Impaired erythrocyte transmembrane potential in diabetes mellitus and its possible improvement by resorcylidene aminoguanidine

β-Resorcylidene aminoguanidine (RAG) dilates coronary arteries in an endothelium-independent manner

BACKGROUND

β-Resorcylidene aminoguanidine (RAG), a highly reactive derivative of aminoguanidine, possesses antithrombotic activity which involves the activation of the vascular COX-2/PGI2 pathway. This endothelium-dependent effect suggests that RAG may demonstrate vasomotor activity in arterial vessels. The aim of the present study was to investigate a possible vasoactive action of RAG in coronary arteries of rat heart.

METHODS

Isolated rat hearts were perfused in the Langendorff model. To investigate the dose dependency of the effect of RAG on coronary flow, the hearts were perfused with RAG at increasing concentrations. Mechanisms of RAG-mediated vasodilation were subsequently tested using selective inhibitors of the endothelium-dependent and endothelium-independent mechanisms responsible for regulation of vascular tone.

RESULTS

RAG dilated coronary arteries at concentrations above 10(-5)mol/l. Inhibition of the endothelium-dependent mechanism of vasodilation by NG-nitro-L-arginine methyl ester, indomethacin and aminobenzotriazole did not affect RAG-mediated vasodilation. Other compounds also had no impact on the vasodilating effect of RAG: the NO-dependent guanylate cyclase inhibitor - 1H-[1,2,4]oxadiazolo[4,3]quinoxalin-1-one, the cAMP-dependent protein kinase inhibitor - PKAi, and the K(+) channel blockers - glibenclamide, tetraethylammonium, charybdotoxin, and apamin.

CONCLUSIONS

RAG is a strong vasodilator that exerts its effect via endothelium-independent mechanisms.

Involvement of membrane fluidity in endogenous protective processes running on subcellular membrane systems of the rat heart

Membrane fluidity is a widely recognized biophysical variable that provides information about structural organization of the subcellular membranes exhibiting physical characteristics of liquid crystals. The term "fluidity" reflects in this case the tightness in packing of acyl parts of the membrane phospholipid molecules, a feature that may influence considerably the molecular mobility and via that also the sensitivity and reactivity of membrane-bound transporters, receptors and enzyme systems. Data presented in this review are aimed to demonstrate the substantial role of changes in membrane fluidity occurring in the processes associated with endogenous protection observed in cardiac sarcolemma and mitochondria in diverse pathologies, particularly in diabetes and hypertension.

Resorcylidene aminoguanidine induces antithrombotic action that is not dependent on its antiglycation activity

There is good evidence supporting the notion that aminoguanidine(AG)-derived compounds prevent glycation/glycooxidation-dependent processes and therefore inhibit late diabetic complications. The aim of the present work was to analyse the antithrombotic action and antiglycation activity of beta-resorcylidene aminoguanidine (RAG) in comparison with another commonly used aminoguanidine (AG)-derived compound, pyridoxal aminoguanidine (PAG). In vitro RAG and PAG prevented exhaustive glycation and glycooxidation of BSA to a similar extent. However, merely RAG showed almost complete binding to sepharose-immobilized heparin, while PAG and other AG derivatives had much poorer affinities. In the model of in vivo thrombosis in Wistar rats with extracorporeal circulation RAG (i.v. 30 mg/kg), but not PAG, produced sustained (2 h) antithrombotic effect, which was abrogated by indomethacin (5 mg/kg) and rofecoxib (1 mg/kg). The 60-day treatment of streptozotocin-diabetic animals with RAG (p.o. 4 mg/kg) significantly decreased plasma concentration of a thromboxane B(2) and reduced whole blood platelet aggregability triggered by ADP or collagen. In conclusion, although RAG and PAG displayed similar antiglycation and antioxidation activities in vitro, only RAG showed antithrombotic activity in vivo that involved activation of COX-2/PGI(2) pathway. Our results indicate that designing novel RAG derivatives with optimal antithrombotic and antiglycation activities may prove useful to treat diabetic complications.

Mitochondrial membrane fluidity, potential, and calcium transients in the myocardium from acute diabetic rats

In this study, we report for the first time concurrent measurements of membrane potential and dynamics and respiratory chain activities in rat heart mitochondria, as well as calcium transients in the hearts of rats in an early phase of streptozotocin diabetes, not yet accompanied with diabetes-induced complications. Quantitative relationships among these variables were assessed. The mitochondria from diabetic rats exhibited decreased fluorescence anisotropy values of diphenylhexatriene. This indicates that hydrophobic core of the membranes was more fluid compared with controls (p<0.05). We discuss the changes in fluidity as having been associated with augmented energy transduction through the diabetic membranes. Reduced ratio of JC-1 fluorescence (aggregates to monomers) in the mitochondria from diabetic hearts reflected descendent transmembrane potential. A significant negative association between membrane fluidity and potential in the diabetic group was found (p<0.05; r=0.67). Further, we observed an increase in calcium transient amplitude (CTA) in the diabetic cardiomyocytes (p=0.048). We conclude that some of the calcium-induced regulatory events that dictate fuel selection and capacity for ATP production in diabetic heart occur at the membrane level. Our findings offer new insight into acute diabetes-induced changes in cardiac mitochondria.

