Comparative effects of vitamin K2 and estradiol on experimental arteriosclerosis with diabetes mellitus

Beneficial Effects of Vitamin K Status on Glycemic Regulation and Diabetes Mellitus: A Mini-Review

Type 2 diabetes mellitus is a chronic disease that is characterized by hyperglycemia, insulin resistance, and dysfunctional insulin secretion. Glycemic control remains a crucial contributor to the progression of type 2 diabetes mellitus as well as the prevention or delay in the onset of diabetes-related complications. Vitamin K is a fat-soluble vitamin that plays an important role in the regulation of the glycemic status. Supplementation of vitamin K may reduce the risk of diabetes mellitus and improve insulin sensitivity. This mini-review summarizes the recent insights into the beneficial effects of vitamin K and its possible mechanism of action on insulin sensitivity and glycemic status, thereby suppressing the progression of diabetes mellitus.

Thiamine pyrophosphate diminishes nitric oxide synthesis in endothelial cells

Although thiamine pyrophosphate (TPP) is considered a protective agent for endothelial cells, it is still unknown if this is associated with nitric oxide (NO) synthesis. Our aim was to evaluate the synthesis of NO in endothelial cells incubated with TPP and high glucose concentrations. Endothelial cells from the umbilical cord vein from newborns (n = 20), were incubated with 5, 15 or 30 mmol/L glucose, in absence or presence of 0.625 mg/ml of TPP. Our results showed a significant increase in cell proliferation (> 40%; P < 0.05), and cell viability (> 90%; P < 0.001) after 48 h in endothelial cells cultured with glucose plus TPP. Likewise, in the presence of glucose and TPP an important rise in the consumption of glucose by the endothelial cells was observed after 24 h (> 7%; P < 0.001) and 48 h (> 10%; P < 0.05). Additionally, the levels of lactate after incubation with glucose and TPP showed only slight variations after 48 h (P < 0.05). However, these changes were clearly different from those observed in the absence of TPP. Interestingly, we found that the changes mentioned were linked with reduced levels of nitrites both at 24 h (< 171 pmol/μg protein; P < 0.001), and 48 h (< 250 pmol/μg protein; P < 0.05), which was associated with a reduced expression of mRNA of eNOS in endothelial cells incubated with TPP and high glucose. In conclusion, the presence of TPP regulates the consumption of glucose and the synthesis of NO, which would explain its protective effect in the endothelium of diabetic patients.

Vitamin K1 prevents diabetic cataract by inhibiting lens aldose reductase 2 (ALR2) activity

This study investigated the potential of vitamin K1 as a novel lens aldose reductase inhibitor in a streptozotocin-induced diabetic cataract model. A single, intraperitoneal injection of streptozotocin (STZ) (35 mg/kg) resulted in hyperglycemia, activation of lens aldose reductase 2 (ALR2) and accumulation of sorbitol in eye lens which could have contributed to diabetic cataract formation. However, when diabetic rats were treated with vitamin K1 (5 mg/kg, sc, twice a week) it resulted in lowering of blood glucose and inhibition of lens aldose reductase activity because of which there was a corresponding decrease in lens sorbitol accumulation. These results suggest that vitamin K1 is a potent inhibitor of lens aldose reductase enzyme and we made an attempt to understand the nature of this inhibition using crude lens homogenate as well as recombinant human aldose reductase enzyme. Our results from protein docking and spectrofluorimetric analyses clearly show that vitamin K1 is a potent inhibitor of ALR2 and this inhibition is primarily mediated by the blockage of DL-glyceraldehyde binding to ALR2. At the same time docking also suggests that vitamin K1 overlaps at the NADPH binding site of ALR2, which probably shows that vitamin K1 could possibly bind both these sites in the enzyme. Another deduction that we can derive from the experiments performed with pure protein is that ALR2 has three levels of affinity, first for NADPH, second for vitamin K1 and third for the substrate DL-glyceraldehyde. This was evident based on the dose-dependency experiments performed with both NADPH and DL-glyceraldehyde. Overall, our study shows the potential of vitamin K1 as an ALR2 inhibitor which primarily blocks enzyme activity by inhibiting substrate interaction of the enzyme. Further structural studies are needed to fully comprehend the exact nature of binding and inhibition of ALR2 by vitamin K1 that could open up possibilities of its therapeutic application.

