Peroxisomes in brain development and function

Peroxisomes contain numerous enzymatic activities that are important for mammalian physiology. Patients lacking either all peroxisomal functions or a single enzyme or transporter function typically develop severe neurological deficits, which originate from aberrant development of the brain, demyelination and loss of axonal integrity, neuroinflammation or other neurodegenerative processes. Whilst correlating peroxisomal properties with a compilation of pathologies observed in human patients and mouse models lacking all or individual peroxisomal functions, we discuss the importance of peroxisomal metabolites and tissue- and cell type-specific contributions to the observed brain pathologies. This enables us to deconstruct the local and systemic contribution of individual metabolic pathways to specific brain functions. We also review the recently discovered variability of pathological symptoms in cases with unexpectedly mild presentation of peroxisome biogenesis disorders. Finally, we explore the emerging evidence linking peroxisomes to more common neurological disorders such as Alzheimer’s disease, autism and amyotrophic lateral sclerosis. This article is part of a Special Issue entitled: Peroxisomes edited by Ralf Erdmann.

Oral administration of a synthetic vinyl-ether plasmalogen normalizes open field activity in a mouse model of rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata (RCDP) is a rare genetic disorder caused by mutations in peroxisomal genes essential for plasmalogen biosynthesis. Plasmalogens are a class of membrane glycerophospholipids containing a vinyl-ether-linked fatty alcohol at the sn-1 position that affect functions including vesicular transport, membrane protein function and free radical scavenging. A logical rationale for the treatment of RCDP is therefore the therapeutic augmentation of plasmalogens. The objective of this work was to provide a preliminary characterization of a novel vinyl-ether synthetic plasmalogen, PPI-1040, in support of its potential utility as an oral therapeutic option for RCDP. First, wild-type mice were treated with ¹³C₆-labeled PPI-1040, which showed that the sn-1 vinyl-ether and the sn-3 phosphoethanolamine groups remained intact during digestion and absorption. Next, a 4-week treatment of adult plasmalogen-deficient Pex7^hypo/null mice with PPI-1040 showed normalization of plasmalogen levels in plasma, and variable increases in plasmalogen levels in erythrocytes and peripheral tissues (liver, small intestine, skeletal muscle and heart). Augmentation was not observed in brain, lung and kidney. Functionally, PPI-1040 treatment normalized the hyperactive behavior observed in the Pex7^hypo/null mice as determined by open field test, with a significant inverse correlation between activity and plasma plasmalogen levels. Parallel treatment with an equal amount of ether plasmalogen precursor, PPI-1011, did not effectively augment plasmalogen levels or reduce hyperactivity. Our findings show, for the first time, that a synthetic vinyl-ether plasmalogen is orally bioavailable and can improve plasmalogen levels in an RCDP mouse model. Further exploration of its clinical utility is warranted.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: This article shows, for the first time, that a synthetic vinyl-ether plasmalogen is orally bioavailable and bioactive in vivo following administration in animals.

Rhizomelic chondrodysplasia punctata: Role of EEG as a biomarker of impending epilepsy

Progressive deterioration of neuroimaging and electroencephalography (EEG) had been described in rhizomelic chondrodysplasia punctata (RCDP); however, serial EEG data showing sequential EEG changes(before and after seizure onset) is lacking. We report a child with a diagnosis of type 1 RCDP, who had a progressive decline in EEG and radiologic findings over a 5 year period. Her first EEG was normal at the age of 8 months. Follow-up EEG at the age of 2 years showed a mild background slowing as well as frequent 1–2 Hz central-parietal spike wave with midline involvement. Just before 3 years of age, she started to seizures, when the EEG showed further worsening with frequent multifocal spikes and bursts of generalized high amplitude spike and spike-wave discharges. The transition of EEG from normal background to the appearance of focal epileptiform abnormality before the seizure onset followed by further deterioration at the seizure onset had not been reported as per our knowledge. This study emphasizes that serial EEGs may provide valuable information about impending seizure activity. Further studies are needed to calculate the lag time between the detection of epileptiform activities and the onset of clinical seizure activities. In addition, research studies are warranted to determine if early (before or at the onset of epileptogenesis rather than after seizure onset) use of replacement therapy or antiepileptic therapy (antiepileptic drugs or diet) can modify epilepsy severity and neurologic prognosis in this devastating disease.

