Percutaneous penetration kinetics of nitroglycerin and its dinitrate metabolites across hairless mouse skin in vitro

Organic nitrate metabolism and action: toward a unifying hypothesis and the future-a dedication to Professor Leslie Z. Benet

This review summarizes the major advances that had been reported since the outstanding contributions that Professor Benet and his group had made in the 1980s and 1990s concerning the metabolism and pharmacologic action of organic nitrates (ORNs). Several pivotal studies have now enhanced our understanding of the metabolism and the bioactivation of ORNs, resulting in the identification of a host of cysteine-containing enzymes that can carry out this function. Three isoforms of aldehyde dehydrogenase, all of which with active catalytic cysteine sites, are now known to metabolize, somewhat selectively, various members of the ORN family. The existence of a long-proposed but unstable thionitrate intermediate from ORN metabolism has now been experimentally observed. ORN-induced thiol oxidation in multiple proteins, called the "thionitrate oxidation hypothesis," can be used not only to explain the phenomenon of nitrate tolerance, but also the various consequences of chronic nitrate therapy, namely, rebound vasoconstriction, and increased morbidity and mortality. Thus, a unifying biochemical hypothesis can account for the myriad of pharmacological events resulting from nitrate therapy. Optimization of the future uses of ORN in cardiology and other diseases could benefit from further elaboration of this unifying hypothesis.

Analysis of cell characterization using cell surface markers in the dermis

BACKGROUND

In recent years, it has been reported that stem cells exist in the mesenchymal tissues of the bone marrow and adipose. These stem cells are thought to express specific cell surface markers such as CD44, CD54, CD105, CD90, and CD271 and have been confirmed to be pluripotent. Furthermore, although it has been reported that stem cells are also present in the dermis, their cell surface markers and characteristics are not fully understood.

OBJECTIVE

To confirm the presence of stem cells in the dermis and their ability, employing the mesenchymal stem cell markers which have previously been reported as an indication.

METHODS

We analyzed the percentages of CD44 (+), CD54 (+), CD90 (+), CD105 (+), and CD271 (+) cells in the dermis of neonatal mice (HR-1 mouse) by performing immunostaining and FACS. Secondly, we isolated each type of marker-positive and -negative cells from dermal tissues and evaluated their proliferation potential and their ability to differentiate into adipocytes, osteoblasts, and chondrocytes.

RESULTS

According to the immunostaining and FACS results, we confirmed that stem cells that express CD44, CD54, CD90, CD105, and CD271 are present in the dermal tissues of neonatal mice. In addition, when we measured the proliferation and differentiation potentials of each type of marker-positive cells, it was revealed that cells expressing CD54 or CD271 have a high proliferation potential and are able to differentiate into adipocytes, osteoblasts, and chondrocytes.

CONCLUSIONS

These results indicated that dermal tissues contain stem cells that express CD44, CD54, CD90, CD105, and CD271 which are stem cell markers. More precisely, it was suggested that both CD54 (+) and CD271 (+) stem cells have high proliferation and differentiation potentials.

Pharmacokinetic characterisation of transdermal delivery systems

The key aspects of the pharmacokinetics of transdermal delivery systems including time lag, steady-state plasma levels and decline phase are illustrated in this review. The 7 currently marketed transdermal systems [nitroglycerin (glyceryl trinitrate), estradiol, clonidine, fentanyl, nicotine, scopolamine (hyoscine) and estradiol/norethisterone acetate] are discussed, as are systems in development. Single-dose absolute bioavailability studies characterise the period of onset, the steady-state plateau and the declining phase, and typify transdermal delivery. More complex temporal profiles result from interactions with enhancers or removal of the system before steady-state conditions are achieved. Clinically these systems are used to achieve multiple peak serum estradiol concentrations after application of transdermal estradiol, and an initial peak systemic concentration of testosterone after application of transdermal testosterone. Multiple-dose, dose proportionality and skin site bioequivalence studies are needed for the full pharmacokinetic characterisation of a transdermal delivery system. The relationship of system design to variability is discussed. Although the data are limited, population factors, cutaneous metabolism and tolerance all appear to influence the disposition of drugs administered transdermally. For example, the route of delivery influences which nitroglycerin metabolite predominates. Furthermore, as a result of tolerance to nitrates, a transdermal delivery system must be removed for 8 to 12 hours for optimal effect. Therefore, transdermal delivery systems, designed on the basis of pharmacokinetic principles and concentration-effect relationships, have the potential to provide optimal therapy for the treatment of some conditions.

Dual sorption model for the nonlinear percutaneous permeation kinetics of timolol

The nonlinear percutaneous permeation kinetics of timolol were studied in vitro with human cadaver skin. In the sorption isotherm (equilibrium) study, the plots of the amount of timolol per unit area of epidermis versus aqueous timolol concentration in equilibrium were curvilinear as the dual sorption model predicts. In the penetration study, several aqueous timolol concentrations were maintained in the donor cell for 25 h. The lag-time was prolonged as the timolol concentration in the donor cell was decreased. The change in the lag time was analyzed by a newly proposed method with the lag-time prolongation factor that is calculated from the parameter values obtained in the sorption isotherm study. The ratio of the lag-time to lag-time prolongation factor was of the same magnitude, indicating that the dual sorption model explains the nonlinear percutaneous permeation kinetics of timolol. Finally, the diffusion parameter for the mobile solute was estimated by fitting the data of the cumulative amount excreted into receptor cell versus time to the numerical solution of the dual sorption model. The observed data were roughly compatible with the values predicted by the dual sorption model.

Simultaneous pharmacodynamic modeling of the non-steady-state effects of three oral doses of 1,3-glyceryl dinitrate upon blood pressure in healthy volunteers

The organic nitrate 1,3-glyceryl dinitrate (1,3-GDN) is one of the primary dinitrate metabolites of the antianginal agent nitroglycerin (GTN). Investigational New Drug Approval was sought to administer oral solution doses of 1,3-GDN to a small number (n = 3) of healthy volunteers; each subject receiving three doses at 1.2, 2.4, and 3.6 mg. With volunteers confined to a semirecumbent posture for the duration of each treatment (4-hr period postdose), diastolic blood pressure (DBP) was recorded and plasma samples collected for 1,3-GDN concentration analysis. Appreciable concentration-related decreases in DBP were observed, with maximal decreases from predose baseline values approximating 11 to 25 mm Hg. For each subject parametric pharmacodynamic modeling was performed with simultaneous analysis utilizing the DBP vs. time data from all three doses; an inhibitory Emax pharmacodynamic model was adopted. The temporal relationship between plasma 1,3-GDN concentrations and DBP displayed rapid equilibration. For subjects 1, 2 and 3, respectively, Emax was predicted as 12.9, 23.4, and 29.7 mm Hg, representing 21.5, 31.6, and 39.5% decreases in DBP from predose baseline values; plasma concentrations at half Emax (C50) were 2.75, 2.43, and 5.93 micrograms/L. Utilizing pharmacokinetic-pharmacodynamic modeling, 1,3-GDN plasma concentrations appear to relate to a systemic "effect measure" that is mechanistically representative of the therapeutic actions of organic nitrates as peripheral vasodilators. The establishment of a GDN plasma concentration-effect relationship together with the relatively high plasma levels of GDN achieved following GTN dosing supports the hypothesis that the GDNs contribute significantly to the hemodynamic effect observed with GTN.