A Case Study of Dysfunctional Nicotinamide Metabolism in a 20-Year-Old Male

We present a case study of a 20-year-old male with an unknown neurodegenerative disease who was referred to the Undiagnosed Diseases Network Vanderbilt Medical Center site. A previous metabolic panel showed that the patient had a critical deficiency in nicotinamide intermediates that are generated during the biosynthesis of NAD(H). We followed up on these findings by evaluating the patient's ability to metabolize nicotinamide. We performed a global metabolic profiling analysis of plasma samples that were collected: (1) under normal fed conditions (baseline), (2) after the patient had fasted, and (3) after he was challenged with a 500 mg nasogastric tube bolus of nicotinamide following the fast. Our findings showed that the patient's nicotinamide N-methyltransferase (NNMT), a key enzyme in NAD(H) biosynthesis and methionine metabolism, was not functional under normal fed or fasting conditions but was restored in response to the nicotinamide challenge. Altered levels of metabolites situated downstream of NNMT and in neighboring biochemical pathways provided further evidence of a baseline defect in NNMT activity. To date, this is the only report of a critical defect in NNMT activity manifesting in adulthood and leading to neurodegenerative disease. Altogether, this study serves as an important reference in the rare disease literature and also demonstrates the utility of metabolomics as a diagnostic tool for uncharacterized metabolic diseases.

Comparison of Untargeted Metabolomic Profiling vs Traditional Metabolic Screening to Identify Inborn Errors of Metabolism

IMPORTANCE

Recent advances in newborn screening (NBS) have improved the diagnosis of inborn errors of metabolism (IEMs); however, many potentially treatable IEMs are not included on NBS panels, nor are they covered in standard, first-line biochemical testing.

OBJECTIVE

To examine the utility of untargeted metabolomics as a primary screening tool for IEMs by comparing the diagnostic rate of clinical metabolomics with the recommended traditional metabolic screening approach.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study compares data from 4464 clinical samples received from 1483 unrelated families referred for trio testing of plasma amino acids, plasma acylcarnitine profiling, and urine organic acids (June 2014 to October 2018) and 2000 consecutive plasma samples from 1807 unrelated families (July 2014 to February 2019) received for clinical metabolomic screening at a College of American Pathologists and Clinical Laboratory Improvement Amendments-certified biochemical genetics laboratory. Data analysis was performed from September 2019 to August 2020.

EXPOSURES

Metabolic and molecular tests performed at a genetic testing reference laboratory in the US and available clinical information for each patient were assessed to determine diagnostic rate.

MAIN OUTCOMES AND MEASURES

The diagnostic rate of traditional metabolic screening compared with clinical metabolomic profiling was assessed in the context of expanded NBS.

RESULTS

Of 1483 cases screened by the traditional approach, 912 patients (61.5%) were male and 1465 (98.8%) were pediatric (mean [SD] age, 4.1 [6.0] years; range, 0-65 years). A total of 19 families were identified with IEMs, resulting in a 1.3% diagnostic rate. A total of 14 IEMs were detected, including 3 conditions not included in the Recommended Uniform Screening Panel for NBS. Of the 1807 unrelated families undergoing plasma metabolomic profiling, 1059 patients (58.6%) were male, and 1665 (92.1%) were pediatric (mean [SD] age, 8.1 [10.4] years; range, 0-80 years). Screening identified 128 unique cases with IEMs, giving an overall diagnostic rate of 7.1%. In total, 70 different metabolic conditions were identified, including 49 conditions not presently included on the Recommended Uniform Screening Panel for NBS.

CONCLUSIONS AND RELEVANCE

These findings suggest that untargeted metabolomics provided a 6-fold higher diagnostic yield compared with the conventional screening approach and identified a broader spectrum of IEMs. Notably, with the expansion of NBS programs, traditional metabolic testing approaches identify few disorders beyond those covered on the NBS. These data support the capability of clinical untargeted metabolomics in screening for IEMs and suggest that broader screening approaches should be considered in the initial evaluation for metabolic disorders.

Precision of a Clinical Metabolomics Profiling Platform for Use in the Identification of Inborn Errors of Metabolism

BACKGROUND

The application of whole-exome sequencing for the diagnosis of genetic disease has paved the way for systems-based approaches in the clinical laboratory. Here, we describe a clinical metabolomics method for the screening of metabolic diseases through the analysis of a multi-pronged mass spectrometry platform. By simultaneously measuring hundreds of metabolites in a single sample, clinical metabolomics offers a comprehensive approach to identify metabolic perturbations across multiple biochemical pathways.

METHODS

We conducted a single- and multi-day precision study on hundreds of metabolites in human plasma on 4, multi-arm, high-throughput metabolomics platforms.

RESULTS

The average laboratory coefficient of variation (CV) on the 4 platforms was between 9.3 and 11.5% (median, 6.5-8.4%), average inter-assay CV on the 4 platforms ranged from 9.9 to 12.6% (median, 7.0-8.3%) and average intra-assay CV on the 4 platforms ranged from 5.7 to 6.9% (median, 3.5-4.4%). In relation to patient sample testing, the precision of multiple biomarkers associated with IEM disorders showed CVs that ranged from 0.2 to 11.0% across 4 analytical batches.

CONCLUSIONS

This evaluation describes single and multi-day precision across 4 identical metabolomics platforms, comprised each of 4 independent method arms, and reproducibility of the method for the measurement of key IEM metabolites in patient samples across multiple analytical batches, providing evidence that the method is robust and reproducible for the screening of patients with inborn errors of metabolism.

Global biochemical analysis of plasma, serum and whole blood collected using various anticoagulant additives

Introduction

Analysis of blood for the evaluation of clinically relevant biomarkers requires precise collection and sample handling by phlebotomists and laboratory staff. An important consideration for the clinical application of metabolomics are the different anticoagulants utilized for sample collection. Most studies that have characterized differences in metabolite levels in various blood collection tubes have focused on single analytes. We define analyte levels on a global metabolomics platform following blood sampling using five different, but commonly used, clinical laboratory blood collection tubes (i.e., plasma anticoagulated with either EDTA, lithium heparin or sodium citrate, along with no additive (serum), and EDTA anticoagulated whole blood).

Methods

Using an untargeted metabolomics platform we analyzed five sample types after all had been collected and stored at -80°C. The biochemical composition was determined and differences between the samples established using matched-pair t-tests.

Results

We identified 1,117 biochemicals across all samples and detected a mean of 1,036 in the sample groups. Compared to the levels of metabolites in EDTA plasma, the number of biochemicals present at statistically significant different levels (p<0.05) ranged from 452 (serum) to 917 (whole blood). Several metabolites linked to screening assays for rare diseases including acylcarnitines, bilirubin and heme metabolites, nucleosides, and redox balance metabolites varied significantly across the sample collection types.

Conclusions

Our study highlights the widespread effects and importance of using consistent additives for assessing small molecule levels in clinical metabolomics. The biochemistry that occurs during the blood collection process creates a reproducible signal that can identify specimens collected with different anticoagulants in metabolomic studies.

Impact statement

In this manuscript, normal/healthy donors had peripheral blood collected using multiple anticoagulants as well as serum during a fasted blood draw. Global metabolomics is a new technology being utilized to draw clinical conclusions and we interrogated the effects of different anticoagulants on the levels of biochemicals from each of the donors. Characterizing the effects of the anticoagulants on biochemical levels will help researchers leverage the information using global metabolomics in order to make conclusions regarding important disease biomarkers.

Assessment of the effects of repeated freeze thawing and extended bench top processing of plasma samples using untargeted metabolomics

INTRODUCTION

Clinical metabolomics has utility as a screen for inborn errors of metabolism (IEM) and variant classification in patients with rare disease. It is important to understand and characterize preanalytical factors that influence assay performance during patient sample testing.

