Angiotensin converting enzyme gene polymorphism and renal hemodynamic function in early diabetes

Genetically increased angiotensin I-converting enzyme alters peripheral and renal vascular reactivity to angiotensin II and bradykinin in mice

Angiotensin I-converting enzyme (ACE) levels in humans are under strong genetic influence. Genetic variation in ACE has been linked to risk for and progression of cardiovascular and renal diseases. Causality has been documented in genetically modified mice, but the mechanisms underlying causality are not completely elucidated. To further document the vascular and renal consequences of a moderate genetic increase in ACE synthesis, we studied genetically modified mice carrying three copies of the ACE gene (three-copy mice) and littermate wild-type animals (two-copy mice). We investigated peripheral and renal vascular reactivity to angiotensin II and bradykinin in vivo by measuring blood pressure and renal blood flow after intravenous administration and also reactivity of isolated glomerular arterioles by following intracellular Ca2+ mobilization. Carrying three copies of the ACE gene potentiated the systemic and renal vascular responses to angiotensin II over the whole range of peptide concentration tested. Consistently, the response of isolated glomerular afferent arterioles to angiotensin II was enhanced in three-copy mice. In these mice, signaling pathways triggered by endothelial activation by bradykinin or carbachol in glomerular arterioles were also altered. Although the nitric oxide (NO) synthase (NOS)/NO pathway was not functional in arterioles of two-copy mice, in muscular efferent arterioles of three-copy mice NOS3 gene expression was induced and NO mediated the effect of bradykinin or carbachol. These data document new and unexpected vascular consequences of a genetic increase in ACE synthesis. Enhanced vasoconstrictor effect of angiotensin II may contribute to the risk for cardiovascular and renal diseases linked to genetically high ACE levels.

NEW & NOTEWORTHY A moderate genetic increase in angiotensin I-converting enzyme (ACE) in mice similar to the effect of the ACE gene D allele in humans unexpectedly potentiates the systemic and renal vasoconstrictor responses to angiotensin II. It also alters the endothelial signaling pathways triggered by bradykinin or carbachol in glomerular efferent arterioles.

Association of Increased Serum ACE Activity with Logical Memory Ability in Type 2 Diabetic Patients with Mild Cognitive Impairment

Background: Angiotensin-converting enzyme (ACE) is involved in the chronic complications of type 2 diabetes mellitus (T2DM) and Alzheimer's disease. This study aimed to assess the pathogenetic roles of ACE and the genetic predisposition of its insertion/deletion (I/D) polymorphism in mild cognitive impairment (MCI) among T2DM patients.

Methods: A total of 210 T2DM patients were enrolled. Among these patients, 116 satisfied the MCI diagnostic criteria and 94 exhibited healthy cognition. The cognitive functions of the patients were extensively assessed. The serum level and activity of ACE were measured via enzyme-linked immunosorbent assay and ultraviolet spectrophotography. The single-nucleotide polymorphisms of I/D gene of ACE were analyzed.

Results: The serum level and activity of ACE in diabetic MCI patients (p = 0.022 and p = 0.008, respectively) were both significantly higher than those in the healthy controls. A significant negative correlation was found between their ACE activity and logical memory test score (LMT) (p = 0.002). Multiple stepwise regression iterated the negative correlation between ACE activity and LMT score (p = 0.035). Although no significant difference was found in the genotype or allele distribution of ACE I/D polymorphism between the groups, the serum levels and activity of ACE were higher in the DD group than in the ID and II groups (p < 0.05).

Conclusions: Serum ACE activity could better predict logical memory in T2DM patients than ACE level. Further investigations on a large population size are necessary to test whether the D-allele of the ACE gene polymorphism is susceptible to memory deterioration.

[Individual renal hemodynamic response to chronic angiotensin II receptor blockade and the influence on the renin-angiotensin system gene polymorphisms]

INTRODUCTION

Our study was aimed at determining whether the polymorphism of genes for different components of the renin-angiotensin-aldosterone system could influence the renal hemodynamic response to losartan treatment.

MATERIAL AND METHOD

The study included 35 patients with type I diabetes mellitus and persistent albuminuria, genotyped for the 1166 A/C polymorphism gene for the angiotensin II type 1 receptor and I/D polymorphism of the angiotensin-converting enzyme gene. The participants were divided into groups according to the combinations of A or C allele: AA, AC, CC; and according to the combinations of I or D allele: II, ID and DD genotype. The patients received losartan therapy for 12 weeks. The renal hemodynamic measurements were determined at baseline and after the examination period.

