Mitochondrial modulators in experimental Huntington’s disease: reversal of mitochondrial dysfunctions and cognitive deficits

Mitostasis in age-associated neurodegeneration

Mitochondria are essential organelles that play crucial roles in various metabolic and signalling pathways. Proper neuronal function is highly dependent on the health of these organelles. Of note, the intricate structure of neurons poses a critical challenge for the transport and distribution of mitochondria to specific energy-intensive domains, such as synapses and dendritic appendages. When faced with chronic metabolic challenges and bioenergetic deficits, neurons undergo degeneration. Unsurprisingly, disruption of mitostasis, the process of maintaining cellular mitochondrial content and function within physiological limits, has been implicated in the pathogenesis of several age-associated neurodegenerative disorders. Indeed, compromised integrity and metabolic activity of mitochondria is a principal hallmark of neurodegeneration. In this review, we survey recent findings elucidating the role of impaired mitochondrial homeostasis and metabolism in the onset and progression of age-related neurodegenerative disorders. We also discuss the importance of neuronal mitostasis, with an emphasis on the major mitochondrial homeostatic and metabolic pathways that contribute to the proper functioning of neurons. A comprehensive delineation of these pathways is crucial for the development of early diagnostic and intervention approaches against neurodegeneration.

A comprehensive perspective of Huntington's disease and mitochondrial dysfunction

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease. It is caused by the expansion of the CAG trinucleotide repeat sequence in the HTT gene. HD mainly manifests as involuntary dance-like movements and severe mental disorders. As it progresses, patients lose the ability to speak, think, and even swallow. Although the pathogenesis is unclear, studies have found that mitochondrial dysfunctions occupy an important position in the pathogenesis of HD. Based on the latest research advances, this review sorts out and discusses the role of mitochondrial dysfunction on HD in terms of bioenergetics, abnormal autophagy, and abnormal mitochondrial membranes. This review provides researchers with a more complete perspective on the mechanisms underlying the relationship between mitochondrial dysregulation and HD.

Pharmacological Progress of Mitophagy Regulation

With the advancement in novel drug discovery, biologically active compounds are considered pharmacological tools to understand complex biological mechanisms and the identification of potent therapeutic agents. Mitochondria boast a central role in different integral biological processes and mitochondrial dysfunction is associated with multiple pathologies. It is, therefore, prudent to target mitochondrial quality control mechanisms by using pharmacological approaches. However, there is a scarcity of biologically active molecules, which can interact with mitochondria directly. Currently, the chemical compounds used to induce mitophagy include oligomycin and antimycin A for impaired respiration and acute dissipation of mitochondrial membrane potential by using CCCP/FCCP, the mitochondrial uncouplers. These chemical probes alter the homeostasis of the mitochondria and limit our understanding of the energy regulatory mechanisms. Efforts are underway to find molecules that can bring about selective removal of defective mitochondria without compromising normal mitochondrial respiration. In this report, we have tried to summarize and status of the recently reported modulators of mitophagy.

Mitochondrial dysfunctions, oxidative stress and neuroinflammation as therapeutic targets for neurodegenerative diseases: An update on current advances and impediments

Neurodegenerative diseases (NDs) such as Alzheimer disease (AD), Parkinson disease (PD), and Huntington disease (HD) represent a major socio-economic challenge in view of their high prevalence yet poor treatment outcomes affecting quality of life. The major challenge in drug development for these NDs is insufficient clarity about the mechanisms involved in pathogenesis and pathophysiology. Mitochondrial dysfunction, oxidative stress and inflammation are common pathways that are linked to neuronal abnormalities and initiation of these diseases. Thus, elucidating the shared initial molecular and cellular mechanisms is crucial for recognizing novel remedial targets, and developing therapeutics to impede or stop disease progression. In this context, use of multifunctional compounds at early stages of disease development unclogs new avenues as it acts on act on multiple targets in comparison to single target concept. In this review, we summarize overview of the major findings and advancements in recent years focusing on shared mechanisms for better understanding might become beneficial in searching more potent pharmacological interventions thereby reducing the onset or severity of various NDs.

Investigation of alpha-lipoic acid effect on memory impairment considering strain-dependent differences in mice

AIMS

Memory impairment is regarded as one of the most challenging neurological disorders. The present study aimed to investigate behavioral and biochemical differences among similar mouse strains following Scopolamine (SCO) exposure as a widespread memory disturbing agent, and a supremely potent antioxidant, alpha-lipoic acid (ALA).

