Sustained Extracellular Electrical Stimulation Modulates the Permeability of Gap Junctions in rd1 Mouse Retina with Photoreceptor Degeneration

Neurons build vast gap junction-coupled networks (GJ-nets) that are permeable to ions or small molecules, enabling lateral signaling. Herein, we investigate (1) the effect of blinding diseases on GJ-nets in mouse retinas and (2) the impact of electrical stimulation on GJ permeability. GJ permeability was traced in the acute retinal explants of blind retinal degeneration 1 (rd1) mice using the GJ tracer neurobiotin. The tracer was introduced via the edge cut method into the GJ-net, and its spread was visualized in histological preparations (fluorescent tagged) using microscopy. Sustained stimulation was applied to modulate GJ permeability using a single large electrode. Our findings are: (1) The blind rd1 retinas displayed extensive intercellular coupling via open GJs. Three GJ-nets were identified: horizontal, amacrine, and ganglion cell networks. (2) Sustained stimulation significantly diminished the tracer spread through the GJs in all the cell layers, as occurs with pharmaceutical inhibition with carbenoxolone. We concluded that the GJ-nets of rd1 retinas remain coupled and functional after blinding disease and that their permeability is regulatable by sustained stimulation. These findings are essential for understanding molecular signaling in diseases over coupled networks and therapeutic approaches using electrical implants, such as eliciting visual sensations or suppressing cortical seizures.

The PKG Inhibitor CN238 Affords Functional Protection of Photoreceptors and Ganglion Cells against Retinal Degeneration

Hereditary retinal degeneration (RD) is often associated with excessive cGMP signalling in photoreceptors. Previous research has shown that inhibition of cGMP-dependent protein kinase G (PKG) can reduce photoreceptor loss in two different RD animal models. In this study, we identified a PKG inhibitor, the cGMP analogue CN238, which preserved photoreceptor viability and functionality in rd1 and rd10 mutant mice. Surprisingly, in explanted retinae, CN238 also protected retinal ganglion cells from axotomy-induced retrograde degeneration and preserved their functionality. Furthermore, kinase activity-dependent protein phosphorylation of the PKG target Kv1.6 was reduced in CN238-treated rd10 retinal explants. Ca2+-imaging on rd10 acute retinal explants revealed delayed retinal ganglion cell repolarization with CN238 treatment, suggesting a PKG-dependent modulation of Kv1-channels. Together, these results highlight the strong neuroprotective capacity of PKG inhibitors for both photoreceptors and retinal ganglion cells, illustrating their broad potential for the treatment of retinal diseases and possibly neurodegenerative diseases in general.

Artificial Vision: The High-Frequency Electrical Stimulation of the Blind Mouse Retina Decay Spike Generation and Electrogenically Clamped Intracellular Ca2+ at Elevated Levels

BACKGROUND

The electrical stimulation (stim) of retinal neurons enables blind patients to experience limited artificial vision. A rapid response outage of the stimulated ganglion cells (GCs) allows for a low visual sensation rate. Hence, to elucidate the underlying mechanism, we investigated different stim parameters and the role of the neuromodulator calcium (Ca2+).

METHODS

Subretinal stim was applied on retinal explants (blind rd1 mouse) using multielectrode arrays (MEAs) or single metal electrodes, and the GC activity was recorded using Ca2+ imaging or MEA, respectively. Stim parameters, including voltage, phase polarity, and frequency, were investigated using specific blockers.

RESULTS

At lower stim frequencies (<5 Hz), GCs responded synaptically according to the stim pulses (stim: biphasic, cathodic-first, -1.6/+1.5 V). In contrast, higher stim frequencies (≥5 Hz) also activated GCs directly and induced a rapid GC spike response outage (<500 ms, MEA recordings), while in Ca2+ imaging at the same frequencies, increased intracellular Ca2+ levels were observed.

CONCLUSIONS

Our study elucidated the mechanisms involved in stim-dependent GC spike response outage: sustained high-frequency stim-induced spike outage, accompanied by electrogenically clamped intracellular Ca2+ levels at elevated levels. These findings will guide future studies optimizing stim paradigms for electrical implant applications for interfacing neurons.

Using Micro-Electrode-Array Recordings and Retinal Disease Models to Elucidate Visual Functions: Simultaneous Recording of Local Electroretinograms and Ganglion Cell Action Potentials Reveals the Origin of Retinal Oscillatory Potentials

BACKGROUND

The electroretinogram (ERG) is an essential diagnostic tool for visual function, both in clinical and research settings. Here, we establish an advanced in vitro approach to assess cell-type-specific ERG signal components.

METHODS

Retinal explant cultures, maintained under entirely controlled conditions, were derived from wild-type mice and rd10 rod- and cpfl1 cone-degeneration mouse models. Local micro-ERG (µERG) and simultaneous ganglion cell (GC) recordings were obtained from the retinal explants using multi-electrode arrays. Band-pass filtering was employed to distinguish photoreceptor, bipolar cell, amacrine cell (AC), and GC responses.

RESULTS

Scotopic and photopic stimulation discriminated between rod and cone responses in wild-type and mutant retina. The 25 kHz sampling rate allowed the visualization of oscillatory potentials (OPs) in extraordinary detail, revealing temporal correlations between OPs and GC responses. Pharmacological isolation of different retinal circuits found that OPs are generated by inner retinal AC electrical synapses. Importantly, this AC activity helped synchronise GC activity.

CONCLUSION

Our µERG protocol simultaneously records the light-dependent activities of the first-, second-, and third-order neurons within the native neuronal circuitry, providing unprecedented insights into retinal physiology and pathophysiology. This method now also enables complete in vitro retinal function testing of therapeutic interventions, providing critical guidance for later in vivo investigations.

