Bioactive lipids are altered in the kidney of chronic undernourished rats: is there any correlation with the progression of prevalent nephropathies?

BACKGROUND: Undernutrition during childhood leads to chronic diseases in adult life including hypertension, diabetes and chronic kidney disease. Here we explore the hypothesis that physiological alterations in the bioactive lipids pattern within kidney tissue might be involved in the progression of chronic kidney disease. METHODS: Membrane fractions from kidney homogenates of undernourished rats (RBD) were submitted to lipid extraction and analysis by thin layer chromatography and cholesterol determination. RESULTS: Kidneys from RBD rats had 25% lower cholesterol content, which disturb membrane microdomains, affecting Ca2+ homeostasis and the enzymes responsible for important lipid mediators such as phosphatidylinositol-4 kinase, sphingosine kinase, diacylglicerol kinase and phospholipase A2. We observed a decrease in phosphatidylinositol(4)-phosphate (8.8 ± 0.9 vs. 3.6 ± 0.7 pmol.mg-1.mim-1), and an increase in phosphatidic acid (2.2 ± 0.8 vs. 3.8 ± 1.3 pmol.mg-1.mim-1), being these lipid mediators involved in the regulation of key renal functions. Ceramide levels are augmented in kidney tissue from RBD rats (18.7 ± 1.4 vs. 21.7 ± 1.5 fmol.mg-1.min-1) indicating an ongoing renal lesion. CONCLUSION: Results point to an imbalance in the bioactive lipid generation with further consequences to key events related to kidney function, thus contributing to the establishment of chronic kidney disease.

The endocannabinoid system in renal cells: regulation of Na(+) transport by CB1 receptors through distinct cell signalling pathways.

BACKGROUND AND PURPOSE: The function of the endocannabinoid system (ECS) in renal tissue is not completely understood. Kidney function is closely related to ion reabsorption in the proximal tubule, the nephron segment responsible for the re-absorption of 70-80% of the filtrate. We studied the effect of compounds modulating the activity of cannabinoid (CB) receptors on the active re-absorption of Na(+) in LLC-PK1 cells. EXPERIMENTAL APPROACH: Changes in Na(+) /K(+) -ATPase activity were assessed after treatment with WIN55,212-2 (WIN), a non-selective lipid agonist, and haemopressin (HP), an inverse peptide agonist at CB1 receptors. Pharmacological tools were used to investigate the signalling pathways involved in the modulation of Na(+) transport. KEY RESULTS: In addition to CB1 and CB2 receptors and TRPV1 channels, the mRNAs encoding for enzymes of the ECS were also expressed in LLC-PK1. WIN (10(-7) M) and HP (10(-6) M) altered Na(+) re-absorption in LLC-PK1 in a dual manner. They both acutely (after 1 min) increased Na(+) /K(+) -ATPase activity in a TRPV1 antagonist-sensitive way. WIN's stimulating effect persisted for 30 min, and this effect was partially blocked by a CB1 antagonist or a PKC inhibitor. In contrast, HP inhibited Na(+) /K(+) -ATPase after 30 min incubation, and this effect was attenuated by a CB1 antagonist or a PKA inhibitor. CONCLUSION AND IMPLICATIONS: The ECS is expressed in LLC-PK1 cells. Both CB1 receptors and TRPV1 channels regulate Na(+) /K(+) -ATPase activity in these cells, and are modulated by lipid and peptide CB1 receptor ligands, which act via different signalling pathways.

Mitochondrial respiration and genomic analysis provide insight into the influence of the symbiotic bacterium on host trypanosomatid oxygen consumption.

