The kidney in diabetes

Diabetic nephropathy in insulin-dependent diabetic patients: renal hemodynamics and derived treatment strategies

Late complications such as retinopathy and neuropathy contribute substantially to the morbidity of patients with diabetes mellitus but have only moderate effect on their life expectancy. However, once diabetic nephropathy occurs, life expectancy of patients with diabetes mellitus is shortened considerably. This review discusses briefly several possible pathogenetic mechanisms involved in the development of diabetic nephropathy. Changes in renal hemodynamics as the initiating and contributing factor to the development of diabetic nephropathy are discussed in more detail. Finally, the article reviews possible therapeutic measures to prevent the development of diabetic nephropathy, or to slow down its progression.

No microalbuminuria or other adverse effects of long-standing hyperfiltration in humans with one kidney

Hypertrophy and hyperfiltration are characteristic features of single kidneys and kidneys of patients with insulin-dependent diabetes mellitus (IDDM). In both cases the hyperfiltration has been suggested to be involved in the pathogenesis of renal functional deterioration. We studied the effect of long-standing hyperfiltration on kidney function in 29 subjects with one kidney, three of whom were insulin-dependent diabetics. Four groups were studied: (1) uninephrectomized less than 10 years since uninephrectomy (UN) (n = 7; age, 30 +/- 6 years); (2) uninephrectomized greater than or equal to 10 years since UN (19 +/- 11 years, 10 to 52); n = 14; age, 38 +/- 15 years; (3) congenital unilateral renal agenesis (n = 5, age, 39 +/- 16 years); and (4) IDDM patients with one kidney (n = 3; age, 28 to 52 years; diabetes duration, 8 to 31 years; years with one kidney, 18 to 30). Glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured by the constant infusion technique, kidney volume (KV) by ultrasonic scanning, and urinary albumin excretion rate (UAE) by radioimmunoassay. In all subjects GFR, RPF, and KV were within the normal range, representing a single kidney hyperfiltration of approximately 70% and hypertrophy of approximately 100%. Only one of the subjects with renal agenesis had an elevated UAE (117 micrograms/min); the remainder had a normal UAE, ie, less than 10 micrograms/min, and the diabetics were below the risk level of 20 micrograms/min. Serum creatinine was normal and BP was slightly elevated in only three subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Early glomerular hyperfiltration and the development of late nephropathy in type 1 (insulin-dependent) diabetes mellitus

We performed a follow-up study of the glomerular function in a series of 29 Type 1 (insulin-dependent) diabetic patients who had been studied 18 years previously. Initial median duration of diabetes was 2 years (range 0-9) and at follow-up 21 (17-27) years. At follow-up, 8 diabetic patients exhibited increased urinary albumin excretion rate 515 (32-3234) micrograms/min with glomerular filtration rates significantly lower than 21 diabetic patients with normal urinary albumin excretion (85 vs 126 ml/min/1.73 m2; p less than 0.01). The patients with increased urinary albumin excretion rate also had higher arterial blood pressure (145/90 vs 120/80) mm Hg; p less than 0.02) and increased frequency of proliferative retinopathy (7 out of 8 vs 2 out of 21; p = 0.0001) as compared to the group with normal urinary albumin excretion. However, we found no association of increased urinary albumin excretion rate (incipient or overt nephropathy) to early glomerular hyperfiltration as median initial glomerular filtration rate was 142 ml/min/1.73 m2 in the diabetic patients with increased urinary albumin excretion and 147 ml/min/1.73 m2 in the patients with normal excretion rate (p greater than 0.05).

Some lessons from the studies of renal biopsies in patients with insulin-dependent diabetes mellitus

The authors have studied relationships of renal structure and function in more than 100 patients with insulin-dependent diabetes mellitus (IDDM), aged 13-55 years (mean, 30 years) with diabetes for 1-30 years (mean, 19 years). The authors confirmed the unique nature of the diabetic lesions that, in constellation, occur in no other disease. It was found that increased fractional mesangial volume (Vv Mes) is strongly associated with decreased glomerular filtration rate (GFR), proteinuria, and hypertension and that all patients with overt diabetic nephropathy have Vv Mes in excess of 0.35 micron 3/micron 3. This relationship results from constriction of the capillary lumen and filtration surface as a consequence of increased Vv Mes. Global glomerulosclerosis (scarring) is common in IDDM patients and appears related to arteriolar hyalinosis. Focal segmental glomerulosclerosis is a rare lesion in these patients. Having a single kidney (transplanted IDDM patients) is not associated with accelerated lesion development. The presence or absence of microalbuminuria (MA), per se, does not predict underlying glomerular structure, which may vary from the normal range to a level of pathology bordering on that regularly associated with overt nephropathy. However, when MA is associated with hypertension, or reduced GFR or both, urine albumin excretion (UAE) generally exceeds 40 mg/24 hr, and glomerular pathology is always present. The authors concluded that diabetic nephropathy is a unique renal disorder that cannot be caused by hemodynamic factors alone. The authors further conclude that MA becomes a predictor only when other features of overt nephropathy are already present and that serious diabetic glomerular lesions can be present in patients with normal UAE.

