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Arch Dermatol Res (2004) 296:97–104
DOI 10.1007/s00403-004-0480-5
ORIGINAL PAPER
Meenakshi S. Venkatraman · Amar Chittiboyina ·
Josef Meingassner · Christopher I. Ho · James Varani ·
Charles N. Ellis · Mitchell A. Avery ·
Harrihar A. Pershadsingh · Theodore W. Kurtz ·
Stephen C. Benson
a-Lipoic acid-based PPARg agonists
for treating inflammatory skin diseases
Received: 7 November 2003 / Revised: 20 April 2004 / Accepted: 6 May 2004 / Published online: 24 June 2004
Springer-Verlag 2004
Abstract Novel thiazolidinedione derivatives of the po-
tent antioxidant, a-lipoic (thioctic, 1,2-dithiolane) acid,
were prepared. The prototype N-(2-{4-[2,4-dioxo(1,3-thi-
azolidin-5-yl)methyl]phenoxy}ethyl)-5-(1,2-dithiolan-3-
yl)-N-methylpentanamide (designated BP-1003), and di-
thioester derivatives thereof were shown to be potent ac-
tivators of peroxisome proliferator-activated receptor
gamma (PPARg) (EC
50
range 15–101 nM) and modest
activators of PPARa (EC
50
5 mM). Both the relatively
hydrophobic dithiolane prototype, BP-1003, and its water-
soluble dithioglycinate derivative, BP-1017, were shown
to inhibit the proliferation of human keratinocytes and
suppress the production of interleukin-2 by human pe-
ripheral lymphocytes to a greater extent than the antidia-
betic thiazolidinedione, rosiglitazone. Both oral and topi-
cal administration of BP-1017 showed significant antiin-
flammatory effects in the oxazolone-sensitized mouse
model of allergic contact dermatitis (ACD). These find-
ings suggest that water-soluble lipoic acid-based thiazo-
lidinediones may be efficacious as oral and topical agents
for treating inflammatory skin conditions such as contact
dermatitis, atopic dermatitis, and psoriasis.
Keywords Thiazolidinedione · Peroxisome
proliferator-activated receptor-g · a-Lipoic acid ·
Inflammation · Dermatitis · Psoriasis
Abbreviations ACD: Allergic contact dermatitis ·
ATCC: American Type Culture Collection · FRET:
Fluorescence resonance transactivation · LBD: Ligand
binding domain · LDH: Lactate dehydrogenase ·
PBMC: Peripheral blood mononuclear cells ·
PHA: Phytohemagglutinin · PPARg: Peroxisome
proliferator-activated receptor-gamma · TZD:
Thiazolidinedione
M. S. Venkatraman · A. Chittiboyina · M. A. Avery
Department Medicinal Chemistry,
University of Mississippi,
University, MS, USA
J. Meingassner
Novartis Forschungsinstitut GmbH,
Vienna, Austria
C. I. Ho · S. C. Benson (
)
)
Department of Biological Sciences,
California State University,
25800 Carlos Bee Blvd, Hayward, CA 94542, USA
e-mail: sbenson@csuhayward.edu
Tel.: +1-510-8853470
Fax: +1-510-8854747
J. Varani
Department of Pathology,
University of Michigan Medical School,
Ann Arbor, MI, USA
C. N. Ellis
Department of Dermatology,
University of Michigan Medical School,
Ann Arbor, MI, USA
H. A. Pershadsingh
Department of Family Medicine,
Kern Medical Center,
Bakersfield, CA, USA
H. A. Pershadsingh
Department of Family Medicine,
University of California,
Irvine, CA, USA
T. W. Kurtz
Bethesda Pharmaceuticals, Inc,
Bakersfield, CA, USA
T. W. Kurtz
Department of Laboratory Medicine,
University of California,
San Francisco, CA, USA
Introduction
The thiazolidinediones (TZDs) are under continuing de-
velopment as insulin-sensitizing pharmacological agents
for the treatment of type 2 (non-insulin-dependent) dia-
betes mellitus [1]. TZDs are high-affinity ligands for the
nuclear receptor, peroxisome proliferator-activated re-
ceptor-gamma (PPARg), a transcription factor that regu-
lates genetic programs involved in glucose and lipid ho-
meostasis, energy metabolism, and adipocyte growth and
differentiation [2]. In addition to regulating lipid and
glucose metabolism, PPARg ligands exert antiinflamma-
tory and antiproliferative effects through their ability to
influence an array of important signaling pathways [3, 4].