OBJECTIVES

To evaluate the impact of extended thawing of human EDTA plasma samples on ice prior to extraction as well as repeated freeze-thaw cycling of samples to identify compounds that are unstable prior to metabolomic analysis.

METHODS

Twenty-four (24) donor EDTA plasma samples were collected and immediately frozen at - 80 °C. Twelve samples were thawed on ice and extracted for analysis at time 0, 2, 4, and 6 h. Twelve other donor samples were repeatedly thawed and frozen up to four times and analyzed at each cycle. Compound levels at each time point/freeze-thaw cycle were compared to the control samples using matched-paired t tests to identify analytes affected by each condition.

RESULTS

We identified 1026 biochemicals across all samples. Incubation of thawed EDTA plasma samples on ice for up to 6 h resulted in < 1% of biochemicals changing significantly. Freeze-thaw cycles affected a greater percentage of the metabolome; ~ 2% of biochemicals changed after 3 freeze-thaw cycles.

CONCLUSIONS

Our study highlights that the number and magnitude of these changes are not as widespread as other aspects of improper sample handling. In total, < 3% of the metabolome detected on our clinical metabolomics platform should be disqualified when multiple freeze-thaw cycles or extended thawing at 4 °C are performed on a given sample.

Untargeted metabolomics as an unbiased approach to the diagnosis of inborn errors of metabolism of the non-oxidative branch of the pentose phosphate pathway

Inborn errors of metabolism (IEM) involving the non-oxidative pentose phosphate pathway (PPP) include the two relatively rare conditions, transketolase deficiency and transaldolase deficiency, both of which can be difficult to diagnosis given their non-specific clinical presentations. Current biochemical testing approaches require an index of suspicion to consider targeted urine polyol testing. To determine whether a broad-spectrum biochemical test could accurately identify a specific metabolic pattern defining IEMs of the non-oxidative PPP, we employed the use of clinical metabolomic profiling as an unbiased novel approach to diagnosis. Subjects with molecularly confirmed IEMs of the PPP were included in this study. Targeted quantitative analysis of polyols in urine and plasma samples was accomplished with chromatography and mass spectrometry. Semi-quantitative unbiased metabolomic analysis of urine and plasma samples was achieved by assessing small molecules via liquid chromatography and high-resolution mass spectrometry. Results from untargeted and targeted analyses were then compared and analyzed for diagnostic acuity. Two siblings with transketolase (TKT) deficiency and three unrelated individuals with transaldolase (TALDO) deficiency were identified for inclusion in the study. For both IEMs, targeted polyol testing and untargeted metabolomic testing on urine and/or plasma samples identified typical perturbations of the respective disorder. Additionally, untargeted metabolomic testing revealed elevations in other PPP metabolites not typically measured with targeted polyol testing, including ribonate, ribose, and erythronate for TKT deficiency and ribonate, erythronate, and sedoheptulose 7-phosphate in TALDO deficiency. Non-PPP alternations were also noted involving tryptophan, purine, and pyrimidine metabolism for both TKT and TALDO deficient patients. Targeted polyol testing and untargeted metabolomic testing methods were both able to identify specific biochemical patterns indicative of TKT and TALDO deficiency in both plasma and urine samples. In addition, untargeted metabolomics was able to identify novel biomarkers, thereby expanding the current knowledge of both conditions and providing further insight into potential underlying pathophysiological mechanisms. Furthermore, untargeted metabolomic testing offers the advantage of having a single effective biochemical screening test for identification of rare IEMs, like TKT and TALDO deficiencies, that may otherwise go undiagnosed due to their generally non-specific clinical presentations.

2-Pyrrolidinone and Succinimide as Clinical Screening Biomarkers for GABA-Transaminase Deficiency: Anti-seizure Medications Impact Accurate Diagnosis

Broad-scale untargeted biochemical phenotyping is a technology that supplements widely accepted assays, such as organic acid, amino acid, and acylcarnitine analyses typically utilized for the diagnosis of inborn errors of metabolism. In this study, we investigate the analyte changes associated with 4-aminobutyrate aminotransferase (ABAT, GABA transaminase) deficiency and treatments that affect GABA metabolism. GABA-transaminase deficiency is a rare neurodevelopmental and neurometabolic disorder caused by mutations in ABAT and resulting in accumulation of GABA in the cerebrospinal fluid (CSF). For that reason, measurement of GABA in CSF is currently the primary approach to diagnosis. GABA-transaminase deficiency results in severe developmental delay with intellectual disability, seizures, and movement disorder, and is often associated with death in childhood. Using an untargeted metabolomics platform, we analyzed EDTA plasma, urine, and CSF specimens from four individuals with GABA-transaminase deficiency to identify biomarkers by comparing the biochemical profile of individual patient samples to a pediatric-centric population cohort. Metabolomic analyses of over 1,000 clinical plasma samples revealed a rich source of biochemical information. Three out of four patients showed significantly elevated levels of the molecule 2-pyrrolidinone (Z-score ≥2) in plasma, and whole exome sequencing revealed variants of uncertain significance in ABAT. Additionally, these same patients also had elevated levels of succinimide in plasma, urine, and CSF and/or homocarnosine in urine and CSF. In the analysis of clinical EDTA plasma samples, the levels of succinimide and 2-pyrrolidinone showed a high level of correlation (R = 0.73), indicating impairment in GABA metabolism and further supporting the association with GABA-transaminase deficiency and the pathogenicity of the ABAT variants. Further analysis of metabolomic data across our patient population revealed the association of elevated levels of 2-pyrrolidinone with administration of vigabatrin, a commonly used anti-seizure medication and a known inhibitor of GABA-transaminase. These data indicate that anti-seizure medications may alter the biochemical and metabolomic data, potentially impacting the interpretation and diagnosis for the patient. Further, these data demonstrate the power of combining broad scale genotyping and phenotyping technologies to diagnose inherited neurometabolic disorders and support the use of metabolic phenotyping of plasma to screen for GABA-transaminase deficiency.

Untargeted metabolomics identifies unique though benign biochemical changes in patients with pathogenic variants in UROC1

Urocanic aciduria is caused by a deficiency in the enzyme urocanase (E.C. 4.2.1.49) encoded by the gene UROC1. In the past, deficiency of urocanase has been associated with intellectual disability in a few case studies with some suggestion that the enzyme deficiency was the causative etiology. Here, we describe two phenotypically normal siblings with compound heterozygous pathogenic variants in UROC1 and characteristic biochemical evidence of urocanase deficiency collected utilizing untargeted metabolomic analysis. These findings suggest that urocanic aciduria may represent an otherwise benign biochemical phenotype and that those individuals with concurrent developmental delay should continue to be evaluated for other underlying causes for their symptoms.

Metabolomics in the clinic: A review of the shared and unique features of untargeted metabolomics for clinical research and clinical testing

Metabolomics is the untargeted measurement of the metabolome, which is composed of the complement of small molecules detected in a biological sample. As such, metabolomic analysis produces a global biochemical phenotype. It is a technology that has been utilized in the research setting for over a decade. The metabolome is directly linked to and is influenced by genetics, epigenetics, environmental factors, and the microbiome-all of which affect health. Metabolomics can be applied to human clinical diagnostics and to other fields such as veterinary medicine, nutrition, exercise, physiology, agriculture/plant biochemistry, and toxicology. Applications of metabolomics in clinical testing are emerging, but several aspects of its use as a clinical test differ from applications focused on research or biomarker discovery and need to be considered for metabolomics clinical test data to have optimum impact, be meaningful, and be used responsibly. In this review, we deconstruct aspects and challenges of metabolomics for clinical testing by illustrating the significance of test design, accurate and precise data acquisition, quality control, data processing, n-of-1 comparison to a reference population, and biochemical pathway analysis. We describe how metabolomics technology is integral to defining individual biochemical phenotypes, elaborates on human health and disease, and fits within the precision medicine landscape. Finally, we conclude by outlining some future steps needed to bring metabolomics into the clinical space and to be recognized by the broader medical and regulatory fields.

