- Email: [email protected]
Food-added monosodium glutamate does not alter brain structure or antioxidant status
Pathophysiology 23 (2016) 303–305
Contents lists available at ScienceDirect
Pathophysiology journal homepage: www.elsevier.com/locate/pathophys
Review
Food-added monosodium glutamate does not alter brain structure or antioxidant status Miro Smriga International Glutamate Technical Committee (IGTC), 142 Ave. J. Bordet, 1100 Brussels, Belgium
a r t i c l e
i n f o
Article history: Received 30 June 2016 Accepted 21 October 2016 Keywords: Monosodium glutamate Brain Safety
a b s t r a c t The International Glutamate Technical Committee (IGTC) comments on a recent publication in “Pathophysiology” entitled “Evidence of alterations in brain structure and antioxidant status following “low-dose” monosodium glutamate ingestion” (authored by Onaolapo, Onaolapo, Akanmu and Gbola) [1]. In particular, IGTC highlights that, in the view of published scientific literature [2–12], the methods of this study were inappropriate and did not support conclusions drawn by the authors. © 2016 Elsevier B.V. All rights reserved.
Contents 1.
Methodology and results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 1.1. IGTC expresses reservations to the methods used to analyze brain histology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 2. Interpretation and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 Declaration of interests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
The manuscript of Onaolapo et al. [1] described the results of a single 4-week-long study conducted in mice which were daily intubated with distilled water, various doses of monosodium glutamate (MSG) or L-glutamic acid. Mice were weighted weekly. At the end of the whole experiment, plasma and whole brain levels of glutamate, glutamine, nitric oxide and superoxide dismutase were determined. Several brain regions were stained and microscopically examined. 1. Methodology and results It is difficult to understand why distilled water, rather than sodium chloride solution, was used as a control. A molecule of MSG is made of sodium (12%) and l-glutamate (88%). Therefore mice which were forcibly intubated with the highest tested dose of MSG (80 mg/kg) received 10 mg/kg of sodium. A possibility of sodium impacting the observed outcomes was neither discussed nor controlled for. Secondly, it is difficult to interpret the need for using l-glutamate (10 mg/kg) as an additional test group. If l-glutamate was intended as a “positive control”, it would have been appro-
E-mail addresses: [email protected], miro [email protected] http://dx.doi.org/10.1016/j.pathophys.2016.10.003 0928-4680/© 2016 Elsevier B.V. All rights reserved.
priate to use it at a dose that corresponded to the highest dose of MSG tested. Lastly, it is noticeable that diet and water intake were not reported, and therefore one could not interpret body weighty changes. Timing of daily forced intubations was not indicated in the method section of the article [1]. The authors claimed that tested substances were not infused into empty stomach, but since mice are nocturnal animals, it is difficult to see how that was ensured. On the other hand, the authors discussed in some detail dosing of the intubated MSG and argued that the applied doses corresponded to human exposure to food-added MSG. IGTC does not object to the choice of MSG doses. However, we argue that forced intubation into an empty stomach does not represent an appropriate model for food intake of MSG. Moreover, IGTC argues that orally intubated dose was irrelevant, because of the following considerations: (A) Assuming that the authors used adult mice that normally ingest diet at more than 12% of their body weight [2], we conclude that the tested mice of all groups consumed daily at least 2.65 g of standard chaw diet. (B) If that diet was based on milk casein, as is usually the case, it contained 10% glutamate, so the mice were ingesting approximately 0.26 g of glutamate from the diet itself (without regards to test-group). (C) The group of mice intubated with MSG at the highest dose (80 mg/kg body weight) received additional 1.7 mg of glutamate. This dose corresponds to a tiny fraction (0.7%) of glu-
304
M. Smriga / Pathophysiology 23 (2016) 303–305
tamate already ingested by all groups from the experimental diet, thus it is not probable that such a fractional addition, if intubated without causing nonspecific stress, would affect morphology of the brain. Authors reported that plasma glutamate levels were doubled in the animals receiving MSG at 40 and 80 mg/kg body weight, when compared to the values observed in controls. These results are difficult to comment on, because it is not clear when the blood was withdrawn; vis-à-vis the intubation. Forced intubation of MSG into an empty stomach increases plasma levels of glutamate, but considering that the dose was low, plasma glutamate was most probably normalized within 1–2 h after the offset of intubation [3,4]. At this point, one needs to consider that less than five percent of orally ingested glutamate is absorbed from the gut