with (99m)Tc-labeled cRGD as a tracer demonstrated that the radioactivity ratio of liver to heart increased progressively along with severity of hepatic fibrosis.

CONCLUSION

Hepatic integrin αvβ3 expression in fibrotic liver reflects HSC activity and its imaging using (99m)Tc-labeled cRGD as a SPECT radiotracer may distinguish different stages of liver fibrosis in rats.

Sterically stable liposomes improve the therapeutic effect of hepatic stimulator substance on fulminant hepatic failure in rats

BACKGROUND AND AIMS

Few drugs have been confirmed to be effective for fulminant hepatic failure (FHF). The purpose of this study was to prepare sterically stable liposomes (SSL) encapsulating hepatic stimulator substance (HSS) and determine their therapeutic effect on FHF.

METHODS

HSS were encapsulated into SSL (HSS-SSL). FHF was induced in rats by thioacetamide (TAA) injection (400mg/kg, three times with a 24-h interval). The agents, including HSS-SSL, SSL, HSS, and sodium chloride (NS), were each injected intravenously 2h after the second and the third TAA injection.

RESULTS

Freshly prepared HSS-SSL had a mean size of 93.59nm and the average encapsulation efficiency was 37.20%. HSS encapsulated in SSL showed a longer half life and more potent target to injured livers than free HSS. Twenty-four hours after the third TAA-injection, the survival rate of HSS-SSL-treated rats (80%) was significantly higher than that of rats treated with NS (20%), SSL (25%), or HSS (50%). Histopathologic examination showed that there was the least necrosis and inflammation in the livers of HSS-SSL-treated rats. The incidence of stage 3 or 4 hepatic encephalopathy in HSS-SSL-treated rats was significantly lower than that in rats treated with other agents. The serum pro-inflammatory cytokine levels and hepatic lipid peroxidation levels were both markedly reduced, while hepatocyte proliferative rate was markedly increased after HSS-SSL treatment.

CONCLUSION

Encapsulation by SSL markedly improved the therapeutic effect of HSS on FHF in rats. Encapsulation by SSL may be an effective approach to enhance the therapeutic potency of drugs for FHF.

N-Boc-histidine-capped PLGA-PEG-PLGA as a smart polymer for drug delivery sensitive to tumor extracellular pH

A pH-sensitive polymer was synthesized by introducing the N-Boc-histidine to the ends of a PLGA-PEG-PLGA block copolymer. The synthesized polymer was confirmed to be biodegradable and biocompatible, well dissolved in water and forming micelles above the CMC. DOX was employed as a model anticancer drug. In vitro drug release from micelles of N-Boc-histidine-capped PLGA-PEG-PLGA exhibited significant difference between pH = 6.2 and pH = 7.4, whereas DOX release from micelles composed of un-capped virgin polymers was not significantly sensitive to medium pH. Uptake of DOX from micelles of the new polymer into MDA-MB-435 solid tumor cells was also observed, and pH sensitivity was confirmed. Hence, the N-Boc-histidine capped PLGA-PEG-PLGA might be a promising material for tumor targeting.

Cyclic RGD-poly(ethylene glycol)-polyethyleneimine is more suitable for glioblastoma targeting gene transfer in vivo

Arginine-glycine-aspartic acid (RGD) is a widely chosen ligand to improve the specific gene targeting transfection efficiency of polyethyleneimine (PEI) in vivo. However, the optimal RGD conjugating mode, RGD-poly(ethylene glycol)-PEI (RGD-PEG-PEI) or RGD-PEI-methoxyl poly(ethylene glycol) (RGD-PEI-mPEG) still remains controversial. In this study, RGD-PEG-PEI and RGD-PEI-mPEG were synthesized and compared with respects to their glioblastoma cell-binding capability and tumor-targeting ability of their complexes with plasmid DNA. These results demonstrated that RGD-PEG-PEI/plasmid enhanced green fluorescent protein (pEGFP)-N2 complexes had higher binding affinities with U87 cells than RGD-PEI-mPEG/pEGFP-N2 complexes. The gene transfection was also performed on U87 cells in vitro and in vivo. In vitro, both of the RGD-modified PEI derivatives enhanced the gene transfection efficiency to some extent. However, all of the complexes (with or without RGD modification) had high transfection efficiency. The biodistribution of RGD-PEG-PEI/pEGFP-N2 complexes in mice bearing subcutaneous glioblastomas were significantly greater than that of RGD-PEI-mPEG/pEGFP-N2 complexes, suggesting a more efficient gene transfection in vivo. In the RGD-PEG-PEI, the use of a PEG spacer was particularly important. These results indicated that RGD-PEG-PEI was more suitable for targeted gene transfer in vivo.

Loop 2 of Ophiophagus hannah toxin b binds with neuronal nicotinic acetylcholine receptors and enhances intracranial drug delivery

