Changes in receptor response by the effect of disease on membrane fluidity

Currently, changes that occur in receptor function under (patho-) physiological conditions are being investigated. The molecular mechanisms causing the observed variations are largely unknown. It is suggested that the pivotal role of the fluidity of the membrane has been neglected in the literature. It is hypothesized that aberrations in receptor function in diseases that are associated with a concomitant mild oxidative stress can be explained by membrane wavering.     

Steroids decrease granulocyte membrane fluidity,while phorbol ester increases membrane fluidity

High concentrations of corticosteroids inhibit granulocyte responses and disrupt agonist receptor function. Dose-response and time-course considerations make it unlikely that these effects are mediated via the glucocorticoid receptor, a concept further supported by the ability of sex steroids to work similar effects. We postulated that steroids nonspecifically altered granulocyte membrane fluidity, which we measured directly by electron paramagnetic resonance. As predicted, methylprednisolone caused a dose-dependent increase in order parameter (decrease in fluidity) calculated on the basis of EPR spectra, using 5-doxylstearic acid (5-DS) as a probe of resting PMN membranes. This trend was highly significant (P < 0.001; P at 0.5 mg/ml < 0.01). Qualitatively similar results (but with different dose-response features) were obtained with conjugated estrogen. Granulocyte agonists (such as PMA) showed an opposite effect, which was not oxidatively mediated and which was steroid-inhibitable. 16-DS showed less prominent effects, suggesting that the membrane leaflets were more strongly affected than was the deep region of the membrane. Ibuprofen, which has similar effects to those of methylprednisolone on PMN aggregation and receptor function, caused a fluidizing rather than a stiffening of the membrane; this surprising result may indicate that there is a critical range of membrane fluidity for normal function, outside of which-in either direction-agonist receptor dysfunction occurs. We conclude that the immediate effects of very high doses of steroids are probably not mediated by corticoid receptors; instead, they may be due to changes in membrane fluidity.     

Age and membrane fluidity

Male rats aged 1, 9 and 19 months were used to study changes in membrane fluidity with age, employing the fluorescence polarization technique with 1,6-diphenyl-1,3,5-hexatriene (DPH) as the fluorescent probe. The intestinal microvillus membranes derived from the 19-month-old rats were found to possess lower fluidity than that observed with the membranes derived from the younger animals. The decrease in fluidity with age was also reflected in a corresponding increase in the gel-to-liquid crystalline transition temperature. Only small insignificant changes with age, were observed in the fluidity of the red blood cell membrane.     

硒对高脂血症大鼠红细胞膜流动性的影响

观察了由两种不同膳食脂肪所致的高脂血症大鼠在添加硒以后其红细胞膜荧光偏振度、血浆和肝脏丙二醛、血清总胆固醇、甘油三酯含量及血清谷胱甘肽过氧化物酶活性的变化。结果表明：补硒组大鼠红细胞膜荧光偏振度及血清谷胱甘肽过氧化物酶活性变化。     

Food restriction and membrane fluidity.

The fluidity of the erythrocyte membrane derived from growing rats raised under restricted food intake was found to be higher than the fluidity of the respective membranes from ad libitum fed animals. Considering the apparent relationship between the decrease in membrane fluidity and aging, the results point to the possible beneficial effects of food restriction at a young age.     

Hyperglycemia-induced alterations in synaptosomal membrane fluidity and activity of membrane bound enzymes: beneficial effect of N-acetylcysteine supplementation

Diabetic encephalopathy is characterized by impaired cognitive functions that appear to underlie neuronal damage triggered by glucose driven oxidative stress. Hyperglycemia-induced oxidative stress in diabetic brain may initiate structural and functional changes in synaptosomal membranes. The objective of the present study was to examine the neuroprotective role of N-acetylcysteine (NAC) in hyperglycemia-induced alterations in lipid composition and activity of membrane bound enzymes (Na⁺,K⁺-ATPase and Ca²⁺-ATPase) in the rodent model of type 1 diabetes. Male Wistar rats weighing between 180 and 200 g were rendered diabetic by a single injection of streptozotocin (50 mg/kg body weight, i.p.). The diabetic animals were administered NAC (1.4–1.5 g/kg body weight) for eight weeks and lipid composition along with membrane fluidity were determined. A significant increase in lipid peroxidation was observed in cerebral cortex of diabetic rats. NAC administration on the other hand lowered the hyperglycemia-induced lipid peroxidation to near control levels. The increased lipid peroxidation following chronic hyperglycemia was accompanied by a significant increase in the total lipids which can be attributed to increase in the levels of cholesterol, triglycerides and glycolipids. On the contrary phospholipid and ganglioside levels were decreased. Hyperglycemia-induced increase in cholesterol to phospholipid ratio reflected decrease in membrane fluidity. Fluorescence polarization (p) with DPH also confirmed decrease in synaptosomal membrane fluidity that influenced the activity of membrane bound enzymes. An inverse correlation was found between fluorescence polarization with the activities of Na⁺,K⁺-ATPase (r²=0.416, P<0.05) and Ca²⁺ ATPase (r²=0.604, P<0.05). NAC was found to significantly improve lipid composition, restore membrane fluidity and activity of membrane bound enzymes. Our results clearly suggest perturbations in lipid composition and membrane fluidity as a major factor in the development of diabetic encephalopathy. Furthermore, NAC administration ameliorated the effect of hyperglycemia on oxidative stress and alterations in lipid composition thereby restoring membrane fluidity and activity of membrane bound enzymes.     

