Staining of cerebral amyloid plaque glycoproteins in patients with Alzheimer's disease with the microglia-specific lectin from mistletoe

In Vitro Methodologies to Study the Role of Advanced Glycation End Products (AGEs) in Neurodegeneration

Advanced glycation end products (AGEs) can be present in food or be endogenously produced in biological systems. Their formation has been associated with chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. The implication of AGEs in neurodegeneration is related to their ability to bind to AGE-specific receptors and the ability of their precursors to induce the so-called “dicarbonyl stress”, resulting in cross-linking and protein damage. However, the mode of action underlying their role in neurodegeneration remains unclear. While some research has been carried out in observational clinical studies, further in vitro studies may help elucidate these underlying modes of action. This review presents and discusses in vitro methodologies used in research on the potential role of AGEs in neuroinflammation and neurodegeneration. The overview reveals the main concepts linking AGEs to neurodegeneration, the current findings, and the available and advisable in vitro models to study their role. Moreover, the major questions regarding the role of AGEs in neurodegenerative diseases and the challenges and discrepancies in the research field are discussed.

Loranthus ferrugineus: a Mistletoe from Traditional Uses to Laboratory Bench

Objectives:

Loranthus ferrugineus (L. ferrugineus) from Loranthaceae, a mistletoe, is a medicinal herb used for a variety of human ailments. Traditionally, decoctions of this parasitic shrub have been mainly used to treat high blood pressure (BP) and gastrointestinal complaints; usage which is supported by experimental based pharmacological investigations. Nonetheless, there is still limited data available evaluating this plant’s traditions, and few studies have been scientifically translated toward evidence based phytomedicine. We therefore provide a concise review of the currently available L. ferrugineus literature and discuss potential directions for future areas of investigation.

Methods:

We surveyed available literature covering ethnopharmacological usage of L. ferrugineus and discussed relevant findings, including important future directions and shortcomings for the medicinal values of this parasitic shrub.

Results:

Evidence based pharmacological approaches significantly covered the medicinal application of L. ferrugineus for hypertension and gastrointestinal complaint management, with a particular focus on the active hydrophilic extract of this herb.

Conclusion:

Understanding the sites of action of this plant and its beneficial effects will provide justification for its use in old traditional treatments, and potentially lead to the development of therapies. Other medicinal applicative areas of this parasitic shrub, such as wound healing, gerontological effects, and antiviral and anticancer activities, are yet to be researched.

Induction of neuronal death by microglial AGE-albumin: implications for Alzheimer's disease

Advanced glycation end products (AGEs) have long been considered as potent molecules promoting neuronal cell death and contributing to neurodegenerative disorders such as Alzheimer’s disease (AD). In this study, we demonstrate that AGE-albumin, the most abundant AGE product in human AD brains, is synthesized in activated microglial cells and secreted into the extracellular space. The rate of AGE-albumin synthesis in human microglial cells is markedly increased by amyloid-β exposure and oxidative stress. Exogenous AGE-albumin upregulates the receptor protein for AGE (RAGE) and augments calcium influx, leading to apoptosis of human primary neurons. In animal experiments, soluble RAGE (sRAGE), pyridoxamine or ALT-711 prevented Aβ-induced neuronal death in rat brains. Collectively, these results provide evidence for a new mechanism by which microglial cells promote death of neuronal cells through synthesis and secretion of AGE-albumin, thereby likely contributing to neurodegenerative diseases such as AD.

Activated microglial cells synthesize and secrete AGE-albumin

A holy grail of curing neurodegenerative diseases is to identify the main causes and mechanisms underlying neuronal death. Many studies have sought to identify these targets in a wide variety of ways, but a more important task is to identify critical molecular targets and their origins. Potential molecular targets include advanced glycation end products (AGEs) that can promote neuronal cell death, thereby contributing to neurodegenerative disorders such as Alzheimer disease or Parkinson disease. In this study, we showed that AGE-albumin (glycated albumin) is synthesized in microglial cells and secreted in the human brain. Our results provide new insight into which microglial cells can promote the receptor for AGE-mediated neuronal cell death, eventually leading to neurodegenerative diseases.

