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Cutting Edge |
-o-methyl)-Fluoromethylketone1


*
Keratinocyte Laboratory, Imperial Cancer Research Fund, London, United Kingdom;
Department of Medicine and Therapeutics, University College Dublin, Dublin, Ireland; and
Department of Histopathology, Imperial College of Science, Technology, and Medicine, London, United Kingdom
| Abstract |
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in the epidermis develop
inflammatory skin disease and features of SLE that have striking
parallels with the human condition. We have now tested the effects
of a pan-caspase inhibitor,
carbobenzoxy-valyl-alanyl-aspartyl-(
-o-methyl)-fluoromethylketone,
on disease progression. Daily s.c. administration of
carbobenzoxy-valyl-alanyl-aspartyl-(
-o-methyl)-fluoromethylketone
to female transgenic mice over a 3-wk period resulted in significant
amelioration of both glomerular and interstitial renal damage,
independent of the effects on autoantibody levels or skin inflammation.
We propose that apoptosis inhibitors could be beneficial in the
treatment of human SLE. | Introduction |
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We have previously shown that transgenic mice expressing IFN-
in the
suprabasal layers of the epidermis, under the control of the involucrin
promoter, develop a lupus-like syndrome (4). As in the
naturally occurring human disease, the production of pathogenic IgG ANA
in this model is largely restricted to females, is T cell dependent,
and is tightly correlated with the development of a proliferative
glomerulonephritis (5). In addition, there is
circumstantial evidence that apoptotic keratinocytes act as the source
of self nuclear Ag triggering ANA production (5). IFN-
transgenics seem, therefore, to be an excellent model in which to study
the effects of pharmacological apoptosis inhibition.
Carbobenzoxy-valyl-alanyl-aspartyl-(
-o-methyl)-fluoromethylketone
(ZVAD-fmk) is a pan-caspase inhibitor that irreversibly inhibits
enzymatic function and is effective in blocking apoptosis in a
variety of cell types in vitro and in vivo (6, 7, 8). We have
studied the effects of ZVAD-fmk administration on the lupus phenotype
in IFN-
-transgenic mice.
| Materials and Methods |
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Thirty-seven female IFN-
-transgenic mice (CBA x
C57/BL10 F1s) from three different founder lines
(9) were assigned to receive either ZVAD-fmk
(n = 19) or saline (n = 18) by daily
s.c. injection for 21 days. Thirty-four animals completed the study.
All animals were 6 mo of age or older at the start of the experiment
(the mean age of the treatment group was 8 mo, and the mean age of the
control group was 7 mo; Table I
) and
produced significant levels of IgG anti-dsDNA Abs on ELISA (OD
>0.1 at a 1/100 dilution; Table I
). Starting serum levels of
anti-dsDNA Abs were comparable in the treatment and saline control
groups, with mean OD on IgG anti-dsDNA ELISA of 0.360 and 0.320,
respectively (Table I
).
|
Anti-dsDNA and histone ELISA
Blood was taken from all animals for estimation of anti-dsDNA and anti-histone levels 1 wk before the onset of treatment and on days 2, 9, 16, and 21 after the start of the trial. The levels of IgG anti-dsDNA and anti-histone Abs in serum were measured as described previously (4, 5).
TUNEL staining
TUNEL staining of paraffin sections of skin was conducted as
described previously (5), and sections were counterstained
with propidium iodide. Sections from 15 saline-treated controls
(1820, 2227, and 2934 in Table I
) and 15 ZVAD-fmk-treated animals
(17 and 917 in Table I
) were analyzed by a single observer (J.
P. Seery) blinded to the treatment status of the animals. Only
TUNEL-positive cells in the interfollicular epidermis that showed
definite evidence of nuclear fragmentation were counted. The length of
the epidermis on each section was measured, and the number of apoptotic
cells per centimeter of epidermis was calculated (in total, 24.3 cm for
saline-treated controls and 20.9 cm for ZVAD-fmk-treated animals).
