Betulinic acid regulates generation of neuroinflammatory mediators responsible for tissue destruction in multiple sclerosis in vitro

Novel anti-inflammatory compounds that alleviate experimental autoimmune encephalomyelitis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disease primarily characterized by inflammatory demyelination. Despite significant research efforts, effective therapies for MS remain limited. Drug screening offers a promising approach to rapidly identifying potential therapeutic compounds.

PURPOSE

This study aimed to screen compounds that can exert anti-inflammatory effects and alleviate experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

STUDY DESIGN

A fundamental research in vitro and in vivo. A high-throughput screen was performed to screen drugs that can mitigate EAE and the molecular mechanism was explored.

METHODS

Based on our previous research highlighting the crucial role of AXL, a receptor tyrosine kinase, in microglial function, we constructed an AXL-GFP reporter gene in BV2 microglia cells. A high-throughput screen of an FDA-approved compound library was performed to identify potential AXL-targeting compounds. The effects of candidate compounds on cellular morphology, cell cycle, apoptosis, mitochondrial function, inflammatory cytokine production, polarization, and phagocytic activity of BV2 cells were assessed. To investigate the in vivo effects of AXL modulation, EAE mice were generated. AXL was either upregulated using recombinant Gas6 protein or knocked out using CRISPR/Cas9. The impact of AXL modulation on disease progression and underlying molecular mechanisms was explored.

RESULTS

Primary and secondary screenings identified three potential AXL-targeting compounds: Betulin, Clofibric acid, and Isosorbide. Molecular docking analysis revealed that Isosorbide exhibited poor binding affinity with AXL at the molecular level and was excluded from further studies. Betulin and Clofibric acid were found to promote M2 polarization, reduce inflammation, enhance phagocytosis, extend the S phase of the cell cycle, inhibit apoptosis, and improve mitochondrial structure in BV2 cells. In vivo studies demonstrated that Betulin (20 mg/kg) alleviated EAE, while AXL gene knockout reversed its protective effects.

CONCLUSION

This study elucidates the molecular mechanism underlying Betulin's therapeutic effects in MS, both in vitro and in vivo. Betulin exerts its beneficial effects by upregulating the AXL/SOCS3 pathway and inhibiting the JAK2/STAT1 signaling pathway. These findings suggest that Betulin holds significant promise as a potential therapeutic agent for multiple sclerosis.

Neuroprotective properties of Betulin, Betulinic acid, and Ursolic acid as triterpenoids derivatives: a comprehensive review of mechanistic studies

Cognitive deficits are the main outcome of neurological disorders whose occurrence has risen over the past three decades. Although there are some pharmacologic approaches approved for managing neurological disorders, it remains largely ineffective. Hence, exploring novel nature-based nutraceuticals is a pressing need to alleviate the results of neurodegenerative diseases, such as Alzheimer's disease (AD) and other neurodegenerative disorders. Some triterpenoids and their derivates can be considered potential therapeutics against neurological disorders due to their neuroprotective and cognitive-improving effects. Betulin (B), betulinic acid (BA), and ursolic acid (UA) are pentacyclic triterpenoid compounds with a variety of biological activities, including antioxidative, neuroprotective and anti-inflammatory properties. This review focuses on the therapeutic efficacy and probable molecular mechanisms of triterpenoids in damage prevention to neurons and restoring cognition in neurodegenerative diseases. Considering few studies on this concept, the precise mechanisms that mediate the effect of these compounds in neurodegenerative disorders have remained unknown. The findings can provide sufficient information about the advantages of these compounds against neurodegenerative diseases.

Evaluation of betulinic acid effects on pain, memory, anxiety, catalepsy, and oxidative stress in animal model of Parkinson's disease