MATERIALS AND METHODS

Three sets of mouse strains (i.e. SW, NMRI, and NIH mice) were subjected to 2 mg/kg intraperitoneal SCO and/or 50 mg/kg ALA 30 min before each Morris Water Maze (MWM) trial for five consecutive days. Upon completion of the trials, the hippocampal region of the animals was dissected for histopathological and biochemical analyses.

KEY FINDINGS

The results exhibited significant impairments caused by SCO in behavioral tests, including probe test, escape latency, and distance traveled in two strains of NMRI and NIH. Nevertheless, at swimming speed, SCO had no meaningful effect on SW and NIH strains. The level of oxidative stress parameters including MDA, ROS, and SOD increased, FRAP and TTM levels related to the hippocampus decreased. There was also a significant increase in hippocampal acetylcholinesterase levels, ADP/ATP ratio, p-NFkB, and Cyt-c. Conversely, ALA administration resulted in a significant improvement in SCO-induced spatial learning and memory impairments only in the SW and NIH mice, which was associated with a significant reduction in hippocampal AChE activity, ADP/ATP ratio, ROS and MDA levels, and SOD activity.

SIGNIFICANCE

In addition of highlighting the efficacious role of ALA in cognitive functions, the findings of this study signified the behavioral dissimilarities among similar animal strains in case of different chemical exposures.

Natural products targeting mitochondria: emerging therapeutics for age-associated neurological disorders

Mitochondria are the primary source of energy production in the brain thereby supporting most of its activity. However, mitochondria become inefficient and dysfunctional with age and to a greater extent in neurological disorders. Thus, mitochondria represent an emerging drug target for many age-associated neurological disorders. This review summarizes recent advances (covering from 2010 to May 2020) in the use of natural products from plant, animal, and microbial sources as potential neuroprotective agents to restore mitochondrial function. Natural products from diverse classes of chemical structures are discussed and organized according to their mechanism of action on mitochondria in terms of modulation of biogenesis, dynamics, bioenergetics, calcium homeostasis, and membrane potential, as well as inhibition of the oxytosis/ferroptosis pathway. This analysis emphasizes the significant value of natural products for mitochondrial pharmacology as well as the opportunities and challenges for the discovery and development of future neurotherapeutics.

Naringenin mitigates behavioral alterations and provides neuroprotection against 3-nitropropinoic acid-induced Huntington's disease like symptoms in rats

BACKGROUND

Naringenin is a powerful antioxidant and anti-inflammatory flavonoid which has been widely used as a therapeutic agent in various toxic models. However, few studies have clearly discussed the neuromodulatory effects of naringenin against different neurodegenerative disorders.

AIM

We investigated the neuroprotective efficacy of naringenin against 3-nitropropionic acid (3-NP)-induced neurobehavioral, biochemical and histopathological alterations in rats.

METHODS

Albino Wistar rats were randomly divided into three experimental groups. Group 1, the vehicle administered group, received saline. Group 2 received 3-NP (20 mg/kg body weight, i.p.) for 4 consecutive days. Group 3 received naringenin (50 mg/kg body weight, p.o.) twice daily for a period of 4 days, 30 min before and 6 h after the 3-NP administration. On the 5th day, neurobehavioral experiments were performed to access the behavioral outcomes and the striatum tissue was used for analysis of the monoamine oxidase (MAO) activity and serotonin (5-HT) levels. In addition, astrocytes activation was observed by glial fibrillary acidic protein (GFAP) immunostaining.

RESULTS

Our results showed that naringenin co-treatment provides neuroprotection against 3-NP-induced neurological disorders. Naringenin also increased the MAO activity and 5-HT levels in the striatum. Moreover, co-treatment with naringenin reduced the expression of GFAP protein in the striatal part and significantly attenuated the neuronal cell death. The findings of the present study suggest that naringenin provides neuroprotection and mitigates neurobehavioral alterations in experimental rats.

CONCLUSION

The results show that co-treatment with naringenin ameliorates 3-NP-induced HD-like symptoms in rats.

Effects of lipoic acid supplementation on age- and iron-induced memory impairment, mitochondrial DNA damage and antioxidant responses

PURPOSE

To investigate the effects of lipoic acid (LA) supplementation during adulthood combined with supplementation later in life or LA administration only at old age on age-induced cognitive dysfunction, mitochondrial DNA deletions, caspase 3 and antioxidant response enzymes expression in iron-treated rats.

