Lipid modulation in insulin-dependent diabetes mellitus: effect on microvascular outcomes

Neuronal Nitric Oxide Synthase Mediates Statin-Induced Restoration of Vasa Nervorum and Reversal of Diabetic Neuropathy

Background— Peripheral neuropathy is a frequent and major complication of diabetes.

Methods and Results— Severe peripheral neuropathy developed in type II diabetic mice, characterized by significant slowing of motor and sensory nerve conduction velocities. Rosuvastatin restored nerve vascularity, including vessel size, and nerve function also recovered to the levels of nondiabetic mice. Neuronal nitric oxide synthase expression in sciatic nerves was reduced in diabetic mice but was preserved by rosuvastatin. Coadministration of a nitric oxide synthase inhibitor with rosuvastatin attenuated the beneficial effects of rosuvastatin on nerve function and limited the recovery of vasa nervorum and nerve function. In vitro, rosuvastatin inhibited downregulation of neuronal nitric oxide synthase expression induced by high-glucose conditions in cultured Schwann cells. Furthermore, Akt phosphorylation in Schwann cells, downregulated by high-glucose conditions, was also restored by rosuvastatin, consistent with the change of neuronal nitric oxide synthase expression. Akt inhibition independently reduced neuronal nitric oxide synthase expression in Schwann cells in low-glucose cultures.

Conclusions— These data indicate that the HMG-CoA reductase inhibitor rosuvastatin has a favorable effect on diabetic neuropathy independent of its cholesterol-lowering effect. Our data provide evidence that this effect may be mediated in part via neuronal nitric oxide synthase/nitric oxide and phosphatidylinositol 3-kinase/Akt-signaling pathways and also suggest that restoration or preservation of the microcirculation of the sciatic nerve may be involved.

Role of lipid control in diabetic nephropathy

Patients with diabetic nephropathy are known to be associated with many lipoprotein abnormalities, including higher plasma levels of very low-density lipoprotein, low-density lipoprotein and triglycerides, and lower levels of high-density lipoprotein. Many studies have reported that lipids may induce both glomerular and tubulointerstitial injury through mediators such as cytokines, reactive oxygen species, chemokines, and through hemodynamic changes. Clinical studies in patients with diabetic nephropathy showed that lipid control can be associated with an additional effect of reduction in proteinuria. Experimental studies demonstrated that lipid-lowering agents exerted a certain degree of renoprotection, through both indirect effects from lipid lowering and a direct effect on cell protection. Therefore, lipid control appears to be important in the prevention and treatment of diabetic nephropathy. Diabetic nephropathy has become the leading cause of end-stage renal failure in many countries, including Taiwan. One of the major risk factors for the development and progression of diabetic nephropathy is dyslipidemia. In this paper we will review the role of lipid in mediating renal injury and the beneficial effects of lipid control in diabetic nephropathy.

Treatment of lipids and type 2 diabetes

The development of type 2 diabetes is increasing in epidemic proportions. There is a significant risk for cardiovascular disease, which is the most prevalent and detrimental complication for the diabetic population. Serum lipid abnormalities are common in patients with diabetes, and due to this increased vascular risk, it is recommended to aggressively treat the hyperlipidemia. Therefore, intensive lipid-lowering therapy should be used for primary and secondary prevention against macrovascular complications for patients with type 2 diabetes. In this article some of the key studies justifying the need for lipid reduction in patients with type 2 diabetes are reviewed and practical guidelines for management of the dyslipidemia are suggested.

The role of lipids in the development of diabetic microvascular complications: implications for therapy

