Bo Feldt-Rasmussen

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.

EFFECT OF TWO YEARS OF STRICT METABOLIC CONTROL ON PROGRESSION OF INCIPIENT NEPHROPATHY IN INSULIN-DEPENDENT DIABETES

36 patients with insulin-dependent diabetes mellitus who had Albustix-negative urine but raised urinary albumin excretion (30 to 300 mg/24 h) were randomly assigned to either remaining on conventional insulin treatment or continuous subcutaneous insulin infusion and followed up for 2 years. The insulin-infusion group showed a significant, sustained improvement in metabolic control, with a median glycosylated haemoglobin of 7.2% (range 5.9-8.8), but there was no change in the conventional-treatment group (median 8.6%, range 7.2-13.4) (p less than 0.001). Clinical diabetic nephropathy (a urinary albumin excretion rate above 300 mg/24 h in at least two of three 24 h urine collections) developed in 5 patients in the conventional-treatment group, but not in the insulin-infusion group (p less than 0.05, two-tailed). Fractional albumin clearance (mean and range X 10(7] increased in the conventional-treatment group from 160 (35-468) to 360 (29-1580) and was unchanged in the insulin-infusion group (170 [31-608] before to 160 [26-460] after) (p less than 0.05). Insulin infusion had an overall beneficial effect on the annual increase in urinary albumin excretion (p less than 0.05), and the mean glycosylated haemoglobin values correlated positively with annual change in albumin excretion (r = 0.57, p less than 0.0001). The diastolic blood pressure rose significantly in the conventional-treatment group (p less than 0.001), and annual change in mean blood pressure correlated with change in urinary albumin excretion (r = 0.49, p less than 0.001).

Enzyme immunoassay: an improved determination of urinary albumin in diabetics with incipient nephropathy

An enzyme linked immunoadsorbent assay for urinary albumin using commercially available reagents is described. The assay range is 2.5-120 micrograms/l. When samples are analysed in two standard dilutions, the assayable albumin concentration range is 2.5-240 mg/l, covering the clinical range from normoalbuminuria to overt clinical nephropathy. Intra-assay variation was 2.1% and interassay variation 8.3%. Recovery of added albumin to urine was 95%-106% and dilution of urine was linear. The correlation to urinary albumin determined by immunodiffusion was excellent (n = 80, r = 0.99). Intraindividual variation of the 24 h urine albumin excretion of different days was high in patients with incipient diabetic nephropathy (51.5%) and was only slightly reduced by taking the variation of creatinine excretion into account (39.5%). No correlation was found between albumin excretion, and HbA1c or urine glucose excretion, indicating that minor metabolic variations are not responsible for the huge intraindividual day-to-day variations of UalbV. The study shows that more than one UalbV measurement must be done before classifying patients into groups with or without incipient diabetic nephropathy.

FEATURES OF ENDOTHELIAL DYSFUNCTION IN EARLY DIABETIC NEPHROPATHY

The release of tissue plasminogen activator (tPA) by vascular endothelial cells during exercise was studied in forty men with insulin-dependent diabetes. Three groups, matched for age and diabetes duration, were defined as: group I (n = 19), normal urinary albumin excretion (less than 30 mg/24 h); group II (n = 11), incipient diabetic nephropathy (30-300 mg albumin excreted per 24 h); and group III (n = 10), clinical diabetic nephropathy (more than 300 mg albumin excreted per 24 h). Nine non-diabetic men served as controls. The rise in tPA antigen with exercise was similar in the controls and group I but significantly smaller in groups II and III (p less than 0.01). The albumin transcapillary escape rate was significantly higher in groups II and III than in group I and normal controls (p less than 0.01). The basal plasma level of von Willebrand factor was higher in groups III (p less than 0.01) and II (difference not significant, p = 0.06) than in group I and normal controls. These findings suggest that insulin-dependent diabetic patients with only slightly raised urinary albumin excretion have general endothelial cell dysfunction or damage. It is not yet clear whether these changes are important in the pathogenesis of thrombosis and atherosclerosis in these patients.

Central role for sodium in the pathogenesis of blood pressure changes independent of angiotensin, aldosterone and catecholamines in type 1 (insulin-dependent) diabetes mellitus.

