David L. Murray

Intracranial Gadolinium Deposition after Contrast-enhanced MR Imaging

PURPOSE To determine if repeated intravenous exposures to gadolinium-based contrast agents (GBCAs) are associated with neuronal tissue deposition. MATERIALS AND METHODS In this institutional review board-approved single-center study, signal intensities from T1-weighted magnetic resonance (MR) images and postmortem neuronal tissue samples from 13 patients who underwent at least four GBCA-enhanced brain MR examinations between 2000 and 2014 (contrast group) were compared with those from 10 patients who did not receive GBCA (control group). Antemortem consent was obtained from all study participants. Neuronal tissues from the dentate nuclei, pons, globus pallidus, and thalamus of these 23 deceased patients were harvested and analyzed with inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy, and light microscopy to quantify, localize, and assess the effects of gadolinium deposition. Associations between cumulative gadolinium dose, changes in T1-weighted MR signal intensity, and ICP-MS-derived tissue gadolinium concentrations were examined by using the Spearman rank correlation coefficient (ρ). RESULTS Compared with neuronal tissues of control patients, all of which demonstrated undetectable levels of gadolinium, neuronal tissues of patients from the contrast group contained 0.1-58.8 μg gadolinium per gram of tissue, in a significant dose-dependent relationship that correlated with signal intensity changes on precontrast T1-weighted MR images (ρ = 0.49-0.93). All patients in the contrast group had relatively normal renal function at the time of MR examination. Gadolinium deposition in the capillary endothelium and neural interstitium was observed only in the contrast group. CONCLUSION Intravenous GBCA exposure is associated with neuronal tissue deposition in the setting of relatively normal renal function. Additional studies are needed to investigate the clinical significance of these findings and the generalizability to other GBCAs. Online supplemental material is available for this article.

Using Mass Spectrometry to Monitor Monoclonal Immunoglobulins in Patients with a Monoclonal Gammopathy

A monoclonal gammopathy is defined by the detection a monoclonal immunoglobulin (M-protein). In clinical practice, the M-protein is detected by protein gel electrophoresis (PEL) and immunofixation electrophoresis (IFE). We theorized that molecular mass could be used instead of electrophoretic patterns to identify and quantify the M-protein because each light and heavy chain has a unique amino acid sequence and thus a unique molecular mass whose increased concentration could be distinguished from the normal polyclonal background. In addition, we surmised that top-down MS could be used to isotype the M-protein because each immunoglobulin has a constant region with an amino acid sequence unique to each isotype. Our method first enriches serum for immunoglobulins followed by reduction using DTT to separate light chains from heavy chains and then by microflow LC-ESI-Q-TOF MS. The multiply charged light and heavy chain ions are converted to their molecular masses, and reconstructed peak area calculations for light chains are used for quantification. Using this method, we demonstrate how the light chain portion of an M-protein can be monitored by molecular mass, and we also show that in sequential samples from a patient with multiple myeloma the light chain portion of the M-protein was detected in all samples, even those negative by PEL, IFE, and quantitative FLC. We also present top-down MS isotyping of M-protein light chains using a unique isotype-specific fragmentation pattern allowing for quantification and isotype identification in the same run. Our results show that microLC-ESI-Q-TOF MS provides superior sensitivity and specificity compared to conventional methods and shows promise as a viable method of detecting and isotyping an M-protein.

Quantitation of serum monoclonal proteins: relationship between agarose gel electrophoresis and immunonephelometry.

