Artemisinin is a sesquiterpene lactone compound with a peroxide group structure extracted from the leaves of Artemisia annua, a plant belonging to the Asteraceae family. The major derivatives of artemisinin include artemether, arteether, artesunate, dihydroartemisinin, and others. Artemisinin-based drugs are primarily used to treat malaria, but with further research, it has been discovered that artemisinin compounds also possess numerous other functions, such as anti-tumor, antibacterial, anti-parasitic, antipyretic, anti-inflammatory, and immune-modulating effects.

1. Anti-malarial Effect

Research has found that the mechanisms of action of artemisinin compounds in exerting anti-malarial effects include: ① With the catalysis of hemoglobin Fe2+, artemisinin undergoes peroxide bridge bond breakage, generating oxygen and carbon radicals. These radicals can bind to amino acid residues near organic alkylation sites, blocking the nutritional absorption of malaria parasites. At the same time, autophagy vesicles are rapidly formed to expel parasites lacking nutrition due to amino acid starvation, thus eliminating malaria parasites. ② Under the catalysis of a certain amount of Fe2+, artemisinin produces carbon-centered radicals. Activated artemisinin relies on its hydrophobic skeleton to target Plasmodium falciparum calcium ATP protein 6 (PfATP6), causing an increase in the concentration of calcium ions in the cytoplasm of malaria parasites, exerting an insecticidal and anti-malarial effect. ③ Artemisinin drugs also have a killing effect on malaria parasite gametocytes, inhibiting the development of gametocytes at different stages, rapidly killing the early gametocytes of malaria parasites, and simultaneously interrupting the development of immature gametocytes.

2.Bacteriostatic and Insecticidal Effects

Artemisinin-based injections have good prevention and treatment effects on various blood parasitic diseases in pigs, especially for diseases caused by Eperythrozoon suis, Toxoplasma suis, Babesia suis, and Trypanosoma suis. They also show good therapeutic effects on coccidiosis in chickens. Artemisinin and its derivatives can block the digestion, absorption, and metabolism of nutrients in the early stages of parasites, causing amino acid deficiency, ultimately leading to damage to the parasite's cell membrane and death. Further research has found that artemisinin and its derivatives can effectively inhibit the transcription and expression of mRNA related to the microneme genes of coccidian schizonts, thereby reducing the number of coccidian parasites. Additionally, artemisinin-based compounds can effectively promote the transformation of lymphocytes in the body, significantly increasing the number of red blood cells, white blood cells, and hemoglobin in the blood. Other studies have found that artemisinin can alter mitochondrial membrane potential, causing it to stagnate in the G0/G1 phase of the cell cycle, ultimately leading to the death of Leishmania donovani promastigotes.

3.Antipyretic and Anti-inflammatory Effects

Artemisinin and its derivatives also have positive effects on relieving heat stress. Research results show that compared to being in a heat stress environment, adding enzymatically hydrolyzed artemisinin to the feed can significantly improve the apparent utilization rate of crude fat, crude protein, and organic matter in the feed for broiler chickens, increase intestinal enzyme activity, and have a positive effect on relieving heat stress in chickens. Adding enzymatically hydrolyzed artemisinin to the feed of broiler chickens can alleviate the increase in blood pH, decline in production performance, and elevation of corticosterone, alanine aminotransferase, and aspartate aminotransferase in the serum caused by heat stress. It can also enhance antioxidant capacity and relieve heat stress by increasing the antioxidant enzyme activity in serum and liver and regulating the expression levels of related mRNAs. Some scholars have studied and compared the anti-inflammatory effects and molecular mechanisms of artemisinin and dihydroartemisinin: Dihydroartemisinin exerts anti-inflammatory activity by downregulating the expression of inducible nitric oxide synthase (iNOS) protein and inhibiting the release of inflammatory factors such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and inflammatory mediator NO from macrophages. On the other hand, artemisinin may exert its anti-inflammatory effects by metabolizing into dihydroartemisinin. Research has found that artemisinin can exert anti-inflammatory effects by regulating the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways.

