Monday, December 31, 2012

The Good Things About Oxidation


This is incomplete but I really want to be done with it for now. Expect difficulties, provide criticism.

For decades we have been assailed with the evils of oxidation. This paper argues that we are mistaken, that oxidation is not always bad but is an adaptive mechanism to address pathological insults. It is a challenging and fascinating hypothesis. The author provides some interesting insights that help elucidate the current contradictions between cellular based studies and epidemiological studies, the former indicating benefits from antioxidants and the latter finding no evidence, or even evidence of harm, from heavy anti-oxidant loading.

Oxidative Shielding or Oxidative Stress
Vol. 342, No. 3

In this review I report evidence that the mainstream field of oxidative damage biology has been running fast in the wrong direction for more than 50 years. Reactive oxygen species (ROS) and chronic oxidative changes in membrane lipids and proteins found in many chronic diseases are not the result of accidental damage. Instead, these changes are the result of a highly evolved, stereotyped, and protein-catalyzed “oxidative shielding” response that all eukaryotes adopt when placed in a chemically or microbially hostile environment. The machinery of oxidative shielding evolved from pathways of innate immunity designed to protect the cell from attack and limit the spread of infection. Both oxidative and reductive stress trigger oxidative shielding. In the cases in which it has been studied explicitly, functional and metabolic defects occur in the cell before the increase in ROS and oxidative changes. ROS are the response to disease, not the cause. Therefore, it is not the oxidative changes that should be targeted for therapy, but rather the metabolic conditions that create them. This fresh perspective is relevant to diseases that range from autism, type 1 diabetes, type 2 diabetes, cancer, heart disease, schizophrenia, Parkinson’s disease, and Alzheimer disease. Research efforts need to be redirected. Oxidative shielding is protective and is a misguided target for therapy. Identification of the causal chemistry and environmental factors that trigger innate immunity and metabolic memory that initiate and sustain oxidative shielding is paramount for human health.
This metabolic mismatch diverts electron flow away from mitochondria in the cell and decreases intramitochondrial electron flow, and mitochondrial oxygen consumption falls. When mitochondrial oxygen consumption (extraction) falls and the cell is still surrounded by 30 Torr (2–4%) oxygen supplied by capillaries, the concentration of oxygen in the cell rises sharply
Only last week a friend of mine sent me a fascinating account of how bacteria create electron conduits spanning vast distances - centimeters! As one wit stated: life is just an electron looking for a home. Electron management is a cardinal feature  of biology. Too many or too few and problems emerge. Last week I looked at studies indicating how "body grounding" may be important to human health because it allows electron transfer from the earth to our bodies. I even wonder if electro convulsive therapy is primarily about electron donation.

Mitochondrial dysfunction is a cardinal marker for many chronic conditions, especially those above the neck. Parkinsons is considered to be at root a mitochondrial issue.Mitochondrial dysfunction is strongly implicated in some cancers.

What the author is arguing here certainly accords with various studies into pathological conditions. The excess oxygen is oxidising molecules. Perhaps this can explain reperfusion injury, where restoring blood flow to an ischemic tissue can induce great damage to that tissue. I wonder if providing mitochondrial agonists like carnitine might help overcome this problem by maxmising oxygen uptake by mitochondria thereby preventing high oxygen loading in the reperfused tissues.

Thus it is surmised ...
Herein, we assume that gradual reperfusion can reduce the reperfusion injury by reducing the production of free radicals during reperfusion.
So considering the author's hypothesis of oxidation as a defensive mechanism reperfusion injury seems to challenge that hypothesis. Perhaps not, in my searches I came across this little gem which immediately pointed to the potential source of the reperfusion injury problem:
The CB2 receptor agonist COR167 potently protected rat brain cortical slices against OGD and reperfusion injury, partly through CB2 receptors activation.
. OGD: oxygen-glucose deprivation
CB2: cannabinoid receptor 2 - very common throughout the body, not so much in the CNS, probably only on micorglia in the CNS. It has no psychotropic effect. Very important regulator of inflammation in immunological processes. CB2 receptor agonists like cannabidiol have demonstrated promise in the treatment of autoimmune diseases, allergies, cancers, pain, neurodegenerative conditions.

Note that in the above study there is no chemical intervention but rather a physiological intervention that had the "potent" effect. Presumably, given that cannabidiol, also an CB2 agonist, is a potent antioxidant, it is possible that the drug used here is an antioxidant. Interestingly the effect of this drug was partly receptor independent, an observation that has also been made with cannabidiol. What this "receptor independent" function is remains unclear, at least to me. There are two clear possibilities: the antioxidant function of the molecule, and the role of cannabinoids in regulating fatty acid synthesis especially in relation to prostaglandin synthesis and arachidonic acid.Limiting inflammatory prostaglandin production is a rate limiting factor in the production of inflammatory mediators, so the potent effect may very well be an immediate shutting down of any inflammatory response.

