Sildenafil Ameliorates Advanced Glycation End Products-Induced Mitochondrial Dysfunction in HT-22 Hippocampal Neuronal Cells

OBJECTIVE: Accumulation of advanced glycation end-products (AGE) and mitochondrial glycation is importantly implicated in the pathological changes of the brain associated with diabetic complications, Alzheimer disease, and aging. The present study was undertaken to determine whether sildenafil, a type 5 phosphodiesterase type (PDE-5) inhibitor, has beneficial effect on neuronal cells challenged with AGE-induced oxidative stress to preserve their mitochondrial functional integrity. METHODS: HT-22 hippocampal neuronal cells were exposed to AGE and changes in the mitochondrial functional parameters were determined. Pretreatment of cells with sildenafil effectively ameliorated these AGE-induced deterioration of mitochondrial functional integrity. RESULTS: AGE-treated cells lost their mitochondrial functional integrity which was estimated by their MTT reduction ability and intracellular ATP concentration. These cells exhibited stimulated generation of reactive oxygen species (ROS), disruption of mitochondrial membrane potential, induction of mitochondrial permeability transition, and release of the cytochrome C, activation of the caspase-3 accompanied by apoptosis. Western blot analyses and qRT-PCR demonstrated that sildenafil increased the expression level of the heme oxygenase-1 (HO-1). CoPP and bilirubin, an inducer of HO-1 and a metabolic product of HO-1, respectively, provided a similar protective effects. On the contrary, the HO-1 inhibitor ZnPP IX blocked the effect of sildenafil. Transfection with HO-1 siRNA significantly reduced the protective effect of sildenafil on the loss of MTT reduction ability and MPT induction in AGE-treated cells. CONCLUSION: Taken together, our results suggested that sildenafil provides beneficial effect to protect the HT-22 hippocampal neuronal cells against AGE-induced deterioration of mitochondrial integrity, and upregulation of HO-1 is involved in the underlying mechanism.

Cilostazol Protects Endothelial Cells Against Lipopolysaccharide-Induced Apoptosis Through ERK1/2- and P38 MAPK-Dependent Pathways

BACKGROUND/AIMS: We examined the effects of cilostazol on mitogen-activated protein kinase (MAPK) activity and its relationship with cilostazol-mediated protection against apoptosis in lipopolysaccharide (LPS)-treated endothelial cells. METHODS: Human umbilical vein endothelial cells (HUVECs) were exposed to LPS and cilostazol with and without specific inhibitors of MAPKs; changes in MAPK activity in association with cell viability and apoptotic signaling were investigated. RESULTS: Cilostazol protected HUVECs against LPS-induced apoptosis by suppressing the mitochondrial permeability transition, cytosolic release of cytochrome c, and subsequent activation of caspases, stimulating extracellullar signal-regulated kinase (ERK1/2) and p38 MAPK signaling, and increasing phosphorylated cAMPresponsive element-binding protein (CREB) and Bcl-2 expression, while suppressing Bax expression. These cilostazol-mediated cellular events were effectively blocked by MAPK/ERK kinase (MEK1/2) and p38 MAPK inhibitors. CONCLUSIONS: Cilostazol protects HUVECs against LPS-induced apoptosis by suppressing mitochondriadependent apoptotic signaling. Activation of ERK1/2 and p38 MAPKs, and subsequent stimulation of CREB phosphorylation and Bcl-2 expression, may be responsible for the cellular signaling mechanism of cilostazolmediated protection.

P2 Receptor-mediated Inhibition of Vasopressin-stimulated Fluid Transport and cAMP Responses in AQP2-transfected MDCK Cells

We cultured canine kidney (MDCK) cells stably expressing aquaporin-2 (AQP2) on collagen-coated permeable membrane filters and examined the effect of extracellular ATP on arginine vasopressin (AVP)-stimulated fluid transport and cAMP production. Exposure of cell monolayers to basolateral AVP resulted in stimulation of apical to basolateral net fluid transport driven by osmotic gradient which was formed by addition of 500 mM mannitol to basolateral bathing solution. Pre-exposure of the basolateral surface of cell monolayers to ATP (100 ?M) for 30 min significantly inhibited the AVP-stimulated net fluid transport. In these cells, AVP-stimulated cAMP production was suppressed as well. Profile of the effects of different nucleotides suggested that the P2Y2 receptor is involved in the action of ATP. ATP inhibited the effect of isoproterenol as well, but not that of forskolin to stimulate cAMP production. The inhibitory effect of ATP on AVP-stimulated fluid movement was attenuated by a protein kinase C inhibitor, calphostin C or pertussis toxin. These results suggest that prolonged activation of the P2 receptors inhibits AVP-stimulated fluid transport and cAMP responses in AQP2 transfected MDCK cells. Depressed responsiveness of the adenylyl cyclase by PKC-mediated modification of the pertussis-toxin sensitive Gi protein seems to be the underlyihng mechanism.

