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Biomedical subjects

Michael Mengel

Publications and source records attributed to Michael Mengel.

At least 37 records · Page 2Linked to original sources
PubMed2005

Local complement C3 expression is upregulated in humoral and cellular rejection of renal allografts.

Evidence on the role of the complement system in transplantation pathology has been accelerated by the discovery of C4d as an in situ marker of antibody-mediated rejection. However, a local or systemic source of complement expression during acute rejection is under discussion. Thus, we quantitatively analyzed local RNA expression of complement component C3 as a pivotal molecule in active humoral and cellular rejection of renal allografts. After laser microdissection, real-time RT-PCR was performed for C3 using RNA extracted from tubuli and glomeruli of 68 paraffin-embedded renal allograft biopsies. Protocol and indication biopsies with signs of humoral and/or cellular rejection were investigated. Quantitative expression analysis of cytokines (IFN gamma, MCP-1, IL2, IL8) potentially influencing local C3 expression was performed. We observed a significant increase in median expression level of C3 mRNA in tubuli of C4d-positive indication biopsies, and in tubuli from indication biopsies with signs of T-cell-mediated cellular rejection. Highest expression levels were found in C4d-positive indication biopsies with signs of cellular rejection. Biopsies with upregulated C3 showed increased IFN gamma expression, suggesting allograft-infiltrating T-cells as potential stimulus for local C3 expression. Therefore, locally synthesized complement component C3 contributes to both humoral and cellular rejection, with tubular epithelial cells being a major source.

Biopsy↗
PubMed2005

Early calcification of renal allografts detected by protocol biopsies: causes and clinical implications.

Interstitial calcification has been described in renal allografts, however, the etiology and significance of this finding for the graft are unclear. The aim of this study was to examine calcification in serial protocol biopsies, to test the hypothesis that calcification is related to parameters of calcium homeostasis in these patients and to analyze a possible relation between calcification and graft function at 1 year. We studied 213 patients with 586 protocol biopsies obtained 6 weeks, 3 and 6 months after transplantation. Calcifications increased over time, from 6.1% at 6 weeks to 17.8% at 6 months. Out of the 213 patients, 56 had calcification in one or more biopsies. Patients age and gender, underlying renal disease, dialysis mode and duration, previous transplantations, donor type, age and gender, HLA matches and ischemia time had no influence on calcification. Calcification was not related to rejection episodes, acute tubular lesions, calcineurin inhibitor toxicity or tubulointerstitial fibrosis and tubular atrophy. Patients with calcification had significantly higher serum parathormone and calcium levels. In patients with calcification, high PTH levels correlated with an inferior outcome of graft function at 1 year after transplantation (p<0.05). Therefore, treatment of hyperparathyroidism should be considered earlier and more often in these patients.

Adult↗
PubMed2005

Safety and adequacy of renal transplant protocol biopsies.

The protocol biopsy strategy has been criticized because of risks and marginal utility. We tested the risk. We performed 1171 protocol biopsies in 508 patients at 6, 12 and 26 weeks after renal transplantation, as well as 499 biopsies as indicated in 429 transplant patients. Biopsies were done as an outpatient procedure using an 18- or 16-gauge automated biopsy needle followed by 4 h bed rest. Complications were: gross hematuria 3.5%, perirenal hematomas 2.5%, arterio-venous fistulas 7.3% and vasovagal reactions 0.5%. Major complications requiring invasive procedures such as blood transfusions or urinary catheter were seen in 1% of cases. The hospitalization rate for observation was 1.9%. According to the Banff criteria of specimen adequacy, biopsies with 18-gauge needles yielded >7 glomeruli and at least one artery in 53% of cases. Changing the needle size in October 2003, those biopsies done with 16-gauge needles yielded >7 glomeruli and at least one artery in 76% of cases, while the rate of major complications did not change. In conclusion, transplant protocol biopsies with 16-gauge needles provide better utility and similar risk as biopsies with 18-gauge needles. A 4-h recovery after biopsy appears adequate for discharge.

