Effects of the Hybridization of Opioid and Neurotensin Pharmacophores on Cell Survival in Rat Organotypic Hippocampal Slice Cultures

Comparative Study of Chemical Stability of a PK20 Opioid-Neurotensin Hybrid Peptide and Its Analogue [Ile9]PK20-The Effect of Isomerism of a Single Amino Acid

Chemical stability is one of the main problems during the discovery and development of potent drugs. When ignored, it may lead to unreliable biological and pharmacokinetics data, especially regarding the degradation of products’ possible toxicity. Recently, two biologically active drug candidates were presented that combine both opioid and neurotensin pharmacophores in one entity, thus generating a hybrid compound. Importantly, these chimeras are structurally similar except for an amino acid change at position 9 of the peptide chain. In fact, isoleucine (C₆H₁₃NO₂) was replaced with its isomer tert-leucine. These may further lead to various differences in hybrids’ behavior under specific conditions (temperature, UV, oxidative, acid/base environment). Therefore, the purpose of the study is to assess and compare the chemical stability of two hybrid peptides that differ in nature by way of one amino acid (tert-leucine vs. isoleucine). The obtained results indicate that, opposite to biological activity, the substitution of tert-leucine into isoleucine did not substantially influence the compound’s chemical stability. In fact, neither hydrolysis under alkaline and acidic conditions nor oxidative degradation resulted in spectacular differences between the two compounds—although the number of potential degradation products increased, particularly under acidic pH. However, such a modification significantly reduced the compound’s half-life from 204.4 h (for PK20 exposed to 1M HCl) to 117.7 h for [Ile⁹]PK20.

Contribution of opioid and neurotensin receptors in the anti-inflammatory activity of PK20 hybrid compound in murine airways

PK20 is an anti-inflammatory hybrid compound, composed of an endomorphin-2-like and neurotensin-like fragments. The aim of the present study is to assess the contribution of particular pharmacophores to the activity of the hybrid tested. For this purpose, airway hyperresponsiveness, accumulation of inflammatory cells in bronchoalveolar lavage fluid (BALF), concentration of mouse mast cell protease, malondialdehyde and secretory phospholipase 2 activity in lung tissue, as well as production of pro-inflammatory cytokines in BALF and lung were determined by using murine model of non-atopic asthma. Blocking either neurotensin receptors or mu opioid receptors did not alter the potential of PK20 in reducing airway hyperresponsiveness. In studies of inflammatory cells, the beneficial effect of the entire peptide occurs to be mediated by the stimulation of neurotensin receptors. However, regarding cytokine and biochemical assays, pretreatment with both receptor antagonists resulted in a different effect on its activity depending on the parameter studied. To conclude, the activation of both the opioid and neurotensin receptors seems to be necessary to induce the full anti-inflammatory activity of the hybrid compound.

Novel opioid-neurotensin-based hybrid peptide with spinal long-lasting antinociceptive activity and a propensity to delay tolerance development

The behavioral responses exerted by spinal administration of the opioid-neurotensin hybrid peptide, PK23, were studied in adult male rats. The antinociceptive effect upon exposure to a thermal stimulus, as well as tolerance development, was assessed in an acute pain model. The PK23 chimera at a dose of 10 nmol/rat produced a potent pain-relieving effect, especially after its intrathecal administration. Compared with intrathecal morphine, this novel compound was found to possess a favourable side effect profile characterized by a reduced scratch reflex, delayed development of analgesic tolerance or an absence of motor impairments when given in the same manner, though some animals died following barrel rotation as a result of its i.c.v. administration (in particular at doses higher than 10 nmol/rat). Nonetheless, these results suggest the potential use of hybrid compounds encompassing both opioid and neurotensin structural fragments in pain management. This highlights the enormous potential of synthetic neurotensin analogues as promising future analgesics.

