Photoreduction and Ketone-sensitized Reduction of Alkaloids

Indirect photodegradation of typical pyrrolizidine alkaloids in water induced by triplet states of dissolved organic matter

The occurrence of pyrrolizidine alkaloids (PAs) in the aquatic environment has received growing attention due to their persistent mutagenicity and carcinogenicity. In this study, the photooxidation processes of four representative PAs (senecionine, senecionine N-oxide, europine, and heliotrine) in the presence of dissolved organic matter (DOM) were investigated. The excited triplet DOM (3DOM*) was demonstrated to play a dominant role in the phototransformation of PAs. The observed degradation rates of PAs largely depended on the DOM concentration. Alkaline conditions and the presence of HCO3-/CO32- were conducive to the photodegradation. Based on kinetic modeling, the second-order reaction rate constants of PAs with 3DOM* were predicted to be (1.7∼5.3)×108 M-1 s-1, nearly two orders of magnitude higher than those with singlet oxygen (1O2). The monoester structure and electron-withdrawing substituent (e.g., -O atom) substantially affected the one-electron oxidation potential of PAs, which dictates the reaction rates of PAs with 3DOM*. Finally, a tentative degradation pathway of PAs was proposed, involving the formation of an N-centered radical cation through one-electron transfer, which then likely deprotonated and further oxidized to more persistent and toxic phototransformation products with an added oxygen atom into the pyrrole ring.

Highlighting the Phototherapeutical Potential of Fungal Pigments in Various Fruiting Body Extracts with Informed Feature-Based Molecular Networking

Fungal pigments are characterized by a diverse set of chemical backbones, some of which present photosensitizer-like structures. From the genus Cortinarius, for example, several biologically active photosensitizers have been identified leading to the hypothesis that photoactivity might be a more general phenomenon in the kingdom Fungi. This paper aims at testing the hypothesis. Forty-eight fruiting body-forming species producing pigments from all four major biosynthetic pathways (i.e., shikimate-chorismate, acetate-malonate, mevalonate, and nitrogen heterocycles) were selected and submitted to a workflow combining in vitro chemical and biological experiments with state-of-the-art metabolomics. Fungal extracts were profiled by high-resolution mass spectrometry and subsequently explored by spectral organization through feature-based molecular networking (FBMN), including advanced metabolite dereplication techniques. Additionally, the photochemical properties (i.e., light-dependent production of singlet oxygen), the phenolic content, and the (photo)cytotoxic activity of the extracts were studied. Different levels of photoactivity were found in species from all four metabolic groups, indicating that light-dependent effects are common among fungal pigments. In particular, extracts containing pigments from the acetate-malonate pathway, e.g., extracts from Bulgaria inquinans, Daldinia concentrica, and Cortinarius spp., were not only efficient producers of singlet oxygen but also exhibited photocytotoxicity against three different cancer cell lines. This study explores the distribution of photobiological traits in fruiting body forming fungi and highlights new sources for phototherapeutics.

Elucidating Berberine's Therapeutic and Photosensitizer Potential through Nanomedicine Tools

Berberine, an isoquinoline alkaloid extracted from plants of the Berberidaceae family, has been gaining interest due to anti-inflammatory and antioxidant activities, as well as neuro and cardiovascular protective effects in animal models. Recently, photodynamic therapy demonstrated successful application in many fields of medicine. This innovative, non-invasive treatment modality requires a photosensitizer, light, and oxygen. In particular, the photosensitizer can selectively accumulate in diseased tissues without damaging healthy cells. Berberine's physicochemical properties allow its use as a photosensitising agent for photodynamic therapy, enabling reactive oxygen species production and thus potentiating treatment efficacy. However, berberine exhibits poor aqueous solubility, low oral bioavailability, poor cellular permeability, and poor gastrointestinal absorption that hamper its therapeutic and photodynamic efficacy. Nanotechnology has been used to minimize berberine's limitations with the design of drug delivery systems. Different nanoparticulate delivery systems for berberine have been used, as lipid-, inorganic- and polymeric-based nanoparticles. These berberine nanocarriers improve its therapeutic properties and photodynamic potential. More specifically, they extend its half-life, increase solubility, and allow a high permeation and targeted delivery. This review describes different nano strategies designed for berberine delivery as well as berberine's potential as a photosensitizer for photodynamic therapy. To benefit from berberine's overall potential, nanotechnology has been applied for berberine-mediated photodynamic therapy.

