Neurodegenerative diseases, in which neuronal cells disintegrate, bring about deteriorations in cognitive functions as is evidenced in millions of Alzheimer patients. A major neuropeptide, vasoactive intestinal peptide (VIP), has been shown to be neuroprotective and to play an important role in the acquisition of learning and memory. A potent lipophilic analogue to VIP now has been synthesized, [stearyl- (6)(7)(8). Cholinergic blockade, resulting in impairment of learning and memory, has been used as a model of this disease (9). Ethylcholine aziridium (AF64A) is a blocker of choline uptake and it is well established that intracerebroventricular (i.c.v.) administration of this drug can induce loss in cholinergic neurons at the basal forebrain (9-11). Despite this apparent progress, successful treatment of neurodegeneration associated with Alzheimer dementia remains elusive (1,2,12,13).In the present study, we have explored the possibility that a neurotrophic peptide, vasoactive intestinal peptide (VIP) (14-16), might provide neuroprotection in models of degeneration/cognitive impairment related to Alzheimer disease. This strategy is based on the demonstrated ability of VIP to protect neurons in the central nervous system from a variety of neurotoxic substances including tetrodotoxin (17)

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NAD+-dependent lactate dehydrogenase (LDH) is assembled onto a pyrroloquinoline quinone-NAD+ monolayer. The redox active monolayer is assembled via covalent attachment of pyrroloquinoline quinone (PQQ) to a cystamine monolayer associated with a Au electrode, followed by covalent linkage of N 6-(2-aminoethyl)-NAD+ to the monolayer. The surface coverage of PQQ and NAD+ units is ca. 1.2 × 10-10 mol cm-2. The surface coverage of LDH bound to the redox active monolayer is ca. 3.5 × 10-12 mol cm-2. The assembled LDH monolayer is active in the bioelectrocatalytic oxidation of lactate. The bioelectrocatalyzed process involves the PQQ-mediated oxidation of the immobilized NADH in the presence of Ca2+ ions. The LDH associated with the PQQ-NAD+ monolayer assembled on the electrode surface exhibits moderate stability, and the biocatalyst dissociates to the electrolyte solution. Dissociation of LDH is enhanced in the presence of solubilized NAD+. Cross-linking of the monolayer-bound LDH with glutaric dialdehyde yields an integrated stable enzyme electrode for the bioelectrocatalyzed oxidation of lactate. The electrode acts as an amperometric biosensor for lactate. Affinity binding of NAD+-dependent alcohol dehydrogenase to the PQQ-NAD+-monolayer-modified Au electrode, followed by cross-linking of the enzyme, yields an enzyme electrode for the bioelectrochemical detection of ethanol.

A novel method for the sensitive and specific electrochemical analysis of DNA is described using Faradaic impedance spectroscopy. A thiol−thymine-tagged oligonucleotide (1) capable of forming only one double-stranded turn with the target DNA analyte (2) is assembled on a Au electrode and acts as the sensing interface. The resulting functionalized electrode is reacted with a complex between the target DNA (2) and a biotinylated oligonucleotide (3) to yield a bifunctional double-stranded assembly on the electrode support. The Faradaic impedance spectra, using Fe(CN)6 3- as redox probe, reveal an increase in the electron-transfer resistance at the electrode surface upon the construction of the double-stranded assembly. This is attributed to the electrostatic repulsion of Fe(CN)6 3- upon formation of the negatively charged double-stranded superstructure. Binding of an avidin−HRP conjugate to the oligonucleotide−DNA assembly further insulates the electrode and increases the interfacial electron-transfer resistance. The HRP-mediated biocatalyzed oxidation of 4-chloro-1-naphthol (4) by H2O2 yields a precipitate (5) on the conductive support and stimulates a very high barrier for interfacial electron transfer, R et = 14.7 kΩ. Thus, the precipitation of 5 confirms and amplifies the sensing process of the target DNA (2). The analyte DNA (2) corresponds to the mutated gene fragment characteristic of the Tay-Sachs genetic disorder. The normal gene (2a) is easily discriminated by the sensing interface. The sensor device enables detection of the target DNA (2) with a sensitivity of at least 20 × 10-9 g·mL-1. Cyclic voltammetry experiments further confirm the formation of barriers for the interfacial electron transfer upon the buildup of the double-stranded oligonucleotide-DNA structure and upon the biocatalytic deposition of 5 on the electrode surface.

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