High-throughput measurement of the content and properties of nano-sized bioparticles with single-particle profiler

We introduce a method, single-particle profiler, that provides single-particle information on the content and biophysical properties of thousands of particles in the size range 5-200 nm. We use our single-particle profiler to measure the messenger RNA encapsulation efficiency of lipid nanoparticles, the viral binding efficiencies of different nanobodies, and the biophysical heterogeneity of liposomes, lipoproteins, exosomes and viruses.

The shift to a proteinopenia paradigm in neurodegeneration

The toxic proteinopathy paradigm has defined neurodegenerative disorders for over a century. This gain-of-function (GOF) framework posited that proteins become toxic when turned into amyloids (pathology), predicting that lowering its levels would translate into clinical benefits. Genetic observations used to support a GOF framework are equally compatible with a loss-of-function (LOF) framework, as the soluble pool of proteins rendered unstable by these mutations (e.g., APP in Alzheimer's disease, SNCA in Parkinson's disease) aggregate, becoming depleted. In this review, we highlight misconceptions that have prevented LOF from gaining currency. Some of these misconceptions include no phenotype in knock-out animals (there is neurodegenerative phenotype in knock-out animals) and high levels of proteins in patients (patients have lower levels of the proteins involved in neurodegeneration than healthy age-matched controls). We also expose the internal contradictions within the GOF framework, namely that (1) pathology can have both pathogenic and protective roles; (2) the neuropathology gold standard for diagnosis can be present in normal individuals and absent in those affected; (3) oligomers are the toxic species even if they are ephemeral and decrease over time. We therefore advocate for a paradigm shift from proteinopathy (GOF) to proteinopenia (LOF) based on the universal depletion of soluble functional proteins in neurodegenerative diseases (low amyloid-β 42 in Alzheimer's disease, low α-synuclein in Parkinson's disease, and low tau in progressive supranuclear palsy) and supported by the confluence of biologic, thermodynamic, and evolutionary principles with proteins having evolved to perform a function, not to become toxic, and where protein depletion is consequential. Such shift to a Proteinopenia paradigm is necessary to examining the safety and efficacy of protein replacement strategies instead of perpetuating a therapeutic paradigm with further antiprotein permutations.

The allure and pitfalls of the prion-like aggregation in neurodegeneration

Prion diseases are fatal neurodegenerative disorders where the formation of amyloids is thought to be infectious by templating their conformation on to natively-folded counterparts. Postulated nearly four decades ago, the search for the mechanism behind the conformational templating has proceeded to no avail. Here, we extend the thermodynamic hypothesis of protein folding (Anfinsen's dogma) to the amyloid phenomenon and illustrate that the amyloid conformation (cross-β) is one of two conformational states that are thermodynamically accessible to any protein sequence depending on concentration. A protein spontaneously assumes its native conformation below supersaturation and the amyloid cross-β conformation above supersaturation. The information to adopt the native conformation and the amyloid conformation is present in the primary sequence and the backbone of the protein, respectively, and does not require templating. The rate-limiting step for proteins to adopt the cross-β conformation of amyloid is termed nucleation, which can be catalyzed by surfaces (heterogeneous nucleation) or preformed amyloid fragments (seeding). Irrespective of the nucleation pathway, once triggered, amyloid formation proceeds spontaneously in fractal-like fashion, where the surfaces of the growing fibrils act as heterogeneous nucleation catalysts for new fibrils, a phenomenon known as secondary nucleation. This pattern is in contrast to the linear growth assumptions that the prion hypothesis necessitates for faithful prion strain replication. Additionally, the cross-β conformation buries the majority of the protein side chain inside the fibrils, making the fibrils inert, generic, and extremely stable. As such, the source of toxicity in prion disorders may come to a greater extent from the loss of proteins in their normal, soluble, and therefore functional state rather than from their transformation into stable, insoluble, nonfunctioning amyloids.

Inferior Alveolar Nerve Block Success of 2% Mepivacaine versus 4% Articaine in Patients with Symptomatic Irreversible Pulpitis in Mandibular Molars: A Randomized Double-Blind Single-Centre Clinical Trial

AIM

To assess inferior alveolar nerve block (IANB) success of 2% mepivacaine (Scandonest 2%, Septodont, France) and 4% articaine (Septanest 4%, Septodont) in patients with symptomatic irreversible pulpitis (SIP) in mandibular molars during access cavity preparation and instrumentation.

METHODOLOGY

Three hundred and thirty patients with moderate-to-severe pain in mandibular molars with SIP randomly received either 3.6 mL 2% mepivacaine hydrochloride with 1:100 000 adrenalin or 3.4mL 4% articaine hydrochloride with 1:100 000 adrenalin (n=165). Intraoperative pain (IOP) intensity was assessed during access cavity preparation and canal instrumentation using 11-point numerical rating scale (NRS). Overall success was considered if the patient felt no-to-mild pain without the need of supplemental anaesthesia throughout treatment; the incidence of need for supplemental anaesthesia was also recorded. Data were statistically analyzed using Mann Whitney U and Chi² (χ² ) tests. Relative risk (RR) and 95% confidence interval (CI) of anaesthetic failure was calculated. The effect of predisposing factors on outcome variables was assessed using multivariable regression analyses. None of the participants reported any adverse effects.

