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Willis
Member since Feb-16-07
13 posts
Apr-16-07, 07:23 AM (PST)
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"Effectiveness of dichloroacetate against certain cancer"
 
   I will preface this by saying that I am not a scientist. Having said that, I have read the Michelakis paper and several others and I believe I have a fairly good understanding of what the Alberta group describes as the mechanism for dichloroacetate. The key to the whole mechanism is the normalization of the mitochondrial membrane potential. This is why the Cancer Cell article discusses the 1988 paper by Chen, et al. regarding rhodamine 123 accumulation by various cancer and normal cells. I have attached a link to a 1982 paper by Chen, which is available online. Rhodamine 123 is a positively-charged dye. Because the rhodamine 123 molecule carries a net positive charge, it is accumulated and retained in areas of the cell that are more negatively charged in greater amounts and for longer periods of time than in less negatively charged areas. Michelakis, et al. discuss the Chen paper because the retention of rh123 by the mitochondria of many carcinomas suggests that the mitochondria in such cells are hyperpolarized (that is the mitochondrial membrane potential in these cells is substantially more negative than normal).

My point in posting is to call attention to the chart on page 5 of the 1982 Chen paper. From this chart, it appears that two types of cancer do not retain rh123: sarcoma and oat cell lung cancer. I believe that oat cell is another name for small cell lung cancer. The 1988 paper also mentions as exceptions “large cell carcinomas of the lung” and “poorly differentiated carcinoma of the colon.” This is not definitive since there is certainly much variation among all types of cancer cells, but in light of the data contained in the Chen papers, and given the importance of the normalization of mitochondrial membrane potential to the apoptosis-inducing mechanism described by Michelakis, et al., it is reasonable to think that sarcomas, small cell lung cancers, and the others mentioned are unlikely to respond to dichloroacetate. Let me be clear: this does not in any way prove that dichloroacetate will work in cancers that do exhibit hyperpolarized mitochondria. I cannot say that it will work in any cancer, I can only say that even if the Alberta group is correct in their science, based on the available evidence I would not expect dichloroacetate to work against the cancers mentioned above.

http://www.pnas.org/cgi/reprint/79/17/5292


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MZ
Member since Mar-19-07
12 posts
Apr-16-07, 06:41 PM (PST)
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1. "two questions for better understanding"
In response to message #0
 
   1. This is quoted from your post:
"it appears that two types of cancer do not retain rh123: sarcoma and oat cell lung cancer. I believe that oat cell is another name for small cell lung cancer. The 1988 paper also mentions as exceptions “large cell carcinomas of the lung”"

question: Does it mean that "...I would not expect dichloroacetate to work against the cancers mentioned above", including lung cancer (small cell and large cell lung cancer)?

But Michelakis group planted human lung cancer cells to the rat which thrink 75% in 3 weeks. How should I interpret all these ?

2. Forgive my rusty high school chemical knowledge. When NaDCA is in water, it will exist with the form of negative ion (DCA-), and positive ion (Na+). Am I right so far?

Below are two quotes from your post:
"The key to the whole mechanism is the normalization of the mitochondrial membrane potential."

"that is the mitochondrial membrane potential in these cells is substantially more negative than normal"

The effective part of NaDCA is the negative DCA-.

But how can the negative DCA- normalize the negative mitochondrial membrane potential to cure cancer?


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Willis
Member since Feb-16-07
13 posts
Apr-16-07, 07:31 PM (PST)
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2. "RE: two questions for better understanding"
In response to message #1
 
   For your first question, it is confusing, but the descriptions “small cell” and “large cell” lung cancer do not exhaust all types of lung cancers. In fact, the lung cancer line used by Michelakis (A549, non-small-cell lung cancer) is listed on the table in Chen 1982 as retaining rh123.