METHODS

Male rats were submitted to iron treatment (30 mg/kg body wt of Carbonyl iron) from 12 to 14th post-natal days. Iron-treated rats received LA supplementation (50 mg/kg, daily) in adulthood and old age or at old age only for 21 days. Memory, mitochondrial DNA (mtDNA) complex I deletions, caspase 3 mRNA expression and antioxidant response enzymes mRNA expression were analyzed in the hippocampus.

RESULTS

LA administration in adulthood combined with treatment later in life was able to reverse age-induced effects on object recognition and inhibitory avoidance memory, as well as on mtDNA deletions, nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression, and antioxidant enzymes disruption induced by iron in aged rats. LA treatment only at old age reversed iron-induced effects to a lesser extent when compared to the combined treatment.

CONCLUSION

The present findings support the view that LA supplementation may be considered as an adjuvant against mitochondrial damage and cognitive decline related to aging and neurodegenerative disorders.

Neuroprotective Effects of Carnitine and Its Potential Application to Ameliorate Neurotoxicity

Carnitine is an essential metabolite that is absorbed from the diet and synthesized in the kidney, liver, and brain. It ferries fatty acids across the mitochondrial membrane to undergo β-oxidation. Carnitine has been studied as a therapy or protective agent for many neurological diseases and neurotoxicity (e.g., prolonged anesthetic exposure-induced developmental neurotoxicity in preclinical models). Preclinical and clinical data support the notion that carnitine or acetyl carnitine may improve a patient's quality of life through increased mitochondrial respiration, release of neurotransmitters, and global gene expression changes, showing the potential of carnitine beyond its approved use to treat primary and secondary carnitine deficiency. In this review, we summarize the beneficial effects of carnitine or acetyl carnitine on the central nervous system, highlighting protective effects against neurotoxicity-induced damage caused by various chemicals and encouraging a thorough evaluation of carnitine use as a therapy for patients suffering from neurotoxicant exposure.

Dietary Intake, Mediterranean Diet Adherence and Caloric Intake in Huntington's Disease: A Review

Decades of research and experimental studies have investigated Huntington’s disease (HD), a rare neurodegenerative disease. Similarly, several studies have investigated whether high/moderate adherence to the Mediterranean Diet and specific macro and micronutrients can decrease cognitive loss and provide a neuroprotective function to neurons. This review systematically identifies and examines studies that have investigated Mediterranean Diet adherence, micro- and macronutrients, supplementation and caloric intake in people with HD, in order to identify if dietary exposures resulted in improvement of disease symptoms, a delay in age of onset or if they contributed to an earlier age of onset in people with HD. A systematic search of PubMed, Directory of open access journal and HubMed was performed independently by two reviewers using specific search terms criteria for studies. The identified abstracts were screened and the studies were included in the review if they satisfied predetermined inclusion criteria. Reference screening of included studies was also performed. A total of 18 studies were included in the review. A few studies found that patients who had high/moderate adherence to Mediterranean Diet showed a slight improvement in their Unified Huntington’s Disease Rating Scale and Total Functional Capacity. In addition, people with HD who had high Mediterranean Diet adherence showed an improvement in both cognitive and motor scores and had a better quality of life compared to patients who had low Mediterranean Diet adherence. Furthermore, a few studies showed that supplementation with specific nutrients, such as triheaptanoin, L-acetyl-carnitine and creatine, had no beneficial effect on the patients’ Unified Huntington’s Disease Rating Scale score. A few studies suggest that the Mediterranean Diet may confer a motor and cognitive benefit to people with HD. Unfortunately, there was little consistency among study findings. It is important for more research to be conducted to have a better understanding of which dietary exposures are beneficial and may result delaying age of onset or disease progression in people with HD.

Mitochondrial biology and the identification of biomarkers of Huntington's disease

Apart from finding novel compounds for treating Huntington's disease (HD) an important challenge at present consists in finding reliable read-outs or biomarkers that reflect key biological processes involved in HD pathogenesis. The core elements of HD biology, for example, HTT RNA levels or protein species can serve as biomarker, as could measures from biological systems or pathways in which Huntingtin plays an important role. Here we review the evidence for the involvement of mitochondrial biology in HD. The most consistent findings pertain to mitochondrial quality control, for example, fission/fusion. However, a convincing mitochondrial signature with biomarker potential is yet to emerge. This requires more research including in peripheral sources of human material, such as blood, or skeletal muscle.

