Synthetic nanocarriers for the delivery of polynucleotides to the eye

This review is a comprehensive analysis of the progress made so far on the delivery of polynucleotide-based therapeutics to the eye, using synthetic nanocarriers. Attention has been addressed to the capacity of different nanocarriers for the specific delivery of polynucleotides to both, the anterior and posterior segments of the eye, with emphasis on their ability to (i) improve the transport of polynucleotides across the different eye barriers; (ii) promote their intracellular penetration into the target cells; (iii) protect them against degradation and, (iv) deliver them in a long-term fashion way. Overall, the conclusion is that despite the advantages that nanotechnology may offer to the area of ocular polynucleotide-based therapies (especially AS-ODN and siRNA delivery), the knowledge disclosed so far is still limited. This fact underlines the necessity of more fundamental and product-oriented research for making the way of the said nanotherapies towards clinical translation.

Short-interference RNAs: becoming medicines

RNA interference is a cellular mechanism by which small molecules of double stranded RNA modulate gene expression acting on the concentration and/or availability of a given messenger RNA. Almost 10 years after Fire and Mello received the Nobel Prize for the discovery of this mechanism in flat worms, RNA interference is on the edge of becoming a new class of therapeutics. With various phase III studies underway, the following years will determine whether RNAi-therapeutics can rise up to the challenge and become mainstream medicines. The present review gives a thorough overview of the current status of this technology focusing on the path to the clinic of this new class of compounds.

Differential expression and localization of transient receptor potential vanilloid 1 in rabbit and human eyes

INTRODUCTION

The superfamily of transient receptor potential (TRP) cation channels is involved in nociception. Members of this family, such as the vanilloid receptor type 1 (TRPV1) channel, are activated by a wide range of stimuli including heat (⟩43°C), low pH (⟨6.5), hypoxia, and hypertonicity. Here we report TRPV1 expression in rabbit and human eyes.

MATERIAL AND METHODS

We analyzed the expression of TRPV1 mRNA by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and protein by immunohistochemistry in eyes of New Zealand White rabbits and humans.

RESULTS

In rabbit and human eyes, TRPV1 protein was present in all layers of the corneal epithelium, but only in the basal layer of the conjunctiva. It was also in the ciliary and lens epithelia of both species as well as in the secretory cells of the rabbit lacrimal gland. The retinal pigment epithelium was positive for this protein in both species. TRPV1 was also present in rabbit Müller cells, where it had a similar pattern of expression to vimentin intermediate filaments. Analysis by qRT-PCR showed that TRPV1 mRNA was found in all of the structures where the protein was present. The highest level was in the lens and the lowest in the retina.

CONCLUSION

TRPV1 is expressed in cells that are particularly active in Ca²⁺ exchange as well as in cells with significant water transport activity. Because TRPV1 is a Ca²⁺ channel, it probably functions in the regulation of both water and Ca²⁺ movements in ocular tissues.

Silencing human genetic diseases with oligonucleotide-based therapies

RNA interference is an endogenous mechanism present in most eukaryotic cells that enables degradation of specific mRNAs. Pharmacological exploitation of this mechanism for therapeutic purposes attracted a whole amount of attention in its initial years, but was later hampered due to difficulties in delivery of the pharmacological agents to the appropriate organ or tissue. Advances in recent years have to a certain level started to address this specific issue. Genetic diseases are caused by aberrations in gene sequences or structure; these particular abnormalities are in theory easily addressable by RNAi therapeutics. Sequencing of the human genome has largely contributed to the identification of alterations responsible for genetic conditions, thus facilitating the design of compounds that can address these diseases. This review addresses the currently on-going programs with the aim of developing RNAi and other antisense compounds for the treatment of genetic conditions and the pros and cons that these products may encounter along the way. The authors have focused on those programs that have reached clinical trials or are very close to do so.

