Renal function in long-duration type I diabetes

Discoveries from the study of longstanding type 1 diabetes

Award programmes that acknowledge the remarkable accomplishments of long-term survivors with type 1 diabetes have naturally evolved into research programmes to determine the factors associated with survivorship and resistance to chronic complications. In this review, we present an overview of the methodological sources of selection bias inherent in survivorship research (selection of those with early-onset diabetes, incidence-prevalence bias and bias from losses to follow-up in cohort studies) and the breadth and depth of literature focusing on this special study population. We focus on the learnings from the study of longstanding type 1 diabetes on discoveries about the natural history of insulin production loss and microvascular complications, and mechanisms associated with them that may in future offer therapeutic targets. We detail descriptive findings about the prevalence of preserved insulin production and resistance to complications, and the putative mechanisms associated with such resistance. To date, findings imply that the following mechanisms exist: strategies to maintain or recover beta cells and their function; activation of specific glycolytic enzymes such as pyruvate kinase M2; modification of AGE production and processing; novel mechanisms for modification of renin-angiotensin-aldosterone system activation, in particular those that may normalise afferent rather than efferent renal arteriolar resistance; and activation and modification of processes such as retinol binding and DNA damage checkpoint proteins. Among the many clinical and public health insights, research into this special study population has identified putative mechanisms that may in future serve as therapeutic targets, knowledge that likely could not have been gained without studying long-term survivors.

Gender difference in albuminuria and ischemic heart disease in type 2 diabetes

OBJECTIVE

The value of urinary albumin excretion in the prediction of myocardial ischemia in men and women with type 2 diabetes is not well understood. We questioned whether gender influences the albuminuria-ischemic heart disease relationship in patients with type 2 diabetes.

METHODS

We designed a matched case-control study of 926 patients with albuminuria (cases) and 926 age and body mass index matched patients without albuminuria (controls). Ischemic heart disease was defined as the presence of (1) history of angina pectoris or angina equivalent symptoms and critical care unit admission, (2) myocardial infarction and/or electrocardiographic evidence of Q-wave myocardial infarction, (3) coronary revascularization and/or stenting, (4) positive myocardial single-photon emission computed tomography scan, (5) ischemic ST-segment or T-wave changes, and (6) positive stress testing.

RESULTS

Patients with albuminuria had a lower glomerular filtration rate and a longer diabetes duration than patients without albuminuria. In the group of cases, there were a greater number of men with ischemic heart disease (120 of 370; 32.4%) compared to women (97 of 559; 17.4%) (P<0.001). The odds ratio of having ischemic heart disease according to the presence or absence of albuminuria was 1.25 [95% CI: 1.01-1.56] (P<0.05) in all studied populations, 0.79 [95% CI: 0.51-1.21] (P=0.14) in women, and 2.84 [95% CI: 1.68-4.79] (P<0.001) in men. We showed that diabetes duration, high-density lipoprotein, low-density lipoprotein, and hemoglobin A(1c) influence albuminuria in women, while diabetes duration, fasting blood sugar, and diastolic blood pressure influence albuminuria in men.

CONCLUSIONS

Men with albuminuria are at increased risk of ischemic heart disease compared to women. This may be related to the role of high-density lipoprotein on the albuminuria-gender relationship.

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.

Characteristics of Type 1 diabetes of over 50 years duration (the Golden Years Cohort)

BACKGROUND

Type 1 diabetes mellitus is associated with high levels of premature morbidity and mortality. Prolonged survival is possible, however, and some patients appear to be protected from the long-term complications of this condition.

METHODS

Diabetes UK awards medals to patients who have had Type 1 diabetes for 50 years or more. By examining medal-holders, we have established the clinical and biochemical features of a group of 400 subjects (54% male) with Type 1 diabetes of long duration.

RESULTS

Mean age of the subjects was 68.9 years and mean age-at-onset of diabetes 13.7 years. Features of long duration diabetes in this cohort include normal body mass (mean BMI 25.0 kg m-2), low insulin dose (mean 0.52 units kg-2) and greatly elevated HDL-cholesterol (mean 1.84 mmol/l). Mean HbA1c was 7.6% (normal range 3.8-5.0%) and no patient had a normal HbA1c at the time of venesection. As a group, they have long-lived parents and consume moderate amounts of alcohol. Medical contact has often been sporadic. A significant proportion (29%) were taking anti-hypertensive medication. Screening for micro- and macroalbuminuria was positive in 35.7%.

CONCLUSIONS

Patients with long-duration (> 50 years) Type 1 diabetes are relatively protected from clinical diabetic nephropathy and large vessel disease; our data are consistent with protection possibly being genetically determined in part via elevated HDL-cholesterol levels. An abnormal urinary albumin/creatinine ratio is common in these patients, despite their low risk of significant renal deterioration; this may have implications for microalbuminuria screening programmes.

