Efficacy and safety of dronedarone in patients with amiodarone-induced hyperthyroidism: a clinical study.

OBJECTIVE: The aim of the study was to examine the safety and efficacy of dronedarone in patients with a history of atrial fibrillation and amiodarone-induced hyperthyroidism. PATIENTS AND METHODS: We conducted a prospective study to evaluate the use of amiodarone and dronedarone in 124 patients with a history of paroxysmal atrial fibrillation who had no additional structural heart disease. All patients received amiodarone 200 mg qd. Out of 124 patients, 56 (45%) switched to dronedarone 400 mg bid due to amiodarone-induced hyperthyroidism and the remaining 68 patients (55%), with normal thyroid function, continued to receive amiodarone. The follow-up period was 12 months, and the patients were regularly monitored. RESULTS: The primary outcome after 6 months dronedarone and amiodarone group was 56 and 68, including 38 (68%) and 54 (79.4%) (Odds ratio [OR] = 1.17, 95% confidence interval [95% CI] = 0.68-2.02) patients with sinus rhythm (SR) and 18 (32.14%) and 14 (28.6%) (odds ratio [OR] = 0.64, confidence interval [95% CI] = 0.29-1.40) patients with atrial fibrillation (AF). The secondary outcome after 12 months showed significant difference in thyroid function in the dronedarone group. Out of 46 patients, 24 (56.18%) patients reduced hyperthyroidism compared to the amiodarone group; out of 68, 6 (8.9%) patients were observed to have hyperthyroidism. At 12 months, there were 24 (43%) and 22 (62%) (odds ratio [OR] = 0.75, confidence interval [95% CI] = 0.38-1.49) patients with SR, and 32 (57%) and 26 (38%) (odds ratio [OR] = 0.67, confidence interval [95% CI] = 0.36-1.25) patients with AF. CONCLUSIONS: In our study, dronedarone appears to be a good therapeutic option in the treatment of atrial fibrillation in patients with amiodarone-induced hyperthyroidism. However, long-term studies are needed to estimate the efficacy and toxicity of both drugs.

Senescence of the brain: focus on cognitive kinases.

Ageing is characterized by alterations in brain anatomy and physiology, finally contributing to an impairment in cognitive functions, such as memory. The most relevant observations indicate that senescent-related cognitive decline is not only due to neuronal loss, instead, functional changes occurring over time play a key role. Overall, these modifications are indeed responsible for an altered interneuronal communication that can represent, rather than morphological modifications, the primum movens leading to cognitive decline. Among the age-induced changes underlying alterations in neuronal communication and synaptic plasticity, those related to neurotransmitter/neurotrophin systems and downstream signalling pathways are of great relevance. In particular, considering that protein kinases play a strategic role aimed to convert the extracellular signals into biological responses, functional alterations on kinases may directly contribute to age-dependent neuronal dysfunctions. Within this context, numerous studies point out on several kinases as positive regulators for memory function and suggest that various memory disturbances are the result of a deficit in kinase signalling pathways. Many kinases associated with synaptic function are indeed age-sensitive; in fact, various studies in senescent animals indicate that a reduction in kinases expression/function in some brain areas correlates with ageing and memory decline. In line with these concepts, pharmacological modulation of kinases may lead to neuroprotective effects that can prevent or counteract age-related memory impairment. This review will mainly focus on the age-induced changes on Protein Kinase C (PKC), Protein Kinase A (PKA), Calcium/calmodulin-dependent Protein Kinase (CaMK), Tyrosine Kinase, widely accepted as key actors in signalling pathways associated with memory.

Antibody response after vaccination with antigen-pulsed dendritic cells.

Dendritic cells (DCs) are the most potent antigen-presenting cells of the immune system capable of initiating immune responses to antigens. It is also well documented that cancer patients often experience anergy against tumor antigens. In this study we selected the best protocol for inducing the production of antibodies against the HER2 oncoprotein using DCs to overcome anergy. Murine DCs were pulsed in vitro, using different protocols, with recombinant HER2 fused to a human Fc (in order to improve DC antigen uptake) and were used to vaccinate mice. The obtained results indicate that antigen-pulsed DCs can induce an antibody response and that adding CpG after antigen pulsing greatly increases anti-HER2 antibody production.

Protein kinase C isoforms as therapeutic targets in nervous system disease states.

