Mitochondrial matrix densities in myocardial ischemia and autolysis

Mitochondrial morphology in the mouse adrenal cortex: Influence of chronic psychosocial stress

Mitochondria within the adrenal cortex play a key role in synthesizing steroid hormones. The adrenal cortex is organized in three functionally specialized zones (glomerulosa, fasciculata, and reticularis) that produce different classes of steroid hormones in response to various stimuli, including psychosocial stress. Given that the functions and morphology of mitochondria are dynamically related and respond to stress, we applied transmission electron microscopy (TEM) to examine potential differences in mitochondrial morphology under basal and chronic psychosocial stress conditions. We used the chronic subordinate colony housing (CSC) paradigm, a murine model of chronic psychosocial stress. Our findings quantitatively define how mitochondrial morphology differs among each of the three adrenal cortex zones under basal conditions, and show that chronic psychosocial stress mainly affected mitochondria in the zona glomerulosa, shifting their morphology towards the more typical glucocorticoid-producing zona fasciculata mitochondrial phenotype. Analysis of adrenocortical lipid droplets that provide cholesterol for steroidogenesis showed that chronic psychosocial stress altered lipid droplet diameter, without affecting droplet number or inter-organellar mitochondria-lipid droplet interactions. Together, our findings support the hypothesis that each adrenal cortex layer is characterized by morphologically distinct mitochondria and that this adrenal zone-specific mitochondrial morphology is sensitive to environmental stimuli, including chronic psychosocial stressors. Further research is needed to define the role of these stress-induced changes in mitochondrial morphology, particularly in the zona glomerulosa, on stress resilience and related behaviors.

Diagnosis of sudden cardiac death due to early myocardial ischemia: An ultrastructural and immunohistochemical study

The aim of this post-mortem ultrastructural and immunohistochemical study is to explore the characteristics of acute myocardial ischemia in the context of sudden death, using the combination of two different methods, both more insightful than ordinary histology. Transmission electron microscopy and immunohistochemistry, in addition to the traditional histology, were applied to study human heart specimens collected during forensic autopsies. The whole series was sub-grouped into cases (n=17) and controls (N=10). The control group consisted of unnatural death with a short agonal period (immediately lethal injuries). Heart samples of the two cohorts of subjects were prepared for electron microscopy. On the other hand, each specimen, formalin fixed and paraffin embedded, was stained with haematoxylin and eosin and immunoreacted with the following primary antibodies: anti-Fibronectin, anti- Connexin-43, anti-npCx43 (dephosphorylated form of Connexin43), anti-Zonula occludens-1. Immunopositivity for each marker in the myocardium was semi-quantitatively graded. Electron microscopy revealed a number of interesting differences, statistically significant, between acute myocardial ischemia and controls, regarding the morphology of nucleus, mitochondria and intercellular junctions. By immunohistochemistry, fibronectin was found to be increased in the extracellular matrix of the acute myocardial ischemia cases, with a statistically significant difference compared to the controls. Connexin 43 staining disclosed a slight increase (not statistically significant) in the cytoplasm of acute myocardial ischemia cases compared to the controls, whereas no significant differences were seen between cases and controls at intercellular junctions. npCx43 showed an evident difference of intensity and pattern (even though not statistically significant) in cases compared to controls and overall this difference was more evident in the cytoplasm. Zonula occludens 1, described as an important marker for functional modification of cardiac muscle fibers, resulted negative or very weak in the vast majority of both cases and controls. The present study attempts to simultaneously apply electron microscopy and immunohistochemistry, in order to figure out the morphological changes that might lead to pathological processes underlying the sudden, unexpected death due to acute myocardial ischemia, and consequently to find useful diagnostic markers of very early ischemic injury. Both methods showed significant differences between acute myocardial ischemia and controls, regarding, overall nuclei, mitochondria, and intercellular junctions.

