Vet. World, 2012, Vol.5(4): 248-254 REVIEW Saponin: Role in Animal system

Saponins are common in a large number of plants and plant products. It is having important role in human and animal nutrition. Saponins have biological role as membrane-permeabilising, immunostimulant and hypocholesterolaemic properties and it has found to have significant affect growth and feed intake in animals. These compounds have been observed to kill protozoans, to impair the protein digestion and the uptake of vitamins and minerals in the gut and to act as hypoglycemic agent. These compounds thus affect animals in both positive and negative ways.


Introduction Chemical Structure
The word 'saponin' is derived from the Latin Chemically, saponins are high-molecular-weight letters 'sapo' means soap and traditionally saponinglycosides in which sugars (1-8 residues) are linked to containing plants have been utilized for washing.The a triterpene or steroidal aglycone moiety (Hostettmann saponins are naturally occurring surface-active glycosides.and Marston, 1995).Saponins possess a variety of They are mainly produced by plants (Alfalfa, Soyabean, glycosyl groups covalently bound to the C3 position Lucerne, Berseem, Yucca, Mahua, Guar etc.), but also but some saponin contain two sugar chains attached at by lower marine animals (sea cucumbers, starfish etc.) the C3 and C17 (via C28) position (Vincken et al., and some rhizo bacteria (Yoshiki et al., 1998).They 2007).A large number of saponins could be possible derive their name from their ability to form stable, depending upon the modifications of the ring structure soap-like foams in aqueous solutions.This easily of aglycone moieties and number of sugars added to it, observable character has attracted human interest and in turn producing different biological properties.from ancient times.Saponins consist of a sugar moiety Saponin glycosides are divided into 2 types based on usually containing glucose, galactose, glucuronic acid, the chemical structure of their aglycones (sapogenins).xylose, rhamnose or methylpentose, glycosidically Saponins on hydrolysis yield an aglycone known as linked to a hydrophobic aglycone (sapogenin) which "sapogenin".may be triterpenoid or steroid in nature.The aglycone SAPONIN= SUGAR + SAPOGENIN may contain one or more unsaturated C-C bonds.The glycone aglycone oligosaccharide chain is normally attached at the C3 position (monodesmosidic), but many saponins have The so-called neutral saponins are an additional sugar moiety at the C26 or C28 position derivatives of steroids with spiroketal side chains.The (bidesmosidic).The great complexity of saponin acid saponins possess triterpenoid structures.structure arises from the variability of the aglycone The main pathway leading to both types of structure, the nature of the side chains and the position sapogenins is similar and involves the head-to-tail coupling of acetate units.However, a branch occurs, of attachment of these moieties on the aglycone.

Figure -1. Components of Saponin
used for their detection.The haemolytic action of saponins is believed to be the result of the affinity of the aglycone moiety for membrane sterols, particularly cholesterol with which they form insoluble complexes.The lesions that are caused by saponins are thought to be a micelle-like aggregation of saponins and cholesterol in the plane of the membrane, possibly with saponin molecules arranged in a ring with their hydrophobic moieties combined with cholesterol around the outer perimeter.The membrane pores or defects produced by saponins were long lasting and such membranes were then permanently permeable to large molecules like ferritin (Seeman, 1974).Besides, soyasaponins I and III, and dehydrosoyasaponin I have been shown to be able to open large Ca-dependent K conductance channels causing membrane hyperpolarization, suppression of electrical activity and relaxation of smooth muscle (McManus et al., 1993).
Effects on nutrient uptake through the intestinal membrane: Dietary saponins are poorly absorbed, so their biological effects occur in the digestive tract (Cheeke, 1996).Johnson et al., (1986) found that some saponins increase the permeability of intestinal mucosal cells in vitro, and inhibit active mucosal transport and facilitate uptake of substances that are normally not absorbed.Saponins (from Gypsophila, Quillaja, clover, guar and lucerne) also reduces transmural potential difference (TPD, the electrochemical gradient that acts as a driving force for active nutrient transport across the brush border membrane of the intestine) across the small intestine of the rat (Gee et al., 1989).An increase in the apparent permea-bility of the brush border observed at sublethal levels of saponins may have important implications for the uptake of macromolecules, such as allergens, whose passage through the epithelium is normally somewhat restricted (Gee et al., 1996).The presence of Gypsophila saponins enhanced the uptake of β lactoglobulin, a milk allergen in the jejunal loops' tips of brown Norway rats (Gee et al., 1997).
Some reports describe obstruction of the absorption after the formation of the triterpenoid hydrocarbon, of micronutrients by dietary saponins.Like, Gypsophila squalene, that leads to steroids in one direction and to saponins in the diet depressed mean liver iron (Fe) cyclic triterpenoids in the other.
concentrations and total liver Fe by impairing Fe