Biopsy, Needle↗
PubMed2005

Polyoma virus nephropathy in native kidneys after lung transplantation.

Polyoma virus nephropathy is recognized as an emerging clinical problem in renal transplantation; however, polyoma in native kidneys is unusual. We report a patient who developed polyoma nephropathy in his native kidneys 15 months after successful lung transplantation. His immunosuppression consisted of tacrolimus, mycophenolate mofetil, and large doses of steroids because of three rejection episodes. When the condition was recognized, cidofovir was an effective treatment (3 doses of 2-3mg/kg); however, his renal function deteriorated nonetheless. Tubulitis and interstitial cell infiltration in his native kidneys were evidence that the changes were in response to viral injury. Polyoma nephropathy of native kidneys is unusual. An earlier course of cisplatin treatment because of metastatic seminoma prior to lung transplantation may have been contributory to pre-existing renal injury. After cidofovir was begun, the polyoma viral load in serum and urine decreased substantially; however, after high-dose steroid treatment of two rejection episodes, each time a significant increase in viral load was seen. We stained biopsies of native kidneys from 30 recipients of other organs. The biopsies were done for various reasons but not because polymoma virus was suspected. We found no additional cases.

Adult↗
PubMed2005

Detection of acute tubulointerstitial rejection by proteomic analysis of urinary samples in renal transplant recipients.

This study investigates proteomic analysis of urinary samples as a non-invasive method to detect acute rejection of renal allografts. Capillary electrophoresis coupled to mass spectrometry (CE-MS) was used to analyze urinary samples in 19 patients with different grades of subclinical or clinical acute rejection (BANFF Ia to IIb), 10 patients with urinary tract infection and 29 patients without evidence of rejection or infection. A distinct urinary polypeptide pattern identified 16 out of 17 cases of acute tubolointerstitial rejection, but was absent in two cases of vascular rejection. Urinary tract infection resulted in a different polypeptide pattern that allowed to differentiate between infection and acute rejection in all cases. Potentially confounding variables such as acute tubular lesions, tubular atrophy, tubulointerstitial fibrosis, calcineurin inhibitor toxicity, proteinuria, hematuria, allograft function and different immunosuppressive regimens did not interfere with test results. Blinded analysis of samples with and without rejection showed correct diagnosis by CE-MS in the majority of cases. Detection of acute rejection by CE-MS offers a promising non-invasive tool for the surveillance of renal allograft recipients. Further investigation is needed to establish polypeptide patterns in vascular rejection and to explore whether changes in the urinary proteome occur before the onset of histologically discernible rejection.

Adult↗
PubMed2004

Low-dose therapy with the long-acting erythropoietin analogue darbepoetin alpha persistently activates endothelial Akt and attenuates progressive organ failure.

BACKGROUND: The hematopoietic cytokine erythropoietin has cytoprotective effects in endothelial cells in vitro that are mediated through direct activation of the pro-survival Akt tyrosine kinase signaling pathway. We tested the hypothesis that low-dose therapy with the long-acting recombinant human erythropoietin analogue darbepoetin alpha protects vascular endothelium in vivo in a classic remnant kidney rat model characterized by severe endothelial damage, progressive vascular sclerosis, and ischemia-induced tissue fibrosis. METHODS AND RESULTS: Using a parallel group study design, we randomly assigned animals after 5/6 nephrectomy to treatment with either saline (n=36) or 0.1 microg/kg body wt darbepoetin (n=24) subcutaneously once weekly. We monitored hematocrit, blood pressure, and serum creatinine regularly and obtained renal tissue 6 weeks after nephrectomy for morphological and immunohistochemical analysis. Darbepoetin-treated animals had significantly improved survival compared with saline-treated controls (63% versus 33%; P<0.05), although hematocrit levels were similar in both groups. Darbepoetin treatment ameliorated endothelial damage; attenuated the composite tissue injury score (saline 1.9+/-0.4; darbepoetin 0.4+/-0.2; P<0.001), which included vascular sclerosis, glomerulosclerosis, and tubulointerstitial damage; and preserved renal function. We found persistent activation of the pro-survival Akt signaling pathway in endothelial and epithelial glomerular cells in darbepoetin-treated animals, accompanied by a significant reduction of apoptotic cell death in renal tissue. CONCLUSIONS: Low-dose darbepoetin treatment confers vascular and tissue protection that is associated with persistent stimulation of the pro-survival Akt signaling pathway. The use of recombinant human erythropoietin or analogues may have utility in preventing ischemia-related progressive vascular injury and organ failure.