Commentary on Selected Aspects of Cardioprotection

Three aspects of cardioprotection are discussed in this article. The first is myocyte death as a function of the duration and severity of ischemia in experimental acute myocardial infarction in the dog heart. The short period of time during which reperfusion with arterial blood will salvage myocytes is demonstrated along with data showing that this period diminishes significantly if collateral flow is very low or absent. The second topic is a discussion of potential mechanisms underlying postconditioning. It begins with a review of the changes that lead to irreversible injury during acute ischemia in the dog heart along with a discussion of the genesis of contraction band necrosis and no reflow when myocardium is salvaged by unrestricted reperfusion with arterial blood in order to provide a basis to discuss the potential mechanisms underlying postconditioning, a situation in which reflow is intermittent and restricted. Postconditioning is reported to achieve greater myocyte salvage than unrestricted reflow. Potential explanations for this beneficial effect include: first, sufficient sarcolemmal repair occurring during the intermittent reflow (reoxygenation) to prevent cell death by explosive cell swelling, and second, prevention of the opening of the mitochondrial permeability transition pore, thereby preventing mitochondrial failure and cell death in the reperfused tissue. Since there is no way available to identify and specifically study the myocytes that would have died if not protected by postconditioning, direct demonstration of mechanisms is difficult or impossible. Finally, the third topic in this commentary is an analysis of the obstacles faced by investigators using small rodent hearts to establish cardioprotective mechanisms. Such studies provide valid data but the relationship of the changes and the proposed mechanisms underlying these changes are not necessarily directly transferable to ischemic large animal hearts including the heart of man.

Role of nitric oxide in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) occurs upon restoration of hepatic blood flow after a period of ischemia. Decreased endogenous nitric oxide (NO) production resulting in capillary luminal narrowing is central in the pathogenesis of IRI. Exogenous NO has emerged as a potential therapy for IRI based on its role in decreasing oxidative stress, cytokine release, leukocyte endothelial-adhesion and hepatic apoptosis. This review will highlight the influence of endogenous NO on hepatic IRI, role of inhaled NO in ameliorating IRI, modes of delivery, donor drugs and potential side effects of exogenous NO.

Ischemia/reperfusion injury in kidney transplantation: mechanisms and prevention

Ischemia has been an inevitable event accompanying kidney transplantation. Ischemic changes start with brain death, which is associated with severe hemodynamic disturbances: increasing intracranial pressure results in bradycardia and decreased cardiac output; the Cushing reflex causes tachycardia and increased blood pressure; and after a short period of stabilization, systemic vascular resistance declines with hypotension leading to cardiac arrest. Free radical-mediated injury releases proinflammatory cytokines and activates innate immunity. It has been suggested that all of these changes-the early innate response and the ischemic tissue damage-play roles in the development of adaptive responses, which in turn may lead to an acute font of kidney rejection. Hypothermic kidney storage of various durations before transplantation add to ischemic tissue damage. The final stage of ischemic injury occurs during reperfusion. Reperfusion injury, the effector phase of ischemic injury, develops hours or days after the initial insult. Repair and regeneration processes occur together with cellular apoptosis, autophagy, and necrosis; the fate of the organ depends on whether cell death or regeneration prevails. The whole process has been described as the ischemia-reperfusion (I-R) injury. It has a profound influence on not only the early but also the late function of a transplanted kidney. Prevention of I-R injury should be started before organ recovery by donor pretreatment. The organ shortage has become one of the most important factors limiting extension of deceased donor kidney transplantation worldwide. It has caused increasing use of suboptimal deceased donors (high risk, extended criteria [ECD], marginal donors) and uncontrolled non-heart-beating (NHBD) donors. Kidneys from such donors are exposed to much greater ischemic damage before recovery and show reduced chances for proper early as well as long-term function. Storage of kidneys, especially those recovered from ECD (or NHBD) donors, should use machine perfusion.

