In vitro Effect of Harmine Alkaloid and Its N-Methyl Derivatives Against Toxoplasma gondii

In Vitro Effect of 9,9'-Norharmane Dimer against Herpes Simplex Viruses

Herpes simplex virus (HSV) infections are highly widespread among humans, producing symptoms ranging from ulcerative lesions to severe diseases such as blindness and life-threatening encephalitis. At present, there are no vaccines available, and some existing antiviral treatments can be ineffective or lead to adverse effects. As a result, there is a need for new anti-HSV drugs. In this report, the in vitro anti-HSV effect of 9,9'-norharmane dimer (nHo-dimer), which belongs to the β-carboline (βC) alkaloid family, was evaluated. The dimer exhibited no virucidal properties and did not impede either the attachment or penetration steps of viral particles. The antiviral effect was only exerted under the constant presence of the dimer in the incubation media, and the mechanism of action was found to involve later events of virus infection. Analysis of fluorescence lifetime imaging data showed that the nHo-dimer internalized well into the cells when present in the extracellular incubation medium, with a preferential accumulation into perinuclear organelles including mitochondria. After washing the host cells with fresh medium free of nHo-dimer, the signal decreased, suggesting the partial release of the compound from the cells. This agrees with the observation that the antiviral effect is solely manifested when the alkaloid is consistently present in the incubation media.

Exploring potooxidative degradation pathways of harmol and harmalol alkaloids in water: effects of pH, excitation sources and atmospheric conditions

This work explores the photochemical degradation of cationic species of 7-hydroxy-1-methyl-2H-pyrido[3,4-b]indole or harmol (1C) and the corresponding partially hydrogenated derivative 7-hydroxy-1-methyl-3,4-dihydro-2H-pyrido[3,4-b]indole or harmalol (2C) in aqueous solution. UV-visible absorption and fluorescence emission spectroscopy coupled with multivariate data analysis (MCR-ALS and PARAFAC), HPLC and HRESI-MS techniques were used for both quantitative and qualitative analysis. The formation of hydrogen peroxide reactive oxygen species (ROS) was quantified, and the influence of pH, oxygen partial pressure and photoexcitation source on the photochemical degradation of both compounds was assessed. The potential implications on the biosynthesis of βCs and their biological role in living systems are discussed.

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.

Triclabendazole and clofazimine reduce replication and spermine uptake in vitro in Toxoplasma gondii

Toxoplasmosis is a worldwide zoonosis caused by the protozoan parasite Toxoplasma gondii. Although this infection is generally asymptomatic in immunocompetent individuals, it can cause serious clinical manifestations in newborns with congenital infection or in immunocompromised patients. As current treatments are not always well tolerated, there is an urgent need to find new drugs against human toxoplasmosis. Drug repurposing has gained considerable momentum in the last decade and is a particularly attractive approach for the search of therapeutic alternatives to treat rare and neglected diseases. Thus, in this study, we investigated the antiproliferative effect of several repurposed drugs. Of these, clofazimine and triclabendazole displayed a higher selectivity against T. gondii, affecting its replication. Furthermore, both compounds inhibited spermine incorporation into the parasite, which is necessary for the formation of other polyamines. The data reported here indicate that clofazimine and triclabendazole could be used for the treatment of human toxoplasmosis and confirms that drug repurposing is an excellent strategy to find new therapeutic targets of intervention.

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.

Synthesis of harmine-nitric oxide donor derivatives as potential antitumor agents

To further improve the anti-tumor activity of Harmine (HM), we took the hybridization approach and synthesized harmine derivatives-furoxan hybrids containing nitric oxide (NO) releasing parts by connecting NO donors with anti-tumor active fragments to harmine. Then, the synthesized compounds were evaluated for their in vitro cytotoxicity against five human cancer cell lines. Among them, compound 10 was found to have the strongest antiproliferative activity against HepG2 (IC₅₀ = 1.79 µM). In addition, compound 10 produced high levels of NO in vitro, verifying that the release of NO was closely correlated to the antiproliferative activity. In addition, Compound 10 also showed good plasma stability. Finally, we also preliminarily investigated the acute toxicity of compound 10 in mice and assessed the absorption of compound 10 by Caco-2 cell permeability assay. In brief, the remarkable biological characteristics of the new harmine derivatives-furoxan hybrids may make them promising candidates for human cancer intervention.