Catalpol: A Comprehensive Encyclopedic Reference
1. Identity and Chemical Characterization
1.1 Names and Classification
Catalpol is an iridoid glycoside predominantly derived from the fresh or dried root tuber of Rehmannia glutinosa Libosch, a member of the Scrophulariaceae family. Catalpol is an iridoid glucoside, a class of natural products that are simply monoterpenes with a glucose molecule attached. First isolated in 1962, catalpol was named for plants in the genus Catalpa in which it was first discovered. In 1971, Kitagawa Hiroshi first isolated catalpol from Rehmannia glutinosa and proved its hypoglycemic effect.
Catalpol is characterized by its polar structure, high solubility in water, and a molecular formula of C₁₅H₂₂O₁₀ with a molecular weight of 362.45. Because of its polar functional groups, catalpol is highly hydrophilic and soluble in water and methanol. Catalpol is a naturally occurring 7,8-cyclopentane iridoid and one of the metabolites formed by the fusion of a cyclopentane ring and a pyran ring skeleton, including an acetal structure, mainly in the form of glycosides.
1.2 Botanical Sources
Catalpol is widely distributed in many plant families and is primarily obtained from the root of Rehmannia glutinosa Libosch. However, it is not exclusive to this species. The compound is distributed in various plant families, such as Plantaginaceae, Lamiaceae, and Bignoniaceae. Catalpol was also isolated from the aqueous extracts of Plantago lanceolata (rib-grass, ribwort plantain) and leaves of Buddleia species. Other sources of catalpol include Radix Scrophulariae and Lancea tibetica.
Iridoids are a class of naturally occurring monoterpenoids that are acetal derivatives of iridodial, originally isolated from the defensive secretions of ants. These compounds are found extensively in dicotyledonous plants, including families such as Scrophulariaceae, Rubiaceae, Lamiaceae, Gentianaceae, Verbenaceae, and Oleaceae. Iridoids have been recognized as defense chemicals of plants against herbivores due to their bitter taste and anti-growth inhibitory activities against insects and pathogens.
1.3 Biosynthesis
S. R. Jensen described a possible biosynthetic pathway for catalpol. With iridoids stemming from a terpenoid origin, epi-iridodial, derived from geraniol, serves as a precursor. Addition of a glucose at carbon 1 (C1) of the iridoid backbone and oxidation of the aldehyde at C4 of epi-iridotrial produces 8-epiloganic acid. A subsequent hydrolysis at C8 yields mussaenosidic acid, followed by a dehydration to yield deoxyngeniposidic acid. The next precursor, geniposidic acid, is furnished via hydrolysis of C10, and then a decarboxylation to remove the carboxylic acid at C4 provides bartsioside. The very widely known and accepted precursor to catalpol, aucubin, is then furnished via hydroxylation at C6.
1.4 Quality Control and Regulatory Status
Catalpol is the representative compound with the highest content in Rehmannia glutinosa Libosch, and is also a key index component for evaluating the quality of the plant. Since 2005, it has been continuously included in various editions of the China Pharmacopoeia. Medicinal uses of Plantago lanceolata leaves, from which catalpol is also isolated, are described in the European Pharmacopoeia. It is used as an anticatarrhal agent for upper and lower respiratory tract conditions and for its anti-inflammatory and antimicrobial effects.
"Catalpol tablets," as the first type of TCM new drug based on this compound, obtained clinical study approval from the China Food and Drug Administration on January 25, 2017, primarily for use in the treatment of diabetes due to its glucose-lowering effect. A new class I Chinese medicine developed on the basis of this monomer component has been approved to enter the clinical trial stage in China.
2. Traditional and Historical Use
2.1 Traditional Chinese Medicine (TCM)
Rehmannia glutinosa, catalpol's primary botanical source, is a plant very commonly used in Chinese and Korean traditional medicine for various disorders, including diabetes mellitus, neuronal disorders, and inflammation. It was first recorded in Shennong's Classic of Materia Medica (Shennong Bencao Jing), one of the oldest foundational texts of Chinese herbal medicine. Rehmannia glutinosa ranks among Traditional Chinese Medicine's 50 fundamental herbs, used for over 2,000 years to nourish kidney yin and support blood health.
