Safety evaluation of titanium dioxide nanoparticles by their absorption and elimination profiles

If titanium dioxide nanoparticles are inert and non-biodegradable, they must be evaluated similarly to fullerenes, carbon nanotubes and asbestos. We surveyed the titanium level in typical raw food materials, and then intravenously injected titanium dioxide nanoparticles (primary particle diameter: 15 nm; secondary particle size: 220 nm) in mice and determined their tissue distribution and elimination. As a result, an unexpectedly high titanium concentration was observed in several foods. It was also detected in blood and tissues of healthy mice without administration of titanium dioxide nanoparticles. Then, forced i.v. injection of the nanoparticles was performed in mice. The titanim level was significantly increased in blood and tissues, but no increase was found in the brain after i.v. injection. Most titanium was concentrated in the liver after injection, but the liver level decreased over time (ca. 30% decrease in 1 month). These data show that titanium must be eliminated from the body, and suggest that we should reconsider an evaluation method for toxicity of titanium dioxide nanoparticles.

Skin Permeation of Lidocaine from Crystal Suspended Oily Formulations

In vitro permeation of lidocaine (lidocaine base, LID) through excised rat skin was investigated using several LID-suspended oily formulations. The first skin permeation of LID from an LID-suspended oily solution such as liquid paraffin (LP), isopropyl myristate (IPM), polyoxyethylene (2) oleylether (BO-2), and diethyl sebacate (DES) was evaluated and compared with that from polyethylene glycol 400 (PEG400) solution, a hydrophilic base. The obtained permeation rate of LID, Japp, from PEG400, LP, IPM, BO-2, and DES was in the order of DES>BO-2=IPM>LP>PEG400, and increased with LID solubility in the oily solvents, although LID crystals were dispersed in all solvents. Subsequently, oily formulations that consisted of different ratios of the first oily solvent (IPM, BO-2, or DES) (each 0-20%), the second oily solvent (LP) and an oily mixture of microcrystalline wax/white petrolatum/paraffin (1/5/4) were evaluated. BO-2 groups at a concentration of 5% and 10% had the highest Japp among the oily formulations, although a higher BO-2 resulted in lower skin permeation. In addition, pretreatment with BO-2 increased the skin permeation of LID. These results suggest that the penetration enhancing effect by the system may be related to the skin penetration of BO-2 itself. Finally, mathematical analysis was done to evaluate the effect of BO-2, and it was shown that BO-2 improved the LID solubility in stratum corneum lipids to efficiently enhance the LID permeation through skin.

Development of Sustained-Release Tablets Containing Sodium Valproate: In Vitro and In Vivo Correlation

We have developed a 200 mg and 400 mg sustained-release sodium valproate tablet that allows effective blood concentration of the active drug with once-a-day dosing. The controlled dissolution or sustained release of the drug was attained by a membrane-controlled system. A single-coating system did not adequately control the dissolution rate, and therefore double-coated tablets were prepared and a human pharmacokinetic study was conducted. With the 200 mg VPA-Na tablets, the nonfasting C(max) was only 20% higher than the fasting C(max). An in vitro dissolution test was conducted to predict the effects of food on drug dissolution after administration of this tablet. A relatively good correlation was observed between the absorption profiles and the dissolution profiles of the drug.

Pretreatment effects of moxibustion on the skin permeation of FITC-dextran

This study was conducted to evaluate the pretreatment effects of different in vivo moxibustion on the permeation of a model high molecular compound, FITC-dextran, with a mean molecular weight of 4 kDa (FD-4), through excised hairless rat skin. Direct or indirect moxibustion (0.10 g moxa) was pretreated consecutively 4 times every 5 min on the abdomen of hairless rats, and the permeation of FD-4 was determined through the excised skin over 8h from 30 min after starting the first moxibustion. This consecutive moxibustion pretreatment showed a significant increase in the skin temperature as well as skin permeation of FD-4 compared with the control group (no moxibustion pretreatment). Quantitative parameters showed an increase in skin temperature and skin permeation: the area under the skin temperature over control temperature-time curve during one burning cycle (5.0 min) (AUCtemp) or the maximum skin temperature during moxibustion (Tmax) and the cumulative amount of FD-4 permeated through skin over 8h (Q8) or steady-state flux were increased by moxibustion pretreatment. Then, the effect of pedestal thickness (distance from the moxa cylinder and skin surface), shape of the moxa cylinder (5mm diameter, 13 mm height or 9 mm diameter, 7 mm height), burning materials (moxa or aromatic incense), pedestal component (paper, potato or ginger) and moxibustion pretreatment method (direct or indirect moxibustion) was evaluated on the AUCtemp or Tmax and Q8 or flux. The amount of protein leached from the skin surface was also determined as an inflammatory index by this moxibustion pretreatment. When the skin temperature was increased to 60 degrees C, the Q8 or flux as well as the amount of protein leached were markedly increased. When the skin temperature was controlled to 42 to 45 degrees C by an adequate selection of pedestal thickness, shape of the moxa cylinder, burning materials, pedestal component and moxibustion pretreatment method, on the other hand, protein leaching remained unaltered, but the Q8 or flux significantly increased with the Tmax. This study thus provides credible evidence that moxibustion pretreatment increases the skin permeation of high molecular compounds.

