Biomarkers in diabetes:hemoglobin A1c, vascular and tissue markers

Biomarkers are conventionally defined as "biological molecules that represent health and disease states." They typically are measured in readily available body fluids (blood or urine), lie outside the causal pathway, are able to detect subclinical disease, and are used to monitor clinical and subclinical disease burden and response to treatments. Biomarkers can be "direct" endpoints of the disease itself, or "indirect" or surrogate endpoints. New technologies (such as metabolomics, proteomics, genomics) bring a wealth of opportunity to develop new biomarkers. Other new technologies enable the development of nonmolecular, functional, or biophysical tissue-based biomarkers. Diabetes mellitus is a complex disease affecting almost every tissue and organ system, with metabolic ramifications extending far beyond impaired glucose metabolism. Biomarkers may reflect the presence and severity of hyperglycemia (ie, diabetes itself) or the presence and severity of the vascular complications of diabetes. Illustrative examples are considered in this brief review. In blood, hemoglobin A1c (HbA1c) may be considered as a biomarker for the presence and severity of hyperglycemia, implying diabetes or prediabetes, or, over time, as a "biomarker for a risk factor," ie, hyperglycemia as a risk factor for diabetic retinopathy, nephropathy, and other vascular complications of diabetes. In tissues, glycation and oxidative stress resulting from hyperglycemia and dyslipidemia lead to widespread modification of biomolecules by advanced glycation end products (AGEs). Some of these altered species may serve as biomarkers, whereas others may lie in the causal pathway for vascular damage. New noninvasive technologies can detect tissue damage mediated by AGE formation: these include indirect measures such as pulse wave analysis (a marker of vascular dysfunction) and more direct markers such as skin autofluorescence (a marker of long-term accumulation of AGEs). In the future, we can be optimistic that new blood and tissue-based biomarkers will enable the detection, prevention, and treatment of diabetes and its complications long before overt disease develops.

Are gatekeepers to renal services referring patients equitably?

Objective: Patients with chronic kidney disease (CKD) benefit from specialist interventions to retard progression of renal failure and prevent cardiovascular events. Certain patient groups have poor access to specialist renal services when dialysis is required. This study used a population-based laboratory database to investigate access to and timeliness of referral to renal specialists relatively early in the course of the disease.

Methods: All tests for serum creatinine and haemoglobin (Hb) A1c in Northern Ireland in a two-year period (2001 and 2002) were retrieved for 345,441 adults. Of these, 16,856 patients had at least one serum creatinine level above 150 µmol/L in 2001 not deemed to be due to acute renal failure (crude prevalence 1.42%). This cohort was followed until the end of 2002 and the differences in the time to referral to a specialist were assessed using Cox's proportional hazards regression.

Results: Diabetic patients, older patients and those living in deprived areas were significantly more likely to have serum creatinine testing, compared with non-diabetic, younger and those living in more affluent areas. Delays in referral to renal specialists for patients with raised serum creatinine levels were significantly shorter among diabetic patients, women, younger individuals, those living in rural areas, those living close to renal centres and those living in deprived areas. Overall, only 19% of diabetic patients and 6% of non-diabetic patients who had CKD had seen a renal specialist within 12 months of their index creatinine test.

Conclusion: Contrary to other diseases, disadvantaged patients do not seem to be under-investigated for renal disease compared with their more affluent neighbours and are generally referred earlier for specialist assessment. However, the absolute rate of timely specialist assessment is low. Recent changes in referral criteria for CKD will result in more referrals and will have serious resource implications. Opportunities for health gain among patients with declining renal function are being missed, particularly among the old and those living furthest from specialist centres.

Optimal glycaemic control, pre-eclampsia and gestational hypertension in women with type 1 diabetes in the Diabetes and Pre-Eclampsia Intervention Trial

OBJECTIVE
To assess the relationship between glycemic control, pre-eclampsia, and gestational hypertension in women with type 1 diabetes.

