Therapeutic potential of RNAi in metabolic diseases

Advantages and disadvantages of RNA therapeutics

RNA therapeutics is an innovative and rapidly evolving field at the forefront of medical research and biotechnology. Recently, many studies have shown that diverse RNA types play important roles in cells. Besides the protein translation coding, they also express and regulate a variety of cellular pathways. Indeed, along with the research and studies, many drugs and vaccines were developed from RNAs, including both coding and non-coding RNA. Some cases were approved to be medicines or under clinical trial. After years of use and application, they have shown a bright opportunity to prevent and treat many fatal and rare diseases with many strong points, such as fast production and long-term effects. Besides, they still have some drawbacks that need to be overcome, like stability or delivery to become the new generation of medicine. Therefore, this chapter focuses on providing an overview of the advantages and disadvantages of RNA therapeutics as well as some crucial points for future development.

Design of a Biocompatible Hydroxyapatite-Based Nanovehicle for Efficient Delivery of Small Interference Ribonucleic Acid into Mouse Embryonic Stem Cells

The small interference RNA (siRNA)-assisted RNA interference approach in stem cells for differentiating into cell-specific lineages is gaining importance for its therapeutic potential. An effective gene delivery platform is crucial to achieve this goal. In this context, self-fluorescent, cell-penetrating peptide (CPP)-functionalized hydroxyapatite nanoparticles (R8HNPs) were synthesized by a modified sol gel technique. R8HNPs were crystalline, displayed characteristic bands, and exhibited broad emission spectra from 350 to 750 nm corresponding to green and red fluorescence. The biocompatible R8HNPs displayed robust binding with siRNA and excellent uptake in R1 ESCs. This was attributed to functionalization with CPP. Moreover, the R8HNP-complexed siRNA exhibited excellent serum and room temperature stability. The NPs protected the siRNA from sonication, pH, and temperature-induced stress and efficiently delivered siRNA to trigger 80% silencing of a pluripotency marker gene, Oct4, in R1 ESCs at 48 h. The transient downregulation was also observed at the protein level. Our findings demonstrate R8HNPs as a promising delivery agent for siRNA therapeutics with the potential for lineage-specific differentiation and future applications in regenerative medicine.

Introducing an In Vitro Liver Stability Assay Capable of Predicting the In Vivo Pharmacodynamic Efficacy of siRNAs for IVIVC

There has been a renewed interest in therapeutic small interfering RNAs (siRNAs) over the past few years. This is particularly the result of successful and efficient delivery of N-acetylgalactosamine (GalNAc)-conjugated siRNAs to the liver. In general, the lead selection process for siRNA drugs is faster and more straightforward than traditional small molecules. Nevertheless, many siRNAs of different sequences and chemical modification patterns must still be evaluated before arriving at a final candidate. One of the major difficulties in streamlining this workflow is the well-known phenomenon that the in vitro data obtained from oligonucleotides transfected into cells are not directly predictive of their in vivo activity. Consequently, all oligonucleotides with some degree of in vitro activity are typically screened in vivo before final lead selection. Here, we demonstrate that the stability of liver-targeting GalNAc-conjugated siRNAs in a mouse liver homogenate shows an acceptable correlation to their in vivo target knockdown efficacy. Therefore, we suggest the incorporation of an in vitro liver homogenate stability assay during the lead optimization process for siRNAs. The addition of this assay to a flow scheme may decrease the need for animal studies, and it could bring cost savings and increase efficiency in siRNA drug development.

