Original articlesBrain-to-blood efflux transport of estrone-3-sulfate at the blood-brain barrier in rats
Abstract
Efflux transport of estrogens such as estrone-3-sulfate (E1S), and estrone (E1) across the blood-brain barrier (BBB) was evaluated using the Brain Efflux Index (BEI) method. The apparent BBB efflux rate constant (Keff) of [3H]E1S, and [3H]E1 was 6.63 × 10−2 ± 0.77 × 10−2 min−1, and 6.91 × 10−2 ± 1.23 × 10−2 min−1, respectively. The efflux transport of [3H]E1S from brain across the BBB was a saturable process with Michaelis constant (Km) of 96.0 ± 34.4 μM and 93.4 ± 22.0 μM estimated by two different methods. By determining [3H]E1S metabolites using high performance liquid chromatography (HPLC) after intracerebral injection, significant amounts of [3H]E1S were found in the jugular venous plasma, providing direct evidence that most of [3H]E1S is transported from brain across the BBB in intact form. To compare the apparent efflux clearance across the BBB of E1S with that of E1, the brain distribution volume of E1S and E1 was estimated using the brain slice uptake method. The apparent efflux clearance of [3H]E1S was determined to be 74.9 ± 3.8 μl/(min·g brain) due to the distribution volume of 1.13 ± 0.06 ml/g brain. By contrast, the apparent efflux clearance of E1 was more than 227 ± 3 μl/(min·g brain), since the distribution volume of [3H]E1 at 60 min was 3.28 ± 0.13 ml/g. The E1S efflux transport process was inhibited by more than 40% by coadministration of bile acids (taurocholate, and cholate), and organic anions (sulfobromophthalein, and probenecid), whereas other organic anions did not affect the E1S efflux transport. The [3H]E1S efflux was significantly reduced by 48.6% after preadministration of 5 mM dehydroepiandrosterone sulfate. These results suggest that E1S is transported from brain to the circulating blood across the BBB via a carrier-mediated efflux transport system.
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Preliminary evidence of altered steroidogenesis in women with Alzheimer's disease: Have the patients "OLDER" adrenal zona reticularis?
2016, Journal of Steroid Biochemistry and Molecular BiologyCitation Excerpt :SULT2A1 is highly expressed in the adrenal zona reticularis and liver [31]. In this study we used these ratios and the recent available knowledge on steroid conjugation in the literature, which is as follows: pregnenolone C/U [17–46], 20α-dihydropregnenolone C/U [17,52], DHEA C/U [17,46–48,52–59], androstenediol C/U [17–47,52], allopregnanolone C/U [17,50,52], isopregnanolone C/U [17–52], androsterone C/U [17–47,52], epiandrosterone C/U [46,47,52], etiocholanolone C/U [17,49,52], epietiocholanolone C/U [52], 5α-androstane-3α,17β-diol C/U [47,52], 5α-androstane-3β,17β-diol C/U [47,52]. This balance is regulated by the reductive and oxidative isoforms of 17β-hydroxysteroid dehydrogenases (HSD17Bs) and by the aldoketoreductases of subfamily 1C (AKR1Cs) (the corresponding references can be found further in the text).
Alzheimer’s disease (AD) represents more than half of total dementias. Various factors including altered steroid biosynthesis may participate in its pathophysiology. We investigated how the circulating steroids (measured by GC–MS and RIA) may be altered in the presence of AD. Sixteen women with AD and 22 age- and BMI-corresponding controls aged over 65 years were enrolled in the study. The steroid levels (47 steroids and steroid polar conjugates) and their ratios in AD female patients indicated increased CYP11A1 activity, weakened activity of the CYP17A1C17,20 lyase metabolic step and attenuated sulfotransferase SULT2A1 activity at higher activity of the CYP17A1 17-hydroxylase step. The patients showed diminished HSD3B2 activity for C21 steroids, abated conversion of 17-hydroxyprogesterone to cortisol, and significantly elevated cortisol. The women with AD had also attenuated steroid 7α-hydroxylation forming immunoprotective Δ5-C19 steroids, attenuated aromatase activity forming estradiol that induces autoimmunity and a shift from the 3β-hydroxy-5α/β-reduced C19 steroids to their neuroinhibitory and antiinflammatory GABAergic 3α-hydroxy- counterparts and showed higher levels of the 3α-hydroxy-5α/β-reduced C21 steroids and pregnenolone sulfate (improves cognitive abilities but may be both protective and excitotoxic). Our preliminary data indicated functioning of alternative “backdoor” pathway in women with AD showing higher levels of both 5α/β-reduced C21 steroids but reduced levels of both 5α/β-reduced C21 steroids, which implied that the alternative “backdoor” pathway might include both 5α- and 5β-reduced steroids. Our study suggested relationships between AD status in women based on the age of subjects and levels of 10 steroids measured by GC–MS.
