Icariin ameliorates streptozotocin-induced diabetic retinopathy in vitro and in vivo

Exploring the combined therapeutic efficacy of bexarotene and icariin in type 2 diabetic rats

OBJECTIVES

The aim of this study was to determine the single and combined antidiabetic activity and side effects of the retinoid X receptor agonist bexarotene and the thioredoxin-interacting protein inhibitor and peroxisome proliferator-activated receptor γ and AMP-activated protein kinase activator icariin.

METHODS

The rats were grouped as healthy (control), diabetes, diabetes + bexarotene (20 mg/kg), diabetes + icariin (60 mg/kg), diabetes + bexarotene (10 mg/kg) + icariin (30 mg/kg) low-dose combination and diabetes + bexarotene (20 mg/kg) + icariin (60 mg/kg) high-dose combination groups.

KEY FINDINGS

Icariin treatment led to a significant reduction in glucose levels compared with the diabetes control group, a remarkable outcome observed 45 days after the initial application. HbA1c levels of the icariin and low-dose combination treatment groups were significantly lower than in the diabetes group. Notably, icariin treatment also significantly elevated HOMA-β levels, which is indicative of improved β-cell function. Icariin significantly decreased glucose levels at 30 and 120 min in the oral glucose tolerance test. Moreover, it ameliorated hepatocyte degeneration, hepatic cord dissociation, congestion, mononuclear cell infiltration in the liver, and degeneration in the pancreas.

CONCLUSIONS

Icariin treatment exhibited robust antidiabetic effects with fewer side effects than other treatment options in this study. In future studies, long-term and varying doses of icariin will contribute to the development of novel antidiabetic drugs.

Icariin alleviates diabetic renal interstitial fibrosis aggravation by inhibiting miR-320a-3p targeting BMP6

Diabetic nephropathy is a common complication of diabetes, accumulating evidence underscores the pivotal role of tubulointerstitial fibrosis in the progression of diabetic nephropathy. However, the underlying mechanisms remain incompletely understood. Although the mechanisms in diabetic nephropathy fibrosis have been the focus of many studies, only limited information is currently available concerning microRNA regulation in tubulointerstitial fibrosis. In this study, we aimed to investigate the roles of miR-320a-3p and bone morphogenetic protein-6 (BMP6) in tubulointerstitial fibrosis. After inducing fibrosis with high glucose in HK-2 cells, we found that miR-320a-3p is significantly up-regulated, whereas BMP6 is markedly down-regulated. These changes suggest close link between miR-320a-3p and BMP6 in tubulointerstitial fibrosis. To elucidate this phenomenon, miR-320a-3p mimic, inhibitor and siBMP6 were employed. We observed in miR-320a-3p mimic group the fibrosis marker include alpha smooth muscle actin and type I collagen was significantly up-regulated, whereas BMP6 exhibited the opposite trend. Additionally, we found icariin could alleviate tubulointerstitial fibrosis by downregulation the miR-320a-3p expression. In conclusion, miR-320a-3p promotes tubulointerstitial fibrosis during the development of DN by suppressing BMP signal pathway activity via inhibiting BMP6 expression. Suggesting that miR-320a-3p represents a potential therapeutic target for tubulointerstitial fibrosis induced by diabetic nephropathy.

The lack of homology domain and leucine rich repeat protein phosphatase 2 ameliorates visual impairment in rats with diabetic retinopathy through regulation of the AKT-GSK-3β-Nrf2 signal cascade

Pleckstrin homology domain and leucine rich repeat protein phosphatase 2 (PHLPP2) is an emerging player in diverse disorders. Our previous findings have documented that reducing PHLPP2 levels in cultured retinal ganglion cells protects against cellular damage caused by high glucose, indicating a possible link between PHLPP2 and diabetic retinopathy (DR). The present work was dedicated to the investigation of PHLPP2 in DR through in vivo experiments with rat models induced by intraperitoneal injection of streptozotocin. Compared to normal rats, the retinas of rats with DR exhibited a notable increase in the level of PHLPP2. The reduction of PHLPP2 levels in the retina was achieved by the intravitreal administration of adeno-associated viruses expressing specific shRNA targeting PHLPP2. Decreasing the expression of PHLPP2 ameliorated visual function impairment and improved the pathological changes of retina in DR rats. Moreover, decreasing the expression of PHLPP2 repressed the apoptosis, oxidative stress and proinflammatory response in the retinas of rats with DR. Reduction of PHLPP2 levels led to an increase in the levels of phosphorylated AKT and glycogen synthase kinase-3β (GSK-3β). Decreasing the expression of PHLPP2 resulted in increased activation of nuclear factor erythroid 2-related factor 2 (Nrf2), which was reversed by suppressing AKT. Notably, the protective effect of reducing PHLPP2 on DR was eliminated when Nrf2 was restrained. These observations show that the down-regulation of PHLPP2 has protective effects on DR by preserving the structure and function of the retina by regulating the AKT-GSK-3β-Nrf2 signal cascade. Therefore, targeting PHLPP2 may hold promise in the treatment of DR.

Why Is Iron Deficiency/Anemia Linked to Alzheimer's Disease and Its Comorbidities, and How Is It Prevented?

Impaired iron metabolism has been increasingly observed in many diseases, but a deeper, mechanistic understanding of the cellular impact of altered iron metabolism is still lacking. In addition, deficits in neuronal energy metabolism due to reduced glucose import were described for Alzheimer's disease (AD) and its comorbidities like obesity, depression, cardiovascular disease, and type 2 diabetes mellitus. The aim of this review is to present the molecular link between both observations. Insufficient cellular glucose uptake triggers increased ferritin expression, leading to depletion of the cellular free iron pool and stabilization of the hypoxia-induced factor (HIF) 1α. This transcription factor induces the expression of the glucose transporters (Glut) 1 and 3 and shifts the cellular metabolism towards glycolysis. If this first line of defense is not adequate for sufficient glucose supply, further reduction of the intracellular iron pool affects the enzymes of the mitochondrial electron transport chain and activates the AMP-activated kinase (AMPK). This enzyme triggers the translocation of Glut4 to the plasma membrane as well as the autophagic recycling of cell components in order to mobilize energy resources. Moreover, AMPK activates the autophagic process of ferritinophagy, which provides free iron urgently needed as a cofactor for the synthesis of heme- and iron-sulfur proteins. Excessive activation of this pathway ends in ferroptosis, a special iron-dependent form of cell death, while hampered AMPK activation steadily reduces the iron pools, leading to hypoferremia with iron sequestration in the spleen and liver. Long-lasting iron depletion affects erythropoiesis and results in anemia of chronic disease, a common condition in patients with AD and its comorbidities. Instead of iron supplementation, drugs, diet, or phytochemicals that improve energy supply and cellular glucose uptake should be administered to counteract hypoferremia and anemia of chronic disease.