Microalbuminuria and mortality in long-duration type 1 diabetes

OBJECTIVE

Microalbuminuria is a recognized risk factor for increased mortality and renal failure in type 1 diabetes. Whether it remains a powerful predictor in patients with a long duration of type 1 diabetes is not known. We ascertained the prognostic significance of abnormal urinary albumin excretion in a cohort of patients with at least 30 years of type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 190 patients with a disease duration of type 1 diabetes of at least 30 years with baseline and 5 years of follow-up.

RESULTS

At baseline 66% were normoalbuminuric, and at 5 years 11% of this cohort had died. Of the 22% who were microalbuminuric at baseline, 26% had died, and of the 8% with persistent proteinuria at baseline, 44% had died. Of the 4% with end-stage renal failure at baseline, 71% had died within 5 years. Death was attributable to a cardiovascular cause in two-thirds of the cases in all groups.

CONCLUSIONS

Even in those with a long duration of type 1 diabetes, the presence of abnormal urinary excretion remains a powerful predictor of increased mortality.

Significance of microalbuminuria in long-duration type 1 diabetes

OBJECTIVE

The value of microalbuminuria (MA) in predicting renal disease and premature mortality in longer duration type 1 diabetes is unclear.

RESEARCH DESIGN AND METHODS

We followed 135 patients with long-standing type 1 diabetes (>30 years' duration) over a 7-year period, recording albuminuria and other clinical variables. Vital status was ascertained and cause of death was recorded.

RESULTS

A total of 27 of 135 patients (20%) died during the follow-up period. Patients with MA (10 of 30, 33.3%) or proteinuria (5 of 6, 83.3%) at initial examination were more likely to die during follow-up than patients who had normal albumin excretion at baseline (12 of 99, 12%; chi(2) for trend 21.9, P < 0.0001). The presence of abnormal albumin excretion and low BMI were independent risk factors of premature death. The causes of death were similar in patients with normal and abnormal urine albumin excretion. A total of 24.4% of initially normoalbuminuric survivors developed MA, and persistent proteinuria developed in 3.5%. Progressors had significantly higher albumin excretion rate at baseline compared with those who remained normoalbuminuric: 9.0 microg/min (3.8-18) vs. 4.0 microg/min (0.4-17.5); P < 0.001. A total of 21% of patients with MA at baseline reverted to normoalbuminuria, and persistent proteinuria developed in 32%. The likelihood of progression to persistent proteinuria was significantly greater in those with baseline MA compared with those with normal albumin excretion (P < 0.001).

CONCLUSIONS

Even in long-standing type 1 diabetes of >30 years' duration, MA and proteinuria predict all-cause mortality. MA is a good predictor of persistent proteinuria.

Smoking is associated with renal impairment and proteinuria in the normal population: the AusDiab kidney study. Australian Diabetes, Obesity and Lifestyle Study

BACKGROUND

Smoking has been associated with the prevalence, development, and progression of kidney disease. The effect of smoking on kidney function in the healthy population is unclear. We examined the relationship between smoking and indicators of kidney damage in a healthy population without impaired fasting glucose levels, impaired glucose tolerance, diabetes mellitus, or hypertension.

METHODS

This is a randomly selected, population-based, cross-sectional study of 11,247 Australian adults. Smoking status was determined by questionnaire. Subjects were tested for indicators of kidney damage: renal impairment by Cockcroft-Gault-estimated glomerular filtration rate less than 60 mL/min/1.73 m2 and proteinuria by urine protein-creatinine ratio of 0.20 mg/mg or greater.

RESULTS

After adjusting for potential confounding factors, smoking was significantly associated with renal impairment in men with an odds ratio of 3.59, but not in women. Smoking was significantly associated with proteinuria in subjects with high-normal systolic blood pressure, with odds ratios ranging from 3.64 at 131.5 mm Hg to 5.76 at 139.5 mm Hg, and in subjects with high-normal 2-hour glucose levels, with odds ratios ranging from 1.76 at 7.0 mmol/L to 10.84 at 7.7 mmol/L. Lifetime exposure, but not current level of smoking, correlated with lower estimated glomerular filtration rate and greater urine protein-creatinine ratio.

CONCLUSION

Smoking is associated with renal impairment and proteinuria in a population without hypertension or abnormal glucose metabolism. A dose-response relationship was found between cumulative amount of smoking and indicators of kidney damage. In conjunction with other studies and plausible biological mechanisms, this study suggests that smoking may cause kidney damage, even in a healthy population.

