Effect of coadministration of single and multiple doses of rifampicin on the pharmacokinetics of fexofenadine enantiomers in healthy subjects
- Drug metabolism and disposition: the biological fate of chemicals
- Published almost 8 years ago
The effect of rifampicin on the pharmacokinetics of fexofenadine enantiomers was examined in healthy subjects who received fexofenadine alone or with single or multiple doses of rifampicin (600 mg). A single coadministered dose of rifampicin significantly decreased the oral clearance (CL(tot)/F) and renal clearance (CL®) of S- and R-fexofenadine by 76 and 62%, and 73 and 62%, respectively. Even after multiple doses, rifampicin significantly decreased these parameters, although the effect on the CL(tot)/F was slightly blunted. Multiple doses of rifampicin abolished the difference in the CL(tot)/F of fexofenadine enantiomers, whereas the stereoselectivity in the CL® persisted. Rifampicin inhibited the uptake of fexofenadine enantiomers by human hepatocytes via organic anion transporter (OAT) OATP1B3 and its basal-to-apical transport in Caco-2 cells, but not OAT3-mediated or multidrug and toxic compound extrusion 1 (MATE1)-mediated transport. The plasma-unbound fraction of S-fexofenadine was 1.8 times higher than that of R-fexofenadine. The rifampicin-sensitive uptake by hepatocytes was 1.6 times higher for R-fexofenadine, whereas the transport activities by OATP1B3, OAT3, MATE1, or P-glycoprotein were identical for both enantiomers. S-fexofenadine is a more potent human histamine H1 receptor antagonist than R-fexofenadine. In conclusion, rifampicin has multiple interaction sites with fexofenadine, all of which contribute to increasing the area under the curve of fexofenadine when they are given simultaneously, to surpass the effect of the induction of P-glycoprotein elicited by multiple doses.
Airway hyperresponsiveness (AHR) and airway inflammation are key pathophysiological features of asthma. Bronchial provocation tests (BPTs) are objective tests for AHR that are clinically useful to aid in the diagnosis of asthma in both adults and children. BPTs can be either “direct” or “indirect,” referring to the mechanism by which a stimulus mediates bronchoconstriction. Direct BPTs refer to the administration of pharmacological agonist (e.g., methacholine or histamine) that act on specific receptors on the airway smooth muscle. Airway inflammation and/or airway remodeling may be key determinants of the response to direct stimuli. Indirect BPTs are those in which the stimulus causes the release of mediators of bronchoconstriction from inflammatory cells (e.g., exercise, allergen, mannitol). Airway sensitivity to indirect stimuli is dependent upon the presence of inflammation (e.g., mast cells, eosinophils), which responds to treatment with inhaled corticosteroids (ICS). Thus, there is a stronger relationship between indices of steroid-sensitive inflammation (e.g., sputum eosinophils, fraction of exhaled nitric oxide) and airway sensitivity to indirect compared to direct stimuli. Regular treatment with ICS does not result in the complete inhibition of responsiveness to direct stimuli. AHR to indirect stimuli identifies individuals that are highly likely to have a clinical improvement with ICS therapy in association with an inhibition of airway sensitivity following weeks to months of treatment with ICS. To comprehend the clinical utility of direct or indirect stimuli in either diagnosis of asthma or monitoring of therapeutic intervention requires an understanding of the underlying pathophysiology of AHR and mechanisms of action of both stimuli.