Neurobehavioral consequences of prenatal antiepileptic drug exposure

Despite elevated rates of birth defects associated with prenatal antiepileptic drug exposure, pharmacotherapy is typically continued throughout pregnancy because of the risks posed to mother and child by recurrent seizures. Emerging data suggest that prenatal exposure to valproate or polytherapy may also be associated with increased risk of cognitive impairment. However, our understanding of the longer-term sequelae of prenatal antiepileptic drug exposure remains incomplete. Improved understanding of the neurobehavioral consequences of prenatal antiepileptic drug exposure is essential to ensure accurate information is available for women with epilepsy planning a pregnancy, and to achieve optimal outcomes for mothers and children.     

Protein-kinase C-dependent phosphorylation inhibits the effect of the antiepileptic drug topiramate on the persistent fraction of sodium currents

We investigated the interference of protein-kinase C (PKC)-dependent Na(+) channel phosphorylation on the inhibitory effect that the antiepileptic drug topiramate (TPM) has on persistent Na(+) currents (I(NaP)) by making whole cell patch-clamp and intracellular recordings of rat sensorimotor cortex neurons. The voltage-dependent activation of I(NaP) was significantly shifted in the hyperpolarizing direction when PKC was activated by 1-oleoyl-2-acetyl-sn-glycerol (OAG). TPM reduced the peak amplitude of I(NaP), but it did not counteract the OAG-induced shift in I(NaP) activation. Firing property experiments showed that the firing threshold was lowered by OAG. TPM was unable to counteract this effect, which may be due to OAG-dependent enhancement of the contribution of subthreshold I(NaP). These data suggest that PKC activation may limit the effect of the anticonvulsant TPM on the persistent fraction of Na(+) currents. The channel phosphorylation that may occur in cortical neurons as a result of physiological or pathological (e.g. epileptic) events can modulate the action of TPM on Na(+) currents.     

Macrophage phagocytosis and membrane fluidity in mice: the effect of age and dietary protein

Male C57BL/6NNia mice were used to investigate the effects of age and dietary protein intake on Fc and C3b receptor-mediated phagocytosis and on membrane fluidity. Six-month-old (adult) and 24-month-old (aged) mice were fed a 6% or 25% protein diet for 3, 5, or 6 weeks at which time thioglycollate elicited peritoneal macrophages were isolated. Both binding of IgG-coated sheep red blood cells to the macrophages and ingestion via the Fc-receptor were identical in all 4 groups after 3 and 6 weeks of feeding but were decreased at 5 weeks in the aged animals fed 6% protein. Phagocytosis via the C3b receptor was not depressed in either age group fed the low protein diet; it was, however, augmented significantly in the aged animals fed the 25% protein diet for 5 and 6 weeks. Membrane fluidity of the plasma membrane outer hemileaflet was monitored with an impermeant fluorescent probe. No changes were observed between adult and aged mice maintained up to 6 weeks on the diets.     

Effect of proteolipid protein on central nervous system myelin membrane fluidity

The effect which intrinsic (proteolipid) protein has on fluidity of central nervous system myelin membrane was measured through differences in temperature-dependent anisotropy of the lipid-soluble fluorescence probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), in multilamellar vesicles (MLV) prepared from total myelin lipids in the presence and absence of proteolipid protein. Very little difference was observed in the anisotropies of DPH incorporated into intact myelin membrane vesicles compared with MLV reconstituted from total myelin lipid plus proteolipid protein but excluding myelin basic protein. In contrast, a significant decrease (P less than 0.01) in anisotropy was observed when MLV prepared from total myelin lipids depleted of proteolipid protein were compared with vesicles containing proteolipid protein. Given the different distributions of myelin basic protein and proteolipid protein suggested by freeze-fracture, neutron and X-ray diffraction studies, and the fact that the hydrophobic DPH probe is known to distribute in the non-polar regions of lipid bilayers, we interpret the marked decrease in anisotropy when proteolipid protein is excluded from MLV to suggest that at least part of the proteolipid is distributed in the hydrocarbon region of the MLV. These findings are consistent with the earlier physical studies and recent postulations that extensive hydrophobic segments exist in proteolipid protein and that these hydrophobic segments are buried in the myelin lipid bilayer and alternate with hydrophilic extra-membrane segments.     

