Central and Peripheral Inflammation: Connecting the Immune Responses of Parkinson’s Disease

Herbal Interventions in Parkinson's Disease: A Systematic Review of Preclinical Studies

Parkinson's disease (PD) is the second most common neurodegenerative disorder, characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra of the midbrain. With its incidence rising annually, the multi-mechanistic pathogenesis of PD presents new opportunities for the development of multi-target therapies. While previous studies have explored the therapeutic potential of natural products in PD, existing reviews often focus on single mechanisms or a limited number of compounds. While previous studies have explored the therapeutic potential of natural products in PD, existing reviews often focus on single mechanisms or a limited number of compounds. This article systematically evaluates preclinical studies published between 2018 and 2025, encompassing 32 bioactive components and 10 categories of traditional Chinese medicine (TCM) formulas. It highlights the therapeutic potential of TCM active ingredients for PD by examining key mechanisms, including oxidative stress, ferroptosis, neuroinflammation, gut microbiota imbalance, mitochondrial dysfunction, autophagy, and endoplasmic reticulum stress. By integrating these insights, this review provides an interdisciplinary perspective to guide the development of next-generation botanical drugs for PD.

Allogenic transplantation therapy of iPS cell-derived dopamine progenitors for Parkinson's disease -Current status of the Kyoto Trial and future perspectives

Transplantation therapy using induced pluripotent stem cell (iPS) cell-derived dopamine (DA) progenitors for Parkinson's disease (PD) has attracted attention as an innovative treatment to restore DA neurons in PD, which leads to the improvement of motor disturbance. iPS cells are multipotent stem cells with very high proliferation activity, created by reprogramming mature somatic cells through the transduction of four transcription factors. Relative to fetal midbrain DA neurons, iPS cells have advantages in terms of ethical aspects and availability. On the other hand, the most serious concern associated with therapies with ES/iPS cells is the risk of tumor growth that is caused by the proliferation of undifferentiated ES/iPS cells. Human ES cells that differentiate into DA neurons have been shown to form teratomas. Another concern is graft-induced dyskinesia (GID). GID, which is likely caused by several factors including contamination with serotonergic neurons, developed in the recipients of fetal ventral midbrain (VM) in randomized controlled trials. To enrich the DA progenitor cells and eliminate unwanted cells, a protocol for sorting midbrain DA neurons with antibodies against CORIN, a marker for floor plates, was developed. CORIN-sorted dopamine progenitors were transplanted into the bilateral putamina of MPTP-treated Parkinson models of cynomolgus monkeys, resulting in 18F-DOPA PET-positive graft formation and motor improvement without tumor formation two years after the surgeries. Very recently, a phase I/II trial of iPSC-derived, CORIN-sorted dopaminergic cells for Parkinson's disease was completed (The Kyoto Trial) (Takahashi, 2020; Sawamoto et al., 2025) [1,2]. Based on the results of the trial, we would like to discuss the current status and future perspectives of iPS cell therapy for PD.

Peripheral Immune-Inflammatory Parameters in Parkinson's Disease. Dependence on the Stage of Progression

According to the modern concepts, neuroinflammation and peripheral immune dysfunction play key roles in the onset and progression of Parkinson's disease (PD), one of the most common and severe neurodegenerative diseases. However, changes in the cellular and molecular immune parameters during the development of PD are still poorly understood. This work is devoted to analysis of the immune cell populations (monocytes, T- and B-cells and their subtypes), expression of Toll-like receptors (TLR), and spontaneous and mitogen-induced production of pro- and anti-inflammatory cytokines in the peripheral blood of the patients at different stages of idiopathic PD and healthy individuals. It was shown that the stage II of PD is characterized by the decrease in amount of the CD3+ T-cells, increase in the TLR2 expression on CD4+CD25+ Tregs, as well as increase in the spontaneous production of proinflammatory cytokines IFNγ and IL-17A. The stage III of PD is associated with the decrease in production of mitogen-induced IFNγ. Relative number of the CD19+CD25+ Breg cells in the patients with PD increased regardless of the disease stage. Thus, the obtained results indicate differences in the cellular and molecular immune parameters in the patients with PD and in the healthy individuals, which are dependent on the stage of the disease. These data are important for understanding molecular basis of PD development and prognosis of its course, and may be useful in identifying biomarkers of the disease severity and developing new treatment approaches depending on the stage of the disease.

