ApoE4.Info

Juliegee wrote:I have much more to share on this tomorrow- specifically the importance of a specialized B1, thiamine, to optimize our brain's utilization of glucose. (It looks like Dr. Bredesen is already on to this- phew.)

Conclusion: Our results show that, though benfotiamine strongly increases thiamine levels in blood and liver, it has no significant effect in the brain. This would explain why beneficial effects of benfotiamine have only been observed in peripheral tissues, while sulbutiamine, a lipid-soluble thiamine disulfide derivative, that increases thiamine derivatives in the brain as well as in cultured cells, acts as a central nervous system drug. We propose that benfotiamine only penetrates the cells after dephosphorylation by intestinal alkaline phosphatases. It then enters the bloodstream as S-benzoylthiamine that is converted to thiamine in erythrocytes and in the liver. Benfotiamine, an S-acyl derivative practically insoluble in organic solvents, should therefore be differentiated from truly lipid-soluble thiamine disulfide derivatives (allithiamine and the synthetic sulbutiamine and fursultiamine) with a different mechanism of absorption and different pharmacological properties.

Wada et al. already noted that benfotiamine was sparingly soluble in organic solvents such as benzene, chloroform and methanol, but was readily soluble in aqueous media at pH≥8.0.[31] This is not surprising as the phosphoryl group of benfotiamine has two negative charges at alkaline pH. Here, we confirm that benfotiamine is sparingly soluble in water at pH≤7.0 and cannot be dissolved in octanol or oils. Thus benfotiamine should not be classified as a "lipophilic" compound as many authors still do.[10,24,25,38] Indeed, benfotiamine appears unable to diffuse across cell membranes. We have shown here that intracellular thiamine content is not increased in cultured neuroblastoma incubated in the presence of 10 µM benfotiamine, while it was increased ten-fold after incubation with 10 µM sulbutiamine.[29] Moreover, after a chronic treatment of rats with sulbutiamine intracellular thiamine derivatives were increased by respectively 250% (thiamine), 40% (ThMP), 25% (ThDP) and 40% (ThTP).[14]

This is in apparent contradiction with results obtained with cultured cells of endothelial origin,[18-20,39] showing that benfotiamine is able to counteract glucose toxicity in these cells by increasing transketolase activity. However, the benfotiamine concentrations used were 50-100µM, much higher than in our study. Hammes et al. even report that there was no effect on transketolase activity in cultured endothelial cells at 10 or 25µM.[18] In any event, this is no proof that benfotiamine is able to cross the membranes: indeed, cultured endothelial cells seem to possess an ecto-alkaline phosphatase.[40] It is therefore likely that, in these cells, the added benfotiamine is at least partially dephosphorylated to S-benzoylthiamine that can enter the cells as in the case of the intestinal mucosa. The slow dephosphorylation to S-benzoylthiamine might also explain the lag period observed between the addition of benfotiamine to thiamine-depleted Neuro 2a cells and the increase in intracellular thiamine derivatives (Fig. 6). In erythrocytes, it was shown that fursultiamine, a lipophilic disulfide, is rapidly incorporated into the cells while benfotiamine is not.[41] Taken together, these results strongly suggest that benfotiamine is unable to cross plasma membranes unless it is dephosphorylated.

Furthermore our results on cultured neuroblastoma cells show that benfotiamine, in contrast to sulbutiamine, does not easily cross cell membranes (Figs 5 and 6). It would therefore be interesting to test whether a thiamine disulfide compound such as sulbutiamine or fursultiamine, would not be more efficient and act at lower concentrations than benfotiamine in counteracting diabetic complications.

Stavia wrote:Merouleau what formulation do you use, and where do you get it from?

