High-performance liquid chromatographic determination of 1,1'-ethylidenebis(L-tryptophan) in L-tryptophan preparations

How do Time, Tannin, and Moisture Content Influence Toxicogenic Fungal Populations during the Storage of Sorghum Grains?

ABSTRACT

Cereal grains are usually ensiled to improve their nutritional value and are one of the main sources of feed for dairy cattle. However, during storage, grains can be contaminated with toxicogenic fungi. Sorghum is one of the most economically important cereals in the world. Therefore, the aim of this work was to evaluate the influence of storage duration and tannin and moisture content (MC) on toxicogenic fungal populations in sorghum grain storage. Samples that were prepared with varieties high in tannins (genotypes Morgan 108 and ACA 558, >5 g/kg dry matter) and with varieties low in tannin content (genotypes Flash 10 and ACA 546, <1 g/kg dry matter) were collected and manually compacted in experimental laboratory silos where they received different MC treatments: low (15 to 25%), medium (26 to 32%), and high (33 to 42%). Freshly harvested grains were analyzed at time 0, and stored grains were analyzed at 30, 90, and 180 days. Fungal isolation and identification were performed following conventional mycological methods. Penicillium citrinum (34%), Aspergillus flavus (60%), and Fusarium nygamai (68%) were the most abundant species. Rapid detection of aflatoxins and fumonisins in each sample was performed using enzyme-linked immunosorbent assay according to the AOAC method, and the quantification of aflatoxin B1 was performed using high-performance liquid chromatography. In four samples of pre- and poststorage grains, aflatoxins were detected with levels of 6.7 to 28.8 μg/kg and aflatoxin B1 with a level of 2 to 14 μg/kg. Fumonisins were only detected in two freshly harvested samples, with levels of 500 to 900 μg/kg. In general, storage time favored the increase of Penicillium populations and reduced Aspergillus and Fusarium. Conversely the abundance of the three populations was not affected by the MC. The results of this study show that fungal populations must be analyzed at different times.

HIGHLIGHTS

Mood effects of the amino acids tryptophan and tyrosine: 'Food for Thought' III

OBJECTIVE

Reflecting increased scientific interest in any nutritional contribution to the onset and treatment of mood disorders, we overview research into two neurotransmitter precursors - the amino acids tryptophan and tyrosine - particularly examining whether any deficiency increases risk to depression and whether those amino acids have any antidepressant properties.

METHOD

The theoretical relevance of the two amino acids was overviewed by considering published risk and intervention studies, technical papers and reviews.

RESULTS

There is some limited evidence, suggesting that depressed patients, especially those with a melancholic depression, have decreased tryptophan levels. Whether such findings reflect a causal contribution or are a consequence of a depressed state remains an open question. There is a small database supporting tryptophan preparations as benefitting depressed mood states. There is no clear evidence as to whether tyrosine deficiency contributes to depression, while the only randomized double-blind study examining tyrosine supplementation did not show antidepressant benefit.

CONCLUSION

Acute tryptophan depletion continues to provide a research tool for investigating the relevance of serotonin to depression onset. There is limited evidence that tryptophan loading is effective as a treatment for depression through its action of increasing serotonin production. Most clinical studies are dated, involve small sample sizes and/or were not placebo controlled. The development of the new serotonin reuptake inhibitor drugs seemingly signalled an end to pursuing such means of promoting increased serotonin as a treatment for depression. The evidence for tyrosine loading promoting catecholamine production as a possible treatment for depression appears even less promising, and depletion studies less informative.

Can nutrient supplements modify brain function?

Over the past 40 y, several lines of investigation have shown that the chemistry and function of both the developing and the mature brain are influenced by diet. Examples are the effect of folate deficiency on neural tube development during early gestation, the influence of essential fatty acid deficiency during gestation and postnatal life on the development of visual function in infants, and the effects of tryptophan or tyrosine intake (alone or as a constituent of dietary protein) on the production of the brain neurotransmitters derived from them (serotonin and the catecholamines, respectively). Sometimes the functional effects are clear and the underlying biochemical mechanisms are not (as with folate and essential fatty acids); in other cases (such as the amino acids tyrosine and tryptophan), the biochemical effects are well understood, whereas the effect on brain function is not. Despite the incomplete knowledge base on the effects of such nutrients, investigators, physicians, and regulatory bodies have promoted the use of these nutrients in the treatment of disease. Typically, these nutrients have been given in doses above those believed to be required for normal health; after they have been given in pure form, unanticipated adverse effects have occasionally occurred. If this pharmacologic practice is to continue, it is important from a public safety standpoint that each nutrient be examined for potential toxicities so that appropriate purity standards can be developed and the risks weighed against the benefits when considering their use.

