A liposomal MRI contrast agent: phosphatidylethanolamine-DTPA

The chelating agent, diethylenetriaminepentaacetic acid (DTPA), was attached via one -COOH group to the amino headgroup of phosphatidylethanolamine to produce a phospholipid which is also a powerful chelating agent. It readily assembles into the walls of lipid bilayer structures as a liposome-associated carrier of cations for MR contrast or radioisotope studies. Freeze-etch electron microscopy showed that phosphatidylethanolamine-DTPA formed satisfactory sonicated vesicles when mixed with natural phospholipids at up to 50 wt%. The resultant structures with bound gadolinium effectively shortened T1 and T2 of surrounding water protons. When sonicated liposomes bearing chelating agent with bound 111In3+ were injected intravenously into rats, uptake was primarily by liver and spleen. By 24 h postinjection there was biliary excretion of this material. Phosphatidylethanolamine-DTPA may have some general utility as an amphiphilic liposomal chelating agent for polyvalent cations.

Evidence that trans-bilayer interdigitation of glycosphingolipid long chain fatty acids may be a general phenomenon

'Interdigitation' is a term coined to describe the phenomenon whereby pure phosphatidylcholines with intramolecular fatty acid chain length heterogeneity when hydrated to form bilayers may insert the methyl ends of long fatty acids from one side across more than half of the membrane thickness to protrude amongst the acyl chains of the opposite side of the bilayer (Keough, K.M.W. and Davis, P.J. (1979) Biochemistry 18, 1453-1459; Huang, C. and Mason, J.T. (1986) Biochim. Biophys. Acta 864, 423-470). In this article we address the fate of long fatty acid chains of glycosphingolipids present as minor components in membranes of non-interdigitating phosphatidylcholines. In this pursuit, derivatives of galactosyl ceramide, lactosyl ceramide, globoside and GM1 were synthesized having either 18-carbon or 24-carbon fatty acid with a spin label covalently attached at C-16. Labelled glycolipids were incorporated at 1-2 mol% into bilayers of synthetic phosphatidylcholines, their mixtures with cholesterol, or natural egg phosphatidylcholine. In each case the C-16 carbon of the glycolipid long chain fatty acid showed considerably greater 'order' and immobility than did C-16 of the fatty acid which was similar in length to the host matrix phospholipids. We interpret this as strong evidence that the long chain fatty acid interdigitates across the mid point of the bilayer in the systems studied. Clearly this phenomenon did not require that the phospholipid host matrix have mixed chain lengths. Furthermore it was totally independent of glycolipid family: for a given host matrix and (glycolipid) fatty acid chain length the order parameter values found were the same amongst all four glycolipid families tested.

A long chain spin label for glycosphingolipid studies: transbilayer fatty acid interdigitation of lactosyl ceramide

16-Carbon and 18-carbon fatty acids with covalently attached nitroxide free radicals have seen wide usage in membrane studies of phospholipid dynamics, orientation, and associations. However, they are inadequate for dealing with some very important questions that relate to glycosphingolipids. We report here the synthesis of a long chain (24-carbon) spin-labelled fatty acid designed for such problems. We have used both the new 24-carbon and the more conventional 18-carbon spin-labelled fatty acids to replace the natural fatty acid of lactosyl ceramide so that we may begin to compare short and long chain derivatives to analyse the molecular basis of their functional differences. Spectra seen are consistent with the view that in a bilayer host matrix the methyl end of the long fatty acid crosses the hydrophobic membrane center and interdigitates with fatty acids of phospholipids of the opposing monolayer.

Effects of fatty acid alpha-hydroxylation on glycosphingolipid properties in phosphatidylcholine bilayers

