The serotonin 5-HT 1A receptor (5-HT 1A R) and dopamine D 2 receptor (D 2 R) have been implicated as important sites of action in antipsychotics. Several lines of evidence indicate the key role of G protein-coupled receptors (GPCRs) heteromers in pathophysiology of schizophrenia and highlight these complexes as novel drug targets. Because heterodimers can form only on those cells co-expressing constituent receptors, they present a target of high pharmacological specificity in the context of biochemical effects induced by antipsychotic drugs. In studies conducted in the HEK 293 cell line, we demonstrated that 5-HT 1A R and D 2 R are able to form constitutive heterodimers, and antipsychotic drugs (clozapine, olanzapine, aripiprazole, and lurasidone) enhanced this process, with clozapine being most effective. Various functional tests (cAMP and IP 1 as well as ERK activation) indicated that the drugs had different effects on signal transduction by the heteromer. Interestingly, co-incubation of heterodimer-expressing HEK 293 cells with clozapine and the 5-HT 1A R agonist 8-OH DPAT potentiated post-synaptic effects, especially with respect to ERK activation. Our results indicate that the D 2 -5-HT 1A complex possesses biochemical, pharmacological, and functional properties distinct from those of mono-and homomers. This result has implications for the development of improved pharmacotherapy for schizophrenia or other disorders (activating the heteromer might be cognitive enhancing, since it is expressed in frontal cortex) through the specific targeting of heterodimers.

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The use of polymeric nanoparticles (NPs) in pharmacology provides many benefits because this approach can increase the efficacy and selectivity of active compounds. However, development of new nanocarriers requires better understanding of the interactions between NPs and the immune system, allowing for the optimization of NP properties for effective drug delivery. Therefore, in the present study, we focused on the investigation of the interactions between biocompatible polymeric NPs and a murine macrophage cell line (RAW 264.7) and a human monocytic leukemia cell line (THP-1). NPs based on a liquid core with polyelectrolyte shells were prepared by sequential adsorption of polyelectrolytes (LbL) using AOT (docusate sodium salt) as the emulsifier and the biocompatible polyelectrolytes polyanion PGA (poly-l-glutamic acid sodium salt) and polycation PLL (poly l-lysine). The average size of the obtained NPs was 80 nm. Pegylated external layers were prepared using PGA-g-PEG (PGA grafted by PEG poly(ethylene glycol)). The influence of the physicochemical properties of the NPs (charge, size, surface modification) on viability, phagocytosis potential, and endocytosis was studied. Internalization of NPs was determined by flow cytometry and confocal microscopy. Moreover, we evaluated whether addition of PEG chains downregulates particle uptake by phagocytic cells. The presented results confirm that the obtained PEG-grafted NPs are promising candidates for drug delivery.

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An investigation of the interactions between bio-polymeric nanoparticles (NPs) and the RAW 264.7 mouse murine macrophage cell line has been presented. The cell viability, immunological response, and endocytosis efficiency of NPs were studied. Biopolymeric NPs were synthesized from a nanoemulsion using the phase inversion composition (PIC) technique. The two types of biopolymeric NPs that were obtained consisted of a biocompatible polymer, polycaprolactone (PCL), either with or without its copolymer with poly(ethylene glycol) (PCL-b-PEG). Both types of synthesized PCL NPs passed the first in vitro quality assessments as potential drug nanocarriers. Non-pegylated PCL NPs were internalized more effectively and the clathrin-mediated pathway was involved in that process. The investigated NPs did not affect the viability of the cells and did not elicit an immune response in the RAW 264.7 cells (neither a significant increase in the expression of genes encoding pro-inflammatory cytokines nor NO (nitric oxide) production were observed). It may be concluded that the synthesized NPs are promising candidates as nanocarriers of therapeutic compounds.

Binge-eating disorder is the most common eating disorder. Various neuropeptides play important roles in the regulation of feeding behavior, including relaxin-3 (RLN3), which stimulates food intake in rats through the activation of the relaxin-family peptide-3 receptor (RXFP3). Here we demonstrate that a likely mechanism underlying the orexigenic action of RLN3 is RXFP3-mediated inhibition of oxytocin-and arginine-vasopressin-synthesizing paraventricular nucleus (PVN) magnocellular neurosecretory cells. Moreover, we reveal that, in male and female rats, this action depends on M-like potassium conductance. Notably, higher intra-and peri-PVN RLN3 fiber densities were observed in females, which may constitute an anatomic substrate for observed sex differences in binge-eating disorder. Finally, in a model of binge-eating in female rats, RXFP3 blockade within the PVN prevented binge-eating behavior. These data demonstrate a direct RLN3/RXFP3 action in the PVN of male and female rats, identify the associated ionic mechanisms, and reveal that hypothalamic RLN3/RXFP3 signaling regulates binge-eating behavior.

Background G protein-coupled receptor (GPCR) signaling via heterotrimeric G proteins plays an important role in the cellular regulation of responses to external stimuli. Despite intensive structural research, the mechanism underlying the receptor–G protein coupling of closely related subtypes of Gαi remains unclear. In addition to the structural changes of interacting proteins, the interactions between lipids and proteins seem to be crucial in GPCR-dependent cell signaling due to their functional organization in specific membrane domains. In previous works, we found that Gαs and Gαi3 subunits prefer distinct types of membrane-anchor lipid domains that also modulate the G protein trimer localization. In the present study, we investigated the functional selectivity of dopamine D2 long receptor isoform (D2R) toward the Gαi1, Gαi2, and Gαi3 subunits, and analyzed whether the organization of Gαi heterotrimers at the plasma membrane affects the signal transduction. Methods We characterized the lateral diffusion and the receptor–G protein spatial distribution in living cells using two assays: fluorescence recovery after photobleaching microscopy and fluorescence resonance energy transfer detected by fluorescence-lifetime imaging microscopy. Depending on distribution of data differences between Gα subunits were investigated using parametric approach–unpaired T-test or nonparametric–Mann–Whitney U test. Results Despite the similarities between the examined subunits, the experiments conducted in the study revealed a significantly faster lateral diffusion of the Gαi2 subunit and the singular distribution of the Gαi1 subunit in the plasma membrane. The cell membrane partitioning of distinct Gαi heterotrimers with dopamine receptor correlated very well with the efficiency of D2R-mediated inhibition the formation of cAMP. Conclusions This study showed that even closely related subunits of Gαi differ in their membrane-trafficking properties that impact on their signaling. The interactions between lipids and proteins seem to be crucial in GPCR-dependent cell signaling due to their functional organization in specific membrane domains, and should therefore be taken into account as one of the selectivity determinants of G protein coupling.

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