Progression of diabetic nephropathy in normotensive type 1 diabetic patients

Gender differences in renal responses to hyperglycemia and angiotensin-converting enzyme inhibition in diabetes

BACKGROUND

Diabetes mellitus reduces female gender-mediated protection against progression of renal disease but the mechanisms responsible for this loss of protection are unknown. The impact of gender on the diabetic hyperfiltration state has not previously been studied. Since hyperfiltration is a factor in the development of diabetic renal disease, and is influenced by hyperglycemia and renin-angiotensin system (RAS) blockade, we examined gender differences in the renal response to hyperglycemia and angiotensin-converting enzyme (ACE) inhibition in young males and females with uncomplicated type 1 diabetes mellitus.

METHODS

Ten male and 12 female normoalbuminuric, normotensive, adolescents with type 1 diabetes mellitus were studied before ACE inhibition during clamped euglycemia and hyperglycemia, and then after 21 days treatment with enalapril (0.1 mg/kg daily x 1 week and then 0.1 mg/kg twice a day x 2 weeks).

RESULTS

During clamped euglycemia, males exhibited significantly higher effective renal plasma flow (ERPF) and renal blood flow (RBF) and a lower renal vascular resistance (RVR). During clamped hyperglycemia, females exhibited reductions in ERPF and RBF, and increased RVR and filtration fraction (FF). Males exhibited no significant renal hemodynamic changes during hyperglycemia. After ACE inhibition treatment, both genders exhibited significant declines in arterial pressure, but only females displayed a reduction in glomerular filtration rate (GFR) and FF.

CONCLUSION

The renal responses to hyperglycemia and ACE inhibition appear to differ between male and female adolescents with uncomplicated type 1 diabetes mellitus. Hyperglycemia-induced changes in RVR and FF in women may account, at least in part, for the loss of gender-based protection in diabetic renal disease.

Preventing end stage renal disease in diabetic patients--genetic aspect (part I)

Diabetic nephropathy is a major cause of diabetes- related morbidity and mortality; however the clinical course of the disease and the renal prognosis is highly variable among individuals. The current review will discuss the genetic influence on the development of end stage renal disease (ESRD) in diabetic patients and potential improvements to the current treatment strategy to slow the loss of kidney function in these patients. In this first part, the growing evidence that glucose-induced activation of the intra-renal and systemic renin-angiotensin systems plays an essential role in processes leading to destruction of renal function is summarised. Genetic variations, especially the angiotensin-converting enzyme (ACE)/ID polymorphisms in the gene coding for ACE, are involved in activation of the renin-angiotensin system and seem to influence the clinical course of diabetic nephropathy during treatment with ACE inhibitors. In addition, this polymorphism may interact with other polymorphisms within the renin-angiotensin system, leading to high risk of ESRD. As new genetic approaches and methods develop, further understanding of diabetic nephropathy will evolve and genotyping will help prevent ESRD in diabetic patients.

Diabetic nephropathy: of mice and men

Accumulating evidence supports intrinsic genetic susceptibility as an important variable in the progression of diabetic nephropathy in people. Mice provide an experimental platform of unparalleled power for dissecting the genetics of mammalian diseases; however, phenotypic analysis of diabetic mice lags behind that already established for humans. Standardized benchmarks of hyperglycemia, albuminuria, and measurements of renal failure remain to be developed for different inbred strains of mice. The most glaring deficiency has been the lack of a diabetic mouse model that develops progressively worsening renal insufficiency, the sine qua non of diabetic nephropathy in humans. Differences in susceptibility of these inbred strains to complications of diabetes mellitus provide a possible avenue to dissect the genetic basis of diabetic nephropathy; however, the identification of those strains and/or mutants most susceptible to renal injury from diabetes mellitus is lacking. Identification of a mouse model that faithfully mirrors the pathogenesis of DN in humans will undoubtedly facilitate the development of new diagnostic and therapeutic interventions.

