The impact of reversal of hypoxia by revascularization on the peripheral nerve function of diabetic patients

Rubrometabolic Syndrome

Metabolic syndrome (MS), a conglomeration of several conditions including obesity, type 2 diabetes mellitus (T2DM), insulin resistance, elevated blood pressure, and dyslipidemia is reaching epidemic proportions. Anemia is caused by iron deficiency or dysregulation of iron homeostasis, leading to tissue hypoxia. Coexistence of anemia and MS or its components has been reported in the literature. The term "rubrometabolic syndrome" acts as a unifying entity linking the importance of blood in health and anemia in MS; it justifies two principles - redness of blood and low-grade inflammation. Chronic low-grade inflammation in MS affects iron metabolism leading to anemia. Tissue hypoxia that results from the anemic condition seems to be a major causative factor for the exacerbation of several microvascular and macrovascular components of T2DM, which include diabetic neuropathy, nephropathy, retinopathy, and cardiovascular complications. In obesity, anemia leads to malabsorption of micronutrients and can complicate the management of the condition by bariatric surgery. Anemia interferes with the diagnosis and management of T2DM, obesity, dyslipidemia, or hypertension due to its effect on pathological tests as well as medications. Since anemia in MS is multifaceted, the management of anemia is challenging as overcorrection of anemia with erythropoietin-stimulating agents can cause detrimental effects. These limitations necessitate availability of an effective and safe therapy that can maintain and elevate the hemoglobin levels along with maintaining the physiological balance of other systems. This review discusses the physiological links between anemia and MS along with diagnosis and management strategies in patients with coexistence of anemia and MS.

Anemia: an independent risk factor of diabetic peripheral neuropathy in type 2 diabetic patients

AIMS

Recently, the association between anemia and diabetic microvascular complications has been studied. Diabetic peripheral neuropathy (DPN) is also a common complication of type 2 diabetes mellitus (T2DM), while the relationship between anemia and DPN is rarely investigated. The aim of this study is to evaluate the association between anemia and DPN in T2DM.

METHODS

In this cross-sectional study, 1134 T2DM inpatients were enrolled. The diagnosis of DPN was based on neuropathy system score (NSS) and neuropathy disability score (NDS). Logistic regression was conducted to analyze the association between anemia and DPN.

RESULTS

The proportions of anemia in DPN and non-DPN group were 25.4 and 15.2%, respectively. Compared with non-anemia group, the proportions of moderate/severe NSS (42.7 vs. 24.5%, P < 0.001) and moderate/severe NDS (51.5 vs. 38.0%, P < 0.001) were higher while the nerve conduction velocity (NCV) was lower in anemia group. Univariate logistic regression analysis showed patients with anemia possessed an increased risk of DPN [OR = 1.906, 95%CI: 1.416, 2.567, P < 0.001]. Multivariate logistic regression analysis suggested anemia was an independent risk factor of DPN in model 1 and model 2 [model 1: OR = 1.472, 95%CI: 1.047, 2.070, P = 0.026; model 2: OR = 1.448, 95%CI: 1.013, 2.071, P = 0.043].

CONCLUSIONS

Anemia is an independent risk factor of DPN in T2DM patients.

Declining Skeletal Muscle Function in Diabetic Peripheral Neuropathy

PURPOSE

The present review highlights current concepts regarding the effects of diabetic peripheral neuropathy (DPN) in skeletal muscle. It discusses the lack of effective pharmacologic treatments and the role of physical exercise intervention in limb protection and symptom reversal. It also highlights the importance of magnetic resonance imaging (MRI) techniques in providing a mechanistic understanding of the disease and helping develop targeted treatments.

METHODS

This review provides a comprehensive reporting on the effects of DPN in the skeletal muscle of patients with diabetes. It also provides an update on the most recent trials of exercise intervention targeting DPN pathology. Lastly, we report on emerging MRI techniques that have shown promise in providing a mechanistic understanding of DPN and can help improve the design and implementation of clinical trials in the future.

FINDINGS

Impairments in lower limb muscles reduce functional capacity and contribute to altered gait, increased fall risk, and impaired balance in patients with DPN. This finding is an important concern for patients with DPN because their falls are likely to be injurious and lead to bone fractures, poorly healing wounds, and chronic infections that may require amputation. Preliminary studies have shown that moderate-intensity exercise programs are well tolerated by patients with DPN. They can improve their cardiorespiratory function and partially reverse some of the symptoms of DPN. MRI has the potential to bring new mechanistic insights into the effects of DPN as well as to objectively measure small changes in DPN pathology as a result of intervention.