RESEARCH DESIGN AND METHODS
Pregnancy outcome (pre-eclampsia or gestational hypertension) was assessed prospectively in 749 women from the randomized controlled Diabetes and Pre-eclampsia Intervention Trial (DAPIT). HbA1c (A1C) values were available up to 6 months before pregnancy (n = 542), at the first antenatal visit (median 9 weeks) (n = 721), at 26 weeks’ gestation (n = 592), and at 34 weeks’ gestation (n = 519) and were categorized as optimal (<6.1%: referent), good (6.1–6.9%), moderate (7.0–7.9%), and poor (=8.0%) glycemic control, respectively.

RESULTS
Pre-eclampsia and gestational hypertension developed in 17 and 11% of pregnancies, respectively. Women who developed pre-eclampsia had significantly higher A1C values before and during pregnancy compared with women who did not develop pre-eclampsia (P < 0.05, respectively). In early pregnancy, A1C =8.0% was associated with a significantly increased risk of pre-eclampsia (odds ratio 3.68 [95% CI 1.17–11.6]) compared with optimal control. At 26 weeks’ gestation, A1C values =6.1% (good: 2.09 [1.03–4.21]; moderate: 3.20 [1.47–7.00]; and poor: 3.81 [1.30–11.1]) and at 34 weeks’ gestation A1C values =7.0% (moderate: 3.27 [1.31–8.20] and poor: 8.01 [2.04–31.5]) significantly increased the risk of pre-eclampsia compared with optimal control. The adjusted odds ratios for pre-eclampsia for each 1% decrement in A1C before pregnancy, at the first antenatal visit, at 26 weeks’ gestation, and at 34 weeks’ gestation were 0.88 (0.75–1.03), 0.75 (0.64–0.88), 0.57 (0.42–0.78), and 0.47 (0.31–0.70), respectively. Glycemic control was not significantly associated with gestational hypertension.

CONCLUSIONS
Women who developed pre-eclampsia had significantly higher A1C values before and during pregnancy. These data suggest that optimal glycemic control both early and throughout pregnancy may reduce the risk of pre-eclampsia in women with type 1 diabetes.

Clinical and technical factors associated with skin intrinsic fluorescence in subjects with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study

The Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications(EDIC) studies have established multiyear mean hemoglobin A1c (HbA1c) as predictive of microvascular complications in persons with type 1 diabetes. However, multiyear mean HbA1c is not always available in the clinical setting. Skin advanced glycation end products (AGEs) are thought to partially reflect effects of hyperglycemia over time, and measurement of skin AGEs might be a surrogate for multiyear mean HbA1c. As certain AGEs fluoresce and skin fluorescence has been demonstrated to correlate with the concentration of skin AGEs, noninvasive measurement by skin intrinsic fluorescence(SIF) facilitates the exploration of the association of mean HbA1c and other clinical/technical factors with SIF using the detailed phenotypic database available in DCCT/EDIC.

Apolipoprotein C-III protein concentrations and gene polymorphisms in type 1 diabetes:associations with lipoprotein subclasses

Serum apolipoprotein C-III (apoCIII) concentration and apoCIII gene polymorphisms have been shown to be a risk factor for cardiovascular disease; however, the underlying mechanisms remain unclear. In addition, no studies have been performed that address these issues in type 1 diabetes. The current study investigated apoCIII protein and apoCIII gene variation in a normotriglyceridemic (82 +/- 57 mg/dL) population of patients with type 1 diabetes, the Diabetes Control and Complications Trial/Epidemiology of Diabetes Intervention and Complications (DCCT/EDIC) cohort. Blood samples were obtained in 409 patients after an overnight fast. Serum apoCIII concentration was highly correlated with multiple changes in lipids and lipoproteins that resulted in an adverse cardiovascular disease risk profile. Higher apoCIII concentrations were associated (P <.0001) with increased triglycerides (r = 0.78), total (r = 0.61) and low-density lipoprotein (LDL) (r = 0.40) cholesterol, apoA-I (r = 0.26), and apoB (r = 0.50), and these relationships persisted after controlling for age, gender, body mass index (BMI), and hemoglobin A1c (HbA1c). Nuclear magnetic resonance (NMR) lipoprotein subclass analyses demonstrated that apoCIII was correlated with an increase in very-low-density lipoprotein (VLDL) subclasses (P = .0001). There also was a highly significant positive relationship between serum apoCIII concentration and the LDL particle concentration in both men (r = 0.49, P = .001) and women (r = 0.40, P = .001), and a highly significant negative relationship between serum apoCIII levels and average LDL particle size in both men (r = -0.37, P = .001) and women (r = -0.22, P = .001) due primarily to an augmentation in the small L1 subclass (r = 0.42, P = .0001). Neither the T(-455) --> C polymorphism affecting an insulin response element in the apoCIII gene promoter nor a SacI polymorphism in the 3'UTR were associated with any alterations in circulating apoCIII concentrations, serum lipids, apolipoprotein concentrations, lipoprotein composition, or parameters measured by NMR lipoprotein subclass analyses. In summary, elevated apoCIII concentration was associated with risk factors for cardiovascular disease in normolipidemic type 1 diabetic patients through associated changes in lipoprotein subfraction distributions, which were independent of apoCIII genotype.