An Atypical form Rhizomelic Chondrodysplasia Punctata in a Newborn

Rhizomelic Chondrodysplasia punctata (RCDP) is an autosomal recessive metabolic disorder affecting mainly peroxisomal function. We describe a case of RCDP in a 12 days old newborn based on the clinical and radiological ground without any major systemic structural or functional abnormalities.

Human Genetics of Atrial Septal Defect

Although atrial septal defects (ASD) can be subdivided based on their anatomical location, an essential aspect of human genetics and genetic counseling is distinguishing between isolated and familiar cases without extracardiac features and syndromic cases with the co-occurrence of extracardiac abnormalities, such as developmental delay. Isolated or familial cases tend to show genetic alterations in genes related to important cardiac transcription factors and genes encoding for sarcomeric proteins. By contrast, the spectrum of genes with genetic alterations observed in syndromic cases is diverse. Currently, it points to different pathways and gene networks relevant to the dysregulation of cardiomyogenesis and ASD pathogenesis. Therefore, this chapter reflects the current knowledge and highlights stable associations observed in human genetics studies. It gives an overview of the different types of genetic alterations in these subtypes, including common associations based on genome-wide association studies (GWAS), and it highlights the most frequently observed syndromes associated with ASD pathogenesis.

Development and evaluation of RhizoQOL, a quality-of-life caregiver-reported survey for rhizomelic chondrodysplasia punctata, a rare peroxisomal disorder

BACKGROUND

Rhizomelic chondrodysplasia punctata (RCDP) is a rare genetic disorder characterized by symptoms such as respiratory dysfunction, seizures, orthopedic issues, and neurodevelopmental delay. Potential therapeutics for RCDP warrant the development of clinical outcome assessments to assess the efficacy of treatment and the well-being of patients. Our study aimed to develop a valid quality-of-life (QOL) caregiver-reported survey instrument, RhizoQOL, to be used as a supportive endpoint in RCDP clinical trials.

METHODS

Development of the RhizoQOL survey tool included three RCDP caregiver focus groups to elicit concepts to serve as potential domains in a QOL survey instrument for RCDP, pilot survey development and initial testing, cognitive interviewing of revised survey drafts to determine content validity, as well as a three-month longitudinal study for reliability and internal consistency of the survey instrument.

RESULTS

Twenty-eight caregivers participated in the focus groups, reporting that concepts that could be appropriate domains of QOL in RCDP include psychosocial behavior, feeding symptoms, mobility symptoms, respiratory symptoms, seizures and related activity, and impact of treatment. Following pilot survey testing (n = 22) and stakeholder feedback, a revised pilot survey instrument was administered to five caregivers for cognitive interviewing. This resulted in a revised survey instrument with 31 question items, six domains, and a 1-5 Likert scale item response assessing frequency or severity of event in the question item. Longitudinal testing (n = 18) of the revised survey instrument found the average response score was 1.98 ± 0.97 for all question items, and a Cronbach's alpha value of 0.856, suggesting strong intra-survey question reliability. Using individual question item results from reliability testing, linear regression modeling, and testing for required magnitude of significant treatment effects, eight question items were removed from the survey instrument, resulting in a total of 23 question items within 6 discrete domains.

CONCLUSIONS

The final RhizoQOL survey instrument, consisting of 23 questions, assesses the symptoms and experiences of RCDP patients as observed by caregivers and serves as a novel clinical outcome assessment for RCDP therapeutic clinical trials to assess the impacts of RCDP and support the overall effectiveness of treatments.

