Assessment of a Plasma Amyloid Probability Score to Estimate Amyloid Positron Emission Tomography Findings Among Adults With Cognitive Impairment

IMPORTANCE

The diagnostic evaluation for Alzheimer disease may be improved by a blood-based diagnostic test identifying presence of brain amyloid plaque pathology.

OBJECTIVE

To determine the clinical performance associated with a diagnostic algorithm incorporating plasma amyloid-β (Aβ) 42:40 ratio, patient age, and apoE proteotype to identify brain amyloid status.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study includes analysis from 2 independent cross-sectional cohort studies: the discovery cohort of the Plasma Test for Amyloidosis Risk Screening (PARIS) study, a prospective add-on to the Imaging Dementia-Evidence for Amyloid Scanning study, including 249 patients from 2018 to 2019, and MissionAD, a dataset of 437 biobanked patient samples obtained at screenings during 2016 to 2019. Data were analyzed from May to November 2020.

EXPOSURES

Amyloid detected in blood and by positron emission tomography (PET) imaging.

MAIN OUTCOMES AND MEASURES

The main outcome was the diagnostic performance of plasma Aβ42:40 ratio, together with apoE proteotype and age, for identifying amyloid PET status, assessed by accuracy, sensitivity, specificity, and area under the receiver operating characteristic curve (AUC).

RESULTS

All 686 participants (mean [SD] age 73.2 [6.3] years; 368 [53.6%] men; 378 participants [55.1%] with amyloid PET findings) had symptoms of mild cognitive impairment or mild dementia. The AUC of plasma Aβ42:40 ratio for PARIS was 0.79 (95% CI, 0.73-0.85) and 0.86 (95% CI, 0.82-0.89) for MissionAD. Ratio cutoffs for Aβ42:40 based on the Youden index were similar between cohorts (PARIS: 0.089; MissionAD: 0.092). A logistic regression model (LRM) incorporating Aβ42:40 ratio, apoE proteotype, and age improved diagnostic performance within each cohort (PARIS: AUC, 0.86 [95% CI, 0.81-0.91]; MissionAD: AUC, 0.89 [95% CI, 0.86-0.92]), and overall accuracy was 78% (95% CI, 72%-83%) for PARIS and 83% (95% CI, 79%-86%) for MissionAD. The model developed on the prospectively collected samples from PARIS performed well on the MissionAD samples (AUC, 0.88 [95% CI, 0.84-0.91]; accuracy, 78% [95% CI, 74%-82%]). Training the LRM on combined cohorts yielded an AUC of 0.88 (95% CI, 0.85-0.91) and accuracy of 81% (95% CI, 78%-84%). The output of this LRM is the Amyloid Probability Score (APS). For clinical use, 2 APS cutoff values were established yielding 3 categories, with low, intermediate, and high likelihood of brain amyloid plaque pathology.

CONCLUSIONS AND RELEVANCE

These findings suggest that this blood biomarker test could allow for distinguishing individuals with brain amyloid-positive PET findings from individuals with amyloid-negative PET findings and serve as an aid for Alzheimer disease diagnosis.

The PrecivityAD™ test: Accurate and reliable LC-MS/MS assays for quantifying plasma amyloid beta 40 and 42 and apolipoprotein E proteotype for the assessment of brain amyloidosis

BACKGROUND

There is an unmet need for an accessible, less invasive, cost-effective method to facilitate clinical trial enrollment and aid in clinical Alzheimer's disease (AD) diagnosis. APOE genotype affects the clearance and deposition of amyloid-beta (Aβ) with APOE4 carriers having increased risk while APOE2 alleles appear to be protective. Lower plasma Aβ42/40 correlates with brain amyloidosis. In response, C₂N has developed the PrecivityAD™ test; plasma LC-MS/MS assays for Aβ isoform quantitation and qualitative APOE isoform-specific proteotyping.

METHODS

In accord with CLIA standards, we developed and validated assay performance: precision, accuracy, linearity, limit of detection (LoD), interferences.

