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Andrew N Hoofnagle

Publications and source records attributed to Andrew N Hoofnagle.

10 recordsLinked to original sources
PubMed2026

Interlaboratory Comparison of a Glucagon and Oxyntomodulin Immuno-LC-MS/MS Assay: Implications for Diabetes Research.

BACKGROUND: The quantification of plasma glucagon and oxyntomodulin is important in the assessment of α-cell function, which is impaired in patients with diabetes. We aimed to transfer between laboratories a novel assay that uses liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the sensitive and specific measurement of these highly homologous hormones. METHODS: Simultaneous measurement of glucagon and oxyntomodulin used immunoaffinity enrichment and LC-MS/MS. Immunoenrichment used monoclonal antibodies that are available at-cost to researchers (deposited at the Developmental Studies Hybridoma Bank). Pure synthetic glucagon, characterized for purity and concentration, was used as a calibrant and is available to others. A detailed standard operating procedure was shared between 3 laboratories and the performance of the method was evaluated with samples collected from patients with and without diabetes. Method comparison was made with 2 commercially available, FDA-registered glucagon immunoassays. RESULTS: The method was linear over the normal range (1-20 pM). When measured in duplicate, the median interlaboratory imprecision (%CV) of the measurement of 40 samples was 6.3% (IQR 4.5%) and 14.4% (IQR 12.4%) for glucagon and oxyntomodulin, respectively. Method comparison with commercially available immunoassays demonstrated good (Mercodia, R = 0.92) or fair (Ansh, R = 0.70) agreement. Multivariable linear regression using LC-MS/MS glucagon and oxyntomodulin concentrations to predict immunoassay results indicated significant cross-reactivity of each immunoassay with oxyntomodulin. CONCLUSION: We have validated a sensitive and specific assay for glucagon and oxyntomodulin that can be deployed in high-complexity clinical laboratories for research or the care of patients. Commercially available glucagon immunoassays have significant interference from molecules other than glucagon.

Journal Article↗
PubMed2025

Genetic Variants Associated With the Biochemical Response to Vitamin D3 in the Multi-Ethnic Study of Atherosclerosis.

CONTEXT: The response to treatment with vitamin D varies between patients. OBJECTIVE: To identify genetic variants associated with the biochemical response to vitamin D3 supplementation. DESIGN: Randomized placebo-controlled trial conducted between 2017 and 2019. SETTING: The trial was nested in an ongoing community-based cohort study, the Multi-Ethnic Study of Atherosclerosis. INTERVENTION: 2000 International Units of vitamin D3 or placebo daily for 16 weeks. PARTICIPANTS: The analytic sample included 427 participants assigned to vitamin D3 (mean age, 73 years; 54% females) and was 36% White, 33% Black, 18% Hispanic, and 14% Chinese. MAIN OUTCOME MEASURES: The biochemical response to vitamin D3 included changes in serum concentrations of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], PTH, and 25-hydroxyvitamin D3 [25(OH)D3]. RESULTS: In genome-wide analyses, single nucleotide polymorphisms in 8 regions of the genome had significant association (P < 5E-08) with 1 of the traits (2 with change in 1,25(OH)2D3, 1 with change in PTH, and 5 with change in 25(OH)D3). rs16867276 within an intergenic region on 2q31 was associated with change in serum 1,25(OH)2D3 (+8.37&#x2005;pg/mL difference per effect allele; P = 4.93E-08) and was the only locus that achieved genome-wide significance in transethnic meta-analysis. rs114044709 adjacent to FAM20A, which encodes a protein required for biomineralization, was associated with change in PTH among Black participants (+20.32&#x2005;pg/mL difference per effect allele; P = 1.34E-08). In candidate analyses, single nucleotide polymorphisms within SULT2A1 and CYP24A1 had significant association (P < .05&#xf7;36 = .0014) with the changes in 1,25(OH)2D3 and PTH, respectively. CONCLUSION: Our results reveal potential new pathways of vitamin D regulation that require replication in other vitamin D trials.

Humans↗
PubMed2006

Online database for documenting clinical pathology resident education.

