Converting enzyme inhibitor temocaprilat prevents high glucose-mediated suppression of human aortic endothelial cell proliferation

Continuous or Transient High Level of Glucose Exposure Differentially Increases Coronary Artery Endothelial Cell Proliferation and Human Colon Cancer Cell Proliferation

We studied effect of high glucose levels on coronary artery endothelial cell proliferation and human colon cancer cell proliferation. To examine the long-term effect of glucose exposure on cell growth, cells were cultured for 14 days in the absence or presence of 183 mg/dL D-glucose addition in the culture medium. Short effect of elevated glucose levels was examined by addition of 183 mg/dL D-glucose addition in the culture medium for just one hour per day followed by changing the culture to standard medium (5.5 mM D-glucose) during the next 23-hours period. Cell proliferation was estimated by 2,3-Bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carbox-anilide (XTT) assay and phosphor-Erk western blot analysis. We found that coronary artery endothelial cell proliferation was significantly increased in the culture medium with the acute one-hour addition of 183 mg/dL D-glucose compared to the absence or chronic presence of 183 mg/dL D-glucose addition in the culture medium. In contrast, colon cancer cell proliferation was significantly increased in the continuous presence of 183 mg/dL D-glucose addition in the culture medium compared to the acute one-hour addition of glucose. The extent of Erk2 phosphorylation paralleled with the relative changes in cellular proliferation in both cell types. Taken together, these results suggested that continuous or transient high level of glucose exposure differentially effects coronary artery endothelial and human colon cancer cell proliferation.

High glucose decreases endothelial cell proliferation via the extracellular signal regulated kinase/p15INK4b pathway

High glucose inhibits endothelial cell proliferation. Thus, we studied cyclin-dependent kinase inhibitor p15(INK4b) in high glucose-induced effects in human umbilical endothelial cells at 24h. High glucose decreased cell proliferation while arresting cells in G(0)/G(1) phase of the cell cycle. High glucose increased phospho-extracellular signal regulated kinase (ERK)1/2, p15(INK4b) protein and mRNA expression. High glucose-inhibited cell proliferation was attenuated by antisense p15(INK4b) oligonucleotide. Moreover, PD98059 attenuated high glucose-induced p15(INK4b) protein expression. High glucose increased transforming growth factor-beta (TGF-beta) gene transcriptional activity and mRNA expression. However, neither SB431542 (type I TGF-beta receptor blocker) nor TGF-beta1 antibody affected high glucose-induced p15(INK4b) protein expression. Additionally, N-acetylcysteine (an antioxidant) attenuated high glucose-induced growth arrest and p15(INK4b) protein expression. Thus, high glucose-induced growth arrest is dependent on p15(INK4b) and oxidative stress in endothelial cells. Moreover, high glucose-induced p15(INK4b) protein expression is dependent on ERK1/2 and oxidative stress.

Pharmacological and Clinical Studies with Temocapril, an Angiotensin Converting Enzyme Inhibitor that is Excreted in the Bile

Temocapril is an angiotensin converting enzyme inhibitor (ACEI), a prodrug with a thiazepine ring. Its active form, temocaprilat, is slightly more potent than enalaprilat in inhibiting ACE isolated from rabbit lung. The inhibitory potency of temocaprilat on isolated rat aorta is 3 times that of enalaprilat. Temocapril is excreted in the bile and urine and can be used in patients with renal insufficiency. It reduces blood pressure without causing any significant change in heart rate or cardiac output. Temocapril has been reported to improve endothelial dysfunction in vitro by suppressing increased oxidative stress. In vivo it improves reactive hyperemia in patients with essential hypertension. It has been reported to prevent coronary vascular remodeling in vivo by suppressing local ACE and increased oxidative stress. In humans temocapril has been found to improve insulin resistance partly by increasing adiponectin levels. Cardiac remodeling was improved by temocapril not only in experiment animals but also in humans. It improves renal function and decreases urinary albumin excretion in diabetics as well as in hypertensive patients. Temocapril is currently marketed only in Japan. Considering its beneficial effects and unique pharmacokinetics, temocapril, is likely to be introduced in other countries as well.

Senescence-associated phenotypes in Akita diabetic mice are enhanced by absence of bradykinin B2 receptors

We have previously reported that genetically increased angiotensin-converting enzyme levels, or absence of the bradykinin B2 receptor, increase kidney damage in diabetic mice. We demonstrate here that this is part of a more general phenomenon - diabetes and, to a lesser degree, absence of the B2 receptor, independently but also largely additively when combined, enhance senescence-associated phenotypes in multiple tissues. Thus, at 12 months of age, indicators of senescence (alopecia, skin atrophy, kyphosis, osteoporosis, testicular atrophy, lipofuscin accumulation in renal proximal tubule and testicular Leydig cells, and apoptosis in the testis and intestine) are virtually absent in WT mice, detectable in B2 receptor-null mice, clearly apparent in mice diabetic because of a dominant mutation (Akita) in the Ins2 gene, and most obvious in Akita diabetic plus B2 receptor-null mice. Renal expression of several genes that encode proteins associated with senescence and/or apoptosis (TGF-beta1, connective tissue growth factor, p53, alpha-synuclein, and forkhead box O1) increases in the same progression. Concomitant increases occur in 8-hydroxy-2'-deoxyguanosine, point mutations and deletions in kidney mitochondrial DNA, and thiobarbituric acid-reactive substances in plasma, together with decreases in the reduced form of glutathione in erythrocytes. Thus, absence of the bradykinin B2 receptor increases the oxidative stress, mitochondrial DNA damage, and many senescence-associated phenotypes already present in untreated Akita diabetic mice.

