In vivo EPR of topical delivery of a hydrophilic substance encapsulated in multilamellar liposomes applied to the skin of hairless and normal mice

Abstract

In vivo low frequency EPR was used to measure the enhancement of topical delivery of hydrophilic substances by use of multilamellar liposomes. The contribution of transepidermal or/and transfollicular routes of transport was investigated using hairless and normal mice. Two liposome dispersions that previously had been shown to have different enhancement properties on ex vivo skin were used. The kinetics of the reduction of hydrophilic spin probe GluSL ( N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)-2,3,4,5,6-pentahydroxy-hexaneamide) applied to the skin encapsulated into the liposomes was measured. To distinguish the reduction of GluSL on the skin surface from its reduction inside the skin, the oxidizing agent potassium ferricyanide (KFeCN) was used. This does not penetrate into the skin and therefore it oxidizes hydroxylamines back to nitroxide only on the surface of the skin. We observed significant differences in the properties of the two types of liposomes with respect to their stability when in contact with skin and their transport characteristics. The results measured in vivo are consistent with those obtained ex vivo, indicating that in vivo L-band EPR is a powerful technique for following pharmacokinetics in the skin of live animals. The results also show that clearance by blood flow and possible alterations of skin after sacrifice of animal do not influence the results of penetration of liposome entrapped substances into the skin during the time of our experiment (typically around 60 min). The reduction of GluSL in the skin of hairless vs. normal mice was similar, indicating that the transfollicular penetration was not of major importance in vivo in this experimental model.