Amelioration of diabetic nephropathy by oral administration of d-α-tocopherol and its mechanisms

Hayashi D, Ueda S, Yamanoue M, Ashida H, Shirai Y

Biosci Biotechnol Biochem. 2018 Jan;82(1):65-73. doi: 10.1080/09168451.2017.1411184. Epub 2018 Jan 3.

Abstract

Diabetic nephropathy (DN) is a diabetic vascular complication, and abnormal protein kinase C (PKC) activation from increased diacylglycerol (DG) production in diabetic hyperglycemia is one of the causes of DN. Diacylglycerol kinase (DGK) converts DG into phosphatidic acid. In other words, DGK can attenuate PKC activity by reducing the amount of DG. Recently, we reported that intraperitoneally administered d-α-tocopherol (vitamin E, αToc) induces an amelioration of DN in vivo through the activation of DGKα and the prevention of podocyte loss. However, the effect of the oral administration of αToc on DN in mice remains unknown. Here, we evaluated the effect of oral administration of αToc on DN and its molecular mechanism using streptozocin-induced diabetic mice. Consequently, the oral administration of αToc significantly ameliorated the symptoms of DN by preventing the loss of podocytes, and it was revealed that the inhibition of PKCactivity was involved in this amelioration.

Alshiek JA, Dayan L, Asleh R, Blum S, Levy AP, Jacob G

Diabetes Res Clin Pract. 2017 Sep;131:200-207. doi: 10.1016/j.diabres.2017.06.026. Epub 2017 Jul 13.

Abstract

Vascular dysfunction in both conduit arteries and small vessels is a major contributor to the development of cardiovascular disease (CVD) in diabetes mellitus (DM). In diabetes there is a process of systemic chronic inflammation accompanied by high oxidative stress causing a subsequent decrease in vascular reactivity and negatively affect the metabolic processes responsible for functioning of the microvasculature. Vitamin E is classified as an antioxidant due to its ability to scavenge lipid radicals and terminate oxidative chain reactions. We conducted a double-blinded cross-over study with vitamin E versus placebo in individuals with type 2DM and the Hp2-2 genotype and assessed different aspects of peripheral vascular function in these patients. Twenty patients completed the study with 10 individuals in each study cohort. We were able to show significant improvement of indirect indices of vascular function following 8weeks of treatment with vitamin E. This improvement was consistent for weeks even after stopping the vitamin E treatment. We concluded that a pharmacogenomic rationale utilizing the Hp genotype might potentially provide cardiovascular benefit with vitamin E.

Chia LL, Jantan I, Chua KH

Curr Pharm Biotechnol. 2017 Aug 8. doi: 10.2174/1389201018666170808144703. [Epub ahead of print]

Abstract

BACKGROUND:

Tocotrienols (T3) are the natural occurring vitamin E derivatives that possess antioxidant properties and therapeutic potential in diabetic complications. The bioactivities of the derivatives are determined by the number and arrangement of methyl substitution on the structure.

OBJECTIVE:

The objective of this study was to determine the effects of T3 derivatives, δ-T3, γ-T3 and α-T3 on insulin secretion of rat pancreatic islets in a dynamic culture.

METHOD:

Pancreatic islets isolated from male Wistar rats were treated with T3 for 1 h at 37 oC in a microfluidic system with continuous operation that provided a stable cell culture environment. Glucose (2.8 mM and 16.7 mM, as basal and stimulant, respectively) and potassium chloride (KCl) (30 mM) were added to the treatment in calcium free medium. The supernatant were collected for insulin measurements.

RESULTS:

Short-term exposure (1 h) of δ-T3 to β cells in the stimulant glucose condition significantly potentiated insulin secretion in a dose-dependent manner. γ-T3 and α-T3 also displayed dose-dependent effect but less effective in the activation of insulin secretion. Essentially, KCl, a pancreatic β cell membrane depolarizing agent, added into the treatment further enhanced the insulin secretion of δ-T3, γ-T3 and α-T3 with ED50 values of 504, 511 and 588 µM, respectively.

CONCLUSION:

The findings suggest the potential of δ-T3 in regulating glucose-stimulated insulin secretion (GSIS) in response to the intracellular calcium especially in the presence of KCl.

Hochberg I, Berinstein EM, Milman U, Shapira C, Levy AP

Curr Diab Rep. 2017 Jun;17(6):42. doi: 10.1007/s11892-017-0868-1.

