Anti-inflammatory and anti-arthritic effects of yucca schidigera: A review

PR Cheeke¹ ,² , S Piacente³ and W Oleszek⁴

Abstract

Yucca schidigera is a medicinal plant native to Mexico. According to folk medicine, yucca extracts have anti-arthritic and anti-inflammatory effects. The plant contains several physiologically active phytochemicals. It is a rich source of steroidal saponins, and is used commercially as a saponin source. Saponins have diverse biological effects, including anti-protozoal activity. It has been postulated that saponins may have anti-arthritic properties by suppressing intestinal protozoa which may have a role in joint inflammation. Yucca is also a rich source of polyphenolics, including resveratrol and a number of other stilbenes (yuccaols A, B, C, D and E). These phenolics have anti-inflammatory activity. They are inhibitors of the nuclear transcription factor NFkappaB. NFkB stimulates synthesis of inducible nitric oxide synthase (iNOS), which causes formation of the inflammatory agent nitric oxide. Yucca phenolics are also anti-oxidants and free-radical scavengers, which may aid in suppressing reactive oxygen species that stimulate inflammatory responses. Based on these findings, further studies on the anti-arthritic effects of Yucca schidigera are warranted.

Introduction

Yucca schidigera is an herbaceous plant of the lily family, native to the deserts of the south-western United States and northern Mexico. This plant was used in traditional medicine by Native Americans to treat a variety of ailments including arthritis. Yucca products are currently used in a number of applications. Yucca powder and yucca extract are used as animal feed additives, as discussed in detail by Cheeke and Otero [1]. Beneficial effects in livestock and poultry production include: increased growth rate and improved feed conversion efficiency, reduction in atmospheric ammonia in confinement animal and poultry facilities, anti-protozoal and nematocidal activity, modification of ruminal microbe populations, inhibition of Gram-positive bacteria, reductions in stillbirths in swine, reduction in egg and tissue cholesterol contents, and anti-arthritic activity in horses and dogs. Other applications include the use of yucca extract as a foaming agent in beverages, and use in crop production as nematode and fungi-control agents, as a soil wetting agent, and crop growth stimulant. Yucca products have GRAS status, so are FDA-approved for use in humans.

Yucca saponins

Yucca contains a number of phytochemicals which contribute to these effects. The best known are the steroidal saponins. Saponins are natural detergents [2] that form stable foams. Saponins contain a lipophilic nucleus (the sapogenin) and one or more side chains of hydrophilic carbohydrate (Fig. 1). Thus the intact saponin molecule is a surfactant, with both fat-soluble and water-soluble moities. It has been known for many years [3] that saponins form insoluble complexes with cholesterol. The hydrophobic portion of the saponin (the aglycone or sapongenin) associates (lipophilic bonding) with the hydrophobic sterol nucleus of cholesterol in a stacked micellar aggregation [4].

Interactions of saponins with cholesterol and other sterols account for many of their biological effects, particularly those involving membrane activity. It was demonstrated more than 45 years ago that dietary saponin reduces blood cholesterol levels [5,6]. This effect is a result of the saponins binding to cholesterol excreted in bile, thus inhibiting entero-hepatic cholesterol recycling. Dietary yucca extracts lower total and LDL cholesterol levels in hypercholesterolemic humans [7]. Saponins affect the permeability of intestinal cells by forming complexes with cholesterol in mucosal cell membranes [8]. In a similar manner, saponins have anti-protozoal activity by complexing with cholesterol in protozoal cell membranes, causing damage to the integrity of the membrane, and cell lysis. This has been well demonstrated with rumen protozoa in vivo [9-11]; and in vitro [12,13]. The antiprotozoal (cholesterol-binding) activity requires the intact saponin structure with both nucleus and side chain present.

Protozoal diseases in which part of the life cycle occurs in the gastrointestinal tract respond to the anti-protozoal activity of saponins. For example, yucca saponins are as effective as the drug metronidazole in killing tropozoites of Giardia lamblia in the intestine [14]. Yucca schidigera contains as much as 10% of steroidal saponins in its stem dry matter, making this plant one of the richest commercial sources of saponins. Acid hydrolysed fractions of yucca contain both furostanol and spirostanol aglycones. These include sarsapogenin, markogenin, smilagenin, samogenin, gitogenin and neogitogenin [15]. In the plant they can be found in a multi-component mixture of glycosides [16,17]. They can be found both as monodesmosides with one sugar chain attached at 3-O- and bidesmosides with two sugar chains at 3-O- and 26-O- positions (Fig. 1). Tanaka and co-workers identified as many as 13 structurally different saponins, but all of them were monodesmosides, given trivial names YS-I-XIII [16]. In the work of Oleszek and co-workers, eight individual saponins were isolated and identified out of which five were known spirostanol and three new furostanol structures [17]. However, monodesmosides made up about 93% of total saponins present.