Key indices of glycaemic variability for application in diabetes clinical practice

Near normal glycaemic control in diabetes consists to target daily glucose fluctuations and quarterly HbA1c oscillations in addition to overall glucose exposure. Consequently, the prerequisite is to define simple, and mathematically undisputable key metrics for the short- and long-term variability in glucose homeostasis. As the standard deviations (SD) of either glucose or HbA1c are dependent on their means, the coefficient of variation (CV = SD/mean) should be applied instead as it that avoids the correlation between the SD and mean values. A CV glucose of 36% is the most appropriate threshold between those with stable versus labile glucose homeostasis. However, when near normal mean glucose concentrations are achieved a lower CV threshold of <27 % is necessary for reducing the risk for hypoglycaemia to a minimal rate. For the long-term variability in glucose homeostasis, a CVHbA1c < 5 % seems to be a relevant recommendation for preventing adverse clinical outcomes.

The obesity treatment dilemma: Why dieting is both the answer and the problem? A mechanistic overview

Restricted-calorie diets are the most worldwide used treatments for obesity. Although such strategies are based on the first law of thermodynamics, the real life clinical practice demonstrates that the observed weight losses are divergent from those theoretically predicted. Loosely adherence to recommendations is one of the main causes for the limited efficacy of dieting, but many additional factors can be involved in the hurdles to weight loss. According to the second law of thermodynamics any restriction in dietary energy intake results in energy sparing with a diminution in the basal metabolic rate and a concomitant loss in the lean body mass. This "thrifty" energetic adaptation is associated with a progressive reduction in the difference between levels of energy intake and expenditure, thus resulting in a drastic fall in weight loss rates on the medium and long-term regardless of the dietary carbohydrate/fat ratio. This loss of efficacy is aggravated by the misadaptation of the production and action of anti-obesity hormones such as leptin. During the latest past decades the discovery of changes in the gut microbiota of obese people referred to as "obese dysbiosis" has raised the question as to whether these alterations can participate to diet-resistance. Combined with the behavioral and psychological barriers to low-calorie diets, there is a broad physiologic spectrum of evidence indicating that weight loss is a hard challenge. Consequently, the answer would be primarily to prevent the development of obesity and at worst to avoid its ominous progression from metabolically healthy to unhealthy stages.

Review of methods for detecting glycemic disorders

Prediabetes (intermediate hyperglycemia) consists of two abnormalities, impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) detected by a standardized 75-gram oral glucose tolerance test (OGTT). Individuals with isolated IGT or combined IFG and IGT have increased risk for developing type 2 diabetes (T2D) and cardiovascular disease (CVD). Diagnosing prediabetes early and accurately is critical in order to refer high-risk individuals for intensive lifestyle modification. However, there is currently no international consensus for diagnosing prediabetes with HbA1c or glucose measurements based upon American Diabetes Association (ADA) and the World Health Organization (WHO) criteria that identify different populations at risk for progressing to diabetes. Various caveats affecting the accuracy of interpreting the HbA1c including genetics complicate this further. This review describes established methods for detecting glucose disorders based upon glucose and HbA1c parameters as well as novel approaches including the 1-hour plasma glucose (1-h PG), glucose challenge test (GCT), shape of the glucose curve, genetics, continuous glucose monitoring (CGM), measures of insulin secretion and sensitivity, metabolomics, and ancillary tools such as fructosamine, glycated albumin (GA), 1,5- anhydroglucitol (1,5-AG). Of the approaches considered, the 1-h PG has considerable potential as a biomarker for detecting glucose disorders if confirmed by additional data including health economic analysis. Whether the 1-h OGTT is superior to genetics and omics in providing greater precision for individualized treatment requires further investigation. These methods will need to demonstrate substantially superiority to simpler tools for detecting glucose disorders to justify their cost and complexity.

Respective Contributions of Glycemic Variability and Mean Daily Glucose as Predictors of Hypoglycemia in Type 1 Diabetes: Are They Equivalent?

OBJECTIVE

To evaluate the respective contributions of short-term glycemic variability and mean daily glucose (MDG) concentration to the risk of hypoglycemia in type 1 diabetes.

RESEARCH DESIGN AND METHODS

People with type 1 diabetes (n = 100) investigated at the University Hospital of Montpellier (France) underwent continuous glucose monitoring (CGM) on two consecutive days, providing a total of 200 24-h glycemic profiles. The following parameters were computed: MDG concentration, within-day glycemic variability (coefficient of variation for glucose [%CV]), and risk of hypoglycemia (presented as the percentage of time spent below three glycemic thresholds: 3.9, 3.45, and 3.0 mmol/L).

RESULTS

MDG was significantly higher, and %CV significantly lower (both P < 0.001), when comparing the 24-h glycemic profiles according to whether no time or a certain duration of time was spent below the thresholds. Univariate regression analyses showed that MDG and %CV were the two explanatory variables that entered the model with the outcome variable (time spent below the thresholds). The classification and regression tree procedure indicated that the predominant predictor for hypoglycemia was %CV when the threshold was 3.0 mmol/L. In people with mean glucose ≤7.8 mmol/L, the time spent below 3.0 mmol/L was shortest (P < 0.001) when %CV was below 34%.

CONCLUSIONS

In type 1 diabetes, short-term glycemic variability relative to mean glucose (i.e., %CV) explains more hypoglycemia than does mean glucose alone when the glucose threshold is 3.0 mmol/L. Minimizing the risk of hypoglycemia requires a %CV below 34%.

