A mitochondrial uncoupler prodrug protects dopaminergic neurons and improves functional outcome in a mouse model of Parkinson's disease

Sorafenib extends the lifespan of C. elegans through mitochondrial uncoupling mechanism

Sorafenib is a targeted anticancer drug in clinic. Low-dose sorafenib has been reported to activate AMPK through inducing mitochondrial uncoupling without detectable toxicities. AMPK activation has been the approach for extending lifespan, therefore, we investigated the effect of sorafenib on lifespan and physical activity of C. elegans and the underlying mechanisms. In the present study, we found that the effect of sorafenib on C. elegans lifespan was typically hermetic. Sorafenib treatment at higher concentrations (100 μM) was toxic but at lower concentrations (1, 2.5, 5 μM) was beneficial to C. elegans. Sorafenib (1 μM) treatment for whole-life period extended C. elegans lifespan and improved C. elegans physical activity as manifested by increasing pharyngeal pumping and body movement, preserving intestinal barrier integrity, muscle fibers organization and mitochondrial morphology. In addition, sorafenib (1 μM) treatment enhanced C. elegans stress resistance. Sorafenib activated AMPK through inducing mitochondrial uncoupling in C. elegans. Sorafenib treatment activated DAF-16, SKN-1, and increased SOD-3, HSP-16.2, GST-4 expression in C. elegans. Sorafenib treatment induced AMPK-dependent autophagy in C. elegans. We conclude that low-dose sorafenib protects C. elegans against aging through activating AMPK/DAF-16 dependent anti-oxidant pathways and stimulating autophagy responses. Low-dose sorafenib could be a strategy for treating aging and aging-related diseases.

The hormesis principle of neuroplasticity and neuroprotection

Animals live in habitats fraught with a range of environmental challenges to their bodies and brains. Accordingly, cells and organ systems have evolved stress-responsive signaling pathways that enable them to not only withstand environmental challenges but also to prepare for future challenges and function more efficiently. These phylogenetically conserved processes are the foundation of the hormesis principle, in which single or repeated exposures to low levels of environmental challenges improve cellular and organismal fitness and raise the probability of survival. Hormetic principles have been most intensively studied in physical exercise but apply to numerous other challenges known to improve human health (e.g., intermittent fasting, cognitive stimulation, and dietary phytochemicals). Here we review the physiological mechanisms underlying hormesis-based neuroplasticity and neuroprotection. Approaching natural resilience from the lens of hormesis may reveal novel methods for optimizing brain function and lowering the burden of neurological disorders.

Postictal hypoxia involves reactive oxygen species and is ameliorated by chronic mitochondrial uncoupling

Prolonged severe hypoxia follows brief seizures and represents a mechanism underlying several negative postictal manifestations without interventions. Approximately 50% of the postictal hypoxia phenomenon can be accounted for by arteriole vasoconstriction. What accounts for the rest of the drop in unbound oxygen is unclear. Here, we determined the effect of pharmacological modulation of mitochondrial function on tissue oxygenation in the hippocampus of rats after repeatedly evoked seizures. Rats were treated with mitochondrial uncoupler 2,4 dinitrophenol (DNP) or antioxidants. Oxygen profiles were recorded using a chronically implanted oxygen-sensing probe, before, during, and after seizure induction. Mitochondrial function and redox tone were measured using in vitro mitochondrial assays and immunohistochemistry. Postictal cognitive impairment was assessed using the novel object recognition task. Mild mitochondrial uncoupling by DNP raised hippocampal oxygen tension and ameliorated postictal hypoxia. Chronic DNP also lowered mitochondrial oxygen-derived reactive species and oxidative stress in the hippocampus during postictal hypoxia. Uncoupling the mitochondria exerts therapeutic benefits on postictal cognitive dysfunction. Finally, antioxidants do not affect postictal hypoxia, but protect the brain from associated cognitive deficits. We provided evidence for a metabolic component of the prolonged oxygen deprivation that follow seizures and its pathological sequelae. Furthermore, we identified a molecular underpinning of this metabolic component, which involves excessive oxygen conversion into reactive species. Mild mitochondrial uncoupling may be a potential therapeutic strategy to treat the postictal state where seizure control is absent or poor.

2,4-Dinitrophenol does not exert neuro-regenerative potential in experimental autoimmune neuritis

OBJECTIVE

We evaluated the potential neuro-regenerative effects of the mitochondrial uncoupler 2,4-Dinitrophenol in experimental autoimmune neuritis, an animal model for an acute autoimmune neuropathy.