Skin permeation and metabolism of a new antipsoriatic vitamin D(3) analogue of structure 16-en-22-oxa-24-carboalkoxide with low calcemic effect

A new vitamin D(3) analogue, SMD-429, is an antipsoriatic candidate of structure 16-en-22-oxa-24-carboalkoxide exhibiting fewer side effects than known vitamin D(3) analogues. In this study, the permeation of SMD-429 through excised rat skin and three-dimensional cultured human skin model (LSE-high) was evaluated. The cumulative amount of SMD-429 permeated through the skin membranes was lower than that of either maxacalcitol or calcipotriol, whereas the amount of SMD-429 in the skin was the same. It was found from in vitro rat skin permeation experiment using [(3)H]SMD-429 that SMD-429 was permeated through skin mainly in its metabolized form. The skin permeation profiles of vitamin D(3) analogues obtained were analyzed based on a one-layer diffusion model to estimate permeation parameters. The apparent diffusion coefficient of SMD-429 was 1.30 x 10(-5) cm(2)/h, which was 10-fold lower than that of maxacalcitol. The apparent metabolic rate constant of SMD-429 in skin was 1.01 x 10(-1) h(-1), the same as maxacalcitol. Low apparent diffusivity of SMD-429 in skin might cause an increase in the probability of bioconversion. The same amount of SMD-429 in skin as known vitamin D(3) analogues would achieve sufficient therapeutic efficacy in skin. Such low skin permeability and high metabolic conversion in skin of SMD-429 would contribute to a reduction in the systemic side effects.

Structure-permeability relationship analysis of the permeation barrier properties of the stratum corneum and viable epidermis/dermis of rat skin

The purpose of this study was to evaluate structure-permeability relationships for chemicals through stratum corneum (SC) and viable epidermis/dermis (VED). In vitro skin permeation of ten compounds through excised rat skin was analyzed based on a two-layer diffusion model and the diffusion coefficients in SC (D(SC)) and VED (D(VED)) were determined. The relationships between the permeation parameters and the physicochemical parameters (octanol-water partition coefficient (log K(o/w)), and hydrogen bond donor number (HBD)) of the compounds were analyzed. D(SC) increased as lipophilicity increased, whereas D(VED) decreased for log K(o/w) > 2. Increases in log K(o/w) caused a decrease in the permeability coefficient from SC through VED (P(VED/SC)) for log K(o/w) > 1. The simulation study suggests that the in vitro skin permeation of a highly lipophilic compound is strongly controlled by skin thickness due to low diffusivity in VED. The present study suggests that VED act as a considerable permeation barrier for highly lipophilic compounds due to low diffusivity.

Dermatopharmacokinetics of salicylate following topical injection in rats: Effect of osmotic pressure and injection volume on salicylate disposition

Using advanced topical formulations containing potential chemical enhancer(s) or physical penetration-enhancing tools capable of delivering entrapped drug(s) directly into skin tissues with little influence of the stratum corneum barrier, local and systemic drug disposition may be markedly similar to direct injection into the skin and muscle. The objective of this study is to investigate the dermatopharmacokinetics and systemic drug disposition after topical application and topical injection. Salicylate (SA) disposition in the skin and muscle as administration sites, and in the systemic circulation were evaluated following intracutaneous (i.c.) injection of an isotonic solution of SA-Na (dose; 3.08 micromol). Subcutaneous (s.c.) and intramuscular (i.m.) injection were also evaluated for comparison. Dermatopharmacokinetics and systemic disposition of SA after i.c. and s.c. injections were analyzed using a 4-compartment model consisting of skin, muscle, and central and peripheral compartments, whereas SA disposition after i.m. injection was analyzed using a 3-compartment model consisting of muscle, and central and peripheral compartments. Moreover, the absorption rate constant of SA after i.c. injection (0.073 min(-1)) was slightly lower than that after s.c. injection (0.083 min(-1)), and much lower than that after i.m. injection (0.327 min(-1)). In addition, higher osmolarity and a larger volume of SA-Na injectant increased the retention of SA in the skin and decreased the absorption rate to the systemic circulation after i.c. injection. The effect of injection volume on SA disposition after i.c. injection was not so marked compared with that of osmotic pressure. These results are useful to design an injection-type topical delivery system.

