Roy DN, Mandal S, Sen G, Mukhopadhyay S, Biswas T.
Cell Biology and Physiology Division, Indian Institute of Chemical
Biology, A Unit of Council of Scientific and Industrial Research,
Kolkata, India.
BACKGROUND AND PURPOSE Andrographis paniculata (AP) has been found to
display hepatoprotective effect, although the mechanism of action of
the active compounds of AP in this context still remains unclear.
Here, we evaluated the hepatoprotective efficacy of
14-deoxyandrographolide (14-DAG), a bioactive compound of AP,
particularly its role in desensitization of hepatocytes to tumour
necrosis factor-alpha (TNF-alpha)-induced signalling of apoptosis.
EXPERIMENTAL APPROACH TNF-alpha-mediated ligand receptor interaction
in hepatocytes in the presence of 14-DAG was studied in vitro in
primary hepatocyte cultures, with the help of co-immunoprecipitation,
confocal microscopy and FACS analysis. Events associated with
14-DAG-induced TNFRSF1A release from hepatocytes were determined using
immunoblotting, biochemical assay and fluorimetric studies.
Pulse-chase experiments with radiolabelled TNF-alpha and detection of
apoptotic nuclei by terminal transferase-mediated dUTP nick-end
labelling were performed under in vivo conditions. KEY RESULTS 14-DAG
down-regulated the formation of death-inducing signalling complex,
resulting in desensitization of hepatocytes to TNF-alpha-induced
apoptosis. Pretreatment of hepatocytes with 14-DAG accentuated
microsomal Ca-ATPase activity through induction of NO/cGMP pathway.
This resulted in enhanced calcium influx into microsomal lumen with
the formation of TNFRSF1A-ARTS-1-NUCB2 complex in cellular vesicles.
It was followed by the release of full-length 55 kDa TNFRSF1A and a
reduction in the number of cell surface TNFRSF1A, which eventually
caused diminution of TNF-alpha signal in hepatocytes. CONCLUSION AND
IMPLICATION Taken together, the results demonstrate for the first time
that 14-DAG desensitizes hepatocytes to TNF-alpha-mediated apoptosis
through the release of TNFRSF1A. This can be used as a strategy
against cytokine-mediated hepatocyte apoptosis in liver dysfunctions.
PMID: 20649583 [PubMed - in process]
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