Parkinson's disease (PD) is known for motor impairments. Betulinic acid (BA) is a natural compound with antioxidant activity. The present study addresses the question of whether BA affects motor and non-motor dysfunctions and molecular changes in the rat model of PD. The right medial forebrain bundle was lesioned by injection of 6-hydroxydopamine in Male Wistar rats (10-12 weeks old, 270-320 g). Animals were divided into Sham, PD, 3 treated groups with BA (0.5, 5, and 10 mg/kg, IP), and a positive control group received L-dopa (20 mg/kg, P.O) for 7 days. rigidity, anxiety, analgesia, and memory were assessed by bar test, open-field, elevated plus-maze (EPM), tail-flick, and shuttle box. Additionally, the malondialdehyde (MDA), Superoxide dismutase (SOD), glutathione peroxidase (GPx) activity, Brain-derived neurotrophic factor (BDNF) and Interleukin 10 (IL10) levels in the whole brain were measured. BA significantly reversed the 6-hydroxydopamine-induced motor and memory complication in the bar test and shuttle box. It modified anxiety-like behavior neither in open-field nor in EPM. It only decreased the time spent in open arms. Moreover, no significant changes were found in the tail-flick between treatment and sham groups. On the other hand, the level of MDA & IL10 were decreased, while the activity of GPx levels of SOD & BDNF in the rats' brains was increased. Our results showed that BA as a free radical scavenger can account for a possible promise as a good therapeutic agent for motor and non-motor complications in PD however further studies may be needed.

Anti-Inflammatory Activities of Betulinic Acid: A Review

Inflammatory diseases have a high prevalence and has become of great interest due to the increase in life expectancy and the costs to the health care system worldwide. Chronic diseases require long-term treatment frequently using corticosteroids and non-steroidal anti-inflammatory drugs, which are associated with diverse side effects and risk of toxicity. Betulinic acid, a lupane-type pentacyclic triterpene, is a potential lead compound for the development of new anti-inflammatory treatments, and a large number of derivatives have been produced and tested. The potential of betulinic acid and its derivatives has been shown in a number of pre-clinical studies using different experimental models. Moreover, several molecular mechanisms of action have also been described. Here we reviewed the potential use of betulinic acid as a promissory lead compound with anti-inflammatory activity and the perspectives for its use in the treatment of inflammatory conditions.

Neonatal Rat Glia Cultured in Physiological Normoxia for Modeling Neuropathological Conditions In Vitro

Cell culture conditions were proven to highly affect crucial biological processes like proliferation, differentiation, intercellular crosstalk, and senescence. Oxygen tension is one of the major factors influencing cell metabolism and thus, modulating cellular response to pathophysiological conditions. In this context, the presented study aimed at the development of a protocol for efficient culture of rat neonatal glial cells (microglia, astrocytes, and oligodendrocytes) in oxygen concentrations relevant to the nervous tissue. The protocol allows for obtaining three major cell populations, which play crucial roles in sustaining tissue homeostasis and are known to be activated in response to a wide spectrum of external stimuli. The cells are cultured in media without supplement addition to avoid potential modulation of cell processes. The application of active biomolecules for coating culturing surfaces might be useful for mirroring physiological cell interactions with extracellular matrix components. The cell fractions can be assembled as cocultures to further evaluate investigated mechanisms, intercellular crosstalk, or cell response to tested pharmacological compounds. Applying additional procedures, like transient oxygen and glucose deprivation, allows to mimic in vitro the selected pathophysiological conditions. The presented culture system for neonatal rat glial cells is a highly useful tool for in vitro modeling selected neuropathological conditions.

Oleogel Formulations for the Topical Delivery of Betulin and Lupeol in Skin Injuries-Preparation, Physicochemical Characterization, and Pharmaco-Toxicological Evaluation

The skin integrity is essential due to its pivotal role as a biological barrier against external noxious factors. Pentacyclic triterpenes stand as valuable plant-derived natural compounds in the treatment of skin injuries due to their anti-inflammatory, antioxidant, antimicrobial, and healing properties. Consequently, the primary aim of the current investigation was the development as well as the physicochemical and pharmaco-toxicological characterization of betulin- and lupeol-based oleogels (Bet OG and Lup OG) for topical application in skin injuries. The results revealed suitable pH as well as organoleptic, rheological, and textural properties. The penetration and permeation of Bet and Lup oleogels through porcine ear skin as well as the retention of both oleogels in the skin were demonstrated through ex vivo studies. In vitro, Bet OG and Lup OG showed good biocompatibility on HaCaT human immortalized cells. Moreover, Bet OG exerted a potent wound-healing property by stimulating the migration of the HaCaT cells. The in ovo results demonstrated the non-irritative potential of the developed formulations. Additionally, the undertaken in vivo investigation indicated a positive effect of oleogels treatment on skin parameters by increasing skin hydration and decreasing erythema. In conclusion, oleogel formulations are ideal for the local delivery of betulin and lupeol in skin disorders.