Reactive Species in Huntington Disease: Are They Really the Radicals You Want to Catch?

Huntington disease (HD) is a neurodegenerative condition and one of the so-called rare or minority diseases, due to its low prevalence (affecting 1–10 of every 100,000 people in western countries). The causative gene, HTT, encodes huntingtin, a protein with a yet unknown function. Mutant huntingtin causes a range of phenotypes, including oxidative stress and the activation of microglia and astrocytes, which leads to chronic inflammation of the brain. Although substantial efforts have been made to find a cure for HD, there is currently no medical intervention able to stop or even delay progression of the disease. Among the many targets of therapeutic intervention, oxidative stress and inflammation have been extensively studied and some clinical trials have been promoted to target them. In the present work, we review the basic research on oxidative stress in HD and the strategies used to fight it. Many of the strategies to reduce the phenotypes associated with oxidative stress have produced positive results, yet no substantial functional recovery has been observed in animal models or patients with the disease. We discuss possible explanations for this and suggest potential ways to overcome it.

Reviewing Biochemical Implications of Normal and Mutated Huntingtin in Huntington's Disease

Huntingtin (Htt) is a multi-function protein of the brain. Normal Htt shows a common alpha-helical structure but conformational changes in the form with beta strands are the principal cause of Huntington's disease. Huntington's disease is a genetic neurological disorder caused by a repeated expansion of the CAG trinucleotide, causing instability in the N-terminal of the gene coding for the Huntingtin protein. The mutation leads to the abnormal expansion of the production of the polyglutamine tract (polyQ) resulting in the form of an unstable Huntingtin protein commonly referred to as mutant Huntingtin. Mutant Huntingtin is the cause of the complex neurological metabolic alteration of Huntington's disease, resulting in both the loss of all the functions of normal Huntingtin and the genesis of abnormal interactions due to the presence of this mutation. One of the problems arising from the misfolded Huntingtin is the increase in oxidative stress, which is common in many neurological diseases such as Alzheimer's, Parkinson's, Amyotrophic Lateral Sclerosis and Creutzfeldt-Jakob disease. In the last few years, the use of antioxidants had a strong incentive to find valid therapies for defence against neurodegenerations. Although further studies are needed, the use of antioxidant mixtures to counteract neuronal damages seems promising.

Sodium selenite protects from 3-nitropropionic acid-induced oxidative stress in cultured primary cortical neurons

Selenium (Se) is an essential trace element for humans; its intake is needed to allow the proper synthesis of 25 different selenoproteins that are necessary to the normal functioning of several organs, including the brain. Accordingly, decreased Se levels have been associated with neurological disorders. In the present study, we investigated the potential beneficial effects of Se, as sodium selenite, against 3-nitropropionic acid (3-NP)-induced oxidative stress in primary cultures of mouse cortical neurons. 3-NP treatment caused a significant decrease in cellular viability, which was accompanied by decreases in mitochondrial complex II activity and reduced glutathione (GSH) content, as well as increases in reactive oxygen species (ROS) generation and oxidized glutathione (GSSG) levels. Sodium selenite pretreatment (6 days) attenuated 3-NP-induced decrease in cell viability. In addition, sodium selenite pretreatment significantly protected against 3-NP-induced increase in ROS generation and decrease in GSH/GSSG ratio. Of note, sodium selenite pretreatment did not change 3-NP-induced decrease of mitochondrial complex II activity, suggesting that Se modulates secondary events resultant from 3-NP-induced mitochondrial dyshomeostasis. In addition, sodium selenite pretreatment significantly increased glutathione peroxidase (GPx) activity. Our data provide insights into the mechanism of protection by sodium selenite, which is related, at least in part, to GPx induction.