Pharmaceutical fingerprinting in phase space. 1. Construction of phase fingerprints

The present study proposes a general method for constructing pharmaceutical fingerprints in the analysis of HPLC trace organic impurity patterns. The approach considers signals in phase space and accounts for two different types of noise: additive and perturbative. The first type, additive noise, contributes to distortion of the absolute values of signal peaks. The second type, perturbative noise, contributes to variations of the retention times of signal peaks and distorts the time scale of the trace organic impurity patterns. The ability of the proposed approach to consider both types of noise significantly distinguishes it from existing methods of data analysis that are usually designed to treat only the additive noise. Analysis of the HPLC signals in phase space eliminates the problem of perturbation noise and enables detection and comparison of similar signal segments recorded at different retention times. The current study analyzes the chromatographic trace organic impurity patterns collected from six different manufacturers of L-tryptophan using three HPLC columns. For five manufacturers the variability of data recorded with the same column are in perfect agreement with the proposed model. A significant variance of parameters is detected for one manufacturer, thus indicating a possible change in its product consistency. The analysis in phase space is also used to explain the previously detected variability of HPLC signals across columns. The accompanying paper reports an application of the proposed approach for the pattern recognition of HPLC data.

Rapid HPLC screening method for contaminants found in implicated L-tryptophan associated with eosinophilia myalgia syndrome and adulterated rapeseed oil associated with toxic oil syndrome

In 1981 a massive food-borne epidemic, termed the toxic oil syndrome (TOS), occurred in Spain. Eight years later a closely related disease, the eosinophilia myalgia syndrome (EMS), was reported in the USA with many additional cases being reported worldwide. Although EMS was linked to the ingestion of contaminated L-tryptophan and TOS to aniline denatured rapeseed oil, the etiological agent(s) responsible for both diseases remains unknown. However, contaminants in both the oil and the dietary supplement are believed to have triggered these diseases, and there has been much speculation that a common contaminant may have caused both epidemics. In this report, methods for the facile preparation and HPLC analysis of EMS-implicated L-tryptophan and adulterated rapeseed oil samples associated with TOS are described which allow a direct comparison between the contaminants of both foodstuffs. A combination of solvent and solid phase extraction methods are demonstrated along with the application of C18 reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with on-line UV and MS detection. These methods have allowed us to determine for the first time, based upon this work, that there are no detectable common contaminants that possess a UV response, between EMS implicated L-tryptophan and TOS implicated rapeseed oil samples.

Contaminants in biotechnologically manufactured L-tryptophan

The epidemic outbreak of a new disease, the eosinophilia-myalgia syndrome (EMS), was traced back to the intake of L-tryptophan (Trp) of certain lots from a single manufacturer. Since some trace contaminants were related to EMS, it appeared to be necessary to identify and find the origin of most trace contaminants in the EMS related Trp in order to apply this knowledge to a prospective manufacturing practice. Seventeen contaminants were determined in an implicated Trp lot by a single reversed-phase high-performance liquid chromatography run using UV and fluorescence detection. Most of these contaminants were classified as Trp metabolites, non-physiological oxidation or carbonyl condensation compounds of Trp. The amount and the pattern of contaminants were compared with recently manufactured Trp and Trp-containing preparations.

Pharmaceutical fingerprinting: evaluation of neural networks and chemometric techniques for distinguishing among same-product manufacturers

The present study was undertaken to evaluate several computer-based classifiers as potential tools for pharmaceutical fingerprinting by utilizing normalized data obtained from HPLC trace organic impurity patterns. To assess the utility of this approach, samples of L-tryptophan (LT) drug substance were analyzed from commercial production lots of six different manufacturers. The performance of several artificial neural network (ANN) architectures was compared with that of two standard chemometric methods, K-nearest neighbors (KNN) and soft independent modeling of class analogy (SIMCA), as well as with a panel of human experts. The architecture of all three computer-based classifiers was varied with respect to the number of input variables. The ANNs were also optimized with respect to the number of nodes per hidden layer and to the number of hidden layers. A novel preprocessing scheme known as the Window method was devised for converting the output of 899 data entries extracted from each chromatogram into an appropriate input file for the classifiers. Analysis of the test set data revealed that an ANN with 46 inputs (i.e., ANN-46) was superior to all other classifiers evaluated, with 93% of the chromatograms correctly classified. Among the classifiers studied in detail, the order of performance was ANN-46 (93%) > SIMCA-46 (87%) > KNN-46 (85%) = ANN-899 (85%) > "human experts" (83%) > SIMCA-899 (78%) > or = ANN-22 (77%) = KNN-22 (77%) > or = KNN-899 (76%) > SIMCA-22 (73%). These results confirm that ANNs, particularly when used in conjunction with the Window preprocessing scheme, can provide a fast, accurate, and consistent methodology applicable to pharmaceutical fingerprinting. Particular attention was paid to variations in the HPLC patterns of same-manufacturer samples due to differences in LT production lots, HPLC columns, and even run-days to quantify how these factors might hinder correct classifications. The results from these classification studies indicate that the chromatograms evidenced variations across LT manufacturers, across the three HPLC columns and, for one manufacturer, across lots. The extent of column-to-column variations is particularly noteworthy in that all three columns had identical specifications with respect to their stationary-phase characteristics and two of the three columns were from the same vendor.