3.  CYCLIC  AMP  or  GMP 
		9.  ***  REDOX  STATUS  *** 

	Prooxidant conditions trigger the induction 
	of various antioxidant enzymes such as:
		- glutathione reductase
		- glutathione synthase
		- glutathione peroxidase
		- superoxide dismutase
		- catalase
	Temporary prooxidant conditions if not beyond 
	the organism's ability to resist and adapt will:
		- redistribute reducing equivalents
		    passively and actively
		- enhance resistance to oxyradical damage
		- inhibit pathology dependent syntheses

Superoxide Dismutase: 
	-OO* +  Enz (Cu++)  -->  O2  +  Enz (Cu+) 
	-OO* +  Enz (Cu+)  +  2 H+  --> H2O2  + Enz(Cu++)
	2H2O2 + Enz (Fe) --> O2 + H2O + Enz (Fe) 
Glutathione Peroxidase: 
	2 GSH  +  HOOH --> GSSG  +  2 HOH 
	2 GSH  +  LOOH  --> GSSG + LOH + HOH 

Reduced glutathione (GSH) is converted to the 
    disulfide (GSSG) by the action of oxyradicals 
    and by glutathione peroxidase. 
The presence of elevated levels of GSSG triggers a 
    change in glucose metabolism in an effort to shift 
    the utilization of hydrogen towards GSSG reduction. 
This change results indirectly in higher levels 
    of 2,3-diphosphoglycerate (2,3-DPG). 
2,3-DPG attaches to oxyhemoglobin in such a way as to 
    enhance dissociation or release of diatomic oxygen. 
Thus mildly pro-oxidant conditions enhances 
    the delivery of diatomic oxygen to tissues. 

To review a list of known toxic agents produced 
    by the putrifying action of colonic anaerobes, 
    one of the most toxic is hydrogen sulfide (H2S). 
Similar to cyanide (CN-), carbon monoxide (CO), and 
    azide (NN-) the bisulfide anion (HS-) attaches 
    to the copper of cytochrome a3 as a ligand. 
This shuts down the action of an entire respiratory 
    electron transport chain. 
This also results in failure to phosphorylate ADP, 
    plus a rapid and profound accumulation of reductants. 
Pro-oxidant conditions, however, can increase 
    the RSSR' / RSH ratio. 
All disulfides readily absorb hydrogen sulfide. 
        R'SSR" +  HSH  --->  R'SSH  +  HSR" 
Thus a hypothetical mechanism of H2S detoxification, 
    rescue of mitochondrial phosphorylation, 
    and restoration of normal redox potentials 
    should result from treatment with oxidants. 

Leukotrienes are long acting promotors of inflammation.
Many of these are produced by combining glutathione
    with certain proinflammatory docosoids.
Oxidation of reduced glutathione hypothetically 
    inhibits this process.
This opens the possibility for mildly oxidizing conditions 
    to have significant antiinflammatory effects.

Reduced glutathione acting as a nucleophile spontaneously
adds to methylglyoxal producing a thiohemiacetal.
                  O  O                OH O
       G-S-H  +  HC--C--CH3  -->  G-S-C--C--CH3
Glyoxalase I tautomerizes the thiohemiacetyl as shown.
                  OH O                O  OH
              G-S-C--C--CH3  -->  G-S-C--C--CH3
                  H                      H
Glyoxalase II hydrolyses the alpha-hydroxy-acyl product
of glyoxalase I yeilding reduced glutathione and lactic acid.
          O  OH                                O  OH
      G-S-C--C--CH3  +  HOH  -->  G-S-H  +  H0-C--C--CH3
             H                                    H

Methylglyoxal was discovered by Albert Szent-Gyorgyi, 
    et al, to be a physiologic inhibitor of cell division. 
Its level is controlled by the enzyme "glyoxalase", 
    which converts methylglyoxal to lactic acid. 
However, glyoxalase requires reduced glutathione 
    (GSH) as a cofactor. 
Oxidation of glutathione inhibits the action 
    of glyoxalase. 
As the levels of methylglyoxal rise proliferation 
    is inhibited. 

