Ultrasensitive Detection of SARS-CoV-2 Spike Proteins Using the Thio-NAD Cycling Reaction: A Preliminary Study before Clinical Trials

Ultrasensitive protein-level detection for respiratory infectious viruses

Influenza virus, adenovirus, and respiratory syncytial virus cause major respiratory infections. These infections have similar initial symptoms making it difficult to differentiate them based on symptoms alone. PCR is currently used as the standard diagnostic test for these infections, however, it has its limitations such as non-specific and false-negative amplifications, high cost, and the inability to distinguish between a live or dead virus. Therefore, there is a need for alternative diagnostic methods that focus on protein. Here, we introduce TN-cyclon™, which is an enzyme-linked immunosorbent assay combined with thio-nicotinamide adenine dinucleotide cycling to amplify signals, rather than the protein itself. Using this method, we were able to detect extremely low levels of viruses such as influenza A, influenza B, adenovirus, and RS virus, with LODs of 2.96 × 10-18 moles/assay, 2.98 × 10-18 moles/assay, 2.36 × 10-18 moles/assay, and 3.55 × 10-18 moles/assay, respectively. Furthermore, we successfully detected viruses diluted with extract buffer, with a significant difference to the blank at concentrations of 3 pfu/mL for influenza A, 1000 pfu/mL for influenza B, 43.8 pfu/mL for adenovirus, and 125 pfu/mL for RS virus. This shows that our low-cost and easy-to-use technique has sufficient sensitivity in diagnosing respiratory infections.

Ultrafast and highly sensitive detection of SARS-CoV-2 spike protein by field-effect transistor graphene-based biosensors

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), etiological agent for the coronavirus disease 2019 (COVID-19), has resulted in over 775 million global infections. Early diagnosis remains pivotal for effective epidemiological surveillance despite the availability of vaccines. Antigen-based assays are advantageous for early COVID-19 detection due to their simplicity, cost-effectiveness, and suitability for point-of-care testing (PoCT). This study introduces a graphene field-effect transistor-based biosensor designed for high sensitivity and rapid response to the SARS-CoV-2 spike protein. By functionalizing graphene with monoclonal antibodies and applying short-duration gate voltage pulses, we achieve selective detection of the viral spike protein in human serum within 100 µs and at concentrations as low as 1 fg ml-1, equivalent to 8 antigen molecules perµl of blood. Furthermore, the biosensor estimates spike protein concentrations in serum from COVID-19 patients. Our platform demonstrates potential for next-generation PoCT antigen assays, promising fast and sensitive diagnostics for COVID-19 and other infectious diseases.

Removal of Soluble ACE2 in VeroE6 Cells by 17β-Estradiol Reduces SARS-CoV-2 Infectivity

Women are less susceptible than men to coronavirus disease 2019 (COVID-19), which might be due to the female steroid hormone 17β-estradiol. We hypothesized that 17β-estradiol removes the soluble portion of angiotensin-converting enzyme 2 (sACE2) to which severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds in host cells and that sACE2 then binds to the virus, thereby reducing the infectivity. In the present study, VeroE6/serine protease 2 transmembrane protein (TMPRSS2) cells were infected with pseudo SARS-CoV-2 viruses and used as our model system. This infectivity was reduced by the application of 17β-estradiol. After applying 17β-estradiol to the VeroE6/TMPRSS2 cells, we used a sandwich enzyme-linked immunosorbent assay (ELISA) to measure the sACE2 concentration in the culture medium. Our findings revealed that 17β-estradiol removes sACE2 from VeroE6/TMPRSS2 cells. Furthermore, the pseudo SARS-CoV-2 viruses were incubated in culture medium with ACE2 collected from 17β-estradiol-treated VeroE6/TMPRSS2 cells, and the viruses were measured with an ultrasensitive ELISA using anti-spike protein antibodies. The amount of spike proteins decreased according to the concentration of 17β-estradiol applied. These results clearly demonstrated that the soluble portion of ACE2, which was removed from 17β-estradiol-treated VeroE6/TMPRSS2 cells, bound to the spike proteins of SARS-CoV-2, thereby reducing COVID-19 infectivity.