Endomorphin-2- and Neurotensin- Based Chimeric Peptide Attenuates Airway Inflammation in Mouse Model of Nonallergic Asthma

We examined anti-inflammatory potency of hybrid peptide-PK20, composed of neurotensin (NT) and endomorphin-2 (EM-2) pharmacophores in a murine model of non-atopic asthma induced by skin sensitization with 2,4-dinitrofluorobenzene and intratracheal challenge of cognate hapten. Mice received intraperitoneally PK20, equimolar mixture of its structural elements (MIX), dexamethasone (DEX), or NaCl. Twenty-four hours following hapten challenge, the measurements of airway responsiveness to methacholine were taken. Bronchoalveolar lavage (BALF) and lungs were collected for further analyses. Treatment with PK20, similarly to dexamethasone, reduced infiltration of inflammatory cells, concentration of mouse mast cell protease, IL-1β, IL-12p40, IL-17A, CXCL1, RANTES in lungs and IL-1α, IL-2, IL-13, and TNF-α in BALF. Simple mixture of NT and EM-2 moieties was less potent. PK20, DEX, and MIX significantly decreased malondialdehyde level and secretory phospholipase 2 activity in lungs. Intensity of NF-κB immunoreactivity was diminished only after PK20 and DEX treatments. Neither PK20 nor mixture of its pharmacophores were as effective as DEX in alleviating airway hyperresponsiveness. PK20 effectively inhibited hapten-induced inflammation and mediator and signaling pathways in a manner seen with dexamethasone. Improved anti-inflammatory potency of the hybrid over the mixture of its moieties shows its preponderance and might pose a promising tool in modulating inflammation in asthma.

Organotypic slice culture based on in ovo electroporation for chicken embryonic central nervous system

Organotypic slice culture is a living cell research technique which blends features of both in vivo and in vitro techniques. While organotypic brain slice culture techniques have been well established in rodents, there are few reports on the study of organotypic slice culture, especially of the central nervous system (CNS), in chicken embryos. We established a combined in ovo electroporation and organotypic slice culture method to study exogenous genes functions in the CNS during chicken embryo development. We performed in ovo electroporation in the spinal cord or optic tectum prior to slice culture. When embryonic development reached a specific stage, green fluorescent protein (GFP)-positive embryos were selected and fluorescent expression sites were cut under stereo fluorescence microscopy. Selected tissues were embedded in 4% agar. Tissues were sectioned on a vibratory microtome and 300 μm thick sections were mounted on a membrane of millicell cell culture insert. The insert was placed in a 30-mm culture dish and 1 ml of slice culture media was added. We show that during serum-free medium culture, the slice loses its original structure and propensity to be strictly regulated, which are the characteristics of the CNS. However, after adding serum, the histological structure of cultured-tissue slices was able to be well maintained and neuronal axons were significantly longer than that those of serum-free medium cultured-tissue slices. As the structure of a complete single neuron can be observed from a slice culture, this is a suitable way of studying single neuronal dynamics. As such, we present an effective method to study axon formation and migration of single neurons in vitro.

Neurokinin-1 receptor-based bivalent drugs in pain management: The journey to nowhere?

Hybrid compounds (also known as chimeras, designed multiple ligands, bivalent compounds) are chemical units where two active components, usually possessing affinity and selectivity for distinct molecular targets, are combined as a single chemical entity. The rationale for using a chimeric approach is well documented as such novel drugs are characterized by their enhanced enzymatic stability and biological activity. This allows their use at lower concentrations, increasing their safety profile, particularly when considering undesirable side effects. In the group of synthetic bivalent compounds, drugs combining pharmacophores having affinities toward opioid and neurokinin-1 receptors have been extensively studied as potential analgesic drugs. Indeed, substance P is known as a major endogenous modulator of nociception both in the peripheral and central nervous systems. Hence, synthetic peptide fragments showing either agonism or antagonism at neurokinin 1 receptor were both assigned with analgesic properties. However, even though preclinical studies designated neurokinin-1 receptor antagonists as promising analgesics, early clinical studies revealed a lack of efficacy in human. Nevertheless, their molecular combination with enkephalin/endomorphin fragments has been considered as a valuable approach to design putatively promising ligands for the treatment of pain. This paper is aimed at summarizing a 20-year journey to the development of potent analgesic hybrid compounds involving an opioid pharmacophore and devoid of unwanted side effects. Additionally, the legitimacy of considering neurokinin-1 receptor ligands in the design of chimeric drugs is discussed.

