An Overview of the Pathophysiological Mechanisms of 3-Nitropropionic Acid (3-NPA) as a Neurotoxin in a Huntington's Disease Model and Its Relevance to Drug Discovery and Development.

Animal models are used to better understand the various mechanisms involved in the pathogenesis of diseases and explore potential pathways that will aid in discovering therapeutic targets. 3-Nitropropionic Acid (3-NPA) is a neurotoxin used to induce Huntington's disease (HD)-like symptoms in experimental animals. The 3-NPA is a fungus toxin that impairs the complex II (succinate dehydrogenase) activity of the mitochondria and reduces ATP synthesis, leading to excessive production of free radicals resulting in the degeneration of GABAergic medium spiny neurons (MSNs) in the striatum. This is characterized by motor impairments a key clinical manifestation of HD. 3-NPA has the potential to alter several cellular processes, including mitochondrial functions, oxidative stress, apoptosis, and neuroinflammation mimicking HD-like pathogenic conditions in animals. This review strives to provide a new insight towards the 3-NPA induced molecular dysfunctioning in developing an animal model of HD. Moreover, we summarise several preclinical studies that support the use of the 3-NPA-induced models for drug discovery and development in HD. This review is a collection of various articles that were published from 1977 to 2022 on Pubmed (1639), Web of Science (2139), and Scopus (2681), which are related to the 3-NPA induced animal model.

The Crosstalk between HepG2 and HMC-III Cells: In Vitro Modulation of Gene Expression with Conditioned Media.

Epidemiological studies have postulated an inverse correlation between developing cancer and neurodegeneration. It is known that the secretome plays a vital role in cell-cell communication in health and disease; the microglia is the resident macrophage of the central nervous system which maintains neuronal integrity by adapting as the microenvironment changes. The present study aimed to identify, in a cell model, biomarkers that link neurodegenerative diseases to cancer or vice versa. Real-time PCR and western blot analysis were used to characterize the effects on gene and protein expression of human hepatoblastoma (HepG2) and human microglia (HMC-III) cells after exchanging part of their conditioned medium. Biomarkers of the endoplasmic reticulum, and mitophagy and inflammatory processes were evaluated. In both cell types, we observed the activation of cytoprotective mechanisms against any potential pro-oxidant or pro-inflammatory signals present in secretomes. In contrast, HepG2 but not HMC-III cells seem to trigger autophagic processes following treatment with conditioned medium of microglia, thus suggesting a cell-specific adaptive response.

Structural and Functional Characterization of the ABCC6 Transporter in Hepatic Cells: Role on PXE, Cancer Therapy and Drug Resistance.

Pseudoxanthoma elasticum (PXE) is a complex autosomal recessive disease caused by mutations of ABCC6 transporter and characterized by ectopic mineralization of soft connective tissues. Compared to the other ABC transporters, very few studies are available to explain the structural components and working of a full ABCC6 transporter, which may provide some idea about its physiological role in humans. Some studies suggest that mutations of ABCC6 in the liver lead to a decrease in some circulating factor and indicate that PXE is a metabolic disease. It has been reported that ABCC6 mediates the efflux of ATP, which is hydrolyzed in PPi and AMP; in the extracellular milieu, PPi gives potent anti-mineralization effect, whereas AMP is hydrolyzed to Pi and adenosine which affects some cellular properties by modulating the purinergic pathway. Structural and functional studies have demonstrated that silencing or inhibition of ABCC6 with probenecid changed the expression of several genes and proteins such as NT5E and TNAP, as well as Lamin, and CDK1, which are involved in cell motility and cell cycle. Furthermore, a change in cytoskeleton rearrangement and decreased motility of HepG2 cells makes ABCC6 a potential target for anti-cancer therapy. Collectively, these findings suggested that ABCC6 transporter performs functions that modify both the external and internal compartments of the cells.

Effect of Quercetin on ABCC6 Transporter: Implication in HepG2 Migration.