Known as Dihuang, it has been historically utilized to nourish the kidney and liver, cool the blood, treat anemia, improve vitality, and address symptoms of chronic illness or aging. In the TCM tradition, Rehmannia (Di Huang) was used to treat blood loss, bone injuries, lower back pain, uterine bleeding, and to regulate menses.
Rehmanniae radix preparata — produced by wine-steaming the Rehmannia root — has been used for thousands of years with effects attributed to nourishing kidney-yin, benefiting essence, and filling marrow based on traditional Chinese medicine theory. Recorded in the China Pharmacopoeia, it is often used to treat consumptive thirst — namely thirst and dry mouth associated with diabetes — and also has a recognized improvement effect on kidney inflammation and fibrosis.
In traditional Chinese medicine, osteoporosis falls under the categories of "bone flaccidity" and "bone impediment," with the pathogenesis linked to a deficiency of essence leading to inadequate nourishment of the bones. Chinese herbal medicine for this condition has shown advantages due to its significant efficacy, minimal toxic side effects, and suitability for long-term use. Common anti-osteoporosis herbal prescriptions often emphasize kidney-nourishing herbs including Rehmannia glutinosa, Epimedium, Drynaria, Cornus officinalis, and Astragalus.
2.2 Korean and Other East Asian Traditions
Rehmannia glutinosa has been very commonly used in both Chinese and Korean traditional medicine for various disorders, including diabetes mellitus, neuronal disorders, and inflammation. The plant's root, catalpol-rich in its fresh form, has played a role in classical East Asian preparations for conditions that modern science now associates with metabolic, neurological, and inflammatory mechanisms.
2.3 Traditional Forms and Preparations
Traditional preparations of catalpol's primary source plant include multiple distinct forms. Rehmanniae radix preparata is extracted from wine-steaming the Rehmannia root, a Scrophulariaceae plant. In classical TCM, the root is prepared in three primary forms: fresh root (Xian Dihuang), dried raw root (Sheng Dihuang), and processed steamed root (Shu Dihuang), each assigned distinct therapeutic properties in classical formulas. The processed form undergoes multiple rounds of steaming and drying, which affects the catalpol content; catalpol levels are significantly higher in the raw, unprocessed root compared with processed preparations.
Catalpol also appears in classical compound prescriptions. The traditional Chinese medicine compound Liuwei Dihuang Decoction (Six-Ingredient Rehmannia Pill) has been shown to improve the learning and memory ability of mice with senile dementia, and catalpol, the main active ingredient in it, can inhibit the apoptosis of neural stem cells through the blood-brain barrier.
3. Key Constituents, Chemistry, and Mechanisms of Action
3.1 Chemical Identity of Catalpol
Catalpol is an iridoid glycoside characterized by its polar structure, high solubility in water, and a molecular formula of C₁₅H₂₂O₁₀ with a molecular weight of 362.45. The compound belongs to the iridoid class of monoterpenoids and carries a glucose moiety attached to the iridoid skeleton, classifying it as an iridoid glucoside. Iridoid glycosides are terpene-derived bioactive compounds that possess a structure related to iridodial.
Co-occurring constituents in Rehmannia glutinosa alongside catalpol include other iridoid glycosides such as aucubin, as well as phenylethanoid glycosides (e.g., acteoside/verbascoside), oligosaccharides, polysaccharides, and various amino acids. Rehmannia contains several bioactive compounds, including iridoid glycosides such as catalpol, with anti-inflammatory and neuroprotective activity; phenylethanoid glycosides with antioxidant effects; and amino acids and sterols that contribute to its overall tonic effect.
3.2 Core Mechanisms of Action
Catalpol operates through multiple molecular pathways simultaneously, which accounts for its broad spectrum of reported biological activities.
Anti-inflammatory Mechanisms
The nuclear translocation of NF-κB dimers is involved in the expressions of genes linked to inflammation and apoptosis. NF-κB is an important transcription factor which is expressed in brain cells, including neurons, microglia, and astrocytes, and participates in several brain functions. Catalpol inhibits this pathway. In models of LPS-induced inflammation, including RAW264.7 cells, cow endometrial epithelial cells (bEECs), and a mouse endometritis model, catalpol inhibits the secretion and expression of inflammatory factors by targeting TLR4. This inhibition prevents the inflammatory process in RAW264.7 and bEECs and provides an anti-inflammatory effect in endometritis.
