Early urinary markers of diabetic kidney disease: a nested case-control study from the Diabetes Control and Complications Trial (DCCT).

BACKGROUND: Urinary markers were tested as predictors of macroalbuminuria or microalbuminuria in patients with type 1 diabetes. STUDY DESIGN: Nested case-control of participants in the Diabetes Control and Complications Trial (DCCT). SETTING & PARTICIPANTS: 87 cases of microalbuminuria were matched to 174 controls in a 1:2 ratio, while 4 cases were matched to 4 controls in a 1:1 ratio, resulting in 91 cases and 178 controls for microalbuminuria. 55 cases of macroalbuminuria were matched to 110 controls in a 1:2 ratio. Controls were free of micro-/macroalbuminuria when their matching case first developed micro-/macroalbuminuria. PREDICTORS: Urinary N-acetyl-beta-d-glucosaminidase (NAG), pentosidine, advanced glycation end product (AGE) fluorescence, and albumin excretion rate (AER). OUTCOMES: Incident microalbuminuria (2 consecutive annual AERs > 40 but < or = 300 mg/d) or macroalbuminuria (AER > 300 mg/d). MEASUREMENTS: Stored urine samples from DCCT entry and 1-9 years later when macro- or microalbuminuria occurred were measured for the lysosomal enzyme NAG and the AGE pentosidine and AGE fluorescence. AER and adjustor variables were obtained from the DCCT. RESULTS: Submicroalbuminuric AER levels at baseline independently predicted microalbuminuria (adjusted OR, 1.83; P < 0.001) and macroalbuminuria (adjusted OR, 1.82; P < 0.001). Baseline NAG excretion independently predicted macroalbuminuria (adjusted OR, 2.26; P < 0.001) and microalbuminuria (adjusted OR, 1.86; P < 0.001). Baseline pentosidine excretion predicted macroalbuminuria (adjusted OR, 6.89; P = 0.002). Baseline AGE fluorescence predicted microalbuminuria (adjusted OR, 1.68; P = 0.02). However, adjusted for NAG excretion, pentosidine excretion and AGE fluorescence lost the predictive association with macroalbuminuria and microalbuminuria, respectively. LIMITATIONS: Use of angiotensin-converting enzyme inhibitors was not directly ascertained, although their use was proscribed during the DCCT. CONCLUSIONS: Early in type 1 diabetes, repeated measurements of AER and urinary NAG excretion may identify individuals susceptible to future diabetic nephropathy. Combining the 2 markers may yield a better predictive model than either one alone. Renal tubule stress may be more severe, reflecting abnormal renal tubule processing of AGE-modified proteins, in individuals susceptible to diabetic nephropathy.

Serum vitamin E and oxidative protein modification in hemodialysis: a randomized clinical trial.

BACKGROUND: Patients with end-stage renal disease have increased circulating concentrations of oxidatively modified circulating proteins. Therefore, we examined the ability of vitamin E alpha (alpha-tocopherol) to alter levels of these modified proteins. STUDY DESIGN: Randomized clinical trial. SETTING & PARTICIPANTS: 27 clinically stable patients treated by means of hemodialysis in 4 freestanding outpatient dialysis units. INTERVENTION: Oral administration of 800 IU of vitamin E alpha or placebo daily. OUTCOMES & MEASUREMENTS: Plasma levels of alpha- and gamma-tocopherol and oxidative protein modifications reflecting 2 pathways for protein-oxidant damage. The advanced glycation end product pentosidine reflects glycoxidation. The lipid peroxidation products iso[4]-levuglandin E(2), (E)-4-hydroxy-2-nonenal, and (E)-4-oxo-2-nonenal are formed through covalent adduction. RESULTS: Circulating levels of all oxidative protein modifications were increased in patients with end-stage renal disease. Supplementation with alpha-tocopherol caused alpha-tocopherol levels to rise (13.2 +/- 3.7 to 27.3 +/- 14 mug/mL), but gamma-tocopherol levels to decrease (4.1 +/- 1.6 to 3.5 +/- 1.1 mug/mL). Control values were unchanged. There was no effect on oxidative protein modifications (placebo versus treatment; mean for pentosidine, 15.6 +/- 11.4 (SD): 95% confidence interval (CI), 8.2 to 23.1 versus 21.3 +/- 9.0 pg/mg protein; 95% CI, 16.1 to 26.6; iso[4]-levuglandin E(2), 8.31 +/- 2.55; 95% CI, 6.77 to 9.85 versus 8.46 +/- 2.37 nmol/mL; 95% CI, 7.09 to 9.84; (E)-4-hydroxy-2-nonenal, 0.51 +/- 0.11; 95% CI, 0.45 to 0.57 versus 0.51 +/- 0.08 nmol/mL; 95% CI, 0.46 to 0.56; (E)-4-oxo-2-nonenal, 189 +/- 44; 95% CI, 162 to 215 vs 227 +/- 72 pmol/mL; 95% CI, 183 to 271). LIMITATIONS: Sample size was adequate to show changes in alpha- and gamma-tocopherol levels in response to treatment. However, power was insufficient to show an effect on oxidative protein modifications. CONCLUSIONS: Intervention of oral supplementation with alpha-tocopherol did not result in changes in circulating oxidative protein modifications. A larger study may be required to show an effect in this clinical setting.

