The mechanical and biochemical effects of pentoxifylline on the perfused rat heart

[Anti-inflammatory effects of pentoxifylline: importance in cardiac surgery]

Initially introduced as a rheologic agent for use in intermittent claudication due to peripheral artery disease and in ischemic cerebrovascular disease, the methylxanthine derivative pentoxifylline (PTX) has been shown to possess several anti-inflammatory properties which make this drug an interesting immunomodulating adjunct for the management of patients undergoing cardiac surgery. As an unspecific phosphodiesterase inhibitor PTX ameliorates the inflammatory response following a septic stimulus and blunts organ dysfunction after ischemia-reperfusion injury. Apart from this several small clinical studies have shown that the use of PTX may blunt the inflammatory response induced by cardiac surgery using a cardiopulmonary bypass. Additionally it has been shown that the perioperative application of this drug may improve postoperative function of organs at risk, such as the kidneys and liver.

Myocardial phosphodiesterases and regulation of cardiac contractility in health and cardiac disease

Phosphodiesterase (PDE) inhibitors are potent cardiotonic agents used for parenteral inotropic support in heart failure. Contractile effects of these agents are mediated through cAMP-protein kinase A-induced stimulation of I (Ca2+) which ultimately results in increased Ca(2+)-induced sarcoplasmic reticulum Ca(2+) release. A number of additional effects such as increases in sarcoplasmic reticulum Ca(2+) stores, stimulation of reverse mode Na(+)-Ca(2+) exchange, direct or cAMP-mediated effects on sarcoplasmic reticulum ryanodine receptor, stimulation of the voltage-sensitive sarcoplasmic reticulum Ca(2+) release mechanism, as well as A(1) adenosine receptor blockade could contribute to positive inotropic responses to PDE inhibitors. Moreover, some PDE inhibitors exhibit Ca(2+) sensitizer properties as they could increase the affinity of troponin C Ca(2+)-binding sites as well as reduce Ca(2+) threshold for thin myofilament sliding and facilitate cross-bridge cycling. Inotropic responses to PDE inhibitors are significantly reduced in cardiac disease, an effect largely attributed to downregulation of cAMP-mediated signalling due to sustained sympathetic activation. Four PDE isoenzymes (PDE1, PDE2, PDE3 and PDE4) are present in myocardial tissue of various mammalian species, of which PDE3 and PDE4 are particularly involved in regulation of cardiac myocyte contraction. PDE cAMP-hydrolysing activity is preserved in compensated cardiac hypertrophy but significantly reduced in animal models of heart failure. However, clinical studies have not revealed any changes in distribution profile as well as kinetic and regulatory properties of myocardial PDEs in failing human hearts. A reduction of PDE inhibitors-induced contractile responses in heart failure has therefore been ascribed to reduced cAMP synthesis due to uncoupling of adenylyl cyclase from beta-adrenoreceptor. In cardiac myocytes, PDEs are targeted to distinct subcellular compartments by scaffolding proteins such as myomegalin, mAKAP and beta-arrestins. Over subcellular microdomains, cAMP hydrolysis by PDE3 and PDE4 allows to control the activity of local pools of protein kinase A and therefore the extent of protein kinase A-mediated phosphorylation of cellular proteins.

Pentoxifylline Improves Reoxygenation-induced Contractile Recovery Through a Nitric Oxide-dependent Mechanism in Rat Papillary Muscles

In this study, the protective effect of pentoxifylline against hypoxia-reoxygenation injury and the possible involvement of nitric oxide (NO)-mediated pathways in this protection were investigated in isolated rat papillary muscles. Papillary muscles were excised and isolated in Krebs-Henseleit solution aerated with 95% O2 and 5% CO2. Hypoxia was simulated by substituting O2 with argon. Three sets of experiments, testing 30, 60, and 90 min of hypoxia, were performed. The effects of different pentoxifylline concentrations on papillary muscle contractile parameters and responsiveness to isoproterenol were assessed. To investigate the role of NO, N(omega)-nitro-L-arginine methyl ester was added before pentoxifylline treatment. Pentoxifylline did not show any inotropic effect on papillary muscles. Hypoxia caused a profound depression of contractile parameters, which was not affected by pentoxifylline treatment. Reoxygenation resulted in significant partial recovery of contractile parameters after 30 and 60 but not 90 min of hypoxia. In experiments with 30 and 60 min of hypoxia, reoxygenation-induced contractile recovery and responsiveness to isoproterenol were improved by pentoxifylline in a concentration-dependent fashion. These functional improvements were completely blocked by N(omega)-nitro-L-arginine methyl ester pretreatment. No improvement was observed in 90-min hypoxia experiment. In conclusion, pentoxifylline improved contractile recovery during reoxygenation and postreoxygenation responsiveness to beta-adrenergic stimulation through the NO-dependent mechanism.

Phosphodiesterase inhibition promotes the transition from compensated hypertrophy to cardiac dilatation in rats

The cellular signaling pathways responsible for the transition from compensated left ventricular hypertrophy (LVH) to LV dilatation (remodeling) and heart failure are unclear. As chronic administration of a beta-adrenoreceptor (beta-AR) agonist mediates the premature onset of cardiac remodeling without myocyte necrosis or myocardial dysfunction in LVH, we suggest that beta-AR activation is critical in promoting the transition from compensated LVH to cardiac dilatation. However, beta-AR mediated effects in the heart can occur via either the cyclic adenosine monophosphate (cAMP) system or via cAMP independent signaling pathways. To determine the role of cAMP in promoting adverse cardiac chamber remodeling, we evaluated whether phosphodiesterase inhibition (PDEI) promotes LV dilatation in rats with compensated LVH. The impact of chronic administration of the PDEI, pentoxifylline, on LV remodeling and function was assessed in spontaneously hypertensive rats (SHR) with compensated LVH. The PDEI mediated inotropic effects and increased cAMP concentrations in SHR. This dose of the PDEI administered for 4 months to SHR did not modify LV weight or influence intrinsic myocardial systolic function (as assessed in the absence of the PDEI) in SHR. However, the PDEI mediated the development of a right shift in LV end diastolic (LVED) pressure-internal dimension and LVED pressure-volume relations, LV wall thinning, and increments in myocardial soluble (non-cross-linked) collagen concentrations. In conclusion, chronic PDEI administration induces adverse geometric and interstitial cardiac remodeling in SHR, a finding that supports the notion that the beta-AR-cAMP system is important in mediating the progression to heart failure by promoting interstitial remodeling and LV dilatation in LVH.

Pharmacology of pentoxifylline, a hemorheologic agent for the treatment of intermittent claudication

Physiological and pathophysiological aspects of systemic and cardiac haemodynamics are reviewed with appraisal of Carl J. Wiggers merits and contributions to the research and developments in this field and his early recognition of the significance of the flow properties of blood in impaired circulation. Pharmacological agents involved in treatment of peripheral vascular diseases are discussed with special regard to the haemorheologically active xanthine derivative pentoxifylline. The profile of pentoxifylline as it emerges from experimental pharmacological and clinical studies is presented paying special attention to the haemorheological properties of the drug. Pharmacokinetic features of pentoxifylline are surveyed touching absorption, blood levels, metabolism and excretion aspects. Basing on the available data pentoxifylline is regarded as a promising drug in the treatment of circulatory ischemic disorders, especially in intermittent claudication.