Animals↗
PubMed2004

Prognostic value of cytotoxic T-lymphocytes and CD40 in biopsies with early renal allograft rejection.

After renal transplantation, different immunological and non-immunological factors lead to long-term allograft deterioration. Acute rejection episodes are one risk factor for chronic renal allograft dysfunction (CRAD). Following the current Banff classification the histological grade in acute rejection episodes is of limited prognostic value, therefore, additional morphological surrogate markers would be helpful. We investigated the biopsies of 91 patients with early acute rejection episodes for the immunohistochemical expression of key molecules (perforin, granzyme B, TIA-1, CD40) in the T cell-mediated rejection process. Staining results were correlated to long-term allograft outcome. Patients with greater than 2% of granzyme B or greater than 25% of CD40-positive cells in the interstitial infiltrate showed significantly shorter allograft survival. Patients with a CD40-positive vascular rejection or greater than 2% of granzyme B-positive cells in the interstitial infiltrate were significantly correlated with an earlier onset of CRAD. Our findings provide potential morphological surrogate markers in biopsies with early acute rejection episodes after renal transplantation. These could become part of combined clinical and histological algorithms, allowing patient-specific risk estimation and customized therapy options to be made.

Acute Disease↗
PubMed2004

Thrombopoietin receptor (Mpl) expression by megakaryocytes in myeloproliferative disorders.

The thrombopoietin receptor (Mpl) is involved in the pathogenesis of chronic myeloproliferative disorders (CMPD). In this study, we determined Mpl expression by bone marrow cells and megakaryocytes in CMPD by applying laser microdissection, real-time RT-PCR, and immunohistochemistry. Mpl mRNA expression was significantly increased up to 9-fold in total bone marrow cells (p < 0.001) and up to 4-fold in megakaryocytes in chronic myeloproliferative disorders (n = 73) compared to normal controls (n = 26, p = 0.01). Immunohistochemistry revealed heterogeneous Mpl expression by megakaryocytes in CMPD with a stronger accentuation in idiopathic myelofibrosis (IMF) in comparison to polycythaemia vera (PV) and essential thrombocythemia (ET). In addition to megakaryocytes, the erythropoietic lineage was prominently labelled by Mpl antiserum, with considerably stronger staining in polycythaemia vera. We conclude that, in CMPD, megakaryocytes and erythroid cells exhibit increased Mpl expression levels which may contribute to the sustained proliferation of both cell lineages in CMPD.

Adult↗
PubMed2004

Chimerism of metanephric adenoma but not of carcinoma in kidney transplants.

Recipient-derived cells integrate into renal allografts inducing organ-specific microchimerism. Circulating pluripotent progenitor cells with high plasticity for differentiation were suggested as a potential source of allograft chimerism. Whether or not these cells also contribute to tumor formation in renal transplants is unknown. We analyzed six histologically different tumors in renal allografts for the presence of recipient-derived cells. To circumvent dependency on gender mismatch, a polymerase chain reaction assay for highly polymorphic short tandem repeat marker (DNA fingerprinting) in combination with laser microdissection was applied. Pure tumor cell populations were harvested by laser microdissection after immunohistochemical (CD45/CD68) marking of contaminating leukocytes. In cases of gender mismatch (n = 2), results were confirmed by sex chromosome in situ hybridization. Two metanephric adenomas demonstrated microchimerism comprising both donor- and recipient-derived tumor cells. Two clear cell carcinomas, one transitional cell carcinoma, and one renal cortical adenoma were all of donor origin without chimerism. We conclude that except for metanephric adenomas, tumors arising in renal transplants originate completely from graft cells. The mixed derivation of metanephric adenomas indicates an incorporation of recipient-derived progenitor cells. This finding suggests that adult stem cells can assume neoplastic phenotypes.

