Structure—Function Relationship among Quillaja Saponins Serving as Excipients for Nasal and Ocular Delivery of Insulin

Abstract

The purpose of this investigation was to explore the structure-function relationship among naturally occurring Quillaja saponins and derivatives for their ability to stimulate insulin delivery from nosedrops and eyedrops and to test the hypothesis that stimulation of peptide drug delivery was correlated with surfactant strength. Native saponins, including QS-21, were purified from an aqueous extract of Quillaja saponaria bark by adsorption chromatography and HPLC. Native saponins were then deacylated by mild alkaline hydrolysis to form DS-1 and DS-2, derivatives that are smaller and more hydrophilic than their parent compounds. DS-1 was further treated either to reduce an aldehyde residue to form DS-1(R) or to remove the fucose-containing oligosaccharide to form QH-957. Rats receiving eyedrops or nosedrops formulated with insulin, but without any Quillaja saponins, showed no hypoglycemic response. Rats receiving eyedrops or nosedrops formulated with insulin plus saponins showed a dose-dependent hypoglycemic response, with the following rank order: QS-21 > DS-1 > DS-1(R) > DS-2 > QH-957. Surfactant strength was determined by measurement of the critical micellar concentration (cmc) and hemolysis of sheep erythrocytes. The cmc was lowest for the parent saponins QS-21 and QS-18, and increased for the deacylated saponin derivatives DS-1, DS-2, and QH-957; hemolysis of sheep erythrocytes was observed at low concentrations (approximately 0.006 mM) of the parent saponins, QS-21 and QS-18, at intermediate concentrations (0.06-0.08 mM) of DS-1 and DS-2, and at higher concentrations of DS-1(R) (0.45 mM) and QH-957 (1.5 mM). Hence, efficacy as an absorption-enhancing agent was greatest in those saponins with the lowest hemolytic titers and cmc values. However, this relationship was not a strict one, because DS-1, which differs from DS-2 only in the absence of one glucose residue, was significantly more potent than DS-2 in stimulating the absorption of insulin. DS-1 and DS-2 share a similar cmc and hemolytic titer, so this difference in efficacy must be due to some specificity beyond simple surfactant strength. Furthermore, DS-1 does not trigger an immune response when administered to animals, whereas QS-21 is a strong immune system activator. Therefore, DS-1 has emerged as an interesting candidate for inclusion in an eyedrop or nosedrop formulation.

Isolation, Characterization and Study of Enhancing Effects on Nasal Absorption of Insulin in Rat of the Total Saponin from Acanthophyllum squarrosum

“…[16] Pillion et al, found that saponins isolated from Quillaja saponaria bark hemolysed sheep red blood cells at fairly low concentrations. [13] As the results of the present study show, the hemolysis profile of the ATS and QTS were almost identical and complete hemolysis was observed for both compounds at the concentration of 250 µg/ml. Since this concentration is above the CMC of ATS, membrane disruption could be attributed to the formation of mixed micelles and extraction of membrane components by saponin micelles.…”

“…Pillion et al, studied naturally occurring QTS and their derivatives for their ability to stimulate insulin delivery from nose and eye drops. [13] This group of researchers instilled 2 IU insulin in the presence of different concentrations of QTS and derivatives into the nose/eye of rat and assessed insulin absorption by the hypoglycemic response of the animal. [13] They found that all the tested saponins and derivatives showed an enhancing effect on insulin absorption and reduced blood glucose levels in rat, though there were differences in the extent of their effects.…”

“…[13] This group of researchers instilled 2 IU insulin in the presence of different concentrations of QTS and derivatives into the nose/eye of rat and assessed insulin absorption by the hypoglycemic response of the animal. [13] They found that all the tested saponins and derivatives showed an enhancing effect on insulin absorption and reduced blood glucose levels in rat, though there were differences in the extent of their effects. [13] However, the enhancing effect of ATS on the absorption of insulin has not been reported in the literature.…”

“…[5,6] Various substances have been studied for use as absorption enhancers of insulin through nasal mucosa, including bile salts; [7] polyoxyethylene-9-lauryl ether [laureth-9]; [3,8] anionic surfactants, e.g, sodium lauryl sulfate (SLS) and potassium lauryl sulfate; [9] l-α-lysophosphatidyl choline, [10] chitosan [11,12] and Quillaja saponins. [13] Pillion and coworkers studied the enhancing effects of Quillaja total saponin (QTS) and its derivatives on nasal and ocular delivery of insulin. [13] However, no report was found in the literature regarding the absorption-enhancing effects of Acanthophyllum total saponin (ATS).…”

“…[13] Pillion and coworkers studied the enhancing effects of Quillaja total saponin (QTS) and its derivatives on nasal and ocular delivery of insulin. [13] However, no report was found in the literature regarding the absorption-enhancing effects of Acanthophyllum total saponin (ATS).…”