Advances on Ethnobotanical, Phytochemical, and Preclinical Studies of Strobilanthes crispus and Strobilanthes cusia (Acanthaceae) for Drug Development Purpose: A Narrative Review

Introduction

Plant-derived drugs have attracted considerable interest, and the development of phytopharmaceuticals has prevailed through ethnopharmacological approaches. Plants of the genus Strobilanthes (family Acanthaceae) are among the most widespread vegetation types in tropical countries, particularly in Southeast Asia. The genus Strobilanthes comprises approximately 350 species, many of which were used in indigenous medicine.¹ The name Strobilanthes originated from strobilos, meaning “cone”, and anthos, meaning “flower”, in Latin.^2,3 The Strobilanthes genus shrubs are characterized by their hapaxanthic or monocarpic life cycle, meaning they complete their entire reproductive process by a massive flowering and fruiting only once at the end of life before dying.^4,5 According to Plants of the World Online, an online database published by the Royal Botanic Gardens, Kew, there are 469 plants with accepted names that belong to the genus Strobilanthes.⁶ More than 100 metabolites have been reported to be present in Strobilanthes crispus (L). Blume (with homotypic synonyms of Hemigraphis crispa (L). T. Anderson, Ruellia crispa L., and Sericocalyx crispus (L). Bremek., https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:55623-1) (Figure 1a) and Strobilanthes cusia (Nees) Kuntze (with homotypic synonyms of Baphicacanthus cusia (Nees) Bremek. and Goldfussia cusia Nees; https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:55627-1) (Figure 1b). As described, the native range of S. crispus extends from Java to the Lesser Sunda Islands. This plant grows primarily in the wet tropical biome, while the native range of S. cusia extends from the East Himalaya to South China, Indo-China, and Taiwan. It is an annual or subshrub and grows primarily in the temperate biome.⁶

Figure 1 (a) Strobilanthes crispus (Chinese black face general or pecah beling) and (b) Strobilanthes cusia (Assam indigo or Chinese rain bell) of the family Acanthaceae.

The metabolites, including alkaloids, fatty acids and derivatives, flavonoids and flavonoid glycosides, phenolic acids, sterols, and terpenoids, are the most abundant and predominant phytochemicals found across various Strobilanthes species.^7–18 Considering the abundance of phytochemical metabolites in these plants, we searched for relevant scientific information to understand why S. crispus and S. cusia were indigenously used to treat various diseases, as well as the mechanisms underlying their pharmacological properties, by reviewing ethnobotanical, phytochemical, and in silico, in vitro, and in vivo studies of these plants.

Methods

This narrative review is intended to provide thorough information on the pharmacological activities of Strobilanthes plants, particularly S. crispus and S. cusia. Strobilanthes is the second largest genus within the family Acanthaceae. Articles were searched in PubMed and Scopus databases. The PubMed database contains approximately 39 million citations and abstracts in the health science field (https://pubmed.ncbi.nlm.nih.gov/about/), while the Scopus database has indexed thousands of health science titles.¹⁹ The keywords used in the PubMed search box were “Strobilanthes” filtered to publication period from 2015 to 2025, free full-text, and article language English, resulting in 50 articles. Similarly, the keywords used in the Scopus search box within articles, abstracts, and the keywords box were “Strobilanthes”, with publication period limited to between 2015 and 2025, subject area limited to “Medicine” and “Pharmacology, Toxicology, and Pharmaceutics”, document type limited to “Article”, keyword limited to “plant extracts”, and language limited to “English”, resulted in 36 papers. Articles were further screened, and only those reporting pharmacological or biological activities, phytochemical or nutritional compositions, and toxicity studies of the Strobilanthes genus were included to ensure scientific rigor and were thoroughly analyzed in this review. Additional articles were searched in Google Scholar to comprehend the discussion.

