Thilini R. Thrimawithana

Therapeutic uses of somatostatin and its analogues: Current view and potential applications

Somatostatin is an endogeneous cyclic tetradecapeptide hormone that exerts multiple biological activities via five ubiquitously distributed receptor subtypes. Classified as a broad inhibitory neuropeptide, somatostatin has anti-secretory, anti-proliferative and anti-angiogenic effects. The clinical use of native somatostatin is limited by a very short half-life (1 to 3min) and the broad spectrum of biological responses. Thus stable, receptor-selective agonists have been developed. The majority of these somatostatin therapeutic agonists bind strongly to two of the five receptor subtypes, although recently an agonist of wider affinity has been introduced. Somatostatin agonists are established in the treatment of acromegaly with recently approved indications in the therapy of neuroendocrine tumours. Potential therapeutic uses for somatostatin analogues include diabetic complications like retinopathy, nephropathy and obesity, due to inhibition of IGF-1, VEGF together with insulin secretion and effects upon the renin-angiotensin-aldosterone system. Wider uses in anti-neoplastic therapy may also be considered and recent studies have further revealed anti-inflammatory and anti-nociceptive effects. This review provides a comprehensive, current view of the biological functions of somatostatin and potential therapeutic uses, informed by the wide range of pharmacological advances reported since the last published review in 2004 by P. Dasgupta. The pharmacology of somatostatin receptors is explained, the current uses of somatostatin agonists are discussed, and the potential future of therapeutic applications is explored.

The Nerve Growth Factor Signaling and Its Potential as Therapeutic Target for Glaucoma

Neuroprotective therapies which focus on factors leading to retinal ganglion cells (RGCs) degeneration have been drawing more and more attention. The beneficial effects of nerve growth factor (NGF) on the glaucoma have been recently suggested, but its effects on eye tissue are complex and controversial in various studies. Recent clinical trials of systemically and topically administrated NGF demonstrate that NGF is effective in treating several ocular diseases, including glaucoma. NGF has two receptors named high affinity NGF tyrosine kinase receptor TrkA and low affinity receptor p75NTR. Both receptors exist in cells in retina like RGC (expressing TrkA) and glia cells (expressing p75NTR). NGF functions by binding to TrkA or p75NTR alone or both together. The binding of NGF to TrkA alone in RGC promotes RGCs survival and proliferation through activation of TrkA and several prosurvival pathways. In contrast, the binding of NGF to p75NTR leads to apoptosis although it also promotes survival in some cases. Binding of NGF to both TrkA and p75NTR at the same time leads to survival in which p75NTR functions as a TrkA helping receptor. This review discusses the current understanding of the NGF signaling in retina and the therapeutic implications in the treatment of glaucoma.

IGF-1 Signaling via the PI3K/Akt Pathway Confers Neuroprotection in Human Retinal Pigment Epithelial Cells Exposed to Sodium Nitroprusside Insult

The pathological increase in the levels of the second messenger nitric oxide (NO) in the vitreous cavity and retina leads to injury and cell death of the retinal pigment epithelium (RPE) cells and eventually may contribute to the occurrence and development of diabetic retinopathy. In this study, we developed a cellular model of retinopathy using D407 cells (a human RPE cell line) exposed to sodium nitroprusside (SNP) and investigated the protective effect of the insulin-like growth factor-1 (IGF-1) towards this insult. Cell death and apoptosis were examined by the methyl thiazolyl tetrazolium assay and Hoechst staining, respectively. Specific inhibitors were used and phosphorylation of relevant signaling proteins was determined by Western blotting. SNP, in a concentration-dependent fashion, increased the production of reactive oxygen species (ROS) and lipid peroxidation process causing cell death by apoptosis of D407 cells. IGF-1, in a time- and dose-dependent manner, conferred protection towards SNP-mediated insult. Both phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) and mitogen-activated protein kinase (MAPK) were activated by IGF-1 in relation to the protective effect. Blockade of the PI3K/Akt pathway abolished the protective effect of IGF-1 whereas inhibition of the MAPK pathway was ineffective. SNP decreased the phosphorylation of Akt in the cells while IGF-1 reversed this inhibitory effect. These results indicate that the protective effect of IGF-1 on D407 exposed to SNP insult is mediated by the PI3K/Akt pathway. This proposal may be exploited in the clinic to improve the viability of insulted retinal cells for maintaining physiological vision.

The suprachoroidal pathway: a new drug delivery route to the back of the eye

The development of safe and convenient drug delivery strategies for treatment of posterior segment eye diseases is challenging. Although intravitreal injection has wide acceptance amongst clinicians, its use is associated with serious side-effects. Recently, the suprachoroidal space (SCS) has attracted the attention of ophthalmologists and pharmaceutical formulators as a potential site for drug administration and delivery to the posterior segment of the eye. This review highlights the major constraints of drug delivery to the posterior eye segment, key anatomical and physiological features of the SCS and drug delivery applications of this route with emphasis on microneedles along with future perspectives.

Epigenetic modifications as potential therapeutic targets in age-related macular degeneration and diabetic retinopathy.

Recently, aberrant epigenetic modifications have been identified in the pathogenesis of the posterior eye diseases, age-related macular degeneration (AMD) and diabetic retinopathy (DR). This has led to the development of alternative therapies that can alter aberrant chromatin-remodelling processes involved in AMD and DR. These novel therapeutic agents could help to ameliorate the challenges associated with current treatments that are limited by variable patient response and disease heterogeneity. However, research on the use of epigenetic-based therapies in these diseases is relatively young and, therefore, preclinical studies that evaluate their mechanism of action, specificity and adverse effects are warranted.

