CLINICOPATHOLOGICAL CONFERENCE

Proteinuria, Hematuria, Hypertension, and Decreased Renal Function in a Patient With Diabetes for 9 Years Roger A. Rodby, MD, Clinical Discussant Melvin M. Schwartz, MD, Pathologist INDEX WORDS: Diabetic nephropathyj nonenzymatic protein glycosylationj advanced glycosylation end-productsj aminoguanidine.

CASE HISTORY The patient is a 29-year-old white man with a history of insulindependent diabetes mellitus (100M) for 9 years. He had been previously healthy until the age of 20 and was found to be diabetic during a hospitalization for a pilonidal cyst. He has required insulin ever since. A 24-hour urine collection 2 years ago demonstrated 150 mg of protein. Three months ago, a repeat 24-hour urine collection contained 650 mg of protein. Mild hypertension was noted at that time and he was started on captopril. He was told that the onset of hypertension and proteinuria portended a poor prognosis and he sought a second opinion. There is no history of rash, fever, arthralgias, weight loss, photophobia, flank pain, gross hematuria, or drug or nonsteroidal antiinflammatory agent use. His medications include captopril12.5 mg twice daily, insulin (units): 18 NPH, 8 regular in the AM, 8 NPH, 4 regular in the PM , and 325 mg aspirin daily. Diabetic retinopathy had been diagnosed 2 years earlier by an ophthalmologist, but he had not received laser therapy. There is no family history of diabetes, renal disease or deafness. On physical examination, the patient's blood pressure was 140/90 mm Hg with a pulse of80/min. He was well developed and well nourished; his height and weight were 185 cm and 95 kg, respectively. His optic fundi demonstrated bilateral microaneurysms without hemorrhages, exudates, proliferative changes, or cataracts. Examination of the heart, lungs, and abdomen was normal. The vascular examination demonstrated strong pulses in all extremities. A mild sensory deficit of the feet was noted with decreased pinprick sensation in the toes. There was no edema. Laboratory results were sodium 144 mmol/L, K+ 4.3 mmol/ L, Cl- \04 mmol/L, HCO)- 28 mmol/L, blood urea nitrogen (BUN) 5.7 mmol/L (16 mg/dL), creatinine 115 ILmol/L (1.3 mg/dL), albumin 4.3 g/dL, cholesterol 167 mg/dL, hemoglobin A lc 8.7% (5% to 8%), hemoglobin I 5A g/dL, white blood cell count 10,200/ILL, and platelet count 178,000/ILL. Twenty-four-hour urine collection showed 575 mg of pro-

From the Departments 0/ Medicine and Pathology, RushPresbyterian St Luke's Medical Center, Chicago, IL. Received March 26, 1992; accepted in revised form June 30,1992. Address reprint requests to Roger A. R odby, MD, Section o/Nephrology, Rush-Presbyterian St Luke's Medical Center, 1653 W Congress Pkwy, Chicago, IL 60612. © 1992 by the National Kidney Foundation, Inc. 0272-6386/92/2006-0023$3.00/0 658

tein; creatinine clearance was 64 mL/min/1.73 m2 (total creatinine, 1.5 g/24 h). Dipstick urinalysis showed specific gravity 1.020, 2+ protein, I + blood, I + glucose. Microscopic examination of the spun urine sediment showed 5 to 25 red blood cells (RBC)/high power field, no RBC casts. Serologic examination showed antinuclear antibody titer I 4: 0 (normal, < I :40) speckled pattern; ribonucleoprotein, Sm, and antiDNA antibody titers negative; C3 97 mg/dL (normal, 80 to 180 mg/dL), C4 19 mg/dL (normal, 15 to 50 mg/dL), hepatitisB surface antigen negative. A percutaneous renal biopsy was performed.

