Distribution of photoactive β-carboline alkaloids across Passiflora caerulea floral organs

This study reports valuable information regarding the presence and concentration of a series of photoactive β-carboline (βCs) alkaloids (norharmane, harmane, harmine, harmol, harmaline, and harmalol) and their distribution across the floral age and organs of Passiflora caerulea. UHPLC-MS/MS data reported herein reveal that the βCs' content ranged from 1 to 110 μg kg-1 , depending on the floral organ and age. In certain physiologically relevant organs, such as anthers, βCs' content was one order of magnitude higher than in other organs, suggesting a special role for βCs in this specific organ. βCs' content also varied in a structure-dependent manner. Alkaloids bearing a hydroxyl group at position C(7) of the main βC ring were present at concentrations one order of magnitude higher than other βC derivatives investigated. UV-visible and fluorescence spectroscopy of the flower extracts provided complementary information regarding other biologically relevant groups of chromophores (phenolic/indolic derivatives, flavonoids/carotenes, and chlorophylls). Since flowers are constantly exposed to solar radiation, the presence of photoactive βCs in floral organs may have several (photo)biological implications that are further discussed.

Photosensitizing properties and subcellular localisation of 3,4-dihydro-β-carbolines harmaline and harmalol

Harmaline (1) and harmalol (2) represent two 3,4-dihydro-β-carboline (DHβCs) most frequently reported in a vast number of living systems. Fundamental aspects including the photosensitizing properties, cellular uptake, as well as the cyto- and phototoxicity of 1 and 2 were investigated herein. The molecular basis underlying the investigated processes are elucidated. Data reveal that both alkaloids show a distinctive pattern of extracellular DNA photodamage. Compound 1 induces a DNA photodamage profile dominated by oxidised purines and sites of base loss (AP sites), whereas 2 mostly induces single-strand breaks (SSBs) in addition to a small extent of purine oxidative damage. In both cases, DNA oxidative damage would occur through type I mechanism. In addition, a concerted hydrolytic attack is suggested as an extra mechanism accounting for the SSBs formation photoinduced by 2. Subcellular internalisation, cyto- and phototoxicity of 1 and 2 and the corresponding full-aromatic derivatives harmine (3) and harmol (4) also showed quite distinctive patterns in a structure-dependent manner. These results are discussed in the framework of the potential biological, biomedical and/or pharmacological roles reported for these alkaloids.

Graphical abstract

The subtle structural difference (i.e., the exchange of a methoxy group for a hydroxyl substituent at C(7)) between harmaline and harmalol, gives rise to distinctive photosensitizing and subcellular localisation patterns.

Design and synthesis of thiadiazolo-carboxamide bridged β-carboline-indole hybrids: DNA intercalative topo-IIα inhibition with promising antiproliferative activity

The conjoining of salient pharmacophoric properties directing the development of prominent cytotoxic agents was executed by constructing thiadiazolo-carboxamide bridged β-carboline-indole hybrids. On the evaluation of in vitro cytotoxic potential, 12c exhibited prodigious cytotoxicity among the synthesized new molecules 12a-k, with an IC₅₀ < 5 μM in all the tested cancer cell lines (A549, MDA-MB-231, BT-474, HCT-116, THP-1) and the best cytotoxic potential was expressed in lung cancer cell line (A549) with an IC₅₀ value of 2.82 ± 0.10 μM. Besides, another compound 12a also displayed impressive cytotoxicity against A549 cell line (IC₅₀: 3.00 ± 1.40 μM). Further target-based assay of these two compounds 12c and 12a revealed their potential as DNA intercalative topoisomerase-IIα inhibitors. Additionally, the antiproliferative activity of compound 12c was measured in A549 cells by traditional apoptosis assays revealing the nuclear, morphological alterations, and depolarization of membrane potential in mitochondria and externalization of phosphatidylserine in a concentration-dependent manner. Cell cycle analysis unveiled the G0/G1 phase inhibition and wound healing assay inferred the inhibition of in vitro cell migration by compound 12c in lung cancer cells. Remarkably, the safety profile of compound 12c was disclosed by screening against normal human lung epithelial cell line (BEAS-2B: IC₅₀: 71.2 ± 7.95 μM) with a selectivity index range of 14.9-25.26. Moreover, Molecular modeling studies affirm the intercalative binding of compound 12c and 12a in the active pocket of topo-IIα. Furthermore, in silico prediction of physico-chemical parameters divulged the propitious drug-like properties of the synthesized derivatives.

