The Biochemical Basis of Vitamin A Production from the Asymmetric Carotenoid ß-Cryptoxanthin.

Vitamin A serves essential functions in mammalian biology as a signaling molecule and chromophore. This lipid can be synthesized from more than 50 putative dietary provitamin A precursor molecules which contain at least one unsubstituted ß-ionone ring. We here scrutinized the enzymatic properties and substrate specificities of the two structurally related carotenoid cleavage dioxygenases (CCDs) which catalyze this synthesis. Recombinant BCO1 split substrates across the C15,C15' double bond adjacent to a canonical ß-ionone ring site to vitamin A aldehyde. Substitution of the ring with a hydroxyl group prevented this conversion. The removal of methyl groups from the polyene carbon backbone of the substrate did not impede enzyme activity. Homology modeling and site-directed mutagenesis identified amino acid residues at the entrance of the substrate tunnel, which determined BCO1's specificity for the canonical ß-ionone ring site. In contrast, BCO2 split substrates across the C9,C10 double bond adjacent to assorted ionone ring sites. Kinetic analysis revealed a higher catalytic efficiency of BCO2 with substrates bearing 3-hydroxy-ß-ionone rings. In the mouse intestine, the asymmetric carotenoid ß-cryptoxanthin with one canonical and one 3-hydroxy-ß-ionone ring site was meticulously converted to vitamin A. The tailoring of this asymmetric substrate occurred by a stepwise processing of the carotenoid substrate by both CCDs and involved a ß-apo-10'-carotenal intermediate. Thus, opposite selectivity for ionone ring sites of the two mammalian CCDs complement each other in the metabolic challenge of vitamin A production from a chemically diverse set of precursor molecules.

Transcription factor ISX mediates the cross talk between diet and immunity.

The intestinal epithelium is a major site for the conversion of dietary ß-carotene to retinaldehyde by the enzyme BCO1. The majority of retinaldehyde is further metabolized to retinol (vitamin A), esterified and packaged into triacylglycerol-rich chylomicrons for bodily distribution. Some serve on-site for the synthesis of retinoic acid, a hormone-like compound, which exerts pleiotropic and dominant effects on gastrointestinal immunity. We report here that the intestine-specific homeobox protein ISX is critical to control the metabolic flow of ß-carotene through this important branching point of vitamin A metabolism. This transcription factor represses Bco1 gene expression in response to retinoic acid signaling. In ISX-deficient mice, uncontrolled Bco1 gene expression led to increased retinoid production in the intestine. Systemically, this production resulted in highly elevated hepatic retinoid stores. In the intestine, it increased the expression of retinoic acid-inducible target genes such as Aldh1a2, Dhrs3, and Ccr9 The ß-carotene-inducible disruption of retinoid homeostasis affected gut-homing and differentiation of lymphocytes and displayed morphologically in large lymphoid follicles along the intestine. Furthermore, it was associated with an infiltration of the pancreas by gut-derived lymphocytes that manifested as a pancreatic insulitis with ß-islet cell destruction and systemic glucose intolerance. Thus, our study identifies an important molecular interlink between diet and immunity and indicates that vitamin A homeostasis must be tightly controlled by ISX to maintain immunity and tolerance at the intestinal barrier.

Violent criminal behavior and perspectives on treatment of criminality in opiate treatment.

PURPOSE: This study describes and compares the characteristics of patients within a VA Opiate Substitution Therapy Program (OSTP) who report arrests for non-violent and violent crimes and describes patients' attitudes and preferences of criminal treatment within an OSTP. METHODS: An anonymous survey was distributed to all veterans at one VA-OSTP. Analyses were conducted to describe the sample characteristics and their associations with prior violent and non-violent criminal behavior. RESULTS: A majority of participants were Caucasian, male, middle-aged, unemployed, and had a history of injection drug use. Participants reported arrests for violent (44%), non-violent (47%), and unspecified crimes (16%). There were few significant differences on demographic and drug use characteristics between participants who reported arrests for any violent and only non-violent crimes, and no arrests. Slightly fewer than half the subjects were satisfied with their ability to access treatment for past criminal behavior within or outside of the VA treatment settings. More veterans reporting violent arrests were satisfied with services addressing criminal behavior within the VA-OSTP than were veterans reporting only nonviolent arrests. Nearly equal proportions of veterans reporting violent (45%) and non-violent (44%) arrests reported dissatisfaction with such services received outside of the VA-OSTP. CONCLUSIONS: Prior violent criminal behavior is common among participants of a VA-OSTP. Many individuals with criminal histories seek treatment for criminality within VA-OSTP.