Neuronal tissues display high levels of protein kinase C (PKC) activity and isoform expression. The activation of this enzymatic system is important in the control of short and long term brain functions (ion channel regulation, receptor modulation, neurotransmitter release, synaptic potentiation/depression, neuronal survival) that are related to diverse brain pathologies. This review will describe recent developments in PKC regulation and changes in levels, isoforms and activation in acute and chronic neurodegenerative pathologies as well as in affective and psychic disorders. The recent availability of isoform selective inhibitors and activators may help to understand better the relevance of PKC in central nervous system (CNS) physiology and pathology and to identify new and safer pharmacologic strategies to be tested in different disease states.

STAT signalling in the mature and aging brain.

Activation of the Janus kinases (JAK) and signal transducers and activator of transcription (STAT) proteins in response to specific cytokines and growth factors has been investigated primarily in cells of non-neuronal origin. More recently, the JAKs and the STATs have also been found to be active in the developing and mature brain, providing evidence for important roles played by these molecules in the control of neuronal proliferation, survival and differentiation. Nothing, however, is known about their occurrence and role(s) in the aged brain. We, therefore, investigated the presence of Stat3 and Stat1 in aged-rat brain, and have found that the Stat3 protein was markedly down regulated with respect to adult tissue, while Stat1 remained invariant. We also investigated the potential role of some growth factors in the activation of the JAK/STAT in mature neurons, exposing primary neuronal cells to ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Besides CNTF, which is known to recruit Stat3, we found that Stat3 was also tyrosine phosphorylated by bFGF. These data are indicative of an important role of Stat3 and Stat1 in regulating the physiological status of mature neurons.

Protein kinase C anchoring deficit in postmortem brains of Alzheimer's disease patients.

Protein kinase C (PKC) has been implicated in the pathophysiology of Alzheimer's disease (AD). The levels of particular isoforms and the activation of PKC are reduced in postmortem brain cortex of AD subjects. Receptors for activated C kinase (RACK) are a family of proteins involved in anchoring activated PKCs to relevant subcellular compartments. Recent evidence has indicated that the impaired activation (translocation) of PKC in the aging brain is associated with a deficit in RACK1, the most well-characterized member of this family. The present study was conducted to determine whether alterations in RACK1 occurred in cortical areas where an impaired translocation of PKC has been demonstrated in AD. Here we report the presence of RACK1 immunoreactivity in human brain frontal cortex for the first time and demonstrate a decrease in RACK1 content in cytosol and membrane extracts in AD when compared with non-AD controls. By comparison, the levels of the RACK1-related PKCbetaII were not modified in the same membrane extracts. These observations add a new perspective in understanding the disease-associated defective PKC signal transduction and indicate that a decrease in an anchoring protein for PKC is an additional determinant of this deficit.

A defective protein kinase C anchoring system underlying age-associated impairment in TNF-alpha production in rat macrophages.

The ability of macrophages to secrete cytokines is important in host responses to infections inflammatory stimuli, both of which are altered with aging. In this study, age-associated changes in the release of TNF-alpha from LPS-stimulated rat alveolar macrophages were determined and correlated with a decrease in the level of RACK1, the anchoring protein involved in protein kinase C translocation and activation. Macrophages from aged rats produced approximately 50% less TNF-alpha than those from young rats. This effect was observed independently from the concentration of LPS used and the time considered. The decrease observed was associated with a defective PKC translocation, due to a reduction in the expression of RACK1, whereas no differences were detected in the expression of LPS receptor (CD14) or total PKC isoforms (alpha and betaIotaIota) in old and young rats. Use of RACK1 antisense oligonucleotide reduced the ability of young macrophages to respond to LPS, further supporting the idea that a deficit in RACK1 contributes to the functional impairment in aged macrophages and that age-induced macrophage immunodeficiencies are associated with alteration in signal transduction pathways.

Very low density lipoprotein-mediated signal transduction and plasminogen activator inhibitor type 1 in cultured HepG2 cells.

In normal subjects and in patients with cardiovascular disease, plasma triglycerides are positively correlated with plasminogen activator inhibitor type 1 (PAI-1) levels. Moreover, in vitro studies indicate that VLDLs induce PAI-1 synthesis in cultured cells, ie, endothelial and HepG2 cells. However, the signaling pathways involved in the effect of VLDL on PAI-1 synthesis have not yet been investigated. We report that VLDLs induce a signaling cascade that leads to an enhanced secretion of PAI-1 by HepG2 cells. In myo-[(3)H]inositol-labeled HepG2 cells, VLDL (100 microg/mL) caused a time-dependent increase in [(3)H]inositol phosphates, the temporal sequence being tris>bis>monophosphate. VLDL brought about a time-dependent stimulation of membrane-associated protein kinase C (PKC) activity and arachidonate release. Finally, VLDL stimulated mitogen-activated protein (MAP) kinase, and this effect was reduced by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), which suggests that PKC plays a pivotal role in MAP kinase phosphorylation. VLDL-induced PAI-1 secretion was completely prevented by U73122, a specific inhibitor of phosphatidylinositol-specific phospholipase C, by H7 or by PKC downregulation, and by mepacrine (all P<0.01 versus VLDL-treated cells). 3,4,5-Trimethoxybenzoic acid 8-(diethylamino)-octyl ester, which prevents Ca2+ release from intracellular stores, inhibited VLDL-induced PAI-1 secretion by 60% (P<0.05), and the MAP kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor PD98059 completely suppressed both basal and VLDL-induced PAI-1 secretion. These data demonstrate that VLDL-induced PAI-1 biosynthesis results from a principal signaling pathway involving PKC-mediated MAP kinase activation.

