Metabolic memory in diabetes--focus on insulin

Metabolic memory in diabetes - from in vitro oddity to in vivo problem: role of apoptosis

Retinal capillary cells undergo apoptosis before pathology characteristic of retinopathy can be observed, and the appearance of apoptotic capillary cell can predict the development of pathology. The purpose of this study is to investigate the effect of reversal of hyperglycemia on retinal capillary cell apoptosis, and identify the apoptosis encoding genes. Streptozotocin-diabetic rats were maintained either in poor glycemic control (PC, glycated hemoglobin, GHb >11%) or in good glycemic control (GC, GHb <6%) for 12 months, or allowed to be in PC for 6 months followed by GC for 6 additional months (PC-GC). Capillary cell apoptosis was determined in the trypsin-digested retinal microvasculature by TUNEL staining, and the genes encoding apoptosis were identified by Oligo GEArray rat apoptosis microarray that profiles 113 genes. Six months of good glycemic control that followed 6 months of poor control failed to attenuate the number of TUNEL-positive capillary cells in the retinal microvasculature. Twenty-three retinal genes, mainly from TNF ligand and receptor, caspase, Bcl-2 and death domain subfamilies that were upregulated by least a two-fold in PC rats remain upregulated after reversal of hyperglycemia. Thus, the continued activation of apoptosis plays a major role in the resistance of retinopathy to halt after re-institution of good glycemic control, and the regulation apoptosis machinery could help retard the progression of diabetic retinopathy.

Late effect of treatment for reducing cardiovascular risk--a hypothesis on cardiometabolic therapeutic memory

Several clinical studies were carried out in order to decrease cardiovascular morbidity and mortality. Occasionally, long-term observational follow-up was performed after terminating the randomized, controlled clinical trials and it was found that the beneficial effect of the active treatment has been maintained in the follow-up period. This prolonged effect was originally observed in patients with type 1 or type 2 diabetes by using intensive versus conventional treatment and called metabolic memory or metabolic legacy. Nevertheless, cardiovascular risk reduction is not restricted to antihyperglycaemic treatment; therefore, it can be hypothesised that other treatment options such as lifestyle changes, antihypertensive or lipid lowering treatment may have similar effects. In fact, a late beneficial effect of lifestyle changes was observed in controlled clinical studies in subjects with impaired glucose tolerance. Moreover, sustained beneficial effect of ACE-inhibitors, statins or fibrates in subjects with high cardiovascular risk was documented in the follow-up period of randomized, controlled clinical trials. Finally, the long-term advantage of intensified versus conventional multifactorial cardiovascular intervention was proven in patients with type 2 diabetes. Taken together, this phenomenon could be called cardiometabolic therapeutic memory. The concept provides further support for initiating proper therapy for patients with moderate or high cardiovascular risks as early as possible. Following this strategy, not only immediate and short-term but, according to the concept of cardiometabolic therapeutic memory, even long-term beneficial effect of the intervention could be expected.

The pro-inflammatory environment in recalcitrant diabetic foot wounds

Lower extremity ulceration is one of the serious and long-term diabetic complications rendering a significant social burden in terms of amputation and quality-of-life reduction. Diabetic patients experience a substantial wound-healing deficit. These lesions are featured by an exaggerated and prolonged inflammatory reaction with a significant impairment in local bacterial invasion control. Experimental and clinical evidences document the deleterious consequences of the wound's pro-inflammatory phenotype for the repair process. From a biochemical standpoint, hyperinflammation favours wound matrix degradation, thus, amplifying a pre-existing granulation tissue productive cells' invasiveness and recruitment deficit. Tumour necrosis factor perpetuates homing of inflammatory cells, triggers pro-apoptotic genes and impairs reepithelialisation. Advanced glycation end-products act in concert with inflammatory mediators and commit fibroblasts and vascular cells to apoptosis, contributing to granulation tissue demise. Therapeutic approaches aimed to downregulate hyperinflammation and/or attenuate glucolipotoxicity may assist in diabetic wound healing by dismantling downstream effectors. These medical interventions are demanded to reduce amputations in an expanding diabetic population.

Role of glyceraldehyde 3-phosphate dehydrogenase in the development and progression of diabetic retinopathy

OBJECTIVE

Mitochondrial superoxide levels are elevated in the retina in diabetes, and manganese superoxide dismutase overexpression prevents the development of retinopathy. Superoxide inhibits glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which activates major pathways implicated in diabetic complications, including advanced glycation end products (AGEs), protein kinase C, and hexosamine pathway. Our aim is to investigate the role of GAPDH in the development and progression of diabetic retinopathy and to elucidate the mechanism.

