Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance.

Non-nutritive sweeteners (NNS) are commonly integrated into human diet and presumed to be inert; however, animal studies suggest that they may impact the microbiome and downstream glycemic responses. We causally assessed NNS impacts in humans and their microbiomes in a randomized-controlled trial encompassing 120 healthy adults, administered saccharin, sucralose, aspartame, and stevia sachets for 2 weeks in doses lower than the acceptable daily intake, compared with controls receiving sachet-contained vehicle glucose or no supplement. As groups, each administered NNS distinctly altered stool and oral microbiome and plasma metabolome, whereas saccharin and sucralose significantly impaired glycemic responses. Importantly, gnotobiotic mice conventionalized with microbiomes from multiple top and bottom responders of each of the four NNS-supplemented groups featured glycemic responses largely reflecting those noted in respective human donors, which were preempted by distinct microbial signals, as exemplified by sucralose. Collectively, human NNS consumption may induce person-specific, microbiome-dependent glycemic alterations, necessitating future assessment of clinical implications.

Identify old drugs as selective bacterial ß-GUS inhibitors by structural-based virtual screening and bio-evaluations.

Irinotecan (CPT-11) is a cytotoxic drug that has wide applicability and usage in cancer treatment. Despite its success, patients suffer dose-dependent diarrhea, limiting the drug's efficacy. No effective therapy is available for this unmet medical need. The bacterial ß-glucuronidase (ß-GUS) plays pivotal role in CPT-11-induced diarrhea (CID) via activating the non-toxic SN-38G to toxic SN-38 inside intestine. By using structural-based virtual screening, three old drugs (N-Desmethylclozapine, Aspartame, and Gemifloxacin) were firstly identified as selective bacterial ß-GUS inhibitors. The IC50 values of the compounds in the enzyme-based and cell-based assays range from 0.0389 to 3.6040 and 0.0105 to 5.3730 µM, respectively. The compounds also showed good selectivity against mammalian ß-GUS and no significant cytotoxicity in bacteria. Molecular docking and molecular dynamics simulations were performed to further investigate the binding modes of compounds with bacterial ß-GUS. Binding free energy decomposition revealed that the compounds formed strong interactions with E413 in catalytic trail from primary monomer and F365' on the bacterial loop from the other monomer of bacterial ß-GUS, explaining the selectivity against mammalian ß-GUS. The old drugs identified here may be used as bacterial ß-GUS inhibitors for CID or other bacterial ß-GUS-related disorders.

High-dose chromium(III) supplementation has no effects on body mass and composition while altering plasma hormone and triglycerides concentrations.

Chromium is generally believed to be an essential element and is often claimed to have value as a weight loss or muscle building agent. Recent studies in humans and rats have failed to demonstrate effects on body composition, although recent studies with pharmacological doses of the cation [Cr(III)3O(O2CCH2CH3)6(H2O)3]+ (or Cr3) (< or =1 mg Cr/kg body mass) in rats have noted a trend toward body mass loss and fat mass loss. Thus, the effects of large gavage doses of Cr3 (1-10 mg Cr/kg) on body mass, organ mass, food intake, and blood plasma variables (insulin, glucose, leptin, cholesterol, and triglycerides) were examined over a 10-wk period using male Sprague-Dawley rats. No effects on body composition were noted, although Cr3 administration lowered (p < 0.05) plasma insulin, leptin, and triglycerides concentrations. As Cr3 is absorbed greater than 10-fold better than commercially available nutritional supplements, the lack of an effect of the Cr(III) compound at these levels of administration clearly indicates that Cr(III) supplements do not have an effect on body composition at any reasonable dosage.

Functional magnetic resonance imaging of human hypothalamic responses to sweet taste and calories.

