Peptide hydrogels are a highly promising class of materials for biomedical application, albeit facing many challenges with regard to stability and tunability. Here, we report a new class of ...amphipathic peptide hydrogelators, namely mixed α/β-peptide hydrogelators. These mixed α/β-gelators possess good rheological properties (high storage moduli) and form transparent self-supporting gels with shear-thinning behavior. Infrared spectroscopy indicates the presence of β-sheets as the underlying secondary structure. Interestingly, self-assembled nanofibers of the mixed α/β-peptides display unique structural morphologies with alteration of the C-terminus (acid vs amide) playing a key role in the fiber formation and gelation properties of the resulting hydrogels. The incorporation of β3-homoamino acid residues within the mixed α/β-peptide gelators led to an increase in proteolytic stability of the peptides under nongelating conditions (in solution) as well as gelating conditions (as hydrogel). Under diluted conditions, degradation of mixed α/β-peptides in the presence of elastase was slowed down 120-fold compared to that of an α-peptide, thereby demonstrating beneficial enzymatic resistance for hydrogel applications in vivo. In addition, increased half-life values were obtained for the mixed α/β-peptides in human blood plasma, as compared to corresponding α-peptides. It was also found that the mixed α/β-peptides were amenable to injection via needles used for subcutaneous administrations. The preformed peptide gels could be sheared upon injection and were found to quickly reform to a state close to that of the original hydrogel. The shown properties of enhanced proteolytic stability and injectability hold great promise for the use of these novel mixed α/β-peptide hydrogels for applications in the areas of tissue engineering and drug delivery.
This paper provides an overview of the different classes of chiral selectors that are used in CE. The main properties of every class are described, together with the mechanism of enantioseparation. ...Newly introduced selectors are also discussed. Pharmaceutical and biomedical applications published from January 2004 till March 2005 are summarized.
The ghrelin system was previously proposed to mediate an independent branch of the stress response that curbs fear processing. Interestingly, the ghrelin system was also shown to control the activity ...of midbrain dopamine neurons. Given that dopamine neurons of the ventral tegmental area appear to have a critical role in fear processing, we aimed to investigate their contribution to the effects of ghrelin on fear processing. Our data show that systemic administration of the ghrelin receptor agonist MK0677, in a dose that induces food intake, has no significant effect on auditory fear processing and does not significantly affect dopamine release in the nucleus accumbens of male C57BL/6J mice. Local administration of the ghrelin receptor agonist MK0677 into the ventral tegmental area significantly increases food intake and it also significantly increased dopamine release in the nucleus accumbens, the medial prefrontal cortex and the amygdala. Nevertheless, it did not significantly affect auditory fear extinction. Our data indicate that pharmacological activation of midbrain dopamine neurons using a ghrelin receptor agonist does not affect auditory fear extinction. We also investigated the effect of non‐pharmacological manipulation of the ghrelin system on auditory fear processing. However, we found that neither overnight food deprivation nor genetic ablation of the ghrelin receptor had a significant effect on auditory fear extinction. We conclude that the effects of manipulation of the ghrelin system on fear processing are subject to boundary conditions that remain poorly understood.
We explored the effects of ghrelin receptor activation on auditory fear processing and forebrain dopamine release. Systemic administration of MK0677 had no significant effect on auditory fear processing and did not significantly affect dopamine release. Local administration of MK0677 into the ventral tegmental area significantly increased dopamine release but did not significantly affect fear extinction. In addition, overnight food deprivation had no significant effect on fear extinction either. We conclude that the effects of manipulation of the ghrelin system on fear processing are subject to boundary conditions that remain poorly understood.
The neuromedin U peptide sequence is highly conserved between various species. Neuromedin U is involved in a variety of physiological processes. It exerts its effects via two neuromedin U receptors, ...NMUR1 and NMUR2. These receptors are characterized by a distinct, yet complementary, tissue distribution with NMUR1 mostly found in the periphery, while NMUR2 is most abundant in the central nervous system. The capability of the neuropeptide to reduce food intake in rodents triggered the design and synthesis of a broad range of modified peptide ligands. The purpose of these ligands is to develop novel therapeutics which could be beneficial in the treatment of obesity and diabetes. Most compounds are derived either from the full-length neuromedin U sequence or are based on the truncated orthologs of this neuropeptide. Only a few non-peptidic ligands were developed. This review provides an overview on various neuromedin U analogs and mimetics that have been reported to date.
