development-quantitative-recombinase-polymerase-amplification-assay

Development of a Quantitative Recombinase Polymerase Amplification Assay with an Internal Positive Control

It was recently demonstrated that recombinase polymerase amplification (RPA), an isothermal amplification platform for pathogen detection, may be used to ...

Rice University

Treatment of sickle-cell anemia by hydroxyurea has been shown to decrease patient mortality by 40%. In a rate-limiting step, hydroxyurea reacts with hemoglobin to form the nitroxide radical, which then decomposes to yield nitric oxide (NO). In this paper, we examine derivatives of hydroxyurea and their radicals by quantum chemical methods to identify derivatives that generate NO-producing radicals at a faster rate than hydroxyurea. The molecules are treated with Hartree-Fock theory, correlated wave function methods such as perturbation theory and coupled-cluster methods, and density functional theory. We observe that the inclusion of the correlation energy is important for an accurate comparison of the energy changes associated with modifications of the hydroxyurea molecule and its radical. The computational results are compared with available experimental data. All 19 derivatives of hydroxyurea, including a new medication for asthma Zileuton, manifest changes in their electronic energies that mark them as candidates for a faster formation of NO-producing radicals.

Quantum chemical design of hydroxyurea derivatives for the treatment of sickle-cell anemia.

Molecular pathways regulating rapid proliferation and persistence are fundamental for pathogens but are not elucidated fully in Toxoplasma gondii. Promoters of T. gondii ribosomal proteins (RPs) were analyzed by EMSAs and ChIP. One RP promoter domain, known to bind an Apetela 2, bound to nuclear extract proteins. Promoter domains appeared to associate with histone acetyl transferases. To study effects of a RP gene's regulation in T. gondii, mutant parasites (Δrps13) were engineered with integration of tetracycline repressor (TetR) response elements in a critical location in the rps13 promoter and transfection of a yellow fluorescent-tetracycline repressor (YFP-TetR). This permitted conditional knockdown of rps13 expression in a tightly regulated manner. Δrps13 parasites were studied in the presence (+ATc) or absence of anhydrotetracycline (-ATc) in culture. -ATc, transcription of the rps13 gene and expression of RPS13 protein were markedly diminished, with concomitant cessation of parasite replication. Study of Δrps13 expressing Myc-tagged RPL22, -ATc, showed RPL22 diminished but at a slower rate. Quantitation of RNA showed diminution of 18S RNA. Depletion of RPS13 caused arrest of parasites in the G1 cell cycle phase, thereby stopping parasite proliferation. Transcriptional differences ±ATc implicate molecules likely to function in regulation of these processes. In vitro, -ATc, Δrps13 persists for months and the proliferation phenotype can be rescued with ATc. In vivo, however, Δrps13 could only be rescued when ATc was given simultaneously and not at any time after 1 week, even when L-NAME and ATc were administered. Immunization with Δrps13 parasites protects mice completely against subsequent challenge with wildtype clonal Type 1 parasites, and robustly protects mice against wildtype clonal Type 2 parasites. Our results demonstrate that G1 arrest by ribosomal protein depletion is associated with persistence of T. gondii in a model system in vitro and immunization with Δrps13 protects mice against subsequent challenge with wildtype parasites.

T. gondii RP promoters & knockdown reveal molecular pathways associated with proliferation and cell-cycle arrest.

Despite the importance of early diagnosis and treatment of HIV, only a small fraction of HIV-exposed infants in low- and middle-income countries are tested for the disease. The gold standard for early infant diagnosis, DNA PCR, requires resources that are unavailable in poor settings, and no point-of-care HIV DNA test is currently available. We have developed a device constructed of layers of paper, glass fiber, and plastic that is capable of performing isothermal, enzymatic amplification of HIV DNA. The device is inexpensive, small, light-weight, and easy to assemble. The device stores lyophilized enzymes, facilitates mixing of reaction components, and supports recombinase polymerase amplification in five steps of operation. Using commercially available lateral flow strips as a detection method, we demonstrate the ability of our device to amplify 10 copies of HIV DNA to detectable levels in 15 min. Our results suggest that our device, which is designed to be used after DNA extraction from dried-blood spots, may serve in conjunction with lateral flow strips as part of a point-of-care HIV DNA test to be used in low resource settings.

A paper and plastic device for performing recombinase polymerase amplification of HIV DNA.

Although the accessibility of HIV treatment in developing nations has increased dramatically over the past decade, viral load testing to monitor the response of patients receiving therapy is often unavailable. Existing viral load technologies are often too expensive or resource-intensive for poor settings, and there is no appropriate HIV viral load test currently available at the point-of-care in low resource settings. Here, we present a lateral flow assay that employs gold nanoparticle probes and gold enhancement solution to detect amplified HIV RNA quantitatively. Preliminary results show that, when coupled with nucleic acid sequence based amplification (NASBA), this assay can detect concentrations of HIV RNA that match the clinically relevant range of viral loads found in HIV patients. The lateral flow test is inexpensive, simple and rapid to perform, and requires few resources. Our results suggest that the lateral flow assay may be integrated with amplification and sample preparation technologies to serve as an HIV viral load test for low-resource settings.

A lateral flow assay for quantitative detection of amplified HIV-1 RNA.

