Skin permeation of buprenorphine and its ester prodrugs from lipid nanoparticles: lipid emulsion,nanostructured lipid carriers and solid lipid nanoparticles

The aim of this study was to develop and characterize lipid nanoparticle systems for the transdermal delivery of buprenorphine and its prodrugs. A panel of three buprenorphine prodrugs with ester chains of various lengths was synthesized and characterized by solubility, capacity factor (log K′), partitioning between lipids and water and the ability to penetrate nude mouse skin. Colloidal systems made of squalene (lipid emulsion, LE), squalene + Precirol (nanostructured lipid carriers, NLC) and Precirol (solid lipid nanoparticles, SLN) as the lipid core material were prepared. Differential scanning calorimetry showed that the SLN had a more-ordered crystalline lattice in the inner matrix compared to the NLC. The particle size ranged from 220–300 nm, with NLC showing the smallest size. All prodrugs were highly lipophilic and chemically stable, but enzymatically unstable in skin homogenate and plasma. The in vitro permeation results exhibited a lower skin delivery of drug/prodrug with an increase in the alkyl chain length. SLN produced the highest drug/prodrug permeation, followed by the NLC and LE. A small inter-subject variation was also observed with SLN carriers. SLN with soybean phosphatidylcholine (SLN-PC) as the lipophilic emulsifier showed a higher drug/prodrug delivery across the skin compared to SLN with Myverol, a palmitinic acid monoglyceride. The in vitro permeation of the prodrugs occurred in a sustained manner for SLN-PC. The skin permeation of buprenorphine could be adjusted within a wide range by combining a prodrug strategy and lipid nanoparticles.     

Sun protection enhancement of titanium dioxide crystals by the use of carnauba wax nanoparticles: the synergistic interaction between organic and inorganic sunscreens at nanoscale

Carnauba wax is partially composed of cinnamates. The rational combination of cinnamates and titanium dioxide has shown a synergistic effect to improve the sun protection factor (SPF) of cosmetic preparations. However, the mechanism of this interaction has not been fully understood. In this study, an ethanolic extract of the carnauba wax and an ethanolic solution of a typical cinnamate derivative, ethylcinnamate, were prepared and their UV absorption and SPF either alone or in the presence of titanium dioxide were compared. The titanium dioxide crystals and the cinnamates solutions were also distributed into a matrix composed of saturated fatty acids to emulate the structure of the crystallized carnauba wax. SPF, differential scanning calorimetry (DSC) and X-ray studies of these matrices were performed. Additionally, carnauba wax nanosuspensions containing titanium dioxide either in the lipid phase or in the aqueous phase were prepared to evaluate their SPFs and their physical structure. Strong UV absorption was observed in diluted suspensions of titanium dioxide after the addition of cinnamates. The saturated fatty acid matrices probably favored the adsorption of the cinnamates at the surface of titanium dioxide crystals, which was reflected by an increase in the SPF. No modification of the crystal structure of the fatty acid matrices was observed after the addition of cinnamates or titanium dioxide. The distribution of the titanium dioxide inside the lipid phase of the nanosuspensions was more effective to reach higher SPFs than that at the aqueous phase. The close contact between the carnauba wax and the titanium dioxide crystals after the high-pressure homogenization process was confirmed by transmission electron microscopy (TEM).     

Skin photoprotection by green tea: antioxidant and immunomodulatory effects

Because of a characteristic aroma and health benefits, green tea is consumed worldwide as a popular beverage. The epicatechin derivatives, commonly called polyphenols, present in green tea possess antioxidant, anti-inflammatory and anti-carcinogenic properties. The major and most highly chemopreventive constituent in green tea responsible for the biochemical or pharmacological effects is (-)-epigallocatechin-3-gallate (EGCG). Epidemiological, clinical and biological studies have implicated that solar ultraviolet (UV) light is a complete carcinogen and repeated exposure can lead to the development of various skin disorders including melanoma and nonmelanoma skin cancers. We and others have shown that topical treatment or oral consumption of green tea polyphenols (GTP) inhibit chemical carcinogen- or UV radiation-induced skin carcinogenesis in different laboratory animal models. Topical treatment of GTP and EGCG or oral consumption of GTP resulted in prevention of UVB-induced inflammatory responses, immunosuppression and oxidative stress, which are the biomarkers of several skin disease states. Topical application of GTP and EGCG prior to exposure of UVB protects against UVB-induced local as well as systemic immune suppression in laboratory animals, which was associated with the inhibition of UVB-induced infiltration of inflammatory leukocytes. Prevention of UVB-induced suppression of immune responses by EGCG was also associated with the reduction in immunosuppressive cytokine interleukin (IL)-10 production at UV irradiated skin and draining lymph nodes, whereas IL-12 production was significantly enhanced in draining lymph nodes. Antioxidant and anti-inflammatory effects of green tea were also observed in human skin. Treatment of EGCG to human skin resulted in the inhibition of UVB-induced erythema, oxidative stress and infiltration of inflammatory leukocytes. We also showed that treatment of GTP to human skin prevents UVB-induced cyclobutane pyrimidine dimers formation, which are considered to be mediators of UVB-induced immune suppression and skin cancer induction. The in vitro and in vivo animal and human studies suggest that green tea polyphenols are photoprotective in nature, and can be used as pharmacological agents for the prevention of solar UVB light-induced skin disorders including photoaging, melanoma and nonmelanoma skin cancers after more clinical trials in humans.     

