Peripheral iron metabolism in patients with Parkinson's disease

Metal Exposure and Risk of Parkinson Disease: A Systematic Review and Meta-Analysis

Metal exposure has been suggested as a possible environmental risk factor for Parkinson disease (PD). We searched the PubMed, EMBASE, and Cochrane databases to systematically review the literature on the relationship between metal exposure and PD risk and to examine the overall quality of each study and the exposure assessment method. A total of 83 case-control studies and 5 cohort studies published during the period 1963-July 2021 were included, of which 73 were graded as being of low or moderate overall quality. Investigators in 69 studies adopted self-reported exposure and biomonitoring after disease diagnosis for exposure assessment approaches. The meta-analyses showed that concentrations of copper and iron in serum and concentrations of zinc in either serum or plasma were lower, while concentrations of magnesium in CSF and zinc in hair were higher, among PD cases as compared with controls. Cumulative lead levels in bone were found to be associated with increased risk of PD. We did not find associations between other metals and PD. The current level of evidence for associations between metals and PD risk is limited, as biases from methodological limitations cannot be ruled out. High-quality studies assessing metal levels before disease onset are needed to improve our understanding of the role of metals in the etiology of PD.

Biological fluid levels of iron and iron-related proteins in Parkinson's disease: Review and meta-analysis

BACKGROUND AND PURPOSE

Several studies suggested a role or iron in the pathogenesis or Parkinson's disease (PD), and substantia nigra iron concentrarions have been found increased in PD. However, the results on cerebrospinal (CSF) and serum/plasma iron levels in PD patients have been controversial. The aim of this systematic review and meta-analysis was to establish the CSF and serum/plasma levels of iron and iron-related proteins (ferritin, transferrin, lactoferrin, haptoglobin, and hepcidine) levels, and the urine levels of iron, in patients with PD.

METHODS

Four databases (PubMed, EMBASE, MedLine, and Web of Science - Core Collection) were reviewed for studies published from 1966 to October 5, 2020. References of interest were identified. A meta-analysis of eligible studies was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines, using the R software package meta.

RESULTS

A non-significant trend towards higher CSF iron levels and marginally significantly lower serum/plasma iron levels was observed in patients with PD compared with age- and sex-matched controls. CSF and serum/plasma ferritin and transferrin concentrations, and serum/plasma lactoferrin and haptoglobin concentrations did not differ significantly between PD patients and controls.

CONCLUSION

The findings of this study suggest an association between decreased serum/plasma iron levels and, possibly, higher CSF iron levels with risk of PD.

Shared perturbations in the metallome and metabolome of Alzheimer's, Parkinson's, Huntington's, and dementia with Lewy bodies: A systematic review

Despite differences in presentation, age-related dementing diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases (HD), and dementia with Lewy bodies (DLB) may share pathogenic processes. This review aims to systematically assemble and compare findings in various biochemical pathways across these four dementias. PubMed and Google Scholar were screened for articles reporting on brain and biofluid measurements of metals and/or metabolites in AD, PD, HD, or DLB. Articles were assessed using specific a priori-defined inclusion and exclusion criteria. Of 284 papers identified, 198 met criteria for inclusion. Although varying coverage levels of metals and metabolites across diseases and tissues made comparison of many analytes impossible, several common findings were identified: elevated glucose in both brain tissue and biofluids of AD, PD, and HD cases; increased iron and decreased copper in AD, PD and HD brain tissue; and decreased uric acid in biofluids of AD and PD cases. Other analytes were found to differ between diseases or were otherwise not covered across all conditions. These findings indicate that disturbances in glucose and purine pathways may be common to AD, PD, and HD. However, standardisation of methodologies and better coverage in some areas - notably of DLB - are necessary to validate and extend these findings.

