Physiological, pharmacological and toxicological considerations of drug-induced structural cardiac injury.

The incidence of drug-induced structural cardiotoxicity, which may lead to heart failure, has been recognized in association with the use of anthracycline anti-cancer drugs for many years, but has also been shown to occur following treatment with the new generation of targeted anti-cancer agents that inhibit one or more receptor or non-receptor tyrosine kinases, serine/threonine kinases as well as several classes of non-oncology agents. A workshop organized by the Medical Research Council Centre for Drug Safety Science (University of Liverpool) on 5 September 2013 and attended by industry, academia and regulatory representatives, was designed to gain a better understanding of the gaps in the field of structural cardiotoxicity that can be addressed through collaborative efforts. Specific recommendations from the workshop for future collaborative activities included: greater efforts to identify predictive (i) preclinical; and (ii) clinical biomarkers of early cardiovascular injury; (iii) improved understanding of comparative physiology/pathophysiology and the clinical predictivity of current preclinical in vivo models; (iv) the identification and use of a set of cardiotoxic reference compounds for comparative profiling in improved animal and human cellular models; (v) more sharing of data (through publication/consortia arrangements) on target-related toxicities; (vi) strategies to develop cardio-protective agents; and (vii) closer interactions between preclinical scientists and clinicians to help ensure best translational efforts.

Developing strategies to link basic cardiovascular sciences with clinical drug development: another opportunity for translational sciences.

Driven, at least in part, by the National Institutes of Health roadmap, an increasing number of studies has bridged the chasm between observations in the basic research laboratory and the clinical bedside. These studies have been an integral part in "translating" new discoveries into therapeutic initiatives. However, "translational medicine" has been used less frequently in the development of cardiovascular drugs or in predicting the potential cardiovascular toxicity of non-cardiac agents. Studies in animal models can provide important clues as to the potential cardiotoxicity of new therapeutic agents, as well as providing a template for the rational design of clinical trials. Three examples of drug development programs that might have been altered by clues available from laboratory studies include the development programs for the anti-cancer drug trastuzumab, the cyclooxygenase inhibitors, and the adenosine-receptor agonists and antagonists. Although mouse models may not always represent the physiology of humans, they provide important information that clinical scientists can utilize in designing safe programs for the evaluation of new pharmacologic agents.

Akt activation preserves cardiac function and prevents injury after transient cardiac ischemia in vivo.

BACKGROUND: The serine-threonine kinase Akt is activated by several ligand-receptor systems previously shown to be cardioprotective. Akt activation reduces cardiomyocyte apoptosis in models of transient ischemia. Its role in cardiac dysfunction or infarction, however, remains unclear. METHODS AND RESULTS: We examined the effects of a constitutively active Akt mutant (myr-Akt) in a rat model of cardiac ischemia-reperfusion injury. In vivo gene transfer of myr-Akt reduced infarct size by 64% and the number of apoptotic cells by 84% (P<0.005 for each). Ischemia-reperfusion injury decreased regional cardiac wall thickening as well as the maximal rate of left ventricular pressure rise and fall (+dP/dt and -dP/dt). Akt activation restored regional wall thickening and +dP/dt and -dP/dt to levels seen in sham-operated rats. To better understand this benefit, we examined the effects of myr-Akt on hypoxic cardiomyocyte dysfunction in vitro. myr-Akt prevented hypoxia-induced abnormalities in cardiomyocyte calcium transients and shortening. Akt activation also enhanced sarcolemmal expression of Glut-4 in vivo and increased glucose uptake in vitro to the level seen with insulin treatment. CONCLUSIONS: Akt activation exerts a powerful cardioprotective effect after transient ischemia that probably reflects its ability to both inhibit cardiomyocyte death and improve function of surviving cardiomyocytes. Akt may represent an important nodal target for therapy in ischemic and other heart disease.

Complications of exercise and pharmacologic stress tests: differences in younger and elderly patients.

