Ph.D., Biochemistry, VMSRF-University of Mysore , India

M.Sc., Biochemistry, University of Mysore , India

B.Sc., Biology, University of Mysore , India

RESEARCH PERSONNEL

Hema Vunta (Graduate Student-Pathobiology)

Dharanija Rao (Graduate Student –Pathobiology)

Pradeep Bodumalla (Graduate Student-Pathobiology)

Dr. Uma Palempalli (Postdoctoral Scholar)

Dr. Ryan J. Arner (Research Associate)

Dr. Channa Reddy (Professor Emeritus)

Dr. K. Sandeep Prabhu (Principal Investigator)

TEACHING:

VBSC 514 Prostaglandins and Leukotrienes

The course provides an in-depth coverage of how fatty acids are metabolized in eukaryotes by various enzymatic and non-enzymatic mechanisms. The course will emphasize on the physiological roles of these fatty acid oxidation products in general health, inflammation, and reproduction along with their cellular basis of action via receptor-dependent and -independent mechanisms.

VBSC 4xx Immunotoxicology of Drugs and Chemicals (Course being developed) (Co-instructor: Dr. Na Xiong)

The immunotoxicology course will focus primarily on the effects of environmental chemicals, therapeutics, and recreational drugs on the immune system. Immunomodulatory mechanisms will be examined at systemic, cellular and molecular levels. Discussions will include theory, principles, and methodology and key issues in immunotoxicology.

RESEARCH:

Regulation of gene expression by oxidative, glycative, and hypertonic stressors; Molecular mechanisms underlying the antioxidant role of selenium; Lipid biochemistry-prostaglandins, leukotrienes, and oxidized fatty acids as nuclear receptor ligands.

Regulation of pro-inflammatory gene expression by oxidative stress-dependent mechanisms and the role of selenium in macrophages

Respiratory burst and the reactions of the electron transport system in mitochondria have the ability to produce a variety of oxygen and nitrogen radicals, commonly called reactive oxygen (ROS) or nitrogen (RNS) species by different mechanisms. Although these ROS/RNS play an important role in the defense of the host, increased production of these radicals is thought to be one of the major mechanisms accompanying inflammation, as seen in atherosclerosis, cancer, asthma, Alzheimer's disease and arthritis. It is increasingly recognized that many cellular signaling pathways are oxidation-sensitive, and that ROS may provide a common link between proinflammatory pathways and pathologies. Extensive evidence from many laboratories, including ours, indicates that ROS can regulate gene expression by modulating a large number of redox-sensitive transcription factors. Therefore, the antioxidant capacity of immune cells (e.g., macrophages) is very important to maintain optimal overall redox or oxidative tone. This is accomplished by a multi-tier system in which selenium (Se) in the form of Se-glutathione peroxidases, thioredoxin reductases, and other selenoproteins. However, the exact mechanism of antioxidant protection by Se is still unclear.

Current projects in this area:

1) The regulation of cyclooxygenase-2 (COX-2), a prototypical proinflammatory gene, by Se. We are trying to understand how Se abrogates the endotoxin- and cytokine-mediated COX-2 expression by interfering with the activation of the redox-sensitive transcription factor, nuclear factor-kappa B (NF-kB). These studies are mainly performed in bone marrow-derived macrophages from mice that are maintained on a Se-deficient and Se-supplemented diets.

2) Statins are drugs used in the treatment of hypercholesterolemia and these have been hypothesized to decrease the expression of selenoproteins, which might explain some of the side-effects (like myopathy, rhabdomyolysis, and depression) of these promising drugs. We are trying to understand the role of Se in alleviating these side effects, the molecular effects that are commonly seen in in-vitro culture systems, and whether these changes have a “signature pattern” like those observed during Se deficiency.

3) Increased oxidative stress leads to increased activation of NF-kB, which can modulate several transcription factors by a mechanism known as “transcription factor squelching”. Using proteomic and genetic approaches, we are making an attempt to identify these NF-kB interacting proteins. One such example is the interaction of p65 subunit with peroxisome proliferator-activated receptor- a and its role on the expression of apolipoprotein A-I (apoA-I) in the hepatocytes.

Through these studies, we hope to gain understanding of the anti-oxidant property of Se and its role as a therapeutic agent in human and animal health.

Isolation and characterization of endogenous ligands for the peroxisome proliferator-activated receptors (PPARs)

The PPARs have enjoyed the spotlight for many reasons. These transcription factors are ligand-inducible nuclear receptors that modulate gene expression in response to a broad spectrum of compounds. The recognition that PPARs are indeed nuclear receptors for polyunsaturated fatty acids, some eicosanoids and also lipid-lowering and antidiabetic drugs, has opened many exciting avenues of research and drug discovery. Recent studies on the PPAR function have extended the role of these transcription factors beyond energy homeostasis to master gene in adipogenesis and also determinants in inflammation control. Using our expertise in the large-scale synthesis of oxidized lipids, we are involved in a collaborative project with the Molecular Toxicology Group in the Department to evaluate some of the promising compounds as ligands for nuclear receptors, including PPARs.