Elevated CXCL1 triggers dopaminergic neuronal loss in the substantia nigra of C57BL/6J mice: Evaluation of a novel Parkinsonian mouse model

Substantial evidence points to the early onset of peripheral inflammation in the development of Parkinson's disease (PD), supporting the "body-first" hypothesis. However, there remains a notable absence of PD-specific animal models induced by inflammatory cytokines. This study introduces a novel mouse model of PD driven by the proinflammatory cytokine CXCL1, identified in our previous research. The involvement of CXCL1 in PD pathogenesis was validated using subacute and chronic MPTP-induced mouse models. Based on these findings, 2-month-old C57BL/6J mice were intravenously administered CXCL1 (20 ng/kg/day) for 2 weeks (5 days per week), successfully replicating motor deficits and pathological alterations in the substantia nigra observed in the chronic MPTP model. These results demonstrate the potential of CXCL1-induced inflammation as a mechanism for PD modeling. The model revealed activation of the PPAR signaling pathway in CXCL1-mediated neuronal damage by CXCL1. Linoleic acid, a PPAR-γ activator, significantly mitigated MPTP- and CXCL1-induced toxicity and reduced serum CXCL1 levels. In addition, the CXCL1-injected mouse model shortened the timeline for developing chronic PD mouse model to 2 weeks, offering an efficient platform for studying inflammation-driven processes in PD. The findings provide critical insights into the inflammatory mechanisms underlying PD and identify promising therapeutic targets for intervention.

Crosstalk between peripheral inflammation and brain: Focus on the responses of microglia and astrocytes to peripheral challenge

A growing body of evidence supports the link between peripheral inflammation and impairment of neurologic functions, including mood and cognitive abilities. The pathogenic event connecting peripheral inflammation and brain dysfunction is represented by neuroinflammation, a pathogenic phenomenon that provides an important contribution to neurodegeneration and cognitive decline also in Alzheimer's, Parkinson's, Huntington's diseases, as well as in Multiple Sclerosis. It is driven by resident brain immune cells, microglia and astrocytes, that acquire an activated phenotype in response to proinflammatory molecules moving from the periphery to the brain parenchyma. Although a huge progress has been made in clarifying cellular and molecular mechanisms bridging peripheral and central inflammation, a clear picture has not been achieved so far. Therefore, experimental models are of crucial relevance to clarify knowledge gaps in this regard. Many findings demonstrate that systemic inflammation induced by pathogen-associated molecular patterns, such as lipopolysaccharide (LPS), is able to trigger neuroinflammation. Therefore, LPS-administration is widely considered a useful tool to study this phenomenon. On this basis, the present review will focus on in vivo studies based on acute and subacute effects of systemic administration of LPS, with special attention on the state of art of microglia and astrocyte response to peripheral challenge.

Monocyte to high-density lipoprotein cholesterol ratio reflects the peripheral inflammatory state in parkinsonian disorders

BACKGROUND

In Parkinson's disease (PD) and Parkinson plus syndrome (PPS), inflammation is recognized as a relevant or contributing factor in the advancement of the diseases. For this reason, numerous biomarkers signaling immune alteration in both the central and peripheral nervous systems have been evaluated in PD and PPS. Nonetheless, the comprehensive inflammatory indices derived from readily available standard blood tests in PD, PPS, and healthy controls (HC) were rarely evaluated especially in the early stage of the diseases.

OBJECTIVE

The aim of this study is to explore the serum level of peripheral inflammatory markers among the patients and investigate whether these markers contribute to symptoms.