Iron and inflammation: in vivo and post-mortem studies in Parkinson's disease

In these present studies, in vivo and and post-mortem studies have investigated the association between iron and inflammation. Early-stage Parkinson's disease (PD) patients, of less than 5 years disease duration, showed associations of plasmatic ferritin concentrations with both proinflammatory cytokine interleukin-6 and hepcidin, a regulator of iron metabolism as well as clinical measures. In addition ratios of plasmatic ferritin and iron accumulation in deep grey matter nuclei assessed with relaxometry T2* inversely correlated with disease severity and duration of PD. On the hand, post-mortem material of the substantia nigra compacta (SNc) divided according to Braak and Braak scores, III-IV and V-VI staging, exhibited comparable microgliosis, with a variety of phenotypes present. There was an association between the intensity of microgliosis and iron accumulation as assayed by Perl's staining in the SNc sections. In conclusion, markers of inflammation and iron metabolism in both systemic and brain systems are closely linked in PD, thus offering a potential biomarker for progression of the disease.

Iron Concentration Does Not Differ in Blood but Tends to Decrease in Cerebrospinal Fluid in Parkinson's Disease

Background

Iron accumulation in the substantia nigra in PD patients was acknowledged, but the studies on alteration of iron levels in blood and cerebrospinal fluids (CSF) reported inconsistent results.

Objective

To determinate the alterations of blood and CSF levels of iron in PD patients, a case-control study and a meta-analysis both in blood and CSF were conducted.

Methods

In the case-control study, 43 PD patients and 33 controls were recruited to test iron metabolism, 15 normal and 12 PD patients donated CSF. Levels in iron were quantified by inductively coupled atomic emission spectrometry. Iron metabolism was analyzed by routine blood tests. In the meta-analysis, a comprehensive literature search was performed on relevant studies published from Jan 1980 to Dec 2018 in PubMed, Web of Science and EMBASE databases. The pooled standard mean difference (SMD) with random effects model was selected to estimate the association between iron levels and PD.

Results

In the case-control study, the iron level in serum in the controls and PD patients were 110.00 ± 48.75 μg/dl and 107.21 ± 34.25 μg/dl, respectively, no significant difference was found between them (p = 0.850), with a small effect size (Cohen’s d: 0.12; 95% CI: 0.08–0.17). Ferritin level in PD patients was lower than controls (p = 0.014). The CSF levels of iron in control and the PD patients were 20.14 ± 3.35 ng/dl and 16.26 ± 4.82 ng/dl, respectively. CSF levels of iron were lower in PD compared with that of controls (p = 0.021), with a moderate effect size (Cohen’s d: 0.51; 95% CI: 0.43–0.65). In the meta-analysis, 22 eligible studies and a total of 3607 participants were identified. Blood levels of iron did not differ significant between PD patients and the controls [SMD (95% CI): −0.03 (−0.30, 0.24)], but CSF iron levels tended to be lower in PD patients compared with that in the controls [SMD (95% CI): −0.33 (−0.65, −0.00)].

Conclusion

Iron homeostasis may be disturbed in CSF, but not in the peripheral blood in PD.

Brain iron concentrations in regions of interest and relation with serum iron levels in Parkinson disease

Brain iron has been previously found elevated in the substantia nigra pars compacta (SNpc), but not in other brain regions, of Parkinson's disease (PD) patients. However, iron in circulation has been recently observed to be lower than normal in PD patients. The regional selectivity of iron deposition in brain as well as the relationship between SNpc brain iron and serum iron within PD patients has not been completely elucidated. In this pilot study we measured brain iron in six regions of interest (ROIs) as well as serum iron and serum ferritin, in 24 PD patients and 27 age- gender-matched controls. Brain iron was measured on magnetic resonance imaging (MRI) with a T2 prime (T2') method. Difference in brain iron deposition between PD cases and controls for the six ROIs were calculated. SNpc/white matter brain iron ratios and SNpc/serum iron ratios were calculated for each study participant, and differences between PD patients and controls were tested. PD patients overall had higher brain iron than controls in the SNpc. PD patients had significantly higher SNpc/white matter brain iron ratios than controls, and significantly higher brain SNpc iron/serum iron ratios than controls. These results indicate that PD patients' iron metabolism is disrupted toward a higher partitioning of iron to the brain SNpc at the expenses of iron in the circulation.

