Prodrugs of peptides. 7. Transdermal delivery of thyrotropin-releasing hormone (TRH) via prodrugs

Skin permeability, a dismissed necessity for anti-wrinkle peptide performance

The skin offers various benefits and potential for peptide delivery if its barrier performance can be reduced temporarily and reversibly. Since peptides possess high molecular weight, hydrophilic nature (in most cases), and ionizable groups in the structure, their skin delivery is highly challenging. Apart from this, they are susceptible to the proteolytic enzymes in the skin. Anti-wrinkle peptides, like other peptides, suffer from insufficient skin permeability, while most of them must penetrate deep in the skin to present their efficacy. Although the cellular studies indicate the effectiveness of such peptides, without the ability to permeate the skin sufficiently, this efficacy is useless. Poor skin permeability of anti-wrinkle peptides has led to ongoing research for finding feasible and noninvasive enhancement methods that would be desirable for consumers of cosmetic products. In this paper, the possibility of skin permeation of anti-wrinkle peptides as well as the chemical, physical, and encapsulation approaches that have been employed to date to increase permeability of these difficult molecules are thoroughly reviewed.

Dispersible hydrolytically sensitive nanoparticles for nasal delivery of thyrotropin releasing hormone (TRH)

Nose-to-brain delivery of drugs is affected by nanoparticles (NPs) deposited on the olfactory surface and absorbed directly into the brain. Thyrotropin releasing hormone (TRH), a water soluble drug used for treating suicidal patients, was incorporated into a fast degrading poly(sebacic anhydride) (PSA) NPs. NPs were prepared by a solvent-antisolvent process under strict anhydrous environment to obtain high TRH loading and to avoid premature PSA degradation and TRH release. PSA and TRH were dissolved in a mixture of dichloromethane and ethanol and added dropwise to a dispersion of mannitol particles in heptane as an antisolvent. Mannitol powder was included in the antisolvent, so that formed NPs adhered to the mannitol microparticles for easy isolation and immediate dispersion in water prior to use. The size, surface charge, and morphology of the TRH-PSA NPs were determined using dynamic light scattering (DLS), zeta-potential, and Scanning Electron Microscopy (SEM), respectively. The NPs prepared were uniform and spherical of ~250 nm. Further, the in vitro release profile of TRH from NPs lasted for 12 h with most TRH released within the first hour in water. Concentration dependent cell toxicity studies revealed low toxicity level at low concentrations of the NPs. Surface adsorption of the NPs was also uniform on the cell surface as examined through the odyssey near infrared fluorescence (NIR) images using Indocyanine green (ICG). The NPs are designed to enable direct delivery to the olfactory epithelium using a refillable nasal atomizer that deposits mist onto the olfactory neuro-epithelium.

Transdermal and Skin-Targeted Drug Delivery

Background:

The application of therapeutic agents to the skin addresses three general objectives: (a) the treatment of a variety of dermatologic diseases; (b) the “targeted” delivery of drugs to deeper subcutaneous tissues, with a concomitant reduction in systemic exposure; and (c) socalled transdermal administration to elicit a systemic pharmacologic effect.

Objective:

Recently, significant progress towards all three goals has been recorded and the level of research and development activity remains high. We aim to discuss these advances from mechanistic and clinical standpoints.

Results:

For the topical treatment of skin disease, novel vehicles (e.g., stabilized, supersaturated systems and liposomal formulations) have led to dramatic improvements in local drug bioavailability. Transdermal delivery of drugs for systemic effect, though limited in terms of the number of compounds, is perhaps the most commercially successful (in terms of the number of products) of the controlled release technologies. Considerable activity continues to enhance drug delivery (and hence to extend the range of drugs for which transdermal delivery can be used). Existing patches use formulations that contain solvents and adjuvants capable of reducing the barrier function of the skin. Much effort is directed at iontophoresis (electrically enhanced transport), particularly for small peptides that are difficult to administer by other routes. “Reverse iontophoresis” may allow the extraction of glucose (without skin puncture) so that continuous, noninvasive monitoring of blood sugar in diabetics approaches realization.

Conclusion:

In the not too distant future, the skin may also play a role not only in drug delivery, but also with respect to measurements in clinical chemistry.

Improvement of Intestinal Absorption of Thyrotropin-releasing Hormone by Chemical Modification with Lauric Acid

Intestinal absorption of 125I-labelled lauryl thyrotropin-releasing hormone (Lau-TRH), a novel lipophilic derivative of TRH, was examined by rat in-situ closed intestinal loops. At a dose of 1 μmol per rat into the small intestine, a significant increase in percent of dose in plasma radioactivity of Lau-TRH was observed in comparison with that of TRH. A dose-dependent decrease in percent of dose in plasma radioactivity of TRH was noted, suggesting a saturable process of TRH transport. In contrast, the percent of dose in plasma radioactivity of Lau-TRH increased with increasing dose of Lau-TRH. The stability of TRH and Lau-TRH was studied in plasma and rat small intestinal homogenates. Lau-TRH was more stable than TRH in rat plasma. These results suggest that chemical modification of TRH with lauric acid may not only increase the lipophilicity of TRH but also reduce the degradation of TRH, resulting in the increased plasma radioactivity of TRH. On the other hand, Lau-TRH was gradually converted to TRH in the intestinal mucosal homogenate. These findings indicate that chemical modification of TRH with lauric acid might be a useful approach for improving the intestinal absorption of this peptide.