4.Antitumor Effects

It is generally believed that the mechanisms of the antitumor effects of artemisinin compounds are: ① inhibiting angiogenesis; ② inducing apoptosis; ③ blocking cell cycles; ④ Fe2+-mediated cytotoxicity; ⑤ being related to oncogenes and tumor suppressor genes; ⑥ acting on specific target proteins; ⑦ counteracting multidrug resistance. Research has found that artemisinin derivatives can inhibit the proliferation and promote apoptosis of cervical cancer HeLa cells in vitro, and their mechanisms are related to downregulating the phosphorylation level of extracellular regulated protein kinases 1/2 (ERK1/2) and upregulating the phosphorylation level of p38 protein, respectively. Dihydroartemisinin inhibits the proliferation of human glioma U251 cells by inhibiting the Wnt/β-catenin pathway, thus inhibiting the epithelial-mesenchymal transition (EMT) process. The mechanism of inhibiting the proliferation of pancreatic cancer JF-305 cells may be related to the mitochondrial apoptosis pathway caused by the increased level of reactive oxygen species (ROS) in JF-305 cells. Artesunate may induce apoptosis in human gastric cancer HGC27 cells by inhibiting the activation of the Wnt/β-catenin signaling pathway.

5.Immunomodulatory Effects

Research results indicate that artemisinin and its derivatives not only act directly on T lymphocytes but also significantly inhibit the proliferation of mouse spleen lymphocytes induced by the T lymphocyte mitogen ConA. Artesunate, a derivative of artemisinin, can reduce the brain edema index and blood-brain barrier permeability in rats, hinder the downregulation of the expression of endothelial cell tight junction proteins Occludin and ZO-1, while alleviating early brain tissue damage in rat models after subarachnoid hemorrhage and improving neurological function. Studies have found that artemisinin has immunomodulatory effects on experimental autoimmune myasthenia gravis (EAMG) rats, and its mechanism is related to reducing serum R97-116 antibody levels directly or indirectly, inhibiting the secretion of proinflammatory factors such as gamma interferon (IFN-γ) and IL-17 from lymph node mononuclear cells. Artemisinin can significantly inhibit the proliferation of T lymphocytes induced by ConA, reduce the organ index of immune organs in type IV or delayed-type hypersensitivity (DTH) model mice, and reduce ear swelling, suggesting that artemisinin exerts an immunosuppressive effect by downregulating cellular immune responses. Additionally, artemisinin and its derivatives have good therapeutic effects on systemic lupus erythematosus (SLE). Studies have found that dihydroartemisinin increases the DNA methylation level of CD4+ T cell genomes in SLE mice by upregulating DNA methyltransferase 1 (DNMT1) expression and downregulating Gadd45a expression, thereby reducing the production of autoimmune antibodies and playing a role in treating SLE.

6.Immunomodulatory Effects

Research findings suggest that artemisinin and its derivatives can not only act directly on T lymphocytes but also significantly inhibit the proliferation of mouse spleen lymphocytes induced by the T-lymphocyte mitogen ConA. The artemisinin derivative artesunate can reduce the brain edema index and blood-brain barrier permeability in rats, hinder the downregulation of the expression of endothelial cell tight junction proteins Occludin and ZO-1, and simultaneously alleviate early brain tissue damage in rat models after subarachnoid hemorrhage, thereby improving neurological function. Studies have discovered that artemisinin exhibits immunomodulatory effects on experimental autoimmune myasthenia gravis (EAMG) rats, and its mechanism is related to reducing serum R97-116 antibody levels directly or indirectly, inhibiting the secretion of proinflammatory factors such as gamma interferon (IFN-γ) and IL-17 from lymph node mononuclear cells. Artemisinin can significantly inhibit the proliferation of T lymphocytes induced by ConA, reduce the organ index of immune organs in type IV or delayed-type hypersensitivity (DTH) model mice, and alleviate ear swelling. It is speculated that artemisinin exerts an immunosuppressive effect by downregulating cellular immune responses in the body. Furthermore, artemisinin and its derivatives have demonstrated good therapeutic effects on systemic lupus erythematosus (SLE). Research has found that dihydroartemisinin increases the DNA methylation level of CD4+ T cell genomes in SLE mice by upregulating the expression of DNA methyltransferase 1 (DNMT1) and downregulating the expression of Gadd45a, thereby reducing the production of autoimmune antibodies and playing a role in treating SLE.