Increased natural killer cell cytotoxicity in Alzheimer's disease may involve protein kinase C dysregulation.

Increased cytokine-mediated cytotoxic natural killer (NK) cell activity has recently been demonstrated in patients with senile dementia of the Alzheimer's type (SDAT). In the present study, we evaluated whether protein-kinase C (PKC), a main regulatory enzyme involved in the mechanism of exocytosis by NK cells, has a role in the cytotoxic response of NK cells (during IL-2 and IFN-beta exposure) from SDAT patients. Our data demonstrate the presence of an increased cytotoxic response by NK cells to IL-2 (mean increase +102%) and IFN-beta (mean increase +132%) in SDAT patients in comparison with healthy elderly subjects (+75% and +88% for IL-2 and IFN-beta, respectively). A smaller suppression of NK cytotoxicity after cortisol was also observed in SDAT (mean decrease -24%) than in the control group (-44%). The NK cell activity of SDAT patients was inversely correlated with the cognitive status as evaluated by the analysis of MMSE (Mini Mental State Examination) score. A comparison of young and elderly healthy subjects revealed no variations in NK cell activity. A physiological decrease in cytosolic PKC activity was demonstrated in healthy old subjects after IL-2 and IFN-beta incubation, but not in SDAT patients, while no variations in kinase activity were observed after cortisol incubation. The decreased activity with cytokines was associated with reduced levels of PKC alpha and betaII isoforms. An alteration in cytokine-mediated NK cell activity associated with PKC dysregulation is therefore suggested to occur in patients with SDAT. These changes may indicate the existence of an immunological component to the pathogenesis and progression of the disease.

Age-related alteration of PKC, a key enzyme in memory processes: physiological and pathological examples.

Brain aging is characterized by a progressive decline of the cognitive and memory functions. It is becoming increasingly clear that protein phosphorylation and, in particular, the activity of the calcium-phospholipid-dependent protein kinase C (PKC) may be one of the fundamental cellular changes associated with memory function. PKC is a multigene family of enzymes highly expressed in brain tissues. The activation of kinase C is coupled with its translocation from the cytosol to different intracellular sites and recent studies have demonstrated the key role played by several anchoring proteins in this mechanism. PKC-phosphorylating activity appears to be impaired during senescence at brain level in a strain-dependent fashion in rodents. Whereas the levels of the various isoforms do not show age-related alterations, the enzyme translocation upon phorbol-ester treatment is deficitary among all strains investigated. Anchoring proteins may contribute to this activation deficit. We discuss also modifications of the PKC system in Alzheimer's disease that may be related to pathological alterations in neurotransmission. A better insight of the different factors controlling brain-PKC activation may be important not only for elucidating the molecular basis of neuronal transmission, but also for identifying new approaches for correcting or even preventing age-dependent changes in brain function.

Cytosolic hippocampal PKC and aging: correlation with discrimination performance.

Adult and aged mice were submitted to a discrimination task in a radial maze (regular trials), and then to probe trials requiring them to form relational representations. Three weeks later, animals were again tested for regular and probe trials. Following another interval of 3 weeks, individual hippocampal cytosolic calcium-dependent and -independent PKC activities were measured. Performance of aged animals was impaired on probe but not regular trials and aged mice had lower hippocampal cytosolic calcium-dependent and -independent PKC activities than adults. Performance on probe trials was specifically correlated with calcium-dependent PKC activity. This suggests a specific relationship between the ability to form relational representations and hippocampal cytosolic calcium-dependent PKC activity.

Moderate Alcohol Intake: Behavioral and Neurochemical Correlates in Rats.

