Protective effect of coconut water concentrate and its active component shikimic acid against hydroperoxide mediated oxidative stress through suppression of NF-κB and activation of Nrf2 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Conventionally coconut water has been used as an 'excellent hydrating' drink that maintain the electrolyte balance and help in treating diverse ailments related to oxidative stress including liver function. The present study was aimed to elucidate whether and how the coconut water concentrate (CWC) and its major active phytoconstituent shikimic acid (SA) can effectively protect murine hepatocytes from the deleterious effect of hydroperoxide-mediated oxidative stress.

MATERIALS AND METHODS

Bioactivity guided fractionation of CWC resulted in the isolation of a couple of known compounds. Freshly isolated murine hepatocytes were exposed to hydrogen peroxide (H2O2) (1 and 3mM) in the presence or absence of CWC (200 and 400 μg/ml) and SA (40 μM) for the determination of antioxidative, DNA protective, cellular ROS level by modern methods, including immunoblot and flowcytometry to find out the possible mechanism of action.

RESULTS

Pre-treatment of hepatocyte with CWC and SA showed significant prevention of H2O2-induced intracellular ROS generation, nuclear DNA damage along with the formation of hepatic TBARS and cellular nitrite. Further, the H2O2 induced cell death was arrested in the presence of CWC through the inhibition of CDC42 mediated SAPK/JNK pathways and activation of other molecules of apoptotic pathways, including Bax and caspase3. Moreover, CWC and SA help in maintaining the GSH level and endogenous antioxidants like Mn-SOD, to support intracellular defense mechanisms, probably through the transcriptional activation of Nrf2; and inhibition of nuclear translocation of NF-κB.

CONCLUSION

CWC and its active components SA reversed the H2O2 induced oxidative damage in hepatocytes, probably through the inhibition of NF-κB, with the activation of PI3K/Akt/Nrf2 pathway and reduction of apoptosis by interfering the SAPK/JNK/Bax pathway.

Ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs) are acquired from their diet by medaka fish (Oryzias latipes) but not by SKH-1 hairless mice

To assess whether vertebrates can acquire, from their diet, ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs), medaka fish and hairless mice were maintained for 150 and 130 days, respectively, on diets either including Mastocarpus stellatus (rich in MAAs) or the same diets without this red alga. In medaka, the MAAs palythine and asterina-330, present in trace quantities in the diet with added M. stellatus, were present in significantly greater quantities in the eyes of fish fed this diet than in the eyes of control fish. Only traces of MAAs were present in the skin of medaka fed the diet containing MAAs. Shinorine, the principal MAA in M. stellatus, was not found in any tissues of medaka, which raises questions about the specificity of transport of MAAs. In hairless mice, no dietary MAAs were found in the tissues of the eyes, skin, or liver after maintenance on the experimental diet. Low concentrations of shinorine were present only in the tissues of the small and large intestines. These results indicate that MAAs are acquired from their diet and translocated to superficial tissues by teleost fish, but that mammals may be incapable of such. Thus, dietary supplementation with MAAs may be useful in aquacultured species of fish, but MAAs as 'dietary sunscreens' may not be an option for mammals, including humans. Nevertheless, our demonstration of the uptake of shinorine by human skin cancer cells in culture raises evolutionary questions regarding the organ specificity of the capacity for the cellular transport of MAAs.

Genotoxicity studies of quercetin and shikimate in vivo in the bone marrow of mice and gastric mucosal cells of rats

Bracken fern (Pteridium aquilinum) causes acute and chronic toxicity in animals and is associated with a high incidence of stomach and esophageal tumors in humans in countries where it is consumed as food, yet the toxic constituent(s) has not been unequivocally identified. None of the toxic constituents so far isolated from bracken have individually reproduced all the disease syndromes typical of the plant. The carcinogenicity of the plant has at one time or another been attributed to quercetin, shikimate or ptaquiloside. Studies to determine whether or not the genotoxicity of quercetin, shikimate (and its metabolite cyclohexane-carboxylate) could be enhanced in combined application were conducted in vivo using the micronucleus test in mice and the unscheduled DNA synthesis in rat gastric mucosal cells. None of these compounds were genotoxic; simultaneous administration of the compounds did not influence their in vivo genotoxicity. Plasma concentrations of quercetin after p.o. and i.p. administration at 200 mg/kg were below 0.1 microgram/ml, suggesting that the negative in vivo results may have been due to limited bioavailability of the compound.