Glycyrrhizic acid prevents ultraviolet-B-induced photodamage: a role for mitogen-activated protein kinases, nuclear factor kappa B and mitochondrial apoptotic pathway.

Glycyrrhizic acid (GA), a natural triterpene, has received attention as an agent that has protective effects against chronic diseases including ultraviolet UV-B-induced skin photodamage. However, the mechanism of its protective effect remains elusive. Here, we used an immortalized human keratinocyte cell line (HaCaT) and a small animal model (BALB/c mice), to investigate the protective effects of GA against UV-B-induced oxidative damage, and additionally, delineated the molecular mechanisms involved in the UV-B-mediated inflammatory and apoptotic response. In the HaCaT cells, GA inhibited the UV-B-mediated increase in intracellular reactive oxygen species (ROS) and down-regulated the release of pro-inflammatory cytokines interleukin (IL)-1α, -1ß and -6, tumor necrosis factor (TNF)-α and prostaglandin E2 (PGE2). GA inhibited UV-B-mediated activation of p38 and JNK MAP kinases, COX-2 expression and nuclear translocation of NF-κB. Furthermore, GA inhibited UV-B-mediated apoptosis by attenuating translocation of Bax from the cytosol to mitochondria, thus preserving mitochondrial integrity. GA-treated HaCaT cells also exhibited elevated antiapoptotic Bcl-2 protein, concomitant with reduced caspase-3 cleavage and decreased PARP-1 protein. In BALB/c mice, topical application of GA on dorsal skin exposed to UV-B irradiation protected against epidermal hyperplasia, lymphocyte infiltration and expression of several inflammatory proteins, p38, JNK, COX-2, NF-κB and ICAM-1. Based on the above findings, we conclude that GA protects against UV-B-mediated photodamage by inhibiting the signalling cascades triggered by oxidative stress, including MAPK/NF-κB activation, as well as apoptosis. Thus, GA has strong potential to be used as a therapeutic/cosmeceutical agent against photodamage.

Oxidative stress mediated Ca(2+) release manifests endoplasmic reticulum stress leading to unfolded protein response in UV-B irradiated human skin cells.

BACKGROUND: Exposure of skin to ultraviolet (UV) radiation, an environmental stressor induces number of adverse biological effects (photodamage), including cancer. The damage induced by UV-irradiation in skin cells is initiated by the photochemical generation of reactive oxygen species (ROS) and induction of endoplasmic reticulum (ER) stress and consequent activation of unfolded protein response (UPR). OBJECTIVE: To decipher cellular and molecular events responsible for UV-B mediated ER stress and UPR activation in skin cells. METHODS: The study was performed on human skin fibroblast (Hs68) and keratinocyte (HaCaT) cells exposed to UV-B radiations in lab conditions. Different parameters of UVB induced cellular and molecular changes were analyzed using Western-blotting, microscopic studies and flow cytometry. RESULTS: Our results depicted that UV-B induces an immediate ROS generation that resulted in emptying of ER Ca(2+) stores inducing ER stress and activation of PERK-peIF2α-CHOP pathway. Quenching ROS generation by anti-oxidants prevented Ca(2+) release and subsequent induction of ER stress and UPR activation. UV-B irradiation induced PERK dependent G2/M phase cell cycle arrest in Hs68 and G1/S phase cell cycle arrest in HaCaT. Also our study reflects that UV-B exposure leads to loss of mitochondrial membrane potential, activation of apoptotic cascade as evident by AnnexinV/PI staining, decreased expression of Bcl-2 and increased cleavage of PARP-1 protein. CONCLUSION: UV-B induced Ca(2+) deficit within ER lumen was mediated by immediate ROS generation. Insufficient Ca(2+) concentration within ER lumen developed ER stress leading to UPR activation. These changes were reversed by use of anti-oxidants which quench ROS.

Ethanolic extract of Alternanthera sessilis (AS-1) inhibits IgE-mediated allergic response in RBL-2H3 cells.