RESULTS

Losartan therapy significantly reduced the filtration fraction from the baseline by 0.018 +/- 0.024 (p = 0.012) only in the AC genotype. The glomerular filtration rate remained unchanged in all genotype groups. A significant increase in the effective renal plasma flow was obtained only in AC genotype (544 +/- 88 vs 575 +/- 90 ml/min; p = 0.02), while significant reductions in the renal vascular resistance were found in AA group (115 +/- 25 vs 95 +/- 21 mmHg x l(-1) x min(-1), p = 0.001) and in AC group (118 +/- 30 vs 101 +/- 28 mmHg x l(-1) x min(-1); p = 0.001). A significant reduction of the glomerular filtration rate by 8 +/- 10 ml/min was obtained only in the DD genotype (p = 0.016), and only the DD genotype achieved a significant reduction of the filtration fraction by 0.019 +/- 0,022 (p = 0.008). The most pronounced increase of the effective renal plasma flow was found only in the ID genotype (536 +/- 75 vs 591 +/- 63 ml/min; p = 0.01). The reduction of the renal vascular resistance was independent of ACE gene polymorphism.

CONCLUSION

Our study shows that individual renal vascular response to losartan treatment in diabetic patients with persistent albuminuria, could be influenced by genetic polymorphisms.

Endothelial nitric oxide synthase gene polymorphisms and the renal hemodynamic response to L-arginine

Nitric oxide is generated from L-arginine by nitric oxide synthase (NOS), an enzyme that exists in several isoforms. Some studies found that a polymorphism (G894T) in the endothelial NOS gene was associated with decreased nitric oxide bioactivity and vascular complications. However, it is not known whether the enzyme had a reduced activity. Here we measured the effect of an infusion of L-arginine on renal hemodynamic function in subjects segregated by the presence or absence of the T allele. If this polymorphism represented a functional variant, subjects with the GT/TT form should exhibit a blunted renal hemodynamic response to L-arginine compared to those with a GG allele. All subjects were given a diet controlled for sodium and protein intake. GG subjects had lower mean arterial pressure and an augmented glomerular filtration rate at baseline. In response to a graded L-arginine infusion, this group had significant changes in effective renal plasma flow, glomerular filtration rate, filtration fraction, renal vascular resistance, and renal blood flow. The renal response to L-arginine in GT/TT subjects was blunted. Circulating cGMP levels and endothelial NOS mRNA expression, measured in skin biopsies by real-time PCR, did not differ between the groups. Our study shows that the G894T allele of endothelial NOS is associated with a blunted response to L-arginine, suggesting this polymorphism may be a functional variant in humans.

The effect of cyclooxygenase-2 inhibition on renal hemodynamic function in humans with type 1 diabetes

OBJECTIVE

Studies in animal models suggest that cyclooxygenase-2 (COX2) plays a role in the regulation of the renal microcirculation in diabetes. Accordingly, we examined the role of COX2 in the control of renal hemodynamic function and in the renal response to hyperglycemia in humans with uncomplicated type 1 diabetes. We hypothesized that COX2 inhibition would alleviate the hyperfiltration state and would abrogate the hyperglycemia-mediated rise in glomerular filtration rate (GFR). RESEARCH DESIGN AND METHODS; Renal function was assessed during clamped euglycemia and hyperglycemia on 2 consecutive days before and then again after 14 days of COX2 inhibition using 200 mg celecoxib once daily by mouth. For analysis, the cohort was then divided into two groups based on the baseline GFR: 9 subjects exhibited hyperfiltration (GFR >or=135 ml/min per 1.73 m(2)), and 12 subjects exhibited normofiltration (GFR <135 ml/min per 1.73 m(2)).

RESULTS

Under euglycemic conditions, COX2 inhibition resulted in a significant decline in GFR in the hyperfiltration group (150 +/- 5 to 139 +/- 5 ml/min per 1.73 m(2)) but increased GFR in the normofiltration group (118 +/- 5 to 138 +/- 5 ml/min per 1.73 m(2)). COX2 inhibition did not blunt the hyperglycemia-associated rise in GFR in the normofiltration group and was instead associated with an augmented rise in GFR.

CONCLUSIONS

In summary, our results support the hypothesis that COX2 is an important determinant of renal hemodynamic function in subjects with type 1 diabetes. The renal response to COX2 inhibition emphasizes that hyperfiltration and normofiltration are distinct physiological states.