Activation of the intrinsic cell death pathway, increased apoptosis and modulation of astrocytes in the cerebellum of diabetic rats

Poorly controlled diabetes mellitus results in structural and functional changes in many brain regions. We demonstrate that in streptozotocin-induced diabetic rats cell death is increased and proliferation decreased in the cerebellum, indicating overall cell loss. Levels of both the proform and cleaved forms of caspases 3, 6 and 9 are increased, with no change in caspases 7, 8 or 12. Colocalization of glial fibrillary acidic protein (GFAP) and cleaved caspase 3 and GFAP in TUNEL-positive cells increased in diabetic rats. Changes in GFAP levels paralleled modifications in proliferating cell nuclear antigen (PCNA), increasing at 1 week of diabetes and decreasing thereafter, and proliferating GFAP-positive cells were decreased in the cerebellum of diabetic rats. These results suggest that astrocytes are dramatically affected in the cerebellum, including an increase in cell death and a decrease in proliferation, and this could play a role in the structural and functional changes in this brain area in diabetes.

Growth hormone-releasing peptide-6 increases insulin-like growth factor-I mRNA levels and activates Akt in RCA-6 cells as a model of neuropeptide Y neurones

Chronic systemic administration of growth hormone (GH)-releasing peptide-6 (GHRP-6), an agonist for the ghrelin receptor, to normal adult rats increases insulin-like growth factor (IGF)-I mRNA and phosphorylated Akt (pAkt) levels in various brain regions, including the hypothalamus. Because neuropeptide Y (NPY) neurones of the arcuate nucleus express receptors for ghrelin, we investigated whether these neurones increase their IGF-I and p-Akt levels in response to this agonist. In control rats, immunoreactive pAkt was practically undetectable; however, GHRP-6 increased p-Akt immunoreactivity in the arcuate nucleus, with a subset of neurones also being immunoreactive for NPY. Immunoreactivity for IGF-I was detected in NPY neurones in both experimental groups. To determine if activation of this intracellular pathway is involved in modulation of NPY synthesis RCA-6 cells, an embryonic rat hypothalamic neuronal cell line that expresses NPY was used. We found that GHRP-6 stimulates NPY and IGF-I mRNA synthesis and activates Akt in this cell line. Furthermore, inhibition of Akt activation by LY294002 treatment did not inhibit GHRP-6 induction of NPY or IGF-I synthesis. These results suggest that some of the effects of GHRP-6 may involve stimulation of local IGF-I production and Akt activation in NPY neurones in the arcuate nucleus. However, GHRP-6 stimulation of NPY production does not involve this second messenger pathway.

The corticotropin-releasing factor-hypocretin connection: implications in stress response and addiction

The hypothalamic neuropeptides hypocretins (orexins) play a crucial role in the stability of arousal and alertness. Recent data have raised the hypothesis that hypocretin neurons are also part of the circuitries that mediate the hypothalamic stress response. In particular, we have recently demonstrated that corticotrophin-releasing factor (CRF)-immunoreactive terminals make direct synaptic contacts with hypocretin-expressing neurons and that numerous hypocretinergic neurons express the CRF-R1/2 receptors. Furthermore, CRF excites hypocretinergic cells ex vivo through CRF-R1 receptors. Activation of hypocretinergic neurons in response to acute stress is severely impaired in CRF-R1 knockout mice. Moreover, the stress response is impaired in hypocretin-deficient mice. We propose that upon stressor stimuli, CRF stimulates the release of hypocretins, and this circuit contributes to activation and maintenance of arousal associated with the stress response and addiction.

