Increased retinoid signaling in vascular smooth muscle cells by proinflammatory cytokines

Homology Models and Molecular Modeling of Human Retinoic Acid Metabolizing Enzymes Cytochrome P450 26A1 (CYP26A1) and P450 26B1 (CYP26B1)

Homology models of cytochrome P450 26A1 and cytochrome P450 26B1 were constructed using the crystal structures of human, CYP2C8, CYP2C9, and CYP3A4 as templates for the model building. The homology models generated were investigated for their docking capacities against the natural substrate all-trans-retinoic acid (atRA), five different tetralone-derived retinoic acid metabolizing blocking agents (RAMBAs), and R115866. Interaction energies (IE) and linear interaction energies (LIE) were calculated for all inhibitors in both homology models after molecular dynamics (MD) simulation of the enzyme-ligand complexes. The results revealed that the homologues had the capacity to distinguish between strong and weak inhibitors. Important residues in the active site were identified from the CYP26A1/B1-atRA complexes. Residues involved in hydrophobic interactions with atRA were Pro113, Phe222, Phe299, Val370, Pro371, and Phe374 in CYP26A1 and Leu88, Pro118, Phe222, Phe295, Ile368, and Tyr272 in CYP26B1. Hydrogen bonding interactions were observed between the atRA carboxylate group and Arg 90 in CYP26A1 and with Arg76, Arg95, and Ser369 in CYP26B1.

Maternal inhalation of surface-coated nanosized titanium dioxide (UV-Titan) in C57BL/6 mice: effects in prenatally exposed offspring on hepatic DNA damage and gene expression

We investigated effects of maternal pulmonary exposure to titanium dioxide (UV-Titan) on prenatally exposed offspring. Time-mated mice (C57BL/6BomTac) were inhalation exposed (1 h/day to 42 mg UV-Titan/m(3) aerosolised powder or filtered air) during gestation days (GDs) 8-18. We evaluated DNA strand breaks using the comet assay in bronchoalveolar lavage (BAL) cells and livers of the time-mated mice (5 and 26-27 days after inhalation exposure), and in livers of the offspring (post-natal days (PND) 2 and 22). We also analysed hepatic gene expression in newborns using DNA microarrays. UV-Titan exposure did not induce DNA strand breaks in time-mated mice or their offspring. Transcriptional profiling of newborn livers revealed changes in the gene expression related to the retinoic acid signalling pathway in the females, while gene expression in male offspring was unaffected. Changes may be a secondary response to maternal inflammation although no direct link was evident through gene expression analysis.

Differences in Retinol Metabolism and Proliferative Response between Neointimal and Medial Smooth Muscle Cells

Vascular disease is multifactorial and smooth muscle cells (SMCs) play a key role. Retinoids have been shown to influence many disease-promoting processes including proliferation and differentiation in the vessel wall. Phenotypic heterogeneity of vascular SMCs is a well-known phenomenon and phenotypic modulation of SMCs precedes intimal hyperplasia. The SMCs that constitute the intimal hyperplasia demonstrate a distinct phenotype and differ in gene expression compared to medial SMCs. Cellular retinol-binding protein-1 (CRBP-I), involved in retinoid metabolism, is highly expressed in intimal SMCs, indicating altered retinoid metabolism in this subset of cells. The aim of this study was to evaluate the metabolism of all-trans ROH (atROH), the circulating prohormone to active retinoids, in vascular SMCs of different phenotypes. The results show an increased uptake of atROH in intimal SMCs compared to medial SMCs as well as increased expression of the retinoid-metabolizing enzymes retinol dehydrogenase-5 and retinal dehydrogenase-1 and, in conjunction with this gene expression, increased production of all-trans retinoic acid (atRA). Furthermore, the retinoic acid-catabolizing enzyme CYP26A1 is expressed at higher levels in medial SMCs compared to intimal SMCs. Thus, both retinoid activation and deactivation processes are in operation. To analyze if the difference in ROH metabolism was also correlated to differences in the biological response to retinol, the effects of ROH on proliferation of SMCs with this phenotypic heterogeneity were studied. We found that intimal SMCs showed a dose- and time-dependent growth inhibition when treated with atROH in contrast to medial SMCs, in which atROH had a mitogenic effect. This study shows, for the first time, that (1) vascular SMCs are able to synthesize biologically active atRA from the prohormone atROH, (2) intimal SMCs have a higher capacity to internalize atROH and metabolize atROH into atRA compared to medial SMCs and (3) atROH inhibits growth of intimal SMCs, but induces medial SMC growth.

Characterization of a cyclooxygenase-2-765G???C promoter polymorphism in human neural cells

Direct sequencing of the human cyclooxygenase-2 gene promoter revealed a common single nucleotide substitution, cyclooxygenase-2-765G-->C, in 24.5% of the populations analyzed. This change introduced a 20 base pair polypyrimidine/polypurine element and a partial recognition feature for RXRalpha, the 9-cis retinoic acid receptor, into the polymorphic promoter. Cyclooxygenase-2-765G-->C constructs, when transfected into human neural cells, exhibited a 1.4-fold higher level of basal expression, while the proinflammatory factors interleukin-1beta and 9-cis retinoic acid synergistically induced polymorphic promoter activity 2.4-fold over wild type. These results suggest that under specific conditions of cellular stress, a common variation in cyclooxygenase-2 promoter structure may enhance cyclooxygenase-2 transcription, and this may contribute to the proliferation of an inflammatory response in brain cells.