Structural changes in the renal vasculature in streptozotocin-induced diabetic rats without hypertension

BACKGROUND/AIM

We evaluated in diabetic-streptozotocin rats (STZR) the structural changes of glomeruli, preglomerular vessels, glomerular tuft and renal parenchyma in order to determine the degree of renal injury and the presence of remodeling in afferent arterioles developed by diabetes without overimposed hypertension.

METHODS

Renal mass index and histological score (glomerular number, density, tubular lesions and degree of arteriosclerosis) were estimated. In afferent arterioles the ratio of wall thickness/lumen was obtained by stereological methods.

RESULTS

STZR developed diabetes without hypertension; renal mass index increased and matched changes in glomeruli (decrease of capillary number and enlargement of mesangium and basement capillary membrane). Both glomerular number and density as well as afferent arteriole number were diminished. Degenerative changes in both proximal (glycogenic and hyaline degeneration) and distal tubules (hyaline casts) were also observed. At variance with preglomerular vessels, the efferent arterioles only presented initial arteriosclerosis. Finally, the stereological study of afferent arterioles showed a significantly lower arteriolar lumen area and arteriolar wall thickness in STZR, resulting in a remodeling without modification of wall/lumen ratio.

CONCLUSION

Diabetes, uncomplicated by hypertension, is associated with (1) a reduction in glomerular number; (2) degeneration in parenchyma and renal tubules, and (3) a specific pattern of remodeling in preglomerular vessels different from that induced by hypertension. Although this work demonstrated that these changes are not triggered by hypertension, further investigations are required in order to determine which mediators are involved in diabetic-vascular renal dysfunction.

Pancreas transplantation: indications and consequences

Pancreas transplantation continues to evolve as a strategy in the management of diabetes mellitus. The first combined pancreas-kidney transplant was reported in 1967, but pancreas transplant now represents a number of procedures, each with different indications, risks, benefits, and outcomes. This review will summarize these procedures, including their risks and outcomes in comparison to kidney transplantation alone, and how or if they affect the consequences of diabetes: hyperglycemia, hypoglycemia, and microvascular and macrovascular complications. In addition, the new risks introduced by immunosuppression will be reviewed, including infections, cancer, osteoporosis, reproductive function, and the impact of immunosuppression medications on blood pressure, lipids, and glucose tolerance. It is imperative that an endocrinologist remain involved in the care of the pancreas transplant recipient, even when glucose is normal, because of the myriad of issues encountered post transplant, including ongoing management of diabetic complications, prevention of bone loss, and screening for failure of the pancreas graft with reinstitution of treatment when indicated. Although long-term patient and graft survival have improved greatly after pancreas transplant, a multidisciplinary team is needed to maximize long-term quality, as well as quantity, of life for the pancreas transplant recipient.

From secondary to primary prevention of progressive renal disease: The case for screening for albuminuria

Many subjects nowadays present with end-stage renal failure and its attendant cardiovascular complications without known prior renal damage. In this report we review the evidence available to strongly suggest that the present practice of secondary prevention in those with known prior renal disease should be extended to primary prevention for those subjects in the general population who are at risk for progressive renal failure, but who had never suffered from a primary renal disease. We show that such subjects can be detected by screening for albuminuria. Elevated urinary albumin loss is an indicator not only of poor renal, but also of poor cardiovascular prognosis. In addition to diabetic subjects who are at risk for albuminuria, we also show that hypertensive, obese, and smoking subjects are more susceptible. We suggest that therapies that have been shown to lower albumin excretion, such as ACE inhibitors, angiotensin II receptor antagonists, and statins be started early in such patients to prevent them from developing clinical renal disease and its attendant cardiovascular complications.

Mouse models of diabetic nephropathy

Mice provide an experimental model of unparalleled flexibility for studying mammalian diseases. Inbred strains of mice exhibit substantial differences in their susceptibility to the renal complications of diabetes. Much remains to be established regarding the course of diabetic nephropathy (DN) in mice as well as defining those strains and/or mutants that are most susceptible to renal injury from diabetes. Through the use of the unique genetic reagents available in mice (including knockouts and transgenics), the validation of a mouse model reproducing human DN should significantly facilitate the understanding of the underlying genetic mechanisms that contribute to the development of DN. Establishment of an authentic mouse model of DN will undoubtedly facilitate testing of translational diagnostic and therapeutic interventions in mice before testing in humans.

