Arsenic trioxide liposomes: encapsulation efficiency and in vitro stability

The use of arsenic-containing compounds in cancer therapy is currently being re-considered, after the recent approval of arsenic trioxide (Trisenox) for the treatment of relapsed promyelocytic leukemia (PML). In an attempt to prepare a carrier system to minimize the toxicity of this drug, the aim of this study is to prepare and characterize liposomes encapsulating arsenic trioxide (ATO). For this, we prepared different types of liposomes entrapping ATO: large multilamellar (MLV), sonicated (SUV) and dried reconstituted vesicles (DRV). The techniques used were: thin film hydration, sonication and the DRV method, respectively. Two lipid compositions were studied for each liposome type, EggPC/Chol (1:1) and DSPC/Chol (1:1). After liposome preparation, drug encapsulation was evaluated by measuring arsenic in liposomes. For this, energy-dispersive X-ray fluorescence spectroscopy or atomic absorption was used. In addition, the retention of the drug in the liposomes was evaluated after incubating the liposomes in buffer at 37 degrees C. The experimental results reveal that encapsulation of ATO in liposomes ranges between 0.003 and 0.506 mol/ mol of lipid, and is highest in the DRV vesicles and lowest in the small unilamellar vesicles, as anticipated. Considering the in vitro stability of ATO-encapsulating liposomes: 1) For the PC/Chol liposomes (DRV and MLV), after 24 hours of incubation, more than 70% (or 90% in some cases) of the initially encapsulated amount of ATO was released. 2) The liposomes composed of DSPC/Chol could retain substantially higher amounts of ATO, especially the DRV liposomes (54% retained after 24 h). 3) In the case of PC/Chol, temperature of incubation has no effect on the ATO release after 24 hours, but affects the rate of ATO release in the MLV liposomes, while for the DSPC/Chol liposomes there is a slight increase (statistically insignificant) of ATO release at higher temperature.     

Colloidal stability of carbon nanotubes in an aqueous dispersion of phospholipid

Within the family of nanomaterials, carbon nanotubes (CNTs) have emerged as a new efficient scaffold for studying molecular interactions at interfaces. Poor dispersability of CNTs in any solvent presents a considerable drawback for the development of novel functional composite structures. Previous studies have demonstrated that the solubility of CNTs can be greatly enhanced by employing appropriate surfactants, some of them being biological molecules. In this work, we study the noncovalent wrapping of lipid chains onto the graphitic surface of single-walled material (SWCNTs) by electron microscopy and Raman spectroscopy. Stable and homogenous aqueous suspensions of SWCNTs in the presence of lipids have been prepared, whereas their electrophoretic mobility was confirmed by zeta-potential measurements. Raman measurements revealed that smaller diameter SWCNTs are preferentially dispersed by lipid molecules in the aqueous supernatant part of the prepared suspension.     

Oxidative stress biomarkers responses to physical overtraining: implications for diagnosis

Overtraining syndrome is characterized by declining performance and transient inflammation following periods of severe training with major health implications for the athletes. Currently, there is no single diagnostic marker for overtraining. The present investigation examined the responses of oxidative stress biomarkers to a resistance training protocol of progressively increased and decreased volume/intensity. Twelve males (21.3+/-2.3 years) participated in a 12-week resistance training consisting of five 3-week periods (T1, 2 tones/week; T2, 8 tones/week; T3, 14 tones/week; T4, 2 tones/week), followed by a 3-week period of complete rest. Blood/urine samples were collected at baseline and 96 h following the last training session of each period. Performance (strength, power, jumping ability) increased after T2 and declined thereafter, indicating an overtraining response. Overtraining (T3) induced sustained leukocytosis, an increase of urinary isoprostanes (7-fold), TBARS (56%), protein carbonyls (73%), catalase (96%), glutathione peroxidase, and oxidized glutathione (GSSG) (25%) and a decline of reduced glutathione (GSH) (31%), GSH/GSSG (56%), and total antioxidant capacity. Isoprostanes and GSH/GSSG were highly (r=0.764-0.911) correlated with performance drop and training volume increase. In conclusion, overtraining induces a marked response of oxidative stress biomarkers which, in some cases, was proportional to training load, suggesting that they may serve as a tool for overtraining diagnosis.     

Plant virus infection development as affected by heavy metal stress

The work was focused on the investigation of possible dependencies between the development of viral infection in plants and the presence of high heavy metal concentrations in soil. Field experiments have been conducted in order to study the development of systemic tobacco mosaic virus (TMV) infection in Lycopersicon esculentum L. cv. Miliana plants under effect of separate salts of heavy metals Cu, Zn and Pb deposited in soil. As it is shown, simultaneous effect of viral infection and heavy metals in tenfold maximum permissible concentration leads to decrease of total chlorophyll content in experiment plants mainly due to the degradation of chlorophyll a. The reduction of chlorophyll concentration under the combined influence of both stress factors was more serious comparing to the separate effect of every single factor. Plants' treatment with toxic concentrations of lead and zinc leaded to slight delay in the development of systemic TMV infection together with more than twofold increase of virus content in plants that may be an evidence of synergism between these heavy metal's and virus' effects. Contrary, copper although decreased total chlorophyll content but showed protective properties and significantly reduced amount of virus in plants.     

