Single metal-organic framework-embedded nanopit arrays: A new way to control neural stem cell differentiation

Stable and continuous supply of essential biomolecules is critical to mimic in vivo microenvironments wherein spontaneous generation of various cell types occurs. Here, we report a new platform that enables highly efficient neuronal cell generation of neural stem cells using single metal-organic framework (MOF) nanoparticle-embedded nanopit arrays (SMENA). By optimizing the physical parameters of homogeneous periodic nanopatterns, each nanopit can confine single nMOFs (UiO-67) that are specifically designed for long-term storage and release of retinoic acid (RA). The SMENA platform successfully inhibited physical interaction with cells, which contributed to remarkable stability of the nMOF (RA⊂UiO-67) structure without inducing nanoparticle-mediated toxicity issues. Owing to the continuous and long-term supply of RA, the neural stem cells showed enhanced mRNA expressions of various neurogenesis-related activities. The developed SMENA platform can be applied to other stem cell sources and differentiation lineages and is therefore useful for various stem cell-based regenerative therapies.

Extracorporeal Shock Waves Increase Markers of Cellular Proliferation in Bronchial Epithelium and in Primary Bronchial Fibroblasts of COPD Patients

Chronic obstructive pulmonary disease (COPD) is due to structural changes and narrowing of small airways and parenchymal destruction (loss of the alveolar attachment as a result of pulmonary emphysema), which all lead to airflow limitation. Extracorporeal shock waves (ESW) increase cell proliferation and differentiation of connective tissue fibroblasts. To date no studies are available on ESW treatment of human bronchial fibroblasts and epithelial cells from COPD and control subjects. We obtained primary bronchial fibroblasts from bronchial biopsies of 3 patients with mild/moderate COPD and 3 control smokers with normal lung function. 16HBE cells were also studied. Cells were treated with a piezoelectric shock wave generator at low energy (0.3 mJ/mm², 500 pulses). After treatment, viability was evaluated and cells were recultured and followed up for 4, 24, 48, and 72 h. Cell growth (WST-1 test) was assessed, and proliferation markers were analyzed by qRT-PCR in cell lysates and by ELISA tests in cell supernatants and cell lysates. After ESW treatment, we observed a significant increase of cell proliferation in all cell types. C-Kit (CD117) mRNA was significantly increased in 16HBE cells at 4 h. Protein levels were significantly increased for c-Kit (CD117) at 4 h in 16HBE (p < 0.0001) and at 24 h in COPD-fibroblasts (p = 0.037); for PCNA at 4 h in 16HBE (p = 0.046); for Thy1 (CD90) at 24 and 72 h in CS-fibroblasts (p = 0.031 and p = 0.041); for TGFβ1 at 72 h in CS-fibroblasts (p = 0.038); for procollagen-1 at 4 h in COPD-fibroblasts (p = 0.020); and for NF-κB-p65 at 4 and 24 h in 16HBE (p = 0.015 and p = 0.0002). In the peripheral lung tissue of a representative COPD patient, alveolar type II epithelial cells (TTF‐1+) coexpressing c-Kit (CD117) and PCNA were occasionally observed. These data show an increase of cell proliferation induced by a low dosage of extracorporeal shock waves in 16HBE cells and primary bronchial fibroblasts of COPD and control smoking subjects.

Biochemical and physiological importance of the CYP26 retinoic acid hydroxylases

The Cytochrome P450 (CYP) family 26 enzymes contribute to retinoic acid (RA) metabolism and homeostasis in humans, mammals and other chordates. The three CYP26 family enzymes, CYP26A1, CYP26B1 and CYP26C1 have all been shown to metabolize all-trans-retinoic acid (atRA) it's 9-cisRA and 13-cisRA isomers and primary metabolites 4-OH-RA and 4-oxo-RA with high efficiency. While no crystal structures of CYP26 enzymes are available, the binding of various ligands has been extensively explored via homology modeling. All three CYP26 enzymes are inducible by treatment with atRA in various prenatal and postnatal tissues and cell types. However, current literature shows that in addition to regulation by atRA, CYP26 enzyme expression is also regulated by other endogenous processes and inflammatory cytokines. In humans and in animal models the expression patterns of CYP26 enzymes have been shown to be tissue and cell type specific, and the expression of the CYP26 enzymes is believed to regulate the formation of critical atRA concentration gradients in various tissue types. Yet, very little data exists on direct disease associations of altered CYP26 expression or activity. Nevertheless, data is emerging describing a variety of human genetic variations in the CYP26 enzymes that are associated with different pathologies. Interestingly, some of these genetic variants result in increased activity of the CYP26 enzymes potentially leading to complex gene-environment interactions due to variability in dietary intake of retinoids. This review highlights the current knowledge of structure-function of CYP26 enzymes and focuses on their role in human retinoid metabolism in different tissues.