The effect of oral contraceptives on the nitric oxide system and renal function

We have demonstrated that oral contraceptive (OC) users exhibit elevated angiotensin II levels and angiotensin II type 1 receptor expression, indicative of renin-angiotensin system (RAS) activation, yet the renal and systemic consequences are minimal, suggesting that there is increased vasodilatory activity, counteracting the effect of RAS activation. We hypothesized that the nitric oxide (NO) system would be upregulated in OC users and that this would be reflected by a blunted hemodynamic response to l-arginine infusion. All subjects were studied after a 7-day controlled sodium and protein diet. Inulin and para-aminohippurate clearance techniques were used to assess renal function. l-Arginine was infused at 100, 250, and 500 mg/kg, each over 30 min. Skin endothelial NO synthase mRNA expression was assessed by real-time PCR. While OC nonusers exhibited significant increases in effective renal plasma flow (670.8 +/- 35.6 to 816.2 +/- 59.7 ml.min(-1).1.73 m(-2)) and glomerular filtration rate (133.4 +/- 4.3 to 151.0 +/- 5.7 ml.min(-1).1.73 m(-2), P = 0.04) and declines in renal vascular resistance (81.1 +/- 6.1 to 63.5 +/- 6.2 mmHg.ml(-1).min, P = 0.001) at the lower l-arginine infusion rates, the responses in OC users were blunted. While l-arginine reduced mean arterial pressure at the 250 and 500 mg/kg doses in OC nonusers, OC users only exhibited a decrease in mean arterial pressure at the highest infusion rate. In contrast, tissue endothelial NO synthase mRNA levels were higher in the OC users (P = 0.04). In summary, these findings suggest that the NO system is upregulated by OC use in young, healthy women. Increased activity of the NO pathway may modulate the hemodynamic effects of RAS activation in OC users.

Modulation of the renal response to ACE inhibition by ACE insertion/deletion polymorphism during hyperglycemia in normotensive, normoalbuminuric type 1 diabetic patients

ACE inhibition protects kidney function, but ACE insertion/deletion (I/D) polymorphism affects renal prognosis in type 1 diabetic patients. ACE genotype may influence the renal benefits of ACE inhibition. We studied the impact of ACE I/D polymorphism on the renal hemodynamic changes induced by ACE inhibition in type 1 diabetes. We studied renal hemodynamics (glomerular filtration rate [GFR], effective renal plasma flow [ERPF], filtration fraction [GFR/ERPF], mean arterial pressure [MAP], and total renal resistances [MAP/ERPF]) repeatedly during normoglycemia and then hyperglycemia in 12 normotensive, normoalbuminuric type 1 diabetes and the II genotype (associated with nephroprotection) versus 22 age- and sex-matched subjects with the ACE D allele after three randomly allocated 2- to 6-week periods on placebo, 1.25 mg/day ramipril, and 5 mg/day ramipril in a double-blind, cross-over study. During normoglycemia, the hemodynamic changes induced by ramipril were similar in both genotypes. During hyperglycemia, the changes induced by ramipril were accentuated in the II genotype group and attenuated dose dependently in the D allele group (treatment-genotype interaction P values for ERPF, 0.018; MAP, 0.018; and total renal resistances, 0.055). These results provide a basis to different renal responses to ACE inhibition according to ACE genotype in type 1 diabetes.

The Influence of Angiotensin-Converting Enzyme Gene of Donor and Recipient on the Function of Transplanted Kidney

One of the genes that is supposed to influence renal graft function is the one encoding angiotensin I-converting enzyme (ACE). It shows polymorphism in the presence (I allele) or absence (D allele) of a 287-base pair fragment. The question arises whether ACE gene polymorphism of the recipient and donor influences renal graft survival. This prospective study included 94 recipients who underwent ACE genotyping (DD, DI, II) and measured their creatinine clearance after cimetidine administration. These factors were correlated with the occurrence of acute or chronic rejection and of pharmacologic treatment of hypertension. In 27 recipients it was possible to obtain the ACE genotype of the donor. Among the recipients, 36 proved to be DD genotype, 38 ID, and 20 II. Among the donors, 10 proved to be DD genotype, 10 ID, and 7 II. The changes in creatinine clearance after cimetidine administration were not significantly different among any of the genotype subgroups. Significantly higher creatinine concentrations were found among recipients with II genotype compared to the combined group of ID and DD among patients not treated with ACE inhibitors, but not among those receiving ACE I after kidney transplantation. No differences were found in the frequency of rejection episodes among the subgroups with different ACE genotypes. No significant influence of donor ACE genotype on renal graft function was observed. In summary, the I/D genotype was not an independent prognostic factor for renal graft survival in the first 4 years after transplantation. Possibly the use of ACE I alters the influence of genotype on some parameters.