IMPLICATIONS

Noninvasive exercise intervention is particularly valuable in DPN because of its safety, low cost, and potential to augment pharmacologic interventions. As we gain a better mechanistic understanding of the disease, more targeted and effective interventions can be designed.

Failure to define the pathogenesis and treatment of human diabetic neuropathy

The clinical manifestations, underlying pathology and aetiology of human diabetic neuropathy are varied and complex. Much data has been generated from preclinical models to provide a conceptual framework for the cause and treatment of human diabetic neuropathy. Despite this there remains much debate and controversy on the pathophysiology of the condition. Furthermore, many of the interventions reaching phase III clinical trials have failed to prove effective. To date we have no evidence-based and effective treatment(s) for human diabetic neuropathy.

Toxic stress, inflammation and symptomatology of chronic complications in diabetes

Diabetes affects at least 382 million people worldwide and the incidence is expected to reach 592 million by 2035. The incidence of diabetes in youth is skyrocketing as evidenced by a 21% increase in type 1 diabetes and a 30.5% increase in type 2 diabetes in the United States between 2001 and 2009. The effects of toxic stress, the culmination of biological and environmental interactions, on the development of diabetes complications is gaining attention. Stress impacts the hypothalamus-pituitary-adrenal axis and contributes to inflammation, a key biological contributor to the pathogenesis of diabetes and its associated complications. This review provides an overview of common diabetic complications such as neuropathy, cognitive decline, depression, nephropathy and cardiovascular disease. The review also provides a discussion of the role of inflammation and stress in the development and progression of chronic complications of diabetes, associated symptomatology and importance of early identification of symptoms of depression, fatigue, exercise intolerance and pain.

Inflammation: therapeutic targets for diabetic neuropathy

There are still no approved treatments for the prevention or of cure of diabetic neuropathy, and only symptomatic pain therapies of variable efficacy are available. Inflammation is a cardinal pathogenic mechanism of diabetic neuropathy. The relationships between inflammation and the development of diabetic neuropathy involve complex molecular networks and processes. Herein, we review the key inflammatory molecules (inflammatory cytokines, adhesion molecules, chemokines) and pathways (nuclear factor kappa B, JUN N-terminal kinase) implicated in the development and progression of diabetic neuropathy. Advances in the understanding of the roles of these key inflammatory molecules and pathways in diabetic neuropathy will facilitate the discovery of the potential of anti-inflammatory approaches for the inhibition of the development of neuropathy. Specifically, many anti-inflammatory drugs significantly inhibit the development of different aspects of diabetic neuropathy in animal models and clinical trials.

[Diabetes, heart surgery and the peripheral arteries]

Peripheral arterial disease (PAD) is an under-recognized and underestimated complication of diabetes. Prevalence of PAD in diabetic patients is 25-30%. The main reason for underreporting is the largely asymptomatic nature of PAD in diabetes. It is important to diagnose PAD as soon as possible because PAD is an important marker for systemic atherosclerosis. Patients with claudication have approximately a 30% five-year mortality rate. PAD patients die 10 years earlier than patients without this atherothrombotic disease. About 70% of the PAD patients die from coronary heart disease, 5-11% die from stroke. PAD and diabetes are comorbid conditions and are associated with the risk of death from coronary artery bypass graft surgery. The prevalence of diabetes in patients who undergo cardiac surgery is 30% and the prevalence of PAD is 18%. The presence of PAD in diabetic patients had a similar 2-fold increase in the annual incidence of death compared with diabetic patients without PAD. The theory that diabetes and PAD together is associated with small vessel disease may play a role in the cause of the higher long-term mortality seen in at least two studies (Circulation 2004; suppl II: II/41-II/44).

Anemia in diabetes: marker or mediator of microvascular disease?

