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Department of Immunology and Clinics of Organ Transplantation Ospedali Riuniti Bergamo, Mario Negri Institute for Pharmacological Research, Bergamo, Italy.
Correspondence to Dr. Marina Noris, Mario Negri Institute for Pharmacological Research, Via Gavazzeni 11, 24125 Bergamo, Italy. Phone: +39-035-319888; Fax: +39-035-319331; E-mail: noris{at}marionegri.it
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Lewis rat
kidney transplant model, we sought (1) to compare the relative
efficacy of the novel immunosuppressant, mycophenolate mofetil (MMF), with
that of the AT1 receptor blocker, losartan, in preventing the development of
chronic graft rejection when given for 52 wk; (2) to examine whether
combining MMF with losartan affords better protection than each of the drugs
alone. For comparison, the effect of cyclosporine (CsA) to control chronic
graft rejection was also assessed. Administration of MMF alone or losartan
alone to the kidney allografted rats resulted in a partial decrease in the
amount of proteinuria, preservation of glomerular and tubulo-interstitial
graft structure, limitation of intragraft cell infiltration, and improvement
of graft survival compared with corresponding parameters in untreated,
transplanted control rats. Combined treatment with MMF and losartan completely
prevented the development of proteinuria, largely reduced glomerular and
tubulointerstitial injury, and suppressed intragraft cell infiltration, and
all animals survived at the end of the follow-up. Similarly, CsA treatment
largely prevented graft injury but failed to achieve 100% animal survival. We
have shown that MMF synergizes with the angiotensin II receptor antagonist,
losartan, in simultaneously targeting complementary pathways of chronic
allograft rejection. Combining MMF and angiotensin II receptor blocker offers
superior long-term renoprotection as compared with CsA. Together, these
findings provide the basis to prevent chronic injury and progressive
dysfunction after renal transplantation. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In the Fisher 344Lewis rat model of chronic rejection,
(12) progressive renal lesions
mirror those of the corresponding human condition that manifests with
progressive proteinuria and renal dysfunction associated with lesions of
glomerulosclerosis, interstitial lymphocyte and macrophage infiltration, and
arteriosclerosis (6). It has
been hypothesized that the synergistic effect of macrophages and
alloantibodies producing B cells, both activated by CD4+ T cells,
can promote the typical changes of chronically rejected allografts
(13). The functional and
structural changes of chronic renal allograft rejection also share
similarities with those observed in other forms of chronic progressive renal
disease in which inadequate functioning nephron mass has been considered the
key event (11,
14). This led also to the
hypothesis that the single renal allograft carries a peculiar risk of
developing hemodynamically mediated glomerular injury as a consequence of
inadequate numbers of functioning nephrons surviving the acute sequelae of
transplantation (14).
No effective therapy exists for chronic allograft dysfunction. Immunosuppressive drugs might help limit antigen-dependent determinants of chronic rejection, but the proatherogenic potential of some of them, like calcineurin inhibitors and prednisone, reduces their effectiveness (10). Similarly, attempts to modulate antigen-independent factors for instance by blockade of renin-angiotensin system slowed but did not completely prevent progressive graft dysfunction (15, 16). Failure to achieve full renoprotection with pharmacologic interventions that have been attempted so far can be attributed to a limited efficacy of the tested drugs, the restricted target of the therapeutic intervention, and/or a too brief period of follow-up.
This study was designed in the Fisher 344Lewis rat model with the
following objectives: (1) to compare the efficacy of mycophenolate
mofetil (MMF), a novel immunosuppressive drug recently approved for clinical
use, with that of the AT1 receptor blocker, losartan, in preventing the
development of chronic rejection when given for a prolonged period of
treatment; (2) to examine whether combining MMF with losartan affords
better protection than each of the drugs alone toward chronic allograft
injury. In addition, another group of animals received cyclosporine (CsA) for
comparison because most human allograft recipients are given CsA to control
immune response.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Kidney Transplantation
Kidney transplantation was performed as described previously
(17). Briefly, the left donor
kidney was removed and positioned orthotopically into the recipient, whose
renal vessels had been isolated and clamped and whose left native kidney had
been removed. End-to-end anastomosis of renal artery, vein, and ureter were
performed using 10-O Prolene sutures (Ethicon Inc., Somerville, NJ). Total
ischemia time was < 30 min. The right native kidney was removed on the 11th
postoperative day. Complete allograft failure was defined as death of the
animal because the animals are dependent on the transplanted kidney
function.
