In vitro approaches to evaluation of Sun Protection Factor

The efficacy of sunscreen products has been recognized as an important public health issue. Adequate methods for assessment of the level of protection should be developed and standardised. While the SPF COLIPA testing method in vivo has been used for years, preference should be given to in vitro testing methods as in vivo methods raise ethical concern. The present study aims to assess possible in vitro approaches based on diffuse transmission spectroscopy, published previously by Diffey, and two methods based on measurements of UVB transmission through a defined layer of a sunscreen product applied on various UV-transparent substrates. The attenuated UVB intensity, using different UV light sources, is detected radiometrically and transformed to real SPF value by means of a calibration curve, which is based on an extensive number of measurements performed using both in vivo and in vitro method The outcome of the three in vitro methods employed in the study showed great differences in the obtained SPF values in comparison with reference SPF determined by means of the COLIPA method in vivo. The high variability of in vitro results suggests that main attention should be focused on substrate selection simulating the human skin surface and homogenous product application. The in vitro screening methods may represent a fast and reasonable tool reducing the number of in vivo experiments and risks related to UV exposure of human subjects, when the technical test parameters are adjusted and optimized.

Asparagine, valine, and threonine in the third extracellular loop of muscarinic receptor have essential roles in the positive cooperativity of strychnine-like allosteric modulators

We have investigated allosteric interactions of four closely related strychnine-like substances: Wieland-Gumlich aldehyde (WGA), propargyl Wieland-Gumlich aldehyde, strychnine, and brucine with N-methylscopolamine (NMS) on M(3) subtype of muscarinic receptor genetically modified in the second or the third extracellular loop to corresponding loops of M(2) subtype (M(3)o2 and M(3)o3 chimera). The M(3)o2 chimeric receptor The exhibited no change in either affinity of strychnine, brucine, and WGA or in cooperativity of brucine or WGA, whereas both parameters for propargyl-WGA changed. In contrast, there was a change in affinity of all tested modulators (except for brucine) and in their cooperativity in the M(3)o3 chimera. Directions of affinity changes in both chimeras were always toward values of the donor M(2) subtype, but changes in cooperativity were variable. Compared with the native M(3) receptor, strychnine displayed a slight increase in positive cooperativity and propargyl-WGA a robust decrease in negative cooperativity at M(3)o2 chimera. Similar changes were found in the M(3)o3 chimera. Interestingly, cooperativity of brucine and WGA at the M(3)o3 chimera changed from negative to positive. This is the first evidence of constitution of positive cooperativity of WGA by switching sequences of two parental receptors, both exhibiting negative cooperativity. Gradual replacement of individual amino acids revealed that only three residues (NVT of the o3 loop of the M(2) receptor) are involved in this effect. Data suggest that these amino acids are essential for propagation of a conformation change resulting in positive cooperativity induced by these modulators.

On parameter synthesis by parallel model checking

An important problem in current computational systems biology is to analyze models of biological systems dynamics under parameter uncertainty. This paper presents a novel algorithm for parameter synthesis based on parallel model checking. The algorithm is conceptually universal with respect to the modeling approach employed. We introduce the algorithm, show its scalability, and examine its applicability on several biological models.

Changes of cooperativity between N-methylscopolamine and allosteric modulators alcuronium and gallamine induced by mutations of external loops of muscarinic M(3) receptors

To clarify the involvement of specific domains of muscarinic receptors in the action of allosteric modulators, muscarinic M(3) receptors (on which allosteric interactions are weak) were genetically modified to become more similar to M(2) receptors (on which allosteric interactions are strong) and were expressed in COS-7 cells. Affinity for allosteric modulator gallamine was enhanced 25- to 50-fold by modifications of the third external loop (o3) and the negative effect of gallamine on the affinity for classical antagonist N-[(3)H]methylscopolamine ([(3)H]NMS) was augmented. Affinity for alcuronium became 3-fold higher after the o3 loop of M(3) receptors was made identical with the o3 loop of M(2) receptors, and alcuronium acquired positive influence on the affinity for [(3)H]NMS. This is the first instance of inducing positive cooperativity on muscarinic receptors by genetic manipulation. Transferring whole o2 loop from M(2) to M(3) receptors substantially enhanced affinities for gallamine and alcuronium without augmenting their negative action on [(3)H]NMS binding. In contrast, effects of simply adding two negative charges into the o2 loop of M(3) receptors were small. Removal of Arg from o1 loop abolished the negative effect of gallamine but not of alcuronium on [(3)H]NMS binding at equilibrium. Data point to an important role of o3 loop in the mechanism of the positive and negative cooperativity between [(3)H]NMS and alcuronium and gallamine, respectively, and in the binding of both modulators to M(2) receptors and reveal independence between mutation-induced changes in the affinity for a modulator and in the magnitude and direction of the allosteric effect of the modulator.

Regulation of signal transduction at M2 muscarinic receptor

Muscarinic acetylcholine receptors mediate transmission of an extracellular signal represented by released acetylcholine to neuronal or effector cells. There are five subtypes of closely homologous muscarinic receptors which are coupled by means of heterotrimeric G-proteins to a variety of signaling pathways resulting in a multitude of target cell effects. Endogenous agonist acetylcholine does not discriminate among individual subtypes and due to the close homology of the orthosteric binding site the same holds true for most of exogenous agonists. In addition to the classical binding site muscarinic receptors have one or more allosteric binding sites at extracellular domains. Binding of allosteric modulators induces conformational changes in the receptor that result in subtype-specific changes in orthosteric binding site affinity for both muscarinic agonists and antagonists. This overview summarizes our recent experimental effort in investigating certain aspects of M2 muscarinic receptor functioning concerning i) the molecular determinants that contribute to the binding of allosteric modulators, ii) G-protein coupling specificity and subsequent cellular responses and iii) possible functional assays that exploit the unique properties of allosteric modulators for characterization of muscarinic receptor subtypes in intact tissue. A detailed knowledge of allosteric properties of muscarinic receptors is required to permit drug design that will modulate signal transmission strength of specific muscarinic receptor subtypes. Furthermore, allosteric modulation of signal transmission strength is determined by cooperativity rather than concentration of allosteric modulator and thus reduces the danger of overdose.