Amphipathic polyethyleneglycols effectively prolong the circulation time of liposomes

Incorporation of dioleoyl N-(monomethoxy polyethyleneglycol succinyl)phosphatidylethanolamine (PEG-PE) into large unilamellar liposomes composed of egg phosphatidylcholine:cholesterol (1:1) does not significantly increase the content leakage when the liposomes are exposed to 90% human serum at 37 degrees C, yet the liposomes show a significant increase in the blood circulation half-life (t1/2 = 5 h) as compared to those without PEG-PE(t1/2 less than 30 min). The PEG-PE's activity to prolong the circulation time of liposomes is greater than that of the ganglioside GM1, a well-described glycolipid with this activity. Another amphipathic PEG derivative, PEG stearate, also prolongs the liposome circulation time, although its activity is less than that of GM1. Amphipathic PEGs may be useful for the sustained release and the targeted drug delivery by liposomes.

Electron transfer by domain movement in cytochrome bc1

The cytochrome bc1 is one of the three major respiratory enzyme complexes residing in the inner mitochondrial membrane. Cytochrome bc1 transfers electrons from ubiquinol to cytochrome c and uses the energy thus released to form an electrochemical gradient across the inner membrane. Our X-ray crystal structures of the complex from chicken, cow and rabbit in both the presence and absence of inhibitors of quinone oxidation, reveal two different locations for the extrinsic domain of one component of the enzyme, an iron-sulphur protein. One location is close enough to the supposed quinol oxidation site to allow reduction of the Fe-S protein by ubiquinol. The other site is close enough to cytochrome c1 to allow oxidation of the Fe-S protein by the cytochrome. As neither location will allow both reactions to proceed at a suitable rate, the reaction mechanism must involve movement of the extrinsic domain of the Fe-S component in order to shuttle electrons from ubiquinol to cytochrome c1. Such a mechanism has not previously been observed in redox protein complexes.

Gene therapy progress and prospects: nonviral vectors

The success of gene therapy is largely dependent on the development of the gene delivery vector. Recently, gene transfection into target cells using naked DNA, which is a simple and safe approach, has been improved by combining several physical techniques, for example, electroporation, gene gun, ultrasound and hydrodynamic pressure. Chemical approaches have been utilized to improve the efficiency and cell specificity of gene transfer. Novel gene carrier molecules, which facilitate DNA escape from the endosome into the cytosol, have been developed. Several functional polymers, which enable controlled release of DNA in response to an environmental change, have also been reported. Plasmids with reduced number of CpG motifs, the use of PCR fragments and the sequential injection method have been established for the reduction of immune response triggered by plasmid DNA. Construction of a long-lasting gene expression system is also an important theme for nonviral gene therapy. To date, tissue-specific expression, self-replicating and integrating plasmid systems have been reported. Improvement of delivery methods together with intelligent design of the DNA itself has brought about large degrees of enhancement in the efficiency, specificity and temporal control of nonviral vectors.

A novel cationic liposome reagent for efficient transfection of mammalian cells

A novel cationic derivative of cholesterol, 3 beta [N-(N',N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol), has been synthesized and used to prepare sonicated liposomes with dioleoylphosphatidylethanolamine. This novel cationic liposome reagent facilitates efficient DNA mediated transfection in A431 human epidermoid carcinoma cells, A549 human lung carcinoma cells, L929 mouse fibroblast cells, and YPT minipig primary endothelial cells. The activity was greater than that of a commercial reagent, Lipofectin, and was approximately 4-fold less toxic than Lipofectin when assayed with A431 cells. The reagent is easy to synthesize and stable for at least 6 weeks.

