Myocardial Dysfunction in an Animal Model of Cancer Cachexia

Aims Fatigue is a common occurrence in cancer patients regardless of tumor type or anti-tumor therapies and is an especially problematic symptom in persons with incurable tumor disease. In rodents, tumor-induced fatigue is associated with a progressive loss of skeletal muscle mass and increased expression of biomarkers of muscle protein degradation. The purpose of the present study was to determine if muscle wasting and expression of biomarkers of muscle protein degradation occur in the hearts of tumor-bearing mice, and if these effects of tumor growth are associated with changes in cardiac function. Main methods The colon26 adenocarcinoma cell line was implanted into female CD2F1 mice and skeletal muscle wasting, in vivo heart function, in vitro cardiomyocyte function, and biomarkers of muscle protein degradation were determined. Key findings Expression of biomarkers of protein degradation were increased in both the gastrocnemius and heart muscle of tumor-bearing mice and caused systolic dysfunction in vivo. Cardiomyocyte function was significantly depressed during both cellular contraction and relaxation. Significance These results suggest that heart muscle is directly affected by tumor growth, with myocardial function more severely compromised at the cellular level than what is observed using echocardiography

Losartan Treatment Attenuates Tumor-induced Myocardial Dysfunction

Fatigue and muscle wasting are common symptoms experienced by cancer patients. Data from animal models demonstrate that angiotensin is involved in tumor-induced muscle wasting, and that tumor growth can independently affect myocardial function, which could contribute to fatigue in cancer patients. In clinical studies, inhibitors of angiotensin converting enzyme (ACE) can prevent the development of chemotherapy-induced cardiovascular dysfunction, suggesting a mechanistic role for the renin–angiotensin–aldosterone system (RAAS). In the present study, we investigated whether an angiotensin (AT) 1-receptor antagonist could prevent the development of tumor-associated myocardial dysfunction. Methods and results: Colon26 adenocarcinoma (c26) cells were implanted into female CD2F1 mice at 8 weeks of age. Simultaneously, mice were administered Losartan (10 mg/kg) daily via their drinking water. In vivo echocardiography, blood pressure, in vitro cardiomyocyte function, cell proliferation assays, and measures of systemic inflammation and myocardial protein degradation were performed 19 days following tumor cell injection. Losartan treatment prevented tumor-induced loss of muscle mass and in vitro c26 cell proliferation, decreased tumor weight, and attenuated myocardial expression of interleukin-6. Furthermore, Losartan treatment mitigated tumor-associated alterations in calcium signaling in cardiomyocytes, which was associated with improved myocyte contraction velocity, systolic function, and blood pressures in the hearts of tumor-bearing mice. Conclusions: These data suggest that Losartan may mitigate tumor-induced myocardial dysfunction and inflammation

Particulate Matter Exposure Exacerbates High Glucose-Induced Cardiomyocyte Dysfunction through ROS Generation

Diabetes mellitus and fine particulate matter from diesel exhaust (DEP) are both important contributors to the development of cardiovascular disease (CVD). Diabetes mellitus is a progressive disease with a high mortality rate in patients suffering from CVD, resulting in diabetic cardiomyopathy. Elevated DEP levels in the air are attributed to the development of various CVDs, presumably since fine DEP (<2.5 µm in diameter) can be inhaled and gain access to the circulatory system. However, mechanisms defining how DEP affects diabetic or control cardiomyocyte function remain poorly understood. The purpose of the present study was to evaluate cardiomyocyte function and reactive oxygen species (ROS) generation in isolated rat ventricular myocytes exposed overnight to fine DEP (0.1 µg/ml), and/or high glucose (HG, 25.5 mM). Our hypothesis was that DEP exposure exacerbates contractile dysfunction via ROS generation in cardiomyocytes exposed to HG. Ventricular myocytes were isolated from male adult Sprague-Dawley rats cultured overnight and sarcomeric contractile properties were evaluated, including: peak shortening normalized to baseline (PS), time-to-90% shortening (TPS90), time-to-90% relengthening (TR90) and maximal velocities of shortening/relengthening (±dL/dt), using an IonOptix field-stimulator system. ROS generation was determined using hydroethidine/ethidium confocal microscopy. We found that DEP exposure significantly increased TR90, decreased PS and ±dL/dt, and enhanced intracellular ROS generation in myocytes exposed to HG. Further studies indicated that co-culture with antioxidants (0.25 mM Tiron and 0.5 mM N-Acetyl-L-cysteine) completely restored contractile function in DEP, HG and HG+DEP-treated myocytes. ROS generation was blocked in HG-treated cells with mitochondrial inhibition, while ROS generation was blocked in DEP-treated cells with NADPH oxidase inhibition. Our results suggest that DEP exacerbates myocardial dysfunction in isolated cardiomyocytes exposed to HG-containing media, which is potentially mediated by various ROS generation pathways

Summary data for intracellular ROS generation as shown by changes in ET fluorescence in isolated ventricular myocytes.

<p>Sample size ranged from 100 to 360 cells from 5–8 rats. (*) Significantly different compared to Ctrl, HG+AOX, HG+MI, DEP+AOX, DEP+MI, HG+DEP+MI+Apo; (#) Significantly different compared to HG and DEP (P<0.05).</p

Cell morphology of isolated ventricular myocytes (A–C).

<p>Typical myocytes treated overnight with 0 µg/ml (A); 0.1 µg/ml DEP (B); or 1.0 µg/ml DEP (C).</p

Intracellular reactive oxygen species (ROS) generation in isolated ventricular myocytes.

<p>Typical ET confocal emission images of Ctrl <i>versus</i> Ctrl with AOX (Tiron at 0.25 mM and NAC at 0.5 mM), Ctrl with MI (rotenone at 1 µg/ml and the mitochondrial complex II inhibitor (MI) thenoyltrifluoroacetone (TTFA) at 50 µM), and Ctrl with apocynin (100 µM, Apo); Typical ET emission images treated with HG (25.5 mM) <i>versus</i> HG with AOX, HG with MI, and HG with Apo; Typical ET images of DEP (0.1 µg/ml) <i>versus</i> DEP with AOX, DEP with MI, and DEP with Apo; Typical ET images of HG (25.5 mM) and DEP (0.1 µg/ml) <i>versus</i> HG and DEP with AOX, HG and DEP with MI, HG+DEP with Apo, and HG+DEP with MI and Apo.</p

Shortening and relengthening contractility in isolated ventricular myocytes stimulated at 1 Hz.

<p>Peak shortening (PS) (A) (% cell length), time-to-90% relengthening (TR₉₀) (B) departure (C) and (D) return velocity (±dL/dt µm/s) in control (culture medium overnight; Ctrl), high glucose treatment (25.5 mM overnight; HG), diesel exhaust particle (DEP) treatment (0.1 µg/ml overnight; DEP), HG and DEP treatment (25.5 mM and 0.1 µg/ml overnight); Ctrl with antioxidants (Tiron at 0.25 mM and NAC at 0.5 mM; (AOX)), HG with AOX, DEP with AOX, HG+DEP with AOX. Myocytes were field stimulated with 1 Hz at 37°C. Sample size ranged from 38 to 72 cells per group from 5–8 rats. (*) Significantly compared to Ctrl; (#) significantly compared to HG and DEP (P<0.05).</p