Histamine (HA) is a pleiotropic biogenic amine synthesized exclusively by histidine decarboxylase (HDC) in most mammalian tissues. The literature on the role of HA within the male gonad has expanded over the last years, attracting attention to potential unexpected side-effects of anti-histamines on testicular function. In this regard, HA receptors (HRH1, HRH2 and HRH4) have been described in Leydig cells of different species, including human. Via these receptors, HA has been reported to trigger positive or negative interactions with the LH/hCG signaling pathway depending upon its concentration, thereby contributing to the local control of testicular androgen levels. It should then be considered that anti-histamines may affect testicular homeostasis by increasing or decreasing steroid production. Additionally, HRH1 and HRH2 receptors are present in peritubular and germ cells, and HRH2 antagonists have been found to negatively affect peritubular cells and reduce sperm viability. The potential negative impact of anti-histamines on male reproduction becomes even more dramatic if we consider that HA has also been associated with human sexual behavior and penile erection. What is more, although testicular mast cells are the major source of locally produced HA, recent studies have described HDC expression in macrophages, Leydig cells and germ cells, revealing the existence of multiple sources of HA within the testis. Undoubtedly, the more we learn about the testicular histaminergic system, the more opportunities there will be for rational design of drugs aimed at treating HA-related pathologies, with minimum or nule negative impact on fertility.
Patients with autosomal dominant vibratory urticaria have localized hives and systemic manifestations in response to dermal vibration, with coincident degranulation of mast cells and increased histamine levels in serum. We identified a previously unknown missense substitution in ADGRE2 (also known as EMR2), which was predicted to result in the replacement of cysteine with tyrosine at amino acid position 492 (p.C492Y), as the only nonsynonymous variant cosegregating with vibratory urticaria in two large kindreds. The ADGRE2 receptor undergoes autocatalytic cleavage, producing an extracellular subunit that noncovalently binds a transmembrane subunit. We showed that the variant probably destabilizes an autoinhibitory subunit interaction, sensitizing mast cells to IgE-independent vibration-induced degranulation. (Funded by the National Institutes of Health.).
Mast cell activation syndrome (MCAS) is a condition with signs and symptoms involving the skin, gastrointestinal, cardiovascular, respiratory, and neurologic systems. It can be classified into primary, secondary, and idiopathic. Earlier proposed criteria for the diagnosis of MCAS included episodic symptoms consistent with mast cell mediator release affecting two or more organ systems with urticaria, angioedema, flushing, nausea, vomiting, diarrhea, abdominal cramping, hypotensive syncope or near syncope, tachycardia, wheezing, conjunctival injection, pruritus, and nasal stuffiness. Other criteria included a decrease in the frequency, severity, or resolution of symptoms with anti-mediator therapy including H(1) and H(2)histamine receptor antagonists, anti-leukotrienes, or mast cell stabilizers. Laboratory data that support the diagnosis include an increase of a validated urinary or serum marker of mast cell activation (MCA), namely the documentation of an increase of the marker above the patient’s baseline value during symptomatic periods on more than two occasions, or baseline serum tryptase levels that are persistently above 15 ng/ml, or documentation of an increase of the tryptase level above baseline value on one occasion. Less specific assays are 24-h urine histamine metabolites, PGD(2) (Prostaglandin D(2)) or its metabolite, 11-β-prostaglandin F(2) alpha. A recent global definition, criteria, and classification include typical clinical symptoms, a substantial transient increase in serum total tryptase level or an increase in other mast cell derived mediators, such as histamine or PGD2 or their urinary metabolites, and a response of clinical symptoms to agents that attenuate the production or activities of mast cell mediators.
The peripheral terminals of primary sensory neurons detect histamine and non-histamine itch-provoking ligands through molecularly distinct transduction mechanisms. It remains unclear, however, whether these distinct pruritogens activate the same or different afferent fibers. Using a strategy of reversibly silencing specific subsets of murine pruritogen-sensitive sensory axons by targeted delivery of a charged sodium-channel blocker, we found that functional blockade of histamine itch did not affect the itch evoked by chloroquine or SLIGRL-NH2, and vice versa. Notably, blocking itch-generating fibers did not reduce pain-associated behavior. However, silencing TRPV1(+) or TRPA1(+) neurons allowed allyl isothiocyanate or capsaicin, respectively, to evoke itch, implying that certain peripheral afferents may normally indirectly inhibit algogens from eliciting itch. These findings support the presence of functionally distinct sets of itch-generating neurons and suggest that targeted silencing of activated sensory fibers may represent a clinically useful anti-pruritic therapeutic approach for histaminergic and non-histaminergic pruritus.