Three-finger snake neurotoxins have been widely investigated for their high binding affinities with nicotinic acetylcholine receptors (nAChRs), which are widely expressed in the central nervous system including the blood-brain barrier and thus mediate intracranial drug delivery. The loop 2 segments of three-finger snake neurotoxins are considered as the binding domain with nAChRs, and thus, they may have the potential to enhance drug or drug delivery system intracranial transport. In the present work, binding of the synthetic peptides to the neuronal nAChRs was assessed by measuring their ability to inhibit the binding of (125)I-α-bungarotoxin to the receptor. The loop 2 segment of Ophiophagus hannah toxin b (KC2S) showed high binding affinity, and the competitive binding IC(50) value was 32.51 nM. Furthermore, the brain targeting efficiency of KC2S had been investigated in vitro and in vivo. The specific uptake by brain capillary endothelial cells (BCECs) demonstrated that KC2S could be endocytosized after binding with nAChRs. In vivo, the qualitative and quantitative biodistribution results of fluorescent dyes (DiR or coumarin-6) indicated that KC2S modified poly(ethylene glycol)-poly(lactic acid) micelles (KC2S-PEG-PLA micelles) could enhance intracranial drug delivery. Furthermore, intravenous treatment with paclitaxel-encapsulated KC2S-PEG-PLA micelles (KC2S-PEG-PLA-PTX micelles) afforded robust inhibition of intracranial glioblastoma. The median survival time of KC2S-PEG-PLA-PTX-micelle-treated mice (47.5 days) was significantly longer than that of mice treated by mPEG-PLA-PTX micelles (41.5 days), Taxol (38.5 days), or saline (34 days). Compared with the short peptide derived from rabies virus glycoprotein (RVG29) that has been previously reported as an excellent brain targeting ligand, KC2S has a similar binding affinity with neuronal nAChRs but fewer amino acid residues. Thus, we concluded that the loop 2 segment of Ophiophagus hannah toxin b could bind with neuronal nAChRs and thus enhance intracranial drug delivery for the treatment of central nervous system diseases.

Myristic acid-conjugated polyethylenimine for brain-targeting delivery: in vivo and ex vivo imaging evaluation

To investigate the potential of myristic acid (MC) to mediate brain delivery of polyethylenimine (PEI) as a gene delivery system, a covalent conjugate (MC-PEI) of MC, and PEI was synthesized. A near-infrared fluorescence probe, IR820 was conjugated to MC-PEI to explore its in vivo distribution after intravenous (i.v.) administration in mice. The brain targeting ability of MC-PEI was evaluated by near-infrared fluorescence imaging and analyzed semiquantitatively by fluorescence intensity, respectively. Significant NIR fluorescent signal was detected in the brain 12 h after i.v. administration and further confirmed by imaging the whole brain and brain slices. Semiquantitative results from fluorescence intensity further supported the successful brain delivery of MC-PEI which led to a very significant increase ( approximately 200%) in the brain uptake after i.v. injection in comparison with unmodified PEI. The capability of MC-PEI to condense DNA was further confirmed using agarose gel retardation assay, indicating its potential for gene delivery. The significant in vivo and ex vivo results suggest that MC-PEI is a promising brain-targeting drug delivery system, especially for gene delivery.

Targeted brain delivery of itraconazole via RVG29 anchored nanoparticles

The blood-brain barrier is a major barrier in the neurological diseases treatment and precludes the entry of drugs from blood to brain. Here, we developed 29-amino-acid peptide derived from rabies virus glycoprotein (RVG29) peptide conjugated itraconazole-loaded albumin nanoparticles (RVG29-ITZ-NPs). The RVG29 peptide was conjugated to the albumin NPs using biotin-binding streptavidin as crosslinker. The NPs were characterized in terms of particle size, zeta potential, drug loading and release behavior in vitro. Cellular uptake of RVG29-ITZ-NPs was investigated by flow cytometry. Pharmacokinetics and brain distribution of RVG29-ITZ-NPs were investigated after intravenous administration of NPs. The particle size of RVG29-ITZ-NPs was 89.3 ± 1.9 nm as determined by dynamic light scattering. The zeta potential of RVG29-ITZ-NPs was -33.1 ± 0.9 mV. RVG29-ITZ-NPs exhibited a sustained release profile within 24 h. In vitro cellular uptake studies demonstrated that RVG29 significantly facilitated the intracellular delivery of NPs. A significant (P < 0.05) accumulation of ITZ in brain was observed for RVG29-ITZ-NPs as compared with ITZ-NPs and cyclodextrin formulation of ITZ (ITZ-CD). These results suggested that RVG29-ITZ-NPs can be exploited as a potential therapeutic formulation for the intracranial fungal infection.

EGFP-EGF1 protein-conjugated PEG-PLA nanoparticles for tissue factor targeted drug delivery

In a strategy for anti-thrombotic therapy, we have expressed EGFP-EGF1 fusion protein, in which EGF1 can bind with tissue factor (TF). EGFP has previously been widely used as a fluorescent protein marker. EGFP-EGF1 protein was thiolated and conjugated to the malemide covering on the pegylated nanoparticles (NP) to form the EGFP-EGF1-NP. The EGFP-EGF1-NP was characterized in terms of morphology, size and zeta potential. In vitro cell viability experiment confirmed that the biodegradable EGFP-EGF1-NP was safe. To evaluate the delivering ability of EGFP-EGF1-NP, a fluorochrome dye, Dir, was incorporated into the nanoparticle, and the loading capacity and release property of the particle were examined. In vitro results showed that the binding ability of EGFP-EGF1-NP with TF-expressing cells was significantly stronger than that of non-conjugated NP. In vivo multispectral fluorescent imaging demonstrated that EGFP-EGF1-NP had high specificity and sensitivity in targeting thrombi. Our study demonstrated that EGFP-EGF1-NP is a promising TF-targeting drug delivery system for thrombolytic treatment.

Cyclic RGD conjugated poly(ethylene glycol)-co-poly(lactic acid) micelle enhances paclitaxel anti-glioblastoma effect

