UGT2B17 Genotype and the Pharmacokinetic Serum Profile of Testosterone during Substitution Therapy with Testosterone Undecanoate. A Retrospective Experience from 207 Men with Hypogonadism

Drug-drug interactions that alter the exposure of glucuronidated drugs: Scope, UDP-glucuronosyltransferase (UGT) enzyme selectivity, mechanisms (inhibition and induction), and clinical significance

Drug-drug interactions (DDIs) arising from the perturbation of drug metabolising enzyme activities represent both a clinical problem and a potential economic loss for the pharmaceutical industry. DDIs involving glucuronidated drugs have historically attracted little attention and there is a perception that interactions are of minor clinical relevance. This review critically examines the scope and aetiology of DDIs that result in altered exposure of glucuronidated drugs. Interaction mechanisms, namely inhibition and induction of UDP-glucuronosyltransferase (UGT) enzymes and the potential interplay with drug transporters, are reviewed in detail, as is the clinical significance of known DDIs. Altered victim drug exposure arising from modulation of UGT enzyme activities is relatively common and, notably, the incidence and importance of UGT induction as a DDI mechanism is greater than generally believed. Numerous DDIs are clinically relevant, resulting in either loss of efficacy or an increased risk of adverse effects, necessitating dose individualisation. Several generalisations relating to the likelihood of DDIs can be drawn from the known substrate and inhibitor selectivities of UGT enzymes, highlighting the importance of comprehensive reaction phenotyping studies at an early stage of drug development. Further, rigorous assessment of the DDI liability of new chemical entities that undergo glucuronidation to a significant extent has been recommended recently by regulatory guidance. Although evidence-based approaches exist for the in vitro characterisation of UGT enzyme inhibition and induction, the availability of drugs considered appropriate for use as 'probe' substrates in clinical DDI studies is limited and this should be research priority.

Long-term testosterone undecanoate treatment in the elderly testosterone deficient male: An observational cohort study

BACKGROUND

Quarterly intramuscular injections with long-acting testosterone undecanoate (TU) provide stable serum testosterone concentrations over time and are therefore preferred by many testosterone-deficient patients. However, the use of long-acting TU in elderly patients is limited due to lack of safety and feasibility studies.

OBJECTIVE

To investigate long-acting TU pharmacokinetics and assess differences in treatment regimens and risk of adverse outcomes in younger versus elderly testosterone-deficient patients.

MATERIALS AND METHODS

Single-center longitudinal observational study. Patients who initiated long-acting TU treatment between 2005 and 2010 were included. Elderly patients were born before 1956 and younger patients between 1965 and 1985. TU dose was adjusted yearly through shortening or prolongation of time between injections. Treatment targets were as follows: (1) free testosterone between 0 and -1 SD from the age-adjusted mean, (2) no symptoms of testosterone deficiency, and (3) hematocrit within the normal range.

RESULTS

The study population consisted of 63 elderly and 63 younger patients. Median follow-up time during testosterone replacement was 12.1 years. Increasing intervals between TU injections were performed 44% more often in the elderly compared to younger patients and time between TU injections were prolonged 4% more in the elderly patients. The hematocrit, as well as the hematocrit for a given serum testosterone (hematocrit: testosterone ratio), increased with treatment time but did not differ between age groups. During follow-up, 40% of patients-both elderly and younger-experienced polycythemia. Risk of polycythemia did not differ with age.

DISCUSSION AND CONCLUSION

An increased number of adjustments of TU dose are necessary in elderly patients in order to reach treatment targets. TU treatment in elderly testosterone-deficient patients is not associated with an increased risk of polycythemia compared to younger patients if age-adjusted treatment targets are reached.