Technical feasibility study for production of tailored multielectrode arrays and patterning of arranged neuronal networks

In this manuscript, we first reveal a simple ultra violet laser lithographic method to design and produce plain tailored multielectrode arrays. Secondly, we use the same lithographic setup for surface patterning to enable controlled attachment of primary neuronal cells and help neurite guidance. For multielectrode array production, we used flat borosilicate glass directly structured with the laser lithography system. The multi layered electrode system consists of a layer of titanium coated with a layer of di-titanium nitride. Finally, these electrodes are covered with silicon nitride for insulation. The quality of the custom made multielectrode arrays was investigated by light microscopy, electron microscopy and X-ray diffraction. The performance was verified by the detection of action potentials of primary neurons. The electrical noise of the custom-made MEA was equal to commercially available multielectrode arrays. Additionally, we demonstrated that structured coating with poly lysine, obtained with the aid of the same lithographic system, could be used to attach and guide neurons to designed structures. The process of neuron attachment and neurite guidance was investigated by light microscopy and charged particle microscopy. Importantly, the utilization of the same lithographic system for MEA fabrication and poly lysine structuring will make it easy to align the architecture of the neuronal network to the arrangement of the MEA electrode.. In future studies, this will lead to multielectrode arrays, which are able to specifically attach neuronal cell bodies to their chemically defined electrodes and guide their neurites, gaining a controlled connectivity in the neuronal network. This type of multielectrode array would be able to precisely assign a signal to a certain neuron resulting in an efficient way for analyzing the maturation of the neuronal connectivity in small neuronal networks.

Multi-targeting effects of a new synthetic molecule (JM-20) in experimental models of cerebral ischemia

Ischemic stroke is a major cause of death and disability worldwide. Thrombolysis by tissue plasminogen activator is the only pharmacological treatment approved for clinical practice, but has a narrow therapeutic window and poor efficacy when the cell death cascade is activated. Numerous drugs that are thought to protect neurons against injury have previously failed in human trials despite showing efficacy in experimental models of stroke. Herein, we reviewed the main pre-clinical results of the neuroprotective effects of JM-20, a new hybrid molecule, against brain ischemia. JM-20 appears to protect the brain from ischemic damage by interfering with several elements of the ischemic cascade: antiexcitotoxic, anticalcic, antioxidant, antiapoptotic, and anti-inflammatory. Its ability to protect not only neurons but also glial cells together with its ability to target and preserve mitochondrial function makes JM-20 a promising molecule that may be able to shield the whole neurovascular unit. The multimodal and multi-cell action of JM-20 may explain the high degree of protection observed in a rat model of brain ischemia, as assayed through histological (hematoxylin-eosin, and luxol fast blue staining), neurochemical (glutamate and aspartate levels in cerebrospinal fluid), mitochondrial functionality and behavioural (neurological scale) analysis at doses of 4 and 8mg/kg. Furthermore, the wide therapeutic window of JM-20 of 8h also suggests that this molecule could be of potential interest in situations where brain perfusion is compromised.

Cardiovascular and respiratory activity of PK20, opioid and neurotensin hybrid peptide in anesthetized and awake rats

AIM

Chimeric compound - PK20 despite its therapeutic activity on nociceptive and inflammatory processes may affect respiration and blood pressure. Our objective was to evaluate influence of the hybrid composed of endomorphin-2 and neurotensin fragments on ventilation, heart rate and blood pressure in anesthetized and awake rats.

