Objective-Endothelial cell senescence is an important contributor to vascular aging and is increased under diabetic conditions. Here we investigated whether the antidiabetic hormone glucagon-like peptide 1 (GLP-1) could prevent oxidative stress-induced cellular senescence in endothelial cells. Methods and Results-In Zucker diabetic fatty rats, a significant 2-fold higher level of vascular senescence was observed compared with control lean rats. Dipeptidyl-peptidase 4 (DPP-4) inhibition significantly increased GLP-1 levels in these animals and reduced senescence almost to lean animal levels. In vitro studies with human umbilical vein endothelial cells showed that GLP-1 had a direct protective effect on oxidative stress (H 2 O 2 )-induced senescence and was able to attenuate oxidative stress-induced DNA damage and cellular senescence. The GLP-1 analogue exendin-4 provided similar results, whereas exendin fragment 9 -39, a GLP-1 receptor antagonist, abolished this effect. Intracellular signaling by the phosphoinositide 3-kinase (PI3K)/Akt survival pathway did not appear to be involved. Further analysis revealed that GLP-1 activates the cAMP response element-binding (CREB) transcription factor in a cAMP/protein kinase A (PKA)-dependent manner, and inhibition of the cAMP/PKA pathway abolished the GLP-1 protective effect. Expression analysis revealed that GLP-1 can induce the oxidative defense genes HO-1 and NQO1. Conclusion-Dipeptidyl-peptidase 4 inhibition protects against vascular senescence in a diabetic rat model. In vitro studies with human umbilical vein endothelial cells showed that reactive oxygen species-induced senescence was attenuated by GLP-1 in a receptor-dependent manner involving downstream PKA signaling and induction of antioxidant genes.

Abstract-The renin-angiotensin system is important for cardiovascular homeostasis. Currently, therapies for different cardiovascular diseases are based on inhibition of angiotensin-converting enzyme (ACE) or angiotensin II receptor blockade. Inhibition of ACE blocks metabolism of angiotensin-(1-7) to angiotensin-(1-5) and can lead to elevation of angiotensin-(1-7) levels in plasma and tissue. In animal models, angiotensin-(1-7) itself causes or enhances vasodilation and inhibits vascular contractions to angiotensin II. The function of angiotensin-(1-5) is unknown. We investigated whether angiotensin-(1-7) and angiotensin-(1-5) inhibit ACE or antagonize angiotensin-induced vasoconstrictions in humans. ACE activity in plasma and atrial tissue was inhibited by angiotensin-(1-7) up to 100%, with an IC 50 of 3.0 and 4.0 mol/L, respectively. In human internal mammary arteries, contractions induced by angiotensin I and II and the non-ACE-specific substrate [Pro 11 ,D-Ala 12 ]-angiotensin I were antagonized by angiotensin-(1-7) (10 Ϫ5 mol/L) in a noncompetitive way, with a 60% inhibition of the maximal response to angiotensin II. Contractions to ACE-specific substrate [Pro 10 ]-angiotensin I were also inhibited, an effect only partly accounted for by antagonism of angiotensin II. Angiotensin-(1-5) inhibited plasma ACE activity with a potency equal to that of angiotensin I but had no effect on arterial contractions. In conclusion, angiotensin-(1-7) blocks angiotensin II-induced vasoconstriction and inhibits ACE in human cardiovascular tissues. Angiotensin-(1-5) only inhibits ACE. These results show that angiotensin-(1-7) may be an important modulator of the human renin-angiotensin system. (Hypertension. 1999;34:296-301.)

