Anastasia Zoga

Short-term statin administration in hypercholesterolaemic rabbits resistant to postconditioning: effects on infarct size, endothelial nitric oxide synthase, and nitro-oxidative stress

AIMS The effectiveness of postconditioning (POC) in hypercholesterolaemia is in dispute. We investigated the effects of 3-day lipophilc (simvastatin) or hydrophilic (pravastatin) statin treatment, without or with POC in normocholesterolaemic (Norm) and hypercholesterolaemic (Chol) rabbits. METHODS AND RESULTS Norm or Chol rabbits were subjected to 30 min ischaemia and randomized in two series of 12 groups each: control, simvastatin (Sim), pravastatin (Prav), POC, Sim-POC, Prav-POC, Chol, Sim-Chol, Prav-Chol, POC-Chol, Sim-POC-Chol, Prav-POC-Chol. After ischaemia, rabbits of the first series underwent 3 h reperfusion, followed by infarct size, total cholesterol, and low density lipoprotein plasma level evaluation; animals of the second series underwent 10 min reperfusion followed by tissue sampling for nitrotyrosine (NT), malondialdehyde, endothelial nitric oxide synthase (eNOS), and Akt analyses. N-nitro-l-arginine methylester (L-NAME) was given in two additional groups (POC-L-NAME and Prav-Chol-L-NAME) for infarct size assessment. All interventions reduced infarction in Norm (24.3 ± 1.3, 25.9 ± 2.8, 27.9 ± 3.1, 23.3 ± 2.3, and 33.4 ± 2.5%, in POC, Sim, Prav, Sim-POC, and Prav-POC groups, respectively, vs. 49.3 ± 1.9% in control, P < 0.05), but only Prav did so in Chol animals (25.7 ± 3.3 and 25.3 ± 3.9% in Prav-Chol and Prav-POC-Chol vs. 50.9 ± 1.7, 44.8 ± 4.3, 41.5 ± 3.5, and 49.3 ± 5.5% in Chol, Sim-Chol, POC-Chol, and Sim-POC-Chol, respectively, P < 0.05). L-NAME abolished the infarct size-limiting effect of POC and Prav-Chol. Prav induced the greatest reduction in NT, while it was the only intervention that increased myocardial eNOS and Akt in Chol rabbits (P < 0.05 vs. all others). CONCLUSION Prav, in contrast to same-dose Sim or POC, reduces infarction in Chol rabbits independently of lipid lowering, potentially through eNOS activation and nitro-oxidative stress attenuation.

Conformation and Bioactivity. Design and Discovery of Novel Antihypertensive Drugs

Peptidomimitism is applied to the medicinal chemistry in order to synthesize drugs that devoid of the disadvantages of peptides. AT1 antagonists constitute a new generation of drugs for the treatment of hypertension designed and synthesized to mimic the C-terminal segment of Angiotensin II and to block its binding action on AT1 receptor. An effort was made to understand the molecular basis of hypertension by studying the conformational analysis of Ang II and its derivatives as well as the AT1 antagonists belonging to SARTANs class of molecules. Such studies offer the possibility to reveal the stereoelectronic factors responsible for bioactivity of AT1 antagonists and to design and synthesize new analogs. An example will be given which proves that drugs with better pharmacological and financial profiles may arise based on this rational design.

Acute administration of vitamin C abrogates protection from ischemic preconditioning in rabbits.

Vitamin C is considered to be an antioxidant agent that is broadly used. Free radicals are involved in the protective mechanism of preconditioning (PC), but some antioxidant compounds abolish this benefit. The aim of the present study was to evaluate the effect of vitamin C on the protective effect of PC with respect to infarct size and oxidative stress in anesthetized rabbits. Male rabbits were randomly divided into six groups and subjected to 30 min of myocardial ischemia and 3h of reperfusion with the following interventions per group: (1) Control (no intervention), (2) Vit C 150 group (i.v. vitamin C at a total dose of 150 mg/kg for 75 min, starting 40 min before the onset of long ischemia and lasting up to the 5th min of reperfusion), (3) Vit C 300 group (i.v. vitamin C at a total dose of 300 mg/kg as previously described), (4) PC group (two cycles of 5 min ischemia and 10 min reperfusion), (5) combined PC-Vit C 150 group and (6) combined PC-Vit C 300 group. Blood samples were taken at different time points for malondialdehyde (MDA) assessment as a lipid peroxidation marker and for superoxide dismutase (SOD) activity. At the end of the experiment the infarct size was determined. Vitamin C, at both doses, did not reduce the infarct size (35.5+/-4.1%, 38.3+/-7.0% vs. 44.9+/-3.3% in the control group) and diminished the protection afforded by PC (32.0+/-2.7%, 43.8+/-3.3% vs. 15.7+/-2.9% in the PC group, P<0.05). At reperfusion there was an elevation of circulating MDA levels in the control and PC groups while in both vitamin C groups the levels were decreased. SOD activity was enhanced in the PC group compared to the controls; vitamin C did not change SOD activity during ischemia-reperfusion. Vitamin C abrogates the beneficial effect of ischemic PC on infarct size and elicits antioxidant properties during ischemia-reperfusion.

