New neolignans that inhibit DNA polymerase beta lyase

Discovery of cycloneolignan enantiomers from Isatis indigotica Fortune with neuroprotective effects against MPP+-induced SH-SY5Y cell injury

A pair of new cycloneolignan enantiomers (1a and 1b) were isolated from the leaves of Isatis indigotica Fortune. Their structures were elucidated by extensive spectroscopic data analysis, including 1D and 2D NMR, HRESIMS, MS/MS analysis, together with theoretical electronic circular dichroism (ECD) calculations. Compounds 1a and 1b were then evaluated for their neuroprotective effects against MPP⁺-induced SH-SY5Y cell injury. As a result, compounds 1a (77.64%) and 1b (78.62%) exhibited moderate neuroprotective activity at the concentration of 12.5 µM compared with that of MPP⁺ treated group (62.00% at 1 mM) by MTT assay. Furthermore, Annexin V-FITC/PI analysis showed that apoptosis ratios of 1a and 1b were reduced to 10.99% and 9.31%, respectively.

Novel cycloneolignans from Vernicia fordii with inhibitory effects on over-activation of BV2 cells in vitro

Novel natural products 7R, 8R, 7′R, 9′S-verniciasin A (1a), 7S, 8S, 7′S, 9′R- verniciasin A (1b), 7R, 8R, 7′R, 9′S−7′-methoxylverniciasin A (2a) and 7S, 8S, 7′S, 9′R−7′-methoxylverniciasin A (2b) were characterized from the seed capsule of Vernicia fordii. And the unique 9-O-9′−7, 9′-cyclo-8, 1′-neolignan skeleton with a seven-membered ring, was identified by extensive spectroscopic analysis. Further the possible biosynthetic pathway was briefly discussed. Interestingly, 1a, 2a, 1b and 2b all exhibited significant stereoselective inhibitory effects on NO production in LPS-induced BV2 microglia cell. Then the primary mechanism of the bioactivities and stereoselectivity was explored by means of bioassay and molecular docking.

DNA Polymerases λ and β: The Double-Edged Swords of DNA Repair

DNA is constantly exposed to both endogenous and exogenous damages. More than 10,000 DNA modifications are induced every day in each cell's genome. Maintenance of the integrity of the genome is accomplished by several DNA repair systems. The core enzymes for these pathways are the DNA polymerases. Out of 17 DNA polymerases present in a mammalian cell, at least 13 are specifically devoted to DNA repair and are often acting in different pathways. DNA polymerases β and λ are involved in base excision repair of modified DNA bases and translesion synthesis past DNA lesions. Polymerase λ also participates in non-homologous end joining of DNA double-strand breaks. However, recent data have revealed that, depending on their relative levels, the cell cycle phase, the ratio between deoxy- and ribo-nucleotide pools and the interaction with particular auxiliary proteins, the repair reactions carried out by these enzymes can be an important source of genetic instability, owing to repair mistakes. This review summarizes the most recent results on the ambivalent properties of these enzymes in limiting or promoting genetic instability in mammalian cells, as well as their potential use as targets for anticancer chemotherapy.

Penchinones A–D, two pairs of cis-trans isomers with rearranged neolignane carbon skeletons from Penthorum chinense

Two pairs of cis-trans isomers with new rearranged neolignane carbon skeletons from Penthorum chinense.

DNA polymerase beta (pol β) inhibitors: a comprehensive overview

Base excision repair (BER) is the fundamental pathway responsible for the elimination of damaged DNA bases and repair of DNA single-strand breaks generated spontaneously or produced by DNA-damaging agents. Among the essential enzymes that are required to achieve the BER reaction is DNA polymerase beta (pol β), which has been regarded as a potential therapeutic target. More than 60 pol β-inhibitors have been identified so far; however, most of them are either not potent or not specific enough to become a drug. In this article we compile an essential knowledge base regarding the structures, the modes of inhibition and the activities of these pharmacologically interesting molecules.