Although TZDs have actions unrelated to PPARg, such as
their ability to block voltage-sensitive [5] and receptor-
operated calcium channels [6], their cellular effects ap-
pear to be largely mediated through PPARg activation [1,
2]. Thus, PPARg appears to be an important molecular
target in the development of drugs for the treatment of
diverse endocrine, proliferative and inflammatory dis-
eases [3, 4, 7].
We have previously shown that the antidiabetic TZD
troglitazone improves psoriasis and normalizes models of
inflammatory, proliferative skin disease [8, 9]. Troglita-
zone has the interesting feature of including an antioxi-
dant a-tocopherol headgroup attached to the TZD back-
bone. We designed and synthesized a unique class of
TZDs by linking the antioxidant vitamin, a-lipoic acid
(thioctic, 1,2-dithiolane pentanoic acid) to benzoxy-TZD.
Herein, we report that the prototype, N-(2-{4-[2,4-di-
oxo(1,3-thiazolidin-5-yl)methyl]phenoxy}ethyl)-5-(1,2-
dithiolan-3-yl)-N-methylpentanamide (known as BP-
1003) and its water-soluble dithioglycinate analog (BP-
1017) strongly activate PPARg, and moderately activate
PPARa, and that these drugs can inhibit both the prolif-
eration of cultured human keratinocytes and the produc-
tion of interleukin-2 (IL-2) by activated peripheral lym-
phocytes. The water-soluble derivative BP-1017 showed
significant antiinflammatory properties in a mouse model
of allergic contact dermatitis (ACD). These findings
suggest that lipoic acid-based TZD ligands for PPAR may
be useful in the treatment of diseases involving inappro-
priate keratinocyte proliferation and T lymphocyte acti-
vation such as psoriasis and atopic dermatitis.
Materials and methods
Experimental compounds
The dithiolane thiazolidinedione prototype derivative N-(2-{4-[2,4-
dioxo(1,3-thiazolidin-5-yl)methyl]phenoxy}ethyl)-5-(1,2-dithiolan-
3-yl)-N-methylpentanamide (designated BP-1003) and other di-
thioester analogs are shown in Fig. 1.
Cell Culture
Murine 3T3-L1 preadipocytes (CCL-173) and CV-1 monkey epi-
thelial cells (CCL-70) were from ATCC (Bethesda, Md.), and
human neonatal keratinocytes were obtained from Clonetics
(Walkersville, Md.).
PPAR activation assays
PPAR activity was determined by either cell-based transactivation
assays (PPARg) or by fluorescence resonance energy transfer
(FRET) assays (PPARg, PPARa and PPARd). For the cell-based
transactivation assay, CV-1 cells were maintained in Dulbecco’s
modified Eagle’s medium (DMEM) supplemented with 5% (v/v)
Cosmic calf serum (Hyclone, Logan, Utah) and antibiotics. The
cells were plated at 210
5
cells/well in 24-well dishes. The medium
was replaced 24 h after plating with DMEM containing 0.5% (v/v)
charcoal-dextran-treated fetal bovine serum (Hyclone), and 24 h
later the cells were transfected with 200 ng PPARg receptor ex-
pression plasmid pGAL4-mPPARg LBD, 1 mg luciferase reporter
plasmid pUAS-tk-luc and 400 ng pCMVSport b-gal (Gibco, Grand
Island, N.Y.) as an internal control. Transfections were performed
using the GenePorter reagent (Gene Therapy Systems, San Diego,
Calif.) according to the manufacturer’s instructions. Cells were
treated 24 h after transfection with the ligand and incubated for an
additional 24 h. Cell extracts were prepared and assayed for luci-
ferase and beta-galactosidase activity using the Promega (Madison,
Wis.) luciferase and beta-galactosidase assay systems according to
the manufacturer’s instructions. All treatments were performed in
triplicate, and normalized for b-galactosidase activity. FRET assays
were performed using human constructs for PPARa, PPARd and
PPARg. Ligand concentrations yielding half-maximal activation
(EC
50
values) were calculated using GraphPad Prism version 3.03
(GraphPad Software, San Diego, Calif.).