Experimental Design
Five experimental groups of F344Lewis renal allograft recipients were
examined and compared. All rats received CsA (5 mg/kg per d intramuscularly;
Novartis Pharmaceutical Corp., Milan, Italy) for the first 10 d after
transplantation to prevent early acute rejection
(12). After day 10, animals
were divided into the following groups: Group 1 (n = 12) received no
treatment; Group 2 (n = 8) received MMF (10 mg/kg per d orally;
Roche, Milan, Italy); Group 3 (n = 8) was given the nonpeptide
angiotensin II receptor antagonist losartan (30 mg/kg per d in the drinking
water; Merck Sharpe & Dohme, Rome, Italy); Group 4 (n = 10) was
given MMF (10 mg/kg per d orally) plus losartan (30 mg/kg per d in the
drinking water); Group 5 (n = 8) was treated with CsA (5 mg/kg per d
intramuscularly). An additional group 6 (n = 8) underwent Lewis to
Lewis syngeneic kidney graft.
Rats were followed for 52 wk. The dose of losartan was adjusted as needed to maintain systolic BP within normal range (Table 1). Renal function, as serum creatinine, was monitored before transplantation at monthly intervals and just before sacrifice in dying animals. At the same time points, animals were placed in individual metabolic cages for 24-h urine collection and determination of urine output and protein excretion. Systolic BP was measured serially in conscious rats by the tail-cuff method (18). At the end of the 52 wk follow-up, whole kidney function studies were performed in surviving rats. Thereafter, the animals were killed and the kidney graft was removed and processed for histology and immunohistology of cell infiltrate. Histologic examination of the graft was also done in those animals that were killed at a different time during the follow-up because they had been dying.
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Renal Hemodynamics
Whole kidney function studies were done as described previously
(15). The rats were
anesthetized, placed on a temperature-regulated table, and tracheotomized. A
PE-50 tubing catheter was inserted into the left femoral artery for subsequent
periodic blood sampling and continuous BP monitoring with an electronic
transducer connected to a writing recorder (Battaglia Rangoni, Bologna,
Italy). A catheter was also placed in the left femoral vein for infusion of
clearance markers. Urine was collected by bladder catheterization. After
60-min equilibration, three timed clearance periods of 30 min each were
started. Arterial blood samples were obtained at the midpoint of each
clearance period for evaluation of plasma inulin and p-aminohippurate (PAH)
concentration.
Routine Chemistry
Creatinine concentration was measured by a Reflotron creatinine test (Roche
Molecular Biochemicals, Mannheim, Germany) on whole blood collected from the
tail vein of anesthetized animals. Protein concentrations in 24-h urine
samples was determined by the Coomassie blue G-dye binding method
(19). Inulin and PAH
concentrations in plasma and urine samples were measured by previously
described methods (20,
21).
Routine Histology
Kidney specimens were fixed for 6 h in Dubosq-Brazil and dehydrated in
alcohol. After paraffin embedding, 3-µm sections of the blocks were cut and
stained with periodic acid-Schiff reagent, Masson's trichrome, and hematoxylin
eosin. The frequency of focal and segmental sclerosis and hyalinosis was
determined by examining all glomerular profiles contained within one or two
coronal sections from each kidney and expressed as the percentage of the total
number of glomeruli counted. A minimum of 80 glomeruli per kidney was
evaluated for glomerulosclerosis. Tubular (atrophy, cast, and dilation) and
interstitial (fibrosis and inflammation) changes were graded on a scale of 0
to 4+: 0, no changes; 1+, changes affecting <25% of the sample; 2+, changes
affecting 25 to 50% of the sample; 3+, changes affecting 50 to 75% of the
sample; 4+, changes affecting 75 to 100% of the sample. All renal biopsies
were analyzed by the same pathologist blinded to the nature of the
experimental groups.
