Synthesis and biological evaluation of berberine analogues as novel up-regulators for both low-density-lipoprotein receptor and insulin receptor

Synthesis and biological evaluation of Argemone mexicana-inspired antimicrobials

Due to the lack of new antimicrobial drug discovery in recent years and an ever-growing prevalence of multidrug-resistant "superbugs", there is a pressing need to explore alternative ways to combat pathogenic bacterial and fungal infections. Building upon our previous work in the field of medicinal phytochemistry, the present study is focused on designing, synthesizing, and testing the altered bioactivity of new variants of two original bioactive molecules found in the Argemone mexicana plant. Herein, we report upon 14 variants of berberine and four variants of chelerythrine that have been screened against a pool of 12 microorganisms (five Gram-positive and four Gram-negative bacteria, and three fungi). Additionally, the crystal structures of two berberine variants are described. Several berberine variants show enhanced antibacterial activity compared to the unaltered plant-derived molecule. We also report promising preliminary tumor cytotoxicity effects for a number of the berberine derivatives.

Discovery of the First in Class 9-N-Berberine Derivative as Hypoglycemic Agent with Extra-Strong Action

Berberine is well known for its ability to reduce the blood glucose level, but its high effective dose and poor bioavailability limits its use. In this work we synthesized a new derivative of berberine, 9-(hexylamino)-2,3-methylenedioxy-10-methoxyprotoberberine chloride (SHE-196), and analyzed the profile of its hypoglycemic effects. Biological tests have shown that the substance has a very pronounced hypoglycemic activity due to increased insulin sensitivity after single and multiple dosing. In obese type 2 diabetes mellitus (T2DM) mice, it was characterized by improved glucose tolerance, decreased fasting insulin levels and sensitivity, decreased total body weight and interscapular fat mass, and increased interscapular brown fat activity. All these effects were also confirmed histologically, where a decrease in fatty degeneration of the liver, an improvement in the condition of the islets of Langerhans and a decrease in the size of fat droplets in brown adipose tissue were found. Our results indicate that 9-(hexylamino)-2,3-methylenedioxy-10-methoxyprotoberberine chloride could be the first in a new series of therapeutic agents for the treatment of diabetes mellitus.

Berberine: A Promising Natural Isoquinoline Alkaloid for the Development of Hypolipidemic Drugs

Berberine, as a representative isoquinoline alkaloid, exhibits significant hypolipidemic activity in both animal models and clinical trials. Recently, a large number of studies on the lipid-lowering mechanism of berberine and studies for improving its hypolipidemic activity have been reported, but for the most part, they have been either incomplete or not comprehensive. In addition, there have been a few specific reviews on the lipid-reducing effect of berberine. In this paper, the physicochemical properties, the lipid-lowering mechanism, and studies of the modification of berberine all are discussed to promote the development of berberine as a lipid-lowering agent. Subsequently, this paper provides some insights into the deficiencies of berberine in the study of lipid-lowering drug, and based on the situation, some proposals are put forward.

Structure-activity relationship and biological evaluation of berberine derivatives as PCSK9 down-regulating agents

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein and its deficiency markedly enhanced the survival rate of patient with cardiovascular diseases (CVDs). Forty berberine (BBR) derivatives were synthesized and evaluated for their activities on down-regulating the transcription of PCSK9 in HepG2 cells, taking BBR as the lead. Structure-activity relationship (SAR) analysis revealed that 2,3-dimethoxy moiety might be beneficial for activity. Among them, 9k displayed the most potent activity with IC₅₀ value of 9.5 ± 0.5 μM, better than that of BBR. Also, it significantly decreased PCSK9 protein level at cellular level, as well as in the liver and serum of mice in vivo. Furthermore, 9k markedly increased LDLR expression and LDL-C clearance via down-regulating PCSK9 protein. The mechanism of action of 9k is targeting HNF1α and/or Sp1 cluster modulation upstream of PCSK9, a different one from BBR. Therefore, 9k might have the potential to be a novel PCSK9 transcriptional inhibitor for the treatment of atherosclerosis, worthy for further investigation.

