Allan Kofoed-Enevoldsen

Albuminuria reflects widespread vascular damage

SummaryAlbuminuria in Type 1 (insulin-dependent) diabetes is not only an indication of renal disease, but a new, independent risk-marker of proliferative retinopathy and macroangiopathy. The coincidence of generalised vascular dysfunction and albuminuria, advanced mesangial expansion, proliferative retinopathy, and severe macroangiopathy suggests a common cause of albuminuria and the severe renal and extrarenal complications associated with it. Enzymes involved in the metabolism of anionic components of the extracellular matrix (e.g. heparan sulphate proteoglycan) vulnerable to hyperglycaemia, seem to constitute the primary cause of albuminuria and the associated complications. Genetic polymorphism of such enzymes is possibly the main reason for variation in susceptibility.

Coronary heart disease in young type 1 (insulin-dependent) diabetic patients with and without diabetic nephropathy: incidence and risk factors

SummaryFifty-nine Type 1 (insulin-dependent) diabetic patients with (group I) and 59 patients without nephropathy (group II) pair-matched according to sex (30 males and 29 females), age (33 years, range 15–48) and diabetes duration (19 years, range 6–42) were followed for a period of 10 years from about 5 years before to 5 years after onset of proteinuria. The cumulative incidence of coronary heart disease was estimated, and blood pressure and serum cholesterol were followed. Within six years after onset of proteinuria the cumulative incidence of coronary heart disease was increased eight-fold in group I (40%) compared with group II (5%), (p<0.001). Blood pressure was higher in group I compared with group II from before onset of proteinuria (135/86±17/9 mmHg vs 129/80±15/8 mmHg, p<0.001), and serum cholesterol elevated from onset of proteinuria in group I (6.3±1.2 mmol/l) vs. group II (5.5±1.0 mmol/l), (p<0.005). Patients in group I who developed coronary heart disease had similar age (36 years, range 21–51, vs 38 years, range 21–53), sex (50% males vs. 52% males), smoking frequency (50% vs 49%), diabetes duration (22 years, range 9–39, vs 24 years, range 10–42) and serum creatinine (110 μmol/l, range 69–284, vs 108 μmol, range 72–1024) compared with patients not developing coronary heart disease. However, the patients with coronary heart disease had higher blood pressure (135/87mmHg±16/9 vs 128/82±15/7, p<0.05) and serum cholesterol (7.3 mmol/l+ 1.2 vs 6.4 mmol/l±0.9, p<0.05) than patients without coronary heart disease. Thus, patients developing clinical nephropathy have a highly increased incidence of coronary heart disease compared with patients not developing nephropathy. Patients who developed coronary heart disease were characterized by higher blood pressure and serum cholesterol.

Microalbuminuria: Implications for micro- and macrovascular disease

Microalbuminuria is diagnosed when the UAER is > 20 but < 200 μg/min. The prevalence of microalbuminuria among diabetic patients is 15–20%. Persistent microalbuminuria in diabetic patients is a risk marker not only of renal disease, but also of proliferative retinopathy and cardiovascular morbidity and mortality. Even among nondiabetic individuals, those with microalbuminuria tend to have an increased cardiovascular morbidity. The established cardiovascular risk factors, such as smoking, elevated plasma cholesterol, fibrinogen, and hypertension, are seen more frequently in diabetic patients with persistent microalbuminuria than in normoalbuminuric diabetic patients of similar age, sex, and diabetes duration. However, these risk factors cannot by themselves explain the cardiovascular overmortality in these patients. In addition, insulin resistance or genetic disposition to hypertension or cardiovascular disease fails to be the missing link. Accumulating evidence suggests a common pathogenetic mechanism for microalbuminuria and premature atherosclerosis (i.e., qualitative alterations of the extracellular matrix, including decreased density and sulfation of HS-PG). Decreased density of HS in the glomeruli may lead to albuminuria and mesangial proliferation. In the intima of large vessel walls, decreased density and/or sulfation of HS may enhance several of the processes involved in premature atherosclerosis. Diabetes affects the composition and structure of the extracellular matrix in many ways and leads to decreased density and sulfation of HS-PG by several mechanisms. Genetic differences in the sulfation of HS and/or genetic defects in the coordinated biosynthesis of HS-PG might contribute to decreased concentration and sulfation of HS-PG in susceptible individuals. It is hoped that susceptibility genes can be identified soon, thereby making prevention of severe late diabetic complications more successful.

Incidence of retinopathy in type I (insulin-dependent) diabetes: association with clinical nephropathy.