Ethnobotanical Study

Ethnobotany links between people and plants, including edible plants, medicinal plants, and plants for other utilizations, such as for clothing, shelter, fuel, and furniture. Therefore, ethnobotanical studies are useful in identifying, disseminating, and documenting indigenous knowledge of plants for human and livestock diseases, thus bridging traditional healing practices with research-based pharmacology. Identification and documentation of the plants are thought to be effective in comprehending how diverse indigenous people interact with bioresources, thus gaining benefits for medicinal purposes.²⁰ There were five articles in PubMed and one in Scopus, reporting on ethnobotanical or ethnoveterinary studies of S. cusia and S. crispus. Of those, three studies were conducted in East Asia (China), and two studies in Southeast Asia (Malaysia and Thailand). In these folklore ethnobotanical surveys, the plants were used as colorants, edible plants, and as natural medicines for cattle.^21–25

In the first article, conducted from September 2015 to November 2018, 46 elderly Landian Yao informants (mostly females) from Southwest China were interviewed. The Landian Yao, which in a literal manner refers to blue clothes Yao, is part of the Hmong-Mien language family distributed across Southwest and Southern China, Laos, Thailand, and Vietnam. This study revealed that S. cusia, known as Assam indigo or Chinese rain bell, with its indigo-colored leaves, was the main source of high indigotin (an indole alkaloid natural blue pigment) for clothing dye. S. cusia has been planted in their home gardens by their ancestors.²¹ The traditional indigo dye extraction includes collecting leaves, soaking them in water until they rot and produce coarse indigo, then refining and drying the resulting dye. In the soaking step, an important chemical reaction occurs, in which endogenous β-glucosidase hydrolyzes indole glycoside to produce indole phenol, the source of indigo and indirubin. Modern pharmacological studies have shown that indigotin exhibits anti-inflammatory, antioxidant, antibacterial, and immunomodulatory properties.²⁶

The second article described an ethnoveterinary survey conducted in Baiku Yao communities in Southwest China. UNESCO has recognized the Baiku Yao people as an ethnic group with an intact culture. A total of 53 informants (27 females and 26 males) were interviewed. This study revealed that 39 ethnoveterinary plant species belonging to 27 families and 38 genera were traditionally used by the Baiku Yao people, among which were the leaves of S. cusia to treat external wounds in cattle.²²

In the third article, which was conducted in Telimau, Bukit Terang, and Kampung Sat, in Malaysia, 24 informants were recruited and interviewed using a semi-structured method and ethnobotanical assessment. This study revealed that the most commonly consumed wild edible plants were S. crispus, Sauropus androgynus (L). Merr., Manihot esculenta Crantz, and Diplazium esculentum (Retz). Sw.²³

An ethnobotanical study of plant colorants used by the Karen ethnic people in Chiang Mai province in Thailand, by interviewing 113 informants, revealed that 52 plant species, belonging to 49 genera and 30 families, have been used for dyeing, mostly by hot water extraction. The leaves of S. cusia were described as the source of blue (fidelity level of 70), green (fidelity level of 2), and grey (fidelity level of 2) dyes. The levels of indigotin in S. cusia range from 4 to 36%.²⁴ In addition, another ethnobotanical study has been conducted in 18 districts of Ganzhou, China, from 2016 to 2018. Information was collected through semi-structured interviews, personal conversations with practitioners, and direct observations using standard methods, which revealed 93 plants belonging to 84 genera in 62 families, among which S. cusia was listed.²⁵

Phytochemical and Nutritional Composition

Of the Strobilanthes genus plants, S. crispus has been the most explored for its phytochemical (tabulated in Table 1) and nutritional profiles. Most of the studies described Malaysia as the location of plant sampling, presumably because the indigenous habitat of this plant is the wet tropical biome.^7–14,17 Only a few other Strobilanthes species have been investigated for their phytochemicals, such as Strobilanthes urens,¹⁵ Strobilanthes kalimantanensis,¹⁶ and Strobilanthes cusia,¹⁸ which narrated India, Indonesia, and Thailand as the locations of sampling.^15,16,18 Leaves were the most studied part for their bioactive metabolites, contributing to their numerous pharmacological activities.^7–18

Table 1 Metabolites Isolated from the Strobilanthes Plants of Family Acanthaceae (in Alphabetical Order) and Total Flavonoids and Total Phenols of the Extract