Nature-inspired saccadic-like electrical stimulation paradigm promotes sustained retinal ganglion cell responses by spatiotemporally alternating activation of contiguous multi-electrode patterns

Objective. Retinal electrical stimulation using multi-electrode arrays (MEAs) aims to restore visual object perception in blind patients. However, the rate and duration of the artificial visual sensations are limited due to the rapid response decay of the stimulated neurons. Hence, we investigated a novel nature-inspired saccadic-like stimulation paradigm (biomimetic) to evoke sustained retinal responses. For implementation, the macroelectrode was replaced by several contiguous microelectrodes and activated non-simultaneously but alternating topologically.Approach.MEAs with hexagonally arranged electrodes were utilized to simulate and record mouse retinal ganglion cells (RGCs). Two shapes were presented electrically using MEAs: a 6e-hexagon (six hexagonally arranged 10µm electrodes; 6e-hexagon diameter: 80µm) and a double-bar (180µm spaced, 320µm in length). Electrodes of each shape were activated in three different modes (simultaneous, circular, and biomimetic ('zig-zag')), stimulating at different frequencies (1-20 Hz).Main results.The biomimetic stimulation generated enhanced RGC responses increasing the activity rate by 87.78%. In the spatiotemporal context, the electrical representation of the 6e-hexagon produced sustained and local RGC responses (∼130µm corresponding to ∼2.5° of the human visual angle) for up to 90 s at 10 Hz stimulation and resolved the electrically presented double-bar. In contrast, during conventional simultaneous stimulation, the responses were poor and declined within seconds. Similarly, the applicability of the biomimetic mode for retinal implants (7 × 8 pixels) was successfully demonstrated. An object shape impersonating a smile was presented electrically, and the recorded data were used to emulate the implant's performance. The spatiotemporal pixel mapping of the activity produced a complete retinal image of the smile.Significance.The application of electrical stimulation in the biomimetic mode produced locally enhanced RGC responses with significantly reduced fading effects and yielded advanced spatiotemporal performance reflecting the presented electrode shapes in the mapped activity imprint. Therefore, it is likely that the RGC responses persist long enough to evoke visual perception and generate a seamless image, taking advantage of the flicker fusion. Hence, replacing the implant's macroelectrodes with microelectrodes and their activation in a topologically alternating biomimetic fashion may overcome the patient's perceptual image fading, thereby enhancing the spatiotemporal characteristics of artificial vision.

Interferon-γ signaling synergizes with LRRK2 in neurons and microglia derived from human induced pluripotent stem cells

Parkinson's disease-associated kinase LRRK2 has been linked to IFN type II (IFN-γ) response in infections and to dopaminergic neuronal loss. However, whether and how LRRK2 synergizes with IFN-γ remains unclear. In this study, we employed dopaminergic neurons and microglia differentiated from patient-derived induced pluripotent stem cells carrying LRRK2 G2019S, the most common Parkinson's disease-associated mutation. We show that IFN-γ enhances the LRRK2 G2019S-dependent negative regulation of AKT phosphorylation and NFAT activation, thereby increasing neuronal vulnerability to immune challenge. Mechanistically, LRRK2 G2019S suppresses NFAT translocation via calcium signaling and possibly through microtubule reorganization. In microglia, LRRK2 modulates cytokine production and the glycolytic switch in response to IFN-γ in an NFAT-independent manner. Activated LRRK2 G2019S microglia cause neurite shortening, indicating that LRRK2-driven immunological changes can be neurotoxic. We propose that synergistic LRRK2/IFN-γ activation serves as a potential link between inflammation and neurodegeneration in Parkinson's disease.

Merging organoid and organ-on-a-chip technology to generate complex multi-layer tissue models in a human retina-on-a-chip platform

The devastating effects and incurable nature of hereditary and sporadic retinal diseases such as Stargardt disease, age-related macular degeneration or retinitis pigmentosa urgently require the development of new therapeutic strategies. Additionally, a high prevalence of retinal toxicities is becoming more and more an issue of novel targeted therapeutic agents. Ophthalmologic drug development, to date, largely relies on animal models, which often do not provide results that are translatable to human patients. Hence, the establishment of sophisticated human tissue-based in vitro models is of upmost importance. The discovery of self-forming retinal organoids (ROs) derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) is a promising approach to model the complex stratified retinal tissue. Yet, ROs lack vascularization and cannot recapitulate the important physiological interactions of matured photoreceptors and the retinal pigment epithelium (RPE). In this study, we present the retina-on-a-chip (RoC), a novel microphysiological model of the human retina integrating more than seven different essential retinal cell types derived from hiPSCs. It provides vasculature-like perfusion and enables, for the first time, the recapitulation of the interaction of mature photoreceptor segments with RPE in vitro. We show that this interaction enhances the formation of outer segment-like structures and the establishment of in vivo-like physiological processes such as outer segment phagocytosis and calcium dynamics. In addition, we demonstrate the applicability of the RoC for drug testing, by reproducing the retinopathic side-effects of the anti-malaria drug chloroquine and the antibiotic gentamicin. The developed hiPSC-based RoC has the potential to promote drug development and provide new insights into the underlying pathology of retinal diseases.

An expeditious synthesis of thiazolidinones and tetathiazanones

In the present study, 4-thiazolidinones have been assembled by HBTU mediated three-component reaction of amine, aldehyde and mercapto acid derivatives at room temperature. The final compounds are obtained in excellent yields within 30 minutes.