Quercetin is a member of the flavonoid group of compounds, which is abundantly present in various dietary sources. It has excellent antioxidant properties and anti-inflammatory activity and is very effective as an anti-cancer agent against various types of tumors, both in vivo and in vitro. Quercetin has been also reported to modulate the activity of some members of the multidrug-resistance transporters family, such as P-gp, ABCC1, ABCC2, and ABCG2, and the activity of ecto-5'-nucleotidase (NT5E/CD73), a key regulator in some tumor processes such as invasion, migration, and metastasis. In this study, we investigated the effect of Quercetin on ABCC6 expression in HepG2 cells. ABCC6 is a member of the superfamily of ATP-binding cassette (ABC) transporters, poorly involved in drug resistance, whose mutations cause pseudoxanthoma elasticum, an inherited disease characterized by ectopic calcification of soft connective tissues. Recently, it has been reported that ABCC6 contributes to cytoskeleton rearrangements and HepG2 cell motility through purinergic signaling. Gene and protein expression were evaluated by quantitative Reverse-Transcription PCR (RT-qPCR) and western blot, respectively. Actin cytoskeleton dynamics was evaluated by laser confocal microscopy using fluorophore-conjugated phalloidin. Cell motility was analyzed by an in vitro wound-healing migration assay. We propose that ABCC6 expression may be controlled by the AKT pathway as part of an adaptative response to oxidative stress, which can be mitigated by the use of Quercetin-like flavonoids.

Extracellular Citrate Is a Trojan Horse for Cancer Cells.

The first intermediate in the mitochondrial tricarboxylic acid (TCA) cycle is citrate, which is essential and acts as a metabolic regulator for glycolysis, TCA cycle, gluconeogenesis, and fatty acid synthesis. Within the cytosol, citrate is cleaved by ATP citrate lyase (ACLY) into oxaloacetate (OAA) and acetyl-CoA; OAA can be used for neoglucogenesis or in the TCA cycle, while acetyl-CoA is the precursor of some biosynthetic processes, including the synthesis of fatty acids. Accumulating evidence suggests that citrate is involved in numerous physiological and pathophysiological processes such as inflammation, insulin secretion, neurological disorders, and cancer. Considering the crucial role of citrate to supply the acetyl-CoA pool for fatty acid synthesis and histone acetylation in tumors, in this study we evaluated the effect of citrate added to the growth medium on lipid deposition and histone H4 acetylation in hepatoma cells (HepG2). At low concentration, citrate increased both histone H4 acetylation and lipid deposition; at high concentration, citrate inhibited both, thus suggesting a crucial role of acetyl-CoA availability, which prompted us to investigate the effect of citrate on ACLY. In HepG2 cells, the expression of ACLY is correlated with histone acetylation, which, in turn, depends on citrate concentration. A decrease in H4 acetylation was also observed when citrate was added at a high concentration to immortalized human hepatic cells, whereas ACLY expression was unaffected, indicating a lack of control by histone acetylation. Considering the strong demand for acetyl-CoA but not for OAA in tumor cells, the exogenous citrate would behave like a trojan horse that carries OAA inside the cells and reduces ACLY expression and cellular metabolism. In addition, this study confirmed the already reported dual role of citrate both as a promoter of cell proliferation (at lower concentrations) and as an anticancer agent (at higher concentrations), providing useful tips on the use of citrate for the treatment of tumors.

Glucagon-like Peptide-1 (GLP-1) and neurotransmitters signaling in epilepsy: An insight review.

