Despite efforts spanning four decades, the therapeutic potential of thyroid hormone receptor (TR) agonists as lipid-lowering and anti-obesity agents remains largely unexplored in humans because of dose-limiting cardiac effects and effects on the thyroid hormone axis (THA), muscle metabolism, and bone turnover. TR agonists selective for the TR␤ isoform exhibit modest cardiac sparing in rodents and primates but are unable to lower lipids without inducing TR␤-mediated suppression of the THA. Herein, we describe a cytochrome P450-activated prodrug of a phosphonatecontaining TR agonist that exhibits increased TR activation in the liver relative to extrahepatic tissues and an improved therapeutic

Non-alcoholic fatty liver disease (NAFLD) is one of the most common forms of chronic liver disease, with a prevalence ranging from 10% to 30%. The use of thyroid hormone receptor (TR) agonists for the treatment of NAFLD has not been considered viable because thyroid hormones increase free fatty acid (FFA) flux from the periphery to the liver, induce hepatic lipogenesis, and therefore could potentially cause steatosis. MB07811 is an orally active HepDirect prodrug of MB07344, a liver-targeted TR-␤ agonist. The purpose of these studies was to assess the effects of MB07811 on whole body and liver lipid metabolism of normal rodents and rodent models of hepatic steatosis. In the current studies, MB07811 markedly reduced hepatic steatosis as well as reduced plasma FFA and triglycerides. In contrast to MB07811, T 3 induced adipocyte lipolysis in vitro and in vivo and had a diminished ability to decrease hepatic steatosis. This suggests the influx of FFA from the periphery to the liver may partially counteract the antisteatotic activity of T 3 . Clearance of liver lipids by MB07811 results from accelerated hepatic fatty acid oxidation, a known consequence of hepatic TR activation, as reflected by increased hepatic mitochondrial respiration rates, changes in hepatic gene expression, and increased plasma acyl-carnitine levels. Transaminase levels remained unchanged, or were reduced, and no evidence for liver fibrosis or other histological liver damage was observed after treatment with MB07811 for up to 10 weeks. Additionally, MB07811, unlike T 3 , did not increase heart weight or decrease pituitary thyroid-stimulating hormone beta (TSH␤) expression. Conclusion: MB07811 represents a novel class of liver-targeted TR agonists with beneficial low-density lipoprotein cholesterollowering properties that may provide additional therapeutic benefit to hyperlipidemic patients with concomitant NAFLD. (HEPATOLOGY 2009;49:407-417.)

Cardiac fibroblasts (CF) express adenosine (ADO) receptors, and pharmacological evidence suggests the possible involvement of the A2 (A2a and A2b) receptor (A2aR and A2bR) subtypes in inhibiting cell functions involved in fibrosis. The main objective of this study was to define the contributions of A2a and/or A2b receptors in modulating ADO-induced decreases in CF functions. For this purpose, CF were either treated pharmacologically or had the A2aR or A2bR levels modified through the use of recombinant adenovirus or siRNA. The assessment of mRNA expression in adult rat CF yielded evidence for A1R, A2bR, A2a), and A3R. Endogenously or exogenously enhanced ADO significantly inhibits CF proliferation, collagen, and protein synthesis. A2R and A2aR agonists, although capable of inhibiting CF protein and collagen synthesis, were unable to define the contributions derived from A2aR or A2bR. Overexpression of A2bR in CF yielded significant decreases in basal levels of collagen and protein synthesis and correlated with increases in cAMP levels. However, at higher doses of ADO receptor agonists, significant increases in protein and collagen synthesis were observed. CF with underexpression of A2bR yielded increases in protein and collagen synthesis. In contrast, A2aR underexpression did not modify ADO-induced decreases in CF protein or collagen synthesis. In conclusion, results derived from the molecular manipulation of receptor levels indicate that A2bR are critically involved in ADO-mediated inhibition of CF functions.

Transient coronary occlusion (15 minutes) does not result in irreversible myocardial injury but is associated with a depression of contractile function sustained for several hours to days ("stunned myocardium"). The defect in the contractile process responsible for this phenomenon has been suggested to be causally related to a reduced energetic state, altered excitation or excitation-contraction coupling, or damaged contractile filaments. The purpose of this study was to attempt to exclude one or more of these hypotheses by evaluating the contractile reserve of reperfused myocardium. Regional subendocardial segment function was measured (sonomicrometry) in a control region and in an area (treatment region) perfused by a carotid artery to anterior descending coronary artery bypass in 13 chloralose-anesthetized dogs. Dose-response curves were constructed from changes in segment shortening (%SS) in response to intracoronary calcium infusion before ischemia and following 5 or 15 minutes of occlusion and reperfusion (30 minutes). Calcium infusion before ischemia resulted in dose-dependent increases in %SS in the treatment area to a maximum value of 36.6% from a preinfusion value of 25.5% (p less than 0.01), in the absence of changes in control region shortening (23.7%). After 15 minutes of occlusion and reperfusion, treatment area %SS had fallen to a depressed but stable level (46% of preischemic values; p less than 0.01). Subsequent calcium infusion at the same doses as in the preischemic trial produced increases in treatment segment function with return of shortening to control levels at an intermediate dose. At the highest dose, %SS was 35.4%, which was not different from the maximal value found in the preischemic trial. Alterations in heart rate and left ventricular systolic and diastolic pressures during calcium infusion were minor and similar before and after ischemia. Calcium-induced increases in regional segment shortening above control levels (113% of control) in reperfused myocardium were sustained with continuous infusion (30 minutes) without deleterious effects on subsequent function. These results demonstrate that stunned myocardium in this model retains a normal contractile reserve in response to calcium, suggesting that the mechanism responsible for postischemic contractile dysfunction involves calcium.