Cigarette smoking: an important renal risk factor - far beyond carcinogenesis

In recent years, it has become apparent that smoking has a negative impact on renal function, being one of the most important remediable renal risk factors. It has been clearly shown that the risk for high-normal urinary albumin excretion and microalbuminuria is increased in smoking compared to non-smoking subjects of the general population. Data from the Multiple Risk Factor Intervention Trial (MRFIT) indicate that at least in males, smoking increases the risk to reach end-stage renal failure. Smoking is particularly "nephrotoxic" in older subjects, subjects with essential hypertension and patients with preexisting renal disease. Of interest, the magnitude of the adverse renal effect of smoking seems to be independent of the underlying renal disease. Death-censored renal graft survival is decreased in smokers, indicating that smoking also damages the renal transplant. Cessation of smoking has been show to reduce the rate of progression of renal failure both in patients with renal disease or a renal transplant. The mechanisms of smoking-induced renal damage are only partly understood and comprise acute hemodynamic (e.g., increase in blood pressure and presumably intraglomerular pressure) and chronic effects (e.g., endothelial cell dysfunction). Renal failure per se leads to an increased cardiovascular risk. The latter is further aggravated by smoking. Particularly survival of smokers with diabetes mellitus on hemodialysis is abysmal. In the present review article the current state of knowledge about the renal risks of smoking is reviewed. It is the aim of the article to point out that smoking not only increases the risk of renal cell carcinoma or uroepithelial cell carcinoma, but also the risk of a faster decline of renal function. The latter is a relatively new negative aspect which has not been widely recognized.

Near-normal urinary albumin concentrations predict progression to diabetic nephropathy in Type 1 diabetes mellitus

AIMS

To determine urinary albumin concentrations that predict progression to diabetic nephropathy and sight-threatening diabetic retinopathy and identify baseline parameters associated with progression.

METHODS

One thousand two hundred and one Type 1 diabetic patients aged 35 years or younger at diagnosis attending six hospital diabetes clinics in Scotland and included on the Royal College of Physicians of Edinburgh Diabetes Register were followed for a median (interquartile range) of 4.0 (2.5-5.5) years. Diabetic nephropathy was defined as the geometric mean of two consecutive urinary albumin values > 200 mg/l or a single value > 1,000 mg/l. Retinopathy was defined as clinician-determined maculopathy or proliferative retinopathy.

RESULTS

Forty-six patients developed nephropathy (4%) and 98 retinopathy (8%). Cox proportional hazards analyses demonstrated that a baseline urinary albumin concentration above 7.4 mg/l, longer duration of diabetes and higher HbA1c levels predicted the development of nephropathy. Higher baseline urinary albumin concentrations were the most powerful predictor for the development of nephropathy. Longer duration of diabetes, baseline blood pressure > 140/90 mmHg and higher HbA1c levels all predicted the development of sight-threatening retinopathy whereas baseline urinary albumin concentration did not.

CONCLUSIONS

Elevation of urinary albumin concentration just above the normal range is associated with an increased risk of developing diabetic nephropathy. Identifying patients with any abnormalities of urinary albumin excretion will provide a clear rationale for early therapeutic interventions.

Microalbuminuria in diabetes

Microalbuminuria is still the only early abnormality of the diabetic kidney that has an established prognostic value. Microalbuminuria evolves into clinical nephropathy and renal failure in a majority of cases of insulin-dependent diabetic patients, and is defined by the detection of urinary albumin excretion rates of 20-200 microg/min in timed urine collections. The occurrence of microalbuminuria at rates of 5-27 % of non-proteinuric patients and cost-benefit considerations justify the screening for microalbuminuria in diabetic outpatient clinics. Both near-normalisation of glycaemic control and treatment with ACE-inhibitors are indicated in patients with insulin-dependent diabetes to correct the progression of micro- to macroalbuminuria. Other therapeutic perspectives are being considered, but the current notion that the available therapies may not arrest the course of nephropathy at this stage suggests that earlier interventions may be required. Prevention of microalbuminuria and overt nephropathy may require a primary approach to the subset of patients with a genetic predisposition to this complication, and several studies (candidate gene or genomic scan with microsatellite probes) now address the chromosomal loci and the nature of the genes that may be involved.

Nephropathy and hypertension in diabetes

The treatment of the patient with diabetes, with or without hypertension, is complex and challenging. Hyperglycemic treatment should ideally not only control blood glucose, but also prevent the chronic complications and associated metabolic derangements that can lead to increased morbidity and mortality. Hypertensive treatment should not only decrease blood pressure, but also reduce the risk of macrovascular and microvascular disease. The use of antihypertensive agents that improve insulin resistance, dyslipidemia, glycemic control, and nephropathy is preferred whenever possible. The real key to success in the care of the hypertensive diabetic patient is adequate screening and appropriate, early treatment. Currently, there is ample evidence to support the use of intensive management with the goal of near-normalization of blood glucose levels in most patients with diabetes. Similarly, aggressive treatment of hypertension is the current standard. Accomplishing these goals helps to prevent the development of chronic diabetic complications, including nephropathy. ESRD need not be the inevitable outcome for individuals with early diabetic nephropathy. Interventions currently available that are targeted at the known modifiable risk factors underlying the development and progression of diabetic nephropathy offer the best hope for reducing the incidence and severity of this complication. Prevention of the complications of diabetes, including nephropathy, must be the goal for the future on behalf of all those who now have diabetes.