Polyphenols isolated from Broussonetia kazinoki prevent cytokine-induced β-cell damage and the development of type 1 diabetes

The significance of glutaredoxins for diabetes mellitus and its complications

Diabetes mellitus is a non-communicable metabolic disease hallmarked by chronic hyperglycemia caused by beta-cell failure. Diabetic complications affect the vasculature and result in macro- and microangiopathies, which account for a significantly increased morbidity and mortality. The rising incidence and prevalence of diabetes is a major global health burden. There are no feasible strategies for beta-cell preservation available in daily clinical practice. Therefore, patients rely on antidiabetic drugs or the application of exogenous insulin. Glutaredoxins (Grxs) are ubiquitously expressed and highly conserved members of the thioredoxin family of proteins. They have specific functions in redox-mediated signal transduction, iron homeostasis and biosynthesis of iron-sulfur (FeS) proteins, and the regulation of cell proliferation, survival, and function. The involvement of Grxs in chronic diseases has been a topic of research for several decades, suggesting them as therapeutic targets. Little is known about their role in diabetes and its complications. Therefore, this review summarizes the available literature on the significance of Grxs in diabetes and its complications. In conclusion, Grxs are differentially expressed in the endocrine pancreas and in tissues affected by diabetic complications, such as the heart, the kidneys, the eye, and the vasculature. They are involved in several pathways essential for insulin signaling, metabolic inflammation, glucose and fatty acid uptake and processing, cell survival, and iron and mitochondrial metabolism. Most studies describe significant changes in glutaredoxin expression and/or activity in response to the diabetic metabolism. In general, mitigated levels of Grxs are associated with oxidative distress, cell damage, and even cell death. The induced overexpression is considered a potential part of the cellular stress-response, counteracting oxidative distress and exerting beneficial impact on cell function such as insulin secretion, cytokine expression, and enzyme activity.

Nutraceuticals as Modulators of Immune Function: A Review of Potential Therapeutic Effects

Dietary supplementation with nutraceuticals can promote optimal immune system activation, modulating different pathways that enhance immune defenses. Therefore, the immunity-boosting effects of nutraceuticals encompass not only immunomodulatory but also antioxidant, antitumor, antiviral, antibacterial, and antifungal properties, with therapeutic effects against diverse pathological conditions. However, the complexity of the pathways that regulate the immune system, numerous mechanisms of action, and heterogeneity of the immunodeficiencies, and subjects treated make their application in the clinical field difficult. Some nutraceuticals appear to safely improve immune system function, particularly by preventing viral and bacterial infections in specific groups, such as children, the elderly, and athletes, as well as in frail patients, such as those affected by autoimmune diseases, chronic diseases, or cancer. Several nutraceuticals, such as vitamins, mineral salts, polyunsaturated omega-3 fatty acids, many types of phytocompounds, and probiotic strains, have the most consolidated evidence in humans. In most cases, further large and long-term randomized clinical trials are needed to confirm the available preliminary positive data.

The Genus Broussonetia: An Updated Review of Phytochemistry, Pharmacology and Applications

The Broussonetia genus (Moraceae), recognized for its value in many Chinese traditional herbs, mainly includes Broussonetia papyrifera (L.) L’Hér. ex Vent. (BP), Broussonetia kazinoki Siebold (BK), and Broussonetia luzonica (Blanco) Bureau (BL). Hitherto, researchers have found 338 compounds isolated from BP, BK, and BL, which included flavonoids, polyphenols, phenylpropanoids, alkaloids, terpenoids, steroids, and others. Moreover, its active compounds and extracts have exhibited a variety of pharmacological effects such as antitumor, antioxidant, anti-inflammatory, antidiabetic, anti-obesity, antibacterial, and antiviral properties, and its use against skin wrinkles. In this review, the phytochemistry and pharmacology of Broussonetia are updated systematically, after its applications are first summarized. In addition, this review also discusses the limitations of investigations and the potential direction of Broussonetia. This review can help to further understand the phytochemistry, pharmacology, and other applications of Broussonetia, which paves the way for future research.