Synthesis of cationic branched tea polysaccharide derivatives for targeted delivery of siRNA to hepatocytes

The cationic branched tea polysaccharide (CTPSA) derivative bearing N-acylurea and 3-(dimethylamino)-1-propylamine residues was synthesized and characterized using FTIR and ¹H NMR spectroscopy. A nonspecific siRNA (NsiRNA) was used as a model molecule of functional siRNA that could downregulate over-expressed glycometabolism enzymes in the liver. The result from the agarose gel electrophoresis confirmed that the CTPSA and NsiRNA could form stable complexes when their weight ratio was larger than 18. The zeta potentials and sizes of the complexes were in the range of +8-+15 mv and 120-150 nm, respectively. The CTPSA/NsiRNA complex was observed as nanoparticles with a spherical shape of approximately 100 nm using scanning electron microscopy. The CTPSA derivative and the CTPSA/NsiRNA complexes exhibited lower cytotoxicity in HL-7702 cells when compared with the branched PEI (bPEI) and bPEI/NsiRNA complexes assessed by the Cell Counting Kit-8 assay. The results of flow cytometric analysis and laser confocal microscopy indicated that the CTPSA derivative could effectively target the transfer of the NsiRNA to HL-7702 cells. This work provides a potential approach to promote the CTPSA derivative as a nonviral vector for targeted delivery of functional siRNA to hepatocytes.

[Treatment of Acanthamoeba keratitis]

In recent years, Acanthamoeba keratitis (AK) has became a clinically significant problem because of the broad use of contact lenses that are the major risk factor of the disease. The treatment presents considerable difficulties due to similarity of clinical manifestations of AK to other keratites (bacterial, herpetic, and fungal). This often leads to late diagnosis and formation of drug-resistant cysts. There is currently no specific drug universally suitable for monotherapy of AK. Instead, 2 agents (usually chlorhexidine and poligexametilen biguanide) are used that, if combined, are effective against both trophozoites and cysts. If necessary (severe keratitis, insufficient treatment effect), diamidines (propamidine and its analogs), antifungals (fluconazole, itrakonazol), certain antibiotics (Neomycinum), and iodine-containing medications (povidone-iodine) can be prescribed. The use of corticosteroids is considered unjustified because of the risk of rapid progression (due to disturbance of local immunity and also provocation of excystation of the amoebas). The penetrative keratoplasty may be required, especially if a descemetocele or corneal perforation occurs, however, its results are generally worse than those in other keratites because of a higher risk of complications (iridocyclitis, secondary glaucoma, AK recurrence in the graft). In some cases, good results are achieved with minimally invasive surgeries, such as mechanical epithelial debridement, conjunctivoplasty and cryopreserved amniotic membrane transplantation, excimer laser phototherapeutic keratectomy, and cross-linking. In the future, gene therapy and specific chemotherapy of AK may well be developed.

An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment

Free-living amoebae of the genus Acanthamoeba are causal agents of a severe sight-threatening infection of the cornea known as Acanthamoeba keratitis. Moreover, the number of reported cases worldwide is increasing year after year, mostly in contact lens wearers, although cases have also been reported in non-contact lens wearers. Interestingly, Acanthamoeba keratitis has remained significant, despite our advances in antimicrobial chemotherapy and supportive care. In part, this is due to an incomplete understanding of the pathogenesis and pathophysiology of the disease, diagnostic delays and problems associated with chemotherapeutic interventions. In view of the devastating nature of this disease, here we present our current understanding of Acanthamoeba keratitis and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be potential targets for improved diagnosis, therapeutic interventions and/or for the development of preventative measures. Novel molecular approaches such as proteomics, RNAi and a consensus in the diagnostic approaches for a suspected case of Acanthamoeba keratitis are proposed and reviewed based on data which have been compiled after years of working on this amoebic organism using many different techniques and listening to many experts in this field at conferences, workshops and international meetings. Altogether, this review may serve as the milestone for developing an effective solution for the prevention, control and treatment of Acanthamoeba infections.

Acanthamoeba keratitis: an emerging disease gathering importance worldwide?