A1 Receptor-mediated Protection against Amyloid Beta-induced Injury in Human Neuroglioma Cells

Adenosine has been reported to provide cytoprotection in the central nervous systems as well as myocardium by activating cell surface adenosine receptors. However, the exact target and mechanism of its action still remain controversial. The present study was performed to examine whether adenosine has a protective effect against Abeta-induced injury in neuroglial cells. The astrocyte-derived human neuroglioma cell line, A172 cells, and Abeta25~35 were employed to produce an experimental Abeta-induced glial cell injury model. Adenosine significantly prevented Abeta-induced apoptotic cell death. Studies using various nucleotide receptor agonists and antagonists suggested that the protection was mediated by A1 receptors. Adenosine attenuated Abeta-induced impairment in mitochondrial functional integrity as estimated by cellular ATP level and MTT reduction ability. In addition, adenosine prevented Abeta-induced mitochondrial permeability transition, release of cytochrome c into cytosol and subsequent activation of caspase-9. The protective effect of adenosine disappeared when cells were pretreated with 5-hydroxydecanoate, a selective blocker of the mitochondrial ATP-sensitive K+ channel. In conclusion, therefore we suggest that adenosine exerts protective effect against Abeta-induced cell death of A172 cells, and that the underlying mechanism of the protection may be attributed to preservation of mitochondrial functional integrity through opening of the mitochondrial ATP-sensitive K+ channels.

Development and Assessment of Multimedia Learning Tool on Clinical Microbiology for Undergraduate Medical Students / 한국의학교육

PURPOSE: Insufficient teaching of clinical microbiology, often caused by limited resources in medical schools, might be a reason for inaccurate diagnosis and treatment of infectious diseases by doctors. The purpose of this study is to develop and assess a multimedia self learning tool (MSLT) for clinical microbiology course. METHODS: We developed the MSLT based on existing self-directed learning tools. This tool was used by second- and third-year medical students. We randomly assigned 67 participating students to two groups: one (29) with lectures only and the other (38) with the MSLT only. We conducted pre- and post-tests. RESULTS: There are no differences in the pre- and post-test scores between the lecture group and the MSLT group in knowledge of bacterial classification, understanding of infectious diseases, proper use of laboratory tests, and proper selection of antimicrobials. However, post-test scores were significantly higher in both groups. CONCLUSION: The MSLT was found to be as equally effective as lectures, at least, test scorewise. Teachers could use either this tool alone or combined with conventional lectures to improve and enhance teaching in clinical microbiology. The results shed new insights into the possibility of introducing new teaching methods in clinical microbiology for future medical education.

A Study on Using Questions during Lectures in Medical School: Reality vs. Awareness of the Professors / 한국의학교육

PURPOSE: Questions are known to be an important teaching technique. And, waiting for the answers is essential in making questions effective and valuable. The objective of this study is to evaluate the status of the use of questions during lectures and to survey the level of awareness of the professors regarding the questioning method including waiting time in one medical college. METHODS: The study subjects were 42 medical college professors who have been lecturing to second year medical students from February to June 2004. The questionnaire consisted of 28 items on the questions used during their lectures. The lecturers were observes by an appointed student to get data on the characteristics of questions used. RESULTS: Most of the professors observed in this study used questions during lectures, predominantly questions requiring answers. The waiting time, however, for answers was too short than reported in the literature. About 50% of the professors answered that their usual waiting time is between 6 to 10 seconds but the results of the observation showed that the average waiting time was 0.6 second. CONCLUSION: There was significant discrepancy about waiting time between the results of the questionnaire and the data from the observation. Because the average waiting time was much shorter than expected, follow up studies after feedback and education would be recommended.

