Mechanisms of nerve cell death: apoptosis or necrosis after cerebral ischaemia

Abstraction and Idealization in Biomedicine: The Nonautonomous Theory of Acute Cell Injury

Neuroprotection seeks to halt cell death after brain ischemia and has been shown to be possible in laboratory studies. However, neuroprotection has not been successfully translated into clinical practice, despite voluminous research and controlled clinical trials. We suggested these failures may be due, at least in part, to the lack of a general theory of cell injury to guide research into specific injuries. The nonlinear dynamical theory of acute cell injury was introduced to ameliorate this situation. Here we present a revised nonautonomous nonlinear theory of acute cell injury and show how to interpret its solutions in terms of acute biomedical injuries. The theory solutions demonstrate the complexity of possible outcomes following an idealized acute injury and indicate that a "one size fits all" therapy is unlikely to be successful. This conclusion is offset by the fact that the theory can (1) determine if a cell has the possibility to survive given a specific acute injury, and (2) calculate the degree of therapy needed to cause survival. To appreciate these conclusions, it is necessary to idealize and abstract complex physical systems to identify the fundamental mechanism governing the injury dynamics. The path of abstraction and idealization in biomedical research opens the possibility for medical treatments that may achieve engineering levels of precision.

DL-2-amino-3-phosphonopropionic acid protects primary neurons from oxygen-glucose deprivation induced injury

Cerebral infarction is a type of ischemic stroke and is one of the main causes of irreversible brain damage. Although multiple neuroprotective agents have been investigated recently, the potential of DL-2-amino-3-phosphonopropionic acid (DL-AP3) in treating oxygen-glucose deprivation (OGD)-induced neuronal injury, has not been clarified yet. This study was aimed to explore the role of DL-AP3 in primary neuronal cell cultures. Primary neurons were divided into four groups: (1) a control group that was not treated; (2) DL-AP3 group treated with 10 μM of DL-AP3; (3) OGD group, in which neurons were cultured under OGD conditions; and (4) OGD + DL-AP3 group, in which OGD model was first established and then the cells were treated with 10 μM of DL-AP3. Neuronal viability and apoptosis were measured using Cell Counting Kit-8 and flow cytometry. Expressions of phospho-Akt1 (p-Akt1) and cytochrome c were detected using Western blot. The results showed that DL-AP3 did not affect neuronal viability and apoptosis in DL-AP3 group, nor it changed p-Akt1 and cytochrome c expression (p > 0.05). In OGD + DL-AP3 group, DL-AP3 significantly attenuated the inhibitory effects of OGD on neuronal viability (p < 0.001), and reduced OGD induced apoptosis (p < 0.01). Additionally, the down-regulation of p-Akt1 and up-regulation of cytochrome c, induced by OGD, were recovered to some extent after DL-AP3 treatment (p < 0.05 or p < 0.001). Overall, DL-AP3 could protect primary neurons from OGD-induced injury by affecting the viability and apoptosis of neurons, and by regulating the expressions of p-Akt1 and cytochrome c.

D-Glucose-Induced Cytotoxic, Genotoxic, and Apoptotic Effects on Human Breast Adenocarcinoma (MCF-7) Cells

Introduction

Glucose is a simple sugar that plays an important role in energy production in biological systems. However, it has been linked to many long-term health problems including the risk of heart disease and stroke, erectile dysfunction in men and pregnancy complications in women, and damage to the kidneys, nerves, eye and vision. Also, the underlying mechanisms of diabetic complications are poorly understood.

Methods

In the present study, D-glucose-induced cytotoxic, genotoxic, and apoptotic effects were studied using MCF-7 cells as an in vitro test model. Cell viability was determined by MTT assay. Genotoxic damage was tested by the means of alkaline single cell gel electrophoresis (Comet) assay. Cell apoptosis was measured by flow cytometry assessment (Annexin-V/PI assay).

Results

The results of MTT assay indicated that D-glucose significantly reduces the viability of MCF-7 cells in a dose and time-dependent manner. Similar trend was obtained with the trypan blue exclusion test. Data obtained from the Comet assay indicated that D-glucose causes DNA damage in MCF-7 cells in a dose-dependent manner. The flow cytometry assessment (Annexin V FITC/PI) showed a strong dose-response relationship between D-glucose exposure and annexin V positive MCF-7 cells undergoing early apoptosis.