Direct gene transfer with DNA-liposome complexes in melanoma: expression, biologic activity, and lack of toxicity in humans

Direct gene transfer offers the potential to introduce DNA encoding therapeutic proteins to treat human disease. Previously, gene transfer in humans has been achieved by a cell-mediated ex vivo approach in which cells from the blood or tissue of patients are genetically modified in the laboratory and subsequently returned to the patient. To determine the feasibility and safety of directly transferring genes into humans, a clinical study was performed. The gene encoding a foreign major histocompatibility complex protein, HLA-B7, was introduced into HLA-B7-negative patients with advanced melanoma by injection of DNA-liposome complexes in an effort to demonstrate gene transfer, document recombinant gene expression, and determine the safety and potential toxicity of this therapy. Six courses of treatment were completed without complications in five HLA-B7-negative patients with stage IV melanoma. Plasmid DNA was detected within biopsies of treated tumor nodules 3-7 days after injection but was not found in the serum at any time by using the polymerase chain reaction. Recombinant HLA-B7 protein was demonstrated in tumor biopsy tissue in all five patients by immunochemistry, and immune responses to HLA-B7 and autologous tumors could be detected. No antibodies to DNA were detected in any patient. One patient demonstrated regression of injected nodules on two independent treatments, which was accompanied by regression at distant sites. These studies demonstrate the feasibility, safety, and therapeutic potential of direct gene transfer in humans.

The role of dioleoyl phosphatidylethanolamine in cationic liposome mediated gene transfer

In a reported gene assay, cationic liposomes containing the cationic lipid 3 beta-(N-(N',N'-dimethylaminoethane)carbamoyl)cholesterol (DC-Chol) and a neural phospholipid dioleoylphosphatidylethanolamine (DOPE) showed high transfection activity. DNA/liposome complex which contained low amount of liposomes could bind to the cell surface but failed to transfect the cells. We have designed a two-step protocol to examine this phenomenon in more detail. A431 human cells were incubated on ice (pulse) with DNA complexed to a low level of cationic liposomes. The cells were washed and incubated at 37 degrees C (chase) with or without free cationic liposomes of various composition (helper liposomes). Only liposomes enriched with DOPE showed helper activity; liposomes containing dioleoylphosphatidylcholine (DOPC), a structural analog of DOPE, had no helper activity. The delivery was inhibited by the lysosomotropic agent chloroquine and was optimal if the helper liposome chase was initiated immediately after the pulse. An endocytosis model of DNA delivery by cationic liposomes is proposed in which the principal function of the chase liposomes is to destabilize the endosome membrane and allow the release of DNA into the cytosol. This model is consistent with the known activity of DOPE to assume non-bilayer structures, hence destabilizing the endosome membrane.

Constitutive activation of Stat3 signaling abrogates apoptosis in squamous cell carcinogenesis in vivo

Field cancerization predisposes the upper aerodigestive tract mucosa to the formation of multiple primary tumors, when exposed to environmental carcinogens. Up-regulation of epidermal growth factor receptor occurs early in squamous cell carcinogenesis and is critical for the loss of growth control in a variety of human cancers, including head and neck squamous cell carcinomas. In these tumor cells in culture, epidermal growth factor receptor stimulation initiates signaling via persistent activation of selective STAT proteins. To determine the timing of Stat3 activation in head and neck carcinogenesis, we studied the expression and constitutive activation of Stat3 in tumors and normal mucosa from patients with head and neck cancer compared with mucosa from controls without cancer. Stat3 was up-regulated and constitutively activated in both primary human head and neck tumors as well as in normal mucosa from these cancer patients compared with control normal mucosa from patients without cancer. In vivo liposome-mediated gene therapy with a Stat3 antisense plasmid efficiently inhibited Stat3 activation, increased tumor cell apoptosis, and decreased Bcl-x(L) expression in a head and neck xenograft model. These findings provide evidence that constitutively activated Stat3 is an early event in head and neck carcinogenesis that contributes to the loss of growth control by an anti-apoptotic mechanism.

Structure of an E6AP-UbcH7 complex: insights into ubiquitination by the E2-E3 enzyme cascade

The E6AP ubiquitin-protein ligase (E3) mediates the human papillomavirus-induced degradation of the p53 tumor suppressor in cervical cancer and is mutated in Angelman syndrome, a neurological disorder. The crystal structure of the catalytic hect domain of E6AP reveals a bilobal structure with a broad catalytic cleft at the junction of the two lobes. The cleft consists of conserved residues whose mutation interferes with ubiquitin-thioester bond formation and is the site of Angelman syndrome mutations. The crystal structure of the E6AP hect domain bound to the UbcH7 ubiquitin-conjugating enzyme (E2) reveals the determinants of E2-E3 specificity and provides insights into the transfer of ubiquitin from the E2 to the E3.