BACKGROUND: Evidence exists that beverages do not trigger appropriate anticipatory physiologic responses, such as cephalic phase insulin release. Therefore, it is of interest to elucidate the food properties necessary for triggering adaptive responses. Previously, we found a prolonged dose-dependent decrease in the hypothalamic functional magnetic resonance imaging signal after ingestion of a glucose solution. OBJECTIVES: The aims of the present study were to measure the effects of sweet taste and energy content on the hypothalamic response to glucose ingestion and to measure the concomitant changes in blood glucose and insulin concentrations. DESIGN: Five healthy, normal-weight men participated in a randomized crossover design trial. The subjects were scanned 4 times for 37 min on separate days with functional magnetic resonance imaging. After 7 min, they ingested 1 of the following 4 stimuli (300 mL of each): water (control), a glucose solution, an aspartame (sweet taste) solution, or a maltodextrin (nonsweet carbohydrate) solution. RESULTS: Glucose ingestion resulted in a prolonged and significant signal decrease in the upper hypothalamus (P < 0.05). Water, aspartame, and maltodextrin had no such effect. Glucose and maltodextrin ingestions resulted in similar increases in blood glucose and insulin concentrations. However, only glucose triggered an early rise in insulin concentrations. Aspartame did not trigger any insulin response. CONCLUSIONS: Our findings suggest that both sweet taste and energy content are required for a hypothalamic response. The combination of sweet taste and energy content could be crucial in triggering adaptive responses to sweetened beverages.

Effect of aspartame on circadian oscillations of calcium and inorganic phosphorus in rats.

The effect of aspartame on circadian rhythms of calcium and inorganic phosphorus levels was studied in rats. Acrophase delays in calcium rhythms and advances in inorganic phosphorus rhythms and alteration in mesor values in both rhythms were observed in aspartame-treated rats. However, no change in amplitude values was observed. Oral administration of aspartame leads to increased levels of aspartate in the brain, which could alter the characteristics of calcium and inorganic phosphorus rhythms, possibly by modulating transmission in several areas/nuclei in brain, including retinohypothalamic tract (RHT) and suprachiasmatic nuclei (SCN).

Effects of long-term ingestion of aspartame on hypothalamic neuropeptide Y, plasma leptin and body weight gain and composition.

The aim of this study was to determine the effects of the chronic ingestion of aspartame (ASP) on brain neuropeptide Y (NPY) concentrations, plasma hormones, food intake and body fat. Two groups of male Long-Evans rats, fed on a control (C) well-balanced diet, had to drink either a 0.1% ASP solution or water for a period of 14 weeks starting at weaning. Food intake and body weight were weekly recorded. At the end of the experiment, fat pads were sampled, leptin and insulin were measured in the plasma and NPY in several microdissected brain areas. Substituting ASP for water led to lower body weight (-8%; P<.004) and lower fat depot weight (-20%; P<.01) with no differences in energy intake or plasma insulin concentrations. Plasma leptin was significantly reduced by 34% (P<.05). Leptin concentrations were well-correlated with final body weight (r=.47; P<.025) and fat pad mass (r=.53; P<.01). NPY concentrations were 23% lower (P<.03) in the arcuate nucleus of ASP rats with no differences in other brain areas. The beneficial effects on body composition could be related to the decreased effects of NPY on lipid and energy metabolism, independently of insulin. The reasons for the NPY decrease (regulatory or toxicological) are not obvious. The constitutive amino acids of the ASP molecule might participate in the NPY regulation.

Acute effects of aspartame on aggression and neurochemistry of rats.

The inverse relationship between serotonin and aggression was investigated in rats treated with aspartame, a sweetener thought to interfere with the synthesis of this neurotransmitter. Eleven adult, male Long-Evans rats received either aspartame (200-800 mg/kg, IP) or the vehicle prior to testing in a standard resident-intruder paradigm. Contrary to our hypothesis, aspartame significantly decreased aggression as shown by increased latencies to the first attack and decreased number of bites per session. Corresponding with the effects on aggression, aspartame significantly increased striatal levels of serotonin. It was concluded that high doses of aspartame reduced aggressive attack via a serotonergic mechanism while the lower dose was without effect on either variable.

Effects of alcohol and chronic aspartame ingestion upon performance in aviation relevant cognitive tasks.