into the systemic circulation and the rest is used as an oxidative substrate by the intestinal mucosa [5–7]. During normal eating behavior, other food components, which are inevitably ingested along with food-added MSG, further suppress circulating glutamate levels [3,8]. Even in pharmacological conditions, when MSG is intubated at a high dose, the excess glutamate that might be leaving the gastrointestinal tract is completely metabolized in the liver into urea, alanine or glutamine [9], so that systematic plasma levels are normalized very efficiently. Among others, oral ingestion of MSG (150 mg/kg body weight) in humans at empty stomach transiently increased plasma glutamate levels for only 105 min [10]. Even though body weight was measured weekly, only the final body weight (at day 28 of experiment) was provided. All values were expressed in relative terms [1,Fig. 1]. MSG dose of 40 mg/kg resulted in a 5–6% decrease of body weight when compared to body weight of controls, while the highest tested dose of 80 mg/kg resulted in a 2–3% increase of body weight. Those changes were not statistically significant, but considering the terminal body weight variances between the two groups with highest MSG intake; it is not clear how to interpret minor (<0.1%) difference in relative brain weight of the two MSG groups and controls [1,Fig. 2]. This author presumes that the relative brain weight changes were random and completely independent of the treatment.
1.1. IGTC expresses reservations to the methods used to analyze brain histology
2. Interpretation and discussion The authors hypothesized that “permissible consumption limits” on MSG in humans could be exceeded in near future. However, there are no permissible limits on MSG intake from food. First of all, flavor-enhancing effects of MSG are strongly dose-dependent and self-limiting. Use of MSG in food is over the range of 0.2–0.8% of food as consumed [13,14]. Higher concentrations would be detrimental to flavor properties of food and therefore are not used. In addition, the effects of MSG depend on the food matrix [15], which means that MSG cannot be used to enhance flavor of every food item or improve taste of poor foods. The second reason for the absence of “permissible consumption limits” on MSG is in the general safety of the substance – when used in food. Glutamate itself is present in almost all savory ingredients. Adult humans ingest about 10–12 g glutamate per day from a normal diet e.g. [16]. This volume includes 0.5–1.0 g per day of glutamate added to food as a flavor enhancer, whether in a form of MSG or included in other condiments rich in glutamate (e.g., bouillon cubes, soy sauces and cheeses). In simple words, the condiment-type glutamates in a daily diet represent minor portion of all ingested glutamates. Finally, it is noteworthy that the Joint FAO/WHO Expert Committee on Food Additives (JECFA) assessed the safety, including the central nervous system safety, of MSG as early as 1988 [17]. JECFA concluded that the total dietary intake of food glutamate did not represent a hazard to health and that the establishment of a numerical Acceptable Daily Intake (ADI) was not necessary. It is very important to monitor and study safety of food substances. However, IGTC argues that the research reported by Onaolapo et al. [1] did not apply appropriate methodology to reflect on food use of MSG. Declaration of interests The author is a member of IGTC secretariat. IGTC is an observer organization of Codex dedicated to supporting MSG research. The author is also employed by Ajinomoto Co., Inc. (Tokyo, Japan); a producer of MSG. References
First, the brains were not perfused prior to dissection and therefore it is not possible to determine if the measured substances, such as glutamate, glutamine and nitric oxide originated from the periphery or from the brain itself. Indeed, the interstitial glutamate content in the brain extracellular space is normally below 1 mM [11] and therefore the observed results (in the control group as well as MSG groups) indicate that at least some penetration of peripheral glutamate into the brain happened during the brain dissection. The authors stated that there were no treatment-related differences in the brain glutamate content, except for those differences observed “visually”. The same comment was made for other measurements, such as body weight. It is not clear what “visual difference” mean in the case of a measured parameter, such as glutamate content in the brain or body weight. Second, due to an absence of a stereotaxic brain atlas for inbred Swiss mice, dissections and consequent brain slice histology would have been difficult to compare rigorously in terms of cell count. Therefore, it was somehow surprising that the observations of cell counts in various brain regions [1,Tab. 4–7] were provided with as low standard error as <2% of the measured values. For a sake of comparison, a new study in Sprague-Dawley rats [12], which applied a comparable methodology to count total cells or neurons in the hippocampus, reported results with standard error of 23–33% of the measured values.