Kazinol C from Broussonetia kazinoki stimulates autophagy via endoplasmic reticulum stress-mediated signaling

Autophagy modulators are considered putative therapeutic targets because of the role of autophagy in cancer progression. Kazinol C, a 1,3-diphenylpropane from the plant Broussonetia kazinoki, has been shown to induce apoptosis in colon cancer cells through the activation of AMPK at high concentrations. In the present study, we found that Kazinol C induced autophagy through endoplasmic reticulum stress-mediated unfolded protein response signaling in several normal and cancer cell lines at low concentrations of Kazinol C that did not induce apoptosis. Kazinol C activated the transducers of unfolded protein response signaling, leading to target gene expression, LC3-II conversion, and TFEB nuclear translocation. Chemical inhibition of endoplasmic reticulum stress reduced LC3-II conversion. In addition, blockade of autophagy by knockout of Atg5 or treatment with 3-MA enhanced Kazinol C-induced apoptosis. In summary, we have uncovered Kazinol C as a novel autophagy inducer and confirmed the role of autophagy as a cellular stress protector.

In vitro anti-cancer effect of marmesin by suppression of PI3K/Akt pathway in esophagus cancer cells

BACKGROUND

Marmesin, an important coumarin isolated from Broussonetia kazinoki, has been proposed to possess many pharmacological activities including anti-tumor activity. However, the anti-cancer effect of marmesin on esophageal cancer (EC) has not been characterized. The study aimed to explore the anti-cancer role of marmesin using EC cell lines in vitro.

METHODS AND RESULTS

Cell proliferation was evaluated by CCK-8 and Edu cell proliferation assays and apoptosis was detected by TUNEL assay. Western blot analysis was used to determine the expression of Ki67, proliferating cell nuclear antigen (PCNA), Bcl-2, Bax, phosphatidylinositol 3-kinase (PI3K), phosphoryrated-PI3K (p-PI3K), protein kinase B (Akt), and phosphoryrated-Akt (p-Akt). The mechanism of action of marmesin was analyzed using network pharmacology approach. Marmesin exhibited anti-proliferative effect against EC cells, which was further confirmed by the reduced expression of Ki67 and PCNA. Marmesin exerted pro-apoptotic activity on EC cells by downregulating Bcl-2 and upregulating Bax. According to the results from network pharmacology approach, we speculated that PI3K/Akt pathway may participate in the effect of marmesin on EC cells. Additionally, the PI3K/Akt pathway was suppressed by marmesin in EC cells. Moreover, forced expression of Akt reversed the inhibition of cell proliferation and induction of apoptosis induced by marmesin in EC cells.

CONCLUSIONS

Marmesin exerted anti-cancer activity in EC cells by inhibiting the PI3K/Akt pathway.

Immunomodulatory Effects of Dietary Polyphenols

Functional and nutraceutical foods provide an alternative way to improve immune function to aid in the management of various diseases. Traditionally, many medicinal products have been derived from natural compounds with healing properties. With the development of research into nutraceuticals, it is becoming apparent that many of the beneficial properties of these compounds are at least partly due to the presence of polyphenols. There is evidence that dietary polyphenols can influence dendritic cells, have an immunomodulatory effect on macrophages, increase proliferation of B cells, T cells and suppress Type 1 T helper (Th1), Th2, Th17 and Th9 cells. Polyphenols reduce inflammation by suppressing the pro-inflammatory cytokines in inflammatory bowel disease by inducing Treg cells in the intestine, inhibition of tumor necrosis factor-alpha (TNF-α) and induction of apoptosis, decreasing DNA damage. Polyphenols have a potential role in prevention/treatment of auto-immune diseases like type 1 diabetes, rheumatoid arthritis and multiple sclerosis by regulating signaling pathways, suppressing inflammation and limiting demyelination. In addition, polyphenols cause immunomodulatory effects against allergic reaction and autoimmune disease by inhibition of autoimmune T cell proliferation and downregulation of pro-inflammatory cytokines (interleukin-6 (IL-6), IL-1, interferon-γ (IFN-γ)). Herein, we summarize the immunomodulatory effects of polyphenols and the underlying mechanisms involved in the stimulation of immune responses.