Histological assessment of renal disease
Kidneys were fixed in formalin and were paraffin embedded, then sections were stained with H&E. The severity of renal disease in the treated and control groups was assessed as follows. The cellularity of the glomeruli was graded (0, +, ++, +++, and ++++) by an experienced renal histopathologist (V. Cattell) blinded to the treatment status of the animals. A score of 0 or + was seen in nontransgenic littermate controls and was therefore considered normal. Additional histological features of renal damage including interstitial infiltrates and glomerular sclerosis and necrosis were recorded. Immune deposits were evaluated in frozen sections of kidneys, essentially as described previously (4), using anti-mouse IgG conjugated with Alexa 488.
Statistics
The incidence of interstitial renal disease in ZVAD-fmk-treated
and saline-treated animals was compared using the
2 test. The degree of glomerular cellularity
and percentage changes in anti-dsDNA levels in the two groups were
compared using the unpaired Student t test.
| Results |
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-transgenic mice assigned to
receive ZVAD-fmk and 17 of the 18 assigned to receive saline injections
completed the study (Table I
ZVAD-fmk treatment had no effect on the macroscopic skin disease of the
animals. After treatment, the mice still had persistent skin erythema,
hair hypopigmentation, and histological evidence of dermal inflammation
(Fig. 1
, A, C, and
E; Ref. 9 ; and data not shown). However, the
number of TUNEL-positive cells in the interfollicular epidermis and
underlying dermis was lower in the ZVAD-fmk-treated animals than in
saline-treated controls (1.20 vs 1.73 per centimeter of interfollicular
epidermis, respectively; average of 15 animals/group; compare Fig. 1
, B and D). One mouse was treated with ZVAD-fmk for
3 wk and was sacrificed 4 days after the final treatment; that animal
had large numbers of apoptotic cells in the skin (>3 cells per
centimeter of interfollicular epidermis), demonstrating that the
suppressive effect of the drug was dependent on continuous application
(compare Fig. 1
, B and F). The reduction in the
number of TUNEL-positive cells in the skin of ZVAD-fmk-treated mice
provided evidence that the amount of drug given to the animals and
frequency of application were sufficient to have an inhibitory effect
on apoptosis.
|
-transgenic
mice showed a high degree of variability (Table I
|
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-transgenic animals demonstrated a marked
reduction in the severity of renal disease compared with saline-treated
controls (Table I
|
The kidneys of six ZVAD-fmk-treated and six saline-treated control
animals were examined for glomerular deposition of autoantibodies. As
reported previously (4), both capillary (Fig. 4
E) and mesangial deposits were found in the control mice.
In the ZVAD-fmk-treated mice, only mesangial deposits were observed
(Fig. 4
F), but the sample size was too small to conclude
whether there had been any reduction in IgG deposition. However, it was
clear that drug treatment did not abolish immune complex
deposition.
| Discussion |
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model of SLE. This finding is of interest because the severity
of renal disease is the primary determinant of prognosis in the human
condition (2).
TUNEL labeling was reduced in the skin of treated transgenic mice,
indicating that the ZVAD-fmk regimen was indeed inhibiting
apoptosis. The residual apoptosis observed could be
occurring via a caspase-independent mechanism involving PML
(10). ZVAD-fmk did not prevent an anuclear stratum corneum
from forming in the epidermis, in contrast to the reported effects of
caspase inhibitors on keratinocytes in culture (11). The
epidermal hyperproliferation and inflammation characteristic of
IFN-
-transgenic animals was not affected by ZVAD-fmk, reinforcing
our earlier conclusions that these aspects of the skin phenotype are
independent of the kidney phenotype (4, 5).