RESULTS

Within-day precision varied from 1.5-3.0% (Aβ40) and 2.5-8.4% (Aβ42). Total (within-lab) variability was 2.7-7.7% (Aβ40) and 3.1-9.5% (Aβ42). Aβ40 quantitation was linear from 10 to 1780 pg/mL; Aβ42 was linear from 2 to 254 pg/mL. LoD was 11 and 2 pg/mL for Aβ40 and Aβ42, respectively. APOE proteotypes were 100% concordant with genotype, while LoD (fM) was much lower than APOE concentrations observed in plasma (mM).

CONCLUSIONS

The PrecivityAD™ assays are precise, accurate, sensitive, and linear over a wide analytical range, free from significant interferences, and suitable for use in the clinical laboratory.

A blood-based diagnostic test incorporating plasma Aβ42/40 ratio, ApoE proteotype, and age accurately identifies brain amyloid status: findings from a multi cohort validity analysis

BACKGROUND

The development of blood-based biomarker tests that are accurate and robust for Alzheimer's disease (AD) pathology have the potential to aid clinical diagnosis and facilitate enrollment in AD drug trials. We developed a high-resolution mass spectrometry (MS)-based test that quantifies plasma Aβ42 and Aβ40 concentrations and identifies the ApoE proteotype. We evaluated robustness, clinical performance, and commercial viability of this MS biomarker assay for distinguishing brain amyloid status.

METHODS

We used the novel MS assay to analyze 414 plasma samples that were collected, processed, and stored using site-specific protocols, from six independent US cohorts. We used receiver operating characteristic curve (ROC) analyses to assess assay performance and accuracy for predicting amyloid status (positive, negative, and standard uptake value ratio; SUVR). After plasma analysis, sites shared brain amyloid status, defined using diverse, site-specific methods and cutoff values; amyloid PET imaging using various tracers or CSF Aβ42/40 ratio.

RESULTS

Plasma Aβ42/40 ratio was significantly (p < 0.001) lower in the amyloid positive vs. negative participants in each cohort. The area under the ROC curve (AUC-ROC) was 0.81 (95% CI = 0.77-0.85) and the percent agreement between plasma Aβ42/40 and amyloid positivity was 75% at the optimal (Youden index) cutoff value. The AUC-ROC (0.86; 95% CI = 0.82-0.90) and accuracy (81%) for the plasma Aβ42/40 ratio improved after controlling for cohort heterogeneity. The AUC-ROC (0.90; 95% CI = 0.87-0.93) and accuracy (86%) improved further when Aβ42/40, ApoE4 copy number and participant age were included in the model.

CONCLUSIONS

This mass spectrometry-based plasma biomarker test: has strong diagnostic performance; can accurately distinguish brain amyloid positive from amyloid negative individuals; may aid in the diagnostic evaluation process for Alzheimer's disease; and may enhance the efficiency of enrolling participants into Alzheimer's disease drug trials.

Effects of Aryl Hydrocarbon Receptor Deficiency on PCB-77-Induced Impairment of Glucose Homeostasis during Weight Loss in Male and Female Obese Mice

BACKGROUND

Lipophilic polychlorinated biphenyls (PCBs) accumulate with obesity, but during weight loss, liberated PCBs act as ligands of the aryl hydrocarbon receptor (AhR) to negatively influence health. Previous studies demonstrated that PCB-77 administration to obese male mice impaired glucose tolerance during weight loss. Recent studies indicate higher toxic equivalencies of dioxin-like PCBs in exposed females than males.

OBJECTIVES

We compared effects of PCB-77 on weight gain or loss and glucose homeostasis in male vs. female mice. We defined effects of AhR deficiency during weight gain or loss in male and female mice exposed to PCB-77.

