Silkworms for Medicine & Good Health

August 17, 2014

A SILKWORM A DAY may not keep the doctor away, but for some in South Korea silkworm proteins are the pathway towards reduced Alzheimer’s disease, less diabetes, less fatigue, stronger muscles and perhaps eventually gold and silver Olympic swimming medals; much the way ghost moth caterpillars naturally infected with cordyceps fungi are used by Chinese athletes and herbal medicine practitioners. Silkworm production dates back several thousand years, and likely came to the Korean Peninsula via China, where over a thousand years ago bolts of silk (30 ft/bolt; one day’s production by a skilled weaver) were equal to silver and gold as hard currencies. A director of the International Dunhuang Project (IDP) investigating ancient Silk Road links between Asia, the Middle East and Europe, Susan Whitfield, wrote in her book, Life Along the Silk Road, that distrust of promissory notes led to demands that horse buyers pay with bolts of silk. According to A Guide to Korean Cultural Heritage (Korean Information Service, 2001): “In Korea, ma (hemp) and ppong (mulberry) trees were cultivated; myeonpo (cotton cloth) and mapo (hemp cloth), as well as hapsa (twisted thread)” and jasu (embroidery) on silk date back well over a thousand years to a time when China imported fine silks from Korea.

Medically, biodegradable silkworm fibers are highly valued for their biocompatiblity (i.e. minimal immune response) when sewn with human tissues as sutures or stitches. Various formulations of silk are also useful in surgical or bioengineering operations such as growing new bones, nerves or blood vessels. “As has been documented over decades, silk protein exhibits high mechanical strength and flexibility, permeability to water and oxygen and can be made into nets, sponges or membranes, being easily handled, manipulated and sterilized…especially in tissue engineering for the generation of artificial bones or ligaments,” write researchers at China’s Nantong University investigating “silk-based or silk-coated materials for peripheral nerve repair.” The idea being to use silk “as scaffold material to prepare the tissue engineered nerve grafts for promoting peripheral nerve regeneration.” Silk scaffolds or blood vessels can also be designed to release various drugs (e.g. anti-coagulants, antimicrobials, anti-inflammatory agents).

Silks can also be naturally colored or made luminescent (fluorescent) by incorporating coloring agents into silkworm mulberry leaf diets: Hence, “novel silk-based material (that) not only maintains the superior properties of natural silk but can also be imbued with additional properties to perform sensing and monitoring functions” such as measuring changes in wound or tissue pH (i.e. acidity, alkalinity), says Dr. Han Mingyong, Senior Scientist at Singapore’s Institute of Materials Research and Engineering (IMRE). “The novel silk material can be used as fabrics in apparel, and furnishing. In biomaterials, it can add function to sutures, wound dressings, and tissue engineering scaffolds.” All this at “minimal cost and with little modification” of centuries-old standard silkworm production practices, but with real environmental benefits because: “The lengthy dyeing process and post-processing steps in conventional silk making are completely removed.”

Silkworm silk production involves getting the adult female silkworm moths, which are flightless and can no longer live in the wild after centuries of domestication, to lay eggs that hatch into caterpillars living on mulberry (some species prefer oak) leaves. When the silkworms pupate, they spin a silken cocoon which is dropped in boiling water so that the outer silk threads unravel and can be spun into the fibers of commerce. “According to legend, 5,000 years ago Chinese Empress Xi Ling-Shi discovered silk when a silkworm cocoon fell into her hot cup of tea,” says Ecoworldly.com. “She unraveled the strange cocoon and, wrapping the thread around her finger, soon realized what an exquisite cloth it would make…If this is true, the silkworm that haplessly fell into the empress’ cup on that fateful day met a fate very similar to that of modern day silkworms.” Being insects, which are animals, they are not vegetarian fare; those concerned with animal cruelty and animal rights activists need to consider that these silkworms are in essence a human-created species (almost a symbiosis) and unable to survive in the wild.

Beondegi (번데기), the boiled or steamed silkworm chrysalis, are served as a snack food on the streets in Korea, and University of Florida, Gainesville, entomology professor Nan-Yao Su, who donated termite trap (Sentricon) royalties to establish the Entomological Society of America’s (ESA) “Nan-Yao Su Award for Innovation and Creativity in Entomology,” told me of eating silkworm snacks as a student in Japan. Dr. Su was not that impressed, an opinion shared by a South Korean and her Brazilian guest’s “gag me with a spoon response” on Izumislife vlog on YouTube; though an older Korean lady in the background, presumably more well-versed in beondegi’s medicinal properties was gulping down the boiled insects sold by the street vendor like there was no tomorrow (increased longevity may indeed be a beondegi benefit). Evidently, silkworms or beondegi (번데기) are a cultivated taste. But Dr. Su, with Professor Marjorie Hoy as my witness, professed not to be a Trader Joe’s fan either. So, I kept to my plan to attend the Tuesday night ESA Annual Meeting Korean Young Entomologists networking meeting, which led off with drones for delivering biocontrol insects and concluded with a trio of researchers fresh off the plane from South Korea to talk (in Korean; with slides in English) about their impressive latest research on the medical benefits of eating silkworm proteins. I was impressed with the research, and spent the last few months reading the English language scientific literature on silkworms for medicine and good health. The result is an overly long blog, like those 3-hour articles I used to read in the New Yorker instead of going to sleep at night; but since the blog readers mainly come here via search engines looking for information on a topic, I figure overly long is okay.