Prognostic implications of renal hypertrophy in diabetes mellitus

Early in the course of type 1 diabetes mellitus, hypertrophy of the kidney is a consistent finding that is easily diagnosed using current noninvasive methods, especially ultrasonography. Renal functional changes occur in association with hypertrophy, most notably glomerular hyperfiltration. The structural counterpart of this functional change is an early increase in capillary filtration surface area. In most forms of nondiabetic renal hypertrophy, kidney size is closely linked to GFR. In contrast, in diabetes, persistence of hypertrophy after the clinical onset of overt kidney disease (microalbuminuria, hypertension, decreased GFR, etc.) suggests that sustained release of one or more growth factors may continue even after kidney function declines. The fact that growth factors can act in both an autocrine and paracrine fashion raises the possibility that the local effects of such substances may act as local mediators of kidney growth. Failure of renal hypertrophy to reverse following strict glycemic control for a few months may turn out to be an important prognostic indicator of future progression of the renal disease, but this remains to be established. Prospective studies of kidney size in patients with newly diagnosed type 1 diabetes, using accurate noninvasive methods, may be helpful in establishing whether irreversible ("autonomous") hypertrophy of the kidney is indeed a useful prognostic indicator. As therapies are developed that target the different microvascular complications of diabetes (retinopathy, nephropathy, neuropathy), a noninvasive estimation of kidney size may be a cost-effective method of predicting ultimate renal involvement. Since microalbuminuria occurs relatively late in the disease process, early and persistent hypertrophy of the kidney may become a useful prognostic test in the earliest stages of the disease.

Metallothionein metabolism in the liver and kidney of the streptozotocin-diabetic rat

1. Elevated levels of metallothionein (MT)-I and -II were identified in the liver and kidney of insulin-deficient diabetic rats. 2. The relative rate of MT synthesis and the turnover of cytoplasmic MT were both accelerated in the liver of diabetic rats. 3. The rate of synthesis of MT, but not its cytoplasmic turnover, was increased in diabetic kidney. 4. Maximal relative rates of MT synthesis in liver and kidney were first observed at 4 and 10 days, respectively, after inducing the diabetic condition. 5. The altered metabolism of hepatic MT in diabetic rats was attributed primarily to disturbances in endocrine status, while the altered metabolism of renal MT was largely due to accumulation of excessive dietary copper in the kidney.

Epithelial crescent in diabetic glomeruli. A case report

The kidney as a target organ for secondary microvascular complications of diabetes mellitus represents a major problem. The pathology of diabetic glomerulopathy is well known. The coexistence of immunocomplex-mediated glomerulonephritis and diabetes mellitus has rarely been reported. The presence of crescents in glomerular disease of diabetes mellitus has been usually ignored in the literature. The present study describes one patient with epithelial crescentic diabetic glomerulopathy with rapidly progressive renal failure.

Diabetes mellitus associated changes in glomerular glycocompounds: a fluorescence microscopical study

Renal biopsy specimens showing histological alterations typical of advanced diabetic glomerulopathy were studied for changes in glomerular glycoconjugates, using fluorochrome-coupled lectins as probes. All samples studied showed a marked reduction in the binding of Triticum vulgaris (WGA) lectin in the glomerular basement membranes. On the other hand, 'new' glomerular binding sites for the lectins of Dolichos biflorus (DBA), Helix pomatia (HPA) and Arachis hypogaea (PNA), recognizing galactosyl moieties of glycoconjugates and giving no reaction in normal glomeruli, were seen in all samples studied. In addition, Wistaria floribunda lectin (WFA), recognizing galactosyl and, N-acetylgalactosaminyl configurations in glycoconjugates, gave a typical linear binding along the glomerular basement membranes, differing markedly from its reaction with normal kidney. Ulex europaeus (UEA I) showed reduced binding in the glomeruli of diabetic nephropathy. The results show that changes in glomerular glycoconjugates may appear in diabetic nephropathy, suggesting a disturbance in the turnover of the non-reducing terminal saccharide residues. In addition, the results show that lectins are useful probes for studying these changes further.

Impact of metabolic control in progression of clinical diabetic nephropathy

Renal clearance of 51Cr-EDTA as a measure of glomerular filtration rate was followed prospectively for 21 months in 18 Type 1 (insulin-dependent) patients with juvenile-onset diabetes and nephropathy. Hypertension was treated aggressively, attaining a mean blood pressure of 154/88 mmHg in the supine and 126/82 mmHg in the standing position. The mean glycosylated haemoglobin value (HbA1c) during the observation period was found to correlate well with the mean of random blood glucose values (r = 0.72). It also correlated to the rate of glomerular filtration rate decline over time, whether the latter was calculated as slope coefficient for all available data (r = -0.52, p less than 0.05) or based on the first and last observations only (r = -0.57, p less than 0.05). In a multiple linear stepwise regression analysis also including mean arterial blood pressure, the correlation between glomerular filtration rate decline and HbA1c was significant at p less than 0.01; this explained one-third of the progression, while mean arterial pressure could not be shown to contribute. It is concluded that hyperglycaemia, contrary to the general belief, is a risk factor for the progression of clinical diabetic nephropathy with reduced glomerular filtration rate.