Electrical activation of degenerated photoreceptors in blind mouse retina elicited network-mediated responses in different types of ganglion cells

Electrical (e-) stimulation is explored in schemes to rescue the vision of blind people, e.g. those affected by Retinitis Pigmentosa (RP). We e-activated subretinally the surviving degenerated photoreceptors (d-Phrs) of the rd1 mouse (RP model) and evoked visual responses in the blind retina. The e-stimulation was applied with a single platinum/iridium electrode. The d-Phrs (calcium-imaging) and ganglion cells (GC) activity (MEA-recording) were recorded in simultaneous multilayer recordings. The findings of this study confirm that the d-Phrs responded to e-stimulation and modulated the retinal network-activity. The application of blockers revealed that the synaptic interactions were dependent on voltage-gated calcium channels and mediated by the transmitters glutamate and GABA. Moreover, the gap junctions coupled networks promoted the lateral-spread of the e-evoked activity in the outer (~60 µm) and inner (~120 µm) retina. The activated GCs were identified as subtypes of the ON, OFF and ON-OFF classes. In conclusion, d-Phrs are the ideal interface partners for implants to elicit enhanced visual responses at higher temporal and spatial resolution. Furthermore, the retina's intact circuity at the onset of complete blindness makes it a tempting target when considering the implantation of implants into young patients to provide a seamless transition from blinding to chip-aided vision.

Feasibility study for a glutamate driven subretinal prosthesis: local subretinal application of glutamate on blind retina evoke network-mediated responses in different types of ganglion cells

OBJECTIVE

A feasibility study for a transmitter based subretinal prosthesis, generating visual responses in blind mouse retina is presented.

APPROACH

Degenerated rd1 mouse retina were stimulated in subretinal configuration by local glutamate (Glu) or NMDA application via micropipettes (~1.5 μm) and thereby the outer retinal activity was recorded by calcium-imaging or the ganglion cell (GC) activity was recorded by the multi-electrode array system. The network mediated activation of GC via bipolar cells was approved by the administration of Glu receptor blockers.

MAIN RESULTS

Data of the degenerated and blind rd1 mouse retina reveals that the outer retina is Glu sensitive and that the subretinal Glu stimulation promotes network mediated GC responses. Analysis of the spatial activity-spread indicates that the Glu induced cell activation radius in the outer retina (~12.5 μm) and postsynaptically activated GC (~40 μm) is focal to the stimulation pipette tip. Moreover, the application of NMDA in subretinal space also evoked network mediated GC responses. The Glu-activated GC were identified as ON-OFF, OFF and two ON cells types.

SIGNIFICANCE

This study evaluates the prerequisite for the function of a transmitter based implant, that after the loss of the photoreceptors, the remnant blind retinal network is Glu sensitive and functional, positively. The differential activation of ON (hyperpolarisation) and OFF (depolarisation) bipolar cells by transmitter Glu is a unique feature and of high interest for retinal implants. Therefore, the respective bipolar cell types could only be driven by glutamatergic stimulation accurately and not by electrical stimulation. The preserved functionality of the blind retina at the onset of complete blindness is motivating to continue research on a transmitter-based prosthesis. Since the artificial Glu stimulation mimics the natural retinal input, early implantation of a Glu-prosthesis might delay the devastating retinal remodelling positively, due to the neuronal-plasticity.

Quality and learning curve of handheld versus stand-alone non-mydriatic cameras

Purpose

Nowadays, complex digital imaging systems allow detailed retinal imaging without dilating patients’ pupils. These so-called non-mydriatic cameras have advantages in common circumstances (eg, for screening or emergency purposes) but present limitations in terms of image quality and field of view. We compare the usefulness of two non-mydriatic camera systems (ie, a handheld versus a stand-alone device) for fundus imaging. The primary outcome was image quality. The secondary outcomes were learning effects and quality grade-influencing factors.

Methods

The imaging procedures followed standard protocol and were all performed by the same investigator. Camera 1 (DRS^®) was a stand-alone system, while Camera 2 (Smartscope^® PRO) was a mobile system. In order to evaluate possible learning effects, we selected an examiner with no prior training in the use of these systems. The images were graded separately by two experienced and “blinded” ophthalmologists following a defined protocol.

Results

In total, 211 people were enrolled. Quality grade comparisons showed significantly better grades for Camera 1. Both systems achieved better quality grades for macular images than for disc-centered images. No remarkable learning effects could be demonstrated.

Conclusions

Both camera systems are useful for fundus imaging. The greater mobility of Camera 2 was associated with lower image quality. For screening scenarios or telemedicine, it must be determined whether image quality or mobility is more important.

Synaptic remodeling generates synchronous oscillations in the degenerated outer mouse retina

During neuronal degenerative diseases, neuronal microcircuits undergo severe structural alterations, leading to remodeling of synaptic connectivity. The functional consequences of such remodeling are mostly unknown. For instance, in mutant rd1 mouse retina, a common model for Retinitis Pigmentosa, rod bipolar cells (RBCs) establish contacts with remnant cone photoreceptors (cones) as a consequence of rod photoreceptor cell death and the resulting lack of presynaptic input. To assess the functional connectivity in the remodeled, light-insensitive outer rd1 retina, we recorded spontaneous population activity in retinal wholemounts using Ca(2+) imaging and identified the participating cell types. Focusing on cones, RBCs and horizontal cells (HCs), we found that these cell types display spontaneous oscillatory activity and form synchronously active clusters. Overall activity was modulated by GABAergic inhibition from interneurons such as HCs and/or possibly interplexiform cells. Many of the activity clusters comprised both cones and RBCs. Opposite to what is expected from the intact (wild-type) cone-ON bipolar cell pathway, cone and RBC activity was positively correlated and, at least partially, mediated by glutamate transporters expressed on RBCs. Deletion of gap junctional coupling between cones reduced the number of clusters, indicating that electrical cone coupling plays a crucial role for generating the observed synchronized oscillations. In conclusion, degeneration-induced synaptic remodeling of the rd1 retina results in a complex self-sustained outer retinal oscillatory network, that complements (and potentially modulates) the recently described inner retinal oscillatory network consisting of amacrine, bipolar and ganglion cells.