The impact of renin-angiotensin system polymorphisms on physiological and pathophysiological processes in humans

PURPOSE OF REVIEW

The renin-angiotensin system plays a central role in health and disease but the determinants of renin-angiotensin system activity have not been fully elucidated. Physiologic genomics continues to be an active area of research that emphasizes definition of phenotype and clarification of non-genomic factors that influence the genotype-phenotype correlation. A common variant of the angiotensinogen gene (T235) predicts elevated levels of circulating angiotensinogen, and polymorphisms of this gene have been linked to physiologic responses and to the risk of cardiovascular disease. The angiotensin-converting-enzyme gene insertion/deletion polymorphism, although not considered functional, has been associated with physiologic responses and disease risk in hypertension and diabetes. A polymorphism of the angiotensin type 1 receptor gene, A1166C, has been the focus of several physiologic studies. These authors will focus on mechanistic studies in normal humans and those with diabetes mellitus or hypertension that examine the impact of these polymorphisms on physiologic responses.

RECENT FINDINGS

Recent studies provide divergent results. Many have shown that mediating factors interfere with the genotype-phenotype correlation. Studies in normal individuals and in those with diabetes mellitus have shown that sodium status and glycemia can alter the impact of genotype. In individuals with essential hypertension, the pathway between genotype and physiology can be disrupted by gender and/or race.

SUMMARY

Divergent results in many studies may be attributable to various non-genomic and environmental influences on the pathway between gene polymorphism and physiology. Clarification of these factors should allow a better understanding of genotype-phenotype correlation.

Vascular injury in systemic sclerosis: Angiotensin-converting enzyme insertion/deletion polymorphism

The microvascular involvement in systemic sclerosis (SSc) is characterized by endothelial damage and smooth muscle cell migration in the intima. The vascular pathologic modifications in SSc are strikingly similar to those of atherosclerosis. SSc also is characterized by an accelerated macrovascular disease. The gene encoding for angiotensin-converting enzyme (ACE) is a 21-kb, 26-exon gene, localized on chromosome 17 (17q23). Polymorphic sites are an insertion/deletion (I/D) that consists of three genotypes: DD and II homozygotes, and ID heterozygote. ACE gene polymorphisms have been linked to vascular disorders (coronary artery disease, hypertension, cerebrovascular disease, hypertrophic cardiomyopathy, and diabetic or nondiabetic nephropathy). In particular, the possession of ACE D allele was associated with an increased risk of developing malignant vascular injury. ACE D allele frequency of the I/D polymorphism was associated with an increased risk of SSc, suggesting a genetic contribution to the disease. The discrepancy between the high prevalence of D allele and reduced ACE plasma levels in SSc demonstrate the lack of knowledge on the regulation and function of renin-angiotensin system in SSc.

Microarray analysis of gene expression in the kidneys of new- and post-onset diabetic NOD mice

We profiled the expression of 5,760 clones from a kidney subtraction library in the kidneys of three groups of NOD mice: nondiabetic, new-onset, and long-term diabetic. A total of 27 genes had lower expression and 1 gene (Gpx3) had higher expression in the new-onset diabetic mice compared with nondiabetic control NOD mice (P < 0.001). Similarly, 19 of the above 27 genes and 7 additional genes had higher expression and the Gpx3 gene had lower expression in long-term diabetic mice compared with controls (P < 0.001). Interestingly, only three genes may be different between new-onset and long-term diabetic mice (P < 0.0004). These genes are from diverse functional groups, including oxidative phosphorylation, free radical neutralization, channels, pumps, lipid processing, transcription and translation machinery, protein trafficking, constitutive protein processing, and immune function. The majority of these genes fall into four signaling pathways: insulin, transforming growth factor-beta, tumor necrosis factor-alpha, and peroxisome proliferator-activated receptor. The most significant expression change was found for the stearoyl-coenzyme A desaturase 1 (SCD1) gene (P < 10(-7)). The lower expression levels of the SCD1 gene in both diabetic groups compared with controls were further confirmed by Northern blot analysis and immunohistochemistry.