Renal lesions in a strain of spontaneously diabetic WBN/Kob rats

In WBN/Kob strain rats, only males spontaneously develop hyperglycemia, glycosuria, hypoinsulinemia and glucose intolerance from about nine months of age. The kidneys of male rats of this strain were histopathologically studied to evaluate the changes which appeared as complications of diabetes mellitus. Thickening of the basement membrane, increase of the mesangial matrix and fibrin-cap lesions were noted in the glomeruli. Armanni-Ebstein degeneration was occasionally found in the tubules. Linear deposition of plasma components such as IgG and albumin in the basement membrane of the glomeruli, tubules and Bowman's capsule characterized the immunohistological pattern. These findings are similar to the findings in diabetic nephropathy in humans. Since the onset of diabetes mellitus in the strain is slow and symptoms are generally mild, insulin administration is usually not necessary for survival. This strain, therefore, appears to be an important animal model for the study of complications of diabetes in humans.

Clinical diabetic nephropathy: natural history and complications

Diabetic nephropathy develops in about 45% of insulin dependent diabetics of whom two-thirds will develop renal failure, the rest dying from cardiovascular disease. Most of the excess mortality of insulin dependent diabetics occurs in those with proteinuria. Among non-insulin dependent diabetics nephropathy is also an important cause of increased mortality but this is mainly from cardiovascular disease. Once diabetic nephropathy is established it progresses relentlessly to end-stage renal failure over about seven years, but ranging from five to 20 years. The explanation for the different rates of progression in individual patients is not understood. Hypertension accompanies diabetic nephropathy and its treatment may retard the progression of renal failure. Other forms of intervention include glycaemic control which has not been shown to have any effect, and protein restriction for which no conclusions can be drawn at present. The diagnosis of diabetic nephropathy is straightforward in the presence of a typical history and clinical features. Non-diabetic renal disease is sometimes the cause of renal failure and may require specific treatment; prognosis for renal failure treatment may be better than for nephropathy patients with other diabetic complications. Other diabetic complications develop as diabetic nephropathy progresses, most notably cardiac and peripheral vascular disease. Proliferative retinopathy and neuropathy are considerable problems and their management needs attention both before and after renal failure treatment.

Glomerular membranopathy in adolescents with insulin-dependent diabetes

Kidney biopsy specimens from 15 patients ranging in age from 11 to 19 years with two- to 14-year histories of insulin-dependent diabetes mellitus were evaluated electron microscopically. Although the mean duration of disease was only eight years, the glomerular basement membrane (GBM) in these patients showed a variety of alterations typical of insulin-dependent diabetes mellitus. Saccular glomerular microaneurysms, previously little recognized, were seen in six of the specimens. These lesions, always associated with breaks in the paramesangial BM, were morphologically distinct from the ectatic capillary loops and glomerular capillary aneurysms described previously in diabetic glomerulopathy. All of the patients with such aneurysms also had other severe GBM alterations. Lytic or mechanical injury to the structurally and biochemically altered diabetic GBM may be responsible for the formation of microaneurysms.

Renal vessel changes in diabetic KK-mice

Glomerular hyperfiltration is thought to be of pathogenic importance in the structural abnormalities seen in diabetic nephropathy but its cause is not known. It has been suggested that the changes in the preglomerular vascular system may lead to a disturbance of glomerular blood flow in diabetes. We therefore examined the potential role of changes in the vascular system supplying the glomerulus in diabetic mice. The kidneys of 15 diabetic KK-mice (aged 2, 5 and 12 months) were studied and compared with those of 15 non-diabetic NMRI-mice. We determined vessel cross-sectional, wall and lumen areas of 408 small intrarenal arteries, 5,140 arterioles and 518 preglomerular afferent arterioles using a morphometric method. At 2 months, diabetic arteries and arterioles were considerably smaller than the controls, while preglomerular afferent arterioles were the same size. At 12 months, however, all diabetic vessels measured were much larger than the controls. This was chiefly due to an excessive increase in lumen area: in the diabetic arteries the mean (+/- SEM) lumen area at 12 months was 1,057 +/- 142 vs 616 +/- 72 sq mu in controls (P less than 0.001), in arterioles 176 +/- 7 vs 115 +/- 4 sq mu (P less than 0.001) and in preglomerular afferent arterioles (at 5 months) 131 +/- 8 vs 95 +/- 7 sq mu (P less than 0.001). The dilatation of small intrarenal arteries and arterioles in diabetic mice may result from progressive impairment of vasoconstriction and may be a cause of the glomerular hyperfiltration in diabetes.