Release kinetics of somatostatin from self-assembled nanostructured hydrogels

Somatostatin‐14 is a native neuropeptide with widespread functions in the body. Self‐assembly of somatostatin‐14 into amyloid‐like nanofibrils has been previously demonstrated in aqueous media. We here hypothesize that the somatostatin nanofibrils can form a stable depot that release monomers in a controlled manner. This study aims to investigate if somatostatin monomers are released from physical hydrogels formed in water and in the presence of electrolytes. The release kinetics of the somatostatin monomers is investigated for the first time. This is correlated with the rheological properties of the hydrogels formed. We demonstrate that at the concentrations tested, there is release of somatostatin monomers from the hydrogels following a novel hybrid model of zero‐order and first‐order release. In the presence of electrolytes, somatostatin hydrogels demonstrated higher elastic moduli (G′) which correlates to the narrower and higher density of nanofibrils observed with TEM. The presence of electrolytes resulted in a slower release of the somatostatin monomers and in a lower cumulative percentage released over 48 hrs. It is questionable that the concentrations released will be therapeutically effective. However, self‐assembled somatostatin hydrogels have the potential to act as a depot for ocular drug delivery.

Critical appraisal of commercially available suspending vehicles for extemporaneous compounding of cardiovascular medicines: physical and chemical stability mini review

Abstract Oral liquid formulations are compounded by pharmacists to meet the needs of patients when a suitable commercially available product is not available. To minimize the errors associated with measuring multiple excipients and to enhance the shelf-life of the medicines, commercially available suspending bases are commonly used. This review aims to compare the stability and shelf life of commercially available extemporaneous formulation to traditional formulation methods. Five (5) databases were searched (Pubmed, SCOPUS, Science direct, Embase, and EBSCOhost). Twelve articles, comprising of seven cardiovascular medications (amiodarone, captopril, carvedilol, furosemide, nifedipine, sotalol, and valsartan), met the study inclusion criteria and were reviewed. Chemical stability of the drugs was comparable between the two formulation methods except for furosemide, captopril, and valsartan. The traditional compounding method provided superior stability for furosemide (90 vs. 14 days) and captopril (50 vs. 14 days), while the commercial vehicles provided superior stability for valsartan (90 vs. 14 days). Physical stability tests indicated that sedimentation does occur with both formulation methods. Microbial studies within the data were lacking and further research can be undertaken in this area. This review highlights the importance of assessing the suitability of compounding ingredients prior to preparation of the formulation.

L-Sulforaphane Confers Protection Against Oxidative Stress in an In Vitro Model of Age-Related Macular Degeneration

BACKGROUND In age-related macular degeneration, oxidative damage and abnormal neovascularization in the retina are caused by the upregulation of vascular endothelium growth factor and reduced expression of Glutathione-S-transferase genes. Current treatments are only palliative. Compounds from cruciferous vegetables (e.g. L-Sulforaphane) have been found to restore normal gene expression levels in diseases including cancer via the activity of histone deacetylases and DNA methyltransferases, thus retarding disease progression. OBJECTIVE To examine L-Sulforaphane as a potential treatment to ameliorate aberrant levels of gene expression and metabolites observed in age-related macular degeneration. METHOD The in vitro oxidative stress model of AMD was based on the exposure of Adult Retinal Pigment Epithelium-19 cell line to 200μM hydrogen peroxide. The effects of L-Sulforaphane on cell proliferation were determined by MTS assay. The role of GSTM1, VEGFA, DNMT1 and HDAC6 genes in modulating these effects was investigated using quantitative real-time polymerase chain reaction. The metabolic profiling of L-Sulforaphane-treated cells via gas-chromatography massspectrometry was established. Significant differences between control and treatment groups were validated using one-way ANOVA, student t-test and post-hoc Bonferroni statistical tests (p<0.05). RESULTS L-Sulforaphane induced a dose-dependent increase in cell proliferation in the presence of hydrogen peroxide by upregulating Glutathione-S-Transferase μ1 gene expression. Metabolic profiling revealed that L-Sulforaphane increased levels of 2-monopalmitoglycerol, 9, 12, 15,-(Z-Z-Z)- Octadecatrienoic acid, 2-[Bis(trimethylsilyl)amino]ethyl bis(trimethylsilyl)-phosphate and nonanoic acid but decreased β-alanine levels in the absence or presence of hydrogen peroxide, respectively. CONCLUSION This study supports the use of L-Sulforaphane to promote regeneration of retinal cells under oxidative stress conditions.

Drug delivery to the lens for the management of cataracts

Abstract Cataracts are one of the most prevalent diseases of the lens, affecting its transparency and are the leading cause of reversible blindness in the world. The clarity of the lens is essential for its normal physiological function of refracting light onto the retina. Currently there is no pharmaceutical treatment for prevention or cure of cataracts and surgery to replace the affected lens remains the gold standard in the management of cataracts. Pharmacological treatment for prevention of cataracts is hindered by many physiological barriers that must be overcome by a therapeutic agent to reach the avascular lens. Various therapeutic agents and formulation strategies are currently being investigated to prevent cataract formation as access to surgery is limited. This review provides a summary of recent research in the field of drug delivery to the lens for the management of cataracts including models used to study cataract treatments and discusses the future perspectives in the field. &NA; Graphical abstract Figure. No Caption available.

Stability of warfarin sodium tablets repackaged in dose administration aids

Dose administration aids (DAAs) are designed to assist patients to better manage their medicines. However, removal of a medicine from the original packaging invalidates the physicochemical stability guaranteed by the manufacturer. A few studies have investigated the stability of warfarin sodium; nevertheless there is no data available to suggest the stability of warfarin sodium in DAAs.