Tau-66: evidence for a novel tau conformation in Alzheimer's disease

We have characterized a novel monoclonal antibody, Tau-66, raised against recombinant human tau. Immunohistochemistry using Tau-66 reveals a somatic-neuronal stain in the superior temporal gyrus (STG) that is more intense in Alzheimer's disease (AD) brain than in normal brain. In hippocampus, Tau-66 yields a pattern similar to STG, except that neurofibrillary lesions are preferentially stained if present. In mild AD cases, Tau-66 stains plaques lacking obvious dystrophic neurites (termed herein 'diffuse reticulated plaques') in STG and the hippocampus. Enzyme-linked immunosorbent assay (ELISA) analysis reveals that Tau-66 is specific for tau, as there is no cross-reactivity with MAP2, tubulin, Abeta(1-40), or Abeta(1-42), although Tau-66 fails to react with tau or any other polypeptide on western blots. The epitope of Tau-66, as assessed by ELISA testing of tau deletion mutants, appears discontinuous, requiring residues 155-244 and 305-314. Tau-66 reactivity exhibits buffer and temperature sensitivity in an ELISA format and is readily abolished by SDS treatment. Taken together these lines of evidence indicate that the Tau-66 epitope is conformation-dependent, perhaps involving a close interaction of the proline-rich and the third microtubule-binding regions. This is the first indication that tau can undergo this novel folding event and that this conformation of tau is involved in AD pathology.

Ligands for Viscum album agglutinin and galectin-1 in human lung cancer: is there any prognostic relevance?

Viscum album agglutinin (VAA) is an extract component of mistletoe. It belongs to the plant lectin family and exerts various biological effects such as cytotoxic properties for tumor cells in culture. VAA as well as galectin-1, an endogenous lectin, possess galactose-specific surface-binding sites. We therefore investigated 159 cases of lung cancer for their capacity to bind VAA and galectin-1 and for Lewis antigen reactivity. Three different methods were used for detection of VAA: a two-step method with biotinylated VAA; an immune complex three-step method, and a four-step method. The most sensitive results were obtained with the four-step method utilising VAA, a goat-anti-VAA antibody and a biotinylated rabbit-anti-goat antibody. Intensity and distribution of staining were assessed using an immunoreactive score index (0-12). Approximately 70% of all tumors exhibited moderate to strong binding capacity for VAA. Adenocarcinomas and bronchiolo-alveolar carcinomas were more frequently labeled than squamous carcinomas. No relationship between expression of binding sites for VAA and galectin-1 as well as of Lewis antigens was found. Moreover, there was no correlation between VAA-binding capacity and survival, whereas expression of galectin-1-binding sites was of prognostic significance. Patients showing expression of galectin-1-binding sites revealed a better prognosis than those lacking binding sites or showing a weak reactivity (P = 0.0257 log rank test of Kaplan-Meier statistics).

Binding patterns of mistletoe lectins I, II and III to microglia and Alzheimer plaque glycoproteins in human brains

Glycoconjugates of microglial cells and in some cases those glycoconjugates present in the amyloid plaques in Alzheimer's disease in the cerebral cortex can be stained with a lectin from mistletoe (ML-I) using a labour-intensive and time-consuming indirect immunoperoxidase technique. In order to simplify the staining method and to test the staining characteristics of the other recently isolated mistletoe lectins (ML-II, ML-III) biotinylated MLs I-III were used together with an avidin-alkaline phosphatase-complex for visualisation. Our findings indicate that this new improved technique can also be used for detection of microglial cells and is considerably faster than the old method. In addition to microglial cells, ML-I labelled plaque glycoproteins possibly indicating that glycoconjugates derived from microglia can be detected in plaques. In contrast to ML-I, both ML-II and ML-III did not stain microglial cells.