The glomerular hyperfiltration of diabetes is not associated with elevated plasma levels of glucagon and growth hormone

Plasma concentrations of glucagon, growth hormone and glucose were measured hourly during an ordinary treatment day in 11 Type 1 (insulin-dependent) diabetic patients with high glomerular filtration rate, 11 Type 1 diabetic patients with normal glomerular filtration rate matched for age, diabetes duration and sex, and five healthy control subjects, simultaneously with the measurement of the glomerular filtration rate using 51Cr EDTA clearance. Plasma glucagon profiles were not statistically distinguishable (p = 0.49) from control values in either group, although they were somewhat lower in the hyperfiltering group. Plasma growth hormone values were higher than control (p = 0.07) in both diabetic groups, but were not different between these two groups (p = 0.94). All indices of glycaemic control (glycosylated haemoglobin, urinary glucose excretion, and plasma glucose concentration) were higher in the hyperfiltering group, although no single index reached statistical significance. No correlations between concentrations of these substances and glomerular filtration rate were found. Elevated plasma concentrations of glucagon and growth hormone do not characterise those diabetic patients with high glomerular filtration rate.

The changing natural history of nephropathy in type I diabetes

Events in the natural history of diabetic nephropathy (including the onset of persistent proteinuria and end-stage renal failure) were studied in a cohort of 292 patients with juvenile-onset type I diabetes who were followed for 20 to 40 years. The risk of persistent proteinuria increased rapidly between the fifth and 15th years of diabetes and declined thereafter. This pattern suggests that susceptibility to this complication was limited to a subset of patients and was exhausted over time. Patients with the most frequent severe hyperglycemia (the highest quartile) during the first 15 years of diabetes had a risk of persistent proteinuria that was four and a half times higher than that for those with the least frequent hyperglycemia (the lowest quartile). Patients whose diabetes was diagnosed in the 1930s had twice the risk of persistent proteinuria as those in whom the condition was diagnosed in later decades. Once persistent proteinuria appeared, progression to renal failure almost always followed. Half reached this stage within 10 years, and the interval for progression did not vary according to sex, frequency of hyperglycemia, or calendar year of diagnosis of diabetes. This period, however, was significantly shorter (eight versus 14 years) for patients whose diabetes was diagnosed after puberty than for those who were younger at onset. In conclusion, the development of diabetic nephropathy consists of at least two stages. The onset of proteinuria, although related to the level of exposure to hyperglycemia, appears to be influenced by genetic and/or environmental factors. The second stage, progression to renal failure, seems to be influenced by processes related to maturation or aging.

Correlates of biopsy-studied nephropathy in young patients with insulin-dependent diabetes mellitus

We have correlated pathologic findings in kidney biopsies from 12 adolescents with proteinuria or hypertension with severity of limited joint mobility (LJM) and retinopathy. We compared mean glucosylated hemoglobin (GHB) and clinical findings in these patients with those in patients without proteinuria or hypertension. Severity of LJM correlated with basement membrane thickening. Protein excretion correlated with degree of mesangial matrix increase and basement membrane changes. Retinal changes were related to basement membrane thickness and duplication. Despite treatment, blood pressures were significantly higher in patients with nephropathy than in the comparison group. Glycemic control status was generally poor and did not correlate with pathologic changes. The narrow spectrum of control did not permit assessment of possible effects of milder metabolic derangement. However, the similarity of GHB values in the groups with and without nephropathy implicates other factors. The group with clinical nephropathy had more LJM than did the comparison group, reaffirming LJM as a risk factor for early microvascular disease. Biopsy changes of nephropathy may begin relatively early in the course of diabetes (less than 7 years in three of our patients) and is already advanced when proteinuria appears.

A comparison of kidney disease in type I and type II diabetes

Diabetes is the most important cause of ESRD in the Western world. Type I and II diabetes appear to contribute importantly to ESRD although, obviously, the prevalence of ESRD is higher in Type I. Microalbuminuria may predict later development of overt clinical nephropathy in both Type I and Type II patients. In both diabetes subtypes current evidence favours the dysmetabolism of diabetes as causative. There are clinical observations in Type I and renal morphologic evidence in Type II indicating that risk of nephropathy is, in part, related to the magnitude of hyperglycemia. Institution of strict glycemic control fails to reverse established clinical nephropathy in Type I diabetes. Efforts to determine if precise regulation of blood sugar can prevent nephropathy in patients with Type I and Type II diabetes are currently incomplete.

