Correlation of glutamate plus aspartate dose, plasma amino acid concentration and neuronal necrosis in infant mice

Association of Glutamate Infusion With Risk of Acute Kidney Injury After Coronary Artery Bypass Surgery: A Pooled Analysis of 2 Randomized Clinical Trials

Importance

Acute kidney injury (AKI) after cardiac surgery is associated with increased morbidity and mortality, and measures to prevent AKI have had limited success. Glutamate has been reported to enhance natural postischemic recovery of the heart, but not among animals and humans with diabetes.

Objective

To summarize pooled results from the GLUTAMICS (Glutamate for Metabolic Intervention in Coronary Surgery) trials regarding the effect of glutamate on postoperative AKI among patients without diabetes undergoing coronary artery bypass graft (CABG) surgery.

Design, Setting, and Participants

Data on a total of 791 patients without diabetes from 2 prospective, randomized, double-blind multicenter trials performed at 5 cardiac surgery centers in Sweden between October 4, 2005, and November 12, 2009, and between November 15, 2015, and September 30, 2020, were pooled. Patients had acute coronary syndrome, left ventricular ejection fraction of 0.30 or less, or a European System for Cardiac Risk Evaluation II score of 3.0 or more and underwent CABG with or without additional valve procedure. Statistical analysis was performed from May to November 2023.

Interventions

Intravenous infusion of 0.125-M l-glutamic acid or saline at 1.65 mL/kg/h for 2 hours during reperfusion, after which the infusion rate was halved and an additional 50 mL was given.

Main Outcomes and Measures

The primary end point was AKI, defined as postoperative increase of plasma creatinine of 50% or more, corresponding to the Risk stage or higher in the Risk, Injury, Failure, Loss, and End-Stage kidney disease (RIFLE) criteria.

Results

A total of 791 patients without diabetes (391 who received glutamate [mean (SD) age, 69.3 (9.1) years; 62 women (15.9%)] and 400 controls [mean (SD) age, 69.6 (9.5) years; 73 women (18.3%)]) were randomized. Baseline data did not differ between groups. Glutamate was associated with a significantly lower risk of AKI (relative risk, 0.49 [95% CI, 0.29-0.83]). Dialysis was required for 2 patients in the glutamate group and 5 patients in the control group. In multivariable analysis, glutamate remained significantly associated with a protective effect against AKI (odds ratio, 0.47 [95% CI, 0.26-0.86]). In the glutamate and control groups, the rate of postoperative mortality at 30 days or less was 0.5% (2 of 391) vs 1.0% (4 of 400), and the rate of stroke at 24 hours or less was 0.8% (3 of 391) vs 1.8% (7 of 400).

Conclusions and Relevance

In this pooled analysis of 2 randomized clinical trials, infusion of glutamate was associated with a markedly lower risk of AKI after CABG among patients without diabetes. The findings are exploratory and need to be confirmed in prospective trials.

Trial Registration

ClinicalTrials.gov Identifiers: NCT00489827 and NCT02592824.

Re-evaluation of glutamic acid (E 620), sodium glutamate (E 621), potassium glutamate (E 622), calcium glutamate (E 623), ammonium glutamate (E 624) and magnesium glutamate (E 625) as food additives

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of glutamic acid-glutamates (E 620-625) when used as food additives. Glutamate is absorbed in the intestine and it is presystemically metabolised in the gut wall. No adverse effects were observed in the available short-term, subchronic, chronic, reproductive and developmental studies. The only effect observed was increased kidney weight and increased spleen weight; however, the increase in organ weight was not accompanied by adverse histopathological findings and, therefore, the increase in organ weight was not considered as an adverse effect. The Panel considered that glutamic acid-glutamates (E 620-625) did not raise concern with regards to genotoxicity. From a neurodevelopmental toxicity study, a no observed adverse effect level (NOAEL) of 3,200 mg monosodium glutamate/kg body weight (bw) per day could be identified. The Panel assessed the suitability of human data to be used for the derivation of a health-based guidance value. Although effects on humans were identified human data were not suitable due to the lack of dose-response data from which a dose without effect could be identified. Based on the NOAEL of 3,200 mg monosodium glutamate/kg bw per day from the neurodevelopmental toxicity study and applying the default uncertainty factor of 100, the Panel derived a group acceptable daily intake (ADI) of 30 mg/kg bw per day, expressed as glutamic acid, for glutamic acid and glutamates (E 620-625). The Panel noted that the exposure to glutamic acid and glutamates (E 620-625) exceeded not only the proposed ADI, but also doses associated with adverse effects in humans for some population groups.