BACKGROUND: Training of clinical pathologists is evolving and must now address the 6 core competencies described by the Accreditation Council for Graduate Medical Education (ACGME), which include patient care. A substantial portion of the patient care performed by the clinical pathology resident takes place while the resident is on call for the laboratory, a practice that provides the resident with clinical experience and assists the laboratory in providing quality service to clinicians in the hospital and surrounding community. Documenting the educational value of these on-call experiences and providing evidence of competence is difficult for residency directors. An online database of these calls, entered by residents and reviewed by faculty, would provide a mechanism for documenting and improving the education of clinical pathology residents. METHODS: With Microsoft Access we developed an online database that uses active server pages and secure sockets layer encryption to document calls to the clinical pathology resident. Using the data collected, we evaluated the efficacy of 3 interventions aimed at improving resident education. RESULTS: The database facilitated the documentation of more than 4 700 calls in the first 21 months it was online, provided archived resident-generated data to assist in serving clients, and demonstrated that 2 interventions aimed at improving resident education were successful. CONCLUSIONS: We have developed a secure online database, accessible from any computer with Internet access, that can be used to easily document clinical pathology resident education and competency.

Clinical Competence↗
PubMed2006

Fisher ratio method applied to third-order separation data to identify significant chemical components of metabolite extracts.

This report is about applying a Fisher ratio method to entire four dimensional (4D) data sets from third-order instrumentation data. The Fisher ratio method uses a novel indexing scheme to discover the unknown chemical differences among known classes of complex samples. This is the first report of a Fisher ratio analysis procedure applied to entire 4D data sets of third-order separation data, which, in this case, is comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry analyses of metabolite extracts using all of the collected mass channels. Current analysis methods for third-order separation data use only user-defined subsets of the 4D data set. First, in a validation study, the Fisher ratio method was demonstrated to objectively evaluate and determine the chemical differences between three controlled urine samples that differed by known spiked chemical components. It was determined that, out of more than 600 recognizable chemical components in a single sample, the six spiked components, along with only two other matrix components, differed most significantly in concentration among the control samples. In a second study, the Fisher ratio method was used in a novel application to discover the unknown chemical differences between urine metabolite samples from pregnant women and nonpregnant women. A brief list of the top 11 components that were most significantly different in concentration between the pregnant and nonpregnant samples was generated. Because the Fisher ratio calculation statistically differentiates regions of the chromatogram with large class-to-class variations from regions containing large within-class variations, the Fisher ratio method should generally be robust against biological diversity in a sample population. Indeed, application of principal component analysis in this second study failed due to biological diversity of the samples.

Algorithms↗
PubMed2006

Specific detection of anabasine, nicotine, and nicotine metabolites in urine by liquid chromatography-tandem mass spectrometry.

The sensitive and specific detection of nicotine, its metabolites, and the tobacco alkaloid, anabasine, is useful in evaluating the success of smoking cessation treatments and detecting tobacco use, passive exposure, and nontobacco nicotine exposure in potential transplant recipients, insurance clients, and elective surgical patients. Rapid sample preparation and extended high-performance liquid chromatographic separation of tobacco alkaloids and metabolites was interfaced with tandem mass spectrometry. By using deuterated internal standards and appropriate confirmatory ion mass transitions, direct injection of centrifugally clarified urine was possible. The method had excellent precision, limit of quantitation, and linearity. The rigorous separation method revealed an interferent of nicotine that had coeluted with anabasine in more rapid chromatography and that may result in tobacco use misclassification. The method provides more specific detection of tobacco exposure and illustrates the potential of centrifugal clarification for sample preparation in the detection of multiple analytes in urine.

Anabasine↗
PubMed2005

Hydrogen exchange solvent protection by an ATP analogue reveals conformational changes in ERK2 upon activation.

