Haem-responsive gene transporter enables mobilization of host haem in ticks

Ticks, notorious blood-feeders and disease-vectors, have lost a part of their genetic complement encoding haem biosynthetic enzymes and are, therefore, dependent on the acquisition and distribution of host haem. Solute carrier protein SLC48A1, aka haem-responsive gene 1 protein (HRG1), has been implicated in haem transport, regulating the availability of intracellular haem. HRG1 transporter has been identified in both free-living and parasitic organisms ranging from unicellular kinetoplastids, nematodes, up to vertebrates. However, an HRG1 homologue in the arthropod lineage has not yet been identified. We have identified a single HRG1 homologue in the midgut transcriptome of the tick Ixodes ricinus, denoted as Ir HRG, and have elucidated its role as a haem transporter. Data from haem biosynthesis-deficient yeast growth assays, systemic RNA interference and the evaluation of gallium protoporphyrin IX-mediated toxicity through tick membrane feeding clearly show that Ir HRG is the bona fide tetrapyrrole transporter. We argue that during evolution, ticks profited from retaining a functional hrg1 gene in the genome because its protein product facilitates host haem escort from intracellularly digested haemoglobin, rendering haem bioavailable for a haem-dependent network of enzymes.

Acute liver injury associated with Oxyfluorfen toxicity

Oxyfluorfen is a phenoxyphenyl-type herbicide which is used for broad-spectrum control of broadleaf and grassy weeds. Ingestion of toxic dose of oxyfluorfen can be fatal among animals. However, toxicity to humans are rare in literature. The alterations in haem biosynthesis (anaemia) and in liver are the primary toxic effects. There are no specific antidotes and none of the current treatments have proven efficacious till date. Therefore, prevention needs to be the utmost priority, and on exposure, aggressive decontamination should be initiated. Herein, we described an oxyfluorfen toxicity with acute hepatic injury in a young woman who presented with a deliberate self-harming with an oxyfluorfen poisoning in Sri Lanka.

Disruption of Plasmodium falciparum histidine-rich protein II may affect haem metabolism in the blood stage

Background. Haem is a key metabolic factor in the life cycle of the malaria parasite. In the blood stage, the parasite acquires host haemoglobin to generate amino acids for protein synthesis and the by-product haem for metabolic use. The malaria parasite can also synthesize haem de novo by itself. Plasmodium falciparum-specific histidine-rich protein 2 (PfHRP2) has a haem-binding site to mediate the formation of haemozoin, a biocrystallized form of haem aggregates. Notably, the gene regulates the mechanism of haemoglobin-derived haem metabolism and the de novo haem biosynthetic pathway in the Pfhrp2-disrupted parasite line during the intraerythrocytic stages. Methods. The CRISPR/Cas9 system was used to disrupt the gene locus of Pfhrp2. DNA was extracted from the transgenic parasite, and polymerase chain reaction (PCR), Southern blotting and Western blotting were used to confirm the establishment of transgenic parasites. RNA-Seq and comparative transcriptome analysis were performed to identify differences in gene expression between 3D7 and Pfhrp2- 3D7 parasites.Results. Pfhrp2- transgenic parasites were successfully established by the CRISPR/Cas9 system. A total of 964, 1261, 3138, 1064, 2512, and 1778 differentially expressed genes (DEGs) were identified in the six comparison groups, and a total of 373, 520, 1499, 353, 1253, and 742 of the DEGs were upregulated, and 591, 741, 1639, 711, 1259, and 1036 of the DEGs were downregulated, respectively. Five DEGs related to haem metabolism and synthesis were identified in the comparison groups of six time points (0, 8, 16, 24, 32, and 40 h after merozoite invasion). The genes encoding ALAS and FC, related to haem biosynthesis, were found to be significantly upregulated in the comparison groups, and the HO, SPP, and PBGD genes were found to be significantly downregulated. No GO terms were significantly enriched in haem-related processes (Q value=1).Conclusion: In this study, our findings revealed changes in the transcriptome expression profile of the Pfhrp2-3D7 parasite during the intraerythrocytic stages. The results suggested that disruption of Pfhrp2 alters the parasite’s haem metabolic and biosynthesis pathways at the gene transcript level. A cooperative mechanism exists between the haem biosynthesis and metabolic pathways for parasite growth and survival in the blood stage. It is difficult to treat malaria patients by inhibiting only one pathway with traditional antimalarial drugs. The above findings provide insight at the gene transcript level for further research and development of anti-malaria drugs.

Variegate Porphyria Triggered by Acute Hepatitis A Infection

Background: Variegate porphyria (VP) is a rare disorder of haem biosynthesis. We report a novel association with hepatitis A infection. Patient and methods: A 31-year-old man was diagnosed with acute hepatitis A infection. During recovery, he presented with abdominal pain and a photoaggravated blistering skin eruption. Results: Urine porphyrin precursors were markedly raised with high coproporphyrin III isomer levels. Faecal protoporphyrin levels were markedly increased and a maximum plasma fluorescence emission at 629 nm was noted. Discussion: Acute hepatitis A infection, and the associated metabolic stress exerted on the haem biosynthetic pathway, induced overt presentation of latent VP.

Acute intermittent porphyria: analgesia can be dangerous

Acute intermittent porphyria (AIP) is a rare condition, a metabolic disorder of the haem biosynthesis. An acute crisis of AIP can present as a combination of symptoms, such as abdominal pain, autonomic dysfunction, hyponatremia, muscle weakness and neurological symptoms in the absence of others obvious causes. We report the case of a 53-year-old woman, who was previously diagnosed with AIP 5 weeks after therapeutic suspension has developed an acute disease exacerbation. During hospitalisation, further exacerbation has occurred after analgesia with metamizole. Glucose and hemin infusions resulted in slow improvement. Physical rehabilitation was crucial to peripheral polyneuropathy recovery. Taking into account the porphyrinogenic effect described for metamizole, this drug might have triggered the second attack. Clinical history was sufficient to suspect the diagnosis and to start the treatment immediately, preventing important sequelae.

The coproporphyrin ferrochelatase of Staphylococcus aureus: mechanistic insights into a regulatory iron-binding site

The majority of characterised ferrochelatase enzymes catalyse the final step of classical haem synthesis, inserting ferrous iron into protoporphyrin IX. However, for the recently discovered coproporphyrin-dependent pathway, ferrochelatase catalyses the penultimate reaction where ferrous iron is inserted into coproporphyrin III. Ferrochelatase enzymes from the bacterial phyla Firmicutes and Actinobacteria have previously been shown to insert iron into coproporphyrin, and those from Bacillus subtilis and Staphylococcus aureus are known to be inhibited by elevated iron concentrations. The work herein reports a Km (coproporphyrin III) for S. aureus ferrochelatase of 1.5 µM and it is shown that elevating the iron concentration increases the Km for coproporphyrin III, providing a potential explanation for the observed iron-mediated substrate inhibition. Together, structural modelling, site-directed mutagenesis, and kinetic analyses confirm residue Glu271 as being essential for the binding of iron to the inhibitory regulatory site on S. aureus ferrochelatase, providing a molecular explanation for the observed substrate inhibition patterns. This work therefore has implications for how haem biosynthesis in S. aureus is regulated by iron availability.