Meta-analysis of the association between serum iron levels and Parkinson's disease: Evidence from 11 publications

BACKGROUND

There is no consensus on the serum iron levels and Parkinson's disease (PD). The aim of this study is to conduct a systematic review and meta-analysis to analyse the relationship between serum iron levels and PD risk.

METHODS

We searched the databases of PubMed, Web of knowledge, Embase, the Cochrane Library, China National Knowledge Infrastructure (CNKI) and China Biology Medical literature to assess the association between serum iron levels and PD risk. Standardized mean differences (SMD) and 95% confidence intervals (CI) with random-effect model were used to combine the results.

RESULTS

Eleven related articles met our selection criteria and contained a total of 829PD patients and 1219 healthy controls. Our meta-analysis results revealed that the serum iron levels in PD patients were significantly higher than those in healthy controls (SMD=0.27, 95% CI=0.18, 0.37, P<0.001). Subgroup analysis by ethnicity showed that the serum iron levels in PD patients were significantly higher than controls both in Asian populations and European populations. Significant associations were also found in prospective studies and case-control studies.

CONCLUSIONS

Our meta-analysis showed strong evidence that a significantly higher serum iron levels are present in PD patients when compared to the healthy controls.

Haptoglobin phenotype modifies serum iron levels and the effect of smoking on Parkinson disease risk

INTRODUCTION

Haptoglobin is a hemoglobin-binding protein that exists in three functionally different phenotypes, and haptoglobin phenotype 2-1 has previously been associated with Parkinson disease (PD) risk, with mechanisms not elucidated. Some evidence is emerging that low levels of serum iron may increase PD risk. In this study we investigated whether PD patients have lower serum iron and ferritin than controls, and whether this is dependent on haptoglobin phenotype. We also investigated the effect of Hp phenotype as a modifier of the effect of smoking on PD risk.

METHODS

The study population consisted of 128 PD patients and 226 controls. Serum iron, ferritin, and haptoglobin phenotype were determined, and compared between PD cases and controls. Stratified analysis by haptoglobin phenotype was performed to determine effect of haptoglobin phenotype on serum iron parameter differences between PD cases and controls and to investigate its role in the protective effect of smoking on PD risk.

RESULTS

PD cases had lower serum iron than controls (83.28 ug/100 ml vs 94.00 ug/100 ml, p 0.006), and in particular among subjects with phenotype 2-1. The protective effect of smoking on PD risk resulted stronger in subjects with phenotype 1-1 and 2-2, and weakest among subjects with phenotype 2-1. Ferritin levels were higher in PD cases than controls among subjects of White ethnicity.

CONCLUSIONS

Our results report for the first time that the haptoglobin phenotype may be a contributor of iron levels abnormalities in PD patients. The mechanisms for these haptoglobin-phenotype specific effects will have to be further elucidated.

Serum vitamins and heavy metals in blood and urine, and the correlations among them in Parkinson's disease patients in China

BACKGROUND

Some heavy metals are suspected to be pathogenic and some vitamins protective against Parkinson's disease (PD), and the interaction between heavy metals and vitamins could be associated with the pathophysiology of PD.

METHODS

Subjects comprised PD patients and sex- and age-matched controls recruited from an outpatient clinic in China. Morning blood and urine samples were used to measure concentrations of metals and vitamins.

RESULTS

The serum iron, whole-blood manganese, urine iron and copper levels were significantly higher in the PD patients than in the controls. The correlation coefficient between serum and urine concentrations of iron in the PD patients was significant. The serum vitamin E/urine copper ratio was significantly lower in the PD patients than in the controls. Serum vitamin E was negatively correlated with serum copper and was positively correlated with urine copper in the PD patients. Serum vitamin B(12) was positively correlated with serum zinc in the PD patients and was negatively correlated with urine zinc in the controls.

CONCLUSIONS

Excessive intake of iron and copper, accumulation of manganese, vitamin E/copper imbalance in intake, and vitamin B(12) decrease by zinc deficiency in the body might be involved in the etiology of PD.