Thiazolidin-4-one and thiazinan-4-one derivatives analogous to rosiglitazone as potential antihyperglycemic and antidyslipidemic agents

A number of thiazolidin-4-one and thiazinan-4-one derivatives were prepared by three component condensation in one pot reaction method. These compounds were evaluated for anti-hyperglycemic activity by in vitro and in vivo assay systems. The compounds with thiazolidin-4-one and thiazinan-4-one moieties exhibited significant anti-hyperglycemic activity. A few compounds (3a, 3b, 4a and 4b) have exhibited both anti-hyperglycemic and anti-dyslipidemic activities. Among them the thiazinan-4-one derivative 4a showed maximal (45%) improvement in oral glucose tolerance test in db/db mice at 30 mg/kg oral dose.

Design and synthesis of 3-[(7-chloro-1-oxidoquinolin-4-ylamino)alkyl]-1,3-thiazolidin-4-ones as antimalarial agents

A new series of quinoline analogs have been synthesized and found active against P. falciparum in vitro and P. yoelli in vivo. Compounds 8, 10 and 11 exhibited superior in vitro activity compared to chloroquine. Selected compounds 8, 10 and 11 exhibited significant suppression of parasitaemia in vivo assay. These analogs form a complex with hematin and inhibit the β-hematin formation, suggesting that this class of compounds act on a heme polymerization target. Further this study confirms that quinoline ring nitrogen is essential for both transportation of the molecule across the membrane as well as for tight binding to hematin.

Design, synthesis of 4-aminoquinoline-derived thiazolidines and their antimalarial activity and heme polymerization inhibition studies

The present study describes the synthesis of a series of new 4-aminoquinoline-derived thiazolidines and evaluation of their antimalarial activity against a NF-54 strain of Plasmodium falciparum in vitro and N-67 strain of Plasmodium yoelii in vivo. Among the series, two compounds, 2-(4-chloro-phenyl)-thiazolidine-4-carboxylic acid [2-(7-chloro-quinolin-4-ylamino)-ethyl]-amide hydrochloride (14) and 2-(2,6-dichloro-phenyl)-thiazolidine-4-carboxylic acid [2-(7-chloro-quinolin-4-ylamino)-ethyl]-amide hydrochloride (22) exhibited significant suppression of parasitaemia in the in vivo assay. All the analogues were found to form strong complex with haematin and inhibited the β-haematin formation in vitro. These results suggest that these compounds act on heme polymerization target.

4-Aminoquinoline derived antimalarials: synthesis, antiplasmodial activity and heme polymerization inhibition studies

A new series of 4-aminoquinoline derivatives have been synthesized and found to be active against both susceptible and resistant strains of Plasmodium falciparum in vitro. Compound 1-[3-(7-chloro-quinolin-4-ylamino)-propyl]-3-cyclopropyl-thiourea (7) exhibited superior in vitro activity against resistant strains of P. falciparum as compared to chloroquine (CQ). All the compounds showed resistance factor between 0.59 and 4.31 as against 5.05 for CQ. Spectroscopic studies suggested that this class of compounds act on heme polymerization target.

CpG oligodeoxynucleotide augments the antileishmanial activity of miltefosine against experimental visceral leishmaniasis

OBJECTIVES

To evaluate the combination of CpG oligodeoxynucleotide (CpG ODN) and miltefosine for the treatment of experimental visceral leishmaniasis (VL).

METHODS

The experiments were carried out using BALB/c mice and hamsters, infected with Leishmania donovani. CpG ODN was administered at various doses by the intraperitoneal (ip) route. The dose of CpG ODN (1 nM/single dose) showing best antileishmanial activity was given as free and liposomal forms with a subcurative dose of miltefosine, namely 2.5 and 5 mg/kg x 5 days in mice and hamsters, respectively.

RESULTS

Among the various groups of mice, co-administered liposomal CpG ODN and miltefosine showed the best inhibitory effect (85% inhibition) compared with free CpG ODN and miltefosine, and miltefosine, free CpG ODN and liposomal CpG ODN separately. Production of Th1 cytokines, nitric oxide (NO), reactive oxygen species (ROS) and H(2)O(2) was enhanced. A remarkable increase in the phagocytosis index was also observed, indicating overall immunological support to antileishmanial activity of miltefosine by CpG ODN. Similar responses were observed in hamsters.

CONCLUSIONS

Promising antileishmanial efficacy was observed in animals treated with liposomal CpG ODN and miltefosine, strongly supported by enhancement of Th1 cytokines as well as NO, ROS and H(2)O(2) levels. The correlation of experimental findings in both the models (mouse and hamster) strengthens the potential of CpG ODN as an immunomodulator in combination with miltefosine against VL.

Derivatives of human beta-casein fragments (54-59) exhibit highly potent immunosuppressant activity

Human beta-casein fragment (54-59) having the amino acid sequence Val-Glu-Pro-Ile-Pro-Tyr, has shown potent immunostimulant activity. Several analogs of this hexapeptide have been synthesized with modification at the N-terminal region and two analogs, viz. peptide I and peptide II have shown significant immunosuppressant activity in-vivo mouse model. Effect on cell mediated immunity (CMI) and humoral immunity was studied in mouse/SRBC model. Both the peptides failed to stimulate immune response in vivo and showed inhibition of CMI and humoral response to sheep red blood cells (SRBC). Peptides showed inhibition in alloantigen induced lymphocyte proliferation, i.e., mixed lymphocyte reaction (MLR) in vitro. Treatment with peptides inhibited the production of interferon-gamma (IFN-gamma), and increased the production of interleukin-4 (IL-4) as well as improved the skin graft survival. Cyclosporine a known immunosuppressant showed similar effect on mouse model. Present study thus provides a lead for the development of safe and effective immunosuppressant.