Discovery of 7,9-Disulfatetrahydroberberine as Novel Lipid-Lowering Agents

Berberine (BBR), a well-known alkaloid, exhibits various pharmacological activities, especially hypolipidemic activity, which has attracted much interest from medicinal chemists in the past decade. However, little progress was made on the structural modification of BBR for improving lipid-lowering activity, mainly due to its unclear biological target and low safety. In this study, a new scaffold of 7,9-disulfatetrahydroberberine was discovered unexpectedly, provided with extremely low cytotoxicity. Hence, a novel series of highly safe 7,9-disulfatetrahydroberberines were designed, synthesized, and evaluated for their hypolipidemic activities. In order to investigate the significance of the 9-position substituent, another new series of 7-sulfatetrahydroberberines were designed and synthesized. Lipid-lowering experiments showed that among these compounds, 5f exhibited the best lipid-lowering activity based on two cell models, 3T3-L1 cells and HepG2 cells. Compared with the blank control, the inhibition rate of compound 5f against total cholesterol was over 60%, the inhibition rate against triglyceride was over 70%, the inhibition rate against low-density lipoprotein cholesterol was approximately 75%, and the inhibition rate against high-density lipoprotein cholesterol was close to 50%, which were far superior to the positive control BBR. This result also verified the feasibility of the development of BBR as a lipid-lowering drug via disubstituted modification at the 7- and 9-position.

Berberine and its structural analogs have differing effects on functional profiles of individual gut microbiomes

The understanding of the effects of compounds on the gut microbiome is limited. In particular, it is unclear whether structurally similar compounds would have similar or distinct effects on the gut microbiome. Here, we selected berberine (BBR), an isoquinoline quaternary alkaloid, and 16 structural analogs and evaluated their effects on seven individual gut microbiomes cultured in vitro. The responses of the individual microbiomes were evaluated by metaproteomic profiles and by assessing butyrate production. We show that both interindividual differences and compound treatments significantly contributed to the variance of metaproteomic profiles. BBR and eight analogs led to changes in proteins involved in microbial defense and stress responses and enrichment of proteins from Verrucomicrobia, Proteobacteria, and Bacteroidetes phyla. It also led to a decrease in proteins from the Firmicutes phylum and its Clostridiales order which correlated to decrease proteins involved in the butyrate production pathway and butyrate concentration. Three of the compounds, sanguinarine, chelerythrine, and ethoxysanguinarine, activated bacterial protective mechanisms, enriched Proteobacteria, increased opacity proteins, and markedly reduced butyrate production. Dihydroberberine had a similar function to BBR in enriching the Akkermansia genus. In addition, it showed less overall adverse impacts on the functionality of the gut microbiome, including a better maintenance of the butyrate level. Our study shows that ex vivo microbiome assay can assess differential regulating effects of compounds with subtle differences and reveals that compound analogs can have distinct effects on the microbiome.

Phytopharmacology and Clinical Updates of Berberis Species Against Diabetes and Other Metabolic Diseases

The incidences of diabetic mellitus and other metabolic diseases such as hypertension and hyperlipidemia are increasing worldwide; however, the current treatment is not able to control the rapidly increasing trend in diabetes mortality and morbidity. Studies related to the effectiveness of extracts and pure compounds obtained from plants have shown promising responses in preclinical and clinical studies related to these metabolic diseases. Plants belonging to the genus Berberis (Family: Berberidaceae) are widely distributed with nearly 550 species worldwide. Extracts and compounds obtained from Berberis species, especially Berberine alkaloid, showed effectiveness in the management of diabetes and other metabolic diseases. Various pharmacological experiments have been performed to evaluate the effects of Berberis extracts, berberine, and its natural and chemically synthesized derivatives against various cell and animal disease models with promising results. Various clinical trials conducted so far also showed preventive effects of Berberis extracts and berberine against metabolic diseases. The present review focuses on i) research updates on traditional uses, ii) phytopharmacology and clinical studies on Berberis species, and iii) active metabolites in the prevention and treatment of diabetes and other metabolic diseases with a detailed mechanism of action. Furthermore, the review critically analyzes current research gaps in the therapeutic use of Berberis species and berberine and provides future recommendations.

