Improper Remodeling of Organelles Deputed to Ca2+ Handling and Aerobic ATP Production Underlies Muscle Dysfunction in Ageing.

Proper skeletal muscle function is controlled by intracellular Ca2+ concentration and by efficient production of energy (ATP), which, in turn, depend on: (a) the release and re-uptake of Ca2+ from sarcoplasmic-reticulum (SR) during excitation-contraction (EC) coupling, which controls the contraction and relaxation of sarcomeres; (b) the uptake of Ca2+ into the mitochondrial matrix, which stimulates aerobic ATP production; and finally (c) the entry of Ca2+ from the extracellular space via store-operated Ca2+ entry (SOCE), a mechanism that is important to limit/delay muscle fatigue. Abnormalities in Ca2+ handling underlie many physio-pathological conditions, including dysfunction in ageing. The specific focus of this review is to discuss the importance of the proper architecture of organelles and membrane systems involved in the mechanisms introduced above for the correct skeletal muscle function. We reviewed the existing literature about EC coupling, mitochondrial Ca2+ uptake, SOCE and about the structural membranes and organelles deputed to those functions and finally, we summarized the data collected in different, but complementary, projects studying changes caused by denervation and ageing to the structure and positioning of those organelles: a. denervation of muscle fibers-an event that contributes, to some degree, to muscle loss in ageing (known as sarcopenia)-causes misplacement and damage: (i) of membrane structures involved in EC coupling (calcium release units, CRUs) and (ii) of the mitochondrial network; b. sedentary ageing causes partial disarray/damage of CRUs and of calcium entry units (CEUs, structures involved in SOCE) and loss/misplacement of mitochondria; c. functional electrical stimulation (FES) and regular exercise promote the rescue/maintenance of the proper architecture of CRUs, CEUs, and of mitochondria in both denervation and ageing. All these structural changes were accompanied by related functional changes, i.e., loss/decay in function caused by denervation and ageing, and improved function following FES or exercise. These data suggest that the integrity and proper disposition of intracellular organelles deputed to Ca2+ handling and aerobic generation of ATP is challenged by inactivity (or reduced activity); modifications in the architecture of these intracellular membrane systems may contribute to muscle dysfunction in ageing and sarcopenia.

Arsenic trioxide toxicity in H9c2 myoblasts--damage to cell organelles and possible amelioration with Boerhavia diffusa.

Arsenic trioxide (ATO) has been long used as a chemotherapeutic agent because of its significant anticancer property. Unfortunately, the use of ATO is limited due to its cardiotoxic effects. The present study evaluates the protective property of ethanolic extract of Boerhavia diffusa (BDE) against ATO-induced toxicity on various cell organelles in H9c2 cardiomyocytes. The effects of different concentrations of ATO (5, 7.5 and 10 µM) on cell organelles like mitochondria, endoplasmic reticulum (ER), lysosome and actin, generation of reactive oxygen species, antioxidant enzyme status and intracellular calcium overload were evaluated. ATO significantly (P ≤ 0.05) altered mitochondrial transmembrane potential, intracellular calcium level, ER, lysosomal activity and F-actin network in addition to induction of oxidative stress. Co-treatment with BDE protected the cardiomyocytes from the adverse effects of ATO, especially at 5 µM concentration, which was evident from decreased activity of lactate dehydrogenase (5 µM ATO + 20 µg/mL BDE: 6.61 ± 1.97 µU/mL, respective control group: 16.15 ± 1.92 µU/mL), reduced oxidative stress, calcium influx and organelle damage. Results obtained from the present study allow for a better characterization of the effects of ATO on H9c2 myoblasts. In conclusion, our data suggest that cell organelles are also the targets of ATO-induced cardiotoxicity in addition to other reported targets like ion channels, and BDE has the potential to protect the cardiotoxicity induced by ATO.

Evaluation of the effects of various chemicals on discharge of and pain caused by jellyfish nematocysts.

