Lieselot Vercruysse

Angiotensin I-converting enzyme inhibitory activity of gelatin hydrolysates and identification of bioactive peptides

In this project we report on the angiotensin I-converting enzyme (ACE)-inhibitory activity of a bovine gelatin hydrolysate (Bh2) that was submitted to further hydrolysis by different enzymes. The thermolysin hydrolysate (Bh2t) showed the highest in vitro ACE inhibitory activity, and interestingly a marked in vivo blood pressure-lowering effect was demonstrated in spontaneously hypertensive rats (SHR). In contrast, Bh2 showed no effect in SHR, confirming the need for the extra thermolysin hydrolysis. Hence, an angiotensin I-evoked contractile response in isolated rat aortic rings was inhibited by Bh2t, but not by Bh2, suggesting ACE inhibition as the underlying antihypertensive mechanism for Bh2t. Using mass spectrometry, seven small peptides, AG, AGP, VGP, PY, QY, DY and IY or LY or HO-PY were identified in Bh2t. As these peptides showed ACE inhibitory activity and were more prominent in Bh2t than in Bh2, the current data provide evidence that these contribute to the antihypertensive effect of Bh2t.

Ala-Val-Phe and Val-Phe: ACE inhibitory peptides derived from insect protein with antihypertensive activity in spontaneously hypertensive rats

In this study, we evaluated the stability/bioavailability and in vivo antihypertensive activity of the tripeptide, Ala-Val-Phe, that was recently purified from insect protein (Spodoptera littoralis; Lepidoptera) and that showed in vitro angiotensin converting enzyme (ACE) inhibitory activity. This tripeptide is partly hydrolyzed by mucosal peptidases to Val-Phe, a more potent in vitro ACE inhibitor. In organ bath experiments using rat aorta, Val-Phe showed ACE inhibition, while Ala-Val-Phe did not. Single oral administration (5mg/kg body weight) to spontaneously hypertensive rats led to a significant decrease in blood pressure for both peptides. Docking experiments indicated an active character for Val-Phe and an inactive character for Ala-Val-Phe as potential inhibitors of human ACE. From our results, it can be suggested that after oral administration of Ala-Val-Phe, Val-Phe is released by in vivo peptidases and is responsible for in vivo activity of Ala-Val-Phe. To the best of our knowledge this is the first report of in vivo antihypertensive activity of peptides derived from insect protein.

Critical evaluation of the use of bioinformatics as a theoretical tool to find high-potential sources of ACE inhibitory peptides

A bioinformatics analysis to screen for high-potential sources of angiotensin converting enzyme (ACE) inhibitory peptides was conducted in the area of insect muscle proteins. Vertebrate muscle proteins are reported as good sources of ACE inhibitory peptides, while the research on invertebrate muscle proteins is limited. A phylogenetic tree constructed with actin sequences of both vertebrate and invertebrate species indicated a high homology. Furthermore, a quantitative in silico ACE inhibition analysis suggested that actin proteins of invertebrates have potentials as new sources of ACE inhibitory peptides. On one insect, Bombyx mori, a more detailed in silico analysis was done followed by a small experimental study. The in silico analysis indicated B. mori as a high-potential source of ACE inhibitory peptides and this was supported by the ACE inhibitory activity of the partially purified actin preparation. In conclusion, in food science, in silico analysis can be used as fast initial screening tool to look for high-potential sources of ACE inhibitory peptides and other peptidic bioactivities.

Antihypertensive mechanism of the dipeptide Val-Tyr in rat aorta.

Antihypertensive peptides received much interest over the last decade. These peptides are known to be angiotensin converting enzyme (ACE) inhibitors in vitro, but the actual antihypertensive mechanisms in vivo are still unclear. In this research, we used rat aortic rings in organ bath experiments to investigate five potential vascular antihypertensive mechanisms of the dipeptide Val-Tyr. Only one significant effect was observed, namely preincubation of the aorta with Val-Tyr led to a significant shift of the concentration-response curve evoked by angiotensin I (Ang I). Val-Tyr had no effect on the angiotensin II receptor or the alpha-adrenergic receptor. Furthermore, it did not interact with voltage-operated Ca2+ channels, or with nitric oxide production/availability. In conclusion, our results show that Val-Tyr specifically inhibits Ang I-evoked contraction through ACE inhibition and that four other main mechanisms of vascular tone regulation are not affected.

Production and enrichment of bioactive peptides derived from milk proteins.

Abstract: In this chapter, information is given on the production of bioactive peptides from milk proteins. After defining bioactive peptides, the necessity to release bioactive peptides from the parent protein is discussed. Then, the two main approaches for release, namely enzymatic hydrolysis and microbial fermentation are reviewed. Next, an overview is given of the main unit operations that can be applied for the enrichment and selective isolation of bioactive peptides from the protein hydrolysates, including membrane filtration, chromatography and precipitation. Attention is given mainly to ACE-inhibitory peptides, and to processes that show potential for application in the dairy industry.

ACE inhibitor captopril reduces ecdysteroids and oviposition in moths.

Abstract: By using the selective ACE inhibitor captopril, we studied the effect of the angiotensin converting enzyme (ACE) on larval growth, metamorphosis, and reproduction in a lepidopteran species, the cotton leafworm, Spodoptera littoralis. Captopril was detrimental to adult formation and oviposition, and in female moths it elicited decreasing ecdysteroid levels, but increasing trypsin activities. Our results suggest that captopril downregulates oviposition by two independent pathways. Apparently, oviposition is influenced by a complex interaction of ACE, trypsin activity, and ecdysteroid levels.