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Autotaxin (ATX) generates the lipid mediator lysophosphatidic acid (LPA). ATX-LPA signalling is involved in multiple biological and pathophysiological processes, including vasculogenesis, fibrosis, cholestatic pruritus and tumour progression. ATX has a tripartite active site, combining a hydrophilic groove, a hydrophobic lipid-binding pocket and a tunnel of unclear function. We present crystal structures of rat ATX bound to 7α-hydroxycholesterol and the bile salt tauroursodeoxycholate (TUDCA), showing how the tunnel selectively binds steroids. A structure of ATX simultaneously harbouring TUDCA in the tunnel and LPA in the pocket, together with kinetic analysis, reveals that bile salts act as partial non-competitive inhibitors of ATX, thereby attenuating LPA receptor activation. This unexpected interplay between ATX-LPA signalling and select steroids, notably natural bile salts, provides a molecular basis for the emerging association of ATX with disorders associated with increased circulating levels of bile salts. Furthermore, our findings suggest potential clinical implications in the use of steroid drugs.

A derivatization procedure with (3-dimethylaminophenyl)dihydroxyborane (DAPB) was introduced to enhance the detectability of steroids having a vicinal diol in LC/electrospray ionization (ESI)-MS/MS. DAPB reacted with the vicinal diol on the steroids [4β-hydroxycholesterol (4-HCh), pregnanetriol (PT) and 20R,22R-dihydroxycholesterol] in pyridine at 50°C within 1 h. The resulting DAPB-derivatives were highly responsive in ESI-MS operating in the positive-ion mode and gave characteristic product ions during MS/MS, which enabled sensitive detection using a selected reaction monitoring mode; the detection responses of the DAPB-derivatives were increased by 20-160-fold over those of the intact steroids and the limits of detection were in the low femtomole or attomole range. The derivatization procedure was successfully applied to biological sample analysis; the derivatization followed by LC/ESI-MS/MS enabled the specific detection of trace amounts of 4-HCh in human plasma and PT in human urine with a small sample volume, simple pretreatment and short chromatographic run time.

The transverse motion of molecules from one leaflet to the other of a lipid bilayer, or flip-flop, represents a putative mechanism for their transmembrane transport and may contribute to the asymmetric distribution of components in biomembranes. However, a clear understanding of this process is still missing. The scarce knowledge derives from the difficulty of experimental determination. Because of its slow rate on the molecular time scale, flip-flop is challenging also for computational techniques. Here, we report a study of the passive transbilayer diffusion of steroids, based on a kinetic model derived from the analysis of their free energy surface, as a function of their position and orientation in the bilayer. An implicit membrane description is used, where the anisotropy and the nonuniformity of the bilayer environment are taken into account in terms of the gradients of density, dielectric permittivity, acyl chain order parameters, and lateral pressure. The flip-flop rates are determined by solving the Master Equation that governs the time evolution of the system, with transition rates between free energy minima evaluated according to the Kramers theory. Considering various steroids (cholesterol, lanosterol, ketosterone, 5-cholestene, 25-hydroxycholesterol, and testosterone), we can discuss how differences in molecular shape and polarity affect the pathway and the rate of flip-flop in a liquid crystalline 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) bilayer, at low steroid concentration. We predict time scales ranging from microseconds to milliseconds, strongly affected by the presence of polar substituents and by their position in the molecular skeleton.

Using 22R-hydroxycholesterol as a sub-structure to screen natural compound databases, we identified a naturally occurring steroid (sc-7) with a 16-acetoxy-22R-hydroxycholesterol moiety, in which the hydroxyl groups in positions 3 and 22 are esterified by an acetoxy group and in which the carbon in position 26 carries a functional diacetylamino. sc-7 is an analog of the sex steroids dehydro-oogoniol and antheridiol, can be isolated from the water mold Achlya heterosexualis, and promoted neurogenesis in vitro and in vivo. Mouse embryonic teratocarcinoma P19 cells exposed to sc-7 for 2days followed by a 5-day wash-out differentiated into cholinergic neurons that expressed specific neuronal markers and displayed axonal formation. Axons continued growing up to 28days after treatment. In vivo, infusion of sc-7 for 2weeks into the left ventricle of the rat brain followed by a 3-week wash-out induced bromodeoxyuridine uptake by cells of the ependymal layer and subventricular zone that co-localized with doublecortin and glial fibrillary acidic protein immunostaining, demonstrating induction of proliferation and differentiation of neuronal progenitors. Migrating neuroblasts were also observed in the corpus callosum. Thus, under these experimental conditions, adult ependymal cells resumed proliferation and differentiation. Taken together, these results suggest that sc-7 is an interesting molecule for stimulating in situ neurogenesis from resident neuronal progenitors as part of neuron replacement therapy. sc-7 did not bind to nuclear steroid receptors and was not metabolized as a steroid, supporting our hypothesis that the neurogenic effect of sc-7 is not likely due to a steroid-like effect., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In this study, cholest-5-en-3β,7β-diol and 3β-hydroxy-cholest-5-en-7-one were isolated from Oviductus Ranae by column chromatographies on Sephadex LH-20, octadecylsilyl (ODS) and pre high-performance liquid chromatography (HPLC). Their structures were elucidated on the basis of chemical and spectral analyses, including electrospray ionisation-mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR). The above two compounds were obtained from Oviductus Ranae for the first time.

