Haem oxygenase-1 and haemopexin gene polymorphisms and the risk of anti-tuberculosis drug-induced hepatotoxicity in China

Objective: To assess whether the risk of anti-tuberculosis drug-induced hepatotoxicity (ATDH) might be influenced by haem oxygenase-1 (HMOX1) and haemopexin (HPX) gene polymorphisms. Methods: A dynamic anti-tuberculosis treatment cohort was constructed, and the 1:4 matched nested case-control study was analysed. Eight single nucleotide polymorphisms (SNPs) of the two genes were selected for genotyping and Bonferroni correction was performed to correct for multiple comparison. Results: Overall, 7.8% of patients developed ATDH. SNP rs1807714 in the HMOX1 gene had decreased effects on the risk of moderate and severe hepatotoxicity under the dominant and additive models, and hepatocellular injury under the additive model. SNP rs2682099 in the HPX gene had increased effects on the risk of moderate and severe hepatotoxicity under the recessive model. However, these associations disappeared after Bonferroni correction. Conclusion: HMOX1 and HPX gene polymorphisms might not be associated with susceptibility to ATDH in the Chinese population.

Chronic activation of anti-oxidant pathways and iron accumulation in epileptogenic malformations

Aims

Oxidative stress is evident in resected epileptogenic brain tissue of patients with developmental brain malformations related to mammalian target of rapamycin activation: tuberous sclerosis complex (TSC) and focal cortical dysplasia type IIb (FCD IIb). Whether chronic activation of anti‐oxidant pathways is beneficial or contributes to pathology is not clear.

Methods

We investigated oxidative stress markers, including haem oxygenase 1, ferritin and the inflammation associated microRNA‐155 in surgically resected epileptogenic brain tissue of TSC (n = 10) and FCD IIb (n = 8) patients and in a TSC model (Tsc1^GFAP−/− mice) using immunohistochemistry, in situ hybridization, real‐time quantitative PCR and immunoblotting. Using human foetal astrocytes we performed an in vitro characterization of the anti‐oxidant response to acute and chronic oxidative stress and evaluated overexpression of the disease‐relevant pro‐inflammatory microRNA‐155.

Results

Resected TSC or FCD IIb tissue displayed higher expression of oxidative stress markers and microRNA‐155. Tsc1^GFAP−/− mice expressed more microRNA‐155 and haem oxygenase 1 in the brain compared to wild‐type, preceding the typical development of spontaneous seizures in these animals. In vitro, chronic microRNA‐155 overexpression induced haem oxygenase 1, iron regulatory elements and increased susceptibility to oxidative stress. Overexpression of iron regulatory genes was also detected in patients with TSC, FCD IIb and Tsc1^GFAP−/− mice.

Conclusion

Our results demonstrate that early and sustained activation of anti‐oxidant signalling and dysregulation of iron metabolism are a pathological hallmark of FCD IIb and TSC. Our findings suggest novel therapeutic strategies aimed at controlling the pathological link between both processes.

Recurrent attacks of acute hepatic porphyria: major role of the chronic inflammatory response in the liver

BACKGROUND

Acute intermittent porphyria (AIP) is an inherited disorder of haem metabolism characterized by life-threatening acute neurovisceral attacks due to the induction of hepatic δ-aminolevulinic acid synthase 1 (ALAS1) associated with hydroxymethylbilane synthase (HMBS) deficiency. So far, the treatment of choice is hemin which represses ALAS1. The main issue in the medical care of AIP patients is the occurrence of debilitating recurrent attacks.

OBJECTIVE

The aim of this study was to determine whether chronic hemin administration contributes to the recurrence of acute attacks.

METHODS

A follow-up study was conducted between 1974 and 2015 and included 602 French AIP patients, of whom 46 had recurrent AIP. Moreover, we studied the hepatic transcriptome, serum proteome, liver macrophage polarization and oxidative and inflammatory profiles of Hmbs^-/- mice chronically treated by hemin and extended the investigations to five explanted livers from recurrent AIP patients.

RESULTS

The introduction of hemin into the pharmacopeia has coincided with a 4.4-fold increase in the prevalence of chronic patients. Moreover, we showed that both in animal model and in human liver, frequent hemin infusions generate a chronic inflammatory hepatic disease which induces HO1 remotely to hemin treatment and maintains a high ALAS1 level responsible for recurrence.

CONCLUSION

Altogether, this study has important impacts on AIP care underlying that hemin needs to be restricted to severe neurovisceral crisis and suggests that alternative treatment targeting the liver such as ALAS1 and HO1 inhibitors, and anti-inflammatory therapies should be considered in patients with recurrent AIP.

Cytotoxic and cytoprotective effects of tryptamine-4,5-dione on neuronal cells: a double-edged sword

Serotonin (5-hydroxytryptamine) is a putative substrate for myeloperoxidase, which may convert it into the reactive quinone tryptamine-4,5-dione (TD). In this study, we found that the viability of human SH-SY5Y neuroblastoma cells treated with 25 μM TD was increased to approximately 117%. On the other hand, the cell viability was significantly decreased by exposure to TD (150-200 μM), with an increase in intracellular reactive oxygen species (ROS). Interestingly, pre-treatment of SH-SY5Y cells with 100 μM TD prevented cell death and suppressed intracellular ROS generation evoked by the addition of hydrogen peroxide (H₂O₂). Expression of the phase-II antioxidant enzyme NAD(P)H: quinone oxidoreductase 1 and haem oxygenase 1 were upregulated by TD at a concentration of 50-100 μM. Nuclear factor erythroid 2-related factor 2 (Nrf2), the regulator of these enzyme, was translocated from the cytosol to the nucleus by 100 μM TD. In summary, moderate concentrations of TD may increase the self-defence capacity of neuronal cells against oxidative stress.

Activation of human biliverdin-IXα reductase by urea: generation of kinetically distinct forms during the unfolding pathway

Activation of enzymes by low concentrations of denaturants has been reported for a limited number of enzymes including lipocalin-type prostaglandin D synthase (L-PGDS) and adenylate kinase. During unfolding studies on human biliverdin-IXα reductase it was discovered that the enzyme is activated at low concentrations of urea. Under standard assay conditions the native enzyme displays pronounced substrate inhibition with biliverdin as variable substrate; however in the presence of 3M urea, the substrate inhibition is abolished and the enzyme exhibits Michaelian kinetics. When the initial rate kinetics with NADPH as variable substrate are conducted in 3M urea, the Vmax is increased 11-fold to 1.8μmol/min/mg and the apparent Km for biliverdin increases from 1 to 3μM. We report the existence of two kinetically distinct folded intermediates between the native and unfolded forms. When the period of incubation with urea was varied prior to measuring enzyme activity, the apparent Vmax was shown to decay to half that seen at zero time with a half life of 5.8minutes, while the apparent Km for NADPH remains constant at approximately 5μM. With NADH as cofactor the half life of the activated (A) form was 2.9minutes, and this form decays in 3M urea to a less active (LA) form. The apparent Km for NADH increases from 0.33mM to 2mM for the A and LA forms. These kinetically distinct species are reminiscent of the activity-enhanced and inactive forms of L-PGDS observed in the presence of urea and guanidine hydrochloride.