Neurotransmitter CART as a New Therapeutic Candidate for Parkinson's Disease

Neurotransmitter systems in the etiology of major neurological disorders: Emerging insights and therapeutic implications

Neurotransmitters serve as chemical messengers playing a crucial role in information processing throughout the nervous system, and are essential for healthy physiological and behavioural functions in the body. Neurotransmitter systems are classified as cholinergic, glutamatergic, GABAergic, dopaminergic, serotonergic, histaminergic, or aminergic systems, depending on the type of neurotransmitter secreted by the neuron, allowing effector organs to carry out specific functions by sending nerve impulses. Dysregulation of a neurotransmitter system is typically linked to a specific neurological disorder. However, more recent research points to a distinct pathogenic role for each neurotransmitter system in more than one neurological disorder of the central nervous system. In this context, the review provides recently updated information on each neurotransmitter system, including the pathways involved in their biochemical synthesis and regulation, their physiological functions, pathogenic roles in diseases, current diagnostics, new therapeutic targets, and the currently used drugs for associated neurological disorders. Finally, a brief overview of the recent developments in neurotransmitter-based therapeutics for selected neurological disorders is offered, followed by future perspectives in that area of research.

Emerging targets signaling for inflammation in Parkinson's disease drug discovery

Parkinson's disease (PD) patients not only show motor features such as bradykinesia, tremor, and rigidity but also non-motor features such as anxiety, depression, psychosis, memory loss, attention deficits, fatigue, sexual dysfunction, gastrointestinal issues, and pain. Many pharmacological treatments are available for PD patients; however, these treatments are partially or transiently effective since they only decrease the symptoms. As these therapies are unable to restore dopaminergic neurons and stop the development of Parkinson's disease, therefore, the need for an effective therapeutic approach is required. The current review summarizes novel targets for PD, that can be utilized to identify disease-modifying treatments.

DMHF (2,5-dimethyl-4-hydroxy-3(2H)-furanone), a volatile food component generated by the Maillard reaction, promotes appetite and changes gene expression in the rat brain through inhalation

Inhalation of odors can affect physiological parameter and change gene expression-related specific function. 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) is one of the major odor compounds generated by the Maillard reaction. We previously reported that the inhalation of DMHF decreased systolic blood pressure via the autonomic nervous system in rats. The autonomic nervous system is also closely related to appetite regulation. The present study investigated the effects of DMHF on dietary intake and gene expression. The inhalation of DMHF increased the dietary intake of rats during the feeding period. However, body weight did not change after 6 weeks feeding. A DNA microarray analysis showed that DMHF altered gene expression associated with feeding behavior and neurotransmission in the rat brain. DMHF inhalation promotes appetite and changes gene expression in rats. Furthermore, phenotypic changes may regulate neurotransmission and appetite at the mRNA level in addition to controlling the autonomic nervous system. PRACTICAL APPLICATION: DMHF is an important flavor component in the food industry. In this study, we first observed that the inhalation of DMHF promotes appetite. This finding is directly connected with the industrial application.

The neuroprotective effect of NeuroAid on morphine-induced amnesia with respect to the expression of TFAM, PGC-1α, ΔfosB and CART genes in the hippocampus of male Wistar rats