Prevention of Oxidative Stress-Induced Pancreatic Beta Cell Damage by Broussonetia Kazinoki Siebold Fruit Extract Via the ERK-Nox4 Pathway

Pancreatic beta cells are vulnerable to oxidative stress, which causes beta cell death and dysfunction in diabetes mellitus. Broussonetia kazinoki Siebold (BK) is a widely used herbal medicine, but its potential effects against beta cell death-induced diabetes have not been studied. Therefore, we investigated the protective effect of an ethanolic extract of BK fruit (BKFE) against streptozotocin (STZ)-induced toxicity in pancreatic beta cells. Intraperitoneal injection of STZ in mice induced hyperglycemia; however, oral administration of BKFE significantly decreased the blood glucose level as well as HbA1c levels. BKFE treatment improved glucose tolerance and increased body weight in diabetic mice. Moreover, BKFE treatment resulted in increased serum insulin levels and insulin expression in the pancreas as well as decreased 4-hydroxynonenal levels induced by oxidative stress. Treatment with STZ decreased cell viability of mouse insulinoma cells (MIN6), which was blocked by BKFE pretreatment. BKFE significantly inhibited apoptotic cells and decreased the expression levels of cleaved-caspase-3 and cleaved-poly (ADP-ribose) polymerase (PARP) induced by STZ treatment. Production of reactive oxygen species in STZ-treated MIN6 cells was also significantly decreased by treatment with BKFE. Erk phosphorylation and Nox4 levels increased in STZ-treated MIN6 cells and the pancreas of mice injected with STZ and this increase was inhibited by treatment with BKFE. Inhibition of Erk phosphorylation by treatment with the PD98059 inhibitor or siRNA Erk also blocked the expression of Nox4 induced by STZ treatment. In conclusion, BKFE inhibits Erk phosphorylation, which in turn prevents STZ-induced oxidative stress and beta cell apoptosis. These results suggested that BKFE can be used to prevent or treat beta cell damage in diabetes.

Reduction of blood glucose by plant extracts and their use in the treatment of diabetes mellitus; discrepancies in effectiveness between animal and human studies

ETHNOPHARMACOLOGICAL RELEVANCE

The global problem of diabetes, together with the limited access of large numbers of patients to conventional antidiabetic medicines, continues to drive the search for new agents. Ancient Asian systems such as traditional Chinese medicine, Japanese Kampo medicine, and Indian Ayurvedic medicine, as well as African traditional medicine and many others have identified numerous plants reported anecdotally to treat diabetes; there are probably more than 800 such plants for which there is scientific evidence for their activity, mostly from studies using various models of diabetes in experimental animals.

AIM OF THE REVIEW

Rather than a comprehensive coverage of the literature, this article aims to identify discrepancies between findings in animal and human studies, and to highlight some of the problems in developing plant extract-based medicines that lower blood glucose in patients with diabetes, as well as to suggest potential ways forward.

METHODS

In addition to searching the 2018 PubMed literature using the terms 'extract AND blood glucose, a search of the whole literature was conducted using the terms 'plant extracts' AND 'blood glucose' AND 'diabetes' AND 'double blind' with 'clinical trials' as a filter. A third search using PubMed and Medline was undertaken for systematic reviews and meta-analyses investigating the effects of plant extracts on blood glucose/glycosylated haemoglobin in patients with relevant metabolic pathologies.

FINDINGS

Despite numerous animal studies demonstrating the effects of plant extracts on blood glucose, few randomised, double-blind, placebo-controlled trials have been conducted to confirm efficacy in treating humans with diabetes; there have been only a small number of systematic reviews with meta-analyses of clinical studies. Qualitative and quantitative discrepancies between animal and human clinical studies in some cases were marked; the factors contributing to this included variations in the products among different studies, the doses used, differences between animal models and the human disease, and the impact of concomitant therapy in patients, as well as differences in the duration of treatment, and the fact that treatment in animals may begin before or very soon after the induction of diabetes.

CONCLUSION

The potential afforded by natural products has not yet been realised in the context of treating diabetes mellitus. A systematic, coordinated, international effort is required to achieve the goal of providing anti-diabetic treatments derived from medicinal plants.