Immunohistochemical Analysis
Mouse monoclonal antibodies were used for the detection of the following
antigens: (1) ED1 antigen present in the rat monocytes and
macrophages (Chemicon, Temecula, CA); (2) a rat MHC class II antigen
monomorphic determinant (OX6; Serotec, Oxford, United Kingdom); (3)
CD4 cell surface glycoprotein, a 55-kD molecule expressed by helper T cells,
thymocytes, and macrophages (W3/25; Serotec), and (4) rat CD8 cell
surface glycoprotein expressed by T cytotoxic suppressor cells (OX8; Serotec),
(5) rat dendritic cells—
restricted antigen (OX62; Serotec). All antigens were analyzed by indirect
immunofluorescence technique. The tissue fragments were frozen in liquid
nitrogen. Tissue sections (3-µm thick) were cut with a Mikrom 500 O
cryostat (Walldorf, Germany) and fixed with acetone. The sections were blocked
with phosphate-buffered saline (PBS)/1% bovine serum albumin, incubated
overnight at 4°C with the primary antibody (ED1, 14 mg/ml; OX6, 5
µg/ml; W3/25, 40 µg/ml; OX8, 1:100 OX62; undiluted), washed with PBS,
and then incubated with Cy3-conjugated donkey antimouse IgG antibodies
(affinity-purified, absorbed with rat IgG, 5 µg/ml in PBS; Jackson
Immuno-Research, West Grove, PA) for 1 h at room temperature. For each marker,
the number of cells was counted in at least 10 randomly selected high-power
microscope fields (x400) for each animal.
Statistical Analyses
Results are given as a mean ± SD. Survival data were analyzed by
PROC LIFETEST of SAS 6.12, (SAS Institute, Cary, NC), and multiple comparisons
between groups were assessed by the log-rank test. For other functional
parameters, the significance of differences between individual group means,
after two-way ANOVA, was established by using the Tukey-Cicchetti test for
multiple comparison (22).
Values for urinary protein excretion, which were not normally distributed,
were log-transformed before statistical analysis. Estimates of renal injury
from morphologic studies and immunohistochemical results were analyzed by the
nonparametric Kruskal-Wallis test for multiple comparisons. Statistical
significance was defined as P < 0.05.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Proteinuria
Although several assays of sequential renal function have been studied in
the established F344Lewis model of chronic rejection, urinary protein
excretion is the most convenient and accurate
(12).
Figure 2 shows the 24-h protein
excretion data of the different experimental groups as a function of time
after transplant.
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The evolution of proteinuria in control untreated group 1 is characteristic of the pattern previously reported for this model (12). In this group, protein excretion progressively increased during the 52-wk study period. In MMF-treated rats (group 2), proteinuria at 26 wk after transplant was increased as compared with baseline (67.9 ± 25.9 versus 9.6 ± 0.6 mg/24 h; P < 0.05), but the value was significantly lower than in control group 1 at the same point in time (224.9 ± 98.4 mg/24 h, P < 0.01). Thereafter, however, in this MMF group, the urinary protein excretion markedly increased (at 39 wk: 238.3 ± 119.0 mg/24 h), reaching values comparable to those of control untreated animals at the end of the follow-up period.
Similarly, animals treated with losartan alone (group 3) had an increase of protein excretion over baseline values at 26 wk after surgery (60.4 ± 55.9 versus 10.9 ± 1.5 mg/24 h). At this time point, mean protein excretion values were significantly reduced compared with those of untreated control rats (P < 0.01). A moderate but progressive increase in urinary protein excretion was found thereafter (at 39 wk: 99.9 ± 29.5 mg/24 h, P < 0.05 versus control), so that at the end of the study period proteinuria was numerically, but not significantly, lower than in untreated control animals.
