Phosphatidic Acid Reduces Whey-Induced Acute Protein Synthesis - Rodent Study Appears to Suggest Antagonism Not Synergism Between PA & Whey - What's the Verdict?

If we take the study at hand as a bench-mark, it appears as if you cannot really recommend PA supplements to serious gymrats. Due to a bunch of short-comings and a lot of open questions, I have to caution you not to jump to preliminary & potentially flawed conclusions.

If you are a "regular" here, at the SuppVersity, you will have heard about the mTOR-promoting effects of Phosphatidic Acid (PA) before (learn more). If you've also been following the SV News on Facebook, you will also know that I have repeatedly highlighted that we need studies that go beyond the mere provision of phosphatidic acid to mouse or man and assess whether adding PA to whey will ameliorate the whey-protein induced increases in protein synthesis, muscle and strength gains. Why would that be important if we do have studies that indicate that PA is effective? Well, anyone who even remotely considers paying the $$$ for a PA product will already be taking whey protein. If adding PA on top of his whey protein shake does not yield extra benefits (or worse), he would - and I would even say he should - not spend extra cash on phosphatidic acid... but before we get to any conclusions, let's take a close look at the latest research.

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To understand why one may even expect that there was a synergism between whey protein (or leucine) and phosphatidic acid, one has to be aware of the fact that both trigger mTOR, albeit via different pathways: While leucine activates mTOR through RAG GTPase, PA is thought to independently activate mTOR through competitive binding with the mTOR inhibitor FKBP38. As Mobley et al. point out in the introduction to their latest paper in the Journal of the ISSN it does thus "stand[...] to reason that whey protein could synergistically activate mTOR if co-ingested with PA" (Mobley. 2015). Accordingly, ...

"the purpose of this study was to examine if PA acutely increases anabolic signaling markers and muscle protein synthesis (MPS) in gastrocnemius with and without whey protein concentrate (WPC) supplementation" (Mobley. 2015).

In view of the fact that previous studies did not do a detailed analysis of the skeletal muscle transcriptomic response to PA and considering the fact that the latter may be important with respect to finding explanations for any - positive or negative - findings, Mobley et al. ran detailed analysis of the skeletal muscle mRNA response to PA and/or WPC, as well. Their goal was to assess whether PA or PA + whey would affect key genes involved in muscle mass maintenance (myostatin (Mstn) and p21Cip1), metabolism (PGC-1α and GLUT-4), and skeletal muscle atrophy (Atrogin-1 and MuRF-1). To get this data, the researchers randomly assigned male Wistar rats to four different treatments groups groups in which they were gavaged with one of the following "supplements":

• control (CON) - 1 ml of tap water
• phosphatidic acid (PA) - 0.029 g soy-derived PA (S-PA, Mediator®, ChemiNutra, Austin, TX, USA) suspended in 1 ml of tap water; this being a human equivalent dose of 1.5 g per the species conversion calculations of ReaganShaw et al. (learn more)
• whey protein concentrate (WPC) - 0.193 g WPC (standardized to 80 %, donated graciously by C.M.L.) suspended in 1 ml of tap water; this being a human equivalent dose of 10 g 
• combined (PA + WPC) - 0.029 g soy-derived PA + 0.193 g WPC suspended in 1 ml of tap water

Three hours post-feeding, the gastrocnemius muscle was removed and analyzed for markers of Akt-mTOR signaling, gene expression patterns related to skeletal muscle mass regulation and metabolism, and muscle protein synthesis (MPS) analysis (note: there was no training involved!).

Why is it important that there was no training involved? With training we'd have a third factor that affects protein synthesis and net muscle gains via the mTOR cascade. It is well possible that it does not make much of a difference and the results would be similar. In view of the fact that it is yet also possible that the results would be reversed, no athlete should make his supplement choices based on studies that do not involve a form of physical exercise that's at least remotely similar to his / her own training.

Figure 1: Effects of PA with or without the co-ingestion of WPC on skeletal muscle mRNA expression patterns. Legend: Data are presented as means ± standard error. Bars not sharing similar superscript letters are significantly different (p < 0.05 | Mobley. 2015).

In our discussion of the results, I'd like to start with the less controversial data (if there is any) in Figure 1. The figure depicts the 6 graphs that illustrate the skeletal muscle mRNA expression in response to the four different treatments. If you know something about reading graphs like this you will realize that the PA+WPC combo had a potentially anabolic advantage in terms of myostatin suppression. Just like the increase in glucose transporter GLUT-4, where the PA+WPC group shows significantly higher levels than any other group, this would be a clear sign of the expected beneficial synergism. However, no relevant differences were found for the potentially "atrophic" proteins MuRF-1 and atrogen-1 (learn more), and the mitochondria builder PGC-1a (for a discussion of the potential relevance of the significant increase of the cell-cycle arrest protein p21Cip1 in the PA only group see blue box).

