The effect of residual beta-cell function on the development of diabetic retinopathy

Potential beneficial effects of a gluten-free diet in newly diagnosed children with type 1 diabetes: a pilot study

AIM

Gluten-free diet has shown promising effects in preventing type 1 diabetes (T1D) in animals as well as beneficial effects on the immune system. Gluten-free diet at diabetes onset may alter the natural course and outcome of autoimmune diseases such as T1D.

METHODS

In a 12-month study, 15 children newly diagnosed with T1D were instructed to follow a gluten-free diet. Questionnaires were used to evaluate adherence to the gluten-free diet. Partial remission (PR) was defined by insulin dose-adjusted A1c (IDAA1c) ≤9 or stimulated C-peptide (SCP) >300 pmol/L measured 90 min after a liquid mixed meal at the inclusion, six and 12 months after onset. The intervention group was compared with two previous cohorts. Linear mixed models were used to estimate differences between cohorts.

RESULTS

After 6 months, more children on a gluten-free diet tended to have SCP values above 300 pmol/L compared to the European cohort (p = 0.08). The adherence to a gluten-free diet decreased during the 12-month study period. After 1 year there was no difference in SCP levels or percentage in remission according to SCP (p > 0.1). Three times as many children were still in PR based on IDAA1c (p < 0.05). Twelve months after onset HbA1c were 21 % lower and IDAA1c >1 unit lower in the cohort on a gluten-free diet compared to the two previous cohorts (p < 0.001).

CONCLUSION

Gluten-free diet is feasible in highly motivated families and is associated with a significantly better outcome as assessed by HbA1c and IDAA1c. This finding needs confirmation in a randomized trial including screening for quality of life. (Clinicaltrials.gov number NCT02284815).

Residual C-peptide in type 1 diabetes: what do we really know?

Connecting peptide, or C-peptide, is a protein that joins insulin's α and B chains in the proinsulin molecule. During insulin synthesis, C-peptide is cleaved from proinsulin and secreted in an equimolar concentration to insulin from the β cells. Because C-peptide experiences little first-pass clearance by the liver, and because levels are not affected by exogenous insulin administration, it may be used as a marker of endogenous insulin production and a reflection of β-cell function. Residual β-cell function, as measured by C-peptide in those with type 1 diabetes (T1D), has repeatedly been demonstrated to be clinically important. The Eisenbarth model of type 1 diabetes postulated immune-mediated linear loss of β cells, with clinical diagnosis occurring when there was insufficient insulin secretion to meet glycemic demand. Moreover, the model also implied that all individuals with T1D rapidly and inevitably progressed to absolute insulin deficiency. Correspondingly, it was assumed that most people with longstanding T1D would show little to no residual C-peptide secretion. While more than a quarter century of data confirms that this model remains largely true and appropriately serves as the basis for prevention studies, accumulating evidence suggests that the natural history of β-cell function before, during and after diagnosis is more complex. In this review, we discuss the clinical benefits of residual insulin secretion and present recent data about the natural history of insulin secretion in those with, or at risk for T1D.

The clinical utility of C-peptide measurement in the care of patients with diabetes

C-peptide is produced in equal amounts to insulin and is the best measure of endogenous insulin secretion in patients with diabetes. Measurement of insulin secretion using C-peptide can be helpful in clinical practice: differences in insulin secretion are fundamental to the different treatment requirements of Type 1 and Type 2 diabetes. This article reviews the use of C-peptide measurement in the clinical management of patients with diabetes, including the interpretation and choice of C-peptide test and its use to assist diabetes classification and choice of treatment. We provide recommendations for where C-peptide should be used, choice of test and interpretation of results. With the rising incidence of Type 2 diabetes in younger patients, the discovery of monogenic diabetes and development of new therapies aimed at preserving insulin secretion, the direct measurement of insulin secretion may be increasingly important. Advances in assays have made C-peptide measurement both more reliable and inexpensive. In addition, recent work has demonstrated that C-peptide is more stable in blood than previously suggested or can be reliably measured on a spot urine sample (urine C-peptide:creatinine ratio), facilitating measurement in routine clinical practice. The key current clinical role of C-peptide is to assist classification and management of insulin-treated patients. Utility is greatest after 3-5 years from diagnosis when persistence of substantial insulin secretion suggests Type 2 or monogenic diabetes. Absent C-peptide at any time confirms absolute insulin requirement and the appropriateness of Type 1 diabetes management strategies regardless of apparent aetiology.

