Maria A. Vlasova

In vivo delivery of a peptide, ghrelin antagonist, with mesoporous silicon microparticles.

Peptides may represent potential treatment options for many severe illnesses. However, they need an effective delivery system to overcome rapid degradation after their administration. One possible way to prolong peptide action is to use particulate drug delivery systems. In the present study, thermally hydrocarbonized mesoporous silicon (THCPSi) microparticles (38-53 microm) were studied as a peptide delivery system in vivo. D-lys-GHRP6 (ghrelin antagonist, GhA) was used as a model peptide. The effects of GhA-loaded THCPSi microparticles on food intake (s.c., GhA dose 14 mg/kg) and on blood pressure (s.c., GhA dose 4 mg/kg) were examined in mice and rats, respectively. In addition, the effects of THCPSi microparticles (2 mg) on cytokine secretion in mice after single s.c. administration were examined by determining several cytokine plasma concentrations. The present results demonstrate that GhA can be loaded into THCPSi microparticles with a high loading degree (20% w/w). GhA loaded THCPSi microparticles inhibited food intake for a prolonged time, and increased blood pressure more slowly than encountered with a GhA solution. Furthermore, THCPSi microparticles did not increase cytokine activity. The present results suggest that THCPSi might be used as a drug delivery system for peptides.

Nanostructured porous silicon microparticles enable sustained peptide (Melanotan II) delivery

Peptide molecules can improve the treatment of a number of pathological conditions, but due to their physicochemical properties, their delivery is very challenging. The study aim was to determine whether nanostructured porous silicon could sustain the release and prolong the duration of action of a model peptide Melanotan II (MTII). Thermally hydrocarbonized nanoporous silicon (THCPSi) microparticles (38-53 μm) were loaded with MTII. The pore diameter, volume, specific surface area and loading degree of the microparticles were analyzed, and the peptide release was evaluated in vitro. The effects of MTII on heart rate and water consumption were investigated in vivo after subcutaneous administration of the MTII loaded microparticles. A peptide loading degree of 15% w/w was obtained. In vitro studies (PBS, pH 7.4, 37 °C) indicated sustained release of MTII from the THCPSi microparticles. In vivo, MTII loaded THCPSi induced an increase in the heart rate 2 h later than MTII solution, and the effect lasted 1 h longer. In addition, MTII loaded THCPSi changed the water consumption after 150 min, when the immediate effect of MTII solution was already diminished. The present study demonstrates that MTII loading into nanosized PSi pore structure enables sustained delivery of an active peptide.

Novel Delivery Systems for Improving the Clinical Use of Peptides

Peptides have long been recognized as a promising group of therapeutic substances to treat various diseases. Delivery systems for peptides have been under development since the discovery of insulin for the treatment of diabetes. The challenge of using peptides as drugs arises from their poor bioavailability resulting from the low permeability of biological membranes and their instability. Currently, subcutaneous injection is clinically the most common administration route for peptides. This route is cost-effective and suitable for self-administration, and the development of appropriate dosing equipment has made performing the repeated injections relatively easy; however, only few clinical subcutaneous peptide delivery systems provide sustained peptide release. As a result, frequent injections are needed, which may cause discomfort and additional risks resulting from a poor administration technique. Controlled peptide delivery systems, able to provide required therapeutic plasma concentrations over an extended period, are needed to increase peptide safety and patient compliancy. In this review, we summarize the current peptidergic drugs, future developments, and parenteral peptide delivery systems. Special emphasis is given to porous silicon, a novel material in peptide delivery. Biodegradable and biocompatible porous silicon possesses some unique properties, such as the ability to carry exceptional high peptide payloads and to modify peptide release extensively. We have successfully developed porous silicon as a carrier material for improved parenteral peptide delivery. Nanotechnology, with its different delivery systems, will enable better use of peptides in several therapeutic applications in the near future.