Rh(iii)-catalyzed synthesis of tetracyclic isoquinolinium salts via C–H activation and [4+2] annulation of 1-phenyl-3,4-dihydroisoquinolines and alkynes in ethanol

An efficient and convenient method to construct tetracyclic isoquinolinium salts via [Cp*RhCl₂]₂ catalyzed C–H activation and [4 + 2] annulation reactions in ethanol is described. This reaction is very fast and highly efficient in the green solvent ethanol. The reaction works with a broad substrate scope affording the products in good to excellent yields in a short time. Moreover, a ratio of S/C up to 10 000 could be achieved with gram scale synthesis.

An efficient method to construct tetracyclic isoquinolinium salts via C–H activation and [4 + 2] annulation reactions in ethanol is described.

Transforming berberine into its intestine-absorbable form by the gut microbiota

The gut microbiota is important in the pathogenesis of energy-metabolism related diseases. We focused on the interaction between intestinal bacteria and orally administered chemical drugs. Oral administration of berberine (BBR) effectively treats patients with metabolic disorders. However, because BBR exhibits poor solubility, its absorption mechanism remains unknown. Here, we show that the gut microbiota converts BBR into its absorbable form of dihydroberberine (dhBBR), which has an intestinal absorption rate 5-fold that of BBR in animals. The reduction of BBR to dhBBR was performed by nitroreductases of the gut microbiota. DhBBR was unstable in solution and reverted to BBR in intestine tissues via oxidization. Heat inactivation of intestinal homogenate did not inhibit dhBBR oxidization, suggesting the process a non-enzymatic reaction. The diminution of intestinal bacteria via orally treating KK-Ay mice with antibiotics decreased the BBR-to-dhBBR conversion and blood BBR; accordingly, the lipid- and glucose-lowering efficacy of BBR was reduced. Conclusively, the gut microbiota reduces BBR into its absorbable form of dhBBR, which then oxidizes back to BBR after absorption in intestine tissues and enters the blood. Thus, interaction(s) between the gut microbiota and orally administrated drugs may modify the structure and function of chemicals and be important in drug investigation.

A New Benzylisoquinoline Alkaloid from Leontice altaica

A new benzylisoquinoline alkaloid, lincangenine-4- β -D-glucopyranoside (1), has been isolated from the roots of Leontice altaica, together with 5 known alkaloids. Its structure was elucidated on the basis of D and 2D NMR data, and chemical means.

A room-temperature protocol to access isoquinolines through Ag(i) catalysed annulation of o-(1-alkynyl)arylaldehydes and ketones with NH4OAc: elaboration to berberine and palmatine

A silver catalysed protocol for the synthesis of a wide range of isoquinolines from o-(1-alkynyl)arylaldehydes has been developed under mild conditions and elaborated to the synthesis of berberine and palmatine.

Knockdown of the NHR-8 nuclear receptor enhanced sensitivity to the lipid-reducing activity of alkaloids in Caenorhabditis elegans

Caenorhabditis elegans is a versatile, whole-organism model for bioactivity screening. However, this worm has extensive defensive mechanisms against xenobiotics which limit its use for screening of pharmacologically active compounds. In this study, we report that knockdown of nhr-8, a gene involved in the xenobiotic response, increased the worm's sensitivity to the lipid-reducing effects of some isoquinoline alkaloids, especially berberine. On the other hand, crude extract of rhizome and cultured cells showed enhanced biological activity compared to the pure alkaloids in wild type worm, but this enhanced activity was not detected in nhr-8 RNAi worm, suggesting that some components in cell extracts might interfere with the defense response in this worm. The possibility of using C. elegans as a model for screening bioactive chemicals is discussed.

Nutraceuticals in Lipid-Lowering Treatment

Lipid-lowering drugs may cause adverse effects and, although lipid targets may be achieved, a substantial residual cardiovascular (CV) risk remains. Treatment with agents mimicking proteins present in the body, such as incretin-based therapies, provided promising results. However, in order to improve lipids and CV risk, lifestyle measures remain important. Some researchers focused on nutraceuticals that may beneficially affect metabolic parameters and minimize CV risk. Chitosan, a dietary fiber, can regulate lipids with benefit on anthropometric parameters. The beneficial properties of dietary supplements (such as green tea extract, prebiotics, plant sterols, and stanols) on plasma lipids, lipoproteins, blood pressure, glucose, and insulin levels and their anti-inflammatory and anti-oxidant effects are documented. However, larger, prospective clinical trials are required to confirm such benefits. Such treatments may be recommended when lipid-lowering drugs are neither indicated nor tolerated as well as in order to achieve therapeutic targets and/or overcome residual CV risk.

