Protection of the vascular endothelium in experimental situations.

One of the factors proposed as mediators of vascular dysfunction observed in diabetes is the increased generation of reactive oxygen species (ROS). This provides support for the use of antioxidants as early and appropriate pharmacological intervention in the development of late diabetic complications. In streptozotocin (STZ)-induced diabetes in rats we observed endothelial dysfuction manifested by reduced endothelium-dependent response to acetylcholine of the superior mesenteric artery (SMA) and aorta, as well as by increased endothelaemia. Changes in endothelium-dependent relaxation of SMA were induced by injury of the nitric oxide radical (·NO)-signalling pathway since the endothelium-derived hyperpolarising factor (EDHF)-component of relaxation was not impaired by diabetes. The endothelial dysfunction was accompanied by decreased ·NO bioavailabity as a consequence of reduced activity of eNOS rather than its reduced expression. The results obtained using the chemiluminiscence method (CL) argue for increased oxidative stress and increased ROS production. The enzyme NAD(P)H-oxidase problably participates in ROS production in the later phases of diabetes. Oxidative stress was also connected with decreased levels of reduced glutathione (GSH) in the early phase of diabetes. After 10 weeks of diabetes, adaptational mechanisms probably took place because GSH levels were not changed compared to controls. Antioxidant properties of SMe1EC2 found in vitro were partly confirmed in vivo. Administration of SMe1EC2 protected endothelial function. It significantly decreased endothelaemia of diabetic rats and improved endothelium-dependent relaxation of arteries, slightly decreased ROS-production and increased bioavailability of ·NO in the aorta. Further studies with higher doses of SMe1EC2 may clarify the mechanism of its endothelium-protective effect in vivo.

Distinct lethal arrhythmias susceptibility is associated with sex-related difference in myocardial connexin-43 expression.

OBJECTIVES: To elucidate gender-related differences in occurrence of sudden cardiac death the myocardial connexin-43 (Cx43) and the susceptibility of male and female rat hearts to ventricular fibrillation (VF) were investigated. METHODS AND RESULTS: Ventricular tissues taken from male and female normotensive Wistar and spontaneously hypertensive (SHR) rats were processed for immuno-fluorescence and immuno-blotting of Cx43. Susceptibility to ventricular fibrillation was examined in isolated heart preparation using either electrical stimulation or low K+ perfusion. Results showed that VF susceptibility of male either normotensive or hypertensive rats was significantly increased comparing to female counterparts. In correlation, ventricular expression of Cx43 was markedly lower in males of both normotensive and hypertensive rats comparing to females. SHR in addition exhibited abnormal myocardial Cx43 distribution due to structural remodelling. CONCLUSIONS: Findings indicate that higher level of myocardial Cx43 expression is linked with lower lethal arrhythmia susceptibility and vice versa. It appears that Cx43 can be involved in sex-related differences in incidence of life-threatening arrhythmias.

Role of inflammatory cytokines and chemoattractants in the rat model of streptozotocin-induced diabetic heart failure.

OBJECTIVE: It is not yet clear how oxidative stress, free radicals, inflammatory cytokines and chemoattractants produced in the heart induce chronic heart failure. The myocardial damage caused by chronic diabetes results either from the persistence of inflammatory signaling directly in the heart or from the dysregulation of anti-inflammatory signaling systems. In the rat model of streptozotocin-induced diabetes (STZD) we investigated 1/ the concentration of free radicals (FR), 2/ reduced glutathione (GSH), 3/ lysozomal enzymes, 4/ inflammatory cytokines (tumor necrosis factor-? (TNF-?) and interleukin-6 (IL-6)), and monocyte chemoattractant protein-1 (mcp-1) in the myocardium. METHODS: Diabetes was induced in 12 male Wistar rats by injection of streptozotocin (STZ). The free radical scavenger and cardiac protectant SMe1EC2 (10 mg/kg/d.) was given orally for 5 days and 5 weeks and these animals were compared with the diabetic and non-diabetic controls. RESULTS: We found reduced heart rate and rate dependent functions of the rat heart, early release of free radicals triggering the release of cytotoxic inflammatory cytokines (like TNF-? and IL-6) and chemoattractants (mcp-1) as an example of this type of pathogens, resulting in the initiation and progression of cardiac pathology. The reduced myocardial contractility after STZD was accompanied with the increased reactive responsiveness of isolated aorta and mesenteric artery to phenylephrine, with increased production of chemoattractive proteins directly in the myocardium, with increased activity of peripheral beta-N-acetyl-glucosaminidase (NAGA), as representative of lysosomal activation processes. The pretreatment of SME1EC2 reduced increase in vascular reactivity, reduced myocardial depression and protected against myocardial toxicity. CONCLUSION: The newly identified and specific cardiac protectant SMe1EC2 could serve as a prospective target in the treatment of increased myocardial cytokine and chemoattractive proteins in diabetic cardiomyopathy.