Computational investigations of physicochemical, pharmacokinetic, toxicological properties and molecular docking of betulinic acid, a constituent of Corypha taliera (Roxb.) with Phospholipase A2 (PLA2)

BACKGROUND

Betulinic acid (BA) is a natural triterpenoid compound and exhibits a wide range of biological and medicinal properties including anti-inflammatory activity. Therefore, this theoretical investigation is performed to evaluate (a) physicochemical properties such as acid dissociation constant (pKa), distribution coefficient (logD), partition coefficient (logP), aqueous solubility (logS), solvation free energy, dipole moment, polarizability, hyperpolarizability and different reactivity descriptors, (b) pharmacokinetic properties like human intestinal absorption (HIA), cellular permeability, skin permeability (P_Skin), plasma protein binding (PPB), penetration of the blood brain barrier (BBB), (c) toxicological properties including mutagenicity, carcinogenicity, risk of inhibition of hERG gene and (d) molecular mechanism of anti-inflammatory action which will aid the development of analytical method and the synthesis of BA derivatives.

METHODS

The physicochemical properties were calculated using MarvinSketch 15.6.29 and Gaussian 09 software package. The pharmacokinetic and toxicological properties were calculated on online server PreADMET. Further, the molecular docking study was conducted on AutoDock vina in PyRx 0.8.

RESULTS

The aqueous solubility increased with increasing pH due to the ionization of BA leading to decrease in distribution coefficient. The solvation energies in water, dimethyl sulfoxide (DMSO), acetonitrile, n-octanol, chloroform and carbon tetrachloride were - 41.74 kJ/mol, - 53.80 kJ/mol, - 66.27 kJ/mol, - 69.64 kJ/mol, - 65.96 kJ/mol and - 60.13 kJ/mol, respectively. From the results of polarizability and softness, it was clear that BA is less stable and hence, kinetically more reactive in water. BA demonstrated good human intestinal absorption (HIA) and moderate cellular permeability. Further, BA also exhibited positive CNS activity due to high permeability through BBB. The toxicological study revealed that BA was a mutagenic compound but noncarcinogenic in mice model. Moreover, molecular docking study of BA with PLA2 revealed that BA interacts with GLY22 & GLY29 through hydrogen bond formation and LEU2, PHE5, HIS6, ALA17, ALA18, HIS47 and TYR51 through different types of hydrophobic interactions. The binding affinity of BA was - 41.00 kJ/mol which is comparable to the binding affinity of potent inhibitor 6-Phenyl-4(R)-(7-Phenyl-heptanoylamino)-hexanoic acid (BR4) (- 33.89 kJ/mol).

CONCLUSIONS

Our computed properties may assist the development of analytical method to assay BA or to develop BA derivatives with better pharmacokinetic and toxicological profile.

The effects of betulinic acid on neurobehavioral activity, electrophysiology and histological changes in an animal model of the Alzheimer's disease

Alzheimer's disease (AD) is a common disorder characterized by aggregation and conversion of amyloid beta (Aβ) monomers to fibrils. Betulinic acid (BA) strongly accelerated this pathway through circumventing the oligomeric intermediate state. BA at doses of 0.2 and 0.4μM/10μl/rat (intra-hippocampal or i.h injection, vehicle: DMSO) was bilaterally administrated 180 and 10min before co-administration of Aβ (0.1μM/5μl/rat, i.h injection, vehicle: PBS) and Streptozotocin (STZ, 1.5mg/kg/10μl/rat, intracerebroventricular or i.c.v. injection, vehicle: aCSF). The behavioral assessments (spatial and passive avoidance memory, anxiety, locomotion, depression, and motor coordination), electrophysiological evaluations (hippocampal long- term potentiation (LTP)) as well as histological changes were evaluated 30days after injections. The indices of spatial and passive avoidance memory, anxiety/depression and LTP records were significantly impaired in AD rats in comparison with the sham. Pretreatment of BA (0.4μM) showed a more significant effect on memory, anxiety, all LTP parameters, and histological damage compared to a low dose in contrast to the AD group. Overall, BA pretreatment was able to prevent AD-induced neurobehavioral and LTP deficits in rats and the best effect was observed in molar ratio of 1:4 (Aβ to BA).