Acute dosing studies of aspartame, known commercially as "NutraSweet," have failed to demonstrate any neuropsychological changes that would imply performance decrements in flight operations. Such studies may be criticized on the grounds that the administration of a single, if large, dose of aspartame is not ecologically valid. Accordingly, a double-blind chronic dosing study of aspartame was conducted using ethanol (at 0.1% BAL) as the positive control. No detectable cognitive performance decrements were associated with the aspartame condition. However, the alcohol results exhibited a pattern of asymmetric lateral brain impairment that closely resembles that observed in studies of depressive patients. These results have operational implications as well as theoretical importance.

Biochemical and clinical effects of aspartame in patients with chronic, stable alcoholic liver disease.

Aspartame is an artificial sweetener completely metabolized in the gut and absorbed as aspartate, phenylalanine, and methanol. Phenylalanine is thought to mediate or exacerbate hepatic encephalopathy, and an impaired liver may not be able to cope with the ammoniagenic properties of the amino acid constituents, or adequately metabolize methanol. Thus, we compared the clinical and biochemical effects of a single ingestion of aspartame (15 mg/kg) to skim milk (phenylalanine content equimolar to aspartame) and placebo in patients with chronic, alcoholic liver disease in a randomized, crossover study. Aspartame produced an elevation of plasma phenylalanine significantly greater than milk and placebo (Cmax 14.55 +/- 7.38, 10.95 +/- 4.95, 8.84 +/- 4.55 mumol/dl, respectively; p < 0.01). However, quantified encephalopathic changes were observed only with milk (p < 0.05). Plasma aspartate, methanol, formate, and ammonia levels remained unchanged after all treatments. The lack of clinical derangements in encephalopathic indices, methanol accumulation, or biochemical changes in liver status suggests that a single large dose of aspartame (representing 5 times the average daily intake of adults) may be used safely by patients with chronic, stable liver disease.

Effect of aspartame and protein, administered in phenylalanine-equivalent doses, on plasma neutral amino acids, aspartate, insulin and glucose in man.

Six human males each received 0.56 g phenylalanine (Phe) in the form of 1.0 g aspartame or 12.2 g bovine albumin in 200 ml water or water alone. Venous blood samples collected before consumption and during the following 4 hr were assayed for plasma levels of large, neutral amino acids (LNAA), aspartate, insulin and glucose. The area under the curve for plasma Phe was 40% greater, although not significant, after aspartame compared with albumin intake. The indicated increased clearance rate of plasma Phe after albumin may be caused by the significant increase of insulin, on which aspartame had no effect. There was a significant main effect of aspartame for plasma tyrosine but not for tryptophan, valine, isoleucine or leucine. Plasma aspartate was significantly increased at 0.25 hr after the aspartame intake. The percentage Phe/LNAA decreased slightly in response to albumin but increased 55% after aspartame and remained significantly increased for 2 hr. Tyrosine/LNAA increased and tryptophan/LNAA decreased modestly after aspartame intake. The study showed that the intake of aspartame in a not unrealistically high dose produced a marked and persistent increase of the availability of Phe to the brain, which was not observed after protein intake. The study indicated, furthermore, that Phe was cleared faster from the plasma after consumption of protein compared with aspartame.

Aspartame and its constituent amino acids: effects on prolactin, cortisol, growth hormone, insulin, and glucose in normal humans.

Because large doses of phenylalanine stimulate prolactin secretion in man, we studied the acute effects of oral doses of aspartame (0.534 g, equivalent to the amount of aspartame in approximately 1 L beverage), aspartic acid (0.242 g), and phenylalanine (0.3 and 1.0 g) on serum prolactin and other hormones in normal humans. Prolactin was not stimulated by any of the aspartame meals, aspartic acid, or 0.3 g phenylalanine; a small rise in serum prolactin, similar to that produced by a high-protein mixed meal, followed ingestion of 1.0 g phenylalanine. Serum growth hormone showed no statistically significant changes in response to any of the experimental meals whereas cortisol and insulin fell slightly and glucose rose slightly during each of the meals. We conclude that these doses of aspartame do not alter secretion of prolactin, cortisol, growth hormone, or insulin in normal individuals.

Aspartame and the rat brain monoaminergic system.