Advanced Detection Method for Dengue NS1 Protein Using Ultrasensitive ELISA with Thio-NAD Cycling

Dengue fever, a mosquito-borne disease in tropical and subtropical climates caused by the dengue virus (DENV), has become a major social and economic burden in recent years. However, current primary detection methods are inadequate for early diagnosis of DENV because they are either time-consuming, expensive, or require training. Non-structural protein 1 (NS1) is secreted during DENV infection and is thus considered a suitable biomarker for the development of an early detection method. In the present study, we developed a detection method for the NS1 protein based on a previously reported thio-NAD cycling ELISA (i.e., ultrasensitive ELISA) and successfully achieved a LOD of 1.152 pg/mL. The clinical diagnosis potential of the detection system was also evaluated by using 85 patient specimens, inclusive of 60 DENV-positive and 25 DENV-negative specimens confirmed by the NAAT method. The results revealed 98.3% (59/60) sensitivity and 100% (25/25) specificity, which was in almost perfect agreement with the NAAT data with a kappa coefficient of 0.972. The present study demonstrates the diagnostic potential of using an ultrasensitive ELISA as a low-cost, easy-to-use method for the detection of DENV compared with NAAT and could be of great benefit in low-income countries.

Non-amplification nucleic acid detection with thio-NAD cycling

The PCR technique is indispensable in biology and medicine, but some difficulties are associated with its use, including false positive or false negative amplifications. To avoid these issues, a non-amplification nucleic acid detection protocol is needed. In the present study, we propose a method in which nucleic-acid probe hybridization is combined with thio-NAD cycling to detect nucleic acids without amplification. We report our application of this method for the detection of the gene of MPT64 in Mycobacterium tuberculosis. Two different cDNA probes targeted the mpt64 gene: the first probe was used to immobilize the mpt64 gene, and the second probe, linked with alkaline phosphatase (ALP), was hybridized to a target sequence in the mpt64 gene. A substrate was then hydrolyzed by ALP, and a cycling reaction was conducted by a dehydrogenase with its co-factors (thio-NAD and NADH). The single-stranded DNA, double-stranded DNA, plasmid DNA for the mpt64 gene, and whole genome of M. tuberculosis var. BCG were detected at the level of 10⁵-10⁶ copies/assay, whereas the non-tuberculosis mycobacteria (e.g., M. avium, M. intracellulare, M. kansasii, and M. abscessus) were below the limits of detection. The present method enables us to avoid the errors inherent in nucleic acid amplification methods.

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

Simple Summary

Cancer cells release exosomes to their surrounding cells, and it is believed that trace amounts of proteins included in exosomes promote cancer stemness. In the present study, we note 78-kDa glucose-regulated protein (GRP78), which is involved in cancer progression, and present the protocol for measurements of trace amounts of GRP78 in exosomes released from cultured gastric cancer cells using an ultrasensitive ELISA with thio-NAD cycling. We found that when high-GRP78-containing exosomes were incubated with cultured cancer cells, these cells increased their stemness, for example, an increase in indices of both an MTT assay and a wound healing assay. The technique for quantifying proteins in exosomes described here will advance our understanding of cancer stemness progression via exosomes.

Abstract

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.

Effectiveness of SARS-CoV-2 Vaccines for Short- and Long-Term Immunity: A General Overview for the Pandemic Contrast

BACKGROUND

The recent COVID-19 pandemic produced a significant increase in cases and an emergency state was induced worldwide. The current knowledge about the COVID-19 disease concerning diagnoses, patient tracking, the treatment protocol, and vaccines provides a consistent contribution for the primary prevention of the viral infection and decreasing the severity of the SARS-CoV-2 disease. The aim of the present investigation was to produce a general overview about the current findings for the COVID-19 disease, SARS-CoV-2 interaction mechanisms with the host, therapies and vaccines' immunization findings.

METHODS

A literature overview was produced in order to evaluate the state-of-art in SARS-CoV-2 diagnoses, prognoses, therapies, and prevention.

RESULTS

Concerning to the interaction mechanisms with the host, the virus binds to target with its Spike proteins on its surface and uses it as an anchor. The Spike protein targets the ACE2 cell receptor and enters into the cells by using a special enzyme (TMPRSS2). Once the virion is quietly accommodated, it releases its RNA. Proteins and RNA are used in the Golgi apparatus to produce more viruses that are released. Concerning the therapies, different protocols have been developed in observance of the disease severity and comorbidity with a consistent reduction in the mortality rate. Currently, different vaccines are currently in phase IV but a remarkable difference in efficiency has been detected concerning the more recent SARS-CoV-2 variants.

CONCLUSIONS

Among the many questions in this pandemic state, the one that recurs most is knowing why some people become more seriously ill than others who instead contract the infection as if it was a trivial flu. More studies are necessary to investigate the efficiency of the treatment protocols and vaccines for the more recent detected SARS-CoV-2 variant.

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.