Mitochondrial mechanisms of estrogen neuroprotection.

Mitochondria have become a primary focus in our search not only for the mechanism(s) of neuronal death but also for neuroprotective drugs and therapies that can delay or prevent Alzheimer's disease and other chronic neurodegenerative conditions. This is because mitochrondria play a central role in regulating viability and death of neurons, and mitochondrial dysfunction has been shown to contribute to neuronal death seen in neurodegenerative diseases. In this article, we review the evidence for the role of mitochondria in cell death and neurodegeneration and provide evidence that estrogens have multiple effects on mitochondria that enhance or preserve mitochondrial function during pathologic circumstances such as excitotoxicity, oxidative stress, and others.

A current practice for predicting ocular toxicity of systemically delivered drugs.

The ability to predict ocular side effects of systemically delivered drugs is an important issue for pharmaceutical companies. Although animal models involving standard clinical ophthalmic examinations and postmortem microscopic examinations of eyes are still used to identify ocular issues, these methods are being supplemented with additional in silico, in vitro, and in vivo techniques to identify potential safety issues and assess risk. The addition of these tests to a development plan for a potential new drug provides the opportunity to save time and money by detecting ocular issues earlier in the program.

Biguanide-induced mitochondrial dysfunction yields increased lactate production and cytotoxicity of aerobically-poised HepG2 cells and human hepatocytes in vitro.

As a class, the biguanides induce lactic acidosis, a hallmark of mitochondrial impairment. To assess potential mitochondrial impairment, we evaluated the effects of metformin, buformin and phenformin on: 1) viability of HepG2 cells grown in galactose, 2) respiration by isolated mitochondria, 3) metabolic poise of HepG2 and primary human hepatocytes, 4) activities of immunocaptured respiratory complexes, and 5) mitochondrial membrane potential and redox status in primary human hepatocytes. Phenformin was the most cytotoxic of the three with buformin showing moderate toxicity, and metformin toxicity only at mM concentrations.

Effect of the multitargeted tyrosine kinase inhibitors imatinib, dasatinib, sunitinib, and sorafenib on mitochondrial function in isolated rat heart mitochondria and H9c2 cells.

Cardiovascular disease has recently been suggested to be a significant complication of cancer treatment with several kinase inhibitors. In some cases, the mechanisms leading to cardiotoxicity are postulated to include mitochondrial dysfunction, either as a primary or secondary effect. Detecting direct effects on mitochondrial function, such as uncoupling of oxidative phosphorylation or inhibition of electron transport chain components, as well as identifying targets within the mitochondrial electron transport chain, can be accomplished in vitro.

In vitro assessment of mitochondrial dysfunction and cytotoxicity of nefazodone, trazodone, and buspirone.

Mitochondrial toxicity is increasingly implicated in a host of drug-induced organ toxicities, including hepatotoxicity. Nefazodone was withdrawn from the U.S.

The significance of mitochondrial toxicity testing in drug development.

Mitochondrial dysfunction is increasingly implicated in the etiology of drug-induced toxicities. Members of diverse drug classes undermine mitochondrial function, and among the most potent are drugs that have been withdrawn from the market, or have received Black Box warnings from the FDA. To avoid mitochondrial liabilities, routine screens need to be positioned within the drug-development process.

Mitochondrial impairment by PPAR agonists and statins identified via immunocaptured OXPHOS complex activities and respiration.

Mitochondrial impairment is increasingly implicated in the etiology of toxicity caused by some thiazolidinediones, fibrates, and statins. We examined the effects of members of these drug classes on respiration of isolated rat liver mitochondria using a phosphorescent oxygen sensitive probe and on the activity of individual oxidative phosphorylation (OXPHOS) complexes using a recently developed immunocapture technique. Of the six thiazolidinediones examined, ciglitazone, troglitazone, and darglitazone potently disrupted mitochondrial respiration.

Mitochondrial mechanisms of estrogen neuroprotection.

Oxidative stress, bioenergetic failure and mitochondrial dysfunction are all implicated in the etiology of neurodegenerative diseases such as Alzheimer's disease (AD). The mitochondrial involvement in neurodegenerative diseases reflects the regulatory role mitochondrial failure plays in both necrotic cell death and apoptosis. The potent feminizing hormone, 17 beta-estradiol (E2), is neuroprotective in a host of cell and animal models of stroke and neurodegenerative diseases.

Circumventing the Crabtree effect: replacing media glucose with galactose increases susceptibility of HepG2 cells to mitochondrial toxicants.

Many highly proliferative cells generate almost all ATP via glycolysis despite abundant O(2) and a normal complement of fully functional mitochondria, a circumstance known as the Crabtree effect. Such anaerobically poised cells are resistant to xenobiotics that impair mitochondrial function, such as the inhibitors rotenone, antimycin, oligomycin, and compounds like carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), that uncouple the respiratory electron transfer system from phosphorylation. These cells are also resistant to the toxicity of many drugs whose deleterious side effect profiles are either caused, or exacerbated, by impairment of mitochondrial function.

Strategies to reduce late-stage drug attrition due to mitochondrial toxicity.

Mitochondrial dysfunction is increasingly implicated in the etiology of drug-induced toxicities and negative side-effect profiles. Early identification of mitochondrial liabilities for new chemical entities is therefore crucial for avoiding late-stage attrition during drug development. Limitations of traditional methods for assessing mitochondrial dysfunction have discouraged routine evaluation of mitochondrial liabilities.