Isotretinoin administration improves sperm production in men with infertility from oligoasthenozoospermia: a pilot study

There is currently no effective medical therapy for men with infertility due to oligoasthenozoospermia. As men with abnormal sperm production have lower concentrations of 13-cis-retinoic acid in their testes, we hypothesized that men with infertility from oligoasthenozoospermia might have improved sperm counts when treated with isotretinoin (13-cis-retinoic acid). We conducted a single-site, single-arm, pilot study to determine the effect of therapy with isotretinoin on sperm indices in 19 infertile men with oligoasthenozoospermia. Subjects were men between 21 and 60 years of age with infertility for longer than 12 months associated with sperm concentrations below 15 million sperm/mL. All men received isotretinoin 20 mg by mouth twice daily for 20 weeks. Subjects had semen analyses, physical examinations, and laboratory tests every 4 weeks during treatment. Nineteen men enrolled in the study. Median (25th, 75th) sperm concentration increased from 2.5 (0.1, 5.9) million/mL at baseline to 3.8 (2.1, 13.0) million/mL at the end of treatment (p = 0.006). No significant changes in sperm motility were observed. There was a trend toward improved sperm morphology (p = 0.056). Six pregnancies (three spontaneous and three from intracytoplasmic sperm injection) and five births occurred during the study. Four of the births, including all three of the spontaneous pregnancies, were observed in men with improvements in sperm counts with isotretinoin therapy. Treatment was well tolerated. Isotretinoin therapy improves sperm production in some men with oligoasthenozoospermia. Additional studies of isotretinoin in men with infertility from oligoasthenozoospermia are warranted.

The safety of isotretinoin in patients with lupus nephritis: a comprehensive review

Oral isotretinoin (13-cis-retinoinc acid) is a derivative of vitamin A and belongs to the first generation of retinoids, which act as synthetic isomers of retinoic acid (RA). It is a very effective agent in a treatment of acne vulgaris; however, multiple side effects related to therapy with retinoids preclude the use of isotretinoin in less severe acne vulgaris. A significant limitation for the administration of isotretinoin appears in case of concomitant kidney disease with a special attention regarding the safety of the agent in patients with lupus nephritis (LN). The aim of this review is an assessment of the safety of isotretinoin for the treatment of acne vulgaris in patients with LN. We searched both MEDLINE and SCOPUS databases, as well as several dermatological textbooks, to present all limitations and benefits of therapy with isotretinoin or its isomer (ATRA) for patients with kidney diseases. Several mouse models of SLE revealed a significant modulatory influence of retinoids on autoimmune injury of the glomerular unit. Retinoids were demonstrated to affect mononuclear cell infiltrations of renal tissue allowing for a reduction in the overall glomerular damage. Presumptively, they can affect a synthesis of autoantibodies significantly limiting their deposition in the glomerular unit. Moreover, retinoids were also shown to affect the synthesis of different cytokines specific both for lymphocytes Th1 (IL-2, IL-12, INFγ) ant Th2 (IL-4, IL-10). The influence of retinoids on the course of LN seems to be more multidimensional than only restricted to immune aspects and these synthetic RA isomers manifest also antiproteinuric activity in comparable extent to steroidal agents. The agents were demonstrated to counteract a loss of podocytes after the injury of the glomerular unit. They can promote a differentiation of renal progenitor cells (RPCs) within the Bowman capsule into mature podocytes leading to regeneration of podocyte number. Additionally, retinoids can probably protect podocytes from injury limiting their apoptosis, as well as reducing foot process effacement. Although, an endogenous production of RA isomers increases after the injury of the glomerular unit aiming to the restoration of podocyte number, it can be significantly impaired by a loss of albumins into urine. RA isomers are progressively sequestered by albumin within the Bowman's space and therefore, they are quickly eliminated with urine. It was demonstrated that the administration of exogenous RA isomers (retinoids) can bypass the activity of albumins enhancing the regeneration of podocytes. Finally, retinoids can regulate the production of vasoactive substances influencing on different vascular functions in the kidney. They can beneficially change a balance of angiotensin metabolites through by down-regulation of angiotensin-converting enzyme type 1 and the enhancement of an expression of angiotensin-converting enzyme type 2. Another studies revealed that retinoids could also alter the activity of renal endothelin pathway; however, the significance of this effect requires further elucidation. Taken all these presented effects of retinoids in the kidney into consideration, we can conclude that isotretinoin can be the safe treatment option of acne vulgaris in patients with LN.