Berberine moderates glucose metabolism through the GnRH-GLP-1 and MAPK pathways in the intestine

Background

Berberine is known to improve glucose and lipid metabolism disorders, but it poorly absorbed into the blood stream from the gut. Therefore, the exact underlying mechanism for berberine is still unknown. In this study, we investigated the effect of berberine on glucose metabolism in diabetic rats and tested the hypothesis that berberine acts directly in the terminal ileums.

Methods

Rats were divided into a control group, diabetic group (DM), low dose of berberine group (BerL) and high dose of berberine group (BerH). Ileum samples were analyzed using a Roche NimbleGen mRNA array, qPCR and immunohistochemistry.

Results

We found that 8 weeks of treatment with berberine significantly decreased fasting blood glucose levels. An oral glucose tolerance test (OGTT) showed that blood glucose was significantly reduced in the BerL and BerH groups before and at 30 min, 60 min and 120 min after oral glucose administration. Plasma postprandial glucagon-like peptide-1 (GLP-1) levels were increased in the berberine-treated groups. The ileum from the BerH group had 2112 genes with significantly changed expression (780 increased, 1332 decreased). KEGG pathway analyses indicated that all differentially expressed genes included 9 KEGG pathways. The top two pathways were the MAPK signaling pathway and the GnRH signaling pathway. Q-RT-PCR and immunohistochemistry verified that glucagon-like peptide 1 receptor (Glp1r) and mitogen activated protein kinase 10 (Mapk10) were significantly up-regulated, in contrast, gonadotropin releasing hormone receptor (Gnrhr) and gonadotropin-releasing hormone 1 (Gnrh1) were down-regulated in the BerH group.

Conclusion

Our data suggest that berberine can improve blood glucose levels in diabetic rats. The mechanisms involved may be in the MAPK and GnRh-Glp-1 pathways in the ileum.

Synthesis and spectroscopic studies of berberine immobilized modified cellulose material

This report describes the synthesis, characterization and spectroscopic studies of berberine immobilized modified cellulose materials, which could be a promising new biocompatible fluorescence material because berberine is a natural fluorescent molecule having important pharmacological aspects including selective binding with DNA G-quadruplex.

Synthesis and structure-activity relationship of 8-substituted protoberberine derivatives as a novel class of antitubercular agents

Background

The emergence of multi-drug resistant tuberculosis (MDR-TB) has heightened the need for new chemical classes and innovative strategies to tackle TB infections. It is urgent to discover new classes of molecules without cross-resistance with currently used antimycobacterial drugs.

Results

Eighteen new 8-substituted protoberberine derivatives were synthesized and evaluated for their anti-mycobacterial activities against Mycobacterium tuberculosis (M. tuberculosis) strain H₃₇Rv. Among them, compound 7g was the most effective antitubercular agent with minimum inhibitory concentration (MIC) of 0.5 μg/mL. Moreover, it also afforded a potent antitubercular effect against clinically isolated MDR strains of M. tuberculosis with MICs ranging from 0.25 to 1.0 μg/mL, suggesting a novel mode of action.

Conclusions

The structure−activity relationship (SAR) analysis revealed that introduction of a substituent at the 8-position in pseudoprotoberberine, especially an n-decyl, could significantly enhance the anti-TB activity. We consider 8-n-decylberberines to be a novel family of anti-tubercular agents with an advantage of inhibiting MDR strains of M. tuberculosis.