RESULTS

Baseline variables were balanced between groups (p>0.05). The IOP intensity during access cavity preparation and canal instrumentation was similar for both groups (p>0.05). IOP intensity was associated with preoperative pain intensity and tooth type (p<0.05). Overall anaesthetic success rate was 35.8% for mepivacaine and 41.2% for articaine (p>0.05) with a relative risk of failure [95%CI] 1.09 [0.92, 1.30]. The need for supplemental anaesthesia occurred 43.6% and 38.2% with mepivacaine and articaine respectively (p>0.05; RR [95%CI]: 1.14 [0.88, 1.48]). Preoperative pain level and age were associated with the need for supplemental anaesthesia.

CONCLUSIONS

2% mepivacaine and 4% articaine demonstrate similar IANB success rates for mandibular molars with SIP. Intraoperative pain experience during endodontic treatment can be associated with preoperative pain, tooth type and age.

Proteins Do Not Replicate, They Precipitate: Phase Transition and Loss of Function Toxicity in Amyloid Pathologies

Protein aggregation into amyloid fibrils affects many proteins in a variety of diseases, including neurodegenerative disorders, diabetes, and cancer. Physicochemically, amyloid formation is a phase transition process, where soluble proteins are transformed into solid fibrils with the characteristic cross-β conformation responsible for their fibrillar morphology. This phase transition proceeds via an initial, rate-limiting nucleation step followed by rapid growth. Several well-defined nucleation pathways exist, including homogenous nucleation (HON), which proceeds spontaneously; heterogeneous nucleation (HEN), which is catalyzed by surfaces; and seeding via preformed nuclei. It has been hypothesized that amyloid aggregation represents a protein-only (nucleic-acid free) replication mechanism that involves transmission of structural information via conformational templating (the prion hypothesis). While the prion hypothesis still lacks mechanistic support, it is also incompatible with the fact that proteins can be induced to form amyloids in the absence of a proteinaceous species acting as a conformational template as in the case of HEN, which can be induced by lipid membranes (including viral envelopes) or polysaccharides. Additionally, while amyloids can be formed from any protein sequence and via different nucleation pathways, they invariably adopt the universal cross-β conformation; suggesting that such conformational change is a spontaneous folding event that is thermodynamically favorable under the conditions of supersaturation and phase transition and not a templated replication process. Finally, as the high stability of amyloids renders them relatively inert, toxicity in some amyloid pathologies might be more dependent on the loss of function from protein sequestration in the amyloid state rather than direct toxicity from the amyloid plaques themselves.

High Soluble Amyloid-β42 Predicts Normal Cognition in Amyloid-Positive Individuals with Alzheimer's Disease-Causing Mutations

BACKGROUND

In amyloid-positive individuals at risk for Alzheimer's disease (AD), high soluble 42-amino acid amyloid-β (Aβ42) levels are associated with normal cognition. It is unknown if this relationship applies longitudinally in a genetic cohort.

OBJECTIVE

To test the hypothesis that high Aβ42 preserves normal cognition in amyloid-positive individuals with Alzheimer's disease (AD)-causing mutations (APP, PSEN1, or PSEN2) to a greater extent than lower levels of brain amyloid, cerebrospinal fluid (CSF) phosphorylated tau (p-tau), or total tau (t-tau).

METHODS

Cognitive progression was defined as any increase in Clinical Dementia Rating (CDR = 0, normal cognition; 0.5, very mild dementia; 1, mild dementia) over 3 years. Amyloid-positivity was defined as a standard uptake value ratio (SUVR) ≥1.42 by Pittsburgh compound-B positron emission tomography (PiB-PET). We used modified Poisson regression models to estimate relative risk (RR), adjusted for age at onset, sex, education, APOE4 status, and duration of follow-up. The results were confirmed with multiple sensitivity analyses, including Cox regression.

RESULTS

Of 232 mutation carriers, 108 were PiB-PET-positive at baseline, with 43 (39.8%) meeting criteria for progression after 3.3±2.0 years. Soluble Aβ42 levels were higher among CDR non-progressors than CDR progressors. Higher Aβ42 predicted a lower risk of progression (adjusted RR, 0.36; 95% confidence interval [CI], 0.19-0.67; p = 0.002) better than lower SUVR (RR, 0.81; 95% CI, 0.68-0.96; p = 0.018). CSF Aβ42 levels predicting lower risk of progression increased with higher SUVR levels.

CONCLUSION

High CSF Aβ42 levels predict normal cognition in amyloid-positive individuals with AD-causing genetic mutations.