Retinoids and rexinoids in cancer prevention: from laboratory to clinic

Early in the age of modern medicine the consequences of vitamin A deficiency drew attention to the fundamental link between retinoid-dependent homeostatic regulation and malignant hyperproliferative diseases. The term "retinoid" includes a handful of endogenous and a large group of synthetic derivatives of vitamin A. These multifunctional lipid-soluble compounds directly regulate target genes of specific biological functions and critical signaling pathways to orchestrate complex functions from vision to development, metabolism, and inflammation. Many of the retinoid activities on the cellular level have been well characterized and translated to the regulation of processes like differentiation and cell death, which play critical roles in the outcome of malignant transformation of tissues. In fact, retinoid-based differentiation therapy of acute promyelocytic leukemia was one of the first successful examples of molecularly targeted treatment strategies. The selectivity, high receptor binding affinity and the ability of retinoids to directly modulate gene expression programs present a distinct pharmacological opportunity for cancer treatment and prevention. However, to fully exploit their potential, the adverse effects of retinoids must be averted. In this review we provide an overview of the biology of retinoid (activated by nuclear retinoic acid receptors [RARs]) and rexinoid (engaged by nuclear retinoid X receptors [RXRs]) action concluded from a long line of preclinical studies, in relation to normal and transformed states of cells. We will also discuss the past and current uses of retinoids in the treatment of malignancies, the potential of rexinoids in the cancer prevention setting, both as single agents and in combinations.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Induction of CYP26A1 by metabolites of retinoic acid: evidence that CYP26A1 is an important enzyme in the elimination of active retinoids

All-trans-retinoic acid (atRA), the active metabolite of vitamin A, induces gene transcription via binding to nuclear retinoic acid receptors (RARs). The primary hydroxylated metabolites formed from atRA by CYP26A1, and the subsequent metabolite 4-oxo-atRA, bind to RARs and potentially have biologic activity. Hence, CYP26A1, the main atRA hydroxylase, may function either to deplete bioactive retinoids or to form active metabolites. This study aimed to determine the role of CYP26A1 in modulating RAR activation via formation and elimination of active retinoids. After treatment of HepG2 cells with atRA, (4S)-OH-atRA, (4R)-OH-atRA, 4-oxo-atRA, and 18-OH-atRA, mRNAs of CYP26A1 and RARβ were increased 300- to 3000-fold, with 4-oxo-atRA and atRA being the most potent inducers. However, >60% of the 4-OH-atRA enantiomers were converted to 4-oxo-atRA in the first 12 hours of treatment, suggesting that the activity of the 4-OH-atRA was due to 4-oxo-atRA. In human hepatocytes, atRA, 4-OH-atRA, and 4-oxo-atRA induced CYP26A1 and 4-oxo-atRA formation was observed from 4-OH-atRA. In HepG2 cells, 4-oxo-atRA formation was observed even in the absence of CYP26A1 activity and this formation was not inhibited by ketoconazole. In human liver microsomes, 4-oxo-atRA formation was supported by NAD(+), suggesting that 4-oxo-atRA formation is mediated by a microsomal alcohol dehydrogenase. Although 4-oxo-atRA was not formed by CYP26A1, it was depleted by CYP26A1 (Km = 63 nM and intrinsic clearance = 90 μl/min per pmol). Similarly, CYP26A1 depleted 18-OH-atRA and the 4-OH-atRA enantiomers. These data support the role of CYP26A1 to clear bioactive retinoids, and suggest that the enzyme forming active 4-oxo-atRA may be important in modulating retinoid action.