Effect of acetylcholine and ischaemia/reperfusion injury on the heart of rats with STZ-induced experimental diabetes.

OBJECTIVES: To investigate the effect of acetylcholine (ACh) and ischaemia/reperfusion injury on functional changes and dysrhythmias of the isolated diabetic rat heart. METHODS AND RESULTS: On retrogradely perfused hearts isolated from 10-week-old diabetic rats (streptozotocin 30 mg/kg b.w. for three consecutive days i.p.), two types of experiments were done: /1/ The effect of acetylcholine (ACh; 3 x 10(-7) mol/l) was evaluated both during and after infusion, and /2/ the influence of the ischaemia/reperfusion injury (I/R) was studied. At the end of both experiments the hearts were electrically stimulated to evoke sustained ventricular fibrillation (VF). An increase of coronary arterial pressure, bradycardia and decreased total number of severe dysrhythmias of both types, spontaneous and evoked ones, were recorded in the diabetic hearts. ACh increased the force of contraction (LVP) and induced vasoconstriction, which persisted in the diabetic hearts even after removal of ACh from the perfusion solution. CONCLUSIONS: The isolated diabetic rat heart was more resistant against severe dysrhythmias. After washing out the ACh, the vasoconstriction of coronary arteries still lasted, along with increased inotropic effect on the left ventricle.

Cardiovascular toxicity of the first line cancer chemotherapeutic agents: doxorubicin, cyclophosphamide, streptozotocin and bevacizumab.

OBJECTIVES: Although the mechanisms responsible for the occurrence of congestive heart failure after anti-cancer therapy are largely unknown, both the formation of free radicals in the myocardium and inflammatory cytokines with resultant production of neurohormones could be operative. The common manifestations of cardiovascular toxicity after anti-cancer therapy may include cardiac ischemia, ST-segment elevation, or depression, serious hypotension and bradyarrhythmias with resultant cardiac depression and congestive heart failure, or hyper-tension, serious ventricular tachycardia, cardiac edema, QT prolongation and thrombo-embolism. METHODS & RESULTS: The mechanisms of cardiotoxicity of four representative anti-cancer agents 1) anthracycline doxorubicin, 2) and 3) alkylating agents cyclophosphamine and streptozotocin and 4) the new humanized monoclonal antibody bevacizumab (directed solely against myocardial and vascular endothelial growth factors), were investigated in chronic experiments on rodents for the occurrence and intensity of early electrocardiographic signs of cardiotoxicity, for late biochemical markers, and for the late production of congestive heart failure. Our results suggested a sneaking ascension of long-term multifactorial cardiotoxicity of the four anti-cancer agents tested. Of these quasi-selective bevacizumab (Avastin) that binds to and inhibits endothelial growth factor and thus neoangiogenicity in rats showed unexpectedly high overexpression of inflammatory cytokines and monocyte chemoattractant protein (mcp-1), both in plasma and in the myocardium. CONCLUSIONS: Thus, suddenly increased and coincidental expression of inflammatory cytokines, neurohormones and chemoattractants in plasma during anti-cancer therapy could be the long-awaited markers of imminent cardiotoxicity.

L-thyroxine increases susceptibility of adult rats to low K+-induced ventricular fibrillation, and sinus rhythm restoration in old rats.