Novel mechanisms for estrogen-induced neuroprotection.

Estrogens are gonadal steroid hormones that are present in the circulation of both males and females and that can no longer be considered within the strict confines of reproductive function. In fact, the bone, the cardiovascular system, and extrahypothalamic regions of the brain are now well-established targets of estrogens. Among the numerous aspects of brain function regulated by estrogens are their effects on mood, cognitive function, and neuronal viability.

Neuroprotective effects of 17beta-estradiol and nonfeminizing estrogens against H2O2 toxicity in human neuroblastoma SK-N-SH cells.

Neuroprotective effects of estrogens have been shown in various in vitro and in vivo models, but the mechanisms underlying protection by estrogen are not clear. Mounting evidence suggests antioxidant effects contribute to the neuroprotective effects of estrogens. In the present study, we assessed the protective effects of estrogens against H2O2-induced toxicity in human neuroblastoma cells and the potential mechanisms involved in this protection.

High-throughput assessment of mitochondrial membrane potential in situ using fluorescence resonance energy transfer.

Mitochondrial dysfunction causes dozens of debilitating diseases, and is implicated in the etiology of type 2 diabetes, Parkinson's, and Alzheimer's diseases, among others. However, development of mitochondrially targeted therapeutic agents has been impeded by the lack of high-throughput screening techniques that are capable of distinguishing in intact cells the mitochondrial membrane potential (deltapsi(m)) from the plasma membrane potential, (deltapsi(p)). We report here a fluorescence resonance energy transfer (FRET) assay that specifically monitors deltapsi(m) that is not confounded by background signal arising from potentiometric dye responding to deltapsi(p).

Development of 17alpha-estradiol as a neuroprotective therapeutic agent: rationale and results from a phase I clinical study.

17alpha-estradiol (17alpha-E2) differs from its isomer, the potent feminizing hormone 17beta-estradiol (17beta-E2), only in the stereochemistry at one carbon, but this is sufficient to render it at least 200-fold less active as a transactivating hormone. Despite its meager hormonal activity, 17alpha-E2 is as potent as 17beta-E2 in protecting a wide variety of cell types, including primary neurons, from a diverse array of lethal and etiologically relevant stressors, including amyloid toxicity, serum withdrawal, oxidative stress, excitotoxicity, and mitochondrial inhibition, among others. Moreover, both estradiol isomers have shown efficacy in animal models of stroke, Alzheimer's disease (AD), and Parkinson's disease (PD).

Mitochondria play a central role in estrogen-induced neuroprotection.

Oxidative stress, bioenergetic impairment and mitochondrial failure have all been implicated in the etiology of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD), as well as retinal degeneration in glaucoma and retinitis pigmentosa. Moreover, at least 75 debilitating, and often lethal, diseases are directly attributable to deletions or mutations in mitochondrial DNA, or in nuclear-encoded proteins destined for delivery to the mitochondria. Such widespread mitochondrial involvement in disease reflects the regulatory position mitochondrial failure plays in both acute necrotic cell death, and in the less catastrophic process of apoptosis.

Photoreceptor preservation in the S334ter model of retinitis pigmentosa by a novel estradiol analog.

The cytoprotective activity of MITO-4565, a novel, non-hormonal, estradiol derivative, was evaluated in the S334ter transgenic model of retinitis pigmentosa (RP). Progressive blindness in RP is due to apoptotic death of the photoreceptors, a process mimicked by the animal models [Portera-Cailliau C, Sung C-H, Nathans J, Adler R. Apoptotic photoreceptor cell death in mouse models of retinitis pigmentosa.

Mitochondrial localization of estrogen receptor beta.

Estrogen receptors (ERs) are believed to be ligand-activated transcription factors belonging to the nuclear receptor superfamily, which on ligand binding translocate into the nucleus and activate gene transcription. To date, two ERs have been identified: ERalpha and ERbeta. ERalpha plays major role in the estrogen-mediated genomic actions in both reproductive and nonreproductive tissue, whereas the function of ERbeta is still unclear.

Oxidative damage to human lens epithelial cells in culture: estrogen protection of mitochondrial potential, ATP, and cell viability.

Purpose: Epidemiologic studies demonstrate a higher incidence of cataracts in estrogen-deprived postmenopausal women, but the mechanism for the increased risk of cataracts is unclear. An elevated level of H(2)O(2) in aqueous humor and whole lenses has been associated with cataractogenesis. In the present study, for the first time, the protective effect of estrogens against oxidative stress were tested in cultured human lens epithelial cells (HLECs).

PHOTOBIOLOGY OF THE SYMBIOTIC SEA ANEMONE, ANTHOPLEURA ELEGANTISSIMA: DEFENSES AGAINST PHOTODYNAMIC EFFECTS, AND SEASONAL PHOTOACCLIMATIZATION.

The sea anemone Anthopleura elegantissima, which contains photosynthetic symbionts (zooxanthellae), responds both biochemically and behaviorally to the combined environmental stresses of exposure to sunlight and photosynthetically generated hyperbaric O. Activities of the enzymes superoxide dismutase (SOD) and catalase, which act in concert as defenses against oxygen toxicity, parallel the distribution of chlorophyll. A.