Insulin's stimulation of endothelial superoxide generation may reflect up-regulation of isoprenyl transferase activity that promotes rac translocation

Association between cardiac autonomic function, oxidative stress and inflammatory response in impaired fasting glucose subjects: cross-sectional study

Background

The worldwide burden of diabetes in 2030 is projected around 552 million. Diabetes leads to higher risk for cardiovascular diseases (CVD). Altered cardiac autonomic function (CAF) measured by heart rate variability (HRV) is observed in early stages of diabetes but the relationship between impaired fasting glucose (IFG) and HRV is still debatable. The aim of the study was to evaluate the association between CAF, oxidative stress, insulin resistance (IR), and inflammatory response in IFG subjects.

Subjects and Methods

Cross-sectional blinded study. Volunteers recruited from health awareness camps underwent CAF and biochemical tests. Based on fasting plasma glucose (FPG) participants (n = 123) were divided into two groups, normal fasting glucose (n = 76) and IFG (n = 47). The comparison of parameters between the groups was carried out using student t test and Mann-Whitney U test for parametric and non-parametric data respectively. The correlation between the parameters was analyzed by Spearman’s rank correlation using SPSS 13.0.

Results

The resting cardiovagal modulation parameters, heart rate response to forced timed breathing, and orthostatic stress were reduced in IFG subjects. Fasting plasma lipid profile, coronary atherogenic lipid risk factors, IR, thiobarbituric acid reactive substance (TBARS), high sensitive C-reactive protein, and tumor necrosis factor alpha were increased and total antioxidant capacity (TAC) was decreased significantly in IFG group but no significant alteration was observed in high-density lipoprotein (HDL-c). Cardiovagal modulation parameters were negatively correlated with triglycerides, FPG, insulin, IR, TBARS, and inflammatory markers and positively with TAC.

Conclusion

There is a continuous interplay between the altered CAF, hyperinsulinemia, IR, oxidative stress parameters, inflammatory response, and IFG in which one factor perpetuates another leading to the progression of disease.

HMG-CoA reductase inhibitors: do they have potential in the treatment of polycystic ovary syndrome?

Many women of reproductive age are affected by polycystic ovary syndrome (PCOS), a heterogeneous endocrinopathy characterized by androgen excess, chronic oligo-anovulation and/or polycystic ovarian morphology. In addition, PCOS is often associated with insulin resistance, systemic inflammation and oxidative stress, which, on one hand, lead to endothelial dysfunction and dyslipidaemia with subsequent cardiovascular sequelae and, on the other hand, to hyperplasia of the ovarian theca compartment with resultant hyperandrogenism and anovulation. Traditionally, HMG-CoA reductase inhibitors (statins) have been used to treat dyslipidaemia by blocking HMG-CoA reductase (the rate-limiting step in cholesterol biosynthesis); however, they also possess pleiotropic actions, resulting in antioxidant, anti-inflammatory and anti-proliferative effects. Statins offer a novel therapeutic approach to PCOS in that they address the dyslipidaemia associated with the syndrome, as well as hyperandrogenism or hyperandrogenaemia. These actions may be due to an inhibition of the effects of systemic inflammation and insulin resistance/hyperinsulinaemia. Evidence to date, both in vitro and in vivo, suggests that statins have potential in the treatment of PCOS; however, further clinical trials are needed before they can be considered a standard of care in the medical management of this common endocrinopathy.

Statins in the treatment of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy affecting reproductive-aged women. The hyperandrogenemia associated with the syndrome is a result of excessive growth and steroidogenic activity of theca-interstitial tissues in response to various factors, including elevated gonadotropins, hyperinsulinemia, and oxidative stress. PCOS frequently coexists with other cardiovascular risk factors, such as dyslipidemia and systemic inflammation. Statins inhibit the synthesis of mevalonate, the key precursor to cholesterol biosynthesis, and reduce cardiovascular morbidity and mortality. Blockade of mevalonate production may also lead to decreased maturation of insulin receptors, inhibition of steroidogenesis (e.g., via limiting the amount of substrate: cholesterol), and alteration of signal transduction pathways that mediate cellular proliferation. The latter depend upon posttranslational modification of proteins (prenylation), a process mediated by mevalonate derivatives. Statins also have intrinsic antioxidant properties. Given the pleiotropic actions of statins, they are likely not only to improve the dyslipidemia associated with PCOS but may also exert other beneficial metabolic and endocrine effects.