In contrast, protein excretion at 26 wk after transplant in animals given the combined treatment of MMF and losartan remained at near-baseline levels (27.4 ± 5.6 versus 9.7 ± 1.2 mg/24 h). At this time point, proteinuria was significantly lower than in control group 1 animals (P < 0.01). Urinary protein excretion in these MMF-plus-losartan rats only minimally increased thereafter (at 39 wk: 33.2 ± 30.8 mg/24 h, P < 0.05 versus control). At the end of the 52-wk observation period, the mean proteinuria was still significantly (P < 0.05) lower than in untreated control rats but comparable to that of syngeneic grafted rats (group 6).
Similarly, in rats treated with CsA alone, protein excretion at 26-wk follow-up was comparable to baseline values (21.6 ± 5.6 versus 13.5 ± 1.1 mg/24 h). At this time point, proteinuria in group-5 animals was significantly lower than in untreated control group 1 (P < 0.01). Although thereafter in the CsA-treated rats a tendency to increase of protein excretion was documented (at 39 wk: 86.3 ± 52.0 mg/24 h, P < 0.05 versus control), mean value at the end of the study period was markedly (P < 0.05) reduced as compared to that of untreated control animals. In these CsA-treated animals, the level of proteinuria was numerically similar to that of animals receiving the combined MMF and losartan treatment (group 4) or undergoing syngeneic kidney graft (group 6). A minor age-related increase in protein excretion was found in group-6 animals with syngeneic kidney graft over the 52-wk follow-up.
Serum Creatinine
Table 3 reports the time
course of serum creatinine concentration in animals from individual groups
that were alive at given time points after transplant. Untreated control
animals of group 1 showed a progressive increase in serum creatinine, taken as
a marker of renal function, during the 52-wk study period. A similar trend
toward progressively deteriorating renal function with time was also found in
MMF-treated rats. However, in animals given losartan alone, serum creatinine
concentration remained quite stable up to the 52 wk after transplant.
Similarly, in rats given the combined treatment of MMF and losartan serum
creatinine did not change to a significant extent over the entire observation
period. At variance, in animals treated with CsA alone, there was a slight
increase in the serum creatinine level at the end of follow-up. This was not
seen in rats with syngeneic kidney grafts, in which serum creatinine remained
near baseline value during the 52 wk after transplant. That differences in
graft function between the experimental groups observed at the end of the
study period are not minimized by the relatively small number of animals still
alive at this time point is supported by a similar trend in the difference of
mean serum creatinine values found at an earlier time point (39 wk after
transplant, Table 3), when
enough time after transplantation was elapsed and significant mortality has
not yet occurred in any of the groups.
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Renal Hemodynamics
GFR and renal plasma flow (RPF) were measured at the end of the study in
all surviving animals. As shown in Figure
3A, GFR in MMF-treated rats was comparable to that of untreated
control animals. Rats given losartan alone or its combination with MMF had a
numerically higher GFR than untreated control animals, but the values in both
groups did not reach statistical significance. At variance, GFR was lower in
animals given CsA alone than in all other groups, achieving statistical
significance (P < 0.05) only as compared with rats receiving the
combined treatment of MMF and losartan. In rats with syngeneic kidney grafts,
GFR was slightly higher than in untreated control animals.
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Similar results were obtained for RPF (Figure 3B), which was numerically higher in the combined treatment with MMF and losartan than in all other groups and attained statistical significance (P < 0.05) as compared with CsA alone group.