Glycosylation of low density lipoprotein in patients with type 1 (insulin-dependent) diabetes:correlations with other parameters of glycaemic control

Glycosylation of low density lipoproteins obtained from 16 patients with Type 1 (insulin-dependent) diabetes and from 16 age-, sex-, and race-matched controls, was determined. The diabetic patients were normolipaemic and were in good or fair glycaemic control. Eleven patients performed home blood glucose monitoring. Glycosylation of low density lipoproteins in the diabetic patients was significantly higher (p less than 0.001) than in the control subjects, and was significantly correlated with haemoglobin A1c, (p less than 0.01), glycosylation of plasma proteins, (p less than 0.001), and mean home blood glucose, (p less than 0.01). This study confirms that, in diabetic patients, increased glycosylation of low density lipoprotein occurs to an extent which correlates closely with other commonly used indices of glycaemic control.

Evaluation of an algorithm to guide patients with type 1 diabetes treated with continuous subcutaneous insulin infusion on how to respond to real-time continuous glucose levels:A randomized controlled trial

OBJECTIVE - To evaluate an algorithm guiding responses of continuous subcutaneous insulin infusion (CSII)-treated type 1 diabetic patients using real-time continuous glucose monitoring (RT-CGM). RESEARCH DESIGN AND METHODS - Sixty CSII-treated type 1 diabetic participants (aged 13-70 years, including adult and adolescent subgroups, with A1C =9.5%) were randomized in age-, sex-, and A1C-matched pairs. Phase 1 was an open 16-week multicenter randomized controlled trial. Group A was treated with CSII/RT-CGM with the algorithm, and group B was treated with CSII/RT-CGM without the algorithm. The primary outcome was the difference in time in target (4-10 mmol/l) glucose range on 6-day masked CGM. Secondary outcomes were differences in A1C, low (=3.9 mmol/l) glucose CGM time, and glycemic variability. Phase 2 was the week 16-32 follow-up. Group A was returned to usual care, and group B was provided with the algorithm. Glycemia parameters were as above. Comparisons were made between baseline and 16 weeks and 32 weeks. RESULTS - In phase 1, after withdrawals 29 of 30 subjects were left in group A and 28 of 30 subjects were left in group B. The change in target glucose time did not differ between groups. A1C fell (mean 7.9% [95% CI 7.7-8.2to 7.6% [7.2-8.0]; P <0.03) in group A but not in group B (7.8% [7.5-8.1] to 7.7 [7.3-8.0]; NS) with no difference between groups. More subjects in group A achieved A1C =7% than those in group B (2 of 29 to 14 of 29 vs. 4 of 28 to 7 of 28; P = 0.015). In phase 2, one participant was lost from each group. In group A, A1C returned to baseline with RT-CGM discontinuation but did not change in group B, who continued RT-CGM with addition of the algorithm. CONCLUSIONS - Early but not late algorithm provision to type 1 diabetic patients using CSII/RT-CGM did not increase the target glucose time but increased achievement of A1C =7%. Upon RT-CGM cessation, A1C returned to baseline. © 2010 by the American Diabetes Association.