Interaction of cardiovascular risk factors with myocardial ischemia/reperfusion injury, preconditioning, and postconditioning

Therapeutic strategies to protect the ischemic myocardium have been studied extensively. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate lethal tissue injury, a process termed "reperfusion injury." Ischemia/reperfusion injury may lead to myocardial infarction, cardiac arrhythmias, and contractile dysfunction. Ischemic preconditioning of myocardium is a well described adaptive response in which brief exposure to ischemia/reperfusion before sustained ischemia markedly enhances the ability of the heart to withstand a subsequent ischemic insult. Additionally, the application of brief repetitive episodes of ischemia/reperfusion at the immediate onset of reperfusion, which has been termed "postconditioning," reduces the extent of reperfusion injury. Ischemic pre- and postconditioning share some but not all parts of the proposed signal transduction cascade, including the activation of survival protein kinase pathways. Most experimental studies on cardioprotection have been undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of other disease processes. However, ischemic heart disease in humans is a complex disorder caused by or associated with known cardiovascular risk factors including hypertension, hyperlipidemia, diabetes, insulin resistance, atherosclerosis, and heart failure; additionally, aging is an important modifying condition. In these diseases and aging, the pathological processes are associated with fundamental molecular alterations that can potentially affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Among many other possible mechanisms, for example, in hyperlipidemia and diabetes, the pathological increase in reactive oxygen and nitrogen species and the use of the ATP-sensitive potassium channel inhibitor insulin secretagogue antidiabetic drugs and, in aging, the reduced expression of connexin-43 and signal transducer and activator of transcription 3 may disrupt major cytoprotective signaling pathways thereby significantly interfering with the cardioprotective effect of pre- and postconditioning. The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenous cardioprotection by pre- and postconditioning (i.e., drug applied as trigger or to activate signaling pathways associated with endogenous cardioprotection) and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardioprotection conferred by preconditioning and postconditioning. We emphasize the critical need for more detailed and mechanistic preclinical studies that examine car-dioprotection specifically in relation to complicating disease states. These are now essential to maximize the likelihood of successful development of rational approaches to therapeutic protection for the majority of patients with ischemic heart disease who are aged and/or have modifying comorbid conditions.

Ultrastructural and cytochemical changes in the heart of iron-deficient rats

Male Sprague-Dawley rats aged 3 weeks that were maintained on an iron-deficient diet for 4-5 weeks developed severe anemia with markedly reduced hemoglobin levels (3.94 +/- 0.14 Hb g% versus controls 12.9 +/- 0.11 Hb g%). Iron-deficiency resulted in marked cardiac hypertrophy (cardiomegaly). On sacrifice, the hearts were processed for light and transmission electron microscopy. The major ultrastructural changes were found in the hypertrophied left ventricle and left papillary muscles. Iron-deficiency caused marked edema in myocytes, sarcomeres were out of register, and degeneration and discontinuities in myofilaments were common. Iron-deficiency resulted in the enlargement of the interfibrillar mitochondria, changes in the matrix and the formation of electron-dense amorphous bodies. The ultrastructural changes in myocytes in response to experimental iron-deficiency were similar to those described by others in cases of experimental ischemia or hypoxia. Mitochondrial changes were also found in the atria of iron-deficient rats. Quantitative cytochemical measurement of succinate dehydrogenase activity was determined and was shown to be substantially reduced in the iron-deficient heart. In severely iron-deficient rats restored to a normal iron-sufficient diet for two weeks, hemoglobin levels recovered, however the myocytes of the hypertrophied left ventricles and papillary muscles continued to show severe degenerative changes.

Reperfusion-induced arrhythmias in isolated rat heart: an index of cellular damage or viability of cardiomyocytes?

