Mulberry leaf multi-components exert hypoglycemic effects through regulation of the PI-3K/Akt insulin signaling pathway in type 2 diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Phytochemicals have unique advantages in the treatment of diabetes due to their multi-target activity and low toxicity. Mulberry leaves, a traditional Chinese herbal medicine, have been used in the prevention and treatment of diabetes for centuries. The main active ingredients in mulberry leaves with regards to the hypoglycemic effect are 1-deoxynojirimycin, flavonoids, and polysaccharides. However, the combined hypoglycemic effects and mechanisms of mulberry leaf multi-components remain unclear.

AIM OF THE STUDY

This study explored the anti-diabetic effects of mulberry leaf multi-components (MMC) and the role of the PI-3K/Akt insulin signalling pathway in improving insulin resistance.

MATERIALS AND METHODS

The main chemical components of MMC were analyzed using the phenol-sulfuric acid method, aluminum nitrate-sodium nitrite method, and HPLC-ultraviolet/fluorescence detection method. The T2DM rat model was created via feeding a high-fat diet and peritoneal injection of streptozotocin. T2DM rats were divided into four groups: model, model plus metformin, model plus low-dose, and model plus high-dose MMC groups (100 and 200 mg/kg body weight/day, respectively), and plus normal group for a total of five groups. MMC was administered by oral gavage for six weeks. Fasting blood glucose and serum lipid profiles were measured using a glucometer and an automatic biochemistry analyzer, respectively. Serum insulin and adipocytokine levels were analyzed by ELISA. Hepatic glucose metabolizing enzyme activity was evaluated by ELISA and the double antibody sandwich method. Expression of PI-3K/Akt signalling pathway proteins was analyzed by RT-PCR and Western blotting.

RESULTS

Extracted 1-deoxynojirimycin, flavonoid, and polysaccharide purity was 70.40%, 52.34%, and 32.60%, respectively. These components were then mixed at a ratio of 1:6:8 to form MMC. MMC significantly reduced serum glucose, insulin, and lipid levels. In diabetic rats, MMC enhanced insulin sensitivity and alleviated inflammatory and oxidative damage by lowing adipocytokine levels and increasing anti-oxidative enzyme activity. Insulin resistance was also mitigated. MMC regulated the activity of key downstream enzymes of hepatic glucose metabolism via activating the expression of PI-3K, Akt, PDX-1, and GLUT4 at the mRNA and protein levels, thereby correcting hepatic glucolipid metabolism disorders and exerting a hypoglycemic effect.

CONCLUSION

MMC ameliorated hepatic glucolipid metabolism disorders and improved insulin resistance in T2DM rats by activating the PI-3K/Akt signaling pathway. These results highlight the multi-component, multi-target, and combined effects of MMC, and suggest it may be further developed as a hypoglycemic drug.

Trelagliptin succinate: DPP-4 inhibitor to improve insulin resistance in adipocytes

Trelagliptin inhibits the enzyme dipeptidyl-4 (DPP-4) to treat type 2 diabetes and it may possess the potential to improve insulin resistance. However, the molecular mechanism is not known. In this study, the effect of trelagliptin succinate in improving insulin resistance was investigated. The differentiation system of 3T3-L1 mouse preadipocytes was used to determine the content of adipokines and the content of GLUT4 in the outer membrane. The expression of AKT, P-AKT, IRS-1 and P-IRS-1 in differentiated 3T3-L1 adipocytes was determined by western blotting. Our results demonstrated that trelagliptin succinate increased the expression of AKT, P-AKT, IRS-1 and P-IRS-1 in the PI-3K/AKT insulin signaling pathway. These events promote the trans-membrane function of GLUT4 and concomitant glucose intake in adipocytes. In addition, the secretion of free fatty acids and resistin were decreased. In conclusion, our study suggested that trelagliptin succinate improved insulin resistance in adipocytes via regulation of PI-3K/AKT/GLUT4 insulin signaling pathway.

