Sex and heredity are determinants of oral oxycodone self-administration in 36 Inbred Rat Strains: correlations with behavioral tests of anxiety and novelty-seeking.

Most individuals affected in the national epidemic of oxycodone abuse began taking oral oxycodone by prescription. We studied vulnerability to oxycodone intake in a rat model of oral drug self-administration (SA), since pharmacokinetics affect abuse potential. Females (33 inbred strains) and males (26) obtained oxycodone at increasing concentrations in operant sessions (FR5; 1-16-h) followed by extinction and reinstatement. Active spout licks were greater in females than males during 4-h and 16-h sessions (p< 0.001 for all). Across all stages of oxycodone SA, intake/session was greater in females (p<0.001). Both sexes escalated intake during 16-h extended access vs 4-h sessions (p<2e-16). Intake and active licks varied greatly by strain. The heritability (h2) of active licks/4-h at increasing oxycodone dose was larger in males (h2 females: 0.30-0.39 vs. males: 0.41-0.53). Under a progressive ratio schedule, breakpoints differed by strain (p<2e-16) and by sex in some strains (p=0.018). For cue-induced reinstatement, active licks were greater in females than males (p<0.001). Behavior in naive rats was assessed using elevated plus maze (EPM), open field (OF) and novel object interaction. (NOI) tests. We correlated these behaviors with 28 parameters of oxycodone SA. EPM-defining traits were most commonly associated with SA in both sexes, whereas more OF and NOI traits were SA-associated in males. Overall, sex and heredity are major determinants of the motivation to take and seek oxycodone, which escalates during extended access. The correlation of EPM, a measure of anxiety, with multiple SA parameters indicates the influence of pleiotropic genes.

Hepatocyte nuclear factor-4 mediates apolipoprotein A-IV transcriptional regulation by fatty acid in newborn swine enterocytes.

Hepatocyte nuclear factor-4alpha (HNF-4alpha) regulates transcription of several genes involved in lipid metabolism, including that of apolipoprotein (apo) A-IV, which is tightly regulated by lipid absorption and enhances enterocyte chylomicron secretion. Studies were performed to define the role of HNF-4alpha in the regulation of apo A-IV gene transcription by dietary fatty acid in neonatal swine small intestine. HNF-4alpha mRNA was expressed in liver > intestine > kidney in suckling, weanling, and weaned pigs. Jejunal HNF-4alpha mRNA and protein and apo A-IV and swine microsomal triglyceride transfer protein (MTP) large subunit mRNA expression were induced in parallel in 2-day-old swine by a 24-h high-fat intraduodenal infusion. In IPEC-1 cells, incubation with oleic acid (OA) resulted in coordinate induction of both HNF-4alpha, apo A-IV, and MTP mRNA, similar to that observed in vivo. When HNF-4alpha expression was driven by doxycycline by using the TET-On system in the absence of OA to observe the effect of HNF-4alpha directly on apo A-IV and MTP mRNA levels in the absence of other factors that might be concomitantly induced by fatty acid absorption, apo A-IV and MTP expression were increased. In luciferase reporter gene assays in IPEC-1 cells using apo A-IV/C-III intergenic region constructs, TET-On-regulated HNF-4alpha expression without OA increased luciferase activity, and incubation with OA did not further increase activity. These data suggest that acute induction of the apo A-IV and MTP genes by dietary lipid in newborn intestine occurs, at least in part, via ligand-independent transactivation by HNF-4alpha that is itself induced by a lipid-mediated mechanism.

Overexpression of apolipoprotein A-IV enhances lipid secretion in IPEC-1 cells by increasing chylomicron size.

Intestinal apolipoprotein A-IV expression is highly regulated by dietary lipid in newborn swine, suggesting a role in lipid absorption. Constitutive overexpression of apoA-IV in newborn swine enterocytes enhances basolateral secretion of triacylglycerol (TG) in TG-rich lipoproteins 4.9-fold (Lu, S., Yao, Y., Meng, S., Cheng, X., and Black, D. D. (2002) J. Biol. Chem. 277, 31929-31937). To investigate the mechanism of this enhancement, IPEC-1 cells were transfected with a tetracycline-regulatable expression system (Tet-On). In cells incubated with oleic acid, a dose response relationship was observed between medium doxycycline concentration and basolateral apoA-IV and TG secretion. Similarly regulated expression of apoA-I did not enhance lipid secretion. The mean diameter of TG-rich lipoproteins secreted from doxycycline-treated cells was larger than from untreated cells (87.0 nm versus 53.4 nm). Basolateral apoB secretion decreased. Using the same expression system, full-length human apoA-IV (376 amino acids); a "pig-like" human apoA-IV, lacking the C-terminal EQQQ repeats (361 amino acids); and a "chicken-like" apoA-IV, further truncated to 343 amino acids, were expressed in IPEC-1 cells. With increasing protein secretion, cells expressing the full-length human apoA-IV displayed a 2-fold increase in TG secretion; in sharp contrast, cells expressing the pig-like human apoA-IV displayed a 25-fold increase in TG secretion and a 27-fold increase in lipoprotein diameter. When human apoA-IV was further truncated to yield a chicken-like protein, TG secretion was inhibited. We conclude that overexpression of swine apoA-IV enhances basolateral TG secretion in a dose-dependent manner by increasing the size of secreted lipoproteins. These data suggest that the region in the human apoA-IV protein from residues 344 to 354 is critical to its ability to enhance lipid secretion, perhaps by enabling the packaging of additional core TG into chylomicron particles. The EQQQ-rich region may play an inhibitory or modulatory role in chylomicron packaging in humans.