Influential Parameters for the Analysis of Intracellular Parasite Metabolomics.

Metabolomics is increasingly popular for the study of pathogens. For the malaria parasite Plasmodium falciparum, both targeted and untargeted metabolomics have improved our understanding of pathogenesis, host-parasite interactions, and antimalarial drug treatment and resistance. However, purification and analysis procedures for performing metabolomics on intracellular pathogens have not been explored. Here, we purified in vitro-grown ring-stage intraerythrocytic P. falciparum parasites for untargeted metabolomics studies; the small size of this developmental stage amplifies the challenges associated with metabolomics studies as the ratio between host and parasite biomass is maximized. Following metabolite identification and data preprocessing, we explored multiple confounding factors that influence data interpretation, including host contamination and normalization approaches (including double-stranded DNA, total protein, and parasite numbers). We conclude that normalization parameters have large effects on differential abundance analysis and recommend the thoughtful selection of these parameters. However, normalization does not remove the contribution from the parasite's extracellular environment (culture media and host erythrocyte). In fact, we found that extraparasite material is as influential on the metabolome as treatment with a potent antimalarial drug with known metabolic effects (artemisinin). Because of this influence, we could not detect significant changes associated with drug treatment. Instead, we identified metabolites predictive of host and medium contamination that could be used to assess sample purification. Our analysis provides the first quantitative exploration of the effects of these factors on metabolomics data analysis; these findings provide a basis for development of improved experimental and analytical methods for future metabolomics studies of intracellular organisms.IMPORTANCE Molecular characterization of pathogens such as the malaria parasite can lead to improved biological understanding and novel treatment strategies. However, the distinctive biology of the Plasmodium parasite, including its repetitive genome and the requirement for growth within a host cell, hinders progress toward these goals. Untargeted metabolomics is a promising approach to learn about pathogen biology. By measuring many small molecules in the parasite at once, we gain a better understanding of important pathways that contribute to the parasite's response to perturbations such as drug treatment. Although increasingly popular, approaches for intracellular parasite metabolomics and subsequent analysis are not well explored. The findings presented in this report emphasize the critical need for improvements in these areas to limit misinterpretation due to host metabolites and to standardize biological interpretation. Such improvements will aid both basic biological investigations and clinical efforts to understand important pathogens.

Penicillin Encephalopathy: An Unlikely Adversary in the Treatment of Neurosyphilis--Case Report and Review of the Literature.

UNLABELLED: Penicillin encephalopathy is a rare, potentially reversible phenomenon of drug-induced neurotoxicity. CASE: A 65-year-old female with a history of HIV was admitted with a three-day history of worsening headache, confusion, and lethargy. On examination she was awake but confused. Cerebrospinal fluid (CSF) and serum venereal disease research laboratory (VDRL) test returned positive and the patient was started on intravenous penicillin G with probenecid. On the second day of therapy, she developed myoclonic jerking, consistent with penicillin neurotoxicity. Repeat labs also showed new onset renal failure. Penicillin and probenecid therapy were stopped with a resolution of symptoms. Subsequently, therapy without probenecid was reinstituted uneventfully. DISCUSSION: Herein, we describe a female who developed penicillin neurotoxicity after initiation of intravenous penicillin therapy with probenecid for neurosyphilis. It is important that penicillin-induced toxicity be considered if characteristic myoclonic movements accompany encephalopathy. The presence of coexistent renal compromise should heighten the vigilance of clinicians.