Helenalin

J Biol Chem. 1998 Dec 11;273(50):33508-16.

The anti-inflammatory sesquiterpene lactone helenalin inhibits the transcription factor NF-kappaB by directly targeting p65.[Pubmed: 9837931]

The sesquiterpene lactone Helenalin is a potent anti-inflammatory drug whose molecular mechanism of action remains unclear despite numerous investigations. We have previously shown that Helenalin and other sesquiterpene lactones selectively inhibit activation of the transcription factor NF-kappaB, a central mediator of the human immune response. These drugs must target a central step in NF-kappaB pathway, since they inhibit NF-kappaB induction by four different stimuli. It has previously been reported that sesquiterpene lactones exert their effect by inhibiting degradation of IkappaB, the inhibitory subunit of NF-kappaB. These data contradicted our report that IkappaB is not detectable in Helenalin-treated, ocadaic acid-stimulated cells.
METHODS AND RESULTS:
Here we use confocal laser scanning microscopy to demonstrate the presence of IkappaB-released, nuclear NF-kappaB in Helenalin-treated, tumor necrosis factor-alpha stimulated cells.
CONCLUSIONS:
These data show that neither IkappaB degradation nor NF-kappaB nuclear translocation are inhibited by Helenalin. Rather, we provide evidence that Helenalin selectively alkylates the p65 subunit of NF-kappaB. This sesquiterpene lactone is the first anti-inflammatory agent shown to exert its effect by directly modifying NF-kappaB.

Vet Microbiol. 2007 Jan 31;119(2-4):330-8.

Helenalin reduces Staphylococcus aureus infection in vitro and in vivo.[Pubmed: 17010538 ]

Staphylococcus (S.) aureus is a major udder pathogen causing bovine mastitis. Some pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), enhance extracellular and intracellular growth of S. aureus, indicating that the inflammatory process favors S. aureus infection. Helenalin is a sesquiterpene lactone with potent anti-inflammatory properties.
METHODS AND RESULTS:
This study was designed to evaluate the effects of Helenalin on S. aureus infection. First, in vitro experiments were conducted. These studies revealed that proliferation of S. aureus in bovine mammary epithelial MAC-T cells treated in the presence or absence of TNF-alpha was markedly reduced in the presence of Helenalin. Secondly, in vivo effects of Helenalin were investigated. Lactating mice treated in the presence or absence of Helenalin were challenged by the intramammary route with S. aureus and the bacteria in the mammary glands were counted 12 h after infection. Significantly less numbers of bacteria were recovered from the infected glands of Helenalin-treated mice compared with untreated mice. Moreover, histological examination of mammary tissue from Helenalin-treated mice that were challenged with S. aureus indicated that Helenalin is able to significantly reduce leukocyte infiltration in the mammary gland following S. aureus inoculation.
CONCLUSIONS:
Our results show that Helenalin reduces S. aureus intracellular growth and experimental S. aureus infection. We conclude that Helenalin may be of potential interest in the treatment of S. aureus-induced mastitis in the bovine species.

Cancer Res. 2001 Aug 1;61(15):5817-23.

Helenalin triggers a CD95 death receptor-independent apoptosis that is not affected by overexpression of Bcl-x(L) or Bcl-2.[Pubmed: 11479221]

Apoptosis is required for proper tissue homeostasis. Defects in apoptosis signaling pathways, thus, contribute to carcinogenesis and chemoresistance. A major goal in chemotherapy is, therefore, to find cytotoxic agents that restore the ability of tumor cells to undergo apoptosis.
METHODS AND RESULTS:
We show here that the sesquiterpene lactone Helenalin (10-50 microM) induces apoptosis in leukemia Jurkat T cells even if they lack the CD95 death receptor or overexpress the antiapoptotic proteins Bcl-x(L) or Bcl-2. Activated peripheral blood mononuclear cells, however, are not affected (10-50 microM Helenalin). Helenalin led to a time-dependent (0-24 h) cleavage of the specific caspase-3-like substrate Asp-Glu-Val-Asp-7-amino-4-trifluoromethylcoumarin as well as to the proteolytic processing of procaspase-3 and -8. Caspase activation was a necessary requirement for apoptosis because the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk, 50 microM) completely abrogated Helenalin-induced DNA fragmentation as well as phosphatidylserin translocation. Although the initiator caspase-8 was activated, the Helenalin-induced signaling pathway did not require the CD95 death receptor as shown using cells without or with an antibody (ZB4)-blocked CD95 receptor. Helenalin also did not induce CD95 or CD95-ligand expression. On the other hand, Helenalin was found to induce the release of cytochrome c from mitochondria that was not inhibited by the caspase inhibitor zVAD-fmk, which indicated that cytochrome c release precedes caspase activation. Cytochrome c release was accompanied by dissipation of the mitochondrial transmembrane potential (DeltaPsi(m)), which was partly inhibited by zVAD-fmk, which suggests that caspases are involved in loss of DeltaPsi(m). Most importantly, overexpression of the mitochondria protecting proteins Bcl-x(L) or Bcl-2 failed to confer resistance to Helenalin-induced apoptosis, although the data presented here suggest that Helenalin induces a mitochondria-dependent pathway.
CONCLUSIONS:
Thus, Helenalin is a promising experimental cytotoxic agent that possibly points to new strategies to overcome apoptosis resistance attributable to overexpression of antiapoptotic Bcl-2 proteins.

BMC Complement Altern Med. 2012 Jul 11;12:93.

NF-κB p65 repression by the sesquiterpene lactone, Helenalin, contributes to the induction of autophagy cell death.[Pubmed: 22784363 ]

To deduce the mechanistic action of Helenalin, cancer cells were treated with the drug at various concentrations and time intervals.
METHODS AND RESULTS:
Using western blot, FACS analysis, overexpression and knockdown studies, cellular signaling pathways were interrogated focusing on apoptosis and autophagy markers. We show here that Helenalin induces sub-G1 arrest, apoptosis, caspase cleavage and increases the levels of the autophagic markers. Suppression of caspase cleavage by the pan caspase inhibitor, Z-VAD-fmk, suppressed induction of LC3-B and Atg12 and reduced autophagic cell death, indicating caspase activity was essential for autophagic cell death induced by Helenalin. Additionally, Helenalin suppressed NF-κB p65 expression in a dose and time dependent manner. Exogenous overexpression of p65 was accompanied by reduced levels of cell death whereas siRNA mediated suppression led to augmented levels of caspase cleavage, autophagic cell death markers and increased cell death.
CONCLUSIONS:
Taken together, these results show that Helenalin mediated autophagic cell death entails inhibition of NF-κB p65, thus providing a promising approach for the treatment of cancers with aberrant activation of the NF-κB pathway.