A high dose of aspartame (APM) was administered to rats to study possible effects on brain monoaminergic systems. APM and its metabolite phenylalanine (Phe) were given orally at doses of 1000 and 500 mg/kg, respectively. Significant increases were seen in brain Phe and tyrosine (Tyr) levels. Two different approaches were used to study monoaminergic systems: whole tissue measurements by HPLC-ED and in vivo voltammetry in freely moving rats. Dopamine, serotonin and their metabolites were taken as indexes of neuronal activity. In spite of the high dose used, no modification was found in monoamines or their metabolites in striatum, hippocampus and nucleus accumbens.

The effects of various carbohydrates on sympathetic activity in heart and interscapular brown adipose tissue of the rat.

The present studies were undertaken to determine the effect of various carbohydrates on sympathetic nervous system (SNS) activity. Tritiated-norepinephrine (3H-NE) turnover was measured in heart and interscapular brown adipose tissue (IBAT) of rats fed either chow or chow plus 50% caloric supplements of fructose, sucrose, dextrose, or corn starch. Additional studies were performed to examine whether absorption of carbohydrate plays a role in the SNS response, and to determine whether sweet taste in the form of artificial sweeteners may influence SNS activity. After five to ten days on the respective diets, 3H-NE turnover was increased to a similar extent by all carbohydrates tested (from 38% to 160% greater than controls in different studies). Addition of acarbose (which impairs sucrose absorption) to a sucrose-supplemented diet abolished the SNS stimulatory response, whereas cholestyramine (a drug that blocks fat absorption) had no effect. Finally, the addition of saccharin or aspartame to a chow diet failed to alter SNS activity. Thus, caloric supplementation with several carbohydrates, in addition to sucrose, stimulates both cardiac and IBAT SNS activity, absorption of carbohydrate is required for this effect, and noncaloric sugar substitutes do not alter SNS function.

Drinking behavior and the development of hypothalamic lesions from aspartame ingestion in water-restricted weanling mice.

Wealing mice that had been deprived overnight of water, or of water and diet, were offered a solution containing L-aspartyl-L-phenylalanine-methylester (APM) or monosodium L-aspartate monohydrate (MSA) as the sole source of drinking water, and/or a diet containing large amounts of APM and/or MSA for 30 min, and were killed subsequently. Only those animals exposed to concentrated (6.64% W/V) MSA solutions developed neuronal lesions in the hypothalamic arcuate nuclei. Those offered MSA in the diet only, or APM either in the diet and/or in solution, failed to develop such lesions. Apparently water-restricted weanling mice lose their ability to regulate subsequent drinking behavior, and consume hyperosmolar MSA or APM solutions whose osmolarity or sweetness would be aversive to humans. Such animals are unsuitable for the safety evaluation of APM.

Aspartame administration to the infant monkey: hypothalamic morphology and plasma amino acid levels.

Infant monkeys received 2 gm/kg body weight of aspartame (APM) or 2 gm/kg body weight APM plus 1 gm/kg body weight monosodium glutamate (MSG) by gastric tube. Blood samples were obtained at intervals over the ensuing 4 hours and analyzed for amino acid levels. At this time, each infant was perfused with glutaraldehyde. The hypothalamus was embedded in plastic and then serially sectioned at 1 mu. Hypothalamic morphology was normal in all eight infants given 2 gm/kg body weight APM and in the six infants given 2 gm/kg body weight APM plus 1 gm/kg body weight MSG. By light microscopy, no pycnotic nuclei, neuronal degeneration, or dendritic swelling was noted. In both experimental and control brains, localized areas of poor perfusion exhibited abnormal morphology. Elevated plasma levels of aspartate, glutamate, and phenylalanine indicated that the test compounds were administered and absorbed. Variable rates of absorption were evident, probably due to the necessity of administering APM as a slurry, due to its low solubility. On the basis of blood absorption curves, it appears that infant monkeys metabolize aspartate and glutamate and phenylalanine somewhat more rapidly than man. It is concluded that APM given alone or with MSG, in large acute doses, does not result in hypothalamic damage in the newborn monkey.