Challenges and lessons learned from four years of planning and implementing pharmacovigilance enhancement in sub-Saharan Africa.

Pharmacovigilance (PV) systems in many countries in sub-Saharan Africa (SSA) are not fully functional. The spontaneous adverse events (AE) reporting rate in SSA is lower than in any other region of the world, and healthcare professionals (HCPs) in SSA countries have limited awareness of AE surveillance and reporting procedures. The GSK PV enhancement pilot initiative, in collaboration with PATH and national PV stakeholders, aimed to strengthen passive safety surveillance through a training and mentoring program of HCPs in healthcare facilities in three SSA countries: Malawi, Côte d'Ivoire, and Democratic Republic of Congo (DRC). Project implementation was country-driven, led by the Ministry of Health via the national PV center or department, and was adapted to each country's needs. The implementation phase for each country was scheduled to last 18 months. At project start, low AE reporting rates reflected that awareness of PV practices was very low among HCPs in all three countries, even if a national PV center already existed. Malawi did not have a functional PV system nor a national PV center prior to the start of the initiative. After 18 months of PV training and mentoring of HCPs, passive safety surveillance was enhanced significantly as shown by the increased number of AE reports: from 22 during 2000-2016 to 228 in 18 months to 511 in 30 months in Malawi, and ~ 80% of AE reports from trained healthcare facilities in Côte d'Ivoire. In DRC, project implementation ended after 7 months because of the SARS-CoV-2 pandemic. Main challenges encountered were delayed AE report transmission (1-2 months, due mainly to remoteness of healthcare facilities and complex procedures for transmitting reports to the national PV center), delayed or no causality assessment due to lack of expertise and/or funding, negative perceptions among HCPs toward AE reporting, and difficulties in engaging public health programs with the centralized AE reporting processes. This pilot project has enabled the countries to train more HCPs, increased reporting of AEs and identified KPIs that could be flexibly replicated in each country. Country ownership and empowerment is essential to sustain these improvements and build a stronger AE reporting culture.

Glutamate release from astrocytes in physiological conditions and in neurodegenerative disorders characterized by neuroinflammation.

Although glial cells have been traditionally viewed as supportive partners of neurons, studies of the last 20 years demonstrate that astrocytes possess functional receptors for neurotransmitters and other signaling molecules and respond to their stimulation via release of chemical transmitters (called gliotransmitters) such as glutamate, ATP, and d-serine. Notably, astrocytes react to synaptically released neurotransmitters with intracellular calcium ([Ca(2+)](i)) elevations, which result in the release of glutamate via regulated exocytosis and possibly other mechanisms. These findings have led to a new concept of neuron-glia intercommunication where astrocytes play an unsuspected dynamic role by integrating neuronal inputs and modulating synaptic activity. The additional discovery that glutamate release from astrocytes is controlled by molecules linked to inflammatory reactions, such as the cytokine tumor necrosis factor-alpha (TNF-alpha) and prostaglandins, suggests that glia-to-neuron signaling may be sensitive to changes in production of these mediators in pathological conditions. Indeed, a local, parenchymal brain inflammatory reaction (neuroinflammation) characterized by astrocytic and microglial activation has been reported in several neurodegenerative disorders, including Alzheimer's disease and AIDS dementia complex. This transition to a reactive state may be accompanied by a disruption of the cross talk normally occurring between astrocytes and neurons and so contribute to disease development. The findings reported in this chapter suggest that a better comprehension of the glutamatergic interplay between neurons and glia may provide information about normal brain function and also highlight possible molecular targets for therapeutic interventions in pathology.

Bioenergetics of mitochondria in cultured neurons and their role in glutamate excitotoxicity.