Design and synthesis of novel antihypertensive drugs.

AT1 antagonists constitute a new generation of drugs for the treatment of hypertension and are designed and synthesized to mimic the C-terminal segment of Angiotensin II (Ang II) and to block its binding action on AT1 receptor. For this reason, the conformational analysis of Ang II and its derivatives as well as the AT1 antagonists belonging to SARTANs class of molecules were studied. Such studies offer the possibility to reveal the stereoelectronic factors responsible for bioactivity of AT1 antagonists and to design and synthesize new analogues with better pharmacological and financial profiles. An example of a novel synthetic non-peptide molecule is given which mimics the His(6)-Pro(7)-Phe(8) part of Ang II and is based on the (S)-pyroglutamic acid.

Differential activation of mitogen-activated protein kinases in ischemic and nitroglycerin-induced preconditioning

Previous studies have shown that the cardioprotective effect of ischemic preconditioning (IPC) can be mimicked pharmacologically with clinically relevant agents, including nitric oxide (NO) donors. However, whether pharmacological preconditioning shares the same molecular mechanism with IPC is not fully elucidated. The present study aimed to determine the activation of mitogen-activated protein kinases (MAPKs) (ERK1/2, p38 MAPK and p46/p54 JNKs) during ischemia and at reperfusion in nitroglycerin-induced preconditioning as compared to IPC and to correlate this with the conferred cardioprotection in anesthetized rabbits. Sixty minutes of intravenous administration of nitroglycerin was capable of inducing both early and late phase preconditioning in anesthetized rabbits, as it was expressed by the reduction of infarct size. Despite the cardioprotective effect conferred by both ischemic and nitroglycerin-induced preconditioning, there was a differential phosphorylation of MAPKs between the studied groups. p38 MAPK was activated early in ischemia in both ischemic and the early nitroglycerin-induced preconditioning while JNKs were markedly increased only after IPC. Furthermore, in these groups, ERK1/2 were activated during reperfusion. A different profile was observed in the late preconditioning induced by nitroglycerin with increased p38 MAPK and ERK1/2 phosphorylation during late ischemia. No activation of JNKs was observed at any time point in this group. It seems that activation of individual MAPK subfamilies depends on the nature of preconditioning stimulus.

Efforts to Understand the Molecular Basis of Hypertension Through Drug:Membrane Interactions

Biological membranes play an essential role in the drug action. They constitute the first barrier for drugs to exert their biological action. AT1 antagonists are amphiphilic molecules and are hypothesized to act on AT1 receptor through incorporation (first step) and lateral diffusion through membrane bilayers (second step). Various biophysical methods along with Molecular Modelling were applied in order to explore the plausible two step proposed mechanism of action for this class of antihypertensive drugs.

Oral nicorandil recaptures the waned protection from preconditioning in vivo

Protection from preconditioning (PC) wanes and is eventually lost when multiple bouts of short ischemia or a prolonged reperfusion interval precedes the following sustained ischemia. The activation of mitochondrial KATP channels plays a pivotal role in the intracellular signaling of PC. We tested whether the KATP channel opener nicorandil (nic) preserves the given protection from PC in conditions where this benefit decays and is lost. Eight groups of rabbits were divided into two equal series of experiments, one without nic (placebo) and one with nic treatment. Nic was given orally for 5 consecutive days in a dose of 5 mg kg−1 d−1. In a second step, four additional groups were treated with nic plus the KATP channel blocker 5HD and 1 additional control group with nitroglycerin only. All the animals were anesthetized and then subjected to 30 min of myocardial ischemia and 2 h of reperfusion with one of the following interventions before the sustained ischemia: Control groups to no intervention; 3PC groups to three cycles of 5‐min ischemia–10‐min reperfusion; 8PC groups to eight cycles of 5‐min ischemia – 10‐min reperfusion; and 3PC90 groups to the same interventions as the 3PC groups but with a prolonged (90 min) intervening reperfusion interval before the sustained ischemia. The infarcted and the risk areas were expressed in percent. There was no significant change in infarct size between the placebo, the nic and the 5HD‐nic in the control groups (41.5±4.7, 43.9±7.1 and 48.7±6.4%) and 3PC groups (10.3±3.4, 12.2±3.9 and 12.6±4.5%). However, there was a significant decrease after nic treatment in groups 8PC (47.7±8.8% vs 13.0±2.6%, P<0.01) and 3PC90 (37.3±6.0% vs 14.2±2.4%, P<0.01), which was abrogated (38.2±4.7 and 42.7±4.4%, respectively, for 8PC and 3PC90 groups). Nitroglycerin had no effect on infarct size (39.1±3.1%, P=NS vs other controls). Oral treatment with nic recaptures the waned protection of PC, both after repetitive bouts of short ischemia or after a prolonged reperfusion interval, preserving the initially obtained benefit. Nic by itself is insufficient to initiate PC in vivo.

