Renin-angiotensin system gene expression in post-transplant hypertension predicts allograft function

Mast cell renin and a local renin-angiotensin system in the airway: role in bronchoconstriction

We previously reported that mast cells express renin, the rate-limiting enzyme in the renin-angiotensin cascade. We have now assessed whether mast cell renin release triggers angiotensin formation in the airway. In isolated rat bronchial rings, mast cell degranulation released enzyme with angiotensin I-forming activity blocked by the selective renin inhibitor BILA2157. Local generation of angiotensin (ANG II) from mast cell renin elicited bronchial smooth muscle contraction mediated by ANG II type 1 receptors (AT(1)R). In a guinea pig model of immediate type hypersensitivity, anaphylactic mast cell degranulation in bronchial rings resulted in ANG II-mediated constriction. As in rat bronchial rings, bronchoconstriction (BC) was inhibited by a renin inhibitor, an AT(1)R blocker, and a mast cell stabilizer. Anaphylactic release of renin, histamine, and beta-hexosaminidase from mast cells was confirmed in the effluent from isolated, perfused guinea pig lung. To relate the significance of this finding to humans, mast cells were isolated from macroscopically normal human lung waste tissue specimens. Sequence analysis of human lung mast cell RNA showed 100% homology between human lung mast cell renin and kidney renin between exons 1 and 10. Furthermore, the renin protein expressed in lung mast cells was enzymatically active. Our results demonstrate the existence of an airway renin-angiotensin system triggered by release of mast-cell renin. The data show that locally produced ANG II is a critical factor governing BC, opening the possibility for novel therapeutic targets in the management of airway disease.

Risk factors for hypertension 3 years after renal transplantation in children

We performed a case-control study in renal transplant patients between 1998 and 2003 to identify risk factors for arterial hypertension over the medium term in pediatric patients undergoing renal transplantation. Three years after transplant, patients were classified into hypertensive or control groups. The following risk factors were analyzed: hypertension before transplant, glomerular filtration rate at sixth posttransplant month, acute rejection episodes, renal artery stenosis, accumulated prednisone and calcineurin inhibitor doses, presence of native kidneys, donor type (living or cadaver), body mass index at 1 year posttransplant, and glomerular disease as renal insufficiency etiology. Of 161 transplants, 124 fulfilled the inclusion criteria; 63 were hypertensive, and 61 were controls. Univariate analysis showed hypertension before transplant (52/63 vs. 27/61, p < 0.001), glomerulopathies (23/63 vs. 12/61, p = 0.001), glomerular filtration rate at 6 months (71 +/- 18 vs, 80 +/- 18 ml/min per 1.73 m(2), p = 0.003) as risk factors. A tendency to statistical significance was observed with regard to body mass index (SDS) in the first year (0.40 +/- 1.10 vs, 0.04 +/- 1.10, p = 0.072). Multivariate analysis showed statistical significance concerning previous hypertension and glomerular filtration rate at 6 months. Hypertension before transplant and early graft function are the major risk factors for hypertension in the medium term following renal transplant.

Prevention of chronic allograft nephropathy with vitamin D

Chronic allograft nephropathy (CAN) is the leading cause of late allograft loss in kidney transplantation. Interstitial fibrosis and glomerulosclerosis are characteristic of CAN. Transforming growth factor beta-1 (TGFbeta-1) is associated with both of these histologic findings in the transplant setting. Recent studies have suggested that vitamin D signaling pathways may interact with and regulate TGFbeta-1 mediated events. We examined the efficacy of 1,25-dihydroxyvitamin D(3), the active metabolite of vitamin D [1,25-(OH)(2)D(3)], the active metabolite of vitamin D, as monotherapy to prolong allograft survival and preserve renal function in a rat model of CAN, the Fisher 344 to Lewis model. Recipients went without treatment or were treated with cyclosporine A (CSA; 10 days) or 1,25(OH)(2)D(3) (1000, 500 or 250 ng/kg/day). Grafts were harvested at the time of rejection or at 24 weeks post-transplant. A portion of the graft was processed for histology and immunohistochemistry and a second portion was analyzed for protein expression by western blotting. Not only did 1,25-(OH)(2)D(3) treatment significantly prolong graft survival, but it also prevented histological changes associated with CAN. 1,25-(OH)(2)D(3) treatment significantly decreased Smad 2 expression. This TGFbeta signaling molecule is likely involved in fibrosis. Moreover, 1,25-(OH)(2)D(3) treatment increased Smad 7 expression, an important feedback molecule in the TGFbeta-1 signaling pathway. This suggests that 1,25-(OH)(2)D(3) interacts with TGFbeta-1 in limiting histological injury in this model of CAN. Furthermore, 1,25-(OH)(2)D(3), treatment increased expression of matrix metalloproteinase 2 (MMP-2), thus directly affecting levels of another important matrix molecule. Taken together our data suggests that 1,25-(OH)(2)D(3) mitigates CAN in this model by altering TGFbeta-1 and matrix-regulating molecules.