As to your second question, I will give a summary of the mechanism described by Michelakis, et al. for the action of dichloroacetate. It has taken me some time to get to where I understand the concepts in the paper sufficiently to make this summary. A very easy mistake to make is to think of dichloroacetate as somehow starving the cancer cell of energy. Based on my understanding, this is not the action at all. What the Alberta group has claimed to discover is a metabolic-electrical remodeling of certain cancers. My understanding of what this means is that they claim that the metabolic pathways of these cells have been altered from normal in such a way that they maintain their mitochondria in a hyperpolarized state, and that the hyperpolarized state of their mitochondria confers at least some of these cells’ apoptosis resistance.

The Alberta paper describes the effects by which DCA promotes apoptosis as follows: (1) DCA inhibits pyruvate dehydrogenase kinase (PDK), the action of which is to inhibit pyruvate dehydrogenase (PDH); (2) inhibition of PDK leads to more PDH; (3) more PDH results in larger amounts of pyruvate being converted to acetyl-coA (essentially, the raw material of mitochondrial respiration); (4) the increased amounts of acetyl-coA enter the mitochondria where their oxidation results in the production of larger amounts of reactive oxygen species (ROS) (particularly H2O2); (5) the larger amounts of ROS damage Complex I of mitochondrial respiration; (6) the damage to Complex I results in inhibited efflux of H+ (a hydrogen atom without an electron, otherwise known as a proton; this is where the positive charge comes from); (7) because H+ is not being pumped out as quickly, the mitochondrial membrane potential becomes more positive, ultimately dissipating completely; (8) the mitochondrial transition pore (MTP), which Michelakis, et al. describe as voltage-sensitive, can now open, releasing pro-apoptotic factors and cytochrome c; (9) the cytochrome c and the increased ROS generated by the mitochondria activate Kv1.5 channels (a type of voltage-gated potassium ion channel) in the cell's plasma membrane; (10) the activated potassium channels in the cell membrane allow increased efflux of potassium ions from the cell; and (11) the decreased intracellular concentration of potassium ions exerts a decreased inhibitory effect on caspases ()which are essentially triggers for apoptosis). This is the mechanism described by Michelakis, et al. in Cancer Cell. As you can see, Michelakis, et al. describe two pro-apoptotic pathways: the normalization of the mitochondrial membrane potential and the activation of Kv1.5 channels in the cell membrane. I believe they attribute approximately two thirds of the effect of dichloroacetate to the normalization of the mitochondrial membrane potential and one third to the activation of Kv1.5 channels. I do not believe, however, that this means that dichloroacetate would be expected to have some effect against non-hyperpolarized mitochondria; the key to all of the apoptotic effects attributed to dichloroacetate is the normalization of previously hyperpolarized mitochondrial membrane potential. In cells that do not exhibit hyperpolarized mitochondria, I think the implication is that something other than hyperpolarized mitochondria is responsible for the apoptosis resistance.

I've probably left some steps out, but I think I’ve hit the high points. It is definitely complicated, and I am sure I have misstated somethings. I have read the paper from beginning to end probably eight times and spent a little time with a molecular biology textbook. To be clear: all I have done here is, to the best of my abilities, summarize the mechanism for the effects of dichloroacetate described by Michelakis, et al. This does not in any way confirm anything. It remains an open question whether Michelakis, et al. are correct in their description of a metabolic-electrical remodeling of some cancers and, if so, whether dichloroacetate will work safely and effectively in humans as it appears to have in rats.


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rtshinn
Member since Mar-7-07
30 posts
Apr-16-07, 08:30 PM (PST)
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3. "RE: two questions for better understanding"
In response to message #2
 
   Is it really THAT simple??? ;>


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DerekSmith
Member since Mar-30-07
42 posts
Apr-17-07, 09:23 PM (PST)
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4. "RE: two questions for better understanding"
In response to message #2
 
   Hi Willis.

I have a problem with this perception of the function of DCA and the proposal that this limits its functionality to Rhodamine 123 retentive cells. I would appreciate your thoughts on this perspective.

In a number of publications (the following included) the function of DCA is defined as having a simple and direct action vis. that it inhibits the function of PDC kinase (PDK) -- and that is ALL that it does. It does not involve itself in membrane potential modification, it just inhibits PDK, the rest of the mitochondrial activation cascade happens as a consequence of the inhibition of PDK.