Anti-Diabetic Effects of Acankoreagenin from the Leaves of Acanthopanax Gracilistylus Herb in RIN-m5F Cells via Suppression of NF-κB Activation

Diabetes mellitus is a chronic degenerative disease that causes long-term complications and represents a serious public health problem. In this manuscript, acankoreagenin isolated from the leaves of Acanthopanax gracilistylus (LAG) is thought to possess excellent anti-diabetic properties. In vitro, anti-diabetic activities were assessed based on the inhibitory activities with α-glucosidase (IC₅₀ 13.01 μM), α-amylase (IC₅₀ 30.81 μM), and PTP1B (IC₅₀ 16.39 μM). Acankoreagenin showed better anti-diabetic effects. Then, an investigation was performed to analyze the insulin secretion effects of the insulin-secreting cell line in RIN-m5F cells. It was found that acankoreagenin could increase the insulin release in RIN-m5F cells. It was also found that acankoreagenin reduced NO production, activity of caspase-3, and the reactive oxygen species levels in the cells injured by processing of cytokines. In western blotting, inactivation of NF-κB signaling was confirmed. Acankoreagenin (20 μM) showed a higher I-κBα expression and lower NF-κB expression than the control group and showed a better expression than the positive control L-NAME (1 mM) (p < 0.05). This study demonstrates the anti-diabetic effects of acankoreagenin in vitro and suggests acankoreagenin might offer therapeutic potential for treating diabetes mellitus.

Protective effect of cirsimaritin against streptozotocin-induced apoptosis in pancreatic beta cells

Objectives

Maintaining glucose homoeostasis is essential for the survival of cells. Despite the various health benefits of Korean thistle (Cirsium japonicum var. maackii), their effects on pancreatic β-cell apoptosis in type 1 diabetes mellitus and the underlying mechanisms remain unclear, and experimentally investigated in this study.

Methods

The effects of C. japonicum var. maackii and its active component cirsimaritin against streptozotocin (STZ)-induced cytotoxicity were assessed in INS-1 cells. By Western blotting analysis, protein expressions related to apoptosis were evaluated. The involvement of apoptosis was also confirmed with image-based cytometric assay and caspase activity tests.

Key findings

Cirsium japonicum var. maackii extract and cirsimaritin in non-toxic concentrations improved cell viability to near normal levels and protected INS-1 cells against STZ-induced damage. In addition, cirsimaritin reduced the intracellular oxidative stress induced by STZ. Cirsimaritin effectively suppressed apoptosis in pancreatic β cells by decreasing the activation of caspase-8 and caspase-3, BID and the DNA repair protein poly (ADP-ribose) polymerase (PARP) and increasing anti-apoptotic BCL-2 protein expression.

Conclusions

This study demonstrates the therapeutic potential and action mechanism of cirsimaritin for the prevention and treatment of type 1 diabetes mellitus.

n-3 Polyunsaturated fatty acids protect against pancreatic β-cell damage due to ER stress and prevent diabetes development

SCOPE

In this study, we focus on the effects of n-3 polyunsaturated fatty acids (PUFAs) on tunicamycin-, streptozotocin-, or high fat diet (HFD)-induced β-cell damage and dysfunction.

MATERIALS AND METHODS

Pretreatment with n-3 PUFAs protected RINm5F cells and mouse islets against tunicamycin-induced β-cell damage through suppression of ER stress and apoptosis induction. This protective effect of n-3 PUFAs on β-cells was further demonstrated by the normalization of insulin secretion in response to glucose in tunicamycin-treated islets. In multiple low-dose streptozotocin-induced diabetes models, fat-1 mice, which endogenously synthesize n-3 PUFAs from n-6 PUFAs, were fully resistant to the development of diabetes, with normal islet morphology, high insulin immunoreactivity, and decreased apoptotic cells. In HFD-induced diabetes models, fat-1 mice also exhibited improved glucose tolerance and functional β-cell mass. In both diabetes models, we observed an attenuation of ER stress in fat-1 mice. Interestingly, n-3 PUFAs attenuated the nuclear translocation of lipogenic transcription factors sterol regulatory element-binding protein-1 (SREBP-1) and C/EBPβ, induced by tunicamycin or HFD, suggesting that n-3 PUFAs suppress ER stress via modulation of SREBP-1 and C/EBPβ.

CONCLUSION

Together, these results suggest that n-3 PUFAs block ER stress, thus protecting β cells against diabetogenic insult; therefore, dietary supplementation of n-3 PUFAs has therapeutic potential for the preservation of functional β-cell mass.