[1] O.J. Onaolapo, A.Y. Onaolapo, M.A. Akanmu, O. Gbola, Evidence of alterations in brain structure and antioxidant status following low-dose monosodium glutamate ingestion, Pathophysiology 78 (2016) 42–56. [2] A.A. Bachmanov, D.R. Reed, G.K. Beauchamp, M.G. Tordoff, Food Intake water intake, and drinking spout side preference of 28 mouse strains, Behav. Genet. 32 (2002) 435–443. [3] L.D. Stegink, L.J. Filer, G.L. Baker, Plasma glutamate concentrations in adult subjects ingesting monosodium l-glutamate in consommé, Am. J. Clin. Nutr. 42 (1985) 220–225. [4] L.D. Stegink, L.J. Filer, G.L. Baker, E.F. Bell, Plasma glutamate concentrations in 1-year-old infants and adults ingesting monosodium l-glutamate in consommé, Pediatr. Res. 20 (1986) 53–58. [5] K.D. Neame, G. Wiseman, The transamination of glutamate and aspartate during absorption by the small intestine of the dog in vivo, J. Physiol. 135 (1957) 442–450. [6] P.J. Reeds, D.G. Burrin, F. Jahoor, L. Wykes, J. Henry, E.M. Frazer, Enteral glutamate is almost completely metabolized in first pass by the gastrointestinal tract of infant pigs, Am. J. Physiol. 270 (1996) E413–E418. [7] P.J. Reeds, D.G. Burrin, B. Stoll B, F. Jahoor, Intestinal glutamate metabolism, J. Nutr. 130 (2000) 978S–982S. [8] J.D. Fernstrom, S. Garattini, International symposium on glutamate. Introduction to the symposium proceedings, J. Nutr. 130 (2000) 891S–894S. [9] C. Remesy, Glutamine or glutamate release by the liver constitutes a major mechanism for nitrogen salvage, Am. J. Physiol. 272 (1997) G257–G264. [10] T.E. Graham, V. Sgro, D. Friars, M.J. Gibala, Glutamate ingestion: the plasma and muscle free amino acid pools of resting humans, Am. J. Physiol. Endocrinol. Metab. 278 (2000) E83–E90. ´ [11] J. Bernacki, A. Dobrowolska, K. Nierwinska, A. Małecki, Physiology and pharmacological role of the blood-brain barrier, Pharmacol. Rep. 60 (2008) 600–622.
M. Smriga / Pathophysiology 23 (2016) 303–305 [12] S. Madhavas, S. Subramanian, Cognition enhancing effect of the aqueous extract of Cinnamomum zeylanicum on non-transgenic Alzheimer’s disease rat model: biochemical, histological and behavioural studies, Nutr. Neurosci 19 (2016) 1194593, http://dx.doi.org/10.1080/1028415X.2016.1194593. [13] S. Yamaguchi, K. Ninomiya, Umami and food palatability, J. Nutr. 130 (2000) 921S–926S. [14] S. Yamaguchi, C. Takahashi, Hedonic functions of monosodium glutamate and four basic taste substances used at various concentration levels in single and complex systems, Agric. Biol. Chem. 48 (1984) 1077–1081.
305
[15] N. Barylko-Pikielna, E. Kostyra, Sensory interaction of umami substances with model food matrices and its hedonic effect, Food Qual. Preference 18 (2007) 751–758. [16] J.D. Fernstrom, Dietary amino acids and brain function, J. Am. Diet. Assoc. 94 (1994) 71–77. [17] JECFA, L-glutamic Acid and Its Ammonium, Calcium, Monosodium and Potassium Salts. In: Toxicological Evaluation of Certain Food Additives and Contaminants, Cambridge University Press, New York, 1988, pp. 97–161.
