Biomedical subjects

Michael L Nicholson

Publications and source records attributed to Michael L Nicholson.

6 recordsLinked to original sources

PubMed2003

Cardiac allograft vasculopathy: current concepts and treatment.

Cardiac allograft vasculopathy (CAV) remains the leading limiting factor of patient and graft survival after the first post-operative year. The pathogenesis involves both immunological and non-immunological factors. Here, we present recent advances and discuss potential preventative and treatment regimens. A review of the current literature of heart transplantation, detailing molecular mechanisms, pharmacological risk factors and novel immunosuppression regimens was performed. Recent findings demonstrate the pivotal role of the endothelium, resulting in release of pro-fibrotic cytokines, recruitment of circulating leucocytes, proliferation of vascular smooth muscle cells, and deposition of extracellular matrix proteins (ECMs). The role of HMG-CoA reductase inhibitors and anti-hypertensives remains controversial, but there is increasing evidence advocating their prophylactic use. We can conclude that novel immunosuppressive agents such as rapamycin, mycophenolate mofetil and FTY-720 are experimental immunosuppressive agents that are undergoing evaluation in clinical trials. The prophylactic use of statins and anti-hypertensive drugs needs to be defined but needs to suggest potential strategies to prolong cardiac allograft survival.

Heart Transplantation↗

PubMed2003

The effect of combined rapamycin/cyclosporine on the changes in pro-fibrotic gene expression that occur during the development of allograft vasculopathy in rats, compared with cyclosporine or rapamycin in isolation.

Chronic allograft dysfunction, the leading cause of solid-organ transplant failure, is characterised by histological evidence of extracellular matrix (ECM) accumulation (fibrosis). The aim of this study was to compare the effect of combined rapamycin and cyclosporine therapy on fibrosis-associated gene expression and ECM turnover during the development of allograft vasculopathy, compared with either agent alone. Lewis recipients of F344 rat thoracic-to-abdominal aorta transplants were administered rapamycin, cyclosporine, combined rapamycin and cyclosporine or no treatment. F344-to-F344 isografts served as controls. Six grafts in each group were harvested at 16 weeks. Vascular remodelling and ECM accumulation (Sirius red) were measured by computerised histomorphometry of aortic sections. Messenger RNA was extracted from frozen tissue, and expression of fibrosis-associated genes was studied by means of semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Rapamycin (0.5 mg/kg per day) or cyclosporine (5 mg/kg per day) inhibited intimal hyperplasia, medial ECM accumulation and expansive vascular remodelling (increasing vessel circumference) in rat aortic allografts. This was associated with attenuation of the graft inflammatory infiltrate and a reduction in intra-graft gelatinase, collagen III and tissue inhibitor of metalloproteinase (TIMP)-1 mRNA levels. Combined rapamycin and cyclosporine inhibited intimal hyperplasia; however, there was a lesser effect on vascular remodelling and medial ECM accumulation. Combined-treatment aortic allografts were also seen to have a more-severe inflammatory infiltrate and larger amounts of intra-graft matrix metalloproteinase (MMP)-9, transforming growth factor (TGF)-beta and TIMP-1 mRNA than those treated with monotherapy. Rapamycin and cyclosporine act synergistically to inhibit intimal hyperplasia but not the inflammatory infiltrate, allograft fibrosis or vessel remodelling. In the high-responder F344-to-Lewis rat model, effective immunosuppression is required to reduce graft fibrosis.

Animals↗

PubMed2003

Non-heart beating donor kidneys with delayed graft function have superior graft survival compared with conventional heart-beating donor kidneys that develop delayed graft function.

Delayed graft function may have an association with reduced graft survival, and nonheart-beating donor (NHBD) kidneys have higher rates of delayed graft function (DGF) than heart-beating donor (HBD) kidneys. This study compared outcome of renal transplants from HBDs who developed DGF, with NHBDs who developed DGF. All recipients of HBD and NHBD kidneys who developed DGF were identified during a 10-year period. All patients with graft primary nonfunction were excluded from analysis. Four hundred and fifty-six functioning transplants were performed. Delayed graft function occurred in 69 (17%) HBD and 55 (93%) NHBD kidneys. The grafts developing DGF were well matched for donor and recipient age. The rate of acute rejection was similar; [n = 16/69 (23%) HBD vs. n = 13/55 (24%) NHBD]. Cold ischaemia was 21 h in the HBD group and 17 h in NHBD group (p > 0.05). Serum creatinine was similar for both groups at 1.3 and 6 years (p > 0.05 for all time points). Graft survival in the NHBD recipients with DGF was significantly better at 3 years (84%) compared with recipients of a HBD renal transplant that developed DGF (73%) (p < 0.05), and at 6 years (62% survival for HBDs and 84% survival for NHBDs). This study shows that graft survival was better for NHBD kidneys up to 6 years after transplantation.

Adult↗

PubMed2003

Nonheart-beating kidney donation: current practice and future developments.