Certain trypanosomatids co-evolve with an endosymbiotic bacterium in a mutualistic relationship that is characterized by intense metabolic exchanges. Symbionts were able to respire for up to 4 h after isolation from Angomonas deanei. FCCP (carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone) similarly increased respiration in wild-type and aposymbiotic protozoa, though a higher maximal O2 consumption capacity was observed in the symbiont-containing cells. Rotenone, a complex I inhibitor, did not affect A. deanei respiration, whereas TTFA (thenoyltrifluoroacetone), a complex II activity inhibitor, completely blocked respiration in both strains. Antimycin A and cyanide, inhibitors of complexes III and IV, respectively, abolished O2 consumption, but the aposymbiotic protozoa were more sensitive to both compounds. Oligomycin did not affect cell respiration, whereas carboxyatractyloside (CAT), an inhibitor of the ADP-ATP translocator, slightly reduced O2 consumption. In the A. deanei genome, sequences encoding most proteins of the respiratory chain are present. The symbiont genome lost part of the electron transport system (ETS), but complex I, a cytochrome d oxidase, and FoF1-ATP synthase remain. In conclusion, this work suggests that the symbiont influences the mitochondrial respiration of the host protozoan.

Rat vas deferens SERCA2 is modulated by Ca2+/calmodulin protein kinase II-mediated phosphorylation.

Ca2+ pumps are important players in smooth muscle contraction. Nevertheless, little information is available about these pumps in the vas deferens. We have determined which subtype of sarco(endo)plasmic reticulum Ca2+-ATPase isoform (SERCA) is expressed in rat vas deferens (RVD) and its modulation by calmodulin (CaM)-dependent mechanisms. The thapsigargin-sensitive Ca2+-ATPase from a membrane fraction containing the highest SERCA levels in the RVD homogenate has the same molecular mass (∼115 kDa) as that of SERCA2 from the rat cerebellum. It has a very high affinity for Ca2+ (Ca0.5 = 780 nM) and a low sensitivity to vanadate (IC50 = 41 µM). These facts indicate that SERCA2 is present in the RVD. Immunoblotting for CaM and Ca2+/calmodulin-dependent protein kinase II (CaMKII) showed the expression of these two regulatory proteins. Ca2+ and CaM increased serine-phosphorylated residues of the 115-kDa protein, indicating the involvement of CaMKII in the regulatory phosphorylation of SERCA2. Phosphorylation is accompanied by an 8-fold increase of thapsigargin-sensitive Ca2+ accumulation in the lumen of vesicles derived from these membranes. These data establish that SERCA2 in the RVD is modulated by Ca2+ and CaM, possibly via CaMKII, in a process that results in stimulation of Ca2+ pumping activity.

Rat vas deferens SERCA2 is modulated by Ca2+/calmodulin protein kinase II-mediated phosphorylation

Ca2+ pumps are important players in smooth muscle contraction. Nevertheless, little information is available about these pumps in the vas deferens. We have determined which subtype of sarco(endo)plasmic reticulum Ca2+-ATPase isoform (SERCA) is expressed in rat vas deferens (RVD) and its modulation by calmodulin (CaM)-dependent mechanisms. The thapsigargin-sensitive Ca2+-ATPase from a membrane fraction containing the highest SERCA levels in the RVD homogenate has the same molecular mass (∼115 kDa) as that of SERCA2 from the rat cerebellum. It has a very high affinity for Ca2+ (Ca0.5 = 780 nM) and a low sensitivity to vanadate (IC50 = 41 µM). These facts indicate that SERCA2 is present in the RVD. Immunoblotting for CaM and Ca2+/calmodulin-dependent protein kinase II (CaMKII) showed the expression of these two regulatory proteins. Ca2+ and CaM increased serine-phosphorylated residues of the 115-kDa protein, indicating the involvement of CaMKII in the regulatory phosphorylation of SERCA2. Phosphorylation is accompanied by an 8-fold increase of thapsigargin-sensitive Ca2+ accumulation in the lumen of vesicles derived from these membranes. These data establish that SERCA2 in the RVD is modulated by Ca2+ and CaM, possibly via CaMKII, in a process that results in stimulation of Ca2+ pumping activity.

Nongenomic signaling pathways triggered by thyroid hormones and their metabolite 3-iodothyronamine on the cardiovascular system.