Abstract-An adenine/cytosine (A/C) base substitution at position 1166 in the angiotensin II type 1 receptor (AT 1 R) gene is associated with the incidence of essential hypertension and increased coronary artery vasoconstriction. However, it is still unknown whether this polymorphism is associated with a difference in angiotensin II responsiveness. Therefore, we assessed whether the AT 1 R polymorphism is associated with different responses to angiotensin II in isolated human arteries. Furthermore, we evaluated whether inhibition of the renin-angiotensin system modifies the effect of the AT 1 R polymorphism. One hundred twelve patients who were undergoing coronary artery bypass graft surgery were prospectively randomized to receive an ACE inhibitor or a placebo for 1 week before surgery. Excess segments of the internal mammary artery were exposed to angiotensin II (0.1 nmol/L to 1 mol/L) and KCl (60 mmol/L) in organ bath experiments. Patients homozygous for the C allele (nϭ17) had significantly greater angiotensin II responses (percentage of this maximal KCl-induced response) than did patients genotyped with AAϩAC (nϭ95, PϽ0.05). Although ACE inhibition increased the response to angiotensin II, the difference in the response to angiotensin II, between CC and AAϩAC patients remained intact in ACE inhibitor-treated patients. These results indicate increased responses to angiotensin II in patients with the CC genotype. The mechanism is preserved during ACE inhibition, which in itself also increased the response to angiotensin II. This reveals that the A1166C polymorphism may be in linkage disequilibrium with a functional mutation that alters angiotensin II responsiveness, which may explain the described relation between this polymorphism and cardiovascular abnormalities.

1 Increased vascular resistance in chronic heart failure (CHF) has been attributed to stimulated neurohumoral systems. However, local mechanisms may also importantly contribute to set arterial tone. Our aim, therefore, was to test whether pressure-induced myogenic constriction of resistance arteries in vitro -devoid of acute effects of circulating factors -is increased in CHF and to explore underlying mechanisms. 2 At 12 weeks after coronary ligation-induced myocardial infarction or SHAM-operations in rats, we studied isolated mesenteric arteries for myogenic constriction, determined as the active constriction (% of passive diameter) in response to stepwise increase in intraluminal pressure (20 -160 mmHg), in the absence and presence of inhibitors of potentially involved modulators of myogenic constriction. 3 We found that myogenic constriction in mesenteric arteries from CHF rats was markedly increased compared to SHAM over the whole pressure range, the difference being most pronounced at 60 mmHg (2472 versus 473%, respectively, Po0.001). 4 Both removal of the endothelium as well as inhibition of NO production (l-N G -monomethylarginine, 100 mm) significantly increased myogenic constriction ( þ 16 and þ 25%, respectively), the increase being similar in CHF-and SHAM-arteries (P ¼ NS). Neither endothelin type A (ET A )-receptor blockade (BQ123, 1 mm) nor inhibition of perivascular (sympathetic) nerve conduction (tetrodotoxin, 100 nm) affected the myogenic response in either group. 5 Interestingly, increased myogenic constriction in CHF was fully reversed after angiotensin II type I (AT 1 )-receptor blockade (candesartan, 100 nm; losartan, 10 mm), which was without effect in SHAM. In contrast, neither angiotensin-converting enzyme (ACE) inhibition (lisinopril, 1 mm; captopril, 10 mm) or AT 2 -receptor blockade (PD123319, 1 mm), nor inhibition of superoxide production (superoxide dismutase, 50 U ml À1 ), TXA 2 -receptor blockade (SQ29,548, 1 mm) or inhibition of cyclooxygenase-derived prostaglandins (indomethacin, 10 mm) affected myogenic constriction. 6 Sensitivity of mesenteric arteries to angiotensin II (10 nm -100 mm) was increased (Po0.05) in CHF (pD 2 7.170.4) compared to SHAM (pD 2 6.270.3), while the sensitivity to KCl and phenylephrine was not different. 7 Our results demonstrate increased myogenic constriction in small mesenteric arteries of rats with CHF, potentially making it an important target for therapy in counteracting increased vascular resistance in CHF. Our results further suggest active and instantaneous participation of AT 1 -receptors in increased myogenic constriction in CHF, involving increased sensitivity of AT 1 -receptors rather than apparent ACE-mediated local angiotensin II production.

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