Multiomic Analysis of Neuroinflammation and Occult Infection in Sudden Infant Death Syndrome

Importance

Antemortem infection is a risk factor for sudden infant death syndrome (SIDS)-the leading postneonatal cause of infant mortality in the developed world. Manifestations of infection and inflammation are not always apparent in clinical settings or by standard autopsy; thus, enhanced resolution approaches are needed.

Objective

To ascertain whether a subset of SIDS cases is associated with neuroinflammation and occult infection.

Design, Setting, and Participants

In this case-control study, postmortem fluids from SIDS cases and controls collected between July 2011 and November 2018 were screened for elevated inflammatory markers, specifically cerebrospinal fluid (CSF) neopterin and CSF and serum cytokines. CSF, liver, and brain tissue from SIDS cases with elevated CSF neopterin were subjected to metagenomic next-generation sequencing (mNGS) to probe for infectious pathogens. Brainstem tissue from a subset of these cases was analyzed by single-nucleus RNA sequencing (snRNAseq) to measure cell type-specific gene expression associated with neuroinflammation and infection. All tissue and fluid analyses were performed from April 2019 to January 2023 in a pathology research laboratory. Included was autopsy material from infants dying of SIDS and age-matched controls dying of known causes.

Exposures

There were no interventions or exposures.

Main Outcomes and Measures

CSF neopterin levels were measured by high-performance liquid chromatography. Cytokines were measured by multiplex fluorometric assay. mNGS was performed on liver, CSF, brain, and brainstem tissue. snRNAseq was performed on brainstem tissue.

Results

A cohort of 71 SIDS cases (mean [SD] age, 55.2 [11.4] postconceptional weeks; 42 male [59.2%]) and 20 controls (mean [SD] age, 63.2 [16.9] postconceptional weeks; 11 male [55.0%]) had CSF and/or serum available. CSF neopterin was screened in 64 SIDS cases and 15 controls, with no exclusions. Tissues from 6 SIDS cases were further analyzed. For CSF neopterin measures, SIDS samples were from infants with mean (SD) age of 54.5 (11.3) postconceptional weeks (38 male [59.4%]) and control samples were from infants with mean (SD) age of 61.5 (17.4) postconceptional weeks (7 male [46.7%]). A total of 6 SIDS cases (9.3%) with high CSF neopterin were identified, suggestive of neuroinflammation. mNGS detected human parechovirus 3 (HPeV3) in tissue and CSF from 1 of these 6 cases. snRNAseq of HPeV3-positive brainstem tissue (medulla) revealed dramatic enrichment of transcripts for genes with predominately inflammatory functions compared with 3 age-matched SIDS cases with normal CSF neopterin levels.

Conclusions and Relevance

Next-generation molecular tools in autopsy tissue provide novel insight into pathogens that go unrecognized by normal autopsy methodology, including in infants dying suddenly and unexpectedly.

Exploratory study of the effect of one week of orally administered CNSA-001 (sepiapterin) on CNS levels of tetrahydrobiopterin, dihydrobiopterin and monoamine neurotransmitter metabolites in healthy volunteers

Tetrahydrobiopterin (BH₄) is a cofactor for the enzymes tyrosine hydroxylase and tryptophan hydroxylase, the rate-limiting enzymes in the production of the neurotransmitters, dopamine and serotonin, respectively, in the central nervous system (CNS). Administration of BH₄ is used clinically within the management of persons with genetic BH₄ deficiencies, but the BH₄ molecule does not cross the blood-brain barrier sufficiently. CNSA-001 is a pharmaceutical preparation of sepiapterin, a natural precursor of BH₄ that induced larger increases in plasma BH₄ compared with administration of the same doses of BH₄ itself in healthy volunteers in a randomized trial. Here, we report the effects of 7 days of once-daily treatment with CNSA-001 60 mg/kg (n = 6) or placebo (n = 2) on metabolites of the BH₄ synthetic pathway and on biomarkers of the serotonin (5-hydroxyindoleacetic acid [5-HIAA]) and dopamine (homovanillic acid [HVA]) pathways in cerebrospinal fluid (CSF) in subjects from this trial. There were no notable changes in any metabolite in placebo-treated subjects. Administration of CNSA-001 increased mean BH₄ from 18.1 (SD 3.0) to 35.1 (10.0) nmol/L, and of dihydrobiopterin (BH₂) from 2.1 (0.3) to 7.9 (1.5) nmol/L. Overall, administration of CNSA-001 had little effect on mean levels (pre- vs. post-treatment) of 5-HIAA (76.1 [SD 29.8] vs. 70.1 [23.1] nmol/L) or HVA (177.2 [66.5] vs. 184.8 [35.3]) nmol/L. One subject with low 5-HIAA and HVA at baseline responded with approximately three-fold increases in CNS levels of these metabolites after CNSA-001 treatment, with post-treatment levels within the range of those seen in other subjects. Administration of CNSA-001 60 mg/kg markedly increased levels of BH₄ in the CNS of healthy volunteers, with apparently little overall effect in CNS levels of already normal key neurotransmitter metabolites.