BACKGROUND Previous comparisons of monoclonal protein quantification identified a bias between serum protein electrophoresis (SPEP) and immunonephelometry (NEPH). METHODS We reviewed data from 2845 patients in whom a single sample provided a gamma fraction M-spike by SPEP, a heavy chain isotype by immunofixation electrophoresis (IFE), and an Ig quantification by NEPH. We examined the relationship between SPEP and NEPH. Selected sera with high monoclonal protein concentrations were diluted and reassessed. RESULTS For all isotypes, the relationship between SPEP and NEPH was best fitted with cubic curves. We determined the concentrations of each isotype that fitted a linear relationship. IgA had the best correspondence (slope 0.92, 95% CI 0.87-1.02), whereas IgM demonstrated a systematic bias of higher values by NEPH (slope 1.80, 95% CI 1.68-1.92). IgG demonstrated a nonlinear relationship between SPEP and NEPH, with a linear region <19.2 g/L having a slope of 0.83 (95% CI 0.79-0.89) and a second linear region having a slope of 1.47 (95% CI 1.39-1.53) at higher concentrations. Dilutions of high-concentration IgG monoclonal proteins were linear by NEPH and nonlinear by SPEP. CONCLUSIONS There are systematic differences in the quantification of monoclonal IgM and IgG by SPEP and NEPH. The bias in IgM is from NEPH overestimation. The nonlinearity of SPEP at high monoclonal IgG concentrations may obscure changes in plasma cell populations. Clinicians should be made aware of the biases and nonlinearity in these tests to make proper conclusions regarding treatment response.

Relationship between monoclonal gammopathy and cardiac amyloid type

BACKGROUND Proper identification of cardiac amyloid type is essential for patient management, and has historically relied upon immunohistochemical- or immunofluorescence-based methods, often correlated with serum and urine protein electrophoresis (SPEP and UPEP) with immunofixation electrophoresis (IFE), and/or free light chain immunoassay (FLC). The recent implementation of mass spectrometry-based proteomic analysis for clinical amyloid typing allows us to determine the validity of these tests to predict amyloid type. Validity of SPEP/UPEP/IFE and FLC assays in cardiac amyloid prediction was examined. METHODS Retrospective analysis of two tertiary care populations (n=143, 2001-2010), of cardiac biopsy-proven amyloidosis, was performed. RESULTS Amyloid of transthyretin (ATTR) type was found in 81 (57%) of 143 patients and immunoglobulin light chain amyloid was found in the remaining 62 (43%). SPEP/UPEP/IFE detected a monoclonal gammopathy in 76 individuals, 56 with AL and 20 with ATTR amyloid and was overall a poor predictor of AL amyloid in this patient population: specificity (75%; 95% CI, 65-83%) and positive predictive value (PPV 74%; 95% CI, 63-82%). The FLC assay detected an abnormal kappa/lambda ratio in 61 patients, 53 with AL and 8 with ATTR amyloid and was a better predictor of AL amyloid type in this patient population: specificity (90%, 95% CI, 82-95%) and PPV (87%, 95% CI, 76-93%). CONCLUSIONS ATTR was the predominant amyloid type in this large cohort of endomyocardial biopsies characterized by mass spectrometry. Although FLC performs better than SPEP/UPEP/IFE, the performance of blood and urine studies for monoclonal proteins are not adequate to classify amyloid type. SUMMARY This large-scale retrospective analysis of cardiac amyloidosis shows that blood and urine monoclonal protein studies are not, by themselves, robust predictors of cardiac amyloid type in patients undergoing endomyocardial biopsy.

Gadolinium Deposition in Human Brain Tissues after Contrast-enhanced MR Imaging in Adult Patients without Intracranial Abnormalities

Purpose To determine whether gadolinium deposits in neural tissues of patients with intracranial abnormalities following intravenous gadolinium-based contrast agent (GBCA) exposure might be related to blood-brain barrier integrity by studying adult patients with normal brain pathologic characteristics. Materials and Methods After obtaining antemortem consent and institutional review board approval, the authors compared postmortem neuronal tissue samples from five patients who had undergone four to 18 gadolinium-enhanced magnetic resonance (MR) examinations between 2005 and 2014 (contrast group) with samples from 10 gadolinium-naive patients who had undergone at least one MR examination during their lifetime (control group). All patients in the contrast group had received gadodiamide. Neuronal tissues from the dentate nuclei, pons, globus pallidus, and thalamus were harvested and analyzed with inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy with energy-dispersive x-ray spectroscopy, and light microscopy to quantify, localize, and assess the effects of gadolinium deposition. Results Tissues from the four neuroanatomic regions of gadodiamide-exposed patients contained 0.1-19.4 μg of gadolinium per gram of tissue in a statistically significant dose-dependent relationship (globus pallidus: ρ = 0.90, P = .04). In contradistinction, patients in the control group had undetectable levels of gadolinium with ICP-MS. All patients had normal brain pathologic characteristics at autopsy. Three patients in the contrast group had borderline renal function (estimated glomerular filtration rate <45 mL/min/1.73 m2) and hepatobiliary dysfunction at MR examination. Gadolinium deposition in the contrast group was localized to the capillary endothelium and neuronal interstitium and, in two cases, within the nucleus of the cell. Conclusion Gadolinium deposition in neural tissues after GBCA administration occurs in the absence of intracranial abnormalities that might affect the permeability of the blood-brain barrier. These findings challenge current understanding of the biodistribution of these contrast agents and their safety.