Thiamine is a water soluble compound that does not penetrate membranes very well. This decreases its absorption from the gut and its movement into cells and across the blood brain barrier. Thus, thiamine derivatives that are able to increase cell thiamine more efficiently than thiamine have been developed …

Benfotiamine is perhaps the best studied of these derivatives. … Benfotiamine contains an open thiazole ring that is closed on reduction within the cell. [Yes, this is here based on endothelial cells, as the mouse study authors suggest -- read on! -MR] Benfotiamine enters cells more easily than thiamine and maintains the active form of thiamine (TPP) for longer periods. Thiamine absorption from benfotiamine is about five times as great as from conventional thiamine supplements (Loew, 1996). Peripheral cells take in five- to twenty-five-fold as much thiamine in the form of [thiamin derivatives] as they do of an equal amount of regular thiamine ...

Studies in humans show that benfotiamine increases blood thiamine and thiamine diphosphate much more than equivalent dosages of thiamine (Frank et al., 2000; Loew, 1996). Benfotiamine only penetrates the cells after de-phosphorylation by intestinal alkaline phosphatases. It then enters the bloodstream as S-benzoylthiamine that is converted to thiamine in erythrocytes and in the liver. Following oral administration of 250 mg benfotiamine in humans, thiamine peaks within one hour in blood, and returns to normal by 25 hours. However, thiamine diphosphate [the active form of thiamin -MR] peaks in blood at about 5 hours at about 2 times control value and remains at that level for 25 hours (Ziems et al., 2000) [and mice have roughly the same pharmacokinetics -MR] ... During this time, brain thiamine does not increase. ...

Thiamine normally enters the brain through low capacity transporters. Thiamine is then phosphorylated to thiamine disphosphate ester ( [TDP], frequently referred to as thiamine pyrophosphate, TPP), which is the form of thiamine that is required for thiamine dependent enzymes [ie, that actually carries out the biochemical "work" of thiamin -MR]. …

The reported effects after longer-term administration (10-14 days) vary. In one report, thiamine does not increase in brain (Volvert et al., 2008 [merouleau's quoted study]), whereas in the other (Pan et al., 2010b) brain thiamine is elevated. ... One study showed a 90% increase in thiamine diphosphate levels in brain of rats that received benfotiamine in their diet for 6 months followed by 6 months of thiamine (Netzel et al., 2000 ). In the paper in which plaque levels were diminished (see below) (Pan et al., 2010b), the treatment was over an eight-week period. However, thiamine was only measured one hour after a single dosage or after a 10-day trial. In both, benfotiamine increased the levels of thiamine but not TMP or TDP in brain, whereas the levels of all were increased in blood. [Again, this was after a single dose or 10 days; Netzel et al., 2000 finds TDP elevated in the brain after long-term administration -MR]. As with all the studies, the increase in blood and liver was much larger than in brain (Pan et al., 2010b). Our unpublished studies in mice demonstrate that six months of benfotiamine feeding increases blood thiamine by 40 fold and brain thiamine by over 50% (Dumont et al.).…

Reduced glucose metabolism is an invariant feature of Alzheimer’s Disease (AD) and an outstanding biomarker of disease progression … (FDG-PET) studies in patients with AD show decreased glucose uptake bilaterally in posterior cingulate, precuneus, parietotemporal and frontal cortex. Greater decreases in FDG uptake correlate with greater cognitive impairment along the continuum from normal cognitive status to mild cognitive impairment (MCI) to AD dementia (Langbaum et al., 2009). A great advantage in patients with a disease causing mutation is that the temporal response of the changes can be followed. In patients that are genetically inclined to develop AD, changes in brain glucose metabolism occur decades before the development of symptoms (Reiman et al., 2004). There are no reports of normal glucose metabolism in brains of AD patients.