Briefly reported in a study, the aqueous extract of S. crispus leaves collected from Kelantan, Malaysia, exhibited high values of total phenol content (TPC) of 12.62 mg gallic acid equivalent (GAE)/g extract, total flavonoid content (TFC) of 7.44 mg quercetin equivalent (QE)/g extract, and total saponin content (TSC) of 44.7 mg diosgenin (C₂₇H₄₂O₃) equivalent (DE)/g extract. The ethanol extract contained flavonoids such as, apigenin (C₁₅H₁₀O₅), catechin (C₁₅H₁₄O₆), kaempferol (C₁₅H₁₀O₆), naringenin (C₂₁H₂₂O₉), quercetin (C₁₅H₁₀O₇), and rutin (C₂₇H₃₀O₁₆), and phenolic acids such as, caffeic acid (C₉H₈O₄), chlorogenic acid (C₁₆H₁₈O₉), ferulic acid (C₁₀H₁₀O₄), and gallic acid (C₇H₆O₅).⁷ The phytochemical profile analysis of the leaves from Seremban, Malaysia, revealed a TPC ranging between 10.87 and 12.22 mg GAE/g extract, phytosterols such as α-tocopherol (C₂₉H₅₀O₂), campesterol (C₂₈H₄₈O), desmosterol (C₂₇H₄₄O), lanosterol (C₃₀H₅₀O), β-sitosterol (C₂₉H₅₀O), and stigmasterol (C₂₉H₄₈O), volatile compounds such as 2-hexen-1-ol (C₆H₁₂O), 2-hexenal (C₆H₁₀O), 1-octen-3-ol (C₈H₁₆O), and benzaldehyde (C₇H₆O), and terpenoids such as linalool (C₁₀H₁₈O), p-cymene (C₁₀H₁₄), limonene (C₁₀H₁₆), eucalyptol (C₁₀H₁₈O), and isopulegol (C₁₀H₁₈O).⁸ Three compounds, namely 1-heptacosanol (C₂₇H₅₆O), tetracosanoic acid (C₂₄H₄₈O₂), and stigmasterol (C₂₉H₄₈O), were isolated from the hexane extract of air-dried leaves of S. crispus collected in Malaysia. Four fatty acid esters, namely β-amyrin (C₃₀H₅₀O), and terpenoids, namely taraxerone (C₃₀H₄₈O) and taraxerol (C₃₀H₅₀O), were found in the dichloromethane extract, and 4-acetyl-2,7-dihydroxy-1,4,8-triphenyloctane-3,5-dione and stigmasterol β-D-glucopyranoside were present in the methanol extract.⁹ Fresh leaves and stems of S. crispus collected in Sabah, Malaysia, contained squalene, vitamin E (C₂₉H₅₀O₂), γ-sitosterol (C₂₉H₅₀O), and campesterol (C₂₈H₄₈O),¹⁰ while the leaves collected from Bertam Ulu, Melaka, Malaysia, contained a TPC of 159.85 mg GAE/g extract and TFC of 955.47 mg rutin equivalent (RE)/g extract. HPLC-ESI-QToF-MS/MS identified 20 polyphenolic compounds, among which were bidenoside B (C₂₄H₃₀O₁₀), torosaflavone C (C₂₁H₂₀O₈), euchrenone b3 (C₂₇H₂₆O₇), lupinisol C (C₂₅H₂₆O₇), and xanthoangelol C (C₂₂H₂₂O₅).¹¹ The leaves harvested at the Horticulture Unit of University Putra Malaysia contained potassium, calcium, sodium, iron, and phosphorus minerals and vitamins such as vitamin C (C₆H₈O₆), B1 (C₁₂H₁₇N₄OS), and B2 (C₁₇H₂₀N₄O₆).¹² Another study on the proximate and mineral composition of S. crispus collected in Malaysia revealed 4.2% total ash, 4.6% fiber, less than 0.1% fat, 2.9% protein, 25.6 kcal/100 g energy, and 81.6% moisture. Potassium and calcium minerals were found to be abundant, at 295 mg/100 g and 176 mg/100 g, respectively.¹³ S. crispus leaves harvested from the same horticulture unit contained apigenin (C₁₅H₁₀O₅), catechin (C₁₅H₁₄O₆), kaempferol (C₁₅H₁₀O₆), naringenin (C₂₁H₂₂O₉), epicatechin (C₁₅H₁₄O₆), rutin (C₂₇H₃₀O₁₆), myricetin (C₁₅H₁₀O₈), and luteolin (C₁₅H₁₀O₆).¹⁴ The leaves of S. crispus collected at Kuching, Sarawak, Malaysia, extracted using ethanol, revealed a TPC of 1.88 mg GAE/g and TFC of 0.25 mg RE/g defatted extract.¹⁷

