Single Molecule Assay for Ultrasensitive Detection of Cathepsin B in Human Blood

Cathepsin B (catB) is a lysosomal cysteine protease expressed in several cells and organs, where it plays a role in protein degradation and turnover. Extracellular, secreted catB has utility as a biomarker for a host of pathological or physiological states, including a myriad of cancers or neurological diseases and injuries. Analytical or diagnostic assessment may be limited by biological sample volume availability. Pathologically relevant changes in catB levels may occur at low-moderate concentrations that require accurate measurement to differentiate from basal levels. Furthermore, biological samples like plasma and serum, often occlude accurate catB measurements because of background and high variance, vastly limiting the ability to detect catB as a peripheral biomarker. Techniques for ultrasensitive protein detection that require low volumes of sample are necessary. To overcome these challenges, a digital enzyme-linked immunosorbent assay (ELISA) was developed for differential detection of catB within less than 5 μL of serum and plasma using the single molecule array (SiMoA) platform, which offers 1000-times more sensitivity and vastly reduced variance compared to colorimetric tests. In buffer, curve-fitting estimated the limit of detection (LoD) to be ∼1.56 and ∼8.47 pg/mL using two-step or three-step assay configurations, respectively. After correcting for endogenous levels, the estimated LoD was ∼4.7 pg/mL in the serum or plasma with the two-step assay. The lower limit of quantitation was ∼2.3 pg/mL in the buffer and ∼9.4 pg/mL in the serum or plasma, indicting the ability to measure small changes above endogenous levels within blood samples.

Neurotrauma Biomarker Levels and Adverse Symptoms Among Military and Law Enforcement Personnel Exposed to Occupational Overpressure Without Diagnosed Traumatic Brain Injury

IMPORTANCE

There is a scientific and operational need to define objective measures of exposure to low-level overpressure (LLOP) and concussion-like symptoms among persons with specialized occupations.

OBJECTIVE

To evaluate serum levels of neurotrauma biomarkers and their association with concussion-like symptoms reported by LLOP-exposed military and law enforcement personnel who are outwardly healthy and cleared to perform duties.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study, conducted from January 23, 2017, to October 21, 2019, used serum samples and survey data collected from healthy, male, active-duty military and law enforcement personnel assigned to operational training at 4 US Department of Defense and civilian law enforcement training sites. Personnel aged 18 years or older with prior LLOP exposure but no diagnosed traumatic brain injury or with acute blast exposure during sampling participated in the study. Serum samples from 30 control individuals were obtained from a commercial vendor.

MAIN OUTCOMES AND MEASURES

Serum levels of glial fibrillary acidic protein, ubiquitin carboxyl hydrolase (UCH)-L1, neurofilament light chain, tau, amyloid β (Aβ)-40, and Aβ-42 from a random sample (30 participants) of the LLOP-exposed cohort were compared with those of 30 age-matched controls. Associations between biomarker levels and self-reported symptoms or operational demographics in the remainder of the study cohort (76 participants) were assessed using generalized linear modeling or Spearman correlations with age as a covariate.

RESULTS

Among the 30 randomly sampled participants (mean [SD] age, 32 [7.75] years), serum levels of UCH-L1 (mean difference, 4.92; 95% CI, 0.71-9.14), tau (mean difference, 0.16; 95% CI, -0.06 to 0.39), Aβ-40 (mean difference, 138.44; 95% CI, 116.32-160.56), and Aβ-42 (mean difference, 4.97; 95% CI, 4.10-5.83) were elevated compared with those in controls. Among the remaining cohort of 76 participants (mean [SD] age, 34 [7.43] years), ear ringing was reported by 44 (58%) and memory or sleep problems were reported by 24 (32%) and 20 (26%), respectively. A total of 26 participants (34%) reported prior concussion. Amyloid β-42 levels were associated with ear ringing (F1,72 = 7.40; P = .008) and memory problems (F1,72 = 9.20; P = .003).