Increases in several markers of oxidative stress also indicate altered metabolism in patients with AD. In autopsy brains, markers of oxidative stress such as acrolein are more pervasive than plaques or tangles (Calingasan et al., 1999). Advanced glycation end products (AGE) occur in 75-95% of pyramidal neurons, which far exceeds the percentage of tau positive neurons (Munch et al., 2002). Markers of oxidative stress occur in peripheral cells formation in even mildly cognitively impaired patients (Torres et al., 2011). In animal models of plaque formation, markers of oxidative stress in brain and urine increase before plaques occur in brain (Praticò et al., 2001). Despite major advances in early diagnosis, neuroimaging, and biomarker research, no disease-modifying therapies are currently available …

In spite of the tight linkage of glucose metabolism to brain function and to the decline in AD, only a very limited number of studies have tried to understand why it is diminished. In related efforts, many experiments to enhance mitogenesis [the replication of the energy-producing mitochondria in the cell –MR] (Burchell et al., 2010) or diminish oxidative stress in the brain (Dumont and Beal, 2011; Eckert et al., 2011) have been completed, but none of the therapies have translated to the clinic…

Thiamine (vitamin B1)-dependent processes occupy critical steps in glucose metabolism … that are diminished in patients with AD. … Further, the reductions in thiamine-dependent processes are highly correlated to the decline in clinical dementia rating scales. ... Brain glucose metabolism depends on three thiamine-dependent enzymes (Figure 1): transketolase (TK), the pyruvate dehydrogenase complex (PDHC) and the α-ketoglutarate dehydrogenase complex (KGDHC). [The latter enzyme is the most consistently impaired in AD and AD prodromes -MR] …

In animal models, thiamine deficiency exacerbates plaque formation, promotes phosphorylation of tau and impairs memory.

[Thiamin Derivatives As Potential AD Prophylactics]
Benfotiamine is perhaps the best studied of these derivatives. … Sulbutiamine is a lipophilic derivative of thiamine that more readily crosses membranes than thiamine. Chronic administration of sulbutiamine improves long-term memory formation in mice (Micheau et al., 1985). Chronic treatment with sulbutiamine improves memory in an object recognition task and reduces some amnesic effects of dizocilpine in a spatial delayed-non-match-to-sample task (Bizot et al., 2005). Fursultiamine has not been studied as extensively as sulbutiamine of benfotiamine. Studies show that it increases brain thiamine as effectively as benfotiamine (Pan et al., 2010b).

Measuring thiamine levels in brain may not provide an adequate measure of the functional consequences of thiamine supplements. For example, one group claims benfotiamine increases brain thiamine (Pan et al., 2010a), whereas others claim it does not (Volvert et al., 2008). Another report found slight increases after six months (Netzel et al., 2000). Others report that both benfotiamine and fursultiamine increase brain thiamine, but not thiamine esters, and only benfotiamine diminishes plaques (Pan et al., 2010a). Measures of the functional consequences of thiamine supplementation provide an effective screen for thiamine-mimetics that may correct a functional thiamine deficiency in brain. The reversal of the decline in the activities of KGDHC and transketolase following [thiamin deficiency] provides a measure of the functional consequences of thiamine (Gibson et al., 1984). The various thiamine derivatives have not been tested in this manner. A limitation of any method is that providing thiamine (or a derivative) to thiamine sufficient animal models may not provide an adequate method to test for effects in functional deficient in patients…

Thiamine supplements and AD pathology
The studies described above suggest that supplementation with thiamine or thiamine derivatives may be able to reverse AD pathological processes. Remarkably, supplements with thiamine derivatives decrease plaque formation and improve memory, even in mice that are genetically engineered to make plaques. Specifically, recent studies in mice show supplementing with the thiamine derivative benfotiamine diminish plaque formation and improve memory (Pan et al., 2010b). Another thiamine derivative, fursultiamine, is not effective, and our unpublished studies show that thiamine does not diminish plaque formation. The precise basis for this selectivity between thiamine and different thiamine derivatives is a matter of speculation, and is discussed in more detail later in the review. The inability of thiamine and fursultiamine to reverse plaques may be related to their ability to enhance thiamine dependent processes within the brain....

