Biphasic effect of bimoclomol on calcium handling in mammalian ventricular myocardium

Heat shock proteins and hormesis in the diagnosis and treatment of neurodegenerative diseases

Modulation of endogenous cellular defense mechanisms via the vitagene system represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. The possibility of high-throughoutput screening using proteomic techniques, particularly redox proteomics, provide more comprehensive overview of the interaction of proteins, as well as the interplay among processes involved in neuroprotection. Here by introducing the hormetic dose response concept, the mechanistic foundations and applications to the field of neuroprotection, we discuss the emerging role of heat shock protein as prominent member of vitagene network in neuroprotection and redox proteomics as a tool for investigating redox modulation of stress responsive vitagenes. Hormetic mechanisms are reviewed as possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the neurodegenerative disease process.

Simulation of the undiseased human cardiac ventricular action potential: model formulation and experimental validation

Cellular electrophysiology experiments, important for understanding cardiac arrhythmia mechanisms, are usually performed with channels expressed in non myocytes, or with non-human myocytes. Differences between cell types and species affect results. Thus, an accurate model for the undiseased human ventricular action potential (AP) which reproduces a broad range of physiological behaviors is needed. Such a model requires extensive experimental data, but essential elements have been unavailable. Here, we develop a human ventricular AP model using new undiseased human ventricular data: Ca(2+) versus voltage dependent inactivation of L-type Ca(2+) current (I(CaL)); kinetics for the transient outward, rapid delayed rectifier (I(Kr)), Na(+)/Ca(2+) exchange (I(NaCa)), and inward rectifier currents; AP recordings at all physiological cycle lengths; and rate dependence and restitution of AP duration (APD) with and without a variety of specific channel blockers. Simulated APs reproduced the experimental AP morphology, APD rate dependence, and restitution. Using undiseased human mRNA and protein data, models for different transmural cell types were developed. Experiments for rate dependence of Ca(2+) (including peak and decay) and intracellular sodium ([Na(+)](i)) in undiseased human myocytes were quantitatively reproduced by the model. Early afterdepolarizations were induced by I(Kr) block during slow pacing, and AP and Ca(2+) alternans appeared at rates >200 bpm, as observed in the nonfailing human ventricle. Ca(2+)/calmodulin-dependent protein kinase II (CaMK) modulated rate dependence of Ca(2+) cycling. I(NaCa) linked Ca(2+) alternation to AP alternans. CaMK suppression or SERCA upregulation eliminated alternans. Steady state APD rate dependence was caused primarily by changes in [Na(+)](i), via its modulation of the electrogenic Na(+)/K(+) ATPase current. At fast pacing rates, late Na(+) current and I(CaL) were also contributors. APD shortening during restitution was primarily dependent on reduced late Na(+) and I(CaL) currents due to inactivation at short diastolic intervals, with additional contribution from elevated I(Kr) due to incomplete deactivation.

Role for calcium in heat shock-mediated synaptic thermoprotection in Drosophila larvae

Chemical synaptic transmission is the mechanism for fast, excitation-coupled information transfer between neurons. Previous work in larval Drosophila has shown that transmission at synaptic boutons is protected by heat shock exposure from subsequent thermal stress through pre- and postsynaptic modifications. This protective effect has been, at least partially, ascribed to an up-regulation in the inducible heat shock protein, hsp70. Effects of hsp70 are correlated with changes to intracellular calcium handling, and the dynamics of intracellular calcium regulate synaptic transmission. Consistent with such a relationship, synaptic plasticity increases at locust neuromuscular junctions following heat shock, suggesting an effect of heat shock on residual presynaptic calcium. Intracellular recording from single abdominal muscle fibers of Drosophila larvae showed that prior heat shock imparts thermoprotection by increasing the upper temperature limit for synaptic transmission. Heat shock exposure enhances short-term synaptic plasticity and increases its thermosensitivity. Increasing extracellular calcium levels eliminates the physiological differences between control and heat shock preparations; excess calcium itself induces thermoprotection at elevated concentrations. These data support the hypothesis that stress-induced neuroprotection at the nerve terminal acts, at least partially, through an alteration to the physiological effects of residual presynaptic calcium.