Biological role in animal systems
absorption (Southon et al., 1988).Probably the saponin formed complexes with dietary Fe rendering it unavailable Effects on cell membranes: A large number of the for absorption.Lucerne saponins were shown to biological effects of saponins have been ascribed to increase excretion of Fe and magnesium (Mg) when their action on membranes.In fact, their specific present in rat diets, and reduce plasma calcium (Ca) ability to form pores in membranes has contributed to and zinc (Zn) in pigs (Southon et al., 1988).These their common use in physiological research.Saponins saponins could complex with Fe and Zn in vitro and have long been known to have a lytic action on this complex formation might have hindered their Yucca saponins in ruminant nutrition was attributed to absorption.Triterpenoid saponins from Gypsophila the enhancement of the entrapment of NH -N from 4 and Quillaja included in the diet appeared to interfere urea-supplemented straw (Makkar et al., 1999).This with the absorption of vitamins A and E in chicks increases the availability of nutrients to rumen bacteria (Jenkins and Atwal, 1994).But feeding a steroid and reduces environmental damage by decreasing saponin (sarsasaponin) at the same level had no effect losses of NH to the air.4 on any of these parameters.
The saponins of lucerne origin had a detrimental effect on rumen fermentation and caused a reduction Effects in other single-stomached animals: There in total VFA and acetate to propionate ratio from 1.93 are also numerous reports of negative effects of dietary to 1.37 in the presence of 1% saponin in the medium.saponins.Dietary saponins depressed growth, feed The rumen microbes are able to deglycosylate the consumption and egg production in poultry (Jenkins saponins to release the steroid moiety, which affects and Atwal, 1994).These negative effects have been rumen fermentation.Yucca schidigera extract has ascribed to several properties of saponins such as been found to alter rumen fermentation favourably, reduced feed intake caused by the astringent and increase animal growth and milk production.Thalib et irritating taste of saponins (Oleszek et al., 1994), al., (1996) studied the effect of saponins of Sapindus reduction in intestinal motility (Klita et al., 1996), rarak fruit on rumen microbes of sheep and reported reduction in protein digestibility (Shimoyamada et al., that the methanol extract of seeds caused a 57% 1998) and damage to the intestinal membrane and reduction in the number of protozoa and 69% increase inhibition of nutrient transport described earlier in the in bacterial population which resulted in improved present review.
feed conversion efficiency and better gain in body Effects on protein digestion: Saponins reduce weight of the animals.Dietary saponins were often suspected of having a role in causing ruminant bloat protein digestibility by the formation of sparingly (Cheeke, 1996;Sen et al., 1998), but clear experidigestible saponin-protein complexes (Potter et al., mental proof for this is lacking in the literature.The 1993).Endogenous saponins affected the chymotrypsic absence of any positive effect in experiments where hydrolysis of soyabean protein, particularly glycinin Yucca saponins were fed to ruminants (Wu et al., (Shimoyamada et al., 1998).The digestibility of the 1994) might have been because animals with adapted bovine serum albumin-soyasaponin complex was rumen microbial population were used.much lower than that of free bovine serum albumin indicating that complexing with saponin had an Effect on Defaunation: There has been increased obstructing effect.
interest in saponin containing plants as a possible means of suppressing or eliminating protozoa in the Effect on rumen environment rumen.Saponins react with cholesterol in the Rumen fermentation: Jouany (1996) reported that ciliate protozoa contributed significantly to intra-protozoal cell membrane, causing the cell to rupture ruminal cycling of microbial nitrogen (N) and and lyse (Wina et al., 2005).In ruminants saponins are efficiency of microbial crude protein (MCP) synthesis, differentially toxic to rumen protozoa.The differential so reducing protozoa counts can improve dietary N toxicity may be explained by the presence of cholesterol utilization and increase MCP flow to the intestine.in eukaryotic membranes but not in prokaryotic cells Total concentrations of volatile fatty acids (VFA) were (Kilta et al., 1996).Saponins are degraded in batch reduced by elimination of protozoa.In the defaunated cultures of rumen fluid in vitro (Makkar and Becker, rumen fluid, molar proportion of propionate was 1997), although apparently the resultant sapogenins increased at the apparent expense of butyrate.Because are more resistant to degradation (Wang et al., 1998).protozoa in the rumen cause protein turnover by Sapogenins do not have the anti-protozoal property of predating on bacteria, defaunation increases the the parent saponin (Teferdegne et al., 1998).Foliage nitrogen utilization of the ruminant and may lead to an from Sesbania sesban, a multi-purpose leguminous increase in growth, milk, or wool production (Wina et  protozoal number in vitro studies with saponin supply of NH4 for microbial protein synthesis extracted from S. sesban leaves and dosage was (Hussain and Cheeke, 1995).A positive effect of 174g/kg hay.In contrast, feeding trial carried out in accelerated the metabolism of cholesterol in the liver Ethiopia failed to find any effect on protozoal numbers resulting lower serum levels.Saponins also reduced in the rumen of sheep fed on S. sesban (Odenyo et al., the more harmful LDL-cholesterol selectively in the 1997; Teferedegne et al., 1999).However, when S. serum of rats, gerbils and human (Matsuura, 2001).sesban was placed directly into the rumen via a rumen Other suggested mechanisms of action of saponins cannula, protozoal numbers decreased significantly include delaying the intestinal absorption of dietary fat (Odenyo et al., 1997).This finding suggests that by inhibiting pancreatic lipase activity (Han et al., deactivation of the saponins may have occurred before 2000).reaching the rumen, probably in the mouth by saliva.
