Insulin is an effective endogenous hormone used in the treatment of diabetes mellitus. Due to the low lipophilicity and the easy destruction of insulin molecules by gastric acid or by gastric intestinal enzymes or by both, only minimal amounts of insulin can be absorbed from adult animals' gastrointestinal tracts. The administration of insulin presently is limited to the parenteral methods. In this proposed research project, insulin is modified so that a) a physiologically active insulin molecule can be transported into the systemic circulation when it is administered orally and b) the bioavailability of the orally administered insulin will reach or be close to that of intravenously administered insulin (i.e. approximately 100% bioavailable). To achieve the above goals, lymphatic transport as well as portal vein transport of the modified insulin must be utilized. We propose to modify insulin in the form of sandwich complexes in which insulin first forms """"""""core"""""""" complexes via hydrophobic force with sodium dodecyl sulfate (SDS) either in a high binding ratio of one gram of insulin to 1.4 grams of SDS, or in a low binding ratio where one gram of insulin binds 0.4 gram of SDS. These core complexes are negatively charged, rodlike and not stable in the gastric acidic environment. To protect these core complexes, a positive shell of quaternary ammonium ion, R3N+ -R'(H) in a 1:1 ratio with SDS is provided via electrostatic force. These quaternary ammonium ions can be either protonated tertiary amines or ester-like quaternary ions, i.e. R'-C00-CH(CH3)-+NR3, or quaternary ammonium ions structurally similar to that of 2-monglycerides. Animal experiments include macroscopic gastro-intestinal absorption studies (oral and intravenous administrations) to determine the effectiveness of insulin complexes as orally effective therapeutic agents in terms of half-life, clearance bioavailability and bioequivalence to the iv regular insulin, and microscopic investigations of the factors which facilitate their lymphatic transport; of their resistance against hepatic degradation. As a result of the above investigation, the routes of transport of an insulin complex from the GI tract to the systemic circulation can be characterized, and the extent of its transport can be optimized. Also included in this proposal are the in vitro studies of lipophilicity and stability of complexes. Acute and chronic toxicity of complexes on normal rats will also be investigated.