Indian Ginseng (Withania somnifera) supplementation ameliorates oxidative stress and mitochondrial dysfunctions in experimental model of stroke

Stroke is an increasingly prevalent clinical condition and second leading cause of death globally. The present study evaluated the therapeutic potential of Indian Ginseng, also known as Withania somnifera (WS), supplementation on middle cerebral artery occlusion (MCAO) induced mitochondrial dysfunctions in experimental model of ischemic stroke. Stroke was induced in animals by occluding the middle cerebral artery, followed by reperfusion injury. Ischemia reperfusion injury resulted in increased oxidative stress indicated by increased reactive oxygen species and protein carbonyl levels; compromised antioxidant system; in terms of reduced superoxide dismutase and catalase activity, along with reduction in GSH levels and the redox ratio, impaired mitochondrial functions and enhanced expression of apoptosis markers. Ischemia reperfusion injury induced mitochondrial dysfunctions in terms of (i) reduced activity of the mitochondrial respiratory chain enzymes, (ii) reduced histochemical staining of complex-II and IV, (iii) reduced in-gel activity of mitochondrial complex-I to V, (iv) mitochondrial structural changes in terms of increased mitochondrial swelling, reduced mitochondrial membrane potential and ultrastructural changes. Additionally, an increase in the activity of caspase-3 and caspase-9 was also observed, along with altered expression of apoptotic proteins Bcl-2 and Bax in MCAO animals. MCAO animals also showed significant impairment in cognitive functions assessed using Y maze test. WS pre-supplementation, on the other hand ameliorated MCAO induced oxidative stress, mitochondrial dysfunctions, apoptosis and cognitive impairments. The results show protective effect of WS pre-supplementation in ischemic stroke and are suggestive of its potential application in stroke management.

Age-related defects in short-term plasticity are reversed by acetyl-L-carnitine at the mouse calyx of Held

Hearing acuity and sound localization are affected by aging and may contribute to cognitive dementias. Although loss of sensorineural conduction is well documented to occur with age, little is known regarding short-term synaptic plasticity in central auditory nuclei. Age-related changes in synaptic transmission properties were evaluated at the mouse calyx of Held, a sign-inverting relay synapse in the circuit for sound localization, in juvenile adults (1 month old) and late middle-aged (18-21 months old) mice. Synaptic timing and short-term plasticity were severely disrupted in older mice. Surprisingly, acetyl-l-carnitine (ALCAR), an anti-inflammatory agent that facilitates mitochondrial function, fully reversed synaptic transmission delays and defects in short-term plasticity in aged mice to reflect transmission similar to that seen in juvenile adults. These findings support ALCAR supplementation as an adjuvant to improve short-term plasticity and potentially central nervous system performance in animals compromised by age and/or neurodegenerative disease.

Spermidine ameliorates the neuronal aging by improving the mitochondrial function in vitro

Changes in mitochondrial structure and function are the initial factors of cell aging. Spermidine has an antiaging effect, but its effect on neuronal aging and mitochondrial mechanisms is unclear. In this study, mouse neuroblastoma (N2a) cells were treated with d‑galactose (d‑Gal) to establish cell aging to investigate the antiaging effect and mechanisms of spermidine. Changes in the cell cycle and β-galactosidase activity were analyzed to evaluate the extent of cell aging. Stabilities of mitochondrial mRNA and mitochondrial membrane potential (MMP) were evaluated in the process of cell aging under different treatments. The mitochondrial function was also evaluated using the Seahorse Metabolic Analysis System combined with ATP production. The unfolded protein response (UPR) of the N2a cells was analyzed under different treatments. Results showed that spermidine pretreatment could delay the cell aging and could maintain the mitochondrial stability during d‑Gal treatment. Spermidine increased the proportion of cells in the S phase and maintained the MMP. The oxygen utilization and ATP production in the N2a cells were reduced by d‑Gal treatment but were partially rescued by the spermidine pretreatment. Spermidine ameliorated the N2a cell aging by promoting the autophagy and inhibiting the apoptosis except the UPR. These results showed that spermidine could ameliorate the N2a cell aging by maintaining the mitochondrial mRNA transcription, MMP and oxygen utilization during the d‑Gal treatment.

Mitochondria as pharmacological targets in Down syndrome

Mitochondria play a pivotal role in cellular energy-generating processes and are considered master regulators of cell life and death fate. Mitochondrial function integrates signalling networks in several metabolic pathways controlling neurogenesis and neuroplasticity. Indeed, dysfunctional mitochondria and mitochondrial-dependent activation of intracellular stress cascades are critical initiating events in many human neurodegenerative or neurodevelopmental diseases including Down syndrome (DS). It is well established that trisomy of human chromosome 21 can cause DS. DS is associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, molecular mechanisms responsible for mitochondrial damage and energy deficits have been identified and characterized in several DS-derived human cells and animal models of DS. Therefore, therapeutic strategies targeting mitochondria could have great potential for new treatment regimens in DS. The purpose of this review is to highlight recent studies concerning mitochondrial impairment in DS, focusing on alterations of the molecular pathways controlling mitochondrial function. We will also discuss the effects and molecular mechanisms of naturally occurring and chemically synthetized drugs that exert neuroprotective effects through modulation of mitochondrial function and attenuation of oxidative stress. These compounds might represent novel therapeutic tools for the modulation of energy deficits in DS.

