Protein kinase A-dependent insulinotropic effect of selected flavonoids

Acute Kaempferol Stimulation Induces AKT Phosphorylation in HepG2 Cells

Type 2 diabetes mellitus (T2DM) stands as a prevalent global public health issue caused by deficiencies in the action of insulin and/or insulin production. In the liver, insulin plays an important role by inhibiting hepatic glucose production and stimulating glycogen storage, thereby contributing to blood glucose regulation. Kaempferitrin (KP) and kaempferol (KM), flavonoids found in Bauhinia forficata, exhibit insulin-mimetic properties, showing promise in managing T2DM. In this study, we aimed to assess the potential of these compounds in modulating the insulin signaling pathway and/or glucose metabolism. Cell viability assays confirmed the non-cytotoxic nature of both compounds toward HepG2 cells at the concentrations and times evaluated. Theoretical molecular docking studies revealed that KM had the best docking pose with the IR β subunit when compared to the KP. Moreover, Langmuir monolayer evaluation indicated molecular incorporation for both KM and KP. Specifically, KM exhibited the capability to increase AKT phosphorylation, a key kinase in insulin signaling, regardless of insulin receptor (IR) activation. Notably, KM showed an additional synergistic effect with insulin in activating AKT. In conclusion, our findings suggest the potential of KM as a promising compound for stimulating AKT activation, thereby influencing energy metabolism in T2DM.

The Antidiabetic Mechanisms of Hesperidin: Hesperidin Nanocarriers as Promising Therapeutic Options for Diabetes

A natural flavonoid with exceptional medicinal capabilities, hesperidin, has shown encouraging results in the treatment of diabetes. Thoughts are still being held on the particular processes through which hesperidin exerts its anti-diabetic effects. This work clarifies the complex antidiabetic mechanisms of hesperidin by investigating the molecular pathways involved in glucose homeostasis, insulin signaling, and oxidative stress control. Additionally, the article explores the newly developing field of nanocarrier-based systems as a prospective means of boosting the therapeutic efficiency of hesperidin in the treatment of diabetes. This is because there are difficulties connected with the efficient delivery of hesperidin. These cutting-edge platforms show enormous potential for changing diabetes therapy by utilizing the benefits of nanocarriers, such as enhanced solubility, stability, and targeted delivery. In conclusion, our comprehensive review emphasizes the antidiabetic potential of hesperidin and underscores the intriguing possibilities provided by hesperidin nanocarriers in the search for more effective and individualized diabetes therapies.

Naringin promotes fat browning mediated by UCP1 activation via the AMPK signaling pathway in 3T3-L1 adipocytes

Induction of the brown adipocyte-like phenotype in white adipocytes (fat browning) is considered a promising therapeutic strategy to treat obesity. Naringin, a citrus flavonoid, has antioxidant, anti-inflammatory, and anticancer activities. We examined the application of naringin as an anti-obesity compound based on an investigation of its induction of fat browning in 3T3-L1 adipocytes. Naringin did not induce lipid accumulation in differentiated 3T3-L1 adipocytes. Additionally, naringin reduced the expression levels of proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding protein alpha (C/EBPα) involved in adipogenesis during lipid metabolism and increased the levels of PPARα and adiponectin involved in fatty acid oxidation. The expression levels of fat browning markers uncoupling protein 1 (UCP1; involved in thermogenesis) and PR domain containing 16 (PRDM16) increased. In addition, naringin treatment resulted in the activation of PPARγ coactivator 1-alpha (PGC-1α), a factor related to UCP1 transcription and mitochondrial biogenesis. Moreover, the expression of beige adipocyte-specific genes such as Cd137, Cited1, Tbx1, and Tmem26 was also induced. The small multi-lipid droplets characteristic of beige adipocytes indicated that naringin treatment increased the levels of all lipolysis markers (hormone-sensitive lipase [HSL], adipose triglyceride lipase [ATGL], perilipin [PLIN], and protein kinase A [PKA]). Adenosine monophosphate-activated protein kinase (AMPK) and UCP1 levels increased by treatment with naringin alone; this was possibly mediated by the stimulation of the AMPK signaling pathway. According to mechanistic studies, naringin activated the thermogenic protein UCP1 via the AMPK signaling pathway. In conclusion, naringin induces fat browning and is a promising therapeutic agent for metabolic disorders based on the regulation of lipid metabolism.

Hesperidin Exerts Anxiolytic-like Effects in Rats with Streptozotocin- Induced Diabetes via PKA/CREB Signaling

BACKGROUND

The mechanisms underlying synaptic injury and anxiety-like behavioral changes caused by diabetes and the strategies to reverse these changes are not well understood.