Although artemisinin-based drugs are highly effective against malaria and possess other pharmacological functions, they often face challenges in clinical applications such as poor solubility, low bioavailability, high first-pass effect, high malaria parasite relapse rate, and frequent dosing. Therefore, the research on dosage forms of artemisinin-based drugs has become a current hotspot. With the advancement of pharmaceutical technology, many new techniques have been applied to the formulations of artemisinin and its derivatives, providing potential avenues for the multifaceted therapeutic effects of artemisinin, including nano-formulations, solid dispersions, inclusion complexes, microemulsions, and percutaneous drug delivery systems.

1. Nano-formulations

Nano-drug delivery systems refer to a series of novel, minute drug delivery systems with particle sizes at the nanometer level. Based on the specificity of their dispersive motion status and properties, nano-drug delivery systems primarily include nanoparticles, liposomes, nanoemulsions, polymeric micelles, and nanosuspensions. These systems possess excellent tumor targeting capabilities, long in vivo circulation time, easy cellular uptake, controllable drug release, improved drug solubility, and increased drug stability.

① Nanoemulsion is a stable and transparent colloidal dispersion system composed of surfactants, cosurfactants, oil phase, and aqueous phase, with a particle size ranging from 10 to 100 nm. In a study on the treatment of bovine and sheep theileriosis and babesiosis using artesunate, polysorbate-80 was chosen as the emulsifier, n-butanol as the cosurfactant, and ethyl oleate as the oil phase to prepare artesunate nanoemulsion injections. This resolved issues such as the limited solubility of artesunate in water, the inability to avoid the first-pass effect in the liver when taken orally, the instability of commercially available artesunate sodium salt, and inconvenience in clinical use.

② Nanoparticles (NPs), made from natural or synthetic polymeric materials, are solid colloidal particles with sizes ranging from 1 to 100 nm, including nanospheres and nanocapsules. Active components (drugs, bioactive materials, etc.) are dissolved, encapsulated within the particles, or adsorbed onto their surfaces. Artesunate was formulated into biodegradable nanoparticles suitable for human use using a modified self-emulsifying/solvent diffusion method. Tumor cell surface-specific recognizable ligands, Tf, were combined with the drug-loaded nanoparticles to achieve targeted therapy for tumor tissues (cells). Animal studies have shown that this novel nano-formulation exhibits blood and bone marrow targeting. The preparation of nanocapsules loaded with artemether using the nascent microcrystalline method addresses the issues of insolubility, rapid metabolism, and low utilization of artemether, significantly enhancing its efficacy.

③ Nano-liposomes. Nanostructured lipid carriers (NLC) are a novel nano-drug delivery system with particle sizes ranging from 50 to 1000 nm. They are solid colloidal drug delivery systems that encapsulate drugs in lipid cores using a certain proportion of liquid oils or other different lipids (such as lecithin, triglycerides, etc.) as carriers. Some scholars have studied the inhibitory effect of dihydroartemisinin nano-liposomes and dihydroartemisinin suspensions on liver cancer cell lines using animal tumor models. They confirmed that dihydroartemisinin nano-liposomes have a stronger inhibitory effect on the proliferation of leukemia cells K562 and glioma cells U87 compared to regular suspensions, providing a basis for the development of highly effective and low-toxicity dihydroartemisinin anticancer drugs. Intervention with artesunate nano-liposomes was performed to regulate the expression of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (VEGFR2) in HepG2 cells, demonstrating that artesunate nano-liposomes can inhibit tumor angiogenesis to achieve anti-tumor effects, which is stronger than the raw artesunate drug, suggesting potential value in the treatment of liver cancer.

2.Solid Dispersion

Solid dispersion refers to a solid material in which a drug is highly dispersed in a suitable carrier material, resembling a liquid system. Solid dispersions allow drugs to exist in an amorphous, microcrystalline, molecularly dispersed, or colloidally dispersed state with a high degree of dispersion. When in contact with the fluid in the gastrointestinal tract, the dissolution rate accelerates, leading to faster drug absorption and improved bioavailability. Based on the different properties of the carrier and drug release characteristics, solid dispersions are further classified into immediate-release solid dispersions, sustained- or controlled-release solid dispersions, and enteric-coated solid dispersions.

