Hormonal stimulation of tyrosinase activity in human foreskin organ cultures

Summary A human foreskin organ culture system has been developed to study the response of human skin to hormonal stimulation. Foreskins are maintained in culture on floating plastic supports which allows the epidermal surface to be exposed to air while the dermis is bathed in nutrient medium. Both black and white human foreskins can be maintained in organ culture for at least 1 wk with no change in the tissue structure or cell viability as determined by histochemical staining and by dopa reaction staining. Tyrosinase activity in both black and white human foreskin cultures decays markedly during the first 2 d of culture to a new steady state level which remains stable throughout the culture period. Both black and white foreskin cultures consistently demonstrate 2- to 10-fold increases in tyrosinase activity when treated with theophylline (1 mM). Approximately 90% of all skin cultures examined showed an increase in enzyme activity when treated with this phosphodiesterase inhibitor. Dibutyryl cAMP (0.1 mM) and [Nle⁴, D-phe⁷]-alpha MSH (10⁻⁸ M), were also found to markedly stimulate tyrosinase activity in some skin cultures, whereas alpha-MSH and prostaglandin E₁ produced only an inconsistent and small increase in the activity of the enzyme. Histamine (1 μM), vitamin D₃ (1 μM), and retinoic acid (1μM) failed to stimulate tyrosinase activity in either white or black foreskin cultures. This hormone-responsive organ culture system can be utilized to characterize the molecular processes responsible for the regulation of tyrosinase and pigmentation in human skin. This work was supported by a research contract from the Oklahoma Center for the Advancement of Science and Technology (OCAST) and by a research grant from the Presbyterian Health Foundation.     

Effects of the anesthetics heptanol,halothane and isoflurane on gap junction conductance in crayfish septate axons: A calcium- and hydrogen-independent phenomenon potentiated by caffeine and theophylline,and inhibited by 4-aminopyridine

Summary This study has monitored junctional and nonjunctional resistance. [Ca²⁺] _i and [H^–] _i , and the effects of various drugs in crayfish septate axons exposed to neutral anesthetics. The uncoupling efficiency of heptanol and halothane is significantly potentiated by caffeine and theophylline. The modest uncoupling effects of isoflurane, described here for the first time, are also enhanced by caffeine. Heptanol causes a decrease in [Ca²⁺] _i and [H⁺] _i both in the presence and absence of either caffeine or theophylline. A similar but transient effect on [Ca²⁺] _i is observed with halothane. 4-Aminopyridine strongly inhibits the uncoupling effects of heptanol. The observed decrease in [Ca^2–] _i with heptanol and halothane and negative results obtained with different [Ca²⁺] _o , Ca²⁺-channel blockers (nisoldipine and Cd²⁺) and ryanodine speak against a Ca²⁺ participation. Negative results obtained with 3-isobutyl-l-methylxanthine, forskolin, CPT-cAMP, 8Br-cGMP, adenosine, phorbol ester and H7, superfused in the presence and absence of caffeine and/or heptanol. indicate that neither the heptanol effects nor their potentiation by caffeine are mediated by cyclic nucleotides, adenosine receptors and kinase C. The data suggest a direct effect of anesthetics. possibly involving both polar and hydrophobic interactions with channel proteins. Xanthines and 4-aminopyridine may participate by influencing polar interactions. The potentiating effect of xanthines on cell-to-cell uncoupling by anesthetics may provide some clues on the nature of cardiac arrhythmias in patients treated with theophylline during halothane anesthesia.     

Summary and Perspectives: Sustained-Release Theophylline and Nocturnal Asthma,Once-Daily and Unequal Dosing Schedules

Many asthmatic patients experience aggravation of symptoms overnight resulting in disruption of their sleep. Sustained-release theophylline represents at this time a major bronchodilator medication which possesses a sufficient duration of activity to avert the nocturnal breathing distress of asthma. Circadian rhythm-adapted theophylline schedules consisting of unequal dosing—more or all the drug taken in the evening—have proven efficacious in clinical investigations for certain patients. Although the kinetic behavior of some formulations is affected by food, the circadian rhythm-adapted schedules represent a significant step forward toward the goal of optimizating sustained-release theophyllines for patients who experience nighttime symptoms.     

Modification of theophylline release with alginate gel formed in hard capsules

The aim of this work was to establish whether alginate gel formed spontaneously in hard gelatin capsules which modifies release of a model drug, theophylline. The effects of the alginate composition, the calcium addition, and the dissolution medium on drug release were also investigated. After the capsule shell dissolved in water, at neutral pH the gel layer of sodium alginate was formed immediately as the sodium alginate hydrated and swelled on contact with the aqueous medium. In acidic pH, the contents remained intact and the matrix shape was the same. Theophylline release from capsules containing different grades of alginate demonstrated different release patterns, depending on alginate composition and the pH of the medium. The capsules containing sodium/calcium salts of alginate showed the slowest drug release at neutral pH but the fastest in acidic medium. The presence of calcium acetate in the formulations influenced the drug release kinetics. The drug release in acidic medium showed a non-Fickian diffusion-controlled release, while those in water at neutral pH exhibited a Super Case II transport mechanism. The study also provides evidence that the behavior of alginate in forming the hydrated gel layer may explain the drug release behavior at different pHs. Published: July 6, 2007     