A debate is open in the literature concerning the safety of low (dietary) versus high (intoxicating or addicting) alcohol consumption. Epidemiological data do indeed suggest that moderate ethanol intake may have beneficial effects, at least at cardiovascular level. On the other hand there are few data on the effect of low doses ethanol at brain level and few experimental models to investigate it, in spite of a vast literature on the addicting mechanisms. In the last years we have addressed this question by investigating behavioral and neurochemical parameters in rats consuming low ethanol doses, not producing tolerance and dependence, thus mimicking balanced dietary intake of ethanol. Ethanol exposure (3% vol/vol in drinking water for 8 weeks) ameliorates emotional reactivity, evaluated as decrease in ultrasonic calls, and improves learning in animals undergoing a two-way avoidance task. The concomitant measure of neurochemical parameters indicates plastic changes in receptor (dopamine) and post-receptor (protein kinase C) mechanisms. These changes are in some cases qualitatively different from those observed with intoxicating ethanol doses. This model may be useful for the further characterization of the beneficial versus detrimental effect of moderate ethanol consumption at brain level.

Chronic low doses of ethanol affect brain protein kinase C and ultrasonic calls in rats.

Few studies have investigated neurobehavioral and neurochemical consequences of chronic consumption of low doses of ethanol. The present study shows that in rats exposure to 3% ethanol (v/v in drinking water) for 2 months decreased both calcium-dependent and -independent protein kinase C (PKC) activities in the cortex and in the hippocampus. This treatment also reduced ultrasonic calls (UCs), an index of emotional and motivational states of the animal. In addition, at cortical level of ethanol-treated rats, we observed a correlation between calcium-dependent activities and UCs. These results suggest that nonaddicting doses of ethanol affect brain PKC activities and that this enzyme may be involved in the ethanol modulation of emotional and motivational behaviors.

The role of anchoring protein RACK1 in PKC activation in the ageing rat brain.

High levels of expression of Ca2+/phospholipid-dependent protein kinase C (PKC) occur in neuronal tissues and play a strategic role in the modulation of short- and long-term functions (ion channels, receptor desensitization, neurotransmitter release and synaptic efficiency) that become modified during the brain ageing process. Recent studies have clarified the key role played by the anchoring proteins in mediating subcellular PKC location, that is, in driving the enzyme to specific sites of action. The protein, receptor for activated C-kinase 1 (RACK1) is involved in PKC-mediated signal transduction. A postnatal developmental increase in RACK1 levels indicates their significance in the outgrowth of neuronal processes. In a physiological model of impairment in PKC translocation-the aged rat brain cortex-RACK1 levels are reduced and the PKC isoenzymes known to interact with it do not translocate to membrane compartments upon stimulation. Anchoring proteins might represent new targets for compounds that modulate PKC signal transduction processes.

Functional impairment in protein kinase C by RACK1 (receptor for activated C kinase 1) deficiency in aged rat brain cortex.

Several laboratories have reported a lack of protein kinase C (PKC) activation in response to various stimuli in the brain of aged rats. It has been suggested that changes in lipid membrane composition could be related to this functional deficit. However, recent evidence has indicated that the translocation of PKC to the different subcellular compartments is controlled by protein-protein interactions. Recently, a class of proteins, termed receptors for activated C kinase (RACKs), have been described that bind PKC. The present study was conducted to determine whether alterations in RACK1, the best-characterized member of RACKs, were associated with changes in translocation and expression of PKC. Quantitative immunoblotting revealed that RACK1 content was decreased by approximately 50% in aged rat brain cortex, compared with that in adult and middle-aged animals. The levels of calcium-independent PKC delta and epsilon, interacting with RACK1, and related calcium-independent PKC activity were not modified by the aging process. By comparison, phorbol ester-stimulated translocation of this activity and of PKC delta and epsilon immunoreactivity was absent in cortex from aged animals, as well as the translocation of the calcium-dependent PKC beta, also known to interact with RACK1. These results indicate that a deficit in RACK1 may contribute to the functional impairment in PKC activation observed in aged rat brain.

Fibroblasts of patients affected by Down's syndrome oversecrete amyloid precursor protein and are hyporesponsive to protein kinase C stimulation.