Thyroid hormones play a wide range of important physiological activities in almost all organism. As changes in these hormones levels-observed in hypothyroidism and hyperthyroidism-promote serious derangements of the cardiovascular system, it is important to know their mechanisms of action. Although the classic genomic actions which are dependent on interaction with nuclear receptors to modulate cardiac myocytes genes expression, there is growing evidence about T(3) and T(4)-triggered nongenomic pathways, resulted from their binding to plasma membrane, cytoplasm, or mitocondrial receptors that leads to a rapidly regulation of cardiac functions. Interestingly both actions converge to amplify thyroid hormone effects on cardiovascular system. T(3) and T(4) nongenomic actions modify inotropic and chronotropic effects, cardiac action potential duration, cardiac growth, and myocyte shape by protein translation through protein kinases-dependent signaling cascades, which include PKA, PKC, PI3K, and MAPK, and changes on ion channels and pumps activity. In respect to the decreased systemic vascular resistance seen in hyperthyroidism, T(3) appears to activate NOS or ATP-sensitive K(+) channels. In addition, a novel biologically active T(4)-derived metabolite has been described, 3-iodothyronamine, T(1)AM, which also acts through membrane receptors to mediate nongenomic cardiac effects. This metabolite influences the physiological manifestations of thyroid hormone actions by inducing opposite effects from those stimulated by T(3) and T(4), such as negative inotropic and chronotropic effects. Therefore, beyond genomic and nongenomic effects of thyroid hormones, it is crucial for there to be an equilibrium between T(3) or T(4) and T(1)AM levels for maintaining cardiac homeostasis.

PI-PLCbeta is involved in the modulation of the proximal tubule Na+-ATPase by angiotensin II.

In previous papers we showed that Ang II increases the proximal tubule Na+-ATPase activity through AT1/PKC pathway [L.B. Rangel, C. Caruso-Neves, L.S. Lara, A.G. Lopes, Angiotensin II stimulates renal proximal tubule Na+-ATPase activity through the activation of protein kinase C. Biochim. Biophys. Acta 1564 (2002) 310-316, L.B.A. Rangel, A.G. Lopes, L.S. Lara, C. Caruso-Neves, Angiotensin II stimulates renal proximal tubule Na+)-ATPase activity through the activation of protein kinase C. Biochim. Biophys. Acta 1564 (2002) 310-316]. In the present paper, we study the involvement of PI-PLCbeta on the stimulatory effect of angiotensin II (Ang II) on the proximal tubule Na+-ATPase activity. Western blotting assays, using a polyclonal antibody for PI-PLCbeta, show a single band of about 150 KDa, which correspond to PI-PLCbeta isoforms. Ang II induces a rapid decrease in PIP2 levels, a PI-PLCbeta substrate, being the maximal effect observed after 30 s incubation. This effect of Ang II is completely abolished by 5 x 10(-8) M U73122, a specific inhibitor of PI-PLCbeta. In this way, the effect of 10(-8) M Ang II on the proximal tubule basolateral membrane (BLM) Na+-ATPase activity is completely abolished by 5 x 10(-8) M U73122. The increase in diacylglycerol (DAG) concentration, an product of PI-PLCbeta, from 0.1 to 10 nM raises the Na+-ATPase activity from 6.1+/-0.2 to 13.1+/-1.8 nmol Pi mg(-1) min(-1). This effect is similar and non-additive to that observed with Ang II. Furthermore, the stimulatory effect of 10 nM DAG is completely reversed by 10(-8) M calphostin C (Calph C), an inhibitor of PKC. Taken together these data indicate that Ang II stimulates the Na+-ATPase activity of proximal tubule BLM through a PI-PLCbeta/PKC pathway.

P-glycoprotein-like protein contributes to cadmium resistance in Euglena gracilis.