Effect of P2 Nucleotide Receptor Activation on Phosphate Transport in Rabbit Proximal Tubular Cells / 대한신장학회잡지

BACKGROUND: Extracellular nucleotides act as agonists to regulate a broad range of physiological processes by interacting with P2 receptors in various tissues including the kidney tubules. This study was undertaken to evaluate the effect of P2 receptor activation on PTH-dependent regulation of phosphate transport in the renal proximal tubular cells. METHODS: Proximal tubular cells were isolated from the rabbit kidney and grown as monolayers on 24 well culture plates. Phosphate uptake was determined by measuring the uptake of radiolabeled phosphate into cell monolayers. Cyclic AMP content was determined by radioimmunoassay using [3H]cAMP assay kit. RESULTS: Activation of P2 receptors with ATP exerted differential effects on phosphate uptake and cAMP generation. In the absence of PTH, it inhibited phosphate uptake and stimulated cAMP generation. In contrast, in the presence of PTH, it attenuated PTH-induced stimulation of cAMP generation and inhibition of phosphate uptake. The profile of the effects of different P2 agonists suggested that P2Y1- and P2Y2-like receptors are involved in the effects of ATP. The effect of ATP to interfere with the PTH-induced regulation was significantly blocked by calphostin C, pertussis toxin or PKC-depletion, whereas, the effects of ATP in the absence of PTH were abolished by indomethacin. CONCLUSION: Our results suggest that PKC-dependent modification of Gi proteins and, subsequently, reduced responsiveness of adenylate cyclases is responsible for the attenuating effect of ATP on the PTH-dependent regulation of phosphate transport in rabbit proximal tubule cells.

Extracellular ATP stimulates Na+ and Cl- transport through the activation of multiple purinergic receptors on the apical and basolateral membranes in M-1 mouse cortical collecting duct cells

The mammalian cortical collecting duct (CCD) plays a major role in regulating renal NaCl reabsorption, which is important in Na+ and Cl- homeostasis. The M-1 cell line, derived from the mouse cortical collecting duct, has been used as a mammalian model of the study on the electrolytes transport in CCD. M-1 cells were grown on collagen-coated permeable support and short circuit current (Isc) was measured. M-1 cells developed amiloride-sensitive current 5apprx7 days after seeding. Apical and basolateral addition of ATP induced increase in Isc in M-1 cells, which was partly retained in Na+/-free or Cl--free solution, indicating that ATP increased Na+ absorption and Cl- secretion in M-1 cells. Cl- secretion was mediated by the activation of apical cystic fibrosis transmembrane regulator (CFTR) chloride channels and Ca2+/-activated chloride channels, but Na+ absorption was not mediated by activation of epithelal sodium channel (ENaC). ATP increased cAMP content in M-1 cells. The RT-PCR analysis demonstrated that M-1 cells express P2Y2, P2X3 and P2Y4 receptors. These results showed that ATP regulates Na+ and Cl- transports via multiple P2 purinoceptors on the apical and basolateral membranes in M-1 cells.

Asymmetrical distribution of P2Y nucleotide receptors in rabbit inner medullary collecting duct cells

We cultured the rabbit inner medullary collecting duct (IMCD) cells as monolayers on collagen-coated membrane filters, and investigated distribution of the P2Y receptors by analyzing nucleotide-induced short circuit current (Isc) responses. Exposure to different nucleotides of either the apical or basolateral surface of cell monolayers stimulated Isc. Dose-response relationship and cross-desensitization studies suggested that at least 3 distinct P2Y receptors are expressed asymmetrically on the apical and basolateral membranes. A P2Y2-like receptor, which responds to UTP and ATP, is expressed on both the apical and basolateral membranes. In addition, a uracil nucleotide receptor, which responds to UDP and UTP, but not ATP, is expressed predominantly on the apical membrane. In contrast, a P2Y1-like receptor, which responds to ADP and 2-methylthio-ATP, is expressed predominantly on the basolateral membrane. These nucleotides stimulated intracellular cAMP production with an asymmetrical profile, which was comparable to that in the stimulation of Isc. Our results suggest that the adenine and uracil nucleotides can interact with different P2Y nucleotide receptors that are expressed asymmetrically on the apical and basolateral membranes of the rabbit IMCD cells, and that both cAMP- and Ca2+-dependent signaling mechanisms underlie the stimulation of Isc.