Vitamin K2 Improves Anxiety and Depression but not Cognition in Rats with Metabolic Syndrome: a Role of Blood Glucose?

BACKGROUND

The metabolic syndrome is a socially important disorder of energy utilization and storage, recognized as a factor predisposing to the development of depression, anxiety and cognitive impairment in humans.

AIM

In the present study we examined the effects of vitamin K2 on the behavior of rats with metabolic syndrome and looked for relationships with the effects on blood sugar.

MATERIALS AND METHODS

Male Wistar rats were divided in four groups: a control group on a regular rat chow, a metabolic syndrome (MS) group fed a high-fat high-fructose diet, a control group treated with vitamin K2 and a MS group treated with vitamin K2. Vitamin K2 was given by gavage. At the end of the study (after 10 weeks) behavioral tests were performed and fasting blood glucose was measured. Anxiety was determined using the social interaction test and depression was assessed by the Porsolt test. Memory effects were estimated by the object recognition test. Correlations between fasting blood glucose and behavioral performance were analyzed.

RESULTS

The rats from the MS group had elevated blood glucose. They had anxiety, depression and memory deficit. Vitamin K2 normalized blood glucose, reduced anxiety and depression, but did not improve memory. Time of social interaction (inverse index of anxiety) and memory recognition were negatively correlated with blood glucose in the untreated rats but the immobility time (measure of depression) was not. When vitamin K2-treated rats were added, the correlation of blood glucose with the time of social interaction was kept, but the one with the recognition memory was lost. It might be that the anxiolytic effect of vitamin K2 in this setting is at least partly due to its effects on blood glucose, while the anti-depressant effect is glucose-independent.

CONCLUSION

The present study demonstrated that vitamin K2 prevented the development of anxiety and depression, but did not improve the memory deficit caused by the dietary manipulation in an experimental model of metabolic syndrome. It might be that the anxiolytic effect of vitamin K2 is at least partly due to its effects on blood glucose, while the antidepressant effect is glucose-independent.

Inhibition of diabetic-cataract by vitamin K1 involves modulation of hyperglycemia-induced alterations to lens calcium homeostasis

This study investigated the potential of vitamin K1 against streptozotocin-induced diabetic cataract in Wistar rats. A single, intraperitoneal injection of streptozotocin (STZ) (35 mg/kg) resulted in hyperglycemia, accumulation of sorbitol and formation of advanced glycation end product (AGE) in eye lens. Hyperglycemia in lens also resulted in superoxide anion and hydroxyl radical generation and less reduced glutathione suggesting oxidative stress in lens. Hyperglycemia also resulted in increase in lens Ca2+ and significant inhibition of lens Ca2+ ATPase activity. These changes were associated with cataract formation in diabetic animals. By contrast treatment of diabetic rats with vitamin K1 (5 mg/kg, sc, twice a week) resulted in animals with partially elevated blood glucose and with transparent lenses having normal levels of sorbitol, AGE, Ca2+ ATPase, Ca2+, and oxidative stress. Vitamin K 1 may function to protect against cataract formation in the STZ induced diabetic rat by affecting the homeostasis of blood glucose and minimizing subsequent oxidative and osmotic stress. Thus, these results show that Vitamin K1 inhibits diabetic-cataract by modulating lens Ca2+ homeostasis and its hypoglycemic effect through its direct action on the pancreas.

Vitamin K1 alleviates streptozotocin-induced type 1 diabetes by mitigating free radical stress, as well as inhibiting NF-κB activation and iNOS expression in rat pancreas

OBJECTIVE

The aim of this study was to understand the mechanism of action of vitamin K1 against streptozotocin (STZ)-induced diabetes.

METHODS

Male Wistar rats were administered 35 mg/kg STZ and after 3 d were treated with vitamin K1 (5 mg/kg, twice a week) for 3 months. Blood glucose was monitored twice a month. At the end of the study, animals were sacrificed and pancreas dissected out and analyzed for free radicals, antioxidants, metabolic enzymes related to glucose, membrane ATPases, histopathological evaluation, and expression of nuclear factor (NF)-κB and inducible nitric oxide synthase (iNOS). Glycated hemoglobin, plasma insulin, and islet area were determined at the end of the study.