A metabolomic map of Zellweger spectrum disorders reveals novel disease biomarkers

PURPOSE

Peroxisome biogenesis disorders-Zellweger spectrum disorders (PBD-ZSD) are metabolic diseases with multisystem manifestations. Individuals with PBD-ZSD exhibit impaired peroxisomal biochemical functions and have abnormal levels of peroxisomal metabolites, but the broader metabolic impact of peroxisomal dysfunction and the utility of metabolomic methods is unknown.

METHODS

We studied 19 individuals with clinically and molecularly characterized PBD-ZSD. We performed both quantitative peroxisomal biochemical diagnostic studies in parallel with untargeted small molecule metabolomic profiling in plasma samples with detection of >650 named compounds.

RESULTS

The cohort represented intermediate to mild PBD-ZSD subjects with peroxisomal biochemical alterations on targeted analysis. Untargeted metabolomic profiling of these samples revealed elevations in pipecolic acid and long-chain lysophosphatidylcholines, as well as an unanticipated reduction in multiple sphingomyelin species. These sphingomyelin reductions observed were consistent across the PBD-ZSD samples and were rare in a population of >1,000 clinical samples. Interestingly, the pattern or "PBD-ZSD metabolome" was more pronounced in younger subjects suggesting studies earlier in life reveal larger biochemical changes.

CONCLUSION

Untargeted metabolomics is effective in detecting mild to intermediate cases of PBD-ZSD. Surprisingly, dramatic reductions in plasma sphingomyelin are a consistent feature of the PBD-ZSD metabolome. The use of metabolomics in PBD-ZSD can provide insight into novel biomarkers of disease.

Disturbed phospholipid metabolism in serine biosynthesis defects revealed by metabolomic profiling

Serine biosynthesis defects are autosomal recessive metabolic disorders resulting from the deficiency of any of the three enzymes involved in de novo serine biosynthesis, specifically phosphoglycerate dehydrogenase (PGDH), phosphoserine aminotransferase (PSAT), and phosphoserine phosphatase (PSP). In this study, we performed metabolomic profiling on 4 children with serine biosynthesis defects; 3 with PGDH deficiency and 1 with PSAT deficiency. The evaluations were performed at baseline and with serine and glycine supplementation. Metabolomic profiling performed at baseline showed low phospholipid species, including glycerophosphocholine, glycerophosphoethanolamine, and sphingomyelin. All children had low serine and glycine as expected. Low glycerophosphocholine compounds were found in 4 children, low glycerophosphoethanolamine compounds in 3 children, and low sphingomyelin species in 2 children. Metabolic profiling with serine and glycine supplementation showed normalization of most of the low phospholipid compounds in the 4 children. Phospholipids are the major component of plasma and intracellular membranes, and phosphatidylcholine is the most abundant phospholipid of all mammalian cell types and subcellular organelles. Phosphatidylcholine is of particular importance for the nervous system, where it is essential for neuronal differentiation. The observed low phosphatidylcholine species in children with serine biosynthesis defects that improved after serine supplementation, supports the role of serine as a significant precursor for phosphatidylcholine. The vital role that phosphatidylcholine has during neuronal differentiation and the pronounced neurological manifestations in serine biosynthesis defects suggest that phosphatidylcholine deficiency occurring secondary to serine deficiency may have a significant contribution to the development of the neurological manifestations in individuals with serine biosynthesis defects.

Clinical Metabolomics to Segregate Aromatic Amino Acid Decarboxylase Deficiency From Drug-Induced Metabolite Elevations

BACKGROUND

Phenotyping technologies featured in the diagnosis of inborn errors of metabolism, such as organic acid, amino acid, and acylcarnitine analyses, recently have been supplemented by broad-scale untargeted metabolomic phenotyping. We investigated the analyte changes associated with aromatic amino acid decarboxylase (AADC) deficiency and dopamine medication treatment.

METHODS

Using an untargeted metabolomics platform, we analyzed ethylenediaminetetraacetic acid plasma specimens, and biomarkers were identified by comparing the biochemical profile of individual patient samples to a pediatric-centric population cohort.

RESULTS

Elevated 3-methoxytyrosine (average z score 5.88) accompanied by significant decreases of dopamine 3-O-sulfate (-2.77), vanillylmandelate (-2.87), and 3-methoxytyramine sulfate (-1.44) were associated with AADC deficiency in three samples from two patients. In five non-AADC patients treated with carbidopa-levodopa, levels of 3-methoxytyrosine were elevated (7.65); however, the samples from non-AADC patients treated with DOPA-elevating drugs had normal or elevated levels of metabolites downstream of aromatic l-amino acid decarboxylase, including dopamine 3-O-sulfate (2.92), vanillylmandelate (0.33), and 3-methoxytyramine sulfate (5.07). In one example, a plasma metabolomic phenotype pointed to a probable AADC deficiency and prompted the evaluation of whole exome sequencing data, identifying homozygosity for a known pathogenic variant, whereas whole exome analysis in a second patient revealed compound heterozygosity for two variants of unknown significance.

CONCLUSIONS

These data demonstrate the power of combining broad-scale genotyping and phenotyping technologies to diagnose inherited neurometabolic disorders and suggest that metabolic phenotyping of plasma can be used to identify AADC deficiency and to distinguish it from non-AADC patients with elevated 3-methoxytyrosine caused by DOPA-raising medications.

Analyses of SLC13A5-epilepsy patients reveal perturbations of TCA cycle

OBJECTIVE

To interrogate the metabolic profile of five subjects from three families with rare, nonsense and missense mutations in SLC13A5 and Early Infantile Epileptic Encephalopathies (EIEE) characterized by severe, neonatal onset seizures, psychomotor retardation and global developmental delay.

METHODS

Mass spectrometry of plasma, CSF and urine was used to identify consistently dysregulated analytes in our subjects.

RESULTS

Distinctive elevations of citrate and dysregulation of citric acid cycle intermediates, supporting the hypothesis that loss of SLC13A5 function alters tricarboxylic acid cycle (TCA) metabolism and may disrupt metabolic compartmentation in the brain.

SIGNIFICANCE

Our results indicate that analysis of plasma citrate and other TCA analytes in SLC13A5 deficient patients define a diagnostic metabolic signature that can aid in diagnosing children with this disease.

Elucidation of the complex metabolic profile of cerebrospinal fluid using an untargeted biochemical profiling assay

We sought to determine the molecular composition of human cerebrospinal fluid (CSF) and identify the biochemical pathways represented in CSF to understand the potential for untargeted screening of inborn errors of metabolism (IEMs). Biochemical profiles for each sample were obtained using an integrated metabolomics workflow comprised of four chromatographic techniques followed by mass spectrometry. Secondarily, we wanted to compare the biochemical profile of CSF with those of plasma and urine within the integrated mass spectrometric-based metabolomic workflow. Three sample types, CSF (N=30), urine (N=40) and EDTA plasma (N=31), were analyzed from retrospectively collected pediatric cohorts of equivalent age and gender characteristics. We identified 435 biochemicals in CSF representing numerous biological and chemical/structural families. Sixty-three percent (273 of 435) of the biochemicals detected in CSF also were detected in urine and plasma, another 32% (140 of 435) were detected in either plasma or urine, and 5% (22 of 435) were detected only in CSF. Analyses of several metabolites showed agreement between clinically useful assays and the metabolomics approach. An additional set of CSF and plasma samples collected from the same patient revealed correlation between several biochemicals detected in paired samples. Finally, analysis of CSF from a pediatric case with dihydropteridine reductase (DHPR) deficiency demonstrated the utility of untargeted global metabolic phenotyping as a broad assessment to screen samples from patients with undifferentiated phenotypes. The results indicate a single CSF sample processed with an integrated metabolomics workflow can be used to identify a large breadth of biochemicals that could be useful for identifying disrupted metabolic patterns associated with IEMs.

