Silibinin protects β cells from glucotoxicity through regulation of the Insig-1/SREBP-1c pathway

Silibinin as a major component of milk thistle seed provides promising influences against diabetes and its complications: a systematic review

Silibinin, or silybin, is a polyphenolic flavonoid and the main active component of silymarin, isolated from the seeds of the milk thistle plant (Silybum marianum). It has been shown to have antioxidant, antineoplastic, hepatoprotective, neuroprotective, anti-inflammatory, antimicrobial, and antidiabetic effects. In this systematic review, a literature search was conducted from inception until January 2024 on major electronic databases (PubMed, Scopus, Web of Science, and Google Scholar) to identify studies assessing the effects of silibinin on diabetes and its associated complications in different molecular, cellular, animal, and clinical studies. Silibinin has been shown to improve diabetic conditions through a variety of mechanisms, including reducing insulin resistance (IR), lowering reactive oxygen species (ROS) levels, and affecting glycolysis, gluconeogenesis, and glycogenolysis. Silibinin treatment reduced blood glucose (BG) levels, oxidative stress markers, and inflammatory cytokines while increasing glycosylated hemoglobin (HbA1C) and antioxidative marker levels in various cellular and animal models of diabetes. It also ameliorated levels of triglyceride (TG), cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL). Furthermore, silibinin has been identified as an effective treatment for diabetic complications, including hepatic damage, endothelial dysfunction, neuropathy, nephropathy, retinopathy, and osteoporosis. The promising anti-inflammatory, antioxidant, antidiabetic, and insulin-sensitizing activities of silibinin were also supported in clinical studies. The administration of silibinin could possess multiple protective impacts in improving DM and its complications. Nevertheless, further well-designed investigations are necessary to better understand its mechanisms.

Silibinin as a promising treatment for diabetes: Insights into behavioral and metabolic changes in an animal model

Diabetes mellitus is causing serious health problems in the chronic period. Silibinin is a flavonoid obtained from the milk thistle (Silybum marianum), which is among the herbal ethnopharmacological administrations. In studies with silibinin, it has been reported that it increases the activity of pancreatic beta cells and insulin sensitivity and has a hyperglycemia-reducing effect. However, behavioral parameters have not been evaluated together with insulin levels and liver function tests. Our aim in this study was to examine the effects of silibinin on insulin secretion, anxiety-like behaviors, and learning in a streptozotocin (STZ)-induced rat diabetes model. Wistar albino rats weighing 200-250 g were divided into 4 groups. Control: Saline solution, Diabetes: STZ 45 mg/kg, S 100: STZ 45 mg/kg + Silibinin 100 mg/kg, S 200: STZ 45 mg/kg + Silibinin 200 mg/kg. Administrations were continued for 21 days. On the 21st day, open field and elevated plus maze as unconditional anxiety tests; Barnes maze for learning and memory; and rotarod test for locomotor activity were conducted. Following behavioral tests, blood samples were taken under anesthesia. Blood glucose levels and ALT values were measured. Insulin levels were measured with an ELISA plate reader. Silibinin shortened the time to find the correct hole. Silibinin prevented the decrease in insulin due to STZ, exhibited a hyperglycemia-reducing effect and decreased the elevation of ALT.

Silibinin alleviates ferroptosis of rat islet β cell INS-1 induced by the treatment with palmitic acid and high glucose through enhancing PINK1/parkin-mediated mitophagy

Type 2 diabetes (T2DM) is induced by the abundance of glucose and lipids, which causes glucolipotoxicity to the pancreatic β-cells. Silibinin is a natural flavonoid possessing the regulatory activity on insulin production and therapeutic activity in diabetic mice; however, its effect on glucolipotoxicity is not fully explained. This in vitro study investigates the effects of silibinin on palmitic acid (PA) and high glucose (HG)-induced cell loss and ferroptosis of rat insulinoma INS-1 cells. In the cells treated with PA and HG, expressions of glucose transporter 4 (Glut4) and carnitine acyltransferase I (CPT1) for β-oxidation of fatty acids are reduced. Mitochondria are the metabolic organelles for glucose and fatty acids. The mitochondrial membrane potential (MMP) and ATP production were decreased, while the ROS level was elevated in the cells treated with PA and HG, indicating an induction of mitochondrial disorder. Cell loss was partially rescued by ferroptosis inhibition, suggesting an involvement of ferroptosis in the cells treated with PA and HG. More importantly, the increases in total iron, lipid ROS, MDA and COX-2, and the decrease in ferroptosis inhibitory molecules GSH, GPX4 and FSP1 appeared in the cells treated with PA and HG, confirming the occurrence of ferroptosis. Moreover, PINK1/parkin-mediated mitophagy, a vital process for selective elimination of damaged mitochondria, was blocked. Interestingly, silibinin rescued the mitochondria, restricted the ferroptosis and restored the mitophagy. By using the pharmacological stimulator and inhibitor of mitophagy, and si-RNA transfection to silence PINK1 expression, silibinin's protective effect against ferroptosis caused by PA and HG treatment was found to depend on mitophagy. Collectively, our current study reveals the new mechanisms for the protection of silibinin against the injury of INS-1 cells treated with PA and HG, elucidates the participation of ferroptosis in glucolipotoxicity, highlighting the involvement of mitophagy in defense against ferroptotic cell death.