The application of simple metrics in the assessment of glycaemic variability

The assessment of glycaemic variability (GV) remains a subject of debate with many indices proposed to represent either short- (acute glucose fluctuations) or long-term GV (variations of HbA_1c). For the assessment of short-term within-day GV, the coefficient of variation for glucose (%CV) defined as the standard deviation adjusted on the 24-h mean glucose concentration is easy to perform and with a threshold of 36%, recently adopted by the international consensus on use of continuous glucose monitoring, separating stable from labile glycaemic states. More complex metrics such as the Low Blood Glucose Index (LBGI) or High Blood Glucose Index (HBGI) allow the risk of hypo or hyperglycaemic episodes, respectively to be assessed although in clinical practice its application is limited due to the need for more complex computation. This also applies to other indices of short-term intraday GV including the mean amplitude of glycemic excursions (MAGE), Shlichtkrull's M-value and CONGA. GV is important clinically as exaggerated glucose fluctuations are associated with an enhanced risk of adverse cardiovascular outcomes due primarily to hypoglycaemia. In contrast, there is at present no compelling evidence that elevated short-term GV is an independent risk factor of microvascular complications of diabetes. Concerning long-term GV there are numerous studies supporting its association with an enhanced risk of cardiovascular events. However, this association raises the question as to whether the impact of long-term variability is not simply the consequence of repeated exposure to short-term GV or ambient chronic hyperglycaemia. The renewed emphasis on glucose monitoring with the introduction of continuous glucose monitoring technologies can benefit from the introduction and application of simple metrics for describing GV along with supporting recommendations.

Toward Defining the Threshold Between Low and High Glucose Variability in Diabetes

OBJECTIVE

To define the threshold for excess glucose variability (GV), one of the main features of dysglycemia in diabetes.

RESEARCH DESIGN AND METHODS

A total of 376 persons with diabetes investigated at the University Hospital of Montpellier (Montpellier, France) underwent continuous glucose monitoring. Participants with type 2 diabetes were divided into several groups-groups 1, 2a, 2b, and 3 (n = 82, 28, 65, and 79, respectively)-according to treatment: 1) diet and/or insulin sensitizers alone; 2) oral therapy including an insulinotropic agent, dipeptidyl peptidase 4 inhibitors (group 2a) or sulfonylureas (group 2b); or 3) insulin. Group 4 included 122 persons with type 1 diabetes. Percentage coefficient of variation for glucose (%CV = [(SD of glucose)/(mean glucose)] × 100) and frequencies of hypoglycemia (interstitial glucose <56 mg/dL [3.1 mmol/L]) were computed.

RESULTS

Percentages of CV (median [interquartile range]; %) increased significantly (P < 0.0001) from group 1 (18.1 [15.2-23.9]) to group 4 (37.2 [31.0-42.3]). In group 1, the upper limit of %CV, which served as reference for defining excess GV, was 36%. Percentages of patients with %CVs above this threshold in groups 2a, 2b, 3, and 4 were 0, 12.3, 19.0, and 55.7%, respectively. Hypoglycemia was more frequent in group 2b (P < 0.01) and groups 3 and 4 (P < 0.0001) when subjects with a %CV >36% were compared with those with %CV ≤36%.

CONCLUSIONS

A %CV of 36% appears to be a suitable threshold to distinguish between stable and unstable glycemia in diabetes because beyond this limit, the frequency of hypoglycemia is significantly increased, especially in insulin-treated subjects.

Near normal HbA1c with stable glucose homeostasis: the ultimate target/aim of diabetes therapy

Achieving near normal glucose homeostasis implies that all components of dysglycemia that are present in diabetes states be eliminated. Reducing ambient/overall hyperglycemia is a pre-requisite to eliminate the risk of development and progression of diabetes complications. More controversially however, are the relative and related contributions of postprandial glucose excursions, glucose variability, hypoglycemia and the dawn phenomenon across the spectrum of dysglycemia. For instance, it is likely that the dawn phenomenon contributes to ambient hyperglycemia and that postprandial glucose excursions are at the cross road of ambient hyperglycemia and glucose variability with glucose fluctuations as causative risk factors for hypoglycemia. Proof-of-concept trials such as the ongoing FLAT-SUGAR study are necessary for gaining further insight into the possible harmful effects of some of these features such as excessive glycemic variability and glucose excursions, still considered to be of minor relevance by several diabetologists. Whether their role will be more thoroughly proven through further intervention trials with "hard" endpoints, remains to be seen. In the meantime more consideration should be given to medications aimed at concomitantly reducing ambient/overall hyperglycemia and those additional abnormal glycemic features of dysglycemia.

Ramadan and diabetes: What we see, learn and understand from continuous glucose monitoring

Abstinence from eating and drinking from dawn to sunset characterizes the holy month of Ramadan. For the 50 million Muslims worldwide with diabetes who adhere to this religious fast, the practice results in marked changes in glucose homoeostasis. The sunset meal (Iftar) that breaks the fasting state is followed by exaggerated surges in blood glucose and sustained overnight hyperglycaemia in cases of nocturnal overfeeding. The predawn meal (Suhoor) frequently results in prolonged glucose decay over the daylight hours. These glycaemic disturbances are particularly marked in insulin-treated patients, in those with unsatisfactory diabetes control during the pre-Ramadan period and in patients who are poorly compliant with lifestyle recommendations. Whether such patients should be exempt from the Islamic fast remains an open debate, which might be partially resolved by long-term controlled studies using the technology of continuous glucose monitoring in large populations of patients with diabetes.

"Mild dysglycemia" in type 2 diabetes: to be neglected or not?