That is rather interesting because ...
Kidney histology showed widespread cell swelling and erythrocyte congestion in both cortex and medulla, and cell necrosis/apoptosis and cast formation in medulla. These experimental findings demonstrated that DTI can probe both structural and functional information of kidneys following renal IRI.
So we do see evidence of unregulated ATP production(cell swelling, also noted in other abstracts) and immunological activity(erythrocyte). As noted in Wiki regarding the erythrocyte sedimentation rate:
 When an inflammatory process is present, the high proportion of fibrinogen in the blood causes red blood cells to stick to each other. The red cells form stacks called 'rouleaux,' which settle faster.
The formation of rouleaux structures has been documented in ischemia and as one study noted:
The changes on reperfusion were disruption of blood flow patterns, vortex formation, regional stasis, adhesion and migration of leukocytes, focal hemorrhage, edema, vasospasm, and platelet aggregation.
Imagine the situation at the site of blood flow blockage, the penumbra region(surrounding) of the infarct tissue. Something has happened, something has broken, alarms are are raised, troops are rallied. The damaged but still functioning tissues are emitting "danger signals" which promote clotting and recruit various immune cells to the site of injury, in this case an occluded blood vessel.. The immune cells are becoming activated by the various types of inflammatory cytokines now being produced and some of these cells will in turn emit inflammatory mediators that can act as a paracrine(local region) and autocrine(self stimulating) inflammatory positive feedback loop. At the site of the occluded blood vessel you have stacked erythrocytes, inflammatory cytokine production, and activated immune cells producing their oxidants(the oxidative shielding component). All this is going to rush down that blood vessel to an infarct region that has collapsed ATP production, perturbed calcium regulation(mitochondrial loading), and mitochondria with collapsed membrane potential leading to cytochrome c oxidative release, capable of initiating internal death signals, and proton leakage, so the cells in this region are very vulnerable to any insult. What happens with reperfusion? It is something akin to barbarians breaking down the walls.

At the site of occlusion there is a big inflammatory event occurring and those activated immune cells will be releasing oxidants like OH-, nitrogen species, O2-, nitric oxide, and peroxynitrate, a potent oxidant, is probably created. The blood flows again and with it comes aggregated red blood cells, inflammatory mediators, oxidants, a potentially a higher than usual oxygen loading in that blood because of the aggregated red blood cells. The already seriously challenged ischemic tissues are now confronted with a tide of further insults. The resulting damage will generate ongoing danger signals which will maintain a state of immune mediated inflammation.

The concentration of erythrocytes may involve an unusually high burst of oxygen delivery to the reperfused tissues, thus elevating the risk of oxidative damage. This will be exacerbated because the damaged mitochondria in the infarct zone will not be able to utilise oxygen at anywhere near the same rate as other tissues, so oxygen levels in the reperfused zone may remain uncomfortably high for some time. This perhaps explain the strange findings regarding the use of helium\xenon to reduce reperfusion injury. It may simply be the case that these noble gases displace the oxygen thereby preventing it I state this because the percentages used are quite high, up to 80% of the gas will be one of the noble gases. Noble gases are supposed to be non-reactive. The benefits of noble gas therapy aren't that promising, certainly not "potent". Another good anti-inflammatory agent, and one that plays an important role in regulating calcium, is taurine. It also demonstrates favourable properties in reperfusion injury:
On the contrary, when present throughout the entire experiment, taurine significantly reduced oxygen/glucose deprivation-induced LDH and glutamate release with a maximal effect (45% reduction) between 5 and 20 mM. Taurine antagonised also tissue water gain according to a "U-shaped" concentration-response curve, which was significant within the range of 0.01-1.0 mM concentration.
There are plenty of studies indicating that taurine has significant anti-inflammatory effects.

That a CB 2 agonist and taurine have such notable effects on reperfusion injury raises the question as to the whether the major problem here is the immune driven inflammation which is causing most of the oxidation agents in reperfusion. This is arising primarily through the innate immune response. This arm of immune responses is very old and represents the first responders to potential danger. Whereas the adaptive immune response relies on antibody recognition for function the innate immune responses are much more generalised and inflammatory, often driving localised inflammation as a means of protecting against pathogens. The consequence however is that many self cells are killed or damaged. In many tissues this loss is tolerable, the cells can be replaced, but in the post mitotic cells like those of the brain and heart, the innate immune response comes at a potentially heavy price. This is why so many medical interventions are about addressing inflammation. From aspirin to steroids to painkillers the targets are often molecular processes driving inflammation.