Effects of silibinin on apoptosis and insulin secretion in rat RINm5F pancreatic β-cells

We investigated whether silibinin, a flavonoid, might be useful for treating diabetes mellitus by treating five groups of rat RINm5F β-insulinemia cells as follows: control streptozotocin (STZ) group administered citrate buffer and dimethyl sulfoxide; STZ group administered 20 mM STZ; silibinin group administered 50 µM silibinin; pre-silibinin group administered 50 µM silibinin 5 h before administering 20 mM STZ; simultaneous group administered 50 µM silibinin at the same time as 20 mM STZ. For all groups, MTT assay and flow cytometry were used to evaluate cell viability and necrosis, respectively. Glucose-stimulated insulin secretion (GSIS) and insulin cell content were determined using enzyme-linked immunosorbent assay. Also, expression of genes, pancreatic and duodenal homeobox 1 (pdx1), neuronal differentiation 1 (neurod1), v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog A (mafa), glucose transporter 2 (glut2)) was determined using the real-time polymerase chain reaction. We found that silibinin improved the viability of RINm5F cells and increased GSIS and cellular insulin under glucotoxic conditions. Silibinin increased the expression of neurod1, mafa and glut2, but reduced pdx1 expression. Our findings suggest that silibinin might increase glucose sensitivity and insulin synthesis under glucotoxic conditions, which could be useful for diabetes treatment.

Venom Peptides, Polyphenols and Alkaloids: Are They the Next Antidiabetics That Will Preserve β-Cell Mass and Function in Type 2 Diabetes?

Improvement of insulin secretion by pancreatic β-cells and preservation of their mass are the current challenges that future antidiabetic drugs should meet for achieving efficient and long-term glycemic control in patients with type 2 diabetes (T2D). The successful development of glucagon-like peptide 1 (GLP-1) analogues, derived from the saliva of a lizard from the Helodermatidae family, has provided the proof of concept that antidiabetic drugs directly targeting pancreatic β-cells can emerge from venomous animals. The literature reporting on the antidiabetic effects of medicinal plants suggests that they contain some promising active substances such as polyphenols and alkaloids, which could be active as insulin secretagogues and β-cell protectors. In this review, we discuss the potential of several polyphenols, alkaloids and venom peptides from snake, frogs, scorpions and cone snails. These molecules could contribute to the development of new efficient antidiabetic medicines targeting β-cells, which would tackle the progression of the disease.

Effect of Silibinin on Dyslipidemia and Glycemic Alteration Associated with Polycystic Ovarian Syndrome: An Experimental Study on Rats

PURPOSE

Females with polycystic ovary syndrome (PCOS) are found to have hormonal and metabolic alterations. This study investigated the efficacy of the flavonolignan silibinin in restoring the metabolic alterations associated with letrozole-induced PCOS in rats.

METHODS

The study allocated 42 albino rats into two groups. The first group was a normal control group (n=12) in which only the vehicle was given. The second group, the PCOS group (n=30), received letrozole (1 mg/kg/day) orally for 21 days. On day 21, six animals from the first group and six animals from the second group were sacrificed to confirm the development of PCOS, and the rest of the animals (n=24) in the second group were distributed equally into four groups: the PCOS group received vehicle, the metformin (MET) group received 300 mg/kg metformin orally, and the low-dose silibinin (LD-100) and high-dose silibinin (HD-200) groups received 100 and 200 mg/kg silibinin intraperitoneally, respectively. Blockade of the estrus cycle in the diestrus phase, hyperglycemia, and body weight elevation were related to a positive PCOS induction. An oral glucose tolerance test (OGTT) was also carried out for all animals on day 21 and on the last day of the experiment (day 40) to investigate the effect of silibinin on insulin resistance. The rats' lipid profile, insulin level, estrus cycle patterns, body weight, and weights of the ovaries and uterus were also measured on day 40.

