|Table of abbrevations used throughout paper|
|3xTg-AD||Triple Transgenic Alzheimer's Disease Mouse Model|
|GSM||Gamma secretase modulaor|
|iGSM||inverse GSM (increase Ab42)|
|straight GSM||Decrease Ab42|
|PPI||Proton Pump Inhibitor|
The primary objective of this research is to identify drugs that alter the biology of Alzheimer’s disease (AD). They focused on the effects of Proton Pump Inhibitors (PPI), specifically Lansoprazole, on the production of Amyloid-beta (Ab) species both in vivo and in vitro as they relate to AD. Little is known about the cause of AD but it is believed to be related to soluble Ab. Ab40 is the most common form of amyloid-beta while Ab42 is thought to be the most likely cause of pathogenesis.
The researchers first asked if the PPI lansoprazole was able to increase Ab levels in celluar models. They found that CHO exhibited a dose-dependent response to Lansoprazole, and at high doses found statistically higher concentrations of Ab42, and higher concentrations of Ab40, although those were not statistically significant. They found similar responses to other PPI that are commonly prescribed. Closer inspection of the extracellular environment of these cells showed an increase of relative amounts of Ab42 and decreased relative amounts of Ab38.
It is known that PPI can cross the blood brain barrier, so it is conceivable that they could change the biochemistry of the brain by altering pH levels. The authors suggest that it is possible that this altered pH can change the activity of some proteases. To determine if this response was biologically relevant and tested the response to PPI administration on wild type mice (WT) and on an Alzheimer’s disease triple transgeneic mouse strain (3xTg-AD). Only in acutely treated wild type mice could they find significantly increased levels of Ab40 while Ab42 remained elevated but not significantly so. The 3xTg-AD mice, however, showed significantly greater levels of Ab40 at moderate dosages, but still lacked significant differences in Ab42 production.
The authors then speculated on possible mechanisms. They suggest that the PPI lansoprazole is ascent as an iGSM, increasing the activity of BACE1 by changing the pH and thus the activity of the enzyme. They also suggest that it could be modulating the activity of gamma-secretase to cleave at different cites, increasing soluble levels of unwanted Amyloid species. I have provided a figure below to summarize this interaction.
This research is badly needed. I have personal experience with family who are struggling with dementia and are on PPI because of peptic ulcers. I also have young family members who suffer from heartburn and acid reflux, conditions that I believe are also treated with PPI on occasion. Existing medications have unknown effects on non-target tissues and it would not be surprising to find that these can change brain chemistry like these authors are suggesting.
I thought that many of the experiments were sound and I really applaud them for their use of color, but I did not like how they reported some of their findings textually. For example, I did like how they reported that amyloid species were elevated but not significantly so. It should be reported, but it seemed that they were trying to imply that the results were more important than they were by mentioning them in the same breath as their other data.
While I liked the topic and the experimentation they did perform, I took issue with three portions of their experimentation. First, as they pointed out, they only looked at extracellular levels of Ab species in their in vitro studies; they knew this was a short coming so they should have done the extra work to publish it along with their other data. Second, AD is also usually a late onset disease, and therefore I believe they should have also done some sort of AD age of onset evaluation of treated vs non-treated mice to determine if there was an effect. Finally, I do not believe their highest dosage treatment is truly biologically relevant. They point out that it sometimes used as a treatment for cancer, but this must be only a relatively small portion of the population. In conclusion I believe they may have been trying to make their work seem more significant than it truly is which is unnecessary, because most people can see the implications of their work without the added hype.
Here, the levels of Amyloid beta species 40 and 42 are visually quantified after treatment with varying concentrations of a designated PPI (Panels C and D) and Lansoprazole (Panels A and B). The amount of Amyloid beta species are determined through an ELISA and compared to the levels when only treated with the vehicle. These cells show a dose dependent response to treatment but only at higher concentrations of treatment, above 10 microliters, were the levels of Ab42 statistically significant. Other common PPI were also shown here to have a significant effect on Ab42. Only the extracellular levels of protein were assayed. DAPT is a negative control.
This figure is more involved but is asking exactly what Ab species and enzymes are present, at what levels, and if treatment with NSAIDS can revert the effect of this PPI. These questions are all related to the hypothesis that Lansoprazole is acting as an iGSM by changing the activity of BACE (through the pathway I explained above). Mass spectrometry is performed to determine the Ab species and their relative numbers present in the supernatant after treatment. Panel B is a western blot showing the amount of different forms of Amyloid species after long and short exposure times. Panel C shows the drug interactions between Lansoprazole and R-Flurbiprofen (a NSAID), showing that Lansoprazole was able to significantly undermine the effect that R-Flurbiprofen has on lowering levels of Ab42. Panel D is a western blot of APP and BACE1 (enzyme cleaving APP). This was done to determine if Lansoprazole was acting by increasing endogenous BACE1 levels or activity, this result suggests it is increasing activity. Paned E was a western blot quantifying the levels of APPb and APPa, APPb is the cleavage product from the BACE1 pathway that leads to Ab production. Here it is evident that soluble APPb is increased (although it appears soluble APPa is as well, but not as greatly. This suggests a skewing effect of Lansoprazole.
This is data from in vivo studies on two strains of mice, wild type above and the multi-transgenic AD model mice below. This data was gathered by ELISA on intracellular and extracellular brain tissue from treated mice (as opposed to only the extracellular levels as before). This data shows that only the acute treatment on wild type mice yielded significant results, and only for Ab40. The multi-transgenic AD mice appeared to be more susceptible to Lansoprazole and show a significant difference in Ab 40 at the acute treatment and also at the moderate treatment level. This figure also implies the partial genetic nature of AD, in that the transgenic mice were affected more greatly by the PPI, suggesting that some human populations may be more greatly effect than other populations.
This is a schematic view of the pathway that Lansoprazole is affecting. This figure is similar to the circuit diagram that I provided, but also provides a better cellular context. Essentially this figure presents their hypothesis that Lansoprazole is acting as an iGSM by making BACE1 a more active enzyme and increasing levels of pathogenic Ab species. What they do not show, but is explained in the text, is their supposition that gamma-secretase may also be modulated by Lansoprazole to cut in a different site.
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The Paper: The Proton Pump Inhibitor Lansoprazole Enhances Amyloid Beta Production
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Badiola, Nahuai, Victor Alcalde, Albert Pujol, Lisa-Marie Munter, Gerd Multhaup, Alberto Lleo, Mireia Coma, Montserrat Soler-Lopez, and Patrick Aloy. "The Proton Pump Inhibitor Lansoprazole Enhances Amyloid Beta Production." PLOS One E58837 8.3 (2013): 1-8. Print.