Synthesis and antimalarial activity of novel side chain modified antimalarial agents derived from 4-aminoquinoline

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (de-alklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4-aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4-aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.

Synthesis and antimalarial activity of side chain modified 4-aminoquinoline derivatives

A new series of side-chain modified 4-aminoquinolines have been synthesized and found active against P. falciparum in vitro and P. yoelli in vivo. Compounds 6, 11, 12, and 19 exhibited superior in vitro activity compared to chloroquine. Selected compounds 6, 12, and 19 exhibited significant suppression in the in vivo assay. These analogs form a complex with hematin and inhibit the beta-hematin formation, suggesting that this class of compounds act on a heme polymerization target.

Design, synthesis and antimalarial activity of a new class of iron chelators

Iron is crucial for many biochemical reactions involved in the growth and multiplication of the malaria parasite Plasmodium falciparum. There are many reports indicating that the iron chelators have antimalarial activity in vitro, in vivo and in human studies. However, these compounds suffer from a number of serious problems such as limited membrane permeability, short half-life and require long subcutaneous infusions. To circumvent these drawbacks we have designed a new class of iron chelators, wherein EDTA is tethered to 4-aminoquinoline. Here 4-aminoquinoline scaffold is used as a carrier to penetrate biological membrane and facilitate targetting the compounds to acidic food vacuole of the parasite. This study describes the synthesis of novel iron chelators and their in vitro antimalarial activity against P. falciparum strain of NF-54. The calculated LogP values of these compounds suggest the importance of lipophilicity for the antimalarial activity. The EDTA esters are more active than the corresponding acids. The biophysical studies suggest that these compounds may inhibit the parasite growth by iron chelation mechanism.

Age-dependent changes in the regulation mechanisms for intracellular calcium ions in ganglion cells of the mouse retina

The purpose of this study was to investigate the role of intracellular calcium buffering in retinal ganglion cells. We performed a quantitative analysis of calcium homeostasis in ganglion cells of early postnatal and adult mice by simultaneous patch-clamp recordings in sliced tissue and microfluorometric calcium measurements with Fura-2. Endogenous calcium homeostasis was quantified by using the 'added buffer' approach which uses amplitudes and decay time constants of calcium transients to give a standard for intracellular calcium buffering. The recovery phase of depolarization-induced calcium transients was well approximated by a mono-exponential function with a decay time constant that showed a linear dependence on dye concentration. Endogenous calcium binding ratios were found to be 575 (n = 18 cells) in early postnatal and 121 (n = 18 cells) in adult retinal ganglion cells. With respect to ganglion cell degeneration at early postnatal stages, our measurements suggest that neuroprotection of a majority of developing ganglion cells partially results from a specialized calcium homeostasis based on high buffering capacities. Furthermore, the dramatic decrease of the intracellular calcium buffering capacity during ganglion cell development may enhance their vulnerability to neurodegeneration.

Immunomodulatory activity of analog of muramyl dipeptide and their use as adjunct to chemotherapy of Leishmania donovani in hamster

In search of a potent immunomodulator to be used as an immunoprophylactic agent and as adjunct to chemotherapy against Leishmania infection, two analogs of muramyl dipeptide, viz. N.Ac-norMur-MeVal-D-isoGln (86/448) and N.AcMur-Acc-D-isoGln (89/729) were evaluated for desired activity. Effect of these peptides on cell mediated and humoral immunity was studied by immunizing the peptide treated mouse with sheep red blood cells (SRBC) and determining HA-titer, plaque forming cells assay and delayed type of hypersensitivity (DTH) response after 4-5 days. Both the peptides stimulated cell mediated immunity (CMI), humoral response as well as macrophage function in terms of super oxide anion (O2-) and nitric oxide (NO) generation. Mitogen induced lymphocyte proliferation and production of IL-2 and INF-gamma increased while that of IL-4 and IL-10 decreased by both the peptides showing a typical Th1 type response. After establishing the immunostimulatory activity, these peptides were evaluated for immunoprophylactic efficacy as well as for use as adjunct to chemotherapy with stibanate (SSG) against Leishmania donovani infection in golden hamster. These peptides were found quite effective in both the modes. In adjunct use the treatment may require lower dose of SSG and thereby reduce the chances of drug toxicity.

Tuftsin-Bearing Liposomes as Antibiotic Carriers in Treatment of Macrophage Infections

Tuftsin is a tetrapeptide (Thr-Lys-Pro-Arg) that specifically binds monocytes, macrophages, and polymorphonuclear leukocytes and potentiates their natural killer activity against tumors and pathogens. The antimicrobial activity of this peptide is significantly increased by attaching at the C-terminus a fatty acyl residue through the ethylenediamine spacer arm. This activity is further augmented by incorporating the modified tuftsin in the liposomes. The tuftsin-bearing liposomes not only enhance the host's resistance against a variety of infections but also serve as useful vehicles for the site-specific delivery of drugs in a variety of macrophage-based infections, such as tuberculosis and leishmaniasis.

Adjunct Effect of Immunostimulating Hexapeptide Analogous to Human Beta‐Casein Fragment (54–59) to Sodium Stibogluconate Against Experimental Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a major public health problem in many tropical countries of the world. The available chemotherapeutics require parenteral administration and have other limitations like cost, toxicity, variable efficacy or restricted supplies. There is no effective treatment for immunosuppressed patients with leishmaniasis- HIV co-infection. Hence, new therapies, that are effective when treatment with the currently available drugs fails, must be developed. One of the major strategies for effective and safe treatment of leishmaniasis and other infectious diseases, in the last decade, involves the use of immunomodulators as adjunct to chemotherapy. In this context, we studied the immunomodulatory activity of a hexapeptide Val-Glu-Pro-Ile-Gly-Tyr (CDRI compound 89-215) corresponding to (54-59) fragment of human beta-casein in mice and its efficacy in adjunct chemotherapy with SSG using L. donovani/hamster model. The hexapeptide was found to enhance both humoral and CMI responses. In animal model the hexapeptide per se showed no antileishmanial activity. However, when given alongwith suiboptimal dose of SSG, it enhanced the efficacy of SSG from 24% to 80%. The activity was very close to the efficacy (85%) recorded for curative dose of SSG. Adjunct chemotherapy with immunomodulator in visceral leishmaniasis appears to be a fruitful preposition.