Metal changes in CSF and peripheral compartments of parkinsonian patients

BACKGROUND

Involvement of metals in the risk of developing Parkinson's disease (PD) has been suggested. In the present study, concentration of metals in cerebrospinal fluid (CSF), blood, serum, urine and hair of 91 PD patients and 18 controls were compared.

METHODS

Blood and hair were microwave digested, while CSF, serum and urine were water-diluted. Elements quantification was achieved by Inductively Coupled Plasma Atomic Emission Spectrometry and Sector Field Inductively Coupled Plasma Mass Spectrometry.

RESULTS

Some metal imbalances in PD were observed: i), in CSF, lower Fe and Si; ii), in blood, higher Ca, Cu, Fe, Mg and Zn; iii), in serum, lower Al and Cu; iv), in urine, lower Al and Mn, higher Ca and Fe; and v), in hair, lower Fe. The ROC analysis suggested that blood Ca, Fe, Mg and Zn were the best discriminators between PD and controls. In addition, hair Ca and Mg were at least 1.5 times higher in females than in males of patients and controls. A decrement with age of patients in hair and urine Ca and, with less extent, in urine Si was observed. Magnesium concentration in CSF decreased with the duration and severity of the disease. Elements were not influenced by the type of antiparkinsonian therapy.

CONCLUSIONS

Variation in elements with the disease do not exclude their involvement in the neurodegeneration of PD.

Serum trace element levels and the complexity of inter-element relations in patients with Parkinson's disease

Trace elements have been postulated to play a role in Parkinson's disease (PD). In order to elucidate whether changes in the serum levels of trace elements reflect the progression of PD, we assessed serum levels of 12 elements (Na, K, Fe, Al, Cu, Zn, Ca, Mg, Mn, Si, P and S) in early PD, severe PD and normal subjects, using inductively coupled plasma atomic emission spectrometry. The concentrations in micromol/ml, the relative mole percentage distribution and inter-element relations were computed. Statistical analysis of these data showed a definite pattern of variation among certain elements in early and severe PD compared to controls. In both early and severe PD serum, Al and S concentrations were significantly decreased (p<0.05) compared to the controls. Fe (p<0.01) and Zn (p<0.05) concentrations were significantly lower in severe PD, while K, Mg, Cu (p < 0.01) and P (p < 0.05) concentrations were higher in early and severe PD compared to the controls. The data revealed an imbalance in the inter-element relations in both early and severe PD serum compared to controls, as shown by the direct and inverse correlations. These results suggest a disturbance in the element homeostasis during the progression of PD.

Oxidative stress in Parkinson's disease

Oxidative stress contributes to the cascade leading to dopamine cell degeneration in Parkinson's disease (PD). However, oxidative stress is intimately linked to other components of the degenerative process, such as mitochondrial dysfunction, excitotoxicity, nitric oxide toxicity and inflammation. It is therefore difficult to determine whether oxidative stress leads to, or is a consequence of, these events. Oxidative damage to lipids, proteins, and DNA occurs in PD, and toxic products of oxidative damage, such as 4-hydroxynonenal (HNE), can react with proteins to impair cell viability. There is convincing evidence for the involvement of nitric oxide that reacts with superoxide to produce peroxynitrite and ultimately hydroxyl radical production. Recently, altered ubiquitination and degradation of proteins have been implicated as key to dopaminergic cell death in PD. Oxidative stress can impair these processes directly, and products of oxidative damage, such as HNE, can damage the 26S proteasome. Furthermore, impairment of proteasomal function leads to free radical generation and oxidative stress. Oxidative stress occurs in idiopathic PD and products of oxidative damage interfere with cellular function, but these form only part of a cascade, and it is not possible to separate them from other events involved in dopaminergic cell death.