Four new steroids, stoloniferones R-T (1-3), and (25S)-24-methylenecholestane-3 beta,5 alpha,6 beta-triol-26-acetate (4) were isolated from the methylene chloride solubles of the soft coral Clavularia viridis. The structures of the metabolites were elucidated by extensive spectral analysis and their anti-inflammatory activity was measured in vitro.

Sterols are essential components of virtually all higher eukaryotic organisms, though the exact identity of the dominating sterol varies between species, from the C-27 of cholesterol in vertebrates to the C-28 and C-29 sterols of plants and invertebrates. In addition to their role as structural components of cell membranes these sterols are also converted into a variety of biologically active hormones. This conversion generally involves modifications of the basic structure of the sterol by dealkylation, hydroxylation and/or isomerization. Recent studies have demonstrated that irreversible inactivation of both plant and insect hormones is achieved by a specific C-26 hydroxylation. The concept of sterol deactivation by 26-hydroxylation appears to be an example of an evolutionarily conserved mechanism that has persisted despite the widely varying requirements for sterols in the species where it has been detected.

In artificial membrane bilayers, saturated long acyl chain-containing phospholipids and cholesterol (Chol) interact to form more ordered domains than those in phospholipids with unsaturated or short fatty acyl chains. We have extended the fluorescence techniques of London et al. [Xu, X., and London, E. (2000) Biochemistry 39, 843-849; Xu, X., Bittman, R., Duportail, G., Heissler, D., Vilchezes, C., and London, E. (2001) J. Biol. Chem. 276, 33540-33546] to study the propensity of several steroids to form or disrupt such ordered lipid domains. Temperature-dependent fluorescence quenching and steady-state polarization of the extrinsic fluorescent probe diphenylhexatriene (DPH) in model membranes composed of dipalmitoylphosphatidylcholine (or sphingomyelin), a nitroxide spin-labeled phosphatidylcholine (12-SLPC), and a given steroid were combined to study the influence of the latter on (a) ordered lipid domain formation, (b) stabilization, and (c) the extension of the ordered lipid assemblies. The results of the two totally independent methods, fluorescence quenching by 12-SLPC and fluorescence polarization of DPH, show that all steroids examined, except for Chol and 25-hydroycholesterol, behave as lipid domain-disrupting compounds. Additionally, we found a positive correlation between the hydrophobicity of steroids and their ordered lipid domain-promoting activity. Comparison of the chemical structures disclosed some distinctive traits of ordered lipid domain-promoting steroids: (i) the presence of an isooctyl side chain bond at C17; (ii) the absence of carbons attached to C23 (i.e., C24-C27) in any of the other (domain-disrupting) steroids; (iii) the presence of a small polar group at position C3; and (iv) the absence of polar groups in the fused rings, with the exception of substitutions at position C3 in the A ring.

Two new brassinosteroids, (22R,23R,24S)-22,23-dihydroxy-24-methyl-5alpha-cholest-2-en-6-one (secasterol) and (22R,23R,24S)-22,23-dihydroxy-2alpha,3alpha-epoxy-24-methyl-5alpha-cholest-6-one (2,3-diepisecasterone) have been identified together with a known 2,3-epoxybrassinosteroid, secasterone, in seedlings of Secale cereale. Deuterated secasterol, teasterone, and typhasterol, upon administration to rye seedlings, were incorporated into secasterone and 2,3-diepisecasterone, indicating a biosynthetic route via teasterone/typhasterol to secasterol to 2,3-epoxybrassinosteroids.