Isolation and characterization of anti-inflammatory and immunomodulatory compounds from higher plants

Autoimmunity is a pathological chronic inflammatory state that arises when the immune system mistakenly targets healthy cells and tissues in the human body. Clinically, there are more than 80 types of autoimmune diseases described, including well-known conditions like psoriasis, rheumatoid arthritis, type I diabetes, multiple sclerosis, and Crohn’s disease. The incidence of autoimmune diseases in the human population is around 5−10% and continues to rise. Although current treatment options with immunosuppressant drugs like cyclosporine or biologic agents have shown excellent efficacy, they are often associated with unwanted side effects such as increased susceptibility to infections and malignancies, drug-drug interactions, cytokine release syndrome, hypersensitivity reactions, or anti-drug antibodies. Additionally, current drugs often lose efficacy over time, which leads to non-responsiveness, or to a lack of long-lasting relief of symptoms. Finally, the treatment of autoimmune diseases is very expensive and generates high treatment costs. Thus, there is a need for continued research into new therapies.
In the pathogenesis of chronic inflammation and autoimmune diseases enhanced activation and proliferation of T cells plays a crucial role. To address this issue, targeted therapies that specifically enhance inhibitory pathways in T cells are an attractive approach to treat human autoimmune diseases. Thus, the first aim of this study was to discover novel immune-modulating substances from plant extracts that specifically inhibit human T cell activation and proliferation. To achieve this goal, an in-house library of 600 extracts from plants endemic to Panama was screened for potential T cell inhibition. As one of the hits, an ethyl acetate extract from the aerial parts of Hyptis brachiata Briq. (Lamiaceae) was found to have strong inhibitory effects on T cell activation and proliferation. Seven aryltetralin lignans, five arylnaphthalene lignans, two flavonoids, three triterpenes, and cinnamyl cinnamate were isolated using an HPLC-based activity profiling approach. The aryltetralin lignans inhibited T cell proliferation in a concentration-dependent manner without inducing apoptosis. Additionally, the ethyl acetate extract and isolated triterpenes weakly lowered the secretion of inflammatory cytokines like IL-2 and TNF-α by activated T cells. The suppressive effects on activated T cells could be attributed to a synergistic interplay between the aryltetralin lignans and triterpenes. These findings suggest that the extract from Hyptis brachiata could be further investigated as a potential treatment for T cell-mediated inflammatory and autoimmune diseases. The findings of this study have been published in Biomedicine & Pharmacotherapy, 160 in 2023.
Another aspect of this work aimed to explore the potential use of saffron corms (Crocus sativus L., Iridaceae) that arise as a waste product from saffron cultivation. A 70% ethanol extract of the corms and a sugar-depleted methanol fraction of the extract have been found to inhibit the TNF-α/IFN-γ-induced gene expression and secretion of the chemokines IL-8, MCP-1, and RANTES in human HaCaT keratinocytes. The effects were in part stronger than those of the positive control hydrocortisone. These chemokines are responsible for monocyte and T cell attraction, as well as for keratinocyte proliferation, making them critical in wound healing and in the development of inflammatory skin diseases like psoriasis and atopic dermatitis. A series of unusual bidesmosidic glycosides of echinocystic acid, which bear a 3,16-dihydroxy-10-oxohexadecanoic acid residue attached to the glycosidic moiety at C-28, were isolated using centrifugal partition chromatography and different C18 and HILIC HPLC stationary phases. Two previously reported compounds, azafrines 1 and 2, and eight new congeners named as azafrines 3−10 were identified. Saffron saponins significantly inhibited TNF-α/IFN-γ-induced secretion of RANTES in human HaCaT cells at 1 μM (p < 0.001). In vitro data suggest that saffron saponins possess anti-inflammatory properties by affecting the expression and secretion of chemotactic cytokines, and could therefore potentially be used as topical agents for treating inflammatory skin diseases. These results have been published in the Journal of Natural Products, 84, 2021.
The treatment of wounds is an increasingly important challenge, particularly in the case of chronic wounds associated with complex pathophysiology that may arise from autoimmune diseases such as psoriasis or type I diabetes. These wounds reduce the quality of life of many patients and current wound healing therapies are only partially effective. The lack of effective treatments for non-healing chronic wounds has become a growing clinical concern, and ongoing research is focused on obtaining more effective options to reduce treatment costs, provide long-term relief, and facilitate effective scar healing.
Historically, medicinal plants have been successfully used in wound treatment, and today they remain widely applied. Plant-based products have gained increasing interest as cost-efficient treatment options for wounds, as they represent mixtures of various phytochemicals that could act beneficially in a synergistic manner during the complex wound healing process. In this context, the last project described in this work investigated the wound healing properties of Teucrium polium subsp. capitatum (L.) Arcang (syn. Teucrium capitatum L.; Lamiaceae), a plant traditionally used in Algeria as a decoction or ointment to treat hypertension, diabetes, and wounds. Initially, a wound excision model in rabbits confirmed beneficial wound healing effects of a methanol extract from the aerial parts of T. polium. An ointment prepared from the T. polium extract demonstrated significant wound healing properties, superior to those of the reference drug Cicatryl-Bio containing allantoin as the active ingredient. A comprehensive analysis by HPLC-PDA-ESIMS led to the isolation and identification of 12 flavonoids and two phenylethanoid glycosides as the main constituents of the extract. Further investigation led to the isolation of six acetoxylated neo-clerodane diterpenes, including 20-acetylauropolin and 6-acetylteucjaponin A, along with four previously undescribed congeners. Some of the isolated diterpenes possess unusual structural features in the class of neo-clerodane diterpenes, such as a rare C-20 acetal function that forms an oxepane ring to C-7 of the trans-decalin core structure. The beneficial wound healing effect of T. polium is thought to be due to the combined effects of its polyphenolic constituents. Overall, the data support the use of T. polium as a wound healing agent in Algerian traditional medicine. The results have been published in the South African Journal of Botany, 137, 2021, and the Journal of Molecular Structure, 1284, 2023.
In conclusion, various approaches have been employed to investigate plant extracts and their secondary metabolites in the context of T cell-mediated autoimmunity, inflammatory skin diseases, such as psoriasis and atopic dermatitis, and wound healing. These diseases are challenging to treat due to their complex pathophysiology, involving numerous mechanisms and targets. However, plants, with their complex mixtures of phytochemical substances, can exert their effects on various targets, offering a potential advantage in treating multifactorial diseases. Complementary modes of action from structurally diverse substance classes may act synergistically on different target cell types or proteins, contributing to improved clinical outcomes. Therefore, preparations containing various phytochemical substances from plant extracts may have the potential as alternative treatment options for these complex disorders. This work provides insights into how extracts and pure substances from H. brachiata, C. sativus, and T. polium may exert beneficial effects in the treatment of multifactorial conditions such as T cell-mediated autoimmunity, inflammatory skin diseases, and wound healing.