Morphine is a natural alkaloid which derived from the opium poppy Papaver somniferum. Many studies have reported the effect of morphine on learning, memory and gene expression. CART (cocaine-amphetamine regulated transcript)is an important neuropeptide which has a critical role in physiological processes including drug dependence and antioxidant activity. ΔfosB is a transcription factor which modulates synaptic plasticity and affects learning and memory. TFAM (the mitochondrial transcription factor A) and PGC-1α (Peroxisome proliferator-activated receptor γ coactivator-1α) are critically involved in mitochondrial biogenesis and antioxidant pathways. NeuroAid is a Chinese medicine that induces neuroprotective and anti-apoptotic effects. In this research, we aimed to investigate the effect of NeuroAid on morphine-induced amnesia with respect to the expression of TFAM, PGC-1α, ΔfosB and CART in the rat's hippocampus. In this study, Morphine sulfate (at increasing doses), Naloxone hydrochloride (2.5 mg/kg) and NeuroAid (2.5 mg/kg) were administered intraperitoneal and real-time PCR reactions were done to assess gene expression. The results showed, morphine impaired memory of step-through passive avoidance, while NeuroAid had no effect. NeuroAid attenuated (but not reversed) morphine-induced memory impairment in morphine-addicted rats. Morphine increased the expression of PGC-1α and decreased the expression of CART. However, NeuroAid increased the expression of TFAM, PGC-1α, ΔfosB and CART. NeuroAid restored the effect of morphine on the expression of CART and PGC-1α. In conclusion, morphine impaired memory of step-through passive avoidance and NeuroAid attenuated this effect. The effect of NeuroAid on morphine-induced memory impairment/gene expression may be related to its anti-apoptotic and neuroprotective effects.

Changes in the Neurochemical Characterization of Enteric Neurons in the Porcine Duodenum After Administration of Low-Dose Salmonella Enteritidis Lipopolysaccharides

Lipopolysaccharides (LPS), also known as lipoglycans or endotoxins, form part of the outer membrane of Gram-negative bacteria. Previous studies have described the various harmful impacts of LPS on humans and animals. Nevertheless, many aspects of these effects are still not fully explained. One of them is the influence of endotoxins on the neurochemical characterization of neurons within the enteric nervous system (ENS), which is found in the intestinal wall and plays important adaptive roles during pathological processes and exposures. In this study, the impact of a low single dose of Salmonella Enteritidis LPS on the duodenal enteric neurons immunoreactive to substance P (SP), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating peptide (PACAP-27), and cocaine- and amphetamine-regulated transcript (CART) was studied using a double immunofluorescence technique. During the study, it was shown that even a low dose of LPS affects the number of enteric neurons containing the neuropeptides studied, and these changes were dependent on the type of the enteric plexus. The most visible changes concerned the SP-like immunoreactive (LI) neurons in the outer submucous plexus (LPS caused an increase in the percentage of these neurons from15.74 ± 0.61 to 21.72 ± 0.79%). Furthermore, the VIP-LI neurons in the inner submucous plexus were seen to decrease from 12.64 ± 0.83 to 5.96 ± 0.58%. The mechanisms behind these noted fluctuations are not clear, but it may be connected with the pro-inflammatory and neurotoxic activity of LPS.

Cocaine and amphetamine-regulated transcript prepropeptide gene (CARTPT) polymorphism interacts with Diet Quality Index-International (DQI-I) and Healthy Eating Index (HEI) to affect hypothalamic hormones and cardio-metabolic risk factors among obese individuals

BACKGROUND

Epidemiologic studies show that cocaine- and amphetamine-regulated transcript prepropeptide (CARTPT) gene polymorphism modifies diet-obesity relationships. However, the interaction between CARTPT gene polymorphism and diet quality indices have not been investigated yet. The current study was aimed to evaluate the interaction between major dietary indices including Diet Quality Index-International (DQI-I) and Healthy Eating Index (HEI)-2015 and CARTPT gene rs2239670 variants among apparently healthy obese Iranians.

METHODS

This cross-sectional study was carried out by employing 288 apparently healthy obese adults aged 20-50 years with a BMI of 30-40 kg/m2. Diet quality was evaluated by Diet Quality Index-International (DQI-I) and Healthy Eating Index-2015 (HEI-2015) using a 132-items semi-quantitative validated food frequency questionnaire. The CARTPT gene rs2239670 polymorphism was genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. Blood concentrations of glycemic markers, lipid profile, α-melanocyte stimulating hormone (MSH) and agouti-related peptide (AgRP) were also measured. ANCOVA multivariate interaction model was used to analyze gene-diet interactions.