[GADA persistence and detectable C peptide in patients with long standing diabetes mellitus type 1]

OBJECTIVE

The aim of this study was to evaluate if GADA+ and detectable CP had any influence in other autoimmune diseases, glycemic control, and risks of retinopathy in diabetes mellitus type 1 (T1DM) lasting longer than 3 years of duration.

SUBJECTS AND METHODS

Fifty T1DM subjects were interviewed, performed fundoscopic examination, and measured CP before and after glucagon, HbA1C, and GADA.

RESULTS

GADA+ (n = 17) had a higher frequency of other autoimmune diseases when compared to GADA (p = 0.02). Detectable CP was also associated with a higher prevalence of these diseases (p = 0.03), although, retinopathy was not influenced by either one. Detectable CP had no influence in the glycemic control (mean HbA1C) (p = 0.28). However, insulin daily doses were lower in this group (0.62 vs. 0.91 U/kg/day; p = 0.004).

CONCLUSION

Although not recommend as a marker of other autoimmune diseases, GADA+ seems to be not only a pancreatic autoimmunity signal. Detectable CP may also have some promising influence in detecting these diseases. Neither influenced the presence of retinopathy, but insulin daily requirements were smaller when CP was present.

Review: The importance of residual endogenous beta-cell preservation in type 1 diabetes

Achieving tight glycaemic control in type 1 diabetes remains very challenging for patients. However, some individuals retain a degree of endogenous beta-cell function for 5 or more years after diagnosis, and prospective studies confirm that this is associated not only with lower glycated haemoglobin A1c levels, and less hypoglycaemia, but also a reduced incidence of long-term complications. An independent effect of insulin C-peptide may contribute to this beneficial effect. Retention of even small amounts of endogenous beta-cell function for as long as possible should therefore be a key therapeutic goal in type 1 diabetes. Tight glycaemic control from diagnosis has already been shown to help in this regard, and we argue that the introduction of novel immunotherapies which achieve this important goal should be strongly encouraged, even if they fall short of an insulin-free 'cure'.

Preservation of beta-cell function in autoantibody-positive youth with diabetes

OBJECTIVE

To determine the extent of beta-cell function in youth with diabetes and GAD65 and/or IA2 autoantibodies.

RESEARCH DESIGN AND METHODS

Fasting C-peptide levels from 2,789 GAD65- and/or IA2 autoantibody-positive youth aged 1-23 years from the SEARCH for Diabetes in Youth study were used. Preserved beta-cell function was defined on the basis of cut points derived from the Diabetes Control and Complications Trial (DCCT) (fasting C-peptide > or =0.23 ng/ml) and from the U.S. adolescent population of the National Health and Nutrition Examination Survey (NHANES) 5th percentile for fasting C-peptide (> or =1.0 ng/ml). We compared the clinical characteristics between those with and without preserved beta-cell function.

RESULTS

Within the first year of diagnosis, 82.9% of youth had a fasting C-peptide > or =0.23 ng/ml and 31.2% had values > or =1.0 ng/ml. Among those with > or =5 years of diabetes duration, 10.7% had preserved beta-cell function based on the DCCT cutoff and 1.0% were above the 5th percentile of the NHANES population.

CONCLUSIONS

Within the 1st year of diagnosis, four of five youth with autoantibody-positive diabetes have clinically significant amounts of residual beta-cell function and about one-third have fasting C-peptide levels above the 5th percentile of a healthy adolescent population. Even 5 years after diagnosis, 1 of 10 has fasting C-peptide above a clinically significant threshold. These findings have implications for clinical classification of youth with diabetes as well as clinical trials aimed to preserve beta-cell function after diabetes onset.

[C-peptide residual secretion makes difference on type 1 diabetes management?]