Phosphorylation of glycosyl-phosphatidylinositol by phosphatidylinositol 3-kinase changes its properties as a substrate for phospholipases

Phosphatidylinositol 3-kinases (PI3K) phosphorylate the 3-position of the inositol ring of phosphatidylinositol-4,5-bisphosphate to produce phosphatidylinositol-3,4,5-trisphosphate. It is not clear whether PI3K can phosphorylate the inositol group in other biomolecules. We sought to determine whether PI3K was able to use glycosyl-phosphatidylinositol (GPI) as a substrate. This phospholipid may exist either in free form (GPIfree) or forming a lipid anchor (GPIanchor) for the attachment of extracellular proteins to the plasma membrane. We demonstrate the specific PI3K-mediated phosphorylation of the inositol 3-hydroxyl group within both types of GPI by incubating this phospholipid with immunoprecipitated PI3K. The phosphorylated product behaves in HPLC as a derivative of a PI3K lipid product. To our knowledge, this is the first demonstration that PI3K uses lipid substrates other than phosphoinositides. Further, we show that this has potential functional consequences. When GPIfree is phosphorylated, it becomes a poorer substrate for GPI-specific phospholipase D, but a better substrate for phosphatidylinositol-specific phospholipase C. These phosphorylation events may constitute the basis of a previously undescribed signal transduction mechanism.

Acidic sphingomyelinase downregulates the liver-specific methionine adenosyltransferase 1A, contributing to tumor necrosis factor-induced lethal hepatitis

S-adenosyl-L-methionine (SAM) is synthesized by methionine adenosyltransferases (MATs). Ablation of the liver-specific MAT1A gene results in liver neoplasia and sensitivity to oxidant injury. Here we show that acidic sphingomyelinase (ASMase) mediates the downregulation of MAT1A by TNF-alpha. The levels of MAT1A mRNA as well as MAT I/III protein decreased in cultured rat hepatocytes by in situ generation of ceramide from exogenous human placenta ASMase. Hepatocytes lacking the ASMase gene (ASMase-/-) were insensitive to TNF-alpha but were responsive to exogenous ASMase-induced downregulation of MAT1A. In an in vivo model of lethal hepatitis by TNF-alpha, depletion of SAM preceded activation of caspases 8 and 3, massive liver damage, and death of the mice. In contrast, minimal hepatic SAM depletion, caspase activation, and liver damage were seen in ASMase-/- mice. Moreover, therapeutic treatment with SAM abrogated caspase activation and liver injury, thus rescuing ASMase+/+ mice from TNF-alpha-induced lethality. Thus, we have demonstrated a new role for ASMase in TNF-alpha-induced liver failure through downregulation of MAT1A, and maintenance of SAM may be useful in the treatment of acute and chronic liver diseases.

Growth hormone-releasing peptide-6 inhibits cerebellar cell death in aged rats

Insulin-like growth factor (IGF)-I is essential for cerebellar granule neuron survival and a decline in IGF-I is implicated in various age-dependent processes. Here we show that IGF-I mRNA levels are decreased in the cerebellum of old rats compared with young rats and this was associated with increased cell death and activation of caspases 3 and 9. Growth hormone-releasing peptide (GHRP)-6, a synthetic ligand for the ghrelin receptor, increased IGF-I mRNA levels, decreased cell death and inhibited caspase 3 and 9 activation in the cerebellum of aged rats. These results suggest that increasing IGF-I expression in the cerebellum can decrease cell death in aged rats via inhibition of caspase 3 and 9 activation.

The number of lactotrophs is reduced in the anterior pituitary of streptozotocin-induced diabetic rats

AIMS/HYPOTHESIS

Prolactin secretion is often reduced in insulin dependent diabetes mellitus, but little is known about the mechanism involved. Since changes in the hormonal environment modulate cell proliferation, death and cellular makeup of the anterior pituitary, we have analysed whether the number of lactotrophs is reduced in diabetic rats.

METHODS

Streptozotocin induced diabetic rats were maintained hyperglycaemic for 2 months. Pituitary prolactin, growth hormone, Bcl-2, Bax and PCNA concentrations were analysed by western blot analysis. In situ hybridisation was used for quantification of prolactin and growth hormone mRNA containing cells. Cell death was detected by TUNEL labelling, alone and in combination with immunocytochemistry for prolactin or growth hormone.