Abstract

PURPOSE OF REVIEW:

Despite compelling evidence regarding the importance of oxidant stress in the development of vascular complications and observational studies suggesting that vitamin E may be protective from these complications, multiple clinical trials have failed to show benefit from vitamin E supplementation in the prevention of vascular complications in diabetes. One possible explanation for this failure of vitamin E may have been inappropriate patient selection. This review seeks to provide the clinical evidence and mechanistic basis for why a subset of individuals defined by their haptoglobin (Hp) genotype may derive cardiovascular protection by vitamin E supplementation.

RECENT FINDINGS:

Clinical trial data from the HOPE, ICARE, and WHS studies is presented showing a pharmacogenomic interaction between the Hp genotype and vitamin E on the development of CVD. Specifically, in individuals with diabetes and the Hp2-2 genotype, vitamin E has been shown to be associated with an approximately 35% reduction in CVD. Cardioprotection by vitamin E in individuals with the Hp2-2 genotype appears to be mediated in part by an improvement in HDL functionality as demonstrated in three independent trials in both type 1 diabetes and type 2 diabetes. Vitamin E may provide benefit in reducing CVD in Hp2-2 individuals with diabetes. However, in order for this pharmacogenomic algorithm to be accepted as a standard of care and used clinically, an additional large prospective study will need to be performed.

Hayashi D, Yagi K, Song C, Ueda S, Yamanoue M, Topham M, Suzaki T, Saito N, Emoto N, Shirai Y.

Sci Rep. 2017 Jun 1;7(1):2597. doi: 10.1038/s41598-017-02354-3.

Abstract

Diabetic nephropathy (DN) is one of vascular complications of diabetes and is caused by abnormal protein kinase C activation as a result of increased diacylglycerol (DG) production in diabetic hyperglycaemia. Diacylglycerol kinase (DGK) converts DG into phosphatidic acid. Therefore, it is expected that the activation of DGK would ameliorate DN. Indeed, it has been reported that vitamin E (VtE) ameliorates DN in rat by activating DGK, and we recently reported that VtE specifically activates DGKα isoform in vitro. However, whether DGKα is involved in the VtE-induced amelioration of DN in vivo remains unknown. Therefore, we investigated the VtE-induced amelioration of DN in wild-type (DGKα^+/+) and DGKα-deficient (DGKα^-/-) mice in which diabetes was induced by streptozocin. Several symptoms of DN were ameliorated by VtE treatment in the DGKα^+/+ mice but not in the DGKα^-/- mice. Moreover, transmission electron microscopy of glomeruli and immunofluorescent staining of glomerular epithelial cells (podocytes) indicated that VtE ameliorates podocyte pathology and prevents podocyte loss in the DGKα^+/+ mice but not in the DGKα^-/- mice. We showed that VtE can ameliorate DN in mice and that DGKα is involved in the VtE-induced amelioration of DN in vivo, suggesting that DGKα is an attractive therapeutic target for DN.

Abdul Nasir NA, Agarwal R, Sheikh Abdul Kadir SH, Vasudevan S, Tripathy M, Iezhitsa I, Mohammad Daher A, Ibrahim MI, Mohd Ismail N.

PLoS One. 2017 Mar 28;12(3):e0174542. doi: 10.1371/journal.pone.0174542. eCollection 2017.

Abstract

Cataract, a leading cause of blindness, is of special concern in diabetics as it occurs at earlier onset. Polyol accumulation and increased oxidative-nitrosative stress in cataractogenesis are associated with NFκB activation, iNOS expression, ATP depletion, loss of ATPase functions, calpain activation and proteolysis of soluble to insoluble proteins. Tocotrienol was previously shown to reduce lens oxidative stress and inhibit cataractogenesis in galactose-fed rats. In current study, we investigated anticataract effects of topical tocotrienol and possible mechanisms involved in streptozotocin-induced diabetic rats. Diabetes was induced in Sprague Dawley rats by intraperitoneal injection of streptozotocin. Diabetic rats were treated with vehicle (DV) or tocotrienol (DT). A third group consists of normal, non-diabetic rats were treated with vehicle (NV). All treatments were given topically, bilaterally, twice daily for 8 weeks with weekly slit lamp monitoring. Subsequently, rats were euthanized and lenses were subjected to estimation of polyol accumulation, oxidative-nitrosative stress, NFκB activation, iNOS expression, ATP levels, ATPase activities, calpain activity and total protein levels. Cataract progression was delayed from the fifth week onwards in DT with lower mean of cataract stages compared to DV group (p<0.01) despite persistent hyperglycemia. Reduced cataractogenesis in DT group was accompanied with lower aldose reductase activity and sorbitol level compared to DV group (p<0.01). DT group also showed reduced NFκB activation, lower iNOS expression and reduced oxidative-nitrosative stress compared to DV group. Lenticular ATP and ATPase and calpain 2 activities in DT group were restored to normal. Consequently, soluble to insoluble protein ratio in DT group was higher compared to DV (p<0.05). In conclusion, preventive effect of topical tocotrienol on development of cataract in STZ-induced diabetic rats could be attributed to reduced lens aldose reductase activity, polyol levels and oxidative-nitrosative stress. These effects of tocotrienol invlove reduced NFκB activation, lower iNOS expression, restoration of ATP level, ATPase activities, calpain activity and lens protein levels.