Antioxidant Mechanisms
Catalpol exerts antioxidant effects by elevating endogenous defence enzymes including superoxide dismutase, catalase, and glutathione peroxidase, and by reducing reactive oxygen species, thereby protecting vascular endothelium and organ function. Catalpol significantly attenuates hydrogen peroxide-induced cytotoxicity, cell cycle arrest, and apoptosis in retinal pigment epithelial cells. The overproduction of reactive oxygen species and malondialdehyde stimulated by oxidative stress, and the corresponding reductions in antioxidant glutathione and superoxide dismutase levels, were largely reversed by catalpol pretreatment. Moreover, catalpol pretreatment markedly activated the expression of Nrf2 and its downstream antioxidant enzymes, including catalase, heme oxygenase-1 (HO-1), and NQO1.
Multiple Signaling Pathway Targets
The effects of catalpol are mediated by multi-target modulation of key cellular signalling pathways, including activation of AMP-activated protein kinase (AMPK), PI3K/Akt, and peroxisome proliferator-activated receptors (PPARs), as well as inhibition of pro-inflammatory and oxidative stress cascades such as JNK/NF-κB and AGE/RAGE. Additional vital signaling pathways engaged by catalpol include PGC-1α/TERT, Nrf2/HO-1, estrogen receptor (ER), Nox4/NF-κB, and GRP78/PERK.
Neuroprotective Mechanisms
Catalpol, as an active component of Rehmanniae radix preparata, elevates brain-derived neurotrophic factor (BDNF) and attenuates neuronal apoptosis and energy metabolism failure. Catalpol reverses neuroinflammation through blockade of the NF-κB pathway, upregulates neurotrophic factors via activation of the Tropomyosin Receptor Kinase B (TrkB) pathway, and preserves blood-brain barrier integrity.
Hepatoprotective Mechanisms
Hepatoprotective features of catalpol are strongly linked to its ability to modulate inflammation and apoptosis-related signalling pathways, especially the JAK/STAT signalling pathway. Catalpol can decrease hepatic fibrosis caused by carbon tetrachloride administration through modulating extracellular vesicle content in hepatic cells, improving autophagy in hepatic stellate cells, and decreasing aerobic glycolysis, resulting in reduced hepatic stellate cell activation, migration, and collagen deposition.
Bone-Related Mechanisms
Studies have shown that the anti-disease effect of catalpol in osteoporosis is mainly achieved through various pathways such as Wnt/β-catenin signaling pathways to promote osteogenic differentiation, and RANKL/RANK and other signaling pathways to inhibit osteoclastic differentiation.
4. Scientific Evidence by Area of Use
4.1 Neuroprotection and Neurodegenerative Disease
Preclinical experiments have demonstrated that catalpol and geniposide possess significant neuroprotective activities against Alzheimer's disease, Parkinson's disease, stroke, and depression. The current body of evidence, however, is restricted almost entirely to animal and cell-based models. No completed, published randomized controlled trials specifically investigating isolated catalpol for neurological disease in humans have been identified in the reviewed literature.
Alzheimer's Disease (AD)
A large number of experimental studies in vivo and in vitro have confirmed that catalpol has antioxidant, anti-inflammatory, antiapoptotic, and other neuroprotective effects, and it plays a significant role in the prevention and treatment of AD, with very small side effects and high safety. It may therefore be an ideal candidate drug for the treatment of AD. Mechanistically, catalpol operates on several AD-relevant targets. Research has shown that the traditional Chinese medicine compound Liuwei Dihuang Decoction can improve the learning and memory ability of mice with senile dementia, and catalpol, the main active ingredient in it, can inhibit the apoptosis of neural stem cells through the blood-brain barrier. The evidence supporting catalpol specifically in Alzheimer's disease remains preclinical; clinical trials are absent.
Parkinson's Disease (PD)
MPTP-treated mice were used as a Parkinson's disease model, and catalpol administration was found to mitigate the loss of dopaminergic (DA) neurons induced by MPTP and increased exploratory behavior along with tyrosine hydroxylase (TH) expression, which was accompanied by astrocyte and microglia activation. Catalpol administration significantly inhibited MPTP-triggered oxidative stress, and restored growth-associated protein 43 (GAP43) and vascular endothelial growth factor (VEGF) levels. Catalpol suppressed the activation of MKK4/JNK/c-Jun signaling, and reduced pro-inflammatory factors and inflammasome activation in the mouse model of PD. The results suggest that catalpol relieves MPTP-triggered oxidative stress, which may benefit the avoidance of chronic inflammatory reactions. All PD evidence is from animal models; no human clinical data are available.
