An experimental biomimetic platform for artificial olfaction

Artificial olfactory systems have been studied for the last two decades mainly from the point of view of the features of olfactory neuron receptor fields. Other fundamental olfaction properties have only been episodically considered in artificial systems. As a result, current artificial olfactory systems are mostly intended as instruments and are of poor benefit for biologists who may need tools to model and test olfactory models. Herewith, we show how a simple experimental approach can be used to account for several phenomena observed in olfaction. An artificial epithelium is formed as a disordered distributed layer of broadly selective color indicators dispersed in a transparent polymer layer. The whole epithelium is probed with colored light, imaged with a digital camera and the olfactory response upon exposure to an odor is the change of the multispectral image. The pixels are treated as olfactory receptor neurons, whose optical properties are used to build a convergence classifier into a number of mathematically defined artificial glomeruli. A non-homogenous exposure of the test structure to the odours gives rise to a time and spatial dependence of the response of the different glomeruli strikingly similar to patterns observed in the olfactory bulb. The model seems to mimic both the formation of glomeruli, the zonal nature of olfactory epithelium, and the spatio-temporal signal patterns at the glomeruli level. This platform is able to provide a readily available test vehicle for chemists developing optical indicators for chemical sensing purposes and for biologists to test models of olfactory system organization.     

Metabolism of a novel side chain modified Delta8(14)-15-ketosterol, a potential cholesterol lowering drug: 28-hydroxylation by CYP27A1

The synthetic inhibitors of sterol biosynthesis, 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one and 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one, are of interest as potential cholesterol lowering drugs. Rapid metabolism of synthetic 15-ketosterols may lead to a decrease, or loss, of their potency to affect lipid metabolism. 3beta-Hydroxy-5alpha-cholest-8(14)-en-15-one is reported to be rapidly side chain oxygenated by rat liver mitochondria. In an attempt to reduce this metabolism, the novel side chain modified 15-ketosterol 3beta-Hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one was synthesized. We have examined the metabolism by recombinant human CYP27A1 of this novel side chain modified 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one and compared the rate of metabolism with that of the previously described 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. Both sterols were found to be efficiently metabolized by recombinant human CYP27A1. None of the two 15-ketosterols was significantly metabolized by microsomal 7alpha-hydroxylation. Interestingly, CYP27A1-mediated product formation was much lower with the side chain modified 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one than with the previously described 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. A surprising finding was that this novel side chain modified sterol was metabolized mainly in the C-28 position by CYP27A1. The data on 28-hydroxylation by human CYP27A1 provide new insights on the catalytic properties and substrate specificity of this enzyme. The finding that 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one with a modified side chain is metabolized at a dramatically slower rate than the previously described 15-ketosterol with unmodified side chain may be important for future development of synthetic cholesterol lowering sterols.     

Enzymatic conversions of polar lipids. Principles, problems and solutions

This text provides a brief overview of the principles of enzymatic lipid conversion and some recent advances in the enzymatic conversion of glycerophospholipids and galactolipids. Lipases and phospholipases are used to exchange fatty acids or the polar group in the lipids. The reactions can be carried out either as hydrolysis–esterification sequences or as one-step transferase reactions. The scope and limitations of the different methods are discussed.     

Epstein-Barr virus (EBV) receptors, complement receptors, and EBV infectibility of different lymphocyte fractions of human peripheral blood. I. Complement receptor distribution and complement binding by separated lymphocyte subpopulations.

Human peripheral lymphocytes were fractionated into a variety of B-, T-, and O-cell fractions and were characterized with regard to several surface receptors. There was a strong correlation between the frequency of EAC receptor-positive cells and the percentage of complement membrane fluorescence (CMF)-stained cells following exposure to fresh human serum and subsequent staining with an anti-C3 conjugate. CMF staining did not diminish in C4-deficient or hypogammaglobulinemic serum, or in the presence of EDTA or EGTA-Mg²⁺, but was completely negative with C3-depleted normal human serum. In all likelihood, the staining is therefore due to the direct binding of C3 to preformed receptors on the lymphocyte surface. In addition to the surface Ig-positive B-cell fractions, C3 receptors were also detected on part of the O-cell population and on a proportion of the Fc receptor-positive T cells.     

Epstein-Barr virus (EBV) receptors, complement receptors, and EBV infectibility of different lymphocyte fractions of human peripheral blood. II. Epstein-Barr virus studies.

