1,721,043 research outputs found
Stability studies of new cosmetic formulations with vegetable extracts as functional agents
No full textPhotostability and solubility improvement of beta-cyclodextrin-included tretinoin
No full textIn this work, we investigated the influence of bcyclodextrin
on the photostability of tretinoin and compared
the photo-chemical stability of tretinoin, either in
methanol or complexed with b-cyclodextrin, when exposed
both to UV and fluorescent light. The physico-chemical
characterization of tretinoin-b-cyclodextrin complexes,
prepared by the freeze-drying process, using different
tretinoin:b-cyclodextrin molar ratios (1:1 and 1:3), was
carried out in solution by phase solubility studies, 1HNMR
spectroscopy, and in solid state by infrared spectroscopy
(FT-IR); these analyses confirmed the existence of
an inclusion compound. Solubility study results showed
that tretinoin solubility was enhanced by inclusion in
b-cyclodextrin as a function of increasing concentrations of
b-cyclodextrin in aqueous solution at different pH values
(i.e., 3.0, 5.5, and 7.0). Moreover, the complexation of the
tretinoin with b-cyclodextrin effectively protected the
photolabile drug and reduced the degradation of tretinoin
induced by UV and fluorescent light, improving its photochemical
stability in comparison with free drug in methanol.
Indeed, dissolved tretinoin in methanol degraded very
quickly and completely, while b-cyclodextrin-included
tretinoin decomposition was delayed and, after 30 days
under UV exposure, the percentage of remaining drug was
about 20–25% (depending on the tretinoin concentration).
The photodegradation of tretinoin in methanol under fluorescent
light was slower: after 5 days of irradiation it
reached a photostationary state and intact tretinoin remained
constant (6.6%). In conclusion, the b-cyclodextrin
complexation always led to a reduction of degradation,
depending on the tretinoin:b-cyclodextrin molar ratio and
on the drug concentration (0.2 mg/ml or 0.4 mg/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tretinoin-β-cyclodextrin inclusion complexes: characterization, phase solubility and photodegradation studies
No full textPhospholipid vesicles as carriers in aquaculture: preparation and stability study of thiamine hydrochloride-loaded liposomes
No full textThe aim of this work is to study liposomes as carriers of nutrients and therapeutic agents in aquaculture with Venerupis decussatus and Venerupis pullastra larvae. Multilamellar (MLVs) and large unilamellar (LUVs) vesicles were prepared from a commercial mixture of soy phosphatidylcholine, rich in unsaturated and polyunsaturated fatty acids, cholesterol, and hydrated with a solution of vitamin B1 both in distilled and sea water. Carboxyfluorescein-loaded liposomes were also prepared in order to test the uptake of vesicles by larvae. The stability of formulations was checked by monitoring the size of vesicles and their drug leakage. In order to limit the vitamin loss, liposome freeze-drying was studied. Dried formulations were also prepared by using different amounts of trehalose as cryoprotectant. We found that freeze-dried vesicles, rehydrated after two weeks, had a vitamin retention (R%) equal to 95%, while their diameter significantly increased. By contrast, liposomes freeze-dried in the presence of trehalose displayed a lower R%, but higher bilayer stability. Finally, when CF-loaded vesicles were added to Venerupis decussatus and Venerupis pullastra larvae incubated in filtered sea water, a bright and diffused fluorescence was present in most of the larvae, a fact which can be regarded as evidence of liposome uptake by Venerupis larvae
Liposomes as carriers for denual delivery of tretinoin: in vitro evaluation of drug penneation and vesicle-skin interaction
No full textThe influence of liposome composition, size, lamellarity and charge on the (trans)dermal delivery of tretinoin (TRA) was studied. For this purpose we studied both multilamellar (MLV) or unilamellar (UV) liposomes. Positively or negatively charged liposomes were obtained using either hydrogenated (Phospholipon (R) 90H) or non-hydrogenated soy phosphatidylcholine (Phospholipon (R) 90) and cholesterol, in combination with stearylamine or dicetylphosphate. Liposomal formulations were characterized by transmission electron microscopy (TEM) and optical and light polarized microscopy for vesicle formation and morphology, and by dynamic laser light scattering for size distribution. In order to obtain more information about the stability and the thermodynamic activity of the liposomal tretinoin, TRA diffusion through a lipophilic membrane was investigated. The effect of the vesicular incorporation of tretinoin on its accumulation into the newborn pig skin was also studied. The experiments were performed in vitro using Franz cells in occlusive conditions and were compared to three different controls. The tretinoin amount delivered through and accumulated in the several skin layers was detected by HPLC. Furthermore, TEM in combination with osmium tetroxide was used to visualize the skin structure after the liposomal administration. Overall obtained results showed that liposomes may be an interesting carrier for tretinoin in skin disease treatment, when appropriate formulations are used. In particular, negatively charged liposomes strongly improved newborn pig skin hydration and TRA retention, though no evidence of intact vesicle penetration was found. (c) 2004 Elsevier B.V. All rights reserved
Liposomes for (trans)dermal delivery of tretinoin: influence of drug concentration and vesicle composition
No full textThe influence of drug concentration and vesicel composition on the (trans)dermal delivery of tretinoin (TRA) was studied.To this purpose tretinoin was incorporated at different concentrations in unilamellar liposomes (UVs) prepared by sonication using phospholipids with different transition temperature (T-c): hydrogenated soy phosphatidylcholine (Tc = 51 degrees C) or dipalmitoylphosphatidylcholine (Tc = 41 degrees C). Vesicle dispersions were characterized in terms of morphology size distribution and incorporation efficiency by using respectively optical and polarized light microscopy, transmission electron mciroscopy, dynamic laser light scattering, and HPLC. The effect of the vesicular incorporation of tretinoin at different molar ratios was investigated by zeta potential measurements and differential scanning calorimetry analysis. These analyses inidcated that tretinoin principally interacts with the lipid groups until bilayer saturation. At higher concentration the ionized drug interacts with the polar head. Interactions between new-born pig skin and vesicle containing different amount of tretinoion were evaluated in vitro using Franz cells. The results obtained confirmed that liposomes saturated with TRA (molar fraction = 0.3) are capable of significantly promoting drug accumulation in the pig skin and that (trans)cutaneous delivery is strongly dependent on vesicular stability on the skin
OCTYL/DECYL POLYGLUCOSIDE NIOSOMES AS POTENTIAL CARRIERS FOR THE CUTANEOUS DELIVERY OF 8-METHOXYPSORALEN
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