Ann Mari Holsæter

Successful co-encapsulation of benzoyl peroxide and chloramphenicol in liposomes by a novel manufacturing method - dual asymmetric centrifugation

&NA; Encapsulation of more than one active pharmaceutical ingredient into nanocarriers such as liposomes is an attractive approach to achieve a synergic drug effect and less complicated dosing schedules in multi‐drug treatment regimes. Liposomal drug delivery in acne treatment may improve drug efficiency by targeted delivery to pilosebaceous units, reduce adverse effects and improve patient compliance. We therefore aimed to co‐encapsulate benzoyl peroxide (BPO) and chloramphenicol (CAM) into liposomes using the novel liposome processing method – dual asymmetric centrifugation (DAC). Liposomes were formed from soybean lecithin, propylene glycol and distilled water (2:1:2 w/v/v ratio), forming a viscous liposome dispersion. Liposomes containing both drugs (BPO‐CAM‐Lip), single drug (BPO‐Lip and CAM‐Lip), and empty liposomes were prepared. Drug entrapment of BPO and CAM was determined by a newly developed HPLC method for simultaneous detection and quantification of both drugs. Encapsulation of around 50% for BPO and 60% for CAM respectively was obtained in both single‐drug encapsulated formulations (BPO‐Lip and CAM‐Lip) and co‐encapsulated formulations (BPO‐CAM‐Lip). Liposome sizes were comparable for all liposome formulations, ranging from 130 to 150 nm mean diameter, with a polydispersity index < 0.2 for all formulations. CAM exhibited a sustained release from all liposomal formulations, whereas BPO appeared retained within the liposomes. BPO retention could be attributed to its poor solubility. However, HaCaT cell toxicity was found dependent on BPO released from the liposomes. In the higher concentration range (4% v/v), liposomal formulations were less cytotoxic than the corresponding drug solutions used as reference. We have demonstrated that DAC is a fast, easy, suitable method for encapsulation of more than one drug within the same liposomes. Graphical abstract Figure. No caption available.

The isolated perfused human skin flap model: A missing link in skin penetration studies?

&NA; Development of effective (trans)dermal drug delivery systems requires reliable skin models to evaluate skin drug penetration. The isolated perfused human skin flap remains metabolically active tissue for up to 6 h during in vitro perfusion. We introduce the isolated perfused human skin flap as a close‐to‐in vivo skin penetration model. To validate the models ability to evaluate skin drug penetration the solutions of a hydrophilic (calcein) and a lipophilic (rhodamine) fluorescence marker were applied. The skin flaps were perfused with modified Krebs‐Henseleit buffer (pH 7.4). Infrared technology was used to monitor perfusion and to select a well‐perfused skin area for administration of the markers. Flap perfusion and physiological parameters were maintained constant during the 6 h experiments and the amount of markers in the perfusate was determined. Calcein was detected in the perfusate, whereas rhodamine was not detectable. Confocal images of skin cross‐sections shoved that calcein was uniformly distributed through the skin, whereas rhodamine accumulated in the stratum corneum. For comparison, the penetration of both markers was evaluated on ex vivo human skin, pig skin and cellophane membrane. The proposed perfused flap model enabled us to distinguish between the penetrations of the two markers and could be a promising close‐to‐in vivo tool in skin penetration studies and optimization of formulations destined for skin administration. Graphical abstract Figure. No caption available.

Development and optimization of a new processing approach for manufacturing topical liposomes-in-hydrogel drug formulations by dual asymmetric centrifugation

Abstract Objective: The objective of the present study was to utilize dual asymmetric centrifugation (DAC) as a novel processing approach for the production of liposomes-in-hydrogel formulations. Materials and methods: Lipid films of phosphatidylcholine, with and without chloramphenicol (CAM), were hydrated and homogenized by DAC to produce liposomes in the form of vesicular phospholipid gels with a diameter in the size range of 200−300 nm suitable for drug delivery to the skin. Different homogenization processing parameters were investigated along with the effect of adding propylene glycol (PG) to the formulations prior to homogenization. The produced liposomes were incorporated into a hydrogel made of 2.5% (v/v) soluble β-1,3/1,6-glucan (SBG) and mixed by DAC to achieve a homogenous liposomes-in-hydrogel-formulation suitable for topical application. Results and discussion: CAM-containing liposomes with a vesicle diameter of 282 ± 30 nm and polydispersity index (PI) of 0.13 ± 0.02 were successfully produced by DAC after 50 min centrifugation at 3500 rpm, and homogenously (< 4% content variation) incorporated into the SBG hydrogel. Addition of PG decreased the necessary centrifugation time to 2 min and 55 s, producing liposomes of 230 ± 51 nm and PI of 0.25 ± 0.04. All formulations had an entrapment efficiency of approximately 50%. Conclusion: We managed to develop a relatively fast and reproducible new method for the production of liposomes-in-hydrogel formulations by DAC.