N-Methyl-β-carboline alkaloids: structure-dependent photosensitizing properties and localization in subcellular domains

N-Methyl-β-carboline (βC) alkaloids, including normelinonine F (1b) and melinonine F (2b), have been found in a vast range of living species playing different biological, biomedical and/or pharmacological roles. Despite this, molecular bases of the mechanisms through which these alkaloids would exert their effect still remain unknown. Fundamental aspects including the photosensitizing properties and intracellular internalization of a selected group of N-methyl-βC alkaloids were investigated herein. Data reveal that methylation of the βC main ring enhances its photosensitizing properties either by increasing its binding affinity with DNA as a biomolecular target and/or by increasing its oxidation potential, in a structure-dependent manner. As a general rule, N(9)-substituted βCs showed the highest photosensitizing efficiency. With the exception of 2-methyl-harminium, all the N-methyl-βCs investigated herein induce a similar DNA photodamage profile, dominated largely by oxidized purines. This fact represents a distinctive behavior when comparing with N-unsubstituted-βCs. On the other hand, although all the investigated compounds might accumulate mainly into the mitochondria of HeLa cells, methylation provides a distinctive dynamic pattern for mitochondrial uptake. While rapid (passive) diffusion is most probably reponsible for the prompt uptake/release of neutral βCs, an active transport appears to mediate the (reatively slow) uptake of the quaternary cationic βCs. This might be a consequence of a distinctive subcellular localization (mitochondrial membrane and/or matrix) or interaction with intracellular components. Biomedical and biotechnological implications are also discussed herein.

Light-induced full aromatization and hydroxylation of 7-methoxy-1-methyl-3,4-dihydro-2H-pyrido[3,4-b]indole alkaloid: Oxygen partial pressure as a key modulator of the photoproducts distribution

Full-aromatic and partially hydrogenated β-carboline (βC) derivatives constitute a group of alkaloids widely distributed in a great variety of living systems. In plants and bacteria, tetrahydro-βCs are the primary product of the Pictet-Spengler enzymatically catalyzed condensation. Tetrahydro-βC skeleton is further modified giving rise to the formation of a vast set of derivatives including dihydro- and full-aromatic βCs. However, in most of the cases, the later processes still remain unclear and other sources, such as photo-triggered reactions, deserve to be explored. In this context, the photophysic and photochemistry of 7-methoxy-1-methyl-3,4-dihydro-2H-pyrido[3,4-b]indole or harmaline (Hlina) in aqueous solution is reported herein. UV-visible absorption and fluorescence emission spectroscopy coupled with multivariate data analysis (PARAFAC), HPLC and HRESI-MS techniques were used for both quantitative and qualitative analysis. The formation singlet oxygen and hydrogen peroxide reactive oxygen species (ROS) was quantified and their role together with the influence of pH and oxygen partial pressure on the photochemical degradation of HlinaH⁺ was assessed. We report herein the first study on photochemical full-aromatization of a dihydro-βC derivative. These results can shed some light on the βCs biosynthesis and role in living systems.