The association between the incidence of diabetic retinopathy and the development of diabetic nephropathy was studied in 110 Type I (insulin-dependent) diabetic patients during a period from 10 years before to 5 years after the onset of persistent proteinuria. This group of patients was compared with 110 diabetic patients, who were matched according to sex, age, and diabetes duration, but who were without proteinuria during the observation period. The cumulative incidence of proliferative retinopathy was 74% in patients with clinical nephropathy and 14% in patients free of proteinuria. The incidence of background retinopathy was 93% and 37%, respectively, and the incidence of retinopathy increased dramatically 5 years before the onset of proteinuria. Neither gender, age at onset of diabetes, nor blood pressure seemed to have much influence on the incidence of severe retinopathy. It is concluded that development of clinical diabetic nephropathy implies an extremely high risk of developing severe retinopathy. A common pathogenetic link may be suspected.

Glomerular charge selectivity and the influence of improved blood glucose control in Type 1 (insulin-dependent) diabetic patients with microalbuminuria

SummaryWe first compared glomerular charge selectivity index in two matched groups of Type 1 (insulin-dependent) diabetic patients with micro and normoalbuminuria respectively, and secondly, investigated prospectively in a randomized clinical trial, the influence of improved metabolic control on selectivity index in diabetic patients with microalbuminuria. In Study 1, 27 patients with microalbuminuria (albumin excretion >-15 μg/min in at least two out of three overnight urine samples) were matched (age, diabetes duration, mean 1-year HbA1c, gender) with normoalbuminuria patients (n=24), and in Study 2, 23 microalbuminuric patients were randomly allocated to either intensive (continuous subcutaneous insulin infusion) or conventional treatment. Glomerular charge selectivity index was measured as IgG/IgG4 selectivity index, i.e. total IgG/IgG4 clearance ratio in timed overnight urine samples. The microalbuminuric patients had a significantly reduced selectivity index compared to the normoalbuminuric patients: 1.20 (0.92–1.40) vs 1.68 (1.22–2.21), median and 95% confidence interval (p<0.01). In Study 2, the HbA1c improved in the intensive-treatment group compared to the conventional-treatment group: at 2, 6 and 12 months the difference in mean percentage HbA1c between the groups was 1.1, 1.2 and 1.4, respectively (p<0.01). A sharp 50% increment in IgG/IgG4 selectivity index was seen in the intensive-treatment group during the first 6 months (p<0.05 compared to the conventional group). We conclude that adolescents and young adults in an early stage of diabetic nephropathy have reduced glomerular charge selectivity, which may be improved by reducing the mean blood glucose level.

Possible Genetic Defects in Regulation of Glycosaminoglycans in Patients With Diabetic Nephropathy

The hypothesis of genetic defects in glycosaminoglycan (GAG) regulation among patients with insulin-dependent diabetes mellitus (IDDM) and nephropathy was assessed by studies in tissue cultures of fibroblasts obtained from 7 patients with normal urinary albumin excretion, 11 patients with diabetic nephropathy, and 6 nondiabetic control subjects. The incorporation of [3H] glucosamine and [35S] sulfate into hyaluronic acid (HA), chondroitin sulfate and dermatan sulfate (CS + DS), and heparan sulfate (HS) was measured in cells, matrix, and medium and related to micrograms of tissue protein. Large interindividual variations were seen in all three groups, and the incorporation of [3H] glucosamine into HA, CS + DS, and HS and [35S] sulfate into CS + DS and HS were not significantly different between the three groups. However, the fractional incorporation of [3H]glucosamine into HS was significantly reduced in diabetic patients with nephropathy compared with control subjects. This was the case not only when related to the total amount of GAGs (P = 0.014) but also when related to HA (P = 0.014). No significant difference was seen between control subjects and normoalbuminuric diabetic patients. The degree of N-sulfation of HS was not significantly different between the experimental groups. The results suggest that patients with diabetic nephropathy may suffer from deficiencies of coordinate regulation in the biosynthesis of GAG in fibroblasts, which may lead to a reduced density of HS in the extracellular matrix. If these changes reflect alterations in the biosynthesis of GAG from endothelial, myomedial, and mesangial cells, this observation may be relevant for the pathogenesis of severe diabetic complications.