The use of glioblastoma-targeted drug delivery system facilitates efficient delivery of chemotherapeutic agents to malignant gliomas in the central nervous system while minimizing high systemic doses associated with debilitating toxicities. To employ the high binding affinity of a cyclic RGD peptide (c(RGDyK), cyclic Arginine-Glycine-Aspartic acid-D-Tyrosine-Lysine) with integrin alpha(v)beta(3) over-expressed on tumor neovasculature and U87MG glioblastoma cells, we prepared paclitaxel-loaded c(RGDyK)-Poly(ethylene glycol)-block-poly(lactic acid) micelle (c(RGDyK)-PEG-PLA-PTX). In vitro physicochemical characterization of these novel micelles showed satisfactory encapsulated efficiency, loading capacity and size distribution. In vitro cytotoxicity studies proved that the presence of c(RGDyK) enhanced the anti-glioblastoma cell cytotoxic efficacy by 2.5 folds. The binding affinity of c(RGDyK)-PEG-PLA micelle with U87MG cells was also investigated. The competitive binding IC(50) value of c(RGDyK)-PEG-PLA micelle was 26.30 nM, even lower than that of c(RGDyK) (56.23 nM). In U87MG glioblastoma-bearing nude mice model, biodistribution of (125)I-radiolabeled c(RGDyK)-PEG-PLA or DiR encapsulated micelles and anti-glioblastoma pharmacological effect was investigated after intravenous administration. c(RGDyK)-PEG-PLA micelle accumulated in the subcutaneous and intracranial tumor tissue, and when loaded with PTX (c(RGDyK)-PEG-PLA-PTX), exhibited the strongest tumor growth inhibition among the studied paclitaxel formulations. The anti-glioblastoma effect of c(RGDyK)-PEG-PLA-PTX micelle was also reflected in the median survival time of mice bearing intracranial U87MG tumor xenografts where the median survival time of c(RGDyK)-PEG-PLA-PTX micelle-treated mice (48 days) was significantly longer than that of mice treated with PEG-PLA-PTX micelle (41.5 days), Taxol (38.5 days) or saline (34 days). Therefore, our results suggested that c(RGDyK)-PEG-PLA micelle may be a potential drug delivery system in the treatment of integrin alpha(v)beta(3) over-expressed glioblastoma.

Preparation of albumin nanospheres loaded with gemcitabine and their cytotoxicity against BXPC-3 cells in vitro

AIM

To optimize formulation methods for loading gemcitabine (GEM), the main drug against pancreatic cancer, into albumin nanoparticles for extended blood circulation and improved efficacy.

METHODS

GEM was loaded into two sizes of disolvation-crosslinked bovine serum albumin nanoparticles, with a mean diameter of 109.7 nm and 405.6 nm, respectively, by co-precipitation (the direct method) and follow-up adsorption (the indirect method). The antitumor activities of the two nanoparticulate formulations, were evaluated according to their anti-proliferative effects on the human pancreatic cell line BXPC-3, which were assessed using the MTT assay.

RESULTS

The two nanoparticulate formulations, created by direct co-precipitation and indirect adsorption, possessed smooth surfaces and high drug loading efficiencies, 83% and 93% at 11% and 13% drug loading, respectively. The two formulations released GEM for 8 and 12 h, respectively, and significantly improved anti-BXPC-3 proliferation effects, as compared with the GEM solution and the drug-free albumin particles.

CONCLUSION

Co-precipitating and adsorbing GEM into albumin particles resulted in sustained-release nanoparticulate formulations with improved antitumor cytotoxicity. The result suggests that this is a useful formulation strategy for improving the antitumor efficacy of GEM.

Development and evaluation of novel itraconazole-loaded intravenous nanoparticles

The purpose of this study was to present novel intravenous itraconazole-loaded nanoparticles (ITZ-NPs) using human serum albumin (HSA) as drug carrier materials. The ITZ-NPs were prepared by nanoparticle albumin bound technology involving a series of homogenization and lyophilization procedures. The ITZ-NPs powder could be easily reconstituted and provide stable solutions at a wide range of concentrations at 25 degrees C for 24h. In safety test, the ITZ-NPs caused mild hemolysis below the concentration of 10mg/mL and were well tolerated at the dose of 160 mg/kg in mice, indicating better biocompatibility than cyclodextrin formulation of itraconazole (ITZ-CD). The pharmacokinetic parameters of itraconazole and its major metabolite, hydroxyl-itraconazole, of ITZ-NPs had no differences from those of ITZ-CD in mice. For the ITZ-NPs group, the distributions of itraconazole in the lung, liver and spleen were higher than those for ITZ-CD group. It was of significance that ITZ-NPs increased the drug distribution in lung which was always the portal to fungal infection. These results indicate that the ITZ-NPs can be a potential intravenous formulation of itraconazole.

Deferiprone protects the isolated atria from cardiotoxicity induced by doxorubicin

AIM

To investigate the effects of deferiprone on doxorubicin-induced cardiotoxicity and determine its protection on cardiac contractility in vivo at tissue level.

METHODS

Spontaneously-beating isolated atria from rats were pretreated with deferiprone for 10 min at 1.2 mmol/L or 0.3 mmol/L, respectively before co-incubation with doxorubicin (DOX) at 0.03 mmol/L for 60 min. Contractility (dF/dt) was assessed every 10 min during the incubation. After that, the tissues around the sinuatrial nodes were fixed for ultrastructural study; succinate dehydrogenase (SDH) and Cu, Zn superoxide dismutase (Cu, Zn-SOD) activity, as well as malondialdehyde (MDA) level of the atria were assayed.

RESULTS

Treatment with DOX alone resulted in a 49.34% reduction of the contractility, mitochondria swelling, disruption of mitochondrial crista and decreased electron density of the matrices. Conversely, with the presence of deferiprone, the negative inotropic effect and lesions in the cardiac mitochondria structure induced by DOX were attenuated. Cu, Zn-SOD activity increased by 12.97%-12.11%, the MDA level decreased by 29.12%-39.82% and succinate dehydrogenase (SDH) activity was ameliorated by 25.15%-34.76%.

CONCLUSION

Deferiprone can efficiently preserve cardiac contractility. Moreover, the results of this study indicate that deferiprone is able to protect mitochondrial function and structure form damage induced by DOX. This cardiac protective potential of deferiprone could be due to its defense capability against oxidative damage.