DNA damage photo-induced by chloroharmine isomers: hydrolysis versus oxidation of nucleobases

Photodynamic therapy (PDT) is an emerging clinical treatment currently being used against a wide range of both cancerous and noncancerous diseases. The search for new active photosensitizers as well as the development of novel selective delivery systems are the major challenges faced in the application of PDT. We investigated herein three chloroharmine derivatives (6-, 8- and 6,8-dichloroharmines) with quite promising intrinsic photochemical tunable properties and their ability to photoinduce DNA damage in order to elucidate the underlying photochemical mechanisms. Data revealed that the three compounds are quite efficient photosensitizers. The overall extent of photo-oxidative DNA damage induced by both 8-chloro-substituted β-carbolines is higher than that induced by 6-chloro-harmine. The predominant type of lesion generated also depends on the position of the chlorine atom in the β-carboline ring. Both 8-chloro-substituted β-carbolines mostly oxidize purines via type I mechanism, whereas 6-chloro-harmine mainly behaves as a "clean" artificial photonuclease inducing single-strand breaks and site of base loss via proton transfer and concerted (HO^--mediated) hydrolytic attack. The latter finding represents an exception to the general photosensitizing reactions and, to the best of our knowledge, this is the first time that this process is well documented. The controlled and selective production of different oxygen-independent lesions could be fine-tuned by simply changing the substituent groups in the β-carboline ring. This could be a promising tool for the design and development of novel photo-therapeutic agents aimed to tackle hypoxic conditions shown in certain types of tumours.

Shipment of a photodynamic therapy agent into model membrane and its controlled release: A photophysical approach

Harmine, an efficient cancer cell photosensitizer (PS), emits intense violet color when it is incorporated in well established self assembly based drug carrier formed by cationic surfactants of identical positive charge of head group but varying chain length, namely, dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB). Micelle entrapped drug emits in the UV region when it interacts with non-toxic β-cyclodextrin (β-CD). Inspired by these unique fluorescence/structural switching properties of the anticancer drug, in the present work we have monitored the interplay of the drug between micelles and non-toxic β-CDs. We have observed that the model membranes formed by micelles differing in their hydrophobic chain length interact with the drug differently. Variation in the surfactant chain length plays an important role for structural switching i.e. in choosing a particular structural form of the drug that will be finally presented to their targets. The present study shows that in case of necessity, the bound drug molecule can be removed from its binding site in a controlled manner by the use of non-toxic β-CD and it is exploited to serve a significant purpose for the removal of excess/unused adsorbed drugs from the model cell membranes. We believe this kind of β-CD driven translocation of drugs monitored by fluorescence switching may find possible applications in controlled release of the drug inside cells.

A comprehensive analysis of direct and photosensitized attenuation of Toxoplasma gondii tachyzoites

In the present work, we have evaluated the effect of three different types of radiation: UVC (254±5nm), UVA (365±20nm) and visible (420±20nm) on different morphological and biological functions of Toxoplasma gondii tachyzoites. Briefly, UVC and UVA showed an inhibitory effect on parasite invasion in a dose-dependent manner. UVC showed the strongest effect inducing both structural damage (antigens) and functional inhibition (i.e., invasion and replication). On its own, visible light induces a quite distinctive and selective pattern of parasite-attenuation. This type of incident radiation inhibits the replication of the parasite affecting neither the capability of invasion/attachment nor the native structure of proteins (antigens) on parasites. Such effects are a consequence of photosensitized processes where phenol red might act as the active photosensitizer. The potential uses of the methodologies investigated herein are discussed.

UVA Photoactivation of Harmol Enhances Its Antifungal Activity against the Phytopathogens Penicillium digitatum and Botrytis cinerea