CASE DISCUSSION

Roger A. Rodby, MD (Assistant Professor of Medicine, Rush Medical College)

While diabetic nephropathy would appear to be the most likely cause ofthe renal abnormalities in this patient, there are two aspects of this clinical presentation that deserve discussion. First, whether the presentation of proteinuria and the decrease in glomerular filtration rate are in keeping with the relatively short length of time that this patient is known to have had diabetes, and, second, the presence of microscopic hematuria. It is conceivable that this patient had non-insulin-dependent diabetes for a number of years before the diagnosis of diabetes and therefore the development of nephropathy would not be inconsistent with the duration of this disorder. A C-peptide level would be useful in making this distinction, but as is was not available I will proceed, for the purpose of discussion, with the assumption that this represented insulin-dependent diabetes mellitus (100M). I The majority of the data on the natural history of diabetic nephropathy is from 100M (type 1) patients, and will serve as the basis for the discussion in this case. An understanding of the patterns of proteinuria and their relationship to disease duration is important. The diagnosis of diabetic nephropathy has typically been dependent on the appearance of proteinuria. As a result,

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what is known about the "natural history" of diabetic nephropathy is largely dependent on data related to the appearance and development of these patterns of proteinuria. Clinically apparent or "overt" diabetic nephropathy is considered the end-product of many years of hyperglycemia and develops in about 40% of insulin-dependent diabetic patients. 2 "Non-overt" diabetic nephropathy is now recognized when the diabetic patient demonstrates a persistently elevated urinary albumin excretion rate (UAE), which is too low to be recognized by the routine dipstick ("microalbuminuria") and therefore requires a more sensitive test such as a radioimmunoassay. By convention, most investigators accept UAE rates of 20 to 200 J.lg/min (29 to 290 mg/24 h) to be within the "microalbuminuria" range. Reversibly elevated UAE rates can occur in association with hyperglycemia, hypertension, exercise, and fever. These transient causes of increased albumin excretion must be distinguised from persistent elevations in UAE, which will develop at some point in the course of about 25% of diabetic patients. 3 .4 The majority of the latter patients, if followed for a number of years, will develop overt nephropathy.5,6 These studies have led to the impression that the presence of microalbuminuria was a marker that would predict the future development of clinically overt and anatomically characteristic diabetic nephropathy. It is now believed by many that this early laboratory finding is not predictive, but rather indicative, of early diabetic nephropathy.7,8 Diabetic microalbuminuric patients who undergo renal biopsy often have marked ultrastructural changes in their glomeruli despite a relatively short duration of diabetes. These histopathologic abnormalities are almost universal when microalbuminuria is accompanied by either hypertension or a reduction in glomerular filtration rate (GFR).9 That diabetic nephropathy may be present well before the onset of overt (ie, dipstickpositive) proteinuria is further supported by renal histopathology of the very early diabetic patient. Renal biopsies performed within the first 5 years of the diagnosis of IDDM demonstrate ultrastructural changes in the basement membrane and mesangium even when UAE rates are normal. 10 Patients followed prospectively after the diagnosis of diabetes will only rarely demonstrate

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microalbuminuria within this initial 5-year period and generally have had a history of diabetes for 7 to 15 years before its development. 11,12 Approximately 80% of those patients who develop persistently elevated UAE rates develop progressive nephropathy with a UAE rate of greater than 300 mg/24 h (total proteinuria, >500 mg/24 h)I3 over the next 6 to 14 years. I4 The convention that diabetic nephropathy begins with the onset of dipstick proteinuria must therefore be challenged. The natural history of early diabetic nephropathy appears to be a continuum of very early histopathologic changes followed by persistent elevations oflow levels ofUAE and, finally, by the appearance of overt proteinuria. Overt nephropathy rarely presents during the first decade after diagnosis of IDDM, as· would seem to be the case in this patient. IS White had published an extensive long-term follow-up on 1,072 IDDM patients at the Joslin Clinic. I6 She reported that those patients with IDDM for less than 10 years had a prevalence of proteinuria of 1.5% and hypertension of 1.2%. In fact, the follow-up of these patients for 15 years revealed that only 7% had developed proteinuria and 4.5% had hypertension. Knowles et al confirmed this; they prospectively followed 167 patients for up to 30 years and reported no cases with clinically apparent proteinuria prior to the 10th year of IDDM.I7 In the context of the patient under discussion, if his proteinuria were due to diabetes, it would be unusual. This patient does manifest retinal diabetic vasculopathy. Retinopathy occurs earlier and is more common in the diabetic population than is nephropathy. As many as 50% of IDDM patients will exhibit some degree of retinopathy during the first decade after diagnosis. The incidence of retinopathy continues to increase with time. IS Diabetic nephropathy is usually accompanied by diabetic retinopathy and the absence of retinopathy in the patient with diabetes and renal disease has been used as a clue that a condition other than diabetes may be responsible for the renal disease. I9 However, because retinopathy develops earlier and is more common than nephropathy, its presence does not necessarily aid in the differentiation of diabetic versus nondiabetic renal disease in the patient under discussion. Although the healthy adult may excrete up to 1 million RBCs per day in the urine, it is consid-

