UNFOLDING THE MYSTERIES OF GENETIC SCIENCES IN INCURABLE DISEASES LIKE CORONARY ARTERY DISEASES, CANCER, & RAREST OF THE RARE DISEASES LIKE MOYAMOYA, SLE, TAKAYASU ETC.

          Native oxygen species contribute either beneficial or detrimental effect on cardiac dysfunction & death. This is formed during oxydative phosphorylation in the mitochondria as a byproduct of normal cellular aerobic metabolism. During the Krebs cycle, electrons derived from reduced nicotinamide adenine dinucleotide (NADH2) and flavin adenine dinucleotide (FADH2) flow along the respiratory transport chain through a series of cytochrome-based enzymes (complexes I,III,IV) which transport electrons finally to molecular oxygen. Normally, the high free energy of the electrons are gradually extracted and converted into adenosene triphosphate (ATP). This is the major process by which heart derived energy. But at the same time, only 1% or less than it is converted to form free oxygen radical. Electron chain transfer is blocked at the level of complex I & III and electrons are diverted to oxygen to form free oxygen radical. That means within mitochondria, the primary site of ROS generation is the electron transport chain. There are four protein complexes associated with the respiratory chain. Complex I, or NADH-ubiquinone oxidoreductase, accepts electrons from NADH; these electrons are carried to complex II, succinate dehydrogenase, and used to oxidize succinate to fumarate. Electrons continue to travel down their electrochemical gradient to complex III (ubiquinol-cytochrome c oxidoreductase), and subsequently to complex IV (cytochrome c oxidase), and are finally used to reduce molecular oxygen to water. Although the majority of molecular oxygen is reduced at complex IV to water, 1–4% of the oxygen is incompletely reduced to O2–, which can yield other ROS via various enzymatic or nonenzymatic reactions.

            Reduced Nicotinamide adenine dinucleotide phosphate oxidases in cardiovascular cells continuously produces low level of free radical oxygen, which are aggravated by AngII, alpha-adrenergic agonist, endothelin-1, tumour necrosis factor-alpha and mechanical stress.ROS has major effect on vascular biology and finally involves pathologies including Alzheimer disease, degenerative changes in aging, Parkinson Disease, and type 2 diabetes.

          Mitochondrial reactive oxygen generation has been associated with pathophysiological signaling. Mitochondrial-derived H2O2 is responsible for redox activation of c-Jun N-terminal kinase which inhibits mitochondrial metabolic enzymes. This serves as a potential feedback mechanism to regulate metabolic processes. In endothelial cells, H2O2 derived from mitochondria induces growth factor transactivation including receptors for vascular endothelial growth factor-2 and platelet-derived growth factor. These responses are inhibited by endogenous antioxidants.

            In human coronary arterioles, mitochondrial-derived H2O2 is responsible for flow-mediated vasodilation. Thus ROS are not simply a byproduct of respiration, but can serve as a control mechanism by which the mitochondria signal changes in vascular function and growth.

          Mitochondrial respiration can modulate vasomotor tone by dilation or constriction, establishing this organelle as a regulator of tissue perfusion. However, the cellular responses to mitochondrial membrane potential changes are complex. Large depolarizations inhibit calcium sparks, induce permeability transition pore (PTP) opening, elevate cytosolic calcium, and reduce cellular ATP. Thus responses may vary according to vascular bed and depending on the sensitivity to calcium, calcium spark frequency, and the function of the PTP.

          Several enzymatic mechanism contribute to ROS production in vascular endothelial cells, including NA(D)PH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase, and the mitochondrial electron transport chain. The respiratory chain is the major source of ROS in most mammalian cells, but the role of mitochondria-derived ROS in vascular cell signaling has not given much importance. In addition to producing ATP, mitochondria also play a key role in cell signaling and regulate a variety of cellular functions. ROS such as superoxide (O2–) and hydrogen peroxide (H2O2), are traditionally thought to be toxic by-products of cellular metabolism, which nonspecifically damage nucleic acids, proteins, lipids, and other cellular components. ROS at moderate concentrations act as signaling molecules and play an important role in the regulation of various vascular cell functions . In vascular endothelial cells, ROS regulate vascular tone, oxygen sensing, cell growth and proliferation, apoptosis, and inflammatory responses. The heterogeneous response profile to ROS may reflect localized actions or qualitative differences due to concentration.