Phytopathogenic fungi responsible for post-harvest diseases on fruit and vegetables cause important economic losses. We have previously reported that harmol (1-methyl-9H-pyrido[3,4-b]indol-7-ol) is active against the causal agents of green and gray molds Penicillium digitatum and Botrytis cinerea, respectively. Here, antifungal activity of harmol was characterized in terms of pH dependency and conidial targets; also photodynamic effects of UVA irradiation on the antimicrobial action were evaluated. Harmol was able to inhibit the growth of both post-harvest fungal disease agents only in acidic conditions (pH 5), when it was found in its protonated form. Conidia treated with harmol exhibited membrane integrity loss, cell wall disruption, and cytoplasm disorganization. All these deleterious effects were more evident for B. cinerea in comparison to P. digitatum. When conidial suspensions were irradiated with UVA in the presence of harmol, antimicrobial activity against both pathogens was enhanced, compared to non-irradiated conditions. B. cinerea exhibited a high intracellular production of reactive oxygen species (ROS) when was incubated with harmol in irradiated and non-irradiated treatments. P. digitatum showed a significant increase in ROS accumulation only when treated with photoexcited harmol. The present work contributes to unravel the antifungal activity of harmol and its photoexcited counterpart against phytopathogenic conidia, focusing on ROS accumulation which could account for damage on different cellular targets.

Chemical and photochemical properties of chloroharmine derivatives in aqueous solutions

In water, chloroharmines follow very distinctive thermal and photochemical pH- and O₂-dependent-reaction pathways.

DNA damage induced by bare and loaded microporous coordination polymers from their ground and electronic excited states

We report on interactions of cell free double-stranded DNA (dsDNA) with a selected subgroup of Microporous Coordination Polymers (MCPs). In particular, we have studied the influence of different metal ion constituents and chemically modified linkers using a set of five benzene carboxylate-based MCPs. Our results suggest that the DNA moiety can be structurally modified in two different ways: by direct MCPs-dsDNA interaction and/or through photosensitized processes. The extent of the observed damage was found to be strongly dependent on the charge density of the material. The potential use of the MCPs tested as inert carriers of photosensitizers was demonstrated by analyzing the interaction between dsDNA and harmine-loaded Cr-based materials, both in the absence of light and upon UVA irradiation.

Determining the molecular basis for the pH-dependent interaction between 2'-deoxynucleotides and 9H-pyrido[3,4-b]indole in its ground and electronic excited states

Interaction between norharmane and three different 2'-deoxynucleotides (dNMP) (2'-deoxyguanosine 5'-monophosphate (dGMP), 2'-deoxyadenosine 5'-monophosphate (dAMP) and 2'-deoxycytidine 5'-monophosphate (dCMP)), in aqueous solution, was studied in the ground state by means of UV-vis and (1)H-NMR spectroscopy and in the first electronic excited state using steady-state and time-resolved fluorescence spectroscopy. In all cases, the norharmane-dNMP interaction dependence on the pH was examined. Possible mechanisms for the interaction of both ground and electronic excited states of norharmane with nucleotides are discussed. Spectroscopic, molecular modeling and chemometric analysis were performed to further characterize the chemical structure of the complexes formed and to get additional information concerning the interaction between dNMPs and norharmane.

Supramolecular hydrophobic guest transport system based on pillar[5]arene

A pillar[5]arene-based bioactive guest loading system was developed, which increased the solubility of norharmane in aqueous medium.

Characterizations of cationic γ-carbolines binding with double-stranded DNA by spectroscopic methods and AFM imaging

Two cationic γ-carbolines, 2-methyl-5H-pyrido[4,3-b]indolium iodide (MPII) and 2,5-dimethyl-5H-pyrido[4,3-b]indolium iodide (DPII), were synthesized, and the DNA-binding properties of the cationic γ-carbolines were elucidated. Through a series of experiments, we proved that the two cationic γ-carbolines could strongly interact with DNA by intercalative binding. However, DPII, with a methyl group substituting H atom of 5-NH, has shown a stronger intercalative interaction with DNA compared to MPII. The dissociation of H from the 5-NH of MPII resulted in better water solubility and less binding affinity to DNA. Atomic force microscopy (AFM) images of pBR322 showed that both MPII and DPII strongly interacted with DNA and induced conformational changes in DNA. Moreover, the CT-DNA circular dichroism (CD) spectra changes and the statistics of the node numbers of pBR322 in AFM images indicated that MPII had more profound effects on DNA conformations compared to DPII. Furthermore, our studies have shown that the interactions between cationic γ-carbolines and DNA were sensitive to ionic strength. Increased ionic strength in the buffer caused the DNA helix to shrink, and the base stacking would be more compact, which resulted in minimal intercalation of cationic γ-carbolines into DNA.