The pathologic activation of NMDA receptors by glutamate is a major contributor to neuronal cell death after stroke. Receptor activation causes a massive influx of calcium into the neuron that is accumulated by the mitochondria. The favored hypothesis is that the calcium loaded mitochondria generate reactive oxygen species that damage and ultimately killed the neuron. In this review this hypothesis is critically re-examined with an emphasis on the role played by deficits in ATP generation. Novel techniques are developed to monitor the bioenergetic status of in situ mitochondria in cultured neurons. Applying these techniques to a model of glutamate excitotoxicity suggests that enhanced reactive oxygen species are a consequence rather than a cause of failed cytoplasmic calcium homeostasis (delayed calcium deregulation, [DCD]), but that prior oxidative damage facilitates DCD by damaging mitochondrial ATP generation. This impacts on current hypotheses relating to the neuroprotective effects of mild mitochondrial uncoupling.

Acute glutathione depletion restricts mitochondrial ATP export in cerebellar granule neurons.

Decreases in GSH pools detected during ischemia sensitize neurons to excitotoxic damage. Thermodynamic analysis predicts that partial GSH depletion will cause an oxidative shift in the thiol redox potential. To investigate the acute bioenergetic consequences, neurons were exposed to monochlorobimane (mBCl), which depletes GSH by forming a fluorescent conjugate. Neurons transfected with redox-sensitive green fluorescent protein showed a positive shift in thiol redox potential synchronous with the formation of the conjugate. Mitochondria within neurons treated with mBCl for 1 h failed to hyperpolarize upon addition of oligomycin to inhibit their ATP synthesis. A decreased ATP turnover was confirmed by monitoring neuronal oxygen consumption in parallel with mitochondrial membrane potential (Deltapsi(m)) and GSH-mBCl formation. mBCl progressively decreased cell respiration, with no effect on mitochondrial proton leak or maximal respiratory capacity, suggesting adequate glycolysis and a functional electron transport chain. This approach to "state 4" could be mimicked by the adenine nucleotide translocator inhibitor bongkrekic acid, which did not further decrease respiration when administered after mBCl. The cellular ATP/ADP ratio was decreased by mBCl, and consistent with mitochondrial ATP export failure, respiration could not respond to an increased cytoplasmic ATP demand by plasma membrane Na(+) cycling; instead, mitochondria depolarized. More prolonged mBCl exposure induced mitochondrial failure, with Deltapsi(m) collapse followed by cytoplasmic Ca(2+) deregulation. The initial bioenergetic consequence of neuronal GSH depletion in this model is thus an inhibition of ATP export, which precedes other forms of mitochondrial dysfunction.

Relationships between superoxide levels and delayed calcium deregulation in cultured cerebellar granule cells exposed continuously to glutamate.

The relationship is investigated between superoxide levels in single cultured rat cerebellar granule neurons exposed continuously to glutamate in low KCl medium and the deregulation of cytoplasmic Ca2+. Cells that maintain a regulated cytoplasmic-free Ca2+ and mitochondrial polarization in the presence of glutamate show no increase in superoxide levels until the onset of cytoplasmic Ca2+ deregulation. Oxidative stress of mitochondrial origin is readily detectable, as the inhibitors rotenone and antimycin A markedly increase superoxide levels with no effect on cytoplasmic-free Ca2+. The potent cell-permeant superoxide dismutase/catalase mimetic manganese tetrakis (N-ethylpyridinium-2yl) porphyrin, MnTE-PyP, abolishes the deregulation-related increase in superoxide but has no effect on deregulation itself. A combination of catalase with the free radical scavenger 4-hydroxy-TEMPO also fails to reduce deregulation. Following the loss of Ca2+ homeostasis nuclei undergo condensation; this morphological change is not inhibited by MnTE-PyP and cannot account for the increased ethidium fluorescence. Phospholipase A2 inhibitors decrease the deregulation-related increase in superoxide without protecting against deregulation. In conclusion, our study indicates that deregulation is not caused by NMDA receptor-mediated oxidative stress as NMDA receptor activation does not increase superoxide levels until the onset of deregulation. Furthermore, the majority of superoxide is produced in the cytoplasm rather than in mitochondria.

Alternative, nonapoptotic programmed cell death: mediation by arrestin 2, ERK2, and Nur77.

