Lead toxicity induces autophagy to protect against cell death through mTORC1 pathway in cardiofibroblasts

Heavy metals, such as lead (Pb²⁺), are usually accumulated in human bodies and impair human''s health. Lead is a metal with many recognized adverse health side effects and yet the molecular processes underlying lead toxicity are still poorly understood. In the present study, we proposed to investigate the effects of lead toxicity in cultured cardiofibroblasts. After lead treatment, cultured cardiofibroblasts showed severe endoplasmic reticulum (ER) stress. However, the lead-treated cardiofibroblasts were not dramatically apoptotic. Further, we found that these cells determined to undergo autophagy through inhibiting mammalian target of rapamycin complex 1 (mTORC1) pathway. Moreover, inhibition of autophagy by 3-methyladenine (3-MA) may dramatically enhance lead toxicity in cardiofibroblasts and cause cell death. Our data establish that lead toxicity induces cell stress in cardiofibroblasts and protective autophagy is activated by inhibition of mTORC1 pathway. These findings describe a mechanism by which lead toxicity may promote the autophagy of cardiofibroblasts cells, which protects cells from cell stress. Our findings provide evidence that autophagy may help cells to survive under ER stress conditions in cardiofibroblasts and may set up an effective therapeutic strategy for heavy metal toxicity.     

Mechanically induced electrical storm as a complication of cardiac resynchronization therapy: A case report

BackgroundCardiac resynchronization therapy (CRT) has been shown to improve both the functional status and mortality of heart failure patients with left bundle branch block. Multiple recent studies suggest several mechanisms for proarrhythmia associated with CRT device.Case summaryA 51-year-old male with symptomatic non-ischemic cardiomyopathy and no previous history of ventricular arrhythmias underwent placement of a biventricular cardioverter-defibrillator. The patient developed sustained monomorphic ventricular tachycardia (VT) soon after implantation. The VT recurred despite reprogramming to right ventricular only pacing. The electrical storm resolved only after a subsequent discharge from the defibrillator caused inadvertent dislodgement of the coronary sinus lead. No recurrent VT occurred throughout 10-years follow up after urgent coronary sinus lead revision.DiscussionWe describe the first reported case of mechanically induced electrical storm due to the physical presence of the CS lead in a patient with a new CRT-D device. It is important to recognize mechanical proarrhythmia as a potential mechanism of electrical storm, as it may be intractable to device reprogramming. Urgent coronary sinus lead revision should be considered. Further studies on this mechanism of proarrhythmia are needed.     

Metal localization in water hyacinth roots from an urban wetland

PCA, principal components analysis
MDS, multidimensional scaling
STEM, scanning transmission electron microscopy

Metal localization within and around roots of water hyacinth ( Eichhornia crassipes ) growing in a wetland receiving urban run-off was studied by energy dispersive X-ray microanalysis of sections from freeze-substituted roots. Sampling randomly from an order of magnitude gradient in metal concentrations (Cu and Pb) allowed us the opportunity to identify general patterns of metal localization. Iron was present at high levels at the root surface, and this may have been a root plaque as described for wetland plants with roots anchored in flooded soils. Iron levels decreased centripetally across the root and were higher in cell walls than within cells. Trace metals (Cu, Zn and Pb) were not localized at the root surface. In contrast with iron, trace metal levels increased centripetally across the root, tended to be higher inside cells and were highest within cells in the stele. Variability of localization was high for all metals analysed. Multivariate statistical analyses (principal components analysis and multidimensional scaling) were useful for identifying overall patterns in elemental distribution.     

Biokinetics of lead in various organs of rats using radiotracer technique

Uptake, distribution, and elimination of lead in various organs of rats have been studied using a radiotracer technique. The elimination data for various organs, except whole blood, is fitted to a double-exponential function using a computer program. The biological half-lives along with the percent elimination of lead by two different decay modes in testis, epididymis, prostate, and seminal vesicles are being reported together with that in liver, kidney, blood, and whole body. It is evident from this study that the elimination of lead is limited for all the organs and permits lead accumulation in the bone, where it is stored and becomes almost unavailable for elimination. Lead levels in blood, testis, and femur of lead acetate-fed rats measured using atomic absorption spectroscopy have been correlated to the uptake of²¹⁰Pb in various organs.     

Effect of lead acetate on Sertoli cell lactate production and protein synthesis in vitro

The effects of lead acetate on protein synthesis and lactate production by cultures of rat Sertoli cells in vitro were studied. Sertoli cell cultures prepared from 20 day old Sprague-Dawley rats were exposed to 0.01, 0.05 and 0.10 mM lead acetate. Lactate production was significantly elevated by all concentrations of lead after 3, 6, 9 and 12 hours of exposure. Protein biosynthesis as measured by [³H]-leucine incorporation was significantly depressed by 0.05 and 0.10 mM lead acetate after 2 hours of exposure. These results support the hypothesis that lead acetate may inhibit spermatogenesis by a disturbance of the metabolic activities of the Sertoli cells.Abbreviations MEM minimal essential medium - TCA trichloroacetic acid     

Feed selection and digestibility by captive giraffe

A digestion trial with subsequent examination of feed selection was conducted using two captive giraffe fed four feedstuffs. Apparent digestibility coefficients were relatively high, indicating that the animals were efficiently utilizing the feedstuffs. However, values could be affected by the possible ingestion of soil containing acid-insoluble ash. A high fiber pelleted feed was eaten in a greater quantity than a low fiber feed, even though the constituents in each feed were the same. Gross energy content of residual hay was higher than gross energy content of the offered hay. whereas neutral detergent fiber and acid detergent fiber content were lower in the residual than in the offered hay. The animals did not appear to be selecting for a diet high in energy or low in fiber. Based on these results and other information, re-classification of giraffe as a facultative concentrate selector or as an intermediate feeder may be appropriate.     