SummaryWe studied 73 Type 1 (insulin-dependent) diabetic patients, 18 to 50 years of age, with a diabetes duration of more than five years. Group 1: normal urinary albumin excretion below 30 mg per 24 h (n=19); group 2: microalbuminuria, 30–300 mg per 24 h (n=36); and group 3: diabetic nephropathy, above 300 mg per 24 h (n=18). Fifteen non-diabetic persons matched for sex and age served as control subjects. The sodium intake evaluated on the basis of 24-h urine sodium excretion was similar in patients and control subjects. Blood pressure in groups 1 and 2 and control subjects was below 160/95 mmHg. The blood pressure was increased in group 3 as compared with the other groups (systolic/diastolic 161±22/101±9 mmHg vs 131±13/84±10, mean±SD, p<0.0001). Exchangeable sodium was increased in patients (p<0.01) and correlated to the mean blood pressure (n=70, r=0.41, p<0.01). Extracellular volume was increased in patients (p<0.05), whereas plasma volume was normal. Supine serum angiotensin II was suppressed in the patients (p<0.001). A negative correlation was found between mean blood pressure and supine serum aldosterone (n=68, r=-0.24, p<0.05), and exchangeable sodium and aldosterone (n=66, r=-0.36, p<0.002) in all patients. The catecholamine levels were also suppressed or normal in the patients. These data suggest that sodium retention plays a major role and that the aldosterone, angiotensin II and catecholamine levels are suppressed during the blood pressure rise observed in the very early stages of diabetic renal disease.

Effect of improved metabolic control on loss of kidney function in type 1 (insulin-dependent) diabetic patients: an update of the Steno studies.

SummaryWe re-examined 69 of the 70 patients entering the two independent Steno Studies of effects of improved metabolic control on progression of late diabetic complications. They were analysed according to an intent to treat after follow-up for 8 years (Steno Study 1) and 5 years (Steno Study 2). The glycaemic control had improved in the insulin infusion group compared with the conventional treatment group (mean HbA1c) by 2.0±0.6% vs 0.7±1.2 in Steno Study 1 and by 1.8±1.2% vs 0.4±1.3 (p<0.01) in Steno Study 2. In the insulin infusion groups three patients had died during episodes of ketoacidosis. These were not caused by malfunction of the insulin infusion pumps. In the conventional treatment groups, three patients suffered five cardiovascular events causing two deaths. From the sixth month of Steno Study 1 the annual change of the glomerular filtration rate was −3.7 (−5.4 to −2.0) ml·min−1·1.73 m−2 vs −1.0 (−2.1 to −0.1) (conventional vs insulin infusion group, mean (95% confidence interval, p<0.01)). The change in urinary albumin excretion was associated with the glycaemic control (n=69, r=0.49, p<0.0002). No progression was observed among 32 patients with low range microalbuminuria (30 to 99 mg/24 h). Among the 19 patients with an initial albumin excretion between 100 and 300 mg/24 h, progression of complications was more frequent during conventional treatment (n=10) vs insulin infusion (n=9): Clinical nephropathy (10 of 10 vs 2 of 9, p<0.01) and arterial hypertension (7 of 10 vs 1 of 9, p<0.01). The glomerular filtration rate declined during conventional treatment by −23 (−42 to −4) ml·mm−1·1.73 m−2 (p<0.05) but not during insulin infusion (−13 (−31 to 5) NS). These results suggest that patients at risk of nephropathy should be offered near normal glycaemic control in order to preserve their kidney function.

Elevated Albumin Excretion and Retinal Changes in Children with Type 1 Diabetes are Related to Long-term Poor Blood Glucose Control

All diabetic children (n = 113) under 19 years old and with more than 2 years of diabetes attending the Steno Memorial Hospital in 1987 were studied. Normal urinary albumin excretion (< 30 mg 24 h−1) was found in 96 patients (85%), 15 had microalbuminuria (30–300 mg 24 h−1) (13%), and 2 patients were proteinuric (>300 mg 24 h−1) (2%). Retinal morphology was evaluated by colour fundus photography. Background retinopathy was more frequent in the group with elevated albumin excretion (71%) than in a matched normoalbuminuric group (20%, 2p < 0.001). Long‐term blood glucose control was assessed from all previous HbA1c measurements in the hospital records, an average of nine per patient. The mean observation period was 48 (3–76) months. Children with elevated albumin excretion had a higher mean HbA1c than children with normal urinary albumin excretion (10.3 ± 1.9 vs 9.2 ± 1.3% (± SD), 2p < 0.05). Children with retinopathy had an HbA1c of 9.9 ± 1.7 vs 9.0 ± 1.2% in patients without retinopathy (2p < 0.01).