An Overview of Potential Natural Photosensitizers in Cancer Photodynamic Therapy

Cancer is one of the main causes of death worldwide. There are several different types of cancer recognized thus far, which can be treated by different approaches including surgery, radiotherapy, chemotherapy or a combination thereof. However, these approaches have certain drawbacks and limitations. Photodynamic therapy (PDT) is regarded as an alternative noninvasive approach for cancer treatment based on the generation of toxic oxygen (known as reactive oxygen species (ROS)) at the treatment site. PDT requires photoactivation by a photosensitizer (PS) at a specific wavelength (λ) of light in the vicinity of molecular oxygen (singlet oxygen). The cell death mechanisms adopted in PDT upon PS photoactivation are necrosis, apoptosis and stimulation of the immune system. Over the past few decades, the use of natural compounds as a photoactive agent for the selective eradication of neoplastic lesions has attracted researchers' attention. Many reviews have focused on the PS cell death mode of action and photonanomedicine approaches for PDT, while limited attention has been paid to the photoactivation of phytocompounds. Photoactivation is ever-present in nature and also found in natural plant compounds. The availability of various laser light setups can play a vital role in the discovery of photoactive phytocompounds that can be used as a natural PS. Exploring phytocompounds for their photoactive properties could reveal novel natural compounds that can be used as a PS in future pharmaceutical research. In this review, we highlight the current research regarding several photoactive phytocompound classes (furanocoumarins, alkaloids, poly-acetylenes and thiophenes, curcumins, flavonoids, anthraquinones, and natural extracts) and their photoactive potential to encourage researchers to focus on studies of natural agents and their use as a potent PS to enhance the efficiency of PDT.

Targeted isolation of photoactive pigments from mushrooms yielded a highly potent new photosensitizer: 7,7'-biphyscion

Pigments of fungi are a fertile ground of inspiration: they spread across various chemical backbones, absorption ranges, and bioactivities. However, basidiomycetes with strikingly colored fruiting bodies have never been explored as agents for photodynamic therapy (PDT), even though known photoactive compound classes (e.g., anthraquinones or alkaloids) are used as chemotaxonomic markers. In this study, we tested the hypothesis that the dyes of skin-heads (dermocyboid Cortinarii) can produce singlet oxygen under irradiation and thus are natural photosensitizers. Three photosensitizers based on anthraquinone structures were isolated and photopharmaceutical tests were conducted. For one of the three, i.e., (-)-7,7'-biphyscion (1), a promising photoyield and photocytotoxicity of EC50 = 0.064 µM against cancer cells (A549) was found under blue light irradiation (λexc = 468 nm, 9.3 J/cm2). The results of molecular biological methods, e.g., a viability assay and a cell cycle analysis, demonstrated the harmlessness of 1 in the dark and highlighted the apoptosis-inducing PDT potential under blue light irradiation. These results demonstrate for the first time that pigments of dermocyboid Cortinarii possess a so far undescribed activity, i.e., photoactivity, with significant potential for the field of PDT. The dimeric anthraquinone (-)-7,7'-biphyscion (1) was identified as a promising natural photosensitizer.

Feature-Based Molecular Networking-An Exciting Tool to Spot Species of the Genus Cortinarius with Hidden Photosensitizers

Fungi have developed a wide array of defense strategies to overcome mechanical injuries and pathogen infections. Recently, photoactivity has been discovered by showing that pigments isolated from Cortinarius uliginosus produce singlet oxygen under irradiation. To test if this phenomenon is limited to dermocyboid Cortinarii, six colourful Cortinarius species belonging to different classical subgenera (i.e., Dermocybe, Leprocybe, Myxacium, Phlegmacium, and Telamonia) were investigated. Fungal extracts were explored by the combination of in vitro photobiological methods, UHPLC coupled to high-resolution tandem mass spectrometry (UHPLC-HRMS2), feature-based molecular networking (FBMN), and metabolite dereplication techniques. The fungi C. rubrophyllus (Dermocybe) and C. xanthophyllus (Phlegmacium) exhibited promising photobiological activity in a low concentration range (1-7 µg/mL). Using UHPLC-HRMS2-based metabolomic tools, the underlying photoactive principle was investigated. Several monomeric and dimeric anthraquinones were annotated as compounds responsible for the photoactivity. Furthermore, the results showed that light-induced activity is not restricted to a single subgenus, but rather is a trait of Cortinarius species of different phylogenetic lineages and is linked to the presence of fungal anthraquinones. This study highlights the genus Cortinarius as a promising source for novel photopharmaceuticals. Additionally, we showed that putative dereplication of natural photosensitizers can be done by FBMN.

Treating Chronic Wounds Using Photoactive Metabolites: Data Mining the Chinese Pharmacopoeia for Potential Lead Species

Efficient wound treatment that addresses associated infections and inflammation remains one of the big unmet needs, especially in low- and middle-income countries. One strategy for securing better healthcare can be using medicinal plants if sufficient evidence on their safety and therapeutic benefits can be ascertained. A unique novel opportunity could be photo-enhanced wound treatment with a combination of light-sensitive plant preparations and local exposure to daylight. Data mining strategies using existing resources offer an excellent basis for developing such an approach with many potential plant candidates. In the present analysis, we researched the 535 botanical drugs included in the Chinese pharmacopeia and identified 183 medicinal plant species, 82 for treating open wounds caused by trauma and 101 for inflammatory skin conditions. After further screening for reports on the presence of known photoactive compounds, we determined a core group of 10 scientifically lesser-known botanical species that may potentially be developed into more widely used topical preparations for photodynamic treatment of infected wounds. Our predictive approach may contribute to developing a more evidence-based use of herbal medicines.

