In 1954, Denham Harman proposed the free radical theory of aging (FRTA), which posits that the accumulation of lipid, protein, and nucleic acid damage from free radicals results in a decline of function over time. Although the FRTA is one of the leading theories on aging today, it is still being modified. One major breakthrough was the identification of mitochondria as the major source of oxygen free radicals, such as superoxide and hydroxyl radical, and other reactive oxygen species (ROS), like hydrogen peroxide.
Support for the FRTA includes a decrease in ROS production in calorie restricted (CR) animals, a dietary strategy known to increase lifespan in a whole host of animals. A hot area of research is the search for calorie restriction mimetics, which mimic the lifespan extending effects of CR. By using CR mimetics therapeutically, we may be able to have lower cholesterol, blood glucose, and blood pressure, as well as lower instances of cancer, diabetes, neurodegeneration, and heart disease — and still be able to eat a hot fudge sundae every night.
Caldeira da Silva and Cerqueira suggest that mitochondrial uncoupling is an effective mimic of CR. In mitochondria, the electron transport chain uses electrons from glucose and lipids to pump protons across a membrane. This proton gradient can be used to make energy in the form of ATP through oxidative phosphorylation. The process is kind of like generating hydropower. Uncouplers work by putting a leak in the dam, which lets water through without going to the generator. They “uncouple” the electron transport chain from oxidative phosphorylation, thus reducing the efficiency of energy production. Although animals have uncoupling proteins (these proteins are important for thermogenesis, especially during hibernation), so far there are no known agonists. The researchers instead used low doses of the mitochondria uncoupler DNP. DNP was actually used as a diet pill because the body makes up for inefficient energy production by burning more fat. Unfortunately, all that potential energy in the proton gradient is released as heat, which can cause fatal fevers. (The FDA deemed DNP unfit for human consumption in 1938, although supplements are now sold online to bodybuilders).
Notably, the mice in the study had no change in body temperature. They were given doses 1000X below the lethal dose and plenty of space to let off any extra heat. The DNP treated mice ate the same amount of food as control mice but had lower body mass. The DNP treated mice showed many phenotypes observed in calorie restricted mice. Like CR mice, DNP treated mice had higher rates of respiration with lower production of ROS. These mice also had lower oxidative damage to their DNA and proteins, another hallmark of CR. They showed lowered blood glucose, lower triglycerides, and lower insulin. Most importantly, DNP treated mice showed an extended lifespan. This study suggests that mitochondrial uncouplers are an effective mimic of calorie restriction and might be a realistic therapeutic intervention for delaying aging and extending lifespan. Uncouplers may be even more effective than resveratrol, which may – or may not – only work on mice on a high fat diet.
>>The DNP treated mice ate the same amount of food
>>as control mice but had lower body mass.
They were given/kept at the same amount of food? Or ate the same amount, even though more was available?
They were fed ad libitum, and food and water intake were measured. There was no differences in the amount of food or water ingested between the DNP and control mice.
[…] On Mitochondrial Uncouplers From Ouroboros: researchers “suggest that mitochondrial uncoupling is an effective mimic of [calorie restriction […]
Are the mice on DNP less active, i.e. producing less ATP due to reduced ox-phos?
Actually, the DNP treated mice do not make less total ATP. Their inefficiency in making ATP is made up by burning more fat (hence the lower body weight). The physical activity was not assayed. My guess is that DNP treated mice and control mice would have the same activity.
Like jorboc implied, I don’t see how uncoupling could avoid increased heat production unless proton pumping (and ATP production) was reduced.
The author’s postulate that the internal temperature of the mice on DNP did not increase because they were using very low doses. The interesting thing about uncouplers is that they actually increase the pumping of protons across the mitochondrial inner membrane. The animals metabolize more fat and pump more protons to make up for the fact that the proton gradient is being depleted without making ATP.
This brings us back to the activity question. If the DNP treated mice and the control mice are equally active, they have the same energy needs. The DNP treated mice are less efficient at making energy. Therefore, the mice on DNP need to burn more fat and pump more protons compared to the control mice to make the same amount of ATP.
Another way to think about it is this – what would happen if the mice on DNP did not burn more fat? They would be at a net energy deficit. Then you might guess that that they would be less active. Because DNP treated mice burn more fat, they are able to make up for this energy deficit and have the same activity as the control mice.
I fail to see how this mimics CR. At the molecular level sure (the cell is dealing with less energy availability), but at the whole organism level the differences are huge. For a start, there’s the whole neurohormonal response and gut-driven control over energy expenditure (leptin, Grehlin, PYY etc.) which will be exactly the same in DNP-fed mice but very different in CR mice.
I suspect at least some of the effect on lifespan is not necessarily due to uncoupling decreasing whole body ROS, but rather the effect of mild uncoupling on the outcome of specific age-related diseases. For example it is known that mild uncoupling is protective in ischemia/reperfusion injury. On the other hand, uncoupling has been linked to faster atherosclerosis. I would love to find out what the mice died of, and would bet that there was a significant shift in cause of death between the 2 populations. The DNP mice likely died of things that are refractory to the benefits of uncoupling. So, the question that arises – does DNP mimic the effects of CR on AGING, or the effects of CR on AGING RELATED DISEASES? These are 2 completely different things.
On a side note regarding the human use of DNP, one of the reasons it fell out of popularity was because it kills people. The other reason is it accumulates in the body, resulting in people turning bright orange!
I also would like to have seen more hormonal data, although insulin levels were consistent with CR. I actually think that CR and DNP mice might have similar hormonal profiles. DNP mimics the low energy availability of CR. This could have drastic effects on gene expression that are consistent with CR (NAD-dependent sirtuins come to mind, although there are many possible targets).
I disagree that aging and age related diseases are “completely different” Sure they have distinct properties, but there is definitely overlap in many aging and age related disease pathways. In addition, CR is also known to reduce the instance of many age related disease, so if there is a reduction in age related disease with DNP treated mice, this might instead be consistent with CR.
Although you’re more of an expert on this than me, I think that the effect of uncoupling on ROS could be related to the uncoupling effect on age related diseases. Oxidative damage might not be the key, but these changes in ROS could affect a variety of redox signaling pathways, which may be responsible for the protective effect of lower ROS.
You breeze over the part about the fatal fevers rather easily. The MAJORITY of those taking DNP experienced fevers of 110 degrees F or higher resulting in organ failure. This study also brings to light one of the main issues of research. The physiology and metabolism of rats and mice are in fact drastically different than humans. The enzymes on which I work hold some sequence similarity between the human enzymes and the murine enzyme but those differences are still apparent and cause us to constant re-evaluate every step to make sure our results are not an artifact of one of these differences.
Good discussion, but can we please back up factual claims with references, folks?
Really interesting post. I’m very interested in DNP related studies but don’t pretend to be any kind of expert.
The majority of DNP users do not experience any kind of fatality or even any uncomfortable side effects. I personaly use it and only experience heat when I eat a lot of carbs. As long as you are hydrated, DNP can be a very safe drug. It’s no different than atheletes that experience heat exhaustion-it’s always preventable with proper hydration.
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