Regulation of the atherogenic properties of vascular smooth muscle proteoglycans by oral anti-hyperglycemic agents

Emerging Applications of Metabolomics to Assess the Efficacy of Traditional Chinese Medicines for Treating Type 2 Diabetes Mellitus

Diabetes is a common and complex disease that can exacerbate the complications related to cardiovascular disease, and this is especially true for type 2 diabetes mellitus (T2DM). In addition to the standard pharmacological therapies, T2DM has also been treated with nonconventional regimens such as traditional Chinese medicine (TCM), e.g., herbal medicines and TCM prescriptions, although the mechanisms underlying the therapeutic benefits remain unclear. In this regard, many studies have used metabolomics technology to elucidate the basis for the efficacy of TCM for T2DM. Metabolomics has recently attracted much attention with regard to drug discovery and pharmacologically relevant natural products. In this review, we summarize the application of metabolomics to the assessment of TCM efficacy for treating T2DM. Increasing evidence suggests that the metabolic profile of an individual patient may reflect a specific type of T2DM syndrome, which may provide a new perspective for disease diagnosis. In addition, TCM has proved effective for countering the metabolic disorders related to T2DM, and this may constitute the basis for TCM efficacy. Therefore, further determining how TCM contributes to the reversal of metabolic disorders, such as using network pharmacology or by assessing the contribution of host–gut microbiota interactions, will also provide researchers with new potential targets for pharmacologic-based therapies.

Dry Eye Disease Is More Prevalent in Children with Diabetes than in Those without Diabetes

Purpose: To compare the prevalence of dry eye disease between children with and without diabetes, and analyze the factors associated with dry eye disease in children with diabetes.Materials and methods: 38 children with diabetes were selected as cases, and 40 children without diabetes constituted the control group. The prevalence of dry eye disease in both groups was statistically analyzed. Related factors of dry eye disease were analyzed in children with diabetes.Results: The prevalence of dry eye disease in the case group was significantly higher than that in the control group (P < .01), with the attributable proportion among the exposed (0.827) and the population attributable fraction (0.700). Univariate analysis showed that the diabetes duration, best-corrected visual acuity, corneal sensation, and levels of glycosylated hemoglobin were associated with dry eye disease in children with diabetes. Logistic regression analysis revealed that only diabetes duration and corneal sensation were independent factors associated with dry eye disease. The diabetes duration was significantly higher and the level of corneal sensation was significantly lower in subjects with dry eye disease than in those without dry eye disease.Conclusions: Early screening and close follow-up of dry eye disease in children with diabetes should be strictly implemented, especially in children with a long duration of diabetes and those with peripheral neuropathy.

Ginsenoside Rb1 as an Anti-Diabetic Agent and Its Underlying Mechanism Analysis

Panax ginseng and Panax notoginseng, two well-known medical plants with economic value, have a long history of use for managing various diseases in Asian countries. Accumulating clinical and experimental evidence suggests that notoginsenosides and ginsenosides, which are the major bioactive components of the plants, have a variety of beneficial effects on several types of disease, including metabolic, vascular, and central nervous system disease. Considerable attention has been focused on ginsenoside Rb1 derived from their common ownership as an anti-diabetic agent that can attenuate insulin resistance and various complications. Particularly, in vitro and in vivo models have suggested that ginsenoside Rb1 exerts various pharmacological effects on metabolic disorders, including attenuation of glycemia, hypertension, and hyperlipidemia, which depend on the modulation of oxidative stress, inflammatory response, autophagy, and anti-apoptosis effects. Regulation of these pathophysiological mechanisms can improve blood glucose and insulin resistance and protect against macrovascular/microvascular related complications. This review summarizes the pharmacological effects and mechanisms of action of ginsenoside Rb1 in the management of diabetes or diabetic complications. Moreover, a multi-target effect and mechanism analysis of its antidiabetic actions were performed to provide a theoretical basis for further pharmacological studies and new drug development for clinical treatment of type 2 diabetes. In conclusion, ginsenoside Rb1 exerts significant anti-obesity, anti-hyperglycemic, and anti-diabetic effects by regulating the effects of glycolipid metabolism and improving insulin and leptin sensitivities. All of these findings suggest ginsenoside Rb1 exerts protective effects on diabetes and diabetic complications by the regulation of mitochondrial energy metabolism, improving insulin resistance and alleviating the occurrence complications, which should be further explored. Hence, ginsenoside Rb1 may be developed as a potential anti-obesity, anti-hyperglycemic, and anti-diabetic agent with multi-target effects.