Acanthamoeba keratitis (AK) is increasingly being recognized as a severe sight-threatening ocular infection worldwide. Although contact lens wear is the leading risk factor for AK, Acanthamoeba parasites are also an important cause of keratitis in non-contact lens wearers. Diagnosis of AK is challenging, and the available treatments are lengthy and not fully effective against all strains. The pathogenesis of Acanthamoeba is still under study, and the identification of the key factors involved in this process should be useful for the development of fully effective therapies. This review focuses on recent developments on AK pathogenesis and diagnosis as well as novel strategies for the evaluation of anti-amoebic agents that could be applied in the near future against these pathogens.

Novel liver-specific TORC2 siRNA corrects hyperglycemia in rodent models of type 2 diabetes

The transcription factor TORC2 [transducer of regulated cAMP-responsive element-binding protein (CREB) activity 2] is a major regulator of hepatic gluconeogenesis and is increased in hyperglycemic rodent models. Because chronic hyperglycemia and increased hepatic glucose production, via increased gluconeogenesis, is a key feature of type 2 diabetes, an effective in vivo method to efficiently knock down TORC2 could provide a potential therapy for treating hyperglycemia and type 2 diabetes. To assess this, primary mouse hepatocytes, high-fat diet (HFD)-fed mice, and Zucker diabetic fatty (ZDF) rats were treated with a siRNA against TORC2 (siTORC2), which was delivered via a novel lipid nanoparticle system, or control siRNA (siCON). Compared with siCON, administration of siTORC2 resulted in highly efficient, sustained (1-3 wk) knockdown of TORC2 and its gluconeogenic target genes phosphoenolpyruvate carboxykinase and glucose-6-phophatase in primary mouse hepatocytes and in the livers of HFD-fed mice. In mice, this knockdown was specific to the liver and did not occur in kidney, skeletal muscle, or adipose tissue. In HFD-fed mice, siTORC2 reduced in vivo gluconeogenic capacity, fasting hepatic glucose production, and hyperglycemia, and led to improved hepatic and skeletal muscle insulin sensitivity. siTORC2 treatment also improved systemic hyperglycemia in ZDF rats. In conclusion, these results demonstrate the importance of TORC2 in modulating HGP in vivo and highlight a novel, liver-specific siRNA approach for the potential treatment of hyperglycemia and type 2 diabetes.

Convenient targeting of stealth siRNA-lipoplexes to cells with chelator lipid-anchored molecules

A major obstacle for the use of siRNAs as novel therapeutics is the requirement for functional delivery to specific cells in vivo. siRNA delivery by cationic agents is generally non-specific and a convenient targeting strategy has been lacking. This work explored the potential for using the chelator lipid 3(nitrilotriacetic acid)-ditetradecylamine (NTA(3)-DTDA) with neutral stealth liposomes to target siRNA to cells. A novel method for incorporating siRNAs into lipoplexes was developed which utilised helper lipids and the ionisable lipid 1,2-dioleoyl-3-dimethylammonium-propane (DODAP). This approach results in an efficient (>50%) incorporation of siRNA into lipoplexes, which when incorporated with Ni-NTA(3)-DTDA and engrafted with a His-tagged form of murine CD4 can target siRNA to murine A20 B cells, in vitro. Also, siRNA-lipoplexes engrafted with His-tagged peptides that target receptors on HEK-293 cells, or the receptor for tumour necrosis factor alpha expressed on the murine dendritic cell line DC2.4, could target siRNA and silence the expression of enhanced green fluorescence protein (EGFP). siRNA-lipoplexes produced by this method are approximately 240 nm dia, exhibit low zeta-potential (-1 mV), and target cells in serum-containing media. The results show that NTA(3)-DTDA can be used to target siRNA-lipoplexes to cells, and could provide a convenient approach for targeting siRNA to cells in vivo for therapeutic applications.