Metabolomic Profiling of Human Urine as a Screen for Multiple Inborn Errors of Metabolism

AIMS

We wished to determine the efficacy of using urine as an analyte to screen for a broad range of metabolic products associated with multiple different types of inborn errors of metabolism (IEMs), using an automated mass spectrometry-based assay. Urine was compared with plasma samples from a similar cohort analyzed using the same assay. Specimens were analyzed using two different commonly utilized urine normalization methods based on creatinine and osmolality, respectively.

METHODS

Biochemical profiles for each sample (from both affected and unaffected subjects) were obtained using a mass spectrometry-based platform and population-based statistical analyses.

RESULTS

We identified over 1200 biochemicals from among 100 clinical urine samples and identified clear biochemical signatures for 16 of 18 IEM diseases tested. The two diseases that did not result in clear signatures, X-linked creatine transporter deficiency and ornithine transcarbamylase deficiency, were from individuals under treatment, which masked biomarker signatures. Overall the process variability and coefficient of variation for isolating and identifying biochemicals by running technical replicates of each urine sample was 10%.

CONCLUSIONS

A single urine sample analyzed with our integrated metabolomic platform can identify signatures of IEMs that are traditionally identified using many different assays and multiple sample types. Creatinine and osmolality-normalized data were robust to the detection of the disorders and samples tested here.

Elevations of C14:1 and C14:2 Plasma Acylcarnitines in Fasted Children: A Diagnostic Dilemma

OBJECTIVES

To test whether follow-up testing for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency uncovers a diagnosis in patients with elevations of C14:1 and C14:2 plasma acylcarnitines after a controlled fasting study performed for clinically suspected hypoglycemia and to compare the acylcarnitine profiles from fasted patients without VLCAD deficiency vs patients with known VLCAD deficiency to determine whether metabolite testing distinguishes these groups.

STUDY DESIGN

We performed a retrospective chart review and identified 17 patients with elevated C14:1 and C14:2 plasma acylcarnitine levels after a controlled fast and with testing for VLCAD deficiency (ACADVL sequencing or fibroblast fatty acid oxidation studies). The follow-up testing in all patients was inconsistent with a diagnosis of VLCAD deficiency. We compared the plasma acylcarnitine profiles from these fasted patients vs patients with VLCAD deficiency.

RESULTS

C14:1/C12:1 was significantly lower (P < .001) in fasted patients vs patients with VLCAD deficiency. Metabolomics analysis performed in 2 fasted patients and 1 patient with VLCAD deficiency demonstrated evidence for up-regulated lipolysis and β-oxidation in the fasted state.

CONCLUSIONS

Elevations of plasma C14:1 and C14:2 acylcarnitines appear to be a physiologic result of lipolysis that occurs with fasting. Both metabolomics analysis and/or C14:1/C12:1 may distinguish C14:1 elevations from physiologic fasting-induced lipolysis vs VLCAD deficiency.

Sharpening Precision Medicine by a Thorough Interrogation of Metabolic Individuality

Precision medicine is an active component of medical practice today, but aspirations are to both broaden its reach to a greater diversity of individuals and improve its “precision” by enhancing the ability to define even more disease states in combination with associated treatments. Given complexity of human phenotypes, much work is required. In this review, we deconstruct this challenge at a high level to define what is needed to move closer toward these aspirations. In the context of the variables that influence the diverse array of phenotypes across human health and disease – genetics, epigenetics, environmental influences, and the microbiome – we detail the factors behind why an individual's biochemical (metabolite) composition is increasingly regarded as a key element to precisely defining phenotypes. Although an individual's biochemical (metabolite) composition is generally regarded, and frequently shown, to be a surrogate to the phenotypic state, we review how metabolites (and therefore an individual's metabolic profile) are also functionally related to the myriad of phenotypic influencers like genetics and the microbiota. We describe how using the technology to comprehensively measure an individual's biochemical profile – metabolomics – is integrative to defining individual phenotypes and how it is currently being deployed in efforts to continue to elaborate on human health and disease in large population studies. Finally, we summarize instances where metabolomics is being used to assess individual health in instances where signatures (i.e. biomarkers) have been defined.

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Untargeted biochemical profiling has the potential to phenotype individuals where genetic associations do not seem to show penetrance

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Metabolomics can be leveraged with other ‘omics data to discern phenotype information that is driven by environmental, microbiota, or epigenetic factors.

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Tracking the biochemical profile of individuals may help discern effectiveness or response to treatment or disease progression.

Untargeted metabolomic analysis for the clinical screening of inborn errors of metabolism

Global metabolic profiling currently achievable by untargeted mass spectrometry-based metabolomic platforms has great potential to advance our understanding of human disease states, including potential utility in the detection of novel and known inborn errors of metabolism (IEMs). There are few studies of the technical reproducibility, data analysis methods, and overall diagnostic capabilities when this technology is applied to clinical specimens for the diagnosis of IEMs. We explored the clinical utility of a metabolomic workflow capable of routinely generating semi-quantitative z-score values for ~900 unique compounds, including ~500 named human analytes, in a single analysis of human plasma. We tested the technical reproducibility of this platform and applied it to the retrospective diagnosis of 190 individual plasma samples, 120 of which were collected from patients with a confirmed IEM. Our results demonstrate high intra-assay precision and linear detection for the majority compounds tested. Individual metabolomic profiles provided excellent sensitivity and specificity for the detection of a wide range of metabolic disorders and identified novel biomarkers for some diseases. With this platform, it is possible to use one test to screen for dozens of IEMs that might otherwise require ordering multiple unique biochemical tests. However, this test may yield false negative results for certain disorders that would be detected by a more well-established quantitative test and in its current state should be considered a supplementary test. Our findings describe a novel approach to metabolomic analysis of clinical specimens and demonstrate the clinical utility of this technology for prospective screening of IEMs.

Global metabolomic analysis of human saliva and plasma from healthy and diabetic subjects, with and without periodontal disease

Recent studies suggest that periodontal disease and type 2 diabetes mellitus are bi-directionally associated. Identification of a molecular signature for periodontitis using unbiased metabolic profiling could allow identification of biomarkers to assist in the diagnosis and monitoring of both diabetes and periodontal disease. This cross-sectional study identified plasma and salivary metabolic products associated with periodontitis and/or diabetes in order to discover biomarkers that may differentiate or demonstrate an interaction of these diseases. Saliva and plasma samples were analyzed from 161 diabetic and non-diabetic human subjects with a healthy periodontium, gingivitis and periodontitis. Metabolite profiling was performed using Metabolon's platform technology. A total of 772 metabolites were found in plasma and 475 in saliva. Diabetics had significantly higher levels of glucose and α-hydroxybutyrate, the established markers of diabetes, for all periodontal groups of subjects. Comparison of healthy, gingivitis and periodontitis saliva samples within the non-diabetic group confirmed findings from previous studies that included increased levels of markers of cellular energetic stress, increased purine degradation and glutathione metabolism through increased levels of oxidized glutathione and cysteine-glutathione disulfide, markers of oxidative stress, including increased purine degradation metabolites (e.g. guanosine and inosine), increased amino acid levels suggesting protein degradation, and increased ω-3 (docosapentaenoate) and ω-6 fatty acid (linoleate and arachidonate) signatures. Differences in saliva between diabetic and non-diabetic cohorts showed altered signatures of carbohydrate, lipid and oxidative stress exist in the diabetic samples. Global untargeted metabolic profiling of human saliva in diabetics replicated the metabolite signature of periodontal disease progression in non-diabetic patients and revealed unique metabolic signatures associated with periodontal disease in diabetics. The metabolites identified in this study that discriminated the periodontal groups may be useful for developing diagnostics and therapeutics tailored to the diabetic population.

