Plasma renin activity in renal transplant patients with hypertension

Association of hypertension genotypes and decline in renal function after kidney transplantation

BACKGROUND

Polymorphisms of genes such as angiotensin-converting enzyme (ACE), angiotensinogen (AGT), and angiotensin receptor type I (AGTR1) have been associated with hypertension. Hypertension, in turn, has been associated with decreased renal allograft survival. Therefore, this study investigated whether single nucleotide polymorphisms (SNPs) in these genes are associated with decline in renal function posttransplantation.

METHODS

We enrolled patients from a prospective cohort of renal transplant recipients of deceased donor kidneys being conducted at 9 centers in the Delaware Valley Region. Medical records were assessed every 6 months and estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease equation. Genotypes of 10, 2, and 5 SNPs in the AGTR1, AGT, and ACE gene were analyzed, respectively.

RESULTS

The G and the T alleles of the respective AGTR1 SNPs rs275704 and rs5182 were both associated with 50% decline in eGFR (HR for rs275704: CG=1.22, 95% confidence interval [CI] 0.67-2.25 and GG=2.55, 95% CI 1.22-5.32, overall P=0.03; HR for rs5182: CT=1.26, 95% CI 0.72-2.19 and TT=3.09, 95% CI 1.50-6.37, overall P=0.007) in the adjusted analysis. Similarly, haplotype analysis showed that AGTR1 SNPs were associated with 50% decline in eGFR (global P=0.010). The GG genotype of SNP rs275704 occurred more frequently in African Americans than in non-African Americans (44% vs. 7%, chi2=36.03, P<0.0001). In contrast, the TT genotype of SNP rs5182 occurred more frequently in non-African Americans than in African-Americans (24% vs. 2%, chi2=21.40, P<0.0001). Polymorphisms in the ACE and AGT genes were not associated with renal allograft outcomes.

CONCLUSIONS

SNPs in AGTR1 gene are associated with decline in renal function posttransplantation.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Body Composition Assessed by Impedance Changes Very Early with Declining Renal Graft Function

BACKGROUND

Kidney transplant (Tx) restores renal filtration, although it does not achieve the function of two native kidneys, and with time it may variably involute back to chronic renal failure. We hypothesized that bioelectrical impedance analysis (BIA) might highlight differences for body compartments among Tx with different filtration rates, and we compared them with healthy controls.

METHODS

38 Tx patients (25 males, 13 females) were studied at 75.9 +/- 37.8 months postsurgery and divided into three groups: good creatinine clearance (CrCl, ml/min/1.73 m2; > 65.0), borderline (35.0 < CrCl < 60.0) and bad (CrCl < 35.0). BIA was assessed three times in a year. Total body water, extracellular water (ECW), intracellular water (ICW), Na:K exchange rate (Nae:Ke) and phase angle were studied. Healthy (n = 11) and hemodialysis (n = 11) groups were also studied.

RESULTS

BIA showed no differences between healthy controls and good Tx while both borderline and bad Tx presented a significantly higher ECW and lower ICW than either good Tx or normal controls. Only good CrCl was different from predialysis.

CONCLUSIONS

A good kidney graft manages to restore and maintain normal body composition, even with potential disturbances brought about by steroids and cyclosporine. With mild renal dysfunction a change in body compartments was observed, moving towards the composition of that with chronic renal failure patients.

Increased Expression of Renin in Chronic Allograft Nephropathy

BACKGROUND

Chronic allograft nephropathy (CAN) is the main cause of renal transplant failure in the first decade posttransplant. The precise pathogenetic mechanism for CAN is not completely understood. A possible role of renin-angiotensin system for CAN has been suggested through clinical observations that angiotensin-converting enzyme inhibition and angiotensin II receptor blockers prevent CAN.

METHODS

Distribution of renin-positive cells in allograft biopsy specimens was examined immunohistochemically in 23 renal transplant recipients diagnosed with CAN Biopsy specimens obtained from seven recipients with stable renal function were examined as controls. Histologic evaluation was performed based on the Banff 97 classification.

RESULTS

Renin-positive cells were found in the juxtaglomerular apparatus (JGA) adjoining the afferent arterioles in both groups. When the number of renin-positive cells in JGA was defined as a renin index, it was significantly higher in the CAN than the control group (P = .007). There was no significant difference in age, interval between transplantation and biopsy, and blood pressure between groups. Only a significantly higher serum creatinine was found in the CAN group.