Animal models for assessing the impact of natural products on the aetiology and metabolic pathophysiology of Type 2 diabetes

Type 2 diabetes mellitus is a complex and heterogeneous disorder which in its most common manifestation arises from insulin resistance and later insulin insufficiency. Type 2 diabetes is characterised by impaired insulin sensitivity and diagnosed as hyperglycaemia. Because of its cardiovascular consequences, Type 2 diabetes represents one of the world's leading causes of mortality and morbidity. Drug discovery and development are required to produce better ways to prevent, treat and manage diabetes and its complications. Diabetes is a human, not an animal disease, so animals do not get Type 2 diabetes. However there are animal models which are variously suitable for the investigation of new agents for the treatment of Type 2 diabetes. In this Review we have examined the various models that are available for the study of natural products with a focus on models (genetic, nutritional and spontaneous) for the metabolic abnormities of diabetes. These models are also relevant to the investigation of Western medicines for the treatment of diabetes. A suitable experimental model plays an important role in drug discovery for translational studies leading to increased understanding of the molecular basis and management of diabetes.

Effect of Momordica charantia fruit extract on vascular complication in type 1 diabetic rats

Diabetes mellitus is one of the risk factors in the development of vascular complications. Decreased nitric oxide (NO) production and increased lipid peroxidation in diabetes mellitus are the dominant exaggerating factors. Mormodica charantia (MC) was proven to be useful in improving diabetes mellitus and its complications. In the present study, a total of 40 male Sprague-Dawley rats were used. Diabetes was induced by a single dose (50 mg/kg) of streptozotocin (STZ), intramuscularly. Following 4 weeks of STZ induction, the animals were equally divided into five groups (n = 8); Control group (Ctrl), control group treated with MC (Ctrl-MC), diabetic untreated group (DM-Ctrl), diabetic group treated with MC (DM-MC) and diabetic group treated with metformin 150 g/kg (DM-Met). Oral administration of the MC fruit extract (1.5 g/kg) was continued for 28 days. DM-MC group showed a significant decrease (P < 0.05) in blood pressure, total cholesterol and triglyceride levels compared to the DM-Ctrl group. Aortic tissue NO level was significantly increased and malondialdehyde level was decreased in the DM-MC group. Immunohistochemical staining showed an increase in eNOS expression in the endothelial lining of the DM-MC group. Similarly, morphological deterioration of the aortic tissues was reverted to normal. In summary, treatment with the MC fruit extract exerted the significant vasculoprotective effect in the type 1 diabetic rat model.

Atherogenic, fibrotic and glucose utilising actions of glucokinase activators on vascular endothelium and smooth muscle

Background

Pharmaceutical interventions for diabetes aim to control glycaemia and to prevent the development of complications, such as cardiovascular diseases. Some anti-hyperglycaemic drugs have been found to have adverse cardiovascular effects in their own right, limiting their therapeutic role. Glucokinase activity in the pancreas is critical in enhancing insulin release in response to hyperglycaemia. Glucokinase activators (GKAs) are novel agents for diabetes which act by enhancing the formation of glucose-6-phosphate leading to increased insulin production and subsequent suppression of blood glucose. Little, however, is known about the direct effects of GKAs on cardiovascular cells.

Methods

The effect of the GKAs RO28-1675 and Compound A on glucose utilisation in bovine aortic endothelial cells (BAEC) and rat MIN6 was observed by culturing the cells at high and low glucose concentration in the presence and absence of the GKAs and measuring glucose consumption. The effect of RO28-1675 at various concentrations on glucose-dependent signalling in BAEC was observed by measuring Smad2 phosphorylation by Western blotting. The effect of RO28-1675 on TGF-β stimulated proteoglycan synthesis was measured by ³⁵S-SO₄ incorporation and assessment of proteoglycan size by SDS-PAGE. The effects of RO28-1675 on TGF-β mediated Smad2C phosphorylation in BAEC was observed by measurement of pSmad2C levels. The direct actions of RO28-1675 on vascular reactivity were observed by measuring arteriole tone and lumen diameter.

Results

GKAs were demonstrated to increase glucose utilisation in pancreatic but not endothelial cells. Glucose-activated Smad2 phosphorylation was decreased in a dose-dependent fashion in the presence of RO28-1675. No effect of RO28-1675 was observed on TGF-β stimulated proteoglycan production. RO28-1675 caused a modest dilation in arteriole but not contractile sensitivity.

Conclusions

GKA RO28-1675 did not increase glucose consumption in endothelial cells indicating the absence of glucokinase in those cells. No direct deleterious actions, in terms of atherogenic changes or excessive vasoactive effects were seen on cells or vessels of the cardiovascular system in response to GKAs. If reflected in vivo, these drugs are unlikely to have their use compromised by direct cardiovascular toxicity.