Separation of polyethylene glycols and their fluorescein-labeled compounds depending on the hydrophobic interaction by high-performance liquid chromatography

The separation and characterization of fluorescein-labeled polyethylene glycols (PEG) is described. Firstly, the polyethylene glycols labeled with fluorescein isothiocyanate (FITC) were synthesized and separated using Sephadextrade mark LH-20 medium by a step gradient. Secondly, a TSK GEL G4000 PW XL column was developed for determining the FITC derivatives of PEG. The retention mechanism is based on the hydrophobic interaction between the FITC derivatives of PEG and the packing material of the TSK GEL G4000PW XL column. The retention time of the PEG compounds increased by adding of salts in the mobile phase and decreased by adding of organic modifier. In addition, various salts in the eluent can also change the chromatographic behavior of these compounds. Finally, the pH of the mobile phase can have an impact on the retention time of the PEG compounds.

In vitro and in vivo studies on mucoadhesive microspheres of amoxicillin

Amoxicillin mucoadhesive microspheres (Amo-ad-ms) were prepared using ethylcellulose (Ec) as matrix and carbopol 934P as mucoadhesive polymer for the potential use of treating gastric and duodenal ulcers, which were associated with Helicobacter pylori. The morphological characteristics of the mucoadhesive microspheres were studied under scanning electron microscope. In vitro release test showed that amoxicillin released faster in pH 1.0 hydrochloric acid (HCl) than in pH 7.8 phosphate buffer. Yet, it would be degraded to some extent in a pH 1.0 HCl medium at 37 degrees C, which indicated that amoxicillin was not stable in an acidic surrounding. It was also found that amoxicillin entrapped within the microspheres could keep stable. In vitro and in vivo mucoadhesive tests showed that Amo-ad-ms adhered more strongly to gastric mucous layer than nonadhesive amoxicillin microspheres (Amo-Ec-ms) did and could retain in gastrointestinal tract for an extended period of time. Amo-ad-ms and amoxicillin powder were orally administered to rats. The amoxicillin concentration in gastric tissue was higher in the Amo-ad-ms group. In vivo H. pylori clearance tests were also carried out by administering, respectively, Amo-ad-ms or amoxicillin powder, to H. pylori infectious BALB/c mice under fed conditions at single or multiple dose(s) in oral administration. The results showed that Amo-ad-ms had a better clearance effect than amoxicillin powder did. In conclusion, the prolonged gastrointestinal residence time and enhanced amoxicillin stability resulting from the mucoadhesive microspheres of amoxicillin might make contribution to H. pylori clearance.

[Binding characteristics between RGD-containing cyclic peptide and rat hepatic stellate cells: an in vitro study]

OBJECTIVE

To investigate the binding characteristics between an artificial Arg-Gly-Asp (RGD)-containing cyclic peptide [cyclo(CGRGDSPK)] and rat hepatic stellate cells (HSC).

METHODS

An artificial RGD-containing cyclic peptide was labeled with fluorescein isothiocyanate (FITC). HSCs were isolated by collagenase in situ liver recirculating and purified by density gradient centrifugation from normal rats. The cells were cultured for 5 days of primary culture (quiescent phenotype) or for 7 days of secondary culture (activated phenotype). To access the binding and uptake, HSCs were incubated with FITC-cRGD of different concentrations at 4 degree C or 37 degree C, and then the binding and uptake were investigated by flow cytometry. The location of FITC-cRGD in HSC was investigated by fluorescent microscopy. Kd and maximal binding sites per cell were calculated by radioligand binding assay (RBA) of receptors using 3H-cRGD. In the interim, FITC-cAGA was used as a peptide control devoid of any binding site.

RESULTS

The binding between FITC-cRGD and HSC was saturable, time- and dose-dependent and could compete with overdosed unlabeled cRGD. The fluorescence was mainly distributed in cytoplasma, especially near the nuclei. Kd was 7.05 x 10(-9) mol/L and Bmax per cell was nearly 6.79 x 10(5).

CONCLUSIONS

The results demonstrate that cRGD are specifically taken up by HSC through a receptor-mediated pathway. The information is useful for understanding the ligand-receptor interaction of HSC. FITC labeled cyclic RGD-peptides meet the standards of special ligands and FITC does not change the binding activation of cyclic RGD-peptides.

[Antifibrotic effects of cyclic RGD-peptide mediated liposomal interferon: an experimental on rats]

OBJECTIVE

To evaluate the antifibrotic effect of receptor-mediated sterical stability liposome (SSL) targeting hepatic stellate cells (HSCs) and containing recombinant human interferon-alpha 1b (IFNalpha-1b) on hepatic cirrhosis.

METHODS

The ligand, cyclo (RGD) with specific affinity to HSCs, was incorporated via PEG into the lipid bilayers of SSL. Forty male SD rats were randomly divided into 4 equal groups: liver fibrosis model group undergoing double ligation and cutting of the common bile duct (BDL group), BDL + IFN-SSL group, undergoing BDL and injection of IFN 50,000 IU per week via caudal vein for 4 times; IFN-RGD-SSL treatment group, undergoing BDL and injection of IFN-RGD-SSL (equal to 50,000 IU per week) via caudal vein for 4 times; and sham operation group used as control. The rats were killed 24 hours after the last injection. Their livers and serum samples were collected. Pathological changes of the liver were observed with HE and alpha-SMA immunohistochemical staining. Biochemical automatic analyzer was used to test the serum indices of liver function: ALT, AST, total bilirubin (TBIL), alkaline phosphatase, and gamma-glutamine (gamma-GT). Radioimmunoassay method was used to examine the s serum index of liver fibrosis: HA, procollagen III (PCIII), LN, and CIV. Colorimetry was used to examine the level of hydroxyl proline (Hyp). RT-PCR was used to detect the mRNA expression of type I collagen. Western blotting was used to examine the protein expression of alpha-SMA of HSC.