Effects of β-cyclodextrin on the intestinal absorption of berberine hydrochloride, a P-glycoprotein substrate

The major objective of this work is to investigate the enhancing effect of β-cyclodextrin on the intestinal absorption of berberine hydrochloride, a P-glycoprotein (Pgp) substrate. The inclusion complexation behavior of BBH with β-CD was investigated by phase-solubility diagram, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray powder diffractometry, NMR spectroscopy, and molecular modeling studies. Results indicated that the 1,3-benzodioxole of BBH was included into the cavity of β-CD to form an inclusion complex which exhibited higher dissolution rate than BBH in vitro. The intestinal absorption of the inclusion complex in rats was significantly higher than the free drug due to its solubilizing effect and Pgp modulatory activity. The mechanisms of β-CD on Pgp modulation were demonstrated by modifying the Pgp ATPase activity, the Pgp mRNA level and the Pgp expression.

Synthesis and structure-activity relationship of berberine analogues in LDLR up-regulation and AMPK activation

Currently there is no approved medicine for the treatment of metabolic syndrome. A series of new derivatives of berberine (BBR) or pseudoberberine (1) was synthesized and evaluated for their activity on AMP-activated protein kinase (AMPK) activation and up-regulatory low-density-lipoprotein receptor (LDLR) gene expression, respectively. In addition, the four major metabolites of BBR in vivo were also examined for their activity on AMPK in order to further understand the chemical mechanisms responsible for its glucose-lowering efficacy. Among those BBR analogues, compound 1 exhibited the potential effect on AMPK activation and LDLR up-regulation as compared with BBR. The results suggested that compound 1 might be a multiple-target agent for the treatment of metabolic syndrome, and thus was selected as a promising drug candidate for further development.

Synthesis, structure-activity relationship and in vitro anti-mycobacterial evaluation of 13-n-octylberberine derivatives

Twenty-eight new 13-n-octylberberine derivatives were synthesized and evaluated for their activities against drug-susceptible Mycobacterium tuberculosis (M. tuberculosis) strain H(37)Rv. Among these compounds, compound 16e was the most effective anti-tubercular agent with a MIC value of 0.125 μg/mL. Importantly, compound 16e exhibited more potent effect against rifampicin (RIF)- and isoniazid (INH)-resistant M. tuberculosis strains than both RIF and INH, suggesting a new mechanism of action. Therefore, it has been selected as a drug candidate for further investigation, or as a chemical probe for identifying protein target and studying tuberculosis biology. We consider 13-n-octylberberine analogs to be a promising novel class of antituberculars against multi-drug-resistant (MDR) strains of M. tuberculosis.

Hypoglycemic and insulin-sensitizing effects of berberine in high-fat diet- and streptozotocin-induced diabetic rats

Hypoglycemic effects of berberine (BBR) have been reported in several studies in cell and animal models. However, the mechanisms of action are not fully understood. The present study was therefore aimed at determining the effect and underlying mechanisms of action of BBR on diabetes in a high-fat diet- and streptozotocin-induced diabetic rat model. Ninety male Sprague-Dawley rats, 150 to 170 g, were housed individually in cages. Two groups (n = 12 each) were fed the AIN-93G diet (normal control) and the same diet modified to contain 33% fat and 2% cholesterol (high-fat control), respectively. The third group (n = 66) was fed the high-fat diet and injected intraperitoneally 2 weeks later with 35 mg/kg body weight of streptozotocin in citrate buffer (pH 4.5). The rats in both control groups were injected with the vehicle. After 12 days, rats with semifasting (5 hours) blood glucose levels between 14 and 25 mmol/L were divided into 4 groups (n = 12 each) and treated with 0 (diabetic control), 50, 100, and 150 mg/kg/d of BBR for 6 weeks while continuing on the high-fat diet. Hypoglycemic effects of BBR were consistently demonstrated by semifasting and fasting blood glucose levels, and insulin-sensitizing effects were seen during oral glucose tolerance testing. Berberine also reduced food intake while having no effect on body weight in diabetic rats. No effect of BBR was observed on plasma levels of insulin, adipokines (leptin and adiponectin), or inflammatory cytokines (tumor necrosis factor-α and C-reactive protein). Berberine did not affect the state of oxidative stress as assessed by the activity of superoxide dismutase and the concentrations of malondialdehyde and reduced and oxidized glutathione in the liver. These findings demonstrated the hypoglycemic and insulin-sensitizing capabilities of BBR, with the underlying mechanisms awaiting further investigation.