(S)-[6]-Gingerol inhibits TGF-β-stimulated biglycan synthesis but not glycosaminoglycan hyperelongation in human vascular smooth muscle cells

Objectives

(S)-[6]-Gingerol is under investigation for a variety of therapeutic uses. Transforming growth factor (TGF)-β stimulates proteoglycan synthesis, leading to increased binding of low-density lipoproteins, which is the initiating step in atherosclerosis. We evaluated the effects of (S)-[6]-gingerol on these TGF-β-mediated proteoglycan changes to explore its potential as an anti-atherosclerotic agent.

Methods

Purified (S)-[6]-gingerol was assessed for its effects on proteoglycan synthesis by [35S]-sulfate incorporation into glycosaminoglycan chains and [35S]-Met/Cys incorporation into proteoglycans and total proteins in human vascular smooth muscle cells. Biglycan level was assessed by real-time quantitative polymerase chain reactions and the effects of (S)-[6]-gingerol on TGF-β signalling by assessment of the phosphorylation of Smads and Akt by western blotting.

Key findings

(S)-[6]-Gingerol concentration-dependently inhibited TGF-β-stimulated proteoglycan core protein synthesis, and this was not secondary to inhibition of total protein synthesis. (S)-[6]-Gingerol inhibited biglycan mRNA expression. (S)-[6]-Gingerol did not inhibit TGF-β-stimulated glycosaminoglycan hyperelongation or phosphorylation of Smad 2, in either the carboxy terminal or linker region, or Akt phosphorylation.

Conclusions

The activity of (S)-[6]-gingerol to inhibit TGF-β-stimulated biglycan synthesis suggests a potential role for ginger in the prevention of atherosclerosis or other lipid-binding diseases. The signalling studies indicate a novel site of action of (S)-[6]-gingerol in inhibiting TGF-β responses.

Hyaluronan synthesis is inhibited by adenosine monophosphate-activated protein kinase through the regulation of HAS2 activity in human aortic smooth muscle cells

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan (GAG) involved in cell motility, proliferation, tissue remodeling, development, differentiation, inflammation, tumor progression, and invasion and controls vessel thickening in cardiovascular diseases. Therefore, the control of HA synthesis could permit the fine-tuning of cell behavior, but the mechanisms that regulate HA synthesis are largely unknown. Recent studies suggest that the availability of the nucleotide-sugar precursors has a critical role. Because the formation of UDP-sugars is a highly energetically demanding process, we have analyzed whether the energy status of the cell could control GAG production. AMP-activated protein kinase (AMPK) is the main ATP/AMP sensor of mammalian cells, and we mimicked an energy stress by treating human aortic smooth muscle cells (AoSMCs) with the AMPK activators 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside and metformin. Under these conditions, HA synthesis, but not that of the other GAGs, was greatly reduced. We confirmed the inhibitory effect of AMPK using a specific inhibitor and knock-out cell lines. We found that AMPK phosphorylated Thr-110 of human HAS2, which inhibits its enzymatic activity. In contrast, the other two HAS isoenzymes (HAS1 and HAS3) were not modified by the kinase. The reduction of HA decreased the ability of AoSMCs to proliferate, migrate, and recruit immune cells, thereby reducing the pro-atherosclerotic AoSMC phenotype. Interestingly, such effects were not recovered by treatment with exogenous HA, suggesting that AMPK can block the pro-atherosclerotic signals driven by HA by interaction with its receptors.

Transforming growth factor-β regulation of proteoglycan synthesis in vascular smooth muscle: contribution to lipid binding and accelerated atherosclerosis in diabetes

Atherosclerosis is accelerated in the setting of diabetes, but the factors driving this phenomenon remain elusive. Hyperglycemia leads to elevated levels of transforming growth factor (TGF)-β and TGF-β has been implicated as a factor in atherosclerosis. Given the established association between hyperglycemia and elevated TGF-β, it is plausible that elevated TGF-β levels in diabetes play a pathogenic role in the development of accelerated atherosclerosis. TGF-β is a potent regulator of extracellular matrix synthesis, including many actions on proteoglycan synthesis that lead to increased binding to low-density lipoprotein and therefore potentially increased lipid retention in the vessel wall and accelerated atherosclerosis. TGF-β signals through the canonical TGF-β receptor I-mediated phosphorylation of Smad transcription factors and TGF-β signaling is also known to involve, positively and negatively, interactions with the mitogen-activated protein kinase pathways. The focus of the present review is on the effects of TGF-β on proteoglycan synthesis in vascular smooth muscle and particularly the signaling pathways through which TGF-β exerts its effects, because those pathways may be therapeutic targets for the prevention of pathological modifications in the proteoglycan component of the vessel wall in the vascular diseases of diabetes.