METHODS

Experimental autoimmune neuritis was induced in Lewis rats. Different concentrations of 2,4-Dinitrophenol (1 mg/kg, 0.1 mg/kg and 0.01 mg/kg) were applied during the recovery phase of the neuritis (at days 18, 22 and 26) and compared to the vehicle. Any effects were assessed through functional, electrophysiological, and morphological analysis via electron microscopy of all groups at day 30. Additional immune-histochemical analysis of inflammation markers and remyelination of the sciatic nerves were performed for the dosage of 1 mg/kg and control.

RESULTS

No enhancement of functional or electrophysiological recovery was observed in all 2,4-Dinitrophenol-treated groups. Cellular inflammation markers of T cells (CD3+) were comparable to control, and an increase of macrophages (IbA1+) invasion in the sciatic nerves was observed. Treatment with 2,4-Dinitrophenol reduced axonal swelling in myelinated and unmyelinated fibers with an increased production of brain-derived neurotrophic factor.

CONCLUSION

Our findings do not support the hypothesis that repurposing of the mitochondrial uncoupler 2,4-Dinitrophenol exerts functionally relevant neuro-regenerative effects in autoimmune neuritis.

Mild pentachlorophenol-mediated uncoupling of mitochondria depletes ATP but does not cause an oxidized redox state or dopaminergic neurodegeneration in Caenorhabditis elegans

Aims

Mitochondrial dysfunction is implicated in several diseases, including neurological disorders such as Parkinson's disease. However, there is uncertainty about which of the many mechanisms by which mitochondrial function can be disrupted may lead to neurodegeneration. Pentachlorophenol (PCP) is an organic pollutant reported to cause mitochondrial dysfunction including oxidative stress and mitochondrial uncoupling. We investigated the effects of PCP exposure in Caenorhabditis elegans, including effects on mitochondria and dopaminergic neurons. We hypothesized that mild mitochondrial uncoupling by PCP would impair bioenergetics while decreasing oxidative stress, and therefore would not cause dopaminergic neurodegeneration.

Results

A 48-hour developmental exposure to PCP causing mild growth delay (∼10 % decrease in growth during 48 h, covering all larval stages) reduced whole-organism ATP content > 50 %, and spare respiratory capacity ∼ 30 %. Proton leak was also markedly increased. These findings suggest a main toxic mechanism of mitochondrial uncoupling rather than oxidative stress, which was further supported by a concomitant shift toward a more reduced cellular redox state measured at the whole organism level. However, exposure to PCP did not cause dopaminergic neurodegeneration, nor did it sensitize animals to a neurotoxic challenge with 6-hydroxydopamine. Whole-organism uptake and PCP metabolism measurements revealed low overall uptake of PCP in our experimental conditions (50 μM PCP in the liquid exposure medium resulted in organismal concentrations of < 0.25 μM), and no measurable production of the oxidative metabolites tetra-1,4-benzoquinone and tetrachloro-p-hydroquinone.

Innovation

This study provides new insights into the mechanistic interplay between mitochondrial uncoupling, oxidative stress, and neurodegeneration in C. elegans. These findings support the premise of mild uncoupling-mediated neuroprotection, but are inconsistent with proposed broad "mitochondrial dysfunction"-mediated neurodegeneration models, and highlight the utility of the C. elegans model for studying mitochondrial and neurotoxicity.

Conclusions

Developmental exposure to pentachlorophenol causes gross toxicological effects (growth delay and arrest) at high levels. At a lower level of exposure, still causing mild growth delay, we observed mitochondrial dysfunction including uncoupling and decreased ATP levels. However, this was associated with a more-reduced cellular redox tone and did not exacerbate dopaminergic neurotoxicity of 6-hydroxydopamine, instead trending toward protection. These findings may be informative of efforts to define nuanced mitochondrial dysfunction-related adverse outcome pathways that will differ depending on the form of initial mitochondrial toxicity.

