An Investigation into the Gastrointestinal Stability of Exenatide in the Presence of Pure Enzymes, Everted Intestinal Rings and Intestinal Homogenates

Abstract

The purpose of this study was to investigate the gastrointestinal stability of exenatide to determine the key factor(s) contributing to peptide degradation during the oral delivery process. The effects of pH and various digestive enzymes on the degradation kinetics of exenatide were determined. Moreover, the degradation clearances of peptide were also examined using rat everted intestinal rings and intestinal homogenates from various intestinal locations. Exenatide was comparatively stable within a pH range of 1.2-8. However, obvious degradation was observed in the presence of digestive enzymes. The order of enzymes, in terms of ability to degradate exenatide, was chymotrypsin>aminopeptidase N>carboxypeptidase A>trypsin>pepsin. Chymotrypsin showed the greatest ability to degrade exenatide (half-life t 1/2 , 5.784 10 2 h), whereas aminopeptidase N and carboxylpeptidase A gave t 1/2 values of 3.53 and 10.16 h, respectively. The degradation of exenatide was found to be peptide concentration-and intestinal site-dependent, with a lower clearance in the upper part of the duodenum and the lower part of the ileum. When using intestinal homogenates as enzyme sources, the order, in terms of peptide degradation ability, was ileum>jejunum>duodenum. However, no significant difference was observed in the remaining peptide concentrations throughout 2 h of incubation, which may be due to the involvement of cytosolic enzymes. These results revealed key factors contributing to peptide degradation, and suggest that the inhibition of chymotrypsin and site-specific delivery of exenatide might be advantageous in overcoming metabolic obstacles during its oral delivery.Key words exendin-4; enzymatic degradation; gastrointestinal stability; kinetics Exenatide is a synthetic 39-amino-acid peptide amide with the same amino acid sequence as exendin-4 which was originally isolated from lizard venom, and the sequence of exenatide is shown in Fig. 1. 1) It bears a 53% structural homology to glucagon-like peptide-1 (GLP-1) and can be used as a GLP-1 receptor agonist.2) In comparison with GLP-1, exenatide has a longer half-life due to its resistance to dipeptidyl peptidase IV degradation, and is mainly degraded and eliminated in the kidney after absorption into the systemic circulation.3) Exenatide was approved by the U.S. Food and Drug Administration (FDA) for the treatment of type 2 diabetes in 2005.4) Generally, the medication is administrated subcutaneously twice daily. More recently in 2012, exenatide-loaded extended-release microspheres were approved by the FDA, which allowed it to be injected once a week for the treatment of type 2 diabetes. Although this long-acting medication can significantly reduce the frequency of injections, the therapeutic application of exenatide is still limited due to patient noncompliance related to both the expense associated with injection and pain at the site of injection. Therefore, non-injection routes of administration for exenatide have been the focus of attention over the past several years.5-10) Among...

Phase‐Changeable Nanoemulsions for Oral Delivery of a Therapeutic Peptide: Toward Targeting the Pancreas for Antidiabetic Treatments Using Lymphatic Transport

“…Although some of the fluorescence signal from the DiO‐vehicle was observed in the pancreas of each test rat in the group that was orally treated with free Cy5‐EXT + empty PC/NEMs, no significant Cy5‐EXT signal was detected in any major organs. Negatively charged vehicles, such as lipid‐based particles, have been demonstrated to undergo greater intestinal lymphatic uptake than neutral or positively charged vehicles, while free EXT can be readily degraded by proteolytic enzymes following oral delivery, and this degradation is an important barrier to its intestinal absorption . Five hours after the oral administration of EXT@PC/NEMs, the DiO‐vehicle and Cy5‐EXT were both found to have accumulated in the pancreatic tissues, suggesting that at least a fraction of the administered PC/NEMs that carried EXT were translocated through the intestinal epithelium.…”

“…Enzymatic Degradation : EXT is very sensitive to trypsin, which is a proteolytic enzyme in the small intestine . The ability of PC/NEMs to protect EXT against proteolytic attack by trypsin was studied in vitro; free EXT served as a control.…”

Effect of Stabilizers on Encapsulation Efficiency and Release Behavior of Exenatide-Loaded PLGA Microsphere Prepared by the W/O/W Solvent Evaporation Method

“…For example, adverse effects like vomiting may increase with higher rates of exenatide burst release [11]. Many groups are currently attempting to suppress exenatide burst release and the incomplete release of commercial products [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Although many investigations into exenatide formulations and dosages have been performed, there is still a lack of useful information about exenatide stability.…”

Long-term oral administration of Exendin-4 to control type 2 diabetes in a rat model

“…However, liposome aggregation in the simulated gastric fluid under fasting conditions (i.e., FaSSGF) was slightly higher than that in simulated intestinal fluid under fasting conditions (i.e., FaSSIF-V2). Ex-4 is comparatively stable within a pH range of 1.2-8 [52] and CSGcoated liposomes are stable in the GIT after oral administration; these features would play an important role in increased Ex-4 absorption because they increase the opportunity for the Ex-4-loaded nanoparticles to reach the distal small intestine.…”