Cyproterone Acetate Loading to Lipid Nanoparticles for Topical Acne Treatment: Particle Characterisation and Skin Uptake

Purpose Topical cyproterone acetate (CPA) treatment of skin diseases should reduce side effects currently excluding the use in males and demanding contraceptive measures in females. To improve skin penetration of the poorly absorbed drug, we intended to identify the active moiety and to load it to particulate carrier systems. Materials and Methods CPA metabolism in human fibroblasts, keratinocytes and a sebocyte cell line as well as androgen receptor affinity of native CPA and the hydrolysis product cyproterone were determined. CPA 0.05% loaded solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), a nanoemulsion and micropheres were characterized for drug-particle interaction and CPA absorption using human skin ex-vivo. Results Native CPA proved to be the active agent. Application of CPA attached to SLN increased skin penetration at least four-fold over the uptake from cream and nanoemulsion. Incorporation into the lipid matrix of NLC and microspheres resulted in a 2–3-fold increase in CPA absorption. Drug amounts within the dermis were low with all preparations. No difference was seen in the penetration into intact and stripped skin. Conclusion With particulate systems topical CPA treatment may be an additional therapeutic option for acne and other diseases of the pilosebaceous unit.     

Involvement of sphingosine 1-phosphate in palmitate-induced insulin resistance of hepatocytes via the S1P2 receptor subtype

Aims/hypothesis

Enhanced plasma levels of NEFA have been shown to induce hepatic insulin resistance, which contributes to the development of type 2 diabetes. Indeed, sphingolipids can be formed via a de novo pathway from the saturated fatty acid palmitate and the amino acid serine. Besides ceramides, sphingosine 1-phosphate (S1P) has been identified as a major bioactive lipid mediator. Therefore, our aim was to investigate the generation and function of S1P in hepatic insulin resistance.

Methods

The incorporation of palmitate into sphingolipids was performed by rapid-resolution liquid chromatography-MS/MS in primary human and rat hepatocytes. The influence of S1P and the involvement of S1P receptors in hepatic insulin resistance was examined in human and rat hepatocytes, as well as in New Zealand obese (NZO) mice.

Results

Palmitate induced an impressive formation of extra- and intracellular S1P in rat and human hepatocytes. An elevation of hepatic S1P levels was observed in NZO mice fed a high-fat diet. Once generated, S1P was able, similarly to palmitate, to counteract insulin signalling. The inhibitory effect of S1P was abolished in the presence of the S1P₂ receptor antagonist JTE-013 both in vitro and in vivo. In agreement with this, the immunomodulator FTY720-phosphate, which binds to all S1P receptors except S1P₂, was not able to inhibit insulin signalling.

Conclusions/interpretation

These data indicate that palmitate is metabolised by hepatocytes to S1P, which acts via stimulation of the S1P₂ receptor to impair insulin signalling. In particular, S1P₂ inhibition could be considered as a novel therapeutic target for the treatment of insulin resistance.     

Dexamethasone protects human fibroblasts from apoptosis via an S1P3-receptor subtype dependent activation of PKB/Akt and BclXL

Topical used glucocorticoids (GC) represent an important class of steroid hormones for the treatment of a broad range of acute or chronical inflammatory diseases. Most interestingly, GC exert a pronounced anti-apoptotic effect in primary human fibroblasts whereas in variety of hematopoietic cells a pro-apoptotic effect is visible. Recently, it has been discovered that in human fibroblasts the GC dexamethasone (Dex) exerts its protection from programmed cell death via the formation of the lipid mediator sphingosine 1-phosphate (S1P) followed by an activation of the S1P₃-receptor subtype. In the present study, the molecular mechanism of Dex to protect human fibroblasts from apoptosis was elucidated. Thereupon, Dex not only mediates its anti-apoptotic effect via activation of phosphoinositide 3-kinase (PI3K)/Akt signalling but also includes an involvement of the Bcl-2 family protein Bcl_XL. Most interestingly, the use of S1P₃-knockout fibroblasts revealed that the S1P₃-receptor subtype is crucial for activation of PKB/Akt as well as Bcl_XL by Dex.     

The role of the lysophospholipid sphingosine 1-phosphate in immune cell biology

Sphingosine 1-phosphate (S1P) has been shown to be a bioactive lipid mediator intimately involved in mediating a variety of immunological processes. In particular, S1P regulates lymphocyte cell trafficking between the lymphatic system and the blood. The lysophospholipid signals mainly through five related G protein-coupled receptor subtypes, termed S1P₁ to S1P₅. S1P₁ seems to play an essential role in cell trafficking, as this receptor subtype promotes the egress of T and B cells from secondary lymphatic organs. This S1P₁-mediated migratory response is a consequence of different S1P levels in the serum and lymphatic organs. In addition to its direct effects on lymphocyte motility, S1P strengthens cell barrier integrity in sinus-lining endothelial cells, thereby reducing lymphocyte egress out of lymph nodes. Furthermore, S1P modulates cytokine profiles in T and dendritic cells, resulting in an elevated differentiation of T helper-2 cells during the T cell activation process. It is of interest that the mode of molecular action of the novel immunomodulator FTY720 interferes with the signaling of S1P. After phosphorylation, FTY720 shares structural similarity with S1P, but in contrast to the natural ligand, phosphorylated FTY720 induces a prolonged internalization of S1P₁, resulting in an impaired S1P-mediated migration of lymphocytes.     