Anti-secretory, anti-inflammatory and anti-Helicobacter pylori activities of several fractions isolated from Piper carpunya Ruiz & Pav

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Piper carpunya Ruiz & Pav. (syn Piper lenticellosum C.D.C.) (Piperaceae), are widely used in folk medicine in tropical and subtropical countries of South America as an anti-inflammatory, anti-ulcer, anti-diarrheal and anti-parasitical remedy as well as an ailment for skin irritations.

AIMS OF THE STUDY

To study the anti-inflammatory, anti-secretory and anti-Helicobacter pylori activities of different fractions isolated from an ethanolic extract of the leaves of Piper carpunya, in order to provide evidence for the use of this plant as an anti-ulcer remedy. Moreover, to isolate the main compounds of the extract and relate their biological activity to the experimental results obtained with the fractions.

MATERIALS AND METHODS

Sixteen fractions were obtained from the ethanolic extract (F I-XVI) and 16 pure compounds were isolated and identified from these fractions. We studied the effects of the fractions (0.1-400microg/mL) on the release of myeloperoxidase (MPO) enzyme from rat peritoneal leukocytes, on rabbit gastric microsomal H(+), K(+)-ATPase activity and anti-Helicobacter pylori anti-microbial activity using the microdilution method (MM). The main compounds contained in the fractions were isolated and identified by (1)H- and (13)C NMR spectra analysis and comparison with the literature data.

RESULTS

Eight fractions showed inhibition of MPO enzyme (F I-IV, X, XII, XIV and XV). The highest inhibition was observed with F XIV (50microg/mL, 60.9%, p<0.001). F X and XII were the most active ones, inhibiting the gastric H(+), K(+)-ATPase activity with IC(50) values equal to 22.3microg/mL and 28.1microg/mL, respectively. All fractions, except F XV, presented detectable anti-Helicobacter pylori activity, with a diameter of inhibition zones ranging from 11mm up to 50mm. The best anti-Helicobacter pylori activity was obtained with F III and V. Both fractions killed Helicobacter pylori with lowest concentration values, about 6.25mug/mL. Sixteen pure compounds were isolated, five of them are flavonoids that possess strong anti-oxidant and free radical scavenging activity, e.g. vitexin, isovitexin, and rhamnopyranosylvitexin. Terpenoids like sitosterol, stigmasterol and phytol, which have shown gastroprotective activity, and dihydrochalcones, like asebogenin, with anti-bacterial activity, were also isolated. Furthermore, the rare neolignan 1, that is a DNA polymerase beta lyase inhibitor, and (6S, 9S)-roseoside, that shows strong anti-bacterial activity, were isolated, for the first time, from the genus Piper.

CONCLUSIONS

We suggest that the flavonoids isolated from F I and II (vitexin, isovitexin, rhamnopyranosylvitexin and isoembigenin) contribute to the anti-MPO activity, as well as to their anti-Helicobacter pylori activity. These flavonoids may also be responsible for the important inhibition of H(+), K(+)-ATPase activity. Also the phytosterols and phytol obtained from F XIV and XV could be involved in these gastroprotective activities. These results encourage us to continue phytochemical studies on these fractions in order to obtain full scientific validation for this species.

Inhibitors of DNA polymerase beta: activity and mechanism

Bioassay-guided fractionation of extracts prepared from Couepia polyandra and Edgeworthia gardneri resulted in the isolation of the DNA polymerase beta (pol beta) inhibitors oleanolic acid (1), edgeworin (2), betulinic acid (3), and stigmasterol (4). Study of these pol beta inhibitors revealed that three of them inhibited both the lyase and polymerase activities of DNA polymerase beta, while stigmasterol inhibited only the lyase activity. Further investigation indicated that the four inhibitors had substantially different effects on the DNA-pol beta binary complex that is believed to be an obligatory intermediate in the lyase reaction. It was found that the inhibitors potentiated the inhibitory action of the anticancer drug bleomycin in cultured A549 cells, without any influence on the expression of pol beta in the cells. The results of the unscheduled DNA synthesis assay support the thesis that the potentiation of bleomycin cytotoxicity by DNA pol beta inhibitors was a result of an inhibition of DNA repair synthesis.