RESULTS

Compared with the control group, liver fibrosis was seen in the other 3 groups, especially in the BDL group. In comparison with the sham operation group, the levels of serum indices of liver fibrosis, liver hydroxyl proline content, and expression of type I collagen mRNA and alpha-SMA protein in liver were significantly higher in the other groups (all P < 0.05), being significantly lower in the BDL + IFN-RGD-SSL group than in the BDL + IFN-SSL group (all P < 0.05).

CONCLUSION

The receptor-mediated IFN-RGD-SSL displays good targeting antifibrotic effects on liver fibrosis.

[Influence of different doxorubicin-salt aggregates on the leakage of liposomal doxorubicin in vitro and long circulation in vivo]

AIM

To develop liposomes containing doxorubicin with different salts and to investigate their influence on the stability of liposomal doxorubicin in vitro and in vivo.

METHODS

Liposomes were prepared by the film method, treated further by extruded through nuclear membrane. The entrapment efficiency was determined by column chromatography. In vitro drug release experiments were carried out with a dialysis bag (Mw cut-off 12000 - 14000). Reverse-phase HPLC was used to study the pharmacokinetics of liposomal doxorubicin.

RESULTS

The particle size of liposomes with glycinate buffer, citrate buffer and ammonium sulfate as the inner water phase were (103 +/- 8), (102 +/- 12) and (97 +/- 8) nm. The zeta potential and the encapsulation ratio were (-21.3 +/- 0.5), (-21.7 +/- 0.4), (-20.9 +/- 0.7) mV and 47.8%, 96.7%, 98.6%, respectively. The leaking rate of doxorubicin from liposomes was related to the pH value of the release medium. The leaking rate increased at lowered pH. Pharmacokinetic study showed that the MRT (mean retention time) of liposomes with glycinate buffer, citrate buffer and ammonium sulfate as the inner water phase were 12.13, 23.31 and 29.79 h, respectively.

CONCLUSION

Doxorubicin showed different stability in liposomes with different inner water phases, the weaker the acid in the inner water phase, the stabler the liposome.

Separation of polyethylene glycols and their amino-substituted derivatives by high-performance gel filtration chromatography at low ionic strength with refractive index detection

The chromatographic analysis of polyethylene glycols (PEG) and their amino-substituted derivatives, with an average molecular mass of 2000 and 3350 is described. The PEG derivatives were perfectly separated by TSK-GEL G4000PW(XL) column, which was widely used in high-performance size-exclusion chromatography (SEC), at low ionic strength with refractive index detection. It was shown that ion-exchange interactions were mainly involved in the retention mechanism of these compounds on TSK-GEL G4000PW(XL) column, since retention volume decreased when salt concentration were added to the mobile phase and varied with the pH of the eluent. Additionally, size exclusion for PEG chains plays a role. Organic modifiers also had effect on chromatographic behaviors of PEG compounds.

[Diffusion behaviors of drugs in thermosensitive in situ gels]

AIM

To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems.

METHODS

A free diffusion model was used to evaluate the effects of concentration, the property of drugs, as well as the gel compositions on the diffusivity of drugs.

RESULTS

Drug transport through the aqueous channels of the gel followed Fickian mechanism, and no significant influence on the diffusivity was observed when the drug concentration was lowered from 5% to 0.25%. The diffusion coefficients of propranolol, timolol maleate, and salbutamol sulfate were 0.91, 1.32, and 3.30 x 10(-6) cm2 x s(-1), respectively. The flux of hydrophilic drug was 3.6 fold faster than that of the lipophilic one implied the latter partitioned into the hydrophobic micellar core, and consequently the diffusion was retarded. The diffusivity was decreased with increased poloxamer and sodium hyaluronate concentration, due to the distorted aqueous channels and higher microviscosity.

CONCLUSION

The result suggested that sustained release could be achieved for the thermosensitive in situ gel by incorporating lipophilic drug or increasing polymer concentration.

[Targeting therapy of magnetic doxorubicin liposome in nude mice bearing colon cancer]

OBJECTIVE

To investigate the effect of magnetic doxorubicin liposome (MDL) in the targeting treatment of nude mice bearing colon cancer.

METHODS

Human colon cancer line LoVo cells were implanted hypodermically into nude mouse. Two weeks after the mouse was killed and the tumor was taken out and cut into small pieces to be retransplanted into nude mice so as to establish an experimental model. MDL was prepared by reverse-phase evaporation method. The particle size and structure of MDL were evaluated. Eighteen nude mice with colon cancer were divided into 3 groups of 3 mice: free DOX group, MDL (-) group (no magnetic field was added to the tumor surface), and MDL (+) group (magnetic field with the strength of 4,500 G was added). DOX of the dosage of 5 mg/kg was injected through the caudal vein in these 3 groups. Then the mice were killed 30 minutes after. Fluorescence spectrophotometry was used to examine the concentrations of DOX in the tissues and plasma. Another 36 nude mice with colon cancer were divided into 6 groups of 6 mice: normal saline group (as controls), DOX group, blank liposome group, magnetic liposome group, MDL (-) group (non-magnetic alloy was implanted into the tumor), and MDL (+) group (rare earth magnet was implanted into the tumor). The body weight, longest diameter of tumor, and short diameter vertical to the longest diameter were calculated regularly. The mice were killed 11 days after. The tumors were taken out to undergo staining and light microscopy. Flow cytometry was used to examine the apoptosis of tumor cells.

RESULTS

The particle size of MDL was 230 nm and the magnetic particles (Fe(3)O(4)) were evenly distributed within the liposome. The DOX concentration in tumor tissue of the MDL (+) group was remarkably higher than those of the DOX and MDL (-) groups (both P < 0.05). The DOX concentration in heart and kidney of the DOX group were higher than those of the other 2 groups, and the plasma DOX concentrations of the DOX group was significantly lower than those of the other groups (all P < 0.05). The growth speed of tumor in the MDL (+) group was significantly lower, and the tumor weight was significantly less than in other groups.