OBJECTIVES

This study examined the neuroprotective effects of hesperidin on anxiety-like behaviors in diabetic rats and investigated the underlying mechanisms from the perspective of the PKA/CREB pathway.

METHODS

Rats with streptozotocin-induced diabetes were treated orally with hesperidin (50 and 150 mg/kg) for 10 weeks. The elevated plus maze (EPM), hole board test (HBT), and marbleburying test (MBT) were used to assess anxiety-like behaviors. We further examined the effects of hesperidin on the PKA/CREB pathway in vivo and in vitro.

RESULTS

The results show that supplementation with hesperidin exerted anxiolytic effects on the diabetic rats, as evidenced by increased percentages of open arm entries and time spent in the open arms in the EPM; decreased numbers of hole visits in the HBT; decreased numbers of marbles buried; and increased expression of PKA, CREB, BDNF, and synaptic proteins in the amygdala and hippocampus of diabetic rats. Hesperidin was found to reverse the imbalance in the PKA/CREB/BDNF pathway. In vitro, we found that the PKA inhibitor H89 reversed the protective effects of hesperidin against cell injury and reversed the HG-induced expression of PKA, pCREB/CREB, and BDNF.

CONCLUSION

Our results demonstrated that hesperidin could ameliorate the anxiety-like behaviors of diabetic rats and that activating the PKA/CREB/BDNF pathway contributed to the beneficial effects. This study may provide important insights into the mechanisms underlying anxiety-like behaviors in diabetes and identify new therapeutic targets for clinical treatment.

Bioavailability of Hesperidin and Its Aglycone Hesperetin—Compounds Found in Citrus Fruits as a Parameter Conditioning the Pro-Health Potential (Neuroprotective and Antidiabetic Activity)—Mini-Review

Hesperidin and hesperetin are polyphenols that can be found predominantly in citrus fruits. They possess a variety of pharmacological properties such as neuroprotective and antidiabetic activity. However, the bioavailability of these compounds is limited due to low solubility and restricts their use as pro-healthy agents. This paper described the limitations resulting from the low bioavailability of the presented compounds and gathered the methods aiming at its improvement. Moreover, this work reviewed studies providing pieces of evidence for neuroprotective and antidiabetic properties of hesperidin and hesperetin as well as providing a detailed look into the significance of reported modes of action in chronic diseases. On account of a well-documented pro-healthy activity, it is important to look for ways to overcome the problem of poor bioavailability.

Tambulin from Zanthoxylum armatum acutely potentiates the glucose-induced insulin secretion via KATP-independent Ca2+-dependent amplifying pathway

Tambulin, a flavonol isolated from Zanthoxylum armatum, showed potent insulin secretory activity in our preliminary anti-diabetic screening. Here, we explored the insulin secretory mechanism(s) of tambulin focusing in glucose-dependent, K_ATP ‒ and Ca²⁺‒channels dependent, and cAMP-PKA pathways. Mice islets and MIN6 cells were incubated with tambulin in the presence of pharmacological agonists/antagonists and the secreted insulin was measured using mouse insulin ELISA kit. The intracellular cAMP was measured by an acetylation cAMP ELISA kit. Tambulin (200 μM) showed potent insulin secretory activity only at stimulatory glucose (11-25 mM) concentrations; however, no change in insulin release was observed at basal glucose both in mice islets and MIN6 cells. Notably, in the presence of diazoxide, a K_ATP channel opener; the incomplete inhibition of tambulin-induced insulin secretion was observed whereas, complete inhibition was found using verapamil, an L-type Ca²⁺ channel blocker. Furthermore, the insulinotropic potential of tambulin was amplified in tolbutamide treated, and depolarized islets suggest tambulin's target other than tolbutamide. Tambulin showed no additive effect in the IBMX-induced intracellular cAMP; whereas, exerted an additive effect in the IBMX-induced insulin secretion. Furthermore, tambulin-induced insulin secretion was dramatically inhibited by PKA inhibitor (H-89), while moderate inhibition was found by using PKC inhibitor (calphostin C). Molecular docking studies also showed the best binding affinities of tambulin with PKA suggest the PKA dependent signaling cascade is involved more in tambulin-induced insulin secretion. Based on these findings, it is concluded that tambulin stimulates insulin secretion in a Ca²⁺ channel-dependent but K_ATP channel-independent manner, most likely by activating the cAMP-PKA pathway.