Effect of ethanol on Na+-Pi uptake in opossum kidney cells: Role of membrane fluidization and reactive oxygen species

This study was undertaken to examine the effect of ethanol on Na+-dependent phosphate (Na+-Pi) uptake in opossum kidney (OK) cells, an established renal proximal tubular cell line. Ethanol inhibited Na+-dependent component of phosphate uptake in a dose-dependent manner with I50 of 8.4%, but it did not affect Na+-independent component. Similarly, ethanol inhibited Na+-dependent uptakes of glucose and amino acids (AIB, glycine, alanine, and leucine). Microsomal Na+-K+-ATPase activity was not significantly altered when cells were treated with 8% ethanol. Kinetic analysis showed that ethanol increased Km without a change in Vmax of Na+-Pi uptake. Inhibitory effect of n-alcohols on Na+-Pi uptake was dependent on the length of the hydrocarbon chain, and it resulted from the binding of one molecule of alcohol, as indicated by the Hill coefficient (n) of 0.8-1.04. Catalase significantly prevented the inhibition, but superoxide dismutase and hydroxyl radical scavengers did not alter the ethanol effect. A potent antioxidant DPPD and iron chelators did not prevent the inhibition. Pyrazole, an inhibitor of alcohol dehydrogenase, did not attenuate ethanol-induced inhibition of Na+-Pi uptake, but it prevented ethanol-induced cell death. These results suggest that ethanol may inhibit Na+-Pi uptake through a direct action on the carrier protein, although the transport system is affected by alterations in the lipid environment of the membrane.

Effects of ethanol on Na+-dependent solute uptake in rabbit renal brush-border membrane vesicles

This study was undertaken to examine the effect of ethanol on Na+-dependent transport systems (glucose, phosphate, and dicarboxylate) in renal brush-border membrane vesicles (BBMV). Ethanol inhibited Na+-dependent uptakes of glucose, phosphate, and succinate in a dose-dependent manner, but not the uptakes of Na+-independent. The H+/TEA antiport was reduced by 8% ethanol. Kinetic analysis showed that ethanol caused a decrease in Vmax of three transport systems, leaving Km values unchanged. Ethanol decreased phlorizin binding, which was closely correlated with the decrease in Vmax of Na+-glucose uptake. These results indicate that ethanol inhibits Na+-dependent uptakes of glucose, phosphate, and dicaboxylate and that the reduction in Vmax of Na+-glucose uptake is caused by a decrease in the number of active carrier proteins in the membrane.

Role of phospholipase A2 in hypoxia-induced renal cell injury

The present study was designed to assess the roles of PLA2 activation and arachidonic acid (AA) metabolites in hypoxia-induced renal cell injury. Hypoxia increased LDH release in a dose-dependent manner in rabbit renal cortical slices, and this increase was significant after 20-min hypoxia. The hypoxia-induced LDH release was prevented by amino acids, glycine and alanine, and extracellular acidosis (pH 6.0). Buffering intracellular Ca2+ by a chelator, but not omission of Ca2+ in the medium produced a significant reduction in hypoxia-induced LDH release. The effect of hypoxia was blocked by PLA2 inhibitors, mepacrine, butacaine, and dibucaine. A similar effect was observed by a 85-kD cPLA2 inhibitor AACOCF3. AA increased hypoxia-induced LDH release, and albumin, a fatty acid absorbent, prevented the LDH release, suggesting that free fatty acids are involved in hypoxia-induced cell injury. These results suggest that PLA2 activation and its metabolic products play important roles in pathogenesis of hypoxia-induced cell injury in rabbit renal cortical slices.

Activation of SAPK and increase in Bak levels during ceramide and indomethacin-induced apoptosis in HT29 cells

It has been reported that activation of sphingomyelin pathway and nonsteroidal anti-inflammatory drugs (NSAIDS) inhibit the promotion of colon carcinoma. Ceramide, a metabolite of sphingomyelin, and indomethacin were shown to induce apoptosis in colon carcinoma cells. However, the mechanisms of ceramide- and indomethacin-induced apoptosis in the colon carcinoma cells are not clearly elucidated. Recent studys showed that indomethacin-induced apoptosis in colon cancer cells through the cyclooxygenase-independent pathways, and that may be mediated by generation of ceramide. In this study, we compared effects of ceramide and indomethacin on important modulators of apoptotic processes in HT29 cells, a human colon cancer cell line. Ceramide and indomethacin induced apoptosis dose- and time-dependently. Ceramide and indomethacin increased stress-activated protein kinase (SAPK) activity, and decreased mitogen-activated protein kinase (MAPK) activity. The expression of Bak was increased by the treatment of ceramide and indomethacin. The expression of other Bcl-2 related proteins (Mcl-1, Bcl-XL, Bax) which were known to be expressed in colon epithelial cells was not changed during the ceramide- and indomethacin-induced apoptosis. Our results suggest that ceramide and indomethacin share common mechanisms for induction of apoptosis in HT29 cells.

