Biological impacts of arabinogalactans in humans: Ethnopharmacology and modern pharmacognosy.

摘要

Numerous dietary supplements are alleged to modify immune cells and improve health, although relatively few have been tested for in vivo efficacy. The purpose of this work was to investigate the ability of arabinogalactan (AG), a polysaccharide gum from the Western Larch (Larix occidentalis ) and Tamarack (L. laricina) trees to modify hematological and blood cell measures and gastrointestinal microbiology in healthy adults. A review of the ethnopharmacological uses of Larix species by Native Amerindians revealed that these plants have been used by numerous Tribes to treat a variety of bacterial and gastrointestinal illnesses, although no studies exist confirming efficacy. In a clinical setting, one hundred healthy adult volunteers were randomly assigned to receive either 0 g (placebo; rice starch), 1.4g, 4.4g or 8.4g larch AG or 8.4g tamarack AG daily for six months. At baseline and at one-month intervals, blood samples were collected and analyzed. No significant differences were found for white or red blood cell counts, hemoglobin, hematocrit, or cell volumes; no changes in monocytes, neutrophils, lymphocytes, basophils or eosinophils were observed at 1.4g, 4.4g or 8.4g larch AG, although 8.4g tamarack AG containing phenolics increased monocytes. In a separate study, twenty healthy adult volunteers were given 15g and 30g of larch AG in a three-week crossover trial. Both doses resulted in a significant increase in % monocytes (p = 0.02 and p = 0.04, 15g and 30g, respectively). 4.4g/day of larch AG induced both a significant increase in Bifidobacterium spp. and a reduction in Clostridium spp. (p = 0.0002). When equivalent 8.4g doses of larch and tamarack AG were assessed for prebiotic potential, larch AG was more effective than tamarack in increasing Bifidobacteria levels. This increase persisted for three months: at month 6 adaptation occurred. In vitro batch fermentation studies confirmed that larch and tamarack AG differentially alter the gut microflora. It is likely that phenolic contaminants resulting from different processing methods are partly responsible for these physiological effects. Collectively, this work suggests that AG may be useful in modifying the lower bowel microflora, thus acting as a prebiotic. The immune-stimulating potential of Larix AG deserves further study.