The role of glycosphingolipid fatty acid alpha-hydroxylation as a modulator of glycolipid organization and dynamics was considered by 2H-NMR in bilayer membranes. For these experiments, galactosylceramides were prepared in which the natural fatty acid mixture was replaced with perdeuterated 18-carbon hydroxylated or non-hydroxylated stearic acid. The L-stereoisomer of N-(alpha-OH-stearoyl-d34)galactosylceramide and its naturally-occurring D-alpha-OH analogue, were isolated for independent study. Bilayers were formed using 10 mol% galactosylceramide in a shorter chain phospholipid, dimyristoylphosphatidylcholine, in an attempt to reproduce several features of glycolipid-phospholipid interactions typical of cell membranes. Spectra of deuterated galactosylceramide in gel phase phospholipid membranes indicated that alpha-hydroxylation led to greater motional freedom and/or conformational disorder, with no measurable difference between D- and L-alpha-OH fatty acid derivatives. In fluid phosphatidylcholine bilayers the effects were modest. Glycolipid fatty acid hydroxylation led to broadening of the range of order parameters associated with methylene groups near the membrane surface (frequently referred to as the 'plateau region') - this effect being more marked for the naturally-occurring (D) stereoisomer. The degree of overall molecular order sensed by the glycolipid fatty acid chain in a fluid host matrix was minimally affected by alpha-hydroxylation; although the plateau region of the D isomer was slightly more ordered than that of the L isomer and the non-hydroxylated species. These results suggest that a significant aspect of the alpha-hydroxy group effect on glycosphingolipid behaviour in bilayer membranes with low glycolipid content was interference with glycolipid packing amongst host phospholipids in the upper portion of the acyl chains. For the D stereoisomer, there was some evidence that the hydroxy group led to strengthening of interlipid interaction near the membrane surface.

Glycosphingolipids: 2H NMR study of the influence of carbohydrate headgroup structure on ceramide acyl chain behavior in glycolipid-phospholipid bilayers

Galactosyl- and glucosylceramide, globoside, and dihydrolactosylceramide, bearing [2,2-2H2]stearic acid, have been studied at a concentration of 10 mol% in bilayers of dimyristoylphosphatidylcholine by 2H NMR. The quadrupolar splitting delta vQ of the C2 deuterons were measured at several temperatures in the range of 30-60 degrees C. Spin-lattice relaxation times T1 of C2 deuterons were determined in the same temperature range for all lipids but globoside. T1 values at 30 and 50 degrees C were unexpectedly short (6-8 ms), indicating reduced mobility of the ceramide acyl chains compared to that of the host phospholipid. At all temperatures, both delta vQ and T1 were essentially identical for the monoglycosylated species, GalCer and GlcCer, indicating that the order and dynamics of the upper portion of the fatty acyl chain are insensitive to this small change in the headgroup structure. In the case of globoside, where the glycolipid headgroup is equivalent to that of GlcCer extended by three sugar residues, values for the quadrupolar splittings associated with the acyl chain C2-position were very close to those obtained for Gal- and GlcCer. In contrast, the delta vQ values obtained for the diglycosyl species, LacCer, were significantly different at all temperatures. This different behavior of LacCer relative to that of the other glycolipids most likely originates from an orientational change of the acyl chain at the C2-position due to the absence of a 4,5 double bond in dihydrosphingosine. T1 values for the GlcCer and GalCer systems increased with temperature, indicating that the motions responsible for relaxation were in the short correlation time regime.(ABSTRACT TRUNCATED AT 250 WORDS)

A phospholipid spin label used as a liposome-associated MRI contrast agent

Given current clinical use of phospholipid bilayer structures (liposomes/vesicles) as nontoxic drug delivery vehicles, we have addressed the possibility of employing the phospholipids themselves as MRI contrast agents. To this end we have synthesized phosphatidylcholine with a nitroxide spin label replacing one methyl residue of the choline headgroup. This material was mixed with natural phosphatidylcholine in mole ratios from 1:50 to 1:1 and used to prepare sonicated unilamellar vesicles in saline. Expected structural features of these vesicles were verified by freeze-fracture electron microscopy. Proton T1 values of saline were readily decreased to less than 0.3 s by such preparations, yielding a net relaxivity of 0.6 M-1 s-1. The approach seems to be a realistic way of firmly associating a contrast agent of minimal toxicity with ordinary liposomes/vesicles in a manner that is not subject to leakage.

Glycosphingolipid interdigitation in phospholipid bilayers examined by deuterium NMR and EPR

