Interaction between positive allosteric modulators and trapping blockers of the NMDA receptor channel

Background and Purpose

Memantine and ketamine are clinically used, open-channel blockers of NMDA receptors exhibiting remarkable pharmacodynamic similarities despite strikingly different clinical profiles. Although NMDA channel gating constitutes an important difference between memantine and ketamine, it is unclear how positive allosteric modulators (PAMs) might affect the pharmacodynamics of these NMDA blockers.

Experimental Approach

We used two different PAMs: SGE-201, an analogue of an endogenous oxysterol, 24S-hydroxycholesterol, along with pregnenolone sulphate (PS), to test on memantine and ketamine responses in single cells (oocytes and cultured neurons) and networks (hippocampal slices), using standard electrophysiological techniques.

Key Results

SGE-201 and PS had no effect on steady-state block or voltage dependence of a channel blocker. However, both PAMs increased the actions of memantine and ketamine on phasic excitatory post-synaptic currents, but neither revealed underlying pharmacodynamic differences. SGE-201 accelerated the re-equilibration of blockers during voltage jumps. SGE-201 also unmasked differences among the blockers in neuronal networks – measured either by suppression of activity in multi-electrode arrays or by neuroprotection against a mild excitotoxic insult. Either potentiating NMDA receptors while maintaining the basal activity level or increasing activity/depolarization without potentiating NMDA receptor function is sufficient to expose pharmacodynamic blocker differences in suppressing network function and in neuroprotection.

Conclusions and Implications

Positive modulation revealed no pharmacodynamic differences between NMDA receptor blockers at a constant voltage, but did expose differences during spontaneous network activity. Endogenous modulator tone of NMDA receptors in different brain regions may underlie differences in the effects of NMDA receptor blockers on behaviour.     

Comparison of a parasite lactate dehydrogenase-based immunochromatographic antigen detection assay (OptiMAL) with microscopy for the detection of malaria parasites in human blood samples

Microscopic examination of blood smears remains the gold standard for malaria diagnosis, but is labor-intensive and requires skilled operators. Rapid dipstick technology provides a potential alternative. A study was conducted in The Gambia to compare the performance of OptiMAL, an immunochromatographic antigen detection assay for the diagnosis of malaria using parasite lactate dehydrogenase, against standard microscopy in patients with suspected malaria. For initial diagnosis of Plasmodium falciparum, irrespective of stage, this assay had a sensitivity of 91.3%, a specificity of 92%, a positive predictive value of 87.2%, and a negative predictive value of 94.7%. The sensitivity of the test decreased markedly at parasitemias < 0.01%. This assay can be used for the diagnosis of malaria in areas where microscopy is not available and for urgent malaria diagnosis at night and at weekends, when routine laboratories are closed and when relatively inexperienced microscopists may be on duty.     

Disappearance of body fat in normal rats induced by adenovirus-mediated leptin gene therapy

Sustained hyperleptinemia of 8 ng/ml was induced for 28 days in normal Wistar rats by infusing a recombinant adenovirus containing the rat leptin cDNA (AdCMV-leptin). Hyperleptinemic rats exhibited a 30–50% reduction in food intake and gained only 22 g over the experimental period versus 115–132 g in control animals that received saline infusions or a recombinant virus containing the β-galactosidase gene (AdCMV-βGal). Body fat was absent in hyperleptinemic rats, whereas control rats pair-fed to the hyperleptinemic rats retained ≈50% body fat. Further, plasma triglycerides and insulin levels were significantly lower in hyperleptinemic versus pair-fed controls, while fatty acid and glucose levels were similar in the two groups, suggestive of enhanced insulin sensitivity in the hyperleptinemic animals. Thus, despite equivalent reductions in food intake and weight gain in hyperleptinemic and pair-fed animals, identifiable fat tissue was completely ablated only in the former group, raising the possibility of a specific lipoatrophic activity for leptin.     

The efficacy and safety of zidovudine with or without acyclovir in the treatment of patients with AIDS-related complex. The European-Australian Collaborative Group.