Diabetes, AD and thiamine
Diabetes predisposes to AD …. Hyperglycaemia increases the formation of AGE [Advanced glycation end products]. ... AGEs appear to be important components in the pathology of AD and diabetes. In AD brains, intracellular accumulation of AGE occurs in 75-95% of pyramidal neurons, which far exceeds the percentage of tau positive neurons. They also occur by the age of 35-45 years (Munch et al., 2002). In addition, AGEs may represent a driving force in acceleration of amyloid deposition and plaque formation (Loske et al., 2000). High levels of AGEs occur in neurofibrillary tangles (Jono et al., 2002) and CSF (Ahmed et al., 2005). The Mini-Mental State Examination (MMSE) score correlates negatively with oxidant-induced protein modification (Ahmed et al., 2005). Thus, the evidence for AGE is overwhelming for AD. These results raise the question of whether the AGEs in AD are due to a functional [thiamin deficiency] and/or if increasing thiamine availability in brain could overcome these deficits. …

Hyperglycaemia increases the formation of AGE
Thiamine, especially the thiamine derivative benfotiamine, reduces hyperglycemia induced AGE in endothelial cells (La Selva et al., 1996; Stracke et al., 2001; Thornalley et al., 2001). Benfotiamine can also diminish cerebral oxidative stress associated with diabetes (Reggiani et al., 1984). [The cited study doesn't show this; I think they meant to cite (1) below. Note Note that this was quite a high dose, and it was INJECTED rather than oral benfotiamine. Note that this also seems to imply that circulating unmetabolized benfo is able to raise functional thiamin in the brain, perhaps undergoing the needed conversion in circulating cells or BBB endothelial cells -MR] ...

Strong evidence suggests that benfotiamine or thiamine does this [reduces metabolically-generated AGE] by inducing transketolase. The data suggests that activation of transketolase reduces the AGE by activation of non-oxidative branch of the pentose phosphate shunt (Hammes et al., 2003; Stracke et al., 2008). Growing cells in high glucose is one model of diabetes. Culturing cells with high glucose does not significantly depress transketolase, but the addition of thiamine or its derivatives to stressed cells increases transketolase and diminishes the toxic metabolites. If the increase in transketolase is blocked by using antisense oligonucleotides, thiamine is no longer neuro-protective. Thiamine does not increase transketolase in controls (Hammes et al., 2003). [It is not clear to me where they get this from the cited paper; the effect on transketolase in nondiabetic controls in vivo certainly is not reported one way or the other -MR] Successful treatment of diabetic peripheral neuropathy by activation of transketolase with thiamine-mimetics suggests a similar strategy may work in AD.(Hammes et al., 2003; Stracke et al., 2008). … Thiamine may also be protective in AD and diabetes by acting at a transcriptional level. …

Although thiamine-dependent processes appear to be appropriate therapeutic targets, the few previous trials have been minimally effective. One cause of the failure was that all were greatly under-powered so neither positive nor negative results are credible. …The studies with thiamine were for short time periods and had small numbers of patients (i.e., they were poorly powered).

Roie of Transketolase in Cancer
Cancer cells utilize glucose maximally as a main source of energy supply and substrates for proliferation through glycolytic metabolic pathways [1,2]. Inhibition of the activity of the key enzymes (e.g., transketolase/transadolase) in these metabolic networks, resulting in significant limitation of glucose utilization, provides an ideal strategy for an effective therapy of cancer. A number of our previous studies have shown that inhibition of activity of either transketolase in the pentose phosphate cycle, or glycogen phosphorylase causes cell cycle arrest leading to cancer cell apoptosis.Cancer cells utilize glucose maximally as a main source of energy supply and substrates for proliferation through glycolytic metabolic pathway.s Inhibition of the activity of the key enzymes (e.g., transketolase/transadolase) in these metabolic networks, resulting in significant limitation of glucose utilization, provides an ideal strategy for an effective therapy of cancer. A number of our previous studies have shown that inhibition of activity of either transketolase in the pentose phosphate cycle, or glycogen phosphorylase causes cell cycle arrest leading to cancer cell apoptosis.