Intriguingly, another species, S. urens, collected from Kalgi village, Kalaburagi District, Karnataka, India, also showed promising nutritional composition, including 28.62% protein, 17.85% carbohydrates, 12.0% lipids, 14.26% total ash, and 2.35% moisture content. The TPC in the extracts ranged from 199.25 to 270.50 mg GAE/g extract, and TFC from 135.57 to 260.57 mg QE/g extract. Alkaloids and tannins were also present in the extracts.¹⁵ The dry leaves of S. kalimantanensis from West Kutai, Kalimantan, Indonesia, were reported to contain a total ash content of 7.83%. Trans-anethole (C₁₀H₁₂O) was successfully isolated from the leaf extract at a concentration of 23.0% using a GC-MS analysis.¹⁶ It should be taken into consideration that obtaining the phytochemical profiles is necessary, as many studies have reported a good correlation between the levels of phytochemicals of plant extracts and their biological activities.^27–29

In vitro Biological Activity Studies

Radical-Scavenging Activity

S. crispus leaf extracts, regardless of the geographical location of plant harvesting, extraction methods, and solvents (ethanol, methanol, acetone, and chloroform), have been reported to exhibit strong radical-scavenging activity. Different reagents have been used to assay the radical-scavenging activity, such as 2,2′-azinobis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS), ferric-reducing antioxidant power (FRAP), Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), and 2,2-diphenyl-1-picrylhydrazyl (DPPH).^7,8,11,13,17 Free radicals have dual effects: (1) in physiological cell signaling pathways that regulate vascular tone, immune response, and apoptosis; and (2) cause numerous degenerative diseases such as cancer, acute inflammation, hypertension, diabetes mellitus, acute kidney injury, atherosclerosis, Alzheimer’s disease and Parkinson’s disorders, aging, and cardiovascular disorders. The radical-scavenging properties of plant antioxidants contribute to the inhibition of excessive lipid oxidation and the prevention of cell damage in the body.^30,31

Anticancer Activity

The anticancer activity of S. crispus leaf extract, collected from different geographical locations, was confirmed in innumerable human cancer cells, such as the human cervical cancer cells (HeLa),⁷ human breast cancer cells MD Anderson-Metastatic Breast-231 (MDA-MB-231),^32–36 human breast cancer cells (MCF-7),³⁶ human breast cancer cells (T47D),³⁶ human colorectal adenocarcinoma cells (HT29),³⁴ human cervical cancer cells (C33A),³⁶ human colorectal carcinoma cells (HCT116),³⁶ human monocytic leukemia (U937),³⁶ human liver cancer cells (HepG2),³³ human liver cancer cells (SNU-182, SNU-449),³⁶ human ovarian epithelial cancer cells (OVCAR-5, PA-1, SK-OV-3)³⁶ human uterine cancer cells (MES-SA/DX5),³⁶ and mouse breast cancer cells (4T1).³⁷ Additionally, the plant extract was also studied for its anti-carcinogenesis activity via inhibition of CYP3A4 and CYP2E1, the subfamilies of cytochrome P450 that play a vital role in metabolizing drugs, toxins, and endogenous compounds.³⁸ The key factor in the development of cancer is cellular oxidative stress. The accumulation of intracellular reactive oxygen species (ROS) may lead to deoxyribonucleic acid (DNA) damage, instigate inflammatory responses, impede cellular homeostasis, and eventually cause carcinogenesis.³⁹

