Sehamuddin Galadari

Sphingosine analogue FTY720 sensitizes arsenic trioxide-induced autophagic cell death in human malignant glioma cells

Studies over the past two decades have identified ceramide as a multifunctional central molecule in the sphingolipid biosynthetic pathway. Given its diverse tumor suppressive activities, molecular understanding of ceramide action will produce fundamental insights into processes that limit tumorigenesis and may identify key molecular targets for therapeutic intervention. Ceramide can be activated by a diverse array of stresses such as heat shock, genotoxic damage, oxidative stress and anticancer drugs. Ceramide triggers a variety of tumor suppressive and anti-proliferative cellular programs such as apoptosis, autophagy, senescence, and necroptosis by activating or repressing key effector molecules. Defects in ceramide generation and metabolism in cancer contribute to tumor cell survival and resistance to chemotherapy. The potent and versatile anticancer activity profile of ceramide has motivated drug development efforts to (re-)activate ceramide in established tumors. This review focuses on our current understanding of the tumor suppressive functions of ceramide and highlights the potential downstream targets of ceramide which are involved in its tumor suppressive action.

Purification and biochemical characterization of a second type of neutral ceramidase from camel (Camelus dromedarius) brain

Malignant gliomas are extremely resistant to therapies that induce apoptosis, but are less resistant to therapies that induce autophagy. Therefore, drugs targeting autophagy are promising in the management of malignant gliomas. In this study, we investigated the anti‐glioma potential of curcumin in vitro, and further examined the molecular mechanisms of curcumin‐induced cell death in human malignant glioma. Here, we provide evidence that curcumin is cytotoxic against human malignant glioma cell lines, and the mechanism of cell death caused by curcumin is associated with features of autophagy. Curcumin suppresses the growth of human malignant glioma cells via ROS‐dependent prostate apoptosis response‐4 (Par‐4) induction and ceramide generation. Extracellular supplementation of antioxidants such as glutathione and N‐acetylcysteine to glioma cells abrogated the Par‐4 induction, ceramide generation, and in turn, prevented curcumin‐induced autophagic cell death. Moreover, tumor cells transfected with Par‐4 gene sensitized the curcumin‐induced autophagic cell death. Overall, this study describes a novel signaling pathway by which curcumin induces ROS‐dependent Par‐4 activation and ceramide generation, leading to autophagic cell death in human malignant glioma cells.

Diabetes mellitus is a metabolic disease with multiple complications that causes serious diseases over the years. The condition leads to severe economic consequences and is reaching pandemic level globally. Much research is being carried out to address this disease and its underlying molecular mechanism. This review focuses on the diverse role and mechanism of ceramide, a prime sphingolipid signaling molecule, in the pathogenesis of type 1 and type 2 diabetes and its complications. Studies using cultured cells, animal models, and human subjects demonstrate that ceramide is a key player in the induction of β-cell apoptosis, insulin resistance, and reduction of insulin gene expression. Ceramide induces β-cell apoptosis by multiple mechanisms namely; activation of extrinsic apoptotic pathway, increasing cytochrome c release, free radical generation, induction of endoplasmic reticulum stress and inhibition of Akt. Ceramide also modulates many of the insulin signaling intermediates such as insulin receptor substrate, Akt, Glut-4, and it causes insulin resistance. Ceramide reduces the synthesis of insulin hormone by attenuation of insulin gene expression. Better understanding of this area will increase our understanding of the contribution of ceramide to the pathogenesis of diabetes, and further help in identifying potential therapeutic targets for the management of diabetes mellitus and its complications.

Ceramidases cleave the N-acyl linkages of ceramide to generate sphingosine and its subsequent product sphingosine-1-phosphate (S1P). Ceramide and S1P are important bioactive lipids, and ceramidases are important in regulating the availability of these lipids. In this study, we report the purification and characterization of camel brain neutral ceramidase (CBCDase). The novel CBCDase was purified from camel brain using sequential chromatography of DEAE-Sepharose, Phenyl-Sepharose, Superdex, and Mono Q column. The Mono Q fractions containing ceramidase activity were used for enzyme characterization. The purified CBCDase showed a single band corresponding to a molecular weight of ~100 kDa, displaying classical Michaelis-Menten kinetics, with maximum enzymatic activity at pH 7.0. Deglycosylation of the enzyme yields an apparent molecular weight of ~80 kDa. The purified CBCDase was inhibited by Zn(2+) and Cu(2+), while Ca(2+) stimulates the activity. Phosphatidic acid, phosphatidylserine and phosphatidylcholine completely inhibited enzyme activity at low concentrations. Thiol-containing compounds inhibited the CBCDase activity. Among the nucleotides, ADP, UMP, and TMP inhibited the enzyme activity at low concentrations, whereas, ATP inhibited the activity at higher concentrations only. The CBCDase catalysed both ceramide hydrolysis and reverse CDase reactions. For the first time, we have purified to apparent homogeneity of a ~100 kDa nCDase from camel brain.

Prostate apoptosis response-4 (Par-4) is a tumor-suppressor protein that selectively activates and induces apoptosis in cancer cells, but not in normal cells. The cancer specific pro-apoptotic function of Par-4 is encoded in its centrally located SAC (Selective for Apoptosis induction in Cancer cells) domain (amino acids 137–195). The SAC domain itself is capable of nuclear entry, caspase activation, inhibition of NF-κB activity, and induction of apoptosis in cancer cells. However, the precise mechanism(s) of how the SAC domain is released from Par-4, in response to apoptotic stimulation, is not well explored.