Cardioprotective effects of Viscum album L. ssp. album (Loranthaceae) on isoproterenol-induced heart failure via regulation of the nitric oxide pathway in rats

The cardioprotective potential of selected species of mistletoe

Mistletoe is an evergreen woody shrub with stems measuring 30-100 cm. It has leathery, yellowish-green strap-shaped leaves, yellowish-green flowers, and bears typical berries. The most common species is Viscum album L., mainly present in Europe and Asia. It is commonly known as European mistletoe or simply, mistletoe. Scientific interest in mistletoe was awakened in the XX century. Mistletoe, especially V. album L., has historically been used in the treatment and prophylaxis of CVD, with its properties being confirmed in recent studies. This mini-review describes new aspects of the cardioprotective properties of various species of mistletoe, especially V. album L. The effect of oral and subcutaneous application of fresh V. album L. extracts on blood pressure has been studied in various models; while the data suggests that mistletoe may be a promising herbal extract with cardioprotective properties, the species has only been tested in vitro and in vivo, on animals. In addition, it is unclear whether the cardioprotective activity of mistletoe may be due to particular chemical components, as the chemical composition of mistletoe extracts can vary depending on inter alia the time of harvest, extraction method and plant part. Hence, this activity may instead result from synergistic interactions between various secondary metabolites. Therefore, further studies are needed to identify the mechanisms of action of mistletoe compounds on CVDs, and determine their interactions with other cardioprotective drugs, their metabolic mechanisms, pharamacokinetics and adverse effects. More research is also needed to determine the therapeutic doses of active ingredients for use in clinical trials; this would require an accurate understanding of the chemical composition of extracts from different species of mistletoe (not only V. album L.) and from various host trees.

Traditional Uses, Phytochemical Constituents and Ethnopharmacological Properties of Mistletoe from Phoradendron and Viscum Species

Plants from the genus Phoradendron and Viscum, also known as American and European mistletoe, are a group of hemiparasitic plants traditionally used to treat many diseases. Mistletoes have a rich content of natural compounds like terpenes, alkaloids, proteins, and phenolic compounds associated with their potential medicinal properties. In this sense, mistletoes have shown antiproliferative, antioxidant, anti-inflammatory, and antimicrobial activity, which has been attributed to their phytochemical constituents. The mechanisms in which mistletoe plants act vary and depend on their phytochemical content and distribution, which in part will depend on the mistletoe species. In this sense, recent literature research is needed to visualize state of the art in the ethnopharmacological potential of mistletoe. Thus, this literature review aims to systematically report recent studies (2010-2023) on the phytochemical characterization and bioactive studies of mistletoe plants, mainly the Viscum and Phoradendron genera. We gather recent information of 140 references selected in our research. Here we report that although there are several bioactivity studies of mistletoe species, bioavailability studies are still scarce, and the precise mechanisms of action are not fully known. We encourage that further studies include a systematic strategy to cover these areas of opportunity.

Phytochemical Profile and Antioxidant Capacity of Viscum album L. Subsp. album and Effects on Its Host Trees

Viscum album L. subsp. album is a hemiparasitic plant that is recognized as a medicinal plant due to its beneficial effects, including anti-tumor activity, antioxidant, anti-inflammatory, anti-hepatotoxic, hypoglycemic, and antimicrobial properties as well as for lowering blood pressure. On the other hand, mistletoe is a biotic stressor for both deciduous trees and conifers. Our main aim was to evidence the influence of mistletoe on the content of chlorophylls, proline, total phenols, flavonoids, and antioxidant capacity of leaves from tree host trees (Malus domestica, Prunus domestica, and Populus alba) that grow on the northwest of Romania. In addition, HPLC-DAD-MS-ESI+ was used to analyze the phenolic acid and flavonoid profiles of V. album L. subsp. album leaves according to their parasitized hosts. A significant decrease in chlorophyll a level of approximately 32% was detected in poplars infested with mistletoe, followed by infested apples and plums with pigment reductions of 29.25% and 9.65%, respectively. The content of total phenols and flavonoids in the parasitized trees was higher compared to the non-parasitized ones. In the case of poplar, which presented the highest incidence of mistletoe infestation (70.37%), the content of total phenols in the leaves was two times higher compared to non-infested leaves. Based on HPLC chromatographic analysis, leaves of mistletoe growing on apple (VAM) had the highest content of phenolic acids (7.833 mg/g dw), followed by mistletoe leaves on poplar (VAO) and plum (VAP) (7.033 mg/g dw and, respectively, 5.559 mg/g dw). Among the flavonols, the predominant component was Rhamnazin glucosides in the amount of 1.025 ± 0.08 mg/g dw in VAO, followed by VAP and VAM (0.514 ± 0.04 and 0.478 ± 0.04 mg/g dw, respectively). Although our results show that mistletoe negatively influences the host trees, it is still a valuable plant that must be exploited to bring benefits to human health.