METHODS

Study design was vehicle (VEH) or PCB-77 administration while fed a high-fat (HF) diet for 12 wk, followed by weight loss for 4 wk. The following groups were examined: male and female C57BL/6 mice administered VEH or PCB-77, female [Formula: see text] and [Formula: see text] mice administered VEH or PCB-77, and male [Formula: see text] and [Formula: see text] mice administered PCB-77. Glucose tolerance was quantified during weight gain (week 11) and loss (week 15); liver and adipose AhR and IRS2 (insulin receptor substrate 2) mRNA abundance, and PCB-77 concentrations were quantified at week 16.

RESULTS

PCB-77 attenuated development of obesity in females but not males. During weight loss, PCB-77 impaired glucose tolerance of males. AhR-deficient females (VEH) were resistant to diet-induced obesity. Compared with VEH-treated mice, HF-fed [Formula: see text] females treated with PCB-77 has less weight gain, and [Formula: see text] females had greater weight gain. During weight loss, [Formula: see text] females but not [Formula: see text] males treated with PCB-77 exhibited impaired glucose tolerance. In [Formula: see text] females administered PCB-77, IRS2 mRNA abundance was lower in adipose tissue compared with VEH-treated mice.

CONCLUSION

Male and female mice responded differently to PCB-77 and AhR deficiency in body weight (BW) regulation and glucose homeostasis. AhR deficiency reversed PCB-77-induced glucose impairment of obese males losing weight but augmented glucose intolerance of females. These results demonstrate sex differences in PCB-77-induced regulation of glucose homeostasis of mice. https://doi.org/10.1289/EHP4133.

Administration of low dose triclosan to pregnant ewes results in placental uptake and reduced estradiol sulfotransferase activity in fetal liver and placenta

Sulfonation is a major pathway of estrogen biotransformation with a role in regulating estrogen homeostasis in humans and sheep. Previous in vitro studies found that triclosan is an especially potent competitive inhibitor of ovine placental estrogen sulfotransferase, with K_ic of <0.1 nM. As the placenta is the main organ responsible for estrogen synthesis in pregnancy in both women and sheep, and the liver is another site of estrogen biotransformation, this study examined the effects of triclosan exposure of pregnant ewes on placental and hepatic sulfotransferase activity. Triclosan, 0.1 mg/kg/day, or saline vehicle was administered to late gestation fetal sheep for two days either by direct infusion into the fetal circulation or infusion into the maternal blood. On the third day, fetal liver and placenta were harvested and analyzed for triclosan and for cytosolic estradiol sulfotransferase activity. Placenta contained higher concentrations of triclosan than liver in each individual sheep in both treatment groups. There was a negative correlation between triclosan tissue concentration (pmol/g tissue) and cytosolic sulfotransferase activity (pmol/min/mg protein) towards estradiol. These findings demonstrated that in the sheep exposed to very low concentrations of triclosan, this substance is taken up into placenta and reduces estrogen sulfonation.

Notch1 loss of heterozygosity causes vascular tumors and lethal hemorrhage in mice

The role of the Notch signaling pathway in tumor development is complex, with Notch1 functioning either as an oncogene or as a tumor suppressor in a context-dependent manner. To further define the role of Notch1 in tumor development, we systematically surveyed for tumor suppressor activity of Notch1 in vivo. We combined the previously described Notch1 intramembrane proteolysis-Cre (Nip1::Cre) allele with a floxed Notch1 allele to create a mouse model for sporadic, low-frequency loss of Notch1 heterozygosity. Through this approach, we determined the cell types most affected by Notch1 loss. We report that the loss of Notch1 caused widespread vascular tumors and organism lethality secondary to massive hemorrhage. These findings reflected a cell-autonomous role for Notch1 in suppressing neoplasia in the vascular system and provide a model by which to explore the mechanism of neoplastic transformation of endothelial cells. Importantly, these results raise concerns regarding the safety of chronic application of drugs targeting the Notch pathway, specifically those targeting Notch1, because of mechanism-based toxicity in the endothelium. Our strategy also can be broadly applied to induce sporadic in vivo loss of heterozygosity of any conditional alleles in progenitors that experience Notch1 activation.

