Inactivation of the first nucleotide-binding fold of the sulfonylurea receptor, and familial persistent hyperinsulinemic hypoglycemia of infancy.

Familial persistent hyperinsulinemic hypoglycemia of infancy is a disorder of glucose homeostasis and is characterized by unregulated insulin secretion and profound hypoglycemia. Loss-of-function mutations in the second nucleotide-binding fold of the sulfonylurea receptor, a subunit of the pancreatic-islet beta-cell ATP-dependent potassium channel, has been demonstrated to be causative for persistent hyperinsulinemic hypoglycemia of infancy. We now describe three additional mutations in the first nucleotide-binding fold of the sulfonylurea-receptor gene. One point mutation disrupts the highly conserved Walker A motif of the first nucleotide-binding-fold region. The other two mutations occur in noncoding sequences required for RNA processing and are predicted to disrupt the normal splicing pathway of the sulfonylurea-receptor mRNA precursor. These data suggest that both nucleotide-binding-fold regions of the sulfonylurea receptor are required for normal regulation of beta-cell ATP-dependent potassium channel activity and insulin secretion.     

NaCl-preferring NZB/B1NJ mice and NaCl-avoiding CBA/J mice have similar amiloride inhibition of chorda tympani responses to NaCl

Integrated chorda tympani nerve responses to NaCl were studied in two mouse strains, an NaCl-preferring NZB/B1NJ and an NaCl-avoiding CBA/J. The NaCl responses of both strains had similar magnitude and were suppressed by amiloride to a similar extent. This suggests that peripheral gustatory responsiveness to NaCl is not the only mechanism underlying mouse strain variation in NaCl acceptance.      

Endocrine disorders of sodium regulation. Role of adrenal steroids in genetic defects causing sodium loss or sodium retention

Salt and water homoeostasis is tightly regulated by a variety of control mechanisms with the adrenal steroid hormone aldosterone playing a central role. Defects or disturbances in these systems lead to either salt loss, which is life threatening in the neonatal period, or sodium retention causing hypertension. Rapid and accurate diagnosis is required to avoid severe complications. During the last few years molecular genetic advances have been identified as the basic genetic defects for a number of clinical syndromes. This knowledge has considerably increased our understanding of the basic pathways involved in sodium and water homoeostasis and of the pathophysiology of these syndromes, particularly the hypertension. In this review we have summarized the biochemical, physiological and genetic basis for clinical syndromes presenting with salt loss and failure to thrive as well as the rare but important genetic syndromes causing sodium retention and hypertension. Early diagnosis and identification will help to prevent severe complications, but it has to be emphasized that the complicated cascade of aldosterone action is still relatively poorly understood. Further syndromes may exist which once identified will help to better understand the basic physiology of aldosterone action.     

Colonic metabolism of dietary polyphenols: influence of structure on microbial fermentation products

The metabolism of chlorogenic acid, naringin, and rutin, representative members of three common families of dietary polyphenols, the hydroxycinnamates, the flavanones, and the flavonols, respectively, was studied in an in vitro mixed culture model of the human colonic microflora. Time- and concentration-dependent degradation of all three compounds was observed, which was associated with the following metabolic events after cleavage of the ester or glycosidic bond: reduction of the aliphatic double bond of the resulting hydroxycinnamate caffeic acid residue; dehydroxylation and ring fission of the heterocyclic C-ring of the resulting deglycosylated flavanone, naringenin, and of the deglycosylated flavonol, quercetin (which differed depending on the substitution). The metabolic events, their sequences, and major phenolic end products, as identified by GC-MS or LC-MS/MS, were elucidated from the structural characteristics of the investigated compounds. The major phenolic end products identified were 3-(3-hydroxyphenyl)-propionic acid for chlorogenic acid, 3-(4-hydroxyphenyl)-propionic acid and 3-phenylpropionic acid for naringin, and 3-hydroxyphenylacetic acid and 3-(3-hydroxyphenyl)-propionic acid for rutin. The degree of degradation of the compounds studied was significantly influenced by the substrate concentration as well as individual variations in the composition of the fecal flora. The results support extensive metabolism of dietary polyphenols in the colon, depending on substrate concentration and residence time, with resultant formation of simple phenolics, which can be considered biomarkers of colonic metabolism if subsequently absorbed. It is also apparent that a relatively small number of phenolic degradation products are formed in the colon from the diverse group of natural polyphenols.     

The metabolic fate of dietary polyphenols in humans

Dietary polyphenols are widely considered to contribute to health benefits in humans. However, little is yet known concerning their bioactive forms in vivo and the mechanisms by which they may contribute toward disease prevention. Although many studies are focusing on the bioavailability of polyphenols through studying their uptake and the excretion of their conjugated forms, few are emphasizing the occurrence of metabolites in vivo formed via degradation by the enzymes of colonic bacteria and subsequent absorption. The purpose of this research was to investigate the relationship between biomarkers of the colonic biotransformation of ingested dietary polyphenols and the absorbed conjugated polyphenols. The results show that the majority of the in vivo forms derive from cleavage products of the action of colonic bacterial enzymes and subsequent metabolism in the liver. Those include the glucuronides of 3-hydroxyphenylacetic, homovanillic, vanillic and isoferulic acid as well as 3-(3-methoxy-4-hydroxyphenyl)-propionic, 3-(3-hydroxyphenyl)-propionic acid, and 3-hydroxyhippuric acid. In contrast, intact conjugated polyphenols themselves, such as the glucuronides of quercetin, naringenin and ferulic, p-coumaric, and sinapic acid were detected at much lower levels. The results suggest that consideration should be given to the cleavage products as having a putative role as physiologically relevant bioactive components in vivo.     

