Cardiac Hypertrophy and Cardiac Cell Death in Chronic Kidney Disease.

BACKGROUND: Chronic kidney disease (CKD) is a prevalent clinical condition affecting 15% of the general population. Cardiorenal syndrome (CRS) type 4 is characterized by an underlying CKD condition leading to impairment of cardiac function and increased risk for major cardiovascular events. To date, the mechanisms leading from CKD to CRS are not completely understood. In particular, it is unclear whether the pathological changes that occur in the heart in the setting of CKD involve enhanced cell death of cardiac cells. OBJECTIVES: To assess whether CKD may mediate loss of cardiac cells by apoptosis. METHODS: We established rat models for CKD, acute myocardial infarction (acute MI), left ventricular dysfunction (LVD), and sham. We measured the cardiac-to-body weight as well as kidney-to-body weight ratios to validate that renal and cardiac hypertrophy occur as part of disease progression to CRS. Cardiac cells were then isolated and the percent of cell death was determined by flow cytometry following staining with annexin-FITC and propidium iodide. In addition, the levels of caspase-3-dependent apoptosis were determined by Western blot analysis using an anti-cleaved caspase-3 antibody. RESULTS: CKD, as well as acute MI and LVD, resulted in significant cardiac hypertrophy. Nevertheless, unlike the increased levels of cell death observed in the acute MI group, in the CKD group, cardiac hypertrophy was not associated with induction of cell death of cardiac cells. Caspase-3 activity was even slightly reduced compared to sham-operated controls. CONCLUSIONS: Our data show that while CKD induces pathological changes in the heart, it does not induce cardiac cell death.

The transient receptor potential vanilloid 2 cation channel is abundant in macrophages accumulating at the peri-infarct zone and may enhance their migration capacity towards injured cardiomyocytes following myocardial infarction.

PURPOSE: A novel family of transient receptor potential (TRP) channels, that may hold a role in calcium homeostasis, has recently been described. By employing a GeneChip array analysis we have demonstrated a clear and specific upregulation of the TRP vanilloid 2 (TRPV2) mRNA in the left ventricles (LV) 3-5 days post-acute myocardial infarction (MI) compared to sham-operated controls, both in rats and in mice. We sought to characterize the cardiac cellular subpopulations in which TRPV2 is overexpressed upon acute MI. METHODS: Lewis rats underwent an acute MI by ligation of the left anterior descending artery or chest opening only (sham). The animals were terminated at various time points and an immunohistochemical (IHC) and immunofluorescent (IFC) staining of the LV sections as well as a flow cytometry analysis of LV-derived cells were carried out, using anti-TRPV2 and anti-monocyte/macrophage antibodies. Rat alveolar macrophage cells, NR8383, transiently transfected with TRPV2 siRNA were allowed to migrate towards hypoxic conditioned media of the rat cardiac myoblast line H9C2 using a trans-well migration assay. The macrophage cells migrating to the bottom side of the inserts were counted. RESULTS: The IHC and IFC staining as well as the flow cytometry data demonstrated a substantial expression of TRPV2 in infiltrating macrophages in the peri-infarct region 3-5 days post-acute MI. The in vitro migration assay data demonstrated that following inhibition of the TRPV2 channel, the number of migrating macrophages towards conditioned medium of hypoxic cardiomyocytes was significantly reduced. CONCLUSIONS: TRPV2 is highly expressed on the peri-infarct infiltrating macrophages and may play an important role in post-MI phagocytosis. Better characterization of this channel may pave the way for identifying a new target for modulating the dramatic post-MI immune reactions.

Effect of vitamin D analogues on acute cardiorenal syndrome: a laboratory rat model.

BACKGROUND: Vitamin D has been shown to induce beneficial effects on cardiovascular and renal morbidity by regulating inflammation and tissue fibrosis. OBJECTIVES: To evaluate the effect of vitamin D analogues on cardiac function and fibrosis in an animal model of cardiorenal syndrome. METHODS: Unilateral nephrectomy was performed and myocardial infarction induced in rats. The rats were treated with vitamin D receptor activator (VDRA, paricalcitol, 40 ng/250 g x 3/week) versus a vehicle. A third group of animals, which served as the control, underwent sham surgery and received no treatment. After 4 weeks of treatment, cardiac function and fibrosis were assessed by trans-thoracic echo and histology, respectively. As a parameter of systemic inflammation, previously shown to be altered in acute coronary syndrome, T regulatory (Treg) cell levels were measured by flow cytometry. Renal dysfunction was documented by standard laboratory tests. RESULTS: After 4 weeks of treatment, no significant improvement in cardiac function parameters was noted following VDRA administration. VDRA treatment did not significantly alter Treg cell systemic levels. Consistently, despite a trend toward less extent of myocardial fibrosis, we found no clear beneficial effects of VDRA on myocardial tissue inflammation and remodeling. CONCLUSIONS: Vitamin D treatment showed no beneficial effects on cardiac function parameters and fibrosis in an animal model of cardiorenal syndrome.

Accelerated renal fibrosis in cardiorenal syndrome is associated with long-term increase in urine neutrophil gelatinase-associated lipocalin levels.

BACKGROUND: Cardiac events are the main cause of death among patients with end-stage renal failure. Even a mild renal disease is currently considered a major risk factor for cardiovascular complications following myocardial infarction (MI). The aim of the present study was to detect histological, sera and urine characteristics of kidney injury in cardiorenal syndrome (CRS) compared to chronic kidney disease (CKD) with an intact cardiac function. METHODS: We employed a rat model for CRS, in which an acute MI (AMI) was induced 4 weeks after establishment of subtotal nephrectomy. Four weeks later, left ventricular function was assessed by echocardiography and changes in renal performance were examined using histological and biochemical parameters. RESULTS: Increased interstitial fibrosis as well as renal inflammation were observed in renal sections derived from CRS rats, compared to subtotal nephrectomy (CKD)-only animals. Moreover, we found that even though AMI on the background of CKD was not associated with a further decrease in creatinine clearance or a further increase in sera BUN levels compared to CKD only, a significant long-term elevation in urine neutrophil gelatinase-associated lipocalin (Ngal) levels was detectable post-MI induction. CONCLUSIONS: AMI in the CKD setting is associated with accelerated renal fibrosis and long-term elevated urine Ngal values, suggesting that cardiac dysfunction contributes to accelerated intrinsic kidney injury in CKD. The data indicate that elevated urine Ngal may potentially serve as an early non-invasive laboratory parameter for a left ventricular dysfunction-related renal injury.