RESEARCH DESIGN AND METHODS

Rats with streptozotocin-induced diabetes were in a state of poor control (GHb >11%) for 12 months, good control (GHb <7) soon after induction of diabetes, or poor control for 6 months with 6 months' good control. Retinal GAPDH, its ribosylation and nitration, AGEs, and PKC activation were determined and correlated with microvascular histopathology.

RESULTS

In rats with poor control, retinal GAPDH activity and expressions were subnormal with increased ribosylation and nitration (25-30%). GAPDH activity was subnormal in both cytosol and nuclear fractions, but its protein expression and nitration were significantly elevated in nuclear fraction. Reinstitution of good control failed to protect inactivation of GAPDH, its covalent modification, and translocation to the nucleus. PKC, AGEs, and hexosamine pathways remained activated, and microvascular histopathology was unchanged. However, GAPDH and its translocation in good control rats were similar to those in normal rats.

CONCLUSIONS

GAPDH plays a significant role in the development of diabetic retinopathy and its progression after cessation of hyperglycemia. Thus, therapies targeted toward preventing its inhibition may inhibit development of diabetic retinopathy and arrest its progression.

Weight change in diabetes and glycemic and blood pressure control

OBJECTIVE

Weight loss in type 2 diabetes is undisputedly important, and data from community settings are limited. We evaluated weight change and resulting glycemic and blood pressure control in type 2 diabetic patients at an HMO.

RESEARCH DESIGN AND METHODS

Using electronic medical records, this retrospective cohort study identified 2,574 patients aged 21-75 years who received a new diagnosis of type 2 diabetes between 1997 and 2002. We estimated 3-year weight trajectories using growth curve analyses, grouped similar trajectories into four categories using cluster analysis, compared category characteristics, and predicted year-4 above-goal A1C and blood pressure by group.

RESULTS

The weight-trajectory groups were defined as higher stable weight (n = 418; 16.2%), lower stable weight (n = 1,542; 59.9%), weight gain (n = 300; 11.7%), and weight loss (n = 314; 12.2%). The latter had a mean weight loss of 10.7 kg (-9.8%; P < 0.001) by 18 months, with near-complete regain by 36 months. After adjusting for age, sex, baseline control, and related medication use, those with higher stable weight, lower stable weight, or weight-gain patterns were more likely than those who lost weight to have above-goal A1C (odds ratio [OR] 1.66 [95% CI 1.12-2.47], 1.52 [1.08-2.14], and 1.77 [1.15-2.72], respectively). Those with higher stable weight or weight-gain patterns were more likely than those who lost weight to have above-goal blood pressure (1.83 [1.31-2.57] and 1.47 [1.03-2.10], respectively).

CONCLUSIONS

A weight-loss pattern after new diagnosis of type 2 diabetes predicted improved glycemic and blood pressure control despite weight regain. The initial period postdiagnosis may be a critical time to apply weight-loss treatments to improve risk factor control.

Effect of early insulin therapy on nuclear factor kappaB and cytokine gene expressions in the liver and skeletal muscle of high-fat diet, streptozotocin-treated diabetic rats

To clarify the effect of early insulin therapy on nuclear factor kappaB (NFkappaB) pathway and inflammatory cytokine responses in the liver and skeletal muscle in type 2 diabetes. High-fat diet and low dose streptozotocin (STZ) induced diabetic rats were given NPH insulin or gliclazide for 3 weeks initiated at the 3rd day after STZ injection as early treatment and NPH for 3 weeks at 1 month as late treatment. Intraperitoneal glucose tolerance test (IPGTT) was performed at 3rd day after the end of treatment. Early interventions caused a decrease in glucose-insulin index in IPGTT, promoted glucose transporter 4 (Glut4) gene and protein expressions in muscle and reduced phosphoenolpyruvate carboxykinase (PEPCK) protein levels in the liver. There was an increase in inhibitor kappaB (IkappaBalpha) protein and a decrease in NFkappaB p65 DNA binding activity. A decreased level in mRNAs encoding tumor necrosis factor (TNF)alpha in the liver and muscle and interleukin (IL)-1beta in the liver were observed. Our results suggested that early insulin treatment inhibits NFkappaB activity and inflammatory cytokine responses in the liver and skeletal muscle that were involved in the amelioration of insulin resistance in type 2 diabetic rats.

