Gastric Cancer Cell-Derived Exosomal GRP78 Enhances Angiogenesis upon Stimulation of Vascular Endothelial Cells.

Exosomes containing glucose-regulated protein 78 (GRP78) are involved in cancer malignancy. GRP78 is thought to promote the tumor microenvironment, leading to angiogenesis. No direct evidence for this role has been reported, however, mainly because of difficulties in accurately measuring the GRP78 concentration in the exosomes. Recently, exosomal GRP78 concentrations were successfully measured using an ultrasensitive ELISA. In the present study, GRP78 concentrations in exosomes collected from gastric cancer AGS cells with overexpression of GRP78 (OE), knockdown of GRP78 (KD), or mock GRP78 (mock) were quantified. These three types of exosomes were then incubated with vascular endothelial cells to examine their effects on endothelial cell angiogenesis. Based on the results of a tube formation assay, GRP78-OE exosomes accelerated angiogenesis compared with GRP78-KD or GRP78-mock exosomes. To investigate the mechanisms underlying this effect, we examined the Ser473 phosphorylation state ratio of AKT, which is involved in the angiogenesis process, and found that AKT phosphorylation was increased by GRP78-OE exosome application to the endothelial cells. An MTT assay showed that GRP78-OE exosome treatment increased the proliferation rate of endothelial cells, and a wound healing assay showed that this treatment increased the migration capacity of the endothelial cells. These findings demonstrated that GRP78-containing exosomes promote the tumor microenvironment and induce angiogenesis.

Ultrasensitive ELISA detection of proteins in separated lumen and membrane fractions of cancer cell exosomes.

Exosomes transfer molecules horizontally to surrounding cells and therefore have a key role in cancer progression. To clarify the role of exosomes in cancer progression, trace amounts of proteins in their lumen and membrane fractions should be analyzed separately. For this purpose, an adequate and easy-to-use method of separating the lumen and membrane fractions of exosomes must be developed. Further, because exosomes contain only trace amounts of proteins, an ultrasensitive protein detection method is necessary. To develop an adequate and easy-to-use lumen and membrane fraction separation method, we applied a commercially available kit originally developed for cells to exosomes and examined the validity of the results compared with those obtained using a conventional, complicated Na2CO3 method. To develop an ultrasensitive protein detection method, we designated GRP78, which is upregulated in cancer cells and contributes to cancer progression, as the target protein and detected it at the subattomolar level using an ultrasensitive ELISA combined with thio-NAD cycling. By applying these methods together, GRP78 was successfully quantified in both the lumen and membrane fractions of exosomes obtained from cultured cancer cells. The present results will facilitate studies to broaden our understanding of the tumor microenvironment.

Ultrasensitive Detection of GRP78 in Exosomes and Observation of Migration and Proliferation of Cancer Cells by Application of GRP78-Containing Exosomes.

Cancer cells communicate with each other via exosomes in the tumor microenvironment. However, measuring trace amounts of proteins in exosomes is difficult, and thus the cancer stemness-promoting mechanisms of exosomal proteins have not been elucidated. In the present study, we attempted to quantify trace amounts of 78-kDa glucose-regulated protein (GRP78), which is involved in cancer progression, in exosomes released from cultured gastric cancer cells using an ultrasensitive ELISA combined with thio-NAD cycling. We also evaluated the cancer stemness-promoting effects by the application of high-GRP78-containing exosomes to cultured gastric cancer cells. The ultrasensitive ELISA enabled the detection of GRP78 at a limit of detection of 0.16 pg/mL. The stemness of cancer cultured cells incubated with high-GRP78-containing exosomes obtained from GRP78-overexpressed cells was increased on the basis of both an MTT assay and a wound healing assay. Our results demonstrated that the ultrasensitive ELISA has strong potential to measure trace amounts of proteins in exosomes. Further, exosomes with a high concentration of GRP78 promote the cancer stemness of surrounding cells. The technique for quantifying proteins in exosomes described here will advance our understanding of cancer stemness progression via exosomes.