RESULTS

Diabetic rats had fewer lactotrophs ( p<0.01). This was coincident with a decrease in overall protein and prolactin content. An increase in pituitary cell death was found and some of the TUNEL labelling co-localised with prolactin immunostaining. No change in the concentration of Bcl-2 or Bax, proteins implicated in apoptosis, was detected. PCNA content was higher in the pituitaries of diabetic rats, suggesting increased proliferation.

CONCLUSION/INTERPRETATION

Anterior pituitary cell turnover is affected in poorly controlled diabetes mellitus. A decrease in the number of lactotrophs, as a result of increased cell death, could underlie, at least in part, the reduction in prolactin secretion observed in diabetic animals.

Growth hormone (GH) and GH-releasing peptide-6 increase brain insulin-like growth factor-I expression and activate intracellular signaling pathways involved in neuroprotection

Beneficial effects of GH on memory, mental alertness, and motivation have been documented. Many actions of GH are mediated through IGF-I; hence, we investigated whether systemic administration of GH or GH-releasing peptide (GHRP)-6 modulates the brain IGF system. Treatment of adult male rats with GHRP-6 or GH for 1 wk significantly increased IGF-I mRNA levels in the hypothalamus, cerebellum, and hippocampus, with no effect in cerebral cortex. Expression of the IGF receptor and IGF-binding protein (IGFBP)-2 were not affected. Phosphorylation of Akt and Bad was stimulated in areas where IGF-I was increased, with no change in MAPK or glycogen synthase kinase-3beta. This suggests that GH and GHRP-6 activate phosphatidylinositol kinase intracellular pathways involved in cell survival in response to growth factors. Indeed, the antiapoptotic protein Bcl-2 was augmented in these same areas, with no change in the proapoptotic protein Bax. IGFBP-5, also reported to be involved in neuron survival processes, was increased mainly in the hypothalamus, suggesting a possible neuroendocrine role. In conclusion, GH and GHRP-6 modulate IGF-I expression in the central nervous system in an anatomically specific manner. This is coincident with activation of intracellular signaling pathways used by IGF-I and increased expression of proteins involved in cell survival or neuroprotection.

Liver cell proliferation requires methionine adenosyltransferase 2A mRNA up-regulation

Regulation of liver cell proliferation is a key event to control organ size during development and liver regeneration. Methionine adenosyltransferase (MAT) 2A is expressed in proliferating liver, whereas MAT1A is the form expressed in adult quiescent hepatocytes. Here we show that, in H35 hepatoma cells, growth factors such as hepatocyte growth factor (HGF) and insulin up-regulated MAT2A expression. HGF actions were time- and dose-response dependent and required transcriptional activity. Mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-phosphate kinase (PI 3-K) pathways were required for both HGF-induced cell proliferation and MAT2A up-regulation. Furthermore, in H35 cells treated with HGF, the inhibition of these pathways was associated with the switch from the expression of fetal liver MAT2A to the adult liver MAT1A isoform. Fetal liver hepatocytes exhibited an identical response pattern. Treatment of H35 hepatoma cells with MAT2A antisense oligonucleotides decreased cell proliferation induced by HGF; this decrease correlated with the decay in MAT2A messenger RNA (mRNA) levels. Finally, growth inhibitors such as transforming growth factor (TGF) beta blocked HGF-induced MAT2A up-regulation while increasing MAT1A mRNA levels in H35 cells. In conclusion, our results show that MAT2A expression not only correlates with liver cell proliferation but is required for this process.

Purification and characterization of insulin-mimetic inositol phosphoglycan-like molecules from grass pea (Lathyrus sativus) seeds

BACKGROUND

Signal transduction through the hydrolysis of glycosyl-phosphatidylinositol (GPI) leading to the release of the water-soluble inositol phosphoglycan (IPG) molecules has been demonstrated to be important for mediating some of the actions of insulin and insulin-like growth factor-I (IGF-I).

MATERIALS AND METHODS

In the present study, GPI from grass pea (Lathyrus sativus) seeds has been purified and partially characterized on the basis of its chromatographic properties and its compositional analysis.