Nonviral vectors in the new millennium: delivery barriers in gene transfer

Development of an efficient method for introducing a therapeutic gene into target cells in vivo is the key issue in treating genetic and acquired diseases by gene therapy. To this end, various nonviral vectors have been designed and developed, and some of them are in clinical trials. The simplest approach is naked DNA injection into local tissues or systemic circulation. Physical (gene gun, electroporation) and chemical (cationic lipid or polymer) approaches have also been utilized to improve the efficiency and target cell specificity of gene transfer by plasmid DNA. After administration, however, nonviral vectors encounter many hurdles that result in diminished gene transfer in target cells. Cationic vectors sometimes attract serum proteins and blood cells when entering into blood circulation, which results in dynamic changes in their physicochemical properties. To reach target cells, nonviral vectors should pass through the capillaries, avoid recognition by mononuclear phagocytes, emerge from the blood vessels to the interstitium, and bind to the surface of the target cells. They then need to be internalized, escape from endosomes, and then find a way to the nucleus, avoiding cytoplasmic degradation. Successful clinical applications of nonviral vectors will rely on a better understanding of barriers in gene transfer and development of vectors that can overcome these barriers.

Nonviral gene therapy: promises and challenges

The last 10 years have seen substantial progress in the development and application of nonviral vectors in gene therapy. However, many problems remain to be resolved before nonviral gene therapy can become a standard clinical practice. This review highlights the major breakthroughs in this field. The problems and future research directions are also discussed. Gene Therapy (2000) 7, 31-34.

Activity of amphipathic poly(ethylene glycol) 5000 to prolong the circulation time of liposomes depends on the liposome size and is unfavorable for immunoliposome binding to target

Dioleoyl-N-(monomethoxy polyethyleneglycol succinyl)-phosphatidylethanolamine (PEG-PE) (mol. wt. of PEG = 5000), an amphipathic polymer, can be incorporated into the liposome membrane and significantly prolong the blood circulation time of the liposome. As little as 3.7 mol% of PEG-PE in liposome resulted in maximal enhancement of liposome circulation time. However, this activity of PEG-PE was only seen with relatively small liposomes (d less than or equal to 200 nm); larger liposomes containing PEG-PE showed an unusually high level (approx. 35% injected dose) of accumulation in the spleen. We have tested whether the small, PEG-PE containing liposomes are suitable for immuno targeting by incorporating a lung-specific monoclonal antibody on the liposome surface. While another amphiphile, ganglioside GM1, which is well known for its activity to prolong the liposome circulation time, significantly enhanced the lung binding of the immunoliposomes, PEG-PE incorporation of immunoliposomes resulted in a low level of target binding. To test if the reduced target binding is due to a steric barrier effect of the surface PEG polymer, we have incorporated a small amount of N-biotinaminocaproylphosphatidylethanolamine into the PEG-PE containing liposomes and examined the liposome agglutination induced by the addition of streptavidin. As little as 0.72 mol% PEG-PE in these liposomes completely abolished agglutination. In contrast, incorporation of GM1 in liposomes only reduced the rate, but not the extent, of liposome agglutination. These results strongly support the hypothesis that PEG-PE prolongs liposome circulation time by providing a strong steric barrier which prevents close contact with another liposome or cell. Since GM1 provides only a weak steric barrier effect, its activity to prolong the liposome circulation time must involve another yet unknown mechanism.

Effect of liposome size on the circulation time and intraorgan distribution of amphipathic poly(ethylene glycol)-containing liposomes