Adenocarcinoma, Clear Cell↗
PubMed2004

Constitutive expression of the FK506 binding protein 51 (FKBP51) in bone marrow cells and megakaryocytes derived from idiopathic myelofibrosis and non-neoplastic haematopoiesis.

OBJECTIVES: Overexpression of FK506 binding protein 51 (FKBP51) in megakaryocytic progenitor cells generated from purified CD34+ cells in patients with idiopathic myelofibrosis (IMF) has been demonstrated. It has been suggested that FKBP51 is involved in the dysregulation of the apoptotic programme with consecutive prolongation of cell survival. The knowledge of FKBP51 and its expression in bone marrow cells and mature megakaryocytes in non-neoplastic haematopoiesis and IMF is sparse. METHODS: To evaluate a potential overexpression of FKBP51 in patients with IMF (n = 37) compared with non-neoplastic haematopoiesis (n = 31), total bone marrow cells as well as single megakaryocytes, isolated by laser microdissection, were quantitatively analysed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). By applying immunohistochemistry, FKBP51 gene expression was correlated with staining pattern and cellular localisation of the corresponding FKBP51 protein. RESULTS: We demonstrated that FKBP51 is constitutively expressed in non-neoplastic haematopoiesis. FKBP51 gene expression by total bone marrow cells as well as megakaryocytes was not significantly different in IMF. FKBP51 protein expression could be localised to myeloid progenitor cells as well as megakaryocytes. In particular, megakaryocytes were stained almost exclusively nuclear for FKBP51. No differences in expression patterns between both IMF and control cases could be demonstrated. CONCLUSIONS: For the first time, FKBP51 expression, in particular gene expression and subcellular localization was described in bone marrow cells of non-neoplastic and neoplastic haematopoiesis grown in vivo. We conclude that FKBP51 could be temporarily overexpressed in megakaryocytic progenitors rather than contribute to the accumulation of mature megakaryocytes in IMF.

Adult↗
PubMed2004

Growth arrest specific protein 6/Axl signaling in human inflammatory renal diseases.

BACKGROUND: Growth arrest-specific gene 6 (Gas6) and its binding partner, the receptor tyrosine kinase Axl, are important mediators in experimental nephritis. The authors tested whether the Gas6/Axl signaling pathway participates in human renal diseases. METHODS: The authors compared 26 human renal specimens from patients with IgA nephritis, acute diffuse immune complex glomerulonephritis, acute lupus nephritis, antineutrophil cytoplasmic antibody--associated glomerulonephritis, acute transplant rejection, and normal renal tissue. Because reactive oxygen species are pivotal in inflammation, the authors tested whether the Axl/Gas6 expression is influenced by NADPH oxidase in vitro. RESULTS: Gas6 and Axl immunofluorescence was barely detectable in normal kidney. However, in disease Axl was copiously expressed in the small vessel media, glomeruli, distal tubules, and collecting ducts. Similarly, Gas6 was upregulated in the small vessel intima and media, all segments of the renal tubules, the brush border, and glomeruli. Gas6 and Axl upregulation was a prominent but nonspecific finding in these renal diseases. Cultured rat vascular smooth muscle cells and immortalized human mesangial cells were stimulated with angiotensin (Ang) II (1 x 10(-7) mol/L) for 6 or 18 hours. Confocal microscopy and Western blot showed Ang II-dependent Gas6 and Axl expression. An antisense probe against the p22 phox unit of NADPH-oxidase suppressed Ang II-induced Gas6 and Axl expression. In addition, in p47 phox knockout cells Ang II-induced Gas6 and Axl expression were blocked. CONCLUSION: GAS6/Axl signaling is involved in human renal disease. The Ang II-induced Gas6 and Axl expression may be dependent on NADPH-oxidase. Gas6 and Axl are important signaling molecules in human renal disease and may be potential therapeutic targets.