Glycosphingolipid fatty acids commonly have up to eight methylene carbons more than do their surrounding phospholipid-attached counterparts. The resultant 'extra' segment may very well modulate glycosphingolipid function as receptor and structural element. As part of an investigation of this phenomenon, galactosylceramide was prepared with a deuterated 18-carbon fatty acid chain. Deuterium-labelled galactosylceramide was assembled at 10 mol% into unsonicated phosphatidylcholine bilayers having all 14-carbon or all 18-carbon saturated fatty acid chains (DMPC and DSPC, respectively). The systems were studied by 2H-NMR spectroscopy above and below the phase transition temperatures, Tm, of the host matrices. At comparable reduced temperatures in fluid membranes the degree of motional order exhibited by the glycolipid fatty acid was significantly higher in the phospholipid host matrix that was four carbons shorter. The fatty acid chain segment least affected by the change from long to short chain host matrix was the terminal (deutero)methyl group (an increase of 8% in quadrupolar splitting for the terminal methyl vs. 16% for deuterons at C17 and 23-28% for the remainder of the chain). Order parameter profiles for galactosylceramide were qualitatively very similar in the two host membranes, arguing against any major conformational difference between the arrangement of the 18-carbon glycolipid fatty acid in the 18-carbon vs. 14-carbon host matrices. Similarly a nitroxide spin probe covalently attached to carbon-12 of the galactosylceramide fatty acid gave clear indication of greater order in the fluid 14-carbon fatty acid phospholipid bilayer. These results are consistent with 'tethering' of the extra length of fatty acid via interdigitation into the opposing monolayer. There was no spectroscopic evidence of any intrinsic difference in glycolipid behaviour in the two fluid host matrices. 2H-NMR spectra of galactosylceramide at comparable reduced temperatures below Tm of the phospholipid bilayer were very different for 14-carbon vs. 18-carbon host matrices. The glycolipid fatty acid showed evidence of relatively reduced mobility in the shorter chain matrix.

Comparative evaluation of two membrane-based liposomal MRI contrast agents

Two phospholipids--one bearing a nitroxide free radical covalently attached to its polar headgroup, and the other bearing a similarly attached chelating agent with bound gadolinium--were compared in vivo as liposomal contrast agents for MR imaging. In each case the phospholipid contrast agent was incorporated into the membranes of sonicated unilamellar vesicles. The agent with bound gadolinium proved to be considerably more potent at highlighting regions of liposome biodistribution than did its spin-labelled analogue. Injected intramuscularly into rats, the spin-label liposomes produced local tissue contrast that persisted for 1 h; while under similar conditions, the liposomal gadolinium persisted for over 24 h. By comparison, water-soluble, nonliposomal DTPA-Gd3+ (dimeglumine), was rapidly cleared from the same intramuscular sites--appearing in kidney bladder within 15 min of injection. When delivered intravenously, maximum effect from both liposomal agents was observed in liver and spleen within 1-2 h, although the spin-label agent produced only marginal contrast. The concomitant use of fat suppression proved a valuable adjunct to liposomal contrast for imaging organs of the reticuloendothelial system.

Identification of Region-Specific Cytoskeletal and Molecular Alterations in Astrocytes of Mecp2 Deficient Animals

Rett syndrome (RTT) is a neurodevelopmental disorder that represents the most common genetic cause of severe intellectual disability in females. Most patients carry mutations in the X-linked MECP2 gene, coding for the methyl-CpG-binding protein 2 (MeCP2), originally isolated as an epigenetic transcriptional factor able to bind methylated DNA and repress transcription. Recent data implicated a role for glia in RTT, showing that astrocytes express Mecp2 and that its deficiency affects their ability to support neuronal maturation by non-cell autonomous mechanisms. To date, some molecular, structural and functional alterations have been attributed to Mecp2 null astrocytes, but how they evolve over time and whether they follow a spatial heterogeneity are two aspects which deserve further investigations. In this study, we assessed cytoskeletal features of astrocytes in Mecp2 deficient brains by analyzing their arbor complexity and processes in reconstructed GFAP⁺ cells at different ages, corresponding to peculiar stages of the disorder, and in different cerebral regions (motor and somatosensory cortices and CA1 layer of hippocampus). Our findings demonstrate the presence of defects in Mecp2 null astrocytes that worsen along disease progression and strictly depend on the brain area, highlighting motor and somatosensory cortices as the most affected regions. Of relevance, astrocyte cytoskeleton is impaired also in the somatosensory cortex of symptomatic heterozygous animals, with Mecp2 ⁺ astrocytes showing slightly more pronounced defects with respect to the Mecp2 null cells, emphasizing the importance of non-cell autonomous effects. We reported a temporal correlation between the progressive thinning of layer I and the atrophy of astrocytes, suggesting that their cytoskeletal dysfunctions might contribute to cortical defects. Considering the reciprocal link between morphology and function in astrocytes, we analyzed the effect of Mecp2 deficiency on the expression of selected astrocyte-enriched genes, which describe typical astrocytic features. qRT-PCR data corroborated our results, reporting an overall decrement of gene expression, which is area and age-dependent. In conclusion, our data show that Mecp2 deficiency causes structural and molecular alterations in astrocytes, which progress along with the severity of symptoms and diversely occur in the different cerebral regions, highlighting the importance of considering heterogeneity when studying astrocytes in RTT.