Phagocytosis and killing of Staphylococcus aureus by human neutrophils

Neutrophils are essential for host defense against Staphylococcus aureus infections. Although significant progress has been made, our understanding of neutrophil interactions with S. aureus remains incomplete. To provide a more comprehensive view of this process, we investigated phagocytosis and killing of S. aureus by human neutrophils using varied assay conditions in vitro. A greater percentage of bacteria were internalized by adherent neutrophils compared to those in suspension, and, unexpectedly, uptake of S. aureus by adherent neutrophils occurred efficiently in the absence of opsonins. An antibody specific for S. aureus promoted uptake of unopsonized bacteria in suspension, but had little or no capacity to enhance phagocytosis of S. aureus opsonized with normal human serum or by adherent neutrophils. Collectively, these results indicate that assay conditions can have a significant influence on the phagocytosis and killing of S. aureus by neutrophils. More importantly, the results suggest a vaccine approach directed to enhance opsonophagocytosis alone is not sufficient to promote increased killing of S. aureus by human neutrophils. With the emergence and reemergence of antibiotic-resistant microorganisms, establishing parameters that are optimal for studying neutrophil-S. aureus interactions will pave the way towards developing immune-directed strategies for anti-staphylococcal therapies.

Metabolomic profiling reveals severe skeletal muscle group-specific perturbations of metabolism in aged FBN rats

Mammalian skeletal muscles exhibit age-related adaptive and pathological remodeling. Several muscles in particular undergo progressive atrophy and degeneration beyond median lifespan. To better understand myocellular responses to aging, we used semi-quantitative global metabolomic profiling to characterize trends in metabolic changes between 15-month-old adult and 32-month-old aged Fischer 344 × Brown Norway (FBN) male rats. The FBN rat gastrocnemius muscle exhibits age-dependent atrophy, whereas the soleus muscle, up until 32 months, exhibits markedly fewer signs of atrophy. Both gastrocnemius and soleus muscles were analyzed, as well as plasma and urine. Compared to adult gastrocnemius, aged gastrocnemius showed evidence of reduced glycolytic metabolism, including accumulation of glycolytic, glycogenolytic, and pentose phosphate pathway intermediates. Pyruvate was elevated with age, yet levels of citrate and nicotinamide adenine dinucleotide were reduced, consistent with mitochondrial abnormalities. Indicative of muscle atrophy, 3-methylhistidine and free amino acids were elevated in aged gastrocnemius. The monounsaturated fatty acids oleate, cis-vaccenate, and palmitoleate also increased in aged gastrocnemius, suggesting altered lipid metabolism. Compared to gastrocnemius, aged soleus exhibited far fewer changes in carbohydrate metabolism, but did show reductions in several glycolytic intermediates, fumarate, malate, and flavin adenine dinucleotide. Plasma biochemicals showing the largest age-related increases included glycocholate, heme, 1,5-anhydroglucitol, 1-palmitoleoyl-glycerophosphocholine, palmitoleate, and creatine. These changes suggest reduced insulin sensitivity in aged FBN rats. Altogether, these data highlight skeletal muscle group-specific perturbations of glucose and lipid metabolism consistent with mitochondrial dysfunction in aged FBN rats.

Toward an understanding of the evolution of Staphylococcus aureus strain USA300 during colonization in community households

Staphylococcus aureus is a frequent cause of serious infections and also a human commensal. The emergence of community-associated methicillin-resistant S. aureus led to a dramatic increase in skin and soft tissue infections worldwide. This epidemic has been driven by a limited number of clones, such as USA300 in the United States. To better understand the extent of USA300 evolution and diversification within communities, we performed comparative whole-genome sequencing of three clinical and five colonizing USA300 isolates collected longitudinally from three unrelated households over a 15-month period. Phylogenetic analysis that incorporated additional geographically diverse USA300 isolates indicated that all but one likely arose from a common recent ancestor. Although limited genetic adaptation occurred over the study period, the greatest genetic heterogeneity occurred between isolates from different households and within one heavily colonized household. This diversity allowed for a more accurate tracking of interpersonal USA300 transmission. Sequencing of persisting USA300 isolates revealed mutations in genes involved in major aspects of S. aureus function: adhesion, cell wall biosynthesis, virulence, and carbohydrate metabolism. Genetic variations also included accumulation of multiple polymorphisms within select genes of two multigene operons, suggestive of small genome rearrangements rather than de novo single point mutations. Such rearrangements have been underappreciated in S. aureus and may represent novel means of strain variation. Subtle genetic changes may contribute to USA300 fitness and persistence. Elucidation of small genome rearrangements reveals a potentially new and intriguing mechanism of directed S. aureus genome diversification in environmental niches and during pathogen-host interactions.

Global changes in Staphylococcus aureus gene expression in human blood

Staphylococcus aureus is a leading cause of bloodstream infections worldwide. In the United States, many of these infections are caused by a strain known as USA300. Although progress has been made, our understanding of the S. aureus molecules that promote survival in human blood and ultimately facilitate metastases is incomplete. To that end, we analyzed the USA300 transcriptome during culture in human blood, human serum, and trypticase soy broth (TSB), a standard laboratory culture media. Notably, genes encoding several cytolytic toxins were up-regulated in human blood over time, and hlgA, hlgB, and hlgC (encoding gamma-hemolysin subunits HlgA, HlgB, and HlgC) were among the most highly up-regulated genes at all time points. Compared to culture supernatants from a wild-type USA300 strain (LAC), those derived from an isogenic hlgABC-deletion strain (LACΔhlgABC) had significantly reduced capacity to form pores in human neutrophils and ultimately cause neutrophil lysis. Moreover, LACΔhlgABC had modestly reduced ability to cause mortality in a mouse bacteremia model. On the other hand, wild-type and LACΔhlgABC strains caused virtually identical abscesses in a mouse skin infection model, and bacterial survival and neutrophil lysis after phagocytosis in vitro was similar between these strains. Comparison of the cytolytic capacity of culture supernatants from wild-type and isogenic deletion strains lacking hlgABC, lukS/F-PV (encoding PVL), and/or lukDE revealed functional redundancy among two-component leukotoxins in vitro. These findings, along with a requirement of specific growth conditions for leukotoxin expression, may explain the apparent limited contribution of any single two-component leukotoxin to USA300 immune evasion and virulence.

Targeting of alpha-hemolysin by active or passive immunization decreases severity of USA300 skin infection in a mouse model

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are predominantly those affecting skin and soft tissues. Although progress has been made, our knowledge of the molecules that contribute to the pathogenesis of CA-MRSA skin infections is incomplete. We tested the hypothesis that alpha-hemolysin (Hla) contributes to the severity of USA300 skin infections in mice and determined whether vaccination against Hla reduces disease severity. Isogenic hla-negative (Deltahla) strains caused skin lesions in a mouse infection model that were significantly smaller than those caused by wild-type USA300 and Newman strains. Moreover, infection due to wild-type strains produced dermonecrotic skin lesions, whereas there was little or no dermonecrosis in mice infected with Deltahla strains. Passive immunization with Hla-specific antisera or active immunization with a nontoxigenic form of Hla significantly reduced the size of skin lesions caused by USA300 and prevented dermonecrosis. We conclude that Hla is a potential target for therapeutics or vaccines designed to moderate severe S. aureus skin infections.

