Diabetic nephropathy: etiology and prevention

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (ε4) and decrease (ε2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

The angiotensin I-converting enzyme (ACE) locus is strongly associated with age and duration of diabetes in patients with type I diabetes

We have investigated the frequency of the angiotensin I-converting enzyme (ACE) insertion/ deletion (I/D) polymorphism in 249 patients with type I diabetes and 162 normal healthy controls. There was no significant difference in the frequency of ACE genotypes between those patients with diabetic nephropathy (n = 72) (nephropaths) compared to those with no proteinuria after 20 years duration of diabetes (n = 86) (normoalbuminurics). There was, however, a significant difference in the frequency of ACE genotypes between the short-duration and long-term normoalbuminuric group (chi = 11.5, p = 0.001). Analysis of the ACE genotypes with respect to age and duration of diabetes showed that homozygosity for the insertion (I/I) genotype was significantly decreased with longer duration of diabetes (r2 = 92.7%, p < 0.009). No association was found with age in the normal controls. In conclusion, these results suggest that the ACE locus may be associated with longevity and survival in patients with type I diabetes rather than diabetic nephropathy or microvascular disease per se.

Relationships between diet control and the development of spontaneous type II diabetes and diabetic nephropathy in OLETF rats

The effect of a 30% restricted diet on the development of diabetes and diabetic nephropathy was examined using the Otsuka Long Evans Tokushima Fatty (OLETF) rat which develops non-insulin-dependent diabetes mellitus (NIDDM) spontaneously after 25-30 weeks of age. The first experimental group that received 30% restricted feeding from six to 80 weeks old, showed complete suppression of spontaneous diabetes up to 40 weeks of age and showed milder histopathological change of pancreatic islets, that those of the control group. The second group which received 30% restricted feeding during 30-80 weeks, showed a gradual decrease in clinical diabetes with age, even though they had already developed diabetes at 25 weeks. In both groups, levels of urinary protein content appeared to decrease, compared with that in control rats, although a gradual increase of urinary protein was observed with age. Histopathologically, glomerular damages were slight to mild in both groups. However, no improvement in nephrotic complication was observed for the group which received a 30% restricted feeding after 70 weeks of age. These results clearly show that the balanced-control diet, given at a 30% restricted feeding level and at an early phase, is effective in the prevention or improvement of NIDDM and nephrotic complications. Diet therapy after 70 weeks of age, however, had little or no effect.

Proteinuria in NIDDM in south India: analysis of predictive factors

There are few data on the risk factors for diabetic nephropathy in the Asian Indian population, although several studies have shown a high prevalence of the disease in this ethnic group. This study also aimed to assess the role of hyperglycaemia and hypertension in the causation and course of nephropathy in this population, which has low rates of obesity. Retrospective analysis of two groups of non-insulin dependent diabetic (NIDDM) patients, one without proteinuria (< 100 mg/day, n = 25) and the other with proteinuria (> or = 500 mg/day, n = 25), matched for age, sex, duration of diabetes and body mass index (BMI) was done to study the factors predisposing to proteinuria and also its progression during a 2 year follow-up. Logistic regression analysis showed that the factors contributory to proteinuria were initial HbA1 and initial systolic blood pressure. The average proteinuria during the follow-up was dependent on the initial and average systolic and diastolic blood pressure values. No correlation was seen between cholesterol or triglyceride values and the change in proteinuria. Creatinine clearance deteriorated in the proteinuric group and this was related to the presence of proteinuria and initial diastolic blood pressure. This study emphasizes the importance of blood pressure in the progression of diabetic nephropathy, even in people who have low BMI. Therefore, good control of blood pressure has an important role to play in the management of this condition.