Microglia: The breakthrough to treat neovascularization and repair blood-retinal barrier in retinopathy

Microglia are the primary resident retinal macrophages that monitor neuronal activity in real-time and facilitate angiogenesis during retinal development. In certain retinal diseases, the activated microglia promote retinal angiogenesis in hypoxia stress through neurovascular coupling and guide neovascularization to avascular areas (e.g., the outer nuclear layer and macula lutea). Furthermore, continuously activated microglia secrete inflammatory factors and expedite the loss of the blood-retinal barrier which causes irreversible damage to the secondary death of neurons. In this review, we support microglia can be a potential cellular therapeutic target in retinopathy. We briefly describe the relevance of microglia to the retinal vasculature and blood-retinal barrier. Then we discuss the signaling pathway related to how microglia move to their destinations and regulate vascular regeneration. We summarize the properties of microglia in different retinal disease models and propose that reducing the number of pro-inflammatory microglial death and conversing microglial phenotypes from pro-inflammatory to anti-inflammatory are feasible for treating retinal neovascularization and the damaged blood-retinal barrier (BRB). Finally, we suppose that the unique properties of microglia may aid in the vascularization of retinal organoids.

Therapeutic effects of icariin and icariside II on diabetes mellitus and its complications

Diabetes mellitus (DM) is a global health issue in the twenty-first century, and there are numerous challenges in preventing and alleviating its chronic complications. The herb Epimedium has beneficial therapeutic effects on various human diseases, including DM. Its major flavonoid component, icariin, has significant anti-DM activity and may help improve pancreatic β-cell dysfunction and insulin resistance. Furthermore, preclinical evidence has shown that icariin and its in vivo bioactive form, icariside II, have preventive and therapeutic effects on several diabetic complications, including diabetic cardiomyopathy, diabetic vascular endothelial disorder, diabetic nephropathy, and diabetic erectile dysfunction. In this review, we present the general and toxicological information concerning icariin and icariside II and review the anti-DM effects of icariin from a molecular perspective. Additionally, we discuss the potential benefits of icariin and icariside II on the important pathological mechanisms of various diabetic complications. Despite positive preclinical evidence, additional investigations are needed before relevant clinical studies can be conducted. Therefore, we conclude with suggestions for future research. Hopefully, this review will provide a comprehensive molecular perspective for future research and product development related to icariin and icariside II in treating DM and diabetic complications.

Glycosides and Vascular Complications of Diabetes

Diabetes is linked with various microvascular and macrovascular complications. Nephropathy, neuropathy and retinopathy are important microvascular complications of diabetes. Different types of secondary metabolites including glycosides have been studied for their effects in diabetic complications. Various glycosides such as flavanoid glycosides and saponin glycosides are reported for their beneficial effects in diabetic nephropathy, neuropathy, retinopathy and cardiomyopathy by action on various pathways involved in the progression of these complications. Coumarin glycosides and cryanogenic glycosides have been studied for their effective role in diabetic nephropathy. Phenolic glycosides and anthraquinone glycosides also have beneficial role in diabetic neuropathy. The present review focuses on various classes of glycosides and their role in the prevention and treatment of vascular complications of diabetes.

TGR5 Activation Ameliorates Mitochondrial Homeostasis via Regulating the PKCδ/Drp1-HK2 Signaling in Diabetic Retinopathy

Background: Diabetic retinopathy (DR) is one of the most important microvascular diseases of diabetes. Our previous research demonstrated that bile acid G-protein-coupled membrane receptor (TGR5), a novel cell membrane receptor of bile acid, ameliorates the vascular endothelial cell dysfunction in DR. However, the precise mechanism leading to this alteration remains unknown. Thus, the mechanism of TGR5 in the progress of DR should be urgently explored.

Methods: In this study, we established high glucose (HG)-induced human retinal vascular endothelial cells (RMECs) and streptozotocin-induced DR rat in vitro and in vivo. The expression of TGR5 was interfered through the specific agonist or siRNA to study the effect of TGR5 on the function of endothelial cell in vitro. Western blot, immunofluorescence and fluorescent probes were used to explore how TGR5 regulated mitochondrial homeostasis and related molecular mechanism. The adeno-associated virus serotype 8-shTGR5 (AAV8-shTGR5) was performed to evaluate retinal dysfunction in vivo and further confirm the role of TGR5 in DR by HE staining, TUNEL staining, PAS staining and Evans Blue dye.

Results: We found that TGR5 activation alleviated HG-induced endothelial cell apoptosis by improving mitochondrial homeostasis. Additionally, TGR5 signaling reduced mitochondrial fission by suppressing the Ca²⁺-PKCδ/Drp1 signaling and enhanced mitophagy through the upregulation of the PINK1/Parkin signaling pathway. Furthermore, our result indicated that Drp1 inhibited mitophagy by facilitating the hexokinase (HK) 2 separation from the mitochondria and HK2-PINK1/Parkin signaling. In vivo, intraretinal microvascular abnormalities, including retinal vascular leakage, acellular capillaries and apoptosis, were poor in AAV8-shTGR5-treated group under DR, but this effect was reversed by pretreatment with the mitochondrial fission inhibitor Mdivi-1 or autophagy agonist Rapamycin.