Research progress of berberine mediated photodynamic therapy

Berberine (BBR) is a plant secondary metabolite that has been used in photodynamic therapy (PDT) in the last few decades. The present review aimed to discuss the research progress of BBR-mediated photodynamic actions. The following key words were searched in several databases: 'Berberine' combined with 'photodynamic therapy', 'sonodynamic therapy (SDT)', 'ultraviolet', 'reactive oxygen' and 'singlet oxygen'. The results demonstrated that both type I and type II reactions participated in the photodynamic progression of BBR derivatives. In addition, the photochemical characteristics of BBR derivatives were affected by the polarity, pH and O2 content of solvents. DNA binding increases the lifespan of the photoexcited BBR state and generation of singlet oxygen (1O2). The chemical properties of substituents in different positions of the BBR skeleton are pivotal for its photochemical properties, particularly the methylenedioxy group at the C-2 and C-3 positions. BBR is a promising agent for mediating both PDT- and SDT-treated diseases, particularly in tumors. However, further studies are required to validate their biological effects. In addition, the molecular mechanisms underlying the antitumor effects of BBR-PDT remain unclear and warrant further investigation. The structural modification and targeted delivery of BBR have made it possible to broaden its applications; however, experimental verification is required. Overall, BBR acts as a sensitizer for PDT and has promising development prospects.

The photoactivity of natural products - An overlooked potential of phytomedicines?

BACKGROUND

Photoactivity, though known for centuries, is only recently shifting back into focus as a treatment option against cancer and microbial infections. The external factor light is the ingenious key-component of this therapy: Since light activates the drug locally, a high level of selectivity is reached and side effects are avoided. The first reported photoactive medicines were plant extracts. Synthetic entities (so-called photosensitizers PSs), however, paved the route towards the clinical approval of the so-called photodynamic therapy (PDT), and thus natural PSs took a backseat in the past.

HYPOTHESIS

Many isolated bioactive phytochemicals hold a hidden photoactive potential, which is overlooked due to the reduced common awareness of photoactivity.

METHODS

A systematic review of reported natural PSs and their supposed medicinal application was conducted by employing PubMed, Scifinder, and Web of Science. The identified photoactive natural products were compiled including information about their natural sources, their photoyield, and their pharmacological application. Furthermore, the common chemical scaffolds of natural PS are shown to enable the reader to recognize potentially overlooked natural PSs.

RESULTS

The literature review revealed over 100 natural PS, excluding porphyrins. The PSs were classified according to their scaffold. Thereby it was shown that some PS-scaffolds were analyzed in a detailed way, while other classes were only scarcely investigated, which leaves space for future discoveries. In addition, the literature revealed that many PSs are phytoalexins, thus the selection of the starting material significantly matters in order to find new PSs.

CONCLUSION

Photoactive principles are ubiquitous and can be found in various plant extracts. With the increasing availability of light-irradiation setups for the identification of photoactive natural products, we anticipate the discovery of many new natural PSs in the near future. With the accumulation of chemically diverse PSs, PDT itself might finally reach its clinical breakthrough as a promising alternative treatment against multi-resistant microbes and cancer types.

Mechanism of coralyne-mediated DNA photo-nicking process

Previously, we reported that coralyne and UVA combination sensitized a wide range of human carcinoma cells regardless of their p53 status. The coralyne induced photosensitization of cancer cells may be clinically attractive, as mutation in the p53 gene is prevalent in many types of tumors. Coralyne mediated photosensitization of cancer cells is attributable to its ability to cause extensive DNA single strand breaks (SSB). However, the precise mechanism of coralyne induced DNA photo-damage is not yet known. The present study was aimed to understand the hitherto unknown mechanism of the coralyne-induced DNA photo-cleavage process. To this end, we compared the DNA photo-nicking properties of berberine, jatrorrhizine and coralyne, and deciphered involvement of the photochemical processes in the photo-nuclease action of coralyne using absorption and electron spin resonance spectroscopy, high performance liquid chromatography and mass spectroscopy (MS) techniques in conjunction with relevant in vitro studies with plasmid DNA. In association with UVA, coralyne, but not berberine and jatrorrhizine induced significant nicking of plasmid DNA via an O₂-independent photo-chemical process. The Job's plot of our spectrophotometric data suggested that one coralyne molecule remains intercalated with two DNA base pairs (i. e., 1:2) and starts forming aggregates beyond this molar ratio. The DNA photo-nicking by the combination of coralyne and UVA (designated as CUVA) was primarily caused by the coralyne aggregates without any significant contribution from the DNA-intercalated coralyne monomer.

Substituent effect on the dynamics of the inclusion complex formation between protoberberine alkaloids and cucurbit[7]uril

The dynamics and activation parameters of alkaloid entry into and exit from cucurbit[7]uril significantly depend on the substitution pattern.

Sequential inclusion of two berberine cations in cucurbit[8]uril cavity: kinetic and thermodynamic studies

The formation and dissociation kinetics of 1 : 1 and 2 : 1 inclusion of berberine in the cucurbit[8]uril cavity is revealed.