Conclusion

Taking together, these data provide clear evidence that D-glucose induces cytotoxic, genotoxic, and apoptotic effects on MCF-7 cells. This finding represents the basis for further studies addressing the pathophysiological mechanisms of action of glucose overdose.

Basic mechanisms of arsenic trioxide (ATO)-induced apoptosis in human leukemia (HL-60) cells

Background

Acute promyelocytic leukemia (APL) is a blood cancer that affects people of all ages and strikes about 1,500 patients in the United States each year. The standard treatment of APL has been based on the combined administration of all-trans retinoic acid and chemotherapy including anthracyclins and cytarabine. However, 10-20% of patients relapse, with their disease becoming resistant to conventional treatment. Recently the Food and Drug Administration has approved the use of arsenic trioxide (ATO) or Trisenox for the treatment of APL, based on clinical studies showing a complete remission, especially in relapsed patients. In a recently published study we demonstrated that ATO pharmacology as an anti-cancer drug is associated with its cytotoxic and genotoxic effects in human leukemia cells.

Methods

In the present study, we further investigated the apoptotic mechanisms of ATO toxicity using the HL-60 cell line as a test model. Apoptosis was measured by flow cytometry analysis of phosphatidylserine externalization (Annexin V assay) and caspase 3 activity, and by DNA laddering assay.

Results

Flow cytometry data showed a strong dose-response relationship between ATO exposure and Annexin-V positive HL-60 cells. Similarly, a statistically significant and dose-dependent increase (p <0.05) was recorded with regard to caspase 3 activity in HL60 cells undergoing late apoptosis. These results were confirmed by data of DNA laddering assay showing a clear evidence of nucleosomal DNA fragmentation in ATO-treated cells.

Conclusion

Taken together, our research demonstrated that ATO represents an apoptosis-inducing agent and its apoptotic mechanisms involve phosphatidylserine externalization, caspase 3 activation and nucleosomal DNA fragmentation.

The fate of “dark” neurons produced by transient focal cerebral ischemia in a non-necrotic and non-excitotoxic environment: Neurobiological aspects

BACKGROUND INFORMATION

We recently proposed novel neurobiological ideas for discussion regarding the common nature (malfunction of a physicochemical phenomenon genetically programmed for the morphological execution of ontogenetic apoptosis), mechanism of formation (phase transition in an intraneuronal gel structure) and mode of death (neither necrosis nor apoptosis) of "dark" neurons. These ideas were deduced from morphological changes in neurons found in a visually undamaged environment after in vivo or postmortem mechanical or electric injuries and after hypoglycemia.

OBJECTIVE

In search of further support, this paper revisits these ideas in the case of transient focal cerebral ischemia by investigating the light- and electron-microscopic changes produced in neurons by a 1-h occlusion of the rat middle cerebral artery in non-necrotic and non-excitotoxic tissue areas, where extraneuronal pathological processes may not influence the intraneuronal events.

RESULTS

In the first hour after restoration of circulation, the soma-dendrite domains of "dark" neurons displayed hyperbasophilia, hyperargyrophilia, hyper-electron density and a dramatic compaction of ultrastructural elements. Between 1 h and 1 day of the restored circulation, the degree of ultrastructural compaction decreased and mitochondrion-derived membranous whorls appeared in several "dark" neurons indicating recovery. Further, the cytoplasm of scattered neurons manifesting the apoptotic condensation pattern of the nuclear chromatin displayed the same morphological features as those of the freshly produced "dark" neurons. After 1 day of restored circulation, both the non-recovering "dark" neurons and the apoptotic neurons fell into membrane-bound, compact and electron-dense fragments, which were subsequently engulfed by phagocytotic cells.

CONCLUSION

These observations support each of the ideas mentioned above.