ACE and PC-1 gene polymorphisms in normoalbuminuric Type 1 diabetic patients: a 10-year prospective study

The aim of this study was to analyze the role of ACE gene insertion/deletion (I/D) and PC-1 gene K121Q polymorphisms in the changes of glomerular filtration rate (GFR), urinary albumin excretion rate (UAER), and blood pressure (BP) levels in a cohort of normoalbuminuric Type 1 diabetic patients. This is a 10.2+/-2.0-year prospective study of 30 normotensive normoalbuminuric Type 1 diabetic patients. UAER (immunoturbidimetry), GFR ((51)Cr-EDTA single injection technique), GHb (ion exchange chromatography), and BP levels were measured at baseline and at 1.7+/-0.6-year intervals. The presence of ACE gene I/D and PC-1 gene K121Q polymorphisms was determined by polymerase chain reaction (PCR) and restriction enzyme techniques. Three patients developed diabetic nephropathy (DN), all carriers of allele D. The presence of allele D was the only predictor (R(2)=.15, F=4.92, P=.035) of the observed GFR decline (-0.29+/-0.34 ml/min/month, P<.05). UAER increased during the study (log UAER=0.0275+/-0.042 microg/min/month, P=.002) and was associated with baseline UAER levels only (R(2)=.17, F=5.72, P=.024). A significant increase (P<.05) in cases of hypertension and retinopathy were observed in ID/DD (n=19) and not in II patients (n=11). Patients with the KQ/QQ genotype (n=8) presented a significant increase (P=.045) in new cases of retinopathy. In conclusion, the presence of the ACE gene D allele in this sample of normoalbuminuric normotensive Type 1 diabetic patients was associated with a higher proportion of microvascular complications and hypertension.

Enhanced responses of blood pressure, renal function, and aldosterone to angiotensin I in the DD genotype are blunted by low sodium intake

Angiotensin-converting enzyme (ACE) activity is increased in the DD genotype, but the functional significance for renal function is unknown. Blunted responses of BP and proteinuria to ACE inhibition among DD renal patients during periods of high sodium intake were reported. It was therefore hypothesized that sodium status affects the phenotype in the ACE I/D polymorphism. The effects of angiotensin I (AngI) and AngII among 27 healthy subjects, with both low (50 mmol sodium/d) and liberal (200 mmol sodium/d) sodium intakes, were studied. Baseline mean arterial pressure (MAP) values, renal hemodynamic parameters, and renin-angiotensin system parameters were similar for all genotypes with either sodium intake level. With liberal sodium intake, the increases in MAP, renal vascular resistance, and aldosterone levels during AngI infusion (8 ng/kg per min) were significantly higher for the DD genotype, compared with the ID and II genotypes (all parameters presented as percent changes +/- 95% confidence intervals), with mean MAP increases of 22 +/- 2% (DD genotype), 13 +/- 5% (ID genotype), and 12 +/- 6% (II genotype) (P < 0.05), mean increases in renal vascular resistance of 100.1 +/- 19.7% (DD genotype), 73.0 +/- 16.3% (ID genotype), and 63.2 +/- 16.9% (II genotype) (P < 0.05), and increases in aldosterone levels of 650 +/- 189% (DD genotype), 343 +/- 71% (ID genotype), and 254 +/- 99% (II genotype) (P < 0.05). Also, the decrease in GFR was more pronounced for the DD genotype, with mean decreases of 17.9 +/- 4.7% (DD genotype), 8.8 +/- 3.4% (ID genotype), and 6.4 +/- 5.9% (II genotype) (P < 0.05). The effective renal plasma flow, plasma AngII concentration, and plasma renin activity values were similar for the genotypes. In contrast, with low sodium intake, the responses to AngI were similar for all genotypes. The responses to AngII were also similar for all genotypes, with either sodium intake level. In conclusion, the responses of MAP, renal hemodynamic parameters, and aldosterone concentrations to AngI are enhanced for the DD genotype with liberal but not low sodium intake. These results support the presence of gene-environment interactions between ACE genotypes and dietary sodium intake.