Sprayable Carbopol hydrogel with soluble beta-1,3/1,6-glucan as an active ingredient for wound healing – Development and in-vivo evaluation

Abstract Chronic wounds represent a significant health problem worldwide. There is a need for advanced‐ and cost‐efficient wound healing products able to increase patient comfort and reduce the healing time. The aim of this study was to develop a sprayable hydrogel dressing with beta‐glucan (&bgr;G) as the active ingredient, targeting future application in the treatment of both chronic and burn wounds. The &bgr;G was chosen as an active ingredient because of its promising wound healing capabilities, whereas Carbopol 971P NF (Carbopol) was chosen as the thickening agent in the formulation due to several attractive characteristics such as its low viscosity, low toxicity, high transparency and good ion tolerance. Four different hydrogel formulations were prepared with varying Carbopol concentrations. The higher Carbopol concentration, 0.5% (w/w), was used to prepare three formulations comprising the HighCP:No&bgr;G, HighCP:Low&bgr;G and the HighCP:Medium&bgr;G formulation, respectively. Lower Carbopol concentration, 0.25% (w/w), was used to prepare the LowCP:High&bgr;G formulation. The content of &bgr;G varied from 0.25% in the HighCP:Low&bgr;G, 0.5% in the HighCP:Medium&bgr;G and 1.0% (w/w) in the LowCP:High&bgr;G formulation, respectively. The first part of the study focused on the rheological characterization of the hydrogels and the fluid affinity testing. All formulations were confirmed to be stable gels; the &bgr;G was shown to augment the gel strength by increasing the yield strength of the gel in a dose dependent manner. The stability of the formulations containing either Carbopol alone or in a combination with &bgr;G did not deteriorate over 26 weeks, and the fluid donation and absorption study indicated a fluid donation profile, which favors healing of dry wounds. The in vivo efficacy of the formulations, evaluated in the modified diabetic male mice (db/db mice), showed that Carbopol alone was unable to induce improved healing and caused adverse reactions in some wounds. The inclusion of &bgr;G increased the epithelialization and wound contraction in the db/db mice when given at high &bgr;G:Carbopol ratio. The positive effect of &bgr;G was, however, not sufficient to counteract the adverse effect of Carbopol, thus a more suitable thickening agent should be investigated for further development of a sprayable wound care product. Graphical abstract Figure. No Caption available.

Old drug, new wrapping - A possible comeback for chloramphenicol?

The antimicrobial drug chloramphenicol (CAM) exhibits activity against resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). However, its use has been limited due to its toxicity. As the threat of antibiotic resistance continues to grow, a promising approach might be to increase the use of historical antimicrobial agents that demonstrate clinical efficacy, but are hampered by toxicity. We therefore aimed to prepare a liposome-in-hydrogel system for dermal delivery of CAM. Chitosan (CS) was used as the hydrogel vehicle due to its antimicrobial activity and excellent biocompatibility. All critical preparation steps were carried out by dual centrifugation (DC). The DC-method proved to be fast and simple, and organic solvents were avoided in all processing steps. Liposomes with high drug entrapment (49-56%), low polydispersity and a size of approximately 120nm were produced. Mixing of liposomes into CS-hydrogel by DC produced a homogenous liposomes-in-hydrogel system. Bioadhesive properties were good and comparable to plain CS-hydrogel formulations. Ex vivo permeation studies using pig skin indicated a sustained release of CAM and limited skin permeation. The in vitro antimicrobial activity of CAM in the new liposome-in-hydrogel formulation was similar or better as compared to CAM in solution. Thus, the new formulation was considered highly promising.

Beta-glucan-loaded nanofiber dressing improves wound healing in diabetic mice

&NA; The increased prevalence of chronic wounds requires novel treatment options. The aim of this study was to develop a beta‐glucan (&bgr;G)‐loaded nanofiber wound dressing. Nanofibers were prepared using the needle‐free Nanospider™ technology, an electrospinning method which enables the production of nanofibers at an industrial scale. The &bgr;G was selected as active ingredient based on its confirmed wound healing potential in both animals and humans. Hydroxypropyl methylcellulose (HPMC) and polyethylene oxide (PEO) were included as copolymers. Rheological profiles of spinning solutions containing HPMC, PEO, &bgr;G, ethanol and water, were optimized. The nanofiber formation was confirmed by Field Emission Scanning Electron Microscopy (FE‐SEM), and both nanofibers with (&bgr;G‐nanofibers) or without &bgr;G (No&bgr;G‐nanofibers) were evaluated by their swelling index and FT‐IR spectroscopy. The formulations, active ingredient and excipients were tested for their possible in vitro toxicity in keratinocytes. Finally, the wound healing potential of the nanofibers was tested in externally induced excisional wounds in male diabetic db/db mice. Three different doses of &bgr;G‐nanofibers and the &bgr;G‐free, No&bgr;G‐nanofibers, were evaluated for their in vivo wound healing efficacy. All nanofiber‐treatments provided improved wound healing as compared to the negative control (water). All &bgr;G‐nanofiber treated groups exhibited significantly improved wound healing as compared to the No&bgr;G‐nanofiber treated group, indicating the potential of &bgr;G‐nanofibers as wound dressing. Graphical abstract Figure. No caption available.

