Bone formation rather than inflammation reflects Ankylosing Spondylitis activity on PET-CT: a pilot study

Introduction

Positron Emission Tomography - Computer Tomography (PET-CT) is an interesting imaging technique to visualize Ankylosing Spondylitis (AS) activity using specific PET tracers. Previous studies have shown that the PET tracers [¹⁸F]FDG and [¹¹C](R)PK11195 can target inflammation (synovitis) in rheumatoid arthritis (RA) and may therefore be useful in AS. Another interesting tracer for AS is [¹⁸F]Fluoride, which targets bone formation. In a pilot setting, the potential of PET-CT in imaging AS activity was tested using different tracers, with Magnetic Resonance Imaging (MRI) and conventional radiographs as reference.

Methods

In a stepwise approach different PET tracers were investigated. First, whole body [¹⁸F]FDG and [¹¹C](R)PK11195 PET-CT scans were obtained of ten AS patients fulfilling the modified New York criteria. According to the BASDAI five of these patients had low and five had high disease activity. Secondly, an extra PET-CT scan using [¹⁸F]Fluoride was made of two additional AS patients with high disease activity. MRI scans of the total spine and sacroiliac joints were performed, and conventional radiographs of the total spine and sacroiliac joints were available for all patients. Scans and radiographs were visually scored by two observers blinded for clinical data.

Results

No increased [¹⁸F]FDG and [¹¹C](R)PK11195 uptake was noticed on PET-CT scans of the first 10 patients. In contrast, MRI demonstrated a total of five bone edema lesions in three out of 10 patients. In the two additional AS patients scanned with [¹⁸F]Fluoride PET-CT, [¹⁸F]Fluoride depicted 17 regions with increased uptake in both vertebral column and sacroiliac joints. In contrast, [¹⁸F]FDG depicted only three lesions, with an uptake of five times lower compared to [¹⁸F]Fluoride, and again no [¹¹C](R)PK11195 positive lesions were found. In these two patients, MRI detected nine lesions and six out of nine matched with the anatomical position of [¹⁸F]Fluoride uptake. Conventional radiographs showed structural bony changes in 11 out of 17 [¹⁸F]Fluoride PET positive lesions.

Conclusions

Our PET-CT data suggest that AS activity is reflected by bone activity (formation) rather than inflammation. The results also show the potential value of PET-CT for imaging AS activity using the bone tracer [¹⁸F]Fluoride. In contrast to active RA, inflammation tracers [¹⁸F]FDG and [¹¹C](R)PK11195 appeared to be less useful for AS imaging.     

Structural and functional organization of the adenylyl cyclase signaling mechanism of insulin-like growth factor 1 revealed in the muscle tissue in vertabrates and invertebrates

Based on the earlier discovered by the authors adenylyl cyclase signaling mechanisms (ACSM) of action of insulin and relaxin, the study was performed of the presence a similar action mechanism of another representative of the insulin superfamily--the insulin-like growth factor 1 (IGF-1) in the muscle tissues of vertebrates (rat) and invertebrates (mollusc). For the first time there was detected participation of ACSM in the IGF-1 action, including the six component signaling cascade: receptor tyrosine kinase --> G(i)-protein (betagamma-dimer) --> phosphatidylinositol-3-kinase (PI-3-K) --> protein kinase Czeta (PKCzeta) --> G(-)protein --> adenylyl cyclase. By this mechanism structural-functional organization at postreceptor stages, in coincides completely with the mechanism of insulin and relaxin, which we revealed in rat skeletal muscle. In smooth muscle of the mollusc Anodonta cygnea this ACSM of action of IGF-1 has only one difference--the protein kinase C included in this mechanism is represented not by PKCzeta isoform, but by another isoform close to PKCepsilon of the vertabrate brain. Earlier we revealed the same differences in muscle of this mollusc in the ACSM of action of insulin and relaxin.     

Certain biochemical characteristics of an insulin-like substance from the bivalve mollusk Anodonta cygnea

An insulin-like substance (ILS) was isolated from the visceral organs of the bivalve mollusc Anodonta cygnea by chromatography on a sulfocationite CU-23 and purified by reverse phase liquid chromatography. ILS was shown to be made up to several fractions with Mr ranging from 9 to 20 kDa which have identical amino acid composition but different hydrophobicity and N-terminal amino acids. It was supposed that the heterogeneity of ILS fractions is due to its genetical or posttranslational polymorphism. ILS has a low (0.02%) affinity for the mammalian insulin receptor and a low immune affinity for mammalian insulin and possesses a mitogenic activity which is commensurate with that of the epidermal growth factor. The data obtained suggest that Anodonta cygnea ILS represents a separate branch of a relatively ancient family of insulin-like hormones and growth factors responsible for metabolism and proliferation of invertebrate tissues.     

Use of Peptide Strategy for Study of Molecular Mechanisms of Hormonal Signal Transduction into Cell

At present the peptide strategy is used extensively to study molecular mechanisms of interaction between signal proteins, components of hormonal signal systems. The strategy is based on use of synthetic peptides as probes corresponding to functionally important sites of these proteins. This review summarizes and analyzes literature data and results of our own works on use of the peptide strategy for studying functional coupling of receptors of serpentine and tyrosine kinase types with heterotrimeric G-proteins. Alongside with peptides derived from the primary structure of cytoplasmic loops and transmembrane domains as well as from different sites of G-protein α, β, and γ-subunits, natural and synthetic peptides are considered which have no homology with receptors and G-proteins, but are able to affect effectively interaction between them.     

Functional characteristics of the adenylate cyclase system of developing skeletal muscles in the rat

The functional development of hormone-sensitive adenylate cyclase system of rat skeletal muscles was studied. It was shown that within 15-17 embryonic days the plasma membrane of the muscle cell contains catecholamine-sensitive adenylate cyclase (isoproterenol greater than epinephrine greater than norepinephrine) which on these ontogenetic stages is represented by functionally active catalytic, regulatory and receptory components. The coupling component, which, according to the authors' view, is presumably an independent (fourth) functional subunit of adenylate cyclase system, is formed only in the postnatal period. A suggestion is put forward that the above process is due to the fact that guanyl nucleotide-binding protein(s) responsible in the mature target cell for the coupling of receptory and catalytic components may appear in the membrane only after birth.     

A new mechanism of inhibiting adenylate cyclase involving a beta-adrenergic receptor]

The previously unknown mechanism of adenylate cyclase activity inhibition by catecholamines has been found. It is realized through a beta-adrenoreceptor in the smooth muscle of fresh-water mollusc Anodonta cygnea. As to its ligand-binding characteristics (one class of binding sites with Kd = 0.35 + 0.06 nM, a competitive series of ligands substitution: isoproterenol greater than adrenalin greater than propranolol greater than noradrenaline greater than serotonin = dopamine greater than phentolamine) as well as to negative regulation of the GTP affinity this receptor is similar to beta-adrenoreceptors of higher vertebrates. The dose-dependent inhibiting effect (to 50-60%) of isoproterenol and noradrenaline on the basal, GTP- and serotonin-stimulated activity of adenylate cyclase and cAMP level which is removed only by beta-adrenergic blockers is shown in vitro and in vivo. It is concluded that inhibition of adenylate cyclase activity by catecholamines in the muscular tissue of the mollusc is realized via beta-adrenoreceptor.