Intestinal absorption and excretion of octapeptidescomposed of D amino acids.

Abstract

Octapeptides ntheized from D amino adds were absorbed from the i id excreted In urine of al rats drinking 5% glucose/1% nineconingthe 12'I-ladbed peptides at 0.1-25 ng/dI. The rats fluid at the rate of about 20 ml/hr and produced urine at 15 ml/hr for several hours during the nocturnal feeding period. Sixty- RATIONALE OF EXPERIMENTS Rats provided with diluted milk or with 5% glucose as the sole source of calories will drink >50% of their body weight during each nocturnal feeding period, producing correspondingly large volumes of urine (11,12). Inert solutes added to the ingestate may be recovered from the urine, thereby providing a minimum estimate of their absorption from the gastrointestinal tract. For example, creatinine or mannitol ingested with 5% glucose can be recovered from urine or other body fluids with a yield of 50-65% in experimental animals (12) and >80%6 in man (13). Experiments of this type provide strong evidence that solutes the size of hexoses or amino acids can be absorbed paracellularly under conditions where fluid absorption and junctional permeability of the small intestine have been increased. In the present investigation we applied this technique to peptides synthesized from D amino acids, anticipating that such molecules would not be recognized by peptidases or transport proteins. For this purpose we synthesized three such peptides having approximately the same molecular weights (octapeptides) but with differing lipid solubilities and net electrical charge (Table 1). Tyrosine (Y) was included in the sequence to permit labeling with 125I, but otherwise the composition and sequences were arbitrary and bear no known relation to biologically active peptides.In preliminary experiments it was found that 30-60% ofthe 125I label from all three of the peptides listed in Table 1 was recovered in urine after ingestion with glucose. However, we soon discovered that the two most lipophilic peptides (DP1 and DP2) were partially converted to polar compounds by the liver and were subsequently recycled in the enterohepatic circulation. Passage of these polar compounds through sizing columns or Bio-Gel Pa (BioRad)] indicated that alteration of the original peptides in liver did not involve major changes of molecular weight. Only the lipid-insoluble peptide DP3 was excreted in urine unaltered, thus providing an uncomplicated test of the hypothesis presented in the Introduction. For this reason the present communication will be concerned mainly with DP3, leaving a detailed description of the more complex behavior of DP1 and DP2 for a subsequent report. METHODSAnimals and Experimental Protocols. Adult male or female rats were maintained on chow pellets at -15 g/day with water ad libitum. This food intake was sufficient to maintain body weight, but the limitation offood made the rats eager to ingest 5% (wt/vol) glucose when they were placed in stainless steel metabolism cages for administration of fluids and collection of feces. Fluid was supplied from weighed bottles, and in Abbreviation: TFA, trif...

Region-Dependent Role of Cell-Penetrating Peptides in Insulin Absorption Across the Rat Small Intestinal Membrane

“…By contrast, the internalization efficiency of penetratin is retained even when its sequence is partially modified as described above, which suggests that fractionated penetratin displays an internalization ability (21,22). The superior enhancing effect of PenetraMax on intestinal insulin absorption may be attributed to the change in the positions of the aromatic amino acid tryptophan (Table I) (21,22,49). This would allow a high degree of conformational flexibility of the interacting moieties, thus stabilizing the conformation of the peptide at the water-lipid interface and facilitating the insertion of PenetraMax into the lipid bilayer (51,52).…”

“…The proteolytic stability of CPPs is a critical requirement for their therapeutic application, and it is essential that they can (13,15,49). In addition to this proteolytic stability, we should consider another factor.…”

Potent D-peptide inhibitors of HIV-1 entry

“…Because D-peptides are not degraded by proteases they have the potential for oral bioavailability (29,30), extended persistence in circulation (28), reduced immunogenicity (36), long shelf life, and use in harsh mucosal environments as a topical prophylactic microbicide. The D-peptides reported here are now sufficiently potent for preclinical studies, which will ultimately determine whether these theoretical advantages translate into a valuable new class of agents for the prevention and treatment of HIV/AIDS.…”

“…In contrast, D-peptides have several theoretical advantages: (i) they are resistant to proteases (27), which can dramatically increase serum half-life (28), (ii) short D-peptides can be absorbed systemically when taken orally (29,30), whereas L-peptides must be injected to avoid digestion, and (iii) D-peptides are a rich unexplored source of structural diversity because they can bind to targets with unique interface geometries not available to L-peptides. Despite these potential advantages, however, the promise of D-peptides has thus far been largely unfulfilled.…”

Characterization of a Proteolytically Stable D-Peptide That Suppresses Herpes Simplex Virus 1 Infection: Implications for the Development of Entry-Based Antiviral Therapy

“…Peptide therapeutics are currently on the rise due to several advantages such as high potency and selectivity and ease of synthesis and modification (20)(21)(22) and, most importantly, a lack of the significant side effects and toxicity associated with conventional antiviral drugs (23)(24)(25). However, the major limitations of peptide therapeutics are their rapid clearance and susceptibility to proteases (13,22,(26)(27)(28). DG2, however, overcomes a major obstacle to in vivo peptide therapy: stability with respect to proteases.…”