Sodium-lithium countertransport in children with diabetes and their families

Abnormalities of sodium-lithium countertransport have been extensively implicated in adult primary hypertension and a relationship between sodium-lithium countertransport and family history of hypertension in children has been previously found. More recently it has been suggested that increased sodium-lithium countertransport may play a part in the pathogenesis of nephropathy in insulin dependent diabetes mellitus (IDDM). Children and adolescents with IDDM and their family members were studied. In those with IDDM (n = 36, median age 14.6 years, range 9.5-19.2 years) there was no relationship between sodium-lithium countertransport (range 0.098-0.585 mmol/l red blood cells/hour) and age, blood pressure as expressed by systolic or diastolic SD scores, glycated haemoglobin, serum lipids, or intracellular sodium concentration. A positive relationship (rs = 0.44) was found between sodium-lithium countertransport and early morning urinary albumin to urinary creatinine ratio (UA/UC), expressed as the logarithm of the geometric mean of two consecutive samples, for each individual (range 0.4-22 mg/mmol). Sodium-lithium countertransport was increased in those with IDDM compared with their non-diabetic siblings, in a paired analysis (n = 26). There was no relationship between UA/UC in the children with diabetes and sodium-lithium countertransport in their parents. These studies in this population of diabetic children indicate that increased sodium-lithium countertransport may play a part in the early stages of the development of nephropathy in IDDM.

Microalbuminuria: pathogenesis, prognosis and management

The development in recent years of sensitive assays specific for albumin has facilitated extensive investigation of the pathophysiology and clinical significance of microalbuminuria. It is now clear that the appearance of microalbuminuria represents a crucial event in the natural histories of diabetes mellitus and essential hypertension. It reflects the presence of generalized vascular damage and is strongly predictive of subsequent renal failure, cardiovascular morbidity, and death. Therapeutic interventions, including strict diabetic and blood-pressure control, can reduce microalbuminuria and improve the overall prognosis. The detection and treatment of microalbuminuria in these high-risk groups should now form an integral part of their management. Large-scale screening programmes are also recommended for insulin-dependent diabetics.

The effect of ejaculation on albumin excretion rate

Microalbuminuria predicts the development of diabetic nephropathy. Large daily variations in albumin excretion rates are frequently observed. Because seminal fluid contains protein and albumin, we reasoned that sexual activity, ejaculation, or residual urethral semen could contribute to albumin content in urine and thus effect determination of albumin excretion rate. Our study was designed to determine the effect of ejaculation of albumin excretion rate and to ascertain if patients routinely should be advised to refrain from sexual activity during or before the urine collection period. Ten normotensive, nondiabetic men (age 31.0 +/- 2.3 years) collected 24-h urine specimens on three occasions: after 3 days of abstinence from sexual activity, during a 24-h period which included one ejaculatory episode, and on a day following sexual activity. Results for albumin excretion rate were: abstinence day: 4.8 +/- 0.7 micrograms/min; sex day: 6.3 +/- 1.1 microgram/min; post-sex day: 4.9 +/- 1.0 micrograms/min. There was no significant difference between these values when compared directly or after log transformation. There also were no differences in urinary creatinine excretion or clearance. We conclude that in nondiabetic individuals ejaculation does not influence albumin excretion rate.

Metabolic abnormalities of the hyperglycemic obese Zucker rat

In a cross-sectional study, we evaluated the metabolic profiles of lean (Fa/?) and obese (fa/fa) Zucker male rats at 4 to 8 months of age. Although all of the obese rats (N = 108) demonstrated glucose intolerance, most of the obese rats exhibited only mild elevations of fasted and fed plasma glucose. Only 14 of the obese rats were severely hyperglycemic, which resulted in substantial elevations of glycohemoglobin (GHb) levels. The nerve and lens levels of glucose, sorbitol, and fructose were elevated, and the myo-inositol was depleted in all hyperglycemic obese rats, but not in the euglycemic obese rats. With increasing duration of hyperglycemia, the neural myo-inositol level approached normal, while the lenses became cataractous. All obese rats had increased urinary albumin excretion (UAE), which was dependent on age (r = .45, P less than .02) and independent of hyperglycemia, glucosuria, and polyuria. In conclusion, although the euglycemic obese rats exhibited some diabetic abnormalities, the hyperglycemic obese Zucker rat more closely resembled the altered metabolic profile associated with type II diabetes mellitus.