Structural-functional relationships in diabetic nephropathy

Renal biopsies in 45 patients with insulin-dependent diabetes mellitus (IDDM) were examined by semiquantitative light microscopy and quantitative electron microscopic stereologic morphometry. In these 14 males and 31 females, aged 13-52 yr, who had had IDDM for 2.5-29 yr there was no strong relationship between either glomerular basement membrane (GBM) thickness or mesangial expansion and duration of IDDM. There was only a weak relationship between the thickness of the GBM and expansion of the mesangium. Thus, GBM thickening and mesangial expansion in IDDM occur at rates that often differ from one another and that vary greatly among patients. The clinical manifestations of diabetic nephropathy, albuminuria, hypertension, and decreased glomerular filtration rate related poorly or not at all to GBM thickening. In contrast, all light and electron microscopic measures of mesangial expansion were strongly related to the clinical manifestations of diabetic nephropathy, although in the absence of these clinical findings, it was not possible to predict the severity of any of the diabetic glomerular lesions. Mesangial expansion had strong inverse correlations with capillary filtering surface area density. It is hypothesized that mesangial expansion could lead to glomerular functional deterioration in IDDM by restricting the glomerular capillary vasculature and its filtering surface. However, capillary closure, glomerular sclerosis, and interstitial fibrosis could also contribute to the clinical manifestations of this disorder.

Comparison of long-term renal hemodynamic effects of methyldopa and propranolol in patients with hypertension and renal insufficiency

Studies were carried out in 15 patients with renal insufficiency and hypertension to compare the long-term effects of methyldopa and propranolol on renal hemodynamics. Inulin and PAH clearance measurements were made under baseline conditions and four to six months of antihypertensive therapy with each of the two drugs. Eight of the 15 patients (group I) were started on methyldopa and then switched to propranolol; and in the other seven (group II), the sequence was reversed. There were no statistical differences in blood pressure or inulin or PAH clearances under baseline conditions between the two groups of patients. Blood pressure was controlled equally with the two drugs in combination with furosemide. In group I, there was no significant effect of either antihypertensive drug on inulin clearance, but PAH clearance was significantly higher during methyldopa than propranolol therapy. In group II, the same higher PAH clearance was found with methyldopa, even though the sequence of drug administration was opposite to that of group I. Challenge with iv furosemide resulted in a greater 3-hour natriuresis during methyldopa than propranolol treatment. The observations indicate that glomerular filtration rate (GFR) is not significantly affected by long-term treatment with methyldopa or propranolol but that renal plasma flow (RPF) is higher during treatment with methyldopa in patients with renal insufficiency and hypertension. The higher RPF apparently enhances the acute natriuretic effect of iv furosemide.

Glycaemia, arterial pressure and micro-albuminuria in type 1 (insulin-dependent) diabetes mellitus

Plasma glucose control and arterial pressure were assessed in 28 Type 1 (insulin-dependent) diabetic patients with different degrees of micro-albuminuria. They were divided into two groups according to their urinary albumin excretion rate: a low micro-albuminuria group (n = 16) with albumin excretion ranging between 12.1 and 28.9 micrograms/min and a high micro-albuminuria group (n = 12) with albumin excretion between 32.4 and 91.3 micrograms/min. The groups were matched for age, sex and duration of diabetes with the same number of normo-albuminuric (2.0-10.4 micrograms/min) diabetic control subjects. Both the low and high micro-albuminuria groups had significantly higher glycosylated haemoglobin levels and mean plasma glucose concentrations during a 24-h profile than their respective normo-albuminuric control subjects. A correlation between glycosylated haemoglobin level and urinary albumin excretion rate was found in the whole study group (r = 0.48; p less than 0.001). Arterial pressure (both systolic and diastolic) was significantly higher in the high micro-albuminuria group than in either the control group or the low micro-albuminuria group. A significant correlation was found between arterial pressure and albumin excretion rate in the whole study population (r = 0.49; p less than 0.001) as well as in the pooled micro-albuminuria groups (r = 0.43; p less than 0.05). Multiple regression analysis showed that glycosylated haemoglobin and arterial pressure levels were independently correlated with albumin excretion rates. Diabetic patients with micro-albuminuria of any degree have worse glycaemic control than normo-albuminuric patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic nephropathy

It is estimated that about 50 per cent of all patients with Type I diabetes mellitus develop uremia during the course of their disease. Glomerular microvasculopathy is the most serious and predictable threat to longevity. Following a discussion of this disorder, the author outlines a plan for overall management of each phase of kidney disease so that the patient, his or her family, and all members of the medical team can achieve an understanding of what can be anticipated and accomplished.

The hyperfiltering glomerulus

The observation has been made that after any of a variety of initial renal injuries, nephron units that have been spared undergo structural and functional compensations. The functional compensation of increased perfusion of residual nephrons may present deleterious, maladaptive stresses to those surviving nephrons and lead to their ultimate destruction. This hypothesis provides a final common pathway for the progression of many different renal diseases to renal failure and explains the tendency of renal insufficiency to progress rather than stabilize.

Are the 'second generation' oral hypoglycemic agents really different?