BCL-XL expression levels influence differential regional astrocytic susceptibility to 1,3-dinitrobenzene

The selective vulnerability of brainstem astrocytes to 1,3-dinitrobenzene is mediated by a 10-fold lower threshold for opening of the cyclosporin A-inhibitable mitochondrial permeability transition pore (mtPTP). BCL-XL, BAX and BCL-2 are members of the BCL-2 protein family known to regulate both apoptotic and necrotic cell death signaling at the mtPTP. The levels at which these proteins are expressed relative to one another, where in the cell they are located and whether they are post-translational modified contributes greatly to the balance in active agonistic to active antagonistic BCL-2 proteins, and this critical balance has been hypothesized to dictate regional astrocytic susceptibility to DNB. The effects of DNB on the balance in expression of the BCL-2 family proteins have been evaluated in F344 rat DNB-sensitive (brainstem) and non-sensitive (cortical) tissue homogenates and primary astrocytes. No significant treatment-related alterations in BCL-XL, BAX or BCL-2 protein expression are observed in rat tissue homogenates or primary astrocytes. However, moderate increases in BCL-XL are observed only in DNB-treated rat cortical astrocytes, and these increases may be sufficient to shift the constitutive balance in expression of antagonistic to agonistic BCL-2 proteins from a ratio which favors BAX to one in which BAX and BCL-XL are comparably expressed. Rat primary brainstem and cortical astrocytes are also transiently transfected with bcl-xl to evaluate whether or not moderate enhancement of BCL-XL protein expression levels are sufficient to alter regional sensitivity to DNB in vitro. BCL-XL overexpression minimizes DNB-induced inhibition of succinate dehydrogenase (complex II) activity and increases significantly the concentration of DNB required to induce MPT onset in primary brainstem and cortical astrocytes. Results from the current investigation suggest that modest region-specific alterations in the balance in expression of antagonistic to agonistic BCL-2 proteins may adequately explain differential regional sensitivity to DNB-induced mitochondrial dysfunction.

Inflammatory mediators and growth factors in obstructive renal injury

Obstruction of the upper urinary tract poses a significant clinical challenge to the urologist, and the cascade of renal cellular and molecular events triggered by upper urinary tract obstruction result in a progressive, and eventually permanent, loss in renal function. These pathological changes include the development of renal fibrosis, tubular atrophy, interstitial inflammation, and apoptotic renal cell death. A myriad of cytokines and growth factors have been identified as major contributors to obstruction-induced renal fibrosis and apoptotic cell death, including transforming growth factor-beta1, angiotensin II, nuclear factor-kappaB, and tumor necrosis factor-alpha. This review examines the role of these mediators in obstruction-induced renal injury.

Synergistic protective effect of caspase inhibitors and bFGF against brain injury induced by transient focal ischaemia

We tested the hypothesis that combined use of trophic factors and caspase inhibitors increases brain resistance to ischaemia in mice. Intracerebroventricular administration of bFGF (>10 ng) 30 min after MCA occlusion decreased infarct size and neurological deficit in a dose-dependent manner following 2 h ischemia and reperfusion (20 h). Combined administration of the subthreshold doses of bFGF (3 ng) and caspase inhibitors (z-VAD.FMK, 27 ng or z-DEVD.FMK, 80 mg) reduced infarct volume by 60%, and reduced neurological deficit. Treatment with a subthreshold dose of bFGF (3 ng) extended the therapeutic window for z-DEVD.FMK (480 ng) from 1 to 3 h after reperfusion. Caspase-3 activity in the ischaemic brain was increased 30 min and 2 h after reperfusion but, was significantly reduced in bFGF-treated animals by 29 and 16%, respectively. Caspase-3 activity was not reduced by a direct bFGF effect because addition of bFGF (10 nM - 2 microM) did not decrease recombinant caspase-3 activity, in vitro. Our data show that combining caspase inhibitors and bFGF lengthens the treatment window for the second treatment, plus lowers the dosage requirements for neuroprotection. These findings are important because low doses of caspase inhibitors or bFGF reduce the possibility of side effects plus extend the short treatment window for ischaemic stroke.