RESULTS

A 19-day silibinin treatment led to the restoration of regular estrus cyclicity, reduced the glucose spike in OGTT analysis, and alleviated insulin resistance in PCOS rats. There was a statistically non-significant decrement in insulin level and lipid profile in the treatment groups.

CONCLUSION

Silibinin flavonolignan ameliorated some metabolic and reproductive alterations associated with PCOS. This could be related to the decreased insulin resistance, and antiandrogenic and phytoestrogenic activity of silibinin. Further study with longer term therapy is recommended to clarify more potential effects of silibinin and its mechanism of action in PCOS.

Methyl Caffeate Isolated from the Flowers of Prunus persica (L.) Batsch Enhances Glucose-Stimulated Insulin Secretion

Phenolic compounds from natural products are considered effective enhancers of insulin secretion to prevent and treat type 2 diabetes (T2DM). The flowers of Prunus persica (L.) Batsch also contain many phenolic compounds. In this study, the extract of flowers of P. persica (PRPE) exhibited an insulin secretion effect in a glucose-stimulated insulin secretion (GSIS) assay, which led us to isolate and identify the bioactive compound(s) responsible for these effects. Compounds isolated from PRPE were screened for their efficacy in INS-1 rat pancreatic β-cells. Among them, caffeic acid (5), methyl caffeate (6), ferulic acid (7), chlorogenic acid (8), naringenin (11), nicotiflorin (12), and astragalin (13) isolated from PRPE increased GSIS without inducing cytotoxicity. Interestingly, the GSIS effect of methyl caffeate (6) as a phenolic compound was similar to gliclazide, an antidiabetic sulfonylurea drug. Western blot assay showed that methyl caffeate (6) enhanced the related signaling proteins of the activated pancreatic and duodenal homeobox-1 (PDX-1) and peroxisome proliferator-activated receptor-γ (PPAR-γ), but also the phosphorylation of the total insulin receptor substrate-2 (IRS-2), phosphatidylinositol 3-kinase (PI3K), and Akt, which influence β-cell function and insulin secretion. This study provides evidence that methyl caffeate (6) isolated from PRPE may aid in the management of T2DM.

Health Benefits of Silybum marianum: Phytochemistry, Pharmacology, and Applications

Silybum marianum (SM), a well-known plant used as both a medicine and a food, has been widely used to treat various diseases, especially hepatic diseases. The seeds and fruits of SM contain a flavonolignan complex called silymarin, the active compounds of which include silybin, isosilybin, silychristin, dihydrosilybin, silydianin, and so on. In this review, we thoroughly summarize high-quality publications related to the pharmacological effects and underlying mechanisms of SM. SM has antimicrobial, anticancer, hepatoprotective, cardiovascular-protective, neuroprotective, skin-protective, antidiabetic, and other effects. Importantly, SM also counteracts the toxicities of antibiotics, metals, and pesticides. The diverse pharmacological activities of SM provide scientific evidence supporting its use in both humans and animals. Multiple signaling pathways associated with oxidative stress and inflammation are the common molecular targets of SM. Moreover, the flavonolignans of SM are potential agonists of PPARγ and ABCA1, PTP1B inhibitors, and metal chelators. At the end of the review, the potential and perspectives of SM are discussed, and these insights are expected to facilitate the application of SM and the discovery and development of new drugs. We conclude that SM is an interesting dietary medicine for health enhancement and drug discovery and warrants further investigation.

Involvement of Estrogen Receptor-α in the Activation of Nrf2-Antioxidative Signaling Pathways by Silibinin in Pancreatic β-Cells

Silibinin exhibits antidiabetic potential by preserving the mass and function of pancreatic β-cells through up-regulation of estrogen receptor-α (ERα) expression. However, the underlying protective mechanism of silibinin in pancreatic β-cells is still unclear. In the current study, we sought to determine whether ERα acts as the target of silibinin for the modulation of antioxidative response in pancreatic β-cells under high glucose and high fat conditions. Our in vivo study revealed that a 4-week oral administration of silibinin (100 mg/kg/day) decreased fasting blood glucose with a concurrent increase in levels of serum insulin in high-fat diet/streptozotocin-induced type 2 diabetic rats. Moreover, expression of ERα, NF-E2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) in pancreatic β-cells in pancreatic islets was increased by silibinin treatment. Accordingly, silibinin (10 μM) elevated viability, insulin biosynthesis, and insulin secretion of high glucose/palmitate-treated INS-1 cells accompanied by increased expression of ERα, Nrf2, and HO-1 as well as decreased reactive oxygen species production in vitro. Treatment using an ERα antagonist (MPP) in INS-1 cells or silencing ERα expression in INS-1 and NIT-1 cells with siRNA abolished the protective effects of silibinin. Our study suggests that silibinin activates the Nrf2-antioxidative pathways in pancreatic β-cells through regulation of ERα expression.