Dr. Gibson asserted that the brain's ability to use glucose (as measured by FDG-PET scan) is the MOST strongly correlated biomarker with Alzheimer's- NOT amyloid plaque. Despite the fact that the brain comprises 2% of the human body, it is the most metabolically demanding organ- using 20% of the the glucose supply. A loss of glucose to the brain is strongly correlated with amyloid plaque and tau. This cerebral glucose hypometabolism can even be measured in skin biopsies (fibroblast cultures) that demonstrate altered internal calcium stores.

Reduced cerebral glucose utilization creates oxidative stress. He asserted that neuronal mitochondria is very sensitive to oxidative stress. Nitration is a marker of this stress that impairs KGDHC (alpha-ketoglutarate dehydrogenase complex ) an important mitochondrial constituent. KGDHC is protective. Strategies to up regulate it include: sirtuins, NAD, and ketones. KGDHC is dependent on Vitamin B1, thiamine. This B vitamin has a function very different than any other B vitamin. A thiamine deficiency is very dangerous. It is exemplified by a condition called Wernicke-Korsakoff Syndrome. ALL diabetics are deficient in thiamine. ALL Alzheimer's patients are deficient in thiamine. Interestingly, Chinese scientists are using thiamine as a biomarker for AD.

Glucose metabolism, and it's subsequent oxidative stress, drive amyloid plaque and tau. A thiamine deficiency impairs glucose metabolism. Supplementing with Vitamin B1 can briefly rectify, but it's quickly used up and the body is unable to hold a steady supply. Benfotiamine can supply a more continuous supply. Supplementing with benfotiamine has also been shown to decrease amyloid plaque and tau. The neurons, which appeared to have died (apoptosis) from lack of cerebral fuel, have been shown to be revived with thiamine supplementation. It has been proven to be safe. A dosage of 300mg, twice daily was recommended. Concurrently supplementing with NAC helps.

merouleau wrote:Michael, 3.5 years after you initiated this discussion on LongeCity, this post suggested that supplementing thiamine allows non-cancerous cells to compete more effectively for glucose and helps starve any nascent tumors as long as blood glucose levels are kept low.

at first we thought we might starve tumors by limiting dietary carbohydrate (CHO), obviously a major source of blood glucose. It took us less than a day of literature review to recognize that CHO restriction would not starve most cancers because they are usually excellent at pirating glucose at blood glucose concentrations way below the normal range. ... We realized that gluconeogenesis and release from glycogen stores would prevent blood glucose concentration from falling to a level low enough to starve cancer cells. However, it became clear that by reducing insulin signaling, dietary CHO reduction would cause many effects which were known to inhibit cancer growth. Some of these were systemic, such as ketosis triggered at CHO restriction to less than 50 grams/day. Ketosis had been reported to inhibit cancer growth in cell culture studies in our lab and others, animal cancer studies and a case study of two children with brain tumors. Other expected effects are changes in all the intracellular signaling molecules downstream of the insulin receptor, which regulate their growth, proliferation, and resistance to apoptosis (cell death signals known in all cells), etc. In the last blogpost, Richard [Feinman] described an animal study which demonstrated insulin’s involvement in downstream signaling and response to diet in cancer. Cancers are now being treated with drugs that individually target these intracellular signaling molecules that are controlled by insulin. These new drugs have shown some efficacy but are often limited by side effects due to the drug interactions with normal tissues. Normal tissues, however, are tolerant of the effects of reduced insulin signaling. This is apparent from the safety of low CHO diet investigations in overweight people and people with diabetes as well as healthy subjects of normal weight. It seemed reasonable to us that a low CHO insulin inhibiting (INSINH) diet could target the same molecules as the drugs and could plausibly inhibit or even kill cancer cells, but would be safe for normal tissues. [all emphasis in original]