CONCLUSION

Magnetic doxorubicin liposome, as a carrier of anticancer drug, has a good targeting function toward the magnetite and has a significant anticancer effect.

Spectrophotometry on measuring the size of liposomes

AIM

To establish a spectrophotometric method for measurement of the sizes of liposomes for evaluating physical stability of liposomes.

METHODS

The sterically stabilized liposomes (SLs) were prepared by ethanol injection method and extrusion method. The mean cumulant diameters (D) of the vesicles were determined by electron microscopy and dynamic light scattering. On the basis of Rayleigh-Gans-Debye theory, the absorbance at 436 nm per unit lipid concentration (A436 nm/Cp) was measured as a function of vesicle diameter.

RESULTS

log(A436 nm/Cp) was closely related to logD (r2 > or = 0.93, n = 5).

CONCLUSION

The absorbance of liposomes reflect their relative sizes and can be used to evaluate physical stability of liposomes.

Convergence of PKC-dependent kinase signal cascades on NMDA receptors

Synaptic plasticity, or long-term potentiation (LTP), of excitatory synapses in the hippocampus contributes to learning and the establishment of spatial memories. In the CA1 region, induction of LTP enhances the function of postsynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs) because of the Ca2+-calmodulin kinase II (CaMKII)-dependent phosphorylation of this subtype of glutamate receptor. Entry of Ca2+, via N-methyl-D-aspartate receptors (NMDARs), during strong synaptic stimulation provides the stimulus to trigger phosphorylation of AMPARs. However, this induction also requires activation of a protein kinase C (PKC)-dependent tyrosine kinase signal cascade and a concomitant upregulation of NMDARs. This review focuses upon NMDARs as potential targets of PKC and/or of the PKC-dependent tyrosine kinase cascade. PKC, acting via the CAKbeta/Src tyrosine kinase cascade, enhances NMDAR activation and may increase the number of receptors expressed in synapses. In contrast, direct phosphorylation of NMDARs by PKC increases the sensitivity of NMDA channel inactivation to intracellular Ca2+. In CAI neurons, PKC provides a point of convergence of control of NMDARs and synaptic plasticity for a wide variety of G-protein coupled and growth factor receptors.

Role of barium nitrate on the sulfur fixation of calcium oxide

In this paper, the effect of Ba(NO3)2 on the efficiency of sulfur fixation of calcium oxide during coal combustion was studied. The results showed that addition of barium nitrate to the CaO can enhance the sulfur removal rate of CaO significantly. The X-ray diffraction spectrum of residual ash of coal added some sulfur fixative expressed that Ba2+ can form a compound of Ba-Al-Si-O which encloses the CaSO4 to prevent it's decomposition, so Ba2+ can improve the action of sulfur fixation of CaO. The combustion character of the original coal and original coal added sulfur fixative was researched with thermal-gravity analyzer and the results expressed that adding some sulfur fixative to the coal will make the combustion character of coal change little.

In CA1 pyramidal neurons of the hippocampus protein kinase C regulates calcium-dependent inactivation of NMDA receptors

The NMDA subtype of the glutamate-gated channel exhibits a high permeability to Ca(2+). The influx of Ca(2+) through NMDA channels is limited by a rapid and Ca(2+)/calmodulin (CaM)-dependent inactivation that results from a competitive displacement of cytoskeleton-binding proteins from the NR1 subunit of the receptor by Ca(2+)/CaM (Zhang et al., 1998; Krupp et al., 1999). The C terminal of this subunit can be phosphorylated by protein kinase C (PKC) (Tingley et al., 1993). The present study sought to investigate whether PKC regulates Ca(2+)-dependent inactivation of the NMDA channel in hippocampal neurons. Activation of endogenous PKC by 4beta-phorbol 12-myristate 13-acetate enhanced peak (I(p)) and depressed steady-state (I(ss)) NMDA-evoked currents, resulting in a reduction in the ratio of these currents (I(ss)/I(p)). We demonstrated previously that PKC activity enhances I(P) via a sequential activation of the focal adhesion kinase cell adhesion kinase beta/proline-rich tyrosine kinase 2 (CAKbeta/Pyk2) and the nonreceptor tyrosine kinase Src (Huang et al., 1999; Lu et al., 1999). Here, we report that the PKC-induced depression of I(ss) is unrelated to the PKC/CAKbeta/Src-signaling pathway but depends on the concentration of extracellular Ca(2+). Intracellular applications of CaM reduced I(ss)/I(p) and occluded the Ca(2+)-dependent effect of phorbol esters on I(ss.) Moreover, increasing the concentration of intracellular Ca(2+) buffer or intracellular application of the inhibitory CaM-binding peptide (KY9) greatly reduced the phorbol ester-induced depression of I(ss). Taken together, these results suggest that PKC enhances Ca(2+)/CaM-dependent inactivation of the NMDA channel, most likely because of a phosphorylation-dependent regulation of interactions between receptor subunits, CaM, and other postsynaptic density proteins.