The Prevalence of Hypercholesterolaemia and its Relationship With Albuminuria in Insulin‐dependent Diabetic Patients: An Epidemiological Study

To assess the prevalence of hypercholesterolaemia and its relationship with metabolic control and urinary albumin excretion in Type 1 diabetic patients, all 1577 insulin‐dependent patients attending the outpatient clinic at the Steno Memorial Hospital were studied. None had previously received lipid‐lowering drugs. Hypercholesterolaemia, defined as plasma concentration of cholesterol above 6.4 mmol I−1 was found in 156 patients (10%) (95%) confidence intervals (CI) 8.4–11.5%) compared with 11% in the Danish background population. Compared with the normolipidaemic diabetic patients, the hyperlipidaemic patients were older (42 vs 37 years: p < 0.001, 95% CI for difference in means 3–7 years), they had a higher glycosylated HbA1C (9.2 vs 8.6%, p < 0.001, 95% CI for difference in means 0.4–1.3%) and their urinary albumin excretion was 32 vs 12 mg 24 h−1, p < 0.001. Of the 1577 diabetic patients, 1084 patients (73%) had normal urinary albumin excretion (UAE < 30 mg 24 h−1), 255 (17%) had microalbuminuria (UAE 30–300 mg 24 h−1) and 136 (9%) had overt clinical nephropathy (UAE > 300 mg 24 h−1). The plasma concentration of cholesterol rose significantly with increasing urinary albumin excretion; normoalbuminuric 4.78 mmol I−1 ± 1.06 (mean ± SD); microalbuminuria 5.12 mmol I−1 ± 1.23 and macroalbuminuric: 4.89 mmol I−1 ± 1.38 (p < 0.001). The influence of metabolic control on the plasma level of cholesterol was of only minor clinical importance.

Natural history of diabetic complications: early detection and progression.

Until recently Type 1 diabetes has been characterized by a considerable degree of mortality, mainly associated with the development of diabetic nephropathy. Diabetic nephropathy is characterized by persistent proteinuria, decreasing glomerular filtration rate (GFR), increasing blood pressure, and morphological changes. Proteinuria represents a late stage in a prolonged process, which begins at the onset of Type 1 diabetes, when urinary albumin excretion is at the lower end of its normal range (< 10 mg 24‐h‐1). However, in those patients who will later develop persistent proteinuria, urinary albumin excretion increases exponentially at about 20% per year. These patients also tend to have rising blood pressure and falling GFR, higher rates of proliferative retinopathy and coronary heart disease, and elevated levels of cardiovascular risk factors. As intervention is possible in all these areas, identification of such patients is required and especially as the imposition of strict metabolic control may postpone or arrest progression to overt nephropathy. Where patients deteriorate despite such control the institution of early antihypertensive therapy and the effective management of end stage renal disease will bring further improvements in the prognosis of diabetic nephropathy.

Inhibition of N-acetylheparosan deacetylase in diabetic rats

The effects on N-acetylheparosan deacetylase (N-deacetylase) activity exerted by poorly and well-regulated diabetes and variation of genetic background were investigated in insulin-treated streptozocin-induced diabetic rats of two different strains (H and U). N-deacetylase plays a key role in heparan sulfate biosynthesis, because N-deacetylation is a prerequisite for N- and further O-sulfation. Specific activity of the enzyme was reduced by 50% in poorly regulated diabetic rats compared with nondiabetic rats (P< 0.001). The decrease in specific activity was accompanied by a reduction in theestimated KM from 34 ± 3 to 27 ± 4 mg/L (P < 0.001). Optimal insulin treatment, leading to near normalization of blood glucose, preventedreduction in N-deacetylase activity. In rat strain U, however, a 20% reduction was found despite optimal insulin treatment (P = 0.01), and the nondiabetic animals of this strain had reduced N-deacetylaseactivity compared with nondiabetic rats from the H strain. This might suggest a genetic difference between the rat strains in the regulation of the enzyme activity. The diabetes-induced inhibition of N-deacetylase may have an important role in the pathogenesis of nephropathy and vascular complications in human diabetes mellitus.

Na+H+ exchanger isoform-1 abundance in skin fibroblasts of type I diabetic patients with nephropathy☆

In diabetic nephropathy and essential hypertension, the cellular Na+/H+ exchanger (NHE) exhibits increased activity. Whether this reflects increased numbers of NHE isoform-1 (NHE-1) transporters or increased turnover per molecule has not been established. We have used a specific polyclonal antibody directed toward the C-terminal of NHE-1 to measure NHE-1 content in cultured skin fibroblasts from diabetic patients with (DN) and without (DCON) nephropathy and normal controls (CON). NHE-1 content in fibroblasts from DN subjects was significantly less than that in the other two groups. This suggests that increased NHE activity in diabetic nephropathy is attributed to increased NHE-1 turnover per site rather than increased NHE-1 expression.