An in silico approach to unveil peptides from Acheta domesticus with potential bioactivity against hypertension, diabetes, cardiac and pulmonary fibrosis

Entomophagy is a sustainable alternative source of proteins for human nutrition. Acheta domesticus is one of the three insect species that complies with the European Union Regulation on novel foods, but to date, there are no reports on their potential bioactive peptides. In this study, an in silico approach was applied to simulate the gastrointestinal (GI) digestion of six A. domesticus proteins and identify new peptides with potential anti-hypertensive and/or anti-diabetic properties, resulting from their capability to inhibit the somatic Angiotensin-I converting enzyme (sACE) and/or dipeptidyl peptidase 4 (DPP-4), respectively. A molecular docking protocol was applied to evaluate the binding interactions between the 43 peptides ranked with high probability of being bioactive and three drug targets: DPP-4 and two catalytic domains (N- and C-) of sACE. Five peptides (AVQPCF, CAIAW, IIIGW, DATW and QIVW) showed high docking scores for both enzymes, suggesting their potential to inhibit the DPP-4 and both catalytic domains of sACE, thus possessing multifunctional bioactive properties. Two peptides (PIVCF and DVW) showed higher docking scores for the N-domain of sACE, indicating a potential action as selective inhibitors and consequently with anti-cardiac and pulmonary fibrosis bioactivities. This is the first study identifying peptides originated from the simulated GI digestion of A. domesticus with potential activities against hypertension, diabetes, cardiac and pulmonary fibrosis.

Anti-hypertensive effects of Radix Rehmanniae and its active ingredients

Radix Rehmanniae (RR) is the root tuber of Rehmannia glutinosa Libosch. Herein, the methanol extracts of dried RR (DRR) and processed RR (PRR) were partitioned to obtain ethyl acetate, aqueous, and n-butanol layers. The angiotensin-I converting enzyme (ACE) inhibition test indicated that the ethyl acetate extracts of DRR (DRRE) and PRR (PRRE) show better inhibitory activity. Therefore, changes in blood pressure were tested over 24 h in spontaneously hypertensive rats, with DRR showing good anti-hypertensive activity. DRRE was further subjected to column chromatography; 28 fractions were separated and tested for ACE inhibition. Ultimately, six compounds were identified by spectral analysis, and literature comparison. Specifically, ursolic acid and oleanolic acid showed better ACE inhibition than the other compounds. This study confirmed that DRR has anti-hypertensive activity. In future, DRR's potential as a health food should be further assessed.

Identification of bioactive peptide from Oreochromis niloticus skin gelatin

Fish skin, one type of wastes generated from Nile tilapia processing, is still a good source of collagen and gelatin. Bioactive peptides can be obtained from Nile tilapia skin gelatin by trypsin digestion. Trypsin hydrolysate was subsequently purified by gel filtration chromatography. Trypsin A fraction showed the greatest reducing power (5.138 ± 1.060 μM trolox/mg peptide) among all hydrolysate fractions, while trypsin B fraction from gel filtration column was found to exhibit the best radical scavenging and angiotensin-I-converting enzyme (ACE) inhibitory activities 8.16 ± 2.18 μg trolox/mg peptide and 59.32 ± 9.97 % inhibition, respectively. The most active fraction was subjected to MALDI-TOF/TOF MS/MS. After annotation by Mascot sequence matching software (Matrix Science) with Ludwig NR Database, two peptide sequences were identified; GPEGPAGAR (MW 810.87 Da) and GETGPAGPAGAAGPAGPR (MW 1490.61 Da). The docking analysis suggested that the shape of the shorter peptide may be slightly more proper, to fit into the binding cleft of the ACE. However, the binding affinities calculated from the docking showed no significant difference between the two peptides. In good agreement with the in silico data, results from the in vitro ACE inhibitory activity with synthetic peptides also showed no significant difference. Both peptides are thus interesting novel candidates suitable for further development as ACE inhibitory and antioxidant agents from the natural source.

Local corticosterone production and angiotensin-I converting enzyme shedding in a mouse model of intestinal inflammation

AIM: To investigate local corticosterone production and angiotensin-I converting enzyme (ACE) protein expression and their interaction in healthy and inflamed intestine.

