Larch Arabinogalactan

Alternative Medicine Review, Oct, 2000

Introduction

Larch arabinogalactan is a polysaccharide powder derived from the wood of the larch tree (Larix species) and comprised of approximately 98 percent arabinogalactan. Arabinogalactans are found in a variety of plants but are more abundant in the Larix genus, primarily Larix occidentalis (Western Larch). The Western Larch is unique among pines in that it loses its needles in the fall. Western Larch is also known as Mountain Larch or Western Tamarack and is native to the Pacific and Inland Northwest United States as well as parts of British Columbia, Canada.[1] Larch arabinogalactan is approved by the U.S. Food and Drug Administration (FDA) as a source of dietary fiber, but also has potential therapeutic benefits as an immune stimulating agent and cancer protocol adjunct.

Description and Biochemistry

Pharmaceutical-grade larch arabinogalactan is a fine, dry, off-white powder with a slightly sweet taste and mild pine-like odor. It dissolves completely in water or juice, is low in viscosity and therefore easy to administer, even to children. It is composed of galactose and arabinose molecules in a 6:1 ratio, with a small amount of glucuronic acid. Arabinogalactans are long, densely branched polysaccharides of varying molecular weights (10,000-120,000). Lower molecular weight polysaccharides typically exhibit an anti-inflammatory, anti-complement, antiallergy effect, while those of higher weights stimulate natural killer (NK) cell cytotoxicity and reticuloendothelial cells. In the case of larch arabinogalactan, molecular weights of the two major fractions are 16,000 and 100,000, perhaps accounting for its wide range of therapeutic properties.[2]

Pharmacokinetics

Human studies on the pharmacokinetics of larch arabinogalactan are few and the amount absorbed following an oral dose remains unclear. Animal studies indicate that intravenous injection of purified larch arabinogalactan results in 52.5 percent of the dose being present in the liver and 30 percent in the urine 90 minutes after dosing. Hepatic clearance occurred with a half-life of 3.42 days.[3] Non-absorbed larch arabinogalactan is actively fermented by intestinal microfiora and is particularly effective at increasing beneficial anaerobes such as Bifidobacteria and Lactobacillus.[4]

Clinical Indications

Dietary Fiber

Larch arabinogalactan is an excellent source of dietary fiber that is able to increase short-chain fatty acid production (primarily butyrate) via its vigorous fermentation by intestinal microflora.[2] It is well documented that butyrate is essential for proper colon health as it is the preferred substrate for energy generation by colonic epithelial cells.[5] Butyrate also acts as a protectant for the intestinal mucosa against disease and cancer-promoting agents.[6] Arabinogalactan added to human fecal homogenates has also been shown to decrease ammonia generation, and therefore may be of clinical value in the treatment of portal-systemic encephalopathy, a disease characterized by ammonia build-up in the liver.[4] Larch arabinogalactan given to human subjects increased levels of beneficial intestinal anaerobes, particularly Bifidobacterium longum, via their fermentation specificity for arabinogalactan compared to other complex carbohydrates.[7,8]

Cancer Protocols

Larch arabinogalactan may be an effective adjunct to cancer therapies due to its ability to stimulate NK cell cytotoxicity, stimulate the immune system, and block metastasis of tumor cells to the liver.[2] Tumor metastasis to the liver is more common than to other organ sites, probably due to tumor cell specificity for lectin-like receptor sites found in liver parenchyma. Animal studies have demonstrated arabinogalactan's ability to inhibit or block lectin receptor sites, thereby reducing tumor cell colonization of the liver and also increasing survival time of the subjects.[9-11] Pretreatment with larch arabinogalactan was found to stimulate NK cell cytotoxicity via potentiation of the cytokine network, primarily via an increase in the release of gamma interferon.[12]

Pediatric Otitis Media

Recurrent otitis media is common in pediatric populations and it appears that improving immune system function might lead to a decrease in both frequency and severity of this condition. Research has demonstrated larch and other arabinogalactans to be capable of enhancing the immune response to bacterial infection via stimulation of phagocytosis, competitive binding of bacterial fimbriae, or bacterial opsonization. This was found to be particularly true for infection by gram negative organisms such as Escherichia coli and Klebsiella species.[2,13] In addition, D'Adamo reports a decrease in occurrence and severity of otitis media in pediatric patients supplemented prophylactically with larch arabinogalactan.[2] Larch arabinogalactan's mild taste and excellent solubility in water and juice make it a relatively easy therapeutic tool to employ in pediatric populations.

Chronic Disease