Dietary artifact

Finally, a note of caution is needed to secure proper handling of biological specimens for GC analysis. Many of the recommendations as well as the rules for GC analysis are similar to the requirements for other clinical determinations (collection rules, sample storage, transportation, etc.), but special needs for GC may sometimes arise. For example, while certain foreign compounds (preservatives, dietary artifacts, therapeutic drugs, etc.) may not matter in conventional determination, they may be a problem in GC analysis. A publication by Jellum [15] discusses this matter in some detail. 

The presence in molluscs of molecules structurally related to typical dietary metabolites could be ascribed either to selective accumulation of minor compounds acquired through the diet, or to an in vivo chemical transformation of major metabolites acquired from the prey. However, all reports on this topic have to be carefully evaluated before drawing hurried conclusions. In particular, interaction among molecules from different organs could favor formation of artifacts when the secondary metabolites are extracted from the whole mollusc and not from individual dissected tissues. Only some cases, where the ability of the molluscs to modify dietary metabolites seems to be well supported, are reported in this chapter. 

Unknown compounds are detected frequently, and laboratories eventually develop some level of comfort in recognizing them as artifacts that are not significant clinically, at least for the purpose of ruling out a possible inborn error of metabolism [21]. However, there are instances when an unknown compound is found in multiple specimens from the same patient and cannot be associated with ongoing drug and known dietary intake. This was the set of circumstances that led to the identification of 2-octenylsuccinic acid as the compound referred to by some laboratories as pseudo-orotic acid [11, 18]. On the other hand, the spectrum shown in Fig. 3.1.10, tentatively identified as 4-hydroxy 2-hexenoic acid by GC-MS/MS, belongs to a compound that appears in the urine of patients with disorders of propionate me-... 

At the other end of the spectrum of serum values, populations with high mean serum carotenoids often are reported to have lower or no different mean retinol levels than found among populations with normal or low carotenoid values. This is illustrated in Table X by comparing data from surveys conducted in Senegal where 98% of the dietary vitamin A activity comes from carotenoids with surveys from the United States where about 50% is from preformed sources. It is difficult to determine if the high blood carotenoids are causally related to a real shift downward in the retinol distribution curve or if this is a methodologic artifact. Several of the colorimetric and fluorometric analytical methods for... 

Despite the mixed results in rats, clinical studies (on hiunans) confirmed that lanthanum carbonate treatment was safe (Finn 2006). Although cognitive function was foimd to decrease in hemodialysis patients during a 2-year study of lanthamun carbonate, this effect was not different from that observed in patients on standard therapy (Altmann, Barnett et al. 2007). On the other hand, Muller and coworkers (Muller, Chantrel et al. 2009) reported a case of confusion in a lanthanum carbonate-treated elderly women, in whom the confusion was resolved after suspension of the lanthamun treatment. A recent study (Damment, Cox et al. 2009) found that brain deposition of lanthanum is a contamination artifact caused by transfer of lanthanum from cranial skin to brain as animals are manipulated during autopsy, and recommended that dietary administration should be avoided in distribution studies of trace elements due to the high contamination risk. 

The curative material, which is abundant in green leafy vegetables, was named folic acid. However, this name is usually reserved for the synthetic compound used in dietary supplementation. The natural forms are largely the coenzymes (Fig. 6), which are collectively called folates. The last of the accepted human vitamins to be discovered was vitamin Bn. A cobalt-containing organic compound needed in very small amounts, it cures and prevents pernicious anemia, which was often a fatal disease of people over 60 years of age. Its complex structure (Fig. 7) was determined by X-ray diffraction after numerous efforts at chemicai characterization had failed. However, cy anocobalamin, the compound isolated and the form used in nutritional supplementation, is an artifact of the isolation and synthesis. The natural vitamin may have OH in place of CN but consists largely of the coenzyme forms. 

We have considered the possibility that these results were due to assay variability or artifact. Several additional experiments were performed which suggest that this is not the case 1) Identification of the product of the reaction mixture (C -imp or C -GMP) was done in 4 different chromatography systems. 2) The standard error of the mean observed from 10 different determinations of HGPRT activity in a single sample of hemolysate from D.C. and V.P. was 2.9% and 5.2% of the mean activity respectively. Also the overall trend of HGPRT activity in all three patients in response to manipulation of dietary purines was consistent. 

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