Amplification-free detection of microRNAs via a rapid microarray-based sandwich assay.

The detection and profiling of microRNAs are of great interest in disease diagnosis and prognosis. In this paper, we present a method for the rapid amplification-free detection of microRNAs from total RNA samples. In a two-step sandwich assay approach, fluorescently labeled reporter probes were first hybridized with their corresponding target microRNAs. The reaction mix was then added to a microarray to enable their specific capture and detection. Reporter probes were Tm equalized, enabling specificity by adjusting the length of the capture probe while maintaining the stabilizing effect brought about by coaxial base stacking. The optimized assay can specifically detect microRNAs in spiked samples at concentrations as low as 1 pM and from as little as 100 ng of total RNA in 2 h. The detection signal was linear between 1 and 100 pM (R2 = 0.99). Our assay data correlated well with results generated by qPCR when we profiled a select number of breast cancer related microRNAs in a total RNA sample.

Plasmodium ovale curtisi and Plasmodium ovale wallikeri circulate simultaneously in African communities.

It has been proposed that ovale malaria in humans is caused by two closely related but distinct species of malaria parasite, Plasmodium ovale curtisi and Plasmodium ovale wallikeri. It was recently shown that these two parasite types are sympatric at the country level. However, it remains possible that localised geographic, temporal or ecological barriers exist within endemic countries which prevent recombination between the genomes of the two species. Here, using conventional and real-time quantitative PCR (qPCR) methods specifically designed to discriminate P. o. curtisi and P. o. wallikeri, it is shown that both species are present among clinic attendees in Congo-Brazzaville, and occur simultaneously both in lake-side and inland districts in Uganda and on Bioko Island, Equatorial Guinea. Thus P. o. curtisi and P. o. wallikeri in these localities are exactly sympatric in both time and space. These findings are consistent with the existence of a biological barrier, rather than geographical or ecological factors, preventing recombination between P. o. curtisi and P. o. wallikeri. In cross-sectional surveys carried out in Uganda and Bioko, our results show that infections with P. ovale spp. are more common than previously thought, occurring at a frequency of 1-6% in population samples, with both proposed species contributing to ovale malaria in six sites. Malaria elimination programmes in Africa need to include strategies for control of P. o. curtisi and P. o. wallikeri.

Two nonrecombining sympatric forms of the human malaria parasite Plasmodium ovale occur globally.

BACKGROUND: Malaria in humans is caused by apicomplexan parasites belonging to 5 species of the genus Plasmodium. Infections with Plasmodium ovale are widely distributed but rarely investigated, and the resulting burden of disease is not known. Dimorphism in defined genes has led to P. ovale parasites being divided into classic and variant types. We hypothesized that these dimorphs represent distinct parasite species. METHODS: Multilocus sequence analysis of 6 genetic characters was carried out among 55 isolates from 12 African and 3 Asia-Pacific countries. RESULTS: Each genetic character displayed complete dimorphism and segregated perfectly between the 2 types. Both types were identified in samples from Ghana, Nigeria, São Tomé, Sierra Leone, and Uganda and have been described previously in Myanmar. Splitting of the 2 lineages is estimated to have occurred between 1.0 and 3.5 million years ago in hominid hosts. CONCLUSIONS: We propose that P. ovale comprises 2 nonrecombining species that are sympatric in Africa and Asia. We speculate on possible scenarios that could have led to this speciation. Furthermore, the relatively high frequency of imported cases of symptomatic P. ovale infection in the United Kingdom suggests that the morbidity caused by ovale malaria has been underestimated.

Mutations in the Plasmodium falciparum cytochrome b gene are associated with delayed parasite recrudescence in malaria patients treated with atovaquone-proguanil.