Dietary retinoic acid induces hindlimb and eye deformities in Xenopus laevis

This study investigated the effects of dietary retinoic acid (RA) on frog hindlimb development. Xenopus laevis (African clawed frog) tadpoles were fed a diet supplemented with 0, 1, 10, or 100 microg of RA/g of food for 2 or 5 d at different stages of metamorphosis. Hindlimb deformities were induced in the group fed 100 microg of RA/g of diet for 5 d. Exposures beginning at mid-hindlimb bud development induced bilaterally bent tibiafibula (bony triangles), while exposures later in hindlimb development induced deformities of the feet, including fusion of the 1st and 2nd clawed digits and reduced length of the 4th and 5th digits (due to reduced, missing, or misplaced phalanges). There were also cases of extra phalanges in the 5th digit. The eye was another target of RA exposure. In one experiment, 58% of the tadpoles fed 10 microg of RA/g had a smaller or absent right eye. Additionally, 11% of the tadpoles fed 100 microg of RA/g of diet developed a smaller or absent left eye. Waterborne heavy metals (Zn or Cu) modified RA effects on the hindlimb and eye. Co-exposure to metals and RA resulted in cases of unilateral bony triangles and reduced rates of smaller eyes. There were also cases of extra hindlimb digits in Zn-exposed animals. Dietary RA exposure in tadpoles can cause some deformities that differ from waterborne RA exposures in previous studies. RA also induced deformities that resemble those in affected wild frog populations (bony triangles), although the patterns of other deformities and missing segments (phalanges and metatarsals) are not similar to those documented in the wild.

The renal retinoid system: time-dependent activation in experimental glomerulonephritis

Retinoids reduce renal damage in rat experimental glomerulonephritis. It is unknown, however, how local and systemic retinoid pathways respond to renal injury. We used a rat model of artificially induced acute anti-Thy1.1-nephritis (THY-GN). We examined the extrarenal and glomerular expression of the retinol (RoDH) and retinal (RalDH) dehydrogenases 1 and 2 as well as the expression of the retinoic acid (RAR) and retinoid X (RXR) receptor subtypes α, β, and γ. Furthermore, we investigated serum and glomerular retinoid concentration patterns. On days 3, 7, and 14, we compared nonnephritic rats (control group; CON) to THY-GN rats with respect to systolic blood pressure and glomerular cell count per cross section. Systolic blood pressure and glomerular cell count were significantly higher in THY-GN rats on days 7 and 14 ( P < 0.001). We found a 60% reduction in expression levels for retinoid receptors and dehydrogenases in nephritic glomeruli on day 3, but a threefold increase on day 7 ( P < 0.001 vs. CON). The same applies to RARα protein. Hepatic expression of retinoid receptors was not influenced. On day 14, glomerular expression levels for retinoid receptors and retinoid-metabolizing enzymes had returned to a normal level, glomerular cell count being still increased. Administering 13- cis retinoic acid (isotretinoin) lowered blood pressure and glomerular cell count in nephritic rats but failed to influence the glomerular expression of retinoid receptors or retinoid-metabolizing enzymes. Our data document a stimulation of glomerular retinoid-synthesizing enzymes and expression of retinoid receptors in the early repair phase of THY-GN, suggesting activation of this system in acute renal disease.

Retinoic acid induces expression of the interleukin-1beta gene in cultured normal human mammary epithelial cells and in human breast carcinoma lines

Retinoic acid (RA) and its derivatives inhibit the proliferation of normal human mammary epithelial cells (HMEC) and some breast carcinoma lines by mechanisms which are not fully understood. To identify genes that mediate RA-induced cell growth arrest, an HMEC cDNA library was synthesized and subtractive screening was performed. We identified the interleukin-1beta (IL-1beta) gene as an RA induced gene in HMEC. Northern blot analyses showed that the IL-1beta gene was up-regulated as early as 2 h after RA treatment. Results from the treatment of HMEC with cycloheximide and actinomycin D indicated that the regulation of the IL-1beta gene by RA occurred at the transcriptional level and that the IL-1beta gene is a direct, downstream target gene of RA. To evaluate the effects of IL-1beta on cell proliferation, the proliferation of HMEC was measured in the presence of RA or IL-1beta, or both. Either RA or IL-1beta could significantly inhibit the proliferation of HMEC. However, the addition of soluble IL-1 receptor antagonist (sIL-1ra) to the cell culture medium did not block RA-induced HMEC growth inhibition, whereas sIL-1ra did block the growth inhibition of HMEC by IL-1beta. IL-1beta expression was not observed in the three carcinoma cell lines, MCF-7, MDA-MB-231, and MDA-MB-468, as compared to the HMEC. Growth curves of the breast carcinoma cell lines showed strong inhibitory effects of RA and IL-1beta on the growth of the estrogen receptor (ER) positive MCF-7 cell line, but only a small effect on the ER negative MDA-MB-231 cells. The expression of the IL-1beta gene was also transcriptionally activated by RA in normal epithelial cells of prostate and oral cavity. Our results suggest that: (a) the IL-1beta gene is a primary target of RA receptors in HMEC; (b) the enhanced expression of the IL-1beta gene does not mediate the RA-induced growth arrest of HMEC; and (c) the expression of the IL-1beta gene is low or absent in all three human breast carcinoma cell lines examined, but the defect in the IL-1beta signaling pathway may be different in ER positive versus ER negative carcinoma cells.