Adolescent↗
PubMed2004

Tubular chimerism occurs regularly in renal allografts and is not correlated to outcome.

Recent studies have demonstrated an integration of recipient-derived progenitor cells into solid allografts with differentiation into parenchymal cells. Whether or to what extent this phenomenon influences allograft outcome has still to be elucidated. To detect epithelial chimerism tubular cells were harvested from sequential renal allograft biopsy samples by laser microdissection in 36 patients. Recipient-derived cells were detected by short-tandem repeat-based genotyping. In cases with gender-mismatched transplantation, chimerism was semiquantitatively evaluated by in situ hybridization for the Y-chromosome. Findings were correlated to different pathomechanisms of epithelial injury as well as to morphologic and clinical outcome. Epithelial chimerism was detectable as early as 8 d after transplantation and lasted for 8 yr. A total of 88% of the patients showed an epithelial chimerism; 72% had a stable chimerism in sequential biopsy samples. Evaluation of Y-chromosome by in situ hybridization revealed low percentages of chimerical tubular epithelial cells (2.4% to 6.6%). No correlation to morphology was found. Chimerism was detectable in inconspicuous protocol biopsy samples, cases of drug toxicity, and rejected allografts with and without chronic changes. No correlation was found to allograft function. Epithelial microchimerism is an early and persistent phenomenon after renal transplantation. There is no correlation to morphologic or functional outcome. Probably recipient-derived stem cells contribute in a minor fashion to tissue homeostasis, and cell turnover in renal allografts is predominantly enabled by donor cell renewal.

Biopsy↗
PubMed2004

Renal arterial resistance index and computerized quantification of fibrosis as a combined predictive tool in chronic allograft nephropathy.

The renal arterial resistance index (RI) and the PicroSirius-Red stained cortical fractional interstitial fibrosis volume (VintFib) proved to be two independent methods that are reliable predictive factors of poor renal allograft outcome. No data have been published, which define the correlation between ultrasound assessment and quantitative morphologic changes. Renal biopsies were performed in 56 children according to increases in s-creatinine >10%. VintFib was calculated by computerized image analysis. RI was determined in two segmental arteries, 1 yr after transplantation and at the time-point of biopsy. RIs 1 yr after transplantation correlated significantly with RIs at time of biopsy (r = 0.58, p < 0.001). VintFib was higher in children with a RI = 80 than in children with a RI < 80 (mean VintFib = 9.5 +/- 3.2% vs. 5.2 +/- 5.1%, p = 0.004). In children with VintFib > 10%, the mean RI was 77 +/- 5 compared with 69 +/- 6 in patients with VintFib < 10% (p = 0.0002). The highest positive predictive value to detect the risk of decline of GFR at 2 yr after biopsy was 98% when an RI = 80% was associated with a VintFib > 10%. For VintFib > 10% or RI = 80 alone, it was 87% or 67%, respectively. The combined measurement of RI and VintFib is a reliable predictive tool for the risk of developing long-term graft dysfunction after kidney transplantation.

Adolescent↗
PubMed2003

Computer-assisted quantification of fibrosis in chronic allograft nephropaty by picosirius red-staining: a new tool for predicting long-term graft function.

BACKGROUND: Chronic allograft nephropathy (CAN) has become the predominant limiting factor for long-term transplant survival. A cardinal histomorphologic correlate for CAN is interstitial fibrosis. Currently, no method has been established in routine use that reliably quantifies the extent of interstitial fibrosis in renal grafts. We have used staining with picrosirius red followed by computerized image analysis to study the correlation between graft fibrosis and future development of glomerular filtration rate (GFR) in a group of children with advanced CAN. METHODS: Renal biopsies were performed in 56 children (mean age, 13.7+/-3.6 years) after a mean period of 4.6+/-3.1 years after transplantation because of significant increases in serum creatinine. All biopsy specimens were stained with picrosirius red. The magnitude of fibrotic tissue was calculated by computerized image analysis. Linear regression analysis was performed correlating the intensity of graft fibrosis and the changes in the GFR at the time points of renal biopsy and 2 years later. RESULTS: There was a significant positive correlation (r=0.62, P<0.001) between the picrosirius red-stained cortical fractional interstitial fibrosis volume (V(intFib)) and the decrease of GFR within 2 years postrenal biopsy. When V(intFib) was below 5%, 82% of the patients had an increase in GFR within 2 years. Ninety-three percent of the patients with greater than 10% of fibrosis experienced a worsening renal function after 2 years. When comparing patients with stable GFR with patients having a decrease in GFR, a highly significant difference in V(intFib) was found (P=0.008). CONCLUSIONS: The quantitative measurement of fibrosis by picrosirius red staining appears to be a useful prognostic indicator for estimating long-term graft function in CAN and may provide an easy, fast, and inexpensive tool helpful for treatment decisions in patients developing CAN.