Soluble Amyloid-β Consumption in Alzheimer's Disease

Brain proteins function in their soluble, native conformation and cease to function when transformed into insoluble aggregates, also known as amyloids. Biophysically, the soluble-to-insoluble phase transformation represents a process of polymerization, similar to crystallization, dependent on such extrinsic factors as concentration, pH, and a nucleation surface. The resulting cross-β conformation of the insoluble amyloid is markedly stable, making it an unlikely source of toxicity. The spread of brain amyloidosis can be fully explained by mechanisms of spontaneous or catalyzed polymerization and phase transformation instead of active replication, which is an enzyme- and energy-requiring process dependent on a specific nucleic acid code for the transfer of biological information with high fidelity. Early neuronal toxicity in Alzheimer's disease may therefore be mediated to a greater extent by a reduction in the pool of soluble, normal-functioning protein than its accumulation in the polymerized state. This alternative loss-of-function hypothesis of pathogenicity can be examined by assessing the clinical and neuroimaging effects of administering non-aggregating peptide analogs to replace soluble amyloid-β levels above the threshold below which neuronal toxicity may occur. Correcting the depletion of soluble amyloid-β, however, would only exemplify 'rescue medicine.' Precision medicine will necessitate identifying the pathogenic factors catalyzing the protein aggregation in each affected individual. Only then can we stratify patients for etiology-specific treatments and launch precision medicine for Alzheimer's disease and other neurodegenerative disorders.

High cerebrospinal amyloid-β 42 is associated with normal cognition in individuals with brain amyloidosis

BACKGROUND

Brain amyloidosis does not invariably predict dementia. We hypothesized that high soluble 42-amino acid β amyloid (Aβ42) peptide levels are associated with normal cognition and hippocampal volume despite increasing brain amyloidosis.

METHODS

This cross-sectional study of 598 amyloid-positive participants in the Alzheimer's Disease Neuroimaging Initiative cohort examined whether levels of soluble Aβ42 are higher in amyloid-positive normal cognition (NC) individuals compared to mild cognitive impairment (MCI) and Alzheimer's disease (AD) and whether this relationship applies to neuropsychological assessments and hippocampal volume measured within the same year. All subjects were evaluated between June 2010 and February 2019. Brain amyloid positivity was defined as positron emission tomography-based standard uptake value ratio (SUVR) ≥1.08 for [18] F-florbetaben or 1.11 for [18]F-florbetapir, with higher SUVR indicating more brain amyloidosis. Analyses were adjusted for age, sex, education, APOE4, p-tau, t-tau, and centiloids levels.

FINDINGS

Higher soluble Aβ42 levels were observed in NC (864.00 pg/ml) than in MCI (768.60 pg/ml) or AD (617.46 pg/ml), with the relationship between NC, MCI, and AD maintained across all amyloid tertiles. In adjusted analysis, there was a larger absolute effect size of soluble Aβ42 than SUVR for NC (0.82 vs. 0.40) and MCI (0.60 vs. 0.26) versus AD. Each standard deviation increase in Aβ42 was associated with greater odds of NC than AD (adjusted odds ratio, 6.26; p < 0.001) or MCI (1.42; p = 0.006). Higher soluble Aβ42 levels were also associated with better neuropsychological function and larger hippocampal volume.

INTERPRETATION

Normal cognition and hippocampal volume are associated with preservation of high soluble Aβ42 levels despite increasing brain amyloidosis.

FUNDING

Please refer to the Funding section at the end of the article.

Phenotype-Agnostic Molecular Subtyping of Neurodegenerative Disorders: The Cincinnati Cohort Biomarker Program (CCBP)

Ongoing biomarker development programs have been designed to identify serologic or imaging signatures of clinico-pathologic entities, assuming distinct biological boundaries between them. Identified putative biomarkers have exhibited large variability and inconsistency between cohorts, and remain inadequate for selecting suitable recipients for potential disease-modifying interventions. We launched the Cincinnati Cohort Biomarker Program (CCBP) as a population-based, phenotype-agnostic longitudinal study. While patients affected by a wide range of neurodegenerative disorders will be deeply phenotyped using clinical, imaging, and mobile health technologies, analyses will not be anchored on phenotypic clusters but on bioassays of to-be-repurposed medications as well as on genomics, transcriptomics, proteomics, metabolomics, epigenomics, microbiomics, and pharmacogenomics analyses blinded to phenotypic data. Unique features of this cohort study include (1) a reverse biology-to-phenotype direction of biomarker development in which clinical, imaging, and mobile health technologies are subordinate to biological signals of interest; (2) hypothesis free, causally- and data driven-based analyses; (3) inclusive recruitment of patients with neurodegenerative disorders beyond clinical criteria-meeting patients with Parkinson's and Alzheimer's diseases, and (4) a large number of longitudinally followed participants. The parallel development of serum bioassays will be aimed at linking biologically suitable subjects to already available drugs with repurposing potential in future proof-of-concept adaptive clinical trials. Although many challenges are anticipated, including the unclear pathogenic relevance of identifiable biological signals and the possibility that some signals of importance may not yet be measurable with current technologies, this cohort study abandons the anchoring role of clinico-pathologic criteria in favor of biomarker-driven disease subtyping to facilitate future biosubtype-specific disease-modifying therapeutic efforts.