Dyslipidemia is a major factor responsible for coronary heart disease and its reduction decreases coronary risk in patients with diabetes mellitus. However, the association of dyslipidemia with microvascular complications and the effect of intervention with lipid-lowering therapy in diabetes have been less investigated. We present the systematic review of association and intervention studies pertaining to dyslipidemia and microvascular disease in diabetes and also review possible mechanisms. Dyslipidemia may cause or exacerbate diabetic retinopathy and nephropathy by alterations in the coagulation-fibrinolytic system, changes in membrane permeability, damage to endothelial cells and increased atherosclerosis. Hyperlipidemia is associated with faster decline in glomerular filtration rate and progression of albuminuria and nephropathy. Recent evidence also suggests a role of lipoprotein(a) in progression of retinopathy and nephropathy in patients with diabetes mellitus. Lipid-lowering therapy, using single agents or a combination of drugs may significantly benefit diabetic retinopathy and diabetic nephropathy. In particular, hydroxymethyl glutaryl coenzyme A reductase inhibitors may be effective in preventing or retarding the progression of microvascular complications because of their powerful lipid-lowering effects and other additional mechanisms. However, most of the data are based on short-term studies, and need to be ascertained in long-term studies. Until more specific guidelines are available, aggressive management of diabetic dyslipidemia, according to currently accepted guidelines, should be continued for the prevention of macrovascular disease which would also benefit microvascular complications.

A review of the efficacy of rosuvastatin in patients with type 2 diabetes

It has been estimated that 92% of individuals with type 2 diabetes, without cardiovascular disease (CVD), have a dyslipidaemic profile. Several guidelines on cardiovascular risk now recommend that patients with diabetes should be considered at high risk of CVD and should thus receive lipid-lowering therapy to reduce low-density lipoprotein cholesterol (LDL-C) to below 2.5 mmol/L. Since their introduction in 1987, statins have revolutionized the management of CVD. The most recent statin to be introduced, rosuvastatin, has been shown to be the most effective at lowering LDL-C, as well as consistently raising HDL-C across the 10-40 mg dose range. This has been confirmed by many studies, including the Measuring Effective Reductions in Cholesterol Using Rosuvastatin Therapy (MERCURY I) study in which rosuvastatin 10 mg was shown to be more effective than commonly used doses of other statins, both for LDL-C reduction and achieving treatment target goals. The effectiveness of rosuvastatin has also been studied in type 2 diabetes patients in three studies: the URANUS (Use of Rosuvastatin vs. Atorvastatin iN type 2 diabetes mellitUS), ANDROMEDA (A raNdomized, Double-blind study to compare Rosuvastatin [10 & 20 mg] and atOrvastatin [10 & 20 Mg] in patiEnts with type II DiAbetes) and CORALL (COmpare Rosuvastatin [10-40 mg] with Atorvastatin [20-80 mg] on apo B/apo A-1 ratio in patients with type 2 diabetes meLLitus and dyslipidaemia) studies. URANUS and ANDROMEDA showed rosuvastatin to be more effective than atorvastatin at reducing LDL-C and achieving treatment target goals. CORALL demonstrated rosuvastatin 10, 20 and 40 mg to be more effective at lowering LDL-C than 20, 40 and 80 mg of atorvastatin, respectively. Ongoing studies will evaluate whether these properties of rosuvastatin translate into beneficial effects on atherosclerosis and significant reductions in cardiovascular events.

Medical management of diabetic retinopathy

Although current treatment and prevention of diabetic retinopathy with laser photocoagulation, and tight metabolic and blood pressure control has reduced the risk of visual loss, there is still a need for additional therapies. A literature review on medical therapies for diabetic retinopathy has been performed, and the following classes of drugs are discussed: blockers of the renin-angiotensin system, protein kinase C-beta inhibitors, glitazones, somatostatin analogues, lipid-lowering drugs and anti-inflammatory drugs. There is experimental and clinical data suggesting beneficial effect from several classes of drugs on diabetic retinopathy, and results from large clinical trials are awaited within the next 3-4 years.

Association of dyslipidemia and effects of statins on nonmacrovascular diseases

BACKGROUND

Statins have mechanisms of action that expand their effects beyond cholesterol lowering and atherosclerotic medical conditions.

OBJECTIVE

This review summarizes clinical evidence for the association of dyslipidemia and the effects of statin use on aortic stenosis, Alzheimer's dementia (AD), osteoporosis, prevention of diabetes mellitus (DM), diabetic retinopathy, age-related macular degeneration, and diabetic/nondiabetic nephropathy.