Fig. 1 Structural formulae of
the pioglitazone, rosiglitazone,
and lipoic acid-based thiazo-
lidinedione derivatives shown
in Table 1
98
Adipocyte differentiation assay
Differentiation assays on preadipocytes were performed by a
modification of the technique described by Smith et al. [10]. In
brief, murine 3T3-L1 cells were plated in DMEM with 5% calf
serum and grown to confluence. After reaching confluence, cells
were incubated in DMEM containing 1.0 mmol/l dexamethasone,
5 mg/ml insulin and 0.5 mmol/l 1-methyl-3-isobutylxanthine with
5% calf serum for 32 h, after which the cells were washed with PBS
and incubated in medium containing the test compound or vehicle,
DMSO (dimethyl sulfoxide). Five days after treatment, cells were
fixed with 10% formalin in PBS and stained with Oil Red O.
Keratinocyte proliferation assay
For proliferation studies, keratinocytes were maintained in kerati-
nocyte growth medium (BioWhittaker, Walkersville, Md.), a low-
calcium (0.15 mM) modification of MCDB-153 medium, supple-
mented with several growth factors, including human recombinant
epidermal growth factor (0.1 ng/ml), insulin (2.5 mg/ml), and 2%
(v/v) pituitary extract. Cells were plated in 24-well dishes at 210
4
cells/well, and 24 h after attachment, the test compound or DMSO
vehicle was added. Control and treated keratinocytes were incu-
bated for 6 days, with one medium change at day 3. Relative cell
numbers were determined in four replicates of each concentration
using the MTS assay as described in the CellTiter 96 Aqueous Non-
Radioactive Cell Proliferation Assay (Promega).
Lymphocyte activation and IL-2 production
T lymphocyte activity was determined as IL-2 production by hu-
man peripheral blood mononuclear cells (PBMCs). Cells were
isolated from the blood of healthy volunteers by Ficoll density
gradient centrifugation, cultured for 24 h in 1 ml RPMI-1640 me-
dium supplemented with glutamine (2 mM), penicillin G (100 U/
ml), streptomycin (100 mg/ml) and 10% (v/v) FBS at 310
6
cells
per well in the presence or absence of test compounds. The cells
were activated 16 h later by exposure to phytohemagglutinin (PHA,
10 mg/ml) and phorbol myristate acetate (PMA, 10 ng/ml) and
cultured for an additional 16 h. The medium was collected and
assayed for IL-2 concentration using a commercial ELISA kit
(R&D Systems).
Effects on ACD
The antiinflammatory effects of topical and oral administration of
BP-1003 and BP-1017 were tested in a mouse model of ACD [11].
ACD was elicited in oxazolone-sensitized NMRI mice with 10 mlof
oxazolone applied to the right ears of 8 to 16 mice per group; the
left ears remained unchallenged. In studies of the antiinflammatory
effects of topically administered BP-1003 or BP-1017, 2% (w/v)
oxazolone was applied; in studies of the antiinflammatory effects of
orally administered compounds, 0.5% (w/v) oxazolone was applied.
ACD was assessed by determining the extent of inflammatory
pinnal swelling by comparison of the weights of both ears in ani-
mals treated with either the test compounds or in negative controls
treated with vehicle only. Positive controls were also included by
treating additional animals with pimecrolimus (SDZ ASM 981), an
ascomycin macrolactam derivative with well-established anti-in-
flammatory properties [11]. Oral treatments were administered
twice (2 h before and concomitant with oxazolone challenge). The
oral doses tested were 30, 10, and 3 mg/kg body weight. In the
topical studies, the treatments were performed once to the right ear,
30 min after oxazolone challenge, using a drug concentration of
1mM. Compounds were dissolved in a mixture of acetone, ethanol,
and dimethylacetamide 1:1:1 and applied in minimal (10 ml) vol-
umes. In all animal experiments, the guidelines in NIH publication
no. 85-23, revised 1985, were followed.
Cytotoxicity assay
Keratinocyte and lymphocyte viability were assessed by LDH re-
lease following 24- and 48-h exposures to PPARg ligands. The
amount of LDH released was determined using a CytoTox 96 non-
radioactive cytotoxicity assay kit (Promega).