Familial true hermaphroditism: paternal and maternal transmission of true hermaphroditism (46,XX) and XX maleness in the absence of Y-chromosomal sequences

We report on 46,XX true hermaphroditism and 46,XX maleness coexisting in the same pedigree, with maternal as well as paternal transmission of the disorder. Molecular genetic analysis showed that both hermaphrodites as well as the 46,XX male were negative for Y-chromosomal sequences. Thus, this pedigree is highly informative and allows the following conclusions: first, the maternal as well as paternal transmission of the disorder allows the possibility of an autosomal dominant as well as an X-chromosomal dominant mode of inheritance; second, testicular determination in the absence of Y-specific sequences in familial 46,XX true hermaphrodites as well as in 46,XX males seems to be due to the varying expression of the same genetic defect; and third, there is incomplete penetrance of the defect.     

Diet-induced endogenous formation of nitroso compounds in the GI tract

Red or processed meat, but not white meat or fish, is associated with colorectal cancer. The endogenous formation of nitroso compounds is a possible explanation, as red or processed meat--but not white meat or fish--causes a dose-dependent increase in fecal apparent total N-nitroso compounds (ATNC) and the formation of nitroso-compound-specific DNA adducts. Red meat is particularly rich in heme and heme has also been found to promote the formation of ATNC. To investigate the underlying mechanism of ATNC formation, fecal and ileal samples of volunteers fed a high red meat or a vegetarian diet were analyzed for nitrosyl iron, nitrosothiols, and heme. To simulate the processes in the stomach, food homogenates and hemoglobin were incubated under simulated gastric conditions. Nitrosyl iron and nitrosothiols were significantly (p < 0.0001) increased in ileal and fecal samples after a high red meat diet compared with a vegetarian diet; significantly more nitrosyl iron than nitrosothiols was detectable in ileal (p < 0.0001) and fecal (p < 0.001) samples. The strong correlation between fecal nitrosyl iron and heme (0.776; p < 0.0001) suggested that nitrosyl heme is the main source of nitrosyl iron, and ESR confirmed the presence of nitrosyl heme in fecal samples after a high red meat diet. Under simulated gastric conditions, mainly nitrosothiols were formed, suggesting that acid-catalyzed thionitrosation is the initial step in the endogenous formation of nitroso compounds. Nitrosyl heme and other nitroso compounds can then form under the alkaline and reductive conditions of the small and large bowel.     

Structurally related (-)-epicatechin metabolites in humans: assessment using de novo chemically synthesized authentic standards

Accumulating data suggest that diets rich in flavanols and procyanidins are beneficial for human health. In this context, there has been a great interest in elucidating the systemic levels and metabolic profiles at which these compounds occur in humans. Although recent progress has been made, there still exist considerable differences and various disagreements with regard to the mammalian metabolites of these compounds, which in turn are largely a consequence of the lack of availability of authentic standards that would allow for the directed development and validation of expedient analytical methodologies. In this study, we developed a method for the analysis of structurally related flavanol metabolites using a wide range of authentic standards. Applying this method in the context of a human dietary intervention study using comprehensively characterized and standardized flavanol- and procyanidin-containing cocoa, we were able to identify the structurally related (-)-epicatechin metabolites (SREM) postprandially extant in the systemic circulation of humans. Our results demonstrate that (-)-epicatechin-3'-β-D-glucuronide, (-)-epicatechin-3'-sulfate, and a 3'-O-methyl-(-)-epicatechin-5/7-sulfate are the predominant SREM in humans and further confirm the relevance of the stereochemical configuration in the context of flavanol metabolism. In addition, we also identified plausible causes for the previously reported discrepancies regarding flavanol metabolism, consisting, to a significant extent, of interlaboratory differences in sample preparation (enzymatic treatment and sample conditioning for HPLC analysis) and detection systems. Thus, these findings may also aid in the establishment of consensus on this topic.     

The diet‐body offset in human nitrogen isotopic values: A controlled dietary study

The “trophic level enrichment” between diet and body results in an overall increase in nitrogen isotopic values as the food chain is ascended. Quantifying the diet–body Δ¹⁵N spacing has proved difficult, particularly for humans. The value is usually assumed to be +3–5‰ in the archaeological literature. We report here the first (to our knowledge) data from humans on isotopically known diets, comparing dietary intake and a body tissue sample, that of red blood cells. Samples were taken from 11 subjects on controlled diets for a 30‐day period, where the controlled diets were designed to match each individual's habitual diet, thus reducing problems with short‐term changes in diet causing isotopic changes in the body pool. The Δ¹⁵N_diet‐RBC was measured as +3.5‰. Using measured offsets from other studies, we estimate the human Δ¹⁵N_{diet‐keratin} as +5.0–5.3‰, which is in good agreement with values derived from the two other studies using individual diet records. We also estimate a value for Δ¹⁵N_{diet‐collagen} of ≈6‰, again in combination with measured offsets from other studies. This value is larger than usually assumed in palaeodietary studies, which suggests that the proportion of animal protein in prehistoric human diet may have often been overestimated in isotopic studies of palaeodiet. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.