Blood Pressure
As shown in Figure 4,
control untreated rats became slightly hypertensive from week 26 after
transplant. Thereafter, systolic BP (SBP) attained overtly hypertensive values
(basal, 114 ± 3 mmHg; week 52, 162 ± 7 mm Hg; P <
0.05). At the end of the study period in these animals, SBP was significantly
higher than in all other experimental groups (P < 0.05). In rats
given MMF alone, SBP tended to slightly increase with time (basal, 115
± 3 mm Hg; week 52, 136 ± 16 mm Hg; P < 0.05), but
the values were significantly different from those of all other treated groups
at only 26 and 39 wk after transplant. In group 3, losartan alone adequately
controlled SBP, which remained within the normal range throughout the study
(basal, 118 ± 5 mm Hg; week 52, 129 ± 7 mm Hg). Also, combined
treatment with MMF and losartan allowed SBP to remain at normal levels during
the entire study period (basal, 116 ± 2 mm Hg; week 52, 125 ± 7
mm Hg). Similarly, animals on CsA alone did not develop any significant change
in SBP over the 52-wk observation period (basal, 117 ± 2 mm Hg; week
52, 128 ± 7 mm Hg). In rats with syngeneic kidney grafts, SBP remained
normal for the entire follow-up (basal, 122 ± 7 mm Hg; week 52, 129
± 7 mm Hg).
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Graft Morphology
Histology findings from animals that survived 52 wk after transplant are
given in Table 4. Grafts from
untreated control animals showed marked glomerular injury with focal and
segmental sclerosis involving 86% of glomeruli. Sections of allografts from
rats given MMF alone showed numerically lower percentage of glomeruli with
sclerotic lesions than in untreated control animals. Further numerical
reduction of the percentage of sclerotic glomeruli was found in rats given
losartan alone. Sclerosis was strikingly limited in rats given the combined
treatment with MMF and losartan, the mean percentage being significantly lower
than in control untreated animals (P < 0.05) or in rats given MMF
alone (P < 0.05). Similarly, only a low percentage of glomeruli
showed focal segmental glomerulosclerosis in animals treated with CsA alone.
Few sclerotic glomeruli were also found in rats receiving syngeneic kidney
grafts.
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In untreated control rats, several tubular casts as well as severe tubulointerstitial injury were documented (Table 4). In animals given MMF alone, a numerically but not statistically significant improvement of the tubulointerstitial injury score was found. Administration of losartan alone significantly (P < 0.05) reduced tubulointerstitial damage as compared with untreated control rats. More importantly, very few tubulointerstitial changes were seen in animals given the combined treatment with MMF and losartan, whose mean score value was even numerically lower than that in animals undergoing syngeneic transplant. Also, in rats given CsA alone, tubulointerstitial architecture was largely preserved, but values were significantly higher than in those receiving the combined MMF and losartan treatment (P < 0.05). Tubulointerstitial injury was minimal in rats receiving syngeneic kidney grafts.
Immunohistology
We also undertook a detailed immunohistology evaluation of allografted and
syngeneic animals studied at the end of the 52-wk follow-up
(Table 5). In kidneys from MMF
alone, or losartan alone-treated hosts, ED1+ cells were markedly decreased as
compared with untreated control rats, with the effect being more prominent in
rats given the angiotensin II receptor antagonist. Moreover, combined
treatment with MMF and losartan completely normalized parenchymal infiltration
of ED1+ cells to the extent that the number of these cells was comparable to
that seen in syngeneic kidney grafts. On the other hand, mononuclear cell
graft infiltration was only partially reduced by the administration of CsA
alone. ED1+ cell infiltration in syngeneic kidney grafts was minimal.
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Similar results were found with dendritic cell (OX62) infiltration that was elevated in grafts from untreated control animals, partially reduced by each single treatment, and completely restored to normal level in rats that had been given the combined treatment with MMF and losartan.
Also MHC class II cell (OX6+) infiltrate was reduced in all treatment groups as compared with grafts from control untreated rats. In these treatment groups, however, cell infiltration was numerically higher than in rats with syngeneic kidney grafts.
As for CD8+ cell infiltrate, animals given MMF alone, losartan alone, or their combination but not CsA alone showed markedly diminished number of this infiltrating cell subpopulation as compared with that in untreated control rats. Interestingly, MMF treatment afforded similar complete protection as well as the combination MMF/losartan regimen to prevent intragraft CD8+ cell infiltration.