METHOD

Clinical data and blood test results from drug naïve, early-stage 139 PD and 87 PPS patients, along with 139 age- and sex-matched healthy controls (HC) to PD were enrolled, with exclusion criteria applied to conditions potentially affecting inflammation. The study examined the disparities in peripheral inflammation among the groups, using total and subpopulation of white blood cells (WBCs), platelet count, red cell distribution width (RDW), high-density lipoprotein cholesterol (HDL-C), and other composite values reflecting inflammation including RDW to platelet ratio (RPR), neutrophil to lymphocyte ratio (NLR), monocyte to lymphocyte ratio (MLR), platelet to lymphocyte ratio (PLR), neutrophil to HDL-C ratio (NHR), monocyte to HDL-C ratio (MHR), lymphocyte to HDL-C ratio (LHR), platelet to HDL-C ratio (PHR), systemic inflammation index (SII), systemic inflammation response index (SIRI), and aggregate index of systemic inflammation (AISI).

RESULT

The MHR values were significantly higher in both PD and PPS groups compared to HC (p < 0.001), and NHR was significantly higher in the PPS group only compared to the HC group (p < 0.001). However, no significant differences in all the inflammatory markers were observed between PPS and PD (p > 0.05). Subgroup analysis of progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) patients revealed significantly higher NHR and MHR levels compared to the HC group (p = 0.025, p = 0.050, respectively), with no significant difference among PSP, MSA, and PD groups. After adjustment for age, sex, and disease duration, MHR was positively associated with H&Y in the total population (β = 0.288, p < 0.001), negatively associated with MMSE in the PD group (β = -0.245, p = 0.017), and positively associated with both H&Y (β = 0.432, p < 0.001) and UPDRS part II (β = 0.295, p = 0.018) in PPS group.

CONCLUSION

NHR and MHR values are not effective as reliable diagnostic markers due to overlap among groups and their limited discriminative capacity in ROC analyses. However, MHR may potentially serve as an indicator reflecting peripheral inflammation in the early stage of PD and PPS compared to HC.

Inflammation and heterogeneity in synucleinopathies

Neurodegenerative diseases represent a huge healthcare challenge which is predicted to increase with an aging population. Synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), present complex challenges in understanding their onset and progression. They are characterized by the abnormal aggregation of α-synuclein in the brain leading to neurodegeneration. Accumulating evidence supports the existence of distinct subtypes based on the site of α-synuclein aggregation initiation, genetics, and, more recently, neuroinflammation. Mediated by both central nervous system-resident cells, peripheral immune cells, and gut dysbiosis, neuroinflammation appears as a key process in the onset and progression of neuronal loss. Sex-based differences add another layer of complexity to synucleinopathies, influencing disease prevalence - with a known higher incidence of PD in males compared to females - as well as phenotype and immune responses. Biological sex affects neuroinflammatory pathways and the immune response, suggesting the need for sex-specific therapeutic strategies and biomarker identification. Here, we review the heterogeneity of synucleinopathies, describing the etiology, the mechanisms by which the inflammatory processes contribute to the pathology, and the consideration of sex-based differences to highlight the need for personalized therapeutics.

Engineered Extracellular Vesicle-Based Nanoformulations That Coordinate Neuroinflammation and Immune Homeostasis, Enhancing Parkinson's Disease Therapy

Although conventional intervention to microglia can mitigate neuroinflammation in the short term, immune disorders by peripheral inflammatory cells can infiltrate continuously, resulting in an overactivated immune microenvironment of Parkinson's disease (PD). Here, we design engineered extracellular vesicle-based nanoformulations (EVNs) to address multiple factors for the management of PD. Specifically, EVN is developed by coating CCR2-enriched mesenchymal stem cell-derived extracellular vesicles (MSCCCR2 EVs) onto a dihydrotanshinone I-loaded nanocarrier (MSeN-DT). The MSCCCR2 EVs (the shell of EVN) can actively show homing to specific chemokines CCL2 in the substantia nigra, which enables them to block the infiltration of peripheral inflammatory cells. Interestingly, MSeN-DT (the core of EVN) can promote the Nrf2-GPX4 pathway for the suppression of the source of inflammation by inhibiting ferroptosis in microglia. In the PD model mice, a satisfactory therapeutic effect is achieved, with inhibition of peripheral inflammatory cell infiltration, precise regulation of inflammatory microglia in the substantia nigra, as well as promotion of behavioral improvement and repairing damaged neurons. In this way, the combinatorial code of alleviation of inflammation and modulation of immune homeostasis can reshape the immune microenvironment in PD, which bridges internal anti-inflammatory and external immunity. This finding reveals a comprehensive therapeutic paradigm for PD that breaks the vicious cycle of immune overactivation.