Ischemic Stroke
Results from preclinical studies showed that catalpol and edaravone significantly facilitated neurological function recovery, reduced infarction volume, and increased cerebral blood flow in stroke mice. The bioavailability of catalpol administered intranasally was higher than that in plasma. In a middle cerebral artery occlusion (MCAO) model, catalpol intranasal administration could significantly reduce cerebral infarction volume, neurological dysfunction, and brain edema. In a rat model of traumatic brain injury induced by controlled cortical impact, catalpol provides neuroprotection against oxidative stress and neuroinflammation, and ameliorates neurological impairment, blood-brain barrier disruption, cerebral edema, and neuronal apoptosis. Again, this evidence is entirely preclinical.
Spinal Cord Injury
Catalpol inhibits apoptosis by enhancing autophagy, thereby reducing neuronal apoptosis and necrosis after acute spinal cord injury in rats, promoting the recovery of motor function. In a weight-drop model of spinal cord injury, catalpol upregulates miR-142 and regulates the HMGB1/TLR4/NF-κB pathway, improving functional recovery. All such evidence is from preclinical animal models.
Evidence Strength: Neuroprotection
The evidence for catalpol's neuroprotective effects is extensive at the in vitro and animal model level and spans multiple mechanistic pathways. No published randomized controlled clinical trials in humans specifically studying isolated catalpol for any neurological condition were identified in the reviewed literature. There is a lack of clinical trials of catalpol for neurological indications. The body of evidence should be classified as preliminary and preclinical.
4.2 Diabetes and Metabolic Disorders
The antidiabetic effects of catalpol represent one of the most studied areas, with a large body of animal evidence and the earliest movement toward clinical investigation.
Preclinical Evidence
In experimental models of type 2 diabetes, catalpol has been shown to lower fasting glucose, enhance insulin sensitivity, and protect pancreatic β-cell integrity. Its lipid-lowering activity reduces circulating triglycerides and cholesterol while preventing hepatic steatosis.
Catalpol may ameliorate high-fat-diet-induced insulin resistance in mice by attenuating adipose tissue inflammation and suppressing the JNK and NF-κB pathways, providing important insights into the underlying mechanisms of the antidiabetic effect of catalpol. Catalpol exhibits the effects of decreasing hepatic gluconeogenesis and increasing hepatic glycogen synthesis both in vivo and in vitro. Additionally, catalpol improved hepatic NADPH oxidase type 4 (NOX4)-mediated oxidative stress and activated hepatic AMP-activated protein kinase (AMPK) and phosphatidylinositol 3-kinase (PI3K)/AKT pathways both in vivo and in vitro.
In a study using the spontaneous diabetes db/db mouse model, results showed that catalpol could significantly improve insulin resistance and decrease the serum concentrations of insulin, glycated serum protein, triglycerides, and total cholesterol. The concentrations of adiponectin in serum, the protein expression of phosphorylation-AMPKα1/2 in liver, and phosphorylation-AMPKα1/2 and GLUT-4 in peripheral tissues were increased. In a separate study investigating skeletal muscle, catalpol at 200 mg/kg significantly (p < 0.05) reduced fasting blood glucose, HbA1c, HOMA-IR index, and the area under the curve of the oral glucose tolerance test, while improving the insulin tolerance test slope.
Clinical Evidence
A Phase IIa clinical trial of catalpol was conducted in Xining City, China. This study investigated the pharmacokinetics of catalpol tablets in patients with type 2 diabetes, assessing their effectiveness and safety at varying doses. "Catalpol tablets," as the first type of TCM new drug, obtained clinical study approval from the China Food and Drug Administration on January 25, 2017, primarily used in the treatment of diabetes due to its glucose-lowering effect. Full published results of pivotal efficacy trials were not available in the sources reviewed.
Evidence Strength: Diabetes
The antidiabetic effects of catalpol are supported by extensive and mechanistically coherent preclinical evidence from multiple animal models and in vitro systems. Catalpol is a well-tolerated natural compound with promising pharmacological actions in protection against diabetes and diabetic complications via multi-targets. Further prospective and well-designed clinical trials will shed light on the potential of clinical usage of catalpol. The clinical evidence base is currently limited and emerging; firm conclusions about efficacy in humans cannot yet be drawn.