Biological activity of mistletoe: in vitro and in vivo studies and mechanisms of action

Mistletoe has been used as treatment of many diseases in traditional and folk medicine. To date, anticancer, immunomodulatory, cardiac, antidiabetic, hepatoprotective, neuropharmacological, antibacterial and antifungal properties of mistletoe extracts have been studied the most. In this review, we summarized in vitro and in vivo studies on the pharmacological activity of Viscum species. Furthermore, we proposed the possible mechanisms of action of this herb, which might include many signalling pathways. Mistletoe could regulate either similar or different targets in various pathways that act on membrane receptors, enzymes, ion channels, transporter proteins and transcriptional targets. Still, pharmacological activities of mistletoe have been investigated mainly for crude extracts. It is a new field for scientists to determined which chemical compounds are responsible for the individual biological activities of mistletoe and how these activities are achieved. As a result, mistletoe might become a source of new complementary therapies supporting the treatment of many diseases.

Identification of Viscum album L. miRNAs and prediction of their medicinal values

MicroRNAs (miRNAs) are a class of approximately 22 nucleotides single-stranded non-coding RNA molecules that play crucial roles in gene expression. It has been reported that the plant miRNAs might enter mammalian bloodstream and have a functional role in human metabolism, indicating that miRNAs might be one of the hidden bioactive ingredients in medicinal plants. Viscum album L. (Loranthaceae, European mistletoe) has been widely used for the treatment of cancer and cardiovascular diseases, but its functional compounds have not been well characterized. We considered that miRNAs might be involved in the pharmacological activities of V. album. High-throughput Illumina sequencing was performed to identify the novel and conserved miRNAs of V. album. The putative human targets were predicted. In total, 699 conserved miRNAs and 1373 novel miRNAs have been identified from V. album. Based on the combined use of TargetScan, miRanda, PITA, and RNAhybrid methods, the intersection of 30697 potential human genes have been predicted as putative targets of 29 novel miRNAs, while 14559 putative targets were highly enriched in 33 KEGG pathways. Interestingly, these highly enriched KEGG pathways were associated with some human diseases, especially cancer, cardiovascular diseases and neurological disorders, which might explain the clinical use as well as folk medicine use of mistletoe. However, further experimental validation is necessary to confirm these human targets of mistletoe miRNAs. Additionally, target genes involved in bioactive components synthesis in V. album were predicted as well. A total of 68 miRNAs were predicted to be involved in terpenoid biosynthesis, while two miRNAs including val-miR152 and miR9738 were predicted to target viscotoxins and lectins, respectively, which increased the knowledge regarding miRNA-based regulation of terpenoid biosynthesis, lectin and viscotoxin expressions in V. album.

Ethyl acetate fraction of Allium hirtifolium improves functional parameters of isolated hearts of diabetic rats

Objective:

Allium hirtifolium (Persian shallot) has a hypoglycemic effect on diabetic animals. The aim of this study was to assess the effect of the ethyl acetate fraction of Allium hirtifolium on the function of isolated hearts of diabetic rats.

Methods:

The control and diabetic animals were randomly divided into four groups: saline- or extract-treated controls (n=10 and n=6, respectively) and saline- or extract-treated diabetic rats (n=8 and n=9, respectively), which received normal saline or extract for four weeks by daily gavage. The hearts were perfused according to the Langendorff method. Cardiac function parameters, including left ventricular developed pressure (LVDP), heart rate (HR), rate pressure product (RPP; LVDP´HR), and dp/dt were measured.

Results

The findings of this study showed that in the extract-treated diabetic rats, LVDP (94.5±9.1 mm Hg, mean±SEM), HR (249±15 beats/min), RPP (22732±1246) and +dp/dt (2598±230) at the baseline were significantly higher than those in the saline-treated diabetic animals, (71.5±4.0), (189±6), (13923±984), and (1701±124), respectively. Furthermore, RPP and HR were also significantly higher than the corresponding values obtained in the saline-treated diabetic rats after ischemia.

Conclusion

Besides blood glucose lowering action, oral administration of the ethyl acetate fraction of Allium hirtifolium significantly improved the baseline and post-ischemic cardiac function parameters in streptozotocin-induced diabetic rats.