Chronic erythropoietin treatment affects different molecular pathways of diabetic cardiomyopathy in mouse.

BACKGROUND: Recent studies in mice experimental models with acute ischaemic injury revealed that erythropoietin (EPO) has numerous tissue-protective effects in the heart, brain and kidneys. We therefore explored the tissue-protective properties of chronic EPO treatment in an experimental model of the db/db mouse with diabetic heart injury. MATERIAL AND METHODS: We randomly treated 11 db/db mice with placebo (saline), 0.4 microg of the continuous erythropoietin receptor activator (CERA) per week (n = 11) or 1.2 microg CERA per week (n = 11) for 14 weeks, and analysed cardiac tissue. The lower CERA dose was a non-haematologically effective dose, whereas the second increased the haematocrit. RESULTS: Compared with mice in the placebo group, CERA-treated mice had a reduction in TGF-beta(1) and collagen I expression in cardiac tissue (P < 0.01 vs. higher dose CERA). In addition, an increased expression of the pro-survival intracellular pathway p-AKT was observed (P < 0.05 vs. higher dose CERA). The values for the lower C.E.R.A had an intermediate nonsignificant effect. Furthermore, we were able to show that atrial natriuretic peptide (ANP) expression was increased in both CERA groups. CONCLUSIONS: Chronic treatment with CERA protects cardiac tissue in diabetic animals, i.e. it inhibits molecular pathways of cardiac fibrosis, and the effects are dose-dependent.

Transferrin and ferritin modulate the activity of brain calcium-calmodulin-dependent phosphodiesterase.

The effect of the key iron homeostasis proteins transferrin and ferritin on the activity of partially purified brain calcium-calmodulin-dependent phosphodiesterase (CaM-PDE, EC 3.4.1.17) were studied. Transferrin and ferritin were found to be potent natural activators of CaM-PDE. The key factor determining the degree of activation by these proteins is their saturation with iron: apotransferrin activated CaM-PDE 6-7-fold; iron-poor brain ferritin and liver apoferritin (taken for comparison) activated the enzyme 4-5- and 2-fold, respectively. Diferric transferrin and iron-rich liver ferritin had no effects on the enzyme activity. Transferrin and ferritin (both in apo- and iron-saturated forms) did not change the activity of calmodulin-phosphodiesterase complex. The data suggest that apotransferrin and iron-poor transferrin are involved in the regulation of cyclic nucleotide content in nervous tissue.

Membranes of retinal microsomes: a new protein of the microsomal monooxigenase system.

A new component, which substitutes cytochrome P-450 as an acceptor of reducing equivalents from NADPH-cytochrome P-450 reductase, was identified in the bovine retina microsomal monooxigenase system, which does not contain cytochrome P-450. This component is a non-heme iron-containing protein with molecular mass of 66 kDa. The properties of the protein from the bovine retina are similar to those of MIP, a non-heme iron-containing protein from the heart microsomal monooxigenase system, in which cytochrome P-450 was not identified, either. Activation of the microsomal monooxigenase system (an increase in the NADPH-cytochrome P-450 reductase activity, an increased rate of microsomal NADPH oxidation) was shown in the retina upon long-term intensive illumination. It was shown also that the development of hereditary degeneration of the retina in rats was accompanied by activation of the specific microsomal monooxigenase system in the target tissues (retina, brain cortex) irrespective of its composition (cytochrome P-450 or non-heme iron-containing protein).

[The NADP.H-cytochrome C reductase and aldose reductase activities in the retina, cerebral cortex and liver of healthy rats and of those with hereditary retinal degeneration in the early postnatal development period]. / Aktivnost' NADF.H-tsditokhrom C reduktazy i al'dozoreduktazy v setchatke, kore golovnogo mozga i pecheni zdorovykh i bol'nykh nasledstvennoi degeneratsiei setchatki krys v rannii period postnatal'nogo razvitiia.

Maximal activity of NADP.H-cytochrome c reductase was found in the liver, the lowest one--in the retina. On the contrary, the highest activity of aldose reductase was observed in the retina, the lowest one--in the liver. The activity of NADP.H-cytochrome c reductase in the retina of rats with hereditary degeneration of the retina increased to the 60th day of postnatal life by 33%, the increase reaching 273% to the 90th day. In the brain cortex, the increase in the activity to the 45-60th days amounted to 22-34%, whereas at the age of 90 days the difference between healthy and patient rats, as well as the difference between males and females became less significant. The activity of aldose reductase in the cortex and retina in patient rats at the 20th day was 35% lower than in healthy animals. In the liver of patient rats, to the age of 45 days, the activity of aldose reductase decreased by 38%. At other periods, no significant differences were observed between healthy and patient animals with respect to the activity of this enzyme.

A new peptide (1150Da) selectively activates the calcium-calmodulin sensitive isoform of cyclic nucleotide phosphodiesterase from human myometrium.

The cyclic nucleotide phosphodiesterase enzymatic system is examined in extracts of human myometrium and four individual phosphodiesterase isoforms have been isolated and characterized. A new thermostable peptide, recently purified in rat and calf myometrium, is able to stimulate up to 55-fold, the calcium-calmodulin dependent phosphodiesterase isoform. Activation of cAMP hydrolysis is by far the most marked with a 55-fold maximal stimulation at a concentration of 0.1 microM peptide and a IC50 value estimated at 30nM. For cGMP hydrolysis, the maximal effect (x25) obtained at 40nM peptide is lesser and the IC50 value is in the 10nM range. Furthermore, we verified that classical calmodulin antagonists such as calmidazolium or trifluoroperazine did not change stimulation of the calcium-calmodulin phosphodiesterase by the peptide, indicating that the myometrial peptide is different from calmodulin. To our knowledge, this is the first evidence for such a strong and selective stimulation of one isoform of the phosphodiesterase enzymatic system by a natural peptide.