It’s open access week and we want to highlight some of the excellent research from MDPI authors that you can read completely for free. This is the first of several posts this week highlighting recent papers that were rated highly during the review process. The first selection, mostly from the field of chemistry, includes some potential benefits of drinking coffee, a new chromotographic method and a fascinating negative result.

For regular readers of the blog, this marks a slight rebranding of the ‘new and notable’ posts.

• Protective Effects of Dihydrocaffeic Acid, a Coffee Component Metabolite, on a Focal Cerebral Ischemia Rat Model
• Adverse-Mode FFF: Multi-Force Ideal Retention Theory
• Identification and Characterization of GABAergic Projection Neurons from Ventral Hippocampus to Amygdala
• Neutrophils Do Not Express IL-17A in the Context of Acute Oropharyngeal Candidiasis
• Identification and Characterization of GABAergic Projection Neurons from Ventral Hippocampus to Amygdala
• Colloidal Stability & Conformational Changes in β-Lactoglobulin: Unfolding to Self-Assembly

Protective Effects of Dihydrocaffeic Acid, a Coffee Component Metabolite, on a Focal Cerebral Ischemia Rat Model

Kyungjin Lee, Beom-Joon Lee, Youngmin Bu,*

We recently reported the protective effects of chlorogenic acid (CGA) in a transient middle cerebral artery occlusion (tMCAo) rat model. The current study further investigated the protective effects of the metabolites of CGA and dihydrocaffeic acid (DHCA) was selected for further study after screening using the same tMCAo rat model. In the current study, tMCAo rats (2 h of MCAo followed by 22 h of reperfusion) were injected with various doses of DHCA at 0 and 2 h after onset of ischemia. We assessed brain damage, functional deficits, brain edema, and blood-brain barrier damage at 24 h after ischemia. For investigating the mechanism, in vitro zymography and western blotting analysis were performed to determine the expression and activation of matrix metalloproteinase (MMP)-2 and -9. DHCA (3, 10, and 30 mg/kg, i.p.) dose-dependently reduced brain infarct volume, behavioral deficits, brain water content, and Evans Blue (EB) leakage. DHCA inhibited expression and activation of MMP-2 and MMP-9. Therefore, DHCA might be one of the important metabolites of CGA and of natural products, including coffee, with protective effects on ischemia-induced neuronal damage and brain edema.

Adverse-Mode FFF: Multi-Force Ideal Retention Theory

Tyler N. Shendruk,* and Gary W. Slater

A novel field-flow fractionation (FFF) technique, in which two opposing external forces act on the solute particles, is proposed. When the two external forces are sufficiently strong and scale differently as a function of the solutes’ property of interest (such as the solute particle size), a sharp peak in the retention ratio (dramatic drop in elution time) is predicted to exist. Because the external forces oppose one another, we refer to this novel technique as adverse-mode FFF. The location of this peak is theoretically predicted and its ideal width estimated. The peak can become quite sharp by simultaneously increasing the strength of both fields, suggesting that adverse-mode FFF could be a useful technique for accurately measuring single species solute size.

Identification and Characterization of GABAergic Projection Neurons from Ventral Hippocampus to Amygdala

Robert Lübkemann 1, Judith Eberhardt 1, Friedrich-Wilhelm Röhl 2, Kathrin Janitzky 3, Sven Nullmeier 1, Oliver Stork 4,5, Herbert Schwegler 1,5 and Rüdiger Linke 1,*

GABAergic local circuit neurons are critical for the network activity and functional interaction of the amygdala and hippocampus. Previously, we obtained evidence for a GABAergic contribution to the hippocampal projection into the basolateral amygdala. Using fluorogold retrograde labeling, we now demonstrate that this projection indeed has a prominent GABAergic component comprising 17% of the GABAergic neurons in the ventral hippocampus. A majority of the identified GABAergic projection neurons are located in the stratum oriens of area CA1, but cells are also found in the stratum pyramidale and stratum radiatum. We could detect the expression of different markers of interneuron subpopulations, including parvalbumin and calbindin, somatostatin, neuropeptide Y, and cholecystokinin in such retrogradely labeled GABA neurons. Thus GABAergic projection neurons to the amygdala comprise a neurochemically heterogeneous group of cells from different interneuron populations, well situated to control network activity patterns in the amygdalo-hippocampal system.

Neutrophils Do Not Express IL-17A in the Context of Acute Oropharyngeal Candidiasis

Anna R. Huppler 1,2, Akash H. Verma 3, Heather R. Conti 3 and Sarah L. Gaffen 3,*

IL-17 protects against pathogens by acting on nonhematopoietic cells to induce neutrophil recruitment through upregulation of chemokines and G-CSF. IL-17- and Th17-deficient humans and mice are susceptible to mucosal Candida albicans infections, linked to impaired neutrophil responses. IL-17 production is traditionally associated with CD4+ Th17 cells. However, IL-17 is also expressed during innate responses to facilitate rapid pathogen clearance. Innate IL-17-expressing cells include various lymphocyte-type subsets, including ILC3, NKT, γδ-T and “natural” Th17 (nTh17) cells. Some reports suggest that neutrophils can express IL-17 during fungal infections. Here, we asked whether neutrophils serve as a source of IL-17 during acute oropharyngeal candidiasis (OPC) using an IL-17A fate-tracking reporter mouse. Mice were subjected to OPC for two days, and oral tissue was analyzed by flow cytometry. IL-17A was expressed by γδ-T cells and TCRβ+ natural Th17 (nTh17) cells, as recently reported. Although infiltrating neutrophils were recruited to the tongue following infection, they did not express the IL-17A reporter. Moreover, neutrophil-depleted mice exhibited normal transcription of both Il17a and downstream IL-17-dependent gene targets after Candida challenge. Thus, in acute OPC, neutrophils are not a measurable source of IL-17 production, nor are they necessary to trigger IL-17-dependent gene expression, although they are essential for ultimate pathogen control.

Colloidal Stability & Conformational Changes in β-Lactoglobulin: Unfolding to Self-Assembly

Steven Blake, Samiul Amin * , Wei Qi, Madhabi Majumdar and E. Neil Lewis

A detailed understanding of the mechanism of unfolding, aggregation, and associated rheological changes is developed in this study for β-Lactoglobulin at different pH values through concomitant measurements utilizing dynamic light scattering (DLS), optical microrheology, Raman spectroscopy, and differential scanning calorimetry (DSC). The diffusion interaction parameter kD emerges as an accurate predictor of colloidal stability for this protein consistent with observed aggregation trends and rheology. Drastic aggregation and gelation were observed at pH 5.5. Under this condition, the protein’s secondary and tertiary structures changed simultaneously. At higher pH (7.0 and 8.5), oligomerizaton with no gel formation occurred. For these solutions, tertiary structure and secondary structure transitions were sequential. The low frequency Raman data, which is a good indicator of hydrogen bonding and structuring in water, has been shown to exhibit a strong correlation with the rheological evolution with temperature. This study has, for the first time, demonstrated that this low frequency Raman data, in conjunction with the DSC endotherm, can be been utilized to deconvolve protein unfolding and aggregation/gelation. These findings can have important implications for the development of protein-based biotherapeutics, where the formulation viscosity, aggregation, and stability strongly affects efficacy or in foods where protein structuring is critical for functional and sensory performance.