Twenty-five years since the discovery of endothelium-derived relaxing factor (EDRF): does a dysfunctional endothelium contribute to the development of type 2 diabetes?

Twenty-five years ago, the discovery of endothelium-derived relaxing factor opened a door that revealed a new and exciting role for the endothelium in the regulation of blood flow and led to the discovery that nitric oxide (NO) multi-tasked as a novel cell-signalling molecule. During the next 25 years, our understanding of both the importance of the endothelium as well as NO has greatly expanded. No longer simply a barrier between the blood and vascular smooth muscle, the endothelium is now recognized as a complex tissue with heterogeneous properties. The endothelium is the source of not only NO but also numerous vasoactive molecules and signalling pathways, some of which are still not fully characterized such as the putative endothelium-derived relaxing factor. Dysfunction of the endothelium is a key risk factor for the development of macro- and microvascular disease and, by coincidence, the discovery that NO was generated in the endothelium corresponds approximately in time with the increased incidence of type 2 diabetes. Primarily linked to dietary and lifestyle changes, we are now facing a global pandemic of type 2 diabetes. Characterized by insulin resistance and hyperglycaemia, type 2 diabetes is increasingly being diagnosed in adolescents as well as children. Is there a link between dietary-related hyperglycaemic insults to the endothelium, blood flow changes, and the development of insulin resistance? This review explores the evidence for and against this hypothesis.

Oxidative stress as a therapeutic target in diabetes: revisiting the controversy

Oxidative stress has been repetitively shown to be a hallmark of many diseases linked with metabolic or vascular disorders. Therefore diabetes represents an ideal candidate for studying the consequences of oxidative stress and its treatment. Indeed diabetes constitutes a multiple source of free radicals, starting very early in the disease process and worsening over the course of disease. In view of the typical characteristics of diabetes, oxidative stress is expected to have a double impact, on both metabolic and vascular functions. It is therefore particularly disappointing to note the dramatic failure of clinical trials with antioxidants, although it must be pointed out that such studies have not been performed with only diabetic patients. This review describes the many different aspects of oxidative stress in diabetes and proposes possible explanations for the apparent lack of efficacy of antioxidant treatments in patients. Some verifications seem warranted before a definitive conclusion can be drawn about the validity of this therapeutic concept.

Antioxidant paraoxonase 1 activity in the metabolic syndrome

Paraoxonase (PON1) is an antioxidant enzyme closely associated with high-density lipoproteins. Low PON1 has been shown in oxidative stress-associated processes such as dyslipidemia, diabetes mellitus, advancing age, and smoking. Indeed, oxidative stress is related to the degree of insulin resistance, a key component of the metabolic syndrome. Therefore, the possible relationship between PON1 activity and the metabolic syndrome was investigated. From 1364 randomly recruited subjects, 285 were found to have the metabolic syndrome, according to the guidelines published by the National Cholesterol Education Program, Adult Treatment Panel III. PON1 activity, lipid peroxides, and PON1 codon 192 genotypes, which strongly modulate PON1 activity, were determined. Serum PON1 activity levels were found to be significantly lower, and lipid peroxide concentrations significantly higher, in subjects with the metabolic syndrome compared with unaffected subjects (P = 0.033 and < 0.001, respectively). Study subjects showed a significant decreasing trend in PON1 activity levels and a significant increasing trend in lipid peroxide concentrations, with the increase in the number of metabolic disturbances. No differences in the prevalence of PON1 codon 192 genotypes were found among the categories of metabolic abnormalities. In conclusion, a greater degree of severity of the metabolic syndrome is associated with a progressively worse antioxidant/oxidant balance, which is consistent with increased oxidative stress and lower antioxidant PON1 enzymatic capacity.