Contents lists available at ScienceDirect
Pathophysiology journal homepage: www.elsevier.com/locate/pathophys
Review
Food-added monosodium glutamate does not alter brain structure or antioxidant status Miro Smriga International Glutamate Technical Committee (IGTC), 142 Ave. J. Bordet, 1100 Brussels, Belgium
a r t i c l e
i n f o
Article history: Received 30 June 2016 Accepted 21 October 2016 Keywords: Monosodium glutamate Brain Safety
a b s t r a c t The International Glutamate Technical Committee (IGTC) comments on a recent publication in “Pathophysiology” entitled “Evidence of alterations in brain structure and antioxidant status following “low-dose” monosodium glutamate ingestion” (authored by Onaolapo, Onaolapo, Akanmu and Gbola) [1]. In particular, IGTC highlights that, in the view of published scientific literature [2–12], the methods of this study were inappropriate and did not support conclusions drawn by the authors. © 2016 Elsevier B.V. All rights reserved.
Contents 1.
Methodology and results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 1.1. IGTC expresses reservations to the methods used to analyze brain histology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 2. Interpretation and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 Declaration of interests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
The manuscript of Onaolapo et al. [1] described the results of a single 4-week-long study conducted in mice which were daily intubated with distilled water, various doses of monosodium glutamate (MSG) or L-glutamic acid. Mice were weighted weekly. At the end of the whole experiment, plasma and whole brain levels of glutamate, glutamine, nitric oxide and superoxide dismutase were determined. Several brain regions were stained and microscopically examined. 1. Methodology and results It is difficult to understand why distilled water, rather than sodium chloride solution, was used as a control. A molecule of MSG is made of sodium (12%) and l-glutamate (88%). Therefore mice which were forcibly intubated with the highest tested dose of MSG (80 mg/kg) received 10 mg/kg of sodium. A possibility of sodium impacting the observed outcomes was neither discussed nor controlled for. Secondly, it is difficult to interpret the need for using l-glutamate (10 mg/kg) as an additional test group. If l-glutamate was intended as a “positive control”, it would have been appro-
E-mail addresses: [email protected], miro [email protected] http://dx.doi.org/10.1016/j.pathophys.2016.10.003 0928-4680/© 2016 Elsevier B.V. All rights reserved.
priate to use it at a dose that corresponded to the highest dose of MSG tested. Lastly, it is noticeable that diet and water intake were not reported, and therefore one could not interpret body weighty changes. Timing of daily forced intubations was not indicated in the method section of the article [1]. The authors claimed that tested substances were not infused into empty stomach, but since mice are nocturnal animals, it is difficult to see how that was ensured. On the other hand, the authors discussed in some detail dosing of the intubated MSG and argued that the applied doses corresponded to human exposure to food-added MSG. IGTC does not object to the choice of MSG doses. However, we argue that forced intubation into an empty stomach does not represent an appropriate model for food intake of MSG. Moreover, IGTC argues that orally intubated dose was irrelevant, because of the following considerations: (A) Assuming that the authors used adult mice that normally ingest diet at more than 12% of their body weight [2], we conclude that the tested mice of all groups consumed daily at least 2.65 g of standard chaw diet. (B) If that diet was based on milk casein, as is usually the case, it contained 10% glutamate, so the mice were ingesting approximately 0.26 g of glutamate from the diet itself (without regards to test-group). (C) The group of mice intubated with MSG at the highest dose (80 mg/kg body weight) received additional 1.7 mg of glutamate. This dose corresponds to a tiny fraction (0.7%) of glu-
304
M. Smriga / Pathophysiology 23 (2016) 303–305
tamate already ingested by all groups from the experimental diet, thus it is not probable that such a fractional addition, if intubated without causing nonspecific stress, would affect morphology of the brain. Authors reported that plasma glutamate levels were doubled in the animals receiving MSG at 40 and 80 mg/kg body weight, when compared to the values observed in controls. These results are difficult to comment on, because it is not clear when the blood was withdrawn; vis-à-vis the intubation. Forced intubation of MSG into an empty stomach increases plasma levels of glutamate, but considering that the dose was low, plasma glutamate was most probably normalized within 1–2 h after the offset of intubation [3,4]. At this point, one needs to consider that less than five percent of orally ingested glutamate is absorbed from the gut into the systemic circulation and the rest is used as an oxidative