CONCLUSIONS AND RELEVANCE

The findings suggest that long-term LLOP exposure acquired during occupational training may be associated with serum levels of neurotrauma biomarkers. Assessment of biomarkers and concussion-like symptoms among personnel considered healthy at the time of sampling may be useful for military occupational medicine risk management.

Penetrating Ballistic-Like Brain Injury Leads to MicroRNA Dysregulation, BACE1 Upregulation, and Amyloid Precursor Protein Loss in Lesioned Rat Brain Tissues

Severe traumatic brain injury (TBI) is a risk factor for neurodegenerative diseases. Yet, the molecular events involving dysregulated miRNAs that may be associated with protein degradation in the brain remains elusive. Quantitation of more than 800 miRNAs was conducted using rat ipsilateral coronal brain tissues collected 1, 3, or 7 days after penetrating ballistic-like brain injury (PBBI). As a control for each time-point, Sham-operated animals received craniotomy alone. Microarray and systems biology analysis indicated that the amplitude and complexity of miRNAs affected were greatest 7 day after PBBI. Arrays and Q-PCR inferred that dysregulation of miR-135a, miR-328, miR-29c, and miR-21 were associated with altered levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), PSEN1, PSEN2, and amyloid precursor protein (APP) genes. These events were followed by increased levels of mature BACE1 protein and concomitant loss of full length APP within 3–7 days, then elevation of amyloid beta (Aβ)-40 7 days after PBBI. This study indicates that miRNA arrays, coupled with systems biology, may be used to guide study design prior validation of miRNA dysregulation. Associative analysis of miRNAs, mRNAs, and proteins within a proposed pathway are poised for further validation as biomarkers and therapeutic targets relevant to TBI-induced APP loss and subsequent Aβ peptide generation during neurodegeneration.

Overpressure Exposure From .50-Caliber Rifle Training Is Associated With Increased Amyloid Beta Peptides in Serum

Background: Overpressure (OP) is an increase in air pressure above normal atmospheric levels. Military personnel are repeatedly exposed to low levels of OP caused by various weapon systems. Repeated OP may increase risk of neurological disease or psychological disorder diagnoses. A means to detect early phase effects that may be relevant to brain trauma remain elusive. Therefore, development of quantitative and objective OP-mediated effects during acute timeframes would vastly augment point-of-care or field-based decisions. This pilot study evaluated the amplitude of traumatic brain injury (TBI)–associated biomarkers in serum as a consequence of repeated OP exposure from .50-caliber rifle use over training multiple days.

Objective: To determine the acute temporal profile of TBI-associated serum biomarkers and their relationship with neurocognitive decrements or self-reported symptoms among participants exposed to low-level, repeated OP from weapons used in a training environment.

Methods: Study participants were enrolled in .50-caliber sniper rifle training and exposed to mild OP (peak pressure 3.8–4.5 psi, impulse 19.27–42.22 psi-ms per day) for three consecutive days (D1–D3). Defense automated neurobehavioral assessment (DANA) neurocognitive testing, symptom reporting, and blood collection were conducted 2–3 h before (pre-) and again 0.45–3 h after (post-) OP exposure. The TBI-associated serum biomarkers, glial fibrillary acidic protein (GFAP), ubiquitin C-terminal hydrolase-L1 (UCH-L1), neurofilament light (Nf-L), tau, and amyloid beta peptides (Aβ-40 and Aβ-42) were measured using digital ELISAs.

Results: Serum GFAP decreased on D1 and D3 but not D2 after OP exposure. Nf-L was suppressed on D3 alone. Aβ-40 was elevated on D2 alone while Aβ-42 was elevated each day after OP exposure. Suppression of GFAP and elevation of Aβ-42 correlated to OP-mediated impulse levels measured on D3.

Conclusions: Acute measurement of Aβ-peptides may have utility as biomarkers of subconcussive OP caused by rifle fire. Fluctuation of GFAP, Nf-L, and particularly Aβ peptide levels may have utility as acute, systemic responders of subconcussive OP exposure caused by rifle fire even in the absence of extreme operational deficits or clinically defined concussion.

