Title: Stability of a liposomal formulation containing lipoyl or dihydrolipoyl acylglycerides† Authors
Submitted to: European Journal of Pharmaceutics and Biopharmaceutics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2014
Publication Date: N/A
Interpretive Summary: A new vegetable oil derivative was found to have good antioxidant properties, which demonstrates that this material may have a positive influence on maintaining the health of cellular tissues. One of our mission objectives is to develop new, value added uses for commodity crops and crop oils through the development of domestically derived, bio-based chemicals and products. The newly developed lipoyl dioleoylglycerol molecule is a skin care product made from vegetable oil and lipoic acid with the potential for delivering protective and energizing activities for improved facial skin health and appearance. In the present research we investigated how stable this molecule may be under storage conditions that resemble commercial transportation and retail display. We found that care must be taken in formulating lipoyl dioleoylglycerol molecule so that it is not exposed to polyunsaturated fatty acids. These findings provide researchers with an enhanced understanding of how such molecules may be included in advanced dermal care products.
Technical Abstract: The acylglycerides of lipoic and dihydrolipoic acids may serve as slow-release sources for cutaneous delivery of these antioxidants when formulated in a liposomal vehicle. Testing was conducted to determine the storage stability of the lipoic derivatives and of the soybean phospholipids in which they were embedded. Lipoyl glycerides, prepared by transesterification of lipoic acid with high oleic sunflower oil, were incorporated into 133-nm diameter, unilamellar liposomes comprised of soy phosphatidylcholine (soyPC). The lipoyl glycerides were stable in the vesicles at 4 °C (90% remaining after five weeks) and decayed with a half-life (t½) of 14 d at 40 °C. In contrast, lipoyl glycerides embedded in liposomes of dioleoylphosphatidylcholine (DOPC) were completely stable for four weeks at 40 °C. Dihydrolipoyl glycerides in soyPC liposomes converted to lipoyl glycerides at 4 °C (t½ = 14 d) over four weeks, and much more rapidly so at 40 °C (t½ = 1 d). An analysis of hydroperoxide accumulation in the liposomes indicated that lipoyl glycerides and dihydrolipoyl glycerides were modified or degraded while suppressing autoxidation of the polyunsaturated fatty acids present in soyPC. Dynamic light scattering measurements of liposomes held at 22 °C and 40 °C determined that soyPC vesicles containing lipoyl glycerides or dihydrolipoyl glycerides did not undergo significant size changes for at least 28 d, while liposomes lacking the glycerides increased in size, reflecting lipid oxidation induced swelling. Substitution of the soyPC with DOPC, which is not readily subject to autoxidation, provided a much more stable storage environment for the lipoyl and dihydrolipoyl glycerides. These findings confirm the expectation that phospholipid liposomes need to be oxidatively stable vehicles for dermal delivery of lipoic acid derivatives.