Involvement of oxidative stress in bee venom-induced inhibition of Na+/glucose cotransporter in renal proximal tubule cells

1. The present study was conducted to examine the involvement of oxidative stress in bee venom-induced inhibition of the Na+/glucose cotransporter (alpha-methyl-d-glucopyranoside (alpha-MG) uptake), a typical functional marker of proximal tubules, in primary cultured rabbit renal proximal tubule cells (PTC). 2. Bee venom (> or = 1 microg/mL) increased lipid peroxide (LPO) formation over 30 min. The increase in [(3)H]-arachidonic acid (AA) release and LPO formation and the inhibition of alpha-MG uptake induced by bee venom (1 microg/mL) and melittin (a major component of bee venom; 0.5 microg/mL) were blocked by N-acetyl-l-cysteine, vitamin C and vitamin E, anti-oxidants. 3. Bee venom- and melittin-induced increases in LPO formation and inhibition of alpha-MG uptake were significantly prevented by mepacrine and AACOCF(3), phospholipase A(2) inhibitors. In addition, nordihydroguaiareic acid (a lipoxygenase inhibitor) and econazole (a cytochrome P-450 epoxygenase inhibitor), but not indomethacin (a cyclo-oxygenase inhibitor), prevented bee venom- and melittin-induced increases in LPO formation and inhibition of alpha-MG uptake. 4. Nordihydroguaiareic acid prevented bee venom- and melittin-induced increases in Ca(2+) uptake. Moreover, anti- oxidants significantly prevented bee venom- and melittin-induced increases in Ca(2+) uptake. 5. In conclusion, bee venom inhibits alpha-MG uptake via the phospholipase A(2)-oxidative stress-Ca(2+) signalling cascade in primary cultured rabbit renal proximal tubule cells.     

Elevation of Na+-K+ ATPase immunoreactivity in GABAergic neurons in gerbil CA1 region following transient forebrain ischemia

In a previous study, we suggested that GABAergic neurons might be resistant to ischemic insult, because of the maintenance of the GABA shunt, which is one of the ATP synthetic pathways in neurons. In the present study, we identified Na(+)-K(+) ATPase immunoreactivity in the gerbil hippocampus in order to determine whether changes in Na(+)-K(+) ATPase immunoreactivity correlate with GABA shunt following ischemic insult. At 12 h after ischemia-reperfusion, Na(+)-K(+) ATPase immunoreactivity accumulated in some neurons in the CA1 region. However, the protein content of Na(+)-K(+) ATPase was not altered. Interestingly, the density of Na(+)-K(+) ATPase immunoreactivity in neurons and the protein content in the CA1 region was intensified in the 24 h post-ischemic group. As a result of double immunofluorescence study, Na(+)-K(+) ATPase immunoreactive neurons were identified with GABAergic neurons. Therefore, our findings suggest that the increase of Na(+)-K(+) ATPase in GABAergic neurons may be able to explain the resistance of these cells to ischemic insult, and support our previous hypothesis that GABA may play an important role as a metabolite in the survival of GABAergic neurons after ischemic insult.     

Cellular proliferation during compensatory renal growth in neonatal rats using flow cytometry

BACKGROUND: Compensatory renal growth consists of cellular enlargement and a small but consistent increase in DNA content. It has been assumed that the increase in the total renal DNA content was due to new cell formation. METHODS: To test the hypothesis of whether cellular hyperplasia is the cause of the compensatory renal growth after the loss of the renal parenchyma and the timing of the DNA increase in neonatal rats, we performed cell cycle analysis using flow cytometry. RESULTS: Following unilateral nephrectomy, the maximum increases of neonatal cortical cells entering the S phase occurred at 72 and 120 h (9.4 and 9.6% compared to 7.0 and 6.1% of the sham-operated group). Peak increases of neonatal kidney cortical cells entering the G2M phase occurred at 48 and 72 h (4.3 and 4.6% compared to 3.3 and 3.9% of the sham-operated group). CONCLUSION: DNA synthesis and replication occurs during compensatory renal growth following unilateral nephrectomy in neonatal rats as evidenced by an increase in cells entering both the S and G2M phases. In neonatal rats these events appear to be completed within 48-120 h after nephrectomy.     