Mevastatin suppresses lipopolysaccharide-induced Rac activation in the human monocyte cell line THP-1

BACKGROUND

Rac is a member of the Rho family of small guanosine triphosphatases that regulate the actin cytoskeleton. Activation of Rac requires lipid modification that can be blocked by statins. Lipopolysaccharide-induced rearrangements in the actin cytoskeleton lead to changes in cell adhesion and motility that play a role in the cellular response to infection. The lipid products of phosphatidylinositol-3 kinase (PI3K) modulate Rac effector pathways and have been linked to the activation of the Rac-guanosine triphosphatase. We hypothesize that lipopolysaccharide stimulation leads to Rac activation and that this may be inhibited by statin pretreatment. Furthermore, signaling downstream of Rac is linked to PI3K; therefore, we hypothesize that a signaling complex between PI3K and Rac may be involved.

METHODS

THP-1 cells were maintained in 1% fetal calf serum with or without 20 micromol/L mevastatin for 24 hours, followed by lipopolysaccharide stimulation. Active Rac was precipitated from THP-1 total cell lysate and then detected by immunoblotting. The PI3K-Rac complex was immunoprecipitated from total cell lysate, and the p85 regulatory subunit of PI3K was detected by immunoblotting.

RESULTS

Lipopolysaccharide stimulation activated Rac. Rac activation was suppressed by pretreatment with mevastatin. The p85 subunit of PI3K was associated with Rac.

CONCLUSIONS

Lipopolysaccharide stimulation leads to Rac activation in THP-1 cells, which may be suppressed with mevastatin pretreatment. There is an association between Rac and PI3K that demonstrates a role for PI3K in the activation of downstream Rac effector pathways.

Policosanol safely down-regulates HMG-CoA reductase - potential as a component of the Esselstyn regimen

Many of the wide-ranging health benefits conferred by statin therapy are mediated, not by reductions in LDL cholesterol, but rather by inhibition of isoprenylation reactions essential to the activation of Rho family GTPases; this may be the mechanism primarily responsible for the favorable impact of statins on risk for ischemic stroke, senile dementia, and fractures, as well as the anti-hypertensive and platelet-stabilizing actions of these drugs. Indeed, the extent of these benefits is such as to suggest that most adults would be wise to take statins; however, owing to the significant expense of statin therapy, as well as to the potential for dangerous side effects that mandates regular physician follow-up, this strategy appears impractical. However, policosanol, a mixture of long-chain aliphatic alcohols extractable from sugar cane wax, has shown cholesterol-lowering potency comparable to that of statins, and yet appears to be devoid of toxic risk. Recent evidence indicates that policosanol down-regulates cellular expression of HMG-CoA reductase, and thus has the potential to suppress isoprenylation reactions much like statins do. Consistent with this possibility, the results of certain clinical and animal studies demonstrate that policosanol has many effects analogous to those of statins that are not likely explained by reductions of LDL cholesterol. However, unlike statins, policosanol does not directly inhibit HMG-CoA reductase, and even in high concentrations it fails to down-regulate this enzyme by more than 50% - thus likely accounting for the safety of this nutraceutical. In light of the fact that policosanol is quite inexpensive and is becoming available as a non-prescription dietary supplement, it may represent a practical resource that could enable the general public to enjoy health benefits comparable to those conferred by statins. In a long-term clinical study enrolling patients with significant symptomatic coronary disease, Esselstyn has demonstrated that a low-fat, whole-food vegan diet, coupled with sufficient statin therapy to maintain serum cholesterol below 150 mg/dL, can stop the progression of coronary disease and virtually eliminate further risk for heart attack. A comparable regimen, in which policosanol is used in place of statins, may represent a practical strategy whereby nearly everyone willing to commit to health-protective eating can either prevent coronary disease, or prevent pre-existing coronary disease from progressing to a life-threatening event.