17beta-Estradiol replacement improves renal function and pathology associated with diabetic nephropathy

The protective factor of female gender appears to be lost in diabetes; the incidence of diabetes and its complications, including diabetic nephropathy, are equal in women and men. This study examined the effects of estrogen deficiency by ovariectomy (OVX) and replacement with 17beta-estradiol (OVX+E2) on renal function and pathology in the nondiabetic (ND) and streptozotocin (STZ)-induced diabetic (D) rat kidneys for 12 wk. Diabetes was associated with an increase in urine albumin excretion (UAE; ND, 0.39 +/- 0.03; D, 5.9 +/- 0.8 mg/day; P < 0.001), decrease in creatinine clearance (CrCl; ND, 0.69 +/- 0.03; D, 0.43 +/- 0.09 mg x min(-1) x 100 g body wt(-1); P < 0.05), increase in the index of glomerulosclerosis [GSI; ND, 0.01 +/- 0.01; D, 0.15 +/- 0.04 arbitrary units (AU); P < 0.01], tubulointerstitial fibrosis (TIFI; ND, 0.04 +/- 0.04; D, 0.68 +/- 0.2 AU; P < 0.01), and transforming growth factor-beta (TGF-beta) protein expression (ND, 0.61 +/- 0.02; D, 1.25 +/- 0.07 AU; P < 0.01). In the D group, the severity of these changes was augmented with OVX (UAE, 8.1 +/- 0.6 mg/day; CrCl, 0.40 +/- 0.04 mg x min(-1) x 100 g body wt(-1); GSI, 0.29 +/- 0.04 AU; TIFI, 0.90 +/- 0.06 AU; TGF-beta, 1.26 +/- 0.10 AU), whereas E2 replacement attenuated these changes (UAE, 6.3 +/- 0.8 mg/day; CrCl, 0.66 +/- 0.03 mg x min(-1) x 100 g body wt(-1); GSI, 0.06 +/- 0.02 AU; TIFI, 0.36 +/- 0.08 AU; TGF-beta, 0.57 +/- 0.08 AU). We conclude that E2 deficiency increases the severity of renal disease in a diabetic animal model and that E2 replacement is renoprotective by attenuating the decline in renal function and pathology associated with diabetes.

Dissociation of renal TGF-beta and hypertrophy in female rats with diabetes mellitus

Prepubertal onset of diabetes mellitus (DM) in male rats delays diabetic renal hypertrophy and suppresses renal transforming growth factor-beta (TGF-beta) compared with onset in adults. Because there are sex differences in normal and pathological renal growth, we performed similar experiments in female rats and examined the effects of prior ovariectomy. As in male rats, adult onset of DM increased renal weight approximately 35%, total renal TGF-beta approximately 35%, and mRNA for TGF-beta inducible gene H3 (betaIG-H3) approximately 200%. TGF-beta levels did not increase with DM in prepubertal animals, but renal weight increased approximately 40%, similar to the enlargement seen in adults. In nondiabetic rats, ovariectomy suppressed renal TGF-beta levels by 25-50% in both age groups, but betaIG-H3 was stable in younger animals and increased by approximately 200% in older animals after ovariectomy. Ovariectomy increased kidney weight approximately 10% in both age groups. DM further increased kidney weight by an additional 40% after ovariectomy with an approximately 150% increase in betaIG-H3, even though TGF-beta levels were not significantly increased. Prepubertal (approximately 99% lower), diabetic (approximately 50% lower), and ovariectomized rats (approximately 90% lower) all tended toward lower estradiol levels than intact adults, although not all differences were statistically significant. Both prepubertal onset and ovariectomy suppress TGF-beta in the kidneys of female rats with DM compared with adult-onset animals, but these states have no effect on renal enlargement. Production of the extracellular matrix component betaIG-H3 is dissociated from TGF-beta under these conditions. These observations may help explain some of the sex differences demonstrated in progressive kidney diseases, including DM.

