GABA Supplementation Improves Glucose Management - Even in Healthy Subjects | Significant Reduction in Glycated Albumin Levels After Only 7 Days on 3x2g GABA per Day

No acute changes in blood glucose, but extreme changes in insulin levels. How can this trigger a reduction in glycated albumin - How's that possible?

You've read about gamma aminobutyric acid (GABA) at the SuppVersity before. While most people think of it mainly as a calming agent, though, SuppVersity readers know that it has the remarkable ability to heal the insulin producing β-cell in rodents by stimulating their replication, protecting them against apoptosis, and attenuating insulitis (Soltani. 2011; Tian. 2013; Prud'homme. 2014; Purwana. 2014). And while these favorable effects were first observed in mice, researchers are quite sure that they are valid in humans, too- that's also because said effects have been confirmed only recently by Tian et al. (2014) and Purwana et al. (2014) in vitro as well as in xenotransplanted human islets.
If you know that, the observations researchers from the Fudan University in Shanghai report in their latest study probably won't come as a surprise. In their investigation into the  pharmacokinetics and pharmacodynamics of GABA in healthy volunteers, the researchers found that the chronic provision of 2g of GABA three times per day triggers a highly significant decrease in glycated albumin (GA) levels, the intermediate measure of blood glucose control (in-between acute blood glucose measurements and HbA1c | Roohk. 2008), within only 7 days.

Figure 1: Acute glucose (top) and insulin (bottom) response after single and repeated administration of 2g of GABA (left). Chronic effects of repeated dose-administration of GABA on glycated albumin (right | Li. 2015).

If you scrutinize the data in Figure 1, though, there are a few questions we still need to find answers to. Obviously, the acute administration of GABA (Figure 1, left) lead to significant increases in insulin - both, under either fasting (1.6-fold, single dose; 2.0-fold, repeated dose; p < 0.01) or fed conditions (1.4-fold, single dose; 1.6-fold, repeated dose; p < 0.01).
Usually, this 1.4-fold or 1.6-fold increase in insulin should trigger a significant (at least transient) decrease in blood glucose. Since the latter wasn't the case in either the fasted or the fed tests the scientists conducted on the twelve subjects, who participated in the open-labeled, three-period trial, it appears more than counter-intuitive that the chronic administration of GABA which does not accumulate in the body and was found to be almost completely absorbed in 60 minutes and to have a half-life of 5h still lead to an GA decrease of approximately 11-12%.

Now this obviously confirms that GABA, due to its ability to increase islet hormonal secretion, has potential therapeutic benefits for diabetes, what the study does not tell us, though, is whether the lack of immediate effects on blood glucose levels can, as the scientists suspect, "in part be attributed to GABA-induced counter regulatory mechanisms, especially elevated glucagon" (Li. 2015) which rose so that the insulin-to-glucagon ratio remained unchanged. Yet while the latter could explain why the subjects did not become hypoglycemic in the face of increased insulin levels, the lack of certainty with respect to the underlying mechanisms makes the study results difficult to interpret.
References:

• Li, Junfeng, et al. "Study of GABA in Healthy Volunteers: Pharmacokinetics and Pharmacodynamics." Frontiers in Pharmacology 6 (2015): 260.
• Prud’homme, Gérald J., et al. "GABA protects human islet cells against the deleterious effects of immunosuppressive drugs and exerts immunoinhibitory effects alone." Transplantation 96.7 (2013): 616-623.
• Prud’homme, Gérald J., et al. "GABA protects pancreatic beta cells against apoptosis by increasing SIRT1 expression and activity." Biochemical and biophysical research communications 452.3 (2014): 649-654.
• Purwana, Indri, et al. "GABA promotes human β-cell proliferation and modulates glucose homeostasis." Diabetes 63.12 (2014): 4197-4205.
• Roohk, H. Vernon, and Asad R. Zaidi. "A review of glycated albumin as an intermediate glycation index for controlling diabetes." Journal of diabetes science and technology 2.6 (2008): 1114-1121.
• Soltani, Nepton, et al. "GABA exerts protective and regenerative effects on islet beta cells and reverses diabetes." Proceedings of the National Academy of Sciences 108.28 (2011): 11692-11697.
• Tian, Jide, et al. "γ-Aminobutyric acid inhibits T cell autoimmunity and the development of inflammatory responses in a mouse type 1 diabetes model." The Journal of Immunology 173.8 (2004): 5298-5304.
• Tian, Jide, et al. "Oral GABA treatment downregulates inflammatory responses in a mouse model of rheumatoid arthritis." Autoimmunity 44.6 (2011): 465-470.
• Tian, Jide, et al. "γ-Aminobutyric acid regulates both the survival and replication of human β-cells." diabetes 62.11 (2013): 3760-3765.
• Tian, Jide, et al. "Combined Therapy With GABA and Proinsulin/Alum Acts Synergistically to Restore Long-term Normoglycemia by Modulating T-Cell Autoimmunity and Promoting β-Cell Replication in Newly Diabetic NOD Mice." Diabetes 63.9 (2014): 3128-3134.