In Vivo Analysis of miR-34a Regulated Glucose Metabolism Related Genes in Megalobrama amblycephala

The Megalobrama amblycephala (M. amblycephala) is one of the most important economic freshwater fish in China. The molecular mechanism under the glucose intolerance responses which affects the growth performance and feed utilization is still confused. miR-34a was reported as a key regulator in the glucose metabolism, but how did the miR-34a exert its function in the metabolism of glucose/insulin in M. amblycephala was still unclear. In this study, we intraperitoneally injected the miR-34a inhibitor (80 nmol/100 g body weight) into M. amblycephala (fed with high starch diet, 45% starch) for 12 h, and then analyzed the gene expression profiling in livers by RNA-seq. The results showed that miR-34a expression in M. amblycephala livers was inhibited by injection of miR-34a inhibitor, and a total of 2212 differentially expressed genes (DEGs) were dysregulated (including 1183 up- and 1029 downregulated DEGs). Function enrichment analysis of DEGs showed that most of them were enriched in the peroxisome proliferator-activated receptor (PPAR), insulin, AMP-activated protein kinase (AMPK) and janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathways, which were all associated with the glucose/lipid metabolic and biosynthetic processes. In addition, we examined and verified the differential expression levels of some genes involved in AMPK signaling pathway by qRT-PCR. These results demonstrated that the inhibition of miR-34a might regulate glucose metabolism in M. amblycephala through downstream target genes.

Influence of Flavonoids on Mechanism of Modulation of Insulin Secretion

BACKGROUND

The development of alternatives for insulin secretion control in vivo or in vitro represents an important aspect to be investigated. In this direction, natural products have been progressively explored with this aim. In particular, flavonoids are potential candidates to act as insulin secretagogue.

OBJECTIVE

To study the influence of flavonoid on overall modulation mechanisms of insulin secretion.

METHODS

The research was conducted in the following databases and platforms: PubMed, Scopus, ISI Web of Knowledge, SciELO, LILACS, and ScienceDirect, and the MeSH terms used for the search were flavonoids, flavones, islets of Langerhans, and insulin-secreting cells.

RESULTS

Twelve articles were included and represent the basis of discussion on mechanisms of insulin secretion of flavonoids. Papers in ISI Web of Knowledge were in number of 1, Scopus 44, PubMed 264, ScienceDirect 511, and no papers from LILACS and SciELO databases.

CONCLUSION

According to the literature, the majority of flavonoid subclasses can modulate insulin secretion through several pathways, in an indication that corresponding molecule is a potential candidate for active materials to be applied in the treatment of diabetes.

SUMMARY

The action of natural products on insulin secretion represents an important investigation topic due to their importance in the diabetes controlIn addition to their typical antioxidant properties, flavonoids contribute to the insulin secretionThe modulation of insulin secretion is induced by flavonoids according to different mechanisms. Abbreviations used: KATP channels: ATP-sensitive K+ channels, GLUT4: Glucose transporter 4, ERK1/2: Extracellular signal-regulated protein kinases 1 and 2, L-VDCCs: L-type voltage-dependent Ca+2 channels, GLUT1: Glucose transporter 1, AMPK: Adenosine monophosphate-activated protein kinase, PTP1B: Protein tyrosine phosphatase 1B, GLUT2: Glucose transporter 2, cAMP: Cyclic adenosine monophosphate, PKA: Protein kinase A, PTK: Protein tyrosine kinase, CaMK II: Ca2+/calmodulin-dependent protein kinase II, GSIS: Glucose-stimulated insulin secretion, Insig-1: Insulin-induced gene 1, IRS-2: Insulin receptor substrate 2, PDX-1: Pancreatic and duodenal homeobox 1, SREBP-1c: Sterol regulatory element binding protein-1c, DMC: Dihydroxy-6'-methoxy-3',5'-dimethylchalcone, GLP-1: Glucagon-like peptide-1, GLP-1R: Glucagon-like peptide 1 receptor.