BACKGROUND: Age characteristics of patients undergoing various types of stress tests are important because of differences in clinical background and exercise performance between the young and elderly. Adverse effects of pharmacologic agents are known to be more common in the elderly, who are less able to perform vigorous exercise stress testing. We investigated the clinical background, performance characteristics, and complication rate of various stress tests in younger (<75 years old) and elderly (>75 years old) patient populations. METHODS: A total of 3412 patients (2796 younger, 616 elderly) underwent 5 types of stress tests with (1) technetium-99m sestamibi (MIBI) single photon emission computed tomography: symptom-limited exercise (Ex, 1598 younger, 173 elderly), (2) dipyridamole infusion (0.14 mg/kg/min, 4 minutes) without exercise (D, 260 younger, 114 elderly), (3) with exercise (DEx, 339 younger, 112 elderly), (4) adenosine infusion (0.14 mg/kg/min, 5 minutes) without exercise (A, 253 younger, 101 elderly), and (5) with exercise (AEx, 346 younger, 116 elderly). RESULTS: Sixty-seven percent of patients in the younger population were able to achieve 85% of the maximum predicted heart rate, whereas 54% of the elderly reached this level of exercise. No patient had life-threatening complications. In both the younger and elderly groups, chest discomfort, feelings of impending syncope, flushing, and fall in blood pressure occurred less frequently in DEx than D and in AEx than A. Sinus bradycardia occurred less frequently in AEx than A in the younger (1.2% vs 4.3%, P < .05) and elderly groups (0.9% vs 6.9%, P < .05). Atrioventricular block was less frequent in AEx than A in the younger group (3.2% vs 7.9%, P < .05) but not so in the elderly group (13.0% vs 17.8%, not significant). The frequency of ischemic electrocardiographic changes in DEx and AEx was very similar to that of Ex in both the younger and elderly groups, although ischemic electrocardiographic changes in D and A are known to be less frequent. CONCLUSION: Of the elderly group who were judged to be fit to exercise to 85% of maximum predicted heart rate, nearly half failed to reach this level. In contrast, the younger patients were able to achieve this level in 67% of tests. Supplementation with modest exercise reduced most of the pharmacologically related adverse effects. The elderly group was not protected from atrioventricular block as effectively as the younger group by additional exercise in the adenosine stress test. Ischemic electrocardiographic changes in the pharmacologic stress test were as frequent as in the exercise stress test when modest supplementary exercise was added to the pharmacologic protocol. There were no deaths, myocardial infarction, or other major complications. These observations suggest that exercise and pharmacologic stress tests are safe in the elderly, including those patients more than 75 years old.

Mitogen regulation of c-Raf-1 protein kinase activity toward mitogen-activated protein kinase-kinase.

The c-raf-1 protooncogene encodes a Ser/Thr protein kinase. A mitogen-activated protein kinase-kinase (MAPKK) purified from bovine brain is phosphorylated and activated 4-9-fold in vitro by c-Raf-1 from mitogen-treated cells. c-Raf-1 protein kinase activity, measured by the phosphorylation of brain MAPKK substrate, is detectably activated within 1 min after addition of platelet-derived growth factor (PDGF) to 3T3 cells, increasing more rapidly than the endogenous NIH 3T3 cell MAPKK activity. c-Raf-1 activation is also induced by insulin, phorbol ester, thrombin, and endothelin. PDGF-, epidermal groth factor-, and insulin-stimulated 32P-c-Raf-1 yield very similar, complex tryptic 32P-peptide maps, wherein only 2 of 10 32P-peptides appear entirely de novo after growth factor addition. Mitogen-activated protein kinase/extracellular signal-regulated kinase-2 can phosphorylate c-Raf-1 in vitro on 4-6 tryptic 32P-peptides, all of which comigrate with tryptic 32P-peptides derived from c-Raf-1 labeled in situ. Mitogen-activated protein kinase phosphorylation of c-Raf-1 in vitro, however, does not 1) generate 32P-peptides that comigrate with those that appear de novo after PDGF or insulin treatment in situ; 2) does not convert c-Raf-1 polypeptides to a slower mobility on SDS-polyacrylamide gel electrophoresis as is seen after PDGF or insulin; 3) does not alter c-Raf-1 kinase activity toward MAPKK. Thus, based on overlapping site specificity, Erk-2 is a viable candidate to be among the PDGF-stimulated c-Raf-1 kinases. Although PDGF/insulin-stimulated c-Raf-1 Ser/Thr phosphorylation may be necessary to sustain the active state, a role for mitogen-activated protein kinase/extracellular signal-regulated kinase-2 phosphorylation in the initiation of c-Raf-1 activation is unlikely.

Coronary ostial stenosis following aortic valve replacement without continuous coronary perfusion.

The development of coronary ostial stenosis following aortic valve replacement has been attributed to intraoperative trauma to the coronary vessels during continuous coronary perfusion. We describe two patients with this lesion in whom continuous coronary perfusion was not used during aortic valve replacement. Both patients were successfully treated with saphenous vein bypass grafting. Intraoperative observation of the aortic root at the time of the bypass operation in one case revealed the left coronary ostium to be pinpoint in size and involved in a dense fibrous reaction extending up from the sewing ring of the prosthesis. The findings in these cases support the hypothesis that coronary ostial stenosis following aortic valve replacement may be due to a fibrous reaction in the aortic root secondary to turbulent flow through the aortic prosthesis.