Prodrug Therapies for Infectious and Neurodegenerative Diseases

Prodrugs are bioreversible drug derivatives which are metabolized into a pharmacologically active drug following chemical or enzymatic modification. This approach is designed to overcome several obstacles that are faced by the parent drug in physiological conditions that include rapid drug metabolism, poor solubility, permeability, and suboptimal pharmacokinetic and pharmacodynamic profiles. These suboptimal physicochemical features can lead to rapid drug elimination, systemic toxicities, and limited drug-targeting to disease-affected tissue. Improving upon these properties can be accomplished by a prodrug design that includes the careful choosing of the promoiety, the linker, the prodrug synthesis, and targeting decorations. We now provide an overview of recent developments and applications of prodrugs for treating neurodegenerative, inflammatory, and infectious diseases. Disease interplay reflects that microbial infections and consequent inflammation affects neurodegenerative diseases and vice versa, independent of aging. Given the high prevalence, personal, social, and economic burden of both infectious and neurodegenerative disorders, therapeutic improvements are immediately needed. Prodrugs are an important, and might be said a critical tool, in providing an avenue for effective drug therapy.

Mild Mitochondrial Uncoupling Decreases Experimental Atherosclerosis, A Proof of Concept

Aim: Atherosclerosis is responsible for high morbidity and mortality rates around the world. Local arterial oxidative stress is involved in all phases of atherosclerosis development. Mitochondria is a relevant source of the oxidants, particularly under certain risky conditions, such as hypercholesterolemia. The aim of this study was to test whether lowering the production of mitochondrial oxidants by induction of a mild uncoupling can reduce atherosclerosis in hypercholesterolemic LDL receptor knockout mice.

Methods: The mice were chronically treated with very low doses of DNP (2,4-dinitrophenol) and metabolic, inflammatory and redox state markers and atherosclerotic lesion sizes were determined.

Results: The DNP treatment did not change the classical atherosclerotic risk markers, such as plasma lipids, glucose homeostasis, and fat mass, as well as systemic inflammatory markers. However, the DNP treatment diminished the production of mitochondrial oxidants, systemic and tissue oxidative damage markers, peritoneal macrophages and aortic rings oxidants generation. Most importantly, development of spontaneous and diet-induced atherosclerosis (lipid and macrophage content) were significantly decreased in the DNP-treated mice. In vitro, DNP treated peritoneal macrophages showed decreased H₂O₂ production, increased anti-inflammatory cytokines gene expression and secretion, increased phagocytic activity, and decreased LDL-cholesterol uptake.

Conclusions: These findings are a proof of concept that activation of mild mitochondrial uncoupling is sufficient to delay the development of atherosclerosis under the conditions of hypercholesterolemia and oxidative stress. These results promote future approaches targeting mitochondria for the prevention or treatment of atherosclerosis.

The neuroprotective effects of isoquercitrin purified from apple pomace by high-speed countercurrent chromatography in the MPTP acute mouse model of Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease. Researchers have shown that oxidative stress and apoptosis play an important role in the Parkinson's disease process. Isoquercitrin (quercetin-3-O-β-d-glucopyranoside) is a natural flavonol compound and one of the main active ingredients of agricultural waste apple pomace. Increasing evidence indicates that this compound possesses anti-oxidation, anti-aging, and anti-inflammation properties. In this study, isoquercitrin was purified from apple pomace by high-speed countercurrent chromatography and its neuroprotective effect on Parkinson's disease was investigated in MPTP-induced acute mouse models. It was found that isoquercitrin ameliorated the animal behaviors against MPTP-induced neurotoxicity, mitigated the loss of dopamine neurons induced by MPTP, increased tyrosine hydroxylase and dopamine transporter expression, reduced the pro-apoptotic signaling molecule bax expression and inhibited MPTP-triggered oxidative stress. Our results demonstrated that isoquercitrin has protective effects on the MPTP subacute model mouse, which might be partially mediated through the actions of anti-oxidation and anti-apoptosis. Isoquercitrin might be a new promising protective drug for the improvement of Parkinson's disease.

Deletion of Mitochondrial Uncoupling Protein 2 Exacerbates Mitochondrial Damage in Mice Subjected to Cerebral Ischemia and Reperfusion Injury under both Normo- and Hyperglycemic Conditions