Synthesis and antimicrobial activity of erythromycin-A oxime analogs

A series of erythromycin-A oxime ether as well as esters have been synthesized. Ether derivatives were synthesized through the epoxy ether intermediate of erythromycin-9-oxime, followed by opening of the epoxy linkage through various amines, whereas esters have been prepared through DCC mediated protocol. These derivatives have been evaluated for antibacterial activity and found to be as active as erythromycin-A.

Generating neutralizing antibodies, Th1 response and MHC non restricted immunogenicity of HIV-I env and gag peptides in liposomes and ISCOMs with in-built adjuvanticity

For enhancing immunogenicity and develop vaccine strategies using peptide based constructs against HIV-1, a chimeric peptide containing V3 loop and transmembrane sequence of gp41 with two glycine motifs as spacer was constructed. The V3-gp41, gp41 peptide and p17 and p24 peptides separately or in a cocktail were entrapped with or without MA729 as an immunoadjuvant in liposomes or ISCOMs. The immunogenicity, antigen induced T-cell proliferation and cytokine profiles of various formulations were studied in four different inbred strains of mice of H-2^d, H-2^b, H-2^k and H-2^q haplotypes, keeping alum as a control adjuvant. Both liposomes and ISCOM preparations elicited high titer and long lasting antibody response (60 days and above). When compared to the alum formulation, the liposomes co-entrapped with MA729 produced high antibody levels, comparable with that induced by ISCOMs. Peptide in alum, liposomes and ISCOMs enhanced both antigen specific IgG2a and IgG2b isotypes and high T-cell stimulation index. Peptide formulations also induced antibodies with high affinity and in vitro neutralizated the formation of HIV-1 syncytia. T-cell supernatants contained high levels of IFN-γ and IL-2. Thus formulation in these adjuvants induced a predominant Th1 like response with MA729 as a versatile novel delivery vehicle for stimulating the appropriate arm of the immune response that can selectively modulate MHC class I or MHC class II response. The above peptide can be of wide vaccination interest as a means to improve immune responses to several other HIV-1 antigens and may serve as candidates for vaccine development.

Reversal of T cell anergy in leprosy patients: in vitro presentation with Mycobacterium leprae antigens using murabutide and Trat peptide in liposomal delivery

Mycobacterium leprae, the causative agent of leprosy resides and multiplies within the host monocytes and macrophages, thereby evading host immune system. Cell-mediated immune response (CMI) plays a vital role as evidenced from the high CMI in BT/TT (borderline and tuberculoid) patients and conversely low in BL/LL (borderline and lepromatous) patients. In the present study, an attempt was made to immunomodulate the anergized T cells of lepromatous leprosy patients by presenting the mycobacterial antigen in combination with T cell adjuvant, murabutide (active analog of muramyl' dipeptide, MDP-BE) and a Trat peptide (T cell epitope of Integral membrane protein (Trat) from Escherichia coli) in particulate form (liposomes) or soluble form (media). PBMNC of normal, BT/TT and BL/LL were stimulated in vitro with five mycobacterial antigens (Ag) in the following formulations, Ag, Ag+murabutide, Ag+murabutide+Trat peptide either in liposomes or in medium. All the five antigen(s) when delivered in liposomes containing murabutide and Trat peptide showed a very high lymphoproliferative response (p<0.001) in all the three groups. IFN-gamma and IL-2 were significantly (p<0.001) high in these culture supernatants compared to IL-10 and IL-4 confirming a shift from CD4+Th2 to Th1 response in leprosy patients with particulate mode of antigen presentation. Interestingly, PBMNC derived from lepromatous patients also showed consistent T cell proliferation with all the formulations. Further, the mechanism of liposomal processing of antigens was studied using different inhibitors that interfere at different stages of antigen presentation. Results indicate that this study may pave way for an immunotherapeutic approach for reverting the anergic T cells of lepromatous patients to proliferating T cells with the release of Th1 cytokines thereby restoring the CMI response in these patients.

A Facile and Simple Method for the Reduction of N-protected Amino Acids and Peptides to the Corresponding Alcohols

A practical and chemoselective method for the reduction of N-protected amino acids and peptides including carboxylic acids to their corresponding alcohols is outlined.

Inhibition of anti-CD3 and interleukin-2 stimulated T lymphocyte proliferation by peptidomimetic opioid compound

In continuation to our earlier studies with peptidomimetic opioid compounds, we have further investigated immunosuppressive properties of one of our peptidomimetic compound (Tyr-NH-CH2-CH2-O-Phe-NH2) using peripheral blood mononuclear cells (PBMCs) of healthy volunteers. Peptidomimetic compound was evaluated for its effect on anti-CD3 and recombinant human interleukin-2 (rhIL-2) stimulated lymphocyte proliferation in vitro and lipopolysaccharide (LPS) induced activation of mitogen activated protein kinase (MAPK, pp42/44) in mouse macrophage cells (RAW 264.7). Our results show the immunosuppressive potential of synthetic peptidomimetic compound. This compound significantly inhibited anti-CD3 and rhIL-2 stimulated lymphocyte proliferation in vitro. However, this peptidomimetic compound did not show any effect on LPS induced MAPK activation. These observations suggest that above peptidomimetic compound has potential to inhibit immune responses mediated by lymphocytes.