Glyceraldehyde-3-phosphate dehydrogenase in neurodegeneration and apoptosis signaling

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a well-studied glycolytic enzyme that plays a key role in energy metabolism. GAPDH catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in the glycolytic pathway. As part of the conversion, GAPDH converts NAD+ to the high-energy electron carrier NADH. GAPDH has been referred to as a "housekeeping" protein and based on the view that GAPDH gene expression remains constant under changing cellular conditions, the levels of GAPDH mRNA have frequently been used to normalize northern blots. In recent years, that view has changed since GAPDH is now known to contribute to a number of diverse cellular functions unrelated to glycolysis. Normative functions of GAPDH now include nuclear RNA export, DNA replication, DNA repair, exocytotic membrane fusion, cytoskeletal organization and phosphotransferase activity. Pathologically, GAPDH has been implicated in apoptosis, neurodegenerative disease, prostate cancer and viral pathogenesis (see Sirover (1999) for a recent review of GAPDH functions). Most recently, it has been shown that GAPDH is a target for deprenyl related compounds (Carlile et al., 2000; Kragten et al., 1998) and may contribute to the neuroprotection offered by those compounds.

Heme oxygenase-2 acts to prevent neuronal death in brain cultures and following transient cerebral ischemia

Heme oxygenase (HO) cleaves the heme ring to form biliverdin, which is rapidly reduced to bilirubin, carbon monoxide, and iron. HO1, the first form of the enzyme discovered, is an inducible protein, concentrated in tissues that are exposed to degrading red blood cells and stimulated by hemolysis and numerous other toxic perturbations to eliminate potentially toxic heme. By contrast, HO2 is constitutive and most highly concentrated in neural tissues. Carbon monoxide, formed from HO2, is a putative neurotransmitter in the brain and peripheral autonomic nervous system. HO1 regulates the efflux of potentially toxic iron from cells, as iron efflux is deficient in mice with targeted deletion of HO1 (HO1(-/-)), and transfection of HO1 facilitates iron efflux. Bilirubin appears to be a physiologic neuroprotectant. Activation of HO2 by phorbol esters, that stimulate protein kinase C to phosphorylate HO2, augments production of bilirubin which protects brain cultures from oxidative stress. Bilirubin itself in nanomolar concentrations is neuroprotective, while HO2 deletion (HO2(-/-)) leads to increased neurotoxicity in brain cultures and increased neural damage following transient cerebral ischemia in intact mice. Mechanisms whereby HO2 provides neuroprotection have not been clarified including whether protection is primarily associated with apoptotic or necrotic cell death. Moreover, the generality of neurotoxic stimuli influenced by HO2 has been unclear. We now demonstrate increased neuronal death in cerebellar granule cultures of HO2(-/-) mice with a selective augmentation of apoptotic death. We also demonstrate that HO2 transfection rescues apoptotic death. In intact mice, we show an increased incidence of apoptotic morphology in the penumbra area surrounding the infarct core in HO2(-/-) mice undergoing transient focal ischemia.

Progression in acute stroke: value of the initial NIH stroke scale score on patient stratification in future trials

BACKGROUND AND PURPOSE

The objective was to determine the occurrence of neurological changes during the first 48 hours after acute stroke as it relates to initial stroke severity.

METHODS

The National Institutes of Health Stroke Scale (NIHSS) was performed serially for the first 48 hours on 127 consecutive ischemic stroke patients (129 strokes) admitted to the neuroscience intensive care unit. Incidence of stroke progression (a >/=3-point increase on the NIHSS) was recorded and analysis performed to determine its association with initial stroke severity and other demographic and physiological variables. Deficit resolution by 48 hours, defined as an NIHSS score of 0 or 1, measured the frequency of functional recovery predicted by the initial deficit.

RESULTS

Overall progression was noted in 31% of events (40/129). Applying Bayes' solution to the observed frequency of worsening, the greatest likelihood of predicting future patient progression occurs with stratification at NIHSS scores of </=7 and >7. Patients with an initial NIHSS of </=7 experienced a 14.8% (13/88) worsening rate versus a those with a score of >7 with a 65.9% (27/41) worsening rate (P<0.000005). Forty-five percent (40/88) of those with an initial score of </=7 were functionally normal at 48 hours, whereas only 2.4% (1/41) of those with scores of >7 returned to a normal examination within this period (chi2, P<0.000005).

