Oxidative Stress and Inflammation

Inflammation is a part of the complex biological response of vascular tissues to harmful stimuli. Debilitating diseases such as atherosclerosis, rheumatoid arthritis, and even cancer are the biggest pharmacological hurdles of today. Targeting inflammation is a broad task, since many mediators are involved in onset of particular disease. Among these many mediators, the reactive oxygen and nitrogen species generated by macrophages and neutrophils are of great interest because of their major contribution in establishment of chronic inflammation and cancer. This review elaborates the pathogenesis of inflammation based on involvement of reactive oxygen and nitrogen species and the activation of signalling cascades in response to oxidative stress. Understanding this would eventually give a clue for target based therapeutic approach in search of new effective anti-inflammatory drugs.

logical studies have shown inflammation as one of the major risk factors in emerging various kinds of neoplastic transformation [1].
Inflammation is s part of the complex biological response of vascular tissues to harmful stimuli [2]. It is a protective reaction of body's cells to injury or infections and allergic or chemical irritation. This is a reaction that is characterized by certain inflammatory features which are redness, pain, swelling, heat, and loss of function because of the blood vessels dilation that leads to the increase of blood flow in that area, thus resulting in the migration of immune cells like neutrophils and macrophages, along with the fluids causing edema toward the inflamed regions. The process of inflammation is quite complex, initiated by several factors which include molecules that ranges from bacteria to chemical and therefore results in cellular trauma or death. Tissue injury induced by this trauma results in the inflammatory mediators release including reactive oxygen species (ROS) like superoxide anion (O 2− ), hydrogen peroxide (H 2 O 2 ), nitric oxide and cytokines [3]- [8]. Immune system disorders have been linked to increased expression of pro-inflammatory mediators, including cytokines, NADPH oxidase, NF kappa B, myeloperoxidase, and Inos [9].
Pharmacological and physiological constituents of the herbal medicines are known to regulate and modulate various functions of inflammatory response in the body either directly or indirectly [10]. The highly complex immune system is however containing well organized set of cells and each cell in this group has a defined function which is particularly essential to protect the body from diseases. Immune cells may interact in a cell to cell manner and also act in response to intercellular messages during the transfer of hormones, and cytokines [11]. Peripheral immune system comprises of, lymphocytes leukocytes, mast cells, and platelets, whereas in central nervous system, the cells that amend inflammatory reactions are, microglial cells, endothelial cells and astrocytes [12] [13] [14] [15].
Major incidents of inflammatory reaction that trigger robust hyperactive immune response could be summarizing in following five categories. First: Nitric Oxide (NO) and prostaglandin synthesis [16], second: NF kappa B expression, third: reactive oxygen species (ROS) [17], fourth: migration of leukocytes [18], and finally the fifth: is increased production of pro-inflammatory cytokines i.e. TNF, IL6 and IL1 [19].

Role of the Free Radicals in Pathology of Inflammation
Reactive oxygen and nitrogen species generated by macrophages and neutrophils Figure 1 upon encounter of an antigen or allergen have been shown its implication in immune system disorders. This phenomenon of generation of free radicals is known as oxidative burst which is accomplished by involvement of NADPH oxidase, present on the surface of neutrophils membrane. The NADPH oxidase which is reactive oxidant producing enzyme or by inducible nitric oxide synthase (iNOS) expressed in activated phagocytic cells both reactive nitrogen and reactive oxygen species are discussed in detail below [20]- [25].

Signaling that Trigger the NO Release by Macrophages
Cell wall of Gram-negative bacteria comprise of good amount of LPS (Lipopolysaccharide), Figure 2 this LPS could serve as an initiator for inflammatory cascades. The LPS upon encounter to a cell, it interacts with LPS Binding Protein LBP, which in turn delivers LPS to CD14, the CD14-LPS complex with the help of MD2 (Lymphocyte antigen 96) interacts with TLR4, leading to initiation of signaling pathway via adaptors molecules that are MyD88 and IRAK p38, TRAF6, and TAB1 by these adaptors is done. Eventually TLR4 activation by LPS leads to NF-κB activation. NF-κB is pleotropic transcription factor which is The IFN-γ also found to provides a synergistic effect to the LPS induction of iNOS transcription because IRF1 interacts with NF-κB, altering the conformation of the NOS2 promoter. They enhances the binding of transcription factors, such as NF-κB and AP-1, by DNA-protein and protein-protein interactions [48].

Reactive Oxygen Species (ROS)
NADPH oxidase is activated during inflammation, resulting in generation of superoxide (•O −2 ) and by action of superoxide dismutase (SOD), it gets connected to H 2 O 2 . Further chloride gets involve and makes H 2 O 2 more toxic, in presence of myeloperoxidase, which usually activated by neutrophils and results in formation of very toxic HOCl, Figure 3. Therefore, the enzymes NADPH Oxidase is normally found in a resting state and function in redox signaling as second messenger. However, under abnormal conditions stimulated phagocytes involved in oxidative stress.
The NADPH oxidase complex is a cluster of proteins that donate an electron from NADPH to molecular oxygen (O 2 ) to produce superoxide ( 2 O − ). This initiates the respiratory burst, a key step in immune defense against bacterial and fungal pathogens. The importance of this process to human health is manifested in chronic granulomatous disease (CGD), which refers to any of several hereditary diseases in which certain oxidase proteins are defective. The result is a reduce superoxide production and impaired clearance of bacterial pathogens, leading to the formation of a granuloma, or fibrotic nodule, around the persistent bacterial infection. While CGD underscores the significance of NADPH oxidase in professional phagocytes, like neutrophils, monocytes, and macrophages, NADPH oxidase has additional roles in other cell types. These non-phagocytic versions of the NADPH oxidase produce less superoxide, which is involved predominantly in the inter-and intra-cellular signaling [49] [50] [51] [52] [53]. Open Journal of Immunology