Selective pressures from polluted environments have led to the development of resistance systems in aquatic organisms. Using different techniques, this study examined a cadmium defense mechanism of the freshwater unicellular protozoa Euglena gracilis, and found it to be an efflux pump similar to the multidrug resistance P-glycoprotein. Cd(2+)-treated E. gracilis were able to extrude Rhodamine 123 at 21 degrees C, but not at 4 degrees C. Furthermore, verapamil, a P-glycoprotein modulator, partially blocked the efflux process (at 21 degrees C), and enhanced the Cd(2+) toxic effects on these cells. Western immunoblots of cell lysates, using the anti-P-glycoprotein antibody JSB-1, revealed a 120-KDa protein, which was expressed, in high amounts on Cd(2+)-exposed cells (74% above the control values). Moreover, cells treated with JSB-1 became more sensitive to the harmful effects of cadmium, showing a decreased survival rate. Taken together, these results suggest that a MDR phenotype has evolved in Euglena as one of the mechanisms for cadmium detoxification.

Inositol metabolism in Trypanosoma cruzi: potential target for chemotherapy against Chagas' disease.

Chagas' disease is a debilitating and often fatal disease caused by the protozoan parasite Trypanosoma cruzi. The great majority of surface molecules in trypanosomes are either inositol-containing phospholipids or glycoproteins that are anchored into the plasma membrane by glycosylphosphatidylinositol anchors. The polyalcohol myo-inositol is the precursor for the biosynthesis of these molecules. In this brief review, recent findings on some aspects of the molecular and cellular fate of inositol in T. cruzi life cycle are discussed and identified some points that could be targets for the development of parasite-specific therapeutic agents.

Activation of host cell phosphatidylinositol 3-kinases by Trypanosoma cruzi infection.

Trypanosoma cruzi, the causative agent of Chagas' disease in humans, is an intracellular protozoan parasite with the ability to invade a wide variety of mammalian cells by a unique and remarkable process in cell biology that is poorly understood. Here we present evidence suggesting a role for the host phosphatidylinositol (PI) 3-kinases during T. cruzi invasion. The PI 3-kinase inhibitor wortmannin marked inhibited T. cruzi infection when macrophages were pretreated for 20 min at 37 degrees C before inoculation. Infection of macrophages with T. cruzi markedly stimulated the formation of the lipid products of the phosphatidylinositol (PI) 3-kinases, PI 3-phospate, PI 3,4-biphosphate, and PI 3,4,5-triphosphate, but not PI 4-phosphate or PI 4,5-biphosphate. This activation was inhibited by wortmannin. Infection with T. cruzi also stimulated a marked increase in the in vitro lipid kinase activities that are present in the immunoprecipitates of anti-p85 subunit of class I PI 3-kinase and anti-phosphotyrosine. In addition, T. cruzi invasion also activated lipid kinase activity found in immunoprecipitates of class II and class III PI 3-kinases. These data demonstrate that T. cruzi invasion into macrophages strongly activates separated PI 3-kinase isoforms. Furthermore, the inhibition of the class I and class III PI 3-kinase activities abolishes the parasite entry into macrophages. These findings suggest a prominent role for the host PI 3-kinase activities during the T. cruzi infection process.

Characterization of the myo-inositol transport system in Trypanosoma cruzi.