Dataset of Rat and Human Serum Proteomes Derived from Differential Depletion Strategies prior to Mass Spectrometry

This article provides information regarding the effect of four common high abundant protein (albumin and immunoglobulins (Ig)) depletion strategies upon serum proteomics datasets derived from normal, non-diseased rat or human serum. After tryptic digest, peptides were separated using C₁₈ reverse phase liquid chromatography-tandem mass spectrometry (rpLC-MS/MS). Peptide spectral matching (PSM) and database searching was conducted using MS Amanda 2.0 and Sequest HT. Peptide and protein false discovery rates (FDR) were set at 0.01%, with at least two peptides assigned per protein. Protein quantitation and the extent of albumin and Ig removal was defined by PSM counts. Venn diagram analysis of the core proteomes, derived from proteins identified by both search engines, was performed using Venny. Ontological characterization and gene set enrichment were performed using WebGestalt. The dataset resulting from each depletion column is provided.

Penetrating Traumatic Brain Injury Triggers Dysregulation of Cathepsin B Protein Levels Independent of Cysteine Protease Activity in Brain and Cerebral Spinal Fluid

Cathepsin B (CatB), a lysosomal cysteine protease, is important to brain function and may have dual utility as a peripheral biomarker of moderate-severe traumatic brain injury (TBI). The present study determined levels of pro- and mature (mat) CatB protein as well as cysteine protease activity within the frontal cortex (FC; proximal injury site), hippocampus (HC; distal injury site), and cerebral spinal fluid (CSF) collected 1-7 days after craniotomy and penetrating ballistic-like brain injury (PBBI) in rats. Values were compared with naïve controls. Further, the utility of CatB protein as a translational biomarker was determined in CSF derived from patients with severe TBI. Craniotomy increased matCatB levels in the FC and HC, and led to elevation of HC activity at day 7. PBBI caused an even greater elevation in matCatB within the FC and HC within 3-7 days. After PBBI, cysteine protease activity peaked at 3 days in the FC and was elevated at 1 day and 7 days, but not 3 days, in the HC. In rat CSF, proCatB, matCatB, and cysteine protease activity peaked at 3 days after craniotomy and PBBI. Addition of CA-074, a CatB-specific inhibitor, confirmed that protease activity was due to active matCatB in rat brain tissues and CSF at all time-points. In patients, CatB protein was detectable from 6 h through 10 days after TBI. Notably, CatB levels were significantly higher in CSF collected within 3 days after TBI compared with non-TBI controls. Collectively, this work indicates that CatB and its cysteine protease activity may serve as collective molecular signatures of TBI progression that differentially vary within both proximal and distal brain regions. CatB and its protease activity may have utility as a surrogate, translational biomarker of acute-subacute TBI.

Brain-related proteins as serum biomarkers of acute, subconcussive blast overpressure exposure: A cohort study of military personnel

Repeated exposure to blast overpressure remains a major cause of adverse health for military personnel who, as a consequence, are at a higher risk for neurodegenerative disease and suicide. Acute, early tracking of blast related effects holds the promise of rapid health assessment prior to onset of chronic problems. Current techniques used to determine blast-related effects rely upon reporting of symptomology similar to that of concussion and neurocognitive assessment relevant to operational decrement. Here, we describe the results of a cross sectional study with pared observations. The concentration of multiple TBI-related proteins was tested in serum collected within one hour of blast exposure as a quantitative and minimally invasive strategy to augment assessment of blast-exposure effects that are associated with concussion-like symptomology and reaction time decrements. We determined that median simple reaction time (SRT) was slowed in accordance with serum Nf-L, tau, Aβ-40, and Aβ-42 elevation after overpressure exposure. In contrast, median levels of serum GFAP decreased. Individual, inter-subject analysis revealed positive correlations between changes in Nf-L and GFAP, and in Aβ-40 compared to Aβ-42. The change in Nf-L was negatively associated with tau, Aβ-40, and Aβ-42. Participants reported experiencing headaches, dizziness and taking longer to think. Dizziness was associated with reaction time decrements, GFAP or NfL suppression, as well as Aβ peptide elevation. UCH-L1 elevation had a weak association with mTBI/concussion history. Multiplexed serum biomarker quantitation, coupled with reaction time assessment and symptomology determined before and after blast exposure, may serve as a platform for tracking adverse effects in the absence of a head wound or diagnosed concussion. We propose further evaluation of serum biomarkers, which are often associated with TBI, in the context of acute operational blast exposures.