The Korean Young Entomologists (KYE) Member Symposium led off with Yong-Lak Park’s “Shooting insects from the sky: Aerial delivery of natural enemies using aerospace engineering,” and finally sometime between 9 and 10 at night (some time changes from ESA Internet site) came the silkworm presentations by Eunyoung Ahn, Hyobin Seo, and Yiseol Kim from South Korea’s Kyungpook National University. Researchers Sungpil Ryu, Taedong Kwon, Yunghi Yeo, and Mihee Cho contributed to the work, but were not present. The researchers made the point that silkworm pupae had a higher protein and amino acid content than soybeans, and were high in desirable unsaturated fatty acids that lowered blood lipid levels (anti-obesity). In rat feeding trials, powdered, freeze-dried silkworm proteins increased skeletal muscle volume when swimming was the exercise. This has obvious appeal to body builders and others involved in exercise and training seeking to increase muscle mass, strength and energy. Specific amino acids (glutamine, branched-chain amino acids, cysteine) were singled out as most important to the immune systems of athletes. A combination of silkworm proteins and exercise had multiple beneficial effects: increased antioxidants; decreased MDA and inflammatory cytokines. Swimming plus silkworm pupae also improved fat metabolism, leading to lower blood lipid levels; so a combination of silkworm protein and exercise was deemed good for promoting weight loss or combating the worldwide epidemic of obesity caused by “excess nutrition” (e.g. the trend towards super-sized portions). Other research indicated benefits involving blood cholesterol, reduced fat synthesis and accumulation, and preventing liver cirrhosis in high-fat diets. Thus, silkworm pupae are potential weight-loss foods or food supplements.

The 25-volume Dong-eui-bo-gam (동의보감) (Mirror of Eastern Medicine), published in 1613 by the legendary Korean royal physician Heo Jun (허준), called silkworm pupa a natural healthy food and nontoxic remedy for diabetes, ischemic disease and “thinning.” Modern medical research indicates Heo Jun knew what he was talking about, and was actually a couple of centuries ahead of modern Western medicine. Our knowledge of the potential medical benefits of silkworms is rapidly expanding, particularly in South Korea, China and Japan; and to a lesser degree in India, where the silkworms are often a different species feeding on oak tree leaves. We have only scratched the surface of the medical benefits of silkworms in this blog.

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Pheromone Revolution Hits Half Century Mark

October 7, 2009

HALF a CENTURY ago the PHEROMONE REVOLUTION commenced in earnest. German chemist Adolf Friedrich Johann Butenandt opened the floodgates as lead author of an article announcing the isolation and chemical identification of a sex pheromone female silkworm moths produce to attract male mates. Butenandt had already shared the 1939 Nobel Prize in chemistry for discovering human reproductive steroid hormones. So the 1959 article announcing the first pheromone in the monthly chemical science journal Zeitschrift für Naturforschung B (14B:283-4) attracted the attention of Rachel Carson and stimulated the efforts and imaginations of many others searching for insecticide-reducing alternatives.

HALF a MILLION virgin female silk moths were sacrificed over a span of almost THREE DECADES to identify that first sex pheromone, named bombykol because Bombyx mori is the scientific name of the Chinese silk moth of textile fame. In the past half century, thousands more pheromones have been identified, mostly from pest insects of economic interest. But also increasingly from beneficial insects providing biological control.

According to researchers like Jeffrey Aldrich at the USDA-ARS Chemicals Affecting Insect Behavior Laboratory (CAIBL) in Beltsville, MD, the potential applications of natural enemy pheromone and semiochemical research, such as herding beneficial insects into crop fields where they are needed, is still in its infancy. Projects include using pheromones to increase biocontrol by predatory spined soldier bugs (Podisus maculiventris). These beneficial stink bugs are capable of biologically controlling pesticide-resistant Colorado potato beetles, Mexican bean beetles, and cabbage and tomato caterpillars.

One idea is using pheromones to trap natural enemies, and then creating mini-insectaries by placing cages full of natural enemies into crop fields and landscapes. Predator production can be maximized with “an in-field nursery where we are putting these trapped bugs right inside of the (mesh) cage” over plants in the field, said Aldrich. “You pick a mesh size where the adults can’t get out, but when they lay eggs then the nymphs can walk out and start feeding on pest species in the vicinity.” In field tests, potato defoliation was reduced and yield significantly increased.

In bean field tests, spined soldier bug nymphs walked upwind towards an aggregation pheromone. In sequential plantings, this technique could be used by farmers to move or herd predators out of maturing fields into more newly planted fields. Pheromone technologies are also being explored to maximize biocontrol by minute pirate bugs, big-eyed bugs, tachinid flies, and other natural enemies.