New aspects on angiotensin-converting enzyme: from gene to disease

Angiotensin-converting enzyme (ACE) is a well known zinc-metallopeptidase that converts angiotensin I to the potent vasoconstrictor angiotensin II and that degrades bradykinin, a powerful vasodilator, both for regulation of vascular tone and cardiac functions. Other natural substrates of ACE were identified broadening the functions of this enzyme within different physiological contexts such as neuronal metabolism, hematopoiesis, digestion and reproduction. Synthetic substrates were developed for the determination of ACE activity in various biological fluids, mostly human plasma, for the diagnosis of sarcoidosis and other granulomatous diseases. After the successful use of captopril, the first ACE inhibitor in the treatment of hypertension, a number of molecules were synthesized and used in the treatment of congestive heart failure and for preventing cardiac impairment after myocardial infarction. This class of antihypertensive drugs benefited from structural data on carboxypeptidases active site, as ACE molecule has not yet been crystallized. In the last two decades ACE gene has been cloned that allowed the identification (i) of two isoenzymes, one called somatic ACE resulting from gene duplication and primarily expressed in endothelial cells, and the other, called germinative or testicular ACE, resulting from the transcription in the male reproductive system of a more simple gene, (ii) of an hydrophobic C-terminal peptide for membrane-anchoring and specifically cleaved by a metalloprotease to release soluble forms of both isoenzymes, and (iii) of several allelic polymorphisms, one of them consisting of an insertion/deletion (I/D) polymorphism in a short intronic Alu sequence that could account for half the variance in plasma ACE level and resulting in a large inter-individual variability; moreover this I/D polymorphism was proposed as a genetic marker for identifying individuals at high risk of ischemic heart disease and of anticipating in one individual the efficacy of the antihypertensive therapy, although conflicting data arose from the past decade literature. Moreover, ACE gene cloning has confirmed the expression of the enzyme in endothelial cell, in particular as an ecto-enzyme facing the vascular lumen, but not to the same extent with regard to the vascular origin of the cells. Plasma ACE in healthy subjects arises essentially from the endothelium. On the other hand, in granulomatous diseases where a local stimulation of macrophages leads to an abnormal ACE secretion, it can also be found in other biological fluids such as cerebrospinal and broncho-alveolar fluids. Low plasma ACE levels result from endothelium impairment such as in deep vein thrombosis or in endothelio-toxic anticancer therapies. Another cause of low, sometimes undetectable, plasma ACE levels is the use of an ACE inhibitor, but this is without any significance with regard to its clinical benefits. Albeit molecular cloning has provided a number of new details on ACE structure and function, many questions still remain, in particular about its tertiary structure including glycosylations, about its tissue-specific expression and regulation, and also about the exact significance of the I/D polymorphism in cardiovascular pathology including the pharmacogenomic field.

Relations between ACE gene and ecNOS gene polymorphisms and resistive index in type 2 diabetic patients with nephropathy

OBJECTIVE

ACE and endothelial cell nitric oxide synthase (ecNOS) genotypes have been reported to be related to the incidence of renal diseases and coronary artery diseases. In order to assess the effect of the gene polymorphism of both ACE and ecNOS on renal hemodynamic abnormality, we examined 155 Japanese patients with type 2 diabetes with various stages of nephropathy.

RESEARCH DESIGN AND METHODS

The patients ranged in age from 40 to 72 years (92 men and 63 women). They were divided into four groups: group 1 consisted of patients with urinary albumin excretion (UAE) <30 mg/day (n = 69), group 2 had 30 < or = UAE < 300 mg/day (n = 44), group 3 had UAE > or =300 mg/day and serum creatinine <1.5 mg/dl (n = 22), and group 4 had serum creatinine >1.5 mg/dl (n = 20). Intrarenal hemodynamics were studied by duplex Doppler sonography in patients with type 2 diabetes. The ACE and ecNOS gene polymorphisms were examined by polymerase chain reaction.

RESULTS

There were no significant differences in sex, BMI, and blood glucose level, but there were differences in HbA(1c) and lipoprotein profiles among the four groups. There were no significant differences in the distribution of ACE genotype or in the frequency of the ecNOS 4a allele among the four groups. Resistive index (RI) values of the interlobar arteries of group 4 were significantly higher than those of groups 1, 2, and 3, whereas the RI values were not significantly different among groups 1, 2, and 3. Multiple regression analysis showed that age, duration of diabetes, systolic and diastolic blood pressure, and creatinine clearance were significantly associated with the increased RI values, but that there was no significant association between RI values and the ecNOS genotype (R(2) = 0.613, P < 0.0001).

CONCLUSIONS

These results suggest that intrarenal hemodynamic abnormalities are present as a feature of the progression of nephropathy in type 2 diabetes, and that they are associated with age, duration of diabetes, decreased creatinine clearance, and blood pressure, but not with the genetic factors of the ACE and ecNOS gene polymorphism in nephropathy of type 2 diabetes.

Glomerular hyperfiltration, high renin, and low- extracellular volume in high blood pressure

Abnormal renovascular resistance and glomerular filtration rate are characteristic of established hypertension and may also be involved in its pathogenesis. To determine renal and body fluid correlates of the predisposition to high blood pressure, we examined 100 healthy young adults with high or low blood pressure. Within each group, half had parents with high blood pressures, and half had parents with low blood pressures. Renal function and hemodynamics, body fluid volumes, and relevant hormones and genotypes were measured. Subjects with high personal and parental blood pressures had the highest levels of glomerular filtration rate (P<0.02) and plasma active renin concentration and low levels of exchangeable sodium and plasma volume (P<0.02). High glomerular filtration rate was not associated with differences in urinary kallikrein or prostaglandins. Polymorphisms of the renin, angiotensin-converting enzyme, and angiotensinogen genes were not associated with differences in glomerular filtration rate or renin. Subjects with high personal, but low parental, blood pressures had low exchangeable sodium and plasma volumes (P<0.02) but normal glomerular filtration rates. In this population, extracellular volume depletion and high renin are correlates of high blood pressure in early adulthood, and glomerular hyperfiltration is a feature of those who also have familial predisposition to high blood pressure.