Conclusion: Overall, our findings indicated that TGR5 inhibited mitochondrial fission and enhanced mitophagy in RMECs by regulating the PKCδ/Drp1-HK2 signaling pathway. These results revealed the molecular mechanisms underlying the protective effects of TGR5 and suggested that activation of TGR5 might be a potential therapeutic strategy for DR.

Icariin improves testicular dysfunction via enhancing proliferation and inhibiting mitochondria-dependent apoptosis pathway in high-fat diet and streptozotocin-induced diabetic rats

BACKGROUND

Diabetes mellitus (DM), a chronic metabolic disease, severely impairs male reproductive function. However, the underpinning mechanisms are still incompletely defined, and there are no effective strategies or medicines for these reproductive lesions. Icariin (ICA), the main active component extracted from Herba epimedii, is a flavonoid traditionally used to treat testicular dysfunction. Whether ICA can improve male reproductive dysfunction caused by DM and its underlying mechanisms are still unclear. In this study, by employing metformin as a comparative group, we evaluated the protective effects of ICA on male reproductive damages caused by DM and explored the possible mechanisms.

METHODS

Rats were fed with a high fat diet (HFD) and then intraperitoneally injected with streptozotocin (STZ) to induce diabetes. Diabetic rats were randomly divided into T2DM + saline group, T2DM + metformin group and T2DM + ICA group. Rats without the treatment of HFD and STZ were used as control group. The morphology of testicular tissues was examined by histological staining. The mRNA expression levels were determined by quantitative real-time PCR. Immunostaining detected the protein levels of proliferating cell nuclear antigen (PCNA), hypoxia-inducible factor 1-alpha (HIF-1α) and sirtuin 1 (SIRT1) in testicular tissues. TUNEL assay was performed to determine cell apoptosis in the testicular tissues. The protein expression levels of HIF-1α and SIRT1 in the testicular tissues were determined by western blot assay.

RESULTS

ICA effectively improved male reproductive dysfunction of diabetic rats. ICA administration significantly decreased fasting blood glucose (FBG) and insulin resistance index (IRI). In addition, ICA increased testis weight, epididymis weight, sperm number, sperm motility and the cross-sectional area of seminiferous tubule. ICA recovered the number of spermatogonia, primary spermatocytes and Sertoli cells. Furthermore, ICA upregulated the expression of PCNA, activated SRIT1-HIF-1α signaling pathway, and inhibited intrinsic mitochondria dependent apoptosis pathway by upregulating the expression of Bcl-2 and downregulating the expression of Bax and caspase 3.

CONCLUSION

These results suggest that ICA could attenuate male reproductive dysfunction of diabetic rats possibly via increasing cell proliferation and decreasing cell apoptosis of testis. ICA potentially represents a novel therapeutic strategy against DM-induced testicular damages.

AMPK/PGC-1α/GLUT4-Mediated Effect of Icariin on Hyperlipidemia-Induced Non-Alcoholic Fatty Liver Disease and Lipid Metabolism Disorder in Mice

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. Therapeutic activity of icariin, a major bioactive component of Epimedii Herba, in NAFLD is still unknown. Herein, the C57BL/6J mice were fed with a high-fat diet for 16 weeks to establish a NAFLD model. Mice were assigned to five groups: control group, NAFLD group, and icariin treatment groups. Effects of icariin on blood indices, glucose tolerance, insulin sensitivity, histopathological morphology, cell apoptosis, lipid accumulation, and AMPK signaling were analyzed. In addition, another cohort of mice were assigned to five groups: control group, NAFLD group, dorsomorphin treatment group, icariin treatment group, and dorsomorphin + icariin treatment group. Expression of proteins in liver tissues associated with AMPK signaling, and levels of ALT and AST were evaluated. Icariin attenuated the NAFLD-induced increase of the TG, TC, LDL-C, ALT, AST levels. HDL-C levels were affected neither by NAFLD nor by icariin. Furthermore, icariin treatment (100-200 mg/kg) counteracted the NAFLD-reduced glucose tolerance and insulin sensitivity and modulated histopathological changes, cell apoptosis, and lipid accumulation in liver tissues. Additionally, icariin mitigated the NAFLD-induced up-regulation of the cleaved caspase 3/9, SREBP-1c, and DGAT-2 levels, and enhanced the expression level of CPT-1, p-ACC/ACC, AMPKα1, PGC-1α, and GLUT4. Effects of icariin on the AMPK signaling and levels of AST and ALT could be reversed by AMPK inhibitor, dorsomorphin. This paper investigates the glucose-reducing and lipid-lowering effects of icariin in NAFLD. Moreover, icariin might function through activating the AMPKα1/PGC-1α/GLTU4 pathway.

The Benefits of Flavonoids in Diabetic Retinopathy

Diabetic retinopathy (DR), one of the most common complications of diabetes, is the leading cause of legal blindness among adults of working age in developed countries. After 20 years of diabetes, almost all patients suffering from type I diabetes mellitus and about 60% of type II diabetics have DR. Several studies have tried to identify drugs and therapies to treat DR though little attention has been given to flavonoids, one type of polyphenols, which can be found in high levels mainly in fruits and vegetables, but also in other foods such as grains, cocoa, green tea or even in red wine. Flavonoids have anti-inflammatory, antioxidant and antiviral effects. Since it is known that diabetes induces oxidative stress and inflammation in the retina leading to neuronal death in the early stages of the disease, the use of these compounds can prove to be beneficial in the prevention or treatment of DR. In this review, we summarize the molecular and cellular effects of flavonoids in the diabetic retina.