Immunomodulator Tuftsin Augments Antifilarial Activity of Diethylcarbamazine Against Experimental Brugian Filariasis

In the present study, we evaluated the potential of an immunomodulator tuftsin in increasing the efficacy of liposomised diethylcarbamazine (DEC) against experimental filarial infection of Brugia malayi. The liposomised form of DEC, when used at sub-optimal dose of 25 mg/kg body weight, successfully eliminated filarial parasite from systemic circulation in animals inflicted with B. malayi infection. However, the formulation was effective upto 60 days post infection only, followed by recurrence of the infection. In contrast, the co-administration of liposomal formulation of DEC along with an immunomodulator tuftsin was found to be competent enough to suppress microfilarial stage of parasite till 90 days post treatment. Interestingly, tuftsin bearing DEC liposomes were found to be effective against adult parasite as well.

Use of tuftsin bearing nystatin liposomes against an isolate of Candida albicans showing less in vivo susceptibility to amphotericin B

In the present study, we evaluated tuftsin bearing nystatin liposomes for their potential against an isolate of Candida albicans (C. albicans) showing less in vivo susceptibility to amphotericin B (Amp B). The liposomised-Amp B in higher doses was found to be effective in elimination of less susceptible strain of C. albicans (C. albicans JMCR) in Balb/c mice, but may not be recommended due to toxicity constraints. On the other hand, liposomal nystatin was shown to possess higher efficacy as compared to that of Amp B, and was pertinent in treatment of C. albicans JMCR strain. The data of present work reveals that the incorporation of nystatin in tuftsin-bearing-liposomes results in a significant increase in its efficacy against experimental murine candidiasis. Interestingly, the pre-treatment of animals with liposomised-tuftsin prior to challenge with C. albicans infection was more effective in elimination of the pathogen from host and shows an advantage in prophylactic perspectives.

Inhibition of antigen specific lymphocyte proliferation and cytokine stimulation by peptidomimetic opioid compound

In sequel to our preliminary observations with peptidomimetic opioid compounds, we have further investigated immunomodulatory activity of one peptidomimetic compound (Tyr-NH-CH2-CH2-O-Phe-NH2) with peripheral blood mononuclear cells (PBMCs) of healthy volunteers/tuberculosis patients. This peptidomimetic compound was evaluated for its effect on purified protein derivative (PPD) stimulated lymphocyte proliferation in vitro, production of Th1 and Th2 cytokines by ELISA and ribonuclease protection assay. Our study shows the immunosuppressive potential of above synthetic peptidomimetic compound. This compound inhibited PPD stimulated human lymphocyte proliferation and this inhibition was reversed by opioid receptor antagonist, naloxone. Its immunosuppressive effect was further demonstrated by inhibition of interleukin-9 (IL-9), IL-10 but failed to influence IL-2, IL-15 and interferon-y (IFN-gamma) in PPD stimulated human PBMCs.

Immunomodulation by biphalin, dimeric synthetic opioid peptide, and its analog

The opioid pentapeptides called enkephalins were originally described as the endogenous ligands for the opioid receptors. Although their precise physiological significance still remains elusive, the enkephalins have been reported to exhibit analgesic, antidepressant, antianxiety and anticonvulsant activities. In addition, enkephalins have also been shown to act as immunomodulator. The first generation of dimeric peptides was derived from enkephalins. Biphalin [(Tyr-D-Ala-Gly-Phe-NH)2] is a bivalent opioid analog containing two tyrosine residues. We have evaluated the immunomodulatory properties of biphalin and its analogs in various in vitro tests. We report that biphalin and one of its analogs [Tyr-D-Ala-Gly-Phe-NH.NH-Phe(p-Cl)-H] stimulate human T cell proliferation, natural killer (NK) cell cytotoxicity in vitro and interleukin-2 (IL-2) production. Biphalin and its analog also released chemokine like factor in the culture supernatant that was responsible for increased chemotaxis of monocytes. Furthermore, these peptides inhibited tumor necrosis factor (TNF-alpha) production in lipopolysaccharide (LPS) stimulated peripheral blood mononuclear cells (PBMC) and nitric oxide (NO) production in mouse macrophage cells, RAW 264.7. Our observations suggest immunomodulatory property of biphalin and its analog.

Enhanced immunostimulant activity and protective effect of a synthetic lipopeptide after liposomization against Plasmodium berghei infection in mice

The immunostimulant activity of non-pyrogenic, sugar-free immunomodulator lipopeptide, Ala-D-Glu(Gly-Lys-CO.C11H23)-NH2 (comp. no 84/201), and its liposomized formulation has been studied. Liposomization of this lipopeptide significantly enhanced its antigen specific as well as nonspecific immune responses, as compared to the free lipopeptide. The liposomized formulation of lipopeptide significantly stimulated both the antibody and delayed-type hypersensitivity responses in Balb/c mice, and also enhanced nonspecifically the macrophage migration index, phagocytic activity and incorporation of 14C glucosamine in peritoneal macrophages of the mice that received pretreatment with this preparation. Further, the mice that received pretreatment with the liposomized preparation strongly resisted lethal P. berghei infection and consequently survived for longer period of times. These results indicate that liposomization of the compound no 84/201 significantly improves its ability to enhance not only antigen-specific immune response but also the nonspecific host's resistance against infections.