Modified ELISA for Ultrasensitive Diagnosis.

An enzyme-linked immunosorbent assay (ELISA) can be used for quantitative measurement of proteins, and improving the detection sensitivity to the ultrasensitive level would facilitate the diagnosis of various diseases. In the present review article, we first define the term 'ultrasensitive'. We follow this with a survey and discussion of the current literature regarding modified ELISA methods with ultrasensitive detection and their application for diagnosis. Finally, we introduce our own newly devised system for ultrasensitive ELISA combined with thionicotinamide adenine dinucleotide cycling and its application for the diagnosis of infectious diseases and lifestyle-related diseases. The aim of the present article is to expand the application of ultrasensitive ELISAs in the medical and biological fields.

Zeptomole Detection of an Enzyme by a Simple Colorimetric Method.

An enzyme immunoassay, in which an enzyme (e.g., alkaline phosphatase, ALP) is conjugated with an antibody, is a precise and simple protein detection method. Precise measurements of enzymes at low concentrations allow for ultrasensitive protein detection. The application of a phosphorylated substrate to ALP, followed by using a dephosphorylated substrate in thionicotinamide-adenine dinucleotide cycling, provides a simple and precise quantification of ALP. We describe a protocol for detecting ALP at the zeptomole level using a simple colorimetric method.

Early diagnosis with ultrasensitive ELISA.

Accurate, rapid and simple detection methods are required to facilitate early diagnosis of various disorders including infectious and lifestyle diseases as well as cancer. These detection approaches reduce the window of infection, i.e., the period between infection and reliable detection. Optimally, these methods should target protein as an indicator of pathogenic microbes as well as other biomarkers. For example, although nucleic acid is easily detected by polymerase chain reaction (PCR), these markers are also present in dead microbes, and, in the case of mRNA, it is not known whether this target was successfully translated. Accordingly, early diagnostic approaches require the development of ultrasensitive protein detection methods. In this chapter, we introduce an ultrasensitive enzyme-linked immunosorbent assay (ELISA) which combines a traditional sandwich-based immunoassay with thionicotinamide adenine dinucleotide (thio-NAD) cycling. The performance characteristics of this unique approach are reviewed as well as its potential role in providing a novel and ultrasensitive diagnostic tool in the clinical laboratory.

Ultrasensitive ELISA Developed for Diagnosis.

For the diagnosis of disease, the ability to quantitatively detect trace amounts of the causal proteins from bacteria/viruses as biomarkers in patient specimens is highly desirable. Here we introduce a simple, rapid, and colorimetric assay as a de novo, ultrasensitive detection method. This ultrasensitive assay consists of a sandwich enzyme-linked immunosorbent assay (ELISA) and thionicotinamide-adenine dinucleotide (thio-NAD) cycling, forming an ultrasensitive ELISA, in which the signal substrate (i.e., thio-NADH) accumulates in a triangular manner, and the accumulated thio-NADH is measured at its maximum absorption wavelength of 405 nm. We have successfully achieved a limit of detection of ca. 10-18 moles/assay for a target protein. As an example of infectious disease detection, HIV-1 p24 could be measured at 0.0065 IU/assay (i.e., 10-18 moles/assay), and as a marker for a lifestyle-related disease, adiponectin could be detected at 2.3 × 10-19 moles/assay. In particular, despite the long-held belief that the trace amounts of adiponectin in urine can only be detected using a radioisotope, our ultrasensitive ELISA was able to detect urinary adiponectin. This method is highly versatile because simply changing the antibody enables the detection of various proteins. This assay system requires only the measurement of absorbance, thus it requires equipment that is easily obtained by medical facilities, which facilitates diagnosis in hospitals and clinics. Moreover, we describe an expansion of our ultrasensitive ELISA to a non-amplification nucleic acid detection method for nucleic acids using hybridization. These de novo methods will enable simple, rapid, and accurate diagnosis.