Genetic Variation in the Renin-Angiotensin System and Progression of Diabetic Nephropathy

ABSTRACT. The impact of polymorphisms in the genes coding for angiotensinogen (M235T), ACE (ID), and angiotensin II type 1 receptor (A1166→C) on decline in GFR and doubling of s-creatinine or development of ESRD in patients with type 1 diabetes and diabetic nephropathy (DN) was tested. From 1985, all patients (n= 169) who had established diabetic nephropathy and were treated with angiotensin-converting enzyme inhibition (ACE-I) were identified consecutively at Steno Diabetes Center. Patients were followed for a median of 6 yr (range, 3 to 15 yr), with nine (range, three to 29) measurements of GFR (51Cr-EDTA). In a Cox proportional hazards model corrected for other risk factors, theDallele (ACE/ID) was associated with time to doubling of s-creatinine/ESRD (rate ratio, 1.81 per allele; 95% confidence interval, 1.09 to 3.03;P= 0.02). A new interaction hypothesis was generated demonstrating that the following variables were associated with accelerated decline in GFR: albuminuria (estimate, 2.12 ml/min per yr per 10-fold increase in albuminuria;P< 0.001), mean BP (estimate, 0.88 ml/min per yr per 10 mmHg;P= 0.02), hemoglobin A1c(estimate, 0.54 min/min per yr per 1%;P= 0.02), and number ofM(M235T)/D(ID)/A(A1166→C) alleles (estimate, 0.45 ml/min per yr per allele;P= 0.049). Number ofM/D/Aalleles also influenced time to doubling of s-creatinine or ESRD. In this study of patients with type 1 diabetes, theDallele of theACE/IDpolymorphism in addition to nongenetic risk factors independently accelerated progression of DN during ACE-I. Interaction between polymorphisms in the renin-angiotensin system also influenced the loss of kidney function. This new genetic interaction model needs to be confirmed in future studies. E-mail: pkjacobsen@dadlnet.dk

Birth weight--a risk factor for progression in diabetic nephropathy?

OBJECTIVES

Intrauterine growth retardation, as seen in individuals with low weight at birth, may give rise to a reduction in nephron number. Oligonephropathy has been linked to hypertension and renal disease in adult life. We tested the concept that low weight at birth acts as a risk factor for progression of diabetic nephropathy.

DESIGN AND SUBJECTS

We performed an observational follow-up study of 161 (97 men) type 1 diabetic patients with diabetic nephropathy [mean age (SD): 35 (11) years, mean duration of diabetes: 22 (8) years]. All patients had been followed for at least 3 years [median (range): 8 (3-20)] with at least three measurements [9 (3-31)] of glomerular filtration rate (GFR) (51Cr-EDTA). Information about birth size was obtained from midwife registrations.

SETTINGS

Steno Diabetes Center, a tertiary referral centre.

MAIN OUTCOME MEASURES

Loss of kidney function according to birth weight and weight/length ratio at birth.

RESULTS

There was no correlation in univariate analysis between birth weight or weight/length ratio and rate of decline in GFR, neither in men nor in women. Furthermore, the 27 patients with birth weights below the 20th centile had a rate of decline in GFR [median (range)] similar to the 134 patients above: 2.6 (-4.7; 9.6) vs. 3.4 (-2.3; 19.3) mL min(-1) year(-1), respectively (NS). A multiple regression analysis revealed that albuminuria, arterial blood pressure, and haemoglobin A1C during follow-up showed a significant correlation with the decline in GFR [R2 (adjusted) = 0.34], whereas birth weight and birth weight/length ratio did not.

CONCLUSIONS

Our study does not suggest that weight at birth is associated with progression of established diabetic nephropathy in type 1 diabetic patients, whilst several other potential modifiable risk factors were identified.