In vitro evaluation of β-carboline alkaloids as potential anti-Toxoplasma agents

Background

Toxoplasmosis is a worldwide infection caused by the protozoan parasite Toxoplasma gondii, which causes chorioretinitis and neurological defects in congenitally infected newborns or immunodeficient patients. The efficacy of the current treatment is limited, primarily by serious host toxicity. In recent years, research has focused on the development of new drugs against T. gondii. β-Carbolines (βCs), such as harmane, norharmane and harmine, are a group of naturally occurring alkaloids that show microbicidal activity. In this work, harmane, norharmane and harmine were tested against T. gondii.

Findings

The treatment of extracellular tachyzoites with harmane, norharmane and harmine showed a 2.5 to 3.5-fold decrease in the invasion rates at doses of 40 μM (harmane and harmine) and 2.5 μM (norharmane) compared with the untreated parasites. Furthermore, an effect on the replication rate could also be observed with a decrease of 1 (harmane) and 2 (norharmane and harmine) division rounds at doses of 5 to 12.5 μM. In addition, the treated parasites presented either delayed or no monolayer lysis compared with the untreated parasites.

Conclusions

The three βC alkaloids studied (norharmane, harmane and harmine) exhibit anti-T. gondii effects as evidenced by the partial inhibition of parasite invasion and replication. A dose–response effect was observed at a relatively low drug concentration (< 40 μM), at which no cytotoxic effect was observed on the host cell line (Vero).

Photosensitized electron transfer within a self-assembled norharmane-2'-deoxyadenosine 5'-monophosphate (dAMP) complex

Norharmane is a compound that belongs to a family of alkaloids called β-carbolines (βCs). These alkaloids are present in a wide range of biological systems, playing a variety of significant photo-dependent roles. Upon UV-A irradiation, βCs are able to act as efficient photosensitizers. In this work, we have investigated the photosensitized oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) by norharmane in an aqueous phase, upon UV-A (350 nm) irradiation. The effect of the pH was evaluated on both the interactions between norharmane and dAMP in the ground and electronic excited states, and on the dAMP photosensitized oxidation. A quite strong static interaction between norharmane and dAMP was observed, especially under those pH conditions where the protonated form of the alkaloid is present (pH < 7). Theoretical studies were performed to further characterize the static complex structure. The participation of reactive oxygen species (ROS) in the photosensitized reaction was also investigated and the photoproducts were characterized by means of UV-LDI-MS and ESI-MS. All the data provided herein indicate that electron transfer (Type I) within a self-assembled norharmane-dAMP complex is the operative mechanism in the dAMP photosensitization.

DNA damage spectra induced by photosensitization

DNA damage induced by photosensitization is not only responsible for the genotoxic effects of various types of drugs in the presence of light, but is also relevant for some of the adverse effects of sunlight, in particular in the UVA and visible range of the spectrum. The types of DNA modifications induced are very diverse and include pyrimidine dimers, covalent adducts, various base modifications generated by oxidation, single-strand breaks and (regular and oxidized) sites of base loss. The ratios in which the various modifications are formed (damage spectra) can be regarded as a fingerprint of the damaging mechanism. Here, we describe the damage spectra of various classes of photosensitizers in relation to the underlying damaging mechanisms. In mammalian cells irradiated with solar radiation, damage at wavelengths <400 nm is characteristic for a (not yet identified) endogenous type-I or type-II photosensitizer. In the UVA range, however, both direct DNA excitation and photosensitized damage appear to be relevant, and there are indications that other chromophore(s) are involved than in the visible range.