SLE is characterized by an ill-defined dysregulation of apoptosis (12). Macromolecular complexes released during apoptosis are found in elevated levels in the serum of patients with the disease; circulating nucleosomes may trigger ANA production, and nucleosome-IgG antinucleosome complexes bind to the glomerular basement membrane (13). Subsequent in situ formation of immune complexes with anti-dsDNA results in complement activation, triggering a destructive inflammatory infiltration (13). Apoptosis plays a key role in linking glomerular injury to interstitial damage. Fas/Fas ligand (FasL)-mediated endothelial cell apoptosis in the peritubular capillaries is an early event in this process (14), and subsequent Fas-dependent apoptosis in the renal tubular epithelium may lead to tubular atrophy and progressive loss of renal function (15).
Consistent with our observations, inhibition of the Fas/FasL pathway by administration of anti-FasL Abs prevents renal disease from developing in the NZB/W F1 murine lupus model (16). In contrast, stimulation of the Fas receptor by anti-Fas mAb reduces autoantibody titers and prevents glomerulonephritis in MRL/gld mice (17). MRL mice are characterized by a genetic defect in the Fas/FasL system with consequent inhibition of immunocyte apoptosis (18), and thus it is not surprising that improvement in the lupus phenotype occurs when apoptosis is promoted. The relevance of such an effect to human disease is open to question, because the rate of immunocyte apoptosis is, if anything, increased in patients with SLE (12), and human subjects with loss of function mutations in the Fas/FasL system in general do not develop lupus (19).
ZVAD-fmk may be acting both systemically and locally to reduce renal
damage in IFN-
-transgenic mice. By decreasing the overall level of
apoptosis in these animals, as evidenced by reduced TUNEL
staining of the skin, the agent may reduce the rate of nucleosome
deposition in the glomeruli. This could result in attenuation of
glomerular damage (20), even in the presence of high
anti-dsDNA levels (e.g., mouse no. 9 in Table I
) and IgG deposits
in the glomeruli (Fig. 4
, E and F).
We have previously argued that apoptotic keratinocytes provide
the source of self-nuclear Ags driving ANA production in
IFN-
-transgenic animals (5). Although anti-dsDNA
levels normalized in four ZVAD-fmk-treated animals, it is unlikely that
removing the source of Ag would switch off a mature T cell-mediated
immune response within a matter of days, and indeed the autoantibody
titers in other mice suggest more complex changes. The reciprocal
relationship between anti-histone and anti-dsDNA levels in
individual transgenics (Ref. 4 and Fig. 3
) raises the
possibility of an idiotypic/antiidiotypic relationship
(21) that might be altered by ZVAD-fmk.
Apoptosis is a normal physiological process, and administration of caspase inhibitors in the long term could result in significant side effects. For this reason, experimental trials have tended to focus on acute conditions under which use of these agents is limited to a well-defined period (7, 8). SLE characteristically runs a relapsing/remitting course with acute exacerbations of both systemic and renal disease (2). Therefore, intensive treatment is pulsatile in the majority of patients, often requiring highly toxic drugs of limited efficacy (2). We propose that intermittent treatment with apoptosis inhibitors might find a role in such regimens.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Fiona M. Watt, Keratinocyte Laboratory, Imperial Cancer Research Fund, 44 Lincolns Inn Fields, WC2A 3PX, London, U.K. E-mail address: watt{at}icrf.icnet.uk ![]()
3 Abbreviations used in this paper: SLE, systemic lupus erythematosus; ANA, antinuclear Ab; ZVAD-fmk, carbobenzoxy-valyl-alanyl-aspartyl-(
-o-methyl)-fluoromethylketone; FasL, Fas ligand. ![]()
Received for publication April 27, 2001. Accepted for publication July 9, 2001.
| References |
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in the epidermis. J. Exp. Med. 186:1451.
T cells in the pathogenesis of murine lupus. J. Immunol. 162:7241.
. Immunol. Lett. 55:5.[Medline]
in the epidermis have eczema, hair hypopigmentation and hair loss. J. Invest. Dermatol. 108:412.[Medline]
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