Diarrheal diseases cause more morbidity and mortality around the world than human immunodeficiency virus (HIV), malaria, or tuberculosis. Given that effective treatment of persistent diarrheal illness requires knowledge of the causative organism, diagnostic tests are of paramount importance. The protozoan parasites of the genus Cryptosporidium are increasingly recognized to be responsible for a significant portion of diarrhea morbidity. We present a novel nucleic acid test to detect the presence of Cryptosporidium species in DNA extracted from stool samples. The assay uses the isothermal amplification technique recombinase polymerase amplification (RPA) to amplify trace amounts of pathogen DNA extracted from stool to detectable levels in 30 min; products are then detected visually on simple lateral flow strips. The RPA-based Cryptosporidium assay (RPAC assay) was developed and optimized using DNA from human stool samples spiked with pathogen. It was then tested using DNA extracted from the stool of infected mice where it correctly identified the presence or absence of 27 out of 28 stool samples. It was finally tested using DNA extracted from the stool of infected patients where it correctly identified the presence or absence of 21 out of 21 stool samples. The assay was integrated into a foldable, paper and plastic device that enables DNA amplification with only the use of pipets, pipet tips, and a heater. The performance of the integrated assay is comparable to or better than polymerase chain reaction (PCR), without requiring the use of thermal cycling equipment. This platform can easily be adapted to detect DNA from multiple pathogens.

Nucleic acid test to diagnose cryptosporidiosis: lab assessment in animal and patient specimens.

Although recombinase polymerase amplification (RPA) has many advantages for the detection of pathogenic nucleic acids in point-of-care applications, RPA has not yet been implemented to quantify sample concentration using a standard curve. Here, we describe a real-time RPA assay with an internal positive control and an algorithm that analyzes real-time fluorescence data to quantify HIV-1 DNA. We show that DNA concentration and the onset of detectable amplification are correlated by an exponential standard curve. In a set of experiments in which the standard curve and algorithm were used to analyze and quantify additional DNA samples, the algorithm predicted an average concentration within 1 order of magnitude of the correct concentration for all HIV-1 DNA concentrations tested. These results suggest that quantitative RPA (qRPA) may serve as a powerful tool for quantifying nucleic acids and may be adapted for use in single-sample point-of-care diagnostic systems.

Quantification of HIV-1 DNA using real-time recombinase polymerase amplification.

The development of isothermal amplification platforms for nucleic acid detection has the potential to increase access to molecular diagnostics in low resource settings; however, simple, low-cost methods for heating samples are required to perform reactions. In this study, we demonstrated that human body heat may be harnessed to incubate recombinase polymerase amplification (RPA) reactions for isothermal amplification of HIV-1 DNA. After measuring the temperature of mock reactions at 4 body locations, the axilla was chosen as the ideal site for comfortable, convenient incubation. Using commonly available materials, 3 methods for securing RPA reactions to the body were characterized. Finally, RPA reactions were incubated using body heat while control RPA reactions were incubated in a heat block. At room temperature, all reactions with 10 copies of HIV-1 DNA and 90% of reactions with 100 copies of HIV-1 DNA tested positive when incubated with body heat. In a cold room with an ambient temperature of 10 degrees Celsius, all reactions containing 10 copies or 100 copies of HIV-1 DNA tested positive when incubated with body heat. These results suggest that human body heat may provide an extremely low-cost solution for incubating RPA reactions in low resource settings.

Equipment-free incubation of recombinase polymerase amplification reactions using body heat.

Recombinase polymerase amplification (RPA) may be used to detect a variety of pathogens, often after minimal sample preparation. However, previous work has shown that whole blood inhibits RPA. In this paper, we show that the concentrations of background DNA found in whole blood prevent the amplification of target DNA by RPA. First, using an HIV-1 RPA assay with known concentrations of nonspecific background DNA, we show that RPA tolerates more background DNA when higher HIV-1 target concentrations are present. Then, using three additional assays, we demonstrate that the maximum amount of background DNA that may be tolerated in RPA reactions depends on the DNA sequences used in the assay. We also show that changing the RPA reaction conditions, such as incubation time and primer concentration, has little effect on the ability of RPA to function when high concentrations of background DNA are present. Finally, we develop and characterize a lateral flow-based method for enriching the target DNA concentration relative to the background DNA concentration. This sample processing method enables RPA of 10(4) copies of HIV-1 DNA in a background of 0-14 μg of background DNA. Without lateral flow sample enrichment, the maximum amount of background DNA tolerated is 2 μg when 10(6) copies of HIV-1 DNA are present. This method requires no heating or other external equipment, may be integrated with upstream DNA extraction and purification processes, is compatible with the components of lysed blood, and has the potential to detect HIV-1 DNA in infant whole blood with high proviral loads.

Article	Year
Quantum chemical design of hydroxyurea derivatives for the treatment of sickle-cell anemia. The journal of physical chemistry. B\| PubMed ID: 16852672	2005
T. gondii RP promoters & knockdown reveal molecular pathways associated with proliferation and cell-cycle arrest. PloS one\| PubMed ID: 21124925	2010
A paper and plastic device for performing recombinase polymerase amplification of HIV DNA. Lab on a chip\| PubMed ID: 22733333	2012
A lateral flow assay for quantitative detection of amplified HIV-1 RNA. PloS one\| PubMed ID: 23029134	2012
Nucleic acid test to diagnose cryptosporidiosis: lab assessment in animal and patient specimens. Analytical chemistry\| PubMed ID: 24479858	2014
Quantification of HIV-1 DNA using real-time recombinase polymerase amplification. Analytical chemistry\| PubMed ID: 24873435	2014
Equipment-free incubation of recombinase polymerase amplification reactions using body heat. PloS one\| PubMed ID: 25372030	2014
Inhibition of recombinase polymerase amplification by background DNA: a lateral flow-based method for enriching target DNA. Analytical chemistry\| PubMed ID: 25560368	2015

Brittany Rohrman

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