Plasma glucose concentration falls only mildly, remaining in the normal range in normal-weight individuals and in those trying to lose weight using low-carbohydrate diets. Simple tumor glucose starvation is therefore unlikely in humans. Strict carbohydrate limitation, however, leads to distinct changes in signaling pathways and downstream metabolism, including moderate ketosis, fatty acid synthase inhibition, reduced secretion of insulin, insulin-like growth factors, and several inflammatory cytokines.(1)

Overexpression of the insulin-independent glucose transporter-1 (GLUT-1) and hexokinase facilitates the increased glucose uptake needed to supply the energy needs of these cancers. … Conversely, we proposed previously that insulin inhibition (INSINH), by altering the metabolic microenvironment, may inhibit many human cancers evolutionarily adapted to a markedly different, specifically hyperinsulinemic, state. We also previously reported on the growth and adenosine triphosphate inhibition in multiple aggressive cancer cell lines when grown in supplemental ketone body medium that are not seen in control fibroblasts. ... [C]alorie restriction shares many of the downstream signaling pathways of the insulin receptor. ... Other insulin receptor ligands, including insulin-like growth factor-1 (IGF-1) and IGF-2, share extensive homology and downstream signaling pathways with insulin, but have more potent mitogenic and antiapoptotic effects. … Conversely, decreased insulin secretion induces metabolic and molecular responses, including the inhibition and downregulation of ... [multiple] proposed cancer therapy targets of drugs such as rapamycin, wortmannin, bevacizumab, metformin, among many others.(2)

merouleau wrote:He doesn't address your primary evidence, the 2001 Comin-Anduix paper

merouleau wrote:I also like the paper he cites. It's too technical for me to follow perfectly, but I think the gist is that tumor cells upregulate one form of transketolase (TKTL1) without the assistance of thiamine; therefore, we are better off optimizing the thiamine status of our non-cancerous cells to upregulate all three forms of transketolase throughout our bodies and thereby optimize overall cellular energy production.

Since we could demonstrate the presence of a second transketolase enzyme in humans, the observed enzymatic results can no longer be interpreted as the consequence of a single transketolase protein unless discrimination between the enzymatic activities of the different transketolase enzymes is performed. Furthermore, if an enzyme needs a cofactor, the enzymatic activity can be altered by the cofactor. If more than a single enzyme with an identical cofactor are present, activation of the enzymatic activity by application of a cofactor is the sum of activation of the different enzymes. Transketolase enzyme activities in tumor cells have been activated by application of thiamine, or inhibited by thiamine analogs [which compete against real thiamin for binding sites on thiamin-dependent enzymes, inhibiting their activity -MR]. The obtained results have been interpreted as the consequence of the TKT [standard transketolase] gene. We could show that only the TKTL1 transketolase is upregulated in tumors, indicating that the TKTL1 transketolase is the relevant transketolase to inhibit. ...

Besides this, transketolase enzyme reactions represent also a target for therapeutic intervention in cancer. Transketolase enzyme reactions of the nonoxidative PPP play a crucial role in nucleic acid ribose synthesis utilizing glucose carbons in tumor cells. ... The importance of transketolases for tumor cell metabolism is underlined by the fact that the application of specific transketolase inhibitors to tumors induces a dramatic reduction in tumor cell proliferation. In addition, the activation of transketolases by application of thiamine stimulates tumor growth. ...

If the TKTL1-based glucose metabolism is important for tumorigenesis, the absence of TKTL1 enzyme activity should inhibit tumor proliferation. Inhibition of TKTL1 enzyme activity can be performed by cofactor analogues, substrate analogues, inhibitory small compounds and depletion of substrates. Inhibition of transketolase enzyme reaction by cofactor analogues (e.g. oxythiamine) and small compounds (Genistein63; AVEMAR64,65) have already been performed, and tumor proliferation could be successfully inhibited. Future analysis will show whether the tumor-inhibitory effect is due to an inhibition of TKTL1 transketolase.

merouleau wrote:This 2013 review cites 150 studies and concludes that we do not know if supplementing thiamine will increase or reduce our cancer risk. Along the way it identifies a number of research gaps.