Which method for quantifying "microalbuminuria" in diabetics? Comparison of several immunological methods (immunoturbidimetric assay, immunonephelometric assay, radioimmunoassay and two semiquantitative tests) for measurement of albumin in urine

We have compared the chemical and clinical characteristics of an immunonephelometric assay (INA), two immunoturbidimetric assays (ITA) and two semi-quantitative methods with those of a solid-phase radioimmunoassay (RIA) for measurement of urinary albumin (UA) concentration in 136 diabetic patients. INA and RIA had similar accuracy, and provided comparable results. However, RIA has slightly greater sensitivity than INA, which is easier and faster. Good agreement was also found between RIA and the two ITA methods, although one of these overestimated RIA values in the low-medium range (5-30 mg/l) of urinary albumin. ITA seems suitable for initial screening of albuminuria in diabetic patients but more sensitive procedures (such as RIA and INA) seem preferable for measurement of UA concentrations in the normal range. The two semi-quantitative methods showed high sensitivity but poor specificity, because of the large number of false positive results. About 50% of diabetic patients "positive" by these methods did not have microalbuminuria. The utility of these methods is questionable, because many samples from diabetic patients need to be reassayed by a more specific and sensitive assay such as the RIA, INA or ITA methods.

Effects of alpha 2-adrenergic blockade on renal hemodynamics in patients with insulin dependent diabetes mellitus

The role of renal alpha 2-adrenoceptors in the regulation of glomerular filtration and renal perfusion is unknown. We studied the effects of alpha 2-adrenergic blockade on renal hemodynamics in six patients with insulin-dependent diabetes mellitus (IDDM) and in six healthy subjects. At the basal state, glomerular filtration rate (GFR) was higher in IDDM although the difference from control levels was not statistically significant. Volume expansion, achieved by infusion of isotonic sodium chloride solution, during placebo infusion induced a significant drop in GFR in healthy subjects but not in IDDM patients. Infusion of the alpha 2-adrenoceptor antagonist idazoxan did not further modify the effect of volume expansion on GFR. Renal plasma and blood flow as well as filtration fraction were not significantly changed by volume expansion or idazoxan infusion. Plasma renin activity and plasma aldosterone levels decreased during volume expansion in both IDDM and control subjects. In conclusion, volume expansion induced decreased GFR in healthy controls but not in IDDM patients. Since infusion of idazoxan did not affect GFR or other parameters of renal hemodynamics, renal alpha 2-adrenoceptors do not seem to be involved in the regulation of renal function. Hence, enhanced renal alpha 2-adrenoceptor activity is not likely to underlie hyperfiltration as seen in IDDM.

Intervention with the aldose reductase inhibitor, tolrestat, in renal and retinal lesions of streptozotocin-diabetic rats

The progressive increase in urinary albumin excretion, which precedes the development of diabetic nephropathy, can be prevented in diabetic rats if the aldose reductase inhibitor, tolrestat, is administered at the initiation and throughout the duration of hyperglycaemia. We therefore determined the ability of tolrestat to intervene in the further progression of already established urinary albumin excretion of streptozotocin-diabetic female Wistar rats. Two months after streptozotocin injection, diabetic rats were grouped as low-urinary albumin excretion (0.2-1.0 mg albumin/day) or high-urinary albumin excretion (1.9-5.9 mg albumin/day), at which time tolrestat intervention (25 mg/kg per day) was begun for half of the diabetic rats in each urinary albumin excretion group. After six months of treatment tolrestat caused a significant reduction in the urinary albumin excretion rate of the low-urinary albumin excretion group only. The diabetes-induced rise of total urinary protein in both groups was significantly reduced by tolrestat. Furthermore, the diabetes-induced increase (49%) in the thickness of the basement membranes of retinal capillaries from the outer plexiform layer was significantly diminished by tolrestat administration. In conclusion, intervention therapy with the aldose reductase inhibitor, tolrestat, can reduce the progression of urinary albumin excretion and retinal basement membrane thickening in long-term diabetic rats.