Deciphering the role of the electrostatic interactions involving Gly70 in eglin C by total chemical protein synthesis

Eglin c from the leech Hirudo medicinalis is a potent protein inhibitor of many serine proteinases including chymotrypsin and subtilisins. Unlike most small protein inhibitors whose solvent-exposed enzyme-binding loop is stabilized primarily by disulfide bridges flanking the reactive-site peptide bond, eglin c possesses an enzyme-binding loop supported predominantly by extensive electrostatic/H-bonding interactions involving three Arg residues (Arg48, Arg51, and Arg53) projecting from the scaffold of the inhibitor. As an adjacent residue, the C-terminal Gly70 participates in these interactions via its alpha-carboxyl group interacting with the side chain of Arg51 and the main chain of Arg48. In addition, the amide NH group of Gly70 donates an H-bond to the carbonyl C=O groups of Arg48 and Arg51. To understand the structural and functional relevance of the electrostatic/H-bonding network, we chemically synthesized wild-type eglin c and three analogues in which Gly70 was either deleted or replaced by glycine amide (NH(2)CH(2)CONH(2)) or by alpha-hydroxylacetamide (HOCH(2)CONH(2)). NMR analysis indicated that the core structure of eglin c was maintained in the analogues, but that the binding loop was significantly perturbed. It was found that deletion or replacement of Gly70 destabilized eglin c by an average of 2.7 kcal/mol or 20 degrees C in melting temperature. As a result, these inhibitors become substrates for their target enzymes. Binding assays on these analogues with a catalytically incompetent subtilisin BPN' mutant indicated that loss or weakening of the interactions involving the carboxylate of Gly70 caused a decrease in binding by approximately 2 orders of magnitude. Notably, for all four synthetic inhibitors, the relative free energy changes (DeltaDeltaG) associated with protein destabilization are strongly correlated (slope = 0.94, r(2) = 0. 9996) with the DeltaDeltaG values derived from a decreased binding to the enzyme.

Distinct roles of synaptic and extrasynaptic NMDA receptors in excitotoxicity

Excitatory synaptic activity governs excitotoxicity and modulates the distribution of NMDA receptors (NMDARs) among synaptic and extrasynaptic sites of central neurons. We investigated whether NMDAR localization was functionally linked to excitotoxicity by perturbing F-actin, a cytoskeletal protein that participates in targeting synaptic NMDARs in dendritic spines. Depolymerizing F-actin did not affect NMDA-evoked whole-cell currents. However, the number of dendritic NMDAR clusters and the NMDAR-mediated component of miniature spontaneous EPSCs were reduced, whereas the number of AMPA receptor clusters and AMPA receptor-mediated component of EPSCs was unchanged. This selective perturbation of synaptically activated NMDARs had no effect on neuronal death or the accumulation of (45)Ca(2+) evoked by applying exogenous NMDA or L-glutamate, which reach both synaptic and extrasynaptic receptors. However, it increased survival and decreased (45)Ca(2+) accumulation in neurons exposed to oxygen glucose deprivation, which causes excitotoxicity by glutamate release at synapses. Thus, synaptically and extrasynaptically activated NMDARs are equally capable of excitotoxicity. However, their relative contributions vary with the location of extracellular excitotoxin accumulation, a factor governed by the mechanism of extracellular neurotransmitter accumulation, not the synaptic activation of NMDARs.

Src potentiation of NMDA receptors in hippocampal and spinal neurons is not mediated by reducing zinc inhibition

The protein-tyrosine kinase Src is known to potentiate the function of NMDA receptors, which is necessary for the induction of long-term potentiation in the hippocampus. With recombinant receptors composed of NR1-1a/NR2A or NR1-1a/2B subunits, Src reduces voltage-independent inhibition by the divalent cation Zn2+. Thereby the function of recombinant NMDA receptors is potentiated by Src only when the Zn2+ level is sufficient to cause tonic inhibition. Here we investigated whether the Src-induced potentiation of NMDA receptor function in neurons is caused by reducing voltage-independent Zn2+ inhibition. Whereas chelating extracellular Zn2+ blocked the Src-induced potentiation of NR1-1a/2A receptors, we found that Zn2+ chelation did not affect the potentiation of NMDA receptor (NMDAR) currents by Src applied into hippocampal CA1 or CA3 neurons. Moreover, Src did not alter the Zn2+ concentration-inhibition relationship for NMDAR currents in CA1 or CA3 neurons. Also, chelating extracellular Zn2+ did not prevent the upregulation of NMDA single-channel activity by endogenous Src in membrane patches from spinal dorsal horn neurons. Taking these results together we conclude that Src-induced potentiation of NMDAR currents is not mediated by reducing Zn2+ inhibition in hippocampal and dorsal horn neurons.

Platelet-derived growth factor receptor-induced feed-forward inhibition of excitatory transmission between hippocampal pyramidal neurons

Growth factor receptors provide a major mechanism for the activation of the nonreceptor tyrosine kinase c-Src, and this kinase in turn up-regulates the activity of N-methyl-D-aspartate (NMDA) receptors in CA1 hippocampal neurons (1). Unexpectedly, applications of platelet-derived growth factor (PDGF)-BB to cultured and isolated CA1 hippocampal neurons depressed NMDA-evoked currents. The PDGF-induced depression was blocked by a PDGF-selective tyrosine kinase inhibitor, by a selective inhibitor of phospholipase C-gamma, and by blocking the intracellular release of Ca(2+). Inhibitors of cAMP-dependent protein kinase (PKA) also eliminated the PDGF-induced depression, whereas a phosphodiesterase inhibitor enhanced it. The NMDA receptor-mediated component of excitatory synaptic currents was also inhibited by PDGF, and this inhibition was prevented by co-application of a PKA inhibitor. Src inhibitors also prevented this depression. In recordings from inside-out patches, the catalytic fragment of PKA did not itself alter NMDA single channel activity, but it blocked the up-regulation of these channels by a Src activator peptide. Thus, PDGF receptors depress NMDA channels through a Ca(2+)- and PKA-dependent inhibition of their modulation by c-Src.

