Pseudopterosin A: Protection of Synaptic Function and Potential as a Neuromodulatory Agent.

Natural products have provided an invaluable source of inspiration in the drug discovery pipeline. The oceans are a vast source of biological and chemical diversity. Recently, this untapped resource has been gaining attention in the search for novel structures and development of new classes of therapeutic agents. Pseudopterosins are group of marine diterpene glycosides that possess an array of potent biological activities in several therapeutic areas. Few studies have examined pseudopterosin effects during cellular stress and, to our knowledge, no studies have explored their ability to protect synaptic function. The present study probes pseudopterosin A (PsA) for its neuromodulatory properties during oxidative stress using the fruit fly, Drosophila melanogaster. We demonstrate that oxidative stress rapidly reduces neuronal activity, resulting in the loss of neurotransmission at a well-characterized invertebrate synapse. PsA mitigates this effect and promotes functional tolerance during oxidative stress by prolonging synaptic transmission in a mechanism that differs from scavenging activity. Furthermore, the distribution of PsA within mammalian biological tissues following single intravenous injection was investigated using a validated bioanalytical method. Comparable exposure of PsA in the mouse brain and plasma indicated good distribution of PsA in the brain, suggesting its potential as a novel neuromodulatory agent.

A cGMP-dependent protein kinase (PKG) controls synaptic transmission tolerance to acute oxidative stress at the Drosophila larval neuromuscular junction.

Increasing evidence demonstrates that modulating the cGMP-dependent protein kinase G (PKG) pathway produces an array of behavioral phenotypes in the fruit fly, Drosophila melanogaster. Altering PKG activity, either genetically via the foraging (for) gene or using pharmacology modifies tolerance to acute abiotic stresses such as hyperthermia and hypoxia. PKG signaling has been shown to modulate neuroprotection in many experimental paradigms of acute brain trauma and chronic neurodegenerative diseases. However, relatively little is known about how this stress-induced neuroprotective mechanism affects neural communication. In this study, we investigated the role PKG activity has on synaptic transmission at the Drosophila larval neuromuscular junction (NMJ) during acute oxidative stress and found that the application of 2.25 mM hydrogen peroxide (H(2)O(2)) disrupts synaptic function by rapidly increasing the rate of neuronal failure. Here, we report that reducing PKG activity through either natural genetic variation or an induced mutation of the for gene increases synaptic tolerance during acute oxidative conditions. Furthermore, pharmacological manipulations revealed that neurotransmission is significantly extended during acute H(2)O(2) exposure upon inhibition of the PKG pathway. Conversely, activation of this signaling cascade using either genetics or pharmacology significantly reduced the time until synaptic failure. Therefore, these findings suggest a potential role for PKG activity to regulate the tolerance of synaptic transmission during acute oxidative stress, where inhibition promotes functional protection while activation increases susceptibility to neurotransmission breakdown.

NO/cGMP/PKG activation protects Drosophila cells subjected to hypoxic stress.

The anoxia-tolerant fruit fly, Drosophila melanogaster, has routinely been used to examine cellular mechanisms responsible for anoxic and oxidative stress resistance. Nitric oxide (NO), an important cellular signaling molecule, and its downstream activation of cGMP-dependent protein kinase G (PKG) has been implicated as a protective mechanism against ischemic injury in diverse animal models from insects to mammals. In Drosophila, increased PKG signaling results in increased survival of animals exposed to anoxic stress. To determine if activation of the NO/cGMP/PKG pathway is protective at the cellular level, the present study employed a pharmacological protocol to mimic hypoxic injury in Drosophila S2 cells. The commonly used S2 cell line was derived from a primary culture of late stage (20-24 h old) Drosophila melanogaster embryos. Hypoxic stress was induced by exposure to either sodium azide (NaN3) or cobalt chloride (CoCl2). During chemical hypoxic stress, NO/cGMP/PKG activation protected against cell death and this mechanism involved modulation of downstream mitochondrial ATP-sensitive potassium ion channels (mitoKATP). The cellular protection afforded by NO/cGMP/PKG activation during ischemia-like stress may be an adaptive cytoprotective mechanism and modulation of this signaling cascade could serve as a potential therapeutic target for protection against hypoxia or ischemia-induced cellular injury.