Going skin deep: A direct comparison of penetration potential of lipid-based nanovesicles on the isolated perfused human skin flap model

Graphical abstract Figure. No Caption available. ABSTRACT Phospholipid‐based nanocarriers are attractive drug carriers for improved local skin therapy. In the present study, the recently developed isolated perfused human skin flap (IPHSF) model was used to directly compare the skin penetration enhancing potential of the three commonly used nanocarriers, namely conventional liposomes (CLs), deformable liposomes (DLs) and solid lipid nanoparticles (SLNs). Two fluorescent markers, calcein (hydrophilic) or rhodamine (lipophilic), were incorporated individually in the three nanosystems. The nanocarrier size ranged between 200 and 300 nm; the surface charge and entrapment efficiency for both markers were dependent on the lipid composition and the employed surfactant. Both carrier‐associated markers could not penetrate the full thickness human skin, confirming their suitability for dermal drug delivery. CLs exhibited higher retention of both markers on the skin surface compared to DLs and SLNs, indicating a depo formation. DLs and SLNs enabled the deeper penetration of the two markers into the skin layers. In vitro and ex vivo skin penetration studies performed on the cellophane membrane and full thickness pig/human skin, respectively, confirmed the findings. In conclusion, efficient dermal drug delivery can be achieved by optimization of a lipid nanocarrier on the suitable skin‐mimicking model to assure system’s accumulation in the targeted skin layer.

Deformable liposomes for skin therapy with human epidermal growth factor: The effect of liposomal surface charge

&NA; The topical administration of exogenous human epidermal growth factor (hEGF) is a promising approach for improved chronic wound therapy. To develop therapeutically superior hEGF formulation, we prepared hEGF‐containing neutral (NDLs), cationic (CDLs) and anionic (ADLs) deformable liposomes (DLs), respectively, since it is expected that the liposomal surface charge can affect both the liposomal physicochemical properties, their skin penetration potential and therapeutic efficacy of liposome‐associated drug. All prepared liposomes were of similar size (300–350 nm) with high hEGF load (˜80% entrapment efficacy). Among the studied DLs, ADLs were found to be most promising for sustained release of hEGF, as assessed in vitro using the polyamide membrane. Ex vivo studies revealed that all DLs were excellent systems for skin therapy with hEGF and no penetration of hEGF through the full thickness human skin was detected. ADLs provided a depot exhibiting the highest hEGF retention onto the human skin surface. ADLs also revealed enhanced mitogenic activities in human fibroblasts compared to both NDLs and CDLs after 48 hrs treatment. Moreover, hEGF‐containing ADLs significantly enhanced mitogenic activity in fibroblast as compared to activity of hEGF solution (positive control). Similar trends were observed in human keratinocytes after 24 hrs of treatment. We proved that the liposomal surface charge affects the therapeutic potential of hEGF‐containing liposomes. hEGF‐containing ADLs can be a promising nanosystem‐based formulation for localized therapy of chronic wounds.

Ceramide-containing liposomes with doxorubicin: time and cell-dependent effect of C6 and C12 ceramide

Doxorubicin, a widely used chemotherapeutic drug, has several potential high-risk side effects including cardiomyopathy. Furthermore, cellular resistance to this drug develops with time. By using liposomes as carrier vesicles both the side effects and drug resistance might be avoided. In this study we have investigated the cytotoxic effect of doxorubicin encapsulated in liposomes with and without ceramides containing 6 or 12 carbon atoms in the N-amidated fatty acyl chains. The short-chain ceramide species were included in the liposomal compositions due to their pro-apoptotic properties, which might cause a synergistic anticancer effect. We demonstrate that the ceramide species enhance the liposomal doxorubicin toxicity in a cell-specific manner. The C6-ceramide effect is most pronounced in cervical cancer cells (HeLa) and colon cancer cells (HCT116), whereas the C12-ceramide effect is strongest in breast cancer cells (MDA-MB-231). Moreover, the study reveals the importance of investigating cell toxicity at several time points and in different cell-lines, to assess drug-and formulation-induced cytotoxic effects in vitro. Furthermore, our data show that the cytotoxicity obtained with the nanocarriers in vitro, does not necessarily reflect their ability to inhibit tumor growth in vivo. We speculate that the larger effect of Caelyx® than our liposomes in vivo is due to a greater in vivo stability of Caelyx®.