Immunomodulating polysaccharides from Lessertia frutescens leaves: isolation, characterization and structure activity relationship.
BACKGROUND
Sutherlandia frutescens (syn. Lessertia frutescens) is an indigenous plant in Southern Africa and has been extensively studied from the ethnobotanical point of view. Amongst the various traditional uses, several illnesses involving the immune system have been reported. Due to some of the therapeutic effects observed, in relation to the traditional uses reported by the "khoi san" and "nama" people on cancer related illnesses, the plant has been given the local name kankerbos (cancerbush). Recently the plant has also been used amongst HIV/AIDS patients to stimulate the immune system.


METHODS
Leaves of Sutherlandia frutescens were extracted sequentially with ethanol, 50% ethanol/water, and water at 50 and 100°C. The polysaccharides were extracted with water and fractionated by ion exchange chromatography and gel filtration to obtain enriched polysaccharide fractions. The bioactivities of the fractions were tested in the complement assay. Some of the fractions were treated with the enzyme pectinase, and the fragments thus produced were separated by gel filtration and their activities tested. Monosaccharide compositions and linkage analyses were determined for the relevant fractions.


RESULTS
The leaves of Sutherlandia frutescens contain polysaccharides of the pectin type. Fractions from both the water extracts of 50 and 100°C were bioactive. Fractions chosen for further studies showed that the fragment with the highest M(W) after the pectinase treatment had a substantially higher biological effect than the parent molecules. Based on a comparison of the different fractions it was concluded that galactose-rich regions were important for the bioactivity, these being of the AGII and AGI type, with the latter probably being more important than the former. Fragments rich in xylose also gave higher activity than those without it.


CONCLUSIONS
Our theory that the polysaccharides present in the leaves of Sutherlandia frutescens could be of importance as immunomodulating agents was confirmed. It was also shown that certain types of polysaccharides had a higher effect in the complement system than others. Thus both the water extracts obtained at 50 and 100°C contain interesting biologically active polysaccharides.
School of Pharmacy, University of Oslo, Oslo, Norway; GIAT-HKU joint Center for Synthetic Biology Engineering Research (CSynBER), Guangzhou Institute of Advanced Technology, Chinese Academy of Sciences, 511458 Nansha, Guangzhou, PR China.
Bingzhao
B
Zhang
School of Pharmacy, University of Oslo, Oslo, Norway.
Wei Kee
WK
Leung
School of Pharmacy, University of Oslo, Oslo, Norway.
Yuanfeng
Y
Zou
South African Herbal Science and Medicine Institute (SAHSMI), University of Western Cape, Bellville, South Africa.
Wilfred
W
Mabusela
Nelson Mandela Metropolitan University, George, Southern Cape, South Africa.
Quinton
Q
Johnson
School of Pharmacy, University of Oslo, Oslo, Norway.
Terje E
TE
Michaelsen
School of Pharmacy, University of Oslo, Oslo, Norway. Electronic address: b.s.paulsen@farmasi.uio.no.
Berit Smestad
BS
Paulsen
D002852:Chromatography, Ion Exchange; D003165:Complement System Proteins / Q000187:drug effects* / Q000276:immunology; D000431:Ethanol / Q000737:chemistry; D007887:Fabaceae / Q000737:chemistry*; D006801:Humans; D007155:Immunologic Factors / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D018515:Plant Leaves; D011134:Polysaccharides / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013696:Temperature; D014867:Water / Q000737:chemistry
D007155:Immunologic Factors; D010936:Plant Extracts; D011134:Polysaccharides; D014867:Water; D000431:Ethanol; D003165:Complement System Proteins
Complement system; Lessertia frutescens; Pectins; Polysaccharides; Sutherlandia frutescens