AT1R blockade reduces IFN-γ production in lymphocytes in vivo and in vitro

BACKGROUND

Type 1 angiotensin II (Ang II) receptor (AT(1)R) signaling induces proinflammatory responses. Recent studies suggest that T lymphocytes express AT(1)R; yet the effects of Ang II binding to AT(1)R on T cells are poorly understood. We examined the effect of AT(1)R blockade on release of the proinflammatory cytokine, interferon-gamma (IFN-gamma) by human lymphocytes in vivo and in vitro.

METHODS

We used an AT(1)R blocker losartan in a randomized clinical trial in kidney transplant recipients over a 12-month period [AT(1)R blocker (N= 11) and control (N= 10)]. Peripheral blood lymphocytes, isolated from both cohorts, were analyzed by enzyme-linked immunosorbent spot assays (ELISPOT) analyses and real-time reverse transcription-polymerase chain reaction (RT-PCR) to enumerate IFN-gamma producing T cells and IFN-gamma mRNA levels. The effects of AT(1)R blockade in vitro were assessed using human alloreactive T cells and an IFN-gamma producing human cytotoxic T-lymphocyte line. Alloreactive T cells were treated with losartan or candesartan and enzyme-linked immunosorbant assay (ELISA) was used to measure IFN-gamma protein release. The cytotoxic T-lymphocyte line also was AT(1)R blocker-treated prior to determining IFN-gamma producing cells by intracellular cytokine staining.

RESULTS

The AT(1)R blocker cohort had a significant decrease in IFN-gamma producing peripheral blood lymphocytes (P< or = 0.05 for each time point) and IFN-gamma mRNA levels (P= 0.01 vs. control patients). Losartan also decreased IFN-gamma production (P < 0.001) in purified alloreactive T cells in vitro as did candesartan. Moreover, Ang II amplified IFN-gamma generation (P < 0.05) in alloreactive T cells while AT(1)R blocker treatment inhibited Ang II's effect (P < 0.04). AT(1)R blocker treatment furthermore also inhibited IFN-gamma production in the cytotoxic T-lymphocyte line.

CONCLUSION

AT(1)R blockers may have a clinically relevant immunomodulatory role by blocking IFN-gamma production in T cells.

Fibrosis and matrix metalloproteinases in rat renal allografts

The temporal activity and gene expression of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinase (TIMP) were investigated in a rat model of chronic allograft nephropathy. Gelatinolytic activity of MMP-2 and -9 were demonstrated by zymography, and MMP-2,-9 and TIMP-3 mRNA by in situ hybridization. The generation of fibrosis was determined as total collagen content/DNA. Significantly more latent and active MMP-2, as well as latent MMP-9, were seen in allografts than in autografts. Intense MMP-2 mRNA expression was demonstrated in the allografts during the first 20 days after transplantation, located mainly in the interstitium of the kidney. In addition, some tubular cells expressed MMP-2 mRNA. After day 20, MMP-2 gene expression was faint. MMP-9 mRNA expression in allografts was located mainly in the glomerulus. TIMP-3 mRNA expression was downregulated in allografts. MMP-2, MMP-9 and TIMP-3 seem to play a critical role in the development of fibrosis in the renal allograft.