Susceptibility of rat myocardium to reperfusion-induced arrhythmias after sustained (4 h) and brief (10 min) durations of regional ischaemia in relation to structurally-related impairment of heart function was studied in isolated Langendorff-perfused rat hearts. Reperfusion arrhythmias after 4 h ischaemia were characterized by low severity accompanied by only partial restoration of coronary flow upon reperfusion (no-reflow). Electron microscopy examination of the ischaemic hearts revealed severely ultrastructure of cardiac myocytes and capillary endothelium. These deteriorations were not reversed upon reperfusion. On the contrary, brief ischaemia resulted in high susceptibility of the heart to severe arrhythmias upon reperfusion with persisting hyperaemia. Ischaemia-induced minor changes in myocardial ultrastructure were reversed upon reperfusion. In conclusion, sustained ischaemia in the rat heart with absent collaterals renders myocardial tissue non-viable with consequent impaired recovery of heart function and loss of excitability of the myocardium upon reperfusion. Accordingly, high susceptibility to arrhythmias may indicate the preservation of viable myocardial cells.

Relationship between sarcolemmal damage and appearance of amorphous matrix densities in mitochondria following occlusion of coronary artery in rats

The relationship between the progression of sarcolemmal damage and the appearance of amorphous matrix densities (AMDs) within myocardial mitochondria in the early phase of ischemia was studied in coronary-ligated rats by means of electron microscopy. The animals were divided into six groups according to the duration of ischemia (from 10 to 120 min). The severity of sarcolemmal damage was graded into four classes according to the ultrastructural ischemic changes, as follows: grade 0, normal cells; grade 1, slight ischemic changes in cellular organelles but intact sarcolemma; grade 2, formation of subsarcolemmal blebs, but overall sarcolemmal integrity; and grade 3, sarcolemmal disruption. In the experiment, grade 1 cells decreased and those of grade 3 increased with a longer period of ischemia. The appearance of grade 3 cells was distinct at 30 min of ischemia. This cellular damage proceeded from the subendocardial layer to the subepicardial layer indicating the "wavefront phenomenon." The number of AMDs within the mitochondria increased as the sarcolemmal damage became more severe. It was noteworthy that AMDs could be found in cells with an intact sarcolemma after subjection to 10 min of ischemia. Myoglobin staining of the myocardium obtained after 10 min of ischemia followed by 6 hr of reperfusion revealed no loss of myoglobin, indicating no irreversible cell damage. This finding suggests that the formation of AMDs may occur prior to the disruption of the sarcolemma or irreversible cell damage.

Use of intermittent dobutamine infusion in congestive heart failure

Dobutamine is a cardiac inotrope useful in the acute treatment of congestive heart failure. Dobutamine improves cardiac output, decreases pulmonary wedge pressure, and decreases total systemic vascular resistance with little effect on heart rate or systemic arterial pressure. Clinical benefit has been observed to continue for weeks to months following the discontinuation of dobutamine. In addition, tolerance to dobutamine has been observed when infusions last 72 hours or longer. This has led investigators to study the effectiveness of chronic intermittent infusions of dobutamine. Studies utilizing dobutamine doses ranging from 1.5 to 15 micrograms/kg/min for 4-48 h/wk have shown sustained clinical and hemodynamic improvement in patients suffering from congestive heart failure. The mechanism by which dobutamine creates this effect is not entirely known; however, studies suggest dobutamine exerts a physical conditioning effect similar to exercise. Dobutamine infusions have also been associated with morphological and metabolic changes in myocardial tissue consistent with improved myocardial structure and function. The intermittent use of dobutamine may be beneficial in the chronic treatment of congestive heart failure in patients who fail to respond to conventional therapy.

Quantitative electron microscopic study of calcium accumulation in cerebral ischemia mitochondria

Formation of calcium deposits in mitochondria is a consistent feature of irreversible injury in ischemic myocardium. We studied calcium accumulation in nerve cell mitochondria in a cat model 30 and 60 minutes after cerebral ischemia localized in the anterior part of the caudate nucleus and adjacent internal capsule. In control animals, calcium deposits were visible in synaptic vesicles, Golgi apparatus, mitochondria, lysosomes, and in glial and neuronal nuclei. After cerebral ischemia, findings included astrocytic swelling and degeneration of neurons, with an increase in calcium pyroantimoniate mitochondrial deposits. Content of intramitochondrial calcium deposits is related to duration of ischemia as well as the amount of cellular lesions.