Multilateral in vivo and in vitro protective effects of the novel heat shock protein coinducer, bimoclomol: results of preclinical studies

Bimoclomol, the recently developed non-toxic heat shock protein (HSP) coinducer, was shown to display multilateral protective activities against various forms of stress or injuries at the level of the cell, tissue or organism. The compound enhanced the transcription, translation and expression of the 70 kD heat shock protein (HSP-70) in myogenic and HeLa cell lines exposed to heat stress, and increased cell survival on exposure to otherwise lethal thermal injury. Bimoclomol increased contractility of the working mammalian heart, this effect was associated with the increased intracellular calcium transients due to increased probability of opening of ryanodine receptors in the sarcoplasmic reticulum (SR). In healthy tissues these cardiac effects were evident only at relatively high concentrations of the drug, while in the ischemic myocardium bimoclomol exerted significant cardioprotective and antiarrhythmic effects at submicromolar concentrations. It decreased ischemia-induced reduction of contractility and of cardiac output, and dramatically decreased the elevation of the ST-segment during ischemia as well as the occurrence of ventricular fibrillation upon reperfusion. Bimoclomol was also active in various pathological animal models subjected to acute or chronic stress. In the spontaneously hypertensive rats chronic pretreatment with bimoclomol restored sensitivity of aortic rings to acetylcholine; this effect was accompanied by accumulation of HSP-70 in the tissues. Bimoclomol pretreatment significantly diminished the consequences of vascular disorders associated with diabetes mellitus. Diabetic neuropathy, retinopathy, and nephropathy were prevented or diminished, while wound healing was enhanced by bimoclomol. Enhancement of wound healing by bimoclomol was observed after thermal injury as well as following ultraviolet (UV) irradiation. In addition to the beneficial effects on peripheral angiopathies, bimoclomol antagonized the increase in permeability of blood-brain barrier induced by subarachnoid hemorrhager or arachidonic acid. A general and very important feature of the above effects of bimoclomol was that the drug failed to cause alterations under physiological conditions (except the enhanced calcium release from cardiac sarcoplasmic reticulum). Bimoclomol was effective only under conditions of stress. Consistent with its HSP-coinducer property, bimoclomol alone had very little effect on HSP production. Its protective activity became apparent only in the presence of cell damage. Currently, bimoclomol reached the end of the Phase II clinical trial in a group of 410 patients with diabetic complications. Results of this trial will answer the question, whether a compound with promising in vitro and in vivo preclinical findings will produce the anticipated beneficial effects in humans. In the event of a positive outcome of this trial, the indications for bimoclomol will be substantially extended.

Heat shock-induced thermoprotection of action potentials in the locust flight system

There is increasing evidence that heat shock (HS) has long-term effects on electrophysiological properties of neurons and synapses. Prior HS protects neural circuitry from a subsequent heat stress but little is known about the mechanisms that mediate this plasticity and induce thermotolerance. Exposure of Locusta migratoria to HS conditions of 45 degrees C for 3 h results in thermotolerance to hitherto lethal temperatures. Locust flight motor patterns were recorded during tethered flight at room temperature, before and after HS. In addition, intracellular action potentials (APs) were recorded from control and HS motoneurons in a semi-intact preparation during a heat stress. HS did not alter the timing of representative depressor or elevator muscle activity, nor did it affect the ability of the locust to generate a steering motor pattern in response to a stimulus. However, HS did increase the duration of APs recorded from neuropil segments of depressor motoneurons. Increases in AP duration were associated with protection of AP generation against failure at subsequent elevated temperatures. Failure of AP generation at high temperatures was preceded by a concomitant burst of APs and depolarization of the membrane. The protective effects of HS were mimicked by pharmacological blockade of I(K+) with tetraethylammonium (TEA). Taken together, these findings are consistent with a hypothesis that HS protects neuronal survival and function via K+ channel modulation.

In vivo and in vitro acute cardiovascular effects of bimoclomol

Effects of bimoclomol, the novel heat shock protein (HSP) coinducer, was studied in various mammalian cardiac and rabbit aortic preparations. Bimoclomol decreased the ST-segment elevation induced by coronary occlusion in anesthetized dogs (56% and 80% reduction with 1 and 5 mg/kg, respectively). In isolated working rat hearts, bimoclomol increased coronary flow (CF), decreased the reduction of cardiac output (CO) and left ventricular developed pressure (LVDP) developing after coronary occlusion, and prevented ventricular fibrillation (VF) during reperfusion. In rabbit aortic preparations, precontracted with phenylephrine, bimoclomol induced relaxation (EC(50)=214 microM). Bimoclomol produced partial relaxation against 20 mM KCl, however, bimoclomol failed to relax preparations precontracted with serotonin, PGF(2) or angiotensin II. All these effects were evident within a few minutes after application of bimoclomol. A rapid bimoclomol-induced compartmental translocation of the already preformed HSPs may explain the protective action of the compound.