Shin J, Yang SJ, Lim Y.

Exp Biol Med (Maywood). 2017 Mar;242(5):505-515. doi: 10.1177/1535370216683836. Epub 2016 Dec 13.

Abstract

Delayed wound healing is one of the major diabetic complications. During wound healing process, the early inflammatory stage is important for better prognosis. One of antioxidant nutrient, gamma-tocopherol (GT) is considered to regulate inflammatory conditions. This study investigated the effect of GT supplementation on mechanism associated with inflammation, oxidative stress, and apoptosis during early cutaneous wound healing in diabetic mice. Diabetes was induced by alloxan injection in ICR mice. All mice were divided into three groups: non-diabetic control mice (CON), diabetic control mice (DMC), and diabetic mice supplemented with GT (GT). After two weeks of GT supplementation, excisional wounds were made by biopsy punches (4 mm). Diabetic mice showed increases in fasting blood glucose (FBG) level, hyper-inflammatory response, oxidative stress, and delayed wound closure rate compared to non-diabetic mice. However, GT supplementation reduced FBG level and accelerated wound closure rate by regulation of inflammatory response-related proteins such as nuclear factor kappa B, interleukin-1β, tumor necrosis factor-α, and c-reactive protein, and oxidative stress-related markers including nuclear factor (erythroid derived 2)-like 2, NAD(P)H dehydrogenase quinone1, heme oxygenase-1, manganese superoxide dismutase, catalase and glutathione peroxidase and apoptosis-related markers such as sirtuin-1, peroxisome proliferator-activated receptor gamma coactivator 1- α, and p53 in diabetic mice. Taken together, GT would be a potential therapeutic to prevent diabetes-induced delayed wound healing by regulation of inflammatory response, apoptosis, and oxidative stress. Impact statement Gamma tocopherol has shown ameliorative effect on diabetic wound healing by regulation of inflammation, oxidative stress, and apoptosis demonstrated by nuclear factor kappa B, nuclear factor (erythroid derived 2)-like 2, and sirtuin-1.

Xu C, Bentinger M, Savu O, Moshfegh A, Sunkari V, Dallner G, Swiezewska E, Catrina SB, Brismar K, Tekle M.

J Diabetes Complications. 2017 Jan;31(1):4-12. doi: 10.1016/j.jdiacomp.2016.10.010. Epub 2016 Oct 18.

Abstract

Diabetes mellitus is characterized by hyperglycemia and capillary hypoxia that causes excessive production of free radicals and impaired antioxidant defense, resulting in oxidative stress and diabetes complications such as impaired wound healing. We have previously shown that modified forms of tocotrienols possess beneficial effects on the biosynthesis of the mevalonate pathway lipids including increase in mitochondrial CoQ. The aim of this study is to investigate the effects of mono-epoxy-tocotrienol-α on in vitro and in vivo wound healing models as well as its effects on mitochondrial function. Gene profiling analysis and gene expression studies on HepG2 cells and human dermal fibroblasts were performed by microarray and qPCR, respectively. In vitro wound healing using human fibroblasts was studied by scratch assay and in vitro angiogenesis using human dermal microvascular endothelial cells was studied by the tube formation assay. In vivo wound healing was performed in the diabetic db/db mouse model. For the study of mitochondrial functions and oxygen consumption rate Seahorse XF-24 was employed. In vitro, significant increase in wound closure and cell migration (p<0.05) both in normal and high glucose and in endothelial tube formation (angiogenesis) (p<0.005) were observed. Microarray profiling analysis showed a 20-fold increase of KIF26A gene expression and 11-fold decrease of lanosterol synthase expression. Expression analysis by qPCR showed significant increase of the growth factors VEGFA and PDGFB. The epoxidated compound induced a significantly higher basal and reserve mitochondrial capacity in both HDF and HepG2 cells. Additionally, in vivo wound healing in db/db mice, demonstrated a small but significant enhancement on wound healing upon local application of the compound compared to treatment with vehicle alone. Mono-epoxy-tocotrienol-α seems to possess beneficial effects on wound healing by increasing the expression of genes involved in cell growth, motility and angiogenes as well as on mitochondrial function.