Effects of endurance training on skeletal muscle mitochondrial function in Huntington disease patients

Background

Mitochondrial dysfunction may represent a pathogenic factor in Huntington disease (HD). Physical exercise leads to enhanced mitochondrial function in healthy participants. However, data on effects of physical exercise on HD skeletal muscle remains scarce. We aimed at investigating adaptations of the skeletal muscle mitochondria to endurance training in HD patients.

Methods

Thirteen HD patients and 11 healthy controls completed 26 weeks of endurance training. Before and after the training phase muscle biopsies were obtained from M. vastus lateralis. Mitochondrial respiratory chain complex activities, mitochondrial respiratory capacity, capillarization, and muscle fiber type distribution were determined from muscle samples.

Results

Citrate synthase activity increased during the training intervention in the whole cohort (P = 0.006). There was no group x time interaction for citrate synthase activity during the training intervention (P = 0.522). Complex III (P = 0.008), Complex V (P = 0.043), and succinate cytochrome c reductase (P = 0.008) activities increased in HD patients and controls by endurance training. An increase in mass-specific mitochondrial respiratory capacity was present in HD patients during the endurance training intervention. Overall capillary-to-fiber ratio increased in HD patients by 8.4% and in healthy controls by 6.4% during the endurance training intervention.

Conclusions

Skeletal muscle mitochondria of HD patients are equally responsive to an endurance-training stimulus as in healthy controls. Endurance training is a safe and feasible option to enhance indices of energy metabolism in skeletal muscle of HD patients and may represent a potential therapeutic approach to delay the onset and/or progression of muscular dysfunction.

Trial registration

ClinicalTrials.gov NCT01879267. Registered May 24, 2012.

Potential Therapeutic Effects of Lipoic Acid on Memory Deficits Related to Aging and Neurodegeneration

The aging process comprises a series of organic alterations, affecting multiple systems, including the nervous system. Aging has been considered the main risk factor for the advance of neurodegenerative diseases, many of which are accompanied by cognitive impairment. Aged individuals show cognitive decline, which has been associated with oxidative stress, as well as mitochondrial, and consequently energetic failure. Lipoic acid (LA), a natural compound present in food and used as a dietary supplement, has been considered a promising agent for the treatment and/or prevention of neurodegenerative disorders. In spite of a number of preclinical studies showing beneficial effects of LA in memory functioning, and pointing to its neuroprotective potential effect, to date only a few studies have examined its effects in humans. Investigations performed in animal models of memory loss associated to aging and neurodegenerative disorders have shown that LA improves memory in a variety of behavioral paradigms. Moreover, cell and molecular mechanisms underlying LA effects have also been investigated. Accordingly, LA displays antioxidant, antiapoptotic, and anti-inflammatory properties in both in vivo and in vitro studies. In addition, it has been shown that LA reverses age-associated loss of neurotransmitters and their receptors, which can underlie its effects on cognitive functions. The present review article aimed at summarizing and discussing the main studies investigating the effects of LA on cognition as well as its cell and molecular effects, in order to improve the understanding of the therapeutic potential of LA on memory loss during aging and in patients suffering from neurodegenerative disorders, supporting the development of clinical trials with LA.

Proinflammatory cytokine MIF plays a role in the pathogenesis of type-2 diabetes mellitus, but does not affect hepatic mitochondrial function

BACKGROUND

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays an important role in the pathogenesis of type 2 diabetes mellitus (T2DM). Although the effect of high glucose on liver function has been described, the role of MIF in hepatic mitochondrial function during T2DM has not been studied.

OBJECTIVE

We examine the influence of MIF to hepatic mitochondrial function in T2DM mouse model.

