Is the glucose-induced phosphate flush in pancreatic islets attributable to gating of volume-sensitive anion channels?

d-Glucose and other nutrient insulin secretagogues have long been known to induce a transient increase in inorganic phosphate release from pancreatic islets, a phenomenon currently referred to as a “phosphate flush”. The objective of this study was to explore the possible participation of volume-sensitive anion channels in such a process. Rat pancreatic islets were preincubated for 60 min in the presence of [³²P]orthophosphate and then perifused for 90 min to measure ³²P fractional outflow rate and insulin secretion. From minutes 46 to 70 inclusive either the concentration of d-glucose was increased from 1.1 to 8.3 mmol L⁻¹ or the extracellular osmolarity was decreased by reducing the NaCl concentration by 50 mmol L⁻¹. The increase in d-glucose concentration induced a typical phosphate flush and biphasic stimulation of insulin release. Extracellular hypoosmolarity caused a monophasic increase in both effluent radioactivity and␣insulin output. The inhibitor of volume-sensitive anion␣channels 5-nitro-2-(3-phenylpropylamino)benzoate (0.1 mmol L⁻¹) inhibited both stimulation of insulin release and phosphate flush induced by either the increase in d-glucose concentration or extracellular hypoosmolarity. It is proposed that gating of volume-sensitive anion channels accounts for the occurrence of the phosphate flush and subsequent stimulation of insulin secretion in response to either an increase in d-glucose concentration or a decrease in extracellular osmolarity.     

A case of thyroid hormone resistance: Prospective follow-up during pregnancy and obstetric outcome

We describe the case of a patient with resistance to thyroid hormone (R243W substitution) and her obstetric outcome. The patient gave birth to a healthy girl, unaffected by the R243W mutation. Two years later, following an uneventful pregnancy, a baby boy was born at term; he presented the same thyroid hormone receptor mutation as his mother. Follow-up of gestational thyroid hormone levels is reported during both pregnancies and related to obstetric outcome.     

Protective effect of prion protein via the N-terminal region in mediating a protective effect on paraquat-induced oxidative injury in neuronal cells

Transmissible spongiform encephalopathies are a group of neurodegenerative disorders caused by a posttranslational, conformational change in the cellular isoform of the prion protein (PrP(C)) into an infectious, disease-associated form (PrP(Sc)). Increasing evidence supports a role for PrP(C) in the cellular response to oxidative stress. We investigated the effect of oxidative stress mediated by paraquat exposure on SH-SY5Y neuroblastoma cells. A loss of mitochondrial membrane potential and subsequent reduction in ATP production were demonstrated in untransfected SH-SY5Y cells, an effect that was ameliorated by the expression of PrP(C). Cells expressing either PrP-DeltaOct, which lacks the octapeptide repeats, or PrP-DA, in which the N-terminus is tethered to the membrane, showed increased sensitivity to paraquat compared with cells expressing wild-type PrP(C) as shown by reduced viability, loss of their membrane integrity, and reduced mitochondrial bioenergetic measurements. Exposure of prion-infected mouse SMB15S cells to paraquat resulted in a reduction in viability to levels similar to those seen in the untransfected SH-SY5Y cells. However, "curing" the cells with pentosan sulfate restored the viability to the level observed in the SH-SY5Y cells expressing PrP(C). These data would indicate that the molecular mechanism promoting cellular resistance to oxidative stress had been compromised in the infected SMB15S cells, which could be reinstated upon curing. Our study supports the hypothesis that PrP(C) expression protects cells against paraquat-induced oxidative injury, demonstrates the significance of the N-terminal region of the protein in mediating this protective effect, and also shows that the biochemical consequences of prion infection may be reversed with therapeutic intervention.     

In vitro resistance of articular chondrocytes to 5-Aminolevulinic acid based photodynamic therapy

OBJECTIVE: 5-Aminolevulinic acid based photodynamic therapy (5-ALA-PDT) has revealed promising results in the treatment of inflammatory joint diseases due to the sensitivity of inflamed synovial tissue. For 5-ALA-PDT to be safe and beneficial for intra-articular applications, resistance of chondrocytes is essential to prevent cartilage damage. As no data yet exist, the aim of the present study was to assess in vitro the response of the chondrocytes to 5-ALA-PDT and to compare with osteoblasts and synovial tissue derived cells. METHODS: Bovine articular chondrocytes, osteoblasts, and synovial cells were subjected to 5-ALA-PDT in cell culture. The PpIX accumulation and the function of the cells were assessed for up to 12 days. RESULTS: Bovine chondrocytes showed lower PpIX fluorescence upon incubation with 5-ALA (0.0-2.0 mM) for 4 hours as compared to osteoblasts and synovial cells suggesting a low PpIX accumulation. After incubation with 0.5 mM 5-ALA and application of light at a dose of 20 J/cm2, chondrocytes were functionally not affected (collagen type II and aggrecan mRNA, glycosaminoglycan synthesis) whereas a decrease in the proportion of viable cells was observed in osteoblasts and synovial cells (2+/-2% and 14+/-8%, respectively; chondrocytes 91+/-13%). Chondrocytes showed a 58% reduction of 5-ALA uptake using [3H]5-ALA as compared to osteoblasts and a lower mitochondrial content as assessed by the activity of the mitochondrial marker enzyme citrate synthase (9.2+/- 3.6 mU/mg protein) than osteoblasts (32.6+/-10.5 mU/mg) and synovial cells (60.0+/-10.8 mU/mg). The reduced uptake of 5-ALA and/or the low mitochondrial content, an adaptation to their in vivo environment and the site of PpIX synthesis, presumably explains the lower PpIX content in chondrocytes and their resistance against 5-ALA-PDT. CONCLUSION: 5-ALA-PDT might represent a treatment strategy in inflammatory joint diseases without endangering the cartilage function. However, further in vitro and in vivo experiments are required to confirm this data in the authentic environment of chondrocytes, the articular cartilage.     

Facial porokeratosis: A series of six patients

Porokeratosis is a disorder of epidermal keratinization characterized by annular plaques with an atrophic centre and hyperkeratotic edges, and includes a heterogeneous group of disorders that are mostly inherited in an autosomal dominant fashion. Facial porokeratosis is rare and is not well documented. We present six cases of facial porokeratosis seen over a period of 15 years in a hospital in Lima, Peru. In most of the cases, porokeratosis was found in younger women without any significant past medical history. Oral isotretinoin showed moderate improvement in two of our patients.     

Conduct disorder symptoms and subsequent pregnancy, child-birth and abortion: A population-based longitudinal study of adolescents

Research on teenage pregnancy and abortion has primarily focused on socio-economic disadvantage. However, a few studies suggest that risk of unwanted pregnancy is related to conduct disorder symptoms. We examined the relationship between level of conduct disorder symptoms at age 15 and subsequent pregnancy, child-birth and abortion. A population-based, representative sample of Norwegian adolescent girls (N = 769) was followed from early adolescence until their mid-20s. Even with control for socio-demographic and family variables, conduct disorder symptoms at age 15 were strongly associated with pregnancy in the 15–19 age group, and a weaker association persisted in the 20–28 age group. Similar results were obtained for abortions, but here a strong relationship with conduct disorder symptoms was found even after age 20. After adjustment, no significant association between conduct disorder symptoms and subsequent child-birth was observed. More targeted preventive programmes aimed at girls with conduct disorder symptoms may be warranted.