Sphingosine 1-phosphate is involved in cytoprotective actions of calcitriol in human fibroblasts and enhances the intracellular Bcl-2/Bax rheostat

Calcitriol is originally known to decrease proliferation rates of several carcinoma cells, partly via induction of apoptosis. On the other hand, the secosteroid is revealed to protect some cell types like thyrocytes, HL-60 cells and melanocytes against programmed cell death. Here we report that calcitriol despite its strong antiproliferative effect on human dermal fibroblasts did not induce apoptosis in these cells. In contrast, calcitriol possessed an antiapoptotic action in dermal fibroblasts. Thus, the ability of the apoptotic stimuli TNFalpha/actinomycin and C2-ceramides (C2-Cer) to induce programmed cell death was drastically diminished in the presence of calcitriol. Moreover, we identified sphingosine 1-phosphate (S1P) as a downstream mediator of calcitriol for its cytoprotective property. Thus, the secosteroid could not protect fibroblasts from apoptosis in the presence of N,N-dimethylsphingosine (DMS), which inhibits sphingosine kinase, the crucial enzyme to form S1P. Like calcitriol, S1P in different concentrations did not induce fibroblast apoptosis and moreover drastically decreased the rates of apoptotic cells after treatment with TNFalpha1/actinomycin. As S1P has been identified to modify the Bcl-2/ Bax ratio in epithelial cells and keratinocytes, we also measured the expression of these proteins in dermal fibroblasts revealing an increased Bcl-2 level after stimulation with S1P while the Bax protein expression was not modified. In conclusion, calcitriol H was revealed to protect human fibroblasts from apoptosis by formation of S1P resulting in a changed Bcl-2/Bax ratio.     

The impact of skin viability on drug metabolism and permeation -- BSA toxicity on primary keratinocytes.

For testing cutaneous absorption of drugs, ingredients of cosmetics and also for risk assessment of industrial compounds predictable in vitro test protocols are under investigation using excised skin or reconstructed human epidermis. Since the metabolizing enzymes expressed by viable skin can influence the absorption behaviour of substances by changing their structure and thereby their physicochemical characteristics, the metabolic capacity should be considered in the design of the test protocols of compounds susceptible to metabolism. Then data, generated using viable reconstructed epidermis may reflect the in vivo situation. Interestingly, bovine serum albumin (BSA) commonly used in receptor media in permeation studies to facilitate solubility of highly lipophilic substances strongly inhibited the metabolism of topically applied prednicarbate in reconstructed epidermis. Here, we show that 5% BSA is toxic to reconstructed epidermis and keratinocytes which was consistent with the earlier findings. While media toxicity (deficiency media) was at least partly the cause of both apoptotic and necrotic processes in keratinocytes, BSA only slightly increased the rate of necrotic cells. Moreover, caspase inhibitors did not reduce BSA toxicity. Yet, the results show that BSA toxicity on keratinocytes has to be carefully considered if this protein is used in permeation studies with reconstructed epidermis.     

Skin Penetration and Metabolism of Topical Glucocorticoids in Reconstructed Epidermis and in Excised Human Skin

Purpose. To investigate pharmacokinetic differences between the non-halogenated double ester prednicarbate (PC) and the fluorinated monoester betamethasone 17-valerate (BM17V) their metabolism in human keratinocytes and fibroblasts as well as their permeation and biotransformation in reconstructed epidermis and excised human skin was compared. Special attention was given to the 17-monoesters because of their high receptor affinity and antiproliferative effects. Methods. Glucocorticoid penetration was determined using Franz diffusion cells, quantifying metabolite concentrations by HPLC. Chemical stability and reactivity of the monoesters was determined by molecular modeling analysis. Results. PC accumulated in the stratum corneum. A considerable amount of penetrating PC was hydrolyzed by viable keratinocytes to prednisolone 17-ethylcarbonate (P17EC). P17EC permeated the skin very rapidly when compared to BM17V. Overall P17EC concentrations in viable tissue were low. Inside of the acceptor fluid, but not within the tissue, P17EC was converted to the more stable prednisolone 21-ethylcarbonate (P21EC). Conclusions. The inactivation of highly potent, but also cell toxic, 17-monoesters to almost inactive 21-congeners seen with isolated cell monolayers appears less important in the skin. In vitro determination of the dermal 17-monoesters concentrations may allow the prediction of the atrophogenic risk in man. BM17V levels exceeding P17EC concentrations about 6-fold may contribute to its lower tolerance when compared to PC.