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ered abnormal to find more than a few RBCs per high-power field in a centrifuged urine specimen. Microscopic hematuria is defined as being present when RBC numbers greater than this are found,20 as was demonstrated in this patient. Microscopic hematuria is generally considered an unlikely consequence of diabetic nephropathy, although the data to support this statement are scant. O'Neill et al 2l reported 30 patients with the clinical diagnosis of "diabetic nephropathy" who were prospectively evaluated for the presence of microscopic hematuria. Nine patients (30%) demonstrated this finding (of which four were reported to have red blood cell casts). However, renal biopsies were not performed to confirm the diagnosis of diabetic nephropathy. Eight other diabetic patients with microscopic hematuria underwent renal biopsy. Three patients had a primary glomerulopathy in addition to diabetic nephropathy, while five had only diabetic nephropathy.2l Reports such as these are often biased, since the decision to biopsy was based on the presence of hematuria. The only conclusion that can be made from these data is that hematuria may be a clue for nondiabetic renal disease, but its presence does not rule out diabetic glomerulopathy. Because of the early onset of proteinuria and microscopic hematuria in this patient, other glomerular lesions must be considered in this case. There is nothing in this patient's clinical history to suggest a systemic disease. The marginally positive antinuclear antibody titer is not supported by any of the other serologic tests for sys-

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Fig 2. Glomerulus with strong diffuse linear deposits of IgG in the GBMs. The deposits are focally enhanced in the paramesangial areas, and the tubular basement membranes and Bowman's capsule are focally and weakly stained. (Fluorescein conjugated anti-human IgGj original magnification x225.)

temic lupus erythematosus and the patient's history does not suggest this diagnosis. Of the primary glomerulopathies seen in this age group, IgA nephropathy would seem to best fit the presentation of mild proteinuria associated with hematuria. Focal segmental glomerular sclerosis and membranous glomerulonephritis are usually seen with greater urinary protein excretion. In summary, by exclusion, the cause of proteinuria, hypertension, and decreasing renal function in a diabetic patient with retinopathy is most likely diabetic nephropathy. However, the relatively early onset of clinically overt renal disease raises some doubt regarding this diagnosis. There are prognostic and therapeutic implications related to the diagnosis of diabetic nephropathy that will certainly impact upon this patient. Therefore, a renal biopsy was performed.

PATHOLOGY Melvin M. Schwartz, MD (Professor of Pathology, Rush Medical College)

Fig 1. Glomerulus with diffuse mesangial expansion by periodiC acid-Schiff-positive mesangial matrix and a mild increase in mesangial cellularity. The basement membranes do not appear thickened. (H&Ej original magnification X225.)

The renal biopsy showed well-preserved cortical architecture with pathological changes confined to the glomeruli and arterioles. The glomeruli had diffuse mesangial expansion with mild hypercellularity (Fig 1). There were no sclerotic glomeruli, nor were there Kimmelstiel-Wilson nodules. Immunofluorescence microscopy demonstrated strong linear deposits oflgG in the glomerular basement membranes (Fig 2). The other immunoglobulins and complement components C3 and C4 were not present. By electron mi-

PROTEINURIA IN A DIABETIC PATIENT

croscopy, the glomerular basal lamina measured 950 nm (normal, 350 nm ± 75 [SD]). In addition to thickening of the basal lamina, there was diffuse mesangial expansion by cell processes and mesangial matrix, and at high magnification the mesangial matrix resolved into discrete randomly arranged micro fibrils measuring approximately 20 nm in diameter (Fig 3). All of these features are consistent with the diagnosis of diabetes mellitus, and there was no evidence for any other glomerular lesions to explain this patient's early onset of protein uria. Thickening of glomerular basal lamina is an early finding in diabetes mellitus that precedes .the onset of albuminuria by many years. to The temporal relationship between the diabetic state and basement membrane thickening is apparent in renal transplants in diabetic recipients, where thickening of the glomerular basement membrane (GBM) has been documented within 2 years of surgery.22,23 Our patient certainly had diabetes long enough to explain the observed pathology. Although greater degrees of basal lamina thickening have been associated with clinically significant proteinuria, basement membrane changes do not correlate with loss of renal function .