The present study was designed to investigate the anti-allergic effects of ethanolic extract of Alternanthera sessilis (AS-1) in rat basophilic leukemia (RBL-2H3) cells. It significantly reduced the ß-hexosaminidase release from anti-DNP-IgE sensitized RBL-2H3 cells. AS-1also inhibited the IgE antibody-induced increase in Interleukin-6 (IL-6), TNF-α, IL-13 and IL-4 production in these cells. The inhibitory effect of AS-1 on these cytokine was found to be nuclear factor-KB (NF-kB) dependent, as it attenuated the degradation of IKBa and nuclear translocation of NFkB. In addition, AS-1 significantly attenuated the DNP HAS-induced intracellular Ca(2+) release from these cells, which makes us speculate strongly that the decreased intracellular Ca(2+) is involved in the inhibitory effect of AS-1 on ß-hexoaminidase release. Taken together, anti-allergic effects of AS-1 suggest possible therapeutic application of this extract in allergic diseases.

Effect of N-acetyl cysteine (NAC), an organosulfur compound from Allium plants, on experimentally induced hepatic prefibrogenic events in Wistar rat.

Aim of present study was to investigate the effect of NAC on experimental chronic hepatotoxicity models induced by carbon tetrachloride (CCl4) and thioacetamide (TAA). CCl4 toxicity was induced by administering 200 µl CCl4 (diluted 2:3 in coconut oil)/100 g body weight, p.o., twice weekly for 8 weeks. TAA toxicity was induced by administering 150 mg/kg b. wt. of TAA i.p., twice weekly for 8 weeks. NAC treatment was started along with toxicants (CCl4 and TAA) for 8 weeks and continued for further 4 weeks. Self reversal group was kept without any treatment for 4 weeks after completion of toxicant treatments. Alanine aminotransferase (ALT), Aspartate aminotransferase (AST), Alkaline phosphatase (ALP), Bilirubin were measured in serum. Hydroxyproline (HP), lipid peroxidation (LPO), catalase (CAT), Glutathione peroxidase (GPx) and Glutathione (GSH) were determined in liver samples by colorimetric methods. Cytochrome P450 2E1 (CYP 450 2E1), activity was determined as hydroxylation of aniline in liver microsomes. General examination and histological analysis were also performed. Serum markers of liver damage (AST, ALT, ALP and Bilirubin) were increased by CCl4 and TAA intoxication (p<0.001), whereas co-treatment with NAC reversed such changes (p<0.001). HP was enhanced in toxicant groups (p<0.001 in CCl4 and TAA), but inhibited by NAC (p<0.001). LPO was increased while as GSH, CAT and GPx decreased by the administration of CCl4 and TAA (p<0.001); co-administration of NAC restored these liver markers to normal levels (p<0.001). Biochemical determinations were corroborated by general and histological findings. Keeping in view the biochemical and histopathological studies, it was concluded that CCl4 and TAA are strong hepatotoxic agents that produce liver fibrosis with close proximity to human etiology (micronodular cirrhosis) and NAC has a significant protective activity against CCl4 and TAA. NAC has also been validated as a model against oxidative burden in chronic liver pathology.

Negundoside, an irridiod glycoside from leaves of Vitex negundo, protects human liver cells against calcium-mediated toxicity induced by carbon tetrachloride.

AIM: To evaluate the protective effect of 2'-p-hydroxybenzoylmussaenosidic acid [negundoside (NG), against carbon tetrachloride (CCl(4))-induced toxicity in HuH-7 cells. METHODS: CCl(4) is a well characterized hepatotoxin, and inducer of cytochrome P450 2E1 (CYP2E1)-mediated oxidative stress. In addition, lipid peroxidation and accumulation of intracellular calcium are important steps in the pathway involved in CCl(4) toxicity. Liver cells (HuH-7) were treated with CCl(4), and the mechanism of the cytoprotective effect of NG was assessed. Silymarin, a known hepatoprotective drug, was used as control. RESULTS: NG protected HuH-7 cells against CCl(4) toxicity and loss of viability without modulating CYP2E1 activity. Prevention of CCl(4) toxicity was associated with a reduction in oxidative damage as reflected by decreased generation of reactive oxygen species (ROS), a decrease in lipid peroxidation and accumulation of intracellular Ca(2+) levels and maintenance of intracellular glutathione homeostasis. Decreased mitochondrial membrane potential (MMP), induction of caspases mediated DNA fragmentation and cell cycle arrest, as a result of CCl(4) treatment, were also blocked by NG. The protection afforded by NG seemed to be mediated by activation of cyclic adenosine monophosphate (cAMP) synthesis and inhibition of phospholipases (cPLA2). CONCLUSION: NG exerts a protective effect on CYP2E1-dependent CCl(4) toxicity via inhibition of lipid peroxidation, followed by an improved intracellular calcium homeostasis and inhibition of Ca(2+)-dependent proteases.