Aloe vera gel and whole leaf extract: functional and versatile excipients for drug delivery?

Abstract

Aloe vera (L.) Burm.f. (Aloe barbadensis Miller) is a perennial xerophyte plant that has many medicinal applications. A. vera leaves contain water storage tissue, which is fundamentally made up of a viscous mucilage contained in the parenchyma cells. A. vera whole leaf extract refers to the product obtained from grinding the entire leaf (i.e. the rind, vascular bundles, and pulp) and removing the anthraquinones such as aloin by means of charcoal filtration. On the other hand, A. vera gel refers to the clear viscous mucilage contained within the parenchyma cells but is sometimes also interchangeably used to describe the complete intact fleshy inner part of the leaf or pulp. The mucilage gel primarily consists of polysaccharides dissolved in water (water content >98%) but also contains other compounds such as enzymes, minerals, and organic acids [1–3].

Materials that can be used as pharmaceutical excipients from renewable, natural sources are sought after due to their sustainable mass production potential. The polysaccharide-rich gel and whole leaf extract materials obtained from A. vera have shown the potential to be used as filler-type excipients in sustained-release matrix tablets. The A. vera leaf materials exhibited sufficient powder flow and compression properties to be used in the manufacture of direct compressible sustained-release matrix-type tablets [4,5].

The absorption enhancement effects of A. vera gel and A. vera whole leaf extract liquid products were first discovered during an in vivo study in human subjects. The randomized, double-blind, cross-over trial consisted of 11 healthy subjects who consumed a 500 mg vitamin C (ascorbic acid) tablet or a 420 mg vitamin E (tocopherol) capsule either with 60 ml of water alone (control) or with an A. vera gel or an A. vera whole leaf liquid product. When comparing the areas under the plasma concentration–time curves (AUC values), it was found that the AUC of vitamin C alone (339 ± 124 μM/h) was increased 3.04-fold (1 031 ± 513 μM/h) when co-administered with the A. vera gel liquid product. The AUC of vitamin E was increased 1.98-fold when co-administered with the A. vera whole leaf extract liquid product, while the A. vera gel product was capable of achieving a 3.69-fold increase in the AUC of vitamin E [2]. These results revealed the potential of A. vera gel and whole leaf products to increase the bioavailability of co-administered compounds.

This article focuses on the current state of research with regard to A. vera gel and whole leaf materials being used as a functional excipient for oral (intestinal), buccal, and transdermal drug delivery