Conformational and biological studies for a pair of novel synthetic AT1 antagonists: stereoelectronic requirements for antihypertensive efficacy

One of the major systems which interferes with the disease of hypertension, is the Renin Angiotensin Aldosterone System (RAS). The octapeptide hormone angiotensin II is the active product of RAS which causes vasoconstriction when binds to the AT(1) receptor. In the last years, there has been a development of drugs which block the Angiotensin II from binding the AT(1) receptor and are called AT(1) antagonists. In an effort to comprehend their stereoelectronic features, a study has been initiated to compare the conformational properties of drugs already marketed for the treatment of hypertension and others which are designed and synthesized in our laboratory possessing structural characteristics necessary for antihypertensive activity. In this study, two synthetic non-peptide AT(1) antagonists, are structurally elucidated and their conformational properties and bioactivity are compared to the prototype and first approved drug of this category in the market; losartan (trade name: COZAAR).

Synthesis and Pharmacological Evaluation of Novel Adenine-Hydrogen Sulfide Slow Release Hybrids Designed as Multitarget Cardioprotective Agents

This work deals with the design, synthesis, and evaluation of the cardioprotective properties of a number of novel hybrid compounds combining the adenine nucleus with a suitable H2S slow-releasing moiety, coupled via a stable ether bond. The H2S release rate of the hybrids and their ability to increase cGMP were estimated in vitro. The most promising derivatives 4 and 11, both containing 4-hydroxythiobenzamide moiety as H2S donor, were selected for further in vivo evaluation. Their ability to release H2S in vivo was recorded using a new fully validated UPLC-DAD method. Both compounds reduced significantly the infarct size when administered at the end of sustained ischemia. Mechanistic studies showed that they conferred enhanced cardioprotection compared to adenine or 4-hydroxythiobenzamide. They activate the PKG/PLN pathway in the ischemic myocardium, suggesting that the combination of both pharmacophores results in synergistic cardioprotective activity through the combination of both molecular pathways that trigger cardioprotection.

Design and synthesis of nitrate esters of aromatic heterocyclic compounds as pharmacological preconditioning agents.

Ischemic preconditioning (IPC) constitutes an endogenous protective mechanism in which one or more brief periods of myocardial ischemia and reperfusion render the myocardium resistant to a subsequent more-sustained ischemic insult. Pharmacological preconditioning represents an ideal alternative of IPC. We now describe the design and synthesis of indole, quinoline, and purine systems with an attached pharmacophoric nitrate ester group. The indole and quinoline derivatives 4 and 5 possess structural features of the nitrate containing K(ATP) channel openers. Purine analogues 11 and 12, substituted at the position 6 by a piperidine moiety and at position 9 by an alkyl nitrate, could combine the effects of the nitrate containing K(ATP) channel openers and those of adenosine. Compound 13 bears the nicotinamide moiety of nicorandil instead of nitrate ester. Compounds 4, 5, and 11 reduced infarction and the levels of malondialdehyde (MDA) at reperfusion in anesthetized rabbits. Compounds 12 and 13 did not significantly reduce the infarct size. Analogues 4 and 5 increased cGMP and MDA during ischemia, while combined analogue 4 and mitoK(ATP) blocker 5-hydroxydecanoic acid (5-HD) abrogated this benefit suggesting an action through mitoK(ATP) channel opening. Treatment with derivative 11 combined with 5-HD as well as treatment with 11 and adenosine receptor blocker 8-(p-sulfophenyl)theophylline (SPT) did not abrogate cardioprotection. Compound 11 is a lead molecule for the synthesis of novel analogues possessing a dual mode of action through cGMP-mitoK(ATP) channel opening-free radicals and through adenosine receptors.