Type 1 diabetes is a chronic disease characterized by progressive destruction of the pancreatic beta cells, what leads to insulin deficiency and hyperglycemia. However, a significant secretory function may persist for long periods in a few patients, what is clinically evident through the detection of serum C peptide. This phenomenon might reduce the risk of chronic complications, severe hypoglycemias and allow easier metabolic control. It is possible that these advantages are caused, at least partially, by C peptide itself, acting directly in its target tissues.

Chronic kidney disease in long duration type 1 diabetes lasting more than 50 years

OBJECTIVE

There is evidence that microalbuminuria and overt nephropathy may progress more slowly in long duration (> 20 years) type 1 diabetes (T1DM). To explore this further, we examined the characteristics of chronic kidney disease (CKD) in a large cohort of long duration T1DM in the United Kingdom (UK).

RESEARCH DESIGN AND METHODS

We studied the UK 'Golden Years' cohort--a group of 400 patients from various parts of the UK with T1DM > 50 years duration. Demographic and clinical information were obtained. HbA(1c), lipids, creatinine and urinary albumin-creatinine ratio (ACR) were measured. Microalbuminuria was defined as 2.5-25.0 mg/mmol for males and 3.5-25.0 mg/mmol for females; macroalbuminuria was defined as an ACR > 25.0 mg/mmol for both sexes.

RESULTS

Mean age was 69 years and duration of diabetes 55 years. Nine percent had macroalbuminuria and 27% microalbuminuria. No patient had stage 5 CKD. Microalbuminuria was associated significantly with increased diabetes duration (p = 0.02), male sex (p = 0.02), smoking (p = 0.002), higher HbA(1c) (p < 0.0001), raised triglycerides (p = 0.04), and peripheral vascular disease (PVD) (p < 0.0001). Macroalbuminuria had significant associations with smoking (p = 0.02), raised triglycerides (p = 0.01), raised creatinine (p = 0.02), PVD (p = 0.01) and hypertension (p = 0.01).

CONCLUSIONS

We conclude that microalbuminuria and CKD are common, even at long duration (> 50 years) of T1DM, and have similar characteristics and associations as they do with shorter disease duration. There is a striking absence, however, of stage 5 CKD, but selection bias may be an important confounder since patients with advanced disease may have not survived.

A community-based study of the relationship between insulin resistance/beta-cell dysfunction and diabetic retinopathy among type II diabetics in Kinmen, Taiwan

PURPOSE

To explore whether insulin resistance and beta-cell dysfunction are both related to diabetic retinopathy (DR) in type II diabetics by using a community-based study in Kinmen, Taiwan.

METHODS

A screening program for DR was performed by a panel of ophthalmologists who used ophthalmoscopy and 45 degrees color retinal photographs on dilated pupils to determine a consensus grade of diabetic retinopathy. Screening, which was conducted between 1999 and 2002, involved 971 patients diagnosed with type II diabetes. The Homeostatis Model Assessment (HOMA) method was used to determine insulin resistance and beta-cell dysfunction.

RESULTS

Seven hundred twenty-five diabetics who attended ophthalmological fundus checkups were studied. The overall response rate was 75%. After excluding 10 insulin-treated diabetics, diabetic retinopathy at first eye screening among the remaining 715 diabetics was 18.5%. Based on the multiple logistic regression, DR was found to be strongly related to both baseline insulin resistance (IR) and beta-cell dysfunction regardless of duration of diabetes. The strength of the relationships was maintained after adjustment for confounders. Those who were in the 2nd, 3rd, and 4th quartile of HOMA IR had 1.38 times (95% CI: 0.62-3.05), 2.37 times (95% CI: 1.19-4.69), and 4.16 times (95% CI: 2.15-8.06) the risk for DR compared to that in the 1st quartile, respectively. A reduced risk for DR in relation to HOMA beta-cell dysfunction for the 2nd, 3rd, and 4th quartile were 64% (95% CI: 27%-82%), 82% (95% CI: 58%-92%), and 82% (95% CI: 60%-92%) compared to that in the 1st quartile, respectively.

CONCLUSIONS

Insulin resistance and beta-cell dysfunction are both associated with diabetic retinopathy in type II diabetes.