Statistical analysis
The results were analyzed using Student’s t-test or ANOVA fol-
lowed by Student-Newman-Keuls testing with statistical signifi-
cance defined as P<0.05.
Results
Structure and relative solubility
of lipoic acid-based TZD derivatives
The structures of rosiglitazone, pioglitazone, and novel
dithiolane-TZD, dithiol-TZD and dithioester-TZD deri-
vatives are shown in Fig. 1. The relative solubilities of the
TZDs were estimated by calculating the oil-water partition
function, C logP. BP-1003 was more hydrophobic than
either rosiglitazone or pioglitazone. The dithiolane ring
was esterified to form various dithioester-TZD derivatives
to increase water solubility. The dithiol- and dithioacetate-
TZD derivatives (BP-1008 and BP-1009) had water sol-
ubilities similar to those of pioglitazone and rosiglitazone,
whereas the dithiosuccinate- and dithioglycinate-TZD
derivatives (BP-1010 and BP-1017) had water solubilities
greater than those of pioglitazone and rosiglitazone (Ta-
ble 1). BP-1017 (dithioglycinate) was most water soluble,
giving it the potential for improved bioavailability,
whereas BP-1009 (dithioacetate) and BP-1010 (dithio-
succinate) had intermediate solubilities, making them po-
tential candidates for topical application.
PPAR transactivation
by a-lipoic acid-based TZD derivatives and induction
of adipocyte differentiation
We first tested the ability of a-lipoic acid-based TZD
derivatives to activate PPARg in a heterologous transac-
tivation assay that eliminates interference from endoge-
nous nuclear receptors. Figure 2 illustrates a typical dose-
response result for BP-1003 and BP-1017 compared to
Table 1 Solubility values (C logP) and potency values for acti-
vating PPARg (EC
50
) of lipoic acid-based TZD derivatives com-
pared to pioglitazone and rosiglitazone
Compound C logP EC
50
(nM)
Pioglitazone 3.53 906
Rosiglitazone 3.02 302
BP-1003 (dithiolane) 4.00 16
BP-1008 (dithiol) 3.30 30
BP-1009 (dithioacetate) 3.25 101
BP-1010 (dithiosuccinate) 2.30 50
BP-1017 (dithioglycinate) 1.23 66
99
pioglitazone and rosiglitazone. An identical analysis was
conducted for the other BP compounds. All BP com-
pounds tested were full agonists of PPARg and were more
potent than pioglitazone and rosiglitazone (Table 1). BP-
1003 was 18 times more potent (EC
50
16 nM) than
rosiglitazone (EC
50
302 nM; Table 1). PPAR activation
data obtained in the cell-free FRET assay yielded results
similar to those obtained in the cell-based transactivation
assay. FRET proximity analyses for activation of PPARg
by BP-1003 and BP-1017 yielded EC
50
values of 1 nM for
both compounds. The EC
50
for PPARa by FRET analysis
was 5 mM also for both compounds, more than three or-
ders of magnitude higher than the EC
50
values for
PPARg. The EC
50
for PPARd by FRET analysis was
determined to be greater than 10 mM for both BP-1003
and BP-1017. Thus both BP-1003 and BP-1017 appear to
be strongly selective for PPARg
Ligand-activated PPARg is required for differentiation
of adipose tissue in vivo and in vitro [12]. Murine 3T3 L1
preadipocytes expressing PPARg were treated with 2 mM
BP-1003, BP-1017, or rosiglitazone, and were observed to
undergo differentiation to Oil Red O-positive adipocytes
(Fig. 3). This demonstrates that these two novel TZDs are
capable of causing functional activation of the endoge-
nous PPARg receptor.