Potent antiprotozoal activity of a novel semi-synthetic berberine derivative

Treatment of diseases such as African sleeping sickness and leishmaniasis often depends on relatively expensive or toxic drugs, and resistance to current chemotherapeutics is an issue in treating these diseases and malaria. In this study, a new semi-synthetic berberine analogue, 5,6-didehydro-8,8-diethyl-13-oxodihydroberberine chloride (1), showed nanomolar level potency against in vitro models of leishmaniasis, malaria, and trypanosomiasis as well as activity in an in vivo visceral leishmaniasis model. Since the synthetic starting material, berberine hemisulfate, is inexpensive, 8,8-dialkyl-substituted analogues of berberine may lead to a new class of affordable antiprotozoal compounds.

Synthesis and structure-activity relationship of N-(2-arylethyl) isoquinoline derivatives as human scavenger receptor CD36 antagonists

By using human scavenger receptor CD36 as the target, twenty-five N-(2-arylethyl) isoquinoline derivatives were designed, synthesized and evaluated for their antagonistic activities for CD36-oxidatively low density lipoprotein (oxLDL) binding. The primary analysis of structure-activity relationship (SAR) indicated a methoxyl at the 7-position and a hydroxyl at the 6- or 8-position could afford good activities. Among these analogs, compounds 7e and 7t showed the potential CD36 antagonistic activities with IC(50) values of 0.2 and 0.8 μg/mL, respectively. Furthermore, both of them could effectively inhibit oxLDL uptake in insect Sf9 cells overexpressing human CD36, and thus have been selected for further investigation. We consider N-(2-arylethyl) isoquinoline analogs to be a family of novel CD36 antagonists.

Berberine regulated Gck, G6pc, Pck1 and Srebp-1c expression and activated AMP-activated protein kinase in primary rat hepatocytes

The effects of hormonal and dietary stimuli on hepatic glucose and lipid homeostasis include regulation of gene expression. Berberine, an effective compound in certain Chinese medicinal herbs, has been reported to lower plasma glucose and lipid levels in diabetic and hypercholesterolemic patients. We hypothesized that it may affect the expression of hepatic genes involved in glucose and lipid metabolism. The effects of berberine hydrochloride on viability, gene expression, and activation of AMP activated protein kinase (AMPK) in primary hepatocytes from Sprague-Dawley (SD), Zucker lean (ZL) or fatty (ZF) rats were examined with MTT assay, real-time PCR, and western blotting, respectively. Berberine hydochloride at 50 µM or higher caused cytotoxic effects on hepatocytes. In SD and ZL hepatocytes, it induced Gck and suppressed G6pc expression at 10 and 25 µM, but not as potent as 1 nM insulin. Its effects on Pck1, and insulin-regulated Gck and G6pc expression depended on the hepatocyte sources and the dosage used. In ZF hepatocytes, it increased Gck, and suppressed Pck1 and G6pc expression without insulin. Its effects on Gck and G6pc, but not Pck1 expression, were additive with insulin. Berberine hydrochloride at 25 µM attenuated insulin-suppressed Pck1 (ZL/ZF cells), and insulin-induced Srebp-1c expression (SD/ZL/ZF cells), suggesting modulation of insulin action. Berberine hydrochloride did not alter these genes' mRNA stability. Its treatment caused a dose-dependent increase of phosphorylation of AMPKα, and its substrate, acetyl-CoA carboxylase, in primary hepatocytes. We conclude that berberine hydrochloride regulated the transcription of hepatic genes involved in glucose and fatty acid metabolism.