Is Hypertension a Major Independent Risk Factor for Retinopathy in Type 1 Diabetes

Hypertension is an established risk factor for retinopathy. Whether it is an independent risk factor or acts only by association with nephropathy is not known. Therefore, we studied 273 Type 1 diabetic patients. They were divided into four groups. Group 1 (n = 55) were normotensive and normoalbuminuric, group 2 (n = 51) had hypertension but were normoalbuminuric, group 3 (n = 33) had nephropathy but were normotensive, and group 4 (n = 134) had nephropathy and hypertension. Hypertensive patients with normoalbuminuria (blood pressure 146 ± 19 (± SD)/87 ± 12 mmHg) had the same prevalence of retinopathy as normoalbuminuric normotensive patients (123 ± 12/75 ± 5 mmHg). Hypertensive nephropathic patients (blood pressure 147 ± 18/87 ± 8 mmHg) had more retinopathy than hypertensive normoalbuminuric patients despite similar blood pressure (normal retina/advanced retinopathy: 3 %/73 % vs 46 %/17 %, p< 0.001). Nephropathic normotensive patients had worse retinal changes than hypertensive normoalbuminuric patients (19 %/49 %, p< 0.001) but fewer than the nephropathic hypertensive patients p < 0.001). Thus hypertension per se is not associated with increased retinal changes but may aggravate these in patients with clinical nephropathy.

Kidney volume in type 1 (insulin-dependent) diabetic patients with normal or increased urinary albumin excretion : effect of long-term improved metabolic control

Forty-seven patients with type 1 (insulin-dependent) diabetes mellitus and 14 normal subjects had renal volume determined by an ultrasonic technique. Renal volume of 299 +/- 49 ml/1.73 m2 (mean +/- SD) in type 1 diabetic patients with normal urinary albumin excretion exceeded that in the normal subjects (245 +/- 53 ml/1.73 m2, p less than 0.05). Compared with diabetic patients with normal urinary albumin excretion, renal volume was significantly higher in patients with microalbuminuria (372 +/- 24 ml/1.73 m2, p less than 0.05) and patients with clinical nephropathy (352 +/- 48 ml/1.73 m2, p less than 0.05). In a multiple linear regression with HbA1c, urinary albumin excretion, age, diabetes duration and mean blood pressure as independent variables, variations in HbA1c could account for 33% of the variations in kidney volume (n = 47, r = 0.57, p less than 0.01). The other variables played no role. When only patients without clinical nephropathy were included, HbA1c and kidney volume remained significantly correlated (n = 34, r = 0.60, p less than 0.01). In those patients a strong correlation between kidney volume and function, i.e. the glomerular filtration rate was found (n = 34, r = 0.70, p less than 0.01); metabolic control and function were also correlated (n = 34, r = 0.62, p less than 0.01). The urinary albumin excretion accounted for only 6% of the variation of the kidney volume (NS). In nine patients with microalbuminuria the kidney volume could be reduced during 2 years of improved metabolic control by means of insulin infusion pumps.(ABSTRACT TRUNCATED AT 250 WORDS)

Micro-ELISA for the quantitation of human urinary IgG

When investigating glomerular changes in the early stages of diabetic renal disease, it is important to be able to estimate low concentrations of urinary immunoglobulins, as well as the albumin/immunoglobulin ratio. For this reason there is a need for highly sensitive and specific routine assays for urinary immunoglobulins. A sandwich enzyme-linked immunoadsorbent assay (ELISA) for the quantitation of urinary immunoglobulin G is described, in which microtest plates are used as the solid phase. The assay is specific, sensitive and simple, and only used commercially available reagents. The assay range was 5-200 micrograms/l. The relative standard deviations within and between assays were 5 and 9%, respectively. Recovery of IgG added to urine was 100-102% (n = 12), and dilution of urine was linear. The assay range allowed for the quantitation of IgG in human urine samples, covering the clinical range from physiological to raised pathological values.