Andreas Wolfram Henkel

Neurochemical diagnosis of Alzheimer’s dementia by CSF Aβ42, Aβ42/Aβ40 ratio and total tau

Cerebrospinal fluid (CSF) concentrations of amyloid β peptides ending at positions 42 and 40 (Aβ42 and Aβ40, respectively), and total tau (tTau) protein were measured by ELISA in order to compare their accuracy in discriminating patients with Alzheimer’s disease (AD, n=22), non-Alzheimer dementia (nAD, n=11) and control subjects (CON, n=35). As compared to the other groups, the concentrations of Aβ42 and tTau were decreased (P<0.001) and increased (P<0.001) in AD, respectively, while Aβ40 did not differ significantly among the groups. Receiver operating characteristic (ROC) analysis was performed to define cut-off values for maximized sensitivity and specificity. For all groups compared the Aβ peptide ratio 42/40 classified more patients correctly, as compared to the concentration of Aβ42 alone: AD versus controls, 94 and 86.7%; AD versus nAD, 90 and 85% and AD versus nAD plus controls, 90.8 and 87%, respectively. The percentage of correctly classified patients was further improved when the Aβ ratio was combined with the analysis of the tTau concentration. Presence of the apolipoprotein E e4 allele, age or degree of mental disability did not significantly influence the parameters studied.

Structural Basis for Guanine Nucleotide Exchange on Ran by the Regulator of Chromosome Condensation (RCC1)

RCC1 (regulator of chromosome condensation), a beta propeller chromatin-bound protein, is the guanine nucleotide exchange factor (GEF) for the nuclear GTP binding protein Ran. We report here the 1.8 A crystal structure of a Ran*RCC1 complex in the absence of nucleotide, an intermediate in the multistep GEF reaction. In contrast to previous structures, the phosphate binding region of the nucleotide binding site is perturbed only marginally, possibly due to the presence of a polyvalent anion in the P loop. Biochemical experiments show that a sulfate ion stabilizes the Ran*RCC1 complex and inhibits dissociation by guanine nucleotides. Based on the available structural and biochemical evidence, we present a unified scenario for the GEF mechanism where interaction of the P loop lysine with an acidic residue is a crucial element for the overall reaction.

Fast steps in exocytosis and endocytosis studied by capacitance measurements in endocrine cells

The past year has witnessed progress in identifying late steps in exocytosis that are so short-lived as to be difficult to study biochemically. Recent studies have also revealed a novel and surprisingly fast mechanism of endocytosis that may be triggered by a rise in the intracellular concentration of Ca2+ and that retrieves exocytosed membrane in seconds.

High activity of acid sphingomyelinase in major depression

Summary.Acid sphingomyelinase (A-SMase) and its reaction product ceramide may play a role in the pathophysiology of depressive disorders and in the therapeutic action of antidepressive drugs. In a prospective case-control study, A-SMase activity was measured in peripheral blood mononuclear cells of 17 patients with a major depressive episode who were free of antidepressant drug therapy for at least 10 days and 8 healthy volunteers. In the patient group, A-SMase activity was correlated to the score (n = 17, r = 0.64, P = 0.005). The patient group exhibited higher A-SMase activity compared to healthy volunteers (T = 2.09, df = 21.33, P<0.05). In addition, we demonstrate that the antidepressants imipramine and amitriptyline induce a long-term reduction of the activity of A-SMase in cultured cells.

Blue light improves cognitive performance

SummaryA newly discovered system of photoreceptors for circadian rhythms works non-visual and responds to blue light (460 nm). We report a longitudinal study in 44 adults, showing that a significant increase in alertness and speed of information processing could be achieved by blue light as compared to normal light.

Rhythmic opening and closing of vesicles during constitutive exo‐ and endocytosis in chromaffin cells

Constitutive exo‐ and endocytic events are expected to increase and diminish the cell surface area in small spontaneous steps. Indeed, cell‐attached patch–clamp measurements in resting chromaffin cells revealed spontaneous upward and downward steps in the electrical capacitance of the plasma membrane. The most frequent step size indicated cell surface changes of <0.04 μm2, corresponding to vesicles of <110 nm diameter. Often downward steps followed upward steps within seconds, and vice versa, as if vesicles transiently opened and closed their lumen to the external space. Transient openings and closings sometimes alternated rhythmically for tens of seconds. The kinase inhibitor staurosporine dramatically increased the occurrence of such rhythmic episodes by making vesicle closure incomplete and by inhibiting fission. Staurosporine also promoted transient closures of large endocytic vesicles possibly representing remnants of secretory granules. We suggest that staurosporine blocks a late step in the endocytosis of both small and large vesicles, and that endocytosis involves a reaction cascade that can act as a chemical oscillator.