Effect of lipoic acid-based TZD derivatives
on keratinocyte growth
Proliferating cultures of normal human keratinocytes
were treated with rosiglitazone, BP-1003 or BP-1017 as
described in Materials and methods. After 6 days expo-
sure to drug, the relative cell numbers were determined by
the MTS assay. Rosiglitazone, BP-1003 and BP-1017 all
inhibited keratinocyte growth in a dose-dependent man-
ner (Fig. 4). The rank-order for the inhibitory effect of
these compounds on keratinocyte proliferation was BP-
1003>BP-1017>rosiglitazone. At all concentrations test-
ed, the BP compounds were more effective at inhibiting
Fig. 2 BP-1003 and BP-1017 are potent PPARg agonists. Trans-
activation of the GAL4-PPARg chimeric receptor by BP-1003, BP-
1017, rosiglitazone and pioglitazone in transiently transfected CV-1
cells. Cells were treated with the indicated concentrations of ligand
for 24 h and normalized total luciferase activity determined (n
rosiglitazone, o pioglitazone, l BP-1003, s BP-1017)
Fig. 3A–D BP-1003 and BP-
1017 induce adipogenesis in
3T3-L1 murine preadipocytes.
Confluent cultures were treated
with insulin, dexamethasone
and IBMX for 32 h. The cells
were then treated with vehicle
(DMSO) or 2 mM of the indi-
cated compound for 5 days.
Following fixation with 10%
formalin in PBS, the cells
were stained with Oil Red O
(A vehicle, 0.004% v/v DMSO;
B rosiglitazone; C BP-1003;
D BP-1017)
100
keratinocyte proliferation than rosiglitazone. At lower
concentrations (0.01–1 mM), BP-1003 was significantly
more effective than BP-1017 while the two compounds
showed similar efficacy at higher concentrations. At the
concentrations tested, none of the compounds appeared
cytotoxic as determined by LDH release into the medium
(data not shown). Removal of medium containing BP-
1003 and BP-1017 resulted in resumption of proliferation,
further confirming the non-injurious nature of these
compounds at the concentrations used.
Effects of BP-1003 and BP-1017 on IL-2 production
by lymphocytes
Human PBMCs are enriched in T lymphocytes. The in-
hibitory effects of BP-1003, BP-1017 and rosiglitazone on
T lymphocyte activation were measured as their ability to
inhibit IL-2 production in PMA/PHA-activated PBMCs
(Table 2). All three compounds significantly inhibited IL-
2 production in a dose-dependent manner. At 10 mM the
inhibitory effects of BP-1003 and BP-1017 (about 90%)
significantly exceeded that of rosiglitazone (75%).
Effects of BP-1003 and BP-1017 on ACD
BP-1003 did not show a significant antiinflammatory ef-
fect when administered either orally or topically in the
ACD mouse model. In contrast, the more water-soluble
molecule, BP-1017, showed significant antiinflammatory
effects with both topical and oral administration (Fig. 5).
Topically applied BP-1017 at 1 mM was associated with
significant inhibition of pinnal swelling (22€4%) although
the effect was less than that observed (37€5%) with top-
ically applied pimecrolimus (SDZ ASM 981), an as-
comycin macrolactam derivative that has been clinically
approved for the topical treatment of atopic dermatitis.
Oral administration of BP-1017 also caused significant
inhibition of pinnal swelling, even at the lowest dose
tested (3 mg/kg, Fig. 5). In contrast, the pimecrolimus
compound approved only for topical use showed no anti-
inflammatory effects at this same oral dose (Fig. 5).
Discussion
The PPARs (a, g and d isoforms) have been under in-
tensive investigation ever since PPARg was identified as
the intracellular high-affinity receptor for the antidiabetic
TZDs [13]. Troglitazone, the first TZD approved in the
USA for the treatment of type 2 diabetes, was later
withdrawn from the market because of liver toxicity. Two
other TZDs, rosiglitazone (Avandia) and pioglitazone
(Actos), marketed since 1999, appear to be free from
hepatotoxicity.
Although originally developed as insulin-sensitizing
agents, TZDs were later shown to have antiinflammatory
[3, 4, 9] and immunomodulatory effects [14, 15, 16].
These compounds also exert antiproliferative effects by
inducing cell cycle withdrawal through G
1
arrest [17] and
by transforming cells from their proliferative (synthetic)
phenotype to their terminally differentiated, mature
(metabolic) phenotype [18].
Ligand activation of PPARg has been shown to inhibit
the production of inflammatory molecules, including IL-
Fig. 4 Inhibitory effect of BP-1003 (shaded bars), BP-1017 (open
bars) and rosiglitazone (filled bars) on keratinocyte proliferation.