Influence of oxidative stress on the antibacterial activity of betulin, betulinic acid and ursolic acid

Contribution of reactive oxygen species and oxidative stress in the antibacterial activities of betulin, betulinic acid and ursolic acid against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus was investigated. The minimum inhibitory concentrations of betulin, betulinic acid and ursolic acid against E. coli, P. aeruginosa and S. aureus are 1024-, 256- and 1024-μg/mL; 512-, 256- and 256 μg/mL; 256-, 256- and 64 μg/mL respectively. Cell viability of betulin-, betulinic acid- and ursolic acid-treated bacteria decrease in time dependent manner. Treatment of bacteria in the presence of 2,2'-bipyrydyl increased cell viability. Superoxide anion radical production increased significantly (p < 0.05) in bacterial cells-treated with betulin, betulinic acid and ursolic acid. Furthermore, NAD+/NADH ratio increased significantly (p < 0.05) in betulin-, betulinic acid- and ursolic acid-treated bacteria. Similarly, level of reduced glutathione in E. coli, P. aeruginosa and S. aureus decreased significantly with corresponding increase in glutathione disulphide, malondialdehyde and fragmented DNA following betulin, betulinic acid and ursolic acid treatments. It is evident from the above findings that betulin, betulinic acid and ursolic acid enhanced electron transport chain activity in E. coli, P. aeruginosa and S. aureus leading to increased ROS generation, Fenton reaction, lipid peroxidation, fragmented DNA and consequentially bacterial death.

Betulinic acid derivative BA5, a dual NF-kB/calcineurin inhibitor, alleviates experimental shock and delayed hypersensitivity

Betulinic acid (BA) is a naturally occurring triterpenoid with several biological properties already described, including immunomodulatory activity. Here we investigated the immunomodulatory activity of eight semi-synthetic amide derivatives of betulinic acid. Screening of derivatives BA1-BA8 led to the identification of compounds with superior immunomodulatory activity than BA on activated macrophages and lymphocytes. BA5, the most potent derivative, inhibited nitric oxide and TNFα production in a concentration-dependent manner, and decreased NF-κB activation in Raw 264.7 cells. Additionally, BA5 inhibited the proliferation of activated lymphocytes and the secretion of IL-2, IL-4 IL-6, IL-10, IL-17A and IFNɣ, in a concentration-dependent manner. Flow cytometry analysis in lymphocyte cultures showed that treatment with BA5 induces cell cycle arrest in pre-G1 phase followed by cell death by apoptosis. Moreover, BA5 also inhibited the activity of calcineurin, an enzyme that plays a critical role in the progression of cell cycle and T lymphocyte activation. BA5 has a synergistic inhibitory effect with dexamethasone on lymphoproliferation, showing a promising profile for drug combination. Finally, we observed immunosuppressive effects of BA5 in vivo in mouse models of lethal endotoxemia and delayed type hypersensitivity. Our results reinforce the potential use of betulinic acid and its derivatives in the search for potent immunomodulatory drugs.

SH479, a Betulinic Acid Derivative, Ameliorates Experimental Autoimmune Encephalomyelitis by Regulating the T Helper 17/Regulatory T Cell Balance

CD4+ T helper cells, especially T helper 17 (TH17) cells, combined with immune regulatory network dysfunction, play key roles in autoimmune diseases including multiple sclerosis (MS). Betulinic acid (BA), a natural pentacyclic triterpenoid, has been reported to be involved in anti-inflammation, in particular having an inhibitory effect on proinflammatory cytokine interleukin 17 (IL-17) and interferon-γ (IFN-γ) production. In this study, we screened BA derivatives and found a BA derivative, SH479, that had a greater inhibitory effect on TH17 differentiation. Our further analysis showed that SH479 had a greater inhibitory effect on TH17 and TH1, and a more stimulatory effect on regulatory T (Treg) cells. To evaluate the effects of SH479 on autoimmune diseases in vivo, we employed the extensively used MS mouse model experimental autoimmune encephalomyelitis (EAE). Our results showed that SH479 ameliorated clinical and histologic signs of EAE in both prevention and therapeutic protocols by regulating the TH17/Treg balance. SH479 dose-dependently reduced splenic lymphocyte proinflammatory factors and increased anti-inflammatory factors. Moreover, SH479 specifically inhibited splenic lymphocyte viability from EAE mice but not normal splenic lymphocyte viability. At the molecular level, SH479 inhibited TH17 differentiation by regulating signal transducer and activator of transcription-3 (STAT3) phosphorylation, DNA binding activity, and recruitment to the Il-17a promoter in CD4+ T cells. Furthermore, SH479 promoted the STAT5 signaling pathway and inhibited the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway. Together, our data demonstrated that SH479 ameliorated EAE by regulating the TH17/Treg balance through inhibiting the STAT3 and NF-κB pathways while activating the STAT5 pathway, suggesting that SH479 is a potential novel drug candidate for autoimmune diseases including MS.

