Pickering emulsions: challenges and opportunities in topical delivery

ABSTRACT

Introduction: Topical drug delivery is a challenging area with many advantages such as avoidance of first passage effect, stabilization of blood concentrations and attainment of local therapeutic effect with fewer side effects. Despite all these advantages, topical drug delivery remains limited to few molecules, since skin acts as a barrier to the delivery of many therapeutic molecules. To overcome this obstacle, a favored strategy relies on selecting suitable vehicles for dermatologic therapy, such as emulsions, gels and, more recently, nanoparticulate systems.

Areas covered: Particle-stabilized emulsions, also known as Pickering emulsions, have garnered interest in recent years. Although most of the investigation on Pickering emulsions has been based on model systems with inorganic or organic solid particles, recent advances have been made regarding the application of nanocarriers, protein-based particles or cyclodextrins for this purpose. This review reports the latest advances in Pickering emulsions technical challenges, and discusses the potential benefits and drawbacks of using these formulations for topical pharmaceutical and cosmetic applications as an alternative to conventional surfactant-based systems.

Expert opinion: Pickering emulsions appear as a multifunctional dosage form with endless advantages. A great deal of progress is expected in this area, which might represent a renewed vision for the pharmaceutical and cosmetic industry.     

针对艾滋病毒的局部杀微生物剂研究进展

高效抗逆转录病毒疗法（HAART）的推广应用使HIV/AIDS的治疗和控制获得了巨大的成功,但至今在艾滋病毒（HIV）感染的预防上却驻足不前,HIV疫苗研究遇到种种困难。在HIV感染者中,女性约占50%,其中绝大多数是通过性途径传播而患病的。本文综述近几年在针对HIV的局部杀微生物剂方面的研究进展：Ⅱ期临床多中心试验结果显示,0.5%PRO2000能使HIV的感染率下降约30%;感染动物试验显示,含1%替诺福韦酯的阴道凝胶剂在预防猴免疫缺陷病毒（SIV）感染方面效果显著。双盲、随机、对照临床试验也证实,含1%替诺福韦酯阴道凝胶剂可使妇女减少39%的HIV感染风险,对高依从性妇女则可将HIV感染风险降低54%,且不良反应发生率未见增加,未出现对替诺福韦酯的耐药。可以预计,针对HIV的局部杀微生物剂有望成为人类阻遏HIV肆虐的又一道有效防线。     

Preventing HIV transmission in drug treatment programs: what works?

The AIDS epidemic has dramatically affected drug treatment programs, creating both an epidemiological crisis and a psychological one. A paramount question for treatment program staff is how to prevent patients from acquiring or spreading HIV. The health belief model has been useful in generating prevention approaches, including programs that raise the threat of infection, provide alternative behaviors, and build social support. Some of these programs have been effective in changing attitudes and reducing the behaviors that put drug users at risk for acquiring or transmitting HIV. Future research will develop collaborative studies, disseminate techniques to drug treatment programs, and develop more powerful interventions for patients who continue with risky behaviors.     

Rotavirus vaccines: opportunities and challenges

Each year rotavirus gastroenteritis episodes in young children cause more than 500,000 deaths and 2.4 million hospital admissions worldwide. Vaccine development became a priority when improved personal hygiene and living standards failed to significantly reduce this disease burden. Rotavirus vaccines were developed mimicking natural immunity by protecting against severe gastroenteritis in young children, which would otherwise lead to health-care attendance, hospitalization or even death. Licensed rotavirus vaccines appear safe and are well-tolerated. In high and middle-income countries they provide 80-100% protection against severe disease and 70-80% protection against rotavirus gastroenteritis of any severity, depending upon the population studied. However, rotavirus vaccines remain to be fully evaluated in low-income countries where reduced immunogenicity of oral vaccines, greater strain diversity and difficulties reaching target populations might decrease immunization program performance. Nevertheless, if these challenges are met, rotavirus vaccines should help reduce the 5% of all childhood deaths attributable to rotavirus gastroenteritis.     

Dengue vaccine: opportunities and challenges

Despite many successes in the field of vaccinology over the past century, several important scourges for which effective vaccines remain elusive continue to be threats to public health. The mosquito-borne dengue virus causes millions of infections in tropical and subtropical regions throughout the world, and is responsible for an annual mortality that measures in the thousands. The ubiquitous presence of dengue virus, and its potentially lethal complications, have made the development of an effective vaccine against the virus a priority. However, before such a vaccine can be created, the basic immunology surrounding dengue infection must be clarified. Such research is underway, including efforts focusing on the response of T-cells and the potentially central role of this response in dengue pathophysiology. 'Shaping' the T-cell response may be the key to successful dengue vaccine design.     

Toward a design of affordable, topical microbicides: acylcarnitine analogues

Most heterosexual women want to reduce the risk of acquiring a sexually transmitted infection; many also want to control their fertility. Several chemical agents have been proposed to dramatically slow the spread of HIV infections. Ideally, vaginal microbicides, with or without contraceptive properties, should be safe, effective, and affordable for women everywhere. Amphiphiles, which are surfactants that can act as detergents, have a long history as microbicides against many pathogens. Amphiphiles have several desirable traits; e.g., they are inexpensive, fast-acting, and capable of a broad spectrum of activity. An "ideal" amphiphilic microbicide will rapidly and selectively inactivate pathogens and sperm without irritating tissue. In this review, we discuss a homologous series of amphiphilic acylcarnitine analogues as microbicides. Two homologues, Z-14 and Z-15, possess excellent spermicidal, anti-HIV, anti-chlamydial, anti-gonorrhea, and anti-Haemophilus activities; both have outstanding anti-Candida activity. A 4% Z-15 gel that is comprised of 3% carboxymethylcellulose in water gives a dramatically low score in a rabbit-vaginal-irritation study. The mechanisms of action of these compounds are not fully understood as yet, but we present several possibilities. Moreover, the results of our limited structure-activity study with a homologous series have stimulated additional questions and ideas for designing the next generation of microbicidal amphiphiles. The above studies support the idea that Z-14 and Z-15 can potentially serve as safe (non-irritating), effective topical microbicides.     

Management of retinoblastoma: opportunities and challenges

Nano-delivery systems have significantly evolved over the last decade for the treatment of cancer by enabling site-specific delivery and improved bioavailability. The widely investigated nanoparticle systems are biodegradable polyesters, dendrimers, liposomes, mesoporous silica and gold nanoparticles. These particles when conjugated with different targeting motifs enhance the therapeutic efficiency of the drug molecules and biocompatibility. However, the application of such systems towards the treatment of retinoblastoma (RB), a rapidly spreading childhood eye cancer, still remains in its infancy. Nanoparticle-based systems that have been investigated for RB therapy have displayed improved drug delivery to the most restricted posterior segment of the eyes and have increased intra-vitreal half-life of the chemotherapy agents highlighting its potential in treatment of this form of cancer. This review focuses on the challenges involved in the treatment of RB and highlights the attempts made to develop nano-dimensional systems for the treatment of RB.