Androgen actions on endothelium functions and cardiovascular diseases

The roles of androgens on cardiovascular physiology and pathophysiology are controversial as both beneficial and detrimental effects have been reported. Although the reasons for this discrepancy are unclear, multiple factors such as genetic and epigenetic variation, sex-specificity, hormone interactions, drug preparation and route of administration may contribute. Recently, growing evidence suggests that androgens exhibit beneficial effects on cardiovascular function though the mechanism remains to be elucidated. Endothelial cells (ECs) which line the interior surface of blood vessels are distributed throughout the circulatory system, and play a crucial role in cardiovascular function. Endothelial progenitor cells (EPCs) are considered an indispensable element for the reconstitution and maintenance of an intact endothelial layer. Endothelial dysfunction is regarded as an initiating step in development of atherosclerosis and cardiovascular diseases. The modulation of endothelial functions by androgens through either genomic or nongenomic signal pathways is one possible mechanism by which androgens act on the cardiovascular system. Obtaining insight into the mechanisms by which androgens affect EC and EPC functions will allow us to determine whether androgens possess beneficial effects on the cardiovascular system. This in turn may be critical in the prevention and therapy of cardiovascular diseases. This article seeks to review recent progress in androgen regulation of endothelial function, the sex-specificity of androgen actions, and its clinical applications in the cardiovascular system.

Delivering enhanced testosterone replacement therapy through nanochannels

Primary or secondary hypogonadism results in a range of signs and symptoms that compromise quality of life and requires life-long testosterone replacement therapy. In this study, an implantable nanochannel system is investigated as an alternative delivery strategy for the long-term sustained and constant release of testosterone. In vitro release tests are performed using a dissolution set up, with testosterone and testosterone:2-hydroxypropyl-β-cyclodextrin (TES:HPCD) 1:1 and 1:2 molar ratio complexes release from the implantable nanochannel system and quantify by HPLC. 1:2 TES:HPCD complex stably achieve 10-15 times higher testosterone solubility with 25-30 times higher in vitro release. Bioactivity of delivered testosterone is verified by LNCaP/LUC cell luminescence. In vivo evaluation of testosterone, luteinizing hormone (LH), and follicle stimulating hormone (FSH) levels by liquid chromatography mass spectrometry (LC/MS) and multiplex assay is performed in castrated Sprague-Dawley rats over 30 d. Animals are treated with the nanochannel implants or degradable testosterone pellets. The 1:2 TES:HPCD nanochannel implant exhibits sustained and clinically relevant in vivo release kinetics and attains physiologically stable plasma levels of testosterone, LH, and FSH. In conclusion, it is demonstrated that by providing long-term steady release 1:2 TES:HPCD nanochannel implants may represent a major breakthrough for the treatment of male hypogonadism.

Detection and effects on serum and urine steroid and LH of repeated GnRH analog (leuprolide) stimulation

Non-steroidal drugs that increase endogenous testosterone (T) may be used to exploit ergogenic effects of androgens in power sports. While superactive GnRH analog use is suspected, neither screening nor detection tests are developed. This study aimed to determine if (a) stimulation for 5 days by leuprolide (a superactive GnRH analog) of serum and urine steroids and urine LH is reproducible at a 2 week interval, (b) nandrolone decanoate (ND) co-administration masks responses to leuprolide administration, (c) performance of urine measurement of leuprolide and M1, its major metabolite, as a detection test. Healthy men were randomized into a 4 week parallel group, open label clinical study in which all men had daily sc injections of leuprolide (1mg) for 4 days in the 1st and 3rd weeks with hormone-free 2nd and 4th weeks. In the 3rd week, men were randomized to either ND injections or no extra treatment. Serum steroids were determined by liquid chromatography, tandem mass spectrometry (LC-MS), urine steroids by gas chromatography, mass spectrometry (GC-MS), urine leuprolide and M1 by high resolution LC-MS and urine LH by immunoassay. Leuprolide stimulated striking, reproducible increases in serum and urine LH and steroids (serum T, dihydroT (DHT), 3α diol; urine T, epitestosterone (E) and androsterone (A). ND suppressed basal serum T, E2, 3α diol, and urinary E but did not mask or change the magnitude of responses to leuprolide. Urine leuprolide and M1 measurement had 100% sensitivity and specificity in detecting leuprolide administration up to one day after cessation of injections with the detection window between 1 and 3 days after last dose. Screening using urine steroid and LH measurements, optimally by urinary log10(LHxT), correctly classified 82% of urine samples. It is concluded that leuprolide stimulation of endogenous testosterone is reproducible after a 10-day interval, is not masked by ND and is reliably detected by urine leuprolide or M1 measurement for at least 1 day after administration.