Lessons in initiating insulin in clinical practice

Insulin therapy in type 2 diabetes (T2DM) can produce greater improvements in fasting plasma glucose (FPG) and glycated haemoglobin (HbA1c) than oral antidiabetic drugs (OADs). There is a growing trend to recommend initiation of insulin in T2DM patients sooner in the course of the disease, and good results have been achieved in insulin-naïve patients during randomised, controlled trials, often using aggressive dose titration algorithms. The Physicians' Routine Evaluation of Safety & Efficacy NovoMix((R)) 30 Therapy (PRESENT) study was a 6-month observational study of the safety and efficacy of biphasic insulin aspart 30 (BIAsp 30) as monotherapy or in combination with OADs in inadequately controlled patients with T2DM. This review article compares results from those patients who entered the study insulin-naïve (either with or without previous OAD treatment), with results from randomised, controlled trials of BIAsp 30 in insulin-naïve T2DM patients. It aims to provide guidance on the initiation of insulin in patients with T2DM, focusing on the efficacy of BIAsp 30 when used for this purpose, and highlighting both the low risk of hypoglycaemia associated with therapy, and the availability of delivery devices that can minimise injection site discomfort and help to overcome psychological insulin resistance.

Effect of intensive insulin therapy on beta-cell function and glycaemic control in patients with newly diagnosed type 2 diabetes: a multicentre randomised parallel-group trial

BACKGROUND

Early intensive insulin therapy in patients with newly diagnosed type 2 diabetes might improve beta-cell function and result in extended glycaemic remissions. We did a multicentre, randomised trial to compare the effects of transient intensive insulin therapy (continuous subcutaneous insulin infusion [CSII] or multiple daily insulin injections [MDI]) with oral hypoglycaemic agents on beta-cell function and diabetes remission rate.

METHODS

382 patients, aged 25-70 years, were enrolled from nine centres in China between September, 2004, and October, 2006. The patients, with fasting plasma glucose of 7.0-16.7 mmol/L, were randomly assigned to therapy with insulin (CSII or MDI) or oral hypoglycaemic agents for initial rapid correction of hyperglycaemia. Treatment was stopped after normoglycaemia was maintained for 2 weeks. Patients were then followed-up on diet and exercise alone. Intravenous glucose tolerance tests were done and blood glucose, insulin, and proinsulin were measured before and after therapy withdrawal and at 1-year follow-up. Primary endpoint was time of glycaemic remission and remission rate at 1 year after short-term intensive therapy. Analysis was per protocol. This study was registered with ClinicalTrials.gov, number NCT00147836.

FINDINGS

More patients achieved target glycaemic control in the insulin groups (97.1% [133 of 137] in CSII and 95.2% [118 of 124] in MDI) in less time (4.0 days [SD 2.5] in CSII and 5.6 days [SD 3.8] in MDI) than those treated with oral hypoglycaemic agents (83.5% [101 of 121] and 9.3 days [SD 5.3]). Remission rates after 1 year were significantly higher in the insulin groups (51.1% in CSII and 44.9% in MDI) than in the oral hypoglycaemic agents group (26.7%; p=0.0012). beta-cell function represented by HOMA B and acute insulin response improved significantly after intensive interventions. The increase in acute insulin response was sustained in the insulin groups but significantly declined in the oral hypoglycaemic agents group at 1 year in all patients in the remission group.

INTERPRETATION

Early intensive insulin therapy in patients with newly diagnosed type 2 diabetes has favourable outcomes on recovery and maintenance of beta-cell function and protracted glycaemic remission compared with treatment with oral hypoglycaemic agents.

Interactions between microvascular and macrovascular disease in diabetes: pathophysiology and therapeutic implications

Convention partitions the complications of diabetes into two main subtypes. First are the diabetes-specific microvascular complications of retinopathy, nephropathy and neuropathy; second are the atherothrombotic macrovascular complications that account for the majority of premature deaths. Pathological interactions between microvascular and macrovascular complications, for example, nephropathy and macrovascular disease, are common. Similar mechanisms and shared risk factors drive the development and progression of both small and large vessel disease. This concept has therapeutic implications. Mounting evidence points to the need for multifactorial strategies to prevent vascular complications in subjects with diabetes and/or the metabolic syndrome. We advocate a combined therapeutic approach that addresses small and large vessel disease. Preferential use should be made of drug regimens that (i) maximize vascular protection, (ii) reduce the risk of iatrogenic vascular damage and (iii) minimize the increasing problem of polypharmacy.