Icariin enhances AMP-activated protein kinase and prevents high fructose and high salt-induced metabolic syndrome in rats

Metabolic syndrome (MetS) is an increasing health threat and often leads to cardiovascular complications. The aim of this study was to evaluate icariin’s ability to combat MetS induced in rats and outline the involved mechanisms of action. Rats were grouped in four batches. The controls received a regular diet and water. MetS was induced in the remaining three groups using a high-salt high-fructose diet. Groups 1 and 2 were given daily doses of saline, while Groups 3 and 4 received 25 and 50 mg/kg icariin, respectively, for 12 weeks in total. The experimental protocol was carried out for 12 weeks consecutively. Icariin significantly decreased body mass index (BMI), adiposity index and body weight. Further, icariin protected against dyslipidemia, hyperglycemia, and hyperinsulinemia and improved insulin resistance as given by the homeostatic model assessment of insulin resistance (HOMA-IR) values. Icariin guarded against the rise in serum interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α). In addition, it significantly inhibited the decrease in mRNA expression of glucose transporter type 4 (GLUT4) and liver kinase B1 (LKB1). These effects were accompanied by decreased liver content of nuclear factor kappa B (NFκB) and enhanced serum levels of phosphorylated 5ʹ-adenosine monophosphate-activated protein kinase (p-AMPK). Further, icariin significantly increased p-AMPK/AMPK ratio in liver tissues. Conclusively, icariin offers protection in experimentally induced MetS, partially due to AMPK activation.

Evaluation of the protective effects of icariin on nicotine-induced reproductive toxicity in male mouse -a pilot study

BACKGROUND

Nicotine, a pharmacologically active component of tobacco adversely affects the male reproductive system and fertility whereas icariin (ICA), the main active ingredient in Epimedium herba has been used in the treatment of several male reproductive problems. This study aimed at evaluating the protective or ameliorative effect of ICA against reproductive toxicity induced by intraperitoneal injection of nicotine in mice.

METHODS

Using simple random allocation, forty male mice were randomly divided into 4 groups: control (received 0.35 mL physiological saline via gastric gavage), nicotine (0.75 mg/kg BW/day intraperitoneally), ICA (75 mg/kg BW/day gastric gavage), and nicotine plus ICA (nicotine, 0.75 mg/kg BW/day intraperitoneally + ICA, 75 mg/kg BW/day gastric gavage) group. After 35 days of treatment, the mice were weighed, sacrificed, and their reproductive organs (testis and epididymis) were collected and examined for further studies.

RESULTS

The nicotine-treated group showed significantly decreased epididymal sperm density and serum testosterone concentration relative to the control group. Nicotine also caused oxidative damage shown by significant reduction in the activities of antioxidant enzymes and elevation in Malondialdehyde (MDA) levels. ICA on the other hand, improved the reduction in sperm density, hormone levels, and activities of antioxidant enzymes altered in the nicotine treated mice.

CONCLUSIONS

These findings indicate that nicotine-induced reproductive toxicity and oxidative damage on male reproductive tissues could be attenuated by ICA.

Icariin affects cell cycle progression and proliferation of human retinal pigment epithelial cells via enhancing expression of H19

Background

Aberrant proliferation of retinal pigment epithelial (RPE) cells under pathologic condition results in the occurrence of proliferative vitreoretinopathy (PVR). Icariin (ICA)-a flavonol glucoside-has been shown to inhibit proliferation of many cell types, but the effect on RPE cells is unknown. This study aimed to clarify the inhibitory effects of ICA on RPE cells against platelet-derived growth factor (PDGF)-BB-induced cell proliferation, and discuss the regulatory function of H19 in RPE cells.

Methods

MTS assay was conducted to determine the effects of ICA on cell proliferation. Flow cytometry analysis was performed to detect cell cycle progression. Quantitative real-time PCR and western blot assay were used to measure the expression patterns of genes in RPE cells.

Results

ICA significantly suppressed PDGF-BB-stimulated RPE cell proliferation in a concentration-dependent manner. Moreover, since administration of ICA induced cell cycle G0/G1 phase arrest, the anti-proliferative activity of ICA may be due to G0/G1 phase arrest in RPE cells. At molecular levels, cell cycle regulators cyclin D1, CDK4, CDK6, p21 and p53 were modulated in response to treatment with ICA. Most importantly, H19 was positively regulated by ICA and H19 depletion could reverse the inhibitory effects of ICA on cell cycle progression and proliferation in PDGF-BB-stimulated RPE cells. Further mechanical explorations showed that H19 knockdown resulted in alternative expressions levels of cyclin D1, CDK4, CDK6, p21 and p53 under ICA treatment.

Conclusions

Our findings revealed that ICA was an effective inhibitor of PDGF-BB-induced RPE cell proliferation through affecting the expression levels of cell cycle-associated factors, and highlighted the potential application of ICA in PVR therapy. H19 was described as a target regulatory gene of ICA whose disruption may contribute to excessive proliferation of RPE cells, suggesting that modulation of H19 expression may be a novel therapeutic approach to treat PVR.

Mechanisms behind Retinal Ganglion Cell Loss in Diabetes and Therapeutic Approach

Diabetes produces several changes in the body triggered by high glycemia. Some of these changes include altered metabolism, structural changes in blood vessels and chronic inflammation. The eye and particularly the retinal ganglion cells (RGCs) are not spared, and the changes eventually lead to cell loss and visual function impairment. Understanding the mechanisms resulting in RGC damage and loss from diabetic retinopathy is essential to find an effective treatment. This review focuses mainly on the signaling pathways and molecules involved in RGC loss and the potential therapeutic approaches for the prevention of this cell death. Throughout the manuscript it became evident that multiple factors of different kind are responsible for RGC damage. This shows that new therapeutic agents targeting several factors at the same time are needed. Alpha-1 antitrypsin as an anti-inflammatory agent may become a suitable option for the treatment of RGC loss because of its beneficial interaction with several signaling pathways involved in RGC injury and inflammation. In conclusion, alpha-1 antitrypsin may become a potential therapeutic agent for the treatment of RGC loss and processes behind diabetic retinopathy.