Liposomal cefoxitin in a porcine model of intra-abdominal sepsis: bactericidal efficacy

The bactericidal effect of free versus liposomal cefoxitin was evaluated in the major reticuloendothelial organs in a porcine model of intra-abdominal sepsis. Yorkshire Landrace pigs were inoculated with 3.2 x 10(10) (n = 5) or 1.4 x 10(11) (n = 7) cfu of Escherichia coli mixed in sterile feces/animal. Two treatment groups inoculated with 1.4 x 10(11) cfu were established: free cefoxitin (n = 9) and liposomal cefoxitin (n = 9). All animals were maintained under anesthesia and euthanized after 24 h. The number of E. coli recovered in the liver, lungs, and spleen was significantly affected by inoculum size (p < .05). The liver had significantly higher numbers of bacteria (p < .05) compared with the other organs, regardless of the inoculum size. The liver and the lung of the liposomal cefoxitin-treated group showed significantly lower numbers of E. coli (5.0 x 10(4) and 6.3 x 10(2), respectively) compared with the untreated (liver, 6.3 x 10(7); lung, 2.0 x 10(6)) and free cefoxitin (liver, 5.0 x 10(6); lung, 7.9 x 10(4))-treated groups (p < .05). At 2 h following the injection of free and liposomal cefoxitin, the decrease of E. coli in peritoneal fluid compared with the nontreated septic group was significant (p < .05). No growth was observed from blood cultures taken 24 h after sepsis induction. All control experiments yielded negative cultures. The results of these experiments demonstrated that liposomal cefoxitin exerts an enhanced bactericidal effect in liver and lungs during Gram-negative sepsis.

Extracellular Vesicles Released by Glioblastoma Cancer Cells Drive Tumor Invasiveness via Connexin-43 Gap Junctions

BACKGROUND

Although invasiveness is one of the major determinants of the poor glioblastoma (GBM) outcome, the mechanisms of GBM invasion are only partially understood. Among the intrinsic and environmental processes promoting cell-to-cell interaction processes, eventually driving GBM invasion, we focused on the pro-invasive role played by Extracellular Vesicles (EVs), a heterogeneous group of cell-released membranous structures containing various bioactive cargoes, which can be transferred from donor to recipient cells.

METHODS

EVs isolated from patient-derived GBM cell lines and surgical aspirates were assessed for their pro-migratory competence by spheroid migration assays, calcium imaging, and PYK-2/FAK phosphorylation. Brain invasiveness was investigated in human cortical organoids-based assembloids and in vivo orthotopic xenografts. EV molecular features were specified by multiplex bead-based flow cytometry.

RESULTS

Results unveil a self-sustaining mechanism triggering migration through autocrine release and engagement of a specific population of EVs of large size (L-EVs), isolated from either patient-derived cell lines or surgical aspirates. L-EVs act through modulation of calcium transients via Connexin 43-Gap Junctions (Cx43-GJ) and phospho-activation of PYK2. Pre-incubation with blocking antibodies targeting Cx43 hemichannels demonstrated a dose-dependent inhibition of the L-EV-mediated GBM migration. By exploiting patients' surgical aspirates, we show that only L-EVs deriving from tumoral cells, and not those with immune origin, promote tumor migration, impacting more prominently the tumoral cells with mesenchymal subtype.

CONCLUSIONS

We demonstrate that L-EVs released by GBM cells, but not by the immune cells of the tumor microenvironment, represent a relevant and unique autocrine pro-migratory input for the tumor.

[A micromethod for assaying HIV reverse transcriptase]

A micromethod for assaying HIV reverse transcriptase was developed. Accuracy, and sensitivity of the micromethod were comparable to those of the traditional macromethod. The micromethod is easy to perform and can be used in non specialised laboratories.

Progress in understanding and using over-the-counter pharmaceuticals for syndromic surveillance

INTRODUCTION

Public health researchers are increasingly interested in the potential use of monitoring data on over-the-counter (OTC) pharmaceutical sales as a source of timely information about community health. However, fundamental uncertainties persist, including how timely such information is and how best to aggregate information about hundreds of products.

OBJECTIVES

This analysis provides new information about OTC timeliness and illustrates a method of OTC product aggregation for surveillance purposes.

