Development and validation of a reliable LC-MS/MS method for quantitative analysis of usnic acid in Cladonia uncialis

Discovery and excavation of lichen bioactive natural products

Lichen natural products are a tremendous source of new bioactive chemical entities for drug discovery. The ability to survive in harsh conditions can be directly correlated with the production of some unique lichen metabolites. Despite the potential applications, these unique metabolites have been underutilized by pharmaceutical and agrochemical industries due to their slow growth, low biomass availability, and technical challenges involved in their artificial cultivation. At the same time, DNA sequence data have revealed that the number of encoded biosynthetic gene clusters in a lichen is much higher than in natural products, and the majority of them are silent or poorly expressed. To meet these challenges, the one strain many compounds (OSMAC) strategy, as a comprehensive and powerful tool, has been developed to stimulate the activation of silent or cryptic biosynthetic gene clusters and exploit interesting lichen compounds for industrial applications. Furthermore, the development of molecular network techniques, modern bioinformatics, and genetic tools is opening up a new opportunity for the mining, modification, and production of lichen metabolites, rather than merely using traditional separation and purification techniques to obtain small amounts of chemical compounds. Heterologous expressed lichen-derived biosynthetic gene clusters in a cultivatable host offer a promising means for a sustainable supply of specialized metabolites. In this review, we summarized the known lichen bioactive metabolites and highlighted the application of OSMAC, molecular network, and genome mining-based strategies in lichen-forming fungi for the discovery of new cryptic lichen compounds.

Analytical Performance Evaluation for Estradiol using Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

There is an increased need for the sensitive and accurate measurement of estradiol levels in patients with estradiol-related endocrine disorders. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a reliable and accurate method for measuring steroid hormone levels. Here, we aimed to establish an LC-MS/MS-based method to quantify estradiol levels without sample derivatization and evaluated its analytical performance.

METHODS

Sciex Triple Quad 6500 + LC-MS/MS was used for estradiol analysis. We evaluated its analytical performance, including linearity, precision, the lower limit of detection and quantification (LoD and LoQ, respectively), accuracy, and carryover. The estradiol results determined by LC-MS/MS were compared with those obtained using a chemiluminescent microparticle immunoassay.

RESULTS

The LC-MS/MS output was linear for serum estradiol concentrations in the range of 0.2-10311.6 pmol/L. The intra-laboratory precision (coefficient of variation) was 3.0-10.1 %. The LoD and LoQ were 2.8 and 7.5 pmol/L, respectively. The overall accuracy was within 15 % of bias, and the carryover was within the acceptable range (<1.0 %). The results of the estradiol analysis determined by LC-MS/MS were comparable to those obtained by the chemiluminescent microparticle immunoassay (r² = 0.9843), although there was a negative bias of - 17.82 (95 % confidence interval, -27.21 to - 8.44).

CONCLUSIONS

A highly sensitive, derivatization-free LC-MS/MS method was successfully developed in this study. This may be beneficial for estradiol measurements in patients with estradiol-related endocrine disorders.

Unraveling usnic acid: a comparison of biosynthetic gene clusters between two reindeer lichen (Cladonia rangiferina and C. uncialis)

Lichenized fungi are known for their production of a diversity of secondary metabolites, many of which have broad biological and pharmacological applications. By far the most well-studied of these metabolites is usnic acid. While this metabolite has been well-known and researched for decades, the gene cluster responsible for its production was only recently identified from the species Cladonia uncialis. Usnic acid production varies considerably in the genus Cladonia, even among closely related taxa, and many species, such as C. rangiferina, have been inferred to be incapable of producing the metabolite based on analysis by thin-layer chromatography (TLC). We sequenced and examined the usnic acid biosynthetic gene clusters, or lack thereof, from four closely related Cladonia species (C. oricola, C. rangiferina, C. stygia, and C. subtenuis), and compare them against those of C. uncialis. We complement this comparison with tiered chemical profile analyses to confirm the presence or absence of usnic acid in select samples, using both HPLC and LC-MS. Despite long-standing reporting that C. rangiferina lacks the ability to produce usnic acid, we observed functional gene clusters from the species and detected usnic acid when extracts were examined by LC-MS. By contrast, C. stygia and C. oricola, have been previously described as lacking the ability to produce usnic acid, lacked the gene cluster entirely, and no usnic acid could be detected in C. oricola extracts via HPLC or LC-MS. This work suggests that chemical profiles attained through inexpensive and low-sensitivity methods like TLC may fail to detect low abundance metabolites that can be taxonomically informative. This study also bolsters understanding of the usnic acid gene cluster in lichens, revealing differences among domains of the polyketide synthase which may explain observed differences in expression. These results reinforce the need for comprehensive characterization of lichen secondary metabolite profiles with sensitive LC-MS methods.