Response to exercise and mechanical efficiency in non-ischaemic stunning, induced by short-term rapid pacing in dogs: a role for calcium?

AIM: Rapid pacing (RP) is a regularly used model to induce heart failure in dogs. The aim of the study was to evaluate Ca2+ handling, left ventricular (LV) contractile response during Ca2+ administration compared to exercise, as well as oxygen consumption and mechanical efficiency after 48 h of RP. METHODS: Fifty-three mongrel dogs were instrumented to measure LV pressure, LV fractional shortening, regional wall thickening and coronary blood flow. Contractile reserve was measured with isoproterenol and intravenous (IV) Ca2+ administration. To assess the function of the sarcoplasmic reticulum (SR), post-extrasystolic potentiation (PESP) and SR Ca2+ uptake were measured. A graded treadmill test was performed in baseline and after RP (n = 14). In a separate group of animals (n = 5), myocardial performance and oxygen consumption were measured using a wide range of loading conditions. RESULTS: Left ventricular contractility was significantly decreased upon cessation of pacing. The contractile response to isoproterenol was blunted compared to a preserved response to IV Ca2+ . Post-extrasystolic potentiation was slightly increased after RP. Maximal velocity (Vmax ) of SR Ca2+ uptake was unchanged. Contractile response during exercise is attenuated after RP. External work is reduced, whereas oxygen consumption is preserved, provoking a reduced mechanical efficiency. CONCLUSION: Forty-eight-hours RP provokes a reversible LV dysfunction, while the SR function and response to exogenous Ca2+ are preserved. This is compatible with an intracellular functional remodelling to counteract Ca2+ overload provoked by RP. Left ventricular dysfunction is accompanied by a reduced contractile reserve, but an unchanged oxygen consumption, illustrating an alteration in oxygen utilization.

Chronic hibernating myocardium in sheep can occur without degenerating events and is reversed after revascularization.

INTRODUCTION: Our goal was to show that blunting of myocardial flow reserve is mainly involved in adaptive chronic myocardial hibernation without apparent cardiomyocyte degeneration. METHODS AND RESULTS: Sheep chronically instrumented with critical multivessel stenosis and/or percutaneous transluminal coronary angioplasty (PTCA)-induced revascularization were allowed to run and feed in the open for 2 and 5 months, respectively. Regional myocardial blood flow (MBF) with colored microspheres, regional and global left ventricular function and dimensions (2D echocardiography), and myocardial structure were studied. In sheep with a critical stenosis, a progressive increase in left ventricular end-diastolic and end-systolic cavity area and a decrease in fractional area change were found. Fraction of wall thickness decreased in all left ventricular wall segments. MBF was slightly but not significantly decreased at rest at 2 months. Morphological quantification revealed a rather small but significant increase in diffusely distributed connective tissue, cardiomyocyte hypertrophy, and presence of viable myocardium of which almost 30 % of the myocytes showed depletion of sarcomeres and accumulation of glycogen. The extent of myolysis in the transmural layer correlated with the degree of left ventricular dilation. Structural degeneration of cardiomyocytes was not observed. Balloon dilatation (PTCA) of one of the coronary artery stenoses at 10 weeks revealed recovery of fraction of wall thickness and near normalization of global subcellular structure at 20 weeks. CONCLUSION: These data indicate that chronic reduction of coronary reserve by itself can induce ischemic cardiomyopathy characterized by left ventricular dilatation, depressed regional and global function, adaptive chronic myocardial hibernation, reactive fibrosis and cardiomyocyte hypertrophy in the absence of obvious degenerative phenomena. SUMMARY: Reduction of myocardial flow reserve due to chronic coronary artery stenosis in sheep induces adaptive myocardial hibernation without involvement of degenerative phenomena.

The effect of antifungal treatment on the vaginal flora of women with vulvo-vaginal yeast infection with or without bacterial vaginosis.