The 5' insulin gene polymorphism and the genetics of vascular complications in type 1 (insulin-dependent) diabetes mellitus

Recent data suggest genetic contributions to the microvascular complications of Type 1 (insulin-dependent) diabetes mellitus. Most research has focused on the HLA region, and the potential role of other genetic loci has not been adequately explored. We examined the possible relationship between DNA polymorphisms in the region 5' to the insulin gene on chromosome 11 and diabetic nephropathy. This was done by comparison of those diabetic patients homozygous for class 1 alleles at the 5' insulin gene polymorphism locus to 1/3 heterozygotes in a well-characterized series of 324 insulin-requiring diabetic patients from the Wisconsin Epidemiologic Study of Diabetic Retinopathy. Proteinuria (defined as greater than or equal to 0.3 g protein/l urine), was used as suggestive evidence for diabetic nephropathy. Hypertension, a frequent associated finding in diabetic patients with nephropathy, was defined as a blood pressure greater than 140/90 or a history of previous treatment of hypertension. The two genotypically defined groups did not differ from each other in regard to sex ratio, age at diagnosis, age at examination, duration of diabetes, body mass, HbAlc or C-peptide. The 1+1 group had a higher prevalence of proteinuria, 29% as compared to 16.2% in other genotypes (p less than 0.05). There was no significant difference in the frequency of hypertension between the two genotypic groups. This finding suggests that the 5' insulin gene polymorphism may be associated with risk for nephropathy, but the pathophysiologic mechanism remains unclear.

Effect of strict glycemic control on renal hemodynamic response to amino acids and renal enlargement in insulin-dependent diabetes mellitus

BACKGROUND

Many patients with insulin-dependent diabetes mellitus have an increase in the glomerular filtration rate and renal enlargement early in the course of their disease. Both these changes may be risk factors for the later development of diabetic nephropathy. Their cause is not known, but they could be due to augmented renal responses to the increase in plasma amino acid concentrations that occurs when dietary protein intake is high, a factor known to increase glomerular filtration and renal blood flow in normal subjects.

METHODS

We measured the glomerular filtration rate and renal plasma flow after an overnight fast and during an infusion of amino acids in 12 patients with insulin-dependent diabetes mellitus and 9 normal subjects. The diabetic patients were studied when they were hyperglycemic, when they were euglycemic after an insulin infusion for 36 hours, and after intensive insulin therapy for 3 weeks. Kidney volume was measured by ultrasonography before and after the period of intensive insulin therapy.

RESULTS

The glomerular filtration rate and renal plasma flow were normal after fasting when the patients were hyperglycemic (mean [+/- SE] fasting plasma glucose level, 11.5 +/- 0.7 mmol per liter). After the amino acid infusion, these values increased more in the patients (glomerular filtration rate, 2.65 +/- 0.07 ml per second per 1.73 m2 of body-surface area; renal plasma flow, 13.30 +/- 0.68 ml per second per 1.73 m2; P less than 0.05 for both) than in the normal subjects (2.25 +/- 0.08 and 11.20 +/- 0.65 ml per second per 1.73 m2, respectively). The 36-hour infusion of insulin in the diabetic patients did not alter the glomerular filtration rate or renal plasma flow either before or during the amino acid infusion. After three weeks of intensive insulin therapy (fasting plasma glucose level, 5.3 +/- 0.2 mmol per liter), the glomerular filtration rate and renal plasma flow after the amino acid infusion (2.33 +/- 0.03 and 11.30 +/- 0.43 ml per second per 1.73 m2, respectively) were similar to those in the normal subjects. The kidney volumes in the normal subjects and the patients with diabetes were 219 +/- 14 and 312 +/- 14 ml per 1.73 m2, respectively (P less than 0.01); the volume decreased to 267 +/- 22 ml per 1.73 m2 (P less than 0.001) in the diabetic patients after three weeks of intensive insulin therapy, which was not significantly different from the volume in the normal subjects (P = 0.1).

CONCLUSIONS

Conventionally treated diabetic patients who have normal renal function while fasting have augmented renal hemodynamic responses to increased plasma amino acid concentrations. The concomitant decrease in these hemodynamic responses and in kidney size with strict glycemic control suggests that these phenomena are related and influenced by the metabolic state.

Strategies in diabetes mellitus. Start of a new era

Important research advances during the last 10 years have improved the quality of life for many patients with diabetes mellitus. The aim at present is not only to further improve glycemic control but also to comprehend basic mechanisms of the disease, define genetic risks, and understand the origins of complications. In this article, Dr Skyler examines current research strategies that may soon become therapeutic options.