Disentangling the Amyloid Pathways: A Mechanistic Approach to Etiology

Amyloids are fibrillar protein aggregates associated with diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), type II diabetes and Creutzfeldt-Jakob disease. The process of amyloid polymerization involves three pathological protein transformations; from natively folded conformation to the cross-β conformation, from biophysically soluble to insoluble, and from biologically functional to non-functional. While amyloids share a similar cross-β conformation, the biophysical transformation can either take place spontaneously via a homogeneous nucleation mechanism (HON) or catalytically on an exogenous surface via a heterogeneous nucleation mechanism (HEN). Here, we postulate that the different nucleation pathways can serve as a mechanistic basis for an etiological classification of amyloidopathies, where hereditary forms generally follow the HON pathway, while sporadic forms follow seed-induced (prions) or surface-induced (including microbially induced) HEN pathways. Critically, the conformational and biophysical amyloid transformation results in loss-of-function (LOF) of the original natively folded and soluble protein. This LOF can, at least initially, be the mechanism of amyloid toxicity even before amyloid accumulation reaches toxic levels. By highlighting the important role of non-protein species in amyloid formation and LOF mechanisms of toxicity, we propose a generalized mechanistic framework that could help better understand the diverse etiology of amyloid diseases and offer new opportunities for therapeutic interventions, including replacement therapies.

Degradation of pristine and oxidized single wall carbon nanotubes by CYP3A4

Carbon nanotubes (CNTs) are a class of carbon based nanomaterials which have attracted substantial attention in recent years as they exhibit outstanding physical, mechanical and optical properties. In the last decade many studies have emerged of the underlying mechanisms behind CNT toxicity including malignant transformation, the formation of granulomas, inflammatory responses, oxidative stress, DNA damage and mutation. In the present investigation, we studied the biodegradation of single-walled carbon nanotubes (SWCNTs) by Cytochrome P450 enzymes (CYP3A4) through using Raman spectroscopy. CYP3A4 is known isozyme accountable for metabolizing various endogenous and exogenous xenobiotics. CYP3A4 is expressed dominantly in the liver and other organs including the lungs. Our results suggest that CYP3A4 has a higher affinity for p-SWNTs compared to c-SWNTs. HEK293 cellular viability was not compromised when incubated with SWNT. However, CYP3A4 transfected HEK293 cell line showed no digestion of c-SWNTs after incubation for 96 h. Cellular uptake of c-SWNTs was observed by electron microscopy and localization of c-SWNTs was confirmed in endosomal vesicles and in the cytoplasm. This is the first study CYP3A4 degrading both p-SWNTs and c-SWNTs in an in vitro setup. Interestingly, our results show that CYP3A4 is more proficient in degrading p-SWNTs than c-SWNTs. We also employed computational modeling and docking assessments to develop a further understanding of the molecular interaction mechanism.

Novel peptide-dendrimer/lipid/oligonucleotide ternary complexes for efficient cellular uptake and improved splice-switching activity

Despite the advances in gene therapy and in oligonucleotide (ON) chemistry, efficient cellular delivery remains an obstacle. Most current transfection reagents suffer from low efficacy or high cytotoxicity. In this report, we describe the synergism between lipid and dendrimer delivery vectors to enhance the transfection efficiency, while avoiding high toxicity. We screened a library of 20 peptide dendrimers representing three different generations and evaluated their capability to deliver a single-stranded splice-switching ON after formulating with lipids (DOTMA/DOPE). The transfection efficiency was analyzed in 5 reporter cell lines, in serum-free and serum conditions, and with 5 different formulation protocols. All formulations displayed low cytotoxicity to the majority of the tested cell lines. The complex sizes were < 200 nm; particle size distributions of effective mixtures were < 80 nm; and, the zeta potential was dependent on the formulation buffer used. The best dendrimer enhanced transfection in a HeLa reporter cell line by 30-fold compared to untreated cells under serum-free conditions. Interestingly, addition of sucrose to the formulation enabled - for the first time - peptide dendrimers/lipid complexes to efficiently deliver splice-switching ON in the presence of serum, reaching 40-fold increase in splice switching. Finally, in vivo studies highlighted the potential of these formulae to change the biodistribution pattern to be more towards the liver (90% of injected dose) compared to the kidneys (5% of injected dose) or to unformulated ON. This success encourages further development of peptide dendrimer complexes active in serum and future investigation of mechanisms behind the influence of additives on transfection efficacy.

Role of autophagy in cell-penetrating peptide transfection model

Cell-penetrating peptides (CPPs) uptake mechanism is still in need of more clarification to have a better understanding of their action in the mediation of oligonucleotide transfection. In this study, the effect on early events (1 h treatment) in transfection by PepFect14 (PF14), with or without oligonucleotide cargo on gene expression, in HeLa cells, have been investigated. The RNA expression profile was characterized by RNA sequencing and confirmed by qPCR analysis. The gene regulations were then related to the biological processes by the study of signaling pathways that showed the induction of autophagy-related genes in early transfection. A ligand library interfering with the detected intracellular pathways showed concentration-dependent effects on the transfection efficiency of splice correction oligonucleotide complexed with PepFect14, proving that the autophagy process is induced upon the uptake of complexes. Finally, the autophagy induction and colocalization with autophagosomes have been confirmed by confocal microscopy and transmission electron microscopy. We conclude that autophagy, an inherent cellular response process, is triggered by the cellular uptake of CPP-based transfection system. This finding opens novel possibilities to use autophagy modifiers in future gene therapy.