myo-inositol is a growth factor for mammalian cells as well as for the pathogenic protozoa Trypanosoma cruzi. Most of the cell surface molecules in this organism rely on myo-inositol as the biosynthetic precursor for phosphoinositides and glycosylated phosphatidylinositols. The aim of this work was to investigate the process of myo-inositol translocation across the parasite cell membrane. myo-Inositol uptake was concentration-dependent in the concentration range 0.1-10 microM with maximal transport obtained at 8 microM. Using sodium-free buffers, where Na+ was replaced by choline or K+, myo-inositol uptake was inhibited by 50%. Furosemide, an inhibitor of the ouabain-insensitive Na+-ATPase, inhibited the Na+-dependent and Na+-independent myo-inositol uptake by 68 and 33%, respectively. In contrast, ouabain, an (Na++/K+) ATPase inhibitor, did not affect transport. Part of the myo-inositol uptake is mediated by active transport as it was inhibited when energy metabolism inhibitors such as carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone (34%), 2,4-dinitrophenol (50%), KCN (71%) and NaN3 (69%) were added to the medium, or the temperature of the medium was lowered to 4 degrees C. The addition of glucose (5-50 mM) or mannose (10 mM) did not change the myo-inositol uptake, whereas the addition of 10 mM nonlabeled myo-inositol totally inhibited this transport, indicating that the transporter is specific for myo-inositol. Phloretin (0.3 mM) and phoridzin (5 mM), but not cytochalasin B, were efficient inhibitors of myo-inositol uptake. A portion of the accumulated myo-inositol is converted to inositol phosphates and phosphoinositides. These data show that myo-inositol transport in T. cruzi epimastigotes is mediated by at least two specific transporters - one Na+-dependent and the other Na+-independent.

Ouabain-insensitive Na(+)-ATPase activity in Trypanosoma cruzi epimastigotes.

In the present paper, the presence of a ouabain-insensitive Na(+)-stimulated, Mg(2+)-dependent ATPase activity in T. cruzi epimastigotes CL14 clone and Y strain was investigated. The increase in Na+ concentration (from 5 to 170 mM), in the presence of 2 mM ouabain, increases the ATPase activity in a saturable manner along a rectangular hyperbola. The Vmax was 18.0 +/- 1.0 and 21.1 +/- 1.1 nmoles Pi x mg-1 x min-1 and the half-activation value (K50) for Na+ was 34.3 +/- 5.8 mM and 37.7 +/- 5.3 in CL14 clone and in Y strain, respectively. The Na(+)-stimulated ATPase activity was inhibited by 5-[aminosulfonyl]-4-chloro-2-[(2-furanylmethyl)-amino] benzoic acid (furosemide) in a dose-dependent manner. The half-inhibition value (I50) was 0.22 +/- 0.03 and 0.24 +/- 0.07 mM, and the Hill number (n) was 0.99 +/- 0.2 and 2.16 +/- 0.29 for CL14 clone and Y strain, respectively. These data indicate that both cell types express the ouabain-insensitive Na(+)-ATPase activity, which might be considered the biochemical expression of the second Na+ pump.

Effects of fluorinated inositols on the phosphoinositide metabolism and the proliferation of Trypanosoma cruzi.

Inositol has been cited as being essential for the growth of micro-organisms and animals. Its action rests mostly in the formation of a set of inositol-containing lipids, including phosphatidylinositol and its phosphorylated derivatives. To evaluate the functional responses coupled to the phosphoinositide metabolism in Trypanosoma cruzi we used myo-inositol and its six fluorinated analogues. Their uptake into epimastigotes was characterised using tritium-labeled myo-inositol and monodeoxyfluoro-myo-inositols. The analogues were tested for their ability to inhibit [3H]-myo-inositol incorporation into phosphoinositides and the proliferation of epimastigotes and amastigotes. The results showed differences between T. cruzi and mammalian systems in the responses to the fluorinated analogues. We found that the 3-, 5- and 6-fluoro analogues did not enter the cells but had an inhibitory effect on the incorporation of the radioactive inositol into lipids and on the amastigotes' and epimastigotes' replication. The most effective inhibitor, 1-D-6-deoxy-6-myo-inositol, had no effect on mammalian cell division.

Distribution of F-actin, alpha-actinin, tropomyosin, tubulin and organelles in Euglena gracilis by immunofluorescence microscopy.