Adding insulin glargine versus rosiglitazone: health-related quality-of-life impact in type 2 diabetes

OBJECTIVE

We sought to assess health-related quality of life (HRQOL) in patients with type 2 diabetes treated with insulin glargine or rosiglitazone as add-on therapy to sulfonylurea plus metformin.

RESEARCH DESIGN AND METHODS

HRQOL was evaluated in 217 subjects uncontrolled with sulfonylurea plus metformin, enrolled in a 24-week, multicenter, randomized, open-label, parallel-group trial of add-on insulin glargine versus rosiglitazone. A 40-item, self-administered questionnaire at baseline and at weeks 2, 6, 12, 18, and 24 was given, including the 34-item Diabetes Symptom Checklist-Revised (DSC-R), a 5-item mental health scale from the 36-item Short-Form Health Survey (SF-36), and a single-item health rating from the SF-36. These assessments do not specify route of therapy.

RESULTS

Both treatment groups showed similar improvements in glycemic control from baseline to week 24 (change in A1C: -1.66% in the insulin glargine group, -1.51% in the rosiglitazone group, P = 0.1446). Both groups also showed improvement in HRQOL, although subjects treated with insulin glargine experienced significantly greater improvements compared with rosiglitazone in the DSC-R total symptom score (P = 0.005), total symptom distress score (P = 0.03), individual domain scores for mood symptoms (P = 0.007), ophthalmologic symptoms (P = 0.007), ophthalmologic distress (P = 0.013), fatigue distress (P = 0.033), and SF-36 perception of general health (P = 0.047).

CONCLUSIONS

Although addition of insulin glargine and rosiglitazone achieved comparable improvements in glycemic control, insulin glargine was associated with greater improvements in HRQOL, indicating that other factors (e.g., safety profile and nonglycemic actions) may further enhance HRQOL in patients with type 2 diabetes.

Metabolic memory phenomenon and accumulation of peroxynitrite in retinal capillaries

AIM

Diabetic retinopathy resists reversal after good glycemic control (GC) is reinitiated, and preexisting damage at the time of intervention is considered as the major factor in determining the outcome of the GC. This study is to investigate the role of peroxynitrite accumulation in the retinal capillaries in the failure of retinopathy to reverse after reestablishment of GC, and to determine the effect of this reversal on the activity of the enzyme responsible for scavenging mitochondrial superoxide, MnSOD.

METHODS

In streptozotocin-diabetic rats, 6 months of poor glycemic control (PC, glycated hemoglobin, GHb > 12.0%) was followed by 6 additional months of GC (GHb about 6%). The trypsin-digested retinal microvessels were prepared for immunostaining of nitrotyrosine (a measure of peroxynitrite) and for counting the number of acellular capillaries (a measure of histopathology). The retina from the other eye was used to quantify nitrotyrosine concentration, MnSOD activity and the total antioxidant capacity.

RESULTS

Reversal of hyperglycemia after 6 months of PC had no significant effect on nitrotyrosine concentration in the retina, on the nitrotyrosine-positive retinal capillary cells and on the number of acellular capillaries; the values were similar in PC-GC and PC groups. In the same rats retinal MnSOD activity remained inhibited and the total antioxidant capacity was subnormal 6 months after cessation of PC.

CONCLUSIONS

Peroxynitrite accumulation in the retinal microvasculature, the site of histopathology, fails to normalize after reversal of hyperglycemia, and superoxide remains inadequately scavenged. This failure of reversal of peroxynitrite accumulation could be, in part, responsible for the resistance of diabetic retinopathy to reverse after termination of PC.