The ease of conversion of thiols to disulfides by oxidation, 
	RSH + R'SH + [O] ---> RSSR' + H2[O] 
And the ease of reversion of disulfides 
back to thiols by reduction, 
	RSSR' + 2[H] ---> RSH + R'SH 
Provide an important mechanism for physiologic control. 
Many enzymes which depend upon a cysteine residue 
    at the active center or as part of the structure 
    can be switched to the [OFF] mode by oxidation.
This may result in an autogenous disulfide 
    or the attachment of an exogenous sulfide.

~~~ ORNITHINE DECARBOXYLASE ~~~ Ornithine decarboxylase (ODC) is an enzyme, which is induced in all proliferating cells. ODC converts ornithine (an amino acid) to putrescine, an essential intermediary in polyamine synthesis. NH2--CH2--CH2--CH2--CH2--NH2 ODC has a cysteine residue, necessary to its function, which is maintained in the reduced state by other thiols. The thiol group of ODC is sensitive to oxidation, and such oxidation inactivates this enzyme. Prooxidant conditions therefore temporarily inhibit ODC activity and polyamine dependent cell proliferation. ~~~ REDOX CONTROL OF POLYAMINE FUNCTION ~~~ REDUCTION FAVORS: Ornithine Decarboxylase Activation Polyamine Synthesis Polyamine Preservation Growth And Proliferation OXIDATION FAVORS: Ornithine Decarboxylase Deactivation Inhibition Of Polyamine Synthesis Oxidative Conversion To Aldehydes Inhibition Of Growth And Proliferation "REDOX SIGNALING AND THE CONTROL OF CELL GROWTH AND DEATH" Advances In Pharmacology [series], Volume 38, pp 329-359, Academic Press, 1997 by Garth Powis, John Gasdaska, Amanda Baker at Arizona Cancer Center, University of Arizona, Tucson CONTENTS: I. oxidation-reduction as a physiologic control mechanism II. cellular redox systems: glutathione, thioredoxin, protein disulfide isomerase, glutaredoxin, Ref-1, metallothionein III.redox targets: ribonucleotide reductase, receptor proteins, transcription factors: OxyR, NFkB, AP-1, p53, kU, v-Ets, E2, Ah, protein folding & degradation IV. cellular responses to redox changes: proliferation, thioredoxin activity, oxidant signaling and apoptosis, oxidative stress, hypoxia Bibliography contains 204 references. ~~~ REDOX ACTIVE PROTEIN THIOLS ~~~ "Thioredoxin" (Trx) is a low molecular weight protein baring two closely situated cysteine residues, which offer two redox active thiol groups. In vivo Trx redox cycles between its reduced dithiol form Trx-(SH)2 and its oxidized disulfide form Trx-SS. Trx-(SH)2 + [O] ---> Trx-SS + H[O]H Trx-SS + 2[H] ---> Trx-(SH)2 The flavoprotein "thioredoxin reductase" utilizes reducing equivalents from NADPH to maintain Trx in the reduced state. NADPH ... FAD / FADH2 ... Trx-SS / Trx-(SH)2 Protein thiols such as Trx, protein disulfide isomerase (PDI), and Ref-1 are important intracellular carriers of hydrogen atoms. These in turn maintain various other proteins in the reduced state, and maintain certain oxidant sensitive enzymes, growth factors, and transcription factors in the active state. Activator-Protein-1 (AP-1) is a transcription factor and is activated by thiol proteins as follows: NADPH ... FAD/FADH2 ... Trx-SS/Trx-(SH)2 ... ... Ref-1-SS/Ref-1-(SH)2 ... AP-1-SS/AP-1-(SH)2 Reduced Trx also serves to convert ribonucleoside-5'-diphosphates to deoxyribonucleoside-5'-diphosphates. RNPP-OH + Trx-(SH)2 ---> dRNPP-H + Trx-SS + H2O The redox sequence is as follows: NADPH ... FAD/FADH2 ... Trx-SS/Trx-(SH)2 ... RNPP-OH/dRNPP-H Glutaredoxin (Grx) performs the same role as thioredoxin (Trx), however, Grx must accept hydrogen from glutathione (GSH). NADPH ... FAD/FADH2 ... GSSG/GSH ... Grx-SS/Grx-(SH)2 ... RNPP-OH/dRNPP-H Thus reductants as supplied by NADPH and carried by thiol