METHODS

An English-language literature search was conducted using MEDLINE (1966-June 2003). Bibliographies of retrieved articles were reviewed. Search terms included statin, HMG-CoA reductase inhibitors, aortic stenosis, Alzheimer's dementia, osteoporosis, prevention of diabetis, diabetic retinopathy, age-related macular degeneration, diabetic nephropathy, and nondiabetic nephropathy.

RESULTS

Three retrospective cohort trials have shown an association between statin use and the progression of aortic stenosis; one of these trials observed a 45% decrease in aortic valve area in 1 year. In AD, one cross-sectional analysis found 60% to 73% lower AD rates in lovastatin or pravastatin recipients ( P<0.001 ). Of the multiple observational studies on the effect of statins on fracture risk, some have shown a decreased risk, with an odds ratio as low as 0.50 (95% CI, 0.33-0.76); others have demonstrated no association. A post hoc analysis of the West of Scotland Coronary Prevention Study found a 30% reduction in the development of DM ( P=0.042 ), but this was not duplicated in the Anglo-Scandinavian Cardiac Outcomes Trial-Lipid Lowering Arm. A small clinical trial of 6 patients (11 eyes) demonstrated improved retinal hard exudates with pravastatin treatment in patients with diabetic retinopathy. In a cross-sectional analysis, age-related macular degeneration was found to be less common among statin users than nonusers (4% [ 1/27 ] vs 22% [ 76/352 ]; P=0.02. Multiple small clinical trials of 19 to 56 patients with diabetic and nondiabetic nephropathy at various stages generated inconsistent results for an association between statin use and decreased albumin excretion rate and decreased rate of decline in glomerular filtration.

CONCLUSION

Data of variable quantity and quality support the use of statins as adjuncts in the treatment of nonmacrovascular diseases.

Lovastatin inhibits bone marrow-derived dendritic cell maturation and upregulates proinflammatory cytokine production

Statins are a group of hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors which are most effective as lipid lowering agents, and are currently extensively used clinically. Recently, it was also shown that statins affect the immune response. We investigated the effects of lovastatin on the maturation and functional changes of bone marrow-derived dendritic cells (BM-DC). Lovastatin inhibited MHC class II and CD40 expression on DC in a dose-dependent manner, but had lesser effects on CD16, CD80, CD86, and CD11b expression. Nuclear extracts of lovastatin treated DC had decreased NF-kappaB DNA binding activity. Although antigen capture capacity of DC was not affected by lovastatin, the T-cell stimulatory activity of DC was inhibited. Lovastatin up-regulated DC pro-inflammatory cytokine production induced by LPS as measured by intracellular cytokine staining, ELISA and cDNA microarrays. Mevalonate, added in vitro, prevented these effects. These results indicate that lovastatin may inhibit BM-DC maturation and up-regulate cytokine production through a mevalonate dependent pathway, and may cause adverse effects on either innate or adaptive immunity.

Current and Future Strategies for the Management of Diabetic Neuropathy

Diabetic neuropathy is common, related to increased morbidity and mortality, and has no effective treatment at present. Interventions based on putative pathways thought to contribute to damage and repair of nerve fibres have yielded little success to date. Pain is a potentially debilitating manifestation of diabetic neuropathy and has many potential sites of origin and, hence, modulation. Its cause is unclear and it does not respond well to traditional pain therapies, proposed to mediate their benefits via multiple peripheral and central mechanisms. A better understanding of the mechanisms leading to nerve fibre degeneration and regeneration as well as pain has recently resulted in the development of a more targeted approach to the treatment of diabetic neuropathy. Thus, specific NMDA receptor antagonists and more specific neuronal serotonin and norepinephrine (noradrenaline) uptake inhibitors offer promise in the treatment of painful diabetic neuropathy. A number of treatments which include the aldose reductase inhibitors and neurotrophins have failed to reach the clinical arena. However, the antioxidant alpha-lipoic acid, as well as compounds which correct vascular dysfunction and hence neuropathy, such as ACE inhibitors and protein kinase C-beta inhibitors, have demonstrated more success.