RESULTS

The significant interactions were identified between CARTPT gene polymorphism and HEI, affecting BMR (PInteraction = 0.003), serum glucose (PInteraction = 0.009) and high density lipoprotein cholesterol HDL concentrations (PInteraction = 0.03) after adjusting for the effects of sex and age. Also we found gene-diet interaction between CARTPT genotypes and DQI-I in terms of fat mass (FM; PInteraction = 0.02), waist circumference (WC; PInteraction < 0.001), body mass index (BMI; PInteraction < 0.001), basal metabolic rate (BMR, PInteraction < 0.001), serum fasting glucose (PInteraction < 0.01) and AgRP (PInteraction = 0.05) in individuals even after adjusting for potential confounders.

CONCLUSION

Current study showed the effects of interaction between CARTPT genotype with adherence to HEI and DQI-I scores on obesity-related anthropometric and metabolic risk-factors.

Neurochemical characterization of the enteric neurons within the porcine jejunum in physiological conditions and under the influence of bisphenol A (BPA)

BACKGROUND

Bisphenol A (BPA) is commonly used in the production of plastics and has multidirectional, negative effects on the living organisms. It may also affect the enteric nervous system (ENS) located in the wall of the gastrointestinal tract. Enteric neurons express many active substances, which regulate majority of intestinal activities not only in physiological conditions but also under the impact of pathological factors.

METHODS

The influence of various doses of BPA on the ENS of jejunum has been investigated using the double immunofluorescence technique. The commercial antibodies against substance P (SP), vasoactive intestinal polypeptide (VIP), galanin (GAL), vesicular acetylcholine transporter (VAChT), and cocaine- and amphetamine-regulated transcript peptide (CART) were used.

KEY RESULTS

Both doses of BPA studied changed the number of the enteric neurons immunoreactive to SP, VIP, GAL, VAChT, and CART, and the intensity of fluctuations depended on the BPA dose and on the type of the enteric plexus. Bisphenol A causes the increase in the number of neurons immunoreactive to the majority of substances studied. The only exception was VAChT-positive neurons, the number of which was lower under the impact of BPA in the comparison with physiological conditions.

CONCLUSIONS & INFERENCES

Even low doses of BPA cause the changes in neurochemical characterization of the enteric neurons in the jejunum. These changes may be the first sign of subclinical BPA intoxication. The mechanisms of observed changes are probably connected with neurotoxic and/or pro-inflammatory activity of BPA, but their exact mechanisms are not fully explained.

Cocaine- and amphetamine-regulated transcript (CART): A multifaceted neuropeptide

Over the last 35 years, the continuous discovery of novel neuropeptides has been the key to the better understanding of how the central nervous system has integrated with neuronal signals and behavioral responses. Cocaine and amphetamine-regulated transcript (CART) was discovered in 1995 in the rat striatum but later was found to be highly expressed in the hypothalamus. The widespread distribution of CART peptide in the brain complicated the understanding of the role played by this neurotransmitter. The main objective of the current compact review is to piece together the fragments of available information about origin, expression, distribution, projection, and function of CART peptides. Accumulative evidence suggests CART as a neurotransmitter and neuroprotective agent that is mainly involved in regulation of feeding, addiction, stress, anxiety, innate fear, neurological disease, neuropathic pain, depression, osteoporosis, insulin secretion, learning, memory, reproduction, vision, sleep, thirst and body temperature. In spite of the vast number of studies about the CART, the overall pictures about the CART functions are sketchy. First, there is a lack of information about cloned receptor, specific agonist and antagonist. Second, CART peptides are detected in discrete sets of neurons that can modulate countless activities and third; CART peptides exist in several fragments due to post-translational processing. For these reasons the overall picture about the CART peptides are sketchy and confounding.