Mechanisms of α-latrotoxin actin

Abstract The major component of black widow spider venom, α-latrotoxin, triggers massive exocytosis in a variety of neurosecretory cells. An important trigger for exocytosis is the calcium influx via α-latrotoxin-induced channels in biological membranes. However, this mechanism fails to explain exocytosis which occurred in the complete absence of extracellular calcium. Recently, sophisticated biochemical and molecular techniques have led to the discovery of novel α-latrotoxin-binding membrane receptors: neurexins and latrophilin/CIRL (calcium-independent receptor for α-latrotoxin). Neurexins are single transmembrane proteins which bind to α-latrotoxin in a calcium-dependent manner and also interact with the synaptic vesicle protein, synaptotagmin. On the other hand, latrophilin is a seven-transmembrane protein and belongs to the family of G-protein-coupled receptors. The multitude of effects of α-latrotoxin on exocytosis in different cell systems and the nature of its membrane targets are discussed in this article. The molecular details of how α-latrotoxin binding is transduced eventually to exocytosis remain to be elucidated.

The role of ceramide in major depressive disorder

Major depression is a severe mood disorder with a lifetime prevalence of more than 10%. The pharmacokinetic hypothesis claims that a slow accumulation of antidepressant drugs by acid trapping mainly into lysosomes is responsible for the therapeutic latency and that a lysosomal target mediates the antidepressant effects. The lysosomal lipid metabolizing enzyme acid sphingomyelinase (ASM) cleaves sphingomyelin into ceramide and phosphorylcholine. In a pilot study, the activity of this enzyme was increased in peripheral blood cells of patients with major depressive disorder (MDD), making the ASM an interesting molecular target of antidepressant drugs. Indeed, several antidepressant drugs functionally inhibit ASM. The ASM/ceramide pathway might be a missing link unifying independent findings in neurobiology and the treatment of MDD such as therapeutic latency, oxidative stress, immune activation and increased risk of cardiovascular disease.

Lipophilic cationic drugs increase the permeability of lysosomal membranes in a cell culture system

Lysosomes accumulate many drugs several fold higher compared to their extracellular concentration. This mechanism is believed to be responsible for many pharmacological effects. So far, uptake and release kinetics are largely unknown and interactions between concomitantly administered drugs often provoke mutual interference. In this study, we addressed these questions in a cell culture model. The molecular mechanism for lysosomal uptake kinetics was analyzed by live cell fluorescence microscopy in SY5Y cells using four drugs (amantadine, amitriptyline, cinnarizine, flavoxate) with different physicochemical properties. Drugs with higher lipophilicity accumulated more extensively within lysosomes, whereas a higher pKa value was associated with a more rapid uptake. The drug‐induced displacement of LysoTracker was neither caused by elevation of intra‐lysosomal pH, nor by increased lysosomal volume. We extended our previously developed numerical single cell model by introducing a dynamic feedback mechanism. The empirical data were in good agreement with the results obtained from the numerical model. The experimental data and results from the numerical model lead to the conclusion that intra‐lysosomal accumulation of lipophilic xenobiotics enhances lysosomal membrane permeability. Manipulation of lysosomal membrane permeability might be useful to overcome, for example, multi‐drug resistance by altering subcellular drug distribution. J. Cell. Physiol. 224:152–164, 2010

Use-Dependent Inhibition of Synaptic Transmission by the Secretion of Intravesicularly Accumulated Antipsychotic Drugs

Antipsychotic drugs are effective for the treatment of schizophrenia. However, the functional consequences and subcellular sites of their accumulation in nervous tissue have remained elusive. Here, we investigated the role of the weak-base antipsychotics haloperidol, chlorpromazine, clozapine, and risperidone in synaptic vesicle recycling. Using multiple live-cell microscopic approaches and electron microscopy of rat hippocampal neurons as well as in vivo microdialysis experiments in chronically treated rats, we demonstrate the accumulation of the antipsychotic drugs in synaptic vesicles and their release upon neuronal activity, leading to a significant increase in extracellular drug concentrations. The secreted drugs exerted an autoinhibitory effect on vesicular exocytosis, which was promoted by the inhibition of voltage-gated sodium channels and depended on the stimulation intensity. Taken together, these results indicate that accumulated antipsychotic drugs recycle with synaptic vesicles and have a use-dependent, autoinhibitory effect on synaptic transmission.