METHODS

WT and Mif^-/- BALB/c mice were treated with a single dose of streptozotocin (STZ). After an 8-week follow-up, serum glucose, proinflammatory cytokines, C-reactive protein (CRP), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzyme quantification, and liver histological analyses were performed. Liver mitochondria were extracted, and mitochondrial function was evaluated by oximetry, swelling and peroxide production.

RESULTS

Following treatment with STZ, WT mice (WT/STZ) developed significant hyperglycemia and high serum levels of MIF, tumor necrosis factor (TNF)-α, interleukin-β (IL-β), and CRP. Liver damage enzymes ALT and AST were found at high levels. In contrast, Mif^-/-STZ lacked serum MIF levels and showed smaller increases in blood glucose, less TNF-α, IL-1β, CPR, ALT and AST, and failure to develop clinical signs of disease compared to the WT/STZ group. Mitochondria extracted from the Mif^-/-STZ liver showed similar respiratory control (RC) to WT/STZ or healthy mice with glutamate/malate or succinate as substrates. The four respiratory chain complexes also had comparable activities. WT/STZ-isolated mitochondria showed low swelling with calcium compared to mitochondria from Mif^-/-STZ or healthy mice. Peroxide production was comparable in all groups.

CONCLUSION

These results show although high systemic levels of MIF contribute to the development of T2DM pathology, the liver mitochondria remain unaltered. Importantly, the absence of MIF reduced the pathology of T2DM, also without altering liver mitochondrial function. These support MIF as a therapeutic target for the treatment of this disease in humans.

Adenyl cyclase activator forskolin protects against Huntington's disease-like neurodegenerative disorders

Long term suppression of succinate dehydrogenase by selective inhibitor 3-nitropropionic acid has been used in rodents to model Huntington's disease where mitochondrial dysfunction and oxidative damages are primary pathological hallmarks for neuronal damage. Improvements in learning and memory abilities, recovery of energy levels, and reduction of excitotoxicity damage can be achieved through activation of Adenyl cyclase enzyme by a specific phytochemical forskolin. In this study, intraperitoneal administration of 10 mg/kg 3-nitropropionic acid for 15 days in rats notably reduced body weight, worsened motor cocordination (grip strength, beam crossing task, locomotor activity), resulted in learning and memory deficits, greatly increased acetylcholinesterase, lactate dehydrogenase, nitrite, and malondialdehyde levels, obviously decreased adenosine triphosphate, succinate dehydrogenase, superoxide dismutase, catalase, and reduced glutathione levels in the striatum, cortex and hippocampus. Intragastric administration of forskolin at 10, 20, 30 mg/kg dose-dependently reversed these behavioral, biochemical and pathological changes caused by 3-nitropropionic acid. These results suggest that forskolin exhibits neuroprotective effects on 3-nitropropionic acid-induced Huntington's disease-like neurodegeneration.

Dihydromyricetin Ameliorates 3NP-induced Behavioral Deficits and Striatal Injury in Rats

Oxidative stress is closely involved in neurodegenerative diseases. The present study aimed to examine the effect of anti-oxidant DHM (dihydromyricetin) on 3NP (3-nitropropionic acid) -induced behavioral deficits of experimental rats and striatal histopathological injury by using behavioral, imaging, biochemistry, histochemistry and molecular biology technologies. The experimental results showed that both motor dysfunctions and learning and memory impairments induced by 3NP were significantly reduced after DHM treatment. 3NP-induced striatal metabolic abnormality was also remarkably improved by DHM treatment, showed as the increased glucose metabolism in PET/CT scan, decreased MDA (malondialdehyde) and increased SOD (superoxide dismutase) activity in enzyme histochemical staining. In addition, the cell apoptosis was evidently detected in the striatum of the 3NP group, while in the 3NP + DHM group, the number of apoptotic cells was remarkably reduced. 3NP treatment obviously induced down-regulation of Bcl-2, and up-regulations of Bax and Cleaved Caspase-3, while these changes were significantly reversed by DHM treatment. The present results suggested that DHM showed its protective effect by anti-oxidant and anti-apoptosis mechanisms.