Fig 3. Glomerular mesangium at high magnification showing cell processes (*) and fibrillar mesangial matrix. The microfibrils measured 20 nm in diameter using a diffraction grating. (Uranyl acetate and lead citrate; original magnification X70,000.)

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In contrast to the lack of structure-function correlation related to GBM abnormalities in diabetes, when mesangial expansion passes a critical point it appears to be associated with loss of renal function. 24,25 It has been suggested that mesangial expansion occurs at the expense of the actual capillary filtration surface and that this may be the critical morphologic feature that predicts loss of filtration function . Microfibrils, such as those seen in Fig 3, have been demonstrated by electron microscopy in the normal mesangium, and they presumably contain some of the normal structural proteins at that site, which include types IV and VI collagen, heparin sulfate, proteoglycan, chondroitin sulfate proteoglycan, laminin, and fibronectin.26 In the diabetic kidney, mesangial microfibrils Me increased in number and, noting their prominence, Sohar et al called the condition " diabetic fibril10sis."27 Mesangial accumulation of microfibrils demonstrated in this case and other diabetics must be differentiated from other types ofpathological extracellular protein deposits, such as amyloidosis28 and immunotactoid glomerulopathy.29 It is possible that they graphically represent the possibility that advanced glycosylation endproduct (AGE)-related cross-linked structural

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proteins are inhibited from normal catabolic turnover and, as a consequence, accumulate in the glomerulus (see below). Pancreas transplantation in humans30 or islet cell transplant in rats 31 have been reported to have a salutary effect on the mesangial changes of the diabetic state. It is conceivable that this is explained by the interruption of biochemical events which lead to the formation of advanced glycosylation end products at this site. Histologic diagnosis: Diabetic nephropathy. Dr Rodby: Given the histopathologic diagnosis of diabetic nephropathy, a number of therapeutic interventions must be considered. The degree of proteinuria in this patient may be considered a marker for early clinical diabetic nephropathy. This was accompanied by a decrease in the creatinine clearance, hypertension, and advanced histopathologic changes associated with the diabetic state. Current therapeutic interventions are thus directed toward retarding the progression of renal pathology. A knowledge of the proposed pathophysiologic mechanisms responsible for the development of diabetic nephropathy is therefore necessary to be able to approach treatment options. I will briefly review these processes, but will focus the discussion on the mechanism of nonenzymatic glycosylation of proteins and the resultant biochemical and histopathologic changes that have been demonstrated both in vitro and in vivo as a result of this pathophysiologic process. The evidence for altered intrarenal hemodynamics playing a pathogenetic role in the development and evolution of the glomerular lesion, as well as the extremely important role of hypertension control in slowing the progression of renal failure, have been reviewed. 32 ,33 Protein restriction may have similar salutary effects. 34 ,35 On the other hand, we do not yet have evidence that improved blood glucose management using insulin will have an impact on disease progression. Pancreas transplantation cures the diabetic hyperglycemic state and has been shown to halt the progression of recurrent diabetic nephropathy histopathologically in the renal transplant. 30 The relevance of this model to the prevention of diabetic nephropathy in the native kidney has not yet been determined. Several biochemical abnormalities common to the diabetic state have been suggested to be the

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pathogenetic link to the development of diabetic microangiopathy and, specificaIly, diabetic glomerulosclerosis (Table 1). These mechanisms are all based on altered carbohydrate metabolism. One of the more popular theories relates to cell injury induced by the intracellular osmotic effects of increased sorbitol accumulation due to activation of the polyol pathway. Aldose reductase is the enzyme responsible for the reduction of aldoses-glucose and galactose-to their corresponding sugar alcohols, sorbitol and galactitol. This reaction is termed the "polyol pathway." Aldose reductase operates at low catalytic rates when glucose concentrations are in the physiologic range, but increases its activity substantially in the presence of hyperglycemia. In the diabetic, this results in an increase in intracellular sorbitol, which may induce cellular injury related to the increase in intracellular osmolality and subsequent ceIlular swelling. 36 ,37 As osmotic swelling proceeds, membrane permeability is altered, with an efflux of myo-inositolleading to intraceIlular myo-inositol deficiency. Also affected as a result of this process are the activities of protein kinase C and sodium-potassium adenosine triphosphatase. 38 ,39 These biochemical alterations have been demonstrated in the diabetic lens, where polyol accumulation leads to cataract formation. 40 Although there is some evidence that the alterations in the polyol pathway are associated with the development of glomerular hyperfiltration in the diabetic,41 reports on the presence of aldose reductase in renal tissue have been variable and its role in the development of nephropathy is yet to be defined. Yet another proposed mechanism of altered glomerular biochemistry involves changes in the sulfated glycoproteins in the GBM and mesangium. 42 -45 Kanwar et al 44 demonstrated that the glomerular sulfate incorporation of perfused kidneys was significantly impaired in the diabetic