A community-based epidemiologic study of gender differences in the relationship between insulin resistance/beta-cell dysfunction and diabetic retinopathy among type 2 diabetic patients in Kinmen, Taiwan

PURPOSE

The purpose of this study was to explore whether there were gender differences in the relation of insulin resistance and beta-cell dysfunction to diabetic retinopathy among type 2 diabetic patients.

METHODS

From 1999 to 2002, a screening regimen for diabetic retinopathy was performed by a panel of ophthalmologists using ophthalmoscopy and 45-degree color fundus photography to examine the fundus in a total of 971 type 2 diabetic patients examined between 1991 and 1993 in Kinmen, Taiwan. Seven hundred and twenty-five type 2 diabetic patients (301 males and 424 females) attended ophthalmological fundus checkup.

RESULTS

The response rate in males and females was 71.3 and 77.2%. The proportion of diabetic retinopathy at the first eye screening was 16.3% in males and 20.1% in females. From the multiple logistic regression, the type of diabetes (known cases vs. new cases) was a significant factor of diabetic retinopathy in both males (OR = 3.65, 95% CI: 1.59-8.37) and females (OR = 3.66, 95% CI: 2.01-6.70). Diabetic retinopathy was also strongly affected by the homeostasis model assessment of insulin resistance (HOMA IR) and homeostasis model assessment of beta-cell dysfunction (HOMA beta-cell) (p < 0.0001 for trend test). In males, those who were in the 2nd quartile, 3rd quartile, and 4th quartile of HOMA IR had 4.87 times (95% CI: 1.18-20.11), 6.83 times (95% CI: 1.91-24.46), and 10.15 times (95% CI: 2.42-42.56) the risk for diabetic retinopathy as compared to those in the 1st quartile. There was a reduced risk for diabetic retinopathy in relation to HOMA beta-cell for the 2nd quartile, 3rd quartile, and 4th quartile of 86% (95% CI: 37-97%), 95% (95% CI: 77-99%), and 96% (95% CI: 78-99%) as compared to that in the 1st quartile. Only the 4th quartile had a significant risk (OR = 2.62, 95% CI: 1.17-5.86) for diabetic retinopathy as compared to that in the 1st quartile in females. The reduced risk for diabetic retinopathy found in relation to HOMA beta-cell for the 3rd and 4th quartiles were 66% (95% CI: 6-88%) and 66% (95% CI: 10-87%) as compared to that in the 1st quartile.

CONCLUSIONS

Gender differences in the relationship between insulin resistance/beta-cell dysfunction and diabetic retinopathy were demonstrated in type 2 diabetic patients.

Beta-cell function and the development of diabetes-related complications in the diabetes control and complications trial

In patients with type 1 diabetes, measurement of connecting peptide (C-peptide), cosecreted with insulin from the islets of Langerhans, permits estimation of remaining beta-cell secretion of insulin. In this retrospective analysis to distinguish the incremental benefits of residual beta-cell activity in type 1 diabetes, stimulated (90 min following ingestion of a mixed meal) C-peptide levels at entry in the Diabetes Control and Complications Trial (DCCT) were related to measures of diabetic retinopathy and nephropathy and to incidents of severe hypoglycemia. Based on the analytical sensitivity of the assay (0.03 nmol/l) and study entry criteria, the DCCT subjects were divided into four groups of stimulated C-peptide responses: <or=0.03, 0.04-0.20, 0.21-0.50 nmol/l at entry, and 0.21-0.50 nmol/l at entry and at least 1 year later (sustained C-peptide secretion). Uniformly in the intensive and partially in the conventional DCCT treatment groups, any C-peptide secretion, but especially at higher and sustained levels of stimulated C-peptide, was associated with reduced incidences of retinopathy (both a single three-step change and a repeated three-step change on the Early Treatment of Diabetic Retinopathy Study [ETDRS] scale at the next 6 month visit) and nephropathy (both albuminuria >40 mg/24 h once and repeated at the next annual visit). There were also differences in severe hypoglycemia across C-peptide levels in both treatment groups. In the intensively treated cohort there were essentially identical prevalences of severe hypoglycemia ( approximately 65% of participants) in the first three groups; however, those subjects with mixed-meal stimulated C-peptide level >0.20 nmol/l for at least baseline and the first annual visit in the DCCT experienced a reduced prevalence of approximately 30%. Therefore, even modest levels of beta-cell activity at entry in the DCCT were associated with reduced incidences of retinopathy and nephropathy. Also, continuing C-peptide (insulin) secretion is important in avoiding hypoglycemia (the major complication of intensive diabetic therapy).