Antibacterial therapy may enhance the risk of symptomatic vulvo-vaginal candidosis in susceptible women. We addressed the question whether oral antifungal treatment for vulvo-vaginal candidosis also influences the bacterial vaginal microflora. One hundred and forty-two patients with a culture-proven acute episode of recurrent vulvo-vaginal candidosis (RVC) were treated with fuconazole according to the ReCiDiF regimen (induction dose of 600 mg orally per week followed by 200 mg per week) or with a single dose of 200 mg pramiconazole, a new potent oral triazole. At inclusion, 1 week and 1 month after the end of antifungal treatment, the bacterial microflora was assessed by microscopy of vaginal fluid to detect lactobacillary grades and bacterial vaginosis (BV). The presence of BV was studied in these patients with vulvo-vaginal candidosis after treatment with antifungal medication. At the start of oral antifungal treatment, 6.3% of women with Candida were co-infected with BV. Of the BV-negative women, 10 out of 133 (8%) developed BV after 1 week and after 1 month 8 of them (7%) were still BV-positive. Although no patients received antibacterial treatment at any moment of the study, 6 out of 9 (66%) of the women with Candida and BV at inclusion no longer had BV 1 week after antifungal treatment and 6 out of 7 (86%) lacked BV after 1 month. Treatment with antifungals may have a beneficial effect on women with concurrent BV, but does not prevent BV from occurring in BV-negative women with Candida vaginitis.

Topical treatment with CYP26 inhibitor talarozole (R115866) dose dependently alters the expression of retinoid-regulated genes in normal human epidermis.

BACKGROUND: An alternative approach to retinoid therapy is to inhibit the cytochrome P450 (CYP)-mediated catabolism of endogenous all-trans retinoic acid in the skin by applying retinoic acid metabolism blocking agents such as talarozole (R115866). OBJECTIVES: To study the effects of topical talarozole on retinoid biomarkers in normal skin in a randomized phase I trial. METHODS: Gels containing talarozole (0.35% or 0.07%) and vehicle were applied once daily for 9 days on either buttock of 16 healthy volunteers. Epidermal shave biopsies (for mRNA analysis) and punch biopsies (for histology and immunofluorescence analysis) were collected from the treatment areas. Genes encoding the following were studied by quantitative real-time polymerase chain reaction: cellular retinoic acid binding protein 2 (CRABP2), cytokeratins (KRT2 and KRT4), CYP26A1, CYP26B1, CYP26C1 and CYP2S1, two enzymes in the retinol metabolism (retinal dehydrogenase-2 and retinol acyltransferase) and two proinflammatory cytokines [interleukin (IL)-1alpha and tumour necrosis factor-alpha]. RESULTS: Talarozole treatment increased the mRNA expression of CRABP2, KRT4, CYP26A1 and CYP26B1 dose dependently, and decreased the expression of KRT2 and IL-1alpha compared with vehicle-treated skin. No mRNA change in retinol-metabolizing enzymes was obtained. There was no induction of epidermal thickness or overt skin inflammation in talarozole-treated skin. Immunofluorescence analysis confirmed an upregulation of KRT4 protein, but no upregulation of CYP26A1 and CYP26B1 expression was detected. CONCLUSIONS: Talarozole influences the biomarker pattern consistently with increased retinoic acid stimulation. The low irritancy of talarozole at the two examined dosages is a possible advantage over topical retinoids.

A new ketoconazole topical gel formulation in seborrhoeic dermatitis: an updated review of the mechanism.

Seborrhoeic dermatitis (SD) is a chronic, inflammatory skin disorder, affecting areas of the head and body where sebaceous glands are most prominent and active. The disorder commonly affects hair-bearing areas of the head, including the scalp. Involvement on the face is usually limited to the hairline, eyebrows, nasolabial folds and ears, and may occur either with or without scalp involvement. Areas of the trunk where SD may occur include the body folds and the presternal area. The aetiology of SD is unknown, although hormones and the Malassezia spp., formerly known as Pityrosporum (naturally occurring yeasts), are thought to be involved in the development of the condition. SD responds to the use of antifungal medications such as ketoconazole, suggesting that the inflammation could be linked to the Malassezia spp. The mechanisms behind the therapeutic effect of ketoconazole for the management of SD form the basis of this review. The broad spectrum activity of Ketoconazole was reported in the early 1980s. Due to its potent effect against Malassezia spp. the development of ketoconazole for the treatment of various skin infections, in which a link was proposed with Malassezia spp., was initiated. Later on, a number of ancillary properties were described for ketoconazole, comprising antibacterial, anti-inflammatory, sebostatic and antiproliferative effects. The incorporation of ketoconazole in an adapted vehicle further promoted its efficacy. Recently, a new anhydrous gel containing 2% ketoconazole (Xolegel) was launched, in which all of the above properties were optimised.