Processing advanced glycation end product-modified albumin by the renal proximal tubule and the early pathogenesis of diabetic nephropathy.

Diabetes is characterized by increased quantities of circulating proteins modified by advanced glycation end products (AGEs). Proteins filtered at the glomerulus and presented to the renal proximal tubule are likely to be highly modified by AGEs. The proximal tubule binds, takes up, and catabolizes AGE-modified albumin by pathways different from those of unmodified albumin. These differences were examined in polarized, electrically resistant proximal tubular cells grown in monolayer culture. In patients with type 1 diabetes, urinary excretion of a lysosomal enzyme predicted the development of nephropathy.

Assessing 24-hour blood glucose patterns in diabetic paitents treated by peritoneal dialysis.

The minute-to-minute effect on blood glucose levels of high-dextrose peritoneal dialysate is not known. We arranged for 7 patients with diabetes, treated by peritoneal dialysis (PD), to wear a continuous glucose monitoring system (CGMS: Medtronic MiniMed, Northridge, CA, U.S.A.). A sensor was inserted subcutaneously into the skin of the patient's abdomen or back to measure glucose in the interstitial fluid. Readings were recorded every 5 minutes for up to 72 hours. The portion of the day during which the patient's blood glucose levels were greater than 180 mg/dL (calculated as a percentage of time) was recorded. Most of the patients participating in the study had elevated levels of glycohemoglobin and hemoglobin A1c, and, for a large percentage of the day, showed blood glucose tracings well above the recommended standards of control. Representative CGMS tracings from patients with type 1 and type 2 diabetes are shown.

Thrombotic events and markers of oxidation and inflammation in hemodialysis.

The goal of this study was to determine whether antioxidant therapy with vitamin E would alter the rate of vascular access complications or other macrovascular complications in hemodialysis (HD) patients. A secondary goal of the study was to explore the relationship between baseline pretreatment markers of oxidative stress (the advanced glycation end product pentosidine and basal levels of vitamin Ealpha and gamma) and the subsequent development of access failure. Thirty-five stable patients treated by HD were recruited for the study. Patients were provided with vitamin E (800 IU) or placebo capsules to be taken daily. Clinical variables, vascular access function (flow meter access flow measurements), and circulating blood markers were obtained initially and every 3 months throughout the study. Vitamin Ealpha levels rose in treated patients from 12.7 +/- 4.4 to 25.1 +/- 15.1 microg/mL at 3 months and 28.6 +/- 14.8 microg/mL at 6 months. Vitamin Egamma levels fell in treated patients from 3.9 +/- 1.7 to 2.3 +/- 1.5 microg/mL at 3 months and 1.7 microg/mL at 6 months. Patients who subsequently developed repeated thrombotic vascular access events were characterized by higher baseline pentosidine content of circulating proteins. Patients who developed a myocardial infarction had higher pentosidine, lower vitamin Ealpha, and much lower vitamin Egamma than patients who did not develop thrombotic events. These findings lead to the speculation that the anti-inflammatory effects of vitamin Egamma may play a more important role in thrombotic vascular events than the antioxidant effects of vitamin Ealpha. Additional studies of these interactions are in progress.

Effect of the peritoneal dialysis prescription on pentosidine in children.

Enhanced formation of advanced glycation end products (AGEs) by peritoneal dialysate containing high dextrose concentrations has been implicated as a source of peritoneal membrane toxicity and loss of viability in patients treated with peritoneal dialysis (PD). The goal of this project was to elucidate the relationship between the structurally defined AGE pentosidine accumulation on peritoneal and plasma proteins and peritoneal membrane function, and to identify clinical factors leading to alterations in these parameters. The study comprised 27 pediatric patients (14 continuous ambulatory PD, 13 chronic cycling PD) on PD for a mean duration of 37.0+/-22.8 months (range 1-120 months) and with a mean age of 13.3+/-4.4 years (range 2.4-20 years). The pentosidine contents of plasma and peritoneal proteins were significantly lower in patients with residual renal function than in patients who were anuric (plasma pentosidine 11.2+/-8.8 vs. 24.1+/-16.6, P=0.02, respectively, peritoneal pentosidine 14.9+/-11.9 vs. 31.1+/-3.7, P=0.01, respectively). There was no effect of treatment modality on plasma pentosidine (18.1+/-11.2, 18.8+/-19.3, CAPD vs. CCPD, P>0.05) or peritoneal pentosidine content (24.1+/-14.1, 24.9+/-19.6, CAPD vs. CCPD, P>0.05). There was no evidence that increased levels of pentosidine on peritoneal proteins reflect or affect peritoneal membrane function in these patients. Furthermore, there was no effect of peritonitis on the pentosidine content of peritoneal proteins or peritoneal function as measured by peritoneal equilibration test. In conclusion, PD represents a well-tolerated therapy in children with no evidence that current practice causes changes in peritoneal membrane function, or in the peritoneal clearance of plasma or peritoneal proteins rich in pentosidine.