Anemia is a common finding in patients with diabetes due to the high burden of chronic kidney disease in this population. Anemia is more prevalent and is found earlier in patients with diabetes than in those with kidney disease from other causes. The increased risk of anemia in diabetes probably reflects changes in the renal tubulointerstitium associated with diabetic kidney disease, which disrupt the delicate interaction between interstitial fibroblasts, capillaries and tubular cells required for normal hemopoietic function. In particular, the uncoupling of the hemoglobin concentration from renal erythropoietin synthesis seems to be the key factor underlying the development of anemia. Systemic inflammation, functional hematinic deficiencies, erythropoietin resistance and reduced red cell survival also drive anemia in the setting of impaired renal compensation. Although anemia can be considered a marker of kidney damage, reduced hemoglobin levels independently identify diabetic patients with an increased risk of microvascular complications, cardiovascular disease and mortality. Nevertheless, a direct role in the development or progression of diabetic complications remains to be clearly established and the clinical utility of correcting anemia in diabetic patients has yet to be demonstrated in randomized controlled trials. Correction of anemia certainly improves performance and quality of life in diabetic patients. In the absence of additional data, treatment should be considered palliative, and any functional benefits must be matched against costs to the patient and the health system.

Is cardiovascular disease a risk factor in the development of axonal polyneuropathy?

OBJECTIVES

To determine if cardiovascular disease may be a risk factor in the development of chronic idiopathic axonal polyneuropathy (CIAP).

METHODS

In this incidence case-control study, the prevalence of cardiovascular disease and risk factors in 97 patients with CIAP (mean age 67.5 (SD 7.9) years) and the prevalence of neuropathic features in 97 patients with peripheral arterial disease (PAD) (mean age 67.1 (SD 7.3) years) were investigated. The results were compared with those for 96 age and sex matched controls without diagnosed PAD or polyneuropathy (mean age 67.5 (SD 9.1) years). In a randomly chosen subgroup of 23 patients with CIAP, 42 patients with PAD, and 48 controls, an electrodiagnostic investigation was performed.

RESULTS

Patients with CIAP more often had manifest cardiovascular disease and cardiovascular risk factors than controls (stroke 18% v 6% of patients, odds ratio (OR) 3.2 (95% confidence interval (CI) 1.8 to 5.9); heart disease 29% v 15%, OR 2.4 (95% CI 1.2 to 4.9); family history of cardiovascular disease 42% v 21%, OR 2.8 (95% CI (1.5 to 5.2); hypertension 56% v 39%, OR 2.0 (95% CI 1.1 to 3.6); hypercholesterolaemia 46% v 21%, OR 3.3 (95% CI 1.5 to 7.3); current smoking 38% v 23%, OR 2.1 (95% CI 1.1 to 3.9)). The prevalence of cardiovascular disease and cardiovascular risk factors was lower than in patients with PAD. Patients with PAD more often had polyneuropathy than controls (15% v 5%, OR 3.3 (95% CI 1.1 to 10.0)). There was a trend towards lower nerve conduction velocities and lower amplitudes on electrodiagnostic investigation compared with controls.

CONCLUSION

This study shows that cardiovascular disease and CIAP often coexist, and therefore cardiovascular disease may be a cofactor in the development of CIAP.

Cutaneous microcirculation in the neuropathic diabetic foot improves significantly but not completely after successful lower extremity revascularization

OBJECTIVE

The purpose of this study was the examination of the effect of successful large vessel revascularization on the microcirculation of the neuroischemic diabetic foot.

RESEARCH DESIGN AND METHODS

We measured the cutaneous microvascular reactivity in the foot in 13 patients with diabetes with peripheral arterial disease and neuropathy (group DI) before and 4 to 6 weeks after successful lower extremity arterial revascularization. We also compared them with age-matched and sex-matched groups of 15 patients with diabetes and neuropathy, seven patients without neuropathy, and 12 healthy patients for control. We used single-point and laser Doppler scan imaging for the measurement of the foot skin vasodilatation in response to heating to 44 degrees C and to iontophoresis of 1% acetylcholine (endothelial-dependent response) and 1% sodium nitroprusside (endothelial-independent response).

RESULTS

The group DI response to heat increased from 289% +/- 90% before surgery (percent increase over baseline measured in volts) to 427% +/- 61% (P <.05) after surgery but was still comparable with the response of the patients with diabetes and neuropathy (318% +/- 51%) and lower than the responses of the patients without neuropathy (766% +/- 220%) and the healthy patients for control (891% +/- 121%; P <.0001). The group DI acetylcholine response also improved from 6% +/- 4% before surgery to 26% +/- 8% after surgery (P <.05) and was similar to the responses of patients with diabetes and neuropathy (18% +/- 3%) and patients without neuropathy (38% +/- 8%) but still lower when compared with the response of the patients for control (48% +/- 9%; P <.001). The sodium nitroprusside response for group DI improved from 10% +/- 4% to 29% +/- 9% (P <.05) and was similar to the responses of the neuropathic (25% +/- 9%), nonneuropathic (32% plus minus 6%), and control (40% +/- 5%) groups. The group DI neurovascular response, which depends on the healthy function of the C-fiber nociceptors, was similar at baseline (5% +/- 9%) and after surgery (14% +/- %10) and in the neuropathic group (33% +/- 21%), but it was dramatically reduced when compared with the nonneuropathic (110% +/- 40%) and control (198% +/- 54%) groups (P <.001).