Oral R115866 in the treatment of moderate to severe facial acne vulgaris: an exploratory study.

BACKGROUND: R115866 (Rambazole; Barrier Therapeutics NV, Geel, Belgium), a new-generation retinoic acid metabolism-blocking agent, is a nonretinoid compound enhancing intracellularly the endogenous levels of all-trans-retinoic acid by blocking its catabolism. By virtue of this property, and the proven positive effects of retinoids in the treatment of acne, R115866 could potentially be a useful drug for acne. OBJECTIVES: To explore the efficacy, safety and tolerability of systemic R115866 in male patients with moderate to severe facial acne vulgaris (at least 15 papules and/or pustules and at least two nodulocystic lesions). METHODS: In this exploratory trial, 17 patients were treated with oral R115866 1 mg once daily for 12 weeks, followed by a 4-week treatment-free period. RESULTS: At the end of treatment (week 12, n = 16) a mean reduction in inflammatory lesion count of 77.4% (P < 0.001), in noninflammatory lesion count of 58.3% (P < 0.001) and in total lesion count of 76.0% (P < 0.001) was observed as compared with baseline. All lesion counts were significantly reduced from week 4 onwards. Mild side-effects were reported occasionally. CONCLUSIONS: The current data indicate that treatment with oral R115866 1 mg once daily for 12 weeks in patients with moderate to severe facial acne vulgaris is efficacious and well tolerated and merits further investigation.

Activity of the triazole antifungal r126638 as assessed by corneofungimetry.

BACKGROUND: R126638 is a novel triazole exhibiting potent in vitro and in vivo antifungal activity against fungal pathogens including dermatophytes and yeasts. OBJECTIVE: To determine the antifungal activity in time in the stratum corneum of healthy volunteers after oral intake of R126638 at a daily dose of 100 or 200 mg for 1 week. METHOD: Sixteen male volunteers were randomly allocated to oral treatment with either 100 or 200 mg of R126638 once daily for 1 week. Five cyanoacrylate skin surface strippings (CSSS) were obtained from the forearm of each subject before drug intake at day 1. CSSS were also collected during treatment at day 2 (24 h after the first drug intake, before the second drug intake), at day 4 (before the fourth drug intake) and at day 7 (10 h after the last drug intake). The post-treatment lingering effect was assessed at day 10 (3 days after treatment) and at day 14 (7 days after treatment). The corneofungimetry bioassay was performed on these CSSS to assess the antifungal profile of R126638. Cells of different fungal species (Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum canis, Candida albicans and Malassezia globosa) were deposited and cultured for 10 days on CSSS in a sterile and controlled environment. The extent of fungal growth on the stratum corneum was determined using computerized image analysis. RESULTS: R126638 clearly reduced the growth of all tested fungal species. The onset of effects of R126638 was evidenced at day 4 when it reached statistical significance for 3 of 5 species. At day 7, significance was reached for 4 of 5 species. During the posttreatment period, R126638 remained effective for 4 of 5 species at day 10, and this activity persisted until day 14 for 2 of 5 species. CONCLUSION: A broad spectrum antifungal activity was rapidly expressed in the stratum corneum after oral intake of R126638. The drug likely reached the upper layers of the stratum corneum by diffusion and persisted in this location for at least 7 days after treatment.

Fungal infections of the skin: infection process and antimycotic therapy.