Serum apolipoprotein AI and B are stronger biomarkers of diabetic retinopathy than traditional lipids

OBJECTIVE - To describe and compare the associations of serum lipoproteins and apolipoproteins with diabetic retinopathy. RESEARCH DESIGN AND METHODS - This was a cross-sectional study of 224 diabetic patients (85 type 1 and 139 type 2) froma diabetes clinic. Diabetic retinopathy was graded from fundus photographs according to the Airlie House Classification system and categorized into mild, moderate, and vision-threatening diabetic retinopathy (VTDR). Serum traditional lipids (total, LDL, non-HDL, and HDL cholesterol and triglycerides) and apolipoprotein AI (apoAI), apolipoprotein B (apoB), and the apoB-to-apoAI ratio were assessed. RESULTS - Diabetic retinopathy was present in 133 (59.4%) individuals. After adjustment for age, sex, diabetes duration, A1C, systolic blood pressure, and diabetes medications, the HDL cholesterol level was inversely associated with diabetic retinopathy (odds ratio 0.39 [95% CI 0.16-0.94], highest versus lowest quartile; P = 0.017). The ApoAI level was inversely associated with diabetic retinopathy (per SD increase, 0.76 [95% CI 0.59-0.98]), whereas apoB (per SD increase, 1.31 [1.02-1.68]) and the apoB-to-apoAI ratio (per SD increase, 1.48 [1.13-1.95]) were positively associated with diabetic retinopathy. Results were similar for mild to moderate diabetic retinopathy and VTDR. Traditional lipid levels improved the area under the receiver operating curve by 1.8%, whereas apolipoproteins improved the area by 8.2%. CONCLUSIONS - ApoAI and apoB and the apoB-to-apoAI ratio were significantly and independently associated with diabetic retinopathy and diabetic retinopathy severity and improved the ability to discriminate diabetic retinopathy by 8%. Serum apolipoprotein levels may therefore be stronger biomarkers of diabetic retinopathy than traditional lipid measures. © 2011 by the American Diabetes Association.

Retinal vascular geometry predicts incident renal dysfunction in young people with type 1 diabetes

OBJECTIVE - To examine the relationship between retinal vascular geometry parameters and development of incident renal dysfunction in young people with type 1 diabetes. RESEARCH DESIGN AND METHODS - This was a prospective cohort study of 511 adolescents with type 1 diabetes of at least 2 years duration, with normal albumin excretion rate (AER) and no retinopathy at baseline while attending an Australian tertiary-care hospital. AER was quantified using three overnight, timed urine specimen collections and early renal dysfunction was defined as AER >7.5 µg/min. Retinal vascular geometry (including length-to-diameter ratio [LDR] and simple tortuosity [ST]) was quantified from baseline retinal photographs. Generalized estimating equations were used to examine the relationship between incident renal dysfunction and baseline venular LDR and ST, adjusting for age, diabetes duration, glycated hemoglobin (A1C), blood pressure (BP), BMI, and cholesterol. RESULTS - Diabetes duration at baseline was 4.8 (IQR 3.3-7.5) years. After amedian 3.7 (2.3-5.7) years follow-up, 34% of participants developed incident renal dysfunction. In multivariate analysis, higher retinal venular LDR (odds ratio 1.7, 95% CI 1.2-2.4; quartile 4 vs. 1-3) and lower venular ST (1.6, 1.1-2.2; quartile 1 vs. 2-4) predicted incident renal dysfunction. CONCLUSIONS - Retinal venular geometry independently predicted incident renal dysfunction in young people with type 1 diabetes. These noninvasive retinal measures may help to elucidate early mechanistic pathways for microvascular complications. Retinal venular geometry may be a useful tool to identify individuals at high risk of renal disease early in the course of diabetes. © 2012 by the American Diabetes Association.

Glycemic targets in the second and third trimester of pregnancy for women with type 1 diabetes

OBJECTIVE: To assess the relationship between second and third trimester glycemic control and adverse outcomes in pregnant women with type 1 diabetes, as uncertainty exists about optimum glycemic targets.

