Plasma concentrations and ACE-inhibitory effects of tryptophan-containing peptides from whey protein hydrolysate in healthy volunteers.

PURPOSE: The tryptophan-containing dipeptides isoleucine-tryptophan (IW) and tryptophan-leucine (WL) are angiotensin-converting enzyme (ACE)-inhibitors in vitro. These peptides are released by enzymatic hydrolysis of bovine whey protein. To exhibit ACE inhibition in vivo, peptides need to be absorbed into the circulatory system. This study aimed to determine the in vivo ACE-inhibitory potency of a whey protein hydrolysate (MPH), containing IW and WL, and to quantify plasma concentrations of these peptides after oral administration of MPH in healthy volunteers. Additionally, changes in blood pressure were investigated. RESULTS: After intake of 5 and 50 g MPH, plasma ACE activity was reduced to 86.4 ± 5.9 and 75.1 ± 6.9% of baseline activity, respectively. Although a clear ACE inhibition was measured, no effect on blood pressure was seen. Basal plasma concentrations of the tryptophan-containing dipeptides were 2.8 ± 0.7 nM for IW and 10.1 ± 1.8 nM for WL. After intake of 5-50 g MPH, peptide concentrations were dose dependently elevated to values between 12.5 ± 8.4 and 99.1 ± 58.7 nM for IW and 15.0 ± 4.3-34.9 ± 19.4 nM for WL. Administration of intact whey protein showed a minor ACE inhibition, probably caused by release of inhibitory peptides during gastrointestinal digestion. The increase of WL in plasma after intake of intact protein was similar to that determined after intake of MPH. In contrast, resulting IW concentrations were much lower after intake of intact whey protein when compared to MPH administration. CONCLUSION: After intake of MPH, plasma ACE activity decreased in parallel to the increase of IW and WL plasma concentrations. However, the resulting peptide concentrations cannot fully explain the reduction of ACE activity in plasma with a direct enzyme inhibition. Therefore, this study points to a gap in the understanding of the inhibitory action of these peptides in vivo. Thus, to further develop innovative food additives with ACE activity diminishing capabilities, it appears mandatory to better characterize the mode of action of these peptides.

Tailoring the Adsorption of ACE-Inhibiting Peptides by Nitrogen Functionalization of Porous Carbons.

Bioactive peptides, such as isoleucyl-tryptophan (IW), exhibit a high potential to inhibit the angiotensin-converting enzyme (ACE). Adsorption on carbon materials provides a beneficial method to extract these specific molecules from the complex mixture of an α-lactalbumin hydrolysate. This study focuses on the impact of nitrogen functionalization of porous carbon adsorbents, either via pre- or post-treatment, on the adsorption behavior of the ACE-inhibiting peptide IW and the essential amino acid tryptophan (W). The commercially activated carbon Norit ROX 0.8 is compared with pre- and postsynthetically functionalized N-doped carbon in terms of surface area, pore size, and surface functionality. For prefunctionalization, a covalent triazine framework was synthesized by trimerization of an aromatic nitrile under ionothermal conditions. For the postsynthetic approach, the activated carbon ROX 0.8 was functionalized with the nitrogen-rich molecule melamine. The batch adsorption results using model mixtures containing the single components IW and W could be transferred to a more complex mixture of an α-lactalbumin hydrolysate containing a huge number of various peptides. For this purpose, reverse-phase high-pressure liquid chromatography with fluorescence detection was used for identification and quantification. The treatment with the three different carbon materials leads to an increase in the ACE-inhibiting effect in vitro. The modified surface structure of the carbon via pre- or post-treatment allows separation of IW and W due to the certain selectivity for either the amino acid or the dipeptide.

Degradation studies of modified inulin as potential encapsulation material for colon targeting and release of mesalamine.

Due to the potential to treat colon specific diseases with reduced side effects, colon targeting has become of high interest over the last decades. Chemical modified inulin was investigated for its potential as encapsulation material regarding its enzymatic degradability and its drug release behavior. Different degrees of acetylated inulin (degree of substitution, DS, 0.3-2.1) were synthesized. The chemical modification leads to a reduction in enzymatic degradability by inulinase and esterase, enzymes which can be expressed by the colon microbiota. Acetylated inulin was only hydrolyzed to fructose units up to DS of 1.3. Microparticles made of native inulin and acetylated inulin (DS 1.8) were loaded with the colon-specific drug mesalamine by spray drying. Compared to the burst release of mesalamine by inulin particles within 6 h, acetylated inulin particles showed less burst release followed by a continuous drug release phase caused by diffusion up to 30% mesalamine after 52 h.

Biotechnological production of the angiotensin-converting enzyme inhibitory dipeptide isoleucine-tryptophan.

Peptides with angiotensin-converting enzyme (ACE)-inhibitory and antihypertensive effects are suggested as innovative food additives to prevent or treat hypertension. Currently, these substances are isolated from food proteins following nonselective hydrolysis as a mixture of ACE-inhibitory peptides and other protein fragments. This study presents an innovative biotechnological method, based on recombinant DNA technology that was established to specifically produce the ACE-inhibitory dipeptide isoleucine-tryptophan. In a first step, a repetitive isoleucine-tryptophan construct fused to the maltose-binding protein was generated and expressed in Escherichia coli BL21 cells. The chromatographically purified recombinant fusion protein was enzymatically hydrolyzed using α-chymotrypsin to liberate the dipeptide isoleucine-tryptophan. The identity of the liberated isoleucine-tryptophan was confirmed by MS and derivatization of its N-terminus. The ACE-inhibitory effect of the recombinant dipeptide on soluble and membrane bound ACE was found to be indistinguishable from the inhibitory potential of the chemically produced commercially available dipeptide. The established experimental strategy represents a promising approach to the biotechnical production of sufficient amounts of recombinant peptide-based ACE-inhibitory and antihypertensive substances that are applicable as functional food additives to delay or even prevent hypertension.