The role of myo-inositol oxygenase in diabetic complications

myo-Inositol (MI), the dominant form of the physiological inositol isomers, is utilized in many tissues and cell types as an organic osmolytes and, more importantly, as a precursor for the synthesis of phosphoinositide second messengers. The first committed step in MI catabolism is catalyzed by a poorly studied enzyme called MI oxygenase (MIOX; EC 1.13.99.1) and it predominantly occurs in the proximal tubular cells of the kidney cortex.

Current projects in this area:

• The transcriptional regulation of expression of MIOX by hyperosmotic and hyperglycemic stress

• Characterization of a multimeric-MIOX complex in cells and its physiological role,

• Understanding the catalytic mechanism of MIOX. Being a unique internal mono-oxygenase, MIOX is one of the enzymes that catalyze the oxidative glycol cleavage reactions of MI and D-chiro-inositol. The elucidation of the catalytic mechanism, using a combination of enzyme kinetic methodologies and X-ray crystallography, is being performed in collaboration with Dr. Martin Bollinger, Associate Professor of Biochemistry and Molecular Biology, at Penn State .

Selected Publications:

G. Xing, Y Diao, L. M. Hoffart, E. W. Barr, K. S. Prabhu , R. J. Arner, C. C. Reddy, K. Krebs, J. M. Bollinger (2006) Evidence for C-H cleavage by an iron-superoxide complex in the glycol cleavage reaction catalyzed by myo -inositol oxygenase. Proc. Natl. Acad. Sci. ( USA ). 103 : 6130-6135.

G. Xing, L. M. Hoffart, Y. Diao, E. W. Barr, K. S. Prabhu , R. J. Arner, C. C. Reddy, K. Krebs, J. M. Bollinger (2006) A coupled dinuclear iron cluster that is perturbed by substrate binding in myo -inositol oxygenase. Biochemistry, 45 : 5393-5401.

G. Xing, E. W. Barr, L. M. Hoffart, K. S. Prabhu , R. J. Arner, C. C. Reddy, K. Krebs, J. M. Bollinger (2006) Oxygen activation by a mixed-valent, diiron (II/III) cluster in the glycol cleavage reaction catalyzed by myo -inositol oxygenase. Biochemistry, 45 : 5402-5412.

D. J. Kim, K. S. Prabhu , F. J. Gonzalez and J.M. Peters (2006) Inhibition of chemically-induced skin carcinogenesis by sulindac is independent of peroxisome proliferator-activated receptor-beta/delta. Carcinogenesis, 27 : 1105-1112.

R. J. Arner, K. S. Prabhu , V. Krishnan, M. Johnson, and C. C. Reddy (2006) Expression of myo -inositol oxygenase in tissues susceptible to diabetic complications. Biochem. Biophys. Res. Commun. 339 : 816-820.

K. S. Prabhu , R. J. Arner, H. Vunta, and C. C. Reddy (2005) Up-regulation of human myo -inositol oxygenase by hyperosmotic stress in renal proximal tubular epithelial cells. J. Biol. Chem. 280: 19895-19901.

R. J. Arner, K. S. Prabhu , and C. C. Reddy (2004) Molecular cloning, expression, and characterization of myo-inositol oxygenase from mouse, rat, and human kidney. Biochem. Biophys. Res. Commun. 324 : 1386-1392.

K. S. Prabhu , P. V. Reddy, E. C. Jones and C. C. Reddy (2004) Characterization of a class Alpha glutathione S-transferase with glutathione peroxidase activity in human liver microsomes. Arch. Biochem. Biophys. 424 : 72-80.

K. S. Prabhu , Padala V. Reddy, Andrew D. Liken, Emily C. Jones, Hemant P. Yennawar, and C. Channa Reddy. (2003) Identification, characterization, and properties of a class alpha microsomal glutathione S-transferase. Adv. Exp. Med. Biol. 525 : 189-192

P. Reddanna, K. S. Prabhu , J. Whelan and C. C. Reddy (2003) Carboxypeptidase catalyzed conversion of leukotriene C 4 to leukotriene F 4 . Arch. Biochem. Biophys. 413 : 158-163.

K. S. Prabhu , F. Zamamiri-Davis, J. Stewart, J. T. Thompson, L. M. Sordillo and C. C. Reddy. (2002) Selenium deficiency increases the expression of inducible nitric oxide synthase (iNOS) in RAW264.7 macrophages: role of nuclear factor-kappa B in up regulation. Biochem. J. 366 : 203-209.

F. Zamamiri-Davis, Y. Lu, J. T. Thompson, K. S. Prabhu , P. V. Reddy, L. M. Sordillo, and C. C. Reddy (2002). Nuclear factor-kappaB mediates over-expression of cyclooxygenase-2 during activation of RAW264.7 macrophages in selenium deficiency. Free Radic. Biol. Med. 32 : 890-97.