Ibrahim Jantan et al.
Immunomodulatory effects of diarylpentanoids
agent (myeloperoxidase–H2O2–Cl- system). MPO is also
involved in the production of highly toxic nitric oxides
(NO).[5] Besides the defensive roles during the infections,
when excessively or inappropriately deployed the phagocyte–
microbe interactions can damage host tissues and contribute
to the pathogeny of various immune and non-immune
chronic inflammatory diseases, including some rheumatoid
disorders. Therefore, inhibitors of phagocyte reactive oxygen
species (ROS) production can be used in the treatment of a
variety of disorders, including inflammation.[6]
A series of 43 diarylpentanoids has been synthesized based
on the chemical structure of curcumin by eliminating the
b-diketone and modifying it into conjugated double bonds,
i.e. two identical aromatic ring regions separated by five
carbon linkers. To the best of our knowledge, curcumin-
related diarylpentanoid analogues have not been investigated
for their immunomodulatory effects. We therefore evaluated
these compounds for their effects on the ROS production of
human whole blood and isolated PMNs, and chemotaxis of
PMNs induced by the bacterial peptide N-formyl-methionyl-
leucyl-phenylalanine (fMLP).
Curcumin
(1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,
6-heptadiene-3,5-dione) is the most studied curcuminoid
of the species Curcuma. Curcumin is well known for its
anti-inflammatory effects and over the past few decades
its numerous biological and pharmacological activities
have been reported.[7,8] Curcumin has been shown to
inhibit the metabolism of arachidonic acid and the activities
of cyclooxygenase-2 (COX-2), lipoxygenase, proinflamma-
tory cytokines,inducible nitric oxide (iNOS),protein kinases,
transcription factors such as nuclear factor-kB and release
of steroids.[9–11] Other activities of curcumin include inhi-
bition of low-density lipoprotein oxidation, reduction of
blood cholesterol level, inhibition of platelet aggregation,
suppression of thrombosis and myocardial infarction, treat-
ment of rheumatoid arthritis, inhibition of HIV replication,
protection from liver injury, as well as anticancer and immu-
nomodulatory activities.[12–14]
Curcumin is known to have a poor bioavailability, as
orally administered curcumin undergoes hepatic conjuga-
tion, leading to the formation of glucoronides and sulphates,
and systematic administration causes it to undergo reduc-
tion.[15] Many studies have been carried out to improve the
bioavailability of curcumin by modifying its molecular struc-
ture, i.e. eliminating the unstable b-diketone moiety and
modifying the heptadiene linker while retaining the phenolic
OH groups.[16,17] The presence of the b-diketone moiety will
result in rapid metabolism by aldo-keto reductase in the liver,
thus limiting the beneficial effects of curcumin on many
types of disease. Various curcumin analogues have been syn-
thesized and evaluated for activity against known biological
targets in order to investigate their structure–activity rela-
tionships (SAR). Recent SAR studies on curcumin analogues
have demonstrated anti-inflammatory, anticancer, antioxi-
dant, anti-tyrosinase and antiosteoporosis properties.[17–20]
The presence of phenolic OH on both phenyl ring structures
has been shown to be important for antioxidant activity.[21]
Our previous studies on synthesized diarylpentanoids and
pyrazoline derivatives have revealed that these compounds
inhibit NO production in IFN-gLPS-activated RAW 264.7
and U937 cells. More importantly, one of the compounds
suppressed both the iNOS gene and enzyme expression while
displaying a strong inhibitory effect on MCP-1 and IL-10
secretion and gene expression.[22,23]
Materials and Methods
Chemicals and equipment
Serum opsonized zymosan A (Sacromyces cerevisae sus-
pensions and serum), luminol (3-aminophthalhydrazide),
phosphate buffer saline tablet (PBS), Hanks balance salt
solutions (HBSS++), fetal calf serum (PAA Laboratories,
USA), Ficoll, Hanks balance salt solution (HBSS–), N-formyl-
methionylleucyl-phenylalanine (fMLP), acetyl salicylic acid
(purity > 99%), ibuprofen (purity > 99%), dimethylsulfox-
ide (DMSO), methanol and ammonium chloride of analyti-
cal grades were purchased from Sigma (St Louis, MO, USA).
Chemiluminescense measurements were carried out on a
Luminoskan Ascent luminometer (Thermo Scientific, UK).
fMLP was stored as a stock solution of 108 m in DMSO at
-80°C and diluted in Hanks solution prior to assay. Haema-
toxylin and xylene for staining were obtained from BDH
(UK). A Boyden 48-well chamber with a 2 mm polycarbonate
membrane filter separating the upper and lower compart-
ments was purchased from Neuro Probe (Cabin John, MD,
USA). A CO2 incubator (Shell Lab, USA) and light micro-
scope (Leitz Watzler, Germany) were used in this assay.
Synthesis of diarylpentanoid analogues
The diarylpentanoid analogues of curcumin were synthe-
sized by direct coupling of the appropriate aromatic aldehyde
with the three ketones, acetone (1–17), cyclohexanone
(18–33) or cyclopentanone (34–43) at a molar ratio of 1 : 2,
using the base-catalysed Claisen–Schmidt condensation
reaction. Figure 1 illustrates the general synthesis of diaryl-
pentanoids. Briefly, the appropriate aromatic aldehyde
(20 mmol, 2 equiv.) and the appropriate ketone (10 mmol, 1
equiv.) were mixed and dissolved in 15 ml of ethanol and
stirred at 5°C for a few minutes. Four drops of 40% NaOH
solution in ethanol was added dropwise over several minutes.
The mixture was stirred at room temperature for 10 h.
The reaction was neutralized with dilute HCl to form a pre-
cipitate, which was subjected to further purification by
recrystallization from appropriate solvents or column chro-
matography. The structures of the synthesized compounds
© 2011 The Authors. JPP © 2011
Royal Pharmaceutical Society 2012 Journal of Pharmacy and Pharmacology, 64, pp. 404–412
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