Strain-specific susceptibility for pulmonary metastasis of sarcoma 180 cells in inbred mice

Most cancer deaths are a result of metastasis. To extend our understanding of the factors that influence the process, we aimed to develop a mouse model of pulmonary metastasis that can be assayed in multiple inbred mouse strains for further use in identification of host genetic variants that influence metastasis. We used i.v. injection of Sarcoma 180 (S180) cells, which can be tracked and quantified by bioluminescence imaging. We observed growth of S180 cells solely in the lung and observed a wide range of pulmonary metastasis among inbred mouse strains. Interestingly, we noted that the BTBRT+tf/J strain exhibited complete clearance and provide evidence that the mechanism of resistance may involve immune factors, as strains subjected to whole-body irradiation are significantly more susceptible to tumor growth. One possible mechanism of resistance to pulmonary metastasis in BTBRT+tf/J mice may require T-cell function. Our experiments present a new mouse model for further characterization of the genetics and mechanisms of pulmonary metastasis.

Immunodeficient mouse strains display marked variability in growth of human melanoma lung metastases

PURPOSE

Immunodeficient mice serve as critical hosts for transplantation of xenogeneic cells for in vivo analysis of various biological processes. Because investigators typically select one or two immunodeficient mouse strains as recipients, no comprehensive study has been published documenting differences in human tumor engraftment. Taking advantage of the increased metastatic potential of RhoC-expressing human (A375) melanoma cells, we evaluate four immunodeficient mouse strains: severe combined immunodeficiency (scid), nonobese diabetic (NOD)-scid, NOD-scid beta2m(null), and NOD-scid IL2Rgamma(null) as xenograft tumor recipients.

EXPERIMENTAL DESIGN

Bioluminescence, magnetic resonance imaging, and histopathology were used to monitor serial tumor growth. Natural killer (NK) cell function was examined in each mouse strain using standard (51)Chromium release assays.

RESULTS

Melanoma metastases growth is delayed and variable in scid and NOD-scid mice. In contrast, NOD-scid beta2m(null) and NOD-scid IL2Rgamma(null) mice show rapid tumor engraftment, although tumor growth is variable in NOD-scid beta2m(null) mice. NK cells were detected in all strains except NOD-scid IL2Rgamma(null), and in vitro activated scid, NOD-scid, and NOD-scid beta2m(null) NK cells kill human melanoma lines and primary melanoma cells. Expression of human NKG2D ligands MHC class I chain-related A and B molecules renders melanoma susceptible to murine NK cell-mediated cytotoxicity and killing is inhibited by antibody blockade of murine NKG2D.

CONCLUSIONS

Murine NKG2D recognition of MICA/B is an important receptor-ligand interaction used by NK cells in immunodeficient strains to limit engraftment of human tumors. The absolute NK deficiency in NOD-scid IL2Rgamma(null) animals makes this strain an excellent recipient of melanoma and potentially other human malignancies.

IMMUNE-DEFICIENT MOUSE STRAINS DISPLAY MARKED VARIABILITY IN GROWTH OF HUMAN MELANOMA LUNG METASTASES (88.6)

Immune-deficient mice are widely used in cancer research to study human cancer biology and evaluate new therapeutics. No comprehensive study has been published documenting differences in human tumor engraftment among immune-deficient strains. Using RhoC-expressing human (A375) melanoma cells, we evaluate scid, NOD-scid (NS), NOD-scid β2mnull (NSB), and NOD-scid IL2Rγnull (NSG) as xenograft tumor recipients. Bioluminescence, magnetic resonance imaging and histopathology were employed to monitor serial tumor growth. Melanoma metastases growth is delayed and variable in scid, and NS mice. In contrast, NSB and NSG mice show rapid tumor engraftment, although tumor growth is variable in NSB mice. NK cells were detected in all strains except NSG, and in vitro activated scid, NS and NSB NK cells kill human melanoma lines and primary melanoma cells. Expression of human NKG2D ligands, MICA and MICB, renders melanoma susceptible to murine NK cell-mediated cytotoxicity and killing is inhibited by antibody blockade of murine NKG2D. Murine NKG2D recognition of MICA/B is an important receptor-ligand interaction employed by NK cells in immune-deficient strains to limit engraftment of human tumors. The absolute NK deficiency in NOD-scid IL2Rγnull animals makes this strain an excellent recipient of melanoma and potentially other human malignancies.