•

Tetrahydrobiopterin (BH₄) is a cofactor of enzymes involved in production of central neurotransmitters dopamine and serotonin

•

Healthy volunteers were randomized to receive a once daily doses of CNSA-001 (sepiapterin) or placebo for 7 days

•

Oral CNSA-001 administration increased levels of BH₄ and 7,8-dihydrobiopterin (BH₂) in cerebrospinal fluid

•

Normal base levels of metabolites of serotonin (5-HIAA) or dopamine (HVA) were unaffected

•

Abnormally low baseline levels of 5-HIAA and HVA in one patient increased to normal ranges following CNSA-001 administration

Phase I clinical evaluation of CNSA-001 (sepiapterin), a novel pharmacological treatment for phenylketonuria and tetrahydrobiopterin deficiencies, in healthy volunteers

Tetrahydrobiopterin (BH4) is the natural cofactor of aromatic amino acid hydroxylases and essential for degradation of phenylalanine and synthesis of catecholamines and serotonin. It can be synthesized either de novo from GTP or through the salvage pathway from sepiapterin. Sepiapterin, a natural precursor of BH4, is a more stable molecule and is transported more efficiently across cellular membranes, thus having potentially significant advantage over BH4 as a pharmacological agent for diseases associated with BH4-deficient conditions. We report the results of a first-in-humans, randomized, double-blind, placebo-controlled, dose-ranging, Phase I clinical trial in 83 healthy volunteers of CNSA-001, a novel formulation of sepiapterin. Single oral doses of 2.5-80 mg/kg CNSA-001 caused dose-related increases in plasma sepiapterin (mean Cmax 0.58-2.92 ng/mL) and BH4 (mean Cmax 57-312 ng/mL). Maximum plasma concentrations were achieved in about 1-2 h (sepiapterin) or about 4 h (BH4) after CNSA-001 oral intake. Increases in plasma BH4 were substantially larger in absolute terms and on a dose-for-dose basis following treatment with CNSA-001 vs. sapropterin dihydrochloride, a synthetic form of BH4. The pharmacokinetics of plasma sepiapterin and BH4 were similar before and after seven days of repeat daily dosing with CNSA-001 at 5, 20 or 60 mg/kg indicating little or no drug accumulation. Oral administration of CNSA-001 resulted in higher concentrations of sepiapterin in fasted vs. fed subjects, but overall BH4 plasma exposure following CNSA-001 intake increased by 1.7-1.8-fold in fed subjects. CNSA-001 was well tolerated, with no clear dose-relationship for adverse events (AE), no serious AE and no study discontinuations for AE. These data indicate that CNSA-001 is rapidly and efficiently converted to BH4 in humans supporting further clinical evaluation of CNSA-001 for the management of PKU, primary BH4 deficiencies and other diseases associated with deficient BH4 metabolism.

Development of a Luminex Bead Based Assay for Diagnosis of Toxocariasis Using Recombinant Antigens Tc-CTL-1 and Tc-TES-26

The clinical spectrum of human disease caused by the roundworms Toxocara canis and Toxocara cati ranges from visceral and ocular larva migrans to covert toxocariasis. The parasite is not typically recovered in affected tissues, so detection of parasite-specific antibodies is usually necessary for establishing a diagnosis. The most reliable immunodiagnostic methods use the Toxocara excretory-secretory antigens (TES-Ag) in ELISA formats to detect Toxocara-specific antibodies. To eliminate the need for native parasite materials, we identified and purified immunodiagnostic antigens using 2D gel electrophoresis followed by electrospray ionization mass spectrometry. Three predominant immunoreactive proteins were found in the TES; all three had been previously described in the literature: Tc-CTL-1, Tc-TES-26, and Tc-MUC-3. We generated Escherichia coli expressed recombinant proteins for evaluation in Luminex based immunoassays. We were unable to produce a functional assay with the Tc-MUC-3 recombinant protein. Tc-CTL-1 and Tc-TES-26 were successfully coupled and tested using defined serum batteries. The use of both proteins together generated better results than if the proteins were used individually. The sensitivity and specificity of the assay for detecting visceral larval migrans using Tc-CTL-1 plus Tc-TES-26 was 99% and 94%, respectively; the sensitivity for detecting ocular larval migrans was 64%. The combined performance of the new assay was superior to the currently available EIA and could potentially be employed to replace current assays that rely on native TES-Ag.

Expression of recombinant antigenic proteins from Angiostrongylus cantonensis: a brief report

Cerebral angiostrongyliasis is an acute inflammation caused by the infection of the nematode Angiostrongylus cantonensis that results in eosinophilic meningitis. The current immunological assay of choice is an immunoblot that detects antibodies to a 31 kDa protein present in crude extracts of the female worm. Recently we have identified diagnostic targets from excretion and secretion products and determined the composition of the 31 kDa antigen after 2-D gel electrophoresis and mass spectrometry. Here we cloned and expressed five proteins in prokaryotic and eukaryotic systems. Recombinant proteins were purified and analysed by Western blot assays and among them 14-3-3, Lec5 and ES7 were recognized by Angiostrongylus-specific serum, although the signal was weak.