4.3 Cardiovascular Protection
Catalpol has gained attention due to its potential use in treating cardio-cerebrovascular diseases (CVDs). Recent studies have investigated catalpol's protective properties in relation to various CVDs, such as atherosclerosis, myocardial ischemia, infarction, cardiac hypertrophy, and heart failure.
Catalpol can protect against cardiovascular injuries by attenuating free radicals, lipid peroxidation, and cell apoptosis. Against cardiovascular diseases, catalpol mainly modulates antioxidant pathways such as Nrf2/HO-1 and inhibits oxidative stress and myocardial injury. In a study examining endothelial protection, catalpol was found to inhibit homocysteine-induced oxidation and inflammation via inhibiting Nox4/NF-κB and GRP78/PERK pathways in human aortic endothelial cells. Although clinical studies specifically addressing catalpol's impact on CVDs are scarce, the compound's established safety and well-tolerated nature suggest that it could be a valuable treatment alternative for CVD patients.
Evidence Strength: Cardiovascular
The cardiovascular evidence for catalpol is preliminary and confined to in vitro and animal studies. No published clinical trials in humans specifically examining catalpol for cardiovascular outcomes were identified in the reviewed literature.
4.4 Hepatoprotection and Liver Fibrosis
Hepatoprotective features of catalpol are strongly linked to its ability to modulate inflammation and apoptosis-related signalling pathways, especially the JAK/STAT signalling pathway. Catalpol can decrease hepatic fibrosis caused by carbon tetrachloride administration through modulating extracellular vesicle content in hepatic cells, improving autophagy in hepatic stellate cells, and decreasing aerobic glycolysis resulting in reduced hepatic stellate cell activation, migration, and collagen deposition.
One study investigated catalpol's role in protecting against fluoxetine-induced hepatotoxicity. It was found that while enhancing fluoxetine's antidepressant activity, catalpol exhibited hepatoprotective properties by decreasing the process of ferroptosis via interfering with the Activating transcription factor 3 (ATF3) and ferroptosis suppressor protein 1 (FSP1) pathway.
Evidence Strength: Hepatoprotection
Evidence is preclinical (in vitro and animal models only). No human clinical trial data were identified for catalpol specifically as a hepatoprotective agent.
4.5 Bone Health and Osteoporosis
Catalpol promotes osteogenic differentiation and inhibits osteoclast differentiation through various molecular mechanisms, thereby achieving therapeutic effects. The anti-osteoporotic effect of catalpol is mainly achieved through pathways such as Wnt/β-catenin signaling to promote osteogenic differentiation, and RANKL/RANK and other signaling pathways to inhibit osteoclastic differentiation.
Clinical trials for Rehmannia glutinosa itself (not isolated catalpol) have been conducted to verify its ameliorating effects on osteoporosis, such as increasing bone mineral density and maintaining the balance between osteoclasts and osteogenesis. The bone-protecting effect of R. glutinosa may be related to its high content of iridoid glycosides such as catalpol.
Evidence Strength: Bone Health
Preclinical evidence (animal models) for catalpol's anti-osteoporotic effects is substantial. Some clinical trials of the parent plant have been conducted, but no published clinical trials specifically assessing isolated catalpol for bone outcomes were identified in the reviewed literature. Evidence is preliminary to moderate for the herb as a whole, preclinical for the isolated compound.
4.6 Anti-Cancer Activity
Catalpol, a natural iridoid glycoside, has been proposed as an anticancer compound due to its anti-proliferative effects. Catalpol targets critical processes involved in cancer cell progression, including malignant proliferation, apoptosis, and metastasis. Additionally, catalpol presents potent anti-inflammatory and antioxidant properties crucial for cancer prevention and intervention.
Due to the absence of clinical trials, investigations have covered in vitro and animal trials encompassing catalpol's effects against several types of cancer, including breast, liver, colorectal, lung, gastric, bladder, and ovarian cancer, as well as osteosarcoma.
A preliminary clinical experimental study explored the safety of catalpol treatment in patients with colon cancer by intraperitoneally injecting 10 mg/kg catalpol twice a day for 12 weeks. Only mild non-fatal adverse reactions, such as nausea, vomiting, gastrointestinal ulcers, and constipation, were observed.