The role of gender in the progression of renal disease

The rate of progression of certain renal diseases in animals is greater in men than in women. In various animal models of renal disease, investigators have concluded that the presence of testosterone explains the worse course in men compared with women, whereas in other diseases, estrogen seems to confer protection for women. The gender disparity in renal disease progression found in animals is seen in certain human renal diseases, including chronic renal disease, membranous nephropathy, immunoglobin A nephropathy, and polycystic kidney disease. In humans, the differences between the genders in renal disease progression cannot be fully explained by differences in blood pressure or serum cholesterol levels. The underlying mechanisms for this gender disparity are potentially related to differences between the sexes in glomerular structure, glomerular hemodynamics, diet, variations in the production and activity of local cytokines and hormones, and/or the direct effect of sex hormones on kidney cells. Further investigation into the contribution of gender to renal disease progression may aid us in developing strategies for slowing this pathological process.

Blood pressure control--effects on diabetic nephropathy progression: how low does blood pressure have to be?

Hypertension and diabetes are independent risk factors for both cardiovascular disease and renal complications. Coexistence of these comorbid conditions predisposes the patient to a much greater risk of progression to end-stage renal disease. Combined with the increased cardiovascular mortality, this has led to recent Joint National Committee-VI recommendations for the initiation of antihypertensive therapy for people with diabetes at a blood pressure of 130/85 mm Hg, a level lower than that recommended for the nondiabetic population. Results of a review of recently published investigations on the effects of blood pressure on diabetic nephropathy progression are presented in this article. This review finds evidence to support reducing the mean arterial blood pressure to levels below 95 mm Hg, a level that is even lower than the blood pressure of 130/80 mm Hg (mean arterial pressure of 97 mm Hg) recommended by the American Diabetes Association and National Kidney Foundation. The effect of blood pressure on renal disease progression is linear and appears to have no lower threshold for the benefits of blood pressure reduction on limiting nephropathy progression. The answer to the question of how low does blood pressure have to be to minimize the effects of blood pressure on diabetic nephropathy progression might be "the lower, the better."

Renoprotective effects of losartan in diabetic nephropathy: interaction with ACE insertion/deletion genotype?

BACKGROUND

The beneficial short- and long-term renoprotective effects of angiotensin I-converting enzyme (ACE) inhibition are lower in albuminuric diabetic patients homozygous for the deletion compared to the insertion polymorphism of the ACE gene. In an attempt to overcome this interaction, we evaluated the short-term renoprotective effect in diabetic nephropathy of the angiotensin II receptor antagonist losartan in patients homozygous for the insertion or the deletion allele.

METHODS

Fifty-four hypertensive type 1 diabetic patients with diabetic nephropathy homozygous for the insertion (I; N = 26) or the deletion (D; N = 28) allele of the ACE/ID polymorphism were included. After four weeks of washout, the patients received losartan 50 mg daily followed by 100 mg in two treatment periods each lasting two months. Patients and investigators were blinded to ACE genotypes. At baseline and in the end of the treatment periods, 24-hour blood pressure, albuminuria and glomerular filtration rate values were determined.

RESULTS

At baseline, blood pressure, albuminuria and glomerular filtration rate (GFR) values were similar in the two genotype groups [II vs. DD, 1134 (238 to 5302) vs. 1451 (227 to 8129) mg/24 h, median (range); 156/82 (17/9) vs. 153/80 (17/11) mm Hg, mean (SD); and 86 (22) vs. 88 (24) mL/min/1.73 m2, respectively]. Both doses of losartan significantly lowered blood pressure, albuminuria, and GFR (P < 0.05 vs. baseline). Losartan 100 mg was more effective than 50 mg in reducing albuminuria, 51% (95% CI; 40 to 61) versus 33% (23 to 42), respectively (P < 0.01). No differences in the impact of losartan between the II and DD groups were observed: Losartan 100 mg lowered systolic/diastolic blood pressure by 12/6 and 10/4 mm Hg, whereas albuminuria decreased by 55% (35 to 68) and 46% (28 to 61), in the II and DD groups, respectively (P = NS).

CONCLUSION

Our data suggest that losartan offers similar short-term renoprotective and blood pressure lowering effects in albuminuric hypertensive type 1 diabetic patients with the ACE II and DD genotypes. However, the long-term renoprotective effects remain to be evaluated.