Algorithms for the automated selection of fragment-like molecules using single-point surface plasmon resonance measurements

Fragment-based approaches have added to the arsenal of tools used to identify novel developable leads for drug discovery with high ligand efficiencies. A variety of label-free technologies have been developed and used throughout the industry for fragment screening. Using surface plasmon resonance (SPR) as a fragment screening platform is a relatively new approach. The miniaturization and automation of this technology has led to an associated problem: the large volume of raw data often makes it challenging to analyze and integrate the results of SPR data into the workflow of project teams engaged in the discovery process in a timely fashion. As such, several sets of equations were derived and implemented on Merck’s intranet to score single sensorgrams to distinguish stable binders from weak or anomalous binders. This set of equations was optimized and validated on simulated data to both capture “fragment-like” behavior from SPR experiments and filter out much of the anomalous behavior commonly observed. It has subsequently been applied successfully to several in-house discovery programs.     

Lead staining in the Golgi complex

Lead ions at similar concentrations to those used for Gomori type phosphatase localization stain some parts of the vacuolar system, particularly compartments of the Golgi complex (GC) and isolation envelopes (im) in a characteristic way in both vertebrates and invertebrates. After fixation in 2.5% glutaraldehyde, lead citrate in acetate or aspartate buffer (pH 5.5-7.2) leaves the contents of GC cisternal compartments with a fine particulate stippling. In the fat body of Calpodes ethlius and in mouse pancreas the staining is faint but definite without further enhancement of contrast, although it is easily overlooked after section staining. The distribution of lead stain differs from that of the lead phosphate precipitated after Gomori type acid phosphatase reactions. Whereas lead stain may be in all GC and im compartments, acid phosphatase is restricted to the innermost saccules and nearby vacuoles. The compartment specific staining by led also differs from the generalized staining in all compartments given by uranyl. Thus the contents of luminal membrane surfaces of some parts of the vacuolar system can be characterized by their ability to bind lead. In cells where protein synthesis has been blocked by cycloheximide, secretory vesicles are absent and the RER and GC from the generalized staining in all compartments given by uranyl. Thus the contents of luminal membrane surfaces of some parts of the vacuolar system can be characterized by their ability to bind lead. In cells where protein synthesis has been blocked by cycloheximide, secretory vesicles are absent and the RER and GC from the generalized staining in all compartments given by uranyl. Thus the contents of luminal membrane surfaces of some parts of the vacuolar system can be characterized by their ability to bind lead. In cells where protein synthesis has been blocked by cycloheximide, secretory vesicles are absent and the RER and GC cisternae are devoid of uranyl stainable material. However, lead staining and acid phosphatase activity in the GC continue. We presume that they mark the environment within these cisternae rather than the proteins passing through them. This environment is itself not static. Several observations suggest that the function of cisternae that is detectable by lead staining is temporally discontinuous and related to a stage of maturation or development. Only early stage ims stain: the staining ceases by the beginning of autophagy after hydrolytic enzymes are presumed to have been added. Condensing vacuoles cease to stain as the central core crystallizes out. Stain may be absent from one or two GC saccules at any position in the stack as though the phase of lead staining (or lack or it) can move progressively through the system. We conclude that in studies characterizing components of the vacuolar system it is necessary to separate those that mark transient occupants of a compartment from those that mark the compartment itself. Both may vary temporally independently from one another.     

Unexpected inhibition of bradycardia pacing due to oversensing in ICD lead fracture associated with spurious tachyarrhythmia detection and discharges

Ιn a 76-year old man with a dual-chamber ICD implanted five years ago, dizzy spells and significant bradycardia on Holter were not initially recognized as inhibition of bradycardia pacing, due to oversensing. Hospital admission was deemed necessary only after repetitive ICD shocks attributed to right ventricular pace-sense lead fracture. The need to ensure adequate ICD antibradycardia backup pacing in pacing-dependent patients when deleterious sensing errors occur, cannot be overemphasized.     

Erythrocyte pyrimidine 5′-nucleotidase inhibition by acute lead exposure in neonatal rats

Inhibition by lead of erythrocyte pyrimidine 5′-nucleotidase (P5N) is thought to contribute to morphological abnormalities observed in red blood cells (RBC) of lead-exposed subjects. However, neither the mechanism of lead inhibition of P5N nor the relationship of this inhibition to blood lead levels attained in exposed subjects is known. In the present investigation, acute in vivo and in vitro lead acetate effects on erythrocyte P5N from 21-day-old rat pups were determined and were related to blood lead concentrations ascertained by atomic absorption spectrophotometry. Acute lead administration to rat pups resulted in a 16% to 21% reduction in erythrocyte P5N, with mean blood lead levels ranging from 77 to 108 μg/dl 24 hours later. Inhibition of erythrocyte P5N was linearly related to blood lead level (r = ?0.67, P < 0.05) following acute lead administration. Lead acetate addition to RBC preparations from 21-day-old rats resulted in concentration-dependent P5N inhibition which was comparable to that produced following acute in vivo exposure. The results indicate that acute P5N inhibition in lead-treated neonatal rats is due to noncompetitive P5N inhibition by lead. The inhibition of P5N produced by acute lead treatment is linearly related to blood lead concentrations.