烧伤中分子物质对豚鼠心肌线粒体膜流动性影响的实验研究

本文应用从正常和烧伤豚鼠血中提取的中分子物质(NMMS,BMMS),以不同浓度干扰豚鼠心肌线粒体,观察中分子物质对线粒体膜流动性的影响。结果表明,NMMS和BMMS,尤其是BMMS在一定浓度下显著抑制膜流动性。作者认为,BMMS参与了烧伤后心泵功能障碍的病理机制。     

Evidence for epistatic interactions in antiepileptic drug resistance

To investigate the epistatic interactions involved in antiepileptic drug (AED) resistance, 26 coding single-nucleotide polymorphisms (SNPs) were selected from 16 candidate genes. A total of 200 patients with drug-resistant localization-related epilepsy and 200 patients with drug-responsive localization-related epilepsy were genotyped individually for the SNPs. Rather than using the traditional parametric statistical method, a new statistical method, multifactor dimensionality reduction (MDR), was used to determine whether gene-gene interactions increase the risk of AED resistance. The MDR method indicated that a combination of four SNPs (rs12658835 and rs35166395 from GABRA1, rs2228622 from EAAT3 and rs2304725 from GAT3) was the best model for predicting susceptibility to AED resistance with a statistically significant testing accuracy of 0.625 (P < 0.001) and cross-validation consistency of 10/10. This best model had an odds ratio of 3.68 with a significant 95% confidence interval of 2.32-5.85 (P < 0.0001). Our results may provide meaningful information on the mechanism underlying AED resistance and, to the best of our knowledge, this is the first report of evidence for gene-gene interactions underlying AED resistance.     

Erythrocyte membrane fluidity in type 1 diabetes mellitus

Erythrocyte membrane fluidity was determined in a group of type 1 diabetics in varying metabolic control. No difference in membrane fluidity, as measured by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, was found between cells from diabetic subjects. In addition, no difference was detected in membrane phospholipid and cholesterol content or the ratio of cholesterol to phospholipid in the diabetic subjects when compared to controls. The present study suggests that changes in erythrocyte membrane fluidity do not play a major role in the alterations of the physical properties of blood seen in type 1 diabetes mellitus.     

抗癫痫药妥泰对大鼠胚胎骨骼发育影响的研究

目的 研究妥泰(TPM)高、低剂量单药及与丙戊酸钠(VPA)合用对大鼠胚胎骨骼发育的影响。方法 采用妊娠雌性SD大鼠随机分为5组。实验组3组，于妊娠6～15d分别经口灌胃给予TPM40mg/kg，TPM80mg/kg和TPM40mg／kg VPA300mg／kg。阴性对照组同期经口灌胃给以等量的蒸馏水。阳性对照组于妊娠第11d一次性腹腔注射环磷酰胺(CP)10mg／kg于妊娠第20d处死孕鼠，将胎仔茜素红和阿利新蓝骨骼双染后，检查全身骨骼发育程度。结果 TPM高剂量组及与丙戊酸钠联合用组仔鼠骨骼发育迟缓，与阴性对照组相比有明显的差异。但TPM低剂量组无显著差异。结论 TPM在低剂量时对大鼠胚胎骨骼发育影响较小，而高剂量及与丙戊酸钠联合用药时影响较大。     

黄柏及其主要成分对细胞膜流动性的影响(英)

目的：观察具有免疫抑制作用的药物黄柏及其3种主要成分：小檗碱、药根碱与巴马汀对正常小鼠脾细胞膜流动性的影响。 方法： 以1，6－二苯基，1，3，5－己三烯（DPH）作为荧光探针，利用荧光偏振法测定脾细胞膜脂质区的流动性。 结果： 在无ConA刺激时，黄柏的水提物可提高小鼠脾细胞膜的流动性，6.25％的浓度与对照组相比有极显著性差异；小檗碱与药根碱可降低脾细胞膜的流动性，与对照组相比均有显著性差异；巴马汀可提高脾细胞膜的流动性，与对照组相比有极显著性差异。经ConA刺激后，黄柏的水提物、小檗碱、药根碱及巴马汀均可降低脾细胞膜流动性，与对照组相比有显著性差异。 结论： 上述结果提示这些药物的免疫抑制作用有可能是通过降低淋巴细胞膜的流动性来实现的。