High glucose down-regulates angiotensin II binding via the PKC-MAPK-cPLA2 signal cascade in renal proximal tubule cells

BACKGROUND: It has been reported that renal renin-angiotensin system contributes to the development of diabetic nephropathy. However, the mechanism of angiotensin II receptor regulation in diabetic condition has not been elucidated. METHODS: The effects of high glucose on [(3)H]-arachidonic acid (AA) release and angiotensin II (Ang II) binding and its related signal pathway were examined in primary cultured rabbit renal proximal tubule cells (PTCs). RESULTS: High glucose down-regulated (125)I-Ang II binding from 12 hours and this response was sustained over 48 hours. Thus, the treatment of 25 mmol/L glucose for 48 hours was used for this study. High glucose-induced down-regulation of (125)I-Ang II binding was reversed by the removal of extracellular glucose, suggesting a role for glucose specificity. The high glucose-induced down-regulation of (125)I-Ang II binding was blocked by mepacrine, AACOCF3, phospholipase A2 inhibitors, indomethacin, ibuprofen, and cyclooxygenase inhibitors. Indeed, high glucose significantly increased prostaglandin E2 synthesis. In addition, the high glucose-induced AA release was blocked by PD 98059, a p44/42 mitogen-activated protein kinase (MAPK) inhibitor. PD 98059 also prevented the down-regulation of (125)I-Ang II binding by high glucose, suggesting a role for p44/42 MAPK. Indeed, high glucose significantly increased p44/42 MAPK activity after the 15-minute time point. Protein kinase C (PKC) inhibitor blocked high glucose-induced activation of p44/42 MAPK, increase of the [(3)H]-AA release, and down-regulation of 125I-Ang II binding. W-7 and KN-62 also blocked the high glucose-induced increase of [(3)H]-AA release and down-regulation of (125)I-Ang II binding. However, phospholipase A2 inhibitor did not block high glucose-induced activation of p44/42 MAPK. CONCLUSION: High glucose down-regulates (125)I-Ang II binding via the PKC-MAPK-cPLA2 signal pathway.     

Chronological changes in pyridoxine-5'-phosphate oxidase immunoreactivity in the seizure-sensitive gerbil hippocampus

To identify the roles of pyridoxine-5'-phosphate (PNP) oxidase in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of PNP oxidase expression was conducted. PNP oxidase immunoreactivity in a preseizure group of seizure-sensitive (SS) gerbils was detected more strongly than that in a seizure-resistant (SR) group. The density of PNP oxidase immunoreactivity in a 30 min postictal group was significantly lower than that in a preseizure group. In a 12 hr postictal group, PNP oxidase immunodensity had recovered to a preseizure level. The overexpression of PNP oxidase in the hippocampus of preseizure SS gerbils suggests that PNP or pyridoxal 5'-phosphate plays an important role in the modulation of glutamic acid decarboxylase activity and gamma-aminobutyric acid reuptake as mediated by membrane transporter via neurons. In addition, this change in the PNP oxidase immunoreactivity following seizure may be a compensatory response designed to reduce epileptic activity in this animal.     

Object activation in semantic memory from visual multimodal feature input.

The human brain's representation of objects has been proposed to exist as a network of coactivated neural regions present in multiple cognitive systems. However, it is not known if there is a region specific to the process of activating an integrated object representation in semantic memory from multimodal feature stimuli (e.g., picture-word). A previous study using word-word feature pairs as stimulus input showed that the left thalamus is integrally involved in object activation (Kraut, Kremen, Segal, et al., this issue). In the present study, participants were presented picture-word pairs that are features of objects, with the task being to decide if together they "activated" an object not explicitly presented (e.g., picture of a candle and the word "icing" activate the internal representation of a "cake"). For picture-word pairs that combine to elicit an object, signal change was detected in the ventral temporo-occipital regions, pre-SMA, left primary somatomotor cortex, both caudate nuclei, and the dorsal thalami bilaterally. These findings suggest that the left thalamus is engaged for either picture or word stimuli, but the right thalamus appears to be involved when picture stimuli are also presented with words in semantic object activation tasks. The somatomotor signal changes are likely secondary to activation of the semantic object representations from multimodal visual stimuli.     

Changes in pyridoxal kinase immunoreactivity in the gerbil hippocampus following spontaneous seizure

To identify the roles of pyridoxal kinase (PLK) in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of PLK expression in the gerbil hippocampus was conducted. PLK immunoreactivity in a pre-seizure group of seizure sensitive (SS) gerbils was more strongly detected than that in a seizure resistant (SR) group. The density of PLK immunoreactivity in a 30-min postictal group was significantly lower than that of a pre-seizure group. In a 12 h postictal group, PLK immunodensity recovered to pre-seizure level. The over-expression of PLK in the hippocampus of pre-seizure SS gerbils suggests that PLP play an important role in the modulation of GAD activity and GABA reuptake as mediated by membrane transporter via neurons.     

Bilateral Multifocal Intraocular Cysticercosis

A 47-year-old male from India was treated for the rare condition of bilateral multifocal intraocular infestation with Cysticercus cellulosae, the larval form of Taenia solium. The intravitreous parasite in the left eye was removed via pars plana vitrectomy. A subretinal cysticercus in the right eye, which caused a rhegmatogenous retinal detachment, was removed via sclerotomy during the scleral buckling procedure. An additional peripapillary subretinal cyst could not be removed. A subconjunctival cysticercus was incidently found and removed at the time of surgery. The patient returned to India six weeks after surgery and is doing well.