The common denominator of the numerous data collected from experimental studies on isolated organs, on healthy subjects and on diabetic patients, is a specific effect of sulfonylureas on insulin release in the presence (or absence) of glucose. However, there are significant differences in the capacity of the various chemical preparations active in that respect. There are biochemical data suggesting that the glyburide- and chlorpropamide-type of preparations are affecting sites of the B-cells that are different from both the glucose and the tolbutamide receptors. Thus, glibenclamide seems to be qualitatively different from the older sulfonylureas, being more a potentiator than a stimulator. Therefore, we called this type the representative of 'the second generation' drugs. The extra-B-cell actions of these drugs, predominantly the stimulation of somatostatin and the inhibition of glucagon, are favorably adding to these antidiabetic actions. In clinical therapy, these specific properties make it possible to diagnose and to treat patients successfully who were regarded before as being non-responsive to sulfonylureas and being insulin-dependent. On the basis of blood glucose decreases and C-peptide increases, a specific glibenclamide-glucose-response-test has been described which is a valuable medium for predicting the outcome of oral antidiabetic therapy.

Copper accumulation in the soluble and particulate fractions of renal cortex in the streptozotocin-diabetic rat

The accumulation and subcellular distribution of copper in the kidney of streptozotocin-diabetic rats were investigated. Male Sprague-Dawley rats received streptozotocin (50 mg/kg body wt on two consecutive days) intraperitoneally and were fed either commercial or purified diet. The concentrations of copper, zinc, iron, and manganese present in intact kidney, renal cortex, and renal medulla were compared at various times. Chow-fed diabetic rats had a renal copper concentration 2.6 times greater than age-matched controls after 2 weeks. The concentration of zinc was only 30% higher in diabetic kidney than in control tissue, whereas the iron and manganese concentrations were similar for both groups. The additional complement of renal copper was localized entirely in the cortex and was significantly reduced by oral treatment with penicillamine, a copper chelating agent. When diabetic rats were fed purified diet (15-20 ppm Cu), the quantity of copper accumulated in the renal cortex increased from 2.3 to 8.7-fold higher than in control tissue from 1 to 4 weeks, respectively, after injection with streptozotocin. Copper levels in. both the soluble and particulate (165, 000g pellet) fractions of diabetic renal cortex were similarly increased at each time. Gel filtration Chromatographic analysis of the cytosol showed that all of the copper accumulated in the soluble fraction was associated with metallothionein. The distribution of excess copper in the particulate fraction was determined by differential centrifugation. The additional quantity of metal was localized in the crude nuclear fraction of renal cortex in the diabetic rat. Further analysis revealed that the lysosomal fraction from 3-weeek diabetic rats had a copper level 16-fold higher than in the controls. The possibility that accumulation of excessive levels of copper in the streptozotocin-diabetic kidney may contribute to the development of diabetic nephropathy is discussed.

Diabetic nephropathy. Is end-stage renal disease inevitable?

The appearance of proteinuria in an insulin-dependent diabetic patient is an ominous sign. Proteinuria heralds the presence of diabetic nephropathy and early death, or chronic renal failure requiring dialysis or transplantation, in 50% of patients. The pathogenesis of diabetic nephropathy is unknown. Adequate insulin administration is the most important preventive measure. Hypertension, if present, should be aggressively treated to delay progression of renal disease. Good nutrition, prompt treatment of urinary tract infections, and caution in the use of radiocontrast agents are other important preventive measures. Hemodialysis, peritoneal dialysis, and transplantation are options for patients with end-stage renal disease. No matter which is selected, the patient may still have multiple amputations, blindness, congestive heart failure, infections, and uncontrolled glycemia. Advancements are being made, however, that promise a better future for insulin-dependent diabetics.

Selective deep nephron hyperfiltration in uninephrectomized spontaneously hypertensive rats

Studies were carried out to determine the effect of uninephrectomy (UNX) on single nephron hemodynamics and proteinuria in the spontaneously hypertensive rat (SHR). Four groups were studied: two-kidney SHR and normotensive WKY controls; SHR + UNX and WKY + UNX. UNX was performed at age 8 to 10 weeks. Blood pressure and protein excretion were measured periodically, and micropuncture experiments of cortical nephrons were carried out at age 32 to 40 weeks. Systolic blood pressure was not significantly different between SHR and SHR + UNX. Protein excretion increased markedly in the SHR + UNX 6 months after UNX, as compared with the other three groups. In cortical nephrons, single nephron glomerular filtration rate (SNGFR) and plasma flow entering the glomeruli (SNPF) was lower in SHR + UNX than in WKY + UNX. Glomerular hydraulic pressure (PG) during stopped flow was closely comparable in all groups, rising only 2 mm Hg after UNX. SNGFR was measured in juxtamedullary (JM) nephrons 2 months after UNX, a stage before heavy proteinuria developed. We found that JM SNGFR was approximately 50% higher in SHR + UNX than in WKY + UNX. The observations suggest that following ablation of renal mass, superficial cortical glomeruli are not exposed to excessively high pressure or flow rates in the SHR. In contrast, JM glomeruli undergo a disproportionate rise in SNGFR, presumably associated with excessively high PG and/or blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Histopathology of argon laser photocoagulation in juvenile diabetic retinopathy

A 24-year-old woman had insulin-dependent juvenile diabetes for 15 years. She developed Sheehan's syndrome (postpartum pituitary necrosis) and diabetic nephropathy at 20 years of age. She had multiple sessions of argon laser photocoagulation for proliferative diabetic retinopathy. Histologically, loss of outer retina and pigmented epithelium occurred at the laser sites. Trypsin retinal digest preparations revealed microaneurysms and markedly decreased numbers of pericytes. The kidneys displayed nodular glomerulosclerosis (Kimmelstiel-Wilson syndrome). The anterior pituitary showed cystic degeneration and old hemorrhage.