Specificity of insulin signalling in human skeletal muscle as revealed by small interfering RNA

Insulin action on metabolically active tissues is a complex process involving positive and negative feedback regulation to control whole body glucose homeostasis. At the cellular level, glucose and lipid metabolism, as well as protein synthesis, are controlled through canonical insulin signalling cascades. The discovery of small interfering RNA (siRNA) allows for the molecular dissection of critical components of the regulation of metabolic and gene regulatory events in insulin-sensitive tissues. The application of siRNA to tissues of human origin allows for the molecular dissection of the mechanism(s) regulating glucose and lipid metabolism. Penetration of the pathways controlling insulin action in human tissue may aid in discovery efforts to develop diabetes prevention and treatment strategies. This review will focus on the use of siRNA to validate critical regulators controlling insulin action in human skeletal muscle, a key organ important for the control of whole body insulin-mediated glucose uptake and metabolism.

RNA interference to target lipid disorders

PURPOSE OF REVIEW

This review focuses on proof-of-principle experiments providing validation of new targets for the development of RNA interference-based therapeutics for dyslipidemia.

RECENT FINDINGS

Over the past few years, RNA interference has become an accepted approach to manipulate gene expression in mammalian systems. Advantage has been taken of the relative tissue specificity of adenovirus for liver, and the genetic specificity of short hairpin RNA-mediated RNA interference to create liver-specific downregulation of different genes. A different approach to target liver has been through the administration of chemically modified short interfering RNAs. For example, apolipoprotein B messenger RNA has been silenced in liver and jejunum resulting in decreased plasma levels of apolipoprotein B and total cholesterol.

SUMMARY

RNA interference has aroused great interest as a powerful experimental tool and a potential therapeutic strategy. Successful animal studies indicate that RNA interference might be useful for the treatment of various human diseases. Clinical studies will soon begin to assess the use of this new class of therapeutics to treat dyslipidemia.

Non-viral siRNA delivery to the lung

SiRNAs exert their biological effect by guiding the degradation of their cognate mRNA sequence, thereby shutting down the corresponding protein production (gene silencing by RNA interference or RNAi). Due to this property, siRNAs are emerging as promising therapeutic agents for the treatment of inherited and acquired diseases, as well as research tools for the elucidation of gene function in both health and disease. Because of their lethality and prevalence, lung diseases have attracted particular attention as targets of siRNA-mediated cures. In addition, lung is accessible to therapeutic agents via multiple routes, e.g., through the nose and the mouth, thus obviating the need for targeting and making it an appealing target for RNAi-based therapeutic strategies. The clinical success of siRNA-mediated interventions critically depends upon the safety and efficacy of the delivery methods and agents. Delivery of siRNAs relevant to lung diseases has been attempted through multiple routes and using various carriers in animal models. This review focuses on the recent progress in non-viral delivery of siRNAs for the treatment of lung diseases, particularly infectious diseases. The rapid progress will put siRNA-based therapeutics on fast track to the clinic.

From genes to systems: new global strategies for the characterization of NCL biology

Neuronal ceroid lipofuscinoses (NCL) are rare neurological disorders with a uniform phenotype, caused by mutations in seven known genes. NCL provide a unique model to characterize molecular pathways critical for normal neuronal development and pathological neuronal degeneration. Systems biology based approach utilizes the rapidly developing tools of genomics, proteomics, lipidomics and metabolomics and aims at thorough understanding of the functions of cells, tissues and whole organisms by molecular analysis and biocomputing-assisted modeling. The systems level understanding of NCL is now possible by utilizing different model organisms. Initial work has revealed disturbed metabolic pathways in several NCL disorders and most analyses have utilized the infantile (INCL/CLN1) and juvenile (JNCL/CLN3) disease modeling and utilized mainly human and mouse samples. To date, the data obtained from transcript and lipidomic profiling has pinpointed the role of lipid metabolism and synaptic function in the infantile NCL. Changes in glutamate utilization and amino acid metabolism have been a common theme emerging from the transcript and metabolite profiling of the juvenile NCL. Further experimental models are being developed and systematic sample collection as well as data integration projects are needed. The combined analyses of the global information should provide means to expose all the NCL-associated molecular pathways.