Epilepsy is one of the most prevalent neurological disorder affecting more than 50 million people worldwide. Numerous studies have suggested that an imbalance in glutamatergic (excitatory) and GABAergic (inhibitory) neurotransmitter system is one of the dominating pathophysiological mechanisms underlying the occurrence and progression of seizures. Further, this alteration in GABAergic and glutamatergic system disrupts the delicate balance of other neurotransmitters system in the brain. Emerging strides have documented the protective role of GLP-1 signaling on altered neurotransmitters signaling in Epilepsy and associated co-morbidities. GLP-1 is neuropeptide and synthesized by preproglucagon (PPG) neurons in the brain. GLP-1 receptors are widely distributed throughout the brain including hippocampus (CA3 and CA1 region) and implicated in various neurological disorders like Epilepsy. A complete understanding of alteration in neurotransmitters signaling will provide essential insight into the basic pathogenic mechanisms of epilepsy and may uncover novel targets for future drug therapies. Presently, treatment of epilepsy is palliative in nature, providing only symptomatic relief to patients. The apparent or traditional approach of treating epileptic subjects with anti-epileptic drugs is associated with variety of adverse effects. Therefore, alternative approaches that can restore altered neurotransmitter signaling are being tried and adopted. Present review is an attempt to highlight the emerging protective role of GLP-1 signaling on altered neurotransmitters signaling in epilepsy. Authors have made significant efforts to discuss effect of various GLP-1 analogs on various neurotransmitters system and associated molecular and cellular pathways as a potential drug target for the management of epilepsy and associated co-morbidities. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Effect of Liraglutide on Corneal Kindling Epilepsy Induced Depression and Cognitive Impairment in Mice.

GLP-1 play important role in neuroprotection and GLP-1 receptor deficit mice showed decreased seizure threshold and increased cognitive impairment. Therefore, study was premeditated to investigate the effect of liraglutide (GLP-1 analogue) on cornel kindling epilepsy induced co-morbidities in mice. Corneal kindling was induced by electrical stimulation (6 mA, 50 Hz, 3 s); twice daily for 13 days. Liraglutide (75 and 150 µg/kg) and phenytoin (20 mg/kg) were administered in corneal kindled groups. On day 14, elevated plus maze, passive shock avoidance paradigms were performed, and on day 15, retention was taken. On day 16 tail suspension test were performed. On 20th day challenge test was performed with same electrical stimulation and retention was observed on elevated plus maze and passive avoidance paradigm. Animal were sacrificed on 21st day for biochemical (LPO, GSH, and nitrite) and neurochemical (GABA, glutamate, DA, NE, 5-HT and their metabolites) estimation. Electrical stimulation by corneal electrode for 13 days developed generalized clonic seizures, increased cognitive impairment, oxidative stress and neurochemical alteration in mice brain. Co-treatment with liraglutide (75 and 150 µg/kg) significantly prevented the seizure severity, restored behavioural activity, oxidative stress and restored the altered level of neurotransmitters observed in corneal kindled mouse.

Neurochemical modulation involved in the beneficial effect of liraglutide, GLP-1 agonist on PTZ kindling epilepsy-induced comorbidities in mice.

Epilepsy is a neurological disorder which occurs due to excessive firing of excitatory neurons in specific region of brain and associated with cognitive impairment and depression. GLP-1 has been reported to maintain hyperexcitability of neurons. Therefore, this study was designed to investigate the neuroprotective effect of liraglutide, GLP-1 analogue in PTZ kindling epilepsy-induced comorbidities and neurochemical alteration in mice. Male albino mice were administered PTZ (35 mg/kg) on every alternate day up to 29th days and challenge test was performed on 33rd day. From 1st day liraglutide (75 and 150 µg/kg) and diazepam (3 mg/kg) were administered up to 33rd day, 30 min prior to PTZ treatment. On 30th day animals were trained on elevated plus maze and passive shock avoidance paradigm and retention was recorded on 31st and 33rd day. On 32nd day tail suspension test was performed. Animals were sacrificed on 34th day for biochemical (LPO, GSH, and nitrite) and neurotransmitters (GABA, glutamate, DA, NE, 5-HT and their metabolites) estimation. Chronic treatment with PTZ developed generalized tonic-clonic seizures, reduced cognitive skills, increased oxidative stress and alteration in the level of neurotransmitters. Pre-treatment with liraglutide (75 and 150 µg/kg) significantly prevented the seizure severity, restored behavioural activity, oxidative defence enzymes, and altered level of neurochemicals in mice brain. The protective effect of liraglutide is attributed to restoration of altered level of GABA, glutamate, DA, NE, and 5-HT by the up-regulation of GLP-1Rs in mice brain.