Anti-Inflammatory, Immunomodulatory, and Wound-Healing Activities

The anti-inflammatory, immunomodulatory, and wound-healing activities of Strobilanthes species extract have been reported in two articles. In the first article, S. crispus leaves collected at Kuching, Sarawak, Malaysia, which were extracted using ethanol, were co-incubated with the pseudo-wound in OUMS-36T-4F human fibroblast cells, revealing a full recovery of the wound after 24 h of incubation.¹⁷ Another species, Strobilanthes cusia, which was collected in Putian City, Fujian Province, China, and extracted with MeOH, contained indole alkaloids, indigodoles A, C, and D, and has shown inhibition towards interleukin 17A (IL-17A) production during the polarization of T helper cells 17 (Th17) at an EC₅₀ of 2.16 μg/mL, or after the polarization at an EC₅₀ of 5.99 μg/mL, without cytotoxicity towards Th17 cells.⁴⁰ Recent investigations have associated Th17/IL-17 with systemic autoimmune diseases, including their role in metabolic dysfunctions, where an excessive pathogenic Th17 cell population and a suppression in CD69+ T regulatory cells intensify low-grade inflammatory conditions.⁴¹ Dysregulation of Th17 cell responses serves as a basis of multiple inflammatory and autoimmune diseases. More specifically, Th17 cells are regulated by IL-17A, which attaches to its binding site on Th17 cells, activating the intracellular nuclear factor-kappaB (NF-κB) signaling pathway and subsequently stimulating the production of IL-24.⁴²

Antidiabetic Activity

The antidiabetic activity of Strobilanthes species extract has been reported in two studies, although not in Strobilanthes crispus or Strobilanthes cusia. In the first article, the whole plant of S. glutinosus was collected in Abbottabad, Pakistan, extracted using methanol, and fractionated with n-hexane, exhibiting a strong inhibitory potential against α-amylase and α-glucosidase.⁴³ Another species of Strobilanthes, as described in the second article, such as the fresh leaves of S. cordifolia, which were collected in the Salem district of Tamil Nadu, India, synthesized in iron and copper nanoparticles, also exhibited inhibitory effects on α-amylase and α-glucosidase enzymes,⁴⁴ thus confirming the antidiabetic effects of the genus Strobilanthes plants. These two enzymes, α-amylase and α-glucosidase, are involved in the degradation of carbohydrates into monosaccharides and disaccharides, leading to an elevation in blood glucose level.⁴⁵

Antimicrobial Activity

S. crispus and S. cusia extracts have been reported to have inhibitory activity against various bacteria, such as Pseudomonas aeruginosa, Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus mutans, and Escherichia coli, against the human coronavirus NL63 (HCoV-NL63), and against the influenza virus. A study reported that S. crispus leaves collected at Kuching, Sarawak, Malaysia, exhibited antibacterial properties against P. aeruginosa on Mueller–Hinton agar.¹⁷ In another study, the leaves of S. cusia were harvested from Guangdong, China, and demonstrated antibacterial effects against clinical penicillin-resistant S. pneumoniae (PRSP) by disrupting cell wall integrity and capsule thickness of the PRSP. Tryptanthrin, an indole alkaloid isolated from the leaf extract, showed the potential to effectively inhibit PRSP F3983 with an MIC of 25 µg/mL. The MIC value of the ethanol extract of the leaves against S. aureus ATCC 29213 and S. pneumoniae ATCC 49619 was 100 μg/mL and 200 μg/mL.⁴⁶ Tryptanthrin isolated from S. cusia leaf was also reported in another study to prevent human coronavirus NL63 (HCoV-NL63) replication by blocking viral ribonucleic acid (RNA) genome synthesis and papain-like protease 2 activity.⁴⁷ The antibacterial activities of synthesized S. crispus-mediated silver nanoparticles (SC-AgNPs) against Streptococcus mutans, Escherichia coli, and P. aeruginosa were also reported.⁴⁸ Furthermore, strobilanthes A, an isocoumarin metabolite which has been isolated from S. cusia cultivated in Guizhou, China, exhibited anti-influenza virus activity in vitro.⁴⁹

Other in vitro Pharmacological Activity Studies

Antiplatelet aggregation using collagen-induced aggregation in human whole blood and the blood coagulation effects of S. crispus collected from the National University of Singapore (NUS) medicinal plant garden were recently reported by Zareisedehizadeh et al (2025). These findings are beneficial for preventing heart attacks and ischemic stroke.⁵⁰ Intriguingly, a low probability of inhibition by S. crispus on CYP2B6, CYP2C19, CYP2D6, and CYP3A4, the cytochrome P450 subfamilies involved in tamoxifen metabolism, was reported. These findings confirm the potential of S. crispus as an adjuvant for breast cancer treatment.⁵¹

In vivo Biological Activity Studies

Anticancer and Chemopreventive Activity

In accordance with the in vitro anticancer results of S. crispus leaf extract, the in vivo anticancer properties of S. crispus were reported in four articles as follows:

S. crispus leaf extract showed protection against colorectal cancer by inhibiting oxidative damage and the following apoptotic cascade, decreasing total colonic aberrant crypt foci formation, malondialdehyde (MDA), and lactate dehydrogenase (LDH), increasing superoxide dismutase (SOD), upregulating adenomatous polyposis coli (APC), BCL2 associated X (Bax), and solute carrier family 24 member 3 (Slc24a3), and downregulating defensin alpha 24 (Defa24) and Bcl-2 in azoxymethane-induced rats.³² S. crispus exhibited antitumorigenic immunogenicity by inducing a significant increase in major histocompatibility complex (MHC) class I and class II molecules, CD4⁺, CD8⁺, and IL-2⁺ cells infiltration, and decreasing the number of CD68⁺ macrophages in the 4T1 cell-induced mammary carcinoma mouse model.³⁷ The active fraction of S. crispus containing lutein and β-sitosterol was described to significantly suppress the total tumor burden and secondary tumor development in metastatic breast cancer without significant toxicities in the 4T1-induced mouse mammary carcinoma model. Histomorphological examination confirmed the safety of the S. crispus fraction.⁵² The in vivo anticancer activity of S. crispus leaves harvested in Malaysia was further confirmed in a study by activating the immune system in rats bearing N-methyl-N-nitrosourea (NMU)-induced mammary tumors, and additionally supports the traditional use of S. crispus leaves to boost the immune system.⁵³ Signaling pathways that are responsible for proliferation, cell cycle arrest, apoptosis, and angiogenesis are thought to be connected with the actions of phytochemicals, such as phenolics, flavonoids, alkaloids, and terpenoids contained in the leaves.⁵⁴

Antidiabetic Activity

The antidiabetic properties of Strobilanthes leaf extract were reported in four studies, two of which were those of S. crispus, and the other two were those of S. sarcorrhiza and S. cuspidata. One study described that S. crispus leaves collected in Pulau Penang, Malaysia, increased lipolysis and fat oxidation in obese mice fed high-fat and low-fat diets, without altering food intake, body weight, and abdominal adipose tissue weight.⁵⁵ Additionally, S. crispus leaves collected in Yogyakarta, Indonesia, at a dose of 16.8% extract/day for 14 days of administration significantly reduced blood glucose levels and improved the lipid profiles in streptozotocin (STZ)-induced diabetes in rats.⁵⁶

Intriguingly, the root of another Strobilanthes species procured in Panan, China, namely S. sarcorrhiza, demonstrated a prevention of diabetic nephropathy in STZ-induced mice by regulating NF-kappaB/IL-1β signaling pathway and glycerophospholipid metabolism. S. sarcorrhiza root extract normalized blood glucose and lipid levels, reduced ALT, creatinine, urea, IL-1β, and IL-17 in the serum, improved pathological damage and fibrosis in the kidneys, and suppressed vascular endothelial growth factor (VEGF), laminin, TNF-α, and NF-kappaB expression in kidney tissue.⁵⁷ S. cuspidata leaves collected at Niligiris, India, at doses of 150 and 300 mg/kg body weight significantly reduced the blood glucose level within 60 min after a glucose load in normoglycemic rats. After 14 days of daily treatment with the extract at a dose of 150 and 300 mg/kg body weight, a significant dose-dependent decrease in blood sugar levels was observed by 38 and 41%, respectively.⁵⁸

Other in vivo Pharmacological Activity Studies

Only one article has described the in vivo anti-inflammatory activities of the Strobilanthes plants, but none in S. crispus or S. cusia. The anti-inflammatory and anti-arthritic activities of lupeol and 19α-H lupeol isolated from S. callosus and S. ixiocephala roots have been reported in India;⁵⁹ however, this publication has not been indexed in the PubMed and Scopus databases. The hepatoprotective activity of S. kunthianus obtained from Nilgiris, India, has also been reported.⁶⁰ In this study, the methanol extract of S. kunthianus normalized the levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, triglyceride, total cholesterol, total bilirubin, and thiobarbiturate-reacting substances, and increased the levels of creatinine, total protein, albumin, catalase, and superoxide dismutase in serum in carbon tetrachloride-induced hepatotoxicity in Wistar albino rats.⁶⁰

