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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
(Oral Abstracts)Soy and Cancer
Soybean Anticarcinogens / Anticancer MechanismsBBI - The Trypsin - and Chymo-trypsin-Inhibitor From Soybeans: Friend or Foe?
Yehudith Birk.
The Hebrew University of Jerusalem, Institute of Biochemistry, Food Science and Nutrition, Rehovot, Israel.BBI, The Bowman-Birk trypsin- and chymotrypsin-inhibitor from soybeans, consists of a polypeptide chain of 71 amino acids highly cross-linked by 7 disulfide bridges. The inhibitor contains two independent inhibitory sites, at Lys16-Ser17 and Leu43-Ser44 against trypsin and chymotrypsin, respectively. BBI and STI, the Kunitz soybean trypsin inhibitor, are the two major protease inhibitors in soybeans. The failure of ingested soybean trypsin inhibitors to cause growth depression was demonstrated in different animal species. However, ingestion of raw soybean meal or soybean trypsin inhibitors caused enlargement of the pancreas in rats, chicks, mice and young guinea pigs but not in adult guinea pigs, dogs, growing swine, calves, monkeys and presumably, humans. The alleged involvement of soybean trypsin inhibitors in the development of pancreatic nodular hyperplasia and acinar adenoma in male Wister rats fed raw soybean meal or unheated soy protein isolates for two years (the "USDA trypsin inhibitor study"), raised considerable criticism. Similar long-term feeding of mice and hamsters failed to induce carcinogenesis in their pancreases even in the presence of chemical carcinogens. In view of the difference in species response to the presence of inhibitors in the diet, the relevance of human remains to be elucidated.
The reports in the last decade of the involvement of BBI in prevention of tumorigenesis in vitro and on the ability of dietary BBI to suppress or prevent carcinogenesis in mice in vivo triggered a series of experiments to clone and express BBI and E. coli and in yeast. Biologically active BBI was resolved by refolding denatured BBI from the inclusion bodies. Attempts to synthesize active BBI point-mutants and fragments are in progress.
In a series of experiments in rats, BBI significantly counteracted the nephrotoxicity induced by the antibiotic drug gentamicin. BBI did not effect the antimicrobial activity of gentamicin when assayed on E. coli and showed no side effects.Finally, failure of stored product pests, such as Tribolium castaneum, to develop on raw soybeans and the full inhibition of Tribolium midgut trypsin by BBI support the hypothesis that BBI comprises a safe insect-control agent during seed storage.
In conclusion, evaluation of the alleged anti-nutritional properties of BBI and of other legume seed protease inhibitors for human nutrition should be placed in perspective
in relation to the level of inhibitors in the diet as well as weighed with respect to their therapeutic and cancer-prevention potential.Soy Symposium Home http://soyfoods.com/symposium/
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