BACKGROUND: Fixed-dose combination antimalarial drugs have played an increasingly important role in the treatment and chemoprophylaxis of falciparum malaria since the worldwide failure of monotherapy with chloroquine. Atovaquone-proguanil is one such combination drug used both for prophylaxis in travellers, and for treatment of acute malaria cases in European hospitals and clinics. METHODS: A series of eight atovaquone-proguanil treatment failures and two prophylaxis breakthroughs from four UK hospitals from 2004-2008 were analysed for evidence of mutations in the pfcyt-b gene, previously found to be associated with failure of the atovaquone component. RESULTS: Parasites carrying pfcyt-b mutations were found in five falciparum malaria patients with recrudescent parasitaemia occurring weeks after apparently successful treatment of a primary infection with atovaquone-proguanil. Four of these cases carried parasites with the Tyr268Cys mutation in pfcyt-b, previously reported in two French patients with malaria. In contrast, mutations in pfcyt-b were not found in three patients treated with atovaquone-proguanil who exhibited delayed clearance of the primary infection, nor in two returning travellers with malaria who had used the combination for prophylaxis. Using current and previously published data, mean time to recrudescence of parasites carrying pfcytb codon 268 mutations was estimated as 28.0 days after treatment (95% C.I. 23.0 - 33.0 days), whereas treatment failures without codon 268 mutations received rescue treatment an average of 4.71 days after initial AP treatment (95% C.I. 1.76 - 7.67 days). CONCLUSION: Genetically-determined parasite resistance to atovaquone is associated with delayed recrudescence of resistant parasites three weeks or more after initial clearance of parasitaemia by atovaquone/proguanil therapy. The 268-Cys allele of pfcyt-b may have been overlooked in previous studies of atovaquone-proguanil treatment failure as it is not detected by current RFLP methods.

Plasmodium malariae in Haitian refugees, Jamaica.

Since 1963, reported malaria transmission in Haiti has been restricted to Plasmodium falciparum. However, screening of Haitian refugees in Jamaica in 2004, by microscopic examination, identified P. falciparum, P. vivax, and P. malariae. PCR confirmed the P. malariae and P. falciparum but not P. vivax infections. DNA sequencing and rRNA gene sequences showed transmission of P. malariae. This report confirms that P. malariae is still being transmitted in Haiti.

Evaluation of the phosphorescent palladium(II)-coproporphyrin labels in separation-free hybridization assays.

Palladium(II)-coproporphyrin label and a set of corresponding monofunctional labeling reagents with different linker arms were evaluated for labeling of oligonucleotides and subsequent use in hybridization assays. The properties of resulting oligonucleotide probes including phosphorescence spectra, quantum yields, lifetimes, and labeling yields were examined as functions of the label and oligonucleotide structures. Upon hybridization with complementary sequences bearing dabcyl, QSY-7, and rhodamine green dyes, the probes displayed strong quenching due to close proximity effects. Intensity and lifetime changes of the phosphorescence, distance, and temperature dependences were investigated in detail. The potential of the new label and probes for sensitive and separation-free hybridization assays was discussed.

Synthesis and evaluation of phosphorescent oligonucleotide probes for hybridisation assays.

Monofunctional, p-isothiocyanatophenyl-derivatives of platinum (II)-coproporphyrin-I (PtCP-NCS) were evaluated as phosphorescent labelling reagents for synthetic oligonucleotides containing a 3'- or 5'-amino modification. Synthesis and purification conditions were optimised to generate high yields and purity of PtCP-labelled oligonucleotide probes. Phosphorescent properties of the PtCP label have been shown to be largely unaffected by conjugation to oligonucleotides of various length, GC composition and label attachment site. 5'-PtCP-labelled oligonucleotides were shown to work efficiently as primers in a standard PCR. A dedicated 532 nm laser-based time-resolved fluorescence plate reader enabled highly sensitive detection of PtCP-labelled oligonucleotides and PCR products, both in solution and in agarose gels, with limits of detection in the order of 0.3 pM. A model system employing two complementary oligonucleotides labelled with PtCP and QSY 7 dye (dark quencher) showed strong (approximately 20-fold) and specific proximity quenching of PtCP label upon hybridisation in solution. The potential applications of PtCP-labelled probes in hybridisation assays were discussed.