Jellyfish tentacles in contact with human skin can produce pain swelling and redness. The pain is due to discharge of jellyfish nematocysts and associated toxins and discharge can be caused by a variety of mechanical and chemical stimuli. A series of tests were carried out with chemicals traditionally used to treat jellyfish stings e.g. acetic acid ammonia meat tenderizer baking soda and urea to determine if these chemicals stimulated or inhibited nematocyst discharge and if they brought relief to testers who were exposed to jellyfish tentacles. Chrysaora quinquecirrha (sea nettle) Chiropsalmus quadrumanus (sea wasp) and Physalia physalis (Portuguese man-of-war) were used in the study. It was found that many of the chemicals traditionally used to treat jellyfish stings stimulated nematocyst discharge and did not relieve the pain. However there was immediate relief when a common anesthetic lidocaine was sprayed on the skin of testers in contact with jellyfish tentacles. Initial exposure of tentacle suspensions to lidocaine prevented the nematocyst discharge by subsequent exposure to acetic acid ethanol ammonia or bromelain. Thus lidocaine in addition to acting as an anesthetic on skin in contact with jellyfish tentacles inhibited nematocyst discharge possibly by blocking sodium and/or calcium channels of the nematocytes.

Green tea modulates reserpine toxicity in animal models.

Reserpine, a natural product extracted from Rauwolfia serpintina or Rauwolfia vomitoria, is a known dopamine depleter that inhibits several neurotransmitters. Reserpine has been used clinically to control hypertension, schizophrenia, insomnia and insanity. The use of this drug, however, has been limited because of its side effects which include oxidative damage to organs, including the liver. Green tea catechins are potent antioxidants that have the potential to counteract reserpine induced oxidative stress. This study investigated the merits of administering green tea concurrently with reserpine to prevent oxidative hepatic damage in Sprague-Dawely (SD) rats. Reserpine was found to cause hepatic damage, with elevated levels of oxidative stress markers, such as Thiobarbituric Acid Reactive Substances (TBARS), transaminases and cholesterol. Reserpine also induced hepatic ultra-structural damage in the cytoplasmic membrane, nuclear envelope, endoplasmic reticulum (rER), ribosomal stripping and mitochondria. Electron microscopy examination showed revival of liver cells as a result of green tea extract administration to experimental rats.

Transmission electron microscopy study of the effects of zinc overdose on mouse liver tissue.

Thirty adult male mice were divided into three groups. The animals in group I were used as controls and drank only water during the entire period of experimentation. Group II animals drank water containing 1.5 g/100 mL zinc as ZnSO4, and group III animals received 2.5 g/100 mL zinc. After 3 wk supplementation with high doses of zinc, the animals were killed and the livers were removed and examined by electron microscopic techniques. After the supplementation period, the animals in groups II and II showed various degrees of degenerative changes in the hepatocytes, such as increased size and the presence of spaces and an abundance of lipid globules in the cytoplasm. The mitochondria showed a crystalline appearance, a diluted matrix, and dense aggregations. Some smooth endoplasmic reticulum tubules showed dilation and were filled with a dense substance. None of these changes were present in the group I control animals.

Ultrastructural apoptotic lesions induced in bone marrow after neptunium-237 contamination.

This study describes the ultrastructure of lesions induced by neptunium-237 (237Np), a by-product of uranium in nuclear reactors, in the bone marrow. A group of rats were given a single injection of 237Np-nitrate solution in order to observe the acute toxicity effects of this actinide. Electron microscopy was used to describe the different lesions. Observations included the swelling of the cell membrane, nuclear membrane lyses, abnormal chromatin condensation or nucleus convolution. These ultrastructural alterations of the nucleus and the cellular membrane appeared shortly after treatment. This study demonstrates the toxic effects of neptunium and its implication in the induction of apoptosis in bone marrow.

Iron toxicity and chelation therapy.