Polymorphisms of angiotensin-converting enzyme and angiotensinogen genes in type 2 diabetic sibships in relation to albumin excretion rate

Familial clustering of altered albumin excretion and nephropathy risk has been described in both type 1 and type 2 diabetes; moreover, an association of micro-macroalbuminuria and diabetic retinopathy has been recently reported in a large number of white families with type 2 diabetes. Conflicting reports, mainly comparing affected with unaffected unrelated subjects, have suggested a possible role of some genotypes of the renin-angiotensin system in conferring nephropathy risk in type 2 diabetes. To examine the role of genetic factors in influencing albuminuria in families, we studied the relation of angiotensin-converting enzymes (ACE) and angiotensinogen (AGN) genotypes with albumin excretion rate in a population of affected siblings of type 2 diabetic probands. We determined ACE insertion/deletion polymorphism and two polymorphisms of the AGN gene (T174M and M235T) in 160 families with at least one affected member. Defining proband as the patient with the longest known duration of diabetes, we compared the allelic distribution in diabetic probands with and without altered albumin excretion and in their siblings. Allelic distribution of these polymorphisms was similar in the two groups of probands, as well as in their siblings. Identity-by-State (IBS) analysis showed a link between AGN locus and arterial hypertension in these siblings, which was independent from the degree of renal involvement. Thus, our findings suggest that in white families with type 2 diabetes, there is no linkage between the degree of albumin excretion and ACE and AGN polymorphisms, whereas the latter is related to arterial hypertension, as previously found in patients without diabetes but with essential hypertension.

Angiotensin II type 1 receptor gene polymorphism predicts response to losartan and angiotensin II

Angiotensin II type 1 receptor gene polymorphism predicts response to losartan and angiotensin II.

BACKGROUND

Most of the known actions of angiotensin II (Ang II) are mediated by the Ang II type 1 receptor (AGT1R). A noncoding polymorphism of the AGT1R gene has been described in which there is either an adenine (A) or cytosine (C) base at position 1166. The functional significance of this polymorphism is unknown, prompting us to examine the relationship between this polymorphism and the systemic and renal responses to AGT1R blockade and subpressor Ang II infusion.

METHODS

Sixty-six healthy Caucasian men and women, genotyped for the AGT1R polymorphism by polymerase chain reaction, were chosen to form two homogeneous groups: AA and AC/CC. Renal hemodynamic function was assessed with inulin and para-aminohippurate clearance before and after AGT1R receptor blockade with losartan and Ang II infusion.

RESULTS

The mean values at baseline for glomerular filtration rate (GFR), renal plasma flow (ERPF), and renal blood flow (RBF) were significantly lower in the AC/CC group compared with the AA group. Losartan increased the GFR and decreased the mean arterial pressure (MAP) in the AC/CC group, but did not influence these parameters in the AA group. The aldosterone responses to losartan were blunted in the AA subgroup. During Ang II infusion, AC/CC subjects maintained GFR despite equivalent declines in RBF, suggesting an enhanced efferent arteriolar constrictive response.

CONCLUSIONS

Taken together, these results suggest that there is a relationship between the AGT1R A1166-->C polymorphism and the humoral and renal hemodynamic responses to AGT1R blockade and to Ang II infusion in the sodium-replete state, and that the C allele is associated with enhanced intrarenal and peripheral Ang II activity. Further studies are required to determine the genetic locus for this effect.

Angiotensin-converting enzyme gene and diabetes mellitus

AIMS

The association of the insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) gene with cardiovascular disease and diabetic nephropathy remains a controversial issue. This review aims to give an overview of the research to date assessing the impact of the ACE polymorphism in Type 1 and Type 2 diabetes mellitus (DM).

METHODS

A systematic review of the literature was performed in the databases of MEDLINE, PubMed and EMBASE for the key words 'diabetes mellitus', 'diabetic nephropathy', 'ACE polymorphism' and 'genotype' and relevant articles were considered.