Mast cells: a unique source of renin

In addition to the traditional renin-angiotensin system, a great deal of evidence favors the existence of numerous independent tissue-specific renin-angiotensin systems. We report that mast cells are an additional source of renin and constitute a unique extrarenal renin-angiotensin system. We use renin-specific antibodies to demonstrate that cardiac mast cells contain renin. Extending this observation to the human mast cell line HMC-1, we show that these mast cells also express renin. The HMC-1 renin RT-PCR product is 100% homologous to Homo sapiens renin. HMC-1 cells also contain renin protein, as demonstrated both by immunoblot and immunocytochemical analyses. Renin released from HMC-1 cells is active; furthermore, HMC-1 cells are able to synthesize renin. It is known that, in the heart, mast cells are found in the interstitium in close proximity to nerves and myocytes, which both express angiotensin II receptors. Inasmuch as myocardial interstitium contains angiotensinogen and angiotensin-converting enzyme, and because we were able to detect renin only in mast cells, we postulate that the release of renin from cardiac mast cells is the pivotal event triggering local formation of angiotensin II. Because of the ubiquity of mast cells, our results represent a unique paradigm for understanding local renin-angiotensin systems, not just in the heart, but in all tissues. Our findings provide a rationale for targeting mast cells in conjunction with renin-angiotensin system inhibitors in the management of angiotensin II-related dysfunctions.

Arterial hypertension following renal transplantation in children-a short-term study

Systemic arterial hypertension is a common complication among transplanted patients. The objective of this study was to investigate the risk factors for arterial hypertension after kidney transplantation in children. A retrospective study was carried out of 70 kidney transplants performed on patients under 18 years of age at the Hospital do Rim and Hipertensão, from January 1998 to June 2001. At the end of 6 months post transplant, the patients were classified into either normotensive ( n=31) or hypertensive ( n=39) groups. The following potential risk factors for arterial hypertension were studied: (1) hypertension before transplantation; (2) the glomerular filtration rate (GFR) at 1, 3, and 6 months post transplant; (3) acute rejection episodes; (4) cumulative dose of corticosteroids; (5) the presence of native kidneys; (6) symptomatic renal artery stenosis; (7) cold ischemia time greater than 24 h; (8) age and sex of the donor; (9) age of the recipient; (10) transplant type (living related or cadaveric donor); (11) the body mass index of recipients at the end of the follow-up period; and (12) delayed graft function. The two groups were comparable in terms of the etiology of renal insufficiency, age, gender, and immunosuppressive drugs. Among the risk factors studied, the sole factor showing a statistically significant association with arterial hypertension was the GFR at 3 and 6 months after transplantation. In the group of normotensive patients, GFRs were 92+/-29 and 83+/-20 ml/min per 1.73 m(2) at 3 and 6 months, respectively, whereas in the hypertensive patients, GFRs were 74+/-23 and 70+/-21 ml/min per 1.73 m(2) respectively. Hence, only the lower GFR can be considered a risk factor for hypertension in children within our sample. However, arterial hypertension might be a risk factor for the early onset of chronic allograft nephropathy; in this case, hypertension should be considered the cause of lower glomerular filtration. Our data do not permit us to distinguish between these two hypotheses. The known risk factors for hypertension following renal transplantation in adults were not confirmed in the present study. It remains unclear to us as to whether this means the etiology of hypertension differs in children, or if this is the result of a bias in patient selection.

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Tumor necrosis factor-alpha and tumor growth factor-beta1 genotype: partial association with intragraft gene expression in two cases of long-term peripheral tolerance to a kidney transplant

Genomic DNA was obtained from peripheral blood samples of patients JB and DS each of whom received a kidney transplant at 16 years of age from a serologically HLA-DR matched and HLA-class I -mismatched donor. Both patients discontinued immunosuppression after 1-2 years and retained good renal function for an additional 5 years or more. DNA was analyzed for genetic polymorphisms in the tumor necrosis factor-alpha (TNFalpha) and tumor growth factor-beta1 (TGFbeta1) loci. Biopsy samples obtained during stable function (DS, JB) and during rejection (JB) were analyzed by RT/PCR for cytokine gene expression. Both patients had a high responder genotype for TGFbeta1. DS had a low responder TNFalpha genotype, while JB and his donor were both genotypically TNFalpha intermediate responders. DS had a high TGFbeta1: TNFalpha mRNA ratio in two biopsies obtained during tolerance, while JB, who eventually lost his graft, had more TNFalpha than TGFbeta1 mRNA. The results suggest a possible role for cytokine immunogenetics in the stability of peripheral tolerance.