Dermatomycoses are among the most widespread and common superficial and cutaneous fungal infections in humans. These typically nonfatal conditions are difficult to treat, especially infections of the nail. Dermatomycoses are caused by filamentous fungi such as Trichophyton, Microsporum or Epidermophyton species. These filamentous fungi have a high affinity for keratin, an important component of hair, skin and nails, which are the primary areas of infection by dermatophytes. The antifungal agents currently marketed for dermatomycoses are mainly inhibitors of ergosterol biosynthesis, except for griseofulvin, which interferes with the cytoplasmic and nuclear microtubular system. Three different types of inhibitors of the ergosterol biosynthetic pathway have been proven to be effective in clinic: the azoles (e.g. topical miconazole and topical/oral ketoconazole, itraconazole and fluconazole), the allylamines (e.g. terbinafine) and morpholines (amorolfine). Even today more effective antifungal azoles with less adverse effects and short-term therapy are deemed necessary to treat dermatophytosis. A promising novel triazole compound in this respect is R126638, which showed potent in vitro and in vivo activity.

End-diastolic myofiber stress and ejection strain increase with ventricular volume overload--Serial in-vivo analyses in dogs with complete atrioventricular block.

BACKGROUND: Myocardial stress and strain are considered primary mechanical stimuli for hypertrophic remodeling. Their values and significance in the intact beating heart during chronic overload remain poorly characterized. METHODS AND RESULTS: Left-ventricular (LV) dimensions (echocardiography) and pressure (invasive) were simultaneously recorded in anesthetized dogs at sinus rhythm (SR), acute and 1, 2, 6, 12 weeks of atrioventricular block (AVB), leading to structural, electrical and contractile remodeling. Mechanical load of the myocardium was quantified as myofiber stress (sigma(f)), being force along myofiber orientation per cross-sectional area, and natural myofiber strain (e(f)), being change in natural logarithm of myofiber length (l) divided by its reference length: e(f) = ln(l/l(ref)). Time courses of sigma(f) and e(f) were calculated from LV pressure and dimensions, using a validated mathematical model of cardiac mechanics. End-diastolic sigmaf increased from 2.0 +/- 0.1 kPa at SR to 3.4 +/- 0.3 kPa at acute AVB, remaining elevated for > 6 weeks. Systolic sigma(f) was not affected by AVB. Ejection strain rose instantly upon AVB, reaching a maximum at 2 weeks: 0.24 +/- 0.02 vs. 0.10 +/- 0.01 at SR. The increase of myofiber stroke work (sigma(f)-e(f) loop area) from 3.1 +/- 0.3 at SR to 6.0 +/- 0.5 kJ/m(3)/beat at 1 week AVB was attributed mainly to an increase of strain during ejection. Stroke work and ejection strain remained elevated up to 12 weeks. The rate of LV-mass increase was maximal (2.2 +/- 0.4 g/day) at 1 week AVB. CONCLUSIONS: Serial mechanical phenotyping is feasible in the intact anesthetized dog with chronic ventricular overload. Our new approach yields values of mechanical load that are comparable to those found in isolated myocardium by others. In chronic AVB, both end-diastolic myofiber stress and ejection strain are increased. Early increases of both parameters coincide with peak hypertrophic growth, suggesting their important role for mechanotransduction. Peak systolic sigmaf is likely not important for hypertrophy in this model, since it does not change throughout the experiment.

Temporal and spatial variations in structural protein expression during the progression from stunned to hibernating myocardium.

BACKGROUND: Dysfunctional and normally perfused remote regions show equal myolysis and glycogen accumulation in pig hibernating myocardium. We tested the hypothesis that these arose secondary to elevations in preload rather than ischemia. METHODS AND RESULTS: Expression of structural protein (desmin, desmoplakin, titin, cardiotin, alpha-smooth muscle actin, lamin-A/C, and lamin-B2) in viable dysfunctional myocardium was analyzed by immunohistochemistry. We performed blinded analysis of paired dysfunctional left anterior descending coronary artery and normal remote subendocardial samples from stunned (24 hours; n=6), and hibernating (2 weeks; n=6) myocardium versus sham controls pigs (n=7). Within 24 hours, cardiac myocytes globally reexpressed alpha-smooth muscle actin. In stunned myocardium, cardiotin was globally reduced, whereas reductions in desmin were restricted to the dysfunctional region. Alterations progressed with the transition to hibernating myocardium, in which desmin, cardiotin, and titin were globally reduced. A qualitatively similar reorganization of cytoskeletal proteins occurred 3 hours after transient elevation of left ventricular end-diastolic pressure to 33+/-3 mm Hg. CONCLUSIONS: Qualitative cardiomyocyte remodeling similar to that in humans with chronic hibernation occurs rapidly after a critical coronary stenosis is applied, as well as after transient elevations in left ventricular end-diastolic pressure in the absence of ischemia. Thus, reorganization of cytoskeletal proteins in patients with viable dysfunctional myocardium appears to reflect chronic and/or cyclical elevations in preload associated with episodes of spontaneous regional ischemia.