Table 1. Biochemical Pathophysiologic Mechanisms Proposed in Diabetic Nephropathy

Abnormal intracellular polyol metabolism36 ,37 Intracellular myoinositol deficiency36,37 Alterations in activity of protein kinase C39 Alterations in activity of Na-K ATPase 38 ,39 Alterations in sulfated glycoproteins42-45 Nonenzymatic protein glycosylation 46-48

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kidney when compared with the nondiabetic kidney. As sulfate is a major component of charge selectivity of the glomerular capillary wall, they proposed that the relative deficiency of these charges may enhance transglomerular passage of plasma proteins. This may allow their adsorption to the glomerular extracellular matrix, thereby "clogging" it with a resultant reduction in GFR. 44 The final mechanism, and the main focus of this discussion, relates to the phenomenon of nonenzymatic glycosylation of proteins. 46-48 This mechanism proposes that disease progression in diabetes mellitus is due to the pathologic accumulation of diverse glycosylated proteins in the blood vessels, manifest in the glomerulus as thickening of the GBMs and increased mesangial matrix. Proteins in contact with glucose (in vitro and in vivo) can spontaneously undergo a reversible nonenzymatic reaction that results in the attachment of glucose to the E-amino group of lysine. The aldimine that is formed is referred to as a Schiff-base. The kinetics of this reaction proceed at a rate proportional to the ambient glucose concentration. This reaction is reversible; however, a Schiff-base can rearrange to form a more stable ketoamine, the Amadori product (Fig 4). Both Schiff-bases and Amadori products are considered early glycosylation end-products. In vitro, equilibrium levels of Schiff-bases are reached within weeks, while those of Amadori products occur over several weeks. 48 Amadori products, if formed on proteins with relatively long half-lives (eg, structural proteins like collagen, elastin, myelin), may spontaneously undergo a series of irreversible nonenzymatic rearrangements, cyclizations, and dehydrations to form advanced glycosylation end-products (AGE) (Fig 4). Because of the irreversible nature of this reaction, the levels of these products remain elevated despite reductions in glucose levels and continue to accumulate over the life of the glycosylated protein. AGEs can be identified by a characteristic brown pigment and by their fluorescent properties. They can also be quantified using a specific macrophage radioreceptor assay for AGEs. 5o AGEs appear to be pathophysiologically important, as they may form irreversible covalent bonds with amino groups on other proteins through nucleophilic addition reactions. This resulting reaction may result in the permanent cross-linking of two structural proteins

BASE

AMADORI PRODUCT

AGE DERIVED CROSSLIN~

Fig 4. The nonenzymatic reaction between glucose and protein results in the reversible formation of the Schiff-base and the Amadori product. Further reactions lead to the irreversible formation of AGE-related protein cross-links.