Betulinic Acid Induces Apoptosis in Differentiated PC12 Cells Via ROS-Mediated Mitochondrial Pathway

Betulinic acid (BA), a pentacyclic triterpene of natural origin, has been demonstrated to have varied biologic activities including anti-viral, anti-inflammatory, and anti-malarial effects; it has also been found to induce apoptosis in many types of cancer. However, little is known about the effect of BA on normal cells. In this study, the effects of BA on normal neuronal cell apoptosis and the mechanisms involved were studied using differentiated PC12 cells as a model. Treatment with 50 μM BA for 24 h apparently induced PC12 cell apoptosis. In the early stage of apoptosis, the level of intracellular reactive oxygen species (ROS) increased. Afterwards, the loss of the mitochondrial membrane potential, the release of cytochrome c and the activation of caspase-3 occurred. Treatment with antioxidants could significantly reduce BA-induced PC12 cell apoptosis. In conclusion, we report for the first time that BA induced the mitochondrial apoptotic pathway in differentiated PC12 cells through ROS.

Development of betulinic acid as an agonist of TGR5 receptor using a new in vitro assay

BACKGROUND

G-protein-coupled bile acid receptor 1, also known as TGR5 is known to be involved in glucose homeostasis. In animal models, treatment with a TGR5 agonist induces incretin secretion to reduce hyperglycemia. Betulinic acid, a triterpenoid present in the leaves of white birch, has been introduced as a selective TGR5 agonist. However, direct activation of TGR5 by betulinic acid has not yet been reported.

METHODS

Transfection of TGR5 into cultured Chinese hamster ovary (CHO-K1) cells was performed to establish the presence of TGR5. Additionally, TGR5-specific small interfering RNA was employed to silence TGR5 in cells (NCI-H716 cells) that secreted incretins. Uptake of glucose by CHO-K1 cells was evaluated using a fluorescent indicator. Amounts of cyclic adenosine monophosphate and glucagon-like peptide were quantified using enzyme-linked immunosorbent assay kits.

RESULTS

Betulinic acid dose-dependently increases glucose uptake by CHO-K1 cells transfected with TGR5 only, which can be considered an alternative method instead of radioligand binding assay. Additionally, signals coupled to TGR5 activation are also increased by betulinic acid in cells transfected with TGR5. In NCI-H716 cells, which endogenously express TGR5, betulinic acid induces glucagon-like peptide secretion via increasing calcium levels. However, the actions of betulinic acid were markedly reduced in NCI-H716 cells that received TGR5-silencing treatment. Therefore, the present study demonstrates the activation of TGR5 by betulinic acid for the first time.

CONCLUSION

Similar to the positive control lithocholic acid, which is the established agonist of TGR5, betulinic acid has been characterized as a useful agonist of TGR5 and can be used to activate TGR5 in the future.

Betulinic Acid: Recent Advances in Chemical Modifications, Effective Delivery, and Molecular Mechanisms of a Promising Anticancer Therapy

An important method of drug discovery is examination of diverse life forms, including medicinal plants and natural products or bioactive compounds isolated from these sources. In cancer research, lead structures of compounds from natural sources can be used to design novel chemotherapies with enhanced biological properties. Betulinic acid (3β-hydroxy-lup-20(29)-en-28-oic acid or BetA) is a naturally occurring pentacyclic triterpene with a wide variety of biological activities, including potent antitumor properties. Non-malignant cells and normal tissues are not affected by BetA. Because BetA exerts its effects directly on the mitochondrion and triggers death of cancerous cells, it is an important alternative when certain chemotherapy drugs fail. Mitochondrion-targeted agents such as BetA hold great promise to circumvent drug resistance in human cancers. BetA is being developed by a large network of clinical trial groups with the support of the U.S. National Cancer Institute. This article discusses recent advances in research into anticancer activity of BetA, relevant modes of delivery, and the agent's therapeutic efficacy, mechanism of action, and future perspective as a pipeline anticancer drug. BetA is a potentially important agent in cancer therapeutics.