CONCLUSIONS

The increased renin-positive cells in JGA suggest a significant role of the intrarenal renin-angiotensin system activation in the development of CAN.

Bioimpedance analysis highlights changes in body composition at the early stages of impairment of kidney transplant function

OBJECTIVE

Kidney transplantation restores renal filtration, although it does not achieve the function of 2 native kidneys, and with time it may involute back to chronic renal failure. We hypothesized that bioelectrical impedance analysis (BIA) might highlight differences for body compartments among kidney transplants (Tx) with different filtration rates.

METHODS

Thirty transplantation patients (19 male, 11 female) were studied at 62.4+/-26.6 months postsurgery and were divided into 3 groups: good creatinine clearance (crCl, mL/min/1.73 m2; >65.0), borderline (35.0<crCl<60.0), and bad (crCl <35.0). BIA was assessed 3 times in 1 year. Total body water, extracellular water (ECW), intracellular water (ICW), Na:K exchangeable ratio (Nae:Ke), and phase angle were studied. Healthy (n=11) and hemodialysis (n=11) groups were studied as well.

RESULTS

BIA showed no differences between healthy controls and good Tx, whereas both borderline and bad Tx presented a significantly higher ECW and lower ICW than either good Tx or normal controls. Only good crCl was different from predialysis.

CONCLUSIONS

A good graft kidney manages to restore and maintain normal body composition, whereas with mild renal dysfunction a change in body compartments was observed, moving toward the body water composition of chronic renal failure patients.

Angiotensinogen M235T genotype predicts progression in chronic renal allograft dysfunction

BACKGROUND

Genotypes of the renin-angiotensin system have been implicated in essential hypertension and in progression of native kidney diseases, but gene effects on progression in chronic renal allograft dysfunction are unclear.

METHODS

To examine gene effects on long-term renal allograft function, we conducted a prospective cohort study of 210 nondiabetic renal allograft recipients younger than 36 years of age who underwent transplantation between 1980 and 1993 and were followed up through 1999. All grafts survived more than 1 year and all subjects received cyclosporine-based immunosuppression. DNA was analyzed by polymerase chain reaction for the angiotensin-converting enzyme insertion/deletion and angiotensinogen (AGT) M235T polymorphisms. Linear regression multivariate modeling of the slope of the inverse creatinine-versus-time, survival analyses for time-to-sustained doubling of baseline serum creatinine, time-to-graft loss, and a composite endpoint including patient death were performed.

RESULTS

Mean follow-up time was 8.4+/-3 years. Genotype frequencies for each marker system did not deviate significantly from the Hardy-Weinberg equilibrium. The slope of the inverse creatinine-versus-time for AGT 235T/T and M/T was significantly increased compared with M/M ( <0.0001). The AGT 235T/T genotype was also associated with a shorter time-to-sustained doubling of serum creatinine ( =0.001). When subjects were divided into quartiles based on slope magnitude, the frequency of the AGT 235T/T genotype was overrepresented in the fastest progressing group compared with the slowest ( =0.001). The AGT 235T/T genotype was also associated with shorter time-to-graft loss ( =0.007) and the composite endpoint ( =0.001).

CONCLUSION

The AGT 235 T allele independently influences long-term decline in renal allograft function.

The effect of angiotensin converting enzyme gene polymorphism on chronic allograft dysfunction in living donor renal transplant recipients

BACKGROUND

Chronic allograft dysfunction (CAD), the major cause of the failure of kidney allografts, may be caused by immunological and non-immunological haemodynamic factors. Renin-angiotensin system has been implicated in the development of intraglomerular hypertension and has a central role on progression in chronic renal disease. Polymorphism in 16th intron of the ACE gene has been reported to predict the circulating angiotensin II levels. The aim of this study was to investigate the effect of the both recipient and donor angiotensin converting enzyme (ACE) genotype on the development of CAD in renal allograft recipients.

PATIENTS AND METHODS

A total of 143 renal transplant recipients (95 male, 48 female, mean age 32 +/- 10 yr) were included. In order to exclude the effect of cold ischaemia, only patients transplanted from living donors were selected. Factors analysed in the development of CAD were donor and recipient age, past history of acute rejection, presence of hypertension and hypercholesterolaemia, serum uric acid level and ACE gene polymorphism.