Diabetic microvascular complications: can patients at risk be identified? A review

People with diabetes have an increased risk of developing microvascular complications, diabetic retinopathy, diabetic nephropathy and diabetic neuropathy, which, if undetected or left untreated, can have a devastating impact on quality of life and place a significant burden on health care costs. In addition, diabetic microvascular complications can reduce life expectancy. The strongest risk factors are glycaemic control and diabetes duration; however, other modifiable risk factors such as hypertension, hyperlipidaemia and smoking, and unmodifiable risk factors including age at onset of diabetes and genetic factors may all play a part. Along with the presence of external risk factors, some associations have also been noted between diabetic microvascular complications themselves. There is evidence that diabetic retinopathy in association with increased blood pressure is an important risk factor for diabetic nephropathy progression. Significant correlations have also been shown between the presence of diabetic peripheral neuropathy and the presence of background or proliferative diabetic retinopathy. Clinical trials are currently in progress looking at a number of approaches to designing treatments to prevent the adverse effects of hyperglycaemia. It is essential however, that risk factors associated with the progression and development of diabetic microvascular complications are detected and treated at an early stage in order to further reduce morbidity and mortality. Considering all three complications as interrelated may well facilitate early detection of microvascular disease. Despite good long-term glycaemic and blood pressure control, diabetes remains a major cause of blindness, renal failure and amputations. As the incidence of diabetes continues to rise, the burden of diabetic microvascular complications will increase in future, hence the need for early detection. Considering the microvascular complications of diabetes as related, and enquiring proactively about complications, may well facilitate early detection of microvascular disease.

Pioglitazone treatment improves nitrosative stress in type 2 diabetes

OBJECTIVE

The purpose of this study was to determine the effect of 24 weeks of treatment with 45 mg/day pioglitazone on peripheral skin blood flow (SkBF) and skin nitric oxide (NO) production in vivo in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

This was a randomized, parallel, cross-over, double-blind, within- and between-subject study designed to compare vascular responses before and after treatment. We studied 12 subjects with type 2 diabetes (average age 58.6 +/- 30.8 years, HbA(1c) 7.9 +/- 00.4%, BMI 31.3 +/- 1.2 kg/m(2)). SkBF was measured using laser Doppler techniques in response to ischemia reperfusion and local skin warming, and NO production was assessed in vivo using an amperometric NO meter inserted directly into the skin. These measurements were performed before treatment and at 6 and 24 weeks.

RESULTS

The SkBF response was not significantly improved after 24 weeks in either of the groups. NO production was significantly decreased in the pioglitazone-treated group in the basal condition (area under the curve 6.4 +/- 1.0 vs. 2.8 +/- 0.8, P < 0.01), after local heat stimulation at 40 degrees C (12.9 +/- 2.2 vs. 5.7 +/- 1.7, P < 0.01), and after nociceptor stimulated flow with local heating at 44 degrees C (36.4 +/- 6.3 vs. 16.6 +/- 3.4). Differences were not significant in the placebo-treated group.

CONCLUSIONS

Treatment of patients with type 2 diabetes with pioglitazone for 24 weeks reduced skin NO production, thus probably reducing nitrosative stress without a demonstrable effect on SkBF. Because nitrosative stress is considered to be a factor in the pathogenesis of neurovascular dysfunction, these findings warrant further investigation.

Treatment escalation and rise in HbA1c following successful initial metformin therapy

OBJECTIVE

To describe secondary failure of initial metformin therapy in patients who achieved initial HbA(1c) (A1C) <8% and to identify predictors of failure.

RESEARCH DESIGN AND METHODS

We identified 1,288 patients who achieved A1C <8% within 1 year of initiating metformin as their first-ever antihyperglycemic drug. Subjects were followed until they added/switched antihyperglycemics, they terminated health plan membership, or 31 December 2004. We defined secondary failure using two separate but overlapping approaches: 1) addition/switch to another antihyperglycemic drug or 2) first A1C measurement >8.0% after at least 6 months on metformin.

RESULTS

The best A1C achieved within 1 year of metformin initiation was the most powerful predictor of avoiding secondary failure. Approximately 50% of subjects whose best A1C was 7-7.9% added/switched antihyperglycemic drugs within 36 months, whereas it took >60 months for those in the 6-6.9% A1C category to reach a 50% failure rate. Those who achieved an A1C <6% did not reach a 50% rate of adding/switching drugs until 84 months. For the alternative secondary failure outcome, about half of those whose best A1C was 7.0-7.9% reached an A1C >8% within 24 months. Only approximately 25% of subjects in the 6-6.9% category failed by 48 months, and >80% of subjects in the <6% category remained below 8% through 60 months.

CONCLUSIONS

Whether defined by adding/switching to another drug or by reaching an A1C of 8%, secondary failure is inversely associated with the reduction of A1C achieved within the 1st year of metformin monotherapy.