or the cross-linking and trapping of a circulating protein to a structural protein 51 ,52 (Fig 5). Two general types of AGE-related cross-links have been characterized. The first involves the condensation of two Amadori products' and resembles the heterocyclic imidazole derivative 2furoyl-4(5)-(2-furanyl) I-H-imidazole51 (Fig 4). The second appears to form from Amadori-derived fragmentation compounds such as 3-deoxyglucosone. These are highly reactive dicarbonyl compounds that appear to cyclize and form electrophilic pyrrole intermediates with highly reactive hydroxyl groups in benzylic positions that react with amino groups to form pyrrolebased cross-links. 52 AGE tissue levels, as quantified by measurement of fluorescence, have been shown to be markedly increased in all tissues of the diabetic compared with the nondiabetic. The degree of nonenzymatic glycosylation of aortic tissue at autopsy of diabetic patients appears to correlate with the degree of vascular complications. 53 Cross-linking of proteins may be manifest clinically in several ways. Cross-linked collagen molecules are less susceptible to enzymatic degradation and this is a mechanism whereby normal turnover may be impaired. 49 This process could be an explanation for the basement membrane thickening and mesangial matrix changes seen in diabetic nephropathy. The presence of AGE in diabetic GBMs 54 and the correlation between the serum levels of AGE peptides and renal dysfunction 55 provide support for this hypothesis. In addition, any number of circulating proteins (eg, albumin, immunoglobulins) may bind to glycosylated collagen. Glycosylated collagen may also bind low-density lipoprotein and it has been proposed that this could also playa role in the development of atherosclerosis. 49 The immuno-

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®®®®®®®

a·t.

b.

t + d.

c.

®-glucose

aminoguanidine

t

@-AGE

A -Lipoprotein

Y-JgG

~-Albumin

Fig 5. (a) Collagen becomes glycosylated by a reversible nonenzymatic reaction with glucose. (b) These glycosylated proteins spontaneously undergo a series of complex nonenzymatic irreversible reactions to form AGEs. (c) These AGEs are then able to irreversibly crossreact with other structural proteins and cross-link them in addition to binding with and permanently trapping circulating proteins, ie, immunoglobulins, lipoproteins, and albumin. (d) Aminoguanidine prevents AGE formation and thereby prevents protein cross-linking and trapping.

fluorescence findings of linear staining ofIgG on the GBM (Fig 2) may represent a nonenzymatic cross-linking of this molecule to type IV collagen. Mesangial expansion could also reflect the process of interaction of circulating glycosylated peptides with structural proteins. Dr Schwartz has offered

the interesting, though speculative, suggestion that the electron micrographic appearance of the lesion of diabetic fibrillosis (Fig 3) represents an exaggeration of cross-linked proteins induced by the process of AGE-related reactions. If substantiated, this would indeed be a graphic morphologic illustration of the biochemical process which we are discussing. Recent studies have demonstrated AGE receptors on macrophages. Coupling of AGE proteins to the receptor results in tumor necrosis factor and interleukin-I synthesis and secretion. This suggests that AGEs may act as a signal for growth-promoting factor secretion, and that a disturbance of this balance may lead to a pathologic proliferative response.56 Mesangial cells in culture have been shown to proliferate in response to mesangial matrix altered by nonenzymatic glycosylation. 57 These cell growth responses to AGE receptor interactions may contribute to the above-mentioned mechanisms of AGE-related tissue damage. Should this pathophysiological explanation for the development of diabetic complications be correct, then pharmacologic agents capable of inhibiting AGE formation would be of obvious benefit. A number ofhydrazine compounds have been tested based on the hypothesis that they would be chemically reactive with early endproducts of the lysine-glucose interaction.58 The goal of this reaction is the formation of an unreactive substituted early glycosylation product rather than an AGE. The nucleophilic hydrazine compound aminoguanidine-HCL (CH 6N 4 • HCl, molecular weight 110.5) is the most studied of these compounds and has been shown to almost completely inhibit AGE formation both in vitro and in vivo (Fig 5). As a result, aortic collagen AGE content58 and rat tail collagen solubility 59 have been normalized in diabetic animals receiving this agent. In addition, animals with diabetes demonstrate glomerular IgG deposits, just as is seen in humans and noted in this patient (Fig 2). GBM IgG content is normalized in the diabetic animal receiving aminoguanidine. 60 More recently, diabetic rats given aminoguanidine were shown to have developed less proteinuria than control diabetic rats. These treated animals did not develop increased mesangial volume as is seen in diabetic animals. 61 As mes-

