The Dawn Phenomenon Revisited: Implications for Diabetes Therapy

Oscillations in joint synchrony of reproductive hormones in healthy men

Negative-feedback (inhibitory) and positive-feedforward (stimulatory) processes regulate physiological systems. Whether such processes are themselves rhythmic is not known. Here, we apply cross-approximate entropy (cross-ApEn), a noninvasive measurement of joint (pairwise) signal synchrony, to inferentially assess hypothesized circadian and ultradian variations in feedback coupling. The data comprised simultaneous measurements of three pituitary and one peripheral hormone (LH, FSH, prolactin, and testosterone) in 12 healthy men each sampled every 10 min for 4 days (5,760 min). Ergodicity, due to the time series stationarity of the measurements over the 4 days, allows for effective estimation of parameters based upon the 12 subjects. Cross-ApEn changes were quantified via moving-window estimates applied to 4-day time series pairs. The resultant ordered windowed cross-ApEn series (in time) were subjected to power spectrum analysis. Rhythmicity was assessed against the null hypothesis of randomness using 1,000 simulated periodograms derived by shuffling the interpulse-interval hormone-concentration segments and redoing cross-ApEn windows and spectral analysis. By forward cross-ApEn analysis, paired LH-testosterone, LH-prolactin, and LH-FSH synchrony maintained dominant rhythms with periodicities of 18-22.5, 18, and 22.5 h, respectively (each P < 0.001). By reverse (feedback) cross-ApEn analysis, testosterone-LH, testosterone-prolactin, and testosterone-FSH synchrony cycles were 30, 18, and 30-45 h, respectively (each P ≤ 0.001). Significant 8- or 24-h rhythms were also detected in most linkages, and maximal bihormonal synchrony occurred consistently at ∼0400-0500. Collectively, these analyses demonstrate significant ultradian (<24 h), circadian (∼24 h), and infradian (>24 h) oscillations in pituitary-testis synchrony, wherein maximal biglandular coordination is strongly constrained to the early morning hours.

Fitting dynamic models with forcing functions: application to continuous glucose monitoring in insulin therapy

The artificial pancreas is an emerging technology to treat type 1 diabetes (T1D). It has the potential to revolutionize diabetes care and improve quality of life. The system requires extensive testing, however, to ensure that it is both effective and safe. Clinical studies are resource demanding and so a principle aim is to develop an in silico population of subjects with T1D on which to conduct pre-clinical testing. This paper aims to reliably characterize the relationship between blood glucose and glucose measured by subcutaneous sensor as a major step towards this goal. Blood-and sensor-glucose are related through a dynamic model, specified in terms of differential equations. Such models can present special challenges for statistical inference, however. In this paper we make use of the BUGS software, which can accommodate a limited class of dynamic models, and it is in this context that we discuss such challenges. For example, we show how dynamic models involving forcing functions can be accommodated. To account for fluctuations away from the dynamic model that are apparent in the observed data, we assume an autoregressive structure for the residual error model. This leads to some identifiability issues but gives very good predictions of virtual data. Our approach is pragmatic and we propose a method to mitigate the consequences of such identifiability issues.

Closed-loop insulin delivery: from bench to clinical practice

Automated closed-loop insulin delivery, also referred to as the 'artificial pancreas', has been an important but elusive goal of diabetes treatment for many decades. Research milestones include the conception of continuous glucose monitoring in the early 1960s, followed by the production of the first commercial hospital-based artificial pancreas in the late 1970s that combined intravenous glucose sensing and insulin delivery. In the past 10 years, research into the artificial pancreas has gained substantial momentum and focused on the subcutaneous route for glucose measurement and insulin delivery, which reflects technological advances in interstitial glucose monitoring and the increasing use of the continuous subcutaneous insulin infusion. This Review discusses the design of an artificial pancreas, its components and clinical results, as well as the advantages and disadvantages of different types of automated closed-loop systems and potential future advances. The introduction of the artificial pancreas into clinical practice will probably occur gradually, starting with simpler approaches, such as overnight control of blood glucose concentration and temporary pump shut-off, that are adapted to more complex situations, such as glycemic control during meals and exercise.