Icariin treatment reduces blood glucose levels in type 2 diabetic rats and protects pancreatic function

Icariin, a flavonoid isolated from traditional oriental herbal medicines, has been demonstrated to exhibit several health benefits in animal models and in humans. The aim of the present study was to investigate the effect of Icariin on hyperglycemia in type 2 diabetes mellitus (T2DM) in rats. A model of diabetes was established in 50 Sprague Dawley rats using a high-sugar and high-fat diet and peritoneal injection of streptozotocin. Diabetic rats were divided into five groups: Diabetic control; metformin; and rats treated with three different doses of Icariin, 5, 10 and 20 mg/kg. Body weight and blood glucose levels were measured, and serum adiponectin levels, expression of phospho-AMP mediated protein kinase (p-AMPK) and glucose transporter isoform 4 (GLUT-4) were measured using ELISA, Realtime PCR and western blotting, respectively. Diabetic rats without drug treatment exhibited reduced body weight, increased blood glucose levels and decreased the number of islets. In T2DM rats treated with 10 or 20 mg/kg Icariin, the blood glucose levels were reduced, whereas serum adiponectin levels were not affected. Additionally, the mRNA and protein expression levels of p-AMPK and GLUT-4 protein were increased in the T2DM rats treated with Icariin. In conclusion, in the diabetes rat model, Icariin alleviated the severity of diabetes, and the effects may be associated with reduction of hyperglycemia by activating an AMPK/GLUT-4 pathway.

Rubrofusarin as a Dual Protein Tyrosine Phosphate 1B and Human Monoamine Oxidase-A Inhibitor: An in Vitro and in Silico Study

A number of nature-derived biologically active compounds comprise glycosides. In some cases, the glycosidic residue is needed for bioactivity; however, in other cases, glycosylation just improves some pharmacokinetic/dynamic parameters. The patterns of protein tyrosine phosphatase 1B (PTP1B) and human monoamine oxidase A (hMAO-A) inhibition by rubrofusarin 6-O-β-d-glucopyranoside (1), rubrofusarin 6-O-β-d-gentiobioside (2), rubrofusarin triglucoside (3), and cassiaside B2 (4) were compared with the aglycone, rubrofusarin, isolated from Cassia obtusifolia seeds. Rubrofusarin showed potent inhibition against the PTP1B enzyme (IC₅₀; 16.95 ± 0.49 μM), and its glycosides reduced activity (IC₅₀; 87.36 ± 1.08 μM for 1 and >100 μM for 2-4) than did the reference drug, ursolic acid (IC₅₀; 2.29 ± 0.04 μM). Similarly, in hMAO-A inhibition, rubrofusarin displayed the most potent activity with an IC₅₀ value of 5.90 ± 0.99 μM, which was twice better than the reference drug, deprenyl HCl (IC₅₀; 10.23 ± 0.82 μM). An enzyme kinetic and molecular docking study revealed rubrofusarin to be a mixed-competitive inhibitor of both these enzymes. In a western blot analysis, rubrofusarin increased glucose uptake significantly and decreased the PTP1B expression in a dose-dependent manner in insulin-resistant HepG2 cells, increased the expression of phosphorylated protein kinase B (p-Akt) and phosphorylated insulin receptor substrate-1 (p-IRS1) (Tyr 895), and decreased the expression of glucose-6-phosphatase (G6Pase) and phosphoenol pyruvate carboxykinase (PEPCK), key enzymes of gluconeogenesis. Our overall results show that glycosylation retards activity; however, it reduces toxicity. Thus, Cassia seed as functional food and rubrofusarin as a base can be used for the development of therapeutic agents against comorbid diabetes and depression.

Icariin Prevents Diabetes-Induced Bone Loss in Rats by Reducing Blood Glucose and Suppressing Bone Turnover

Diabetic Osteoporosis (DOP) is a common metabolic bone disease, characterized by decreased bone mineral density (BMD) and destruction of bone microstructure. It has been reported that icariin is beneficial for estrogen deficiency-induced osteoporosis, and alcohol-induced osteoporosis; whether icariin has protective effects on diabetes-induced osteoporosis has not been reported. In this study, a rat model of diabetic osteoporosis was established by streptozotocin injection, the bone protective effects and potential mechanism of icariin on diabetes-induced bone loss was observed. Thirty 8-week-old female Sprague Dawley rats were divided into control group (vehicle treatment), T1DM (diabetic) group and T1DM-icariin (ICA) group (diabetic rats treated with icariin), 10 rats in each group. The bone histomorphometry parameters, bone mineral density (BMD), serum bone turnover markers, and bone marrow adipogenesis were analyzed after 8 weeks of icariin administration. The results showed consumption of icariin at a doses of 100 mg kg⁻¹ decreased blood glucose, and increased the BMD of diabetic rats. Icariin effectively decreased serum bone turnover marker levels, including CTX-1, ALP, TRACP 5b, osteocalcin, and PINP. Meanwhile, the bone histomorphometry parameters, the number of osteoclasts per bone perimeter were turned to be normal level, and the icariin treatment suppressed bone marrow adipogenesis. The runt-related transcription factor 2 (RUNX 2), as well as the osteoprotegerin (OPG)/receptor activator of nuclear factor-κ B ligand (RANKL) ratio in serum and bone tissues were increased significantly after icariin treatment in diabetic rats. All of the above indicate that oral administration of icariin can prevent diabetic osteoporosis; the effect is mainly related to its ability to reduce blood glucose, inhibit bone turnover and bone marrow adipogenesis, as well as up-regulate bone RUNX 2, and OPG expression.

Icariin Attenuates High Glucose-Induced Apoptosis, Oxidative Stress, and Inflammation in Human Umbilical Venous Endothelial Cells

Endothelial dysfunction is closely associated with diabetic complications. Icariin, a flavonoid glycoside isolated from the Epimedium plant species, exhibits antidiabetic properties. However, its impact on endothelial function remains poorly understood, particularly under hyperglycemia. In this study, we investigated the potential protective effect of icariin on high glucose-induced detrimental effects on vascular endothelial cells. Human umbilical venous endothelial cells were incubated in media containing 5.5 mM glucose (normal glucose) or 25 mM glucose (high glucose) in the presence or absence of 50 µM icariin for 72 h. We found that high glucose markedly induced cell apoptosis, enhanced reactive oxygen species generation, and elevated expression levels of inflammatory factors and cell adhesion molecules, which were greatly subdued by icariin supplementation. In conclusion, icariin exerted a beneficial effect on high glucose-induced endothelial dysfunction. This new finding provides a promising strategy for future treatment of diabetic vascular complications.

