New Role for Glutamine in Protein Synthesis? Study Suggests Direct Effects on Mammalian Target of Rapamycin (mTOR) - EAAs Alone Won't Produce Optimal Results

Image 1 (Pumping Iron): The guy in the middle, obviously no one else than the Austrian Oak, took glutamine, the rest of the guys forgot about it in all the craze about leucine... no, just kiddin' ;-) Still, someone who trains like Arnold, is probably most likely to benefit from additional l-glutamine

After all those bad news about allegedly effective supplements, I thought it may be about time to present some good news about an allegedly ineffective supplement: Glutamine! Published ahead of print in the online version of the scientific journal Amino Acids, the results from a 2012 study by Martina Chiu and her colleagues from the Unit of General and Clinical Pathology at the Department of Experimental Medicine of the University of Parma in Italy (Chia. 2012), could well explain a recent comment by Macijec who recounts that he saw great improvements in lean-mass retention on a diet from a combined BCAA + glutamine supplement over taking just plain BCAAs. And while I will get to what I believe is a much more likely explanation for this observation in the conclusion of this blogpost, let's initially take a look at what Chiu et al. bring to the table.

Don't take away my glutamine, man!

Previous studies by Evans et al. had already suggested that glutamine, despite its non-essential nature (meaning that your body can produce it from other amino acids by transamination), plays more than just a facilitative role in the phosphorylation of  the mammalian target of rapamycin (mTOR) and skeletal muscle protein synthesis (Evans. 2007 & 2008). To investigate this hypothesis further Chia et al. incubated HepG2 and HeLa cells (the use of these durable and cheap cells instead of myocytes as they were used by Evans, for example, is certainly a downside of the study) and found that

• the presence / abundance of glutamine influences mTORC1 activity 
• this effect is not mediated by glutamine induced increases in cellular leucine content
• the quantitative contribution of leucine and glutamine to the mTORC1 activation is cell-line specific
• even in the absence of glutamine, mTORC1 activity was not completely suppressed 
• in all cells both glutamine and leucine appear necessary for the maximal stimulation of mTORC1 

The cell-line specificity, is unequestionably problematic, still the general finding that glutamine depletion does not lead to a subsequent depletion or lack of uptake of EAAs, which would then in turn reduce the mTOR-induced phosphorylation of the protein uptake regulating enzyme p70S6K (Ribosomal protein S6 kinase beta-1) is probably valid for muscle cells as well. This suggests that" the signals and transduction pathways involved may be also distinct and their sensitivities different." (Chiu. 2012)

So what does that mean? To take or not to take glutamine - this is the question!

If we discard that the exact mechanism behind these observation still remains to be elucidated and invoke that there was a biphasic reaction to glutamine depletion with a minimum from 3h-6h and a subsequent partial rescue pf p70SK activity later, these results would support the value of the ingestion of supplemental glutamine particularly right after intense workouts or in periods of caloric restriction, where the intramuscular glutamine and EAA pools (muscle, liver, intestines) are drawn upon also as a substrate for hepatic glycogenesis (=production of sugar in the liver) and exogenous glutamine may spare "pro-anabolic" BCAAs/EAAs (Holecek. 2002).

Figure 1: Glutamine synthesis
(Self. 2004)

The study at hand, as well as the findings of Candow et al. who report a slight, but eventually negligibly greater increases in lean mass (+0.3%) and strength with 0.9g/kg glutamine supplementation over a 0.9g/kg bw. maltodextrin control in the absence of dietary restrictions do yet suggest that the effects of glutamine cannot be explained solely based on its energy content. And would warrant further investigations into what would be the threshold and optimal EAA and glutamine levels to propel skeletal muscle protein synthesis in vivo and whether or not, a energetically non-restricted high protein diet alone will not eventually provide enough glutamine and respective substrates for it's "on demand" production (cf. figure 1)

Are you training hard to be "glutamine deficient"?

That in fact the intensity of your exercise regimen may be the fundamental determinant of whether you do or don't need supplemental l-glutamine would be supported by the well-established efficiacy of parentally administered glutamine to critically ill patients. As so often inflammation appears to be, once again, the fundamentally important determinant, as it has been shown to increase in the net release of glutamine from peripheral tissues, such as your muscles, to central tissues and complex systems like the immune system  the liver (as mentioned before), the spleen (!) and wounds (Soeters. 2012). Against that background the longstanding practice of ingesting extra amounts of glutamine may well make sense, if the latter would actually make it to the periphery and would not be absorbed by exactly those previously enumerated "central tissues" that do not just need it the most, but that have a relatively comprehensive amount of scientific data to back the usefulness of glutamine as well as glutamine-(di-)peptides such as l-alanylglutamine (brand name Sustamine).