Protein kinase D activation stimulates the transcription of the insulin receptor gene

Our previous studies proved that berberine (BBR) up-regulates the insulin receptor (InsR) gene by stimulating its promoter and calphostin C blocks this effect. Here, the present study was designed to discover the specific kinase isoform(s) used by berberine. In the blocking experiment, we found that Gö6976, a kinase inhibitor that potently inhibit PKCμ/protein kinase D 1 (PKD1), effectively and specifically reduced the activity of BBR on InsR. PKD1/PKCμ is a member of the PKD family that also covers PKD2 and PKD3/PKCν with high homology. The role of PKD1 in InsR expression was also proved by using another PKD-activator oligomycin. In the RNA interference experiment, we found that the effects of BBR on InsR expression and on cellular glucose consumption were partially eliminated by silencing any one of the three PKDs and were totally abolished by silencing all of them. BBR enhanced the PKD1 catalytic activity, but not its expression. Along with BBR treatment, PKD1 ser916 autophosphorylation was increased time- and dose-dependently, indicating an activation of PKD1 by BBR. BBR also induces PKD1 translocation from cytosol-to-plasma membrane, further verifying the activation of PKD1. These results suggest that the PKD family is involved in the transcriptional regulation of the InsR gene; we consider it to be a potential new target to discover drugs for sugar-related disorders in the future.

Design, synthesis, and cholesterol-lowering efficacy for prodrugs of berberrubine

In order to enhance oral bioavailability of berberine (BBR) for its cholesterol-lowering efficacy in vivo, a series of ester or ether prodrugs of berberrubine (M1), which is an active metabolite of BBR after first-pass metabolism, were designed, semi-synthesized, and evaluated. Among these M1 prodrugs, compound 5g possessing palmitate at the 9-position showed a moderate LogP value and esterase hydrolysis rate for releasing M1 in blood. Its cholesterol-lowering efficacy in vivo was evaluated in hyperlipidemic SD rats. Compound 5g (100mg/kg/d) reduced blood CHO and LDL-c by 35.8% and 45.5%, respectively, similar to that by BBR. It also exhibited a good safety in rats with no side-effect on liver and kidney function. Therefore, the design of M1 prodrug appears to be an effective strategy to improve pharmacokinetic feature of BBR for its lipid-lowering efficacy in vivo.

8,8-Dimethyldihydroberberine with improved bioavailability and oral efficacy on obese and diabetic mouse models

The clinical use of the natural alkaloid berberine (BBR) as an antidiabetic reagent is limited by its poor bioavailability. Our previous work demonstrated that dihydroberberine (dhBBR) has enhanced bioavailability and in vivo efficacy compared with berberine. Here we synthesized the 8,8-dimethyldihydroberberine (Di-Me) with improved stability, and bioavailability over dhBBR. Similar to BBR and dhBBR, Di-Me inhibited mitochondria respiration, increased AMP:ATP ratio, activated AMPK and stimulated glucose uptake in L6 myotubes. In diet-induced obese (DIO) mice, Di-Me counteracted the increased adiposity, tissue triglyceride accumulation and insulin resistance, and improved glucose tolerance at a dosage of 15mg/kg. Administered to db/db mice with a dosage of 50mg/kg, Di-Me effectively reduced random fed and fasting blood glucose, improved glucose tolerance, alleviated insulin resistance and reduced plasma triglycerides, with better efficacy than dhBBR at the same dosage. Our work highlights the importance of dihydroberberine analogs as potential therapeutic reagents for type 2 diabetes treatment.

Berberine inhibits PTP1B activity and mimics insulin action

Type 2 diabetes patients show defects in insulin signal transduction that include lack of insulin receptor, decrease in insulin stimulated receptor tyrosine kinase activity and receptor-mediated phosphorylation of insulin receptor substrates (IRSs). A small molecule that could target insulin signaling would be of significant advantage in the treatment of diabetes. Berberine (BBR) has recently been shown to lower blood glucose levels and to improve insulin resistance in db/db mice partly through the activation of AMP-activated protein kinase (AMPK) signaling and induction of phosphorylation of insulin receptor (IR). However, the underlying mechanism remains largely unknown. Here we report that BBR mimics insulin action by increasing glucose uptake ability by 3T3-L1 adipocytes and L6 myocytes in an insulin-independent manner, inhibiting phosphatase activity of protein tyrosine phosphatase 1B (PTP1B), and increasing phosphorylation of IR, IRS1 and Akt in 3T3-L1 adipocytes. In diabetic mice, BBR lowers hyperglycemia and improves impaired glucose tolerance, but does not increase insulin release and synthesis. The results suggest that BBR represents a different class of anti-hyperglycemic agents.