Unveiling the Journey from the Gut to the Brain: Decoding Neurodegeneration-Gut Connection in Parkinson's Disease

Parkinson's disease, a classical motor disorder affecting the dopaminergic system of the brain, has been as a disease of the brain, but this classical notion has now been viewed differently as the pathology begins in the gut and then gradually moves up to the brain regions. The microorganisms in the gut play a critical role in maintaining the physiology of the gut from maintaining barrier integrity to secretion of microbial products that maintain a healthy gut state. The pathology subsequently alters the normal composition of gut microbes and causes deleterious effects that ultimately trigger strong neuroinflammation and nonmotor symptoms along with characteristic synucleopathy, a pathological hallmark of the disease. Understanding the complex pathomechanisms in distinct and established preclinical models is the primary goal of researchers to decipher how exactly gut pathology has a central effect; the quest has led to many answered and some open-ended questions for researchers. We summarize the popular opinions and some contrasting views, concise footsteps in the treatment strategies targeting the gastrointestinal system.

Integrated Bioinformatics Analysis for Revealing CBL is a Potential Diagnosing Biomarker and Related Immune Infiltration in Parkinson's Disease

Purpose

There is growing evidence that the immune system plays an important role in the progression of Parkinson's disease, the second most common neurodegenerative disorder. This study aims to address the comprehensive understanding of the immunopathogenesis of Parkinson's disease and explore new inflammatory biomarkers.

Patients and Methods

In this study, Immune-related differential expressed genes (DEIRGs) were obtained from GEO database and Immport database. The hub gene was screened in DEIRGs using LASSO regression and random forest algorithm, and the mRNA expression of the identified hub gene was validated using clinical blood samples.

Results

We obtained a total of 157 DEIRGs that played an important role in the immune response. The results of immune cell infiltration analysis showed that the degree of memory B cells infiltration was higher in PD patients, while the degree of Monocytes, resting mast cells and M0 macrophages infiltration was lower (p<0.05). A total of 8 hub genes were screened by machine learning methods, and RT-PCR results showed that the expression level of CBL gene in PD was significantly increased (p<0.05).

Conclusion

Our findings suggest that CBL is a new potential diagnostic biomarker for PD and that abnormal immune cell infiltration may influence PD development.

Causal association between atopic dermatitis and Parkinson's disease: A bidirectional Mendelian randomization study

BACKGROUND

Atopic dermatitis is one of the most common skin disorders. Evidence has suggested an association between skin disorders, such as atopic dermatitis, and Parkinson's disease (PD). However, whether atopic dermatitis has a causal effect on PD remains unknown.

METHODS

The study aimed to determine whether their association between atopic dermatitis and PD is causal, using a bidirectional two-sample Mendelian randomization method. Genetic variants from the public genome-wide association studies for atopic dermatitis (n = 10788 cases and 30047 controls) were selected to evaluate their causal effects on the risk of PD (33,674 cases and 449,056 controls). The inverse variance weighted (IVW) method was used as the primary analysis.

RESULTS

The IVW results indicated that atopic dermatitis was associated with decreased risk of PD {fixed effects: odds ratio [OR] [95% confidence interval (CI)]: .905 [.832-.986], p = .022; OR [95% CI]: .905 [.827-.991], p = .032}. However, we failed to detect the causal effects of PD on risk of atopic dermatitis in the reverse causation analysis.

CONCLUSION

This study indicated causal association of genetically proxied atopic dermatitis with the risk of PD. Future studies are warranted to explore the underlying mechanism and investigate the targeting effect of atopic dermatitis on PD.

