Excretion of catechol after ingestion of quinic and shikimic acids

Modulation of urinary siderophores by the diet, gut microbiota and inflammation in mice

Mammalian siderophores are believed to play a critical role in maintaining iron homeostasis. However, the properties and functions of mammalian siderophores have not been fully clarified. In this study, we have employed Chrome Azurol S (CAS) assay which is a well-established method for bacterial siderophores study, to detect and quantify mammalian siderophores in urine samples. Our study demonstrates that siderophores in urine can be altered by diet, gut microbiota and inflammation. C57BL/6 mice, fed on plant-based chow diets which contain numerous phytochemicals, have more siderophores in the urine compared to those fed on purified diets. Urinary siderophores were up-regulated in iron overload conditions, but not altered by other tested nutrients status. Further, germ-free mice displayed 50% reduced urinary siderophores, in comparison to conventional mice, indicating microbiota biotransformation is critical in generating or stimulating host metabolism to create more siderophores. Altered urinary siderophores levels during inflammation suggest that host health conditions influence systemic siderophores level. This is the first report to measure urinary siderophores as a whole, describing how siderophores levels are modulated under different physiological conditions. We believe that our study opens up a new field in mammalian siderophores research and the technique we used in a novel manner has the potential to be applied to clinical purpose.

Purification and Structural Characterization of "Simple Catechol", the NGAL-Siderocalin Siderophore in Human Urine

The identification of ligands that bind the protein Neutrophil Gelatinase-Associated Lipocalin (NGAL, Siderocalin, Lipocalin-2) have helped to elucidate its function. NGAL-Siderocalin binds and sequesters the iron loaded bacterial siderophore enterochelin (Ent), defining the protein as an innate immune effector. Simple metabolic catechols can also form tight complexes with NGAL-Siderocalin and ferric iron, suggesting that the protein may act as an iron scavenger even in the absence of Ent. While different catechols have been detected in human urine, they have not been directly purified from a biofluid and demonstrated to ligate iron with NGAL-Siderocalin. This paper describes a "natural products" approach to identify small molecules that mediate iron binding to NGAL-Siderocalin. A 10K filtrate of human urine was subjected to multiple steps of column chromatography and reverse-phase HPLC, guided by NGAL-Siderocalin-iron binding assays and LC-MS detection. The co-factor forming a ternary structure with iron and NGAL-Siderocalin was identified as authentic simple catechol (dihydroxybenze) by ESI-HR-Mass, UV, and NMR spectrometric analysis. Comparison of the binding strengths of different catechols demonstrated that the vicinal-dihydroxyl groups were the key functional groups and that steric compatibilities of the catechol ring have the strongest effect on binding. Although catechol was a known NGAL-Siderocalin co-factor, our purification directly confirmed its presence in urine as well as its capacity to serve as an iron trap with NGAL-Siderocalin.

NGAL-Siderocalin in kidney disease

Kidney damage induces the expression of a myriad of proteins in the serum and in the urine. The function of these proteins in the sequence of damage and repair is now being studied in genetic models and by novel imaging techniques. One of the most intensely expressed proteins is lipocalin2, also called NGAL or Siderocalin. While this protein has been best studied by clinical scientists, only a few labs study its underlying metabolism and function in tissue damage. Structure-function studies, imaging studies and clinical studies have revealed that NGAL-Siderocalin is an endogenous antimicrobial with iron scavenging activity. This review discusses the "iron problem" of kidney damage, the tight linkage between kidney damage and NGAL-Siderocalin expression and the potential roles that NGAL-Siderocalin may serve in the defense of the urogenital system. This article is part of a Special Issue entitled: Cell Biology of Metals.

Iron traffics in circulation bound to a siderocalin (Ngal)-catechol complex

The lipocalins are secreted proteins that bind small organic molecules. Scn-Ngal (also known as neutrophil gelatinase associated lipocalin, siderocalin, lipocalin 2) sequesters bacterial iron chelators, called siderophores, and consequently blocks bacterial growth. However, Scn-Ngal is also prominently expressed in aseptic diseases, implying that it binds additional ligands and serves additional functions. Using chemical screens, crystallography and fluorescence methods, we report that Scn-Ngal binds iron together with a small metabolic product called catechol. The formation of the complex blocked the reactivity of iron and permitted its transport once introduced into circulation in vivo. Scn-Ngal then recycled its iron in endosomes by a pH-sensitive mechanism. As catechols derive from bacterial and mammalian metabolism of dietary compounds, the Scn-Ngal-catechol-Fe(III) complex represents an unforeseen microbial-host interaction, which mimics Scn-Ngal-siderophore interactions but instead traffics iron in aseptic tissues. These results identify an endogenous siderophore, which may link the disparate roles of Scn-Ngal in different diseases.