At variance, although all treatments significantly decreased the number of CD4+ cells in the grafts as compared with untreated control animals, only losartan alone and its combination with MMF completely prevented this T cell infiltration, the mean value being similar to that of rats receiving syngeneic kidney grafts.
Renal Function and Graft Morphology in Animals that Died
Prematurely
Table 6 summarizes graft
function and morphology variables in animals that succumbed before the 52-wk
follow-up. Most of animals were from the untreated control recipients (group
1). Functional variables (serum creatinine and proteinuria) represent the last
available measurement before animals were killed because they were moribund.
Rats died between 113 and 345 d after transplant. All of them had high urinary
protein excretion rate and renal insufficiency of different degree ranging
from moderate to severe, depending on the time of their last serum creatinine
measurement in relationship to animal sacrifice or death. Graft histologic
examination at autopsy showed marked glomerular injury, with focal and
segmental sclerosis involving 48 to 100% of glomeruli, associated with severe
tubulointerstitial damage. Overall, these findings would suggest that all the
transplanted animals that died prematurely before the end of the study
succumbed for end-stage renal disease resulting from chronic graft
rejection.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Lewis rats partially protected from the
development of chronic rejection. This finding is in line with a previous
study in the same kidney allograft rat model showing that after 52 wk of MMF
administration, morphologic and immunohistologic manifestations of the chronic
process into the graft were markedly diminished
(23). In models of chronic
rejection, activated macrophages and T cells infiltrating the graft and the
endothelial cells themselves secrete growth factors that cause smooth muscle
cell proliferation, leading to vascular intimal occlusion, interstitial
fibrosis, and, in the case of kidney, renal scarring
(1). Thus, the beneficial
effect of MMF we and others have found in this graft model could be attributed
to the drug's property of inhibiting the expression of adhesion molecules on
the surface of inflammatory cells and ultimately preventing their infiltration
in the graft, as previously shown in other models of kidney diseases
(23,24,25).
This possibility is supported by our observation that MMF treatment
significantly limited the intragraft infiltration of monocytes/macrophages,
CD4+, and CD8+ T cells as compared with control untreated kidney transplants
at the end of the 52-wk follow-up. Moreover, as recently shown in rat remnant
kidney (26), MMF may have
contributed to reduce myofibroblast infiltration and extracellular matrix
accumulation, factors that contribute to renal fibrosis. Interestingly, in MMF-treated animals, we also found that urinary protein excretion rate was within normal range up to 22 wk after transplantation, thereafter progressively increased to level of untreated allografted control animals. We are tempted to speculate that late development of proteinuria in MMF-treated animals occurred mainly as a consequence of non-immunologic factors contributing to nephron loss, which cannot be controlled by an immunosuppressive agent such as MMF. This could also explain why MMF treatment had only a minimally beneficial impact on graft survival as compared with the untreated control group.
We also showed that in the same Fisher 344Lewis kidney transplant
model, treatment with the angiotensin II receptor blocker, losartan, improved
graft survival and partially prevented the development of proteinuria and
glomerular and tubulointerstitial injury that characterize this model. This
result is in harmony with other reports in the Fisher 344Lewis model of
late renal allograft failure that the angiotensin-converting enzyme inhibitor,
cilazapril (16), or the
angiotensin II receptor antagonists, L-158,809
(16), candesartan
(27), or losartan
(15,
28), can significantly help to
prevent chronic graft injury.
Although systemic hypertension is not a prominent feature of Fisher
344Lewis rats, glomerular capillary hydraulic pressure is significantly
elevated (29,
30), and alleviation of
glomerular capillary hypertension with angiotensin-converting enzyme inhibitor
or angiotensin II receptor blocker treatment is believed to be the central
mechanism by which a reduction of proteinuria and prevention of supervening
chronic glomerular and tubulointerstitial injury are achieved
(27,
31).
Beside hemodynamics, when the glomerular permselective property is lost, excessive quantities of filtered proteins reach the lumen of the proximal tubule. The secondary process of reabsorption of filtered proteins can contribute substantially to renal interstitial injury by activating intracellular events, eventually leading to interstitial inflammation (32). It is possible that amelioration of glomerular permeability to proteins also contributed to the observed beneficial effect of losartan in this model.