"Mild dysglycemia" in type 2 diabetes can be defined by the range of HbA1c levels≥6.5% (48 mmol/mol) and<7% (53 mmol/mol), which corresponds to when the risk for vascular complications begins to increase. This "mild dysglycemia" is characterized by both a dawn phenomenon (a spontaneous blood glucose rise in the early morning) and an excess of post-prandial glucose excursions in the absence of abnormal elevation in basal glucose, especially during nocturnal periods. This represents an intermediary stage between pre-diabetes (HbA1c≥5.7%, 39 mmol/mol, and<6.5%, 48 mmol/mol) and those who begin to show a steadily progressive worsening in basal glucose (HbA1c≥7%, 53 mmol/mol). Should this relatively minor intermediate dysglycemic phase deserve more attention, that is the question. The now available incretin-based therapies, and more specifically the DPP-4 inhibitors provide the clinician with the possibility to reduce or eradicate both the dawn phenomenon and post-meal glucose excursions with minimal side effects. The availability of 24-h glycemic profiles in those with "mild dysglycemia" will help to describe their individual glycemic phenotype, based on which the early and appropriate life style changes and/or pharmacological interventions can be introduced.

Residual dysglycemia when at target HbA(1c) of 7% (53mmol/mol) in persons with type 2 diabetes

AIMS

To understand the composition of the residual dysglycemia when HbA1c is between 6.5% (48mmol/mol) and 7% (53mmol/mol), representing the definition of diabetes and the recommended treatment goal, respectively.

METHODS

One hundred persons with type 2 diabetes and a HbA1c<7% (53mmol/mol), treated with diet alone and/or oral hypoglycemic agents underwent continuous glucose monitoring (CGM) and were further divided into two subgroups 1 (n=50) and 2 (n=50) according to whether the HbA1c was <6.5% (48mmol/mol) or 6.5-6.9% (48-52mmol/mol), respectively. A similar analysis was performed in those on diet alone: subgroups A (n=34, HbA1c<6.5%, 48mmol/mol) and B (n=10, HbA1c 6.5-6.9%, 48-52mmol/mol). The residual dysglycemia determined from the CGM was assessed using glucose exposures defined as areas under curves (AUCs) and mean glucose values.

RESULTS

Averaged 2-h postprandial glucose value (averaged PPG, mmol/L, mean±SD) and postprandial glucose exposure (AUCpp, mean±SD, mmol·L(-1)·h) were significantly higher in subgroup 2 (mean HbA1c=6.7%, 50mmol/mol) than in subgroup 1 (mean HbA1c=6.0%, 42mmol/mol): averaged PPG=8.1±1.3 versus 7.3±1.3mmol/L (p<0.002); AUCpp=23.5±8.6 versus 16.2±8.6 (p<0.0001). The percentages of persons with averaged PPG≥7.8mmol/L were 52% and 24% (p<0.01) in subgroups 2 and 1, respectively. Similar results were observed in those (subgroups A and B) who were on diet alone.

CONCLUSIONS

The residual dysglycemia in type 2 diabetes with HbA1c between 6.5 and 6.9% (48-52mmol/mol) inclusive is mainly due to remnant abnormal postprandial glucose excursions. Consequently, HbA1c<6.5% (48mmol/mol) is an achievable goal with therapeutic measures aimed at reducing postmeal glucose when the HbA1c is at 7% (53mmol/mol).

Magnitude of the dawn phenomenon and its impact on the overall glucose exposure in type 2 diabetes: is this of concern?

OBJECTIVE

To assess the magnitude of the dawn phenomenon and its impact on the total glucose exposure in type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 248 noninsulin-treated persons with type 2 diabetes who underwent continuous glucose monitoring were divided into three groups selected by treatments: diet alone (n = 53); insulin sensitizers alone (n = 82); and insulin secretagogues alone or in combination with insulin sensitizers (n = 113). The dawn phenomenon (∂ glucose, mg/dL) was quantified by its absolute increment from nocturnal nadir to prebreakfast value. The participants were secondarily divided into two paired subsets after they had been separated by the presence/absence of a dawn phenomenon based on a threshold of 20 mg/dL and matched for glucose nadir. The impact of the dawn phenomenon was assessed on HbA1c and 24-h mean glucose.

RESULTS

The median of ∂ glucose (interquartile range) was 16.0 (0-31.5 mg/dL) in the 248 subjects, and no differences were observed across groups selected by HbA1c or treatments. In the overall population, the mean impacts on HbA1c and 24-h mean glucose were 4.3 ± 1.3 mmol/mol (0.39 ± 0.12%) and 12.4 ± 2.4 mg/dL, respectively. The mean impact on 24-h mean glucose was not statistically different between those on diet alone (16.7 ± 5.9 mg/dL) compared with the two subsets treated with oral hypoglycemic agents (11.2 ± 5.3 and 8.5 ± 7.5 mg/dL).

CONCLUSIONS

The impact of the dawn phenomenon on overall glycemic control in type 2 diabetes, as depicted by the HbA1c level, was ∼0.4% and not eliminated by any of the currently available armamentarium of oral antidiabetes agents.

Insulin and atherosclerosis: how are they related?