substrate by the intestinal mucosa [5–7]. During normal eating behavior, other food components, which are inevitably ingested along with food-added MSG, further suppress circulating glutamate levels [3,8]. Even in pharmacological conditions, when MSG is intubated at a high dose, the excess glutamate that might be leaving the gastrointestinal tract is completely metabolized in the liver into urea, alanine or glutamine [9], so that systematic plasma levels are normalized very efficiently. Among others, oral ingestion of MSG (150 mg/kg body weight) in humans at empty stomach transiently increased plasma glutamate levels for only 105 min [10]. Even though body weight was measured weekly, only the final body weight (at day 28 of experiment) was provided. All values were expressed in relative terms [1,Fig. 1]. MSG dose of 40 mg/kg resulted in a 5–6% decrease of body weight when compared to body weight of controls, while the highest tested dose of 80 mg/kg resulted in a 2–3% increase of body weight. Those changes were not statistically significant, but considering the terminal body weight variances between the two groups with highest MSG intake; it is not clear how to interpret minor (<0.1%) difference in relative brain weight of the two MSG groups and controls [1,Fig. 2]. This author presumes that the relative brain weight changes were random and completely independent of the treatment.
1.1. IGTC expresses reservations to the methods used to analyze brain histology
2. Interpretation and discussion The authors hypothesized that “permissible consumption limits” on MSG in humans could be exceeded in near future. However, there are no permissible limits on MSG intake from food. First of all, flavor-enhancing effects of MSG are strongly dose-dependent and self-limiting. Use of MSG in food is over the range of 0.2–0.8% of food as consumed [13,14]. Higher concentrations would be detrimental to flavor properties of food and therefore are not used. In addition, the effects of MSG depend on the food matrix [15], which means that MSG cannot be used to enhance flavor of every food item or improve taste of poor foods. The second reason for the absence of “permissible consumption limits” on MSG is in the general safety of the substance – when used in food. Glutamate itself is present in almost all savory ingredients. Adult humans ingest about 10–12 g glutamate per day from a normal diet e.g. [16]. This volume includes 0.5–1.0 g per day of glutamate added to food as a flavor enhancer, whether in a form of MSG or included in other condiments rich in glutamate (e.g., bouillon cubes, soy sauces and cheeses). In simple words, the condiment-type glutamates in a daily diet represent minor portion of all ingested glutamates. Finally, it is noteworthy that the Joint FAO/WHO Expert Committee on Food Additives (JECFA) assessed the safety, including the central nervous system safety, of MSG as early as 1988 [17]. JECFA concluded that the total dietary intake of food glutamate did not represent a hazard to health and that the establishment of a numerical Acceptable Daily Intake (ADI) was not necessary. It is very important to monitor and study safety of food substances. However, IGTC argues that the research reported by Onaolapo et al. [1] did not apply appropriate methodology to reflect on food use of MSG. Declaration of interests The author is a member of IGTC secretariat. IGTC is an observer organization of Codex dedicated to supporting MSG research. The author is also employed by Ajinomoto Co., Inc. (Tokyo, Japan); a producer of MSG. References
First, the brains were not perfused prior to dissection and therefore it is not possible to determine if the measured substances, such as glutamate, glutamine and nitric oxide originated from the periphery or from the brain itself. Indeed, the interstitial glutamate content in the brain extracellular space is normally below 1 mM [11] and therefore the observed results (in the control group as well as MSG groups) indicate that at least some penetration of peripheral glutamate into the brain happened during the brain dissection. The authors stated that there were no treatment-related differences in the brain glutamate content, except for those differences observed “visually”. The same comment was made for other measurements, such as body weight. It is not clear what “visual difference” mean in the case of a measured parameter, such as glutamate content in the brain or body weight. Second, due to an absence of a stereotaxic brain atlas for inbred Swiss mice, dissections and consequent brain slice histology would have been difficult to compare rigorously in terms of cell count. Therefore, it was somehow surprising that the observations of cell counts in various brain regions [1,Tab. 4–7] were provided with as low standard error as <2% of the measured values. For a sake of comparison, a new study in Sprague-Dawley rats [12], which applied a comparable methodology to count total cells or neurons in the hippocampus, reported results with standard error of 23–33% of the measured values.