Acupuncture Alleviates Levodopa-Induced Dyskinesia via Melanin-Concentrating Hormone in Pitx3-Deficient aphakia and 6-Hydroxydopamine-Lesioned Mice

Although L-3,4-dihydroxyphenylalanine (L-DOPA) is currently the most effective medication for treating Parkinson's disease (PD) motor symptoms, its prolonged administration causes several adverse effects, including dyskinesia. To identify the mechanisms underlying the effects of acupuncture on L-DOPA-induced dyskinesia (LID), antidyskinetic effects of acupuncture were investigated in two mouse models of PD. Acupuncture stimulation at GB34 alleviated abnormal involuntary movements (AIMs) in Pitx3-deficient aphakia mice (ak/ak) following L-DOPA administration and these effects were reproduced in 6-hydroxydopamine (6-OHDA)-lesioned mice with LID. A transcriptome analysis of the hypothalamus revealed pro-melanin-concentrating hormone (Pmch) gene was highly expressed in acupuncture-treated mouse from ak/ak model of LID as well as 6-OHDA model of LID. Acupuncture combined with the administration of MCH receptor antagonist did not have any beneficial effects on dyskinesia in L-DOPA-injected ak/ak mice, but the intranasal administration of MCH attenuated LID to the same degree as acupuncture in both ak/ak and 6-OHDA mice with LID. A gene expression profile with a hierarchical clustering analysis of the dyskinesia-induced ak/ak mouse brain revealed an association between the mechanisms underlying acupuncture and MCH. Additionally, altered striatal responses to L-DOPA injection were observed after prolonged acupuncture and MCH treatments, which suggests that these treatment modalities influenced the compensatory mechanisms of LID. In summary, present study demonstrated that acupuncture decreased LID via hypothalamic MCH using L-DOPA-administered ak/ak and 6-OHDA mouse models and that MCH administration resulted in novel antidyskinetic effects in these models. Thus, acupuncture and MCH might be valuable therapeutic candidates for PD patients suffering from LID.

The Influence of High and Low Doses of Bisphenol A (BPA) on the Enteric Nervous System of the Porcine Ileum

Bisphenol A, used in the production of plastic, is able to leach from containers into food and cause multidirectional adverse effects in living organisms, including neurodegeneration and metabolic disorders. Knowledge of the impact of BPA on enteric neurons is practically non-existent. The destination of this study was to investigate the influence of BPA at a specific dose (0.05 mg/kg body weight/day) and at a dose ten times higher (0.5 mg/kg body weight/day), given for 28 days, on the porcine ileum. The influence of BPA on enteric neuron immunoreactive to selected neuronal active substances, including substance P (SP), vasoactive intestinal polypeptide (VIP), galanin (GAL), vesicular acetylcholine transporter (VAChT—used here as a marker of cholinergic neurons), and cocaine- and amphetamine-regulated transcript peptide (CART), was studied by the double immunofluorescence method. Both doses of BPA affected the neurochemical characterization of the enteric neurons. The observed changes depended on the type of enteric plexus but were generally characterized by an increase in the number of cells immunoreactive to the particular substances. More visible fluctuations were observed after treatment with higher doses of BPA. The results confirm that even low doses of BPA may influence the neurochemical characterization of the enteric neurons and are not neutral for living organisms.

Allogeneic/xenogeneic transplantation of peptide-labeled mitochondria in Parkinson's disease: restoration of mitochondria functions and attenuation of 6-hydroxydopamine-induced neurotoxicity