Glomerular manifestations of diabetes in the BB rat

Morphologic characteristics of the renal glomeruli and tubules of BB rats with spontaneous diabetes mellitus were studied at 30 weeks' duration of diabetes. Whereas the glomerular basement membrane (GBM) was significantly thickened, no changes in the diabetic glomeruli were seen in the peripheral capillary wall area and in the fractional volumes of the mesangial cells or of the mesangial matrix. Light microscopy of the diabetic kidneys were normal, and immunofluorescent examination of diabetic glomeruli showed no increased accumulation of albumin, C3, or IgG. Diabetic rats had increased renal blood flow and glomerular filtration rates. Diabetic rats at 7, 17, and 30 weeks excreted normal amounts of urinary albumin. Thus kidneys of the BB diabetic rat differ from other experimental models of diabetes in that GBM thickening occurs in the absence of mesangial changes and of increased albuminuria. These studies suggest that the mesangium may influence glomerular permeability in diabetes, while thickening of the GBM in diabetes does not necessarily coincide with increased urinary albumin excretion. Furthermore, these results are consonant with the hypothesis that genetic factors may influence the pathological expression of diabetic nephropathy in rats.

Diabetic nephropathy: clinical and histological study in 22 patients

Twenty-two patients with insulin-dependent diabetes mellitus and renal involvement were submitted to renal biopsy. Mean age was 42 years; 10 were males, 12 females. The mean interval between clinical manifestation of nephropathy and biopsy was about 2 years. At the time of biopsy, 4 groups were distinguished according to clinical conditions, depending on the presence or absence of nephrotic syndrome and renal failure. Renal lesions were semiquantitatively evaluated, a separate score being considered for glomerular and vascular lesions. Immunofluorescence most frequently showed a pattern of faint linear IgG deposits along glomerular basement membranes. Severity of histological lesions and pattern of urinary abnormalities were not correlated with the duration of diabetes or the patients' age. Both glomerular and vascular lesions were correlated with the presence of renal failure, while no relationship with the pattern of urinary abnormalities was found. Fourteen patients were followed for more than one year after biopsy: 5 had normal renal function, 4 were in chronic renal insufficiency and 5 in end-stage renal failure (3 were in dialysis, 2 died). There was no correlation between the 3 above-mentioned types of evolution and glomerular histological findings. Nevertheless a higher score of vascular impairment at biopsy was observed among patients who subsequently were found to have a more unfavorable prognosis. Therefore renal biopsy, by providing information on the degree of renal vascular damage, may have some value in predicting the clinical course of diabetic nephropathy.

Long term correction of hyperglycaemia and progression of renal failure in insulin dependent diabetes

The effect of long term correction of hyperglycaemia on the rate of deterioration of renal function was studied in six insulin dependent diabetics with proteinuria due to diabetic nephropathy. After a planned run in observation period of 10 to 24 months patients entered a programme of continuous subcutaneous insulin infusion for up to 24 months. Glycaemic control was promptly and significantly improved and optimal glycaemic values sustained throughout the study. Blood pressure was maintained stable. A control group of six nephropathic diabetics was studied receiving conventional insulin injection treatment but also with blood pressure control over the same period.Despite greatly improved metabolic control in the infusion treated group no significant change in the rate of decline of glomerular filtration rate could be shown, the plasma creatinine concentrations continued to increase, and the fractional clearance of albumin and IgG rose progressively, indicating progression of glomerular damage. The conventionally treated control group behaved similarly. In a single patient receiving the continuous infusion the rate of decline of the glomerular filtration rate slowed considerably, suggesting that the response to strict diabetic control may differ in some patients.These findings suggest that by the time glomerular function has started to fail in diabetic nephropathy the process culminating in end stage renal failure has become self perpetuating and is little influenced by the degree of metabolic control. A new definition of potential clinical diabetic nephropathy is proposed that will permit identification of patients at risk and earlier intervention by glycaemic correction in an attempt to arrest diabetic renal disease.