The relationship between insulin and atherosclerosis is complex. People with type 2 diabetes are affected by three main glycaemic disorders: chronic hyperglycaemia; glycaemic variability; and iatrogenic hypoglycaemia. In addition to this triumvirate, the diabetic condition is characterized by lipid disorders, chronic low-grade inflammation and activation of oxidative stress. All these associated disorders reflect the insulin-resistant nature of type 2 diabetes and contribute to the development and progression of cardiovascular (CV) diseases. By both lowering plasma glucose and improving the lipid profile, insulin exerts beneficial effects on CV outcomes. In addition, insulin has several pleiotropic effects such as anti-inflammatory, antithrombotic and antioxidant properties. Insulin per se exerts an inhibitory effect on the activation of oxidative stress and seems able to counteract the pro-oxidant effects of ambient hyperglycaemia and glycaemic variability. However, insulin actions remain a subject of debate with respect to the risk of adverse CV events, which can increase in individuals exposed to high insulin doses. Evidence from the large-scale, long-term ORIGIN trial suggests that early implementation of insulin supplementation therapy in the course of glycaemic disorders, including type 2 diabetes, has a neutral impact on CV outcomes compared with standard management. Thus, the answer to the question "What impact does insulin have on atherosclerosis?" remains unclear, even though it is logical to deduce that insulin should be initiated as soon as possible and that small doses of insulin early on are better than higher doses later in the disease process.

Frequency and severity of the dawn phenomenon in type 2 diabetes: relationship to age

OBJECTIVE

To know whether age has an independent effect on the dawn phenomenon in noninsulin-using type 2 diabetes.

RESEARCH DESIGN AND METHODS

Eighty-one individuals with type 2 diabetes were matched for HbA(1c) and divided by age into three subgroups of 27 individuals (1: ≥70 years; 2: 60-69 years; and 3: ≤59 years). All underwent ambulatory continuous glucose monitoring for quantifying the dawn phenomenon (i.e., the absolute [∂G, mg/dL] or relative [∂G%] increments from nocturnal nadirs to prebreakfast time points).

RESULTS

HbA(1c) levels and 24-h glycemic profiles were similar across the three groups. Glucose increments (mean ± SEM) were identical in the three groups: ∂G (mg/dL), 22.0 ± 4.7 (1), 21.3 ± 3.6 (2), and 18.0 ± 3.6 (3) and δG (%), 19.9 ± 4.9 (1), 21.6 ± 4.4 (2), and 17.6 ± 4.2 (3). Using the most common definition (∂G >10 mg/dL), the prevalence of the dawn phenomenon was 52, 70, and 59% in groups 1, 2, and 3, respectively.

CONCLUSIONS

The dawn phenomenon is present in the elderly.

Add-on therapies to metformin in type 2 diabetes: what modulates the respective decrements in postprandial and basal glucose?

BACKGROUND

Oral hypoglycemic agents (OHAs) are usually divided into postprandial and basal drugs. As their actions are probably more complex, it is important to ascertain which factors can modulate their effects.

SUBJECTS AND METHODS

Thirty-one type 2 diabetes patients treated with metformin (glycosylated hemoglobin [HbA1c] 6.5-9%; median, 7.3%) and enrolled in two randomized controlled studies were allocated to either rosiglitazone (Group 1, n = 8) or glimepiride (Group 2, n = 7) and to either vildagliptin or sitagliptin (Group 3 considered as a whole, n = 16). All patients were investigated using continuous glucose monitoring at baseline and after 8-12 weeks of add-on therapy. Areas under the 24-h glycemic profile curves (AUCs) were determined for assessing postprandial (AUCpp), basal (AUCb), and total (AUCtotal) hyperglycemia. After calculation of decrements in AUCs (∂AUCs) from baseline to end of treatment periods, the following contribution ratios of postprandial and basal decrements to the overall glucose decrement were determined: ∂AUCpp/∂AUCtotal and ∂AUCb/∂AUCtotal (%).

RESULTS

∂AUCpp/∂AUCtotal and ∂AUCb/∂AUCtotal were negatively and positively, respectively, associated (R(2) = 0.195, P = 0.013) with baseline HbA1c. ∂AUCpp/∂AUCtotal was significantly higher (50.8 ± 4.8%) in patients with HbA1c <7.3% than in those with HbA1c ≥ 7.3% (27.0 ± 4.4%) (P = 0.001). After adjustment on baseline HbA1c, ∂AUCpp/∂AUCtotal was greater in Group 3 (44.0 ± 1.6%) than in Group 1 (32.1 ± 4%) and 2 (37.0 ± 3.1%) (P = 0.007).

CONCLUSIONS

Gliptins, glitazones and sulfonylureas concomitantly act on basal and postprandial glucose even though gliptins are more efficient on postprandial glucose. HbA1c appears as a reliable factor for predicting the respective decrements of these two parameters and thus for guiding the choice between the aforementioned drugs.

The glycemic triumvirate and diabetic complications: is the whole greater than the sum of its component parts?

The dysglycemia of diabetes mellitus can be depicted as the glycemic triumvirate with its 3 main components: the sustained chronic (ambient) hyperglycemia, glucose variability and hypoglycemic episodes. The respective contributions of these glycemic disorders to the overall risk for diabetic complications remain a subject of debate. At present, there is cogent evidence for the direct deleterious effect of ambient hyperglycemia while the roles exerted by glucose variability and hypoglycemia remain less documented and only based on observational and pathophysiological studies. In addition, these 3 glycemic disorders could be regarded as components of either an additive or an initiator/accelerator model according to whether each disorder exerts an independent or inter-dependent effect on the development and progression of diabetes-related complications, respectively. In the present review, pros and cons arguments for each model are debated. However it is highly likely that these 3 glycemic disorders have both direct (spoke in a wheel) and indirect (link in a chain) causal effects on clinical cardiovascular outcomes. As a consequence, the relationship between the so-called glycemic triumvirate and diabetic complications might be summarized by the famous Aristotle's aphorism: "the whole is greater than the sum of its parts".

