Nutritional value of D-amino acids, D-peptides, and amino acid derivatives in mice

Effects of Protein-Derived Amino Acid Modification Products Present in Infant Formula on Metabolic Function, Oxidative Stress, and Intestinal Permeability in Cell Models

Proteins present in infant formulas are modified by oxidation and glycation during processing. Modified amino acid residues released from proteins may be absorbed in the gastrointestinal tract, and pose a health risk to infants. In this study, the markers of glycation furosine (1.7-3.5 μg per milligram of protein) and N^ε-(carboxymethyl)lysine (28-81 ng per milligram of protein) were quantitated in infant formulas. The effects of these species, and other amino acid modifications, at the levels detected in infant formulas, on 3T3-L1 (murine preadipocyte) and Caco-2 (human intestinal epithelial) cells were assessed. Incubation of 3T3-L1 cells for 48 h with amino acid side chain oxidation and glycation products (1 and 10 μM) resulted in a loss (up to 40%, p < 0.05) of cell thiols and decreased metabolic activity compared with those of the controls. In contrast, Caco-2 cells showed a stimulation (10-50%, p < 0.05) of cellular metabolism on exposure to these products for 24 or 48 h. A 28% ( p < 0.05) increase in protein carbonyls was detected upon incubation with 200 μM modified amino acids for 48 h, although no alteration in transepithelial electrical resistance was detected. Oxidation products were detected in the basolateral compartments of Caco-2 monolayers when modified amino acids were applied to the apical side, consistent with limited permeability (up to 3.4%) across the monolayer. These data indicate that modified amino acids present in infant formulas can induce effects on different cell types, with evidence of bioavailability and induction of cellular stress. This may lead to potential health risks for infants consistently exposed to high levels of infant formulas.

Analysis, Nutrition, and Health Benefits of Tryptophan

Tryptophan is an essential plant-derived amino acid that is needed for the in vivo biosynthesis of proteins. After consumption, it is metabolically transformed to bioactive metabolites, including serotonin, melatonin, kynurenine, and the vitamin niacin (nicotinamide). This brief integrated overview surveys and interprets our current knowledge of the reported multiple analytical methods for free and protein-bound tryptophan in pure proteins, protein-containing foods, and in human fluids and tissues, the nutritional significance of l-tryptophan and its isomer d-tryptophan in fortified infant foods and corn tortillas as well the possible function of tryptophan in the diagnosis and mitigation of multiple human diseases. Analytical methods include the use of acid ninhydrin, near-infrared reflectance spectroscopy, colorimetry, basic hydrolysis; acid hydrolysis of S-pyridylethylated proteins, and high-performance liquid and gas chromatography-mass spectrometry. Also covered are the nutritional values of tryptophan-fortified infant formulas and corn-based tortillas, safety of tryptophan for human consumption and the analysis of maize (corn), rice, and soybean plants that have been successfully genetically engineered to produce increasing tryptophan. Dietary tryptophan and its metabolites seem to have the potential to contribute to the therapy of autism, cardiovascular disease, cognitive function, chronic kidney disease, depression, inflammatory bowel disease, multiple sclerosis, sleep, social function, and microbial infections. Tryptophan can also facilitate the diagnosis of certain conditions such as human cataracts, colon neoplasms, renal cell carcinoma, and the prognosis of diabetic nephropathy. The described findings are not only of fundamental scientific interest but also have practical implications for agriculture, food processing, food safety, nutrition, and animal and human health. The collated information and suggested research need will hopefully facilitate and guide further studies needed to optimize the use of free and protein-bound tryptophan and metabolites to help improve animal and human nutrition and health.

Genetics of Amino Acid Taste and Appetite

The consumption of amino acids by animals is controlled by both oral and postoral mechanisms. We used a genetic approach to investigate these mechanisms. Our studies have shown that inbred mouse strains differ in voluntary amino acid consumption, and these differences depend on sensory and nutritive properties of amino acids. Like humans, mice perceive some amino acids as having a sweet (sucrose-like) taste and others as having an umami (glutamate-like) taste. Mouse strain differences in the consumption of some sweet-tasting amino acids (d-phenylalanine, d-tryptophan, and l-proline) are associated with polymorphisms of a taste receptor, type 1, member 3 gene (Tas1r3), and involve differential peripheral taste responsiveness. Strain differences in the consumption of some other sweet-tasting amino acids (glycine, l-alanine, l-glutamine, and l-threonine) do not depend on Tas1r3 polymorphisms and so must be due to allelic variation in other, as yet unknown, genes involved in sweet taste. Strain differences in the consumption of l-glutamate may depend on postingestive rather than taste mechanisms. Thus, genes and physiologic mechanisms responsible for strain differences in the consumption of each amino acid depend on the nature of its taste and postingestive properties. Overall, mouse strain differences in amino acid taste and appetite have a complex genetic architecture. In addition to the Tas1r3 gene, these differences depend on other genes likely involved in determining the taste and postingestive effects of amino acids. The identification of these genes may lead to the discovery of novel mechanisms that regulate amino acid taste and appetite.

Antibacterial, antiviral, and antifungal properties of wines and winery byproducts in relation to their flavonoid content

Grapes produce organic compounds that may be involved in the defense of the plants against invading phytopathogens. These metabolites include numerous phenolic compounds that are also active against human pathogens. Grapes are used to produce a variety of wines, grape juices, and raisins. Grape pomace, seeds, and skins, the remains of the grapes that are a byproduct of winemaking, also contain numerous bioactive compounds that differ from those found in grapes and wines. This overview surveys and interprets our present knowledge of the activities of wines and winery byproducts and some of their bioactive components against foodborne (Bacillus cereus, Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus, Yersinia enterocolitica, Vibrio cholerae, Vibrio vulnificus), medical (Helicobacter pylori, Klebsiella pneumoniae), and oral pathogenic bacteria, viruses (adeno, cytomegalo, hepatitis, noro, rota), fungi (Candida albicans, Botrytis cinerea), parasites (Eimeria tenella, Trichomonas vaginalis), and microbial toxins (ochratoxin A, Shiga toxin) in culture, in vivo, and in/on food (beef, chicken, frankfurters, hot dogs, lettuce, oysters, peppers, pork, sausages, soup, spinach) in relation to composition and sensory properties. Also covered are antimicrobial wine marinades, antioxidative and immunostimulating aspects, and adverse effects associated with wine consumption. The collated information and suggested research needs might facilitate and guide further studies needed to optimize the use of wines and byproducts to help improve microbial food safety and prevent or treat animal and human infections.

Racemization in reverse: evidence that D-amino acid toxicity on Earth is controlled by bacteria with racemases

D-amino acids are toxic for life on Earth. Yet, they form constantly due to geochemical racemization and bacterial growth (the cell walls of which contain D-amino acids), raising the fundamental question of how they ultimately are recycled. This study provides evidence that bacteria use D-amino acids as a source of nitrogen by running enzymatic racemization in reverse. Consequently, when soils are inundated with racemic amino acids, resident bacteria consume D- as well as L-enantiomers, either simultaneously or sequentially depending on the level of their racemase activity. Bacteria thus protect life on Earth by keeping environments D-amino acid free.