Elaboration of a fragment library hit produces potent and selective aspartate semialdehyde dehydrogenase inhibitors

Aspartate-β-semialdehyde dehydrogenase (ASADH) lies at the first branch point in the aspartate metabolic pathway which leads to the biosynthesis of several essential amino acids and some important metabolites. This pathway is crucial for many metabolic processes in plants and microbes like bacteria and fungi, but is absent in mammals. Therefore, the key microbial enzymes involved in this pathway are attractive potential targets for development of new antibiotics with novel modes of action. The ASADH enzyme family shares the same substrate binding and active site catalytic groups; however, the enzymes from representative bacterial and fungal species show different inhibition patterns when previously screened against low molecular weight inhibitors identified from fragment library screening. In the present study several approaches, including fragment based drug discovery (FBDD), inhibitor docking, kinetic, and structure-activity relationship (SAR) studies have been used to guide ASADH inhibitor development. Elaboration of a core structure identified by FBDD has led to the synthesis of low micromolar inhibitors of the target enzyme, with high selectivity introduced between the Gram-negative and Gram-positive orthologs of ASADH. This new set of structures open a novel direction for the development of inhibitors against this validated drug-target enzyme.

A cautionary tale of structure-guided inhibitor development against an essential enzyme in the aspartate-biosynthetic pathway

The aspartate pathway is essential for the production of the amino acids required for protein synthesis and of the metabolites needed in bacterial development. This pathway also leads to the production of several classes of quorum-sensing molecules that can trigger virulence in certain microorganisms. The second enzyme in this pathway, aspartate β-semialdehyde dehydrogenase (ASADH), is absolutely required for bacterial survival and has been targeted for the design of selective inhibitors. Fragment-library screening has identified a new set of inhibitors that, while they do not resemble the substrates for this reaction, have been shown to bind at the active site of ASADH. Structure-guided development of these lead compounds has produced moderate inhibitors of the target enzyme, with some selectivity observed between the Gram-negative and Gram-positive orthologs of ASADH. However, many of these inhibitor analogs and derivatives have not yet achieved the expected enhanced affinity. Structural characterization of these enzyme-inhibitor complexes has provided detailed explanations for the barriers that interfere with optimal binding. Despite binding in the same active-site region, significant changes are observed in the orientation of these bound inhibitors that are caused by relatively modest structural alterations. Taken together, these studies present a cautionary tale for issues that can arise in the systematic approach to the modification of lead compounds that are being used to develop potent inhibitors.

Structure of homoserine O-acetyltransferase from Staphylococcus aureus: the first Gram-positive ortholog structure

Homoserine O-acetyltransferase (HTA) catalyzes the formation of L-O-acetyl-homoserine from L-homoserine through the transfer of an acetyl group from acetyl-CoA. This is the first committed step required for the biosynthesis of methionine in many fungi, Gram-positive bacteria and some Gram-negative bacteria. The structure of HTA from Staphylococcus aureus (SaHTA) has been determined to a resolution of 2.45 Å. The structure belongs to the α/β-hydrolase superfamily, consisting of two distinct domains: a core α/β-domain containing the catalytic site and a lid domain assembled into a helical bundle. The active site consists of a classical catalytic triad located at the end of a deep tunnel. Structure analysis revealed some important differences for SaHTA compared with the few known structures of HTA.