The contribution of glucose variability to asymptomatic hypoglycemia in persons with type 2 diabetes

BACKGROUND

The present study was designed to define the relative contributions of glucose variability and ambient glycemia to the incidence of asymptomatic hypoglycemia in type 2 diabetes.

METHODS

Two hundred twenty-two persons with type 2 diabetes were divided into three groups: Group I (n = 53) on insulin sensitizers alone, Group II (n = 87) on oral hypoglycemic agents (OHAs) to include at least one insulin secretagogue, and Group III (n = 82) on insulin alone or in combination with OHAs. Ambient mean glucose concentration (MG) values (in mmol/L) and glycemic variability (SD around the mean glucose value) (in mmol/L) or mean amplitude of glycemic excursions (in mmol/L) were assessed by a continuous glucose monitoring system. Asymptomatic hypoglycemia was recorded over a 48-h period. Poisson regression analysis was used for assessing the potential predictors of hypoglycaemia.

RESULTS

The best model fit was obtained with the two following explanatory variables: MG and SD. Hypoglycemia frequency was negatively associated with MG and positively with SD: Log (number of hypoglycemia episodes) = 1.37 - (0.72 × MG) + (1.33 × SD). Odds ratios (95% confidence interval) for hypoglycemic risk were significantly different from 1 for MG at 0.96 (0.95-0.97) (P < 0.0001) and for SD at 1.08 (1.06-1.10) (P < 0.0001). In addition, the risk for hypoglycemia was completely or virtually eliminated when the SD was <1.7 mmol/L irrespective of the ambient glucose level and treatment modality.

CONCLUSIONS

As the risk of asymptomatic hypoglycemia increases in the presence of increased glucose variability, avoidance of excess glucose fluctuations should be an important consideration for either reducing or preventing the risk of hypoglycemia in type 2 diabetes.

Postprandial and basal glucose in type 2 diabetes: assessment and respective impacts

The independent contribution of postprandial glucose (PPG) excursions to the overall glucose exposure and its role in the development of both micro- and macrovascular complications of diabetes remain subject to continuing debate in type 2 diabetes. Discussion continues on whether postprandial hyperglycemia is the main contributor to the overall hyperglycemia in fairly well-controlled individuals, whereas basal hyperglycemia becomes the preponderant contributor in poorly controlled patients. The concern about the role of PPG as a risk factor for diabetes complications is related to the controversial data obtained in individuals with impaired glucose tolerance. It remains, however, that the total glucose exposure as reflected by hemoglobin A1c (HbA1c) levels is an undoubted major vascular risk factor. Excluding the contribution of PPG is nonsensical. In support of this position is the fact that the absolute impact of PPG on HbA1c, expressed as percentage levels of HbA1c, remains constant at 1% across the HbA1c continuum in non-insulin-treated type 2 diabetes patients. This key feature clearly depicts the absolute contribution of PPG in contrast to its relative contribution and better explains why PPG contributes to the excess of glycation with the basal hyperglycemia.

Insulin therapy has a complex relationship with measure of oxidative stress in type 2 diabetes: a case for further study

BACKGROUND

Because pharmacotherapies in type 2 diabetes exert complex effects, we examined the different anti-diabetic strategies, especially the influence of insulin doses, on the activation of oxidative stress, a key player in atherosclerosis, ageing and the risk of cancer.

METHODS

This observational study included 122 persons with type 2 diabetes, 61 treated with oral hypoglycaemic agents alone (group I), 61 treated with a combination of oral hypoglycaemic agents and insulin at either a low dose (<0.40 unit/kg/day, group IIa, n = 30) or high dose (≥0.40 unit/kg/day, group IIb, n = 31) of insulin. Oxidative stress was estimated from 24-h urinary excretion rates of 8-iso-prostaglandin F2α. Haemoglobin A(1c) (%) was also measured to assess overall diabetic control.

RESULTS

The 24-h excretion rates of 8-iso-prostaglandin F2α [median (range) pmol/mmol of creatinine] were much lower in group IIa [68 (32-220)] than in either group I [120 (26-329) p < 0.001] or group IIb [101 (30-289) p = 0.026]. Considering groups IIa and IIb as a whole, a significant and positive relationship (p = 0.021) was observed between insulin dose and 8-iso-prostaglandin F2α. Haemoglobin A(1c) was comparable in the three groups.

CONCLUSIONS

The main benefit of insulin therapy is the restoration and maintenance of near normal glycaemia. However insulin at elevated doses can promote oxidative stress which is thought to be an important mediator of some of the deleterious effects of insulin. Our study shows that the link between insulin action and oxidative stress in type 2 diabetes is complex and warrants further study.

Regulation of oxidative stress by glycaemic control: evidence for an independent inhibitory effect of insulin therapy

AIMS/HYPOTHESIS

We examined whether type of diabetes and/or insulin treatment can modulate the impact of sustained hyperglycaemia and glycaemic variability as activators of oxidative stress.

METHODS

This was an observational study in 139 patients with diabetes, 48 with type 1, 60 with type 2 treated by oral hypoglycaemic agents (OHAs) alone and 31 with type 2 treated with insulin plus OHAs. In addition, two groups of ten patients with type 2 diabetes were investigated either before and after introducing insulin treatment (add-on insulin group) or before and after add-on OHA therapy to metformin (add-on OHA group). Oxidative stress was estimated from 24 h urinary excretion rates of 8-isoprostaglandin F2alpha (8-iso-PGF2alpha). HbA(1c) was assessed and mean amplitude of glycaemic excursions (MAGE) was estimated by continuous monitoring.