The pentacyclic triterpene Lupeol switches M1 macrophages to M2 and ameliorates experimental inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD), including ulcerative colitis and Crohn's disease, is a chronic inflammatory disease in the lower gastrointestinal tract. Mounting evidence suggests that the predominance of the classically activated (M1) macrophages versus the alternatively activated (M2) macrophages plays a role in the progression of IBD. Thus, agents able to shift pro-inflammatory M1 macrophages to anti-inflammatory M2 macrophages may be beneficial to IBD. The pentacyclic triterpene Lup-20(29)-en-3β-ol (Lupeol), a potent anti-inflammatory natural product, has been shown to inhibit pro-inflammatory cytokine production, suggesting it is potentially able to modulate macrophage polarization, thereby beneficial to IBD.

METHODS

CD4(+) monocytes were differentiated to M1 or M2 macrophages, which were cocultured with epithelial cell lines, T84 and Caco-2, in the absence or presence of Lupeol (10μM). Experimental colitis was induced with dextran sodium sulfate (DSS), with or without oral administration of Lupeol (50mg/kg, q.d.). Cytokines were measured with Luminex kits. M1/M2 genes were measured with real-time polymerase chain reaction. Macrophage phenotypes were defined by measuring M1 and M2 markers with confocal microscopy. Proteins were measured with Western blotting, while cell surface markers were measured with confocal microscopy or flow cytometry. Histology was evaluated with H&E staining.

RESULTS

Treatment of M1 macrophages with Lupeol resulted in a marked decrease in the production of pro-inflammatory cytokines, including IL-12, IL6, IL-1β and TNFα, and a marked increase in the production of IL-10, an anti-inflammatory cytokine. This was associated with a down-regulation of CD86, a typical marker of M1 macrophages, and an up-regulation of CD206, a typical M2 macrophage marker. IRF5, a transcription factor that is critically involved in M1 polarization, was down-regulated in M1 macrophages after being incubated with Lupeol, associated with a marked decrease in the phosphorylation of p38 mitogen activated protein kinase. Coculture of epithelial cells with M1 macrophages resulted in down-regulation of the tight junction protein ZO-1 and disruption of epithelial integrity, which were blocked by Lupeol treatment of the M1 macrophages. Moreover, oral administration of Lupeol to dextran sulfate sodium (DSS)-induced colitis mice resulted in mitigated intestinal inflammation and increased survival from lethal colitis, associated with decreased expression of M1-related genes and increased expression of M2-related genes.

CONCLUSION

Lupeol ameliorates experimental inflammatory bowel disease through, at least in part, inhibiting M1 and promoting M2 macrophages.

Highly lipophilic 3-epi-betulinic acid derivatives as potent and selective TGR5 agonists with improved cellular efficacy

AIM

TGR5 is a G protein-coupled receptor that is expressed in intestinal L-cells and stimulates glucagon-like peptide 1 (GLP-1) secretion. TGR5 may represent a novel target for the treatment of metabolic disorder. Here, we sought to design and synthesize a series of TGR5 agonists derived from the natural product betulinic acid.

METHODS

A series of betulinic acid derivatives were designed and synthesized. A cAMP assay was established using a HEK293 cell line expressing human TGR5. Luciferase reporter assay was established using HEK293 cells transfected with plasmids encoding human FXR and luciferase reporter. A human intestinal L-cell line NCI-H716 was used to evaluate the effects of the betulinic acid derivatives on GLP-1 secretion in vitro.

RESULTS

Biological data revealed that the 3-α-OH triterpenoids consistently show increased potency for TGR5 compared to their 3-β-OH epimers. 3-OH esterification increased the lipophilicity and TGR5 activity of 3-α betulinic derivatives and enhanced the activity differences between 3-α and 3-β derivatives. The 3-α-acyloxy betulinic acids also exhibited a significant dose-dependent GLP-1 secretion effect.

CONCLUSION

This study demonstrates that highly lipophilic 3-epi-betulinic acid derivatives can be potent and selective TGR5 agonists with improved cellular efficacy, and our research here provides a new strategy for the design and development of potent TGR5 agonists.