AMPK and vasculoprotection

AMP-activated protein kinase (AMPK) is proposed to be a key regulator of cellular and organismal metabolism and has reported vasculoprotective effects. In addition, many therapeutic agents used in the treatment of diabetes and atherosclerosis such as metformin, thiazolidinediones and statins may exert their vasculoprotective effects through activation of AMPK. Activation of AMPK has a number of potentially beneficial anti-atherosclerotic effects including reducing adhesion of inflammatory cells to the blood vessel endothelium, reducing lipid accumulation and the proliferation of inflammatory cells caused by oxidised lipids, stimulation of gene expression responsible for cellular antioxidant defenses and stimulation of enzymes responsible for nitric oxide formation. In humans and animals the AMPK cascade triggers vascular protective mechanisms that have been shown to reduce myocardial ischaemic injury and mutations in AMPK can cause familial hypertrophic cardiomyopathy. Taken together, these data suggest that activation and function of AMPK contributes to cardiovascular health. In this review we propose to focus on the vasculoprotective effects of AMPK, the evidence for AMPK activation with currently used therapeutic agents and the potential for agents which specifically activate AMPK as a treatment for vascular disease.

Urinary transforming growth factor-beta(1), collagen IV and the effect of insulin in children at diagnosis of diabetes mellitus

OBJECTIVE

This study investigated whether metabolic derangement at diagnosis of diabetes mellitus affects the function of the basement membrane and the excretion of several components and whether insulin treatment can normalize this. It was designed to evaluate urinary excretion rates of transforming growth factor-beta(1) (TGF-beta(1)), the carboxy-terminal domain of collagen IV (NC1) and albumin in children during the first 20 days of treatment after diagnosis of type 1 diabetes.

MATERIAL AND METHODS

Thirty-four newly diagnosed diabetic children between 4 and 16 years of age and 26 healthy children of matching age were studied with timed overnight urine collections. Urine was collected during the first 20 days of treatment.

RESULTS

Urinary excretion of albumin and TGF-beta(1) in diabetic children were significantly increased at entry but normalized during 20 days of treatment with insulin compared with control children. In contrast, the non-significant high NC1 excretion at diagnosis did not change but became significantly increased after 20 days of insulin treatment. Overall, the kidney size was within normal limits and unaffected by treatment. The largest kidneys had less NC1 excretion (R= - 0.67, p<0.05, n=13) and a lower glomerular filtration rate (R= - 0.77, p<0.01, n=10) than the smallest kidneys. After 20 days of treatment TGF-beta(1) excretion had decreased in children with kidney size > 8.5 cm.

CONCLUSION

Correction of the metabolic derangement with insulin decreased excretion of albumin and TGF-beta(1), but had no effect on kidney size and urine NC1 excretion, presumably because the observation period was too short.

Proteoglycan mediated lipoprotein retention: a mechanism of diabetic atherosclerosis

The response to retention hypothesis outlines the initial stages of atherosclerotic lesion formation. The central theme of the hypothesis is that proteoglycan mediated lipoprotein retention plays a critical step in the initiation of atherosclerosis development. Recent research using human arterial specimens, transgenic mouse models and molecular biology techniques have added to our understanding of atherosclerosis development, and provided experimental data in support of the response to retention hypothesis. In this review we summarize the recent data, in particular that which addresses mechanisms by which diabetes can accelerate atherosclerosis formation, with a focus on proteoglycan-mediated LDL retention.

The effect of PPAR ligands to modulate glucose metabolism alters the incorporation of metabolic precursors into proteoglycans synthesized by human vascular smooth muscle cells

PPAR ligands are important effectors of energy metabolism and can modify proteoglycan synthesis by vascular smooth muscle cells (VSMCs). Describing the cell biology of these important clinical agents is important for understanding their full clinical potential, including toxicity. Troglitazone (10 microM) and fenofibrate (30 microM) treatment of VSMCs reduces ((35)S)-sulphate incorporation into proteoglycans due to a reduction of glycosaminoglycan (GAG) chain length. Conversely, under physiological glucose conditions (5.5 mM), the same treatment increases ((3)H)-glucosamine incorporation into GAGs. This apparent paradox is the consequence of an increase in the intracellular ((3)H)-galactosamine specific activity from 48.2 +/- 3.2 microCi/ micromol to 90.7 +/- 11.0 microCi/ micromol (P < 0.001) and 57.1 +/- 2.6 microCi/ micromol (P < 0.05) when VSMCs were treated with troglitazone and fenofibrate, respectively. The increased specific activity observed with troglitazone (10 microM) treatment correlates with a two-fold increase in glucose consumption, while fenofibrate (50 microM) treatment showed a modest (14.6%) increase in glucose consumption. We conclude that the sole use of glucosamine precursors to assess GAG biosynthesis results in misleading conclusions when assessing the effect of PPAR ligands on VSMC proteoglycan biosynthesis.