Optical imaging of bacterial infection in living mice using a fluorescent near-infrared molecular probe

An optical imaging probe was synthesized by attaching a near-infrared carbocyanine fluorophore to an affinity group containing two zinc(II) dipicolylamine (Zn-DPA) units. The probe has a strong and selective affinity for the surfaces of bacteria, and it was used to image infections of Gram-positive S. aureus and Gram-negative E. coli bacteria in living nude mice. After intravenous injection, the probe selectively accumulates at the sites of localized bacterial infections in the thigh muscles of the mice.

Transglutaminase 2 inhibitor, KCC009, disrupts fibronectin assembly in the extracellular matrix and sensitizes orthotopic glioblastomas to chemotherapy

Transglutaminase 2 (TG2, a.k.a. tissue transglutaminase) belongs to a family of transglutaminase enzymes that stabilize proteins by affecting covalent crosslinking via formation of amide bonds. Cell surface TG2 is directly involved as an adhesive receptor in cell-extracellular matrix (ECM) interactions. Here, we show that TG2 activity is elevated in glioblastomas compared with non-neoplastic brain. Immunofluorescent studies showed increased staining of fibronectin colocalized with TG2 in the ECM in glioblastomas. In addition, small clusters of invading human glioblastoma cells present in non-neoplastic brain parenchyma secrete high levels of TG2 and fibronectin that distinguish them from normal brain stroma. Downregulation of TG2 in U87MG glioblastoma cells with RNAi demonstrated decreased assembly of fibronectin in the ECM. Treatment with KCC009 blocked the remodeling of fibronectin in the ECM in glioblastomas in both in vitro and in vivo studies. KCC009 treatment in mice harboring orthotopic glioblastomas (DBT-FG) sensitized the tumors to N,N'-bis(2-chloroethyl)-N-nitrosourea chemotherapy, as measured by reduced bioluminescence, increased apoptosis and prolonged survival. The ability of KCC009 to interfere with the permissive remodeling of fibronectin in the ECM in glioblastomas suggests a novel target to enhance sensitivity to chemotherapy directed not only at the tumor mass, but also invading glioblastoma cells.

ESTs from the basidiomycete Schizophyllum commune grown on nitrogen-replete and nitrogen-limited media

Lambda phage cDNA libraries were constructed using mRNAs from the basidiomycete Schizophyllum commune grown on media with high or low nitrogen concentrations. A total of 440 clones were sequenced, representing 373 distinct transcripts. Of these, 166 showed significant similarity to annotated genes in GenBank. Those that could be tentatively identified using BLAST searches were classified by function using the Gene Ontology (GO) database. Genes with products involved in cell-cycle processes were more frequent in the nitrogen-limited libraries, while genes with products involved in protein biosynthesis were more frequent in the nitrogen-replete library. Overall, clones showed much greater similarity to the one publicly available basidiomycete genome, Phanerochaete chrysosporium, than to any of the ascomycete genomes.

Use of alkaline phosphatase fusions to study protein secretion in Bacillus subtilis

We have constructed a vector designed to facilitate the study of protein secretion in Bacillus subtilis. This vector is based on a translational fusion between the expression elements and signal sequence of Bacillus amyloliquefaciens alkaline protease and the mature coding sequence for Escherichia coli alkaline phosphatase (phoA). We show that export of alkaline phosphatase from B. subtilis depends on a functional signal sequence and that alkaline phosphatase activity depends upon secretion. The vector design facilitates the insertion of heterologous coding sequences between the signal and phoA to generate three-part translational fusions. Such phoA fusions are easily analyzed by monitoring alkaline phosphatase activity on agar plates or in culture supernatants or by immunological detection. Exploitation of this methodology, which has proven to be extremely useful in the study of protein secretion in E. coli, has a variety of applications for studying protein secretion in B. subtilis.

