The role of APP proteolytic processing in lipid metabolism

Amyloid plaques in brains are one of the major pathological hallmarks of Alzheimer's disease (AD). These plaques are mainly formed by aggregated Aβ, generated by proteolytic cleavage of the amyloid precursor protein (APP). Therefore, APP processing and Aβ production have been one of the central scopes in AD research in the past. Now, accumulating evidence suggests that besides its pathological impact, APP and its cleavage products also contribute to physiological functions. Proteolytic cleavage of APP is tightly regulated, and several lipids such as cholesterol and sphingolipids have been shown to influence APP processing and Aβ generation. In turn, Aβ as well as other APP cleavage products plays an essential role in regulating lipid homeostasis arguing for complex regulatory cycles in which lipids control APP processing and vice versa. This balanced regulation is disrupted under pathological conditions such as in AD. This article will review the physiological function of APP and its proteolytic products, especially Aβ and AICD, in regulating lipid homeostasis and which lipid species modulate APP processing. Furthermore, we summarize the alterations in lipid metabolism observed in AD patients and AD mouse models.     

Unexpected T‐cell recognition of an altered peptide ligand is driven by reversed thermodynamics

The molecular basis underlying T‐cell recognition of MHC molecules presenting altered peptide ligands is still not well–established. A hierarchy of T‐cell activation by MHC class I‐restricted altered peptide ligands has been defined using the T‐cell receptor P14 specific for H‐2D^b in complex with the immunodominant lymphocytic choriomeningitis virus peptide gp33 (KAVYNFATM). While substitution of tyrosine to phenylalanine (Y4F) or serine (Y4S) abolished recognition by P14, the TCR unexpectedly recognized H‐2D^b in complex with the alanine‐substituted semiagonist Y4A, which displayed the most significant structural modification. The observed functional hierarchy gp33 > Y4A > Y4S = Y4F was neither due to higher stabilization capacity nor to differences in structural conformation. However, thermodynamic analysis demonstrated that while recognition of the full agonist H‐2D^b/gp33 was strictly enthalpy driven, recognition of the weak agonist H‐2D^b/Y4A was instead entropy driven with a large reduction in the favorable enthalpy term. The fourfold larger negative heat capacity derived for the interaction of P14 with H‐2D^b/gp33 compared with H‐2D^b/Y4A can possibly be explained by higher water entrapment at the TCR/MHC interface, which is also consistent with the measured opposite entropy contributions for the interactions of P14 with both MHCs. In conclusion, this study demonstrates that P14 makes use of different strategies to adapt to structural modifications in the MHC/peptide complex.     

Rituximab treatment for recurrence of nephrotic syndrome in a pediatric patient after renal transplantation for congenital nephrotic syndrome of Finnish type

Congenital nephrotic syndrome (CNS) of the Finnish type due to mutation in the NPHS-1 gene results in massive proteinuria due to structural abnormality in the glomerular slit diaphragm, and is usually refractory to immunosuppressive therapy. Patients eventually require bilateral nephrectomy and renal replacement therapy, with transplantation being the ultimate goal. Post-transplant recurrence of nephrotic syndrome occurs in about 25% of children and is thought to be immune-mediated secondary to antibodies formed against the nephrin protein in renal allograft. Conventional therapy with calcineurin inhibitors (CNI), cyclophosphamide and corticosteroids with or without plasmapheresis often fails to achieve remission resulting in graft loss in 12-16%. There is limited experience with use of rituximab (RTX) in pediatric organ transplant recipients. We report the first case of post-transplant recurrence of nephrotic syndrome in a 4-yr-old child with CNS due to NPHS-1 mutation in whom CNI, corticosteroid and cyclophosphamide therapy was unsuccessful, but who achieved remission after depletion of B cells with RTX, associated with a decrease in the level of anti-nephrin antibodies. The child remains in remission 5 yr following treatment. Our experience suggests that activated B cells may play a pivotal role in the recurrence of nephrosis after renal transplantation in children with CNS.     

Differentiation of heroin and cocaine using dual-energy CT—an experimental study

Objective

To evaluate if heroin and cocaine can be distinguished using dual-energy CT.

Materials and methods

Twenty samples of heroin and cocaine at different concentrations and standardized compression (SC) were scanned in dual-energy mode on a newest generation Dual Energy 64-row MDCT scanner. CT number, spectral graphs, and dual-energy index (DEI) were evaluated. Results were prospectively tested on six original samples from a body packer. Wilcoxon’s test was used for statistical evaluation.