[1] O.J. Onaolapo, A.Y. Onaolapo, M.A. Akanmu, O. Gbola, Evidence of alterations in brain structure and antioxidant status following low-dose monosodium glutamate ingestion, Pathophysiology 78 (2016) 42–56. [2] A.A. Bachmanov, D.R. Reed, G.K. Beauchamp, M.G. Tordoff, Food Intake water intake, and drinking spout side preference of 28 mouse strains, Behav. Genet. 32 (2002) 435–443. [3] L.D. Stegink, L.J. Filer, G.L. Baker, Plasma glutamate concentrations in adult subjects ingesting monosodium l-glutamate in consommé, Am. J. Clin. Nutr. 42 (1985) 220–225. [4] L.D. Stegink, L.J. Filer, G.L. Baker, E.F. Bell, Plasma glutamate concentrations in 1-year-old infants and adults ingesting monosodium l-glutamate in consommé, Pediatr. Res. 20 (1986) 53–58. [5] K.D. Neame, G. Wiseman, The transamination of glutamate and aspartate during absorption by the small intestine of the dog in vivo, J. Physiol. 135 (1957) 442–450. [6] P.J. Reeds, D.G. Burrin, F. Jahoor, L. Wykes, J. Henry, E.M. Frazer, Enteral glutamate is almost completely metabolized in first pass by the gastrointestinal tract of infant pigs, Am. J. Physiol. 270 (1996) E413–E418. [7] P.J. Reeds, D.G. Burrin, B. Stoll B, F. Jahoor, Intestinal glutamate metabolism, J. Nutr. 130 (2000) 978S–982S. [8] J.D. Fernstrom, S. Garattini, International symposium on glutamate. Introduction to the symposium proceedings, J. Nutr. 130 (2000) 891S–894S. [9] C. Remesy, Glutamine or glutamate release by the liver constitutes a major mechanism for nitrogen salvage, Am. J. Physiol. 272 (1997) G257–G264. [10] T.E. Graham, V. Sgro, D. Friars, M.J. Gibala, Glutamate ingestion: the plasma and muscle free amino acid pools of resting humans, Am. J. Physiol. Endocrinol. Metab. 278 (2000) E83–E90. ´ [11] J. Bernacki, A. Dobrowolska, K. Nierwinska, A. Małecki, Physiology and pharmacological role of the blood-brain barrier, Pharmacol. Rep. 60 (2008) 600–622.
M. Smriga / Pathophysiology 23 (2016) 303–305 [12] S. Madhavas, S. Subramanian, Cognition enhancing effect of the aqueous extract of Cinnamomum zeylanicum on non-transgenic Alzheimer’s disease rat model: biochemical, histological and behavioural studies, Nutr. Neurosci 19 (2016) 1194593, http://dx.doi.org/10.1080/1028415X.2016.1194593. [13] S. Yamaguchi, K. Ninomiya, Umami and food palatability, J. Nutr. 130 (2000) 921S–926S. [14] S. Yamaguchi, C. Takahashi, Hedonic functions of monosodium glutamate and four basic taste substances used at various concentration levels in single and complex systems, Agric. Biol. Chem. 48 (1984) 1077–1081.
305
[15] N. Barylko-Pikielna, E. Kostyra, Sensory interaction of umami substances with model food matrices and its hedonic effect, Food Qual. Preference 18 (2007) 751–758. [16] J.D. Fernstrom, Dietary amino acids and brain function, J. Am. Diet. Assoc. 94 (1994) 71–77. [17] JECFA, L-glutamic Acid and Its Ammonium, Calcium, Monosodium and Potassium Salts. In: Toxicological Evaluation of Certain Food Additives and Contaminants, Cambridge University Press, New York, 1988, pp. 97–161.