Liposomal entrapment of suramin(II): interaction of suramin with phospholipids of various chain lengths

Building Blocks to Design Liposomal Delivery Systems

The flexibility of liposomal carriers does not just simply rely on their capability to encapsulate various types of therapeutic substances, but also on the large array of components used for designing liposome-based nanoformulations. Each of their components plays a very specific role in the formulation and can be easily replaced whenever a different therapeutic effect is desired. It is tempting to describe this by an analogy to Lego blocks, since a whole set of structures, differing in their features, can be designed using a certain pool of blocks. In this review, we focus on different design strategies, where a broad variety of liposomal components facilitates the attainment of straightforward control over targeting and drug release, which leads to the design of the most promising systems for drug delivery. The key aspects of this block-based architecture became evident after its implementation in our recent works on liposomal carriers of antisense oligonucleotides and statins, which are described in the last chapter of this review.

Targeting ischemic penumbra: part I - from pathophysiology to therapeutic strategy

Penumbra is the viable tissue around the irreversibly damaged ischemic core. The purpose of acute stroke treatment is to salvage penumbral tissue and to improve brain function. However, the majority of acute stroke patients who have treatable penumbra are left untreated. Therefore, developing an effective non-recanalizational therapeutics, such as neuroprotective agents, has significant clinical applications. Part I of this serial review on "targeting penumbra" puts special emphases on penumbral pathophysiology and the development of therapeutic strategies. Bioenergetic intervention by massive metabolic suppression and direct energy delivery would be a promising future direction. An effective drug delivery system for this purpose should be able to penetrate BBB and achieve high local tissue drug levels while non-ischemic region being largely unaffected. Selective drug delivery to ischemic stroke penumbra is feasible and deserves intensive research.

The effect of different lipid components on the in vitro stability and release kinetics of liposome formulations

Liposomes are colloidal carriers that form when certain (phospho)lipid molecules are hydrated in an aqueous media with some energy input. The ideal liposome formulation with optimum stability will improve drug delivery by decreasing the required dose and increasing the efficacy of the entrapped drug at the target organ or tissue. The most important parameter of interest in this article was to compare the efficacy of three different liposomes formulated with DSPC, DMPC, and DPPC, all saturated neutral phospholipids with different acyl chain lengths and transition temperatures. DMPC has a phase transition temperature (Tc) below 37 degrees C, whereas the other two phospholipids possess Tcs above the physiological temperature. These lipids were then added to a cholesterol concentration of 21% to optimize the stability of the vesicles. The liposomes were prepared by a sonication and incubated in phosphate buffered saline (PBS) at 4 degrees C and 37 degrees C. The encapsulation efficiency, initial size, and drug retention of the vesicles were tested over a 48-hr period employing radiolabeled inulin as a model drug. The phase transition temperature of liposomes, which depends on the Tc of the constituent lipids, was an important factor in liposome stability. Of all the liposomes tested, the greatest encapsulation efficiency was found for the DSPC liposomes (2.95%) that also had the greatest drug retention over 48 hr at both 4 degrees C (87.1 +/- 6.8%) and 37 degrees C (85.2 +/- 10.1%), none of these values being significantly different from time zero. The lowest drug retention was found for DMPC liposomes for which a significant difference in drug retention was seen after only 15 min at both 4 degrees C (47.3 +/- 6.9%) and 37 degrees C (53.8 +/- 4.3%). The DPPC liposomes showed a significant difference in drug retention after 3 hr at 4 degrees C (62.1 +/- 8.2%) and after 24 hr at 37 degrees C (60.8 +/- 8.9%). Following the initial drop at certain time intervals a plateau was reached for all of the liposome formulations after which no significant difference in drug retention was observed. In conclusion, liposomes with higher transition temperatures appear to be more stable in PBS either at 4 degrees C or 37 degrees C, indicating that the increase in acyl chain length (and therefore transition temperature) is directly proportional to stability.

Preparation of liposomes with glucose binding sites: liposomes containing di-branched amino acid derivatives

Di-branched amino acid derivatives, such as dihexadecyl-glutamate-glutamine (DHD-glu-gln), dihexadecyl-glutamate-asparagine (DHD-glu-asn) and dihexadecyl-glutamate-glutamic acid (DHD-glu-glu), were synthesized, and then incorporated into lipid vesicles (liposomes) using dipalmitoylphosphatidylcholine (DPPC). To form binding sites toward glucose, the liposomes containing amino acid derivatives were mixed with glucose above the phase transition temperature (PTT) of DPPC and subsequently the temperature was lowered below the PTT. The glucose-binding affinity of liposomes containing amino acid derivative with or without glucose imprinting was evaluated by surface plasmon resonance (SPR) and equilibrium dialysis technique. SPR of liposomes containing each amino acid derivative or three amino acid derivatives revealed that only the liposomes containing all three amino acid derivatives had glucose-binding affinity and that the glucose-imprinting process was essential to fix the amino acid derivatives into a glucose binding site on the liposomes. Equilibrium dialysis studies of glucose-imprinted liposomes produced curvilinear Scatchard plots, indicating that the amino acid derivatives play a role in glucose binding. Di-branched amino acid derivatives synthesized in this study are promising agent for the development of biocompatible synthetic glucose binding materials.