Biodegradation of estrone and 17 β-estradiol in grassland soils amended with animal wastes
2006, Soil Biology and BiochemistryThe release of endocrine disrupting chemicals into the environment is of increasing concern due to the formation of an intersex state in freshwater organisms and potential risks to human health. The aim of this study was to investigate the persistence of the naturally occurring hormones, estrone and 17 β-estradiol in three agricultural grassland soils in the presence and absence of cattle and sheep wastes (urine and manure). Biodegradation was investigated using 14C-labelled hormones which were applied to soil in three different solvents (water, artificial urine and natural sheep urine). When applied directly to soil the two hormones degraded at a similar rate, however, the speed of mineralization was soil type and solvent dependant. The half-life () of the hormones in soils ranged from 5 to 25 d. The hormones were also applied to the soils in sheep and cattle manure of different ages (7 d to 2 yr). Generally, the rate of degradation in the animal manure amended soils was more rapid than in the unamended soils (t1/2=1–9 d), with mineralization being largely independent of manure age and type. We conclude that in comparison to many xenobiotics, estrogens are not persistent in agricultural soils. However, our calculations suggest that if they are lost to freshwater via runoff or leaching then they may have an appreciable effect on freshwater organisms. Assuming normal landspreading rates our results suggest that the risk of estrogen contamination of freshwater associated with manure spreading is very low.
Role of drug efflux transporters in the brain for drug disposition and treatment of brain diseases
2005, Progress in NeurobiologyThe blood–brain barrier (BBB) serves as a protective mechanism for the brain by preventing entry of potentially harmful substances from free access to the central nervous system (CNS). Tight junctions present between the brain microvessel endothelial cells form a diffusion barrier, which selectively excludes most blood-borne substances from entering the brain. Astrocytic end-feet tightly ensheath the vessel wall and appear to be critical for the induction and maintenance of the barrier properties of the brain capillary endothelial cells. Because of these properties, the BBB only allows entry of lipophilic compounds with low molecular weights by passive diffusion. However, many lipophilic drugs show negligible brain uptake. They are substrates for drug efflux transporters such as P-glycoprotein (Pgp), multidrug resistance proteins (MRPs) or organic anion transporting polypeptides (OATPs) that are expressed at brain capillary endothelial cells and/or astrocytic end-feet and are key elements of the molecular machinery that confers the special permeability properties to the BBB. The combined action of these carrier systems results in rapid efflux of xenobiotics from the CNS. The objective of this review is to summarize transporter characteristics (cellular localization, specificity, regulation, and potential inhibition) for drug efflux transport systems identified in the BBB and blood–cerebrospinal fluid (CSF) barrier. A variety of experimental approaches available to ascertain or predict the impact of efflux transport on brain access of therapeutic drugs also are described and critically discussed. The potential impact of efflux transport on the pharmacodynamics of agents acting in the CNS is illustrated. Furthermore, the current knowledge about drug efflux transporters as a major determinant of multidrug resistance of brain diseases such as epilepsy is reviewed. Finally, we summarize strategies for modulating or by-passing drug efflux transporters at the BBB as novel therapeutic approaches to drug-resistant brain diseases.
