A new model system for lipid interactions in stratum corneum vesicles: effects of lipid composition, calcium, and pH

We prepared large unilamellar vesicles (LUVs) with three different stratum corneum lipid compositions: constant amounts of ceramides (55 wt %) and fatty acids (15%) with varying amounts of cholesterol sulfate (0-15%) and cholesterol (15-30%). One of the compositions served as a model for normal stratum corneum, while the second one served as a model for recessive X-linked ichthyosis stratum corneum. The third composition consisted of no cholesterol sulfate. Intervesicle lipid interactions in these LUVs were monitored by fluorescence methods for content leakage, and contents mixing at pH 9, in the absence and presence of Ca2+, and at pH 6. Since the content leakage and contents mixing assays were originally developed for phospholipid vesicles, we characterized the probe binding and the probe quenching properties for stratum corneum LUV systems, and modified the assays slightly accordingly. The time-dependent fluorescence intensity changes in the probe-containing LUVs at pH 9 and 6 and in response to the addition of calcium were monitored. Our results demonstrated that all three types of LUVs were relatively stable at pH 9. Addition of Ca2+ or decreasing the pH to 6 activated intervesicle lipid mixing followed by vesicle fusion and lysis. We found that the LUVs with no cholesterol sulfate and 30% cholesterol exhibited a more extensive Ca2+- or low-pH-activated intervesicle lipid interaction than LUVs with either 5% cholesterol sulfate and 25% cholesterol or 15% cholesterol sulfate and 15% cholesterol. These results suggest that fusogenic agents such as Ca2+ and H+ act to neutralize the fatty acids in the lipid bilayer of stratum corneum vesicles. The inclusion of 5-15% cholesterol sulfate helps to prevent the collapse of fused vesicles into other structures.     

Interactions of the alpha-spectrin N-terminal region with beta-spectrin. Implications for the spectrin tetramerization reaction

Spectrin of the erythrocyte membrane skeleton is composed of alpha- and beta-spectrin, which associate to form heterodimers and tetramers. It has been suggested that a fractional domain (helix C) in the amino-terminal region of alpha-spectrin (Nalpha region) bundles with another fractional domain in the carboxyl-terminal region of beta-spectrin (Cbeta region) to yield a triple alpha-helical bundle and that this helical bundling is largely responsible for tetramer formation. However, there are certain objections to assigning a preeminent role to this helical bundling in the tetramerization reactions. We prepared several recombinant peptides of alpha-spectrin fragments spanning only the Nalpha region (lacking the dimer nucleation site) and quantitatively studied their interaction with beta-spectrin. We found that a majority of the interactions were localized, as expected, in the Nalpha-helix C region but that there was also some contribution from the nonhomologous region. More importantly, the temperature and ionic strength dependence of this interaction in our model peptides was different from that in intact spectrin. We suggest that, although the regions involving the putative helical bundling in alpha- and beta-spectrin undoubtedly play a significant role in tetramerization, regions distal to the Nalpha-helix C region in spectrin are also involved in tetramer formation. Structural flexibility and lateral interactions may play a role in spectrin tetramerization.     

Ribonuclease A variants with potent cytotoxic activity

Select members of the bovine pancreatic ribonuclease A (RNase A) superfamily are potent cytotoxins. These cytotoxic ribonucleases enter the cytosol, where they degrade cellular RNA and cause cell death. Ribonuclease inhibitor (RI), a cytosolic protein, binds to members of the RNase A superfamily with inhibition constants that span 10 orders of magnitude. Here, we show that the affinity of a ribonuclease for RI plays an integral role in defining the potency of a cytotoxic ribonuclease. RNase A is not cytotoxic and binds RI with high affinity. Onconase, a cytotoxic RNase A homolog, binds RI with low affinity. To disrupt the RI-RNase A interaction, three RNase A residues (Asp-38, Gly-88, and Ala-109) that form multiple contacts with RI were replaced with arginine. Replacing Asp-38 and Ala-109 with an arginine residue has no effect on the RI-RNase interaction. In addition, these variants are not cytotoxic. In contrast, replacing Gly-88 with an arginine residue yields a ribonuclease (G88R RNase A) that retains catalytic activity in the presence of RI and is cytotoxic to a transformed cell line. Replacing Gly-88 with aspartate also yields a ribonuclease (G88D RNase A) with a decreased affinity for RI and cytotoxic activity. The cytotoxic potency of onconase, G88R RNase A, and G88D RNase A correlate with RI evasion. We conclude that ribonucleases that retain catalytic activity in the presence of RI are cytotoxins. This finding portends the development of a class of chemotherapeutic agents based on pancreatic ribonucleases.     

Dietary conjugated linoleic acid normalizes impaired glucose tolerance in the Zucker diabetic fatty fa/fa rat

Conjugated linoleic acid (CLA) is a naturally occurring fatty acid which has anti-carcinogenic and anti-atherogenic properties. CLA activates PPAR alpha in liver, and shares functional similarities to ligands of PPAR gamma, the thiazolidinediones, which are potent insulin sensitizers. We provide the first evidence that CLA is able to normalize impaired glucose tolerance and improve hyperinsulinemia in the pre-diabetic ZDF rat. Additionally, dietary CLA increased steady state levels of aP2 mRNA in adipose tissue of fatty ZDF rats compared to controls, consistent with activation of PPAR gamma. The insulin sensitizing effects of CLA are due, at least in part, to activation of PPAR gamma since increasing levels of CLA induced a dose-dependent transactivation of PPAR gamma in CV-1 cells cotransfected with PPAR gamma and PPRE X 3-luciferase reporter construct. CLA effects on glucose tolerance and glucose homeostasis indicate that dietary CLA may prove to be an important therapy for the prevention and treatment of NIDDM.     

Scoliosis circa 2000: radiologic imaging perspective. II. Treatment and follow-up

Plain film imaging remains important for the diagnosis and surveillance of scoliosis, as well as for the detection of complications after surgery. New means of treating scoliosis have become established and should be understood by the radiologist. To the well-known postoperative complications, including pneumothorax, pneumonia, and gastrointestinal obstruction, are added new specific potential problems with the new surgical methodology.