The neutrophil-to-lymphocyte ratio, lymphocyte-to-monocyte ratio, and neutrophil-to-high-density-lipoprotein ratio are correlated with the severity of Parkinson's disease

BACKGROUND

Inflammation plays a pivotal role in the pathogenesis of Parkinson's disease (PD). However, the correlation between peripheral inflammatory markers and the severity of PD remains unclear.

METHODS

The following items in plasma were collected for assessment among patients with PD (n = 303) and healthy controls (HCs; n = 303) were assessed for the neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR) and neutrophil-to-high-density-lipoprotein ratio (NHR) in plasma, and neuropsychological assessments were performed for all patients with PD. Spearman rank or Pearson correlation was used to evaluate the correlation between the NLR, the LMR and the NHR and the severity of PD. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic performance of the NLR, LMR and NHR for PD.

RESULTS

The plasma NLR and NHR were substantially higher in patients with PD than in HCs, while the plasma LMR was substantially lower. The plasma NLR was positively correlated with Hoehn and Yahr staging scale (H&Y), Unified Parkinson's Disease Rating Scale (UPDRS), UPDRS-I, UPDRS-II, and UPDRS-III scores. Conversely, it exhibited a negative relationship with Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) scores. Furthermore, the plasma NHR was positively correlated with H&Y, UPDRS, UPDRS-I, UPDRS-II and UPDRS-III scores. Moreover, negative associations were established between the plasma LMR and H&Y, UPDRS, UPDRS-I, UPDRS-II, and UPDRS-III scores. Finally, based on the ROC curve analysis, the NLR, LMR and NHR exhibited respectable PD discriminating power.

CONCLUSION

Our research indicates that a higher NLR and NHR and a lower LMR may be relevant for assessing the severity of PD and appear to be promising disease-state biomarker candidates.

Search in the Periphery for Potential Inflammatory Biomarkers of Dementia with Lewy Bodies and Alzheimer's Disease

Background

Neuroinflammation, with altered peripheral proinflammatory cytokine production, plays a major role in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD), while the role of inflammation in dementia with Lewy bodies (DLB) is less known and the results of different studies are often in disagreement.

Objective

The present study aimed to investigate the levels of TNFα and IL-6 in serum and supernatants, and the related DNA methylation in patients affected by DLB and AD compared to healthy controls (HCs), to clarify the role of epigenetic mechanisms of DNA promoter methylation on of pro-inflammatory cytokines overproduction.

Methods

Twenty-one patients with DLB and fourteen with AD were frequency-matched for age and sex with eleven HCs. Clinical evaluation, TNFα and IL-6 gene methylation status, cytokine gene expression levels and production in serum and peripheral blood mononuclear cell (PBMC) supernatants were performed.

Results

In AD and DLB patients, higher serum levels of IL-6 and TNFα were detected than in HCs. Differences in LPS-stimulated versus spontaneous PBMCs were observed between DLB, AD, and HC in the levels of TNFα (p = 0.027) and IL-6 (p < 0.001). Higher levels were also revealed for sIL-6R in DLB (p < 0.001) and AD (p < 0.001) in comparison with HC.DNA hypomethylation in IL-6 and TNFα CpG promoter sites was detected for DLB and AD patients compared to the corresponding site in HCs.

Conclusions

Our preliminary study documented increased levels of IL-6 and TNFα in DLB and AD patients to HCs. This overproduction can be due to epigenetic mechanisms regarding the hypomethylation of DNA promoters.

Peripheral blood inflammatory cytokines in prodromal and overt α-synucleinopathies: a review of current evidence

While the pathomechanisms of α-synucleinopathies are not completely understood, accumulating evidence suggests a role of neuroinflammation in the development and progression of the diseases. In addition, emerging data provide insights into the potential role of central neuroinflammation in prodromal α-synucleinopathies. Given the considerable bidirectional crosstalk between peripheral and central inflammation, peripheral blood inflammatory cytokines may be a useful tool to understand immune responses in association with α-synucleinopathies. Indeed, the accessibility and practicality of using blood samples have facilitated multiple investigations evaluating peripheral blood inflammatory cytokines in overt α-synucleinopathies, whereas the associations between these biomarkers and prodromal α-synucleinopathies remain unclear. In this review, we provide an overview of the current evidence available for the role of peripheral blood inflammatory cytokines in prodromal and overt α-synucleinopathies.