In vitro and in vivo activities of the novel azole antifungal agent r126638.

R126638 is a new triazole agent with potent antifungal activity in vitro against various dermatophytes, Candida spp., and Malassezia spp. Its activity against Malassezia spp. in vitro was superior to that of ketoconazole, the agent currently used for the treatment of Malassezia-related infections. R126638 showed activity comparable to or lower than that of itraconazole against dermatophytes in vitro; however, in guinea pig models of dermatophyte infections, R126638 given orally consistently showed antifungal activity superior to that of itraconazole, with 50% effective doses (ED(50)s) three- to more than eightfold lower than those of itraconazole, depending on the time of initiation and the duration of treatment. The ED(50) of R126638 in a mouse dermatophytosis model was more than fivefold lower than that of itraconazole. These data indicate that if the effects of R126638 seen when it is used to treat animals can be extrapolated to humans, the novel compound would be expected to show effects at doses lower than those of existing drugs and, hence, present a lower risk for side effects.

Accumulation of ultrasmall superparamagnetic particles of iron oxide in human atherosclerotic plaques can be detected by in vivo magnetic resonance imaging.

BACKGROUND: One of the features of high-risk atherosclerotic plaques is a preponderance of macrophages. Experimental studies with hyperlipidemic rabbits have shown that ultrasmall superparamagnetic particles of iron oxide (USPIOs) accumulate in plaques with a high macrophage content and that this induces magnetic resonance (MR) signal changes. The purpose of our study was to investigate whether USPIO-enhanced MRI can also be used for in vivo detection of macrophages in human plaques. METHODS AND RESULTS: MRI was performed on 11 symptomatic patients scheduled for carotid endarterectomy before and 24 (n=11) and 72 (n=5) hours after administration of USPIOs (Sinerem) at a dose of 2.6 mg Fe/kg. Histological and electron microscopical analyses of the plaques showed USPIOs primarily in macrophages within the plaques in 10 of 11 patients. Histological analysis showed USPIOs in 27 of 36 (75%) of the ruptured and rupture-prone lesions and 1 of 14 (7%) of the stable lesions. Of the patients with USPIO uptake, signal changes in the post-USPIO MRI were observed by 2 observers in the vessel wall in 67 of 123 (54%) and 19 of 55 (35%) quadrants of the T2*-weighted MR images acquired after 24 and 72 hours, respectively. For those quadrants with changes, there was a significant signal decrease of 24% (95% CI, 33% to 15%) in regions of interest in the images acquired after 24 hours, whereas no significant signal change was found after 72 hours. CONCLUSIONS: Accumulation of USPIOs in macrophages in predominantly ruptured and rupture-prone human atherosclerotic lesions caused signal decreases in the in vivo MR images.

Development of a novel fluorescent microsphere technique to combine serial cerebral blood flow measurements with histology in the rat.