There is also plenty of evidence that angiotensin II affects tissue remodeling independently of its effect on BP or hemodynamics (33), through its growth factor modulating properties (34,35,36,37). These findings suggest that the antiproliferative effect of blocking angiotensin II biologic activity could also have contributed to the renoprotective effect of losartan in this model of chronic allograft nephropathy.
Together, these observations can be taken to indicate that alloantigen-independent factors, which operate through excessive angiotensin II production, are important causes of progressive allograft loss after transplantation. Data are also available that angiotensin II may possibly interfere with immune functions. Thus, exposure of T lymphocytes to angiotensin II with no other exogenous stimulus is sufficient to trigger cell proliferation, a response blocked by specific AT1 receptor antagonist and absent in cells from Agtr1a-/- mice, which lack AT1A receptors for angiotensin II (38). This finding may open the possibility that the renoprotective effect of losartan in this model could also be, at least in part, related to the immunomodulatory effect of blocking angiotensin II activity.
Regardless of the mechanisms of protection afforded by MMF or losartan, our findings indicate that each regimen alone failed to provide full protection against chronic graft rejection, raising the possibility that both alloantigen-dependent and alloantigen-independent mechanisms participate in inducing progressive kidney graft loss.
The novelty of our observations is the finding that combined MMF and losartan treatment completely prevented the development of proteinuria and suppressed interstitial accumulation of macrophages, T cells, dendritic cells and MHC class II overexpression at the end of the experiment as well tubulointerstitial injury, so that graft function was well preserved and all animals survived at the end of the follow-up. These findings indicate that combining treatments that target immune and non-immune mechanisms of chronic graft loss preserve allograft structural integrity and function better than each regimen alone. The synergistic effect of simultaneous blockade of monocyte and lymphocyte infiltration with MMF and of the biologic effects of angiotensin II with losartan would convey on down-regulating the expression of several cytokines and growth factors in the graft interstitium, ultimately preventing cellular and molecular events that lead to chronic renal allograft injury in this model.
CsA is currently the most employed antirejection agent in human
transplantation. Therefore, additional experiments were performed to explore
its effect on chronic rejection in the present Fisher 344Lewis rat
model. Our findings document that, in line with previous experimental
observations (16,
39), CsA largely prevents
proteinuria and histopathology manifestations of chronic rejection. Although
these effects are similar to those we observed with the combined MMF and
losartan treatment, CsA administration resulted in significantly lower renal
function (GFR) and graft perfusion (RPF) values than with the combined regimen
and, more importantly, failed to achieve 100% animal survival during the 52-wk
follow-up period. Thus, despite its potential value for modulating chronic
allograft rejection, CsA treatment, which bears intrinsic nephrotoxicity
(40), would contribute to
long-term graft loss, at least for kidney transplant.
In summary, we have demonstrated a substantial protective effect of MMF or
angiotensin II receptor blockade on indices of chronic allograft injury in the
Fisher 344Lewis model of late allograft failure. This implies that
chronic allograft injury in this model is associated with processes that arise
from T cell recognition of alloantigen, leading to B cell and macrophage
activation and from the renal response to inadequate nephron supply. We have
also shown that MMF synergizes with angiotensin II receptor antagonism in
simultaneously targeting complementary pathways of chronic allograft
nephropathy. Together, these findings provide the basis for novel treatment
regimens that are designed to protect transplant kidneys from chronic injury
and progressive dysfunction.
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Acknowledgments |
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Footnotes |
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Lewis rats. J Hypertens15
[Suppl 6]: S21-S25,1997
Lewis rats: Hemodynamics, macrophages, and cytokines.
Kidney Int 57:2618
-2625, 2000[Medline]
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,
P < 0.05 versus control and MMF at the same time point.
, P < 0.05 versus MMF plus losartan at the same
time point.
