Effect of polyamines on protein kinase C activation process

Maternal separation and early social deprivation in Octodon degus: quantitative changes of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive neurons in the prefrontal cortex and nucleus accumbens

The influence of postnatal socio-emotional deprivation on the development of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reactive neurons in prefrontal cortical areas and in subdivisions of the nucleus accumbens was quantitatively investigated in the precocious rodent Octodon degus. Forty-five-days-old O. degus from two animal groups were compared: (i) degus which were repeatedly separated from their mothers during the first three postnatal weeks and after weaning reared in complete isolation; and (ii) degus which were reared under normal undisturbed social conditions. Socially-deprived animals displayed a significant decrease of NADPH-diaphorase-containing neurons in anterior cingulate cortex (85.5%), the same tendency was observed in the infralimbic, precentral medial and prelimbic prefrontal areas. Similarly, the core region of nucleus accumbens expressed reduced NADPH-diaphorase-reactive neuron numbers in deprived animals (70%), whereas the shell region remained unchanged. Since during normal postnatal development the number of NADPH-diaphorase-reactive neurons gradually decreases in all prefrontal cortical and accumbal regions, the observed deprivation-induced changes may reflect either an excessive reduction of NADPH-diaphorase-positive neurons or a down-regulation of the enzyme in neurons that normally express it. Since some NADPH-diaphorase-containing neurons in the prefrontal cortex have been shown to be GABAergic, it is tempting to speculate that a reduction of these inhibitory neurons in the anterior cingulate cortex may result in an enhanced excitatory output activity of disinhibited projection neurons in this cortical region, including those that project to the core region of the nucleus accumbens. Our results indicate a link between early adverse socio-emotional experience and the maturation of NADPH-reactive neurons and further studies are required to analyse the functional implication for this experience-induced brain pathology.

Raised erythrocyte polyamine levels in non-insulin-dependent diabetes mellitus with great vessel disease and albuminuria

Erythrocyte content of polyamines has been previously found increased in insulin-dependent diabetes mellitus with microalbuminuria. Since increased urinary albumin excretion (AER) is associated with the presence of vascular diseases in non-insulin-dependent diabetes mellitus (NIDDM) the aim of this study was to verify the hypothesis that the presence of increased urinary albumin excretion (AER), and of macroangiopathy in NIDDM would be related to a significant modification in polyamine erythrocyte levels. The erythrocyte content of spermine and spermidine was measured by a HPLC method in 39 patients affected with NIDDM and in 24 age- and sex-matched healthy control subjects, evaluating the relationship between erythrocyte polyamines of NIDDM patients with the presence of macroangiopathy as well as with retinopathy or increased AER (> or = 20 micrograms/ml). Both spermidine and spermine were not modified in the group of NIDDM patients while the presence of raised urinary AER was characterised by an increase in erythrocyte spermine (11 +/- 1.7 vs. 7.7 +/- 1.7 nmol/ml packed erythrocytes; P = 0.04) and spermidine (18.9 +/- 1.7 vs. 12.6 +/- 1.5 nmol/ml packed erythrocytes; P = 0.02), being both polyamines significantly related to AER and to metabolic control. Erythrocyte spermidine and spermine were moreover significantly higher in the group of patients with macroangiopathy (22.8 +/- 1.5 vs. 12.3 +/- 1.5 nmol/ml; P = 0.0001 and 11.5 +/- 1.7 vs. 7.8 +/- 1.7 nmol/l packed erythrocytes; P = 0.04) and being, moreover, erythrocyte spermidine augmented in patients with retinopathy (24.2 +/- 1.5 vs. 12.2 +/- 1.5 nmol/ml packed erythrocytes; P = 0.009). In conclusion the levels of erythrocyte spermine and spermidine are both associated with the presence of albuminuria and macroangiopathy in NIDDM, while spermidine is on the average increased in the group of diabetic patients with retinopathy.

Spermine protects protein kinase C from phospholipid-induced inactivation

Phosphatidylserine (PS), an activator of protein kinase C (PKC) in the assay of protein phosphorylation, inhibited this enzyme in a time-dependent manner following preincubation in the absence of Ca2+. The phospholipid-induced inactivation of kinase activity was dependent on the PS content and on the charge density of liposomes. This inactivation of PKC could be reduced, but not completely eliminated, by addition of Ca2+. In the present work the effect of a naturally occurring polyamine (spermine) on the PS-induced inactivation of PKC was investigated. The presence of spermine during preincubation without Ca2+ was effective in suppressing the PS-induced inactivation of PKC over the period (20 min) required for PS to inhibit the enzyme by 95%. PKC exists in two membrane-bound states: a reversible one which can be dissociated by Ca2+ chelators (membrane-associated form) and an irreversible one which is chelator-stable (membrane-inserted form). Gel filtration experiments on the PKC-PS complex formed in the presence of Ca2+ indicated that less insertion of enzyme into liposomes occurred in the presence of spermine and that the kinase activity of the reversibly membrane-associated PKC was protected from PS inactivation.

Effect of spermine on membrane-associated and membrane-inserted forms of protein kinase C

Protein kinase C is reported to exist in two membrane-bound states: a reversible one which can be dissociated by calcium chelators (membrane-associated form) and an irreversible one which is chelator stable (membrane-inserted form). In the present work the effects of a naturally occurring polyamine (spermine) on the membrane-associated and membrane-inserted forms of protein kinase C were investigated using a reconstituted system consisting of partially purified protein kinase C from rat brain and phospholipid vesicles of defined composition. The active membrane-bound complex was conveniently determined by its ability to bind radioactive phorbol ester with an exact 1:1 stoichiometry. Our experimental data show that, in the absence of calcium ions, the amount of enzyme bound to phospholipids vesicles was dramatically reduced by the presence of spermine whereas the PDBu binding affinity was not significantly affected. The addition of the divalent cation increased the affinity of phorbol ester for the active complex but had no effect on Nmax; spermine added in this experimental conditions was no longer able to decrease the total number of enzyme molecules bound to liposomes. Moreover gel filtration experiments of the protein kinase C-phospholipids complex formed in the presence of calcium, indicated that polyamine added during the association process was able to reduce the extent of enzyme insertion into liposomes. Since the increase in phospholipid concentration resulted in a higher level of non-dissociable protein kinase C-liposomes complex we propose that spermine, complexing to membrane binding sites both in the absence and in the presence of Ca++, could promote binding conditions that oppose to the formation of the inserted form of the enzyme. As a consequence the distribution between the reversible and the irreversible membrane-bound forms of protein kinase C is affected.