METHODS

The effects of PK20 (1mg/kg) were studied either after its intravenous administration in anesthetized rats or intraperitoneal injection in awake state. Tidal volume and the timing components of the breathing pattern, arterial blood pressure, and heart rate were recorded.

RESULTS

Intravenous administration of PK20 in the neurally intact rats evoked a dose-dependent apnoea followed by a transient insignificant increase in tidal volume and breathing rate. The blood pressure changes were biphasic: transient increase was replaced by prolonged hypotension. Midcervical vagotomy abrogated all post-PK20 respiratory effects. Hypotension was eliminated after blockade of neurotensin NTS₁ receptor, while respiratory changes were reduced by blockade of both: NTS₁ and μ opioid receptors. After PK20 intraperitoneal injection awake rats did not show any significant changes in ventilation and blood pressure.

CONCLUSION

This chimeric peptide should be used with care via intravenous administration in anesthetized animals since PK20 may evoke respiratory apnoea and hypotension. Nevertheless, applied intraperitoneally in the same dose in conscious rats induced no adverse effects.

Neurotensin-based hybrid peptide's anti-inflammatory activity in murine model of a contact sensitivity response

The objective of the study was to investigate the possibility of modulation of skin inflammation by topical treatment with a novel compound: an opioid-neurotensin hybrid peptide PK20 encompassing endomorphin-2 analog and modified fragment of neurotensin (8-13). Contact sensitivity response was induced in mice by skin sensitization with dinitrofluorobenzene (DNFB) followed by topical hapten application on ears. Mice were treated locally with PK20 or pure cream 2h after the challenge with DNFB. 2 and 24h after hapten exposure, ear thickness was determined. Ears were collected for histology and homogenization. Supernatants were used for measurement of contents of cytokines and lipid peroxidation products. Treatment with PK20 reduced significantly the late phase of contact sensitivity response, which was revealed by ear thickness diminution and reduction of inflammatory cell infiltration. The average concentrations of IL-1α, MCP-1, TNF-α and thiobarbituric acid-reactive substances were significantly decreased in the ears treated with the chimera in comparison to the control cream treated ears in DNFB sensitized/DNFB challenged group. We found that PK20 topical treatment alleviates hypersensitivity responses triggered by DNFB challenge and usage of the hybrid peptide may be a novel therapeutic strategy in the treatment of chronic inflammatory diseases. However, the mechanism remains unclear and needs further investigation.

A method for objectively quantifying propidium iodide exclusion in organotypic hippocampal slice cultures

BACKGROUND

Organotypic hippocampal slice cultures (OHSCs) are an attractive in vitro model to examine mechanisms of neuronal injury, because the normal hippocampal architecture, function and cellular diversity are mostly preserved. The effects of exposure to excitotoxins such as N-methyl-d-aspartate (NMDA) on cell viability can be determined by propidium iodide (PI) staining.

NEW METHOD

We describe a simple method to objectively quantify cell death in NMDA exposed slice cultures using PI that provides a standardized means of quantifying cell death in hippocampal subfields without the need to induce maximal cell death in each slice. The method employs separation of subfields using simple landmarks and densitometric quantification of PI intensity in 10 template-oriented counting fields.

RESULTS

We show that exposure to increasing concentrations of NMDA results in a dose-dependent increase in PI uptake. Additionally, our method facilitates the comparison of cell death in different hippocampal subfields, such as dentate gyrus, CA1 and CA3. Our results show marked differences of PI uptake in the hippocampal regions with the CA1 area being most sensitive to NMDA-induced injury.

COMPARISON WITH EXISTING METHOD(S)

The method provides a standardized format for quantifying PI exclusion in OHSCs that can be applied to cultures of differing shapes and sizes, permits comparisons between hippocampal subfields and does not require induction of maximal cell death.

CONCLUSION

The method of quantifying PI uptake described herein allows for an objective, quantitative and reproducible analysis and comparison of cell death in distinct regions of OHSCs.