Effects of tryptophan-containing peptides on angiotensin-converting enzyme activity and vessel tone ex vivo and in vivo.

PURPOSE: Over-activation of the renin-angiotensin axis and worsening of vascular function are critical contributors to the development of hypertension. Therefore, inhibition of angiotensin-converting enzyme (ACE), a key factor of the renin-angiotensin axis, is a first line treatment of hypertension. Besides pharmaceutical ACE inhibitors, some natural peptides have been shown to exert ACE-inhibiting properties with antihypertensive effects and potentially beneficial effects on vascular function. In this study, the ACE-inhibiting potential and effects on vascular function of tryptophan-containing peptides were evaluated. METHODS: The ACE inhibitory action and stability of tryptophan-containing peptides was tested in endothelial cells-a major source of whole body ACE activity. Furthermore, the efficacy of peptides on vascular ACE activity, as well as vessel tone was assessed both ex vivo and in vivo. RESULTS: In human umbilical vein endothelial cells (HUVEC), isoleucine-tryptophan (IW) had the highest ACE inhibitory efficacy, followed by glutamic acid-tryptophan (EW) and tryptophan-leucine (WL). Whereas none of the peptides affected basal vessel tone (rat aorta), angiotensin I-induced vasoconstriction was blocked. IW effectively inhibited aortic ACE activity ex vivo taken from SHRs after 14-weeks of oral treatment with IW. Furthermore, IW treated SHRs showed better endothelium-dependent vessel relaxation compared to placebo. CONCLUSION: This study shows strong ACE-inhibiting effects of IW, EW and WL in HUVECs and aorta. The peptides effectively counteract angiotensin-induced vasoconstriction and preserve endothelium-dependent vessel relaxation. Thus, tryptophan-containing peptides and particularly IW may serve as innovative food additives with the goal of protection from angiotensin II-induced worsening of vascular function.

Aldosterone Synthase Inhibition Improves Glucose Tolerance in Zucker Diabetic Fatty (ZDF) Rats.

Plasma aldosterone is elevated in type 2 diabetes and obesity in experimental and clinical studies and can act to inhibit both glucose-stimulated insulin secretion by the ß-cell and insulin signaling. Currently mineralocorticoid receptor antagonism is the best characterized treatment to ameliorate aldosterone-mediated effects. A second alternative is inhibition of aldosterone synthase, an approach with protective effects on end-organ damage in heart or kidney in animal models. The effect of aldosterone synthase inhibition on metabolic parameters in type 2 diabetes is not known. Therefore, male Zucker diabetic fatty (ZDF) rats were treated for 11 weeks with the aldosterone synthase inhibitor FAD286, beginning at 7 weeks of age. Results were compared with the mineralocorticoid receptor antagonist eplerenone. Plasma aldosterone was abolished by FAD286 and elevated more than 9-fold by eplerenone. The area under the curve calculated from an oral glucose tolerance test (OGTT) was lower and overall insulin response during OGTT was increased by FAD286. In contrast, eplerenone elevated blood glucose levels and blunted insulin secretion during the OGTT. Fasting glucose was lowered and fasting insulin was increased by FAD286 in the prediabetic state. Glycated hemoglobin was lowered by FAD286, whereas eplerenone showed no effect. We conclude that aldosterone synthase inhibition, in contrast to mineralocorticoid receptor antagonism, has the potential for beneficial effects on metabolic parameters in type 2 diabetes.

The effects of lipid infusion on myocardial function and bioenergetics in l-bupivacaine toxicity in the isolated rat heart.

BACKGROUND: It is unclear whether improved metabolism or a "lipid sink" effect of lipid infusion is responsible for the positive effects in local anesthetic-induced myocardial depression. METHODS: We used an isolated rat heart, constant-pressure perfused, nonrecirculating Langendorff preparation and exposed hearts to 5 mug/mL l-bupivacaine and 9 microL/mL lipid emulsion. Hearts were freeze-clamped and energy was charge measured by HPLC. In a second experiment the effects of pacing hearts was evaluated. The effects of lipid addition on local anesthetic concentrations in Krebs-Henseleit buffer and human plasma were examined by using a mass spectrometer. RESULTS: With spontaneously beating hearts l-bupivacaine led to a significant decrease in heart rate (to 74% +/- 7% of baseline), +dP/dt (69% +/- 7%), systolic pressure (78% +/- 6%), coronary flow (61% +/- 8%), and to an increase in PR (177% +/- 52%) and QRS intervals (166% +/- 36%). Lipid infusion exerted a positive inotropic effect, significantly augmenting +dP/dt and systolic pressure back to 94% +/- 11% and 102% +/- 16% of baseline in l-bupivacaine-treated hearts. Heart rate, coronary flow, PR, and QRS intervals remained unchanged after lipid intervention. Lipid infusion in paced hearts had a significant effect on +dP/dt, systolic pressure, and Mvo2. Neither l-bupivacaine nor lipids had an effect on energy charge. A lipid concentration of 500 muL/mL plasma was necessary to effect changes in the plasma concentration of local anesthetics. CONCLUSION: Lipid application in l-bupivacaine-induced cardiac depression had a significant positive inotropic effect, which we would attribute to a direct inotropic effect. However, in an isolated heart model, indirect, local anesthetic plasma-binding effect of lipids cannot be excluded.

Modulation of adenine nucleotide concentrations in human plasma by erythrocytes and endothelial cells.

The regulation of plasma concentrations of adenine nucleotides is unsettled. We tested the possibility of extracellular adenosine triphosphate (ATP) production from adenosine diphosphate (ADP) at physiological low concentrations by erythrocytes and endothelial cells. Filtered erythrocytes and human umbilical vein endothelial cells (HUVEC) were incubated for 15 to 120 s with ADP (10 microM), supplemented with 3H-ADP (2.85 nM) or 14C-ADP (54.6 nM). Enzymatic conversion of ADP to ATP was detected by recovery of the radioactive label in the ATP fraction. ATP was measured in the supernatant using high performance liquid chromatography (HPLC) separation, scintillation techniques, and luminometry. Using etheno (epsilon)-labeled ADP (10 microM), the extracellular localization of the conversion was further corroborated. Following ADP application in plasma, no radioactivity was detected in the ATP fraction. However, in erythrocyte suspensions, 12.9% and 9.7% of the label were recovered in the ATP fraction after application of 3H- and 14C-ADP, respectively. Between 15 and 120 s after 3H-ADP application, the 3H-ATP fraction was found to be stable at around 10%. For the range of ADP concentrations studied (10-40 microM), no saturation of ATP production was achieved. The extracellular localization of conversion was supported by the recovery of the epsilon -label in the epsilon -ATP fraction. In contrast, on HUVEC a conversion of epsilon -ADP to epsilon -ATP was not observed. In conclusion, on erythrocytes there is rapid enzymatic conversion of extracellular ADP to ATP which may play a significant role in adjusting adenine nucleotide concentrations in human plasma. In endothelial cells, extracellular conversion of ADP to ATP is of quantitatively minor importance, if it contributes at all.