The effect of preoperative oral administration of prednisolone on postoperative pain in patients with symptomatic irreversible pulpitis: a single-centre randomized controlled trial

AIM

This single-centre randomized, double-blind, placebo-controlled clinical trial assessed the effect of a preoperative, single, oral dose of prednisolone on postoperative pain and postoperative analgesic intake in patients with symptomatic, irreversible pulpitis in mandibular molars.

METHODOLOGY

Four hundred participants, randomly assigned to two equal groups, received either 40 mg prednisolone or placebo tablets 30 min before single-visit root canal treatment. Patients recorded their pain level 6, 12 and 24 h after treatment on a 100-mm visual analogue scale. All patients received a sham capsule to take if needed as a postoperative analgesic, and, if the pain persisted, an analgesic was prescribed. The relative risk reduction and 95% confidence intervals (CI) were estimated for binary data. Mann-Whitney U-test was used to compare postoperative pain intensity between groups.

RESULTS

The relative risk reduction in pain incidence was 20.31% (95% CI: 12.03%, 27.82%) at 6 h, 23.39% (95% CI: 14.75%, 31.16%) at 12 h and 28.85% (95% CI: 18.08%, 38.20%) at 24 h. Prednisolone had significantly less post-obturation pain intensity compared to placebo at 6, 12 and 24 h (P < 0.001). The relative risk reduction in sham-capsule intake was 54% (95% CI: 38%, 66%) and of analgesic intake was 55% (95% CI: 3%, 79%). No adverse effects were recorded.

CONCLUSION

Preoperative oral administration of a single dose of 40 mg prednisolone was beneficial to control short-term post-obturation pain after single-visit root canal treatment in patients with symptomatic irreversible pulpitis reducing pain incidence after 24 h by approximately 30% and postoperative analgesic intake by approximately 55%.

C9orf72 and RAB7L1 regulate vesicle trafficking in amyotrophic lateral sclerosis and frontotemporal dementia

A non-coding hexanucleotide repeat expansion in intron 1 of the C9orf72 gene is the most common cause of amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD), however, the precise molecular mechanism by which the C9orf72 hexanucleotide repeat expansion directs C9ALS/FTD pathogenesis remains unclear. Here, we report a novel disease mechanism arising due to the interaction of C9ORF72 with the RAB7L1 GTPase to regulate vesicle trafficking. Endogenous interaction between C9ORF72 and RAB7L1 was confirmed in human SH-SY5Y neuroblastoma cells. The C9orf72 hexanucleotide repeat expansion led to haploinsufficiency resulting in severely defective intracellular and extracellular vesicle trafficking and a dysfunctional trans-Golgi network phenotype in patient-derived fibroblasts and induced pluripotent stem cell-derived motor neurons. Genetic ablation of RAB7L1or C9orf72 in SH-SY5Y cells recapitulated the findings in C9ALS/FTD fibroblasts and induced pluripotent stem cell neurons. When C9ORF72 was overexpressed or antisense oligonucleotides were targeted to the C9orf72 hexanucleotide repeat expansion to upregulate normal variant 1 transcript levels, the defective vesicle trafficking and dysfunctional trans-Golgi network phenotypes were reversed, suggesting that both loss- and gain-of-function mechanisms play a role in disease pathogenesis. In conclusion, we have identified a novel mechanism for C9ALS/FTD pathogenesis highlighting the molecular regulation of intracellular and extracellular vesicle trafficking as an important pathway in C9ALS/FTD pathogenesis.

Effectiveness of stress and burnout management training for employees of an industrial company

Introduction

Burnout is a state of physical and emotional exhaustion. It can occur when people experience long-term stress in job, or when they have worked in a physically or emotionally draining role for a long time. There have been numerous studies done showing the results of stress and burnout in the employee's profession across many areas of health care.

Objectives

The purpose of this study was to investigate the effectiveness of stress and burnout management training on employees using experimental method to help employees to understand available resources and help them find better ways to manage stress in the workplace.

Aims

This study aims to discusses how organizations can assist in combating stress in ways that benefit both the employees involved and the organization itself.

Method

A curriculum-based intervention was developed to provide education in a classroom setting. The sample included 14 nurses with various nursing backgrounds who were selected randomly and were assigned randomly in two experimental and control groups, which contained 7 employees in each group. The experimental group received the training while the control group was in waiting list. The instruments were the General Health Questionnaire and Burnout Checklist, and demographic questionnaire. Data was analyzed by covariance analysis method.

Results

Result indicated that stress and burnout management training was efficient on reducing stress and burnout symptoms in employee.