Urinary protein excretion and renal function in children with IgA nephropathy

Renal haemodynamics and the pattern of urinary protein excretion were studied in 38 children (21 boys, 17 girls) with biopsy-proven IgA nephropathy (IgAN), 0.4-16.8 (median 5.3) years after onset of the disease. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were evaluated by clearances of inulin and para-aminohippuric acid. Serum and urinary albumin, IgG and beta 2-microglobulin (beta 2 mu) were determined and the excretion rates, clearances, and fractional clearances were calculated. The patients were grouped according to the type and the amount of proteinuria. Mean GFR and ERPF were significantly decreased (107 +/- 3 and 580 +/- 17 ml/min per 1.73 m2, respectively) versus controls (119 +/- 2 and 627 +/- 14 ml/min per 1.73 m2, respectively). Grouped according to albumin excretion rates, non-albuminuric patients had normal GFR, while mean GFR was reduced in patients with micro-albuminuria (106 +/- 3 ml/min per 1.73 m2) and albuminuric patients (92 +/- 7 ml/min per 1.73 m2). IgG excretion increased with increasing albuminuria, but the selectivity index was lower in albuminuric patients than in patients with micro-albuminuria. Albuminuric patients had also higher blood pressure than those with micro-albuminuria. beta 2 mu excretion did not discriminate between patients with impaired renal function. The results suggest that childhood IgAN is not a benign kidney disease. After a median duration of 5 years of the disease a number of children had impaired renal function. Mean GFR was reduced most in the albuminuric patients but was also decreased in micro-albuminuric patients, indicating that micro-albuminuria may be a predictor of more severe disease.

Glomerular hyperfiltration in insulin-dependent diabetes mellitus: no evidence for enhanced activity of the renin-angiotensin-aldosterone system

Glomerular hyperfiltration is a characteristic functional abnormality in insulin-dependent diabetes mellitus (IDDM) patients, but the underlying mechanisms remain controversial. Supine and ambulant plasma renin activity (PRA) and aldosterone were measured in ten IDDM patients with normal glomerular filtration rate (GFR), in ten IDDM patients with elevated GFR and in ten nondiabetic controls. Basal and stimulated PRA or aldosterone did not differ significantly between the three groups. These results suggest that in insulin-dependent diabetes the glomerular hyperfiltration is not causally related to hyperactivity of the renin-angiotensin-aldosterone system.

Sodium-lithium countertransport activity in red cells of patients with insulin dependent diabetes and nephropathy and their parents

OBJECTIVE

To determine whether there are familial and genetic aspects of sodium-lithium countertransport activity in red cells in diabetic nephropathy.

DESIGN

Case-control study.

SETTING

Teaching hospital diabetic clinic.

SUBJECTS

40 Patients with insulin dependent diabetes, both of whose parents were alive: 20 with persistent proteinuria and 20 with normal albumin excretion matched for age, duration of diabetes, and body mass index. All 80 parents.

MAIN OUTCOME MEASURES

Sodium-lithium countertransport activity in red cells and arterial blood pressure.

RESULTS

Sodium-lithium countertransport activity in red cells was higher in the patients with proteinuria than in the patients with normoalbuminuria (mean (95% confidence interval) 0.47 (0.39 to 0.54) v 0.33 (0.28 to 0.38) mmol/l red cells/h respectively, p = 0.0036; mean difference 0.14 (0.04 to 0.22)). The mean countertransport activity for the two parents of each patient was calculated, and from this the mean value for each group of parents was calculated; the value was higher in the parents of the patients with proteinuria than in the parents of the patients with normoalbuminuria (0.40 (0.32 to 0.48) v 0.30 (0.26 to 0.33) mmol/l red cells/h respectively, p = 0.016; 0.10 (0.02 to 0.19)). Twenty-eight of the parents of the patients with proteinuria compared with 12 of the parents of the patients with normoalbuminuria had a countertransport activity that was above the median value in all 80 parents (p less than 0.001). Mean arterial blood pressure in the parents of the patients with proteinuria was related to that of their offspring (r = 0.46; p less than 0.01). There was a positive correlation between the sodium-lithium countertransport activity in red cells in the parents and their offspring when all parents and patients were considered (r = 0.37; p less than 0.001).

CONCLUSIONS

Increased sodium-lithium countertransport activity in red cells in the parents of diabetic patients with nephropathy provides further evidence that familial, and possibly genetic, factors related to a predisposition to arterial hypertension have a role in the susceptibility of diabetic renal disease.