Triglyceride-coated nanoparticles: Skin toxicity and effect of UV/IR irradiation on them

Triglyceride (TG) is an important compound on the skin, produced by sebaceous glands, and may change cytotoxicity of different nanoparticles. To date, there is no report about toxicity of nanoparticles coated with TG. On the other hand, the use of ultraviolet (UV) and infrared (IR) with nanoparticles changes nanoparticle cytotoxicity. The combination of nanoparticles with UV or IR is applicable, because it may be used for treatment or detection of local cancers, surface microbial infections and other skin diseases. In this study, different nanoparticles including titanium dioxide, zinc oxide, magnesium oxide, silver, gold, and TG-coated form of these nanoparticles, were added to suspensions of Balb/c skin cells, and then incubated for 24 h at 37 °C. Additionally, TG-coated nanoparticles were treated with UV and IR irradiation for 1 h. Different methods were applied for evaluation of cytotoxicity, including 5-diphenyl-tetrazolium bromide assay, lactate dehydrogenase (LDH) assay, cell metabolic assay, ATP assay, and reactive oxygen species (ROS) generation assay. This research showed that TG-coated nanoparticles had less LDH release and ROS generation with higher cell viability, cell metabolic activity, and ATP level, compared with pristine nanoparticles. In contrast, the combination of UV and IR with TG-coated nanoparticles led to higher LDH release and ROS generation with less cell viability, cell metabolic activity, and ATP level, in comparison with pristine nanoparticles. Overall, pristine metal nanoparticles without irradiation had higher cytotoxicity than metal oxide nanoparticles.     

The mechanism of synergistic interaction between etoposide and cytarabine

The sequence dependency of the antitumor effect of etoposide and cytarabine (ara-C) was investigated against the L1210 ascites tumor in BDF1 mice. Etoposide (7.5 mg/kg or 15 mg/kg) and ara-C (25 mg/kg or 500 mg/kg) were administered intraperitoneally on days 1, 4, and 7 after inoculation of L1210 cells with or without a time interval of 3 or 6 h. Simultaneous administration of etoposide and ara-C produced a 70% cure rate. At every dosage examined, pretreatment with etoposide given 6 h before ara-C was the most effective antitumor schedule in L1210 leukemia. At 1 h after injection of ara-C, 3 h and 6 h pretreatment with etoposide 15 mg/kg increased ara-C incorporation to more than 200% as compared with that of ara-C given alone. Simultaneous administration of etoposide, however, decreased ara-C incorporation to 33% of that of ara-C alone. Deoxycytidine kinase (dCK) is a rate-limiting enzyme for the activation of ara-C. We demonstrated that dCK activity was increased within 1 h after exposure to etoposide. Much more attention must be paid to the timing of the administration of etoposide in combination chemotherapy with etoposide and ara-C.     

可卡因与去甲肾上腺素协同作用的动力学模型

目的：建立药物在失活位点上相互竞争而产生协同作用的动力学模型。方法：测定不同浓度可卡因对去甲肾上腺素收缩豚鼠输精管的量－效曲线的影响，经数理推导，建立失活位点竞争性协同模型，并用最小二乘法拟合实验数据，求算模型参数。结果：可卡因（１～１００μｍｏｌ·Ｌ－１）剂量依赖性增强去甲肾上腺素收缩豚鼠输精管的作用，使其量－效曲线平行左移。模型的理论曲线与实验数据完全拟合。可卡因对去甲肾上腺素的协同指数为６．４。结论：失活位点竞争性协同模型可定量分析可卡因与去甲肾上腺素的协同作用。该模型除能求算一般药效动力学参数（ＥＣ５０，Ｅｍａｘ）外，还能估计协同指数、组织对激动剂的“表观失活容量指数”和激动剂到达受体前的损失率。     