Effects on the immune system: Saponin based Effect on Rumen Bacteria: Newbold et al., (1997) adjuvants have the unique ability to stimulate the cellhave found that bacterial numbers increase when mediated immune system, as well as to enhance foliage from S. sesban is introduced into the diet, antibody production and have the advantage that only presumably as a consequence of the suppression of a low dose is needed for adjuvant activity (Oda et al., protozoal numbers.Valdez et al., (1986) have found a 2000).The mechanisms of immune-stimulating action similar trend with Y. schidigera extract.Steroidal of saponins have not been clearly understood, but saponins from Y. schidigera have no effect on total or many explanations have been put forward.Saponins cellulolytic bacterial counts in Rusitec, however, reportedly induced production of cytokines such as inoculating fluid from the fermenter into a medium interleukins and interferons that might mediate their containing saponins decreases the viable count (Wang immunostimulant effects (Kensil, 1996).There is et al., 1998).
evidence that saponins may increase the immune Experiments using pure cultures of rumen bacteria response by increasing the uptake of antigens from the have indicated that there are also possible antibacterial gut and other membranes.effects of saponins.Y. schidigera extract abolishes Effect on methanogenesis: Many researches had growth of the fibre digester, Butyrivibrio fibrisolvens, been carried out to find ways to lower the methane and prolongs the lag phase of Streptococcus bovis production in ruminant animals.The symbiosis of (Wallace et al., 1994).Similar sensitivity of S. bovis to protozoa with methanogenic archaea was described by Y. schidigera extract has been found by Wang et al., Finlay et al., (1994) and selective suppression of the (2000), who additionally found that cellulose digestion rumen protozoa had been suggested to be a promising by Ruminococcus spp.and Fibrobacter succinogenes approach to reduce methane release (Dohme et al., is inhibited.1999; Moss et al., 2000).Inclusion of saponin significantly Effect on Rumen Fungi: A potentially very important reduced methane production in faunated rumen fluid, observation is that the anaerobic rumen fungi, but not in the defaunated rumen fluid, suggesting that Neocallimastix frontalis and Piromyces rhizinflata, are inhibition of methanogenesis by tea saponins was highly sensitive to Y. schidigera saponins (Wang et al., primarily due to their anti-protozoal activity.Formation 2000).Rumen fungi appear to fill an important niche of acetate and butyrate are usually accompanied by in the digestion of recalcitrant plant fibres, because production of hydrogen and carbon dioxide, whereas they cause physical as well as enzymic disruption of propionate formation involves a net uptake of hydrogen, plant cell walls (Orpin and Joblin, 1997).Thus, it may thus, defaunation decreases the hydrogen supply for well be advantageous to promote the bacterial methanogens in the rumen, leading to lower methane detoxification of the saponins in animals receiving emission.A number of studies have reported that saponins poor-quality forages or crop by-products.
or plants rich in saponins decreased the methane production in the rumen both in vitro (Pen et Holtshausen et al., 2009) studies.Additionally, it has animals including human subjects.Large mixed been suggested that methane production may also be micelles formed by the interaction of saponins with affected by saponins as a result of reduced rate of bile acids account for their increased excretion when methanogenesis via diminished activity of methane saponin-rich foods such as soyabean, lucerne and producing gene without changing the total methachickpea are consumed (Oakenfull and Sidhu, 1990).nogen population (Guo et al., 2008).As the saponin decreases absorption of both endogenous and exogenous chlolesterol and thereby, As a Haemolytic agent: The saponins cause haemolysis of red blood cells perhaps by increasing Isolation of saponins the permeability of the plasma membrane and inhibit Plant saponins are isolated in the following ways; smooth muscle activity.Baumann et al., (2000) investigated the effect of saponins on the membrane

Figure- 2 .
Figure-2.Pathways of saponin synthesis tree from sub-Saharan Africa, inhibited protozoal al., 2005).activity in vitro and transiently depressed the number Yucca extract can also bind NH when ruminal of protozoa in the rumen of sheep in the United 4 NH concentrations are high, and release it again when Kingdom (Newbold et al., 1997; Teferedegne et al., al., 2006, Effects on cholesterol metabolism: A number of 2008; Holtshausen et al., 2009) and in vivo (Pen et al., studies have shown that saponins from different 2007; Santoso et al., 2004; Wang et al., 2009a; sources lower serum cholesterol levels in a variety of