In B-cell fractions isolated from human peripheral blood, the frequency of surface immunoglobulin-positive and of complement receptor-positive cells showed a good correlation with the frequency of EBV-binding cells, as detected by membrane fluorescence or by a quantitative bioassay for infectious virus in the absorbed supernatant fluid. There was a close relationship between all three parameters mentioned, the frequency of EBNA-positive cells 2 or 3 days after the infection, and the stimulation of cellular DNA synthesis. So-called O-cell fractions remaining after the removal of nylon adherent and E-rosetting cells contained a certain frequency of complement receptor-positive cells and absorbed EBV to a limited extent, but did not respond to EBV infection with EBNA induction or stimulation of DNA synthesis. None of the T-cell fractions absorbed EBV to a detectable extent. This includes the T_ea+ fraction that contained a certain proportion of complement receptor-positive cells. It is concluded that the previously demonstrated relationship between EBV receptors and complement receptors on B-lymphoblastoid lines also holds for peripheral B lymphocytes. In these cells, virus absorption is followed by an intracellular infectious process, signaled by the appearance of EBNA and cellular DNA synthesis. O cells carry complement receptors and absorb EBV to a certain extent, but do not respond with EBNA synthesis or DNA stimulation, presumably due to intracellular restrictions. T cells do not bind EBV, and the complement receptors present on some cells of the T_ea+ fraction do not function as EBV receptors.     

Evidence for sex difference in the CSF/plasma albumin ratio in ~20 000 patients and 335 healthy volunteers

Given sex‐related differences in brain disorders, it is of interest to study if there is a sex difference in the permeability of the blood‐cerebrospinal fluid barrier (BCSFB) and the blood‐brain barrier (BBB). The CSF/serum albumin ratio (Q_Alb) is a standardized biomarker that evaluates the function of these barriers. In previous studies, contradictory results have been reported with respect to sex difference using this quotient, possibly because of small population sizes and heterogeneity with respect to ages. Q_Alb measurements in more than 20 000 patients between 1 and 90 years visiting our hospitals revealed a significant sex difference in all age groups also when excluding patients with pathologically high CSF albumin > 400 mg/L. Similar pattern was found in 335 healthy volunteers in similar age intervals. Although also other factors are likely important, our observation is consistent with lower integrity of the brain barriers in males. If the difference in Q_Alb is caused mainly by a difference in barrier function, this may require different drug doses and strategies for efficient central nervous system (CNS) delivery in males and females, as well as it may indicate differences in brain metabolism. Moreover, our study emphasizes that different reference values should be used both for different ages and sexes.     

A 15.6 frames per second 1‐megapixel multiple exposure laser speckle contrast imaging setup

A multiple exposure laser speckle contrast imaging (MELSCI) setup for visualizing blood perfusion was developed using a field programmable gate array (FPGA), connected to a 1000 frames per second (fps) 1‐megapixel camera sensor. Multiple exposure time images at 1, 2, 4, 8, 16, 32 and 64 milliseconds were calculated by cumulative summation of 64 consecutive snapshot images. The local contrast was calculated for all exposure times using regions of 4 × 4 pixels. Averaging of multiple contrast images from the 64‐millisecond acquisition was done to improve the signal‐to‐noise ratio. The results show that with an effective implementation of the algorithm on an FPGA, contrast images at all exposure times can be calculated in only 28 milliseconds. The algorithm was applied to data recorded during a 5 minutes finger occlusion. Expected contrast changes were found during occlusion and the following hyperemia in the occluded finger, while unprovoked fingers showed constant contrast during the experiment. The developed setup is capable of massive data processing on an FPGA that enables processing of MELSCI data in 15.6 fps (1000/64 milliseconds). It also leads to improved frame rates, enhanced image quality and enables the calculation of improved microcirculatory perfusion estimates compared to single exposure time systems.      

7 Alpha-hydroxylation of cholesterol by reconstituted systems from rat liver microsomes

A reconstituted system from rat liver microsomes, consisting of partially purified fractions of cytochrome P-450 and NADPH-cytochrome P-450 reductase was shown to catalyze 7α-hydroxylation of cholesterol in the presence of NADPH and a synthetic phosphatidylcholine. The rate of 7α-hydroxylation of added [4-¹⁴C] cholesterol was linear with the concentration of cytochrome P-450 and increased with the concentration of NADPH-cytochrome P-450 reductase up to a certain level and then remained constant. Omission of phosphatidylcholine resulted only in a 20% decrease in cholesterol 7α-hydroxylase activity of the system. The rate of 7α-hydroxylation was 2–3 times higher in reconstituted systems with cytochrome P-450 from cholestyramine-treated rats than in those with cytochrome P-450 from untreated rats.