CONCLUSIONS

This study suggests that the early clinical course of the neurological deficit after acute stroke is dependent on the initial stroke severity and that a dichotomy in early outcome exists surrounding an initial NIHSS score of 7. These findings may have significant implications for the design and patient stratification in treatment protocols with respect to primary clinical outcome.

Intrathecal expression of proteins regulating apoptosis in acute stroke

BACKGROUND AND PURPOSE

The neuronal death that accompanies an ischemic stroke has previously been attributed to a necrotic process. However, numerous studies in experimental models of ischemia have recently indicated that programmed cell death, also called apoptosis, may contribute to neuronal death. The aim of the present study was to investigate the intrathecal levels of proteins regulating apoptosis in acute stroke and to relate these levels to brain damage and to production of proinflammatory and anti-inflammatory cytokines.

METHODS

Thirty stroke patients were studied prospectively on days 0 to 4, 7 to 9, 21 to 26, and after day 90 with clinical evaluation, radiological assessment, and analysis of cerebrospinal fluid (CSF) levels of soluble (s) Fas/APO-1 and sbcl-2, 2 proteins that regulate apoptosis. In addition, analysis of the intrathecal levels of cytokines interleukin (IL)-1beta, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha was performed. Nineteen CSF samples from healthy subjects were used for control purposes. The patients were examined with MRI 1 to 3 months after stroke onset for measurement of infarct volume

RESULTS

Significantly decreased CSF levels of sFas/APO-1 were observed during the entire observation period, with a maximal decrease on day 21 after the onset of stroke. The intrathecal levels of sFas/APO-1 were significantly negatively correlated with the volume of brain infarct and with the neurological deficit 3 weeks and 3 months after the onset of the stroke. In addition, the intrathecal levels of sFas/APO-1 were significantly correlated with the levels of IL-1beta, IL-6, IL-10, and GM-CSF 3 weeks after the onset of the disease. The intrathecal levels of sbcl-2 were significantly decreased during the first 3 days after stroke onset and at the same time were positively correlated with the levels of IL-6 and tumor necrosis factor-alpha.

CONCLUSIONS

Our study demonstrates decreased intrathecal levels of proteins with antiapoptotic properties, suggesting that patients with acute stroke display a propensity toward apoptosis. Control of factors regulating apoptosis may lead to decreased delayed brain damage in stroke.

Neural apoptosis in the retina during experimental and human diabetes. Early onset and effect of insulin

This study determined whether retinal degeneration during diabetes includes retinal neural cell apoptosis. Image analysis of retinal sections from streptozotocin (STZ) diabetic rats after 7.5 months of STZ diabetes identified 22% and 14% reductions in the thickness of the inner plexiform and inner nuclear layers, respectively (P < 0. 001). The number of surviving ganglion cells was also reduced by 10% compared to controls (P < 0.001). In situ end labeling of DNA terminal dUTP nick end labeling (TUNEL) identified a 10-fold increase in the frequency of retinal apoptosis in whole-mounted rat retinas after 1, 3, 6, and 12 months of diabetes (P < 0.001, P < 0. 001, P < 0.01, and P < 0.01, respectively). Most TUNEL-positive cells were not associated with blood vessels and did not colocalize with the endothelial cell-specific antigen, von Willebrand factor. Insulin implants significantly reduced the number of TUNEL-positive cells (P < 0.05). The number of TUNEL-positive cells was also increased in retinas from humans with diabetes. These data indicate that retinal neural cell death occurs early in diabetes. This is the first quantitative report of an increase in neural cell apoptosis in the retina during diabetes, and indicates that neurodegeneration is an important component of diabetic retinopathy.

Signal transduction in environmental neurotoxicity

Signal transduction is the process by which specific information is transferred from the cell surface to the cytosol and ultimately to the nucleus, leading to changes in gene expression. Since these chains of biochemical and molecular steps control the normal function of each cell, disruption of these processes would have a significant impact on cell physiology. Some of the major signal transduction pathways are briefly reviewed. The interactions of four chemicals (lead, ethanol, polychlorinated biphenyls, and trimethyltin) with different cell signaling systems, particularly the phospholipid hydrolysis/protein kinase C pathway, are discussed. The possible causal relationship of such cellular and molecular interactions with known signs and symptoms of neurotoxicity are highlighted.