Specific coupling of NMDA receptor activation to nitric oxide neurotoxicity by PSD-95 protein

The efficiency with which N-methyl-D-aspartate receptors (NMDARs) trigger intracellular signaling pathways governs neuronal plasticity, development, senescence, and disease. In cultured cortical neurons, suppressing the expression of the NMDAR scaffolding protein PSD-95 (postsynaptic density-95) selectively attenuated excitotoxicity triggered via NMDARs, but not by other glutamate or calcium ion (Ca2+) channels. NMDAR function was unaffected, because receptor expression, NMDA currents, and 45Ca2+ loading were unchanged. Suppressing PSD-95 blocked Ca2+-activated nitric oxide production by NMDARs selectively, without affecting neuronal nitric oxide synthase expression or function. Thus, PSD-95 is required for efficient coupling of NMDAR activity to nitric oxide toxicity, and imparts specificity to excitotoxic Ca2+ signaling.

G-protein-coupled receptors act via protein kinase C and Src to regulate NMDA receptors

The N-methyl-D-aspartate (NMDA) receptor contributes to synaptic plasticity in the central nervous system and is both serine-threonine and tyrosine phosphorylated. In CA1 pyramidal neurons of the hippocampus, activators of protein kinase C (PKC) as well as the G-protein-coupled receptor ligands muscarine and lysophosphatidic acid enhanced NMDA-evoked currents. Unexpectedly, this effect was blocked by inhibitors of tyrosine kinases, including a Src required sequence and an antibody selective for Src itself. In neurons from mice lacking c-Src, PKC-dependent upregulation was absent. Thus, G-protein-coupled receptors can regulate NMDA receptor function indirectly through a PKC-dependent activation of the non-receptor tyrosine kinase (Src) signaling cascade.

Regulation of N-methyl-D-aspartate receptor function by constitutively active protein kinase C

The ability of the constitutively active fragment of protein kinase C (PKM) to modulate N-methyl-D-aspartate (NMDA)-activated currents in cultured mouse hippocampal neurons and acutely isolated CA1 hippocampal neurons from postnatal rats was studied using patch-clamp techniques. The responses of two heterodimeric combinations of recombinant NMDA receptors (NR1a/NR2A and NR1a/NR2B) expressed in human embryonic kidney 293 cells were also examined. Intracellular applications of PKM potentiated NMDA-evoked currents in cultured and isolated CA1 hippocampal neurons. This potentiation was observed in the absence or presence of extracellular Ca2+ and was prevented by the coapplication of the inhibitory peptide protein kinase inhibitor(19-36). Furthermore, the PKM-induced potentiation was not a consequence of a reduction in the sensitivity of the currents to voltage-dependent blockade by extracellular Mg2+. We also found different sensitivities of the responses of recombinant NMDA receptors to the intracellular application of PKM. Some potentiation was observed with the NR1a/NR2A subunits, but none was observed with the NR1a/NR2B combination. Applications of PKM to inside-out patches taken from cultured neurons increased the probability of channel opening without changing single-channel current amplitudes or channel open times. Thus, the activation of protein kinase C is associated with potentiation of NMDA receptor function in hippocampal neurons largely through an increase in the probability of channel opening.

Multiple sites of action of neomycin, Mg2+ and spermine on the NMDA receptors of rat hippocampal CA1 pyramidal neurones

1. The effects of neomycin on NMDA-evoked currents in isolated CA1 hippocampal pyramidal neurones were investigated and single channel activity was examined in outside-out patches taken from cultured hippocampal neurones. The effects of neomycin on two combinations of NMDA receptor subunits (NR1a-NR2A and NR1a-NR2B) expressed in human embryonic kidney (HEK293) cells were also studied. 2. Neomycin (0. 01-1 mM) caused a potentiation of NMDA-activated currents in all neurones examined. No evidence of a voltage-dependent depression was observed in whole-cell recordings. 3. In outside-out patch recordings relatively low concentrations (30 and 100 microM) of neomycin caused a voltage-dependent reduction in single channel current amplitude as well as a large increase in the frequency of channel opening. 4. In saturating concentrations of glycine, neomycin enhanced NMDA-activated currents and this glycine-independent enhancement was confirmed using recombinant NR1a-NR2B receptors. Neomycin substantially increased the potency of glycine for the receptor by reducing the rate of dissociation of glycine from the receptor. Neomycin demonstrated a glycine-dependent enhancement of currents mediated by the NR1a-NR2A combination of subunits but a paradoxical depression was observed in saturating concentrations of glycine. 5. Neomycin increased the rate of deactivation of glutamate-activated currents consistent with neomycin causing a reduction in the affinity of the receptor for agonist. 6. These results indicate that neomycin has multiple and complex effects on NMDA receptors.

Vagal afferent transmission in the NTS mediating reflex responses of the rat esophagus

In urethan-anesthetized rats, esophageal distension evoked volume-dependent reflex contractions with phase-locked multiunit discharges in the central subnucleus of the solitary tract complex (NTSC) and the nucleus ambiguus. During blockade of solitarial, but not peripheral, muscarinic cholinoceptors, the volume-response relationship of reflex contractions was shifted rightward with a depression in pressure wave amplitude. Concurrently, premotor NTSC responses were attenuated and nucleus ambiguus activity was abolished during esophagomotor inhibition. Both NTSC discharges and reflex responses were eliminated, or strongly inhibited, during blockade of excitatory amino acid receptors (EAARs) with 6-cyano-7-nitroquinoxaline-2,3-dione, gamma-glutamylglycine or 2-amino-7-phosphonoheptanoate. In brain stem slice preparations, whole cell recordings in the NTSC region revealed fast excitatory postsynaptic potentials (EPSPS) with spikes in response to electrical stimulation of the solitary tract. Although spiking was facilitated by muscarine, EPSPS were resistant to cholinoceptor antagonists but sensitive to EAAR blockers. We conclude that esophageal vagal afferents excite ipsilateral NTSC interneurons via activation of glutamate receptors of the DL-alpha-amino-3-hydroxy-5-methylisoxazole-propionic acid and N-methyl-D-aspartate subtypes. Cholinergic input to the NTSC probably derives from propriobulbar sources and serves to modulate the responsiveness of reflex interneurons.