Apelin induces the proliferation, migration and expression of cytoskeleton and tight junction proteins in human RPE cells via PI-3K/Akt and MAPK/Erk signaling pathways

Diabetic retinopathy is major cause of vision loss during working age. Breakdown of blood-retinal barrier is an early event in pathogenesis of DR. RPE is the major part of outer BRB. Apelin, an endogenous ligand of APJ, mediates angiogenesis. Our previous study showed that apelin induced proliferation, migration, and collagen I mRNA expression in human RPE cells via PI-3K/Akt and MAPK/Erk signaling pathways. Now we investigate the connection between apelin and RPE in vascular permeability of diabetic retinopathy and its working mechanism. Our study showed that apelin promotes the proliferation, migration and expression of cytoskeleton and tight junction proteins in human RPE cells using MTS and transwell chamber assay. Apelin also activated the expression of PI-3K/Akt and MAPK/Erk signaling pathways proteins, such as PLCγ1, p38, Akt and Erk phosphorylation in RPE cells using laser scanning confocal detection, PCR and western blot. Pretreatment with the inhibitor of apelin receptor APJ, F13A, abolished the apelin-induced activations of the proliferation, migration and expression of cytoskeleton, tight junction and PI-3K/Akt and MAPK/Erk signaling pathways proteins in human RPE cells. It suggested that apelin as a promoter in retinal vascular permeability during early stage of DR, provides further evidence for neurovascular crosstalk in pathogenesis of DR, which may offer a new target in early prevention and treatment of DR.

Neuroprotective efficacy of naringin on 3-nitropropionic acid-induced mitochondrial dysfunction through the modulation of Nrf2 signaling pathway in PC12 cells

Oxidative stress and mitochondrial dysfunction are implicated in neuronal apoptosis associated with Huntington's disease. Naringin is the flavanone present in grapefruit and related citrus species possess diverse pharmacological and therapeutic properties including antioxidant, anti-apoptotic, and neuroprotective properties. The aim of this study was to investigate the protective effect of naringin on 3-nitropropionic acid (3-NP)-induced neurotoxicity in pheochromocytoma cells (PC12) cells and to explore its mechanism of action. Naringin protects PC12 cells from 3-NP neurotoxicity, as evaluated the by cell viability assays. The lactate dehydrogenase release was decreased upon naringin treatment in 3-NP-induced PC12 cells. Naringin treatment enhances the antioxidant defense by increasing the activities of enzymatic antioxidants and the level of reduced glutathione. The increase in levels of reactive oxygen species and lipid peroxidation induced by 3-NP were significantly decreased by naringin. PC12 cells induced with 3-NP showed decrease in the mitochondrial membrane potential and mitochondrial respiratory complex enzymes, succinate dehydrogenase and cytochrome c oxidase activities, and it was significantly altered to near normal upon naringin treatment. Naringin reduced the 3-NP-induced apoptosis through the modulation in expressions of B-cell lymphoma 2 and Bcl-2-associated X protein. Further, naringin enhances the nuclear translocation of Nrf2 and induces the

NAD(P)H

quinone oxidoreductase-1 and Heme oxygenase-1 expressions through the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway. Taken together, the above findings suggest that naringin augments cellular antioxidant defense capacity and reduces the 3-NP-induced neurotoxicity in PC12 cells through the PI-3K/Akt-dependent Nrf2 activation in PC12 cells.

Aspidin PB, a novel natural anti-fibrotic compound, inhibited fibrogenesis in TGF-β1-stimulated keloid fibroblasts via PI-3K/Akt and Smad signaling pathways

Keloid is an overgrowth of scar tissue that develops around a wound. The mechanisms of keloid formation and development still remain unknown, and no effective treatment is available. Searching for active natural resources may develop better prevention and treatment approaches for keloids. Aspidin PB is a natural resource with lower toxicity. We explored its effect on the regulation of TGF-β1-induced expression of type I collagen, CTGF, and α-SMA in keloid fibroblasts (KFs). Western blotting was used to detect the expression levels of type I collagen, CTGF, α-SMA, PI-3K/Akt and Smad-dependent and Smad-independent signaling pathway. The effect of aspidin PB on cell viability in human keloid fibroblasts was measured by MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide). The percentage of the apoptotic cells was studied by flow cytometry. Based on our results, we revealed that aspidin PB inhibited the production of type I collagen, CTGF, and α-SMA in TGF-β1-induced KFs by blocking PI-3K/Akt signaling pathway. The TGF-β1-mediated phosphorylated levels of Smad2/3 were inhibited by aspidin PB pretreatment. Conclusively, our study suggests that aspidin PB has an inhibitory effect on fibrogenesis in TGF-β1-induced KFs. Our findings imply that aspidin PB has a therapeutic potential to intervene and prevent keloids and other fibrotic diseases.