•Ion-pair UHPLC at high flow rates results in peak-splitting.•The peak-splitting phenomenon is due to disturbed ion-pair retention mechanisms.•The influence of several chromatographic parameters is ...investigated.•Under specific conditions, peak-splitting is delayed to higher flow rates.
The use of ion-pair ultra-high performance liquid chromatography (UHPLC) coupled with electrochemical detection (ECD) is of great interest for the fast and sensitive determination of the monoamine neurotransmitters dopamine, noradrenaline and serotonin in microdialysis samples. However, when applying high flow rates in ion-pair UHPLC, other peaks than the initial compound peaks appear on the chromatogram. This peak-splitting phenomenon is caused by disturbed ion-pair retention mechanisms. The influence of several chromatographic parameters is investigated. Peak-splitting is delayed to higher flow rates when increasing the concentration of ion-pair reagent or buffering agent in the mobile phase, when decreasing the percentage of organic modifier in the mobile phase, when applying a stationary phase with a smaller amount of packing material or when increasing the separation temperature. One or a combination of these conditions can be applied to analyze the monoamine neurotransmitters using ion-pair UHPLC–ECD at high flow rates.
Long term treatment with L-3,4-dihydroxyphenylalanine (l-DOPA) is associated with several motor complications. Clinical improvement of this treatment is therefore needed. Lesions or high frequency ...stimulation of the hyperactive subthalamic nucleus (STN) in Parkinson's disease (PD), alleviate the motor symptoms and reduce dyskinesia, either directly and/or by allowing the reduction of the l-DOPA dose. N-methyl-d-aspartate (NMDA) receptor antagonists might have similar actions. However it remains elusive how the neurochemistry changes in the STN after a separate or combined administration of l-DOPA and a NMDA receptor antagonist. By means of in vivo microdialysis, the effect of l-DOPA and/or MK 801, on the extracellular dopamine (DA) and glutamate (GLU) levels was investigated for the first time in the STN of sham and 6-hydroxydopamine-lesioned rats. The l-DOPA-induced DA increase in the STN was significantly higher in DA-depleted rats compared to shams. MK 801 did not influence the l-DOPA-induced DA release in shams. However, MK 801 enhanced the l-DOPA-induced DA release in hemi-parkinson rats. Interestingly, the extracellular STN GLU levels remained unchanged after nigral degeneration. Furthermore, administration of MK 801 alone or combined with l-DOPA did not alter the STN GLU levels in both sham and DA-depleted rats. The present study does not support the hypothesis that DA-ergic degeneration influences the STN GLU levels neither that MK 801 alters the GLU levels in lesioned and non-lesioned rats. However, NMDA receptor antagonists could be used as a beneficial adjuvant treatment for PD by enhancing the therapeutic efficacy of l-DOPA at least in part in the STN.
•Subthalamic nucleus glutamate is unaffected by nigral 6-OHDA injection.•Subthalamic nucleus glutamate is unaffected by MK 801.•Increased l-DOPA-induced dopamine release in parkinsonian subthalamic nucleus.•Potentiation of l-DOPA-induced dopamine release by MK 801 in parkinsonian rats.
Low testosterone (T) in men, especially its free fraction, has been associated with loss of energy. In accordance, orchidectomy (ORX) in rodents results in decreased physical activity. Still, the ...mechanisms through which T stimulates activity remain mostly obscure. Here, we studied voluntary wheel running behavior in three different mouse models of androgen deficiency: ORX, androgen receptor (AR) knock-out (ARKO) and sex hormone binding globulin (SHBG)-transgenic mice, a novel mouse model of "low free T". Our results clearly show a fast and dramatic action of T stimulating wheel running, which is not explained by its action on muscle, as evidenced by neuromuscular studies and in a muscle-specific conditional ARKO mouse model. The action of T occurs via its free fraction, as shown by the results in SHBG-transgenic mice, and it implies both androgenic and estrogenic pathways. Both gene expression and functional studies indicate that T modulates the in vivo sensitivity to dopamine (DA) agonists. Furthermore, the restoration of wheel running by T is inhibited by treatment with DA antagonists. These findings reveal that the free fraction of T, both via AR and indirectly through aromatization into estrogens, stimulates physical activity behavior in male mice by acting on central DA pathways.
