Decreased metabolism of cerebrosides and sulfatides in rat sciatic nerve after intraneural injection of colchicine

Inhibition by sulfatide of 21-kDa protein phosphorylation by protein kinase C in cow mammary gland and its reversal by phosphatidylserine

The effect of sulfatide, a sulfated sphingolipid, on phosphorylation of endogenous proteins by protein kinase C (PKC) was examined in cow mammary gland. Several proteins, including 21-kDa, 43-kDa and 56-kDa proteins in the cytosolic fraction, were found to be substrates for PKC by phosphorylation in the absence or presence of the cofactors 1-oleoyl-2-acetyl-sn-glycerol (OAG), phosphatidylserine (PS) and Ca2+. Sulfatide inhibited the 21-kDa phosphorylation, whereas it enhanced the 56-kDa and 43-kDa phosphorylation. Experiments were then conducted to examine whether other sphingolipids, including sphingosine, dihydrosphingosine, ceramides, galactocerebrosides, psychosine and sphingomyelin, modulated phosphorylation of the PKC substrates. Sphingosine, dihydrosphingosine and psychosine did not inhibit the 21-kDa phosphorylation; however, they enhanced the 56-kDa and 43-kDa phosphorylation. Ceramides, galactocerebrosides and sphingomyelin did not inhibit the 21-kDa or enhance the 56-kDa and 43-kDa phosphorylation. The inhibition by sulfatide of the 21-kDa phosphorylation was reversed by excess addition of PS, but not by OAG or Ca2+; whereas the enhancement by sulfatide, as well as sphingosine, dihydrosphingosine and psychosine, of 56-kDa and 43-kDa phosphorylation was not affected by PS, OAG or Ca2+. It is suggested that sulfatide is involved in the regulation of PKC-dependent phosphorylation by modulating the association of PKC substrates, in particular the 21-kDa protein, with membrane phospholipids in cow mammary gland.

Effects of thiocolchicine on axonal cytoskeleton of the rat peroneus nerve

Thiocolchicine is a colchicine-derivative used in the therapy of some diseases and extensively studied in the field of oncological research as antimitotic agent. Here we studied the activity of thiocolchicine on the cytoskeleton of the peroneus nerve, performing a histological and ultrastructural analysis. We observed a decrease in mean myelinated fiber area in thiocolchicine-treated rats in comparison to controls; this was due to a decrease in mean axoplasm area, while myelin thickness was constant. In the ultrastructural analysis a decrease in microtubule density and an increase in neurofilaments were found; moreover, the myelinated fibers seemed to be more affected in comparison to the unmyelinated axons. These findings are in agreement with the capability of binding to microtubule skeleton shared by all the colchicinoids.

Synthesis, spectral properties and enzymatic hydrolysis of fluorescent derivatives of cerebroside sulfate containing long-wavelength-emission probes

Fluorescent derivatives of cerebroside sulfate (sulfogalactosyl ceramide, sulfatide) containing long-wavelength-emission fluorophores were synthesized. For this purpose a procedure was developed for preparing a cerebroside 3-sulfate derivative with an amino group on the terminal carbon atom of its fatty acyl residue. The latter compound has been used to prepare cerebroside 3-sulfate, coupled to lissamine-rhodamine, fluoresceine, eosine and NBD. The spectroscopic properties of these compounds, in different solvent systems and when incorporated into micelles of a non-ionic detergent or liposomes of a phospholipid, are reported. Incubation of these respective sulfatides with a human leukocyte preparation, resulted in the formation of the corresponding fluorescent cerebrosides.

Alteration of axonal microfilaments alters Schwann cell lipid metabolism

To investigate the importance of the neuronal cytoskeleton in Schwann cell metabolism, three agents acting on the microfilaments (cytochalasin D, brevine, and phalloïdin) were injected into the endoneurium of rat sciatic nerve. Sciatic nerves were removed 24 h later and separated into two pieces: the first one was the injection site and the second was from nerves located distal to the injection site. The pieces of nerve were incubated with [14C] galactose for 3 h. At the site of injection, [14C] incorporation into monogalactosyldiacylglycerol (MGDG) was perturbed by the three agents, whereas in the distal part, sulfatides and phosphatidylserine were affected by cytochalasin D and brevine. These results show that the three compounds acting on microfilaments have a different effect on Schwann cell metabolism, depending on whether incubated Schwann cells were directly in contact with the toxin or they were only in contact with the axons affected by the toxin. In the latter case, axonal microfilaments seem to be involved in the regulation of Schwann cell metabolism.

Altered metabolism of rat contralateral sciatic nerve after microinjection into the endoneurium of the ipsilateral sciatic nerve

Microinjection of substances into the endoneurium of the sciatic nerve is a technique widely used. Because the contralateral nerve is often used as control nerve, we studied the incorporation of [14C]galactose into myelin lipids in normal nerves, saline-injected nerves and their contralateral nerves. Results show that incorporation of radioactivity into contralateral nerve lipids is affected as compared with normal nerves. We conclude that the contralateral nerve of an injected nerve is not a good control.