Soleymani H, Saboury AA, Moosavi-Movahedi AA, Rahmani F, Maleki J, Yousefinejad S, Maghami P.

Int J Biol Macromol. 2016 Dec;93(Pt A):868-878. doi: 10.1016/j.ijbiomac.2016.09.047.

Abstract

Changes in human environment and lifestyle over the last century have caused a dramatic increase in the occurrence of diabetes. Research of past decades illustrated that vitamin D and E have a key role in the improvement of diabetes by reducing oxidative stress, protein glycosylation, insulin resistance and also improving beta cell function. Binding properties and conformational changes of human insulin upon interaction with vitamins D₃ and E (α-tocopherol) were investigated by spectroscopy, differential scanning calorimetry (DSC) and molecular dynamic simulation. Tyrosine fluorescence quenching studies indicates changes in the human insulin conformation in the presence of vitamins. Binding constants of vitamins D₃ and E for human insulin were determined to be 2.7 and 1.5 (×10^-5M^-1) and the corresponding average numbers of binding sites were determined to be 1.3 and 1.2, respectively. Far- and near-UV circular dichroism studies showed that vitamin E can significantly change the secondary and tertiary structures of human insulin via an increase in the content of α-helix structure. Results of DSC showed that both vitamins D₃ and E stabilize the structure of human insulin. Molecular dynamic simulation results indicated that vitamin D₃ decreases the helical and strand structural contents of human insulin, but vitamin E stabilizes more regular secondary structures such as helical and strand structural contents as shown by experimental results.

Jamilian M, Hashemi Dizaji S, Bahmani F, Taghizadeh M, Memarzadeh MR, Karamali M, Akbari M, Asemi Z.

Can J Diabetes. 2016 Nov 21. pii: S1499-2671(16)30266-0. doi: 10.1016/j.jcjd.2016.09.004. [Epub ahead of print]

Abstract

Limited data are available for assessing the effects of omega-3 fatty acids and vitamin E co-supplementation on metabolic profiles and pregnancy outcomes in gestational diabetes (GDM). This study was designed to determine the effects of omega-3 fatty acids and vitamin E co-supplementation on biomarkers of oxidative stress, inflammation and pregnancy outcomes in women with GDM.

This randomized, double-blind, placebo-controlled clinical trial was conducted in 60 patients with GDM who were not taking oral hypoglycemic agents. Patients were randomly allocated to intake either 1000 mg omega-3 fatty acids from flaxseed oil plus 400 IU vitamin E supplements (n=30) or placebo (n=30) for 6 weeks. Fasting blood samples were obtained from the women at the beginning of the study and after the 6-week intervention to quantify related markers.

After 6 weeks of intervention, omega-3 fatty acids and vitamin E co-supplementation, compared with the placebo, resulted in a significant rise in total antioxidant capacity (TAC) (+187.5±224.9 vs. -32.5±136.1 mmol/L; p<0.001); nitric oxide (NO) (+5.0±7.7 vs. -12.0±28.0 µmol/L; p=0.002) and a significant decrease in plasma malondialdehyde (MDA) concentrations (-0.1±0.9 vs. +0.6±1.4 µmol/L; p=0.03). Co-supplementation with omega-3 fatty acids and vitamin E showed no detectable changes in plasma glutathione and serum high-sensitivity C-reactive protein levels. Joint omega-3 fatty acids and vitamin E supplementation resulted in lower incidences of hyperbilirubinemia in newborns (10.3% vs. 33.3%; p=0.03).

Overall, omega-3 fatty acids and vitamin E co-supplementation for 6 weeks in women with GDM had beneficial effects on plasma TAC, MDA and NO and on the incidence of the newborns’ hyperbilirubinemia.