BACKGROUND: Nonheart-beating kidney donation (NHBD) is gaining acceptance as a method of donor pool expansion. However, a number of practitioners have concerns over rates of delayed graft function, acute rejection, and long-term graft survival. The ethical issues associated with NHBD are complex and may be a further disincentive. Tailored strategies for preservation, viability prediction, and immunosuppression for kidneys from this source have the potential to maximize the number of available organs. This review article presents the current practice of NHBD kidney transplantation, examines the results and draws comparisons with cadaveric kidneys, and explores some areas of potential development. METHODS: A review of the current literature on NHBD kidney donation was performed. RESULTS: The renewed interest in NHBD kidneys is driven by a continuing shortfall in available organs. Those centers involved in NHBD report an increase in kidney transplants of the order of 16% to 40% and there is no evidence that the financial costs are higher with NHBDs. The majority of experience comes from Maastricht category 2 NHBDs, where an estimation of warm time is possible. This is generally limited to 40 minutes. There are variations in the technique for kidney preservation prior to retrieval, but most centers use an aortic balloon catheter. Much work has looked at the ideal technique for kidney preservation prior to implantation. Evidence suggests that machine perfusion produces the best initial function rates, decreased use of adjuvant immunotherapy and fewer haemodialysis sessions than static cold storage. CONCLUSION: Despite being associated with poorer initial graft function, the long-term allograft survival of NHBD kidneys does not differ from the results of transplantation from cadaveric kidneys. Further, serum creatinine levels are generally equivalent. Constant reassessment of the ethical issues is required for donation to be increased while respecting public concerns. Use of viability assessment and tailoring of immune suppression for NHBD kidneys may allow a further increase in donation from this source.

Heart Arrest↗

PubMed2003

Intra-renal resistance reflects warm ischaemic damage, and is further increased by static cold storage: a model of non-heart-beating donor kidneys.

BACKGROUND: Non-heart beating donor kidneys increase transplant activity, but their use is associated with a higher rate of both primary non-function and delayed graft function than cadaveric kidneys, due to a period of cold ischaemic damage superimposed on a period of warm ischaemia. We aimed to measure intra-renal resistance in machine perfused porcine kidneys subjected to different periods of warm ischaemic injury, with additional, varying, cold ischaemic times, in an attempt to mimic the injury suffered by NHBD kidneys and test the predictive power of viability testing. MATERIAL/METHODS: Landrace pigs were killed by lethal injection, and the kidneys were subjected to varying WITs of 10-90 minutes prior to explantation. Kidneys were subsequently stored for varying cold times of 2 to 48 hours. IRR (pressure/flow) was calculated during 6 hours cold pulsatile machine perfusion. RESULTS: For all WITs, IRR was higher at the start than at the end of machine perfusion (P<0.001). There was a strong correlation between IRR on MP, and WIT, but no correlation after 6 hours MP. Intra-renal resistance increased as kidneys were exposed to longer CITs; this effect was most marked for the longer WITs (P<0.004), However, the slope gradient was similar for the different WITs. CONCLUSIONS: Early IRR accurately reflects kidney in-situ WIT, and machine perfusion reduces IRR whilst cold ischaemia imposed on periods of warm ischaemia increases IRR and attenuates the beneficial effect of MP. Machine perfusion may partially ameliorate the effects of WIT in terms of IRR, and may prove useful in pre-transplant viability assessment of NHBD kidneys.

Animals↗

PubMed2002

Sequential protocol biopsies from renal transplant recipients show an increasing expression of active TGF beta.

Chronic allograft nephropathy (CAN) is a major cause of graft loss after renal transplantation. Implicated in the pathogenesis of this complication is overproduction of the cytokine transforming growth factor beta (TGF beta). In this study we measured changes in CAN's expression in stable patients early after transplantation, and studied links with established risk factors for CAN, such as delayed graft function, acute rejection, and cyclosporine exposure. We took biopsies from 40 renal allografts at time of transplantation (pre-perfusion), and then, using ultrasound guidance, at 1 week and 6 months after transplantation. An immunofluorescence technique was used to stain sections for active TGF beta. These were then assessed by semi-quantitative scanning laser confocal microscopy. There was very little variation in active TGF-beta expression among patients in their pre-perfusion biopsies. Expression had increased by 1 week and then very significantly by 6 months ( P<0.0001). Patients who suffered delayed graft function had increased TGF-beta expression at both time points. There was no difference regarding donor type, acute rejection, and immunosuppressive drug (cyclosporine or tacrolimus). There was no correlation between the amount of TGF-beta expression at any time-point and isotope glomerular filtration rate (GFR) at 12 months. This study demonstrated that in a group of stable renal allograft recipients, TGF-beta expression in the kidney increased after transplantation. As the study used protocol biopsies, this increase is unlikely to be due to acute events, and probably represents a genuine increase.

Adult↗