Consumption of artificial sweetener- and sugar-containing soda and risk of lymphoma and leukemia in men and women

BACKGROUND

Despite safety reports of the artificial sweetener aspartame, health-related concerns remain.

OBJECTIVE

We prospectively evaluated whether the consumption of aspartame- and sugar-containing soda is associated with risk of hematopoetic cancers.

DESIGN

We repeatedly assessed diet in the Nurses' Health Study (NHS) and Health Professionals Follow-Up Study (HPFS). Over 22 y, we identified 1324 non-Hodgkin lymphomas (NHLs), 285 multiple myelomas, and 339 leukemias. We calculated incidence RRs and 95% CIs by using Cox proportional hazards models.

RESULTS

When the 2 cohorts were combined, there was no significant association between soda intake and risks of NHL and multiple myeloma. However, in men, ≥1 daily serving of diet soda increased risks of NHL (RR: 1.31; 95% CI: 1.01, 1.72) and multiple myeloma (RR: 2.02; 95% CI: 1.20, 3.40) in comparison with men who did not consume diet soda. We observed no increased risks of NHL and multiple myeloma in women. We also observed an unexpected elevated risk of NHL (RR: 1.66; 95% CI: 1.10, 2.51) with a higher consumption of regular, sugar-sweetened soda in men but not in women. In contrast, when sexes were analyzed separately with limited power, neither regular nor diet soda increased risk of leukemia but were associated with increased leukemia risk when data for men and women were combined (RR for consumption of ≥1 serving of diet soda/d when the 2 cohorts were pooled: 1.42; 95% CI: 1.00, 2.02).

CONCLUSION

Although our findings preserve the possibility of a detrimental effect of a constituent of diet soda, such as aspartame, on select cancers, the inconsistent sex effects and occurrence of an apparent cancer risk in individuals who consume regular soda do not permit the ruling out of chance as an explanation.

The S-100B substudy of the GLUTAMICS trial: glutamate infusion not associated with sustained elevation of plasma S-100B after coronary surgery

BACKGROUND & AIMS

Concerns have been raised about potential neurological injury related to exogenous glutamate. In cardiac surgery glutamate has been administered as a putative cardioprotective agent by cardioplegia or intravenous infusion. In the GLUTAMICS trial, in addition to surveillance of clinical neurological injuries, a prespecified subgroup was analyzed with regard to postoperative S-100B levels to detect potential subclinical neurological injury related to glutamate infusion.

METHODS

Sixty-nine patients operated on for unstable coronary syndrome were randomized to intravenous infusion of glutamate (n=35) or saline (n=34) perioperatively. Plasma levels of S-100B were obtained on the third postoperative day.

RESULTS

S-100B in the glutamate group and the control group were 0.079+/-0.034microg/L and 0.090+/-0.042microg/L respectively (p=0.245). There were no patients with stroke or mortality. Three patients in the control group and two in the glutamate group had postoperative confusion. These patients had significantly elevated S-100B compared with those without confusion (0.132+/-0.047vs 0.081+/-0.036microg/L; p=0.003). Overall, 21 patients had S-100B above reference level (> or =0.10microg/L) and these patients had significantly more calcifications in the ascending aorta on epiaortic scanning.

CONCLUSIONS

Intravenous glutamate infusion during surgery for unstable coronary artery disease did not initiate a sustained elevation of plasma S-100B. Thus, no evidence for subclinical neurological injury related to glutamate infusion was found. In contrast, postoperative elevation of plasma S-100B was linked to calcification of the ascending aorta and postoperative confusion.

Toxicity of hypercaloric diet and monosodium glutamate: oxidative stress and metabolic shifting in hepatic tissue

The present study examines the effects of a hypercaloric diet on hepatic glucose metabolism of young rats, with and without monosodium glutamate (MSG) administration, and the association of these treatments with evaluating markers of oxidative stress. Male weaned Wistar rats (21 days old) from mothers fed with a hypercaloric diet or a normal diet, were divided into four groups (n=6): control (C) fed with control diet; (MSG) treated with MSG (4 mg/g) and control diet; (HD) fed with hypercaloric diet and (MSG-HD) treated with MSG and HD. Rats were sacrificed after the oral glucose tolerance test (OGTT), at 45 days of treatments. Serum was used for insulin determination. Glycogen, hexokinase(HK), glucose-6-phosphatase(G6PH), lipid hydroperoxide, superoxide dismutase(SOD) and glutathione peroxidase(GSH-Px) were determined in liver. HD rats showed hypoglycemia, hyperinsulinemia, and high hepatic glycogen, HK and decreased G6PH. MSG and MSG-HD had hyperinsulinemia, hyperglycemia, decreased HK and increased G6PH in hepatic tissue. These animals had impaired OGTT. HD, MSG and MSG-HD groups had increased lipid hydroperoxide and decreased SOD in hepatic tissue. Hypercaloric diet and monosodium glutamate administration induced alterations in metabolic rate of glucose utilization and decreased antioxidant defenses. Therefore, the hepatic glucose metabolic shifting induced by HD intake and MSG administration were associated with oxidative stress in hepatic tissue.