Cellular Activation
A variety of stimuli can lead to superoxide production through NADPH oxidase, but in the phagocytes, a very strong response is known be achieved through ligand that activates Gq-type GPCRs. Some of the molecules that activates specific Gq-coupled receptors include PAF, IL-8, various proteases, nucleotides like ATP, and N-formylated peptides (fMLP). Receptor activation causes Gq to initiate hydrolysis of membrane-associated phosphatidylinositol bisphosphate (PIP 2 ) by phospholipase C β (PLCβ), giving rise to inositol trisphosphate (IP 3 ) and diacylglycerol (DAG). The IP 3 promotes the opening of calcium (Ca 2+ ) channels in the endoplasmic reticulum (ER), leading to a transient rise in intracellular Ca 2+ levels. It is an established fact that both Ca 2+ and DAG activate PKC, which results in its movement from the cytoplasm to a membrane. Ca 2+ also activates cytosolic PLA 2 (cPLA 2 ), which moves to the ER and perinuclear membranes to selectively liberate arachidonic acid (AA) stored in membrane phospholipids. The AA is known to act as a second messenger and is believed to regulate many neutrophil functions, although the underlying mechanisms and its physiologic role are poorly understood. Stimulation of intact neutrophils with exogenous AA leads to activation of PKCs, phosphatidylinositol 3-kinases (PI-3K), PLC, PLD, and mitogen-activated protein kinases (MAPK). Exogenous AA has long been known to activate neutrophil superoxide [54] [55].

Assembly of the NADPH Oxidase Complex
In the resting phagocytes, a portion of the oxidase is integrated in membranes while other components remain soluble in cytoplasm (Figure 4). The membrane-bound section consists of a large glycosylated protein, gp91 phox , and a smaller

Phagocytosis
The phagosome pocket is formed in response to antigen engulfment by phago-

Targeting NADPH Oxidase
In some inflammatory diseases scientist aim to target Activation of NADPH oxidases which may result from the stimulation of a number of cell surface receptors, such as the angiotensin II receptor, which is particularly important in hypertension and heart failure due to the complex mechanisms involved in the activation of NADPH oxidases, these enzymes can be targeted at several different levels of their activity. Firstly, decreasing NADPH oxidase expression can lead to inhibition. Also, the activation of NADPH oxidase can be decreased by blocking the translocation of its cytosolic subunits to the membrane. Another

Prevention from Oxidative Stress and Need Based Research
Overall, imbalance between antioxidant defense mechanism and oxygen-derived species generation in vivo leads to state of oxidative stress. There is evidently no great reserve of antioxidant defenses in mammals, perhaps because some oxygen-derived species may involve in metabolism. Certain compounds or strategies cause an activation of mitochondrial oxygen consumption and promote increased formation of ROS formation. These molecules culminating in increased stress resistance and longevity. During aging the oxidative stress of the organism is increasing and approaches to lower the increased ROS formation in our cells should be implemented. The most efficient preventive step to avoid exogenous free-radical exposure would be to avoid, exogenous toxic molecules cigarette smoke, pollutants and UVR, since it's not always possible, protection could be obtained by adequate antioxidant protection, decreasing the formation of free radicals, or increasing damage-repair systems of the cells [85].
Paradoxically, the efficiency of defense and repair may be enhanced by different measures caloric restriction (with adequate vitamin and mineral intake) for the prolonging of life. On the other hand, the reduction of energy metabolism may actually reduce ROS generation from mitochondria and consequently extend lifespan. In either case, avoiding electron leakage from electron transport and the resultant ROS production seem to be essential for a normal life. In order to reduce endogenous oxidative stress lifestyle approach to be followed. Consumption of vegetables and plant-derived foods and beverages has positive effect on the prevention of age associated diseases like coronary heart disease and atherosclerosis as well as for longevity. Avoiding mental stress, meditation and Open Journal of Immunology limit intake of fats and sugar is another way of preventing from oxidative stress.
Besides that, after consuming a meal, perform work instead of resting should in order to maintain an appropriate electron flow. The regulation of energy by the body's circadian rhythms also plays a significant role in controlling oxidative stress [86] [87] [88]. In addition to this if person suffering from inflammation must to cure using the medication however the medications may limit the symptoms but could not provide a complete healing. With advent of NSAIDs physicians treated successfully Rheumatoid Arthritis patients, unfortunately later developed gastrointestinal bleeding, because of long term administration of aspirin along with cortisone. Since that time, the pharmaceutical industry and researchers are trying to find solution and new ways to overcome the gastrointestinal toxicity caused by this effective drug of choice which is combination of steroids plus NSAIDs. Recently researcher is investigating anti-inflammatory entities that are immunomodulating which possess inhibitory activity against oxidative stress particularly with specific targeted molecule. Eventually, this information can be useful in the theoretical design of drugs with favorable, improved specificity and activity [89] [90] [91].

Conclusion
Targeting inflammation is a broad task, since many mediators are involved in onset of particular disease. Among these many mediators, free radicals are of great interest because of their major contribution in establishment of chronic inflammation and cancer. The well known immunosuppressive and anti-inflammatory drugs that are commercially available are mainly non-selective in their mechanism of action and also exhibit numerous side effects. The purpose of current review is to understand the new target site via targeting oxidative stress in terms of nitric oxide and reactive oxygen species at cellular level. This might work to develop new anti-inflammatory molecules with specific target. As mentioned above, inducible nitric oxide synthase and phagocytic NADPH oxidase can be focused so that specific pathologies can be targeted. Keeping this in mind, the potential of anti-NADPH oxidase and iNOS inhibitors, could serve as promising therapeutic intervention for chronic inflammatory disorders.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.