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.

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.

Ischaemia/reperfusion-induced organ injury in low dose streptozotocin diabetes.

OBJECTIVES: The influence of low dose streptozotocin diabetes on intestinal and vascular injury induced by mesenteric ischaemia/reperfusion (I/R) was studied in rats. The role of reactive oxygen species (ROS) in the exacerbation of ischaemic/postischaemic damage in diabetes was addressed. METHODS: Diabetes was induced by i.p. injection of 3 x 30 mg/kg streptozotocin and after 5 weeks male Wistar rats underwent 60 min ischaemia followed by 30 min reperfusion of the superior mesenteric artery (SMA). The extent of intestinal haemorrhagic injury was assessed macroscopically. Relaxation to acetylcholine of precontracted SMA rings was tested. Chemiluminescence (CL) enhanced by luminol of tissue samples excised from the ileum and SMA was measured. RESULTS: In diabetic rats I/R-induced intestinal injury was significantly more pronounced compared to non-diabetic rats (63.6% potentiation). Decreased endothelial-dependent relaxation of diabetic SMA was not further influenced by I/R. Diabetes itself did not change the CL response of SMA and there was a similar CL increase in the diabetic group with I/R as in the controls. In the intestinal samples CL response was suppressed and I/R only mildly increased CL in the diabetic group. CONCLUSIONS: Diabetes renders the intestinal tissue more vulnerable to the effects of I/R. Endothelial-dependent relaxation of diabetic SMA was not further worsened by I/R. CL responses showed a different involvement of ROS in diabetic intestinal versus vascular tissue.

Participation of reactive oxygen species in diabetes-induced endothelial dysfunction.

OBJECTIVES: In the present study, the relationship between diabetes-induced hyperglycemia, reactive oxygen species production and endothelium-mediated arterial function was examined. The effect of antioxidant on the reactive oxygen species induced damage was tested. METHODS: Diabetes was induced by streptozotocin (STZ), 3 x 30 mg/kg i.p., administered on three consecutive days. After 10 weeks of diabetes, the functional state of the endothelium of the aorta was tested, endothelemia evaluation was performed and systolic blood pressure was measured. Reactive oxygen species (ROS) formation in blood and the aorta was measured using luminol-enhanced chemiluminescence (CL). Levels of reduced glutathione (GSH) were determined in the aorta, kidney, and plasma. To study the involvement of hyperglycemia in functional impairment of the endothelium, aortal rings incubated in solution with high glucose concentration were tested in in vitro experiments. RESULTS: After 10 weeks of diabetes, endothelial injury was observed, exhibited by diminished endothelium-dependent relaxation of the aorta, increased endothelemia and by elevated systolic blood pressure. Using luminol-enhanced CL, a significant increase of ROS production was found in arterial tissue and blood. GSH levels were significantly increased in the kidney, while there were no GSH changes in plasma and the aorta. Incubation of aortic rings in solution with high glucose concentration led to impairment of endothelium-dependent relaxation. The synthetic antioxidant SMe1EC2 was able to restore reduced endothelium-mediated relaxation. CONCLUSIONS: Our results suggest an important role of hyperglycemia-induced ROS production in mediating endothelial dysfunction in experimental diabetes, confirmed by CL and the protective effect of the antioxidant SMe1EC2.

Effect of a novel stobadine derivative on isolated rat arteries.

The antioxidant and reactive-oxygen-species-scavenging activity of stobadine has been demonstrated in previous studies. Recently, chemical modification of this leading structure led to the synthesis of other pyridoindole derivatives with significantly increased intrinsic antioxidant efficacy. Further structural modifications of stobadine provided the opportunity to increase bioavailability and attenuate unwanted side effects, such as α-adrenolytic activity. The aim of the work was to evaluate the direct effect of a novel pyridoindole, SMe1EC2, on the vascular wall ex vivo. The vasomotor effect of SMe1EC2 (1×10(-8)-1×10(-4) mol/l) was measured on isolated and pressurized rat cerebral and coronary arterioles using video-microscopy. The effect of SMe1EC2 (1×10(-6) and 1×10(-5) mol/l) on high potassium-, phenylephrine- or serotonin-induced contraction or acetylcholine-induced relaxation was also determined in aortic rings. We found that SMe1EC2 (1×10(-8)-1×10(-4) mol/l) elicited significant dilatations in both cerebral and coronary arterioles (max dilatation: 25±8% and 18±5% respectively). Yet, SMe1EC2 (1×10(-6) and 1×10(-5) mol/l) did not influence the tone of aortic rings nor did it affect high potassium-, phenylephrine- or serotonin -induced contractions and acetylcholine-induced relaxation. Thus SMe1EC2 was able to dilate resistance arteries but did not affect aortic contractility. It is likely that SMe1EC2 does not possess α1-adrenolytic and anti-serotoninergic activity in the vascular wall.

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.

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.