Deletion of mitochondrial uncoupling protein 2 (UCP2) has been shown to aggravate ischemic damage in the brain. However, the underlying mechanisms are not fully understood. The objective of this study is to explore the impact of homozygous UCP2 deletion (UCP2^-/-) on mitochondrial fission and fusion dynamic balance in ischemic mice under normo- and hyperglycemic conditions. UCP2^-/- and wildtype mice were subjected to a 60 min middle cerebral artery occlusion (MCAO) and allowed reperfusion for 6h, 24h and 72h. Our results demonstrated that deletion of UCP2 enlarged infarct volumes and increased numbers of cell death in both normo- and hyperglycemic ischemic mice compared with their wildtype counterparts subjected to the same duration of ischemia and reperfusion. The detrimental effects of UCP deletion were associated with increased ROS production, elevated mitochondrial fission markers Drp1 and Fis1 and suppressed fusion markers Opa1 and Mfn2 in UCP2^-/- mice. Electron microscopic study demonstrated a marked mitochondrial swolling after 6h of reperfusion in UCP2^-/- mice, contrasting to a mild mitochondrial swolling in wildtype ischemic animals. It is concluded that the exacerbating effects of UCP2^-/- on ischemic outcome in both normo- and hyperglycemic animals are associated with increased ROS production, disturbed mitochondrial dynamic balance towards fission and early damage to mitochondrial ultrastructure.

Hormesis: A potential strategic approach to the treatment of neurodegenerative disease

This review describes neuroprotective effects mediated by pre- and post-conditioning-induced processes that act via the quantitative features of the hormetic dose response. These lead to the development of acquired resilience that can protect neuronal systems from endogenous and exogenous stresses and insult. Particular attention is directed to issues of dose optimization, inter-individual variation, and potential ways to further study and employ hormetic-based preconditioning approaches in medical and public health efforts to treat and prevent neurodegenerative disease.

Therapeutic innovation in Parkinson's disease: a 2020 update on disease-modifying approaches

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting more than 10 million patients worldwide. Despite increasing improvements in disease management, a huge medical need still exists as its relentless progression cannot be delayed by current treatments. Therefore, scientists, clinicians, and pharmaceutical companies are hunting new drugs with 'disease-modifying' properties.

AREAS COVERED

This review concentrates on new therapeutics - excluding cell and gene therapies - under investigation for PD with 'disease-modifying' potential. This is a global, comprehensive picture of the current innovative drug pipeline, where the main preclinical and clinical data available are provided. Drug candidates presented include α-synuclein modulating agents, neuroprotective agents and neuroinflammation modulators, kinase modulators, neurotrophic factors, and drugs acting on emerging targets.

EXPERT OPINION

There is excitement for agents with 'disease-modifying' properties and the authors found more than 130 assets, not including cell and gene therapies under investigation - most of them still in preclinical development - meaning that the science is progressing multiple, diverse new opportunities. Many limitations hamper the successful development of these drug candidates such as the translational accuracy of preclinical models, the current clinical development paradigm as well as the lack of biomarkers to be used in diagnosis and therapy management.

Manipulating Cellular Energetics to Slow Aging of Tissues and Organs

Up to now numerous studies in the field of gerontology have been published. Nevertheless, a well-known food restriction remains the most reliable and efficient way of lifespan extension. Physical activity is also a well-documented anti-aging intervention being especially efficient in slowing down the age-associated decline of skeletal muscle mass. In this review we focus on the molecular mechanisms of the effect of physical exercise on muscle tissues. We also discuss the possibilities of pharmacological extension of this effect to the rest of the tissues. During the exercise, the level of ATP decreases triggering activation of AMP-dependent protein kinase (AMPK). This kinase stimulates antioxidant potential of the cells and their mitochondrial respiratory capacity. The exercise also induces mild oxidative stress, which, in turn, mediates the stimulation via hormetic response. Furthermore, during the exercise cells generate activators of mammalian target of rapamycin (mTOR). The intracellular ATP level increases during the rest periods between exercises thus promoting mTOR activation. Therefore, regular exercise intermittently activates anti-oxidant defenses and mitochondrial biogenesis (via AMPK and the hormetic response) of the muscle tissue, as well as its proliferative potential (via mTOR), which, in turn, impedes the age-dependent muscle atrophy. Thus, the intermittent treatment with activators of (i) AMPK combined with the inducers of hormetic response and of (ii) mTOR might partly mimic the effects of physical exercise. Importantly, pharmacological activation of AMPK takes place in the absence of ATP level decrease. The use of uncouplers of respiration and oxidative phosphorylation at the phase of AMPK activation could also prevent negative consequences of the cellular hyper-energization. It is believed that the decline of both antioxidant and proliferative potentials of the cells causes the age-dependent decline of multiple tissues, rather than only the muscular one. We argue that the approach above is applicable for the majority of tissues in an organism.