Cardiovascular effects of ghrelin antagonist in conscious rats

Ghrelin, a 28 aa growth-hormone-releasing peptide, has been shown to increase food intake and decrease arterial pressure in animals and in humans. Recently, a ghrelin antagonist (GhA), [d-Lys-3]-GHRP-6, was demonstrated to decrease food intake in mice, but its cardiovascular actions have not been described. In the present study, the effects of the GhA on cardiovascular parameters in conscious rats were investigated and the involvement of the sympathetic nervous system evaluated. Mean arterial pressure (MAP) and heart rate (HR) measurements were assessed by radiotelemetry. GhA was administered in doses of 2, 4 and 6 mg/kg subcutaneously (s.c.). MAP as well as HR was dose-dependently elevated after sc application of GhA. Sympathetic blockade of alpha-adrenoreceptors with phentolamine (3 mg/kg, s.c.) and simultaneous antagonism of beta(1)-adrenoreceptors with atenolol (10 mg/kg, s.c.) abolished the increase in MAP and HR induced by GhA (4 mg/kg, s.c.). Administration of phentolamine alone inhibited the increase of MAP, but not HR; atenolol alone abolished the elevation of both MAP and HR evoked by GhA. These results suggest that the peripheral injection of ghrelin antagonist increases arterial pressure and heart rate, at least in part, through the activation of the sympathetic nervous system. Therefore, the use of the ghrelin antagonist system as a therapeutic target for reduction in food intake might lead to serious side effects like elevated blood pressure in humans mostly already having an elevated blood pressure as part of their metabolic syndrome.

Injected nanoparticles: The combination of experimental systems to assess cardiovascular adverse effects

When nanocarriers are used for drug delivery they can often achieve superior therapeutic outcomes over standard drug formulations. However, concerns about their adverse effects are growing due to the association between exposure to certain nanosized particles and cardiovascular events. Here we examine the impact of intravenously injected drug-free nanocarriers on the cardiovasculature at both the systemic and organ levels. We combine in vivo and in vitro methods to enable monitoring of hemodynamic parameters in conscious rats, assessments of the function of the vessels after sub-chronic systemic exposure to nanocarriers and evaluation of the direct effect of nanocarriers on vascular tone. We demonstrate that nanocarriers can decrease blood pressure and increase heart rate in vivo via various mechanisms. Depending on the type, nanocarriers induce the dilation of the resistance arteries and/or change the responses induced by vasoconstrictor or vasodilator drugs. No direct correlation between physicochemical properties and cardiovascular effects of nanoparticles was observed. The proposed combination of methods empowers the studies of cardiovascular adverse effects of the nanocarriers.

Nanocarriers and the delivered drug: Effect interference due to intravenous administration

Intravenously administered nanocarriers are widely studied to improve the delivery of various therapeutic agents. However, recent in vivo studies have demonstrated that intravenously administered nanocarriers that do not contain any drug may affect cardiovascular function. Here we provide an example where the drug and the nanocarrier both affect the same cardiovascular parameters following intravenous administration. The peptide ghrelin antagonist (GhA) increases arterial pressure, while thermally hydrocarbonized porous silicon nanoparticles (THCPSi) transiently decrease it, as assessed with radiotelemetry in conscious rats. As a result, intravenous administration of GhA-loaded THCPSi nanoparticles partially antagonized GhA activity: arterial pressure was not increased. When the cardiovascular effects of GhA were blocked with atenolol pretreatment, GhA-loaded nanoparticles reduced arterial pressure to similar extent as drug-free nanoparticles. These data indicate that the biological activity of a drug delivered within a nanocarrier may be obscured by the biological responses induced by the nanocarrier itself.

Effect of Transmural Pressure on Constrictor Reactions of Caudal Artery in Hypotensive and Hypertensive Rats

Clipping of the abdominal aorta distally to the renal arteries produces a persistent decrease in blood pressure in hindquarter vessels by 35-40%. On week 6-7 postoperation, the reactions of the caudal artery perfused in vitro under constant pressure to norepinephrine were studied. At transmural pressure of 150 mm Hg, the vascular responses in hypotensive rats were reduced compared to those in normotensive control. By contrast, the responses of hypertensive vessels were more pronounced at 75 mm Hg even after deendothelization.