Effect of 3 years of antihypertensive therapy on renal structure in type 1 diabetic patients with albuminuria: the European Study for the Prevention of Renal Disease in Type 1 Diabetes (ESPRIT)

In the treatment of diabetic nephropathy, ACE inhibitor therapy reduces albumin excretion and slows the rate of decline in glomerular filtration rate (GFR). Our study was designed to investigate whether these effects lay in amelioration of the underlying glomerular structural abnormalities. A total of 54 type 1 diabetic patients with albuminuria and blood pressure (BP) <150/90 mmHg were randomized to receive 10 mg enalapril once daily, 10 mg nifedipine retard twice daily, or placebo in a multicenter double-blind study of 3 years' duration. Renal biopsy was performed at baseline and follow-up, and tissue was analyzed by standard morphometric methods. BP, GFR, albumin excretion rate (AER), and HbA1c were measured every 6 months. Enalapril lowered AER after 6 months by 26% (P < 0.05); however, this reduction was not sustained at 3 years. There was no significant effect of nifedipine or placebo on AER. GFR decreased by a similar average rate of 4.1 ml x min(-1) x year(-1) (95% CI 2.6-5.6) in all three groups. BP and HbA1c were unchanged throughout the study in all groups. At baseline, nearly all biopsies showed classic appearances of diabetic glomerulopathy. There was no detectable effect of enalapril compared with either nifedipine or placebo on renal structure over 3 years. However, we found that patients with increased AER have established glomerulopathy and a progressive average decline in GFR of 4.1 ml x min(-1) x year(-1) in the absence of overt hypertension, and baseline AER appeared predictive of subsequent mesangial volume fraction (r = 0.20, P = 0.0018). In this small cohort of nonhypertensive patients studied for 3 years, disease evolution appears unaffected by treatment with either enalapril or nifedipine.

Gender and the progression of renal disease

Many studies of chronic renal disease have reported that men have a more rapid progression of renal insufficiency. However, other studies have found no differences between the sexes, and the true effect of sex on chronic renal disease remains a topic of controversy. There is evidence that women with non-diabetic renal diseases experience a slower progression, but in diabetic renal disease, the effect of gender is not yet established. Sex hormones may mediate the effects of gender on chronic renal disease, through alterations in the renin--angiotensin system, reduction in mesangial collagen synthesis, the modification of collagen degradation, and upregulation of nitric oxide synthesis.

Effects of pulsatile intravenous insulin therapy on the progression of diabetic nephropathy

The purpose of this study was to assess the effects of pulsatile intravenous insulin therapy (PIVIT) on the progression of diabetic nephropathy in patients with type 1 diabetes mellitus (DM). This 18-month multicenter, prospective, controlled study involved 49 type 1 DM patients with nephropathy who were following the Diabetes Control and Complications Trial (DCCT) intensive therapy (IT) regimen. Of these, 26 patients formed the control group (C), which continued on IT, while 23 patients formed the treatment group (T) and underwent, in addition to IT, weekly PIVIT. Blood pressure in all patients was maintained below 140/90 mm Hg on antihypertensive medication, preferentially using angiotensin-converting enzyme (ACE) inhibitors. All study patients were seen in the clinic weekly for 18 months, had monthly glycohemoglobin (HbA1c), and every 3 months, 24-hour urinary protein excretion and creatinine clearance (CrCl) determinations. The HbA1c levels declined from 8.61% +/- 0.33% to 7.68% +/- 0.31% (P = .0028) in the T group and from 9.13% +/- 0.36% to 8.19% +/- 0.33% (P = .0015) in the C group during the study period. CrCl declined significantly in both groups, as expected, but the rate of CrCl decline in the T group (2.21 +/- 1.62 mL/min/yr) was significantly less than in the C group (7.69 +/- 1.88 mL/min/yr, P = .0343). We conclude that when PIVIT is added to IT in type 1 DM patients with overt nephropathy, it appears to markedly reduce the progression of diabetic nephropathy. The effect appears independent of ACE inhibitor therapy, blood pressure, or glycemic control.