Nutraceuticals and Diet-based Phytochemicals in Type 2 Diabetes Mellitus: From Whole Food to Components with Defined Roles and Mechanisms

BACKGROUND

Over the past decades, the development and use of an array of prescription medications have considerably improved the clinical management of type 2 diabetes mellitus and the quality of life of patients. However, as our knowledge of the associated risk factors and approaches to its management increases, the increasing roles of diet and the composition of the diet in the etiology and successful management of diabetes mellitus are being illuminated. Presently, a lot of attention is being given to nutraceuticals and certain phytochemicals that are integral parts of the human diet. It is believed that a clearer understanding of their roles may be crucial to 'non-invasive' or minimallyintrusive management, with regards to daily living of patients. In this review, an overview of nutraceutical components and phytochemicals that may be of benefit, or had been known to be beneficial in diabetes mellitus is given. Also, how the roles of such dietary components are evolving in the management of this disorder is highlighted. Lastly, the obstacles that need to be overcome before nutraceuticals can be considered as options for the clinical management of diabetes mellitus areconsidered.

CONCLUSION

Despite studies that demonstrate their efficacy, no nutraceutical or food-derived compound has been formally adopted as a direct replacement for any class of antidiabetic drugs.

An outline for the pharmacological effect of icariin in the nervous system

Icariin is a major active component of the traditional herb Epimedium, also known as Horny Goat Weed. It has been extensively studied throughout the past several years and is known to exert anti-oxidative, anti-neuroinflammatory, and anti-apoptotic effects. It is now being considered as a potential therapeutic agent for a wide variety of disorders, ranging from neoplasm to cardiovascular disease. More recent studies have shown that icariin exhibits potential preventive and/or therapeutic effects in the nervous system. For example, icariin can prevent the production of amyloid β (1-42) and inhibit the expression of amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE-1) in animal models of Alzheimer's disease (AD). Icariin has been shown to mitigate pro-inflammatory responses of microglia in culture and in animal models of cerebral ischemia, depression, Parkinson's disease (PD), and multiple sclerosis (MS). Icariin also prevents the neurotoxicity induced by hydrogen peroxide (H₂O₂), endoplasmic reticulum (ER) stress, ibotenic acid, and homocysteine. In addition, icariin is implicated in facilitating learning and memory in both normal aging animals and disease models. To date, we still have no consolidated source of knowledge about the pharmacological effects of icariin in the nervous system, though its roles in other tissues have been reviewed in recent years. Here, we summarize the pharmacological development of icariin as well as its possible mechanisms in prevention and/or therapy of disorders afflicting the nervous system in hope of expanding the knowledge about the preventive and/or therapeutic effect of icariin in brain disorders.

Icariin Ameliorates Palmitate-Induced Insulin Resistance Through Reducing Thioredoxin-Interacting Protein (TXNIP) and Suppressing ER Stress in C2C12 Myotubes

Both thioredoxin-interacting protein (TXNIP) and endoplasmic reticulum (ER) stress are implicated in skeletal muscle insulin resistance. Icariin has been found to mimic insulin action in normal skeletal muscle C2C12 cells and display anti-diabetic properties in diet-induced obese mice. However, the underlying molecular mechanism remains to be well-established. Herein, we tested the hypothesis that the protective effects of icariin on free fatty acid-induced insulin resistance were attributed to its regulation on TXNIP protein levels and ER stress in skeletal muscle cells. We found that TXNIP mediated the saturated fatty acid palmitate (PA)-induced insulin resistance in C2C12 myotubes. Icariin treatment significantly restored PA-reduced proteasome activity resulting in reduction of TXNIP protein and suppression of ER stress, as well as improvement of insulin sensitivity. Proteasome inhibition by its specific inhibitor MG132 obviously abolished the inhibitory effect of icariin on PA-induced insulin resistance. In addition, MG132 supplementation markedly abrogated the impacts of icariin on ER stress and TXNIP-mediated downstream events such as inflammation and STAT3 phosphorylation. These results clearly indicate that icariin improves PA-induced skeletal muscle insulin resistance through a proteasome-dependent mechanism, by which icariin downregulats TXNIP levels and inhibits ER stress.

Icariin prevents cytokine-induced β-cell death by inhibiting NF-κB signaling

The loss of insulin secretion in type I diabetes mellitus (T1DM) is caused by autoimmune-mediated destruction of insulin-producing pancreatic β-cells. Inflammatory cytokines and immune cell infiltration activate oxidative and endoplasmic reticulum (ER) stress, resulting in reduced β-cell viability. The current pharmacological agents used to control blood glucose have a limited effective duration and are accompanied by strong side effects. Blocking the inflammatory and immune responses that cause the β-cell damage has been investigated as a novel therapeutic approach to control T1DM. Icariin is a flavonoid component of Chinese medicinal herbs that has anti-inflammatory effects in vitro and in vivo. The results of the present study revealed that icariin abrogates the pro-apoptotic effect of inflammatory cytokines and significantly suppresses the activation of nuclear factor (NF)-κB in rat pancreatic β-cell lines. The present study may provide a basis for the potential use of icariin as a therapeutic agent for T1DM.

Potential of Icariin Metabolites from Epimedium koreanum Nakai as Antidiabetic Therapeutic Agents

The therapeutic properties of Epimedium koreanum are presumed to be due to the flavonoid component icariin, which has been reported to have broad pharmacological potential and has demonstrated anti-diabetic, anti-Alzheimer’s disease, anti-tumor, and hepatoprotective activities. Considering these therapeutic properties of icariin, its deglycosylated icaritin and glycosylated flavonoids (icaeriside II, epimedin A, epimedin B, and epimedin C) were evaluated for their ability to inhibit protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase. The results show that icaritin and icariside II exhibit potent inhibitory activities, with 50% inhibition concentration (IC₅₀) values of 11.59 ± 1.39 μM and 9.94 ± 0.15 μM against PTP1B and 74.42 ± 0.01 and 106.59 ± 0.44 μM against α-glucosidase, respectively. With the exceptions of icaritin and icariside II, glycosylated flavonoids did not exhibit any inhibitory effects in the two assays. Enzyme kinetics analyses revealed that icaritin and icariside II demonstrated noncompetitive-type inhibition against PTP1B, with inhibition constant (K_i) values of 11.41 and 11.66 μM, respectively. Moreover, molecular docking analysis confirmed that icaritin and icariside II both occupy the same site as allosteric ligand. Thus, the molecular docking simulation results were in close agreement with the experimental data with respect to inhibition activity. In conclusion, deglycosylated metabolites of icariin from E. koreanum might offer therapeutic potential for the treatment of type 2 diabetes mellitus.