RESULTS

Treatment of STZ-induced type 1 diabetic rats with vitamin K1 reduced oxidative stress, enhanced antioxidants, and inhibited aldose reductase in pancreas. Vitamin K1 administration rescued endocrine pancreas from STZ-induced cell death, resulting in enhanced insulin secretion and normal blood glucose and glycosylated hemoglobin levels. Histologic analyses also showed the antidiabetic potential of vitamin K1. Measure of pancreatic islet area showed an increase in the islet area upon vitamin K1 treatment when compared with the STZ-administered group, suggesting the possibility of regeneration. To understand the mechanism involved in vitamin K1 mediated changes, we performed immunohistochemical analyses for NF-κB and iNOS enzyme. Vitamin K1 was shown to suppress NF-κB activation and iNOS expression in the islets upon administration of STZ.

CONCLUSION

This work shows, to our knowledge for the first time, the mechanism of action of vitamin K1 against type 1 diabetes and the possible therapeutic use of this vitamin in stimulating islet cell proliferation/regeneration.

Pleiotropic actions of vitamin K: protector of bone health and beyond?

Vitamin K is a nutrient that was originally identified as an essential factor for blood coagulation. Recently, vitamin K has emerged as a potential protector against osteoporosis, atherosclerosis, and hepatocarcinoma. Accumulated evidence indicates that subclinical non-hemostatic vitamin K deficiency in extrahepatic tissues, particularly in bone and possibly in vasculature, exists widely in the otherwise healthy adult population. Vitamins K1 and K2 have been shown to exert protective effects against osteoporosis, although it is important that the beneficial effects will be further confirmed by large-scale, randomized, clinical trials. Increasing evidence implicates a role for vitamin K in calcification of arteries and atherogenesis. Moreover, the therapeutic potential of vitamin K2 as an antihepatoma drug has recently been highlighted. Most of the new biological functions of vitamin K in bone, vasculature, and hepatoma cells are considered attributable to promotion of gamma-carboxylation of glutamic acid residues in vitamin K-dependent proteins, which is shared by vitamins K1 and K2. In contrast, vitamin K2-specific, gamma-carboxylation-unrelated functions have also been demonstrated. Thus, biological differences between vitamins K1 and K2 and potential involvement of gamma-carboxylation-independent actions in the new roles of vitamin K remain open issues. Molecular bases of coagulation-unrelated pleiotropic actions of vitamin K and its implications in human health deserve further investigations.

Atherosclerosis and Matrix Dystrophy

Atherosclerosis is characterized by inflammatory metabolic change with lipid accumulation in the artery. Atherosclerotic plaque occurs at discrete locations in the arterial system and involves the proliferation of smooth muscle cells (SMCs) together with imbalance of the extracellular matrix elements, elastic fiber in particular. The role of elastin in arterial development and disease was confirmed by generating mice that lack elastin. Thus, elastin is a critical regulatory molecule that regulates the phenotypic modulation, proliferation and migration of SMCs. We estimated that elastin expression and SMC proliferation are coupled inversely: potent stimulators of cell proliferation may potentially inhibit elastin expression and potent inhibitors of cell proliferation can stimulate elastin expression. Moreover, elastin was found to be expressed maximally at the G(0) and minimally at the G(2)/M phase during the cell cycle, suggesting that its expression is regulated by the cell growth state. The elastin peptide VPGVG enhanced SMC proliferation, resulting in the reduction of elastin expression. The inhibition of elastin expression by elastin fragments may be reflected in the negative feedback regulatory mechanism. The relationship between cell proliferation and elastin expression may be changed in atherosclerosis. Areas of atherosclerotic plaque show abnormality of elasticity and permeability from the viewpoint of the physiological function of the arterial wall. The etiology was estimated to be that cholesterol and calcium are deposited on the elastic fiber, resulting in decreased elastin synthesis and cross-linking formation. In addition, these dysfunctions of elastin fiber are also associated, in that the down-regulation of elastin and its related components (fibrillin-1 and lysyl oxidase) are directly related to calcification in SMCs. The denatured arterial elastin by cholesterol and calcium accumulation was also susceptible to proteolytic enzymes such as elastase and matrix metalloproteinase (MMP). Therefore, metabolic change in elastic fiber induces decreased elasticity and is associated with essential hypertension. Vitamin K(2) is used in drug therapy against atherosclerosis, or calcification in diabetes mellitus or dialysis, due to its promotion of the carboxylation of the matrix Gla protein.