PDK is normally initiated by the presence of excess acetyl-CoA, it performs the function of a negative feedback control to limit excessive production of acetyl-CoA. For some reason in the cancer cell, the PDK seems to be fully activated, essentially blocking the production of acetyl-CoA and forcing the mitochondria into a starvation stasis.

The application of DCA inhibits the PDK, allowing the PDC pathway to complete the conversion of pyruvate into acetyl-CoA. As the cellular concentration of acetyl-CoA increases it is transported into the mitochondria to potentiate the Kreb's cycle, restarting aerobic respiration.

The mitochondrial membrane potentials are nothing to do with this process, membrane polarisation/depolarisation is a function of the process of apoptosis that is allowed to be innitiated once energy flow is restored via aerobic respiration.

Does this not suggest that DCA will potentiate the restoration of aerobic respiration irrespective of a cells mitochondrial membrane potentials?

Derek

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http://www.stanford.edu/group/hopes/treatmts/ebuffer/j4.html

Dichloroacetate in energy metabolism

Dichloroacetate has been found to decrease lactate production in cells by stimulating the pyruvate dehydrogenase complex (PDC), a critical group of enzymes involved in energy metabolism. The PDC is a large complex that is composed of multiple copies of three enzymes - E1, E2, and E3. The PDC serves as the vital enzyme involved in pyruvate oxidation, the step in aerobic respiration in which pyruvate is converted to acetyl-CoA. Pyruvate is a product of glycolysis, the first step in energy metabolism where sugar molecules from the carbohydrates we eat are transformed into pyruvate to be used for further processing in metabolism.

Each of the three enzymes that make up the PDC performs specific reactions that collectively transform pyruvate to acetyl-CoA. Acetyl-CoA is then transported into the mitochondria and enters the Kreb’s Cycle, a step in aerobic respiration. Once acetyl-CoA enters the Kreb’s Cycle, it undergoes various reactions that ultimately end in the production of large quantities of ATP. The PDC acts as a gatekeeper that facilitates and regulates the entry of pyruvate in to the Kreb’s Cycle.

In essence, the PDC determines whether the pyruvate molecules will be transformed into acetyl-CoA. If pyruvate is converted to acetyl-CoA, the cells can use the acetyl-CoA to undergo aerobic respiration. If pyruvate is unable to be converted to acetyl-CoA, the pyruvate is used in anaerobic respiration. If the PDC is damaged, fewer pyruvate molecules are converted to acetyl-CoA, which results in a decrease in the rate of aerobic respiration and a decrease in the number of ATP molecules produced. Instead, the pyruvate molecules stay in the cytosol and undergo anaerobic respiration, producing increased amounts of lactate. An abnormal lactate buildup results in various symptoms such as severe lethargy (tiredness) and poor feeding, especially during times of illness, stress, or high carbohydrate intake.

How is PDC activity regulated?

A family of enzymes called PDC Kinases acts to add phosphate groups to the E1 enzyme of the PDC. Adding a phosphate group to E1 inhibits the activity of the PDC complex. Acetyl-CoA usually activates these PDC kinases as a way to stop production of more acetyl-CoA when it is already present in large amounts and continued production is no longer needed.

Dichloroacetate therapy has been used to increase the efficiency of aerobic respiration. Researchers have reported that dichloroacetate stimulates the PDC by inhibiting the kinase that inactivates the PDC. Once the kinase is inhibited, the PDC continues to be activated and is able to perform its function of converting pyruvate to acetyl-CoA for use in aerobic respiration.