CONCLUSION

Impaired vasodilation in the diabetic neuropathic lower extremity leads to functional ischemia, which improves considerably but is not completely corrected with successful bypass grafting surgery. Therefore, patients with diabetes and neuropathy may still be at high risk for the development of foot ulceration or the failure to have an existing ulcer heal despite adequate correction of large vessel blood flow.

Is peak expiratory flow rate a predictor of complications in diabetes? The Wisconsin Epidemiologic Study of Diabetic Retinopathy

The Objective of this study was to determine whether peak expiratory flow rate is a predictor of complications of diabetes. Peak expiratory flow rate was measured at the 10-year follow-up (third examination) of a cohort of persons with younger-onset diabetes. The relationships of progression of diabetic retinopathy by two steps, progression to proliferative retinopathy and of incidences of macular edema, sore or ulcers on feet or ankles, lower extremity amputation, proteinuria, and cardiovascular disease 4 years after this examination with respect to peak expiratory flow rate were evaluated. Study procedures including measurements of blood pressure, height and weight, grading of fundus photographs, peak expiratory flow rate, urinalysis, and medical history were performed according to standard protocols. Peak expiratory flow rate was not associated in univariate analyses with progression of retinopathy, incidences of proliferative retinopathy, macular edema or lower extremity amputation, sores or ulcers on feet or ankles, gross proteinuria, or self-reported cardiovascular disease. However, when using multivariable models to include the effects of other risk factors, peak expiratory flow rate was significantly associated with the combined incidences of sores or ulcers on feet and ankles, or lower extremity amputations (OR=0.61, 95% CI 0.42-0.88). These data suggest that peak expiratory flow rate is a predictor of subsequent complications in the lower extremities in those with long duration of younger-onset diabetes. Evaluating this association in an incipient cohort would illuminate whether the relationship we found is likely to be causal.

Can diabetic neuropathy be prevented by angiotensin-converting enzyme inhibitors?

The incidence of diabetes and its complications is increasing to staggering proportions. Presently the WHO estimates an overall prevalence of 130 million, but by 2025 there will be 300 million individuals with diabetes mellitus. The incidence of diabetic neuropathy approaches 50% in most diabetic populations; there is no treatment, and its consequences in the form of foot ulceration and amputation are financially punishing for health care providers. Attempts to develop treatments have faltered for want of an understanding of the aetiology of diabetic neuropathy. As a consequence, 1999 saw the demise of two further compounds: recombinant growth factor by Roche-Genentech and the aldose reductase inhibitor zopolrestat, by Pfizer, both had reached phase III clinical trials. They joined an impressive list of at least 30 other compounds which have reached phase III clinical trials and failed to establish efficacy. The need to establish a viable treatment for human diabetic neuropathy is absolutely paramount. To provide a rational answer as to whether angiotensin-converting enzyme (ACE) inhibitors can prevent human diabetic neuropathy, two major issues need addressing: 1) Does vascular dysfunction cause human diabetic neuropathy? 2) Can ACE inhibitors ameliorate diabetic vascular dysfunction and hence neuropathy? Epidemiological studies support a strong association between neuropathy, retinopathy and nephropathy. Microangiopathy is deemed as the root cause of both nephropathy, and retinopathy and mounting evidence provides support for a vascular basis of diabetic neuropathy. ACE inhibitors appear to correct many of the abnormalities associated with the vascular dysfunction found in diabetes. Thus effective ACE inhibition impacts very positively on cardiovascular outcomes in patients with ischaemic heart disease, particularly in diabetic patients. ACE inhibition also prevents the development and progression of incipient and established diabetic nephropathy and delays progression of background retinopathy. Quinapril improves measures of diabetic autonomic neuropathy. Our recent study has demonstrated a significant improvement in peripheral neuropathy following 12 months of treatment with the ACE inhibitor trandolapril.