           In addition to these regulatory functions under physiological conditions, excessive or sustained ROS have been implicated in the pathogenesis of various cardiovascular diseases, such as atherosclerosis, hypertension, diabetic cardiovascular complications, and ischemia-reperfusion injury.

          A variety of cellular enzyme systems are potential sources of ROS, including NAD(P)H oxidase, xanthine oxidase, uncoupled endothelial nitric oxide (NO) synthase (eNOS), arachidonic acid metabolizing enzymes including cytochrome P-450 enzymes, lipoxygenase and cyclo-oxygenase, and the mitochondrial respiratory chain. Although the contribution of individual sources may depend on the tissues and cells involved, four enzyme systems are thought to predominate in vascular endothelial ROS generation: NAD(P)H oxidase, xanthine oxidase, uncoupled eNOS, and mitochondrial electron leakage.

          The primary ROS produced by mitochondria is O2–, either in the matrix or the intermembrane space. As a charged species, O2– is not readily diffusible across mitochondrial membranes. However, the mitochondrial permeability transition pore, containing the voltage-dependent mitochondrial anion channel, might serve as a conduit for intermembranous mitochondrial O2– to pass through the outer mitochondrial membrane and into the cytosol . Probably a more important mechanism for transmembrane movement of reduced oxygen involves dismutation to H2O2 by superoxide dismutase (SOD). Once generated, the uncharged ROS- H2O2 can easily move across the membrane.

          H2O2 can be further reduced by catalase and glutathione peroxidase. Glutathione peroxidase uses GSH to reduce H2O2 and lipid peroxides to water and corresponding alcohols, respectively. This is the primary mechanism for eliminating H2O2 in cytosol and mitochondria. Catalase is located mainly in peroxisomes and exclusively catalyzes H2O2 to water. Catalase may be an important protective mechanism against a high concentration of H2O2 due to its higher Km for H2O2 compared with glutathione peroxidase. There are other enzymes, such as thioredoxin and gluthathione S-transferase, and antioxidants, such as ubiquinol and cytochrome c, that also help to inactivate ROS generated from the mitochondria. In the presence of transition metals (e.g., copper and iron), H2O2 can generate the highly reactive hydroxyl radical via the Fenton reaction or the Haber-Weiss reaction. Hydroxyl radicals are short-lived, highly reactive, and contribute significantly to local organelle damage through protein modification.

 Intracellular Calcium :

          Mitochondria participate in intracellular Ca2+ homeostasis via several Ca2+ uptake and release pathways. In this context, mitochondria behave as a high-capacity, low-affinity transient Ca2+ store. An increase in cytosolic Ca2+ concentration induces Ca2+ entry across the mitochondrial inner membrane and results in an elevation in the mitochondrial matrix Ca2+ concentration. Although this response serves primarily to buffer large, more pathophysiological changes in intracellular Ca2+ and may not be invoked by smaller transient changes that occur with physiological signaling, recent evidence indicates that mitochondria may act as a facilitating factor in the spreading of Ca2+ signals. These Ca2+-regulating functions are supported by the observations of the close apposition between mitochondria and Ca2+-release channels of endoplasmic reticulum, such as inositol 1,4,5-trisphosphate and ryanodine receptors, as well as proximity between mitochondria and plasma membrane.

          Calcium concentration is usually maintained at a very low level in the cytosol by sequestration in the smooth endoplasmic reticulum and the mitochondria. Ca2+ release from the endoplasmic reticulum into the cytosol results in the binding of the released Ca2+ to signaling proteins that are then activated. There are two combined receptor/ion channel proteins that perform the task of controlled transport of Ca2+:

          Calcium controls muscle contraction, release of neurotransmitter from nerve endings, proliferation, secretion, cytoskeleton structure, cell migration, gene expression and controlling various metabolism The three main pathways that lead to Ca2+ activation are :

   There are two different ways by which Ca2+ can regulate proteins:

     Ca2+ increases mitochondrial ROS production under conditions of partial mitochondrial membrane depolarization or in the presence of some degree of mitochondrial electron transport inhibition. Several mechanisms are thought to be responsible for this situation-

     Cytochrome c is a potent antioxidant, and its loss can result in more ROS liberation from mitochondria.