proteins are necessary for a variety of proliferation related functions. ~~~ TRIGGERING OF APOPTOSIS ~~~ Apoptosis (programmed cell death) is a normal physiologic process whereby certain cells are selected for self-destruction. This may occur as a part of embroyologic developement or as a mechanism to remove aged, damaged, or malfunctioning cells. A beneficial result would be the termination of IgE producing plasma cells or tumor cells. One of the physiologic triggers of apoptosis is an oxidant sensing mechanism. When successful such apoptosis can produce long term beneficial results from oxidative therapies. ~~~ P53 PROTECTOR OR ONCOGENE? ~~~ P53 stands for the genome and corresponding protein involved in several control systems: -- detection of DNA damage -- initiation of DNA repair -- promotion versus suppression of proliferation -- initiation of apoptosis by oxidants, etc. Healthy P53 protein has cysteine residues, which are sensitive to oxidation, making redox control part of normal P53 function. Mutation(s) of the P53 genome in favor of carcinogenesis result in: -- promotion function locked -- apoptosis function locked -- sensitivity to oxidants decreased or absent ~~~ REDOX CONTROL OVER IMMUNOLOGIC TRIGGER MECHANISM ~~~ Most redox sensitive enzymes and transcription factors are inhibited upon oxidation and reactivated upon reduction. Conversely, certain other enzymes (namely protein kinases) are activated upon oxidation and inhibited upon reduction. A wide variety oxidants (including ultraviolet light and GSSG), can activate specialized protein kinases in immune cells. Immune cells have protein complexes composed of "inhibitor kappa B" and "nuclear factor kappa B". Activated protein kinases phosphorylate I-kappa-B. Ubiquitin attaches to phosphorylated proteins. The proteosome subsequently eliminates I-kappa-B by digestion. NF-kappa-B is released and migrates to the nucleus. There it associates with the transcription protein AP-1. Messenger RNA is synthesized which in turn directs the ribosomes to produce cytokines. Cytokines function as alarms which trigger activation of systemic immunity.
~~~ GSSG AS COFACTOR IN IMMUNOACTIVATION ~~~ In many types of cells oxidants can directly activate protein kinases without involving GSSG. However, in certain immune cells GSSG is a necessary cofactor to protein kinase activation. In these cells, deficiency of GSH and/or GSSG results in failure of NFKB transactivation. This explains how glutathione deficiency is associated with immune dysregulation. ~~~ INHIBITION OF HISTAMINE RELEASE ~~~ Histamine is a proinflammatory agent produced by the enzymatic decarboxylation of histidine. Histamine is stored in granules within mast cells. Mast cells degranulate and release histamine upon action of IgE-antigen complexes. The release of histamine from mast cells is inhibited by certain enediols such as: ascorbic acid, quercetin, and other polyphenolic bioflavonoids. Which phase (oxidized or reduced) of the enediol compound is actually responsible for this inhibition remains to be clarified. ~~~ REVIEW OF PHYSIOLOGIC EFFECTS OF OXIDANT EXPOSURE ~~~ 1. Passive and active redistribution of reducing equivalents towards oxidant eliminating pathways. 2. Adaptive induction of oxyradical quenching enzymes. 3. Enhanced oxyhemoglobin dissociation. 4. Temporary detoxification of hydrogen sulfide. 5. Inhibition of leukotriene synthesis. 6. Inhibition of glyoxalase. 7. Reversible inhibition of numerous enzymes and physiologic triggers which utilize thiols in their active centers. 8. Initiation of apoptosis in unwanted cells. 9. Induction of cytokine expression. 10. Modulation of histamine release.