Liposomes containing dioleoyl-N-(monomethoxypoly(ethylene glycol)succinyl)- phosphatidylethanolamine (PEG-PE), and of three characteristic sizes (d > 300 nm, d approximately 150-200 nm, and d < 70 nm), were prepared, injected into mice, and their biodistributions examined following a radioactive lipid phase marker. The large and small liposomes accumulated to elevated levels in spleen and liver, respectively. The intermediate sized liposomes were found to be the longest circulating. Furthermore, when injected into mice bearing murine MC-38 colon carcinoma tumor, an approximate 2-fold increase in the % injected dose per g tumor was observed for the long-circulating liposomes compared to liposomes without PEG-PE. The distribution of the injected liposomes within the tumor was examined by fluorescence microscopy, where the liposomes were labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). The liposomes were found surrounding blood vessels in the tumor, with some degree of extravasation into the tumor mass. A previous explanation for the reduced circulation time of small liposomes has been that they have an ability to pass through the fenestrated liver endothelium and thereby reach the parenchymal cells. DiI-labeled liposomes were therefore used to examine the intrahepatic distribution of the injected liposomes. Liposomes accumulated in liver were localized to Kupffer cells, regardless of liposome size. The small liposomes were not detectable in areas comprised of parenchymal cells when using this fluorescence technique. The reason for reduced long-circulating behavior for the small liposomes may be more directly related to the activity of PEG-PE. Therefore the steric barrier activity of the liposomes was examined by a serum protein binding assay and by streptavidin binding to biotinylated liposomes. The steric barrier was liposome size dependent, with the small liposomes revealing increased protein binding. This decreased steric barrier of the small liposomes may result in increased susceptibility to opsonization and thus explain their more rapid clearance from the circulation. The large liposomes accumulated in spleen were localized in the red pulp and marginal zone. Uptake of the large liposomes may occur by means of a filtration mechanism. These results establish the significance of liposome size in determining liposome circulation time and biodistribution, and are relevant for the optimal design of liposomes for drug delivery.

Potentiation of cationic liposome-mediated gene delivery by polycations

We discovered that several high molecular weight cationic polymers, such as poly(L-lysine) and protamine, can enhance the transfection efficiency of several types of cationic liposomes by 2-28-fold in a number of cell lines in vitro. Small polycations such as spermine and a cationic decapeptide derived from SV40 T-antigen were only moderately active. The addition of poly(L-lysine) and protamine dramatically reduced the particle size of the complex formed between DNA and cationic liposomes and rendered DNA resistant to the nuclease activity. The complexes composed of DNA, poly(L-lysine), and cationic lipids were purified from an excess of free liposomes with sucrose gradient ultracentrifugation. Purified complex formed at low cationic liposome ratio was poor in lipid content and only had weak transfection activity. Addition of free liposome to the purified complex significantly enhanced the transfection activity. In contrast, complexes formed at a higher initial ratio of liposome to DNA had a higher lipid content and were highly active in transfection; the activity was about 3-9-fold more active than the corresponding complex before purification. Negative stain EM studies revealed that the most active complexes prepared from 40 nmol of lipid, 0.5 micrograms of poly(L-lysine), and 1 microgram of DNA and purified by gradient ultracentrifugation were spherical, electron dense, small (< 100 nm in diameter) particles, and some of them were associated with lipid membranes. These highly active, stable, small-sized lipid/poly(L-lysine)/DNA complexes represent a new class of nonviral gene delivery vehicles that might be useful in gene therapy.

Rapid and visual detection of 2019 novel coronavirus (SARS-CoV-2) by a reverse transcription loop-mediated isothermal amplification assay

OBJECTIVE

To evaluate a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and compare it with RT-PCR.

METHODS

We designed primers specific to the orf1ab and S genes of SARS-CoV-2. Total viral RNA was extracted using the QIAamp Viral RNA Mini Kit. We optimized the RT-LAMP assay, and evaluated it for its sensitivity and specificity of detection using real-time turbidity monitoring and visual observation.

RESULTS

The primer sets orf1ab-4 and S-123 amplified the genes in the shortest times, the mean (±SD) times were 18 ± 1.32 min and 20 ± 1.80 min, respectively, and 63°C was the optimum reaction temperature. The sensitivities were 2 × 10¹ copies and 2 × 10² copies per reaction with primer sets orf1ab-4 and S-123, respectively. This assay showed no cross-reactivity with 60 other respiratory pathogens. To describe the availability of this method in clinical diagnosis, we collected 130 specimens from patients with clinically suspected SARS-CoV-2 infection. Among them, 58 were confirmed to be positive and 72 were negative by RT-LAMP. The sensitivity was 100% (95% CI 92.3%-100%), specificity 100% (95% CI 93.7%-100%). This assay detected SARS-CoV-2 in a mean (±SD) time of 26.28 ± 4.48 min and the results can be identified with visual observation.