Role of phospholipase A2 in oxidant-induced alteration in phosphate transport in primary cultured rabbit renal proximal tubule cells

The present study was undertaken to examine the role of phospholipase A2 (PLA2) in oxidant-induced inhibition of phosphate transport in primary cultured rabbit renal proximal tubule cells. Uptakes of phosphate and glucose were dose-dependently inhibited by an oxidant t-butylhydroperoxide (tBHP), and the significant inhibition appeared at 0.025 mM of tBHP, whereas tBHP-induced alterations in lipid peroxidation and cell viability were seen at 0.5 mM. tBHP stimulated arachidonic acid (AA) release in a dose-dependent fashion. A PLA2 inhibitor mepacrine prevented tBHP-induced AA release, but it did not alter the inhibition of phosphate uptake and the decrease in cell viability induced by tBHP. tBHP-induced inhibition of phosphate transport was not affected by a PKC inhibitor, staurosporine. tBHP at 0.1 mM did not produce the inhibition of Na+-K+-ATPase activity in microsomal fraction, although it significantly inhibited at 1.0 mM. These results suggest that tBHP can inhibit phosphate uptake through a mechanism independent of PLA2 activation, irreversible cell injury, and lipid peroxidation in primary cultured rabbit renal proximal tubular cells.

Effect of endothelin-1 on proliferation and differentiation of rat tracheal epithelial cells

A number of substances involved in the proliferation and differentiation of the tracheobronchial epithelium have been identified. The defects in the control of the proliferation and differentiation of tracheobronchial epithelial cells appear to constitute crucial steps in the transition of normal cells to neoplastic ones. Endothelin-1 is produced by tracheal epithelial cells, and its receptors are present in tracheal epithelial cells. However, the effect of endothelin-1 on the proliferation and differentiation of tracheal epithelial cells has not been clearly elucidated. This study was undertaken to investigate these actions of endothelin-1 in primary cultured cells of rat tracheal epithelia. Endothelin-1 stimulated proliferation of tracheal epithelial cells 1.5-fold when compared with that of control cells. Endothelin-1 increased mitogen-activated protein kinase (MAPK) activity. Herbimycin A, a tyrosine kinase inhibitor, inhibited endothelin-1-induced proliferation of epithelial cells. The treatment of endothelin-1 during the primary culture of tracheal epithelial cells increased AB-PAS-stained cell population and ciliated cell population 6.5 fold and 1.5 fold, respectively, when compared with those in control cells. The responsiveness to carbachol and forskolin in the Cl- secretion was increased 1.7 and 1.9 fold, respectively, in the endothelin-treated epithelial cells. These results indicated that endothelin-1 increases proliferation via MAPK pathway and stimulates differentiation to secretory and ciliated cells in rat tracheal epithelial cells.

Functional characteristics of neutral amino acid transporter in opossum kidney (OK) cells

The characteristics of Na+/-dependent cycloleucine uptake was investigated in OK cells with regard to substrate specificity and regulation by protein kinase C (PKC). Inhibition studies with different synthetic and natural amino acids showed a broad spectrum affinity to neutral amino acids regardless of their different side chains including branched or aromatic, indicating that the Na+/-dependent cycloleucine uptake in OK cells is mediated by System B-o or System B degree -like transporter rather than the classical System A or ASC. Phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate, but not 4 alpha-PMA elicited a time-dependent biphasic stimulation of Na+/-dependent cycloleucine uptake, which produced early transient peak at 30 min and late sustained peak at 180 min. Both the early and late stimulations by PMA were due to an increase in Vmax and not due to a change in Km. PKC inhibitors blocked both the early and late stimulation by PMA, while protein synthesis inhibitors blocked the late stimulation only. These results suggest the existence and regulation by PKC of System B degree or System B degree -like broad spectrum transport system for neutral amino acids in OK cells.