Our objective was to evaluate the efficacy and safety of zidovudine (250 mg every 6 h) alone or in combination with acyclovir (800 mg every 6 h) as treatment for AIDS-related complex (ARC). A double-blind, controlled clinical trial of 6 months therapy was conducted at teaching hospital ambulatory clinics in eight European countries and Australia; 199 patients were studied. Time to development of AIDS-defining opportunistic infections (OI) and AIDS-associated neoplasms, survival, performance status, body weight and CD4+ cell counts were measured. During the study six (9%) zidovudine recipients, five (7%) combination recipients and 12 (18%) placebo recipients developed AIDS-defining OI; the probability of developing an OI was 0.23, 0.09 and 0.08 for the placebo, zidovudine and combination recipients, respectively. Four patients in the placebo group, three in the zidovudine group and one in the combination group died during the study. Patients receiving zidovudine with or without acyclovir had moderate increases in CD4+ cell counts compared with placebo recipients and serum HIV p24 antigen level decreased significantly in all those receiving zidovudine. Fourteen (21%) patients in the zidovudine group and 16 (24%) in the combination group experienced bone-marrow suppression compared with three (5%) placebo recipients. Red-cell transfusions were administered to 6, 19 and 13% of placebo, zidovudine and combination recipients, respectively. These data confirm the efficacy of zidovudine therapy after 4 weeks' treatment in the reduction of development of OI in patients with ARC and support the use of a maintenance dose of 250 mg zidovudine 6-hourly. Given the increased development of OI in the treated groups compared with placebo during the first 4 weeks of therapy, we cannot exclude an initial adverse effect of zidovudine and recommend caution in the use of a loading dose of zidovudine. At 6 months there was no apparent difference in efficacy between the combination of zidovudine and acyclovir compared with zidovudine alone. Moreover, the addition of high-dose acyclovir resulted in a minimal increase in the risk of toxicity.     

The role of immune-related myeloid cells in angiogenesis

Macrophage function is not restricted to the innate and adaptive immune responses, but also includes host defence, wound healing, angiogenesis and homeostatic processes. Within the spectrum of macrophage activation there are two extremes: M1 classically activated macrophages which have a pro-inflammatory phenotype, and M2 alternatively activated macrophages which are pro-angiogenic and anti-inflammatory. An important property of macrophages is their plasticity to switch from one phenotype to the other and they can be defined in their polarisation state at any point between the two extremes. In order to determine what stage of activation macrophages are in, it is essential to profile various phenotypic markers for their identification. This review describes the angiogenic role for myeloid cells: circulating monocytes, Tie-2 expressing monocytes (TEMs), myeloid-derived suppressor cells (MDSCs), tumour associated macrophages (TAMs), and neutrophils. Each cell type is discussed by phenotype, roles within angiogenesis and possible targets as a cell therapy. In addition, we also refer to our own research on myeloid angiogenic cells (MACs), outlining their ability to induce angiogenesis and their similarities to alternatively activated M2 macrophages. MACs significantly contribute to vascular repair through paracrine mechanisms as they lack the capacity to differentiate into endothelial cells. Since MACs also retain plasticity, phenotypic changes can occur according to disease states and the surrounding microenvironment. This pro-angiogenic potential of MACs could be harnessed as a novel cellular therapy for the treatment of ischaemic diseases, such as diabetic retinopathy, hind limb ischaemia and myocardial infarction; however, caution needs to be taken when MACs are delivered into an inflammatory milieu.     

Lipid-mediated innate lymphoid cell recruitment and activation in aspirin-exacerbated respiratory disease

ObjectiveTo synthesize investigations into the role of lipid-mediated recruitment and activation of group 2 innate lymphoid cells (ILC2s) in aspirin-exacerbated respiratory disease (AERD).Data SourcesA comprehensive literature review of reports pertaining to cellular mechanisms, cytokine, and lipid mediators in AERD, as well as ILC2 activation and recruitment, was performed using PubMed and Google Scholar.Study SelectionsSelections of studies were based on reports of lipid mediators in AERD, cytokine mediators in AERD, type 2 effector cells in AERD, platelets in AERD, AERD treatment, ILC2s in allergic airway disease, and ILC2 activation, inhibition, and trafficking.ResultsThe precise mechanisms of AERD pathogenesis are not well understood. Greater levels of proinflammatory lipid mediators and type 2 cytokines are found in tissues derived from patients with AERD relative to controls. After pathognomonic cyclooxygenase-1 inhibitor reactions, proinflammatory mediator concentrations (prostaglandin D2 and cysteinyl leukotrienes) are rapidly increased, as are ILC2 levels in the nasal mucosa. The ILC2s, which potently generate type 2 cytokines in response to lipid mediator stimulation, may play a key role in AERD pathogenesis.ConclusionAlthough the literature suggests that lipid-mediated ILC2 activation may occur in AERD, there is a dearth of definitive evidence. Future investigations leveraging novel next-generation single-cell sequencing approaches along with recently developed AERD murine models will better define lipid mediator–induced ILC2 trafficking in patients with AERD.