Clinical experience with insulin glargine in type 1 diabetes

The Diabetes Control and Complications Trial (DCCT) demonstrated the importance of optimal glycemic control achieved through intensive insulin therapy in reducing the microvascular complications associated with type 1 diabetes. However, the DCCT, which was conducted prior to the availability of insulin analogs, also reported a significant increase in severe hypoglycemia with intensive versus conventional therapy. Insulin analogs were developed to aid patients in achieving better diabetes control by providing insulins with optimized pharmacokinetic and pharmacodynamic characteristics. Insulin glargine was the first long-acting insulin analog with a 24-h duration of action, offering once-daily injection, and has now been in clinical use for over 10 years. The authors performed a systematic search of EMBASE, MEDLINE, and Web of Science (Science Citation Index) to determine the efficacy of insulin glargine in type 1 diabetes in basal-bolus insulin regimens. Randomized controlled trials have demonstrated that glycemic control with insulin glargine is at least comparable to that with neutral protamine Hagedorn (NPH) insulin in adults and in children and adolescents, and with continuous subcutaneous insulin infusion in adults. However, these same trials show a significantly lower risk for hypoglycemia with insulin glargine compared with NPH insulin in adults.

Pharmacokinetics following continuous subcutaneous insulin infusion of insulin aspart with or without initial subcutaneous bolus

AIM

To evaluate time to steady state insulin concentration (C(ss)) following continuous subcutaneous insulin infusion (CSII) of insulin aspart (IAsp) with or without an initial s.c. bolus.

METHODS

In random order 10 healthy volunteers were given a basal insulin infusion rate (0.5 U/h) for 8 h with or without an initial s.c. bolus (1.4 U). Serum IAsp was measured until 3 h after infusion was stopped.

RESULTS

An overshoot of IAsp was seen before C(ss) was achieved following an initial bolus of insulin as compared to no bolus. The apparent half-life (t((1/2))) with or without bolus did not differ (p = 0.15). Time to steady state (T(ss)) was evaluated in two ways: (1) T(ss) defined as the first point within an interval of C(ss)+/- 2 x CV was 233 vs. 166 min with and without a bolus respectively (p = 0.068). (2) A t-test was performed for each concentration-time point vs. mean C(ss), and the first point with no significance was defined, T(ss). This gave 208 (p = 0.09) and 178 min (p = 0.24) with and without bolus respectively. Mathematical modelling suggests that an ideal mean bolus should be 0.89 U, and that this bolus dose may result in a shorter T(ss).

CONCLUSION

A bolus of 1.4 U resulted in an overshoot of serum IAsp before C(ss) and a longer period before C(ss) is achieved. Mathematical modelling suggests that a mean bolus of 0.89 U would result in a faster achievement of C(ss) compared to no bolus.

Difference in insulin usage patterns with pubertal development in children with type 1 diabetes during transition from multiple daily injections to continuous subcutaneous insulin infusion (CSII) and through the CSII treatment

OBJECTIVE

This study analyzed the changes in insulin requirement in the transition from multiple daily injections (MDI) to continuous subcutaneous insulin infusion (CSII) and the differences through the CSII treatment in pediatric patients in different pubertal developmental stages.

METHODS

We analyzed, through a longitudinal retrospective study, the insulin usage patterns and glycemic control of 40 patients with type 1 diabetes on CSII treatment for 12 months. The patients were subdivided in three groups: group A, 13 prepubertal subjects (Tanner stage I); group B, 15 pubertal subjects (Tanner stage II-IV); and group C, 12 postpubertal subjects (Tanner stage V).

RESULTS

During the transition from MDI to CSII, the insulin requirements decreased significantly by 21 +/- 5% (0.89 +/- 0.26 U/kg/day vs. 0.70 +/- 0.11 U/kg/day). Through the CSII treatment the percentage of total daily insulin delivered as the basal rate in groups A, B, and C was 54-60%, 52-54%, and 52-54%, respectively. The number of basal rates per day was significantly higher in groups A and B. The overall profile of basal rate differed among the groups. During the night, prepubertal patients required more insulin from 12 p.m. to 2 a.m., whereas pubertal and postpubertal patients required more insulin between 2-3 a.m. to 7 a.m. Prepubertal patients had a maximum basal rate between 9 a.m. to 12 a.m. and 2 p.m. to 4 p.m., in contrast to pubertal and postpubertal patients between 2 p.m. to 3 p.m. and 5 p.m. to 6 p.m. The number of "extra" boluses per day was significantly higher in groups B and C compared to group A.

CONCLUSIONS

Age-related differences exist in insulin usage patterns of pediatric patients on pump treatment. A greater knowledge of these variations may help to obtain optimum conditions in the CSII treatment in pediatric patients.

Identification of intraday metabolic profiles during closed-loop glucose control in individuals with type 1 diabetes

BACKGROUND

Algorithms for closed-loop insulin delivery can be designed and tuned empirically; however, a metabolic model that is predictive of clinical study results can potentially accelerate the process.