Hyperlipidemia in kidney disease: causes and consequences

Dyslipidemias are common in patients with chronic kidney disease. The causes vary with the stage of kidney disease, the degree of proteinuria, and the modality of end-stage renal disease treatment. Dyslipidemias have been associated with kidney disease progression, and a number of small, randomized, controlled trials of lipid-lowering agents have been conducted. Unfortunately, the results of these trials, although encouraging, have been inconclusive because of the small numbers of patients enrolled. Dyslipidemias may also contribute to the high incidence of cardiovascular disease in patients with chronic kidney disease. This is most likely for patients with chronic renal insufficiency and for kidney transplant recipients. Less certain is the role of dyslipidemias in the pathogenesis of cardiovascular disease among dialysis patients.

Dyslipidemia in pediatric renal disease: epidemiology, pathophysiology, and management

Dyslipidemia increases the risk of cardiovascular events among individuals with renal disease, and there is a growing body of evidence that it hastens the progression of renal disease itself. Children with nephrotic syndrome or renal transplants have easily recognized hyperlipidemia. Among those with chronic renal insufficiency or end-stage renal disease, detection of dyslipidemia requires more careful analysis and knowledge of normal pediatric ranges. Disordered lipoprotein metabolism results from complex interactions among many factors, including the primary disease process, use of medications such as corticosteroids, the presence of malnutrition or obesity, and diet. The systematic treatment of dyslipidemia in children with chronic renal disease is controversial because conclusive data regarding the risks and benefits are lacking. Hepatic 3-methylglutaryl coenzyme A reductase inhibitors (statins), fibrates, plant stanols, bile acid-binding resins, and dietary manipulation are options for individualized treatment. Prospective investigations are required to guide clinical management.

Current literature in diabetes

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of diabetes/metabolism. Each bibliography is divided into 17 sections: 1 Books, Reviews & Symposia; 2 General; 3 Genetics; 4 Epidemiology; 5 Immunology; 6 Prediction; 7 Prevention; 8 INTERVENTION: a&rpar General; b&rpar Pharmacology; 9 Pathology: a&rpar General; b&rpar Cardiovascular; c&rpar Neurological; d&rpar Renal; 10 Endocrinology & Metabolism; 11 Nutrition; 12 Animal Studies; 13 Techniques. Within each section, articles are listed in alphabetical order with respect to author (9 Weeks journals - Search completed at 1st Aug 2001)

Lipid and blood pressure treatment goals for type 1 diabetes: 10-year incidence data from the Pittsburgh Epidemiology of Diabetes Complications Study

OBJECTIVE

Subjects with type 1 diabetes are at high risk for many long-term complications, including early mortality and coronary artery disease (CAD). Few data are available on which to base goal levels for two major risk factors, namely blood pressure and lipid/lipoproteins. The objective of this study was to determine at which levels of LDL and HDL cholesterol, triglycerides, and blood pressure the relative risks of type 1 diabetic complications increase significantly.

RESEARCH DESIGN AND METHODS

Observational prospective study of 589 patients with childhood-onset type 1 diabetes (<17 years) aged > or =18 years at baseline; 10-year incidence of mortality, CAD, lower-extremity arterial disease, proliferative retinopathy, distal symmetric polyneuropathy, and overt nephropathy. Relative risks were determined using traditional groupings of blood pressure and lipid/lipoproteins, measured at baseline, using the lowest groupings (<100 mg/dl [2.6 mmol/l] LDL cholesterol, <45 mg/dl [1.1 mmol/l] HDL cholesterol, <100 mg/dl [1.1 mmol/l] triglycerides, <110 mmHg systolic blood pressure, and <80 mmHg diastolic blood pressure) as reference. Adjustments for age, sex, and glycemic control were examined.

RESULTS

Driven mainly by strong relationships (RR range 1.8-12.1) with mortality, CAD, and overt nephropathy, suggested goal levels are as follows: LDL cholesterol <100 mg/dl (2.6 mmol/l), HDL cholesterol >45 mg/dl (1.1 mmol/l), triglycerides <150 mg/dl (1.7 mmol/l), systolic blood pressure <120 mmHg, and diastolic blood pressure <80 mmHG: Age, sex, and glycemic control had little influence on these goals.

CONCLUSIONS

Although observational in nature, these data strongly support the case for vigorous control of lipid levels and blood pressure in patients with type 1 diabetes.