Endothelial antioxidant actions of dihydropyridines and angiotensin converting enzyme inhibitors

Dihydropyridines and angiotensin converting enzyme inhibitor effects on superoxide and nitric oxide (NO) were compared in high glucose (20 mM, 24 h)-treated human Ea.hy 926 endothelial cells. High glucose stimulated superoxide both extracellularly (lucigenin chemiluminescence, cytochrome c reduction) and intracellularly (dihydrorhodamine 123 fluorescence). The dihydropyridines amlodipine, nisoldipine, BayK 8644 or the angiotensin converting enzyme inhibitors captopril and enalaprilat attenuated extra- and intracellular superoxide formation; nifedipine blocked extracellular increases only, ramiprilat was without antioxidant effect. Dihydropyridines and captopril also prevented NADPH-driven superoxide release. Antioxidant actions were blunted by a bradykinin B(2) receptor antagonist or an inhibitor of p38 mitogen activated protein kinase (MAPK), and were accompanied by improved NO release (amperometric sensor). p38MAPK inhibition prevented the NO-sparing actions of dihydropyridines but not angiotensin converting enzyme inhibitors. Thus, dihydropyridines and angiotensin converting enzyme inhibitors limit high glucose-induced superoxide formation and improve NO bioavailability in human endothelial cells, in part via bradykinin and p38MAPK.

Antioxidant and nitric oxide-sparing actions of dihydropyridines and ACE inhibitors differ in human endothelial cells

The effects of dihydropyridine Ca2+ channel blockers (DHP) and ACE inhibitors on superoxide formation and nitric oxide (NO) bioavailability were compared in human EA.Hy926 endothelial cells (EC). EC were stimulated 4 h with angiotensin II (Ang II, 10 nM) +/- study drugs. Specific superoxide formation was measured by lucigenin-enhanced chemiluminescence, reduction of cytochrome c and rhodamine-123 fluorescence. Free NO release was determined with an amperometric NO sensor. NADPH oxidase subunits expression was examined with Western Blot. In untreated EC the intracellular superoxide is -64.3 +/- 6.0% decreased compared to Ang II stimulated EC. Elevated extracellular superoxide formation was on a -43.0 +/- 1.7% lower level in untreated EC. The DHP Ca2+-channel agonist BayK8644 and ACE inhibitors captopril and ramiprilat led extracellular superoxide concentration to control level. Enalaprilat blocked extracellular superoxide, the DHP amlodipine and nisoldipine prevented intracellular increases only (n = 8-9, p < 0.05). Icatibant (HOE 140), a kinin-B2 receptor antagonist, attenuated antioxidant actions of all tested agents except of nisoldipine. Ang II-induced superoxide was elevated by the phorbolester PMA and blocked by the protein kinase C (PKC) inhibitor chelerythrine. Suppression of substance P-evoked NO release by Ang II (>70%, n = 6) was reversed by the PKC inhibitor chelerythrine, the DHP amlodipine and nisoldipine and the ACE inhibitor ramiprilat. Further, Ang II reduces Nox-4 expression by 34.5 +/- 4.9. Nox-2 expression was not regulated. DHP and ACE inhibitors exert different antioxidant effects in human EC stimulated with Ang II, but both improve NO bioavailability via bradykinin and modulation of redox-regulating enzymes.

Putative roles of kinin receptors in the therapeutic effects of angiotensin 1-converting enzyme inhibitors in diabetes mellitus

The role of endogenous kinins and their receptors in diabetes mellitus is being confirmed with the recent developments of molecular and genetic animal models. Compelling evidence suggests that the kinin B(2) receptor is organ-protective and partakes to the therapeutic effects of angiotensin 1-converting enzyme inhibitors (ACEI) and angiotensin AT(1) receptor antagonists. Benefits derive primarily from vasodilatory, antihypertensive, antiproliferative, antihypertrophic, antifibrotic, antithrombotic and antioxidant properties of kinin B(2) receptor activation. Mechanisms include the formation of nitric oxide and prostacyclin and the inhibition of NAD(P)H oxidase activity involving classical and novel signalling pathways. Kinin B(2) receptor also ameliorates insulin resistance by increasing glucose uptake and supply, and by inducing glucose transporter-4 translocation either directly or through phosphorylation of insulin receptor. The kinin B(1) receptor, which is induced by the cytokine network, growth factors and hyperglycaemia, mediates hyperalgesia, vascular hyperpermeability and leukocytes infiltration in diabetic animals. However, emerging data highlight reno- and cardio-protective effects mediated by kinin B(1) receptor under chronic ACEI therapy in diabetes mellitus. Thus, the Janus-faced of kinin receptors needs to be taken into account in future drug development. For instance, locally acting kinin B(1)/B(2) receptor agonists if used in a safe therapeutic window may represent a more rationale strategy in the prevention and management of diabetic complications. Because kinin B(2) receptor antagonists may further increase insulin resistance, the persisting dogma that restricts the development of kinin receptor analogues to antagonists (that is still relevant to abrogate pain and inflammation) needs to be revisited.