Introduction The homeostatic intracellular repair response (HIR2) is an endogenous beneficial pathway that eliminates damaged mitochondria and dysfunctional proteins in response to stress. The underlying mechanism is adaptive autophagy. The purpose of this study was to determine whether the HIR2 response is activated in the heart in patients undergoing cardiac surgery and to assess whether it is associated with the duration of ischemic arrest and predicted surgical outcome. Methods Autophagy was assessed in 19 patients undergoing coronary artery bypass or valve surgery requiring cardiopulmonary bypass (CPB). Biopsies of the right atrial appendage obtained before initiation of CPB and after weaning from CPB were analyzed for autophagy by immunoblotting for LC3, Beclin-1, Atg5-12, and p62. Changes in p62, a marker of autophagic flux, were correlated with duration of ischemia and with the mortality/morbidity risk scores obtained from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (v2.73). Results Heart surgery was associated with a robust increase in autophagic flux indicated by depletion of LC3-I, LC3-II, Beclin-1, and Atg5-12; the magnitude of change for each of these factors correlated significantly with changes in the flux marker p62. Moreover, changes in p62 correlated directly with cross clamp time and inversely with the mortality/morbidity risk scores. Conclusion These findings are consistent with preclinical studies indicating that HIR2 is cardioprotective, and reveal that it is activated in patients in response to myocardial ischemic stress. Strategies designed to amplify HIR2 during conditions of cardiac stress may have therapeutic utility and represent an entirely new approach to myocardial protection in patients undergoing heart surgery.

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We chronically implanted hygroscopic occluders around the left circumflex coronary artery in 49 anesthetized young male domestic pigs and we studied the development of a collateral circulation at 4, 8, 12, and 26 weeks after implantation. At these time intervals groups of animals were again anesthetized, the hearts were explanted and perfused in Langendorff-fashion with leucocyte-filtered pig blood. Maximal coronary vasodilation was induced with adenosine and global (electromagnetic), and regional (tracer microspheres) blood flow was measured at 40, 60, 80, and 100 mm Hg of perfusion pressure. At 4 weeks after occluder implantation maximal left circumflex collateral blood flow was about 20% of normal maximal flow. Collateral flow rose to 60% of maximal normal flow between 4 and 8 weeks and did not improve further with longer time intervals. In contrast to the canine heart numerous small vessels develop in response to ischemia in the pig heart. These vessels develop throughout the entire risk region with a slight preference for the subendocardium. They appear on tomographic angiograms as a dense "blush". The study of the relationship between peripheral coronary pressure vs collateral flow showed a relationship much steeper than that of normal maximal flow vs aortic perfusion pressure which indicates that the minimal resistance of the risk region was decreased as part of the mechanism to ensure adequate blood supply in a situation of progressive coronary narrowing.

Activated complement component C5a causes myocardial ischemia mediated by thromboxane (Tx) A2 and leukotrienes C4/D4. Blood cells are not involved in either the mediator release or the myocardial effects of C5a, suggesting that a C5a-sensitive, cardiac resident inflammatory cell is responsible. The goals of this study were to determine whether 1) cardiac mast cell activation accompanies the C5a response, 2) inhibition of mast cell degranulation inhibits the response, and 3) histamine release plays a role in the C5a-induced myocardial ischemia. The left anterior descending coronary artery (LAD) of open-chest pigs (n = 13) was perfused with arterial blood at constant pressure (95 mmHg). Coronary blood flow (CBF) was measured (in-line flowmeter) and regional function [percent segment shortening (%SS)] determined with sonomicrometry. A coronary vein was cannulated for measurement of plasma TxB2 and histamine (a marker of mast cell degranulation). Intracoronary C5a (500 ng) decreased coronary blood flow (45% of preinfusion levels) and LAD %SS (65% of preinfusion) and was accompanied by increases in coronary venous TxB2 (delta 63.3 ng/ml) and histamine (delta 200 nM). Mast cell inhibition with lodoxamide (2 mg/kg iv, n = 8) attenuated the C5a-induced fall in CBF (14 vs. 53% decrease, P < 0.01) and %SS (10 vs. 38% decrease, P < 0.01) and also reduced the C5a-induced increase in both coronary venous histamine (delta 26 vs. 278 nM, P < 0.05) and TxB2 (delta 0.34 vs. 63.3 ng/ml, P < 0.01). However, histamine H1 (pyrilamine) and H2 (ranitidine) receptor blockade had no effect on the C5a-induced fall in CBF or LAD %SS.(ABSTRACT TRUNCATED AT 250 WORDS)