RESULTS

The results indicate that it shows similarities to GPI previously isolated from other sources such as rat liver. IPG was generated from L. sativus seed GPI by hydrolysis with a GPI-specific phospholipase D (GPI-PLD). This IPG inhibited protein kinase A (PKA) in an in vitro assay, caused cell proliferation in explanted cochleovestibular ganglia (CVG), and decreased 8-Br-cAMP-induced phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression in cultured hepatoma cells.

CONCLUSIONS

Our data indicate that L. sativus seed IPG possess insulin-mimetic activities. This may explain why L. sativus seeds have been used in some traditional medicines to ameliorate diabetic symptoms.

Short-chain ceramide regulates hepatic methionine adenosyltransferase expression

BACKGROUND

The metabolism of methionine plays an important role in regulating hepatic cellular function. Methionine adenosyltransferase (MAT) is the enzyme that catalyses the biosynthesis of S-adenosylmethionine (AdoMet) from ATP and methionine. Liver-specific MAT I/III levels are down-regulated in the regenerating rat liver after partial hepatectomy. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) are two cytokines fundamental for liver regeneration. TNF-alpha stimulates sphingomyelin metabolism and ceramide generation in a variety of cell systems.

AIMS

The role of exogenous cell-permeable ceramide in modifying MAT I/III mRNA levels and its association with TNF-alpha and IL-6 actions were investigated in rat hepatocytes and H35 hepatoma cells.

RESULTS

C2-ceramide (N-acetylsphingosine) at 1-10 microM decreased MAT I/III expression. The effect was maximum after 2 h of treatment and it was maintained up to 24 h. MAT I/III protein levels also decreased. IL-6 (1-10 ng/ml) potentiated C2-ceramide effects in cultured hepatocytes while decreasing by itself MAT I/III levels with a similar time-response curve in both cell types. C2-ceramide actions were not associated with an increase in cell death. TNF-alpha was also a potent antagonist for MAT I/III expression, at 1-20 ng/ml decreased MAT I/III levels and induced endogenous ceramide generation. The decrease of MAT I/III mRNA levels (in all the cases) was not due to a decrease in mRNA half-life which suggests a regulation at the transcriptional level. Finally, the decrease in MAT I/III mRNA levels correlated to a decrease in MAT activity.

CONCLUSION

This work demonstrates that short-chain ceramide can be used as a novel exogenous agonist that can modulate hepatic methionine metabolism in association with cytokines.

Role of diffusible and transcription factors in inner ear development: implications in regeneration

Organogenesis involves a dynamic balance of the mechanisms regulating cell division, differentiation and death. The development of the chicken embryo inner ear offers a well-characterised model at the morphological level to study which signals are implicated in the modulation of cellular activation and commitment. The early developmental decisions that control the origin of the inner ear elements are just beginning to be identified by complementary in vivo and in vitro studies. Insulin-like growth factor-I (IGF-I) and nerve growth factor (NGF) are among the best characterised diffusible factors acting during inner ear development. Although the cellular actions of these factors are beginning to be understood, the signalling pathways triggered by them still remain largely unknown. In this context, viral vehicles can be used to deliver genes and then analyse their functional roles during inner ear development. A model is proposed where the actions of IGF-I and NGF contribute to the combinatorial expression of Jun and Fos family members in particular domains of the otic vesicle. Some of these mechanisms may be also implicated in otic regeneration.

Towards the in vitro reconstitution of caveolae. Asymmetric incorporation of glycosylphosphatidylinositol (GPI) and gangliosides into liposomal membranes

Large unilamellar vesicles consisting of phospholipids with or without cholesterol have been prepared containing GPI and/or gangliosides asymmetrically located in the outer leaflet of the bilayer. Such asymmetric distribution of GPI and gangliosides is found in 'rafts' and caveolae. Using these vesicles, GPI can be readily hydrolysed by phospholipases. Both cholesterol and ganglioside are seen to inhibit, in an additive way, the hydrolytic activity of GPI-specific phospholipase D.