METHODS

Using data from a previously conducted closed-loop insulin delivery study, existing models of meal carbohydrate appearance, insulin pharmacokinetics, and the effect on glucose metabolism were identified for each of the 10 subjects studied. Insulin's effects to increase glucose uptake and decrease endogenous glucose production were described by the Bergman minimal model, and compartmental models were used to describe the pharmacokinetics of subcutaneous insulin absorption and glucose appearance following meals. The composite model, comprised of only five equations and eight parameters, was identified with and without intraday variance in insulin sensitivity (S(I)), glucose effectiveness at zero insulin (GEZI), and endogenous glucose production (EGP) at zero insulin.

RESULTS

Substantial intraday variation in SI, GEZI and EGP was observed in 7 of 10 subjects (root mean square error in model fit greater than 25 mg/dl with fixed parameters and nadir and/or peak glucose levels differing more than 25 mg/dl from model predictions). With intraday variation in these three parameters, plasma glucose and insulin were well fit by the model (R(2) = 0.933 +/- 0.00971 [mean +/- standard error of the mean] ranging from 0.879-0.974 for glucose; R(2) = 0.879 +/- 0.0151, range 0.819-0.972 for insulin). Once subject parameters were identified, the original study could be reconstructed using only the initial glucose value and basal insulin rate at the time closed loop was initiated together with meal carbohydrate information (glucose, R(2) = 0.900 +/- 0.015; insulin delivery, R(2) = 0.640 +/- 0.034; and insulin concentration, R(2) = 0.717 +/- 0.041).

CONCLUSION

Metabolic models used in developing and comparing closed-loop insulin delivery algorithms will need to explicitly describe intraday variation in metabolic parameters, but the model itself need not be comprised by a large number of compartments or differential equations.

Psychosocial problems in adolescents with type 1 diabetes mellitus

Adolescents with diabetes are at increased risk of developing psychiatric (10-20%) or eating disorders (8-30%), as well as substance abuse (25-50%), leading to non-compliance with treatment and deterioration of diabetic control. At high risk are female adolescents with family problems and other comorbid disorders. Impaired cognitive function has also been reported among children with diabetes, mainly in boys, and especially in those with early diabetes diagnosis (< 5 years), or with episodes of severe hypoglycaemia or prolonged hyperglycaemia. Type 1 diabetes mellitus contributes to the development of problems in parent-child relationships and employment difficulties, and negatively affects the quality of life. However, insulin pumps appear to improve patients' metabolic control and lifestyle. The contributions of family and friends to the quality of metabolic control and emotional support are also crucial. In addition, the role of the primary-care provider is important in identifying patients at high risk of developing psychosocial disorders and referring them on to health specialists. At high risk are patients in mid-adolescence with comorbid disorders, low socioeconomic status or parental health problems. Multisystem therapy, involving the medical team, school personnel, family and peer group, is also essential. The present review focuses on the prevalence of nutritional and psychosocial problems among adolescents with diabetes, and the risk factors for its development, and emphasizes specific goals in their management and prevention.

Insulin pump therapy: guidelines for successful outcomes

PURPOSE

Current forms of insulin delivery used in the treatment of diabetes mellitus (diabetes) include syringes, pens, and insulin pumps. Technical advantages of insulin pump therapy, or continuous subcutaneous insulin delivery (CSII), include precise and flexible insulin dosing. In the context of intensive diabetes management, insulin pumps can facilitate improved long-term glycemic control and reduce the risk for diabetes complications, with improved lifestyle flexibility for patients and their families. Comprehensive patient education, carbohydrate counting, and frequent self-monitoring of blood glucose or continuous glucose monitoring are necessary components of successful insulin pump therapy. Technological advances have increased the appeal of pump therapy to patients and clinicians. Physically, current insulin pumps are discreet, ergonomic, and water resistant. Meanwhile, software improvements have yielded smart pumps with features that support pump users in their daily diabetes management. Robust data analysis software packages allow patients and clinicians unprecedented insight into the quality of diabetes control. Furthermore, widespread insurance reimbursement for CSII has expanded access to therapy.

CONCLUSIONS

As the number of pump users and potential users expands, diabetes educators face new challenges and opportunities to improve patients' lives with diabetes. This activity describes the rationale for insulin pump therapy, its potential advantages and disadvantages, and strategies regarding patient selection and education.

Overnight CSII as supplement to oral antidiabetic drugs in type 2 diabetes

AIM

To evaluate the potential advantages of a constant overnight subcutaneous delivery of insulin in type 2 diabetic patients who fail to achieve glycaemic control on oral antidiabetics.

