Activities of angiotensin-converting enzymes ACE1 and ACE2 and inhibition by bioactive peptides in porcine ocular tissues

Plasma and aqueous humor angiotensin-converting enzyme levels in patients with diabetic retinopathy

PURPOSE

To assess angiotensin-converting enzyme (ACE) levels in aqueous humor and plasma of patients with nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR) as another potent ischemia-induced angiogenic factor.

METHODS

The clinical comparative study included 40 patients with diabetic retinopathy and 16 healthy subjects. For all patients, aqueous humors were collected during the cataract surgery or intravitreal injection of triamcinolone acetonide. ACE levels were measured using a solid-phase chemiluminescence immunoassay.

RESULTS

We observed significantly elevated ACE level in aqueous humor of patients with PDR compared with the patients with NPDR and normal subjects (P = 0.023), but no significant difference was detected between nonproliferative diabetics and control group (P = 0.239). There was no significant difference in plasma ACE levels among diabetic and control groups (P = 0.816).

CONCLUSION

Elevated ACE level may induce retinal angiogenesis and proliferative retinopathy in patients with DM. We consider that high levels of ACE in aqueous humor can reflect the association between retinal angiogenesis and DM serve as predictor in the progression of diabetic retinopathy.

Milk Products Containing Bioactive Tripeptides Have an Antihypertensive Effect in Double Transgenic Rats (dTGR) Harbouring Human Renin and Human Angiotensinogen Genes

Tripeptides isoleucyl-prolyl-proline (IPP) and valyl-prolyl-proline (VPP) act as ACE inhibitors in vitro. Double transgenic rats (dTGR) harbouring human renin and human angiotensinogen genes develop malignant hypertension due to increased angiotensin II formation. The present study was aimed to evaluate possible antihypertensive effect of IPP and VPP in this severe model. Four-week-old dTGR were randomized in three groups to receive: (1) water (control), (2) fermented milk containing IPP and VPP, and (3) IPP and VPP dissolved in water for three weeks. Fermented milk, but not peptides in water, attenuated the development of hypertension in dTGR by 19 mmHg versus the control group (P = .023). In vitro vascular function tests showed that high concentrations of the peptides evinced ACE inhibitory properties. In other hypertension related variables, no significant differences between the treatment groups were found. In conclusion, fermented milk product containing IPP and VPP prevents development of malignant hypertension in an animal model.