Clinical administration of rosiglitazone and glimepiride combination in the treatment of type 2 diabetes mellitus

A cardiovascularis halálozás világszerte növekszik. A halálos kimenetelnek egyik legfontosabb kóroki tényezője a diabetes mellitus. E megbetegedés kezelésére alkalmazható gyógyszerek közé tartoznak az inzulin kiválasztását fokozó szerek (insulinsecretagog készítmények), az inzulin hatását növelő (inzulinszenzitizálók) és glükózfelszívódást gátló készítmények. Mindezek alkalmazhatók monoterápiában és különféle kombinációban is. A gyakorlatban nagyon hasznosnak tűnik a roziglitazon és a glimepirid kombinációja. Mivel alkotóik különböző támadáspontokon fejtik ki hatásukat, jól kiegészítik egymást. A glimepirid a béta-sejtek inzulinszekrécióját fokozza, csökkenti a vércukorszintet, a roziglitazon pedig az így megtermelt inzulin iránti érzékenységet fokozza a célszervekben. A két szer additív módon jelentősen javítja a vércukorszintet. A glimepirid és roziglitazon kombinációját a betegek általában jól tolerálják, és a fix kombináció javítja a terápiás adherenciát is.

Anti-proliferative activity of oral anti-hyperglycemic agents on human vascular smooth muscle cells: thiazolidinediones (glitazones) have enhanced activity under high glucose conditions

Background

Inhibition of vascular smooth muscle cell (vSMC) proliferation by oral anti-hyperglycemic agents may have a role to play in the amelioration of vascular disease in diabetes. Thiazolidinediones (TZDs) inhibit vSMC proliferation but it has been reported that they anomalously stimulate [³H]-thymidine incorporation. We investigated three TZDs, two biguanides and two sulfonylureas for their ability of inhibit vSMC proliferation. People with diabetes obviously have fluctuating blood glucose levels thus we determined the effect of media glucose concentration on the inhibitory activity of TZDs in a vSMC preparation that grew considerably more rapidly under high glucose conditions. We further explored the mechanisms by which TZDs increase [³H]-thymidine incorporation.

Methods

VSMC proliferation was investigated by [³H]-thymidine incorporation into DNA and cell counting. Activation and inhibition of thymidine kinase utilized short term [³H]-thymidine uptake. Cell cycle events were analyzed by FACS.

Results

VSMC cells grown for 3 days in DMEM with 5% fetal calf serum under low (5 mM glucose) and high (25 mM glucose) increased in number by 2.5 and 4.7 fold, respectively. Rosiglitazone and pioglitazone showed modest but statistically significantly greater inhibitory activity under high versus low glucose conditions (P < 0.05 and P < 0.001, respectively). We confirmed an earlier report that troglitazone (at low concentrations) causes enhanced incorporation of [³H]-thymidine into DNA but did not increase cell numbers. Troglitazone inhibited serum mediated thymidine kinase induction in a concentration dependent manner. FACS analysis showed that troglitazone and rosiglitazone but not pioglitazone placed a slightly higher percentage of cells in the S phase of a growing culture. Of the biguanides, metformin had no effect on proliferation assessed as [³H]-thymidine incorporation or cell numbers whereas phenformin was inhibitory in both assays albeit at high concentrations. The sulfonylureas chlorpropamide and gliclazide had no inhibitory effect on vSMC proliferation assessed by either [³H]-thymidine incorporation or cell numbers.

Conclusion

TZDs but not sulfonylureas nor biguanides (except phenformin at high concentrations) show favorable vascular actions assessed as inhibition of vSMC proliferation. The activity of rosiglitazone and pioglitazone is enhanced under high glucose conditions. These data provide further in vitro evidence for the potential efficacy of TZDs in preventing multiple cardiovascular diseases. However, the plethora of potentially beneficial actions of TZDs in cell and animal models have not been reflected in the results of major clinical trials and a greater understanding of these complex drugs is required to delineate their ultimate clinical utility in preventing macrovascular disease in diabetes.