RESULTS

The 24 h excretion rate of 8-iso-PGF2alpha (median [range] picomoles per millimole of creatinine) was much higher (p < 0.0001) in type 2 diabetes patients treated with OHAs alone (112 [26-329]) than in the type 1 diabetes group (65 [29-193]) and the type 2 diabetes group treated with insulin (69 [30-198]). It was associated with HbA(1c) (F = 12.9, p = 0.0008) and MAGE (F = 7.7, p = 0.008) in non-insulin-treated, but not in insulin-treated patients. A significant reduction in 24 h excretion rate of 8-iso-PGF2alpha from 126 (47-248) to 62 (35-111] pmol/mmol of creatinine was observed in the add-on insulin group (p = 0.005) but not in the add-on OHA group.

CONCLUSIONS/INTERPRETATION

In type 1 and type 2 diabetes, insulin exerts an inhibitory effect on oxidative stress, a metabolic disorder that is significantly activated by sustained hyperglycaemia and glucose variability in non-insulin-treated type 2 diabetes.

Integrating glycaemic variability in the glycaemic disorders of type 2 diabetes: a move towards a unified glucose tetrad concept

The high incidence of atherosclerosis and cardiovascular disease (CVD) is the leading cause of morbidity and mortality among patients with diabetes. Evidence is accumulating that postprandial hyperglycaemia is an independent risk factor for diabetes-associated complications and mortality, and that worsening diabetes control is characterized by postprandial glucose (PPG) deterioration preceding an impairment in fasting glucose levels. Postprandial and general glucose fluctuations play a major role in activating oxidative stress, leading to the endothelial dysfunction, one of the mechanisms responsible for vascular complications. Therefore, the management of PPG is key for any strategy used in the monitoring and treatment of diabetes. We recommend that any strategy aimed at controlling the glycaemic disorders associated with type 2 diabetes, and limiting the risk of complications, should target the 'glucose tetrad', which comprises the following components: HbA(1c), fasting and postprandial plasma glucose, and markers of glycaemic variability, such as the mean amplitude of glycaemic excursions (MAGE) index. This brings together, in a simple, unified concept, the conventional markers (HbA(1c) and fasting glucose) and the more recently recognized markers of glycaemic control (PPG excursions and acute glycaemic variability).

Glycemic variability: the third component of the dysglycemia in diabetes. Is it important? How to measure it?

THE dysglycemia of diabetes includes two components: (1) sustained chronic hyperglycemia that exerts its effects through both excessive protein glycation and activation of oxidative stress and (2) acute glucose fluctuations. Glycemic variability seems to have more deleterious effects than sustained hyperglycemia in the development of diabetic complications as both upward (postprandial glucose increments) and downward (interprandial glucose decrements) changes activate the oxidative stress. For instance, the urinary excretion rate of 8-iso-PGF2alpha, a reliable marker of oxidative stress, was found to be strongly, positively correlated (r = 0.86, p < .001) with glycemic variability assessed from the mean amplitude of glycemic excursions (MAGE) as estimated by continuous glucose monitoring systems (CGMS). These observations therefore raise the question of whether we have the appropriate tools for assessing glycemic variability in clinical practice. From a statistical point of view, the standard deviation (SD) around the mean glucose value appears as the "gold standard." By contrast, the MAGE index is probably more appropriate for selecting the major glucose swings that are calculated as the arithmetic mean of differences between consecutive peaks and nadirs, provided that the differences be greater than the SD around the mean values. Furthermore, calculating the MAGE index requires continuous glucose monitoring, which has the advantage to detect all isolated upward and downward acute glucose fluctuations. In conclusion, the increasing use of CGMSs will certainly promote better assessment and management of glycemic variability.

Targeting prandial hyperglycemia: how important is it and how best to do this?

The contribution of postprandial glucose (PPG) excursions to the overall hyperglycemia of patients with type 2 diabetes depends on the degree of diabetic control. PPG is a major contributor in patients with hemoglobin A(1c) (HbA(1c)) levels below 7.3%, whereas the contribution of fasting plasma glucose (FPG) is preponderant in poorly controlled patients. In addition, the loss of postprandial glycemic control precedes stepwise degradation of fasting with worsening diabetes. As a consequence, monitoring after meals is particularly important in patients with HbA(1c) levels ranging from 6.5% to 8%. In such patients, targeting PPG below 140 mg/dL should be one of the main objectives to achieve HbA(1c) less than 6.5%. The new hypoglycemic agents, such as the glucagon-like peptide-1 analogues and the dipeptidyl peptidase-4 inhibitors which have a gluco-dependent insulinotropic effect, should normally reinforce our therapeutic armamentarium for achieving the glycemic targets that should include the three components of the glucose triad: HbA(1c), FPG, and PPG.

Glycemic variability: should we and can we prevent it?

Diabetes is characterized by glycemic disorders that include both sustained chronic hyperglycemia and acute glucose fluctuations. There is now cogent evidence for the deleterious effects of sustained chronic hyperglycemia that results in excessive protein glycation and generation of oxidative stress. The role of glucose variability from peaks to nadirs is less documented, but there are many reasons to think that both upward (postprandial) and downward (interprandial) acute fluctuations of glucose around a mean value activate the oxidative stress. As a consequence, it is strongly suggested that a global antidiabetic strategy should be aimed at reducing to a minimum the different components of dysglycemia (i.e., A1C, fasting and postprandial glucose, as well as glucose variability). All the therapeutic agents that act on postprandial glucose excursions seem of particular interest for reducing the latter parameter (i.e., the glucose instability). Particular attention should be paid to such emerging therapeutic agents as the glucagon-like peptide 1 agonists and the dipeptidyl peptidase (DPP)-IV inhibitors that act through the incretin pathway.

