Structural and functional properties of Antarctic fish cytoglobins-1: Cold-reactivity in multi-ligand reactions.

While the functions of the recently discovered cytoglobin, ubiquitously expressed in vertebrate tissues, remain uncertain, Antarctic fish provide unparalleled models to study novel protein traits that may arise from cold adaptation. We report here the spectral, ligand-binding and enzymatic properties (peroxynitrite isomerization, nitrite-reductase activity) of cytoglobin-1 from two Antarctic fish, Chaenocephalus aceratus and Dissostichus mawsoni, and present the crystal structure of D. mawsoni cytoglobin-1. The Antarctic cytoglobins-1 display high O2 affinity, scarcely compatible with an O2-supply role, a slow rate constant for nitrite-reductase activity, and do not catalyze peroxynitrite isomerization. Compared with mesophilic orthologues, the cold-adapted cytoglobins favor binding of exogenous ligands to the hexa-coordinated bis-histidyl species, a trait related to their higher rate constant for distal-His/heme-Fe dissociation relative to human cytoglobin. At the light of a remarkable 3D-structure conservation, the observed differences in ligand-binding kinetics may reflect Antarctic fish cytoglobin-1 specific features in the dynamics of the heme distal region and of protein matrix cavities, suggesting adaptation to functional requirements posed by the cold environment. Taken together, the biochemical and biophysical data presented suggest that in Antarctic fish, as in humans, cytoglobin-1 unlikely plays a role in O2 transport, rather it may be involved in processes such as NO detoxification.

Design, synthesis and in vivo study of novel pyrrolidine-based 11ß-HSD1 inhibitors for age-related cognitive dysfunction.

Recent findings suggest that treatment with 11ß-HSD1 inhibitors provides a novel approach to deal with age-related cognitive dysfunctions, including Alzheimer's disease. In this work we report potent 11ß-HSD1 inhibitors featuring unexplored pyrrolidine-based polycyclic substituents. A selected candidate administered to 12-month-old SAMP8 mice for four weeks prevented memory deficits and displayed a neuroprotective action. This is the first time that 11ß-HSD1 inhibitors have been studied in this broadly-used mouse model of accelerated senescence and late-onset Alzheimer's disease.

Searching for novel applications of the benzohomoadamantane scaffold in medicinal chemistry: Synthesis of novel 11ß-HSD1 inhibitors.

The structural and physicochemical properties of the adamantane nucleus account for its use as a chemical scaffold in multiple drugs. In the last years, we have developed new polycyclic scaffolds as surrogates of the adamantane group with encouraging results in multiple targets. As adamantane is a common structural feature in several 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) inhibitors, we have explored the ability of the 6,7,8,9,10,11-hexahydro-5H-5,9:7,11-dimethanobenzo[9]annulen-7-yl scaffold to act as a surrogate of the adamantane nucleus in a novel series of 11ß-HSD1 inhibitors. Of note, within this family of compounds one derivative is endowed with submicromolar 11ß-HSD1 inhibitory activity. Molecular modeling studies support the binding of the compounds to the active site of the enzyme. However, a fine tuning of the hydrophobicity of the size-expanded nucleus may be beneficial for the inhibitory potency.

Novel 11ß-HSD1 inhibitors: C-1 versus C-2 substitution and effect of the introduction of an oxygen atom in the adamantane scaffold.

The adamantane scaffold is found in several marketed drugs and in many investigational 11ß-HSD1 inhibitors. Interestingly, all the clinically approved adamantane derivatives are C-1 substituted. We demonstrate that, in a series of paired adamantane isomers, substitution of the adamantane in C-2 is preferred over the substitution at C-1 and is necessary for potency at human 11ß-HSD1. Furthermore, the introduction of an oxygen atom in the hydrocarbon scaffold of adamantane is deleterious to 11ß-HSD1 inhibition. Molecular modeling studies provide a basis to rationalize these features.