Skin penetration and photoprotection of topical formulations containing benzophenone-3 solid lipid microparticles prepared by the solvent-free spray-congealing technique

Abstract

Purpose: Solid-lipid microparticles loaded with high amounts of the sunscreen UV filter benzophenone-3 were prepared by spray congealing with the objective of decreasing its skin penetration and evaluate whether the sunscreen’s photoprotection were impaired by the microencapsulation process. Methods: The microparticles were produced using the natural lipids carnauba wax or bees wax and three different concentrations of benzophenone-3 (30, 50 and 70%) using spray congealing technique. Results: The microparticles presented properties suitable for topical application, such as spherical morphology, high encapsulation efficiency (95.53–102.2%), average particle sizes between 28.5 and 60.0?µm with polydispersivities from 1.2 to 2.5. In studies of in vitro skin penetration and preliminary stability, formulations of gel cream containing carnauba wax solid lipid microparticles and 70% benzophenone-3 when compared to the formulation added of bees wax solid-lipid microparticles containing 70% benzophenone-3, was stable considering the several parameters evaluated and were able to decrease the penetration of the UV filter into pig skin. Moreover, the formulations containing solid lipid microparticles with 70% benzophenone-3 increased the photoprotective capacity of benzophenone-3 under UV irradiation. Conclusion: The results show that spray-congealed microparticles are interesting solid forms to decrease the penetration solar filters in the skin without compromising their photoprotection.     

Encapsulation of ethylhexyl methoxycinnamate,a light-sensitive UV filter,in lipid nanoparticles

The aim of this study was to encapsulate ethylhexyl methoxycinnamate (EMC), a commonly used UVB filter, in a solid lipid matrix in order to obtain microparticles and then nanoparticles to reduce its photo-instability under UV light exposure. Glyceryl behenate, rice bran wax and ozokerite were investigated for encapsulating EMC. The suspensions of nanoparticles contained 70% encapsulated EMC (relative to the lipid mass). The absorbance level at 310?nm of suspensions containing nanoparticles was more than twice that of those containing microparticles. So, decreasing the size of particles improved the efficiency of light protection, regardless of the lipid material used. Moreover, free EMC presented a 30% loss of its efficiency after 2?h of irradiation, whereas the three NLC formulations showed a loss of absorbency between 10% and 21%. The in vitro cutaneous penetration test did not show a higher potential penetration for EMC contained in nanosuspensions compared to free EMC.     

Surface of synergistic interaction between dipyrone and morphine in the PIFIR model

The analgesic effects of dipyrone and morphine administered either separately or in 24 different combination were determined in the “Pain-Induced Functional Impairment in the Rat” (PIFIR analgesic model). This allowed the detection of the profile of analgesic interaction of the various combinations. Furthermore, the optimal degree of potentiation obtained with a specific combination of the above drugs was determined by means of the “Surface of Synergistic Interaction” (SSI) of the combinations. This parameter was calculated from the total analgesic effect produced by the combination after having subtracted the analgesic effect produced by each drug alone. Over the dose-ranges used, the analgesic activities of either dipyrone or morphine tended to be smaller than those of their respective combinations. Furthermore, 11 combinations showed various degrees of potentiation (P < 0.05), while the remainder (13) exhibited additive analgesic effects. The combination of dipyrone (562 mg/kg, sc) and morphine (5.6 mg/kg, sc) produced the maximum analgesic effect. However, dipyrone (178 mg/kg) with morphine (3.2 mg/kg) produced the highest potentiation effect (P < 0.001). The surface of synergistic interaction clearly showed which combination of analgesic drugs produced the highest degree of potentiation in the rat. This represents the first study to show that a specific ratio of combination of analgesic drugs can produce an optimal potentiation of their analgesic effects. These findings may have important implications for the treatment of pain. © 1994 Wiley-Liss, Inc.     

Solid lipid nanoparticles (SLN)--a novel carrier for UV blockers.