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angial volume appears to correlate with decreased renal function in human diabetic nephropathy, this may be a finding of great importance. 24 The precise biochemical interactions whereby aminoguanidine prevents AGE formation are now being elucidated. Recently, aminoguanidine has been shown to react with Amadori-derived fragmentation products such as 3-deoxyglucosone in solution, thereby preventing subsequent AGE formation on susceptible proteins. 62 Aminoguanidine may also have an effect by its ability to inhibit either nitric oxide production or the physiologic effect of this compound. Nitric oxide is a potent vasodilator and interference with the physiologic function of this substance could conceivably alter renal blood flow and vascular permeability in the diabetic state. 63 The extent of human clinical benefit from advanced glycosylation end-product inhibition is yet to be determined. The exciting animal data in rodents rendered diabetic make human trials with aminoguanidine mandatory. To date, the use of aminoguanidine in diabetic humans has been limited to dosing and toxicity evaluations. A multicentered, placebo-controlled, doubleblind trial with aminoguanidine in early overt diabetic nephropathy will begin in 1993. Its potential role in earlier diabetic nephropathy cannot be ignored, given the fact that histopathologic changes have been demonstrated to occur within

3 to 5 years of the onset of diabetes. Identification of a subset of patients with very early diabetic nephropathy would depend on the demonstration of persistent elevations of low levels of UAE. Progression of renal failure at this stage may be very slow and measurements of renal function and proteinuria lack the sensitivity to determine efficacy. Therefore, serial renal biopsies with careful histomorphometric measurements may be required to demonstrate an effect at this early stage. 64 In summary, this patient with 100M has a somewhat unusual early presentation of diabetic nephropathy. Advanced clinical and histopathologic disease is present despite a duration of diabetes for only 9 years. His management should be directed at the prolongation of his coarse to renal failure and includes strict blood pressure control and dietary protein restriction. 33-35 By the end of 1992, the results of the Collaborative Study Group Study of Angiotensin-Converting Enzyme Inhibition in Type 1 Diabetic Nephropathy will be known and this may add to the armamentarium. The role of aldose reductase inhibitors is yet to be determined. Reports on their use in diabetic neuropathy and retinopathy have demonstrated inconsistent results. 65 ,66 The question of the benefit of the inhibition of AGE formation will soon be under evaluation and may also offer promise for the future.

REFERENCES I. Ludvigsson J: C-peptide in juvenile diabetics beyond the post initial remission phase. Acta Paediatr Scand 66: 177180,1977 2. Berglund J, Newberg K, Engstrom L, et al: Prevalence of microalbuminuria in a defined Swedish population of insulin-dependent diabetic patients. Kidney Int 37: 1381, 1990 3. Mckenna MJ, Arias C, Feldkamp CS, et al: Microalbuminuria in clinical practice. Arch Intern Med 151: 17451747,1991 4. Anderson AR, Christiansen JS, Andersen JK, et al: Diabetic nephropathy in type I (insulin dependent) diabetes: An epidemiologic study. Diabetologia 25:496-501, 1983 5, Viberti GC, Hill RD, Jarrett RJ, et al: Microalbuminuria as a predictor of clinical nephropathy in insulin-dependent diabetes mellitus. Lancet I: 1430-1432, 1982 6. Mogensen CE, Christensen CK: Predicting diabetic nephropathy in insulin-dependent patients. N Engl J Med 311: 89-93, 1984 7. Steffes MW, Chavers BM, Bilous RW, et al: The predictive value of microalbuminuria. Am J Kidney Dis 13:2528, 1989

8. Jarrett RJ, the Microalbuminuria Collaborative Study Group: Microalbuminuria in type I diabetic patients: Prevalence and clinical characteristics. Diabetes Care 15:495-501, 1992 9. Chavers BM, Bilous RW, Ellis EN, et al: Glomerular lesions and urinary albumin excretion in type I diabetes without overt proteinuria. N Engl J Med 320:966-970, 1989 10. 0sterby R: Early phases in the development of diabetic glomerulosclerosis. Acta Med Scand 574:1-80, 1975(suppl) II. Close CF, MCS Group: Sex, diabetes, duration and microalbuminuria in type I (insulin dependent) diabetes mellitus. Diabetologia 30:508A, 1987 (abstr) 12. Mogensen CE, Mauer SM, Kjellstrand CM: Diabetic nephropathy, in Schrier RW, Gottschalk CW (eds): Diseases of the Kidney. Boston, MA, Little Brown, 1988, pp 23952439 13. Lemann J, Doumas BT, Sasse EA, et al: Diabetic nephropathy: Urinary albumin or total protein? Ann Intern Med III :343-344, 1989 14. Viberti GC, Keen H: The patterns of proteinuria in diabetes mellitus. Relevance to pathogenesis and prevention of diabetic nephropathy. Diabetes 333:686-692, 1984

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