Hypertension is considering a public cardiovascular disease and an important risk factor of myocardial infarction; cerebral infarction, and renal failure. Angiotensin I-converting enzyme (ACE); plays a key role in controlling hypertension. ACE inhibition is an important method often using to treat high blood pressure. Previous studies show that many peptides from food materials have ACE inhibitory (ACEI); activity and decrease blood pressure. This function of peptides has received considerable research attention.

Previous studies showed some bioactive peptides existed good antihypertensive activity in vivo. Bioactive peptides with high ACEI activities in vitro can exert antihypertensive activity in vivo when they are intact in the target organ through the intestinal tract. Although some peptides have in vitro ACEI activity; no antihypertensive activity in spontaneously hypertensive rats (SHRs) has yet observed after oral administration in vivo. Thus, the ACI activities of peptides may affect by the absorption and metabolism vivo.

Transepithelial transports

Caco-2 cells are human colon adenocarcinoma cell clones. The structures and functions of Caco-2 cells are similar to those of differentiated intestinal epithelial cells. Therefore, a Caco-2 cell monolayer model is often using in simulating intestinal transport experiments in vitro. Previous studies have studied the transepithelial transports of antihypertensive peptides by Caco-2 cell monolayer model.

In our previous study, QAGLSPVR was separating and identifing from tilapia skin gelatin hydrolysates; its IC50 for ACEI activity in vitro to 68.35 μM. Bioactive peptides are exposing through systemic circulation in human tissues. Unfortunately, bioactive peptides may hydrolyzed before they reach the target tissues during passage through and absorption by the small intestine.

Antihypertensive activity

While some bioactive peptides show in vitro ACEI activity; they do not exhibit antihypertensive effects in vivo after oral administration to SHRs. For example, FKGRYYP was identified from chicken muscle hydrolysates, and its IC50 for ACEI activity in vitro to 0.55 mM; however, no antihypertensive activity of this peptide after oral administration to SHRs.
Therefore, bioactive peptides must resist systemic peptidase degradation prior to reaching; their target sites to exert their function in vivo. The application of antihypertensive peptides is when they have no ACEI activity after oral administration. The antihypertensive effect in vivo of QAGLSPVR derived from tilapia skin gelatin hydrolysates was determined; the peptide revealed a clear antihypertensive effect on SHRs.
The ability of the peptide to inhibit ACE activity in serum was considering a key factor of the antihypertensive effect of QAGLSPVRin vivo. QAGLSPVR could be transported intact by the Caco-2 cell monolayer and may transport through this layer via the paracellular pathway. Therefore, QAGLSPVR could effectively absorb and regulate hypertension in vivo.