Although restoration of mitochondrial function in mitochondrial diseases through peptide-mediated allogeneic mitochondrial delivery (PMD) has been demonstrated in vitro, the in vivo therapeutic efficacy of PMD in Parkinson's disease (PD) has yet to be determined. In this study, we compared the functionality of mitochondrial transfer with or without Pep-1 conjugation in neurotoxin (6-hydroxydopamine, 6-OHDA)-induced PC12 cells and PD rat models. We injected mitochondria into the medial forebrain bundle (MFB) of the PD rats after subjecting the nigrostriatal pathway to a unilateral 6-OHDA lesion for 21 days, and we verified the effectiveness of the mitochondrial graft in enhancing mitochondrial function in the soma of the substantia nigra (SN) neuron through mitochondrial transport dynamics in the nigrostriatal circuit. The result demonstrated that only PMD with allogeneic and xenogeneic sources significantly sustained mitochondrial function to resist the neurotoxin-induced oxidative stress and apoptotic death in the rat PC12 cells. The remaining cells exhibited a greater capability of neurite outgrowth. Furthermore, allogeneic and xenogeneic transplantation of peptide-labeled mitochondria after 3 months improved the locomotive activity in the PD rats. This increase was accompanied by a marked decrease in dopaminergic neuron loss in the substantia nigra pars compacta (SNc) and consistent enhancement of tyrosine hydroxylase-positive immunoreaction of dopaminergic neurons in the SNc and striatum. We also observed that in the SN dopaminergic neuron in the treated PD rats, mitochondrial complex I protein and mitochondrial dynamics were restored, thus ameliorating the oxidative DNA damage. Moreover, we determined signal translocation of graft allogeneic mitochondria from the MFB to the calbindin-positive SN neuron, which demonstrated the regulatory role of mitochondrial transport in alleviating 6-OHDA-induced degeneration of dopaminergic neurons.

CART modulates the effects of levodopa in rat model of Parkinson's disease

Parkinson's disease (PD) is an age-related disorder characterized by a progressive degeneration of dopaminergic neurons of substantia nigra (SN). The neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to closely interact with the dopamine system and regulate psychomotor activity. We screened the effectiveness of CART in reversing the symptoms of PD in a rat model. PD like condition was induced by administering 6-hydroxydopamine (6-OHDA) directly in the SN of the right side. Fifteen days later, intraperitoneal (IP) treatment with apomorphine hydrochloride to these rats, resulted in contralateral rotations in the rotation test chamber suggesting induction of PD-like symptoms. This action of apomorphine was significantly attenuated by intracerebroventricular (ICV) treatment with CART and potentiated by CART antibody. IP treatment with levodopa also produced contralateral rotation in PD induced rats, and showed anti-Parkinson-like action. Prior treatment with CART via ICV route potentiated the anti-Parkinsonian effects of levodopa, while CART antibody produced opposite effects. CART treatment per se, to PD induced rats produced ipsilateral rotations, suggesting that the peptide may promote the endogenous release of dopamine from intact neurons. While CART-immunoreactivity in arcuate nucleus, paraventricular nucleus, striatum, substantia nigra, ventral tegmental area and locus coeruleus was reduced in the PD induced rats, levodopa treatment restored the expression of CART-immunoreactivity in these nuclei. These results suggest that endogenous CART might closely interact with the dopamine containing SN-striatal pathway which is known to profoundly influence the motor system. The study underscores the importance of CART as a potential therapeutic agent in the treatment of PD.

CART treatment improves memory and synaptic structure in APP/PS1 mice

Major characteristics of Alzheimer’s disease (AD) include deposits of β-amyloid (Aβ) peptide in the brain, loss of synapses, and cognitive dysfunction. Cocaine- and amphetamine-regulated transcript (CART) has recently been reported to attenuate Aβ-induced toxicity. In this study, CART localization in APP/PS1 mice was characterized and the protective effects of exogenous CART treatment were examined. Compared to age-matched wild type mice, 8-month-old APP/PS1 mice had significantly greater CART immunoreactivity in the hippocampus and cortex. A strikingly similar pattern of Aβ plaque-associated CART immunoreactivity was observed in the cortex of AD cases. Treatment of APP/PS1 mice with exogenous CART ameliorated memory deficits; this effect was associated with improvements in synaptic ultrastructure and long-term potentiation, but not a reduction of the Aβ plaques. Exogenous CART treatment in APP/PS1 mice prevented depolarization of the mitochondrial membrane and stimulated mitochondrial complex I and II activities, resulting in an increase in ATP levels. CART treatment of APP/PS1 mice also reduced reactive oxygen species and 4-hydroxynonenal, and mitigated oxidative DNA damage. In summary, CART treatment reduced multiple neuropathological measures and improved memory in APP/PS1 mice, and may therefore be a promising and novel therapy for AD.