Monitoring glomerular function in diabetic nephropathy. A prospective study

Glomerular function was monitored prospectively in 13 patients with insulin-dependent diabetes and diabetic nephropathy for up to 51 months. Glomerular filtration rate, measured by 51Cr-EDTA clearance, showed a linear decline in all patients. Rates of fall ranged between 0.63 and 2.4 ml/minute per month (mean +/- SEM 1.2 +/- 0.16). Plasma creatinine concentration proved to be an insensitive marker of glomerular function, especially in the early phase of nephropathy. A good correlation was found between the rate of change of 51Cr-EDTA glomerular filtration rate and that of inverse creatinine levels when plasma creatinine concentrations exceeded 200 mumol/liter. Inverse plasma beta 2-microglobulin concentrations, however, showed a highly significant correlation (r = 0.93; p less than 0.001) with 51Cr-EDTA glomerular filtration rate over the whole range of values, making it sensitive in screening for early impairment of renal function. A significant relationship (r = 0.85; p less than 0.01) was found between the rates of change of the 51Cr-EDTA glomerular filtration rate and of inverse beta 2-microglobulin levels for plasma beta 2-microglobulin concentrations above 3 mg/liter. A progressive increase in the fractional clearance of albumin, IgG, and beta 2-microglobulin was noted as the glomerular filtration rate fell, indicating an evolving defect in the renal handling of proteins. The rate of decline of the glomerular filtration rate was unrelated to age, sex, duration of diabetes, duration of diabetes before onset of proteinuria, glomerular filtration rate, initial albumin clearance, blood glucose control, and arterial pressure, when diastolic values were below 100 mm Hg. The effect of therapeutic intervention (e.g., blood glucose, blood pressure, or diet) on the progression of diabetic nephropathy can be reliably evaluated by precise measures of rate of decline of glomerular filtration rate and changes in fractional clearance of plasma proteins. The factor(s) determining the individual rate of decline of renal function still remain obscure.

The natural history of diabetic nephropathy in type I diabetes and the role of metabolic control in its prevention, reversibility and clinical course

The authors present a contemporary picture of the pathogenesis and clinical course of diabetic nephropathy in type I diabetics describing the stages of the disease and the possible evidence for reversibility of the kidney damage with tight metabolic control. During the so-called latency period, which is clinically non-detectable, the predominant functional abnormalities (increase in GFR with sub-clinical glomerular proteinuria) can be corrected by strict control although there is no evidence for the regression of the associated anatomical changes such as the enlarged filtration area. As for the described increase in thickness of the glomerular basement membrane, from experimental data and pancreatic transplants in man, delay in its development and to some extent regression of the glomerular lesions can be expected. The problem of how the renal lesions in experimental diabetes mirror the changes in the human kidney is discussed. During the symptomatic period, with intermittent and subsequently constant proteinuria and progressive decline in renal function, which are observed in only about 30% of type I diabetics, the role of arterial hypertension and its effective control is emphasized. Finally, the renal failure period is indicative of irreversible damage to the kidneys. The progression from its early to its late stages is variable between different patients but each individual patient shows a constant rate of deterioration. The evidence for the efficacy of medical treatment in slowing down its progression is very limited at present but much can be done to improve the quality of life by dietary measures, treatment of fluid overload and hypertension. When the end-stage diabetic kidney disease is reached, with serum creatinine above 8 mg/dl, renal transplantation from a living donor offers a good chance for a relatively acceptable quality of life for years. In conclusion, it is stressed that the morbidity of diabetic nephropathy could eventually be reduced through effective control of the metabolic abnormalities of diabetes with the methods presently available.

Focal segmental membranous glomerulonephropathy associated with other glomerular diseases

In four patients with the nephrotic syndrome, renal biopsy revealed focal segmental membranous glomerulonephropathy (FSMGN) associated with the histologic patterns of "nil" disease (two cases), hereditary nephritis and diffuse diabetic glomerulosclerosis. The occurrence of FSMGN in association with other glomerular diseases, presumably unrelated to immune complex deposition, is infrequent in our experience. Rather than necessarily representing an early stage or milder form of membranous glomerulonephropathy, it may be an epiphenomenon. This interpretation has prognostic and therapeutic implications and raises important pathogenetic questions. In particular, this study suggests that in some instances, preexisting functional and structural abnormalities may play a role either in the deposition of preformed circulating immune complexes or in the local formation of immune complexes.

Microalbuminuria as a predictor of clinical nephropathy in insulin-dependent diabetes mellitus

The overnight urinary albumin excretion rate (AER) of 87 patients with insulin-dependent diabetes mellitus was measured in 1966-67, 14 years later information was obtained on 63 of the original cohort; those alive were restudied, and for those who had died relevant clinical information and case of death were recorded. The development of clinical diabetic nephropathy ('Albustix'positive proteinuria) was related to the 1966-67 AER values. Clinical proteinuria developed in only 2 of 55 patients with AER below 30 microgram/min but in 7 of 8 with AER between 30 and 140 microgram/min. The risk of clinical diabetic nephropathy in the latter group was twenty-four time higher than inthe former. 9.1% of patients with AER below 30 microgram/min had died, compared with 37.5% with higher AER. The two groups did not differ significantly in age, sex composition, and initial blood pressure. Mean duration of diabetes was longer, but not significantly so, in those with AER above 30 microgram/min. Thus, elevated levels of microalbuminuria strongly predict the development of clinical diabetic nephropathy. These levels of AER are potentially reversible, and their detection and treatment may prevent diabetic renal disease.