Conclusion

It is concluded that stress and burnout management training is an effective group intervening method for reducing the dysfunctional effects of stress and job burnout in employees.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Peptides for nucleic acid delivery

Nucleic acids and their synthetic oligonucleotide (ON) analogs are a group of gene therapeutic compounds which hold enormous clinical potential. Despite their undoubted potential, clinical translation of these molecules, however, has been largely held back by their limited bioavailability in the target tissues/cells. To overcome this, many different drug delivery systems have been devised. Among others, short delivery peptides, called cell-penetrating peptides (CPPs), have been demonstrated to allow for efficient delivery of nucleic acids and their ON analogs, in both cell culture and animal models. In this review, we provide brief overview of the latest advances in nucleic acid delivery with CPPs, covering the two main vectorization strategies, covalent conjugation and nanoparticle formation-based approach. In conclusion, CPP-based drug delivery systems have the capacity to overcome the hurdle of delivery and thus have the potential to facilitate the clinical translation of nucleic acid-based therapeutics.

Synthetic SiRNA Delivery: Progress and Prospects

Small interfering RNA (siRNA) is a powerful tool for modulating gene expression by RNA interference (RNAi). Duplex RNA oligonucleotides induce cleavage of homologous target transcripts, thereby enabling posttranscriptional silencing of potentially any gene. As such, siRNAs may have utility as novel pharmaceuticals for a wide range of diseases. However, a lack of "drug-likeness," physiological barriers, and potential toxicities have meant that systemic delivery of SiRNAs in vivo remains a major challenge. Here we discuss various strategies that have been employed to solve the problem of SiRNA delivery. These include chemical modification of the SiRNA, direct conjugation to bioactive moieties, and nanoparticle formulations.

Self-Assembly into Nanoparticles Is Essential for Receptor Mediated Uptake of Therapeutic Antisense Oligonucleotides

Antisense oligonucleotides (ASOs) have the potential to revolutionize medicine due to their ability to manipulate gene function for therapeutic purposes. ASOs are chemically modified and/or incorporated within nanoparticles to enhance their stability and cellular uptake, however, a major challenge is the poor understanding of their uptake mechanisms, which would facilitate improved ASO designs with enhanced activity and reduced toxicity. Here, we study the uptake mechanism of three therapeutically relevant ASOs (peptide-conjugated phosphorodiamidate morpholino (PPMO), 2'Omethyl phosphorothioate (2'OMe), and phosphorothioated tricyclo DNA (tcDNA) that have been optimized to induce exon skipping in models of Duchenne muscular dystrophy (DMD). We show that PPMO and tcDNA have high propensity to spontaneously self-assemble into nanoparticles. PPMO forms micelles of defined size and their net charge (zeta potential) is dependent on the medium and concentration. In biomimetic conditions and at low concentrations, PPMO obtains net negative charge and its uptake is mediated by class A scavenger receptor subtypes (SCARAs) as shown by competitive inhibition and RNAi silencing experiments in vitro. In vivo, the activity of PPMO was significantly decreased in SCARA1 knockout mice compared to wild-type animals. Additionally, we show that SCARA1 is involved in the uptake of tcDNA and 2'OMe as shown by competitive inhibition and colocalization experiments. Surface plasmon resonance binding analysis to SCARA1 demonstrated that PPMO and tcDNA have higher binding profiles to the receptor compared to 2'OMe. These results demonstrate receptor-mediated uptake for a range of therapeutic ASO chemistries, a mechanism that is dependent on their self-assembly into nanoparticles.

A convergent uptake route for peptide- and polymer-based nucleotide delivery systems

Cell-penetrating peptides (CPPs) have been used as vehicles to deliver various cargos into cells and are promising as tools to deliver therapeutic biomolecules such as oligonucleotides both in vitro and in vivo. CPPs are positively charged and it is believed that CPPs deliver their cargo in a receptor-independent manner by interacting with the negatively charged plasma membrane and thereby inducing endocytosis. In this study we examine the mechanism of uptake of several different, well known, CPPs that form complexes with oligonucleotides. We show that these CPP:oligonucleotide complexes are negatively charged in transfection-media and their uptake is mediated by class A scavenger receptors (SCARA). These receptors are known to promiscuously bind to, and mediate uptake of poly-anionic macromolecules. Uptake of CPP:oligonucleotide complexes was abolished using pharmacological SCARA inhibitors as well as siRNA-mediated knockdown of SCARA. Additionally, uptake of CPP:oligonucleotide was significantly increased by transiently overexpressing SCARA. Furthermore, SCARA inhibitors also blocked internalization of cationic polymer:oligonucleotide complexes. Our results demonstrate that the previous held belief that CPPs act receptor independently does not hold true for CPP:oligonucleotide complexes, as scavenger receptor class A (SCARA) mediates the uptake of all the examined CPP:oligonucleotide complexes in this study.

