The heavy subunit of ferritin stimulates NLRP3 inflammasomes in hepatic stellate cells through ICAM-1 to drive hepatic inflammation.

Serum ferritin concentrations increase during hepatic inflammation and correlate with the severity of chronic liver disease. Here, we report a molecular mechanism whereby the heavy subunit of ferritin (FTH) contributes to hepatic inflammation. We found that FTH induced activation of the NLRP3 inflammasome and secretion of the proinflammatory cytokine interleukin-1ß (IL-1ß) in primary rat hepatic stellate cells (HSCs) through intercellular adhesion molecule-1 (ICAM-1). FTH-ICAM-1 stimulated the expression of Il1b, NLRP3 inflammasome activation, and the processing and secretion of IL-1ß in a manner that depended on plasma membrane remodeling, clathrin-mediated endocytosis, and lysosomal destabilization. FTH-ICAM-1 signaling at early endosomes stimulated Il1b expression, implying that this endosomal signaling primed inflammasome activation in HSCs. In contrast, lysosomal destabilization was required for FTH-induced IL-1ß secretion, suggesting that lysosomal damage activated inflammasomes. FTH induced IL-1ß production in liver slices from wild-type mice but not in those from Icam1-/- or Nlrp3-/- mice. Thus, FTH signals through its receptor ICAM-1 on HSCs to activate the NLRP3 inflammasome. We speculate that this pathway contributes to hepatic inflammation, a key process that stimulates hepatic fibrogenesis associated with chronic liver disease.

Pyruvate:ferredoxin oxidoreductase and thioredoxin reductase are involved in 5-nitroimidazole activation while flavin metabolism is linked to 5-nitroimidazole resistance in Giardia lamblia.

OBJECTIVES: The mechanism of action of, and resistance to, metronidazole in the anaerobic (or micro-aerotolerant) protozoan parasite Giardia lamblia has long been associated with the reduction of ferredoxin (Fd) by the enzyme pyruvate:ferredoxin oxidoreductase (PFOR) and the subsequent activation of metronidazole by Fd to toxic radical species. Resistance to metronidazole has been associated with down-regulation of PFOR and Fd. The aim of this study was to determine whether the PFOR/Fd couple is the only pathway involved in metronidazole activation in Giardia. METHODS: PFOR and Fd activities were measured in extracts of highly metronidazole-resistant (MTR(r)) lines and activities of recombinant G. lamblia thioredoxin reductase (GlTrxR) and NADPH oxidase were assessed for their involvement in metronidazole activation and resistance. RESULTS: We demonstrated that several lines of highly MTR(r) G. lamblia have fully functional PFOR and Fd indicating that PFOR/Fd-independent mechanisms are involved in metronidazole activation and resistance in these cells. Flavin-dependent GlTrxR, like TrxR of other anaerobic protozoa, reduces 5-nitroimidazole compounds including metronidazole, although expression of TrxR is not decreased in MTR(r) Giardia. However, reduction of flavins is suppressed in highly MTR(r) cells, as evidenced by as much as an 80% decrease in NADPH oxidase flavin mononucleotide reduction activity. This suppression is consistent with generalized impaired flavin metabolism in highly MTR(r) Trichomonas vaginalis. CONCLUSIONS: These data add to the mounting evidence against the dogma that PFOR/Fd is the only couple with a low enough redox potential to reduce metronidazole in anaerobes and point to the multi-factorial nature of metronidazole resistance.

Susceptibility in vitro of clinically metronidazole-resistant Trichomonas vaginalis to nitazoxanide, toyocamycin, and 2-fluoro-2'-deoxyadenosine.

This study investigates the susceptibility of a clinically metronidazole (Mz)-resistant isolate of Trichomonas vaginalis to alternative anti-trichomonal compounds. The microaerobic minimal inhibitory concentration (MIC) of the 5-nitroimidazole (NI) drug, Mz, against a typical Mz-susceptible isolate of T. vaginalis is around 3.2 microM Mz while the clinically, highly Mz-resistant isolate has an MIC of 50-100 microM. This isolate was cross-resistant to other members of the 5-NI family of compounds including tinidazole and other experimental compounds and maintained resistance under anaerobic conditions. In addition, this isolate was cross-resistant to the 5-nitrothiazole compound nitazoxanide and the 5-nitrofuran derivative, furazolidone. Adenosine analogues toyocamycin and 2-fluoro-2'-deoxyadenosine with no nitro group were also less effective against the clinically Mz-resistant isolate than a Mz-susceptible one. Three other isolates which were determined to be Mz-resistant soon after isolation lost resistance in the long term. One other isolate has maintained some level of permanent Mz resistance (MIC of 25 microM). A multi-drug resistance mechanism may be involved in these clinically Mz-resistant isolates.

A new-generation 5-nitroimidazole can induce highly metronidazole-resistant Giardia lamblia in vitro.

The 5-nitroimidazole (NI) compound C17, with a side chain carrying a remote phenyl group in the 2-position of the imidazole ring, is at least 14-fold more active against the gut protozoan parasite Giardialamblia than the 5-NI drug metronidazole (MTR), with a side chain in the 1-position of the imidazole ring, which is the primary drug for the treatment of giardiasis. Over 10 months, lines resistant to C17 were induced in vitro and were at least 12-fold more resistant to C17 than the parent strains. However, these lines had ID(90) values (concentration of drug at which 10% of control parasite ATP levels are detected) for MTR of >200 microM, whilst lines induced to be highly resistant to MTR in vitro have maximum ID(90) values around 100 microM (MTR-susceptible isolates typically have an ID(90) of 5-12.8 microM). The mechanism of MTR activation in Giardia apparently involves reduction to toxic radicals by the activity of pyruvate:ferredoxin oxidoreductase (PFOR) and the electron acceptor ferredoxin. MTR-resistant Giardia have decreased PFOR activity, which is consistent with decreased activation of MTR in these lines, but C17-resistant lines have normal levels of PFOR. Therefore, an alternative mechanism of resistance in Giardia must account for these super-MTR-resistant cells.

Sequence map of the 3-Mb Giardia duodenalis assemblage A chromosome.

The genome of the gut protozoan parasite Giardia duodenalis (assemblage A) has been sequenced and compiled as contigs and scaffolds (GiardiaDB- http://GiardiaDB.org ), but specific chromosome location of all scaffolds is unknown. To determine which scaffolds belong to the 3-Mb chromosome, a library of probes specific for this chromosome was constructed. The probes were hybridised to NotI-cleaved whole chromosomes, and the combined size of different NotI segments identified by the probes was 2,225 kb indicating the probes were well distributed along the 3-Mb chromosome. Six scaffolds (CH991814, CH991779, CH991793, CH991763, CH991764, and CH991761) were identified as belonging to the 3-Mb chromosome, and these scaffolds were ordered and oriented according to scaffold features including I-PpoI sites and hybridisation pattern. However, the combined size of scaffolds was more than 4 Mb. Approximately, 1 Mb of scaffold CH991763 carrying previously identified sequences specific for the 1.5-Mb chromosome(s) including subtelomeric sequence was reassigned, and several other anomalies were addressed such that the final size of the apparently 3-Mb chromosome is estimated to be 2,885 kb. This work addresses erroneous computer-based assignment of a number of contigs and emphasises the need for alternative and confirmatory methods of scaffold construction.