The formulation of safe sunscreen products is of high importance due to their increasing use because of the diminishing ozone layer. Solid lipid nanoparticles (SLN) are introduced as the new generation of carriers for cosmetics, especially for UV blockers for the use on human skin and/or hair and production thereof is described. The crystalline cetylpalmitate SLN particles have the ability of reflecting and scattering UV radiation on their own thus leading to photoprotection without the need for molecular sunscreens. An in vitro assay showed that a placebo cetyl palmitate SLN formulation is twice to three times as potent in absorbing UV radiation as a conventional emulsion. Incorporation of sunscreens into SLN lead to a synergistic photoprotection, i.e. higher than the additive effect of UV scattering caused by the SLN and UV absorption by the sunscreen. The photoprotective effect after incorporation of the molecular sunscreen 2-hydroxy-4-methoxybenzophenone (Eusolex 4360) into the SLN dispersion was observed to be increased threefold compared to a reference emulsion. Further, film formation on the skin was investigated by scanning electron microscopy, showing particle fusion due to water evaporation and formation of a dense film.     

Encapsulation of ethylhexyl methoxycinnamate, a light-sensitive UV filter, in lipid nanoparticles

The aim of this study was to encapsulate ethylhexyl methoxycinnamate (EMC), a commonly used UVB filter, in a solid lipid matrix in order to obtain microparticles and then nanoparticles to reduce its photo-instability under UV light exposure. Glyceryl behenate, rice bran wax and ozokerite were investigated for encapsulating EMC. The suspensions of nanoparticles contained 70% encapsulated EMC (relative to the lipid mass). The absorbance level at 310?nm of suspensions containing nanoparticles was more than twice that of those containing microparticles. So, decreasing the size of particles improved the efficiency of light protection, regardless of the lipid material used. Moreover, free EMC presented a 30% loss of its efficiency after 2?h of irradiation, whereas the three NLC formulations showed a loss of absorbency between 10% and 21%. The in?vitro cutaneous penetration test did not show a higher potential penetration for EMC contained in nanosuspensions compared to free EMC.     

Parasitic diseases: Liposomes and polymeric nanoparticles versus lipid nanoparticles

Parasitic diseases such as malaria, leishmaniasis, and trypanosomiasis represent a significant global burden and pose a great challenge to drug discovery and delivery scientists due to their intracellular nature and disseminated locations. Moreover, poor rate of discovery in the anti-parasitic segment seen in last few decades has necessitated effective management of existing drugs by modulating their delivery. The review focuses on the biological and biopharmaceutical issues to be considered in the design of delivery strategy for treating parasitic infections such as malaria, leishmaniasis, and trypanosomiasis. Also, it describes the role of the colloidal carriers liposomes, polymeric nanoparticles, lipid nanoparticles including lipid drug conjugate (LDC) nanoparticles in optimizing the delivery of anti-malarial, anti-leishmanial and anti-trypanosomial agents. Furthermore, the review emphasizes especially the potential of solid lipid nanoparticles (SLN) in the treatment of parasitic infections with the help of recent reports and our own experience.     

Profile of analgesic interaction between aspirin and d-propoxyphene obtained by means of the surface of synergistic interaction

The analgesic effects of aspirin [acetyl salicylic acid (ASA)] and d-propoxyphene (PROP) administered either separately or in 24 different combinations were determined in the pain-induced functional impairment in the rat (PIFIR) model. This allowed the detection of the profile of analgesic interaction of the combinations. Furthermore, we set out to determine the optimal degree of potentiation obtained with a specific combination of the above drugs by means of the surface of synergistic interaction of the combinations. This parameter was calculated from the total analgesic effect produced by the combination after having subtracted the analgesic effect produced by each drug alone. The ED₅₀ for ASA and PROP were 210.4 ± 1.2 and 66.3 ± 1.2 mg/kg, respectively. Over the dose ranges used, the analgesic activities of either ASA or PROP tended to be smaller than those of their respective combinations. Furthermore, 10 combinations showed various degrees of potentiation (P < 0.01), while the others (14) exhibited additive analgesic effects. The combination of ASA (562.3 mg/kg, po) and PROP (31.6 mg/kg, sc) produced the maximum analgesic effect. However, 5 combinations of ASA with PROP (56.2–56.2, 100–56.2, 177.8–56.2,316.2–56.2, and 177.8–31.6 mg/kg) produced the highest potentiation effects. The surface of synergistic interaction clearly showed which combination of these analgesic drugs produced the highest degree of potentiation in the rat. This study shows that a specific ratio of combination of analgesic drugs can produce optimum potentiation of their analgesic effects. © 1995 Wiley-Liss, Inc.     