Proliferating cultures of normal human keratinocytes in serum-free
growth medium were treated with vehicle, rosiglitazone, BP-1003,
or BP-1017, as described in Materials and methods. After 6 days
exposure to drug, the relative cell numbers were determined
spectrophotometrically using the MTS assay. Rosiglitazone, BP-
1003 and BP-1017 all inhibited keratinocyte growth in a dose-
dependent manner. Data points are means€SEM of quadruplicate
replicate determinations. *P<0.05 vs rosiglitazone, **P<0.05 BP-
1017 vs BP-1003, by ANOVA and Student-Newman-Keuls test
Table 2 Inhibitory effect of
lipoic acid-based TZD deriva-
tives on IL-2 release by human
lymphocytes. Values are mean-
s€SEM of four determinations
in one experiment
Drug and concentration (mM) IL-2 released (pg/ml) Inhibition (%)
Control (no drug) 459€20 –
Rosiglitazone 1 406€12 12
10 114€5* 75
BP-1003 1 362€17
*
22
10 39€5
**
92
BP-1017 1 339€21
*
26
10 45€7** 90
*P<0.05 vs control, **P<0.05 vs control and vs rosiglitazone, by ANOVA and Student-Newman-Keuls
test
101
1b, IL-2, IL-6, tumor necrosis factor-a, interferon-g, nu-
clear factor-kB, inducible nitric oxide synthase, and pro-
teases such as matrix metalloproteinase-9 (gelatinase B)
[3, 4, 14, 15, 16, 19]. Yang et al. [20] have demonstrated
that troglitazone inhibits the activity of NFAT (nuclear
factor of activated T cells) which regulates the IL-2
promoter and downstream IL-2 production by T lym-
phocytes. IL-2 is a key inflammatory component of dis-
orders such as psoriasis, multiple sclerosis and Alzhei-
mer’s disease, in which TZDs have been shown to have
potential therapeutic effects [7, 8, 9, 14, 15, 20, 21, 22].
a-Lipoic acid is a potent antioxidant found endoge-
nously as lipoamide in eukaryotic dehydrogenases where
it is covalently bound to a lysyl residue [23]. Exogenously
supplied lipoic acid is taken up readily by a variety of cells
and tissues where it is reduced rapidly to dihydrolipoic
acid [24]. Unmodified a-lipoic acid has been reported to
have antiinflammatory and cytoprotective effects [24]. In
the study reported here, we demonstrated the feasibility of
linking the methoxybenzyl-2,4-thiazolidinedione moiety
of existing TZDs to lipoic acid via an amide bridge. This
structure provides a flexible scaffold for synthesizing di-
thioester prodrugs or other thiol-based derivatives with a
wide constellation of pharmacokinetic properties including
variable water solubility as illustrated in Table 1.
The pathogenesis of inflammatory skin diseases is
known to be associated with altered signal transduction
pathways involved in keratinocyte proliferation and cu-
taneous T cell-mediated inflammation [25]. We have
previously reported that troglitazone normalizes models
of proliferative skin disease, inhibits keratinocyte prolif-
eration, and improves psoriasis in nondiabetic patients [8,
9]. Similar findings have been observed in pilot studies of
nondiabetic psoriatic patients treated with rosiglitazone
(Pershadsingh et al., unpublished observations) or pi-
oglitazone [22].
In the current studies, we found that both BP-1003 and
BP-1017 are potent activators of PPARg (Table 1). Both
compounds inhibited keratinocyte proliferation (Fig. 3)
and IL-2 production by T lymphocytes (Table 2) to a
greater extent than rosiglitazone. It is important to note
that these results do not conclusively demonstrate that the
effects of these compounds on inflammation and prolif-
eration are due to the activation of PPARg. This obser-
vation is particularly relevant since thiazolidinediones
have been shown to have PPARg-dependent and -inde-
pendent effects on inflammatory responses in macro-
phages [26]. However, these findings do indicate that BP-
1003 and BP-1017 may be efficacious as antiinflamma-
tory and antiproliferative agents. The water-soluble pro-
drug, BP-1017, was also found to exert significant anti-
inflammatory effects when administered either orally or
topically in the mouse model of ACD.