Nondairy creamer, but not milk, delays the appearance of coffee phenolic acid equivalents in human plasma

Chlorogenic acids (CGA) are antioxidants found in coffee. They are becoming of interest for their health-promoting effects, but bioavailability in humans is not well understood. We hypothesized that adding whole milk or sugar and nondairy creamer to instant coffee might modulate the bioavailability of coffee phenolics. Nine healthy participants were asked to randomly drink, in a crossover design, instant coffee (Coffee); instant coffee and 10% whole milk (Milk); or instant coffee, sugar, and nondairy creamer already premixed (Sugar/NDC). All 3 treatments provided the same amount of total CGA (332 mg). Blood was collected for 12 h after ingestion and plasma samples treated using a liquid-liquid extraction method that included a full enzymatic cleavage to hydrolyze all CGA and conjugates into phenolic acid equivalents. Hence, we focused our liquid chromatography-Electrospray ionization-tandem MS detection and quantification on caffeic acid (CA), ferulic acid (FA), and isoferulic acid (iFA) equivalents. Compared with a regular black instant coffee, the addition of milk did not significantly alter the area under the curve (AUC), maximum plasma concentration (C(max)), or the time needed to reach C(max) (T(max)). The C(max) of CA and iFA were significantly lower and the T(max) of FA and iFA significantly longer for the Sugar/NDC group than for the Coffee group. However, the AUC did not significantly differ. As a conclusion, adding whole milk did not alter the overall bioavailability of coffee phenolic acids, whereas sugar and nondairy creamer affected the T(max) and C(max) but not the appearance of coffee phenolics in plasma.

Dose-dependent induction of glandular stomach preneoplastic and neoplastic lesions in male F344 rats treated with catechol chronically

The dose-dependence of catechol glandular stomach carcinogenesis was investigated in male F344 rats. Groups of 30 male animals were fed catechol at dietary levels of 0 (control). 0.1, 0.2, 0.4, and 0.8% for up to 104 weeks. Five rats of each group were killed at 34 weeks and the remaining animals were sacrificed at the termination, all undergoing histopathological examination. Moderate retardation of body weight increase was observed in the 0.8% group. but no adverse effects were found in terms of survival. Submucosal hyperplasias and adenomas of the pyloric glands developed in the 0.4 and 0.8% groups, only very minor changes being noted in the 0.1 and 0.2% groups at week 34. Incidences of adenocarcinoma development in the pylorus were 4% and 8% in 0.4% and 0.8% groups, respectively, and 0 in the 0.1% and 0.2% groups, at the termination. Adenomas and submucosal hyperplasias were found in nearly all animals fed 0.2% catechol or more, the incidences of those in 0.1% group being 0% and 56%, respectively. Serum gastrin levels were significantly increased in the 0.2, 0.4, and 0.8% groups at 34 weeks, and in all treated groups at the termination, at extents comparable with the induction of proliferative lesions in the pylorus. The results thus demonstrated that dietary levels of 0.4% and 0.8% catechol long-term induce adenocarcinomas in the pyloric glands, while 0.1 and 0.2% cause benign proliferative lesions, all accompanied by increase in serum gastrin levels. As a no-effect level could not be decided in the present study, further investigation of lower doses is needed to determine whether a threshold exists.

Changes in the excretion of endogenous glycine conjugate as a possible artifact in toxicological experiments

Changes in the urinary excretion of hippuric acid (HIA) and phenaceturic acid (PUA) as well as their metabolic precursors, i.e. benzoic (BA) and phenylacetic acid (PAA), in rats housed in glass metabolic cages for 4 days were monitored using gas-liquid chromatography. The amount of HIA excreted was 128 +/- 63 mumol/kg for female and 79 +/- 43 mumol/kg for male rats in the first 24 h and decreased to 11 +/- 7 mumol/kg (p less than 0.01) for female and 3.2 +/- 2.4 mumol/kg (p less than 0.001) for male rats on the 2nd day. These values remained nearly at the same level until the end of the experiment. The amount of PUA decreased from 48 +/- 12 mumol/kg on the 1st day to 22 +/- 9 mumol/kg (p less than 0.05) on the 2nd day by male rats, whereas by the females the decrease from 30 +/- 9 mumol/kg to 21 +/- 8 mumol/kg was not significant. The decrease in the excretion of glycine conjugates was compensated by a parallel increase in the level of unconjugated BA and PAA.

Quantitative analysis of catechol and 4-methylcatechol in human urine

A method was developed for the quantitative analysis of catechol and 4-methylcatechol in human urine. [U-14C]Catechol was used as in internal standard. Urine was treated with beta-glucuronidase and sulphatase, acidified and extracted with ether. The ether extract was silylated and analysed by glass capillary gas chromatography. Catechol and 4-methylcatechol occurred in urine primarily as conjugates. Levels of catechol and 4-methylcatechol in the urine of nonsmokers on unrestricted diets were 10 +/- 7.3 (mean +/- 1 SD) and 3.4 +/- 2.3 mg/24 hr, respectively. Nonsmokers on uniform restricted diets, in which the intake of plant-derived products was limited, excreted 4.4 +/- 1.2 mg catechol and 8.1 +/- 1.7 mg 4-methylcatechol/24 hr. Smokers on the same restricted diet excreted 6.8 +/- 3.0 mg catechol and 6.1 +/- 2.6 mg 4-methylcatechol/24 hr. These results indicate that diet is a major factor in determining urinary catechol levels and that the contribution of smoking is comparatively small. Catechol and 4-methylcatechol appear to have different dietary precursors.

The metabolism of shikimate in the rat

In the rat, shikimate was metabolized and excreted as hippurate, hexahydrohippurate, 3,4,5,6-tetrahydrohippurate, t-3,t-4-dihydroxycyclohexane-r-1-carboxylate and c-3,t-4-dihydroxycyclophexane-r-1-carboxylate, conjugates of catechol and CO2. The metabolism was entirely dependent on various initial microbial transformations in the gut, metabolite formation being suppressed in animals pretreated with antibiotics. Shikimate was not metabolized by mammalian tissues, and products of microbial metabolism were excreted either unchanged or after further biotransformation in the animal tissues.