The synergistic interaction between rilmenidine and paracetamol in the writhing test in mice

The aim of the study was to ascertain antinociceptive effects of rilmenidine, a second-generation imidazoline-alpha-2-adrenoreceptor agonist, and to see whether rilmenidine was able to increase the analgesic effects of paracetamol in the writhing test in mice. An acetic acid (0.7%) solution was injected into the peritoneal cavity and the number of writhes was counted. The influence on locomotor performance was tested using the rotarod test. Rilmenidine, paracetamol, and rilmenidine–paracetamol fixed-ratio combinations produced dose-dependent antinociceptive effects. ED₅₀ values were estimated for the individual drugs and an isobologram was constructed. The derived theoretical additive ED₅₀ value for the rilmenidine–paracetamol combination was 109.23 ± 35.05 mg/kg. This value was significantly greater than the observed ED₅₀ value which was 56.35 ± 20.86 mg/kg, indicating a synergistic interaction. Rilmenidine did not impair motor coordination, as measured by the rotarod test, at antinociceptive and higher doses.     

Importance of using solid lipid microspheres as carriers for UV filters on the example octyl methoxy cinnamate

The aim of this study was to prepare solid lipid microspheres (SLM) of octyl methoxy cinnamate (2-ethylhexyl-p-methoxy cinnamate; OMC) to achieve controlled release, decrease penetration of this UV absorber from skin and improve its photostability. The influence of the carrier on the rate of release was studied in vitro with a cellulose acetate membrane and in vivo from excised rat skin with Franz diffusion cells. The release rate was decreased by up to 13-80% with the SLM formulation. In vivo, penetration of OMC into skin was investigated by HPLC method. It was found out that the rate of penetration is significantly dependent upon the formulation and could be decreased by up to 77% in SLM formulations. When different topical vehicles were compared, OMC was released and penetrated into rat skin more quickly and in greater amount from vehicles containing free OMC than in SLM form. Additionally, photostability was shown to be improved in SLM form.     

Skin penetration and safety of nanoparticles

Human beings are exposed or otherwise a subjected to a various chemical compounds. Various nanomaterials are contained in the chemical compounds which are used in many fields. Nanomaterials are also used in cosmetics: titanium dioxide and zinc oxide are examples. Consumers who apply cosmetics to their skin as well as workers at industrial plants may thus be exposed to these nanoparticles. Therefore, it is of great importance to evaluate the safety of these nanoparticles. In this review, we describe the possibility of nanoparticle penetration to skin following exposure, which makes it urgent to evaluate the safety factors. In general, it is necessary to take account of the desquamation rate of the stratum corneum and the permeation pathway and size of nanoparticles when considering such penetration. One layer of the human stratum corneum is peeled off per day. Therefore, a chemical compound of which the skin penetration is lower than the desquamation rate does not permeate through the skin, when the compound infiltrates the stratum corneum. Hence, compounds with a molecular weight of more than 500 Daltons do not permeate through the stratum corneum. However, we must also pay attention to the appendage routes, although the aforementioned layer is the primary permeation route of nanoparticles. The contribution of appendage routes must be taken into consideration.     

Toxicokinetics and metabolisms of benzophenone-type UV filters in rats

Sunscreens containing UV filters are recommended to reduce damage caused by solar UV radiation. Recently, benzophenone (BP)-type UV filters have become widely used as UV stabilizers in skin-moisturizing products and sunscreen lotions; however, very little information is available regarding the potential harmful effects of prolonged exposure to these compounds. Therefore, we investigated the toxicokinetics and metabolism of BP-type UV filters in rats using gas chromatography-mass spectrometry (GC-MS). To examine the metabolism of BP-type UV filters, we analyzed the parent compounds BP and 2-hydroxy-4-methoxybenzophenone (HMB). In rats, BP was mainly converted to benzhydrol (BH) and 4-hydroxybenzophenone (HBP) (i.e., type A UV filters). In contrast, HMB was converted into at least three intermediates, including 2,4-dihydroxybenzophenone (DHB), which was formed via o-demethylation and subsequently converted into 2,3,4-trihydroxybenzophenone (THB), and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB), which formed via the aromatic hydroxylation of HMB (i.e., type B UV filters). Next, the toxicokinetic curve for BP showed a peak concentration (Cmax) of 2.06+/-0.46 microg/ml at approximately 4h after BP administration. After a single oral dose of HMB, the Cmax of HMB reached 21.21+/-11.61 microg/ml within 3h (Tmax), and then declined rapidly compared to the kinetic curve of BP. The concentration of these metabolites in rat blood decreased much more slowly over time compared to the parent compounds. Thus, our results indicate that such metabolites might have more significant adverse effects than the parent compounds over the long term.