Can allopurinol improve retinopathy in diabetic rats? Oxidative stress or uric acid; which one is the culprit?

Allopurinol, an inhibitor of xanthine oxidase, reduces both plasma uric acid and oxidative stress and shows useful effects on some complications of diabetes. However, it is not defined which of the above mentioned properties are involved. Moreover, to the best of our knowledge no study has been done on the effects of allopurinol on diabetic retinopathy. In the present study, the effect of allopurinol on experimental diabetic retinopathy and its possible mechanism has been investigated. Thirty two rats were divided into four groups of eight rats each; (1) normal, (2) diabetic control, (3) diabetic + allopurinol (50 mg/kg.day), (4) diabetic + benzbromarone (10 mg/kg.day). Drugs were administered daily and orally from the day after diabetes induction for eight weeks. Thereafter retinal function and structure were evaluated by electroretinography and microscopic studies. Uric acid and oxidative stress biomarkers were measured biochemically. Diabetes significantly increased plasma uric acid and oxidative stress markers and reduced body weight and amplitude of electroretinogram (ERG) b-wave and oscillatory potentials. Treatment of diabetic rats with allopurinol caused a significant increase in the amplitude of ERG b-wave (87%) and decrease in blood sugar (20%), uric acid (49%), and 8-iso-prostaglandin F2a (56%), but had no effect on the number of retinal ganglionic cells and oscillatory potentials. Benzbromarone showed no significant effects on the considered parameters except the reduction of uric acid. Allopurinol improved the b-wave amplitude of diabetic rats. It seems that this beneficial effect is due to the reduction of oxidative stress rather than its effect on plasma uric acid.

Icariin Promotes Tendon-Bone Healing during Repair of Rotator Cuff Tears: A Biomechanical and Histological Study

To investigate whether the systematic administration of icariin (ICA) promotes tendon-bone healing after rotator cuff reconstruction in vivo, a total of 64 male Sprague Dawley rats were used in a rotator cuff injury model and underwent rotator cuff reconstruction (bone tunnel suture fixation). Rats from the ICA group (n = 32) were gavage-fed daily with ICA at 0.125 mg/g, while rats in the control group (n = 32) received saline only. Micro-computed tomography, biomechanical tests, serum ELISA (calcium; Ca, alkaline phosphatase; AP, osteocalcin; OCN) and histological examinations (Safranin O and Fast Green staining, type I, II and III collagen (Col1, Col2, and Col3), CD31, and vascular endothelial growth factor (VEGF)) were analyzed two and four weeks after surgery. In the ICA group, the serum levels of AP and OCN were higher than in the control group. More Col1-, Col2-, CD31-, and VEGF-positive cells, together with a greater degree of osteogenesis, were detected in the ICA group compared with the control group. During mechanical testing, the ICA group showed a significantly higher ultimate failure load than the control group at both two and four weeks. Our results indicate that the systematic administration of ICA could promote angiogenesis and tendon-bone healing after rotator cuff reconstruction, with superior mechanical strength compared with the controls. Treatment for rotator cuff injury using systematically-administered ICA could be a promising strategy.

The Possible Role of Flavonoids in the Prevention of Diabetic Complications

Type 2 diabetes mellitus is a disease that affects many metabolic pathways. It is associated with insulin resistance, impaired insulin signaling, β-cell dysfunction, abnormal glucose levels, altered lipid metabolism, sub-clinical inflammation and increased oxidative stress. These and other unknown mechanisms lead to micro- and macro-complications, such as neuropathy, retinopathy, nephropathy and cardiovascular disease. Based on several in vitro animal models and some human studies, flavonoids appear to play a role in many of the metabolic processes involved in type 2 diabetes mellitus. In this review, we seek to highlight the most recent papers focusing on the relationship between flavonoids and main diabetic complications.

Pharmacological effects and pharmacokinetic properties of icariin, the major bioactive component in Herba Epimedii

Herba Epimedii is an important medicinal plant which has been used in various traditional Chinese formulations for thousands of years as well as in modern proprietary traditional Chinese medicine products. It has extensive clinical indications, especially for the treatment of sexual dysfunction and osteoporosis. There have been more than 260 chemical moieties identified in the genus Epimedium most of which belong to flavonoids. Icariin is the most abundant constituent in Herba Epimedii. Icariin is pharmacologically bioactive and demonstrates extensive therapeutic capacities such as osteoprotective effect, neuroprotective effect, cardiovascular protective effect, anti-cancer effect, anti-inflammation effect, immunoprotective effect and reproductive function. Particularly, the significant osteogenic effect of icariin made it a promising drug candidate in bone tissue engineering. The current review paper aims to summarize the literatures reporting the pharmacological effects of icariin. The pharmacokinetic properties of bioactive ingredients in Herba Epimedii have also been discussed.

Icariin is a PPARα activator inducing lipid metabolic gene expression in mice

Icariin is effective in the treatment of hyperlipidemia. To understand the effect of icariin on lipid metabolism, effects of icariin on PPARα and its target genes were investigated. Mice were treated orally with icariin at doses of 0, 100, 200, and 400 mg/kg, or clofibrate (500 mg/kg) for five days. Liver total RNA was isolated and the expressions of PPARα and lipid metabolism genes were examined. PPARα and its marker genes Cyp4a10 and Cyp4a14 were induced 2-4 fold by icariin, and 4-8 fold by clofibrate. The fatty acid (FA) binding and co-activator proteins Fabp1, Fabp4 and Acsl1 were increased 2-fold. The mRNAs of mitochondrial FA β-oxidation enzymes (Cpt1a, Acat1, Acad1 and Hmgcs2) were increased 2-3 fold. The mRNAs of proximal β-oxidation enzymes (Acox1, Ech1, and Ehhadh) were also increased by icariin and clofibrate. The expression of mRNAs for sterol regulatory element-binding factor-1 (Srebf1) and FA synthetase (Fasn) were unaltered by icariin. The lipid lysis genes Lipe and Pnpla2 were increased by icariin and clofibrate. These results indicate that icariin is a novel PPARα agonist, activates lipid metabolism gene expressions in liver, which could be a basis for its lipid-lowering effects and its beneficial effects against diabetes.