PepFect14 peptide vector for efficient gene delivery in cell cultures

The successful applicability of gene therapy approaches will heavily rely on the development of efficient and safe nonviral gene delivery vectors, for example, cell-penetrating peptides (CPPs). CPPs can condense oligonucleotides and plasmid DNA (pDNA) into nanoparticles, thus allowing the transfection of genetic material into cells. However, despite few promising attempts, CPP-mediated pDNA delivery has been relatively inefficient due to the unfavorable nanoparticle characteristics or the nanoparticle entrapment to endocytic compartments. In many cases, both of these drawbacks could be alleviated by modifying CPPs with a stearic acid residue, as demonstrated in the delivery of both the pDNA and the short oligonucleotides. In this study, PepFect14 (PF14) peptide, previously used for the transport of shorter oligonucleotides, is demonstrated to be suited also for the delivery of pDNA. It is shown that PF14 forms stable nanoparticles with pDNA with a negative surface charge and size of around 130-170 nm. These nanoparticles facilitate efficient gene delivery and expression in a variety of regular adherent cell lines and also in difficult-to-transfect primary cells. Uptake studies indicate that PF14/pDNA nanoparticles are utilizing class A scavenger receptors (SCARA) and caveolae-mediated endocytosis as the main route for cellular internalization. Conclusively, PF14 is an efficient nonviral vector for gene delivery.

Solid formulation of cell-penetrating peptide nanocomplexes with siRNA and their stability in simulated gastric conditions

Cell-penetrating peptides (CPPs) are short cationic peptides that have been extensively studied as drug delivery vehicles for proteins, nucleic acids and nanoparticles. However, the formulation of CPP-based therapeutics into different pharmaceutical formulations and their stability in relevant biological environments have not been given the same attention. Here, we show that a newly developed CPP, PepFect 14 (PF14), forms non-covalent nanocomplexes with short interfering RNA (siRNA), which are able to elicit efficient RNA-interference (RNAi) response in different cell-lines. RNAi effect is obtained at low siRNA doses with a unique kinetic profile. Furthermore, the solid dispersion technique is utilized to formulate PF14/siRNA nanocomplexes into solid formulations that are as active as the freshly prepared nanocomplexes in solution. Importantly, the nanocomplexes are stable and active in mediating RNAi response after incubation with simulated gastric fluid (SGF) that is highly acidic. These results demonstrate the activity of PF14 in delivering and protecting siRNA in different pharmaceutical forms and biological environments.

Scavenger receptor-mediated uptake of cell-penetrating peptide nanocomplexes with oligonucleotides

Cell-penetrating peptides (CPPs) are short cationic peptides that penetrate cells by interacting with the negatively charged plasma membrane; however, the detailed uptake mechanism is not clear. In contrary to the conventional mode of action of CPPs, we show here that a CPP, PepFect14 (PF14), forms negatively charged nanocomplexes with oligonucleotides and their uptake is mediated by class-A scavenger receptors (SCARAs). Specific inhibitory ligands of SCARAs, such as fucoidin, polyinosinic acid, and dextran sulfate, totally inhibit the activity of PF14-oligonucleotide nanocomplexes in the HeLa pLuc705 splice-correction cell model, while nonspecific, chemically related molecules do not. Furthermore, RNA interference (RNAi) knockdown of SCARA subtypes (SCARA3 and SCARA5) that are expressed in this cell line led to a significant reduction of the activity to <50%. In line with this, immunostaining shows prevalent colocalization of the nanocomplexes with the receptors, and electron microscopy images show no binding or internalization of the nanocomplexes in the presence of the inhibitory ligands. Interestingly, naked oligonucleotides also colocalize with SCARAs when used at high concentrations. These results demonstrate the involvement of SCARA3 and SCARA5 in the uptake of PF14-oligonucleotide nanocomplexes and suggest for the first time that some CPP-based systems function through scavenger receptors, which could yield novel possibilities to understand and improve the transfection by CPPs.

PepFect 14, a novel cell-penetrating peptide for oligonucleotide delivery in solution and as solid formulation

Numerous human genetic diseases are caused by mutations that give rise to aberrant alternative splicing. Recently, several of these debilitating disorders have been shown to be amenable for splice-correcting oligonucleotides (SCOs) that modify splicing patterns and restore the phenotype in experimental models. However, translational approaches are required to transform SCOs into usable drug products. In this study, we present a new cell-penetrating peptide, PepFect14 (PF14), which efficiently delivers SCOs to different cell models including HeLa pLuc705 and mdx mouse myotubes; a cell culture model of Duchenne's muscular dystrophy (DMD). Non-covalent PF14-SCO nanocomplexes induce splice-correction at rates higher than the commercially available lipid-based vector Lipofectamine 2000 (LF2000) and remain active in the presence of serum. Furthermore, we demonstrate the feasibility of incorporating this delivery system into solid formulations that could be suitable for several therapeutic applications. Solid dispersion technique is utilized and the formed solid formulations are as active as the freshly prepared nanocomplexes in solution even when stored at an elevated temperatures for several weeks. In contrast, LF2000 drastically loses activity after being subjected to same procedure. This shows that using PF14 is a very promising translational approach for the delivery of SCOs in different pharmaceutical forms.