Add-on therapy options in asthma not adequately controlled by inhaled corticosteroids: a comprehensive review

Many patients with persistent asthma can be controlled with inhaled corticosteroids (ICS). However, a considerable proportion of patients remain symptomatic, despite the use of ICS. We present systematically evidence that supports the different treatment options. A literature search was made of Medline/PubMed to identify randomised and blinded trials. To demonstrate the benefit that can be obtained by increasing the dose of ICS, dose-response studies with at least three different ICS doses were identified. To demonstrate whether more benefit can be obtained by adding long-acting β₂-agonist (LABA), leukotriene antagonist (LTRA) or theophylline than by increasing the dose of ICS, studies comparing these options were identified. Thirdly, studies comparing the different "add-on" options were identified. The addition of a LABA is more effective than increasing the dose of ICS in improving asthma control. By increasing the dose of ICS, clinical improvement is likely to be of small magnitude. Addition of a LTRA or theophylline to the treatment regimen appears to be equivalent to doubling the dose of ICS. Addition of a LABA seems to be superior to an LTRA in improving lung function. However, addition of LABA and LTRA may be equal with respect to asthma exacerbations. However, more and longer studies are needed to better clarify the role of LTRAs and theophylline as add-on therapies.     

Evidence that the neuroleptic fluphenazine replaces Ca2+ and adjusts the noradrenaline induced cyclic adenosine monophosphate synthesis in the rat retina

Intact rat retinae were incubated in Krebs-Ringer media with noradrenaline (NA) in the presence (0.75 mM) or absence of extracellular Ca²⁺ and at relatively high (10 mM) or low (1 mM) theophylline concentrations. Depending on the incubation conditions we found that the neuroleptic fluphenazine (FLU) affected cAMP-synthesis separately from cAMP-degradation of the NA-cAMP system in the retina. The main results were: At a relatively high theophylline concentration of 10 mM, where cAMP synthesis alone is operative, and at 0.75 Ca²⁺ we measured with 50 μM NA a NA-response of 110 pmol cAMP/mg prot. At a low theophylline concentration of 1 mM and again at 0.75 mM Ca²⁺ both cAMP-synthesis and -breakdown are operative. In this condition we found the NA-response of 26 pmol cAMP/mg prot. to be raised by 10 μM FLU to 130 pmol cAMP/mg prot. This enhancing effect might be due to inhibition of degradation of NA-induced cAMP by FLU. In the absence of extracellular calcium and again at 10 mM theophylline, 10 μM FLU raised the NA response nearly 4-fold from 42 pmol cAMP/mg prot. to 153 pmol cAMP/mg prot. The lowest effective concentration for obtaining this enhancing effect was 10 μM FLU and the effect is characterized by an apparent K_m of 0.5 μM. The use of 10 mM theophylline in this condition suggests that this FLU-Ca²⁺ effect is confined to the synthesis part of the NA-cAMP system. The effect points to a replacement of an intramembraneous Ca²⁺ function by FLU. In conclusion: our results suggest that FLU inhibits degradation of NA-induced synthesis of cAMP and that the neuroleptic renders the NA-response less dependent on extracellular Ca²⁺.     

A novel fluorescent aptasensor for the detection of theophylline based on cryonase-driven signal amplification strategy

In the study, we have developed an expedient and efficient method for the detection of theophylline based on the amplification of the signal intensity of fluorescence based on oxidized single-walled carbon nanohorns (oxSWCNHs)/cryonase. When theophylline was not present in the system, oxSWCNHs can adequately adsorb nucleic acid probes labeled by carboxyfluorescein (FAM). In the presence of theophylline, the nucleic acid probe forms the tertiary probe–theophylline complex, which detaches from the surface of the oxSWCNHs. Then, upon reaction with cryonase, the complex can release the FAM and theophylline into the next cycle. The fluorescence signal of the system exhibits a 1:N magnification, enabling quantitative detection of theophylline. The linear range was 30–150 ng/mL, and the limit of detection (LOD) was 6.04 ng/mL. At the same time, it can also be used to detect theophylline in mouse serum.     

Effect of estradiol on Ca<Superscript>2+</Superscript> release from intracellular stores in porcine oocytes stimulated by prolactin,theophylline, or guanosine triphosphate

The interaction between prolactin and theophylline as well as between prolactin and guanosine triphosphate during Ca²⁺ release from intracellular stores of estradiol-treated porcine oocytes isolated from the ovary at the stage of follicular growth were studied using fluorescent Ca²⁺-sensitive probe chlortetracycline. In the absence of estradiol, prolactin or theophylline induced Ca²⁺ release from intracellular stores; however, no increase in Ca²⁺ release was observed after their combined action. Conversely, Ca²⁺ release from intracellular stores increased only after the combined exposure to prolactin and theophylline in the presence of estradiol. In the absence of estradiol, guanosine triphosphate induced calcium release alone and together with prolactin. Protein kinase C regulated Ca²⁺ release from intracellular stores after the combined exposure to prolactin and theophylline only in the presence of estradiol; while the activation of protein kinase C required no estradiol during the combined exposure to prolactin and guanosine triphosphate. The data obtained indicate the effect of estradiol on Ca²⁺ release from intracellular stores after the combined exposure to prolactin and theophylline, while no such effect was observed after the combined exposure to prolactin and guanosine triphosphate.