First-In-Human Safety, Tolerability, and Pharmacokinetics of PPI-1011, a Synthetic Plasmalogen Precursor

PPI-1011 is a synthetic plasmalogen precursor designed to augment plasmalogen levels in patients with Rhizomelic chondrodysplasia punctata (RCDP), an ultra-rare genetic disorder caused by a plasmalogen deficiency that results in significant physical and mental delays. We report here a Phase I, randomized, double-blind, placebo-controlled study that evaluated the safety, tolerability, and pharmacokinetics (PK) of single (10-100 mg/kg) and multiple (75 and 100 mg/kg/day) ascending doses of PPI-1011 in healthy adults. All treatment-emergent adverse events (TEAEs) were mild, monitorable, and resolved without intervention, suggesting no significant safety concerns. The most common TEAEs were gastrointestinal in both the placebo and PPI-1011 groups, suggesting they were likely related to the oil-based nature of the formulation. PK analysis confirmed that both single (25, 50, 75 and 100 mg/kg) and multiple-dose (75 and 100 mg/kg, once daily) administration of PPI-1011 significantly increased serum levels of the target plasmalogen (PlsEtn 16:0/22:6). With a once-daily regimen, PPI-1011 administration resulted in a sustained increase of PlsEtn 16:0/22:6 serum concentrations in healthy participants over a duration of 14 days and beyond.

Recombinant human dihydroxyacetonephosphate acyl-transferase characterization as an integral monotopic membrane protein

Although the precise functions of ether phospholipids are still poorly understood, significant alterations in their physiological levels are associated either to inherited disorders or to aggressive metastatic cancer. The essential precursor, alkyl-dihydroxyacetone phosphate (DHAP), for all ether phospholipids species is synthetized in two consecutive reactions performed by two enzymes sitting on the inner side of the peroxisomal membrane. Here, we report the characterization of the recombinant human DHAP acyl-transferase, which performs the first step in alkyl-DHAP synthesis. By exploring several expression systems and designing a number of constructs, we were able to purify the enzyme in its active form and we found that it is tightly bound to the membrane through the N-terminal residues.

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Human DHAPAT is associated to peroxisomal membrane through the N-terminal region.

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Recombinant human DHAPAT expressed and purified from P. pastoris cells is active.

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Evidence of the in vitro reconstitution of DHAPAT/ADPS enzymatic complex.

Quantitative analysis of ethanolamine plasmalogen species in red blood cells using liquid chromatography tandem mass spectrometry for diagnosing peroxisome biogenesis disorders

Plasmalogens are glycerophospholipids characterized by a vinyl-ether bond with a fatty alcohol at the sn-1 position, a polyunsaturated fatty acid at the sn-2 position, and a polar head at the sn-3 position, commonly phosphoethanolamine. Plasmalogens play crucial roles in several cellular processes. Reduced levels have been associated with Alzheimer's and Parkinson's disease progression. Markedly reduced plasmalogens are a classic feature of peroxisome biogenesis disorders (PBD) because plasmalogen synthesis requires functional peroxisomes. Particularly, severe plasmalogen deficiency is the biochemical hallmark of rhizomelic chondrodysplasia punctata (RCDP). Traditionally, plasmalogens are evaluated in red blood cells (RBCs) by gas-chromatography/mass-spectrometry (GC-MS), which cannot distinguish individual species. We developed a liquid-chromatography/tandem mass-spectrometry (LC-MS/MS) method to quantify eighteen phosphoethanolamine plasmalogens in RBCs to diagnose PBD patients, especially RCDP. Validation results showed a specific, robust, and precise method with broad analytical range. Age-specific reference intervals were established; control medians were used to assess plasmalogen deficiency in patients' RBCs. Clinical utility was also confirmed in Pex7 deficient mouse models recapitulating severe and milder RCDP clinical phenotypes. To our knowledge, this is the first attempt to replace the GC-MS method in the clinical laboratory. In addition to diagnosing PBDs, structure-specific plasmalogen quantitation could help understand disease pathogenesis and monitor therapy.