Incorporation of PEG-lipids in arsonoliposomes results in formation of highly stable arsenic-containing vesicles

We investigated the effect of pegylation on the physical stability, morphology and membrane integrity of arsonoliposomes. Arsonoliposomes composed of distearoylglycerophosphocholine (DSPC), cholesterol (Chol) and the palmitoyl side chain arsonolipid (with concentrations ranging from 0 mol% [DSPC/Chol vesicles] to 53 mol% of total lipid) containing either 4 or 8 mol% DPPE-PEG2000 or DSPE-PEG2000, were prepared by sonication. Arsonoliposome membrane integrity was evaluated by measuring the retention of encapsulated calcein in vesicles (during incubation in buffer or fetal calf serum [FCS]) while physical stability was evaluated by measuring vesicle dispersion turbidity (during incubation in water or CaCl(2)). Vesicle morphology was studied by cryo-electron microscopy. Experimental results show that: (i) PEG-lipids are incorporated in arsonoliposomes (as confirmed by the vesicle zeta potential modulation), (ii) pegylation of arsonoliposomes prevents their aggregation and fusion in the presence of calcium ions and (iii) when 8 mol% of PEG-DSPE is incorporated in arsonoliposomes based on their arsonolipid content, two groups of pegylated vesicles are formed: low content arsonoliposomes (<20 mol% arsonolipid) which are highly leaky and high content arsonoliposomes (>27 mol% arsonolipid) which are highly stable (70% calcein retention after 24h incubation in fetal calf serum [FCS]). In addition to high membrane integrity, the high content pegylated arsonoliposomes are morphologically perfect round-shaped vesicles without the sharp edges typically observed with non-pegylated DSPC-containing arsonoliposomes.     

Thermal behavior of novel non-sonicated arsonolipid-containing liposomes

The thermal properties of novel arsonolipid-containing liposomes in PBS pH 7.4 and in water in absence and presence of Ca(2+) ions are reported. Liposomes composed of arsonolipids with different acyl chains (C(12), C(16) and C(18)) were prepared by the one step method. Microcalorimetry results showed that (i) the thermotropic transitions of arsonoliposomes (in PBS, pH 7.4, and in water) increase as a function of arsonolipid fatty acyl chain length, (ii) arsonoliposomes of long fatty acyl chain arsonolipids (C(16) and C(18)) showed higher enthalpy and transition temperature in the buffer compared to those observed in water (for arsonoliposomes of C(12)-fatty acyl chain arsonolipid, the order was reversed which might be attributed to their different structure), and (iii) the presence of 2 mM CaCl(2) has more pronounced effects on the thermal properties of arsonoliposomes in distilled water than in buffer, which suggests that the ionic strength of the dispersion medium plays an important role in determining the thermal properties of arsonoliposomes.     

Plant responses to butterfly oviposition partly explain preference–performance relationships on different brassicaceous species

Oecologia - The preference–performance hypothesis (PPH) states that herbivorous female insects prefer to oviposit on those host plants that are best for their offspring. Yet, past attempts to...     

The effect of rearing history and aphid density on volatile‐mediated foraging behaviour of Diaeretiella rapae

1. Parasitoid females foraging for hosts rely on cues derived from the insect host, the host plant and/or their interaction, and all of these can be learned during the immature and adult stages. 2. The present study investigated the importance of rearing history on foraging behaviour of Diaeretiella rapae, an endoparasitoid often associated with aphids feeding on brassicaceous plant species. 3. Parasitoids were reared on one of the four possible combinations, comprising two brassicaceous host plant species, Brassica nigra or Raphanus sativus, and two aphid species Brevicoryne brassicae or Myzus persicae. These parasitoids were tested in a Y‐tube olfactometer and given the choice between volatiles emitted by an aphid‐infested plant (25 or 100 aphids per plant) and an uninfested control plant. The parasitoid's responses were compared when offered: (i) the same plant–aphid combination as the one on which it had been reared; (ii) the same host plant infested with the alternative aphid species; or (iii) an alternative plant with the alternative aphid species. 4. Aphid density did affect the behavioural responses to the various odour sources, but rearing history did not. Diaeretiella rapae only preferred aphid‐induced to non‐induced plant volatiles at low aphid infestation level, whereas they did not discriminate between volatiles at high aphid infestation level. 5. It is concluded that aphid‐induced volatiles of brassicaceous plants play an important role during host habitat location, but seem less important for parasitoids to locate the aphid host itself. The data are discussed in the light of manipulation of host plant defences by aphids.