RESULTS

Forty of the patients (28%) had CAD. Homozygous deletion type ACE gene polymorphism was detected in 59 renal transplant recipients (42%) and in 31 donors of the patients (37%). On comparing patients with and without CAD, donor age, rate of acute rejection and hypertension and serum uric acid levels were significantly higher in CAD (+) groups. Neither recipient nor donor ACE genotype was associated with time to CAD. Cox regression analysis revealed donor age (p < 0.001), presence of hypertension (p=0.002) and serum uric acid levels (p=0.009), but neither donor nor recipient ACE genotype as independent factors for predicting development of CAD.

CONCLUSION

Donor age, presence of hypertension and serum uric acid levels was independent factors. Donor and recipient ACE genotype seemed to have no influence on the development of CAD in living donor transplanted patients.

Recipient RAS gene variants and renal allograft function

BACKGROUND

Genetic variants of the renin-angiotensin system (RAS) have been implicated in the progression of native kidney diseases. A decreased long-term renal allograft function has also been associated with increased activity of RAS, which may be genetically determined.

METHODS

The effect of the angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin type 1 receptor (AGT1R), and aldosterone synthase (CYP11B2) genotypes on renal function was investigated in 223 first-allograft recipients. Graft function was estimated by yearly determinations of serum creatinine. Genotyping was performed for the M235T-AGT, the I/D-ACE, the A1166C-AGT1R, and the -344T/C-CYP11B2 gene polymorphisms using polymerase chain reaction.

RESULTS

The percentage of patients with preserved stable graft function up to 15 years after transplantation was higher when mean blood pressure was <97 mmHg, than when it was >117 mmHg (60 vs. 25% of patients). The CYP11B2 genotype predicted long-term stable graft function with more patients suffering from worsening renal function with the CYP11B2 TT than the CC genotype (P=0.002). There was a weak association between the AGT1R genotype (P=0.037), but not the AGT or ACE genotypes, and a preserved long-term graft function. Cox proportional hazards estimation showed no interactions between the observed effect of CYP11B2 genotype on renal function over time and the number of HLA class I and II matches, other RAS genotypes, graft function, or mean blood pressure at 1 year after transplantation.

CONCLUSIONS

The rate of decline in renal allograft function is strongly associated with the CYP11B2 but not AGT, ACE, or AGT1R genotypes. This finding suggests that certain genetic factors related to the RAS are important determinants of long-term renal allograft function.

Vasoactive substances in renal transplantation

During and after transplantation the kidney experiences a variety of insults that result in functional impairment and structural damage. These changes are mediated or influenced by hormones, cytokines, enzymes and growth factors, which are excreted by endothelial, graft parenchymal as well as by graft infiltrating cells. This review evaluates the pathophysiological role of vasoactive substances (for example, the vasoconstrictors angiotensin II and endothelin, as well as vasodilators such as nitric oxide, adrenomedullin and atrial natriuretic peptide) in kidney transplantation and summarizes recent reports that indicate that targeting vasoactive substances may represent effective therapeutic strategies for the achievement of long-term allograft survival.

Correlation between angiotensin-converting enzyme gene insertion/deletion polymorphism and kidney graft long-term outcome in pediatric recipients: a single-center analysis

BACKGROUND

Despite numerous advances in the areas of organ preservation, histocompatibility, and immunosuppression, chronic deterioration of organ allograft function, referred to as "chronic rejection," still remains the main obstacle to long-term graft survival. The common feature of chronic rejection is a concentric generalized graft arteriosclerosis associated with interstitial fibrosis that reflects an allogeneic injury to graft arteries, possibly worsened by other alloantigen-independent risk factors. The presence of the angiotensin I-converting enzyme (ACE) gene-deleted (D) allele has been associated, when in homozygosity, with increased risk of cardiovascular diseases and with an accelerated progression of organ damage in a variety of kidney diseases. In this study, we analyzed whether the insertion/deletion polymorphism of the ACE gene, because of its negative prognostic impact on cardiovascular and renal pathology, could have any influence on kidney graft survival in pediatric recipients.

METHODS

DNA was isolated from peripheral blood mononuclear cells from 146 pediatric dialysis patients (mean age: 12.9 years) who received a first kidney graft at our center between December 1985 and July 1997. To rule out any bias due to acute graft losses, only 119 patients who reached a minimum of 12 months of graft survival were considered for statistical analysis. The insertion/deletion polymorphism of the ACE gene was detected using a polymerase chain reaction technique with two flanking primers.