Monitoring IgA Multiple Myeloma: Immunoglobulin Heavy/Light Chain Assays

BACKGROUND The use of electrophoresis to monitor monoclonal immunoglobulins migrating in the β fraction may be difficult because of their comigration with transferrin and complement proteins. METHODS Immunoassays specific for IgGκ, IgGλ, IgAκ, IgAλ, IgMκ, and IgMλ heavy/light chain (HLC) were validated for use in the clinical laboratory. We assessed sample stability, inter- and intraassay variability, linearity, accuracy, and reference intervals for all 6 assays. We tested accuracy by verifying that the sum of the concentrations for the HLC-pairs accounted for the total immunoglobulins in each of 129 healthy sera, and that the HLC-pair ratios (rHLCs) were outside the reference interval in 97% of 518 diagnostic multiple myeloma (MM) samples. RESULTS We assessed diagnostic samples and posttreatment sera in 32 IgG and 30 IgA patients for HLC concentrations, rHLC, and total immunoglobulins and compared these nephelometry results with serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE). In sample sets from patients with IgG MM, the sensitivity of SPEP was almost the same as for rHLC, and no additional advantage was conferred by running HLC assays. In pre- and posttreatment samples from patients with IgA MM, the SPEP, rHLC, and IFE identified clonality in 28%, 56%, and 61%, respectively. In addition, when M-spikes were quantifiable, the concentration of the involved HLC was linearly related to that of the SPEP M-spike, with a slope near 1. CONCLUSIONS The use of IgA HLC assays for monitoring β-migrating IgA monoclonal proteins can substitute for the combination of SPEP, IFE, and total IgA quantification.

Serum immunoglobulin G4 level is a poor predictor of immunoglobulin G4-related disease.

Objectives Immunoglobulin G4–related disease (IgG4-RD) is characterized by elevation in serum IgG4 levels, typical multiorgan involvement and dramatic response to steroid therapy. We determined the predictive value of an elevated serum IgG4 for the diagnosis of IgG4-RD. We also sought to identify novel conditions, which have characteristic features of IgG4-RD. Methods We identified all Mayo Clinic Rochester patients with serum IgG4 levels measured between January 2008 and December 2011 (n = 6014). Those with elevated serum IgG4 levels (reference range, 121–140 mg/dL) were included in the analysis and were classified as “definite,” “probable,” or “no” IgG4-RD. Results Serum IgG4 levels were elevated in 390 subjects (6.5%) of whom only 39 (10%) had IgG4-RD (29 “definite,” 10 “probable”). The positive predictive value of an elevated serum IgG4 for IgG4-RD was poor (10%). Subjects with IgG4-RD differed from those without IgG4-RD in mean age (59.6 ± 15.2 vs 54.4 ± 18.3 years, P < 0.05), % males (90% vs 58%, P < 0.05), mean serum IgG4 level (437 ± 471vs 223 ± 194 mg/dL, P < 0.05), and presence of chronic rhinosinusitis (7/39 vs 29/351, P = 0.05). Conclusions Elevated serum IgG4 levels are not specific for IgG4-RD and are likely to be a false-positive. Chronic rhinosinusitis is likely an as yet underrecognized manifestation of IgG4-RD.