METHODS: Acute intestinal inflammation was induced to six weeks old male Balb/c mice by administration of either 3% or 5% dextran sodium sulfate (DSS) in drinking water for 7 d (n = 12 in each group). Healthy controls (n = 12) were given tap water. Corticosterone production and ACE protein shedding were measured from ex vivo incubates of the small and large intestine using EIA and ELISA, respectively. Morphological changes of the intestinal wall were assessed in hematoxylin-eosin stained tissue preparations of jejunum and distal colon. Effects of angiotensin II, captopril and metyrapone on corticosterone production was assessed by incubating pieces of small intestine of healthy mice in the presence of 0.1, 1 or 10 μmol/L angiotensin II, 1, 10 or 100 μmol/L captopril or 1, 10 or 100 μmol/L metyrapone solutions and measuring corticosterone released to the incubation buffer after 90 min (n = 5 in each group).

RESULTS: Both concentrations of DSS induced inflammation and morphological changes in large intestines but not in small intestines. Changes were observed as distortions of the crypt structure, mucosal erosion, immune cell infiltration to the mucosa and submucosal edema. Ex vivo corticosterone production (2.9 ± 1.0 ng/mL vs 2.0 ± 0.8 ng/mL, P = 0.034) and ACE shedding (269.2 ± 97.1 ng/mL vs 175.7 ± 52.2 ng/mL, P = 0.016) were increased in small intestines in 3% DSS group compared to the controls. In large intestine, corticosterone production was increased compared to the controls in both 3% DSS (229 ± 81 pg/mL vs 158 ± 30 pg/mL, P = 0.017) and 5% DSS groups (366 ± 163 pg/mL vs 158 ± 30 pg/mL, P = 0.002). Large intestine ACE shedding was increased in 5% DSS group (41.5 ± 9.0 ng/mL vs 20.9 ± 5.2 ng/mL, P = 0.034). Angiotensin II treatment augmented corticosterone production in small intestine at concentration of 10 μmol/L (0.97 ± 0.21 ng/mg protein vs 0.40 ± 0.09 ng/mg protein, P = 0.036).

CONCLUSION: Intestinal ACE shedding is increased by DSS-induced intestinal inflammation and parallels local corticosterone production. ACE product angiotensin II stimulates corticosterone formation in healthy intestine.

A new high-resolution crystal structure of the Drosophila melanogaster angiotensin converting enzyme homologue, AnCE

Angiotensin converting enzyme (ACE) is a zinc-dependent dipeptidyl carboxypeptidase with an essential role in blood pressure homeostasis in mammals. ACE has long been targeted in the treatment of hypertension through ACE inhibitors, however current inhibitors are known to cause severe side effects. Therefore, there is a requirement for a new generation of ACE inhibitors and structural information will be invaluable in their development. ACE is a challenging enzyme to work with due to its extensive glycosylation. As such, the Drosophila melanogaster ACE homologue, AnCE, which shares ∼60% sequence similarity with human ACE, can be used as a model for studying inhibitor binding. The presence of ligands originating from the crystallisation condition at the AnCE active site has proved an obstacle to studying the binding of new inhibitor precursors. Here we present the crystal structure of AnCE (in a new crystal form) at 1.85 Å resolution, using crystals grown under different conditions. This new structure may be more suitable for studying the binding of new compounds, with the potential of developing a new generation of improved ACE inhibitors.

Serine proteases as candidates for proteolytic processing of angiotensin-I converting enzyme

Somatic angiotensin-I converting enzyme (sACE) is a broadly distributed peptidase which plays a role in blood pressure and electrolyte homeostasis by the conversion of angiotensin I into angiotensin II. N-domain isoforms (nACE) with 65 and 90 kDa have been described in body fluids, tissues and mesangial cells (MC), and a 90 kDa nACE has been described only in spontaneously hypertensive rats. The aim of this study was to investigate the existence of proteolytic enzymes that may act in the hydrolysis of sACE generating nACEs in MC. After the confirmation of the presence of ACE sheddases in Immortalized MC (IMC), we purified and characterized these enzymes using fluorogenic substrates specifically designed for ACE sheddases. Purified enzyme identified as a serine protease by N-terminal sequence was able to generate nACE. In the present study, we described for the first time the presence of ACE sheddases in IMC, identified as serine proteases able to hydrolyze sACE in vitro. Further investigations are necessary to elucidate the mechanisms responsible for the expression and regulation of ACE sheddases in MC and their roles in the generation of nACEs, especially the 90 kDa form possibly related to hypertension.