Structural and kinetic studies have provided extensive information about the molecular mechanisms of kinase activation by phosphorylation. However, it is still unclear how changes in protein dynamics and flexibility contribute to catalytic function. Mass spectrometry was used to probe changes in hydrogen/deuterium exchange in the MAP kinase, ERK2, in the presence and absence of the ATP analogue, AMP-PNP. In both active and inactive forms of ERK2, protection from hydrogen exchange by AMP-PNP binding was observed within conserved ATP binding motifs in the N-terminal lobe, which are known to directly interact with nucleotide in various protein kinases. In contrast, higher protection from exchange by AMP-PNP was observed in active ERK2 compared to inactive ERK2, in a region corresponding to the conserved DFG motif, which is located in the C-terminal lobe and coordinates Mg2+ at the catalytic site. Thus, AMP-PNP binding simultaneously protects residues within the N and C terminus in the active form of ERK2, but not the inactive form. This demonstrates that ERK2 binds nucleotide in two modes, in which active ERK2 adopts a closed conformation following nucleotide binding in solution, while inactive ERK2 adopts an open conformation. The finding provides novel evidence that phosphorylation of ERK2 facilitates interdomain closure, allowing proper orientation between ATP and substrate to facilitate phosphoryl transfer.

Adenosine Triphosphate↗
PubMed2004

Docking motif interactions in MAP kinases revealed by hydrogen exchange mass spectrometry.

Protein interactions between MAP kinases and substrates, activators, and scaffolding proteins are regulated by docking site motifs, one containing basic residues proximal to Leu-X-Leu (DEJL) and a second containing Phe-X-Phe (DEF). Hydrogen exchange mass spectrometry was used to identify regions in MAP kinases protected from solvent by docking motif interactions. Protection by DEJL peptide binding was observed in loops spanning beta7-beta8 and alphaD-alphaE in p38alpha and ERK2. In contrast, protection by DEF binding to ERK2 revealed a distinct hydrophobic pocket for Phe-X-Phe binding formed between the P+1 site, alphaF helix, and the MAP kinase insert. In inactive ERK2, this pocket is occluded by intramolecular interactions with residues in the activation lip. In vitro assays confirm the dependence of Elk1 and nucleoporin binding on ERK2 phosphorylation, and provide a structural basis for preferential involvement of active ERK in substrate binding and nuclear pore protein interactions.

Amino Acid Sequence↗
PubMed2004

Phosphorylation-dependent changes in structure and dynamics in ERK2 detected by SDSL and EPR.

Mitogen-activated protein kinases are regulated by occupancy at two phosphorylation sites near the active site cleft. Previous studies using hydrogen exchange to investigate the canonical mitogen-activated protein kinase, extracellular signal-regulated protein kinase-2, have shown that phosphorylation alters backbone conformational mobility >10 A distal to the site of phosphorylation, including decreased mobility within amino acids 102-105 and increased mobility within 108-109. To further describe changes after enzyme activation, site-directed spin labeling at amino acids 101, 105-109, 111, 112 and electron paramagnetic resonance spectroscopy were used to investigate this region. The anisotropic hyperfine splitting of the spin labels in glassy samples was unchanged by phosphorylation, consistent with previous crystallographic studies that indicate no structural change in this region. At positions 101, 111, and 112, the mobility of the spin label was unchanged by diphosphorylation, consistent with little or no conformational change. However, diphosphorylation caused small but significant changes in rotational diffusion rates at positions 105-108 and altered proportions of probe in a motionally constrained state at positions 105, 107, and 109. Thus, electron paramagnetic resonance indicates reproducible changes in nanosecond side-chain mobilities at specific residues within the interdomain region, far from the site of phosphorylation and conformational change.

Amino Acid Substitution↗
PubMed2003

Protein analysis by hydrogen exchange mass spectrometry.

Mass spectrometry has provided a powerful method for monitoring hydrogen exchange of protein backbone amides with deuterium from solvent. In comparison to popular NMR approaches, mass spectrometry has the advantages of higher sensitivity, wider coverage of sequence, and the ability to analyze larger proteins. Proteolytic fragmentation of proteins following the exchange reaction provides moderate structural resolution, in some cases enabling measurements from single amides. The technique has provided new insight into protein-protein and protein-ligand interfaces, as well as conformational changes during protein folding or denaturation. In addition, recent studies illustrate the utility of hydrogen exchange mass spectrometry toward detecting protein motions relevant to allostery, covalent modifications, and enzyme function.

Amides↗