Management of chronic spontaneous urticaria in real life - in accordance with the guidelines? A cross-sectional physician-based survey study
- Journal of the European Academy of Dermatology and Venereology : JEADV
- Published almost 9 years ago
Background Recently, the updated EAACI/GA(2) LEN/EDF/WAO guidelines for urticaria have been published. Objective To examine how chronic spontaneous urticaria (csU) patients in Germany are diagnosed and treated, and to compare the outcome to the guideline recommendations. Methods During this cross-sectional survey study, most dermatologists, paediatricians and 5149 general practitioners in private practice in Germany were asked to participate. All physicians who agreed were requested to complete a standardized questionnaire about their diagnostic and therapeutic management of csU. Results A total of 776 questionnaires were available for analysis. Most physicians (82%) were attempting to identify underlying causes in their csU patients, but with only limited success. More than 70% reported to check for total serum IgE and to do skin prick testing (not suggested in first line by guideline). In contrast, only 10% applied the autologous serum skin test. The most common first-line treatments were non-sedating antihistamines in standard or higher doses (as recommended). However, many physicians reported still using first generation sedating antihistamines (23%) (not recommended) or systemic steroids (18%). Experience with alternative options was low. Less than one-third of the participants reported to be familiar with the guidelines. Those who did, were found to be more likely to check for underlying causes, to be more experienced with antihistamine updosing and to be more reluctant to use sedating antihistamines or systemic steroids. Conclusion The diagnostic and therapeutic management of csU by private practice physicians does not sufficiently comply with the guidelines. Awareness of the guidelines can lead to improved care.
Lipopolysaccharide (LPS) can exacerbate asthma; however, the mechanisms are not fully understood. This study investigated the effect of LPS on antigen-stimulated mast cell degranulation and the underlying mechanisms. We found that LPS enhanced degranulation in RBL-2H3 cells and mouse peritoneal mast cells upon FcεRI activation, in a dose- and time-dependent manner. Parallel to the alteration of degranulation, LPS increased FcεRI-activated Ca(2+) mobilization, as well as Ca(2+) entry through store-operated calcium channels (SOCs) evoked by thapsigargin. Blocking Ca(2+) entry through SOCs completely abolished LPS enhancement of mast cell degranulation. Consistent with functional alteration of SOCs, LPS increased mRNA and protein levels of Orai1 and STIM1, two major subunits of SOCs, in a time-dependent manner. In addition, LPS increased the mRNA level of Toll-like receptor 4 (TLR4) in a time-dependent manner. Blocking TLR4 with Cli-095 inhibited LPS, increasing transcription and expression of SOC subunits. Concomitantly, the effect of LPS enhancement of Ca(2+) mobilization and mast cell degranulation was largely reduced by Cli-095. Administration of LPS (1 μg) in vivo aggravated airway hyperreactivity and inflammatory reactions in allergic asthmatic mice. Histamine levels in serum and bronchoalveolar lavage fluid were increased by LPS treatment. In addition, Ca(2+) mobilization was enhanced in peritoneal mast cells isolated from LPS-treated asthmatic mice. Taken together, these results imply that LPS enhances mast cell degranulation, which potentially contributes to LPS exacerbating allergic asthma. Lipopolysaccharide increases Ca(2+) entry through SOCs by upregulating transcription and expression of SOC subunits, mainly through interacting with TLR4 in mast cells, resulting in enhancement of mast cell degranulation upon antigen stimulation.
The simpler, the better: H(3) histamine receptor (H(3) R) are of interest as therapeutic targets in cognitive and somnolence disorders. Here, lead optimization of H(3) R inverse agonists bearing a thiazolo[5,4-c]piperidine group gave rise to a clinical candidate with a much simpler unprecedented benzamide scaffold, displaying decreased hERG activity while maintaining high brain receptor occupancies.
Narcolepsy is characterised by excessive daytime sleepiness (EDS) and cataplexy. Histamine neurons are crucial to maintain wakefulness. We assessed the safety and efficacy of pitolisant (previously called BF2.649), a selective histamine H3 receptor inverse agonist that activates these neurons, in patients with narcolepsy.