Acute glucose fluctuations and chronic sustained hyperglycemia as risk factors for cardiovascular diseases in patients with type 2 diabetes

Chronic hyperglycemia, usually assessed from HbA1c determinations, results in excessive glycation and generation of oxidative stress. As a consequence, chronic hyperglycemia has been identified as a risk factor for diabetes complications leading to accelerated atherosclerosis. Both fasting and postprandial hyperglycemia contribute to this process. However the acute glucose fluctuations that occur in diabetes have been recently described as an additional factor that activates the oxidative stress. As a consequence, acute glucose swings, including upward (postprandial) and downward (interprandial) fluctuations can be considered as risk factors for cardiovascular events and should be included in the "dysglycemia" of diabetes in combination with fasting and postprandial hyperglycemia. As postprandial glucose is a contributor of both acute glucose fluctuations and chronic sustained hyperglycemia, it remains difficult to know whether these 2 mechanisms are equivalent or not equivalent risk factors for cardiovascular disease.

Continuous glucose monitoring in patients with type 2 diabetes: Why? When? Whom?

The overall assessment of glycaemic control in patients with type 2 diabetes should normally include the monitoring of three parameters that are usually depicted as the 'glucose triad': HbA(1c), fasting plasma glucose (FPG) and postprandial glucose (PPG) excursions. However one additional marker, the so-called 'glucose variability' might be as important as the three others since it has been demonstrated that both upward and downward glucose fluctuations are potent activators of oxidative stress. Even though many methods have been proposed for assessing glucose fluctuations, the 'mean amplitude glucose excursions' (MAGE) index remains the 'gold standard'. However MAGE estimation requires the use of continuous glucose sensors. Despite the debate on the reliability and cost of the devices that permit glucose monitoring, we suggest that interventional trials designed to evaluate the effects of glucose fluctuations on diabetic complications should benefit from the use of continuous glucose monitoring systems (CGMSs). More prosaically, the use of these technologies could be extended to current clinical care of type 2 diabetic patients especially for motivating them to accept earlier insulin treatments in case of 'oral antidiabetic drug secondary failure', and further for choosing the most appropriate insulin regimen.

The loss of postprandial glycemic control precedes stepwise deterioration of fasting with worsening diabetes

OBJECTIVE

The aim of the study was to determine whether the loss of fasting and postprandial glycemic control occurs in parallel or sequentially in the evolution of type 2 diabetes.

RESEARCH DESIGN AND METHODS

In 130 type 2 diabetic patients, 24-h glucose profiles were obtained using a continuous glucose monitoring system. The individuals with type 2 diabetes were divided into five groups according to A1C levels: 1 (<6.5%, n = 30), 2 (6.5-6.9%, n = 17), 3 (7-7.9%, n = 32), 4 (8-8.9%, n = 25), and 5 (> or =9%, n = 26). The glucose profiles between the groups were compared. The overall glucose concentrations for the diurnal, nocturnal, and morning periods, which represent the postprandial, fasting, and the dawn phenomenon states, respectively, were also compared.

RESULTS

Glucose concentrations increased steadily from group 1 to 5 in a stepwise manner. The initial differences in mean glucose concentrations reaching statistical significance occurred 1) between groups 1 and 2 (6.4 vs. 7.7 mmol/l, P = 0.0004) for daytime postprandial periods, followed by differences; 2) between groups 2 and 3 (7.5 vs. 9.3 mmol/l, P = 0.0003) for the morning periods (dawn phenomenon); and finally 3) between groups 3 and 4 (6.3 vs. 8.4 mmol/l, P < 0.0001) for nocturnal fasting periods.

CONCLUSIONS

The deterioration of glucose homeostasis in individuals with type 2 diabetes progressed from postprandial to fasting hyperglycemia following a three-step process. The first step related to the three diurnal postmeal periods considered as a whole, the second step occurred during the morning period, and the third and final step corresponded to sustained hyperglycemia over the nocturnal fasting periods. Such a description of the key stages in the evolution of type 2 diabetes may be of interest for implementing antidiabetes treatment.

Contribution of postprandial glucose to chronic hyperglycaemia: from the "glucose triad" to the trilogy of "sevens"

Even though fasting and postprandial glucose are both contributors to the overall hyperglycaemia as observed in patients with type 2 diabetes, their respective contributions are varying with the degree of diabetic control. The contribution of postprandial glucose is predominant in patients with satisfactory control of diabetes (HbAlc < 7.3%) whereas the contribution of fasting glucose increases progressively with worsening diabetes. As a consequence an overall picture of the diabetic control should normally be based on the assessment of the "glucose triad" with its three components: HbAlc which integrates the diabetic control over a 3-month period, fasting and postprandial glucose. The two later are good indicators of the glycaemic regulation over the two main physiological periods of daytime: the fasting and postprandial states. Postprandial glucose concentrations should be more particularly tested at mid-morning time since in most patients this period corresponds to the highest glucose concentrations of daytime. However postprandial measurements at 2-h after lunch provide an evaluation of the overall diabetic control since we have demonstrated that glucose concentrations < 7 mmol/L at this time point are excellent predictors of HbAlc levels < 7% (specificity 2 90%). Therefore, in order to simplify the work of health care providers the "glucose triad" concept can be translated into the trilogy of "sevens": HbA1c goals < 7% and postprandial glucose targets < 7 mmol/L 2-h after lunch, both for assessing a satisfactory diabetic control, and fasting glucose < 7 mmol/L for defining the non-diabetic state.