① Immediate-release solid dispersions are prepared using hydrophilic carrier materials. Drugs are highly dispersed in the carrier material, and due to the hydrophilic nature of the carrier, the drug exhibits good wettability, enabling rapid release, improved solubility, accelerated dissolution rate, and higher bioavailability. This is an excellent solution for insoluble drugs. For example, some scholars have prepared solid dispersions of dihydroartemisinin, a poorly water-soluble drug, using polyvinylpyrrolidone as the carrier. Through comparative detection using X-ray diffraction (XRD) and differential scanning calorimetry (DSC), it was found that dihydroartemisinin existed in an amorphous complex state, with its solubility increased by 50 times compared to the raw drug, significantly enhancing its biological activity.

② Sustained- or controlled-release solid dispersions are prepared using water-insoluble or lipid-soluble carriers. This system can be viewed as a dissolution-diffusion system.

③ Enteric-coated solid dispersions are made using enteric carriers to facilitate drug release in the intestine. Due to the specific pH conditions for dissolution of the carrier material, colonic-targeted solid dispersions may not release or release minimally in the stomach and small intestine, achieving rapid drug release only when reaching the colon.

3.Cyclodextrin Inclusion Complex

A cyclodextrin inclusion complex refers to the construction of a complex assembly with intricate structure and specific functions by introducing drug molecules as building blocks into the supramolecular system of cyclodextrin. This allows poorly soluble drugs to be encapsulated by cyclodextrin, enhancing their solubility and stability in water, thus improving the bioavailability of the drugs. By adopting evaporation-precipitation methods, both artemisinin nanoparticles and artemisinin-β-cyclodextrin inclusion complexes have been successfully prepared, both of which can significantly increase the solubility and dissolution rate of artemisinin. Some scholars have synthesized artesunate-cyclodextrin conjugate prodrugs and used the MTT method to evaluate their cellular activity, demonstrating that this series of new compounds exhibit good anti-colorectal cancer activity with a certain degree of targeting.

4.Transdermal Drug Delivery Systems

Transdermal drug delivery systems refer to formulations that deliver drugs through the skin. Currently, two types of formulations are available: ointments and pressure-sensitive adhesive patches. These formulations allow drugs to rapidly penetrate the skin and enter the blood circulation, exerting systemic therapeutic effects while avoiding the "first-pass effect" of the liver and destruction in the gastrointestinal tract. Some scholars have developed transdermal patches with soluble artemether microneedles. Compared to intramuscular injection, these patches provide similar bioavailability but with more stable blood drug concentrations, creating a new anti-malarial formulation with sustained-release effects.

References:

[1] Li Haibo, Qin Dapeng, Ge Wen, Wang Zhenzhong, Cao Liang, Xiao Wei, Yu Yang, Yao Xinsheng. Research Progress on Chemical Constituents and Pharmacological Effects of Artemisia annua L. [J]. Chinese Traditional and Herbal Drugs, 2019, 50(14): 3461-3470.

[2] Zhang Wenfei, Guan Wutai, Chen Fang, Zhang Shihai, Deng Yuelin, Shi Hequn, Xu Guohuan. Research Progress on the Application of Artemisinin and Its Derivatives in Animal Husbandry and Poultry Production [J]. Feed Industry, 2019, 40(15): 22-27. DOI: 10.13302/j.cnki.fi.2019.15.004.

[3] Li Wenting, Zhang Guoli, Zhang Ruiwu, Duan Guolei, Yang Zhaoxiang. Research Progress on New Drug Forms of Artemisinin Drugs [J]. Rural Economy and Science-Technology, 2019, 30(12): 299-300.

About the Author

Xiaomichong, a pharmaceutical quality researcher, has been committed to pharmaceutical quality research and drug analysis method validation for a long time. Currently employed by a large domestic pharmaceutical research and development company, she is engaged in drug inspection and analysis as well as method validation.