Improved sensitivity in homogeneous enzyme immunoassays using a fluorogenic macromolecular substrate: an assay for serum ferritin

A fluorescent probe for specific detection of β-galactosidase in living cells and tissues based on ESIPT mechanism

β-galactosidase is of great significance to living organisms, which is an important marker of primary ovarian cancer and cellular senescence. To detect the activity of β-galactosidase, a novel fluorescent probe ESIPT-GAL which based on excited state intramolecular proton transfer (ESIPT) mechanism for detecting β-galactosidase is developed in this work with low background fluorescence and high sensitivity (Φ_F = 0.0045-0.2409). The fluorescence intensity at 552 nm of this probe increased by ~ 55 times with β-galactosidase addition (0-4 U/mL), and its detection limit is very low (3.9 × 10^-5 U/mL). In addition, the spectral data (pseudo-first-order rate: 1.303 min^-1) and enzyme kinetic parameter (V_max = 69.5 μΜ•S^-1) both show that the probe can achieve rapid response to β-galactosidase. Moreover, the probe has good water solubility, which ensures that it has good biocompatibility and can be easily applied to detect β-galactosidase in living cells and tissues. Importantly, the probe ESIPT-GAL can monitor β-galactosidase in deep mouse tissue sections (90 μm).

Recent Advances of Molecular Optical Probes in Imaging of β-Galactosidase

β-Galactosidase (β-Gal), as a lysosomal hydrolytic enzyme, plays an important physiological role in catalyzing the hydrolysis of glycosidic bonds which convert lactose into galactose. Moreover, upregulation of β-Gal is often correlated with the occurrence of primary ovarian cancers and cell senescence. Thereby, detection of β-Gal activity is relevant to cancer diagnosis. Optical imaging possesses high spatial and temporal resolution, high sensitivity, and real-time imaging capability. These properties are beneficial for the detection of β-Gal in living systems. This Review summarizes the recent progress in development of molecular optical probes for near-infrared fluorescence (NIRF), bioluminescence (BL), chemiluminescence (CL), or photoacoustic (PA) imaging of β-Gal in biological systems. The challenges and opportunities in the probe design for detection of β-Gal are also discussed.

Performance and comparability of laboratory methods for measuring ferritin concentrations in human serum or plasma: A systematic review and meta-analysis

BACKGROUND

Different laboratory methods are used to quantify ferritin concentrations as a marker of iron status. A systematic review was undertaken to assess the accuracy and comparability of the most used methods for ferritin detection.

METHODS AND FINDINGS

National and regional databases were searched for prospective, retrospective, sectional, longitudinal and case-control studies containing the characteristics and performance of at least one method for serum/plasma ferritin determinations in humans published to date. The analysis included the comparison between at least 2 methods detailing: sensitivity, precision, accuracy, predictive values, inter-methods adjustment, and use of international reference materials. Pooled method performance was analyzed for each method and across methods.

OUTCOMES

Search strategy identified 11893 records. After de-duplication and screening 252 studies were assessed, including 187 studies in the qualitative analysis and 148 in the meta-analysis. The most used methods included radiometric, nonradiometric and agglutination assays. The overall within-run imprecision for the most reported ferritin methods was 6.2±3.4% (CI 5.69-6.70%; n = 171), between-run imprecision 8.9±8.7% (CI 7.44-10.35%; n = 136), and recovery rate 95.6% (CI 91.5-99.7%; n = 94). The pooled regression coefficient was 0.985 among all methods analyzed, and 0.984 when comparing nonradiometric and radiometric methods, without statistical differences in ferritin concentration ranging from 2.3 to 1454 μμg/L.

CONCLUSION

The laboratory methods most used to determine ferritin concentrations have comparable accuracy and performance. Registered in PROSPERO CRD42016036222.