Evidence Strength: Anti-Cancer
Evidence is entirely or nearly entirely preclinical (in vitro and animal models). The sole human data point identified relates to a preliminary safety study, not an efficacy trial. Clinical efficacy evidence is absent.
4.7 Depression and Mood
Based on spectrum-effect relationship analysis and activity verification, catalpol has been shown to exert antidepressant effects. In chronic unpredictable mild stress mice, catalpol alleviates depressive symptoms by downregulating the oxidative stress-mediated activation of the NLRP3 inflammasome and neuroinflammation.
Evidence Strength: Depression
Evidence is currently limited to animal and preclinical models. No human clinical trials on catalpol for depression were identified in the reviewed literature.
4.8 Anti-Aging Effects
In aging models using mutant insulin-like receptor gene and mammalian transcription factor family protein homologs in nematodes, catalpol enhanced antioxidant gene expression and the antioxidant response, thus delaying aging by activating the insulin/IGF-1 signaling pathway.
Evidence Strength: Anti-Aging
Evidence is at the preclinical (invertebrate model) level only. This area requires substantially more research before any human application can be considered.
4.9 Respiratory and Other Organ Systems
Among the pharmacological effects attributed to catalpol in experimental settings are lowering blood sugar, treating osteoporosis, anti-tumor activity, improving microcirculation, protecting lung function, improving renal function, preventing intestinal inflammation, improving Sjogren's syndrome, improving cognitive impairment, protecting nerves, radiation protection, delaying ovarian aging, and treating asthma. All of these applications are based on experimental models; clinical evidence ranges from very limited to absent for most of these conditions.
5. Pharmacokinetics and Bioavailability
Studies have shown that catalpol can be rapidly absorbed by the intestine after oral administration, but its bioavailability can be affected by intestinal bacteria that convert it. Catalpol can be distributed to multiple tissues through blood circulation and can even penetrate the blood-brain barrier (BBB). Catalpol is metabolized by hydrogenation after deglycosylation and eliminated quickly by the body.
The compound demonstrates a quick onset, rapid and complete excretion, no accumulation in the body, and no damage to major organs. These properties make it suitable for long-term use without significant drug interactions, positioning it as a TCM hypoglycemic agent with minimal toxicity and side effects.
Preliminary pharmacokinetic assessments indicate good oral bioavailability, blood-brain barrier penetration, and a favourable safety profile, supporting its potential development as a natural scaffold for drug development.
Intranasal delivery has been investigated as an alternative route. After intranasal administration, the brain targeting index (DTI) of catalpol was greater than 1, indicating that catalpol had good brain targeting after intranasal administration. The bioavailability of catalpol administered intranasally was higher than that in plasma.
6. Dosage Forms and Reported Dosages
Important note: The following dosages derive exclusively from preclinical (animal) studies or from the single clinical safety study identified in the reviewed literature. These figures do not constitute clinical recommendations and no widely established human dosage for isolated catalpol exists.
- Animal model dosages (oral/gavage): In a mouse model of type 2 diabetes induced by high-fat diet and streptozotocin, diabetic mice were orally administered catalpol at 100 and 200 mg/kg, metformin at 200 mg/kg, and saline for four weeks.
- Animal model dosages (db/db mice): In a study with spontaneous diabetes db/db mice, animals were divided into groups receiving catalpol at 40, 80, and 120 mg/kg body weight, or metformin at 250 mg/kg.
- Animal model dosages (cardiovascular): Catalpol at 5 mg/kg was administered to mice by intraperitoneal injection one hour before the intratracheal administration of diesel exhaust particles at 30 µg/mouse.
- Long-term toxicology (rat, intravenous): After a long-term intravenous catalpol injection at 10, 20, and 40 mg/kg/day for 90 days, no toxic changes were observed in the biochemical indexes and physiological structure of rat organs.
- Clinical safety study (colon cancer patients): A preliminary clinical study explored the safety of catalpol treatment in patients with colon cancer by intraperitoneally injecting 10 mg/kg catalpol twice a day for 12 weeks.
- Phase IIa clinical trial (type 2 diabetes, catalpol tablets): A Phase IIa clinical trial of catalpol was conducted in Xining City, China, investigating the pharmacokinetics of catalpol tablets in patients with type 2 diabetes, assessing effectiveness and safety at varying doses. Specific dose amounts from this trial were not reported in the reviewed sources.