Alpha Synuclein: Neurodegeneration and Inflammation

Alpha-Synuclein (α-Syn) is one of the most important molecules involved in the pathogenesis of Parkinson's disease and related disorders, synucleinopathies, but also in several other neurodegenerative disorders with a more elusive role. This review analyzes the activities of α-Syn, in different conformational states, monomeric, oligomeric and fibrils, in relation to neuronal dysfunction. The neuronal damage induced by α-Syn in various conformers will be analyzed in relation to its capacity to spread the intracellular aggregation seeds with a prion-like mechanism. In view of the prominent role of inflammation in virtually all neurodegenerative disorders, the activity of α-Syn will also be illustrated considering its influence on glial reactivity. We and others have described the interaction between general inflammation and cerebral dysfunctional activity of α-Syn. Differences in microglia and astrocyte activation have also been observed when in vivo the presence of α-Syn oligomers has been combined with a lasting peripheral inflammatory effect. The reactivity of microglia was amplified, while astrocytes were damaged by the double stimulus, opening new perspectives for the control of inflammation in synucleinopathies. Starting from our studies in experimental models, we extended the perspective to find useful pointers to orient future research and potential therapeutic strategies in neurodegenerative disorders.

Multiple Beneficial Effects of Aloesone from Aloe vera on LPS-Induced RAW264.7 Cells, Including the Inhibition of Oxidative Stress, Inflammation, M1 Polarization, and Apoptosis

Aloesone is a major metabolic compound in Aloe vera, which has been widely used as a food source and therapeutic agent in several countries. Our recent study demonstrated that aloesone has anti-epileptic effects on glutamate-induced neuronal injury by suppressing the production of reactive oxygen species (ROS). Unless ROS are naturally neutralized by the endogenous antioxidant system, they lead to the activation of inflammation, polarization, and apoptosis. This study aimed to identify the multiple beneficial effects of aloesone and explore its molecular mechanism in macrophages. Hence, the murine macrophage cell line RAW264.7 was pretreated with aloesone and then exposed to lipopolysaccharides (LPS). The results demonstrated that aloesone, within a dosage range of 0.1-100 µM, dramatically decreased the LPS-induced elevation of ROS production, reduced nitric oxide (NO) release, inhibited the M1 polarization of RAW264.7 cells, and prevented cells from entering the LPS-induced early and late phases of apoptosis in a dose-dependent manner. Simultaneously, aloesone significantly decreased the mRNA expression of inflammation-related genes (iNOS, IL-1ꞵ, TNF-α) and increased the expression of antioxidant enzymes (Gpx-1 and SOD-1). The core genes HSP90AA1, Stat3, Mapk1, mTOR, Fyn, Ptk2b, and Lck were closely related to these beneficial effects of aloesone. Furthermore, immunofluorescence staining and flow cytometry data confirmed that aloesone significantly repressed the activation of mTOR, p-mTOR, and HIF-1α induced by LPS and inhibited the protein expression of TLR4, which is the target of LPS. In conclusion, aloesone demonstrated multiple protective effects against LPS-induced oxidative stress, inflammation, M1 polarization, and apoptosis in macrophages, suggesting its potential as a prodrug.

The complex role of inflammation and gliotransmitters in Parkinson's disease

Our understanding of the role of innate and adaptive immune cell function in brain health and how it goes awry during aging and neurodegenerative diseases is still in its infancy. Inflammation and immunological dysfunction are common components of Parkinson's disease (PD), both in terms of motor and non-motor components of PD. In recent decades, the antiquated notion that the central nervous system (CNS) in disease states is an immune-privileged organ, has been debunked. The immune landscape in the CNS influences peripheral systems, and peripheral immunological changes can alter the CNS in health and disease. Identifying immune and inflammatory pathways that compromise neuronal health and survival is critical in designing innovative and effective strategies to limit their untoward effects on neuronal health.