Rapid neutrophil destruction following phagocytosis of Staphylococcus aureus

Mechanisms underlying the enhanced virulence phenotype of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are incompletely defined, but presumably include evasion of killing by human polymorphonuclear leukocytes (PMNs or neutrophils). To better understand this phenomenon, we investigated the basis of rapid PMN lysis after phagocytosis of USA300, a prominent CA-MRSA strain. Survival of USA300 clinical isolates after phagocytosis ultimately resulted in neutrophil lysis. PMNs containing ingested USA300 underwent morphological changes consistent with apoptosis, but lysed rapidly thereafter (within 6 h), whereas cells undergoing FAS-mediated apoptosis or phagocytosis-induced cell death remained intact. Phagosome membranes remained intact until the point of PMN destruction, suggesting lysis was not caused by escape of S. aureus from phagosomes or the cytolytic action of pore-forming toxins. Microarray analysis of the PMN transcriptome after phagocytosis of representative community-associated S. aureus and healthcare-associated MRSA strains revealed changes unique to community-associated S. aureus strains, such as upregulation of transcripts involved in regulation of calcium homeostasis. Collectively, the data suggest that neutrophil destruction after phagocytosis of USA300 is in part a form of programmed necrosis rather than direct lysis by S. aureus pore-forming toxins. We propose that the ability of CA-MRSA strains to induce programmed necrosis of neutrophils is a component of enhanced virulence.

Host-microbe interaction systems biology: lifecycle transcriptomics and comparative genomics

The use of microarray and comparative genomic technologies for the analysis of host-pathogen interactions has led to a greater understanding of the biological systems involved in infectious disease processes. Transcriptome analysis of intracellular pathogens at single or multiple time points during infection offers insight into the pathogen intracellular lifecycle. Host-pathogen transcriptome analysis in vivo, over time, enables characterization of both the pathogen and the host during the dynamic, multicellular host response. Comparative genomics using hybridization microarray-based comparative whole-genome resequencing or de novo whole-genome sequencing can identify the genetic factors responsible for pathogen evolutionary divergence, emergence, reemergence or the genetic basis for different pathogenic phenotypes. Together, microarray and comparative genomic technologies will continue to advance our understanding of pathogen evolution and assist in combating human infectious disease.

Effects of feed delivery time on milk production and sorting of dairy cows

The effects of delivery time (0900 or 2100) of a diet consisting of 45% of dry matter as chopped hay and 55% of dry matter as concentrates on milk production of dairy cows were determined in a 6-wk experiment consisting of 3 wk of adaptation and 3 wk of sampling. Feed delivery time did not affect feed intake and milk production. Average milk fat percentage decreased from 2.14% during week 4 to 1.73% during week 6. The low milk fat could was assumed to be caused by the short dietary particle lengths, and could have prohibited effects of feeding time on milk production. The decrease in milk fat over time might have been due to increased sorting against long and medium length feed particles. This increase in sorting was greater in 0900-fed cows than in 2100-fed cows. Key words: Time of feeding, dairy cows, milk production, sorting

Neutrophil apoptosis and the resolution of infection

Polymorphonuclear leukocytes (PMNs) are the most abundant white cell in humans and an essential component of the innate immune system. PMNs are typically the first type of leukocyte recruited to sites of infection or areas of inflammation. Ingestion of microorganisms triggers production of reactive oxygen species and fusion of cytoplasmic granules with forming phagosomes, leading to effective killing of ingested microbes. Phagocytosis of bacteria typically accelerates neutrophil apoptosis, which ultimately promotes the resolution of infection. However, some bacterial pathogens alter PMN apoptosis to survive and thereby cause disease. Herein, we review PMN apoptosis and the ability of microorganisms to alter this important process.

Identification of novel cytolytic peptides as key virulence determinants for community-associated MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major human pathogen. Traditionally, MRSA infections occurred exclusively in hospitals and were limited to immunocompromised patients or individuals with predisposing risk factors. However, recently there has been an alarming epidemic caused by community-associated (CA)-MRSA strains, which can cause severe infections that can result in necrotizing fasciitis or even death in otherwise healthy adults outside of healthcare settings. In the US, CA-MRSA is now the cause of the majority of infections that result in trips to the emergency room. It is unclear what makes CA-MRSA strains more successful in causing human disease compared with their hospital-associated counterparts. Here we describe a class of secreted staphylococcal peptides that have a remarkable ability to recruit, activate and subsequently lyse human neutrophils, thus eliminating the main cellular defense against S. aureus infection. These peptides are produced at high concentrations by standard CA-MRSA strains and contribute significantly to the strains' ability to cause disease in animal models of infection. Our study reveals a previously uncharacterized set of S. aureus virulence factors that account at least in part for the enhanced virulence of CA-MRSA.

Dectin-1 promotes fungicidal activity of human neutrophils

Human polymorphonuclear leukocytes (PMN) are a first line of defense against fungal infections. PMN express numerous pattern recognition receptors (PRR) that facilitate identification of invading microorganisms and ultimately promote resolution of disease. Dectin-1 (beta-glucan receptor) is a PRR expressed on several cell types and has been studied on monocytes and macrophages. However, the role played by dectin-1 in the recognition and killing of fungi by PMN is unknown. We investigated the ability of dectin-1 to mediate human PMN phagocytosis and fungicidal activity. Dectin-1 was expressed on the surface of PMN from all subjects tested (n=29) and in an intracellular compartment that co-sedimented with azurophilic granules in Percoll density gradients. Soluble beta-glucan and mAb GE2 (anti-dectin-1) inhibited binding and phagocytosis of zymosan by human PMN (e.g., ingestion was inhibited 40.1% by 30 min, p<0.001), and blocked reactive oxygen species production. Notably, soluble beta-glucan and GE2 inhibited phagocytosis and killing of Candida albicans by PMN (inhibition of killing was 54.8% for beta-glucan and 36.2% for GE2, p<0.01). Our results reveal a mechanism whereby PMN dectin-1 plays a key role in the recognition and killing of fungal pathogens by the innate immune system.

Accelerating dynamical-fermion computations using the rational hybrid Monte Carlo algorithm with multiple pseudofermion fields

There has been much recent progress in the understanding and reduction of the computational cost of the hybrid Monte Carlo algorithm for lattice QCD as the quark mass parameter is reduced. In this letter we present a new solution to this problem, where we represent the fermionic determinant using n pseudofermion fields, each with an nth root kernel. We implement this within the framework of the rational hybrid Monte Carlo algorithm. We compare this algorithm with other recent methods in this area and find it is competitive with them.

Thrice-Weekly Low-Dose Rituximab Decreases CD20 Loss via Shaving and Promotes Enhanced Targeting in Chronic Lymphocytic Leukemia

Treatment of chronic lymphocytic leukemia (CLL) patients with standard dose infusion of rituximab (RTX), 375 mg/m2, induces clearance of malignant cells from peripheral blood after infusion of 30 mg of RTX. After completion of the full RTX infusion, substantial recrudescence of CLL cells occurs, and these cells have lost > 90% of CD20. To gain insight into mechanism(s) of CD20 loss, we investigated the hypothesis that thrice-weekly low-dose RTX (20 or 60 mg/m2) treatment for CLL over 4 wk would preserve CD20 and enhance leukemic cell clearance. During initial infusions in all 12 patients, the first 30 mg of RTX promoted clearance of > 75% leukemic cells. Four of six patients receiving 20 mg/m2 RTX retained > or = 50% CD20, and additional RTX infusions promoted further cell clearance. However, four of six patients receiving 60 mg/m2 had CD20 levels < 20% baseline 2 days after initial infusions, and additional RTX infusions were less effective, presumably due to epitope loss. Our results suggest that when a threshold RTX dose is exceeded, recrudesced RTX-opsonized cells are not cleared, due to saturation of the mononuclear phagocytic system, but instead are shaved of RTX-CD20 complexes by acceptor cells. Thrice-weekly low-dose RTX may promote enhanced clearance of circulating CLL cells by preserving CD20.