The present study investigates the ability of the pharmacologic activation of protein kinase C (PKC) to modulate amyloid precursor protein (APP) secretion in human skin fibroblasts from patients affected by Down's syndrome (DS). We assessed DS subjects at the Hospital Institute of Sospiro, Cremona, and at the Alzheimer's Disease Unit of the Sacred Heart Hospital in Brescia, and we subdivided them into nondemented (NDS) and demented (DDS) patients. All DS patients were trisomy 21 karyotype. DS fibroblasts had an increased content of APP immunoreactive material as revealed by immunocytochemistry analysis. The basal secretion of soluble APP was higher (+94.6%) in Down's cells with respect to controls. The observation on the fibroblasts prepared from DS is consistent with these patients' possessing an extra copy of the APP gene (mapped on chromosome 21) leading to increased APP expression. Phorbol-12,13-dibutyrate (PdBu, 9 to 150 nM) treatment promoted a dose-dependent increase of secreted APP in the conditioned medium of control fibroblasts. The peak response (+102.2%) was attained using 150 nM PdBu. In Down's fibroblasts, PdBu stimulated APP secretion already maximally at low concentrations (9 nM), but the peak response, due to the higher basal release, was lower on a percentage basis (+16.4%) than in control fibroblasts. The results indicate that in Down's fibroblasts the mechanisms controlling APP release are at least quantitatively altered. In addition, these results suggest caution when using information obtained from Down's patients to model Alzheimer's disease biochemical defects.

Differential isoform-specific regulation of calcium-independent protein kinase C in rat cerebral cortex.

Regulation of the Ca(2+)-independent protein kinase C (PKC) activity and isoforms by phorbol esters was investigated in rat cerebral cortex. Loss of soluble PKC eta immunoreactivity from the soluble fraction was dramatic with only a small increase in the membrane fraction. The kinetics of PKC epsilon and -delta translocation were slower than that for PKC eta, while phorbol esters had no effect on PKC zeta translocation. Despite the translocation of PKC delta, -epsilon and -eta from the soluble to the membrane fraction, both fractions showed a loss of PKC activity. These data indicate that the rates of translocation, inactivation and/or downregulation appear to be different not only among these Ca(2+)-independent isozymes, but also from that reported for the Ca(2+)-dependent PKCs. In addition, these results emphasize the importance of measuring both Ca(2+)-independent PKC activity and immunoreactivity in evaluating activation of these isoforms.

Calcium responses in human fibroblasts: a diagnostic molecular profile for Alzheimer's disease.

We have previously identified alterations of K+ channel function, IP3-mediated calcium release, and Cp20 (a memory-associated GTP binding protein) in fibroblasts from AD patients vs. controls. In the present study we introduce a scoring system based on these response alterations that integrates two or more alterations (and their degree) in AD vs. control fibroblasts. This scoring system generates an index that distinguishes AD patients from controls with both high specificity and sensitivity. We also show that low doses of bradykinin elicit intracellular calcium release almost exclusively in AD cell lines in an all or none fashion that provide a clear measurement of enhanced IP3-mediated function in AD vs. controls.

Influences of hypothyroidism on lipid composition and inositol lipid-linked receptors responsiveness and protein kinase C (PKC) activity in the cerebral cortex of Lewis rats.

The influence of hypothyroidism (HO) induced by treatment with propylthiouracil on lipid composition, receptor responsiveness of M1-muscarinic receptors (M1AChRs) and metabotropic glutamate receptors (mGluRs) as well as on protein kinase C (PKC) activity was investigated in the cerebral cortex of Lewis rats. HO did not influence the lipid composition. There was a significant 2-fold increase of efficacy and 6-fold decrease of potency of carbachol-induced inositol phosphate (IP) accumulation in HO, with respect to control rats. The efficacy of trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD)-induced IP accumulation was also higher in HO (by 50%), without differences in EC50 values. The activities of soluble calcium-dependent and calcium-independent PKC were higher in HO than in control rats (both roughly 30%); membrane-associated PKCs were not modified. The data indicate that HO induces an increased responsiveness of M1AChRs and mGluRs and a rise in the soluble PKC activity that could be available and ready for translocation.

Defective protein kinase C alpha leads to impaired secretion of soluble beta-amyloid precursor protein from Alzheimer's disease fibroblasts.

The present study shows that cultured fibroblasts from sporadic AD patients present: a) reduced (-30%) cytosolic protein kinase C (PKC) activity; b) increased KD of phorbol ester binding (+94%) in cytosolic fractions; c) reduced (-30%) soluble protein kinase C alpha immunoreactivity; d) lower (-27.5%) basal soluble APP secretion and e) reduced soluble APP secretion in response to low phorbol ester concentrations (over threefold difference using 9 nM phorbol-12,13-dibutyrate-PdBu). Since the PKC-stimulated secretion of APP leads to the cleavage of the precursor within the amyloidogenic beta-A4 fragment, the reduced PKC activity in AD patients may lead to accumulation of potentially amyloidogenic or toxic APP fragments. A defect in the secretion of soluble amyloid beta-protein precursor is indeed suggested by literature data on familial AD fibroblasts as well as by the reported results.