Transfer of chimeric plasmids among Salmonella typhimurium strains by P22 transduction

Salmonella typhimurium bacteriophage P22 transduced plasmids having P22 sequences inserted in the vector pBR322 with high frequency. Analysis of the structure of the transducing particle DNA and the transduced plasmids indicates that this plasmid transduction involves two homologous recombination events. In the donor cell, a single recombination between the phage and the homologous sequences on the plasmid inserted the plasmid into the phage chromosome, which was then packaged by headfuls into P22 particles. The transducing particle DNA contained duplications of the region of homology flanking the integrated plasmid vector sequences and lacked some phage genes. When these defective phage genomes containing the inserted plasmid infected a recipient cell, recombination between the duplicated regions regenerated the plasmid. A useful consequence of this sequence of events was that genetic markers in the region of homology were readily transferred from phage to plasmid. Plasmid transduction required homology between the phage and the plasmid, but did not depend on the presence of any specific P22 sequence in the plasmid. When the infecting P22 carried a DNA sequence homologous to the ampicillin resistance region of pBR322, the vector plasmid having no P22 insert could be transduced. P22-mediated transduction is a useful way to transfer chimeric plasmids, since most S. typhimurium strains are poorly transformed by plasmid DNA.

Localization of two functions of the phosphoribosyl anthranilate transferase of Escherichia coli to distinct regions of the polypeptide chain

The trpD gene specifies a polypeptide which has both glutamine amidotransferase and phosphoribosyl anthranilate (PRA) transferase activities. Deletions fusing segments of trpD to the gene preceding it in the operon, trpE, were selected in strains carrying various trpD point mutations. The selection procedure required both that a deletion enter trpE and that it restore the PRA transferase activity which the parent trpD point mutant lacked. Deletion mutants were found which had PRA transferase activity although the first third of trpD was deleted. The existence of the mutants proves that a terminal segment of trpD is sufficient to specify a polypeptide having PRA transferase activity. The location of the deletion end points on the genetic map of trpD defines the extent of the trpD segment required for PRA transferase activity. This segment did not overlap the initial region of trpD required to specify the glutamine amidotransferase function of the trpD polypeptide. These results support the hypothesis (M. Grieshaber and R. Bauerle, 1972; H. Zalkin and L. H. Hwang, 1971) that the bifunctional trpD polypeptide might have evolved by fusion of a gene specifying a glutamine amidotransferase with a gene directing PRA transferase synthesis.

Duplication-translocations of tryptophan operon genes in Escherichia coli

Mutants of Escherichia coli were selected in which a single mutational event had both relieved the polar effect of an early trpE mutation on trpB and simultaneously released the expression of trpB from tryptophan repression. The frequency at which these mutations appeared was roughly equal to the frequency of point mutations. In each of these mutants, the mutation increased the function of trpB and also increased the activity of some, but not all, of the other four tryptophan operon genes. Genetic analysis showed that the mutations were not located within the trp operon since in each case the parental trp operon could be recovered from the mutants. Each mutant was shown to carry a duplication of a trp operon segment translocated to a new position near the trp operon. Polarity is relieved since the trpB duplication-translocation is not in the same operon as the trpE polar mutation. The duplicated and translocated segments are fused to operons not regulated by tryptophan, so trpB function is no longer subject to tryptophan repression. The properties of the mutants indicate that the length of the duplicated segment and the position to which it is translocated differ in each of the seven mutants studied. The duplications are unstable, but the segregation pattern observed is not consistent with a single crossover model for segregation. That such duplication-translocation events generate a variety of new genetic arrangements at a frequency comparable with point mutations suggests they may play an important role in evolution.