Plasma melatonin and insulin-like growth factor-1 responses to dim light at night in dairy heifers

The effect of dim (5, 10 and 50 1x) light at night on night plasma melatonin level (NML) and night plasma insulin-like growth factor-1 (IGF-1) level was determined in 12 prepubertal Holstein heifers (245 +/- 16 days age) using a 4 x 4 Latin Square design with 14-day treatment and 14-day recovery periods. Blood samples were collected at 23:00 hr (prior to the 8 hr night treatment which commenced at mid-night) on days 0, 3 and 13, and throughout the night at 01:00, 02:00, 03:00, 04:00, 06:00 and 08:00 hr on days 1, 4 and 14 of treatment. Plasma was analysed by radioimmunoassay for melatonin (all samples) and IGF-1 (samples for day 14, 04:00 hr only). Treatment (P = 0.03) and treatment x time (P = 0.02) were significant for NML. Exposure to 50 lx suppressed NML by 50% during the initial 2 hr of the night, but not thereafter. Exposure to 5 and 10 lx had no effect on NML. The NML response to 50 lx was found on all treatment days studied (treatment x time x day; P = 0.99). There was no treatment effect on plasma IGF-1 level (P = 0.89), but plasma IGF-1 level was higher (P = 0.001) during period 4. Plasma IGF-1 level and NML tended (P = 0.10) to be negatively correlated. Light intensities of 10 lx or less appear safe for use at night in dairy barns where darkness is recommended.

Selective and efficient inhibition of the alternative pathway of complement by a mAb that recognizes C3b/iC3b

The alternative pathway (AP) of the complement system plays an important role in tissue damage and inflammation associated with certain autoimmune diseases and with ischemia-reperfusion injury. Selective inhibition of the AP could prevent such pathologies while allowing the classical and lectin pathways of complement activation to continue to provide protection. Here we present data describing selective inhibition of the AP of complement by anti-C3b/iC3b monoclonal antibody (mAb) 3E7, and by a chimeric, "deimmunized" form of this mAb, H17, which contains the human IgG1 Fc region and was further modified by substitution of amino acids in order to remove T cell epitopes. Both mAbs block AP-mediated deposition of C3b onto zymosan or Sepharose 4B, and they also inhibit AP-promoted lysis of rabbit erythrocytes. MAbs 3E7 and H17 also successfully compete with both factors B and H for binding to C3b-opsonized substrates, and the ability of both mAbs to inhibit the AP is blocked by pre-incubation with two different sources of C3(H2O). Kinetic measurements demonstrate that mAb 3E7 effectively stops progression of C3b deposition after AP activation is initiated. Our results therefore suggest that these mAbs block activation of the AP by binding to both C3(H2O) and to C3b, and thus prevent binding and activation of factor B. Based on these and other observations, mAb H17 may find future use in therapeutic applications focused on selective inhibition of the AP.

The Shaving Reaction: Rituximab/CD20 Complexes Are Removed from Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia Cells by THP-1 Monocytes

Clinical investigations have revealed that infusion of immunotherapeutic mAbs directed to normal or tumor cells can lead to loss of targeted epitopes, a phenomenon called antigenic modulation. Recently, we reported that rituximab treatment of chronic lymphocytic leukemia patients induced substantial loss of CD20 on B cells found in the circulation after rituximab infusion, when rituximab plasma concentrations were high. Such antigenic modulation can severely compromise therapeutic efficacy, and we postulated that B cells had been stripped (shaved) of the rituximab/CD20 complex by monocytes or macrophages in a reaction mediated by FcgammaR. We developed an in vitro model to replicate this in vivo shaving process, based on reacting rituximab-opsonized CD20(+) cells with acceptor THP-1 monocytes. After 45 min at 37 degrees C, rituximab and CD20 are removed from opsonized cells, and both are demonstrable on acceptor THP-1 cells. The reaction occurs equally well in the presence and absence of normal human serum, and monocytes isolated from peripheral blood also promote shaving of CD20 from rituximab-opsonized cells. Tests with inhibitors and use of F(ab')(2) of rituximab indicate transfer of rituximab/CD20 complexes to THP-1 cells is mediated by FcgammaR. Antigenic modulation described in previous reports may have been mediated by such shaving, and our findings may have profound implications for the use of mAbs in the immunotherapy of cancer.

Subacute ruminal acidosis induces ruminal lipopolysaccharide endotoxin release and triggers an inflammatory response

Subacute ruminal acidosis (SARA) was induced in 3 rumen fistulated Jersey steers by offering them different combinations of wheat-barley pellets and chopped alfalfa hay. Steers were offered 4, 5, and 6 kg/d of pelleted concentrate and 6, 5, and 4 kg/d of chopped alfalfa hay for diets 1, 2, and 3, respectively, during 5-d treatment periods and were fed chopped alfalfa hay between treatment periods. Inducing SARA increased blood concentrations of haptoglobin and serum amyloid-A. Dry matter intake of concentrate and hay decreased from d 1 to 5 in each period. Subacute ruminal acidosis was induced in all steers during d 4 and 5 when concentrate was fed, with ruminal pH remaining below 5.6 for an average of 187 and 174 min/d on these days. Lipopolysaccharide concentration increased significantly during periods of grain feeding compared with times when only hay was fed. Inducing SARA by feeding wheat-barley pellets activated a systemic inflammatory response in the steers.

Short Communication: Infrared Thermography and Visual Examination of Hooves of Dairy Cows in Two Stages of Lactation

Hooves of 16 lactating Holstein cows were examined twice for sole hemorrhages and underrun heels. Images of hooves were taken using infrared thermography to determine the temperatures of the coronary band and that of a control area above the coronary band. To adjust for skin (control) temperature, the difference (DeltaT) between the coronary band and the control area was calculated. Effects of stage of lactation, that is, <or=200 d in milk (DIM) vs. >200 DIM, on temperature of the coronary band, DeltaT, and visual abnormalities were determined. Temperatures of the coronary bands of cows were greater for cows <or=200 DIM (n = 17) than for cows (n = 15) in late lactation (25.5 +/- 1.3 vs. 21.0 degrees C). The DeltaT was also greater for cows <or=200 DIM compared with those >200 DIM (6.1 +/- 0.8 vs. 3.3 +/- 0.9 degrees C). The DeltaT was greater for lateral claws than for medial claws (5.2 +/- 0.6 vs. 4.2 +/- 0.6 degrees C). Chi-square analysis revealed that the frequency of sole hemorrhages in hind lateral claws was significantly higher for cows <or=200 DIM compared with those in late lactation. In contrast, underrun heel was more frequently observed among cows >200 DIM. Increased temperatures of the coronary band and DeltaT in early/midlactation coincided with increased incidence of sole hemorrhages, but not to incidences of underrun heels. Because higher hoof temperatures occurred in cows <or=200 DIM compared with cows later in lactation, measurement of hoof temperatures among cows in early lactation may be useful in monitoring hoof health.

Complement activation and C3b deposition on rituximab-opsonized cells substantially blocks binding of phycoerythrin-labeled anti-mouse IgG probes to rituximab

Binding of rituximab (RTX) to CD20+ B cells activates complement and promotes covalent deposition of C3b fragments on the cells. Previously, we reported that the deposited C3b is substantially co-localized with cell-bound RTX, and therefore C3b may block access of antibody probes specific for RTX. We examined the ability of several commercially available phycoerythrin (PE)-labeled anti-Mouse IgG antibodies to bind to B cells opsonized in milieu which allow or preclude complement activation. Even when large amounts of fluorescently labeled RTX are bound to the cells, binding of the anti-Mouse IgG probes is substantially inhibited if C3b is deposited on the cells. However, cell-bound RTX is still demonstrable on development with a monoclonal antibody (mAb) specific for the human Fc region of RTX. Our findings may provide an alternative explanation for data presented in recent reports suggesting that binding of RTX to cells in plasma leads to internalization of RTX and CD20.

