Calorimetry and Langmuir-Blodgett studies on the interaction of a lipophilic prodrug of LHRH with biomembrane models.

The interaction between an amphiphilic luteinizing hormone-releasing hormone (LHRH) prodrug that incorporated a lipoamino acid moiety (C12-LAA) with biological membrane models that consisted of multilamellar liposomes (MLVs) and phospholipid monolayers, was studied using Differential Scanning Calorimetry (DSC) and Langmuir-Blodgett film techniques. The effect of the prodrug C12[Q1]LHRH on the lipid layers was compared with the results obtained with the pure precursors, LHRH and C12-LAA. Conjugation of LHRH with a LAA promoiety showed to improve the peptide interaction with biomembrane models. Basing on the calorimetric findings, the LAA moiety aided the transfer of the prodrug from an aqueous solution to the biomembrane model.

A novel biomaterial for osteotropic drug nanocarriers: synthesis and biocompatibility evaluation of a PLGA-ALE conjugate.

BACKGROUND & AIMS: Osteotropic drug-delivery systems have been proposed as a means to provide drugs with affinity to bone tissues. Drugs or proteins have been linked chemically to bone-seeking agents, such as bisphosphonates (BPs); alternatively, drug-loaded nanoparticles have been used to target specific tissues, such as tumor areas. In our current research, these approaches were merged by synthesizing a novel bone-seeking polymer conjugate, from which targetable nanoparticles can be produced. MATERIALS & METHODS: An amino-BP, alendronate (ALE) was bound covalently to a biodegradable polymer, poly(lactic-co-glycolide) (PLGA), containing a free end carboxylic group. Blood compatibility and cytotoxicity were assessed in vitro. RESULTS & DISCUSSION: By a classical solvent-evaporation method, nanoparticles with a mean size of 200-300 nm were prepared from the conjugate; sterilization was achieved by gamma-irradiation, confirming their potential as injectable drug nanocarriers. Owing to the presence of the BP residue, PLGA-ALE nanoparticles were adsorbed onto hydroxyapatite to a higher extent than pure PLGA nanoparticles. The PLGA-ALE conjugate did not induce either hemolysis or alterations of the plasmatic phase of coagulation, or cytotoxic effects on endothelial cells and trabecular osteoblasts. CONCLUSION: The prepared conjugate represents a novel biomaterial that is able to provide nanoparticles, which can be further loaded with drugs, such as anticancer agents, and addressed to osteolytic or other bone diseases.

Biocompatibility of poly(D,L-lactide-co-glycolide) nanoparticles conjugated with alendronate.

Nanoparticles made of a conjugate of poly(D,L-lactide-co-glycolide) with alendronate (PLGA-ALE NPs), were prepared by emulsion/solvent evaporation technique. The conjugation yield, determined by MALDI TOF analysis, was 30-35%. PLGA-ALE NPs size, evaluated by photon correlation spectroscopy, was 198.7+/-0.2 nm. Haemocompatibility studies using different concentrations of PLGA-ALE NPs did not show any significant effect on haemolysis, leukocyte number, platelet activation, APTT and complement consumption, in comparison with blood incubated with phosphate buffered saline (PBS). A significant reduction of the prothrombin activity was demonstrated after incubation with 560 microg/ml of PLGA-ALE NPs; a significant increase was observed at the highest dilutions. The viability of human umbilical vein endothelial cells and bone marrow stromal cells (BMSC), evaluated through the neutral red test, was not affected by PLGA-ALE NPs. There were no significant differences in cell-associated alkaline phosphatase between BMSC incubated with PLGA-ALE NP- and PBS-added media. These results demonstrated that PLGA-ALE NPs had an acceptable degree of blood compatibility and were not cytotoxic; therefore, they may be considered suitable for intravenous administration.

Enhancement of drug affinity for cell membranes by conjugation with lipoamino acids II. Experimental and computational evidence using biomembrane models.

Lipoamino acids (LAAs) are promoieties able to enhance the amphiphilicity of drugs, facilitating their interaction with cell membranes. Experimental and computational studies were carried out on two series of lipophilic amide conjugates between a model drug (tranylcypromine, TCP) and LAA or alkanoic acids containing a short, medium or long alkyl side chain (C-4 to C-16). The effects of these compounds were evaluated by monolayer surface tension analysis and differential scanning calorimetry using dimyristoylphosphatidylcholine monolayers and liposomes as biomembrane models. The experimental results were related to independent calculations to determine partition coefficient and blood-brain partitioning. The comparison of TCP-LAA conjugates with the related series of TCP alkanoyl amides confirmed that the ability to interact with the biomembrane models is not due to the mere increase of lipophilicity, but mainly to the amphipatic nature and the kind of LAA residue.

Temperature and pressure dependence of quercetin-3-O-palmitate interaction with a model phospholipid membrane: film balance and scanning probe microscopy study.

The molecular interaction of quercetin-3-O-palmitate (QP) with dimyristoylphosphatidylcholine (DMPC) has been studied. Film balance measurements of the average molecular area vs QP molar fraction in DMPC/QP mixed monolayers showed that relevant positive deviations from ideality, i.e., a less dense monolayer packing, occurred for a temperature of 10 degrees C, below the critical melting transition temperature of DMPC monolayers T c m approximately equal 20 degrees C), while ideal behavior was observed at 37 degrees C, above this phase transition temperature. The positive deviation observed at low temperatures in the average molecular area increased with the surface pressure. Scanning probe microscopy measurements performed on mixed monolayers transferred on mica showed that the deviations from ideality were connected to the formation of nanometric-scale QP-rich domains. However, the formation of aggregates was observed only for relatively high-QP molar fractions X QP > or = 0.25 at 10 degrees C, while it was not observed at 37 degrees C, i.e., when the ideal mixing was found at the air/water interface. The observed effects are explained in terms of a temperature- and surface pressure-dependent phase-separation process based on the predominance at low temperature and low molecular mobility of QP-QP and DMPC-DMPC aggregation forces, prompting the formation of QP-rich domains embedded in a DMPC-rich matrix. High temperature prompts the QP/DMPC ideal mixing.

Structure effect on the interaction of phenylurea herbicides with model biomembrane as an environmental mobility parameter.

During recent years, intensive use of herbicides has raised increasing concern mainly due to their massive pollution of the environment. As these herbicides are directly or indirectly toxic to a wide range of organisms, their potential for contaminating soil, surface water, and groundwater makes these xenobiotics of special interest from a health and environmental point of view. Knowledge of the mechanisms by which they exert their toxic effects is becoming a need. Because of the herbicides' lipophilicity, a possible site of interaction in the cell is represented by biomembranes. The interaction of four herbicides, difenoxuron, diuron, linuron, and metoxuron, with model membranes constituted of dimyristoylphosphatidylcholine multilamellar vesicles was investigated by the differential scanning calorimetry technique. The aim was to study the effects exerted by an increasing amount of the examined compounds on thermotropic behavior of the model phospholipid membranes and to correlate the obtained results with structural features of the herbicides due to their environmental mobility. Among the herbicides studied, linuron is the most effective in perturbing the ordinate structure of vesicles forming phospholipids, whereas metoxuron is the least effective and the others exert an intermediate effect. Linuron exerts its effect both on the transition temperature of the gel to the liquid crystalline phase and on the enthalpy change. Difenoxuron, diuron, and metoxuron cause a change in the transition temperature but have an insignificant effect on the enthalpy change. The calorimetric results, correlated with the structural features of the herbicides, are consistent with their partition coefficient, log K(ow), suggesting that the more hydrophobic compound character causes a greater liposolubility and consequential cellular absorption with more effectiveness on the membrane order.