In silico Biological Activity Studies

Few studies have described the in silico biological activity of phytochemicals in Strobilanthes plants. In one study, six phytochemicals obtained from GC-MS analysis, namely lupeol, beta-amyrin, stigmasterol, gamma sitosterol, 9,12-octadecadienoic acid, and n-hexadecanoic acid, were molecularly docked towards α-glucosidase and α-amylase enzymes, and their binding affinities were compared to the standard acarbose. This study revealed that β-amyrin, stigmasterol, and sitosterol bind strongly to α-glucosidase and α-amylase, leading to their potential in altering carbohydrate degradation.⁴³ In another article, tryptanthrin isolated from the leaf extract was reverse-docked to 623 target proteins obtained from the database of S. pneumoniae, resulting in 63 top proteins, among which β-galactosidase, acetylglucosaminidase, β-hexosaminidase, and α-fucosidase were selected. To provide sufficient space for ligand-free movement, the grid boxes of the molecular docking simulation were constructed to completely cover the binding pockets of S. pneumonia proteins. Tryptanthrin occupies the binding pockets of these four proteins by building hydrogen bonds or aromatic stacking interactions, thus confirming its antibacterial properties by disrupting the growth of S. pneumoniae.⁴⁶

Metabolites and Their Mechanism of Action

Strobilanthes crispus and S. cusia are known for their metabolites, including alkaloids, fatty acids and derivatives, flavonoids and flavonoid glycosides, phenolic acids, sterols, and terpenoids.^7–18 These bioactive metabolites contribute to the plants’ wide range of biological and pharmacological effects.

One of the bioactive metabolites, namely tryptanthrin, which is a natural, indolo-quinazoline alkaloid primarily isolated from S. cusia, has been reported for its strong cytotoxicity against tumor and microbial cells. This alkaloid and its derivatives inhibit the cell cycle of tumor cells from the G₁ phase to the S phase.⁶¹ Tryptanthrin also exhibits anti-microbial, anti-inflammatory, anticancer, antiviral, antiparasitic, antiallergic, and antioxidant.^62–64 Flavonoids have been known for their capability to interact with bacterial proteins and nucleic acids, causing denaturation and inhibition of metabolic processes, and disruption of cell membrane synthesis.⁶⁵ Flavonoids inhibit the growth of numerous pathogenic microorganisms, including multidrug-resistant bacteria. The hydroxylation of C5, C7, C3′, and C4′, and geranylation or prenylation at C6 are attributed to the antibacterial activity.⁶⁶ Most flavonoids exhibit antioxidant activity because of their stable backbone structure. However, the hydroxyl substituents in positions 2’ and 6’ in ring B, and in positions 3 and 5 with the carbonyl substituent in C4, and the double bond between C2 and C3 with the carbonyl in C4, further strengthen the antioxidant properties.^67–69 Moreover, the most abundant phytosterol (β-sitosterol) and fatty acid (α-linolenic acid) in S. crispus have shown a strong antioxidant activity.⁸

Pharmacokinetics

The pharmacokinetics profile of Strobilanthes plants has been described for one of their bioactive phytochemicals, namely tryptanthrin. Tryptanthrin has been studied in male Sprague-Dawley rats administered intravenously at a dose of 2 mg/kg body weight. Tryptanthrin showed a half-life (T1/2) of 40.63 ± 6.66 min and a clearance of 1.00 ± 0.36 L/h/kg, suggesting a fast distribution and clearance.⁷⁰ Additionally, oral administration of tryptanthrin at a dose of 100 mg/kg body weight in rodents revealed that its accumulation is at a higher concentration in the liver than in other tissues. Tryptanthrin was also found to be deposited in the kidneys, lungs, heart, and spleen, but not in the brain, under the experimental conditions.⁷¹ In rats, tryptanthrin underwent a Phase 1 metabolism, as proven by its metabolite, showing mono-hydroxylated on the aromatic ring of the indole moiety of protonated tryptanthrin, structurally confirmed as 8-hydroxytryptanthrin.⁷²

Toxicity Assays

Only one article published between 2015 and 2025 reported that a sub-acute oral toxicity assay of the ethanol extract of S. crispus leaves was performed in young female Sprague Dawley rats. The rats were orally administered a single dose of 150, 300, or 600 mg/kg body weight of the extract for 14 consecutive days. This investigation confirmed the safety of the extract up to the highest dose of 600 mg/kg body weight, as indicated by the absence of adverse effects or death, no significant changes in serum biochemical parameters, and no damage to the liver and kidneys.⁷³