Effect of feed delivery fluctuations and feeding time on ruminal acidosis, growth performance, and feeding behavior of feedlot cattle1,2

Research was conducted to determine whether fluctuations in the amount of feed delivered and timing of feeding affect ruminal pH and growth of feedlot cattle. In Exp. 1, the effects of constant (C) vs. fluctuating (F) daily feed delivery on ruminal pH were assessed in a crossover experiment (two 28-d periods) involving six mature, ruminally cannulated steers. The diet consisted of 86.8% barley grain, 4.9% supplement, and 8.3% barley silage (DM basis) and was offered ad libitum for 2 wk to estimate DMI by individual steers. Steers in group C were offered a constant amount of feed daily equal to their predetermined DMI, whereas steers in group F were offered 10% more or less than their predetermined DMI on a rotating 3-d schedule. Ruminal pH of each steer was measured continuously via an indwelling electrode placed in the rumen during the last 6 d of each period. Mean pH tended to be lower (0.10 units) for F than C (5.63 vs. 5.73; P = 0.15), and ruminal pH of steers in group F tended to remain below 5.8 (P = 0.03) or 5.5 (P = 0.14) for greater proportions of the day than steers in group C. Inconsistent delivery of feed lowered ruminal pH, suggesting increased risk of subclinical acidosis. In Exp. 2, a 2 x 2 factorial was used to study the effects of pattern (C vs. F) and feeding time (morning [0900] vs. evening [2100]) on the feeding behavior and performance of 234 (310 +/- 23 kg) Charolais x Hereford beef steers during backgrounding and finishing phases over 209 d. One pen per treatment was equipped with a radio frequency identification (GrowSafe Systems Ltd., Airdrie, Canada) system that monitored bunk attendance by each steer throughout the trial. Pattern of feed delivery did not affect (P = 0.16) DMI (7.36 kg/d), ADG (1.23 kg/d), G:F (0.17), or time spent at the bunk (141 min/d), nor were pattern of feed delivery x time of feeding interactions observed (P = 0.18). Late feeding increased (P < 0.05) daily DMI (7.48 vs. 7.26 kg), ADG (1.28 vs. 1.00 kg/d), and G:F (0.21 vs. 0.15). These studies indicate that the risk of subclinical acidosis was increased with fluctuating delivery of feed, but the greater risk of acidosis did not impair growth performance by feedlot cattle. Consequently, daily intake fluctuations of 10% DMI or less that do not alter overall intake by feedlot cattle are unlikely to have any negative consequences on growth performance.

Rituximab infusion promotes rapid complement depletion and acute CD20 loss in chronic lymphocytic leukemia

Complement plays an important role in the immunotherapeutic action of the anti-CD20 mAb rituximab, and therefore we investigated whether complement might be the limiting factor in rituximab therapy. Our in vitro studies indicate that at high cell densities, binding of rituximab to human CD20(+) cells leads to loss of complement activity and consumption of component C2. Infusion of rituximab in chronic lymphocytic leukemia patients also depletes complement; sera of treated patients have reduced capacity to C3b opsonize and kill CD20(+) cells unless supplemented with normal serum or component C2. Initiation of rituximab infusion in chronic lymphocytic leukemia patients leads to rapid clearance of CD20(+) cells. However, substantial numbers of B cells, with significantly reduced levels of CD20, return to the bloodstream immediately after rituximab infusion. In addition, a mAb specific for the Fc region of rituximab does not bind to these recirculating cells, suggesting that the rituximab-opsonized cells were temporarily sequestered by the mononuclear phagocytic system, and then released back into the circulation after the rituximab-CD20 complexes were removed by phagocytic cells. Western blots provide additional evidence for this escape mechanism that appears to occur as a consequence of CD20 loss. Treatment paradigms to prevent this escape, such as use of engineered or alternative anti-CD20 mAbs, may allow for more effective immunotherapy of chronic lymphocytic leukemia.

Three new assays for rituximab based on its immunological activity or antigenic properties: analyses of sera and plasmas of RTX-treated patients with chronic lymphocytic leukemia and other B cell lymphomas

Rituximab (RTX) is a monoclonal antibody which targets CD20 and is approved for treatment of non-Hodgkin's lymphoma (NHL), with an approximate 50% overall response rate among NHL patients. Accurate determination of RTX concentrations in patient plasmas is important for proper dosing of patients and for correlating RTX concentrations with clinical responses. There is currently no assay available for RTX which utilizes easily obtainable commercial reagents. Therefore, we sought to develop such an assay, and in this report we describe three new assays for RTX concentration. One assay, based on flow cytometry, quantitates immunologically active RTX based on its ability to bind to CD20 on Raji cells. Two other methods, based on flow cytometry and ELISA, measure RTX based on its antigenic properties. The assays are accurate, in good agreement with one another, and can all measure RTX concentrations as low as approximately 1 microg/ml in both sera and plasmas. Use of these assays reveals that chronic lymphocytic leukemia (CLL) patients receiving RTX treatment have lower plasma RTX concentrations than patients with other B cell lymphomas at all times over the usual 4-week course of therapy. The level in CLL plasmas often declines to <1 microg/ml RTX 1 week after each RTX infusion, substantially lower than the values found in comparable non-CLL patient plasmas. RTX assay results also demonstrate that naïve CLL patient plasmas do not have levels of non-cell associated CD20 sufficient to either interfere with an in vitro assay of RTX or to block the potential therapeutic action of RTX in vivo.

B cell complement receptor 2 transfer reaction

The B cell C receptor specific for C3dg (CR2) shares a number of features with the primate E C receptor (CR1). Previously, we have demonstrated, both in vitro and in animal models, that immune complexes (IC) bound to primate E CR1, either via C opsonization or by means of bispecific mAb complexes, can be transferred to acceptor macrophages in a process that also removes CR1 from the E. We have now extended this paradigm, the transfer reaction, to include B cell CR2. We used both flow cytometry and fluorescence microscopy to demonstrate that IC bound to Raji cell CR2, either via C opsonization or through the use of an anti-CR2 mAb, are transferred to acceptor THP-1 cells. This reaction, which appears to require Fc recognition of IgG bound to Raji cell CR2, also leads to transfer of CR2. Additional support for the B cell transfer reaction is provided in a prototype study in a monkey model in which IC bound to B cell CR2 are localized to the spleen. These findings may have important implications with respect to defining the role of C in IC handling during the normal immune response.

An anti-C3b(i) mAb enhances complement activation, C3b(i) deposition, and killing of CD20+ cells by rituximab

We investigated deposition of the complement protein fragment C3b and its breakdown products (collectively designated as C3b(i)) on CD20-positive cells treated with rituximab (RTX) in the presence of normal human serum (NHS). Radioimmunoassay (RIA) demonstrates that about 500 000 C3b(i) molecules deposit per cell, and fluorescence microscopy reveals that C3b(i) colocalizes with bound RTX. Use of mAb 3E7, specific for C3b(i) bound to substrates, enhances C3b(i) deposition; > 1 million C3b(i) deposit when cells are incubated with NHS, RTX and mAb 3E7. Treatment of Raji cells in NHS plus RTX leads to robust cell killing (95%) after 24 to 48 hours, and mAb 3E7 significantly enhances RTX-mediated killing of Raji and DB cells. A cynomolgus monkey model based on intravenous infusion of RTX followed by mAb 3E7 demonstrated that RTX rapidly binds to B cells and promotes complement activation and C3b(i) deposition; fluorescence microscopy analyses revealed the same pattern of colocalization of C3b(i) on cell-bound RTX in vivo as observed in vitro. Preliminary in vitro studies with blood samples from patients with chronic lymphocytic leukemia lead to similar findings. These experiments suggest that complement plays a key role in the mechanism of action of RTX; moreover, the in vivo molecular form of RTX (and possibly other antitumor mAbs) in the circulation or in tissues may include C3b(i) molecules covalently bound to the therapeutic mAb, thus allowing it to interact with cells containing both Fc and complement receptors.