METHODS

Ten type 2 diabetic patients treated with oral antidiabetic drugs without gaining sufficient glycaemic control were included in this three-period study. All patients received continuous subcutaneous insulin infusion (CSII) with a short-acting insulin analogue, 2 IU/h, for 8 h during three consecutive nights (period A). Based upon the results from period A, two additional dose regimens of three nights (period B and C) were studied in random order. Serum insulin aspart, human insulin and plasma glucose (PG) profiles were recorded.

RESULTS

In period A, fasting plasma glucose (FPG) was reduced from a mean +/- s.d. (mmol/l) value of 11.6 +/- 2.9 to 5.5 +/- 1.6 (p < 0.0001) during the first night. No additional lowering of FPG was seen the two succeeding nights. FPG narrowed as the range before the infusion was 7.3-15.2 mmol/l compared with 3.6-6.1 mmol/l on the last morning after infusion. The variability in PG profile during the first and the last night of CSII was small and not significantly different. The rising insulin aspart was mirrored by a decrease in human insulin. In period B and C, similar tendencies as for period A were seen. In period A, two patients each experienced one mild hypoglycaemic episode.

CONCLUSIONS

CSII with an insulin analogue overnight effectively reduced FPG without occurrence of major hypoglycaemia in type 2 diabetic patients who fail to achieve glycaemic control on oral antidiabetic treatment.

Predicted blood glucose from insulin administration based on values from miscoded glucose meters

OBJECTIVES

The proper use of many types of self-monitored blood glucose (SMBG) meters requires calibration to match strip code. Studies have demonstrated the occurrence and impact on insulin dose of coding errors with SMBG meters. This paper reflects additional analyses performed with data from Raine et al. (JDST, 2:205-210, 2007). It attempts to relate potential insulin dose errors to possible adverse blood glucose outcomes when glucose meters are miscoded.

METHODS

Five sets of glucose meters were used. Two sets of meters were autocoded and therefore could not be miscoded, and three sets required manual coding. Two of each set of manually coded meters were deliberately miscoded, and one from each set was properly coded. Subjects (n = 116) had finger stick blood glucose obtained at fasting, as well as at 1 and 2 hours after a fixed meal (Boost((R)); Novartis Medical Nutrition U.S., Basel, Switzerland). Deviations of meter blood glucose results from the reference method (YSI) were used to predict insulin dose errors and resultant blood glucose outcomes based on these deviations.

RESULTS

Using insulin sensitivity data, it was determined that, given an actual blood glucose of 150-400 mg/dl, an error greater than +40 mg/dl would be required to calculate an insulin dose sufficient to produce a blood glucose of less than 70 mg/dl. Conversely, an error less than or equal to -70 mg/dl would be required to derive an insulin dose insufficient to correct an elevated blood glucose to less than 180 mg/dl. For miscoded meters, the estimated probability to produce a blood glucose reduction to less than or equal to 70 mg/dl was 10.40%. The corresponding probabilities for autocoded and correctly coded manual meters were 2.52% (p < 0.0001) and 1.46% (p < 0.0001), respectively. Furthermore, the errors from miscoded meters were large enough to produce a calculated blood glucose outcome less than or equal to 50 mg/dl in 42 of 833 instances. Autocoded meters produced zero (0) outcomes less than or equal to 50 mg/dl out of 279 instances, and correctly coded manual meters produced 1 of 416.

CONCLUSIONS

Improperly coded blood glucose meters present the potential for insulin dose errors and resultant clinically significant hypoglycemia or hyperglycemia. Patients should be instructed and periodically reinstructed in the proper use of blood glucose meters, particularly for meters that require coding.

[Post-prandial hyperglycemia in type 2 diabetes patients]

OBJECTIVES

Through the analysis of a group of type 2 diabetes patients, the aims of this study are: to evaluate through CGMS (continuous glucose monitoring system) the post-prandial subcutaneous glucose excursions; to analyze the correlations between subcutaneous glucose and capillary glycemia with HbA1c and to evaluate the effectiveness, safety and broad-mindedness of the CGMS.

METHODS

Forty type 2 diabetes patients were analyzed, with HbA1c until 7.3%, in use of oral agents and within less than a ten-year diagnosis. They were submitted to CGMS for 72 h, whose data were compared with HbA1c and capillary glycemia.

RESULTS

The average subcutaneous glucose excursion at breakfast was statistically bigger than at dinner (95%CI -24.96 a -1.66). The subcutaneous glucose excursion/meal carbohydrates content ratio was statistically bigger at breakfast than at other meals (p 0.001). There was no correlation between the levels of subcutaneous glucose and capillary glycemia with HbA1c. There were no complications using CGMS.