Are those dipeptides so much better? You will probably have heard about the "unbelievable", "unique" and "far superior effects" of glutamine dipeptides compared to the regular, dirt cheap free-form l-glutamine. And despite the fact that I am not aware of studies that would compare one to the other in a relevant, exercise related context, these statements do actually have a rationale basis. After all, the transport of intact peptides by the PEPT transporters in the gastrointestinal tract peptides has the major advantage that the cells of the gut do not avail themselves of as much glutamine as they want before it even reaches systemic circulation (Adibi. 1997). Whatever it's exact effects on protein synthesis may be - on a gram per gram base the dipeptides will therefore be more effective than regular l-glutamine. What you should keep in mind though is that you get both glutamine and alanine from sustamine at a ratio of ~3:2. The 40% of alanine are yet by no means useless. Rather, they could, in and out of themselves, exert (if nothing else) EAA and even glutamine sparing effects, since alanine is, next to lactate and pyruvate, the major gluconeogenic precursor during exercise (Brooks. 1987).

Image 2: I what's on this tummy is all you put in your tummy, l-glutamine alone will probably not prevent the highly undesirable transition from slightly chubby to skinny fat. With a dialed in, but calorically and/or carb restricted diet, l-glutamine supplementation could yet spare help you spare tissue protein, get rid of ammonia and maintain a decent amount of muscle.

The two exercise related studies on the latter by Hoffmann et al., which showed beneficial effects of l-alanylglutamine (AG) supplementation on hydration stress during endurance exercise and overall performance during a basketball match do yet suffer from a non-negligible methodological shortcoming: In both trials the AG solution was compared to plain water instead of an isocaloric carbohydrate solution. Against the background hat glutamine and alanine the individual amino acids the peptide is made of are the main substrates for amino acid driven hepatic gluconeogenesis it is at least very questionable whether the observed effects could not have been achieved by the same amount of plain table sugar, since both the  time to exhaustion during a mild hydration stress (Hoffmann. 2010) and the skill performance and visual reaction time (Hoffnmann. 2012) are unquestionably unrelated to the mTOR effects Chiu et al. observed in their study. 

It would thus warrant a longitudinal study in resistance trained individuals consuming a high protein diet on a high volume strength training regimen (>3 sessions per day, which is the maximum I have come across in hitherto published trials), to see whether your gains would benefit from additional glutamine... if you are dieting, on the other hand, you could argue that you better play safe than be sorry and add another tablespoon of glutamine to your BCAAs ;-)

References:

1. Adibi SA. The oligopeptide transporter (Pept-1) in human intestine: biology and function. Gastroenterology. 1997 Jul;113(1):332-40. 
2. Brooks GA. Amino acid and protein metabolism during exercise and recovery. Med Sci Sports Exerc. 1987 Oct;19(5 Suppl):S150-6.
3. Candow DG, Chilibeck PD, Burke DG, Davison KS, Smith-Palmer T. Effect of glutamine supplementation combined with resistance training in young adults. Eur  J Appl Physiol. 2001 Dec;86(2):142-9.
4. Chiu M, Tardito S, Barilli A, Bianchi MG, Dall'asta V, Bussolati O. Glutamine stimulates mTORC1 independent of the cell content of essential amino acids. Amino Acids. 2012 May 8. [Epub ahead of print]
5. Evans K, Nasim Z, Brown J, Clapp E, Amin A, Yang B, Herbert TP, Bevington A. Inhibition of SNAT2 by metabolic acidosis enhances proteolysis in skeletal muscle. J Am Soc Nephrol. 2008 Nov;19(11):2119-29. Epub 2008 Jul 23. 
6. Evans K, Nasim Z, Brown J, Butler H, Kauser S, Varoqui H, Erickson JD, Herbert TP, Bevington A. Acidosis-sensing glutamine pump SNAT2 determines amino acid levels and mammalian target of rapamycin signalling to protein synthesis in L6 muscle cells. J Am Soc Nephrol. 2007 May;18(5):1426-36. Epub 2007 Apr 11. 
7. Holecek M. Relation between glutamine, branched-chain amino acids, and protein metabolism. Nutrition. 2002 Feb;18(2):130-3. 
8. Self JT, Spencer TE, Johnson GA, Hu J, Bazer FW, Wu G. Glutamine synthesis in  the developing porcine placenta. Biol Reprod. 2004 May;70(5):1444-51. Epub 2004 Jan 21. 
9. Soeters PB, Grecu I. Have we enough glutamine and how does it work? A clinician's view. Ann Nutr Metab. 2012;60(1):17-26.