The aim of the study was to evaluate the microsphere technique for the quantitative assessment of regional cerebral blood flow (rCBF) at different time points in the same animal. Yellow-green and red fluorescent microspheres with a diameter of 15 microm were injected into the rat at two different time points via a cannula inserted into the left ventricle of the heart. The reproducibility of the rCBF measurements in normocapnic conditions (n=7) and the responsiveness of the flow to hypercapnia induced by 7% CO(2) (n=7) was examined. The fluorescent spheres were counted on 100 microm vibratome sections of perfusion-fixed brains and rCBF was calculated. The median total CBF in normocapnic rats was 224 ml/min/100 g for the first microsphere injection and 216 ml/min/100 g for the second one. In the hypercapnic group CBF amounted to 400 ml/min/100 g and after 30 min of normocapnia decreased to 178 ml/min/100 g. No differences between the left and right hemisphere were found and there was no indication that the first injection might have influenced the second one. The described approach allows combining the assessment of rCBF at different time points in physiological or pathological conditions with histological evaluation of related morphological alterations in the same brain region of the same animal.

Dissociation of cardiomyocyte apoptosis and dedifferentiation in infarct border zones.

AIMS: Cardiomyocyte apoptosis is known to occur in infarct border zones, where cardiomyocyte dedifferentiation, as seen in hibernating myocardium, can also be observed. The aim of the study is to determine whether dedifferentiated cardiomyocytes represent a population of cells stably surviving or undergoing apoptosis. METHODS AND RESULTS: Microinfarctions were induced in sheep (n=8) by intracoronary injection of polymer macrobeads. The sheep were killed when cardiac function was gradually decreased (ejection fraction 37+/-6%, mean+/-SEM), but not earlier than 6 weeks after embolization. Transmural biopsies were taken from embolized and remote areas, based on flow measurements with positron emission tomography. Cells were classified as dedifferentiated when sarcomere content was depleted by >10% and glycogen content increased. Apoptosis was detected using the Tdt-mediated nick-end labelling (TUNEL) method and activated caspase-3 immunolabelling. Dedifferentiated cardiomyocytes were identified by morphology and by immunohistochemical evaluation of dedifferentiation related expression patterns of desmin, titin, cardiotin and alpha-smooth muscle actin. Cardiomyocyte apoptosis was detected in both the infarction border zones and remote areas. Dedifferentiated cardiomyocytes accounted for up to 30% of the cells in embolized areas and were almost exclusively non-apoptotic. CONCLUSION: In embolization induced microinfarcted tissue, dedifferentiated cardiomyocytes are preferentially spared to undergo apoptosis. It is hypothesized that dedifferentiated cardiomyocytes and apoptotic cardiomyocytes represent two different cell populations. The dedifferentiated cells can be considered as stable surviving cells.

Time course of atrial fibrillation-induced cellular structural remodeling in atria of the goat.

BACKGROUND: Previously we documented cellular structural changes of a non-degenerative nature in atrial myocytes after atrial fibrillation (AF) in the goat. The time course of these changes was not studied. METHODS AND RESULTS: Cellular structural changes were studied by light- and electron microscopy and immunohistochemistry in goat atria after 0-16 weeks AF. The first sign of cellular structural remodeling was a more homogeneous chromatin distribution, at 1 week of AF. Sub-structural changes in mitochondria and sarcoplasmic reticulum occurred gradually. Cellular degeneration was absent. The degree of myolysis and glycogen accumulation increased till 8 weeks of AF and did not increase further from thereon. After 16 weeks of AF, 42% of the myocytes in the right atrial free wall were affected by myolysis. The diameter of the atrial myocytes increased. Dedifferentiation of the atrial myocytes was suggested by altered expression patterns of structural proteins, such as the disappearance of cardiotin (1 week), the A-I junctional part of titin (4 weeks), desmin at the intercalated disk (ID) (8 weeks) and a gradual re-expression of alpha-smooth muscle actin. CONCLUSION: Remodeling of the cellular ultrastructure in atrial myocardium of the goat develops progressively during AF. Re-expression of fetal proteins indicate dedifferentiation of atrial myocytes, analogous to observations in hibernating myocardium of the ventricle.

Transient expression of phosphatidylserine at cell-cell contact areas is required for myotube formation.

