Structural insight into dynamic bypass of the major cisplatin‐DNA adduct by Y‐family polymerase Dpo4

Y‐family DNA polymerases bypass Pt‐GG, the cisplatin‐DNA double‐base lesion, contributing to the cisplatin resistance in tumour cells. To reveal the mechanism, we determined three structures of the Y‐family DNA polymerase, Dpo4, in complex with Pt‐GG DNA. The crystallographic snapshots show three stages of lesion bypass: the nucleotide insertions opposite the 3′G (first insertion) and 5′G (second insertion) of Pt‐GG, and the primer extension beyond the lesion site. We observed a dynamic process, in which the lesion was converted from an open and angular conformation at the first insertion to a depressed and nearly parallel conformation at the subsequent reaction stages to fit into the active site of Dpo4. The DNA translocation‐coupled conformational change may account for additional inhibition on the second insertion reaction. The structures illustrate that Pt‐GG disturbs the replicating base pair in the active site, which reduces the catalytic efficiency and fidelity. The in vivo relevance of Dpo4‐mediated Pt‐GG bypass was addressed by a dpo‐4 knockout strain of Sulfolobus solfataricus, which exhibits enhanced sensitivity to cisplatin and proteomic alterations consistent with genomic stress.     

Text Mining the History of Medicine

Historical text archives constitute a rich and diverse source of information, which is becoming increasingly readily accessible, due to large-scale digitisation efforts. However, it can be difficult for researchers to explore and search such large volumes of data in an efficient manner. Text mining (TM) methods can help, through their ability to recognise various types of semantic information automatically, e.g., instances of concepts (places, medical conditions, drugs, etc.), synonyms/variant forms of concepts, and relationships holding between concepts (which drugs are used to treat which medical conditions, etc.). TM analysis allows search systems to incorporate functionality such as automatic suggestions of synonyms of user-entered query terms, exploration of different concepts mentioned within search results or isolation of documents in which concepts are related in specific ways. However, applying TM methods to historical text can be challenging, according to differences and evolutions in vocabulary, terminology, language structure and style, compared to more modern text. In this article, we present our efforts to overcome the various challenges faced in the semantic analysis of published historical medical text dating back to the mid 19^th century. Firstly, we used evidence from diverse historical medical documents from different periods to develop new resources that provide accounts of the multiple, evolving ways in which concepts, their variants and relationships amongst them may be expressed. These resources were employed to support the development of a modular processing pipeline of TM tools for the robust detection of semantic information in historical medical documents with varying characteristics. We applied the pipeline to two large-scale medical document archives covering wide temporal ranges as the basis for the development of a publicly accessible semantically-oriented search system. The novel resources are available for research purposes, while the processing pipeline and its modules may be used and configured within the Argo TM platform.     

Altered glial function causes neuronal death and increases neuronal susceptibility to 1-methyl-4-phenylpyridinium- and 6-hydroxydopamine-induced toxicity in astrocytic/ventral mesencephalic co-cultures

Altered glial function in the substantia nigra in Parkinson's disease may lead to the release of toxic substances that cause dopaminergic cell death or increase neuronal vulnerability to neurotoxins. To investigate this concept, we examined the effects of subjecting astrocytes to lipopolysaccharide (LPS)-induced activation alone or combined with L-buthionine-[S,R]-sulfoximine-induced glutathione depletion or inhibition of complex I activity by 1-methyl-4-phenylpyridinium (MPP+) on the viability of primary ventral mesencephalic neurones or susceptibility to MPP+ and 6-hydroxydopamine (6-OHDA) in co-cultures. LPS-activated astrocytes caused neuronal death in a time-dependent manner, but glutathione-depleted or complex I-inhibited astrocytes had no effect on neuronal viability. The neurotoxicity of LPS-activated astrocytes was inhibited by the inducible nitric oxide synthase inhibitor aminoguanidine, by the nitric oxide scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, and by reduced glutathione (GSH). MPP+-induced neuronal death was greater in ventral mesencephalic cultures previously cultured with LPS-activated, glutathione-depleted, or complex I-inhibited astrocytes compared with co-cultures containing normal astrocytes. The increased neuronal susceptibility to MPP+ caused by LPS-activated or complex I-inhibited astrocytes and glutathione-depleted astrocytes was inhibited by the NMDA/glutamate antagonist MK-801 and by GSH, respectively. Neuronal death caused by 6-OHDA was increased in ventral mesencephalic cultures previously cultured with LPS-activated and glutathione-depleted, but not complex I-inhibited astrocytes, compared with co-cultures containing normal astrocytes. Treatment of co-cultures with GSH prevented the increased neuronal susceptibility to 6-OHDA. These findings suggest that glial dysfunction may cause neuronal death or render neurones susceptible to toxic insults via a mechanism involving the release of free radicals and glutamate. Such a mechanism may play a role in the development or progression of nigrostriatal degeneration in Parkinson's disease.     

Detoxications in peripatus. Sulphate, phosphate and histidine conjugations

Phenols were detoxified in the Onycophoran Peripatoides novaezealandiae by conjugation with sulphuric acid and phosphoric acid, but no evidence for a glycoside detoxication could be found. [(14)C]Benzoic acid was metabolized in 24h to N(2)-benzoyl-l-histidine, which was identified by electrophoresis, chromatography and dilution analysis. Similar conjugates were formed with p-aminobenzoic acid and p-nitrobenzoic acid. In longer-duration experiments further unidentified metabolites were formed, two of which appeared to result from the further metabolism of the histidine conjugate.     

Evaluation of a peer counselling programme to sustain breastfeeding practice in Hong Kong

Background

Peer counselling is reported to increase breastfeeding rates. We evaluated an intervention consisting of mainly telephone contact peer counselling programme on breastfeeding duration and exclusivity.

Methods

Peer counsellors (PCs) were mothers who had successfully breastfed and had received formal training. Following a postnatal visit, they provided scheduled telephone consultations (Days 1, 4, 7, Weeks 2, 4, 8, and Month 4) to PC group mothers (n = 100) who continued breastfeeding their infants after discharge. Control group mothers (n = 100) received routine care.

Results

After adjusting for mothers' previous breastfeeding experiences, mothers' working status and breastfeeding problems, no statistical differences in mothers' feeding methods (exclusive, almost exclusive or predominant breastfeeding) were noted at the three follow-up times for intervention and control mothers respectively (Day 5: 37%/38%, 46%/53%, 57%/63%; Month 3: 10%/9%, 17%/23%, 20%/26%; Month 6: 2%/1%, 18%/18%, 18%/19%). All differences between the groups were not significant. Also, there was no evidence to suggest that PC intervention prolonged breastfeeding duration.

Conclusion

The lack of effect of our PC intervention may reflect the low baseline breastfeeding rate and low value placed on breastfeeding in our population, the type of PC intervention or group allocation biases.

Trial registration

ISRCTN93605280.