Microalbuminuria development in short-term IDDM

To assess risk factors associated with microalbuminuria development in short-term evolution insulin-dependent diabetes mellitus (IDDM) we undertake a cross-sectional study with retrospective examination of the 34 patients diagnosed with IDDM between 1982 and 1983 and followed up for at least 7 years in an outpatient endocrinology clinic.

MAIN MEASURES

(1) At IDDM diagnosis: age, sex, parameters of metabolic control (fasting glycemia, HbA1), islet-cell antibodies, insulin autoantibodies, endogenous insulin secretion (EIS) and HLA type. (2) At 1 year evolution: EIS re-evaluation. (3) From IDDM diagnosis (every 3-4 month): body mass index, insulin schedule and dose, and parameters of metabolic control. (4) At 7-year evolution: 24-h urinary albumin excretion (UAE) and arterial blood pressure measurements on two consecutive outpatient controls. Microalbuminuria was defined as UAE above 30 micrograms/min on the two consecutive measurements. After 7-year follow-up, 8 (23.5%; 95% Cl: 9.3 to 37.7%) patients developed microalbuminuria. Their metabolic control was worse (7 years mean HbA1: 10.7 vs. 9.7%; P = 0.04) and 1 year EIS lower (1.9 vs. 7.6 ng/ml.10 min; P = 0.03) than in normoalbuminuric patients. They also had higher prevalence of 'high-normal' arterial blood pressure (P = 0.03) and diabetic retinopathy (P = 0.01) than normoalbuminuric patients did. Stepwise logistic regression analysis showed that diabetic retinopathy was the only independent and significant risk factor related to microalbuminuria development (P = 0.01). We conclude that in subjects with short-term evolution IDDM, microalbuminuria development was associated with glycemic control, EIS and arterial blood pressure levels, however the strongest association was found with diabetic retinopathy occurrence.

Pancreatic B-cell function in relation to diabetic retinopathy in Asian Indian NIDDM patients

Pancreatic B-cell function in relation to diabetic retinopathy was studied in 195 NIDDM patients with long-standing diabetes. Background diabetic retinopathy (BDR) was present in 95 (48.7%) and proliferative retinopathy (PDR) in 17 (8.7%) of the subjects. There was no significant difference between the BDR, PDR, and non-retinopathy groups with respect to age, age at diagnosis of diabetes and HbA1 values. Mean duration of diabetes was higher in the PDR group (p less than 0.05). Serum C-peptide values showed no correlation with the presence of retinopathy or with the duration of diabetes. The C-peptide values were widely scattered in patients with BDR and PDR showing no association between pancreatic B-cell reserve and occurrence or severity of retinopathy in NIDDM patients. Thus, decreased pancreatic B-cell reserve does not appear to be a risk factor for diabetic retinopathy in NIDDM patients.

C-peptide: an index of insulin secretion

Insight into the natural history of beta cell function in IDDM patients obtained by C-peptide measurements is reviewed. It is argued that residual insulin secretion of metabolic importance is present in all IDDM patients during the initial course of the disease. After some months, beta cell function reaches its maximum; thereafter it declines at different rates dependent on the age at onset of diabetes and, possibly, on the presence of ICA and HLA-antigens. As many as 15% of IDDM patients retain life-long beta cell function that persists at approximately 10% of that observed in nondiabetic individuals. The residual endogenous insulin secretion is characterized by reduced capacity, as well as abnormal insulin secretory kinetics; these defects in residual insulin secretion can be modulated by changes in metabolic regulation as well as by immunosuppression during the initial course of the disease.