Therapeutic application of peptides and proteins: parenteral forever?

Varied therapeutic peptides and proteins represent a rapidly growing part of marketed drugs and have an undisputed place alongside other established therapies. Nevertheless, such biodrugs have several drawbacks that hinder their therapeutic application. These are undesirable physicochemical properties, such as variable solubility, low bioavailability and limited stability. These issues can be overcome by addition of stabilizing agents and directed injectable administration, which can however result in low patient compliance. Hence, there is a drive in the biotechnology industry to produce needle-free and more user-friendly drugs, and this has led to the growth of nano-enabled drug delivery systems in the last decade. As discussed here, nanobiotechnology is becoming a commercially feasible and promising opportunity for oral, pulmonary and transdermal administration routes.

Synthesis, antitubercular activity and pharmacokinetic studies of some Schiff bases derived from 1-alkylisatin and isonicotinic acid hydrazide (INH)

N'-(1-alkyl-2,3-dihydro-2-oxo-1H-3-indolyliden)-4-pyridinecarboxylic acid hydrazide derivatives, 3(a-g), were synthesized in a trial to overcome the resistance developed with the therapeutic uses of isoniazid (INH). The lipophilicity of the synthesized derivatives supersedes that of the INH as expressed by Clog p values. The synthesized compounds and INH were tested against bovin, human sensitive and human resist strains of Mycobacterium tuberculosis. Compounds 3a, 3d, 3f and 3g with 1-unsubstituted, 1-propyl, 1-propynyl and 1-benzyl groups respectively exhibited equipotent growth inhibitory activity (MIC 10 micromol) against the tested strains as compared with INH however the later has no activity against human resist strain. Pharmacokinetic study revealed that the rate and extent of absorption of the tested derivatives (3d and 3f) significantly higher than that of INH (p < 0.05). The relative bioavailabilities (F(R)%) were 183.15 and 443.25 for 3f and 3d respectively as compared to INH. These results preliminary indicate the possible use of the prepared derivatives for treatment of tuberculosis infections in order to overcome the resistance developed with INH.

New tetrahydro-2H-1,3,5-thiadiazine-2-thione derivatives as potential antimicrobial agents

The deacylated chloramphenicol amine D-(-)-threo-2-amino-1-(4-nitrophenyl)-1,3-diol (D-amine, 1a), and its enantiomer, the L-(+)-threo-form (L-amine, 1b), were introduced into a tetrahydro-2H-1,3,5-thiadiazine-2-thione (THTT) skeleton. They are incorporated in three ways (Chart 1, types I-III) at N3 (type I), N5 (type II) or both N3 and N5 (type III) of the THTT system. These selections were made in order to investigate the effect of combining the structural features of the THTT and the D-amine on the antimicrobial activity, if any.

New carriers for representative peptides and peptide drugs

3,5-Disubstituted tetrahydro-2H-1,3,5-thiadiazine-2-thione (THTT) derivatives; 4a-g were prepared and found to be a promising prodrug approach for peptide drugs. The pH profile for their degradation in aqueous buffer solutions was determined using HPLC technique and accounted for, in terms of specific base-catalyzed reactions. All of the compounds however, showed high acid-stability. Enzymatic (human serum) hydrolysis of the different derivatives offered an advantageous range of t1/2's, the property that permits controlling onset and duration of actions of drugs.

Transdermal therapy and diagnosis by iontophoresis

Iontophoresis, the use of an electric current to drive charged molecules across the skin, has the potential to expand the feasible range of drugs for transdermal administration significantly. This method of delivery is being examined carefully with respect to higher-molecular-weight therapeutics (in particular, peptides and small proteins), which cannot be absorbed following oral administration and for which, at this time, an invasive injection remains the only option. In addition, the procedure of so-called 'reverse' iontophoresis would appear to represent a truly noninvasive approach for diagnostic monitoring of blood chemistry.

Improvement of transdermal delivery of tetragastrin by lipophilic modification with fatty acids

The in-vitro permeability of chemically modified tetragastrin with fatty acids through the rat skin was studied. The permeability of these compounds through intact skin and stripped skin of rat was determined with a Franz-type diffusion cell. The permeation of tetragastrin across the intact skin was improved by chemical modification with acetic acid and butyric acid. However, tetragastrin and caproyl-tetragastrin did not permeate across the intact skin up to the end of experiment. The permeation of tetragastrin across the stripped skin was improved by chemical modification, the skin flux of these acyl derivatives being in the order:acetyl > butyroyl > caproyl. The stability of tetragastrin in skin homogenate was also significantly improved by chemical modification with fatty acids. These results suggest that chemical modifications of tetragastrin with fatty acids increases its lipophilicity, which makes it permeable across the stratum corneum. Moreover, the chemical modification reduced the degradation of tetragastrin in the viable skin, resulting an increase in permeation of tetragastrin across the skin.