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What do we make of the large increase in P21Clp1 mRNA? In view of the fact that the p21Cip1 gene is thought to promote satellite cell differentiation (Hawke. 2003a,b), one could argue that its increase in the PA group could be a harbinger of the reduced muscle protein synthesis in the whey condition. After all, any protein that goes to the myogenic precursor cells in the sarcoplasm is diverted away from the myoplasm and the myoblasts the scientists extracted from the rodents. If that's in fact case, it would be even more interesting to see a long-term study on PA + WPC. Eventually it would mean that PA may increase the recruitement of satellite cells. That's important not just for muscle repair, but also for growth.

In fact, a lack of new satellite cells which can form myonuclei will cause the domain sizes to increase to a critical level, where mostatin will stop further growth in order to prevent the muscle from becoming disfunctional, until new myonuclei have been formed from satellite cells.

So, if this process of muscle "restructuring" was triggered, promoted or enforced by PA this could be a huge plus. One that would be especially valuable for experienced athletes for whom the increase in domain sizes may in fact become a growth limiting factor. Unfortunately, all this remains speculative, until corresponding human long-term studies W/ will have been conducted.

If we think of the p21Cip1 elevation (see discussion in the blue box) as the "standby" for muscle gains, look at the increased myostatin levels and even the mTOR response in Figure 2 everything looks as if the study had hardly been necessary and the expected synergism was there. Unfortunately, the most straight forward marker of real-world benefits, the skeletal muscle protein synthesis (it's not a real-world benefit in and out of itself), tells us a very different story.

Figure 2: Effects of PA with or without the co-ingestion of WPC on mTOR-related signaling markers (a-f) and acute factional muscle protein synthesis (right hand side | Mobley. 2015).

If there was a synergism between whey and PA it does - and the data in Figure 2 leaves no doubt about that - not translate into increases in muscle protein synthesis. In fact, the addition of phosphatidic acid appears to blunt, not increase the acute influx of protein into the muscle. That may be a "shocking" revelation for some of you, but if you've been following the SuppVersity articles for a couple of month you will know that there's a disconnect between the increases in allegedly anabolic signalling molecules like mTOR & co and the actual rate of protein synthesis. That does not change the simple truth, though, that the data in Figure 2 (right) suggests that the provision of PA on top of whey protein impairs the protein anabolic effect of whey.

So, does this mean that phosphatidic acid is a supplemental non-starter? Let's not jump to conclusions we may regret, here. We are not only dealing with a preliminary rodent study, here, we are also dealing with a study without practically relevant study outcomes. Why's that? Well, you should remember that there are two disconnects when it comes to measuring mTOR, protein synthesis and actual muscle size & strength gains. I've already mentioned the first one: Increases in mTOR and related signalling proteins don't necessarily translate to increases in protein synthesis.

From previous SuppVersity articles you should yet also remember that increases in protein synthesis don't necessarily translate into significantly increased muscle gains, either (Burd. 2012 | learn more). Why's that? Well, I guess the answer is more complex than that, but one thing everyone should understand is that muscle gains are the difference between protein synthesis and breakdown. Whether the protein breakdown did in fact increase, though, is something the mere elevation of an allegedly catabolic signalling protein, i.e. MuRF1 (see Figure 1), in the study at hand cannot tell us reliably. What we'd really have to measure would be the net protein accrual (in sarcoplasm and myoplasm | see blue box) over 24h or more - a value that has not been determined in the study at hand. If we had this value and it was significantly lower with PA  + WPC, this would be a reason to be concerned.

On it's own PA has already proven that it works - even in humans, where it doubled the lean mass gains triggered albeit non-significant reductions in body fat at 50% of the dosage used in the study at hand. So, if anything, we may use this study to argue that adding PA to whey could be useless.

The lack of data on the net protein accrual is directly related to another problem Mobley et al. call the "limited post-feeding time point interrogation" and mean that you cannot tell what happens in days / weeks by measuring protein synthesis for a very short period at a "random" point after the ingestion of a supplement. Since we (b) also don't have data on the intramuscular PA levels and are (c) lacking data on different dosages of PA and/or WPC dosages as well as an exercise group (which could be a game changer), the only thing we can tell for sure is that future long-term human studies with relevant outcome markers, i.e. strength and muscle gains, as well as a resistance training component are needed before we can safely conclude that PA joins the ranks of the dozens of supplemental non-starters that have been celebrated in the absence of relevant scientific evidence as "the next best thing" in the past decades | Comment!

References:

• Burd, Nicholas A., et al. "Greater stimulation of myofibrillar protein synthesis with ingestion of whey protein isolate v. micellar casein at rest and after resistance exercise in elderly men." British Journal of Nutrition 108.06 (2012): 958-962.
• Hawke, Thomas J., Nan Jiang, and Daniel J. Garry. "Absence of p21CIP rescues myogenic progenitor cell proliferative and regenerative capacity in Foxk1 null mice." Journal of Biological Chemistry 278.6 (2003a): 4015-4020.
• Hawke, Thomas J., et al. "p21 is essential for normal myogenic progenitor cell function in regenerating skeletal muscle." American Journal of Physiology-Cell Physiology 285.5 (2003b): C1019-C1027.
• Mobley, C. Brooks, et al. "Effects of oral phosphatidic acid feeding with or without whey protein on muscle protein synthesis and anabolic signaling in rodent skeletal muscle." Journal of the International Society of Sports Nutrition 12.1 (2015): 32.