CONCLUSIONS

The subcutaneous glucose excursions were predominant at breakfast. There were no correlations between HbA1c and glycemic control parameters. CGMS showed itself efficient, secure and well tolerated in this group of patients.

Insulin and glucose profiles during continuous subcutaneous insulin infusion compared with injection of a long-acting insulin in Type 2 diabetes

AIMS

To compare insulin and glucose profiles during basal continuous subcutaneous infusion of a rapid-acting insulin analogue and once daily subcutaneous injection of a long-acting insulin analogue in Type 2 diabetes.

METHODS

Twenty-one patients with Type 2 diabetes treated with oral glucose-lowering agents were randomized in this two-period crossover study to an equivalent 24-h dose of continuous subcutaneous infusion of insulin aspart and subsequently once-daily bedtime subcutaneous injection of insulin glargine, or vice versa, for eight consecutive days. Plasma profiles of insulin and glucose were recorded.

RESULTS

On the last day of each treatment period, the area under the curve (AUC) for glucose was 10% lower on the continuous subcutaneous infusion regimen compared with the insulin injection regimen (P = 0.002). This was accomplished by a flat exogenous insulin infusion profile compared with a peaking profile with injected insulin (AUC was 74% higher after injection compared with pre-injection levels (P = 0.001)). During the last 6 days in each treatment period, the intra-subject variability of exogenous fasting insulin levels in the mornings was 41% lower during insulin infusion compared with insulin injection (P = 0.012). The corresponding intra-subject variability for fasting glucose only showed a tendency to be lower during infusion as compared to the injection regimen (28%; P = 0.104). Thirteen symptomatic-only or minor hypoglycaemic episodes were recorded during the entire infusion period compared with three episodes during the injection period.

CONCLUSIONS

Basal continuous subcutaneous infusion of a rapid-acting insulin analogue improved plasma insulin (more flat insulin profile with a lower variability) and glucose (lower AUC) profiles compared with once-daily subcutaneous injection of a long-acting insulin analogue in Type 2 diabetes.

Chronobiology in the endocrine system

Biological signaling occurs in a complex web with participation and interaction of the central nervous system, the autonomous nervous system, the endocrine glands, peripheral endocrine tissues including the intestinal tract and adipose tissue, and the immune system. All of these show an intricate time structure with rhythms and pulsatile variations in multiple frequencies. Circadian (about 24-hour) and circannual (about 1-year) rhythms are kept in step with the cyclic environmental surrounding by the timing and length of the daily light span. Rhythmicity of many endocrine variables is essential for their efficacy and, even in some instances, for the qualitative nature of their effects. Indeed, the continuous administration of certain hormones and their synthetic analogues may show substantially different effects than expected. In the design of drug-delivery systems and treatment schedules involving directly or indirectly the endocrine system, consideration of the human time organization is essential. A large amount of information on the endocrine time structure has accumulated, some of which is discussed in this review.

A prospective evaluation of insulin dosing recommendations in patients with type 1 diabetes at near normal glucose control: Basal dosing

BACKGROUND

Current basal insulin dosing recommendations are based on retrospective studies of Type 1 patients with diabetes in whom the glucose control was not intensely established. Using continuous glucose monitoring (CGM) we prospectively studied these recommendations in patients treated with continuous subcutaneous insulin infusion.

METHODS

With CGM 30 subjects were titrated with daily insulin adjustments to achieve a basal glucose targets of <5% of values <70 mg/dl and <20%, >170 mg/dl. The basal rate during meal time was studied by a sequential daily single meal omission until the glucose goals were achieved.

RESULTS

Glucose targets were achieved in all subjects. The observed ratios of total basal dose (TBD) to total daily dose and TBD to weight, in kilograms, were 0.384 and 0.185, respectively. Previously reported formulas for estimating the TBD resulted in significantly higher values than we observed. The difference between the maximum to the minimum hourly basal insulin infusion rate was more than 100% and the peak rate was reached by 0200 hours in 73% of subjects. During the post study observation period in which there was no further study intervention and in those subjects with baseline A1C >6.9%, the A1C decreased 0.45 % (p = 0.0110) in a mean of 12.8 weeks.

CONCLUSIONS

Current literature overestimates TBD dose and underestimates the degree and the time of onset of the dawn phenomenon. Maintaining near normal glycemia in the ambulatory setting may be achieved in selected Type 1 patients for at least two weeks and maybe longer.