The temporal evolution of hypoglycemic brain damage. I. Light- and electron-microscopic findings in the rat cerebral cortex

In the course of a study on the pathogenesis of neuronal necrosis in severe hypoglycemia, the morphological characteristics reflecting reversible and irreversible neuronal lesions were examined as a function of time following normalization of blood glucose. To that end, closely spaced time intervals were studied in the rat cerebral cortex before, during, and up to 1 year after standardized pure hypoglycemic insults of 30 and 60 min of cerebral isoelectricity. Both the superficial and deep layers of the cerebral cortex showed dark and light neurons during and several hours after the insult. By electron microscopy (EM) the dark neurons were characterized by marked condensation of both karyoplasm and cytoplasm, with discernible, tightly packed cytoplasmic organelles. The light neurons displayed clustering of normal organelles around the nucleus with clearing of the peripheral cytoplasm. Some cells, both dark neurons and neurons of normal electron density, contained swollen mitochondria with fractured cristae. Light neurons disappeared from the cerebral cortex by 4 h of recovery. Some dark neurons in the superficial cortex and almost all in the deep cortex evolved through transitional forms into normal neurons by 6 h recovery. Another portion of the dark neurons in the superficial cortex became acidophilic between 4 and 12 h, and by EM they demonstrated karyorrhexis with stippled electron-dense chromatin. The plasma membrane was disrupted, the cytoplasm was composed of amorphous granular debris, and the mitochondria contained flocculent densities. These definitive indices of irreversible neuronal damage were seen as early as 4-8 h recovery. Subsequently, the acidophilic neurons were removed from the tissue, and gliosis ensued. Thus, even markedly hyperchromatic "dark" neurons are compatible with survival of the cell, as are neurons with conspicuous mitochondrial swelling. Definite nerve cell death is verified as the appearance of acidophilic neurons at which stage extensive damage to mitochondria is already seen in the form of flocculent densities, and cell membranes are ruptured. Our previous results have shown that hypoglycemic neocortical damage affects the superficial laminae, chiefly layer 2. The present results demonstrate that, following the primary insult, this damage evolves relatively rapidly within the first 4-12 h. We have obtained no evidence that additional necrotic neurons are recruited after longer recovery periods.

The temporal evolution of hypoglycemic brain damage. II. Light- and electron-microscopic findings in the hippocampal gyrus and subiculum of the rat

Part I of this paper has documented the evolution of dark neurons into acidophilic neurons in the superficial laminae as well as the reversion of dark neurons to normal neurons in the deep laminae of the cerebral cortex in hypoglycemic brain damage. The present study describes the temporal evolution of hypoglycemic brain damage in the hippocampus. The evolution of dark neurons to acidophilic neurons was confirmed in this brain region. Four additional problems were addressed: Firstly, delayed neuronal death was looked for, and was found to occur in areas of CA1 undergoing mild damage. However, it was not preceded by a morphological free interval, had ultrastructural characteristics distinct from delayed neuronal death in ischemia, and hence should be considered a distinct phenomenon. Secondly, the gradient in the density of neuronal necrosis in the rat hippocampal pyramidal cell band was exploited to test the hypothesis that a more severe insult causes a more rapid evolution of neuronal changes. This was found to be the case, with a temporal spectrum in the timing of neuronal death: Necrosis occurred already after 2 h medially in the subiculum, and was delayed by up to several weeks laterally in CA1. Thirdly, the almost universal sparing of CA3 pyramidal neurons after 30 min hypoglycemic isoelectricity was exploited to address the question of whether reactive changes, which could with certainty be deemed reversible, occur in CA3. Mitochondrial injury was seen in these cells, and was found to be recoverable. No reactive changes of the type previously described following ischemic insults were observed. Fourthly, the astrocytic and vascular response of the tissue was studied. A sequence of astrocytic changes representing structural and probably metabolic activation of astrocytes was seen, consisting of morphological indices of increased turnover of cellular components. Capillaries demonstrated endothelial pits, vesicles, and prominent microvilli hours to days after recovery. The results demonstrate that, in the hippocampal gyrus as in other brain regions, hypoglycemic brain damage is distinct from ischemic brain damage and likely has a different pathogenesis.

