Critical effects of polar fluorescent probes on the interaction of DHA with POPC supported lipid bilayers.

The understanding of lipid bilayer structure and function has been advanced by the application of molecular fluorophores. However, the effects of these probe molecules on the physicochemical properties of membranes being studied are poorly understood. A quartz crystal microbalance with dissipation monitoring instrument was used in this work to investigate the impact of two commonly used fluorescent probes, 1­palmitoyl­2­{12­[(7­nitro­2­1,3­benzoxadiazol­4­yl)amino]dodecanoyl}­sn­glycero­3­phosphocholine (NBD-PC) and 1,2­dipalmitoyl­sn­glycero­3­phosphoethanolamine­n­(lissamine rhodamine­B­sulfonyl) (Lis-Rhod PE), on the formation and physicochemical properties of a 1­palmitoyl­2­oleoyl­sn­glycero­3­phosphocholine supported lipid bilayer (POPC-SLB). The interaction of the POPC-SLB and fluorophore-modified POPC-SLB with docosahexaenoic acid, DHA, was evaluated. The incorporation of DHA into the POPC-SLB was observed to significantly decrease in the presence of the Lis-Rhod PE probe compared with the POPC-SLB. In addition, it was observed that the small concentration of DHA incorporated into the POPC:NBD-PC SLB can produce rearrangement processes followed by the lost not only of DHA but also of POPC or NBD-PC molecules or both during the washing step. This work has significant implications for the interpretation of data employing fluorescent reporter molecules within SLBs.

Real-Time Quartz Crystal Microbalance Monitoring of Free Docosahexaenoic Acid Interactions with Supported Lipid Bilayers.

Docosahexaenoic acid (DHA) is the most abundant polyunsaturated omega-3 fatty acid found in mammalian neuronal cell membranes. Although DHA is known to be important for neuronal cell survival, little is know about how DHA interacts with phospholipid bilayers. This study presents a detailed quartz crystal microbalance with dissipation monitoring (QCM-D) analysis of free DHA interactions with individual and mixed phospholipid supported lipid bilayers (SLB). DHA incorporation and subsequent changes to the SLBs viscoelastic properties were observed to be concentration-dependent, influenced by the phospholipid species, the headgroup charge, and the presence or absence of calcium ions. It was observed that 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) SLBs incorporated the greatest amount of DHA concentration, whereas the presence of phospholipids, phosphatidylserine (PS), and phosphatidylinositol (PI) in a POPC SLB significantly reduced DHA incorporation and changed the SLBs physicochemical properties. These observations are hypothesized to be due to a substitution event occurring between DHA and phospholipid species. PS domain formation in POPC/PS 8:2 SLBs was observed in the presence of calcium ions, which favored DHA incorporation to a similar level as for a POPC only SLB. The changes in SLB thickness observed with different DHA concentrations are also presented. This work contributes to an understanding of the physical changes induced in a lipid bilayer as a consequence of its exposure to different DHA concentrations (from 50 to 200 µM). The capacity of DHA to influence the physical properties of SLBs indicates the potential for dietary DHA supplementation to cause changes in cellular membranes in vivo, with subsequent physiological consequences for cell function.

Functional genome analysis of Bifidobacterium breve UCC2003 reveals type IVb tight adherence (Tad) pili as an essential and conserved host-colonization factor.

Development of the human gut microbiota commences at birth, with bifidobacteria being among the first colonizers of the sterile newborn gastrointestinal tract. To date, the genetic basis of Bifidobacterium colonization and persistence remains poorly understood. Transcriptome analysis of the Bifidobacterium breve UCC2003 2.42-Mb genome in a murine colonization model revealed differential expression of a type IVb tight adherence (Tad) pilus-encoding gene cluster designated "tad(2003)." Mutational analysis demonstrated that the tad(2003) gene cluster is essential for efficient in vivo murine gut colonization, and immunogold transmission electron microscopy confirmed the presence of Tad pili at the poles of B. breve UCC2003 cells. Conservation of the Tad pilus-encoding locus among other B. breve strains and among sequenced Bifidobacterium genomes supports the notion of a ubiquitous pili-mediated host colonization and persistence mechanism for bifidobacteria.

Gestational exposure to a ketogenic diet increases sociability in CD-1 mice.

Postnatal administration of high-fat, low-carbohydrate ketogenic diets (KDs) is an established and effective treatment option for refractory epilepsy, with more recently identified therapeutic potential across a wide range of preclinical models of neurological and psychiatric disorders. However, the impact of gestational exposure to a KD (GKD) on offspring development remains unclear. Previous work has found that GKD exposure reduces depression- and anxiety-like behaviors in CD-1 mice, whereas postnatal KD improves sociability in several different rodent models of autism. Here we examined how sociability is impacted by GKD. Given that the neuropeptide oxytocin positively regulates affect, anxiety, and sociability, we also examined the effects of GKD on brain oxytocin expression. Male and female CD-1 mice exposed to either a standard diet (SD) or a KD gestationally were cross-fostered with SD dams at birth and remained on a SD from that point onward. These offspring were then tested for sociability and social novelty (three-chambered test) and depressive-like behaviors (forced swim test) at 10 weeks of age. At the conclusion of testing, brain tissue was collected and immunohistochemically processed for oxytocin expression in hypothalamic and limbic areas. We found that GKD increased sociability and reduced depressive-like symptoms, without affecting oxytocin expression in quantified areas. By expanding the scope of the lasting impact of gestational exposure to a ketogenic diet to include positive effects on sociability, these results indicate that GKDs may have novel therapeutic applications for individuals at risk for developmental disorders of social behavior, including autism and schizophrenia. (PsycInfo Database Record (c) 2020 APA, all rights reserved).