Aspartame: review of safety

Over 20 years have elapsed since aspartame was approved by regulatory agencies as a sweetener and flavor enhancer. The safety of aspartame and its metabolic constituents was established through extensive toxicology studies in laboratory animals, using much greater doses than people could possibly consume. Its safety was further confirmed through studies in several human subpopulations, including healthy infants, children, adolescents, and adults; obese individuals; diabetics; lactating women; and individuals heterozygous (PKUH) for the genetic disease phenylketonuria (PKU) who have a decreased ability to metabolize the essential amino acid, phenylalanine. Several scientific issues continued to be raised after approval, largely as a concern for theoretical toxicity from its metabolic components--the amino acids, aspartate and phenylalanine, and methanol--even though dietary exposure to these components is much greater than from aspartame. Nonetheless, additional research, including evaluations of possible associations between aspartame and headaches, seizures, behavior, cognition, and mood as well as allergic-type reactions and use by potentially sensitive subpopulations, has continued after approval. These findings are reviewed here. The safety testing of aspartame has gone well beyond that required to evaluate the safety of a food additive. When all the research on aspartame, including evaluations in both the premarketing and postmarketing periods, is examined as a whole, it is clear that aspartame is safe, and there are no unresolved questions regarding its safety under conditions of intended use.

Neurological injury after surgery for ischemic heart disease: risk factors, outcome and role of metabolic interventions

OBJECTIVES

Neurological complication remains a feared and increasing problem in association with cardiac surgery. The aim of this study was to analyze risk factors for neurological complications in a cohort of patients in whom inotropes for weaning from cardiopulmonary bypass was gradually replaced by metabolic treatment.

METHODS

The records of 775 consecutive patients undergoing coronary artery bypass grafting (CABG) or combined CABG+valve procedures were examined. Forward stepwise multiple logistic regression analysis was used for statistical evaluation of independent risk factors.

RESULTS

The incidence of neurological injury was 1.8% in patients undergoing isolated CABG and 5.4% after combined CABG+valve procedures. After cross-validation multivariate analysis identified history of cerebrovascular disease, advanced age and aortic cross-clamp time as independent risk factors for postoperative cerebral complications. Chronic obstructive pulmonary disease and number of bypasses also emerged as risk factors in the primary analysis.

CONCLUSIONS

In general, markers for advanced atherosclerosis, with history of cerebrovascular disease as the most important, emerged as predictors for neurological injury. Although it did not enter the final risk model, the results also suggest that postoperative heart failure deserves further surveillance as a potential risk factor for neurological complications. However, no evidence for untoward neurological effects associated with glutamate or glucose-insulin-potassium treatment was found.

Assessment of myocardial glutamate requirements early after coronary artery bypass surgery

Glutamate is an important substrate for the intermediary metabolism of the heart, particularly in association with ischemia. Early after coronary artery bypass surgery (CABG) myocardial uptake of glutamate seems to be limited by substrate availability (arterial levels). However, glutamate is not an innocuous substrate. As arterial levels of glutamate are important both for myocardial uptake and adverse effects, an attempt was made to determine a minimum dose of glutamate sufficient to supply the needs of the heart after CABG. Ten patients received and infusion of 220-240 ml of 0.1 M L-glutamic acid solution at varying rates during two 30-min periods, starting 2 h after uncomplicated elective CABG. Intravenous glutamate infusion caused a dose-dependent linear increase in arterial glutamate and an increased myocardial uptake of glutamate. However, myocardial uptake of glutamate correlated with arterial levels only at lower infusion rates. Although maximal peak uptake in individual patients (6.6 +/- 1.1 mumol/min) occurred at an average increase of arterial whole blood glutamate of 172 +/- 34 mumol/L, the greatest impact on myocardial glutamate uptake was achieved by increasing arterial whole blood glutamate by less than 100 mumol/L. This implies that an infusion rate of 30-40 mg glutamate/kg BW/h could suffice to achieve a maximal or near maximal myocardial glutamate uptake in most patients after CABG. The adequacy of this dosage remains to be confirmed in high-risk patients.

