Sodium thiosulfate fails to reduce nitrite-induced methemoglobinemia in vitro

On-chip magnetophoretic capture in a model of malaria-infected red blood cells

The search for new rapid diagnostic tests for malaria is a priority for developing an efficient strategy to fight this endemic disease, which affects more than 3 billion people worldwide. In this paper, we characterize systematically an easy-to-operate lab-on-chip, designed for the magnetophoretic capture of malaria-infected red blood cells. The method relies on the positive magnetic susceptibility of infected red blood cells with respect to blood plasma. A matrix of nickel posts fabricated in a silicon chip placed face down is aimed at attracting infected cells, while healthy cells sediment on a glass slide under the action of gravity. Using a model of infected red blood cells, i.e. erythrocytes with methaemoglobin, we obtained a capture efficiency of about 70% after 10 minutes in static conditions. By proper agitation, the capture efficiency reached 85% after just 5 minutes. Sample preparation requires only a 1:10 volume dilution of whole blood, previously treated with heparin, in a phosphate buffered solution. Nonspecific attraction of untreated red blood cells was not observed in the same time interval. This article is protected by copyright. All rights reserved.

A Lab-On-chip Tool for Rapid, Quantitative, and Stage-selective Diagnosis of Malaria

Malaria remains the most important mosquito-borne infectious disease worldwide, with 229 million new cases and 409.000 deaths in 2019. The infection is caused by a protozoan parasite which attacks red blood cells by feeding on hemoglobin and transforming it into hemozoin. Despite the WHO recommendation of prompt malaria diagnosis, the quality of microscopy-based diagnosis is frequently inadequate while rapid diagnostic tests based on antigens are not quantitative and still affected by non-negligible false negative/positive results. PCR-based methods are highly performant but still not widely used in endemic areas. Here, a diagnostic tool (TMek), based on the paramagnetic properties of hemozoin nanocrystals in infected red blood cells (i-RBCs), is reported on. Exploiting the competition between gravity and magnetic forces, i-RBCs in a whole blood specimen are sorted and electrically detected in a microchip. The amplitude and time evolution of the electrical signal allow for the quantification of i-RBCs (in the range 10-105 i-RBC µL-1) and the distinction of the infection stage. A preliminary validation study on 75 patients with clinical suspect of malaria shows on-field operability, without false negative and a few false positive results. These findings indicate the potential of TMek as a quantitative, stage-selective, rapid test for malaria.

L-arginine, a nitric oxide precursor, reduces dapsone-induced methemoglobinemia in rats

Dapsone use is frequently associated to hematological side effects such as methemoglobinemia and hemolytic anemia, which are related to N-hydroxylation mediated by the P450 enzyme system. The aim of the present study was to evaluate the influence of L-arginine supplementation, a precursor for the synthesis of nitric oxide, as single or multiple dose regimens on dapsone-induced methemoglobinemia. Male Wistar rats were treated with L-arginine at 5, 15, 30, 60 and 180 mg/kg doses (p.o., gavage) in single or multiple dose regimens 2 hours prior to dapsone administration (40 mg/kg, i.p.). The effect of the nitric oxide synthase inhibitor L-NAME was investigated by treatment with multiple doses of 30 mg/kg (p.o., gavage) 2 hours before dapsone administration. Blood samples were collected 2 hours after dapsone administration. Erythrocytic methemoglobin levels were assayed by spectrophotometry. The results showed that multiple dose supplementations with 5 and 15 mg/kg L-arginine reduced dapsone-induced methemoglobin levels. This effect is mediated by nitric oxide formation, since the reduction in methemoglobin levels by L-arginine is blocked by simultaneous administration with L-NAME, a nitric oxide synthase inhibitor.

Benzylidene acetal type bridged nucleic acids: changes in properties upon cleavage of the bridge triggered by external stimuli

Four classes of benzylidene acetal type bridged nucleic acids (BA-BNAs) were designed with 2',4'-bridged structures that cleaved upon exposure to appropriate external stimuli. Cleavage of 6-nitroveratrylidene and 2-nitrobenzylidene acetal type BNA bridges occurred upon photoirradiation and subsequent treatment with thiol caused changes in secondary structure to afford 4'-C-hydroxymethyl RNA. Benzylidene and 4-nitrobenzylidene acetal type BNA responded to acids and reducing agents, respectively, resulting in hydrolysis of the acetal-bridged structure. Cleavage of the bridge removed sugar conformational restrictions and changed the duplex- and triplex-forming properties of the BNA-modified oligonucleotides. Moreover, oligonucleotides incorporating a single BA-BNA modification had considerably improved stability toward 3'-exonuclease, which was lost upon cleavage of the bridge. Thus, these new BNAs may be useful as therapeutic and detection tools by sensing various environments.

Case studies in pediatric toxicology

Intentional and unintentional poisonings are encountered commonly in the pediatric population. Providers should be familiar both with the general approach to the poisoned child and with specific interventions required for certain toxic exposures.

Investigation of methaemoglobin reduction by extracellular NADH in mammalian erythrocytes

The effect of extracellular NADH on the rate of reduction of nitrite-induced methaemoglobin in erythrocytes from man, cattle, dog, horse, grey kangaroo, pig and sheep was investigated. Extracellular NADH was found to enhance the rate of methaemoglobin reduction in man, dog, pig and kangaroo erythrocytes, but had essentially no effect on the rate of methaemoglobin reduction in erythrocytes from cattle, horse and sheep. In erythrocytes of those animals affected by extracellular NADH the rate of reduction of metHb in the presence of NADH was the same or greater than that observed in the presence of nutrients such as glucose and inosine. The combination of nutrient and NADH produced a more profound increase in the rate of methaemoglobin reduction. The rate of methaemoglobin reduction in all cases was significantly less than that observed with methylene blue, the standard treatment of methaemoglobinaemia. Extracellular NADH was found to indirectly increase the intracellular NADH concentration through displacement of the pseudo-equilibrium of the intracellular LDH reaction and relied upon the presence of sufficient LDH activity released into the extracellular medium through haemolysis. The lack of response of cattle, horse and sheep RBCs to extracellular NADH was found to derive mainly from their low extracellular LDH activity, but also correlated with their lower NADH-methaemoglobin reductase activity compared to the other species.