The dentate gyrus in hypoglycemia: pathology implicating excitotoxin-mediated neuronal necrosis

A detailed light- and electron-microscopic study of the damage to the rat dentate gyrus in hypoglycemia was undertaken, in view of the previously advanced hypothesis that hypoglycemic nerve cell injury is mediated by a released neurotoxin. The distribution of neuronal necrosis showed a relationship to the subarachnoid cisterns. Electron microscopy of the dentate granule cells and their apical dendrites revealed dendrosomal, axon-sparing neuronal pathology. Dentate granule cells were affected first in the dendrites in the outer layer of the stratum moleculare, sparing axons of passage and terminal boutons. Subsequently, the neuronal perikarya were affected, and Wallerian degeneration of axons followed. Cell membrane abnormalities preceded the appearance of mitochondrial flocculent densities and degradation of the cytoskeleton, and are suggested to be early lethal changes. The observed early dendrotoxic changes, and the dendrosomal, axon-sparing nature of the lesion implicate an excitotoxin-mediated neuronal necrosis in hypoglycemia.

The effects of altered cation balance on the fine structure of hypoxic myocardial cells

To determine whether the changes in intracellular/extracellular cation balance which develop in ischaemic myocardium are responsible for the fine structural changes seen in such tissue, thin slices of normal canine ventricle were incubated under hypoxic conditions at 37 degrees C and physiological pH in balanced salt solution (BSS), isotonic NaCl and isotonic KCl. Slices from each solution were fixed at 10-120 min intervals and examined by light and electron microscopy. For 60 min, tissue from both NaCl and KCl showed good overall preservation of cell architecture and only mild subcellular alterations including aggregation of nuclear chromatin, disappearance of glycogen granules, and swelling of sarcoplasmic reticulum. Tissue from BSS showed early development of intramitochondrial dense inclusions together with focal contraction-band damage similar to that seen in temporarily ischaemic, re-perfused heart muscle and at the margins of infarcts. These changes thus appear to be promoted by divalent cations. The progressive reversal of monovalent cation balance in an area of permanent and severe ischaemia does not appear to be a major determinant of fine structural change.

Relationship between structure and fatty acid metabolism in mitochondria isolated from ischemic rat hearts

We studied mitochondrial structure and intermediates of fatty acid metabolism in mitochondria isolated from ischemic hearts. By electron microscopy, no structural difference was detected between mitochondria isolated from control hearts and from ischemic hearts receiving glucose as the only substrate. However, major differences were observed in mitochondria obtained from control and ischemic hearts receiving both glucose and palmitate. These hearts contained a higher portion of damaged mitochondria. However, measurements of marker enzyme activities failed to show that more mitochondria were lost during the isolation procedure in ischemic than in control hearts. Many densely staining areas (or amorphous densities) were observed in the isolated mitochondria of ischemic hearts. These amorphous densities have an appearance similar to that observed in the intact ischemic heart under the same perfusion conditions. Levels of long-chain acyl-CoA in mitochondria isolated from hearts receiving glucose alone were practically the same for control and ischemic hearts and were only slightly increased in mitochondria of ischemic hearts receiving both glucose and palmitate. On the other hand, levels of long-chain acyl carnitine in mitochondria of ischemic hearts were twice those found in control hearts. The mitochondrial level of long-chain acyl carnitine was approximately four times higher in the ischemic hearts receiving palmitate compared to those receiving no palmitate. This rise in long-chain acyl carnitine levels in mitochondria isolated fom ischemic hearts receiving palmitate may be related to modifications of the mitochondrial structure and to the appearance of amorphous densities.