Inducing a cell-mediated immune response against peptides of the Plasmodium vivax circumsporozoite protein

An attempt was made to generate an unrestricted cellular immune response against peptide antigens of the circumsporozoite protein (CSP) of Plasmodium vivax. The peptides used represent the repeat-region sequences of the type-I variant (AA and DA) or type-II variant (ANG) and the conserved region (region II) containing the hepatocyte-binding region extended to include a T-cell epitope (HBP). The study was conducted in outbred mice and two genetically unrelated inbred strains of mice. Spleen cells, recovered from mice that had been primed either with one peptide or a conjugate formed of HBP linked to one of the repeat-region peptides, were pulsed in vitro with varying amounts of individual peptides/conjugates, both in soluble and particulate form (with and without a human beta-casein bio-active fragment analogue as adjuvant). In the tests using the cells from the mice primed with an individual peptide(s), HBP showed a high proliferation index, and the repeat-region peptides, especially AA, showed T-cell activity in at least one of the mouse strains studied. In vitro, higher concentrations of the free peptides than of liposomal preparations of the peptides had to be used to elicit the optimal proliferation of the cells from each strain of mice. Interestingly, the cells from the conjugate-primed mice showed enhanced proliferation (compared with that observed in the cells from mice primed with individual peptides) when stimulated with each component, and especially the repeat-region sequence, of the relevant conjugate. In such cases there was no evidence of restriction of the immune response by the major histocompatibility complex. The major secreted cytokines were found to be from CD4(+) Th1 (interferon-gamma and interleukin-2), with relatively low levels of the Th-2 cytokines interleukin-4 and interleukin-6. The delivery of cohered 'B-T' peptide(s) sequences from the same protein, ideally with an immunostimulatory adjuvant or as a liposomal preparation, should greatly enhance the cell-mediated immune response and should improve clearance of mosquito-inoculated P. vivax sporozoites.

Modulation of the humoral response to repeat and non-repeat sequences of the circumsporozoite protein of Plasmodium vivax using novel adjuvant and delivery systems

In the use of sub-unit vaccines, it is important to identify the protective epitopes and to generate the optimal immune response by using appropriate immuno-modulatory adjuvants and/or delivery systems. The main aim of the present study was to generate an MHC-non-restricted immune response against one promising vaccine candidate, the circumsporozoite protein (CSP) of Plasmodium vivax. Four synthetic peptides were chosen: three repeat-region sequences (AA, DA and ANG) and a putative T-cell epitope extended from a conserved region (region II) containing a hepatocyte-binding region (HBP). The humoral response against each peptide was studied in outbred mice and three strains of inbred mice (with different genetic backgrounds). Delivery of each peptide in microspheres or inclusion of a bio-active casein-fragment analogue as adjuvant with alum/liposome delivery considerably enhanced the humoral response against the peptide (when compared with the response to the peptide delivered in alum alone). The maximal immune response was observed when the peptide was delivered in microspheres, with no booster doses required; the antibodies raised against peptide delivered with adjuvant or in modulatory delivery vehicles had two-to five-fold lower binding affinities. The predominant IgG isotypes elicited using microspheres or adjuvant with alum/liposome delivery were IgG(2a)/IgG(2b) and/or IgG(1). Importantly, conjugation of HBP to the B-cell repeat peptides increased the titres of peptide-specific antibodies, especially of antibodies against the supposedly cryptic HBP. Delivery of a mix of all four peptides in microspheres elicited an intense immune response in outbred mice, indicating that such a delivery system efficiently presents the peptides to the immune effector cells. That antibodies in the anti-peptide sera bound strongly to air-dried sporozoites of P. vivax was confirmed by immunofluorescence. The present results, based on the use of individual peptides or a conjugate or cocktail of the peptides, highlight the utility of the casein-fragment analogue as an adjuvant, when used with alum/liposome delivery, and also demonstrate the potential of microspheres as a single-shot delivery system for sub-unit peptides.

Immunomodulation by opioid peptidomimetic compound

OBJECTIVE

As a follow-up to our earlier studies on immunomodulation with opioid peptides, we synthesized and evaluated immunomodulatory activity of four peptidomimetic compounds, i.e. Tyr-NH-C(Me)(2)-CH(2)-O-Phe-NH(2 )(1), Tyr-NH-C(6)H(5)-(o)-CH(2)-CH(2)-O-Phe-NH(2) (2), Tyr-NH-CH(2)-CH(2)-O-Phe-NH(2) (3) and Tyr-NH-CH(D-Et)-CH(2)-O-Phe-NH(2) (4).

METHODS

These compounds were synthesized in solution phase and evaluated for their immunomodulatory properties in vitro by mixed lymphocyte reaction (MLR), proliferation of opioid receptor-expressing cells, production of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide.

RESULTS

This study shows the immunosuppressive potential of synthetic peptidomimetic compound 3. This compound inhibited two-way MLR and suppressed the proliferation of the mu-opioid receptor expressing human embryonic kidney cells HEK 293 in vitro. Inhibition of MLR by compound 3 was reversed by naloxone (opioid receptor antagonist) and beta-funaltrexamine hydrochloride (mu-opioid receptor antagonist). The immunosuppressive effect of compound 3 was further demonstrated by inhibition of TNF-alpha and nitric oxide production in lipopolysaccharide-stimulated human PBMCs and mouse macrophage cells RAW 264.7, respectively.

CONCLUSION

These observations suggest that compound 3 inhibits MLR through mu-opioid receptor present on cells.

Antisense peptide interactions studied by electrospray ionization mass spectrometry

Non-covalent interactions between met- and leu-enkephalins and their antisense peptides were studied by electrospray ionization mass spectrometry. Mixtures of sense and antisense peptides gave both the corresponding homodimers and heterodimers. The relative abundance ratios of the heterodimer to that of the homodimer of the sense peptide and the relative stability constants of the heterodimers were compared with the corresponding values from mixtures of the sense peptides and a control peptide. The results show that there is a preferential interaction between the sense and antisense peptides compared with that between the sense and control peptides.