A report of the proceedings of an MSG workshop held August 1991

This report of the proceedings of a workshop on monosodium glutamate (MSG) represents the output of an exchange of scientific information, discussed and debated, by a group of experts representing a variety of disciplines. Experts in the areas of food science, potential adverse reactions to foods, pharmacology, neuroscience, biochemistry, nutrition, pediatrics, and anatomy reviewed the current scientific literature relative to the safe use of MSG in foods. These proceedings supplement the extensive literature compiled by various prestigious international expert committees since the flavor-enhancing properties of MSG were identified around the turn of the century,

Acceptable daily intake vs actual intake: the aspartame example

This article discusses the acceptable daily intake (ADI) and the postmarketing surveillance of consumption levels for a food additive, using the widely used food additive aspartame (APM, L-aspartyl-L-phenylalanine methyl ester) as an example. The safety implications of the ADI and consumption levels are also discussed. Aspartame has been assigned an ADI of 40 mg/kg/day by the World Health Organization and regulatory authorities in Europe and Canada, and of 50 mg/kg/day by the US Food and Drug Administration. A number of different methods have been used to measure consumption levels of food additives. Consumption estimations for aspartame from one such method, the food intake survey, have been done in the United States, Canada, Germany, and Finland. APM consumption in all age groups and selected subpopulations, even at the 90th percentile, is approximately 2-10 mg/kg/day and is thus well below the ADI.

Aspartate-induced neuronal necrosis in infant mice: protective effect of carbohydrate and insulin

Infant mice given large doses of glutamate or aspartate develop hypothalamic neuronal necrosis. Studies by others demonstrated that simultaneous administration of carbohydrate or prior injection with insulin markedly decreased glutamate-induced neuronal damage. We investigated whether carbohydrate and insulin exert a similar protective effect against aspartate-induced neuronal necrosis. Eight-day-old mice administered aspartate at 750 and 1000 mg/kg body weight developed neuronal necrosis (45.9 +/- 7.2 and 80.8 +/- 17.3 necrotic neurons/section, respectively). When carbohydrate (1 g/kg body weight) was administered simultaneously no lesions were detected in mice administered 750 mg/kg body weight aspartate, while 30.1 +/- 14.2 necrotic neurons/section were noted at 1000 mg aspartate/kg body weight. Mice administered 1000 mg/kg body weight aspartate with prior injection of insulin had 28.4 +/- 12.6 necrotic neurons/section, while 4.2 +/- 1.4 necrotic neurons/section were noted in insulin treated mice given 750 mg aspartate/kg body weight. Carbohydrate and insulin treatments has only minimal effects on plasma aspartate concentrations.

Plasma amino acid concentrations in normal adults ingesting aspartame and monosodium L-glutamate as part of a soup/beverage meal

We tested the hypothesis that ingestion of monosodium L-glutamate with aspartame produces a marked increase in plasma glutamate and aspartate concentrations. Twelve normal adults (6 males, 6 females) ingested three different soup/beverage meals in a balanced Latin square design. One meal (A) provided no aspartame (APM) or monosodium L-glutamate (MSG); a second (B) provided 50 mg MSG/kg body weight; while the third (C) provided 50 mg MSG and 34 mg APM per kg body weight. Plasma glutamate (Glu) concentrations were not significantly affected by meal A but increased significantly after meals B and C (no significant difference between B and C). Plasma aspartate (Asp) concentrations were not significantly affected by meal A but increased significantly after meals B and C (values significantly higher after meal C than meal B). Plasma Glu + Asp concentrations were not significantly affected by meal A but increased significantly from a mean (+/- SD) baseline value of 5.64 +/- 2.62 mumol/dL to high mean values of 23.1 +/- 7.29 and 26.8 +/- 9.74 mumol/dL after ingestion of meals B and C, respectively (no significant difference between meals B and C). Similarly, the area under the plasma Glu + Asp concentration-time curve did not differ significantly between meals B and C (624 +/- 197 v 763 +/- 277 mumol/dL x min, respectively). Peak plasma Glu + Asp concentrations for each subject (ignoring time) were also examined. The mean peak plasma Glu + Asp concentrations were 7.39 +/- 2.77, 23.0 +/- 6.61, and 27.3 +/- 9.07 mumol/dL, respectively after meals A, B, and C.