TLR9-signaling is required for turning retinoic acid into a potent stimulator of RP105 (CD180)-mediated proliferation and IgG synthesis in human memory B cells

The role of vitamin A in the various parts of the immune system remains elusive. Toll-like receptors (TLRs) are involved in innate polyclonal activation of B-cells, and as such they are important for maintaining long-lasting first line defense against pathogens. Here we explore the impact of all-trans retinoic acid (RA) on B cell responses mediated via the TLR homolog RP105 (CD180). We show that RA slightly reduces the proliferation and IgG production in CD27+ memory B cells stimulated by anti-RP105 alone. However, co-stimulation with the TLR9-ligand CpG results in turning RA into a potent stimulator of RP105-induced proliferation and IgG synthesis in memory B cells. The results emphasize the important role of RA in stimulating TLR-mediated polyclonal activation and differentiation of B cells, and reveal the complex interplay between various TLRs that may underlie the ability of RA to fight pathogens.

13-cis-Retinoic acid specific down-regulation of angiotensin type 1 receptor in rat liver epithelial and aortic smooth muscle cells

Transcriptional repression through cis- and trans-acting factors enabling an alternate approach to control angiotensin type 1 receptor (AT1 or AGTR1 as listed in the MGI database) expression has not been studied. In previous investigations, treatment with retinoic acid was found to be associated with enhanced insulin sensitivity. In our previous study, expression of AT1 was found to be inversely correlated with intracellular glucose concentrations. Therefore, we hypothesized that 13-cis-retinoic acid (13cRA), an antioxidant, enhances insulin-sensitive glucose-mediated down-regulation of the AT1. In this study, we used continuously passaged rat liver epithelial cells. Our study shows that cells exposed to 13cRA specifically down-regulated the AT1 protein in a dose- and time-dependent manner, independently of any change in receptor affinity. Down-regulation of the AT1 expression leads to reduced AngII-mediated intracellular calcium release, a hallmark of receptor-mediated intracellular signaling. Similarly with receptor down-regulation, we observed a significant reduction in AT1 mRNA; however, the AT1 down-regulation was independent of insulin-sensitive glucose uptake and retinoic acid receptor activation (RAR/RXR). Treatment with 13cRA resulted in phosphorylation of p42/p44 MAP kinases in these cells. Subsequent studies using MEK inhibitor PD98059 prevented 13cRA-mediated AT1 down-regulation and restored AngII-mediated intracellular calcium response. Furthermore, 13cRA-mediated inhibitory effects on AT1 were validated in primary rat aortic smooth muscle cells. In summary, our results demonstrate for the first time that 13cRA has a glucose- and RAR/RXR-independent mechanism for transcriptional inhibition of AT1, suggesting its therapeutic potential in systems in which AT1 expression is deregulated in insulin-sensitive and -insensitive tissues.

Potential of retinoic acid derivatives for the treatment of corticotroph pituitary adenomas

Cushing's disease is a severe clinical condition caused by hypersecretion of corticosteroids due to excessive ACTH secretion from a pituitary adenoma. This complex endocrine disorder still represents a major challenge for the physician in terms of efficient treatment. In the last years there was only little progress in elucidating the molecular mechanisms responsible for the constitutive and autonomous ACTH secretion of pituitary corticotrophinomas. As a consequence, no effective drug therapy is currently available, particularly if surgical excision is not successful. In the present article we examine recent studies that have investigated the therapeutic potential of retinoic acid receptors as nuclear receptor targets for the treatment of Cushing's disease. Retinoic acid is an efficient drug used for the treatment of different types of cancers and it proved to act in animal models of Cushing's disease. The efficiency of this treatment in patients with this disorder still needs to be tested in clinical trials.