Hypokalaemia increases the risk for life-threatening arrhythmias; however, data about interaction with thyroid status are lacking. The aim of this study was to investigate vulnerability of l-thyroxine (T(4))-treated adult and old rats to low K(+)-induced ventricular fibrillation (VF) as well as the ability of the heart to recover sinus rhythm. The experiments were performed on isolated heart preparations using the heart of 4- and 20-month-old female Wistar rats without and with feeding with T(4) 50 microg (100 g day)(-1) over a period of 2 weeks. Perfusion of the isolated heart with oxygenated Krebs-Henseleit solution at constant pressure was followed by perfusion with K(+)-deficient solution until occurrence of VF (< 10 min). After 2 min of sustained VF, the heart was perfused with normal solution for 10 min, during which sinus rhythm was restored. ECG, left ventricular pressure (LVP) and coronary flow were continuously monitored. The results showed that compared with untreated rats, the onset of low K(+)-induced ventricular premature beats was delayed and their number was significantly decreased in both T(4)-treated groups. Nevertheless, VF occurred earlier in T(4)-treated than in non-treated adult rats (6.78 +/- 0.28 vs. 9.59 +/- 0.55 min, P < 0.05), whereas the difference was not significant in aged animals. Furthermore, sinus rhythm appeared earlier in old T(4)-treated rats compared with non-treated rats (7.18 +/- 0.57 vs. 8.94 +/- 0.64 min, P < 0.05), whereas in adult hearts it set in at practically the same time regardless of treatment. In conclusion, our results indicate that administration of a pharmacological dose of T(4) can increase the risk of low K(+)-induced VF in adult but not in old animals; in the latter it even facilitated restoration of sinus rhythm. Moreover, enhanced mechanical function was observed in both adult and old T(4)-treated hearts.

Chemical function based pharmacophore generation of endothelin-A selective receptor antagonists.

Both quantitative and qualitative chemical function based pharmacophore models of endothelin-A (ET(A)) selective receptor antagonists were generated by using the two algorithms HypoGen and HipHop, respectively, which are implemented in the Catalyst molecular modeling software. The input for HypoGen is a training set of 18 ET(A) antagonists exhibiting IC(50) values ranging between 0.19 nM and 67 microM. The best output hypothesis consists of five features: two hydrophobic (HY), one ring aromatic (RA), one hydrogen bond acceptor (HBA), and one negative ionizable (NI) function. The highest scoring Hip Hop model consists of six features: three hydrophobic (HY), one ring aromatic (RA), one hydrogen bond acceptor (HBA), and one negative ionizable (NI). It is the result of an input of three highly active, selective, and structurally diverse ET(A) antagonists. The predictive power of the quantitative model could be approved by using a test set of 30 compounds, whose activity values spread over 6 orders of magnitude. The two pharmacophores were tested according to their ability to extract known endothelin antagonists from the 3D molecular structure database of Derwent's World Drug Index. Thereby the main part of selective ET(A) antagonistic entries was detected by the two hypotheses. Furthermore, the pharmacophores were used to screen the Maybridge database. Six compounds were chosen from the output hit lists for in vitro testing of their ability to displace endothelin-1 from its receptor. Two of these are new potential lead compounds because they are structurally novel and exhibit satisfactory activity in the binding assay.

Potential antimutagenic activity of berberine, a constituent of Mahonia aquifolium.

BACKGROUND: As part of a study aimed at developing new pharmaceutical products from natural resources, the purpose of this research was twofold: (1) to fractionate crude extracts from the bark of Mahonia aquifolium and (2) to evaluate the strength of the antimutagenic activity of the separate components against one of the common direct-acting chemical mutagens. METHODS: The antimutagenic potency was evaluated against acridine orange (AO) by using Euglena gracilis as an eukaryotic test model, based on the ability of the test compound/fraction to prevent the mutagen-induced damage of chloroplast DNA. RESULTS: It was found that the antimutagenicity of the crude Mahonia extract resides in both bis-benzylisoquinoline (BBI) and protoberberine alkaloid fractions but only the protoberberine derivatives, jatrorrhizine and berberine, showed significant concentration-dependent inhibitory effect against the AO-induced chloroplast mutagenesis of E. gracilis. Especially berberine elicited, at a very low dose, remarkable suppression of the AO-induced mutagenicity, its antimutagenic potency being almost three orders of magnitude higher when compared to its close analogue, jatrorrhizine. Possible mechanisms of the antimutagenic action are discussed in terms of recent literature data. While the potent antimutagenic activity of the protoberberines most likely results from the inhibition of DNA topoisomerase I, the actual mechanism(s) for the BBI alkaloids is hard to be identified. CONCLUSIONS: Taken together, the results indicate that berberine possesses promising antimutagenic/anticarcinogenic potential that is worth to be investigated further.