Linking mitochondrial dysfunction, metabolic syndrome and stress signaling in Neurodegeneration

Mounting evidence suggests a link between metabolic syndrome (MetS) such as diabetes, obesity, non-alcoholic fatty liver disease in the progression of Alzheimer's disease (AD), Parkinson's disease (PD) and other neurodegenerative diseases (NDDs). For instance, accumulated Aβ oligomer is enhancing neuronal Ca²⁺ release and neural NO where increased NO level in the brain through post translational modification is modulating the level of insulin production. It has been further confirmed that irrespective of origin; brain insulin resistance triggers a cascade of the neurodegeneration phenomenon which can be aggravated by free reactive oxygen species burden, ER stress, metabolic dysfunction, neuorinflammation, reduced cell survival and altered lipid metabolism. Moreover, several studies confirmed that MetS and diabetic sharing common mechanisms in the progression of AD and NDDs where mitochondrial dynamics playing a critical role. Any mutation in mitochondrial DNA, exposure of environmental toxin, high-calorie intake, homeostasis imbalance, glucolipotoxicity is causative factors for mitochondrial dysfunction. These cumulative pleiotropic burdens in mitochondria leads to insulin resistance, increased ROS production; enhanced stress-related enzymes that is directly linked MetS and diabetes in neurodegeneration. Since, the linkup mechanism between mitochondrial dysfunction and disease phenomenon of both MetS and NDDs is quite intriguing, therefore, it is pertinent for the researchers to identify and implement the therapeutic interventions for targeting MetS and NDDs. Herein, we elucidated the pertinent role of MetS induced mitochondrial dysfunction in neurons and their consequences in NDDs. Further, therapeutic potential of well-known biomolecules and chaperones to target altered mitochondria has been comprehensively documented. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Characterization of age-dependent changes in the striatum: Response to the mitochondrial toxin 3-nitropropionic acid

Neurodegenerative phenomena are associated with mitochondrial dysfunction and this could be exacerbated by aging. Age-dependence of mitochondrial response to toxins could help understand these mechanisms and evolve novel therapeutics. 3-Nitropropionic acid (3-NPA) is a mitochondrial toxin that induces neurotoxicity in the striatum via inhibition of complex II. We investigated the age-related events that contribute to 3-NPA toxicity. 3-NPA induced neuronal death, oxidative stress and altered mitochondrial structure in neuronal cells. 3-NPA injection in vivo caused motor impairment, mitochondrial dysfunction and oxidative damage with different trend in young and adult mice. To understand the age-dependent mechanisms, we carried out proteomic analysis of the striatal protein extract from young mice (control: YC vs. 3-NPA treated: YT) and adult mice (control: AC vs. 3-NPA treated: AT). Among the 3752 identified proteins, 33 differentially expressed proteins (mitochondrial, synaptic and microsomal proteins) were unique either to YT or AT. Interestingly, comparison of the proteomic profile in AC and YC indicated that 161 proteins (linked with cytoskeletal structure, neuronal development, axogenesis, protein transport, cell adhesion and synaptic function) were down-regulated in AC compared to YC. We surmise that aging contributes to the cellular and molecular architecture in the mouse striatum with implications for neurodegeneration.

Mitochondrial modulators improve lipid composition and attenuate memory deficits in experimental model of Huntington's disease

3-Nitropropionic acid (3-NP) is an irreversible inhibitor of succinate dehydrogenase and induces neuropathological changes similar to those observed in Huntington's disease (HD). The objective of the present study was to investigate neuroprotective effect of mitochondrial modulators; alpha-lipoic acid (ALA) and acetyl-L-carnitine (ALCAR) on 3-NP-induced alterations in mitochondrial lipid composition, mitochondrial structure and memory functions. Experimental model of HD was developed by administering 3-NP at sub-chronic doses, twice daily for 17 days. The levels of conjugated dienes, cholesterol and glycolipids were significantly increased, whereas the levels of phospholipids (phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine) including cardiolipin were significantly decreased in the mitochondria isolated from the striatum of 3-NP-treated animals. In addition, the difference in molecular composition of each phospholipid class was also evaluated using mass spectrometry. Mitochondria lipid from 3-NP-treated animals showed increased cholesterol to phospholipid ratio, suggesting decreased mitochondrial membrane fluidity. 3-NP administration also resulted in ultra-structural changes in mitochondria, accompanied by swelling as assessed by transmission electron microscopy. The 3-NP administered animals had impaired spatial memory evaluated using elevated plus maze test. However, combined supplementation with ALA + ALCAR for 21 days normalized mitochondrial lipid composition, improved mitochondrial structure and ameliorated memory impairments in 3-NP-treated animals, suggesting an imperative role of these two modulators in combination in the management of HD.