The 31-kDa antigen of Angiostrongylus cantonensis comprises distinct antigenic glycoproteins

Human angiostrongyliasis results from accidental infection with Angiostrongylus, an intra-arterial nematode. Angiostrongylus cantonensis infections result in eosinophilic meningitis, and A. costaricensis infections cause eosinophilic enteritis. Immunological methodologies are critical to the diagnosis of both infections, since these parasites cannot be isolated from fecal matter and are rarely found in cerebrospinal fluid samples. A. costaricensis and A. cantonensis share common antigenic epitopes which elicit antibodies that recognize proteins present in either species. Detection of antibodies to a 31-kDa A. cantonensis protein present in crude adult worm extracts is a sensitive and specific method for immunodiagnosis of cerebral angiostrongyliasis. The objective of the present work was to isolate and characterize the 31-kDa proteins using soluble protein extracts derived from adult female worms using both one- (1DE) and two-dimensional (2DE) gel electrophoresis. Separated proteins were blotted onto nitrocellulose and probed using sera from infected and non-infected controls. The 31-kDa band present in 1DE gels and the 4 spots identified in 2DE gels were excised and analyzed by electrospray ionization mass spectrometry. Using the highest scores obtained following Mascot analysis, amino acid sequences were obtained that matched four unique proteins: tropomyosin, the 14-3-3 phosphoserine-binding protein, a protein containing a nascent polypeptide-associated complex domain, and the putative epsilon subunit of coatomer protein complex isoform 2. Oxidative cleavage of diols using sodium m-periodate demonstrated that carbohydrate moieties are essential for the antigenicity of all four spots of the 31-kDa antigen. In this article we describe the identification of the 31-kDa antigen, and provide DNA sequencing of the targets. In conclusion, these data suggest that reactivity to the 31-kDa proteins may represent antibody recognition of more than one protein, and recombinant protein-based assays for cerebral angiostrongyliasis diagnosis may require eukaryotic expression systems to maintain antigenicity.

Characterization of Angiostrongylus cantonensis excretory-secretory proteins as potential diagnostic targets

Angiostrongyliasis results from infections with intra-arterial nematodes that accidentally infect humans. Specifically, infections with Angiostrongylus cantonensis cause eosinophilic meningitis and Angiostrongylus costaricensis infections result in eosinophilic enteritis. Immunological tests are the primary means of diagnosing infections with either pathogen since these parasites are usually not recoverable in fecal or cerebrospinal fluid. However, well-defined, purified antigens are not currently available in sufficient quantities from either pathogen for use in routine immunodiagnostic assays. Since A. costaricensis and A. cantonensis share common antigens, sera from infected persons will recognize antigens from either species. In addition to their potential use in angiostrongyliasis diagnosis, characterization of these proteins that establish the host-parasite interphase would improve our understanding of the biology of these parasites. The main objective of the present work was to characterize A. cantonensis excretory-secretory (ES) products by analyzing ES preparations by two-dimensional gel electrophoresis coupled with immunoblotting using pools of positive sera (PS) and sera from healthy individuals (SC). Protein spots recognized by PS were excised and analyzed by electrospray ionization (ESI) mass spectrometry. MASCOT analysis of mass spectrometry data identified 17 proteins: aldolase; CBR-PYP-1 protein; beta-amylase; heat shock protein 70; proteosome subunit beta type-1; actin A3; peroxiredoxin; serine carboxypeptidase; protein disulfide isomerase 1; fructose-bisphosphate aldolase 2; aspartyl protease inhibitor; lectin-5; hypothetical protein F01F1.12; cathepsin B-like cysteine proteinase 1; hemoglobinase-type cysteine proteinase; putative ferritin protein 2; and a hypothetical protein. Molecular cloning of these respective targets will next be carried out to develop a panel of Angiostrongylus antigens that can be used for diagnostic purposes and to further study host-Angiostrongylus interactions.

The sequence of the acidic repeat protein (arp) gene differentiates venereal from nonvenereal Treponema pallidum subspecies, and the gene has evolved under strong positive selection in the subspecies that causes syphilis

Despite the completion of the Treponema pallidum genome project, only minor genetic differences have been found between the subspecies that cause venereal syphilis (ssp. pallidum) and the nonvenereal diseases yaws (ssp. pertenue) and bejel (ssp. endemicum). In this paper, we describe sequence variation in the arp gene which allows straightforward differentiation of ssp. pallidum from the nonvenereal subspecies. We also present evidence that this region is subject to positive selection in ssp. pallidum, consistent with pressure from the immune system. Finally, the presence of multiple, but distinct, repeat motifs in both ssp. pallidum and Treponema paraluiscuniculi (the pathogen responsible for rabbit syphilis) suggests that a diverse repertoire of repeat motifs is associated with sexual transmission. This study suggests that variations in the number and sequence of repeat motifs in the arp gene have clinical, epidemiological, and evolutionary significance.