Adolescent↗
PubMed2003

Protocol biopsy of the stable renal transplant: a multicenter study of methods and complication rates.

BACKGROUND: Clinical trials in renal transplantation must use surrogate markers of long-term graft survival if conclusions are to be drawn at acceptable speed and cost. Morphologic changes in transplant biopsies provide the earliest available evidence of damage, and "protocol" biopsies from stable grafts can be used to reduce the number of patients needed in clinical trials. This approach has been inhibited by concerns over safety, but the risk of biopsy of a stable kidney, with no active inflammation or acute functional impairment, has never been formally estimated. METHODS: In accordance with a predefined set of questions, a retrospective audit of a sequential series of protocol biopsies was performed in four major transplant centers. RESULTS: A total of 2,127 biopsy events were assessed for major complications, and 1,486 were assessed for minor ones. There were no deaths. One graft was lost, under circumstances indicating that the loss should have been prevented. Three episodes of hemorrhage required direct intervention. Three further patients required transfusion. There were two episodes of peritonitis, but one was arguably an unrelated event. All serious complications presented within 4 hr of biopsy. CONCLUSIONS: The incidence of clinically significant complications after protocol biopsy of a stable renal transplant is low. Direct benefits to the patients concerned (irrespective of the benefit that may accrue in clinical trials) were not formally assessed but seem likely to outweigh the risk of the procedure. We believe that it is ethically justifiable to ask renal transplant recipients to undergo protocol biopsies in clinical trials and routine care.

Biopsy↗
PubMed2003

Elevated numbers of circulating endothelial cells in renal transplant recipients.

BACKGROUND: Damage of microvascular endothelial cells is a salient feature of acute vascular rejection and chronic allograft nephropathy, yet specific blood markers of ongoing endothelial injury are currently unavailable. Circulating endothelial cells have recently been established as a novel marker of endothelial damage in a variety of vascular disorders. METHODS: We studied 129 renal transplant recipients who underwent percutaneous graft biopsy. Circulating endothelial cells were isolated with immunomagnetic anti-CD146-coated Dynabeads. Cells were stained with acridine and counted. To verify their endothelial origin, staining for Ulex europaeus lectin 1 (UEA-1) was performed in parallel. Twenty-one healthy controls were also studied. RESULTS: On biopsy, seven patients had acute vascular rejection, 15 patients had acute tubulointerstitial rejection, 14 patients had borderline rejection, and 93 patients had no rejection. Patients with acute vascular rejection had the highest cell numbers (72+/-39 cells/mL) when compared with all other patients (P<0.02). Regardless of their biopsy findings, however, all other renal transplant recipients had significantly higher numbers of circulating endothelial cells (25+/-20 cells/mL) than healthy controls (7+/-5 cells/mL, P<0.001). Finally, there was a significant correlation of cell numbers and serum cyclosporine A trough levels. By contrast, there was no correlation with serum creatinine, age, or the number of immunosuppressive drugs. CONCLUSIONS: The number of circulating endothelial cells is a novel marker of endothelial damage in renal transplant recipients. Further studies must now evaluate the origin of these cells, corroborate the clinical significance of our findings, and delineate the influence of calcineurin inhibitors.

Acute Disease↗