CONCLUSION

These results demonstrate that we developed a rapid, simple, specific and sensitive RT-LAMP assay for SARS-CoV-2 detection among clinical samples. It will be a powerful tool for SARS-CoV-2 identification, and for monitoring suspected patients, close contacts and high-risk groups.

DNA transfection mediated by cationic liposomes containing lipopolylysine: characterization and mechanism of action

The ability of a polycationic lipid, lipopoly(L-lysine) (LPLL), to mediate efficient DNA transfection depended on scraping of the treated cells (Zhou et al. (1991) Biochim. Biophys. Acta 1065, 8-14). It was found that the mechanical treatment could be avoided by including a helper lipid to the liposome composition. Among the helper lipids tested, a hexagonal phase forming lipid, dioleoylphosphatidylethanolamine (DOPE), gave rise to the highest activity. The transfection efficiency was further optimized by varying the lipophilicity of the LPLL and the ratio of the cationic liposome to DNA. Transfection activity of the optimal DNA-liposome complexes was enhanced by up to 6-fold if cells were pretreated with agents interfering with the process of endocytosis. Meanwhile, pretreatment of cells with a peptide which inhibits membrane fusion decreased the activity by about 60%. These results indicated that DNA-liposome complexes are taken up by an endocytosis mechanism and that cytoplasmic delivery of DNA involves a fusion-related event probably in the endosome compartment. The transfection process was visualized by thin-section electron microscopy. It was found that the complexes entered the cytoplasm mainly by destabilizing endosomes and occasionally by penetrating through the plasma membrane. Therefore, our findings differ from a previous hypothesis which suggests that transfection is mediated by fusion of the liposomes with the plasma membrane of the treated cells.

In vivo gene transfer via intravenous administration of cationic lipid-protamine-DNA (LPD) complexes

A novel LPD formulation has been developed for in vivo gene transfer. It involves the interaction of plasmid DNA with protamine sulfate, a cationic polypeptide, followed by the addition of DOTAP cationic liposomes. Compared with DOTAP/DNA complexes, LPD offers better protection of plasmid DNA against enzymatic digestion and gives consistently higher gene expression in mice via tail vein injection. When a luciferase reporter gene was employed, gene expression was found in all tissues examined including lung, heart, spleen, liver and kidney with the highest expression in the lung. The in vivo efficiency of LPD was dependent upon charge ratio and was also affected by the lipid used. Increasing the amount of DNA delivered induced an increase in gene expression. The optimal dose was approximately 50 micrograms per mouse at which concentration approximately 20 ng luciferase protein per milligram extracted tissue protein could be detected in the lung. Increasing the DNA to 100 micrograms per mouse resulted in toxicity and death of the animal. Gene expression in the lung was detected as early as 1 h after injection, peaked at 6 h and declined thereafter. High expression was also found in the spleen 6 h after injection but dropped very rapidly thereafter. The in vivo gene expression by LPD was dependent upon the route of administration since intraportal injection of LPD led to about a 100-fold decrease in gene expression in the lung as compared with i.v. injection. Using lacZ as a reporter gene, it was shown that endothelial cells were the primary locus of transgene expression in both the lung and spleen. No sign of inflammation in these organs was noticed. Since protamine sulfate has been proven to be nontoxic and only weakly immunogenic in humans, this novel vector may be useful for clinical gene therapy.

Protamine sulfate enhances lipid-mediated gene transfer

A polycationic peptide, protamine sulfate, USP, has been shown to be able to condense plasmid DNA efficiently for delivery into several different types of cells in vitro by several different types of cationic liposomes. The monovalent cationic liposomal formulations (DC-Chol and lipofectin) exhibited increased transfection activities comparable to that seen with the multivalent cationic liposome formulation, lipofectamine. This suggests that lipofectamine's superior in vitro activity arises from its ability to condense DNA efficiently and that protamine's primary role is that of a condensation agent, although it also possesses several amino acid sequences resembling that of a nuclear localization signal. While the use of polycations to condense DNA has been previously reported, the of protamine sulfate, USP as a condensation agent was found to be superior to poly-L-lysine as well as to various other types of protamine. These differences among various salt forms of protamine appear to be attributable to structural differences between the protamines and not due to differences in the net charge of the molecule. The appearance of lysine residues within the protamine molecule correlate with a reduction in binding affinity to plasmid DNA as well as an observed loss in transfection enhancing activity. This finding sheds light on the structural requirements of condensation agents for use in gene transfer protocols. Furthermore, protamine sulfate, USP is an FDA-approved compound with a documented safety profile and could be readily used as an adjuvant to a human gene therapy protocol.