Results

Values are given as median and range. Under SC, the CT number of cocaine samples (?29.87 Hounsfield unit (HU) [?125.85; 16.16 HU]) was higher than the CT number of heroin samples (?184.37 HU [?199.81; ?159.25 HU]; p?<?0.01). Slope of spectral curves for cocaine was ?2.36 HU/keV [?7.15; ?0.67 HU/keV], and for heroin, 1.75 HU/keV [1.28; 2.5 HU/keV] (p?<?0.01). DEI was 0.0352 [0.0081; 0.0528] for cocaine and significantly higher than for heroin samples (?0.0127 [?0.0097; ?0.0159]; p?<?0.001). While CT number was inconclusive, all six original packs were correctly classified after evaluation of the spectral curve and DEI. In contrast to the CT number, slope of the spectral curve and DEI were independent of concentration and compression.

Conclusion

The slope of the spectral curve and the DEI from dual-energy CT data can be used to distinguish heroin and cocaine in vitro; these results are independent of compression and concentration in the measured range.     

Diagnostic and therapeutic use of membrane proteins in cancer cells

As proteomics technologies develop, increasing number of membrane-associated proteins specific for cancer cells are being discovered. These proteins are of great interest, particularly because they are rich in targets for antibodies. Amongst them candidate biomarkers for early tumor diagnosis, prognosis and treatment have been detected. The suitability of several membrane-associated proteins as targets for drugs or antibodies has already been tested in preclinical and clinical studies. The results were encouraging in some cases, but not in all. They demonstrate that each type of tumor has its specific "Achilles heel", and that suitable targets of cancer diagnosis and therapy must be found for each kind of neoplasm. This implies that membrane-associated proteins for each type of tumor cell need to be investigated. This review describes the current technologies of membrane protein characterization in a first part and subsequently summarizes the membrane associated proteins currently being tested as targets for diagnosis and treatment in breast, prostate, thyroid, and colon cancer. Their function will be explained and their role in tumor biology will be discussed.     

Genotype–phenotype studies in infantile spinal muscular atrophy (SMA) type I in Germany: implications for clinical trials and genetic counselling

We reviewed the natural history and assessed the SMN2 copy number of 66 patients with infantile spinal muscular atrophy (SMA) type I born between 2000 and 2005 in Germany whose diagnosis was confirmed by a homozygous SMN1 deletion in the first 6 months of life. After excluding patients who had received valproic acid, the median/mean age at disease endpoint was 6.1/7.3 months (range 0.0–34.0). Four (6.1%) patients with one SMN2 copy had severe SMA type '0' with joint contractures and respiratory distress from birth. Median/mean age at onset (months) in 57 (86.3%) patients with two SMN2 copies was 1.2/1.3, and 3.5/3.4 in 5 (7.6%) patients with three SMN2 copies. Median/mean age at disease endpoint was 6.5/7.8 months (range 0.5–30) in patients with two SMN2 copies. All patients with three SMN2 copies were still alive at 10–55 months, two of them under permanent ventilation. Our data are relevant for prognostication and genetic counselling. The observed clinical variability, especially in the group with two SMN2 copies, might be important for clinical trials in SMA I where a possible control group could be defined as follows: age at onset within 4–5 months, age at genetic diagnosis <6 months, two SMN2 copies present, head control in less than 10%, no respiratory distress from birth, disease endpoint either age at death or age at permanent ventilation.     

Effects of systemic or nucleus accumbens-directed dopamine D1 receptor antagonism on sucrose seeking in rats

Rationale  

Conditioned cues can elicit relapse to drug- and food-seeking behavior over prolonged periods of abstinence. If seeking behavior depends on mesolimbic dopamine D1 receptors, blocking these receptors should reduce seeking behavior.     

Absorption, excretion, and metabolism of a potential GABA-A α2/3 receptor modulator in rats

4-Amino-8-(2,5-dimethoxyphenyl)-N-propylcinnoline-3-carboxamide (AZD6280) is a selective GABA-A(α2/3) receptor modulator under development for the treatment of generalized anxiety disorders. Absorption, metabolism, and excretion of [(14)C]-AZD6280 was studied in rats following a single oral (7 mg/kg) or intravenous (i.v., 1 mg/kg) administration of [(14)C]-AZD6280. The results from the bile duct-cannulated study revealed that AZD6280 was well-absorbed in rats. The pharmacokinetic analysis was conducted using unlabelled parent drug that was rapidly absorbed (plasma T(max) ~1 h) and exhibited a mean apparent terminal half-life of ~4.2 h. The overall mean recoveries in the excreta were 98.6% and 100.3% after oral and i.v. administration of [(14)C]-AZD6280, respectively. The major route for elimination of [(14)C]-AZD6280 and its metabolites was through faeces. The radiochromatographic analysis of the excreta demonstrated that AZD6280 underwent extensive biotransformation. A total of 28 metabolites of AZD6280 were detected and profiled in urine, bile, and faeces in this study. The structures of metabolites were elucidated by high-resolution tandem mass spectrometry. Similar metabolite profiles were observed in rats given AZD6280 orally or intravenously.