Cell surface exposure of phosphatidylserine (PS) is shown to be part of normal physiology of skeletal muscle development and to mediate myotube formation. A transient exposure of PS was observed on mouse embryonic myotubes at E13, at a stage of development when primary myotubes are formed. The study of this process in cell cultures of differentiating C2C12 and H9C2 myoblasts also reveals a transient expression of PS at the cell surface. This exposure of PS locates mainly at cell-cell contact areas and takes place at a stage when the structural organization of the sarcomeric protein titin is initiated, prior to actual fusion of individual myoblast into multinucleated myotubes. Myotube formation in vitro can be inhibited by the PS binding protein annexin V, in contrast to its mutant M1234, which lacks the ability to bind to PS. Although apoptotic myoblasts also expose PS, differentiating muscle cells show neither loss of mitochondrial membrane potential nor detectable levels of active caspase-3 protein. Moreover, myotube formation and exposure of PS cannot be blocked by the caspase inhibitor zVAD(OMe)-fmk. Our findings indicate that different mechanisms regulate PS exposure during apoptosis and muscle cell differentiation, and that surface exposed PS plays a crucial role in the process of myotube formation.

Mitochondrial alterations caused by defective peroxisomal biogenesis in a mouse model for Zellweger syndrome (PEX5 knockout mouse).

Zellweger syndrome (cerebro-hepato-renal syndrome) is the most severe form of the peroxisomal biogenesis disorders leading to early death of the affected children. To study the pathogenetic mechanisms causing organ dysfunctions in Zellweger syndrome, we have recently developed a knockout-mouse model by disrupting the PEX5 gene, encoding the targeting receptor for most peroxisomal matrix proteins (M Baes, P Gressens, E Baumgart, P Carmeliet, M Casteels, M Fransen, P Evrard, D Fahimi, PE Declercq, D Collen, PP van Veldhoven, GP Mannaerts: A mouse model for Zellweger syndrome. Nat Genet 1997, 17:49-57). In this study, we present evidence that the absence of functional peroxisomes, causing a general defect in peroxisomal metabolism, leads to proliferation of pleomorphic mitochondria with severe alterations of the mitochondrial ultrastructure, changes in the expression and activities of mitochondrial respiratory chain complexes, and an increase in the heterogeneity of the mitochondrial compartment in various organs and specific cell types (eg, liver, proximal tubules of the kidney, adrenal cortex, heart, skeletal and smooth muscle cells, neutrophils). The changes of mitochondrial respiratory chain enzymes are accompanied by a marked increase of mitochondrial manganese-superoxide dismutase, as revealed by in situ hybridization and immunocytochemistry, suggesting increased production of reactive oxygen species in altered mitochondria. This increased oxidative stress induced probably by defective peroxisomal antioxidant mechanisms combined with accumulation of lipid intermediates of peroxisomal beta-oxidation system could contribute significantly to the pathogenesis of multiple organ dysfunctions in Zellweger syndrome.

Structural remodelling during chronic atrial fibrillation: act of programmed cell survival.

Atrial fibrillation is the most common cardiac arrhythmia with an overall prevalence of almost 1%. Increasing prevalence and associated risks such as stroke and mortality have increased the need for better and more reliable therapeutic treatment. This has stimulated research to elucidate the pathophysiological mechanisms underlying atrial fibrillation. Atrial fibrillation is primarily characterised by electrical remodelling and functional deterioration. Both phenomena are reversible but after prolonged duration of atrial fibrillation, a discrepancy occurs between rapid electrical remodelling and slow recovery of contractile function. Recent studies have indicated that morphological remodelling might underlie this incongruity. In experimental models of lone atrial fibrillation, the remodelling involves cellular changes that are reminiscent of dedifferentiation and are characterised by cellular volume increase, myolysis, glycogen accumulation, mitochondrial changes and chromatin redistribution. The absence of clear signs of degeneration in these models points towards cardiomyocyte adaptation or a mechanism of programmed cell survival. In patients with atrial fibrillation cardiomyocyte degeneration does occur along with dedifferentiation which might be the result of underlying cardiac pathologies or longer duration of atrial fibrillation. In this review we focus on structural remodelling during atrial fibrillation. The different aspects of histological and ultrastructural changes as well as their role in atrial dysfunction and cardiomyocyte survival are discussed. We briefly describe the underlying molecular remodelling. and possible mechanisms responsible for remodelling involving calcium overload and stretch are presented.