For the parent herb Rehmannia glutinosa preparations (which contain catalpol as an active marker), dosage information is more available but relates to the whole herb or extract rather than to isolated catalpol. The catalpol content of raw versus processed Rehmannia preparations varies considerably.
7. Safety, Toxicology, and Drug Interactions
7.1 General Safety Profile
A large number of experimental studies in vivo and in vitro have confirmed that catalpol has very small side effects and high safety. Mice with type 2 diabetes exhibit no toxic symptoms when treated with catalpol, and reasonable doses of catalpol have not shown significant adverse effects in rodents or humans.
Acute toxicity experiments related to catalpol have been conducted in mouse models to determine its safety. The 50% lethal dose (LD₅₀) of catalpol in mice was determined as 206.5 mg/kg after intraperitoneal catalpol injection. After a long-term intravenous catalpol injection at 10, 20, and 40 mg/kg/day for 90 days, no toxic changes were observed in the biochemical indexes and physiological structure of rat organs, indicating that catalpol has no significant side effects at these doses.
The definite toxicity, safety margin, and potential adverse reactions of catalpol in humans have not been fully reported. This represents a critical gap in the safety database for isolated catalpol as a human intervention.
7.2 Reported Adverse Events in Available Human Data
In the preliminary clinical study in patients with colon cancer receiving intraperitoneally injected catalpol at 10 mg/kg twice a day for 12 weeks, only mild non-fatal adverse reactions, such as nausea, vomiting, gastrointestinal ulcers, and constipation, were observed.
In the context of the parent herb Rehmannia glutinosa, broader adverse event profiles have been described. Side effects such as nausea, gas, diarrhea, headache, heart palpitations, dizziness, vertigo, allergies, and fatigue have been reported.
7.3 Potential Drug Interactions and Notable Considerations
Co-administration of catalpol with fluoxetine was found to enhance fluoxetine's antidepressant activity while simultaneously exerting hepatoprotective properties. This interaction, while potentially beneficial in the studied context, illustrates catalpol's capacity to alter the pharmacological and toxicological profile of co-administered drugs. Research in HepaRG cells demonstrated that catalpol can protect against triptolide-induced hepatotoxicity, further demonstrating pharmacodynamic interaction potential with other herbal and pharmaceutical agents.
Catalpol's bioavailability after oral administration can be affected by intestinal bacteria that convert it. This implies that the composition of the gut microbiome may modulate catalpol's in vivo activity and effective exposure.
The compound demonstrates rapid excretion and no accumulation in the body, and no damage to major organs, positioning it as a compound with minimal drug interactions. However, this characterization is derived from animal studies, and formal human drug-interaction studies for isolated catalpol are not yet published in the reviewed literature.
7.4 Contraindications and Special Populations
Formal contraindication data for isolated catalpol are not established in the reviewed scientific literature. In the traditional TCM context for the parent plant, Rehmannia glutinosa, classical texts and practitioners note specific contraindications. Traditional Chinese medicine principles indicate avoidance in individuals with severe diarrhea or spleen deficiency. Rehmannia may also be unsafe for people who have liver disease or pre-existing digestive or immune issues. It is not considered safe for children or pregnant or breastfeeding women. These observations relate to the whole herb and not necessarily to isolated catalpol, and should be understood in that context.
8. Current Research Directions and Regulatory Context
In recent years, the development of different targeted drug delivery formulations and administration routes of catalpol to maximize its efficacy has become a major focus of research. "Catalpol tablets," a new class I Chinese medicine developed on the basis of this monomer component, has been approved to enter the clinical trial stage in China. However, in-depth investigation is required to elucidate the mechanisms of action of catalpol, and more clinical trials are required to assess the clinical value of this compound.
Areas of ongoing experimental study include organ- and tissue-protective actions on the kidneys, bones, nervous system, heart, brain, liver, lungs, uterus, ovaries, and more, alongside notable anti-arthritis, anti-cancer, and anti-diabetic properties.
Catalpol has been shown to counteract bone marrow suppression induced by acetylphenylhydrazine and cyclophosphamide in rats. It has also been reported to outperform methimazole in treating hyperthyroidism in mice while reducing oxidative stress damage to the liver. These are areas of active preclinical investigation.
References
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