Folate-targeted, anionic liposome-entrapped polylysine-condensed DNA for tumor cell-specific gene transfer

We have developed a lipidic gene transfer vector, LPDII, where DNA was first complexed to polylysine at a ratio of 1:0.75 (w/w) and then entrapped into folate-targeted pH-sensitive anionic liposomes composed of dioleoyl phosphatidylethanolamine (DOPE)/cholesteryl hemisuccinate/folate-polyethlene glycol-DOPE (6:4:0.01 mol/mol) via charge interaction. LPDII transfection of KB cells, a cell line overexpressing the tumor marker folate receptor, was affected by both the lipid to DNA ratio and the lipid composition. At low lipid to DNA ratios (e.g. 4 and 6), LPDII particles were positively charged; transfection and cellular uptake levels were independent of the folate receptor and did not require a pH-sensitive lipid composition. Meanwhile, transfection and uptake of negatively charged LPDII particles, i.e. those with high lipid to DNA ratios (e.g. 10 and 12), were folate receptor-dependent and required a pH-sensitive lipid composition. The transfection activity of LPDII was lost when the inverted cone-shaped DOPE was replaced by dioleoyl phosphatidylcholine. LPDII particles with lipid to DNA ratios of 4, 6, 10, and 12 were approximately 20-30 times more active than DNA.3-beta-[N-(N',N'-dimethylethane)carbamoyl]cholesterol cationic liposome complexes in KB cells and were much less cytotoxic. On the sucrose gradient, LPDII particles had a migration rate in between those of the free DNA and the DNA.polylysine complex. An electron micrograph of LPDII showed a structure of spherical particles with a positively stained core enclosed in a lipidic envelope with a mean diameter of 74 +/- 14 nm. This novel gene transfer vector may potentially be useful in gene therapy for tumor-specific delivery.

Role of liposome size and RES blockade in controlling biodistribution and tumor uptake of GM1-containing liposomes

We have examined the effect of liposome size on liposome circulation time in the blood. Liposomes composed of phosphatidylcholine, cholesterol and ganglioside GM1 were prepared in the various size range. Optimal circulation activity (55% injected dose at 4 h post injection) of GM1-containing liposomes, which correlated with a relatively high uptake of liposomes by EMT6 tumor in mouse, was obtained with a size range of 70 to 200 nm in diameter. Increasing the diameter of liposome to greater than 200 nm resulted in an enhancement of the spleen uptake and decrease of the blood level. For liposomes with a diameter of less than 70 nm, 70% of the injected dose were taken up by the liver, presumably by the parenchymal cells. In contrast, the biodistribution of phosphatidylserine-containing liposomes was relatively insensitive to changes in liposome size; most of the injected dose was found in the liver. The effect of RES blockade on the circulation time of large (d greater than 300 nm), GM1-containing liposomes was also studied. Dextran sulfate 500, a commonly used blockade reagent for Kupffer cells, had no effect. On the other hand, preinjection of a large dose of liposomes with a diameter greater than 500 nm showed variable results depending on the lipid composition of the blocking liposomes. Preinjection of liposomes containing GM1, phosphatidylinositol or (N-polyethyleneglycol) phosphatidylethanolamine effectively reduced the spleen uptake of the large GM1-containing liposomes, whereas liposomes containing phosphatidic acid showed no effect. These results indicate that only spleen homing liposomes can be used as a blocking reagent to prolong the circulation time of the large GM1-containing liposomes.

Generation by insulin of a chemical mediator that controls protein phosphorylation and dephosphorylation

Deproteinized skeletal muscle extracts free of major nucleotides from control and insulin-treated rats were fractionated and assayed for inhibition of protein phosphorylation by cyclic adenosine monophosphate (AMP)-dependent and -independent protein kinases. A differential effect of insulin on a particular fraction was observed on cyclic AMP-dependent protein kinase but not on cyclic AMP-independent protein kinases. This fraction that inhibited cyclic AMP-dependent protein kinase also stimulated glycogen synthase phosphoprotein phosphatase. It is proposed that this fraction may contain a mediator substance generateed in the presence of insulin.