Analysis of in vitro skin permeation of 22-oxacalcitriol from ointments based on a two- or three-layer diffusion model considering diffusivity in a vehicle

In the present study, in vitro rat skin permeation of 22-oxacalcitriol (OCT) from ointments having differing compositions was determined and discussed based on a diffusion model. Diffusion coefficients of OCT in two ointments, one containing 3% (w/w) medium chain triglyceride (MCT) (3MO) and the other 30% (w/w) MCT (30MO), were determined using a modified membraneless method resulting in values of 0.89x10(-4) and 1.87x10(-4) cm2/h, respectively. At 24 h after application with 3MO, 7% of the applied OCT dose permeated through full-thickness skin and 22% remained in the ointment, whereas with 30MO, 2% of the applied dose permeated through full-thickness skin and 65% remained in the ointment. The diffusion coefficient of OCT in 3MO was lower than 30MO but the cumulative amount of OCT permeated was higher. From analysis of skin permeation of OCT based on a diffusion model considering diffusivity in an ointment, the partition coefficient of OCT from the ointment to stratum corneum (K(SC/V)) was calculated to be five-fold higher with 3MO than with 30MO. Our simulation study based on a diffusion model suggests that the diffusion coefficients of OCT in both ointments were high enough to have no affect on the skin permeation of OCT in the present case and that the difference in the skin permeations of the ointments was mainly caused by a difference in K(SC/V).

Enhancement of skin permeation of high molecular compounds by a combination of microneedle pretreatment and iontophoresis

A combination of microneedle pretreatment and iontophoresis was evaluated for the potential to increase skin permeation of drugs. Two model compounds with low and high molecular D(2)O and fluorescein isothiocyanate (FITC)-dextrans (FD-4, FD-10, FD-40, FD-70 and FD-2000; average molecular weight of 3.8, 10.1, 39.0, 71.2 and 200.0 kDa), respectively, were used and the effect of microneedle pretreatment and iontophoresis on their in vitro permeability was evaluated using excised hairless rat skin with a 2-chamber diffusion cell. Convective solvent flow through the skin was measured using a set of calibrated capillaries attached to the diffusion cell. The following results were obtained: (1) convective solvent flow (electroosmosis) during iontophoresis through microneedle-pretreated skin, 2.62+/-0.32 microL/cm(2)/h, was almost the same as through intact skin, 2.71+/-0.25 microL/cm(2)/h, and (2) the combination of microneedle pretreatment and subsequent iontophoresis significantly enhanced FD flux compared with microneedle pretreatment alone or iontophoresis alone, whereas no synergistic effect was found on the flux of D(2)O. These results suggest that the combination of iontophoresis with microneedle pretreatment may be a useful means to increase skin permeation of high molecular compounds.

Preparation and evaluation of gene-transfected cultured skin as a novel drug delivery system for severely burned skin

PURPOSE

The purpose of this study is to prepare and evaluate gene-transfected cultured skin to establish a dermal patch consisting of cultured skin as a new and novel delivery system for severely burned skin.

MATERIALS AND METHODS

Plasmid DNA encoding the green fluorescent protein (GFP) gene was used as a model gene and transfected to rat and human cultured dermis models (CDMs) using the hemagglutinating virus of Japan envelope vector (HVJ-E) to prepare gene-transfected CDM and evaluate GFP expression in the CDM. Two kinds of transfection methods were evaluated. In pre-transfection, the gene was first transfected into fibroblasts and then CDM was prepared using these gene-transfected cells. In post-transfection, the gene was transfected directly into CDM.

RESULTS

GFP expression was observed in both the pre- and post-transfected CDMs. The post-transfection method showed higher GFP expression in the CDM than pre-transfection, although no statistically significant difference was observed. The cell viability of these transfected CDMs was also examined with MTT assay. Slight decrease in viability was observed in these transfected CDMs. These methods could be useful in preparing gene-transfected cultured skins with low cell damage.

CONCLUSION

Gene transfection to cultured skin may produce several dermal patches that release potent endogenous bioactive peptides.

Effect of electroporation and pH on the iontophoretic transdermal delivery of human insulin

The synergistic effect of electroporation (EP) and iontophoresis (IP) on the in vivo percutaneous absorption of human insulin was evaluated in rats. Passive diffusion and IP alone (0.4 mA/cm(2)) resulted in almost no skin permeation of insulin at pH 7, whereas EP treatment (150 or 300 V, 10 ms, and 10 pulses) resulted in a high plasma level of insulin and the combined use of EP and IP led to a further increase of the plasma level of insulin compared with that measured after EP alone. Interestingly, a much higher plasma level was observed when the pH of the insulin solution at 7 was increased to 10. One of the reasons was the different aggregation properties of insulin at pH 7 and pH 10. The nonassociation ratio of insulin was significantly higher at pH 10 than at pH 7. Insulin monomers and dimers were observed in addition to the normal form of insulin, hexamer, albeit in low percentages, at pH 10, whereas most of the insulin was in the hexamer form at pH 7. To confirm the influence of the aggregation properties of insulin, the commercially available human insulin analogue insulin lispro was then evaluated. Its skin permeation was found to be extremely high compared to that of conventional human insulin without increasing the solution pH. Marked decreases in blood glucose levels reflecting the increases in the plasma concentration of insulin were also observed after EP/IP treatment. The present study suggests that percutaneous absorption of insulin is synergistically enhanced by a combined use of EP and IP and that altering the aggregation properties of insulin is important to enhance the percutaneous absorption of insulin by IP and/or EP.