Iron is an essential mineral for normal cellular physiology, but an excess can result in cell injury. Iron in low-molecular-weight forms may play a catalytic role in the initiation of free radical reactions. The resulting oxyradicals have the potential to damage cellular lipids, nucleic acids, proteins, and carbohydrates; the result is wide-ranging impairment in cellular function and integrity. The rate of free radical production must overwhelm the cytoprotective defenses of cells before injury occurs. There is substantial evidence that iron overload in experimental animals can result in oxidative damage to lipids in vivo, once the concentration of iron exceeds a threshold level. In the liver, this lipid peroxidation is associated with impairment of membrane-dependent functions of mitochondria and lysosomes. Iron overload impairs hepatic mitochondrial respiration primarily through a decrease in cytochrome C oxidase activity, and hepatocellular calcium homeostasis may be compromised through damage to mitochondrial and microsomal calcium sequestration. DNA has also been reported to be a target of iron-induced damage, and this may have consequences in regard to malignant transformation. Mitochondrial respiratory enzymes and plasma membrane enzymes such as sodium-potassium-adenosine triphosphatase (Na(+) + K(+)-ATPase) may be key targets of damage by non-transferrin-bound iron in cardiac myocytes. Levels of some antioxidants are decreased during iron overload, a finding suggestive of ongoing oxidative stress. Reduced cellular levels of ATP, lysosomal fragility, impaired cellular calcium homeostasis, and damage to DNA all may contribute to cellular injury in iron overload. Evidence is accumulating that free-radical production is increased in patients with iron overload. Iron-loaded patients have elevated plasma levels of thiobarbituric acid reactants and increased hepatic levels of aldehyde-protein adducts, indicating lipid peroxidation. Hepatic DNA of iron-loaded patients shows evidence of damage, including mutations of the tumor suppressor gene p53. Although phlebotomy therapy is effective in removing excess iron in hereditary hemochromatosis, chelation therapy is required in the treatment of many patients who have combined secondary and transfusional iron overload due to disorders in erythropoiesis. In patients with beta-thalassemia who undergo regular transfusions, deferoxamine treatment has been shown to be effective in preventing iron-induced tissue injury and in prolonging life expectancy. The use of the oral chelator deferiprone remains controversial, and work is continuing on the development of new orally effective iron chelators.

Gastric subcellular organelle fragility and impaired gastric energy charge levels in rats with caerulein-induced acute pancreatitis: protective effect of anti-ulcer agent, teprenone.

When rats were given a supramaximal dose of caerulein (infused intravenously at 5 micrograms/kg.h for 4 h) they developed acute pancreatitis characterized by significantly raised amylase levels in the blood. In this model of acute pancreatitis, reduced gastric adenylate energy charge levels were observed, and the leakage of the lysosomal enzyme, cathepsin B, from gastric lysosomes and of the mitochondrial enzyme, malate dehydrogenase, from gastric mitochondria were both significantly accelerated compared with the control group. The intragastric administration of the anti-ulcer agent, teprenone, at a dose of 5 mg/kg (twice before caerulein infusion) significantly inhibited this gastric damage accompanying acute pancreatitis. These results suggest that gastric subcellular organelle fragility may play an important role in the pathogenesis of impaired gastric energy metabolism accompanying acute pancreatitis, and indicate the possible usefulness of teprenone in preventing this gastric damage.

Anoxic hepatocyte injury: role of reversible changes in elemental content and distribution.

Examination of anoxic isolated hepatocytes by light and electron microscopy indicated that initial morphologic changes were largely localized to the periphery of the cells. This early phase consisted of surface bleb formation but was not accompanied by alterations in parameters of plasma membrane integrity (leakage of cellular enzymes, exclusion of trypan blue). The time course of changes in structure was temporally related to alterations in the elemental distribution and content of various subcellular compartments. These studies, which employed electron probe X-ray microanalysis, demonstrated that rapid increases in the sodium and chlorine content and decreases in the potassium content of the cytoplasm, mitochondria and nucleus occurred, whereas no change in the calcium content of any subcellular compartment was detected. Concurrently, two cellular functions known to be dependent upon ion homeostasis, sodium-dependent taurocholate uptake and mitochondrial respiratory control, became markedly impaired. Reoxygenation within 30 min resulted in the restoration of both elemental distribution and the latter two functions to baseline. These data are consistent with the hypothesis that some early functional changes may be mediated by altered ion homeostasis. In contrast, additional studies indicated that sodium and water fluxes could be dissociated from the appearance of plasma membrane blebs. Thus, this study provides direct evidence that the structural and functional changes of early anoxic hepatocyte injury cannot be explained by a single mechanistic cascade, but apparently involve multiple mechanisms which may not be directly linked.