Assessment of plasma lactoferrin in Parkinson's disease

Iron may play an important role in the pathogenesis of Parkinson's disease (PD). Recent studies have shown that the iron-transporting glycoprotein lactoferrin (LF) and its receptor are increased in the substantia nigra (SN) in PD. We investigated whether plasma levels of LF are altered in dopa-responsive PD. Plasma LF was not different between patients with PD (n = 23; 306 +/- 116 [mean +/- standard deviation] ng/ml) and age- and sex-matched healthy control subjects (n = 15; 359 +/- 126 ng/ml ). However, LF was inversely correlated with PD severity (r = -0.68, P = 0.002), an association that remained significant after adjustment for treatment with levodopa, monoaminooxidase inhibitors, and dopa agonists (r = -0.53, P = 0.017). Plasma transferrin and ferritin levels were not different between groups and neither correlated with disease severity nor with LF levels. Together with the result of increased nigral lactoferrin, this finding is compatible with the hypothesis of an imbalance between LF levels in blood and SN in progressing PD. Larger and particularly longitudinal studies and measurements of LF in cerebrospinal fluid are warranted to further examine the role of LF in PD.

Time course of dopaminergic cell death and changes in iron, ferritin and transferrin levels in the rat substantia nigra after 6-hydroxydopamine (6-OHDA) lesioning

Parkinson's disease is characterized by dopaminergic cell death in the substantia nigra. The underlying mechanism is, however, unknown. Though there are increasing lines of evidence showing iron accumulation in the Parkinsonian substantia nigra, it still remains obscure whether increased iron is the primary cause of dopaminergic cell death, or just a consequence of the pathological process. It is also unclear how iron gains access to the Parkinsonian SN. To gain more understanding in these areas, the present study investigated the time course of dopaminergic cell death and of changes in the level of iron, ferritin and transferrin. The results showed that iron was increased after the significant nigral dopaminergic cell death induced by 6-hydroxydopamine injection into the rat substantia nigra. On the other hand, the expression of transferrin was decreased. However, there was a temporal increase in the number of ferritin positive microglia. The results indicated that iron increase was not the primary cause of dopaminergic cell death in the Parkinsonian rat. It was most likely the result of an accumulation of iron-laden microglia.

The role of iron in neurodegeneration: prospects for pharmacotherapy of Parkinson's disease

Although the aetiology of Parkinson's disease (PD) and related neurodegenerative disorders is still unknown, recent evidence from human and experimental animal models suggests that a misregulation of iron metabolism, iron-induced oxidative stress and free radical formation are major pathogenic factors. These factors trigger a cascade of deleterious events leading to neuronal death and the ensuing biochemical disturbances of clinical relevance. A review of the available data in PD provides the following evidence in support of this hypothesis: (i) an increase of iron in the brain, which in PD selectively involves neuromelanin in substantia nigra (SN) neurons; (ii) decreased availability of glutathione (GSH) and other antioxidant substances; (iii) increase of lipid peroxidation products and reactive oxygen (O2)species (ROS); and (iv) impaired mitochondrial electron transport mechanisms. Most of these changes appear to be closely related to interactions between iron and neuromelanin, which result in accumulation of iron and a continuous production of cytotoxic species leading to neuronal death. Some of these findings have been reproduced in animal models using 6-hydroxydopamine, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), iron loading and beta-carbolines, although none of them is an accurate model for PD in humans. Although it is not clear whether iron accumulation and oxidative stress are the initial events causing cell death or consequences of the disease process, therapeutic efforts aimed at preventing or at least delaying disease progression by reducing the overload of iron and generation of ROS may be beneficial in PD and related neurodegenerative disorders. Current pharmacotherapy of PD, in addition to symptomatic levodopa treatment, includes 'neuroprotective' strategies with dopamine agonists, monoamine oxidase-B inhibitors (MAO-B), glutamate antagonists, catechol O-methyltransferase inhibitors and other antioxidants or free radical scavengers. In the future, these agents could be used in combination with, or partly replaced by, iron chelators and lazaroids that prevent iron-induced generation of deleterious substances. Although experimental and preclinical data suggest the therapeutic potential of these drugs, their clinical applicability will be a major challenge for future research.