Human Studies and Case Reports

Unfortunately, there are very limited human studies and case reports on Strobilanthes extracts indexed in the PubMed and Scopus databases. In fact, only one systematic review and meta-analysis study reported the evidence and potential mechanism of action of S. cusia and its active components in the treatment of psoriasis. In their study, Wang et al (2024) included 26 clinical trials comprised six interventions in the form of S. cusia decoctions and Chinese herbal medicine. The Psoriasis Area and Severity Index (PASI) score was considered an indicator of the effectiveness of psoriasis treatment; however, the original articles sourced in this systematic review and meta-analysis study were found to be written in Chinese.⁷⁴ Meanwhile, the other plant, S. crispus, is widely used in Indonesia and Malaysia by directly consuming fresh leaves or boiling them in water to cure numerous ailments, such as diabetes mellitus, kidney stones, high blood pressure, and constipation.^75,76

Limitations of the Study and Future Perspectives

Although this review provides a profound understanding of the potential therapeutic effects of two Strobilanthes plants, namely S. crispus and S. cusia, some limitations were identified during the analysis, such as (1) the fact that there was variability in extraction methods, solvents, and experimental conditions across studies, shows a lack of standardized protocol, and (2) that all data described in the articles were primarily derived from in vitro and in vivo studies, thus may not fully translate to human physiology. Furthermore, animal studies only covered a limited or minimum sample size, different rodent species or strains, such as rats or mice, Wistar or Sprague-Dawley rats, and the heterogeneity of sex used, thus resulting in varying observed effects between sexes caused by hormonal factors such as estrogen. As a serendipitous outcome, only one article reported a sub-acute oral toxicity study, thus unlocking further toxicity studies, such as acute oral single-dose toxicity, sub-chronic oral multiple-dose toxicity, and chronic oral toxicity. In addition, the variety of geographical locations for plant harvesting, extraction methods, solvents used, and mechanisms by which phytochemicals exert their biological properties requires more in-depth exploration to provide data supporting clinical settings and to confirm therapeutic benefits in humans. From a future perspective, clinical trials to bridge the gap between preclinical findings and human applications will validate the pharmacological activity, efficacy, and safety, particularly in vulnerable populations such as pediatric and geriatric patients with comorbidities. Investigations should focus on various demographic populations, considering factors such as age, ethnicity, and sex, in relation to hormonal status, pharmacodynamics, and pharmacokinetics, to clearly understand how these variables influence treatment outcomes.

Conclusion

This study clarifies the multifaceted roles of Strobilanthes crispus and Strobilanthes cusia in alleviating various disorders. Our review of articles published between 2015 and 2025 confirms that these two Strobilanthes plants are still being investigated globally, with the most studied being their leaves, as the active parts. Ethanol and methanol are the commonly used solvents for extraction, and room temperature is a popular choice. More than 100 metabolites have been reported to be present in Strobilanthes crispus and Strobilanthes cusia, including alkaloids, fatty acids and derivatives, flavonoids and flavonoid glycosides, phenolic acids, sterols, and terpenoids. One of the bioactive metabolites, namely tryptanthrin, has shown a strong cytotoxicity against tumor and microbial cells, and the flavonoids and phytosterols exhibited antibacterial and antioxidant properties. Considering the noteworthy findings from preclinical studies, which point to S. crispus, this plant may be established as a plant-based antimicrobial, anti-inflammatory, anticancer, or hypoglycemic agent. As only one article reported a sub-acute oral toxicity study, further toxicity studies are necessary to confirm its safety. Despite promising pharmacological evidence, we cannot locate human studies during the selected publication period; however, several articles describing ethnopharmacological surveys of medicinal plants in China, Malaysia, and Thailand were found, among which Strobilanthes plants were used as colorants, edible plants, and natural medicines for cattle, which is not related to the results of preclinical pharmacological activity assays. The lack of human studies presents challenges in determining its safety, dosage, and long-term effects. Further clinical trials will validate pharmacological activity, efficacy, and safety, and confirm its potential as a therapeutic agent.