Influence of the steric barrier activity of amphipathic poly(ethyleneglycol) and ganglioside GM1 on the circulation time of liposomes and on the target binding of immunoliposomes in vivo

A series of dioleoyl N-(monomethoxy polyethyleneglycol succinyl)phosphatidylethanolamine (PEG-PE) of different polymer chain length was used in this study. Both the activity of PEG-PE in prolonging the circulation time of liposomes and the relative steric barrier activity of amphipathic polymer, measured by a liposome agglutination assay, were found to be directly proportional to the chain length of PEG-PE (PEG5000-PE greater than PEG2000-PE greater than PEG750-PE). However, PEG5000-PE caused a reduced target binding of immunoliposomes in mice due to its overly strong steric barrier activity. The best PEG-PE species supporting the target binding of immunoliposomes was PEG2000-PE, the activity of which was compatible to that of ganglioside GM1. However, GM1 only showed a weak steric barrier activity, suggesting a different mechanism for this glycolipid.

Tas1r3, encoding a new candidate taste receptor, is allelic to the sweet responsiveness locus Sac

The ability to taste the sweetness of carbohydrate-rich foodstuffs has a critical role in the nutritional status of humans. Although several components of bitter transduction pathways have been identified, the receptors and other sweet transduction elements remain unknown. The Sac locus in mouse, mapped to the distal end of chromosome 4 (refs. 7-9), is the major determinant of differences between sweet-sensitive and -insensitive strains of mice in their responsiveness to saccharin, sucrose and other sweeteners. To identify the human Sac locus, we searched for candidate genes within a region of approximately one million base pairs of the sequenced human genome syntenous to the region of Sac in mouse. From this search, we identified a likely candidate: T1R3, a previously unknown G protein-coupled receptor (GPCR) and the only GPCR in this region. Mouse Tas1r3 (encoding T1r3) maps to within 20,000 bp of the marker closest to Sac (ref. 9) and, like human TAS1R3, is expressed selectively in taste receptor cells. By comparing the sequence of Tas1r3 from several independently derived strains of mice, we identified a specific polymorphism that assorts between taster and non-taster strains. According to models of its structure, T1r3 from non-tasters is predicted to have an extra amino-terminal glycosylation site that, if used, would interfere with dimerization.

Stable Superhydrophobic Surface via Carbon Nanotubes Coated with a ZnO Thin Film

We report the formation of a stable superhydrophobic surface via aligned carbon nanotubes (CNTs) coated with a zinc oxide (ZnO) thin film. The CNT template was synthesized by chemical vapor deposition on an Fe-N catalyst layer. The ZnO film, with a low surface energy, was deposited on the CNT template by the filtered cathodic vacuum arc technique. Contact angle measurement reveals that the surface of the ZnO-coated CNTs is superhydrophobic with water contact angle of 159 degrees . Unlike the uncoated CNTs surface, the ZnO-coated CNTs surface shows no sign of water seepage even after a prolonged period of time. The wettability of the surface can be reversibly changed from superhydrophobicity to hydrophilicity by alternation of ultraviolet (UV) irradiation and dark storage.

Mutations in the gene encoding gap junction protein beta-3 associated with autosomal dominant hearing impairment

Hearing impairment is the most commonly occurring condition that affects the ability of humans to communicate. More than 50% of the cases of profound early-onset deafness are caused by genetic factors. Over 40 loci for non-syndromic deafness have been genetically mapped, and mutations in several genes have been shown to cause hearing loss. Mutations in the gene encoding connexin 26 (GJB2) cause both autosomal recessive and dominant forms of hearing impairment. To study the possible involvement of other members of the connexin family in hereditary hearing impairment, we cloned the gene (GJB3) encoding human gap junction protein beta-3 using homologous EST searching and nested PCR. GJB3 was mapped to human chromosome 1p33-p35. Mutation analysis revealed that a missense mutation and a nonsense mutation of GJB3 were associated with high-frequency hearing loss in two families. Moreover, expression of Gjb3 was identified in rat inner ear tissue by RT-PCR. These findings suggest that mutations in GJB3 may be responsible for bilateral high-frequency hearing impairment.