In this day and age it can be difficult to understand why the innate immune responses can be so damaging. Think back to before antibiotics and how much devastation arose in those times. It is humbling to think that an ancient cell form can bring forth so much devastation on we who rule this planet. The innate immune response is so potent, so destructive on normal tissues because that is the price worth paying to maximise the likelihood that in the event of pathogen exposure the pathogen will be killed before it can become established and start dividing. Remember, some single cell creatures can divide every 20 minutes so quite literally every minute counts. It can take 3-7 days for the adaptive arm to generate the appropriate antibody, instruct the T cells, and launch an assault, by which time the pathogen will have well and truly taken over the body. As for the heart and brain, if a pathogen has managed to become established there the problem began long ago and the immune response has already failed; which it does often enough. Fortunately we have hygiene, sanitation, vaccines, and antibiotics.

The problem I have with the author's argument is that irrespective of the cause of increased oxidation events these events are not helping. The innate immune response is primitive and often destructive upon healthy tissues, that had value in the past because the selection advantage favoured a strategy that maximised pathogen protection even at the cost of tissue damage. "Sickness behavior", like depression, which often has a significant inflammatory component, if only because of emergent glucocorticoid resistance, initiates behaviors which isolate the individual from the group, thereby reducing the risk of herd infection, or even that the inflammatory response kills the individual, had selection advantages in the natural pathogen rich environment has left us with an inflammatory response that is presents unique clinical challenges. The problem for modern medicine is that so many medical interventions involve tissue damage which initiates innate immune responses that are always initially inflammatory. But medical interventions are done under sterile environments, those innate responses arose in pathogen rich environments.

Should we then continue to boost our antioxidant intake all the time? No, and here is why. In the same way that the innate immune response is now to some extent maladaptive with respect to the modern environment, over the billions of years cells have developed metabolic processes that are adapted towards at least partially addressing the potentially dangerous consequences of oxidative stress. Various chemical processes have evolved in this environment and are adapted for that environment. So reducing oxidation events may perturb these chemical processes in unfortunate ways. As paradoxical as it seems there are studies indicating that antioxidant therapy, while helping certain conditions, also appear to reduce lifespan. As one bod stated this is probably a class effect. That is, all antioxidants, in excess(whatever that means!), reduce lifespan.

So what are antioxidants doing? The author states:
Just as in the response to exercise,the durable antioxidant effects of botanicals occur because of their acute, but transient, pro-oxidant (electrophilic and/or ROS-generating) effects (Speciale et al., 2011). Electrophiles abstract electrons from (oxidize) other molecules.
The argument here is that the antioxidants create a transient "danger signal" so the cell starts producing protective responses like increased glutathione and SOD production, heat shock protein production, and other defensive processes. I am not convinced by this argument but it helps me think about a question that has long troubled me.

Antioxidants cannot endlessly keep donating electrons, in fact most don't, becomig oxidised in the very process of being an antioxidant. Melatonin appears unique in its capacity to regenerate(receive elections) without additional hlep, whereas some antioxidants can be regenerated with agents like alpha lipoic acid, and endogenously created mitochondrial antioxidant. But the problem still remains, whenceforth all these electrons? Fortunately the author provides some great graphics and text concerning the oxygen tension and millvolts in various regions in the cell.

So we don't have electrons just randomly distributed throughout the cell, there are regions potentially rich in electrons. For example, long ago I read how DNA, being negatively charged, is surrounded by a cloud of positively charged particles. So I presume that the mitochondria with all those circling protons in the intermembrane space might be attracting an electron cloud around their outer membrane. The issue here may not be so much about electron donation but electron distributions within the cell. The author argues that pathogens steal electrons for carbon carbon bond formation. So in infection there is an electron deficit occurring.

This is where I must segway into something a friend of mine piqued my curiousity some weeks ago. He sent me a wiki link for body grounding. I checked the literature. There are some recent reviews arguing that because we now rarely touch the bare earth we are in effect not being sufficiently grounded and so may be suffering from electron deficits. If you think that is strange, when I was data mining on the reperfusion issue I found a study which indicated that one possible way to prevent erythrocyte stacking in cerebral microcirculation post myocardial infarct was through electrostimulation! This stopped the "blood sludge" and according to wiki erythrocytes rely on their negative charges to prevent aggregation! Then there is the perennial mystery of why pulsed magnetic fields, electro shock therapy, and other electrical interventions can have important therapeutic effects.

So I close 2012 with a great big friggin mystery. There is something fascinating going on there, I would like to learn more but I suspect I'm over reaching - again.

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