The astrocytic cystine/glutamate antiporter system x
(with xCT as the specific subunit) imports cystine in exchange for glutamate and has been shown to interact with multiple pathways in the brain ...that are dysregulated in age-related neurological disorders, including glutamate homeostasis, redox balance, and neuroinflammation. In the current study, we investigated the effect of genetic xCT deletion on lactacystin (LAC)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration of the nigrostriatal pathway, as models for Parkinson's disease (PD). Dopaminergic neurons of adult xCT knock-out mice (xCT
) demonstrated an equal susceptibility to intranigral injection of the proteasome inhibitor LAC, as their wild-type (xCT
) littermates. Contrary to adult mice, aged xCT
mice showed a significant decrease in LAC-induced degeneration of nigral dopaminergic neurons, depletion of striatal dopamine (DA) and neuroinflammatory reaction, compared to age-matched xCT
littermates. Given this age-related protection, we further investigated the sensitivity of aged xCT
mice to chronic and progressive MPTP treatment. However, in accordance with our previous observations in adult mice (Bentea et al., 2015a), xCT deletion did not confer protection against MPTP-induced nigrostriatal degeneration in aged mice. We observed an increased loss of nigral dopaminergic neurons, but equal striatal DA denervation, in MPTP-treated aged xCT
mice when compared to age-matched xCT
littermates. To conclude, we reveal age-related protection against proteasome inhibition-induced nigrostriatal degeneration in xCT
mice, while xCT deletion failed to protect nigral dopaminergic neurons of aged mice against MPTP-induced toxicity. Our findings thereby provide new insights into the role of system x
in mechanisms of dopaminergic cell loss and its interaction with aging.
Gaining insights into the pharmacokinetic and pharmacodynamic properties of lead compounds is crucial during drug development processes. When it comes to the treatment of brain diseases, collecting ...information at the site of action is challenging. There are only a few techniques available that allow for the direct sampling from the cerebral interstitial space. This review concerns the applicability of microdialysis and other approaches, such as cerebral open flow microperfusion and electrochemical biosensors, to monitor macromolecules (neuropeptides, proteins, …) in the brain. Microdialysis and cerebral open flow microperfusion can also be used to locally apply molecules at the same time at the site of sampling. Innovations in the field are discussed, together with the pitfalls. Moreover, the 'nuts and bolts' of the techniques and the current research gaps are addressed. The implementation of these techniques could help to improve drug development of brain-targeted drugs.
Due to the essential roles of glutamate, detection and response to a large range of extracellular concentrations of this excitatory amino acid are necessary for the fine-tuning of brain functions. ...Metabotropic glutamate receptors (mGluRs) are implicated in shaping the activity of many synapses in the central nervous system. Among the eight mGluR subtypes, there is increasing interest in studying the mGlu3 receptor which has recently been linked to various diseases, including psychiatric disorders. This receptor displays striking functional properties, with a high and, often, full basal activity, making its study elusive in heterologous systems. Here, we demonstrate that Cl− ions exert strong positive allosteric modulation of glutamate on the mGlu3 receptor. We have also identified the molecular and structural determinants lying behind this allostery: a unique interactive “chloride-lock” network. Indeed, Cl− ions dramatically stabilize the glutamate-induced active state of the extracellular domain of the mGlu3 receptor. Thus, the mGlu3 receptors’ large basal activity does not correspond to a constitutive activity in absence of agonist. Instead, it results mostly from a Cl−mediated amplified response to low ambient glutamate concentrations, such as those measured in cell media. This strong interaction between glutamate and Cl− ions allows the mGlu3 receptor to sense and efficiently react to sub-micromolar concentrations of glutamate, making it the most sensitive member of mGluR family.
•Chloride ions are strong positive allosteric modulators of mGlu3 receptor.•A unique “chloride-lock” network dramatically stabilize the active state of the receptor.•This allows the mGlu3 receptor to sense and react to sub-micromolar concentrations of glutamate.
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