RESULTS

A meta-analysis assessing the influence of the ACE polymorphism on disease susceptibility demonstrated significant odds ratios in individuals with the DD genotype for coronary heart disease, myocardial infarction and both diabetic and nondiabetic renal disease. No association was found for left ventricular hypertrophy or hypertension in nondiabetic subjects.

CONCLUSIONS

The ACE polymorphism appears to have a significant impact on the progression of diabetic nephropathy and may have therapeutic implications for identifying those individuals resistant to the effects of ACE inhibitors. It also appears to be indicative of an increased vascular risk in diabetic patients; however, larger prospective studies are required to clarify this situation.

Angiotensin-converting enzyme gene polymorphism: is there a link to nephropathy in patients with type 1 diabetes?

OBJECTIVE

To evaluate the association between the angiotensin-converting enzyme (ACE) gene polymorphism and diabetic nephropathy in patients with type 1 diabetes.

DATA SOURCES

Citations were selected using the MEDLINE database. Only those citations involving human subjects and available in English were selected. Key search words included angiotensin-converting enzyme (ACE), polymorphism, nephropathy, and type 1 diabetes.

STUDY SELECTION

Selection criteria consisted of all MEDLINE-referenced clinical trials, review articles, and editorial comments assessing the potential link between the ACE gene polymorphism and diabetic nephropathy in insulin-dependent diabetes mellitus published between January 1990 and February 1998.

DATA SYNTHESIS

Because diabetic nephropathy is a serious complication of type 1 diabetes, focus has been placed on the early identification of and intervention with patients genetically susceptible to this complication. Because the ACE gene polymorphism has an effect on plasma ACE concentration variations among individuals, it has been investigated as a potential genetic marker for diabetic nephropathy. The best studies to date are reviewed in order to assess the utility of the ACE polymorphisms as a genetic marker of diabetic nephropathy in patients with type 1 diabetes, and to determine what implications this holds for drug treatment.

CONCLUSIONS

Although the ACE gene polymorphism's potential link to diabetic nephropathy in patients with type 1 diabetes has been debated, the most definitive studies show that an association exists. Large epidemiologic studies must now be conducted to determine the implications this polymorphism holds for the best treatment strategies in the care of these patients.

Renal changes on hyperglycemia and angiotensin-converting enzyme in type 1 diabetes

Hyperglycemia causes capillary vasodilation and high glomerular capillary hydraulic pressure, which lead to glomerulosclerosis and hypertension in type 1 diabetic subjects. The insertion/deletion (I/D) polymorphism of the angiotensin I-converting enzyme (ACE) gene can modulate risk of nephropathy due to hyperglycemia, and the II genotype (producing low plasma ACE concentrations and probably reduced renal angiotensin II generation and kinin inactivation) may protect against diabetic nephropathy. We tested the possible interaction between ACE I/D polymorphism and uncontrolled type 1 diabetes by measuring glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) during normoglycemia ( approximately 5 mmol/L) and hyperglycemia ( approximately 15 mmol/L) in 9 normoalbuminuric, normotensive type 1 diabetic subjects with the II genotype and 18 matched controls with the ID or DD genotype. Baseline GFR (145+/-22 mL/min per 1.73 m2) and ERPF (636+/-69 mL/min per 1.73 m2) of II subjects declined by 8+/-10% and 10+/-9%, respectively, during hyperglycemia; whereas baseline GFR (138+/-16 mL/min per 1.73 m2) and ERPF (607+/-93 mL/min per 1.73 m2) increased by 4+/-7% and 6+/-11%, respectively, in ID and DD subjects (II versus ID or DD subjects: P=0.0007 and P=0.0005, for GFR and ERPF, respectively). The changes in renal hemodynamics of subjects carrying 1 or 2 D alleles were compatible, with a mainly preglomerular vasodilation induced by hyperglycemia, proportional to plasma ACE concentration (P=0.024); this was not observed in subjects with the II genotype. Thus, type 1 diabetic individuals with the II genotype are resistant to glomerular changes induced by hyperglycemia, providing a basis for their reduced risk of nephropathy.

Angiotensin converting enzyme gene polymorphisms and renal disease

In the past year there has been a profusion of reports identifying a possible association between the insertion/deletion polymorphism of the angiotensin converting enzyme and renal diseases. Rather than clarifying the situation, it has become more difficult to interpret its significance owing to small sample sizes and concerns over methodology; hence, studies are frequently contradictory. Despite these concerns there is evidence for a role of this polymorphism in progressive renal disease. This review summarizes the major studies in this field and suggests future strategies that might be employed to identify useful genetic markers in nephrology, for which the angiotensin converting enzyme polymorphism has acted as an important paradigm.