An influenza hemagglutinin A peptide assay based on the enzyme-multiplied immunoassay technique

A practical approach for constructing enzyme-multiplied immunoassay technique (EMIT)-based protein/peptide assays is described. Normally used in small-molecule drug testing, EMIT is a homogeneous assay method that is attractive for its simplicity, sensitivity, and rapidity. The EMIT-based peptide/protein assay was developed by conjugating a cysteine-modified HA peptide (from influenza hemagglutinin A) to the reporter enzyme, glucose-6-phosphate dehydrogenase. The 13-min assay gave a free HA limit of detection of 10 nM and proved effective for detection of a high-molecular-weight model protein tagged with HA. Similar EMIT-based assay approaches may be developed for applications in biotoxin and infectious disease detection.

An enzymatically activated fluorescence probe for targeted tumor imaging

Beta-galactosidase is a widely used reporter enzyme, but although several substrates are available for in vitro detection, its application for in vivo optical imaging remains a challenge. To obtain a probe suitable for in vivo use, we modified our previously developed activatable fluorescence probe, TG-betaGal (J. Am. Chem. Soc. 2005, 127, 4888-4894), on the basis of photochemical and photophysical experiments. The new probe, AM-TG-betaGal, provides a dramatic fluorescence enhancement upon reaction with beta-galactosidase, and further hydrolysis of the ester moiety by ubiquitous intracellular esterases affords a hydrophilic product that is well retained within the cells without loss of fluorescence. We used a mouse tumor model to assess the practical utility of AM-TG-betaGal, after confirming that tumors in the model could be labeled with an avidin-beta-galactosidase conjugate. This conjugate was administered to the mice in vivo, followed by AM-TG-betaGal, and subsequent ex vivo fluorescence imaging clearly visualized intraperitoneal tumors as small as 200 microm. This strategy has potential clinical application, for example, in video-assisted laparoscopic tumor resection.

Lectin-based homogeneous enzyme-linked binding assay for estimating the type and relative amount of carbohydrate within intact glycoproteins

The feasibility of using a new lectin-based homogeneous enzyme-linked binding assay for estimating the type and relative amount of specific carbohydrate structures within intact glycoproteins is examined. Malate dehydrogenase-galactose, -mannose, and -N-acetylglucosamine conjugates are utilized in conjunction with Jacalin, concanavalin A, and wheat germ agglutinin, respectively. The catalytic activity of the glyco-enzyme conjugates is inhibited significantly (greater than 60%) in solution in the presence of the respective lectins. The observed inhibition for each reagent set is reversed in proportion to the type and relative amount of specific carbohydrates present within test glycoproteins added to the assay mixture. Competitive binding ED50 values for a number of synthetic and native model glycoproteins correlate well with the known carbohydrate content of these species. The proposed method is much faster than previous solid-phase lectin-based enzyme-linked methods used to probe carbohydrate content/structure (less than 15 min) and has the potential to be fully automated.

Automated quantitative nephelometric latex immunoassay for determining ferritin in human serum

We describe a rapid and sensitive latex nephelometric immunoassay for quantifying ferritin in human serum. This latex immunoassay procedure uses commercially available ready-for-use reagents [Tina-Quant (a) Ferritin, Boehringer Mannheim] that have a long shelf life. The assay consists of incubating the diluted serum sample (5-fold) for 12 min at room temperature with latex particles covalently coated with anti-ferritin antibodies, and then quantifying the change of light-scatter produced. The assay is fully automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. The method has an analytical range of 3 to 260 micrograms/l. Maximal intra- and inter-assay CVs were 4.0 and 6.2%, respectively. Analytical recoveries ranged from 91.3 to 103.6%. Assay detection limit was less than 3 micrograms/l. Linearity of the test is given throughout the measuring range. There was no interference from bilirubin (up to 340 mumol/l), haemoglobin (up to 7 g/l), or rheumatoid factor (up to 1,100 IU/ml). Turbid and lipemic samples interfere. This interference may be avoided by pretreating these samples prior to assay. Results correlated well with those obtained by an automated ELISA test (r = 0.995) and with those of two commercial RIA methods (r greater than 0.97). This latex nephelometric procedure is a convenient method and represents an interesting alternative to other immunoassays for measuring ferritin in human serum.