RESEARCH DESIGN AND METHODS: Pregnancy outcomes were assessed prospectively in 725 women with type 1 diabetes from the Diabetes and Pre-eclampsia Intervention Trial. HbA1c (A1C) values at 26 and 34 weeks' gestation were categorized into five groups, the lowest, <6.0% (42 mmol/mol), being the reference. Average pre- and postprandial results from an eight-point capillary glucose profile the previous day were categorized into five groups, the lowest (preprandial <5.0 mmol/L and postprandial <6.0 mmol/L) being the reference.

RESULTS: An A1C of 6.0-6.4% (42-47 mmol/mol) at 26 weeks' gestation was associated with a significantly increased risk of large for gestational age (LGA) (odds ratio 1.7 [95% CI 1.0-3.0]) and an A1C of 6.5-6.9% (48-52 mmol/mol) with a significantly increased risk of preterm delivery (odds ratio 2.5 [95% CI 1.3-4.8]), pre-eclampsia (4.3 [1.7-10.8]), need for a neonatal glucose infusion (2.9 [1.5-5.6]), and a composite adverse outcome (3.2 [1.3-8.0]). These risks increased progressively with increasing A1C. Results were similar at 34 weeks' gestation. Glucose data showed less consistent trends, although the risk of a composite adverse outcome increased with preprandial glucose levels between 6.0 and 6.9 mmol/L at 34 weeks (3.3 [1.3-8.0]).

CONCLUSIONS: LGA increased significantly with an A1C ≥6.0 (42 mmol/mol) at 26 and 34 weeks' gestation and with other adverse outcomes with an A1C ≥6.5% (48 mmol/mol). The data suggest that there is clinical utility in regular measurement of A1C during pregnancy.

Cord blood adipokines, neonatal anthropometrics and postnatal growth in offspring of Hispanic and Native American women with diabetes mellitus

BACKGROUND: Offspring of women with diabetes mellitus (DM) during pregnancy have a risk of developing metabolic disease in adulthood greater than that conferred by genetics alone. The mechanisms responsible are unknown, but likely involve fetal exposure to the in utero milieu, including glucose and circulating adipokines. The purpose of this study was to assess the impact of maternal DM on fetal adipokines and anthropometry in infants of Hispanic and Native American women.

METHODS: We conducted a prospective study of offspring of mothers with normoglycemia (Con-O; n = 79) or type 2 or gestational DM (DM-O; n = 45) pregnancies. Infant anthropometrics were measured at birth and 1-month of age. Cord leptin, high-molecular-weight adiponectin (HMWA), pigment epithelium-derived factor (PEDF) and C-peptide were measured by ELISA. Differences between groups were assessed using the Generalized Linear Model framework. Correlations were calculated as standardized regression coefficients and adjusted for significant covariates.

RESULTS: DM-O were heavier at birth than Con-O (3.7 ± 0.6 vs. 3.4 ± 0.4 kg, p = 0.024), but sum of skinfolds (SSF) were not different. At 1-month, there was no difference in weight, SSF or % body fat or postnatal growth between groups. Leptin was higher in DM-O (20.1 ± 14.9 vs. 9.5 ± 9.9 ng/ml in Con-O, p < 0.0001). Leptin was positively associated with birth weight (p = 0.0007) and SSF (p = 0.002) in Con-O and with maternal hemoglobin A1c in both groups (Con-O, p = 0.023; DM-O, p = 0.006). PEDF was positively associated with birth weight in all infants (p = 0.004). Leptin was positively associated with PEDF in both groups, with a stronger correlation in DM-O (p = 0.009). At 1-month, HMWA was positively associated with body weight (p = 0.004), SSF (p = 0.025) and % body fat (p = 0.004) across the cohort.

CONCLUSIONS: Maternal DM results in fetal hyperleptinemia independent of adiposity. HMWA appears to influence postnatal growth. Thus, in utero exposure to DM imparts hormonal differences on infants even without aberrant growth.