Euglena gracilis, a unicellular flagellated alga, can display numerous shape changes. These changes are most probably caused by a pellicle and an internal cytoskeleton. In this paper we studied the distribution of the cytoskeletal proteins actin, alpha-actinin, tropomyosin and tubulin in dark-adapted Euglena, using immunofluorescence microscopy. We found that F-actin, alpha-actinin, tropomyosin and tubulin have a distribution that is coincident in the plasma membrane and, in addition, alpha-actinin and tropomyosin are seen in small patches in the cytoplasm, and tubulin in the flagella. We have also studied the distribution of the endoplasmic reticulum, nucleus, and Golgi apparatus of these cells, using fluorescent probes. Both the endoplasmic reticulum and the Golgi apparatus have a meshwork pattern distributed throughout the cytoplasm, and the nucleus has a chromatin evenly distributed in the nucleoplasm.

Trypanosoma cruzi epimastigotes express the ouabain- and vanadate-sensitive (Na(+)+K+)ATPase activity.

The presence of (Na(+)+K+)ATPase activity in CL14 clone and NIH NTY strain of Trypanosoma cruzi epimastigotes is demonstrated. A Na+ plus K+ stimulated ATPase activity is found in both strains. The optimal Na+/K+ ratio is 5:1 and 9:1 in CL14 clone and NIH NTY strain, respectively. In both strains, vanadate completely inhibits the ouabain-sensitive ATPase activity indicating that it belongs to the P-type (E1/E2) family of ion-transporting ATPases. The I50 for vanadate is 0.66 +/- 0.04 and 0.04 +/- 0.02 microM in CL14 clone and NIH NTY strain, respectively. These data indicate that both strains of T. cruzi epimastigotes express the ouabain- and vanadate-sensitive (Na(+)+K+)ATPase activity. On the other hand, the discrepancy between the parameters analyzed for the inhibitors suggests that they express different isoforms of this enzyme.

Effects of cadmium on Euglena gracilis membrane lipids.

The toxic effects of cadmium (2 micrograms/ml) on membrane lipids and growth of Euglena gracilis were studied using autotrophic (AUTO), heterotrophic (DARK) and mixotrophic (LIGHT) cells. Cadmium caused inhibition of cellular proliferation (IC50 1.2 micrograms/ml) and morphological alterations which were most pronounced in chloroplasts. The chlorophyll content of LIGHT cadmium-treated cells was reduced 42.5%. Cadmium also caused an increase in protein and total lipid content per cell in all three cell types. Among the membrane lipids, cholesterol content was lower in cadmium-treated cells cultivated under illumination (AUTO: 0.40 +/- 0.02 vs 0.64 +/- 0.08 and LIGHT: 0.40 +/- 0.09 vs 0.53 +/- 0.01 microgram/10(5) cells). There were no changes in total phospholipid content, although cardiolipin content was altered in all three cell types, and in mixotrophic cells there was an increase in phosphatidylglycerol, a phospholipid typically found in chloroplasts. These results suggest that cadmium has an overall toxic effect on Euglena gracilis and that part of the effect can be ascribed to defects in the structure of chloroplasts and mitochondrial membranes.

Effects of cadmium on Euglena gracilis membrane lipids

The toxic effects of cadmium (2 mug/ml) on membrane lipids and growth of Euglena gracilis were studied using autotrophic (AUTO), heterotrophic (DARK) and mixotrophic (LIGHT) cells. Cadmium caused inhibition of cellular proliferation (IC50 1.2 mug/ml) and morphological alterations which were most pronounced in chloroplasts. The chlorophyll content of LIGHT cadmium-treated cells was reduced 42.5 per cent. Cadmium also caused an increase in protein and total lipid content per cell in all three cell types. Among the membrane lipids, cholesterol content was lower in cadmium-treated cells cultivated under illumination (AUTO: 0.40 ñ 0.02 vs 0.64 ñ 0.08 and LIGHT: 0.40 ñ 0.09 vs 0.53 ñ 0.01 mug/l0(5) cells). There were no changes in total phospholipid content, although cardiolipin content was altered in all three cell types, and in mixotrophic cells there was an increase in phosphatidylglycerol, a phospholipid typically found in chloroplasts. These results suggest that cadmium has an overall toxic effect on Euglena gracilis and that part of the effect can be ascribed to defects in the structure of chloroplasts and mitochondrial membranes.