Efflux transport systems at the blood-brain barrier and blood CSF barrier
2005, International Congress SeriesDrugs acting in the central nervous system (CNS) have to cross the blood-brain barrier (BBB) and/or blood–cerebrospinal fluid barrier (BCSFB). These two barriers are formed by brain capillary endothelial cells and choroid plexus epithelial cells. P-glycoprotein (P-gp) was initially identified as an efflux transporter at the BBB. It extrudes its substrate drugs into the blood, and acts as one of barrier functions against invasion of xenobiotics into the central nervous system. Thus, recognition by P-gp as a substrate is a major disadvantage for drugs used to treat CNS disease. In addition to P-gp, accumulating evidence has revealed the presence of efflux transport systems for anionic drugs. The transporters involved in the efflux transport of organic anions from the CNS are being identified in the BBB and BCSFB, and include the members of organic anion transporting polypeptides (Oatp1a4 and Oatp1a5) and organic anion transporter (Oat3) which are involved in the efflux of amphipathic and hydrophilic organic anions, respectively. The transporters located on the membranes facing the blood still remain to be identified although several candidate primary active transporters, such as MRP and BCRP, have already been proposed. Further clarification of influx and efflux transporters in the barriers will enable us to deliver drugs efficiently into the brain and to understand the mechanisms of drug–drug interactions and interindividual differences in the therapeutic CNS effects and/or adverse effects caused by drugs. The present manuscript summarizes the recent advance in the characterization of efflux transport systems at the BBB and BCSFB from our laboratory and others.
In the past decade, research into P-glycoprotein involving the blood-brain barrier (BBB) has seen a shift in the concept of the BBB as a structural barrier to that of a functional barrier for xenobiotics and changed simultaneously the strategy for the discovery and development of drugs acting in the CNS. As far as making advances in neurotherapeutics are concerned, the brain-to-blood transport function at the BBB will be one of the most important issues. Knowing the limitations of the in vivo and in vitro methods for BBB efflux research, it is essential to adopt a multidisciplinary approach in investigating the true physiological role of the BBB. Among several methods, the Brain Efflux Index method and the use of conditionally immortalized brain capillary endothelial cell lines, established from transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene, are likely to be very useful tools for the BBB efflux transport research. According to our recent findings using these methods, several transporters in the brain capillary endothelial cells appear to play an important role in reducing the brain level of hydrophilic endogenous substrates produced either in the brain or peripheral organs, e.g., neurotransmitters, neuromodulators, metabolites of neurotransmitters, and uremic toxins. It has been reported also that large hydrophilic molecules, such as IgG, apo-transferrin, and amyloid-β peptide, are susceptible to brain-to-blood efflux transport. In the light of the latest findings, we have formed the hypothesis that the BBB acts as a CNS detoxifying system for both endogenous substrates and xenobiotics in the brain. A fuller understanding of the physiological role of BBB efflux transporters will provide rational insights to assist in the development of safer neurotherapeutics.
The brain uptake of xenobiotics is restricted by the blood-brain brain barrier formed by brain capillary endothelial cells. Active efflux transport systems in the blood-brain barrier work as a detoxification system in the brain by facilitating removal of xenobiotic compounds from the brain. Drugs, acting in the brain, have to overcome such efflux mechanisms to achieve clinically significant concentration in the brain. Multiple transporters are involved in this efflux transport in the brain capillaries. In the past few years, considerable progress has been made in the cloning of these transporters and their functional characterization after heterologous expression. Members of the solute carrier family (SLC) play an important role in the efflux transport, especially for organic anions, which include organic anion transporting polypeptides (OATP/SLCO) and organic anion transporters (OAT/SLC22A). It is believed that coordination of the members of SLC family, and ABC transporters, such as P-glycoprotein, multidrug resistance protein, and breast cancer-resistant protein (BCRP/ABCG2), allows an efficient vectorial transport across the endothelial cells to remove xenobiotics from the brain. In this review, we shall summarize our current knowledge about their localization, molecular and functional characteristics, and substrate and inhibitor specificity.