Taken together, these findings suggest that BP-1017
may be effective as a topical or oral agent for treating
contact dermatitis, atopic dermatitis and psoriasis. The
current findings should also motivate future studies of the
extent to which the antiproliferative and antiinflammatory
effects of these compounds can be attributed to their an-
tioxidant lipoic acid moieties versus their ability to acti-
vate PPARg. Preliminary studies suggest that at least in
the mouse model of ACD, the lipoic acid moiety may be
an important determinant of the antiinflammatory effects
of these compounds (unpublished observations). If so, the
inclusion of the antioxidant moiety in these molecules
may extend their clinical utility beyond that of conven-
tional PPARg ligands.
Fig. 5 Antiinflammatory effects determined in the mouse model of
ACD. The antiinflammatory effects of topical and oral adminis-
tration of BP-1003 and BP-1017 were tested in a mouse model of
ACD. ACD was elicited in oxazolone-sensitized NMRI mice with
10 ml oxazolone applied to the right ears; left ears remained un-
challenged. In studies of the antiinflammatory effects of topically
administered BP-1003 or BP-1017, 2% (w/v) oxazolone was ap-
plied; in studies of the antiinflammatory effects of orally admin-
istered compounds, 0.5% (w/v) oxazolone was applied. ACD was
assessed by determining the extent of inflammatory pinnal swelling
by comparison of the weights of both ears in animals treated with
either the test compounds or vehicle only. Positive controls were
animals treated with pimecrolimus. Oral treatments were adminis-
tered twice (2 h before and concomitant with oxazolone challenge).
Top effect of topical administration, bottom effect of oral admin-
istration. **P<0.01, *P<0.05, vs vehicle-treated controls by t-test;
***P<0.01, vs vehicle-treated controls and BP-1017;
#
P<0.05, vs
pimecrolimus
102
The finding that the hydrophobic BP-1003 was inef-
fective in the ACD model, whereas the hydrophilic BP-
1017 compound was effective whether administered
orally or topically, suggests that administering a-lipoic
acid-based thiazolidinedione derivatives as the water
soluble pro-drugs such as BP-1017 may be important for
enhanced bioavailability. This finding underscores the
flexibility and convenience of synthesizing compounds by
thioesterification of the dithiolane/dithiol scaffold to
produce the desired pro-drug. The glycinate residues
would be cleaved away during metabolism to yield the
lipoic acid/dihydrolipoic acid couple as a functional an-
tioxidant adduct.
Water solubility is but one of the characteristics that
can be explored, as in the case of BP-1017. In addition it
should be possible to exploit the dithiolane/dithiol scaf-
fold to produce “caged” compounds or hybrid (bifunc-
tional) compounds designed for controlled delivery to
specific tissue targets. In this regard, it is of interest to
note that others have shown that the 1,2-dithiolane-3-
pentyl moiety of lipoic acid can function as the “targetor
moiety” for drug targeting to lung tissue [27]. Given that
regulation of PPARg expression in the airway has been
proposed as a therapeutic target in the treatment of asthma
[28] and that PPARg agonists are reported to be associ-
ated with improvement of asthma via downregulation of
allergic inflammation and eosinophil activation [29, 30],
these dithioester-TZD compounds may be useful for
treatment of lower airway diseases by topical delivery
(i.e., by inhalation).
The clinical potential of TZDs has been demonstrated
in nondermatological inflammatory, proliferative diseases
with related immunopathophysiological mechanisms.
Examples include atherosclerosis [31], prevention of
vascular restenosis [32], ulcerative colitis [33], chorio-
retinal neovascularization [34, 35], Alzheimer’s disease
[21] and multiple sclerosis [36]. The current results sug-
gest the potential utility of lipoic acid-based TZD
derivatives for the treatment of inflammatory, prolifera-
tive skin diseases such as psoriasis, contact dermatitis and
atopic dermatitis, and perhaps other inflammatory dis-
eases as well.
Acknowledgements This work was supported by NIH grant
2R42AR44767-02A2 (Bethesda Pharmaceuticals), grants from
Bethesda Pharmaceuticals, Inc. (M.V., A.C.), and a Joint Venture
grant between Bethesda Pharmaceuticals and the California State
University Program for Education and Research in Biotechnology
(S.B.).
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