Leptin levels in patients with Parkinson's disease: A systematic review and meta-analysis

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Recent Advances in the Knowledge of the Mechanisms of Leptin Physiology and Actions in Neurological and Metabolic Pathologies

Excess body weight is frequently associated with low-grade inflammation. Evidence indicates a relationship between obesity and cancer, as well as with other diseases, such as diabetes and non-alcoholic fatty liver disease, in which inflammation and the actions of various adipokines play a role in the pathological mechanisms involved in these disorders. Leptin is mainly produced by adipose tissue in proportion to fat stores, but it is also synthesized in other organs, where leptin receptors are expressed. This hormone performs numerous actions in the brain, mainly related to the control of energy homeostasis. It is also involved in neurogenesis and neuroprotection, and central leptin resistance is related to some neurological disorders, e.g., Parkinson's and Alzheimer's diseases. In peripheral tissues, leptin is implicated in the regulation of metabolism, as well as of bone density and muscle mass. All these actions can be affected by changes in leptin levels and the mechanisms associated with resistance to this hormone. This review will present recent advances in the molecular mechanisms of leptin action and their underlying roles in pathological situations, which may be of interest for revealing new approaches for the treatment of diseases where the actions of this adipokine might be compromised.

Emerging roles of leptin in Parkinson's disease: Chronic inflammation, neuroprotection and more?

An increasing body of experimental evidence implicates a relationship between immunometabolic deterioration and the progression of Parkinson's disease (PD) with a dysregulation of central and peripheral neuroinflammatory networks mediated by circulating adipokines, in particular leptin. We screened the current literature on the role of adipokines in PD. Hence, we searched known databases (PubMed, MEDLINE/OVID) and reviewed original and review articles using the following terms: "leptin/ObR", "Parkinson's disease", "immune-metabolism", "biomarkers" and "neuroinflammation". Focusing on leptin, we summarize and discuss the existing in vivo and in vitro evidence on how adipokines may be protective against neurodegeneration, but at the same time contribute to the progression of PD. These components of the adipose brain axis represent a hitherto underestimated pathway to study systemic influences on dopaminergic degeneration. In addition, we give a comprehensive update on the potential of adjunctive therapeutics in PD targeting leptin, leptin-receptors, and associated pathways. Further experimental and clinical trials are needed to elucidate the mechanisms of action and the value of central and peripheral adipose-immune-metabolism molecular phenotyping in order to develop and validate the differential roles of different adipokines as potential therapeutic target for PD patients.

Parkinson's disease: the nutrition perspective

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease and affects about 1% of the population over the age of 60 years in industrialised countries. The aim of this review is to examine nutrition in PD across three domains: dietary intake and the development of PD; whole body metabolism in PD and the effects of PD symptoms and treatment on nutritional status. In most cases, PD is believed to be caused by a combination of genetic and environmental factors and although there has been much research in the area, evidence suggests that poor dietary intake is not a risk factor for the development of PD. The evidence about body weight changes in both the prodromal and symptomatic phases of PD is inconclusive and is confounded by many factors. Malnutrition in PD has been documented as has sarcopaenia, although the prevalence of the latter remains uncertain due to a lack of consensus in the definition of sarcopaenia. PD symptoms, including those which are gastrointestinal and non-gastrointestinal, are known to adversely affect nutritional status. Similarly, PD treatments can cause nausea, vomiting and constipation, all of which can adversely affect nutritional status. Given that the prevalence of PD will increase as the population ages, it is important to understand the interplay between PD, comorbidities and nutritional status. Further research may contribute to the development of interventional strategies to improve symptoms, augment care and importantly, enhance the quality of life for patients living with this complex neurodegenerative disease.

The Interactions between Adipose Tissue Secretions and Parkinson's disease; The Role of Leptin

Leptin is a hormone that regulates appetite by acting on receptors in the hypothalamus, where it modifies food intake to maintain equilibrium with the body energy resources. Leptin and its receptors are widely distributed in the central nervous system, suggesting that they may give neuronal survival signals. The potential of leptin to decrease/increase neuronal damage and neuronal plasticity in Parkinson's diseases (PD) is the subject of this review, which outlines our current knowledge of how leptin acts in the brain. Although leptin-mediated neuroprotective signaling results in neuronal death prevention, it can affect neuroinflammatory cascades and also neuronal plasticity which contribute to PD pathology. Other neuroprotective molecules, such as insulin and erythropoietin, share leptin-related signaling cascades, and therefore constitute a component of the neurotrophic effects mediated by endogenous hormones. With the evidence that leptin dysregulation causes increased neuronal vulnerability to damage in PD, using leptin as a target for therapeutic modification is an appealing and realistic option.

The potential benefit of leptin therapy against amyotrophic lateral sclerosis (ALS)

BACKGROUND

Targeting leptin could represent a rational strategy to treat amyotrophic lateral sclerosis (ALS), as previously clinical studies have shown its levels to be associated with a lower risk of ALS disease. However, very little is known about the potential influence of leptin in altering disease progression in ALS, as it has thus far been correlated with the protection exerted by increased fat mass stores.

METHODS

We studied the impact of leptin treatment beginning at 42-days of age (asymptomatic stage of disease) in the TDP-43 (TDP43^A315T ) transgenic (Tg) ALS mouse model.

RESULTS

Our study shows that leptin treatment was associated with altered expression of adipokines and metabolic proteins in TDP43^A315T mice. We also observed that weight loss decline was less prominent after leptin treatment in TDP43^A315T mice relative to vehicle-treated animals. In TDP43^A315T mice treated with leptin the disease duration lasted longer along with an improvement in motor performance relative to vehicle-treated animals.

CONCLUSIONS

Collectively, our results support leptin as a potential novel treatment approach for ALS.

Blood and Cerebrospinal Fluid Biomarkers of Inflammation in Parkinson's Disease

Given the clear role of inflammation in the pathogenesis of Parkinson's disease (PD) and its impact on incidence and phenotypical characteristics, this review provides an overview with focus on inflammatory biofluid markers in blood and cerebrospinal fluid (CSF) in PD patient cohorts. In preparation for clinical trials targeting the immune system, we specifically address the following questions: 1) What evidence do we have for pro-inflammatory profiles in blood and in CSF of sporadic and genetic PD patients? 2) Is there a role of anti-inflammatory mediators in blood/CSF? 3) Do inflammatory profiles in blood reflect those in CSF indicative of a cross-talk between periphery and brain? 4) Do blood/CSF inflammatory profiles change over the disease course as assessed in repeatedly taken biosamples? 5) Are blood/CSF inflammatory profiles associated with phenotypical trajectories in PD? 6) Are blood/CSF inflammatory profiles associated with CSF levels of neurodegenerative/PD-specific biomarkers? Knowledge on these questions will inform future strategies for patient stratification and cohort enrichment as well as suitable outcome measures for clinical trials.