Evaluating the validity of blood-based membrane potential changes for the identification of bipolar disorder I

OBJECTIVE

The objective of this study was to develop a diagnostic blood test for bipolar disorder I using membrane potentials as biological markers.

METHODS

We measured the fluorescence intensity of a dye sensitive to membrane potential in whole blood samples from bipolar I, unipolar, schizophrenic patients, and psychiatrically normal controls. Patients were diagnosed through structured clinical interviews according to DSM-IV. Both the t-test and logistic regression analysis were used to analyze the data.

RESULTS

The membrane potential as indicated by the fluorescence intensity of the membrane potential dye in blood cells drawn from patients with bipolar disorder I was significantly different from the blood cells drawn from unipolar and schizophrenic patients, and from psychiatrically normal controls (P<0.001). The specificity and sensitivity were determined to be 0.88 and 0.78 respectively which compared well with the state of the art diagnostic techniques for other diseases. Logistic regression analysis revealed that the membrane potential was a reliable predictor which could be used as a diagnostic marker for bipolar I.

CONCLUSIONS

These results indicate that the membrane potential of blood cells can be used as a diagnostic marker to augment the DSM-IV diagnosis of bipolar disorder I. Expanded clinical trials are needed to establish this technique for general use.

Influences of lovastatin on membrane ion flow and intracellular signaling in breast cancer cells

Lovastatin, an inhibitor of cellular cholesterol synthesis, has an apparent anti-cancer property, but the detailed mechanisms of its anti-cancer effects remain poorly understood. We investigated the molecular mechanism of Lovastatin anti-tumor function through the study of its effect on membrane ion flow, gap junctional intercellular communication (GJIC), and the pathways of related signals in MCF-7 mammary cancer cells. After treatment for 24–72 h with 4, 8 or 16 μmol/L Lovastatin, cellular proliferation was examined via the MTT assay, and changes in membrane potential and cellular [Ca²⁺]_i were monitored using confocal laser microscopy. In addition, the expression of plasma membrane calcium ATPase isoform 1 (PMCA1) mRNA was analyzed via RT-PCR, the GJIC function was examined using the scrape-loading dye transfer (SLDT) technique, and MAPK phosphorylation levels were tested with the kinase activity assay. The results showed that Lovastatin treatment significantly inhibited the growth of MCF-7 breast cancer cells. It also increased the negative value of the membrane potential, leading to the hyperpolarization of cells. Moreover, Lovastatin treatment continuously enhanced [Ca²⁺]_i, although the levels of PMCA1 mRNA were unchanged. GJIC was also upregulated in MCF-7 cells, with transfer of LY Fluorescence reaching 4 to 5 rows of cells from the scraped line after treatment with 16 μmol/L Lovastatin for 72 h. Finally, downregulation of ERK1 and p38^MAPK phosphorylation were found in Lovastatin-treated MCF-7 cells. It could be deduced that Lovastatin can induce changes in cellular hyperpolarization and intracellular Ca²⁺ distributions, and increase GJIC function. These effects may result in changes in the downstream signal cascade, inhibiting the growth of MCF-7 cells.

Fluidity gradient of erythrocyte membranes in diabetics: the effect of resorcylidene aminoguanidine

We estimated in vitro membrane fluidity gradient in erythrocytes (RBC) from diabetic patients, using a fluorescent dye 1,6-diphenyl-1,3,5-hexatriene (DPH). The rate constant of DPH incorporation (k) into the membranes was determined by fitting experimental data to an exponential equation. Four important findings were made. First, membrane fluidity in the hydrocarbon region of RBC from diabetic patients is decreased compared with control cells (P<0.01). Second, the rate constant k of DPH incorporation into the membranes of RBC from diabetic patients was lower (P<0.01), which indicates an altered fluidity gradient in the membranes. Third, resorcylidene aminoguanidine (RAG) decreased significantly (P<0.001) the anisotropy values in RBC membranes from diabetic patients, which means that it apparently acted as a fluidizing agent. Lastly, no significant differences in the rate constants k were found between the control membranes (from RAG untreated RBC) and the membranes isolated from RAG pretreated blood from diabetic patients, as well as between the control membranes and those from RAG pretreated control blood. In conclusion, RAG affects lipid-protein interactions in RBC membranes, which results in membrane lipid bilayer fluidization and leads to the restoration of natural physiological membrane dynamic parameters in RBC from diabetic patients.