RESULTS

The results demonstrated that (i) the distribution of DD and non-DD (ID + II) genotypes was 36.1% (43 patients) and 63.8% (76 patients), respectively; (ii) actuarial graft survival at 7, 8, 9, and 10 years in patients with non-DD genotype was significantly higher than that in patients with DD genotype (7 years: 94.6% vs. 72.4%, P<0.05; 8 years: 94.6% vs. 62%, P<0.025; 9 years: 87.3% vs. 51.4%, P<0.025; 10 years: 76.3% vs. 25.7%, P<0.01).

CONCLUSIONS

In conclusion, the above data indicate that DD genotype is associated in pediatric kidney graft recipients with a shorter long-term kidney graft survival and suggest a possible role of this genotype as a cofactor in the progression of nonimmunological injuries leading to chronic kidney graft failure.

Role of genetic variants of the renin-angiotensin system in chronic renal allograft injury

In the the vast majority of patients undergoing kidney transplantation, long-term success is markedly limited by a gradual decrease in graft function over time, often termed as "chronic rejection" or "chronic allograft injury." Although there have been no formal studies examining the role of genetic factors other than those related to histocompatibility for the development or progression of chronic allograft rejection, it is likely that genetic factors affecting blood pressure regulation, mesangial or vascular proliferation, or aspects of inflammatory response including thrombosis, chemotaxis, or fibrosis may play an important role in this complex syndrome. There is currently little hope that the responsible genes can be identified through sib-pair or linkage studies in families. Therefore, the study of candidate genes selected on the basis of our current understanding of the pathophysiological mechanisms involved in the chronic rejection response appears the only feasible approach. Thus far, studies have focused mainly on the role of functional genetic variants of the renin-angiotensin system on renal allograft funding. These studies, however, have not identified these variants as important determinants of renal allograft survival. Clearly, future studies will have to address the role of other variants of this system as well as genes encoding for other systems deemed to be of pathophysiological significance for the development and progression of chronic transplant injury.

Chronic rejection and late renal allograft dysfunction

Renal transplantation is currently standard therapy for end-stage kidney disease for children. Despite the considerable improvement in short-term results, the expected allograft half-life has remained the same. This is due to chronic rejection/late graft dysfunction which has proved resistant to therapeutic attempts. During the last few years the multifactorial pathogenesis of chronic renal allograft rejection has been clarified to some extent. Early injury by immunological and non-immunological mechanisms is followed by vascular remodelling due to repetitive cycles of cytokine release, upregulation of growth factors, and vascular smooth muscle cell proliferation. This leads to typical concentric arteriosclerosis and ischemia. Secondary kidney-specific mechanisms are initiated by the reduction in functioning renal mass and lead to gradual progression of chronic rejection. There is no single optimal therapy. Several attempts to influence the pathophysiological cascade have been promising. Attention should be focused on minimizing early immunological/non-immunological injury in order to attenuate future progression of chronic rejection. A significant prolongation of allograft half-life may be achieved during the next decade with the introduction of new therapeutic agents and comprehensive approach to treatment. This would be especially beneficial for pediatric recipients, reducing the need for retransplantation in adulthood.

Effects of dietary protein in patients with chronic renal transplant rejection

Dietary protein restriction reduces proteinuria and slows the progression of renal failure in a variety of renal diseases in native kidneys. Such beneficial effects may be mediated by the multiple renal effects of dietary protein including those on glomerular capillary hemodynamics and the renin-angiotensin system. The role of dietary protein restriction in the management of chronic renal transplant rejection is, however, unclear. This study was therefore undertaken to examine the effects of dietary protein restriction in patients with chronic rejection. Fourteen patients with biopsy proven chronic rejection, who had been on a self-selected home diet of 1.0 +/- 0.1 g protein/kg/day, were randomly assigned, using a crossover design to two 11-day periods, one on a low protein diet (0.55 g/kg/day) and the other on a high protein diet (2 g/kg/day). The effect of these diets on renal hemodynamics, proteinuria, plasma renin activity, and nutritional status was examined. The low protein diet was associated with a significant improvement in glomerular permselectivity in all patients as evidenced by a significant fall in the fractional clearance of albumin and IgG and reduction in 24-hour urinary excretion of total protein, albumin and IgG without any change in blood pressure, glomerular filtration rate, or renal plasma flow. Compared to the proteinuria at the beginning of each diet, a high protein diet did not increase but a low protein diet significantly decreased the proteinuria. The low protein diet was also associated with a significant reduction in plasma renin activity, suggesting that part of the beneficial effect of protein restriction was related to the suppression of the renin-angiotensin system.(ABSTRACT TRUNCATED AT 250 WORDS)