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Willis
Member since Feb-16-07
13 posts
Apr-17-07, 10:35 PM (PST)
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5. "RE: two questions for better understanding"
In response to message #4
 
   I think you are correct: the only action of DCA in the cell is the inhibition of PDK. I never meant to suggest it did anything else. All of the effects follow from the inhibition of PDK, and the key event, as far as apoptosis in these cells is concerned, is the normalization of the previously hyperpolarized mitochondrial membrane. I believe the entire point of describing a metabolic-electrical remodeling of cancer is what I set out above. In the cancers that exhibit hyperpolarized mitochondria (which according to the available data would appear to include the majority of carcinomas; that’s part of the reason Michelakis, et al. cite the Chen paper), increasing the amount of acetyl coA being oxidized in the mitochondria results in damage to Complex I. Here is the explanation from Figure 1 of the Cancer Cell paper (ΔΨm is the abbreviation for mitochondrial membrane potential): “Sustained increase in ROS generation can damage the redox-sensitive complex I, inhibiting H+ efflux and decreasing ΔΨm. Opening of the ΔΨm-sensitive mitochondrial transition pore (MTP) allows the efflux of cytochrome c and apoptosis inducing factor (AIF).” They go on to explain, on page 11 of the PDF (page 47 of the Cancer Cell pagination), that “ur work directly shows that this relative increase in ΔΨm is associated with increased resistance to apoptosis, and its ‘‘normalization’’ increases apoptosis and decreases cancer growth.”

I think it is correct to say that DCA would act to inhibit PDK and encourage mitochondrial respiration in any cell, but I do not think there is any reason to expect the apoptosis-inducing effects in cells that do not exhibit hyperpolarized mitochondria. The idea that DCA just turns on the mitochondria and they take care of the rest is a gross simplification in the journalistic coverage. I recommend Figure 1 as a good summary of the action, but I am not exaggerating when I say it took me quite some time to get to the point I thought I understood what it was trying to say. The thing that is preventing apoptosis (at least in part; there could be other mechanisms preventing apoptosis in these cells as well) is the hyperpolarized mitochondrial membrane potential. As I said, in cancers that are not associated with hyperpolarized mitochondria, I think the implication is that something else explains their lack of apoptosis.


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iboy
Member since May-18-07
1 posts
May-18-07, 06:18 PM (PST)
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8. "oxygen deprivation/reperfusion equivalence??"
In response to message #1
 
   >Below are two quotes from your post:
>"The key to the whole mechanism is the normalization of the
>mitochondrial membrane potential."

Something interesting in the news that seems to be related to how DCA works:

http://www.msnbc.msn.com/id/18368186/site/newsweek/

Biologists are still grappling with the implications of this new view of cell death—not passive extinguishment, like a candle flickering out when you cover it with a glass, but an active biochemical event triggered by "reperfusion," the resumption of oxygen supply. The research takes them deep into the machinery of the cell, to the tiny membrane-enclosed structures known as mitochondria where cellular fuel is oxidized to provide energy. Mitochondria control the process known as apoptosis, the programmed death of abnormal cells that is the body's primary defense against cancer. "It looks to us," says Becker, "as if the cellular surveillance mechanism cannot tell the difference between a cancer cell and a cell being reperfused with oxygen. Something throws the switch that makes the cell die."

Reoxygenating deprived cells causes apoptosis. Maybe to the mitochondria, the oxygen starvation and reoxygenation is somehow equivalent to the effect of DCA's membrane potential normalization.


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billn
Member since Apr-27-07
19 posts
May-01-07, 11:37 AM (PST)
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6. "RE: Effectiveness of dichloroacetate against certain ca"
In response to message #0
 
Regards the sentence:

"The key to the whole mechanism is the normalization of the mitochondrial membrane potential."

If you look up Dr Budwigs diet of flaxseed oil and low fat cottage cheese (1950's), you will see that normalization of the mitochondrial/cell membrane potential is the theory that lies behind it.

There is a focus on the impact of hydrogenated fats on the electrical potential of cell membranes and the damage caused during the cell reproductive/division process, resulting in cancerous cells.

The similarities between the process attributed to DCA and that to Flaxseed Oil/Low fat cottage cheese in re-establishing the correct potentials is very interesting.

Billn


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gordon
Member since Apr-27-07
23 posts
May-04-07, 03:09 AM (PST)
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7. "RE: Effectiveness of dichloroacetate against certain ca"
In response to message #6
 
   A general theme found in some research papers on DCA is that the DCA molecule structurally resembles pyruvate and therefore binds the kinase that would otherwise be bound to the dehydrogenase

Gordon


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