Characterization of Sparstolonin B, a Chinese Herb-derived Compound, as a Selective Toll-like Receptor Antagonist with Potent Anti-inflammatory Properties

Abstract

Blockade of excessive Toll-like receptor (TLR) signaling is a therapeutic approach being actively pursued for many inflammatory diseases. Here we report a Chinese herb-derived compound, sparstolonin B (SsnB), which selectively blocks TLR2-and TLR4-mediated inflammatory signaling. SsnB was isolated from a Chinese herb, Spaganium stoloniferum; its structure was determined by NMR spectroscopy and x-ray crystallography. SsnB effectively inhibited inflammatory cytokine expression in mouse macrophages induced by lipopolysaccharide (LPS, a TLR4 ligand), Pam3CSK4 (a TLR1/TLR2 ligand), and Fsl-1 (a TLR2/TLR6 ligand) but not that by poly(I:C) (a TLR3 ligand) or ODN1668 (a TLR9 ligand). It suppressed LPS-induced cytokine secretion from macrophages and diminished phosphorylation of Erk1/2, p38a, IB␣, and JNK in these cells. In THP-1 cells expressing a chimeric receptor CD4-TLR4, which triggers constitutive NF-B activation, SsnB effectively blunted the NF-B activity. Co-immunoprecipitation showed that SsnB reduced the association of MyD88 with TLR4 and TLR2, but not that with TLR9, in HEK293T cells and THP-1 cells overexpressing MyD88 and TLRs. Furthermore, administration of SsnB suppressed splenocyte inflammatory cytokine expression in mice challenged with LPS. These results demonstrate that SsnB acts as a selective TLR2 and TLR4 antagonist by blocking the early intracellular events in the TLR2 and TLR4 signaling. Thus, SssB may serve as a promising lead for the development of selective TLR antagonistic agents for inflammatory diseases. Toll-like receptors (TLRs)2 are key components of innate immunity (1) expressed by macrophages, dendritic cells, and many other cell types (2, 3). TLRs serve as the first line of defense against invading pathogens such as bacteria and viruses. Currently more than a dozen TLRs have been identified, with the first nine being well characterized. Some TLRs, including TLR1, -2, -4, -5, and -6, are mainly located on the plasma membrane and recognize bacterial, fungal, and protozoan pathogens, whereas others, including TLR3, -7, -8, and -9, are mainly located on endosomal/lysosomal membranes where they bind viral RNAs or DNAs (4 -6). All TLRs use leucine-rich repeats to sense the ligands and the Toll/IL-1 receptor homologue (TIR) domain to trigger downstream signaling by binding to adaptor proteins MyD88 (7-9), TIRAP/Mal (10, 11), or TRIF (12, 13). The signaling initiated by TLRs is a double-edged sword. On the one hand, it may lead to confining or eliminating the invading organisms (14, 15); on the other hand, a prolonged and exaggerated response can cause tissue and organ damage (16,17). Moreover, TLR signaling triggered by exogenous or endogenous ligands contributes to the pathogenesis of many chronic inflammatory diseases (18). For example, TLR2 and TLR4 are involved in atherosclerosis (19,20), autoimmune colitis (21), systemic lupus erythematosus (22, 23), diabetes (24, 25), and Alzheimer disease (26,27). Thus, blockade of excessive TLR signaling is a therapeutic approach being actively pursu...

Contrasting Frustrated Lewis Pair Reactivity with Selenium‐ and Boron‐Based Lewis Acids

“…[24,25] Thes tructure of 4 consists of an isobenzofuran bicycle connected by ad ouble bond to an indene moiety.A lthough the isobenzofuran heterocycle and the indene ring are conjugated, they do not lie perfectly in the same plane in the solid state,w ith the angle between the two rings being 17.99(11)8 8.T he fact that this system does not lie in the same plane clearly reflects the steric constraints in the molecule, which is also revealed in the NMR data. In addition, the phenyl substituent in 4 also rotates out of the plane of the indene ring by 67.87(10)8 8,t hus permitting it to adopt an ear coplanar geometry (12.52(9)8 8)w ith one of the C 6 F 5 rings of the B(C 6 F 5 ) 3 moiety with acentroid···centroid distance of just 3.4785 (16) .T his value is somewhat shorter than that observed for other C 6 F 5 ···C 6 H 5 contacts (3.6421(10) ).…”

“…Here we compare the reactivity of methyl-2-{[2-(phenylethynyl)phenyl]ethynyl} benzoate (1) with the soft Se-centered Lewis acid PhSeCl and the hard Bcentered Lewis acid B(C 6 F 5 ) 3 in the pursuit of obtaining novel heterocyclic frameworks such as isocoumarin derivatives. Indeed, isocoumarins are well known for their biological activity and their derivatives have many applications as antimicrobial, [14] anticancer, [15] and anti-inflammatory [16] agents etc. [17] Thed iyne starting material 1 was prepared by ap alladium-catalyzed cross-coupling reaction according to literature procedures.…”

Gegensätzliche Reaktivität frustrierter Lewis‐Paare mit Selen‐ und Bor‐basierten Lewis‐Säuren

“…Viele dieser Elemente sind auch in der Lage gleichzeitig als Lewis-Säuren (durch niedrig liegende freie Orbitale oder s*-Orbitale) und als Lewis-Basen (aufgrund freier Elektronenpaaren im nÀ2-oder nÀ4-Oxidationszustand) zu wirken. Wirv ergleichen hier die Reaktivitätv on Methyl-2-{[2-(phenylethinyl)phenyl]ethinyl}-benzoat (1)m it der weichen Selen-Lewis-Säure PhSeCl, und der harten Bor-Lewis-Säure B(C 6 F 5 ) 3 in der Synthese neuer heterocyclischer Verbindungen wie beispielsweise Isocumarinderivate.I socumarine sind füri hre biologische Aktivität bekannt und haben unter anderem viele Anwendungen als antimikrobielle, [14] Antikrebs- [15] und als entzündungshem-mende [16] Mittel.…”

“…Die Tatsache, dass diese Ringe nicht in der gleichen Ebene liegen, spiegelt deutlich die sterische Einschränkung im Molekülw ider, die sich auch in den NMR-Daten offenbart. Außerdem dreht sich der Phenylsubstituent in 4 auch aus der Ebene des Indenrings heraus (67.87 (10)8 8), was eine nahezu coplanare Geometrie (12.52(9)8 8)m it einem der C 6 F 5 -Ringe der B(C 6 F 5 ) 3 -Einheit mit einem Zentroid···Zentroid-Abstand von nur 3.4785 (16) ermçglicht, der etwas kleiner ist als bei anderen C 6 F 5 ···C 6 H 5 -Kontakten (3.6421(10) ).…”

Total synthesis of Sparstolonin B, a potent anti-inflammatory agent

“…[1][2][3] TLRs play an essential part in the perception of microbes and shape the complex host responses that occur during infection. 4 However, the signalling initiated by TLRs is a double-edged sword since a prolonged and exaggerated response can cause tissue and organ damage.…”