Novel Mechanisms of Anthracycline-Induced Cardiovascular Toxicity: A Focus on Thrombosis, Cardiac Atrophy, and Programmed Cell Death.

Anthracycline antineoplastic agents such as doxorubicin are widely used and highly effective component of adjuvant chemotherapy for breast cancer and curative regimens for lymphomas, leukemias, and sarcomas. The primary dose-limiting adverse effect of anthracyclines is cardiotoxicity that typically manifests as cardiomyopathy and can progress to the potentially fatal clinical syndrome of heart failure. Decades of pre-clinical research have explicated the complex and multifaceted mechanisms of anthracycline-induced cardiotoxicity. It is well-established that oxidative stress contributes to the pathobiology and recent work has elucidated important central roles for direct mitochondrial injury and iron overload. Here we focus instead on emerging aspects of anthracycline-induced cardiotoxicity that may have received less attention in other recent reviews: thrombosis, myocardial atrophy, and non-apoptotic programmed cell death.

Effects of the kinase inhibitor sorafenib on heart, muscle, liver and plasma metabolism in vivo using non-targeted metabolomics analysis.

BACKGROUND AND PURPOSE: The human kinome consists of roughly 500 kinases, including 150 that have been proposed as therapeutic targets. Protein kinases regulate an array of signalling pathways that control metabolism, cell cycle progression, cell death, differentiation and survival. It is not surprising, then, that new kinase inhibitors developed to treat cancer, including sorafenib, also exhibit cardiotoxicity. We hypothesized that sorafenib cardiotoxicity is related to its deleterious effects on specific cardiac metabolic pathways given the critical roles of protein kinases in cardiac metabolism. EXPERIMENTAL APPROACH: FVB/N mice (10 per group) were challenged with sorafenib or vehicle control daily for 2 weeks. Echocardiographic assessment of the heart identified systolic dysfunction consistent with cardiotoxicity in sorafenib-treated mice compared to vehicle-treated controls. Heart, skeletal muscle, liver and plasma were flash frozen and prepped for non-targeted GC-MS metabolomics analysis. KEY RESULTS: Compared to vehicle-treated controls, sorafenib-treated hearts exhibited significant alterations in 11 metabolites, including markedly altered taurine/hypotaurine metabolism (25-fold enrichment), identified by pathway enrichment analysis. CONCLUSIONS AND IMPLICATIONS: These studies identified alterations in taurine/hypotaurine metabolism in the hearts and skeletal muscles of mice treated with sorafenib. Interventions that rescue or prevent these sorafenib-induced changes, such as taurine supplementation, may be helpful in attenuating sorafenib-induced cardiac injury.

BIN1 localizes the L-type calcium channel to cardiac T-tubules.

The BAR domain protein superfamily is involved in membrane invagination and endocytosis, but its role in organizing membrane proteins has not been explored. In particular, the membrane scaffolding protein BIN1 functions to initiate T-tubule genesis in skeletal muscle cells. Constitutive knockdown of BIN1 in mice is perinatal lethal, which is associated with an induced dilated hypertrophic cardiomyopathy. However, the functional role of BIN1 in cardiomyocytes is not known. An important function of cardiac T-tubules is to allow L-type calcium channels (Cav1.2) to be in close proximity to sarcoplasmic reticulum-based ryanodine receptors to initiate the intracellular calcium transient. Efficient excitation-contraction (EC) coupling and normal cardiac contractility depend upon Cav1.2 localization to T-tubules. We hypothesized that BIN1 not only exists at cardiac T-tubules, but it also localizes Cav1.2 to these membrane structures. We report that BIN1 localizes to cardiac T-tubules and clusters there with Cav1.2. Studies involve freshly acquired human and mouse adult cardiomyocytes using complementary immunocytochemistry, electron microscopy with dual immunogold labeling, and co-immunoprecipitation. Furthermore, we use surface biotinylation and live cell confocal and total internal fluorescence microscopy imaging in cardiomyocytes and cell lines to explore delivery of Cav1.2 to BIN1 structures. We find visually and quantitatively that dynamic microtubules are tethered to membrane scaffolded by BIN1, allowing targeted delivery of Cav1.2 from the microtubules to the associated membrane. Since Cav1.2 delivery to BIN1 occurs in reductionist non-myocyte cell lines, we find that other myocyte-specific structures are not essential and there is an intrinsic relationship between microtubule-based Cav1.2 delivery and its BIN1 scaffold. In differentiated mouse cardiomyocytes, knockdown of BIN1 reduces surface Cav1.2 and delays development of the calcium transient, indicating that Cav1.2 targeting to BIN1 is functionally important to cardiac calcium signaling. We have identified that membrane-associated BIN1 not only induces membrane curvature but can direct specific antegrade delivery of microtubule-transported membrane proteins. Furthermore, this paradigm provides a microtubule and BIN1-dependent mechanism of Cav1.2 delivery to T-tubules. This novel Cav1.2 trafficking pathway should serve as an important regulatory aspect of EC coupling, affecting cardiac contractility in mammalian hearts.

Pharmacy-based bone mass measurement to assess osteoporosis risk.

OBJECTIVE: To evaluate elderly women's knowledge of their skeletal status, assess adequacy of calcium intake, determine the prevalence of low bone density, and determine whether peripheral bone density testing led to medical interventions in a group of rural, elderly Wisconsin women recruited in community pharmacies. DESIGN: Recruiting notices were posted in each pharmacy, and eligible women were enrolled in the order in which they volunteered. Each completed a fracture-risk questionnaire. Calcaneal bone density was measured within the following 6 weeks, using peripheral dual-energy X-ray absorptiometry. Mail surveys were used to assess interventions subsequent to the womens' study participation. SETTING: The study was conducted at 5 community pharmacies in rural Wisconsin. RESULTS: Of 133 women, 20% had calcaneal osteoporosis, defined as a T score < or =2.5 (calcaneal bone density <2.5 SDs below the young reference database). Thirty percent of women met National Osteoporosis Foundation (NOF) treatment criteria based on heel bone density and NOF-designated risk factors. Of those meeting treatment criteria, 75% were unaware of their low bone mass. Half of the women received <1200 mg/d of calcium, the recommended dose for osteoporosis prevention. Those who were taking a calcium supplement were much more likely to receive the recommended amount. Women who had discussed bone density test results with their physicians were more likely to receive central dual energy X-ray absorptiometry (DXA) measurements and/or start antiresorptive therapy than women who did not. CONCLUSIONS: Rural, elderly Wisconsin women are at substantial risk for osteoporosis, based on calcaneal bone density, but most are unaware of their risk. Compounding this risk is low calcium intake. Community screening of rural, elderly women by peripheral bone density measurement can lead to medical interventions in such individuals.