METHODS

Timeliness measurements were made by correlating pharmaceutical sales counts with counts of physician encounters, after adjustment to remove seasonal effects from both counts. OTC product aggregations were formed by a two-stage process. In the first stage, individual products were placed into small groups based on qualitative observations. In the second stage, a clustering algorithm was used to form supergroups (i.e., product group clusters) sharing similar sales histories.

RESULTS

Even after seasonal correction, OTC counts correlated with clinical measures of community illness. However, the lead time of nonseasonal fluctuations was substantially shorter than that for uncorrected data. The clustering approach produced 16 meaningful supergroups containing products that behaved approximately alike.

CONCLUSIONS

Measurements of OTC lead time sensitive to the timing of annual cyclic trends in the behavior of persons seeking health care do not reliably indicate the lead time observed for short-term (e. g. weekly or monthly) fluctuations in community health-care utilization.

Mecp2 knock-out astrocytes affect synaptogenesis by interleukin 6 dependent mechanisms

Synaptic abnormalities are a hallmark of several neurological diseases, and clarification of the underlying mechanisms represents a crucial step toward the development of therapeutic strategies. Rett syndrome (RTT) is a rare neurodevelopmental disorder, mainly affecting females, caused by mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene, leading to a deep derangement of synaptic connectivity. Although initial studies supported the exclusive involvement of neurons, recent data have highlighted the pivotal contribution of astrocytes in RTT pathogenesis through non-cell autonomous mechanisms. Since astrocytes regulate synapse formation and functionality by releasing multiple molecules, we investigated the influence of soluble factors secreted by Mecp2 knock-out (KO) astrocytes on synapses. We found that Mecp2 deficiency in astrocytes negatively affects their ability to support synaptogenesis by releasing synaptotoxic molecules. Notably, neuronal inputs from a dysfunctional astrocyte-neuron crosstalk lead KO astrocytes to aberrantly express IL-6, and blocking IL-6 activity prevents synaptic alterations.

Clinical-grade intranasal NGF fuels neurological and metabolic functions of Mecp2-deficient mice

MECP2 deficiency causes a broad spectrum of neuropsychiatric disorders that can affect both genders. Rett syndrome is the most common and is characterized by an apparently normal growth period followed by a regression phase in which patients lose most of their previously acquired skills. After this dramatic period, various symptoms progressively appear, including severe intellectual disability, epilepsy, apraxia, breathing abnormalities and motor deterioration. MECP2 encodes for an epigenetic transcription factor that is particularly abundant in the brain; consequently, several transcriptional defects characterize the Rett syndrome brain. The well-known deficiency of several neurotrophins and growth factors, together with the positive effects exerted by trofinetide, a synthetic analogue of insulin-like growth factor 1, in Rett patients and in mouse models of Mecp2 deficiency, prompted us to investigate the therapeutic potential of nerve growth factor. Initial in vitro studies demonstrated a healing effect of recombinant human GMP-grade NGF (rhNGF) on neuronal maturation and activity in cultured Mecp2-null neurons. Subsequently, we designed in vivo studies with clear translational potential using intranasally administered rhNGF already used in the clinic. The efficacy of rhNGF in vivo in Mecp2-null hemizygous male mice and heterozygous female mice was assessed. General well-being was evaluated by a conventional phenotypic score and motor performance through the Pole and Beam Walking tests, while cognitive function and interaction with the environment were measured by the Novel Object Recognition test and the Marble Burying test, respectively. At the end of the treatment, mouse cortices were dissected and bulk RNA sequencing was performed to identify the molecular pathways involved in the protective effects of rhNGF. In both male and female mouse models of Rett syndrome, rhNGF exerted positive effects on cognitive and motor functions. In male hemizygous mice, which suffer from significantly more severe and rapidly advancing symptoms, the drug's ability to slow the disease's progression was more pronounced. The unbiased research for the molecular mechanisms triggering the observed benefits revealed a strong positive effect on gene sets related to oxidative phosphorylation, mitochondrial structure and function. These results were validated by demonstrating the drug's ability to improve mitochondrial structure and respiration in Mecp2-null cerebral cortices. Furthermore, Gene Ontology analyses indicated that NGF exerted the expected improvement in neuronal maturation. We conclude that intranasal administration of rhNGF is a non-invasive and effective route of administration for the treatment of Rett syndrome and possibly for other neurometabolic disorders with overt mitochondrial dysfunction.