Plant polyphenols in the treatment of age-associated diseases: revealing the pleiotropic effects of icariin by network analysis

Polyphenols are a broad class of compounds. Some are ingested in substantial quantities from nutritional sources, more are produced by medicinal plants, and some of them are taken as drugs. It is becoming clear, that a single polyphenol is impacting several cellular pathways. Thus, a network approach is becoming feasible, describing the interaction of a single polyphenol with cellular networks. Here we have selected icariin to draw a prototypic network of icariin activities. Icariin appears to be a promising drug to treat major age-related diseases, like neurodegeneration, memory and depressive disorders, chronic inflammation, diabetes, and osteoporosis. It interacts with several relevant pathways, like PDE, TGF-ß, MAPK, PPAR, NOS, IGF, Sirtuin, and others. Such networks will be useful to future comparative studies of complex effects of polyphenols.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Expression of adiponectin and its receptors in type 1 diabetes mellitus in human and mouse retinas

PURPOSE

Recent studies have suggested that adiponectin (APN) is associated with several retinal diseases. We studied the expression of APN and its receptors (AdipoRs) in the human retina and in a mouse model of type 1 diabetes mellitus (T1DM).

METHODS

Human eyeball specimens were obtained from the Chongqing Eye Bank. eNOS-knockout (eNOS⁻/⁻) mice were randomly divided into a T1DM group and a control group. The T1DM model was induced with an intraperitoneal injection of streptozotocin. To locate the AdipoRs in the retina, immunofluorescence was performed. Total APN protein and RNA were extracted from the neural retina and the retinal pigment epithelium (RPE)-choroid complex, and the APN protein was detected with enzyme-linked immunosorbent assay (ELISA). The mRNA and the protein of AdipoRs in the retina were detected with qRT-PCR and western blotting, respectively. The unpaired Student t test was used to assess the significance between the T1DM and the control groups, with p<0.05 regarded as statistically significant.

RESULTS

APN, AdipoR1, and AdipoR2 were identified in the neural retina and in the RPE-choroid of humans and mice. AdipoR1 was found in the internal limiting membrane and in the outer segments of the photoreceptors in human and mouse retinas, whereas no noticeable AdipoR2 expression was seen in the retinal frozen sections of human and mouse eyes. Compared to the control group, APN and AdipoR1 expression in the retina was elevated in the T1DM group, but AdipoR2 expression remained unchanged.

CONCLUSIONS

We demonstrated that APN, AdipoR1, and AdipoR2 exist in human and mouse retinas and that retinal APN and AdipoR1 protein levels are elevated in T1DM mice, implying that the APN-AdipoR1 axis may be activated in the diabetic retina. In contrast, AdipoR2 appears to play a minor role in this pathological process.

Impaired hypothalamic insulin signaling in CUMS rats: restored by icariin and fluoxetine through inhibiting CRF system

Epidemiological evidence demonstrates the neuroendocrine link between stress, depression and diabetes. This study observed glucose intolerance of rats exposed to chronic unpredictable mild stress (CUMS) in oral glucose tolerance test (OGTT). CUMS procedure significantly up-regulated corticotropin-releasing factor (CRF)-related peptide urocortin 2 expression and elevated cAMP production, resulting in over-expression of suppressor of cytokine signaling 3 (SOCS3) in hypothalamic arcuate nucleus (ARC) of rats. Furthermore, SOCS3 activation blocked insulin signaling pathway through the suppression of insulin receptor substrate 2 (IRS2) phosphotyrosine and phosphatidylinositol-3-kinase (PI3-K) activation in hypothalamic ARC of CUMS rats after high-level of insulin stimulation. These data indicated that CUMS procedure induced the hyperactivity of CRF system, and subsequently produced conditional loss of insulin signaling in hypothalamic ARC of rats. More importantly, icariin and fluoxetine with the ability to restrain CRF system hyperactivity improved insulin signaling in hypothalamic ARC of CUMS rats, which were consistent with the enhancement of glucose tolerance in OGTT, showing anti-diabetic efficacy. Although effective in OGTT, anti-diabetic drug pioglitazone failed to restore hypothalamic ARC CRF system hyperactivity, paralleling with its inability to ameliorate the loss of insulin signaling and depression-like behavior in CUMS rats. These observations support the hypothesis that signal cross-talk between hypothalamic CRF system and insulin may be impaired in depression with glucose intolerance and suggest that icarrin and fluoxetine aiming at CRF system may have great potential in the prevention and treatment of depression with comorbid diabetes.

Animal models of diabetic retinopathy: summary and comparison

Diabetic retinopathy (DR) is a microvascular complication associated with chronic exposure to hyperglycemia and is a major cause of blindness worldwide. Although clinical assessment and retinal autopsy of diabetic patients provide information on the features and progression of DR, its underlying pathophysiological mechanism cannot be deduced. In order to have a better understanding of the development of DR at the molecular and cellular levels, a variety of animal models have been developed. They include pharmacological induction of hyperglycemia and spontaneous diabetic rodents as well as models of angiogenesis without diabetes (to compensate for the absence of proliferative DR symptoms). In this review, we summarize the existing protocols to induce diabetes using STZ. We also describe and compare the pathological presentations, in both morphological and functional aspects, of the currently available DR animal models. The advantages and disadvantages of using different animals, ranging from zebrafish, rodents to other higher-order mammals, are also discussed. Until now, there is no single model that displays all the clinical features of DR as seen in human. Yet, with the understanding of the pathological findings in these animal models, researchers can select the most suitable models for mechanistic studies or drug screening.