Programmed cell death (pcd) may take the form of apoptosis or of nonapoptotic pcd. Whereas cysteine aspartyl-specific proteases (caspases) mediate apoptosis, the mediators of nonapoptotic cell death programs are much less well characterized. Here we report that alternative, nonapoptotic pcd induced by the neurokinin-1 receptor (NK(1)R) activated by its ligand Substance P, is mediated by a MAPK phosphorylation cascade recruited by the scaffold protein arrestin 2. The activation of the protein kinases Raf-1, MEK2, and ERK2 is essential for this form of nonapoptotic pcd, leading to the phosphorylation of the orphan nuclear receptor Nur77. NK(1)R-mediated cell death was inhibited by a dominant negative form of arrestin 2, Raf-1, or Nur77, by MEK1/2-specific inhibitors, and by RNA interference directed against ERK2 or MEK2 but not ERK1 or MEK1 and against Nur77. The MAPK pathway is also activated in neurons in primary culture undergoing NK(1)R-mediated death, since the MEK inhibitor PD98059 inhibited Substance P-induced death in primary striatal neurons. These results suggest that Nur77, which is regulated by a MAPK pathway activated via arrestin 2, modulates NK(1)R-mediated nonapoptotic pcd.

Interactions between mitochondrial bioenergetics and cytoplasmic calcium in cultured cerebellar granule cells.

The mitochondrion has moved to the center stage in the drama of the life and death of the neuron. The mitochondrial membrane potential controls the ability of the organelle to generate ATP, generate reactive oxygen species and sequester Ca(2+) entering the cell. Each of these processes interact, and their deconvolution is far from trivial. The cultured cerebellar granule cell provides a model in which knowledge gained from studies on isolated mitochondria can be applied to study the role played by the organelles in the maintenance of Ca(2+) homeostasis in the cell under resting, stimulated and pathophysiological conditions. In particular, mitochondria play a complex role in the response of the neuron to excitotoxic stimulation of NMDA and AMPA-kainate selective glutamate receptors. One goal of research in this area is to provide clues as to possible ways in which modulators of mitochondrial function may be used as neuroprotective agents, since mitochondrial Ca(2+) accumulation seems to play a key role in glutamate excitotoxicity.

Barbiturates induce mitochondrial depolarization and potentiate excitotoxic neuronal death.

Barbiturates are widely used as anesthetics, anticonvulsants, and neuroprotective agents. However, barbiturates may also inhibit mitochondrial respiration, and mitochondrial inhibitors are known to potentiate NMDA receptor-mediated neurotoxicity. Here we used rat cortical cultures to examine the effect of barbiturates on neuronal mitochondria and responses to NMDA receptor stimulation. The barbiturates tested, secobarbital, amobarbital, and thiamylal, each potentiated NMDA-induced neuron death at barbiturate concentrations relevant to clinical and experimental use (100-300 microm). By using rhodamine-123 under quenching conditions, barbiturates in this concentration range were shown to depolarize neuronal mitochondria and greatly amplify NMDA-induced mitochondrial depolarization. Barbiturate-induced mitochondrial depolarization was increased by the ATP synthase inhibitor oligomycin, indicating that barbiturates act by inhibiting electron transport sufficiently to cause ATP synthase reversal. Barbiturates similarly amplified the effects of NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence mitochondrial potential or potentiate NMDA neurotoxicity or calcium responses. However, all of the barbiturates attenuated NMDA-induced calcium elevations and cell death when present at millimolar concentrations. Whole-cell patch-clamp studies showed that these effects may be attributable to actions at the cell membrane, resulting in a block of NMDA-induced current flux at millimolar barbiturate concentrations. Together, these findings reconcile previous reports of opposing effects on barbiturates on NMDA neurotoxicity and show that barbiturate effects on neuronal mitochondria can be functionally significant. Effects of barbiturates on neuronal mitochondria should be considered in experimental and clinical application of these drugs.