Diagnosis of complement alternative pathway disorders

Kidney diseases resulting from abnormal control of the complement alternative pathway include atypical hemolytic uremic syndrome, C3 glomerulonephritis, and dense-deposit disease, as well as atypical postinfectious glomerulonephritis. Although clinically diverse, they all result from loss of surface or fluid-phase complement control, caused by acquired or genetic defects in the complement alternative pathway. As such, the diagnostic approach is similar and includes a comprehensive biochemical, genetic, and pathologic analysis of the complement pathway. The biochemical test battery includes functional activity measurements of the entire complement pathway, functional and quantitative analysis of individual components and regulators, and quantification of activation products. In patients with a thrombotic microangiopathy, ADAMTS-13 activity should be determined to exclude a thrombotic thrombocytopenic purpura. The spectrum of genes currently known to be involved in the pathogenesis of alternative pathway disorders is rapidly expanding. Pathologic analysis of a kidney biopsy specimen is sophisticated with ad hoc immunofluorescence studies and laser microdissection with mass spectrometry. The identification of the underlying defect in the alternative pathway based on this comprehensive analysis will allow treatment to be directed to the site of dysregulation.

Comprehensive Assessment of M-Proteins Using Nanobody Enrichment Coupled to MALDI-TOF Mass Spectrometry.

BACKGROUND Electrophoretic separation of serum and urine proteins has played a central role in diagnosing and monitoring plasma cell disorders. Despite limitations in resolution and analytical sensitivity, plus the necessity for adjunct methods, protein gel electrophoresis and immunofixation electrophoresis (IFE) remain front-line tests. METHODS We developed a MALDI mass spectrometry-based assay that was simple to perform, automatable, analytically sensitive, and applicable to analyzing the wide variety of monoclonal proteins (M-proteins) encountered clinically. This assay, called MASS-FIX, used the unique molecular mass signatures of the different Ig isotypes in combination with nanobody immunoenrichment to generate information-rich mass spectra from which M-proteins could be identified, isotyped, and quantified. The performance of MASS-FIX was compared to current gel-based electrophoresis assays. RESULTS MASS-FIX detected all M-proteins that were detectable by urine or serum protein electrophoresis. In serial dilution studies, MASS-FIX was more analytically sensitive than IFE. For patient samples, MASS-FIX provided the same primary isotype information for 98% of serum M-proteins (n = 152) and 95% of urine M-proteins (n = 55). MASS-FIX accurately quantified M-protein to <1 g/dL, with reduced bias as compared to protein electrophoresis. Intraassay and interassay CVs were <20% across all samples having M-protein concentrations >0.045 g/dL, with the ability to detect M-proteins <0.01 g/dL. In addition, MASS-FIX could simultaneously measure κ:λ light chain ratios for IgG, IgA, and IgM. Retrospective serial monitoring of patients with myeloma posttreatment demonstrated that MASS-FIX provided equivalent quantitative information to either protein electrophoresis or the Hevylite(™) assay. CONCLUSIONS MASS-FIX can advance how plasma cell disorders are screened, diagnosed, and monitored.

Quantitation of infliximab using clonotypic peptides and selective reaction monitoring by LC–MS/MS

OBJECTIVES Although therapeutic concentrations of infliximab (chimeric IgG1 kappa) are associated with improved clinical prognosis, clinical laboratory methods for monitoring are limited. Therefore, we aimed to develop a LC-MS/MS method to measure infliximab in serum. METHODS Infliximab was measured using isotope-labeled peptides and horse IgG as a surrogate internal standard. After trypsin digestion, peptides were separated by reverse-phase C8 LC and detected by MS/MS on an ABSciex API 5000; analyte-to-internal standard peak area ratios were used for quantitation. Sera from patients receiving infliximab were collected at different time points in treatment and compared with a commercially available ECLIA method. RESULTS The linear dynamic range of the assay was 1-100 μg/mL (R(2)>0.998); both intra- and inter-assay imprecisions were <20%. Patients undergoing infliximab therapy had trough concentrations of 8.5 ± 8.8 μg/mL (mean ± SD), which substantially increased 48-72 h after infusion (77 ± 40 μg/mL), then fell after 28-32 days (15 ± 11 μg/mL). A comparison of LC-MS/MS and ECLIA methods demonstrated a slope of 0.967 (95% CI: 0.894-1.034, r=0.970). CONCLUSIONS We have demonstrated the ability to quantify infliximab in patients using clonotypic peptides. This approach has the potential to be quickly adaptable to other monoclonal antibodies and to expand the availability of testing for this class of therapeutics in routine clinical practice.