A peptide-based vector for efficient gene transfer in vitro and in vivo

Finding suitable nonviral delivery vehicles for nucleic acid-based therapeutics is a landmark goal in gene therapy. Cell-penetrating peptides (CPPs) are one class of delivery vectors that has been exploited for this purpose. However, since CPPs use endocytosis to enter cells, a large fraction of peptides remain trapped in endosomes. We have previously reported that stearylation of amphipathic CPPs, such as transportan 10 (TP10), dramatically increases transfection of oligonucleotides in vitro partially by promoting endosomal escape. Therefore, we aimed to evaluate whether stearyl-TP10 could be used for the delivery of plasmids as well. Our results demonstrate that stearyl-TP10 forms stable nanoparticles with plasmids that efficiently enter different cell-types in a ubiquitous manner, including primary cells, resulting in significantly higher gene expression levels than when using stearyl-Arg9 or unmodified CPPs. In fact, the transfection efficacy of stearyl-TP10 almost reached the levels of Lipofectamine 2000 (LF2000), however, without any of the observed lipofection-associated toxicities. Most importantly, stearyl-TP10/plasmid nanoparticles are nonimmunogenic, mediate efficient gene delivery in vivo, when administrated intramuscularly (i.m.) or intradermally (i.d.) without any associated toxicity in mice.

Design of a peptide-based vector, PepFect6, for efficient delivery of siRNA in cell culture and systemically in vivo

While small interfering RNAs (siRNAs) have been rapidly appreciated to silence genes, efficient and non-toxic vectors for primary cells and for systemic in vivo delivery are lacking. Several siRNA-delivery vehicles, including cell-penetrating peptides (CPPs), have been developed but their utility is often restricted by entrapment following endocytosis. Hence, developing CPPs that promote endosomal escape is a prerequisite for successful siRNA implementation. We here present a novel CPP, PepFect 6 (PF6), comprising the previously reported stearyl-TP10 peptide, having pH titratable trifluoromethylquinoline moieties covalently incorporated to facilitate endosomal release. Stable PF6/siRNA nanoparticles enter entire cell populations and rapidly promote endosomal escape, resulting in robust RNAi responses in various cell types (including primary cells), with minimal associated transcriptomic or proteomic changes. Furthermore, PF6-mediated delivery is independent of cell confluence and, in most cases, not significantly hampered by serum proteins. Finally, these nanoparticles promote strong RNAi responses in different organs following systemic delivery in mice without any associated toxicity. Strikingly, similar knockdown in liver is achieved by PF6/siRNA nanoparticles and siRNA injected by hydrodynamic infusion, a golden standard technique for liver transfection. These results imply that the peptide, in addition to having utility for RNAi screens in vitro, displays therapeutic potential.

Peptide nanoparticles for oligonucleotide delivery

In the past two decades, different methods have emerged for intervention with gene expression, which can be generally referred to as gene therapy. Oligonucleotides (ONs) and their analogs form the basis of the molecules that can be used to modulate gene expression. Unfortunately, due to their physicochemical properties, these molecules require assistance in their intracellular delivery. Cell-penetrating peptides (CPPs) are one class of nonviral delivery vectors that, because of their remarkable translocation properties, have been intensely utilized for the delivery of ON-based molecules, both in vitro and in vivo. This chapter concentrates on the applications of CPPs that directly form nanoparticles with different ONs and facilitate their intracellular delivery.

Delivery of nucleic acids with a stearylated (RxR)4 peptide using a non-covalent co-incubation strategy

In recent years, oligonucleotide-based molecules have been intensely used to modulate gene expression. All these molecules share the common feature of being essentially impermeable over cellular membranes and they therefore require efficient delivery vectors. Cell-penetrating peptides are a group of delivery peptides that has been readily used for nucleic acid delivery. In particular, polyarginine and derivates thereof, i.e. the (RxR)(4) peptide, have been applied with success both in vitro and in vivo. A major problem, however, with these arginine-rich peptides is that they frequently remain trapped in endosomal compartments following internalization. The activity of polyarginine has previously been improved by conjugation to a stearyl moiety. Therefore, we sought to investigate what impact such modification would have on the pre-clinically used (RxR)(4) peptide for non-covalent delivery of plasmids and splice-correcting oligonucleotides (SCOs) and compare it with stearylated Arg9 and Lipofectamine 2000. We show that stearyl-(RxR)(4) mediates efficient plasmid transfections in several cell lines and the expression levels are significantly higher than when using unmodified (RxR)(4) or stearylated Arg9. Although the transfection efficiency is lower than with Lipofectamine 2000, we show that stearyl-(RxR)(4) is substantially less toxic. Furthermore, using a functional splice-correction assay, we show that stearyl-(RxR)(4) complexed with 2'-OMe SCOs promotes significant splice correction whereas stearyl-Arg9 fails to do so. Moreover, stearyl-(RxR)(4) promotes dose-dependent splice correction in parity with (RxR)(4)-PMO covalent conjugates, but at least 10-times lower concentration. These features make this stearic acid modified analog of (RxR)(4) an intriguing vector for future in vivo experiments.