Activation of oxidative stress by acute glucose fluctuations compared with sustained chronic hyperglycemia in patients with type 2 diabetes

CONTEXT

Glycemic disorders, one of the main risk factors for cardiovascular disease, are associated with activation of oxidative stress.

OBJECTIVE

To assess the respective contributions of sustained chronic hyperglycemia and of acute glucose fluctuations to oxidative stress in type 2 diabetes.

DESIGN, SETTING, AND PARTICIPANTS

Case-control study of 21 patients with type 2 diabetes (studied 2003-2005) compared with 21 age- and sex-matched controls (studied in 2001) in Montpellier, France.

MAIN OUTCOME MEASURES

Oxidative stress, estimated from 24-hour urinary excretion rates of free 8-iso prostaglandin F2alpha (8-iso PGF2alpha). Assessment of glucose fluctuations was obtained from continuous glucose monitoring system data by calculating the mean amplitude of glycemic excursions (MAGE). Postprandial contribution to glycemic instability was assessed by determining the postprandial increment of glucose level above preprandial values (mean postprandial incremental area under the curve [AUCpp]). Long-term exposure to glucose was estimated from hemoglobin A1c, from fasting glucose levels, and from mean glucose concentrations over a 24-hour period.

RESULTS

Mean (SD) urinary 8-iso PGF2alpha excretion rates were higher in the 21 patients with diabetes (482 [206] pg/mg of creatinine) compared with controls (275 [85] pg/mg of creatinine). In univariate analysis, only MAGE (r = 0.86; P<.001) and AUCpp (r = 0.55; P = .009) showed significant correlations with urinary 8-iso PGF2alpha excretion rates. Relationships between 8-iso PGF2alpha excretion rates and either MAGE or AUCpp remained significant after adjustment for the other markers of diabetic control in multiple linear regression analysis (multiple R2 = 0.72 for the model including MAGE and multiple R2 = 0.41 for the model including AUCpp). Standardized regression coefficients were 0.830 (P<.001) for MAGE and 0.700 (P = .003) for AUCpp.

CONCLUSIONS

Glucose fluctuations during postprandial periods and, more generally, during glucose swings exhibited a more specific triggering effect on oxidative stress than chronic sustained hyperglycemia. The present data suggest that interventional trials in type 2 diabetes should target not only hemoglobin A1c and mean glucose concentrations but also acute glucose swings.

Insulin secretion and sensitivity as determinants of HbA1c in type 2 diabetes

BACKGROUND

Defects in insulin secretion and sensitivity, two major determinants of glycaemic control, can occur and progress or not in parallel. The present study was designed to compare the respective roles of both determinants on HbA1c, in type 2 diabetic patients, according to whether or not residual beta-cell function was stimulated with insulin secretagogues.

MATERIALS AND METHODS

Insulin secretion and insulin sensitivity were both estimated using the homeostasis model assessment (HOMA). HbA1c, insulin sensitivity (HOMA2%S) and insulin secretion (HOMA2%B) were determined in 289 noninsulin-using type 2 diabetic patients who were further divided into two groups according to treatment: metformin alone (group I, n = 57) or metformin and glyburide (group II, n = 232). The patients of both groups were further divided into three subsets in order to test the dependence of HbA1c on HOMA2%B and HOMA2%S.

RESULTS

In group I mean HbA1c were greater (8.4%) in patients with HOMA2%B < 50% than in the two subsets with HOMA2%B > or = 50%: 7.2 and 6.8% (P = 0.0013). In group II mean values of stimulated-insulin secretion (HOMA2%B) were lesser (40.7 and 30.1%) in the two subsets of patients with HbA1c > or = 8% than in patients with HbA1c < 8%: 55.1% (P < 0.0001). By contrast, we found no differences in both groups with HOMA2%S. A stepwise multiple regression showed that HOMA2%B contributed to HbA1c more than HOMA2%S both in groups I (33.5% vs. 23.4%) and II (22.7% vs. 8%).

CONCLUSIONS

Although the role of insulin sensitivity is not negligible, insulin secretion appears to be the major determinant of diabetic control in overt type 2 diabetic patients who are treated with metformin alone or with a two-drug therapy combining metformin and glyburide.

Addition of rapid-acting insulin to basal insulin therapy in type 2 diabetes: indications and modalities

There are many reasons to believe that in the near future, the treatment of patients with Type 2 diabetes will be characterised by an increased use of insulin therapy. To ensure that insulin regimens are acceptable to patients, and implemented by physicians, they should be as simple and efficient as possible. Simplicity is synonymous with the regimen of once-daily basal insulin glargine given at any time of the day (at the same time each day). With such a strategy, the dose is adjusted by titrating to target fasting blood glucose values of 5.0 - 7.2 mmol/L (90 - 130 mg/dL). When these targets can no longer be achieved with reasonable doses of long-acting insulin, a rapid-acting insulin analogue should be added at meal times. A step-by-step strategy can be used; it is recommended that initially, a single daily prandial bolus of a rapid-acting insulin analogue is administered before the meal that leads to the highest post-meal blood glucose excursions. Further boluses can be added at other meal times as necessary, i.e, when post-meal blood glucose values remain above 10.0 mmol/L (180 mg/dL) and 7.8 mmol/L (140 mg/dL) at mid-morning and 2h-post-lunch or post-dinner times, respectively. This stepwise strategy may eventually lead to a standard basal-bolus regimen with 3 pre-meal injections of rapid-acting insulin analogues, a potentially small trade-off for achieving fairly-well controlled diabetes.