Growth hormone replacement therapy induces codeine clearance

The effects of growth hormone on therapy resistance in cancer

Pituitary derived and peripherally produced growth hormone (GH) is a crucial mediator of longitudinal growth, organ development, metabolic regulation with tissue specific, sex specific, and age-dependent effects. GH and its cognate receptor (GHR) are expressed in several forms of cancer and have been validated as an anti-cancer target through a large body of in vitro, in vivo and epidemiological analyses. However, the underlying molecular mechanisms of GH action in cancer prognosis and therapeutic response had been sparse until recently. This review assimilates the critical details of GH-GHR mediated therapy resistance across different cancer types, distilling the therapeutic implications based on our current understanding of these effects.

Tacrolimus dose requirements in paediatric renal allograft recipients are characterized by a biphasic course determined by age and bone maturation

AIMS

Despite longstanding recognition of significant age-dependent differences in drug disposition during childhood, the exact course and the underlying mechanisms are not known. Our aim was to determine the course and determinants of individual relative dose requirements, during long-term follow-up in children on tacrolimus.

METHODS

This was a cohort study in a tertiary hospital with standardized annual pharmacokinetic (PK) follow-up (AUC_0-12hr ) in recipients of a renal allograft (≤19 years), between 1998 and 2015. In addition, the presence of relevant pharmacogenetic variants was determined. The evolution of dose-corrected exposure was evaluated using mixed models.

RESULTS

A total of 184 PK visits by 43 children were included in the study (median age: 14.6). AUC_0-12h corrected for dose per kg demonstrated a biphasic course: annual increase 4.4% (CI: 0.3-8.7%) until ±14 years of age, followed by 13.4% increase (CI 8.7-18.3%). Moreover, exposure corrected for dose per m² proved stable until 14 years (+0.8% annually; CI: -3.0 to +4.8%), followed by a steep increase ≥14 years (+11%; CI: 7.0-16.0%). Analysis according to bone maturation instead of age demonstrated a similar course with a distinct divergence at TW2: 800 (P = 0.01). Genetic variation in CYP3A4, CYP3A5, and CYP3A7 was associated with altered dose requirements, independent of age.

CONCLUSIONS

Children exhibit a biphasic course in tacrolimus disposition characterized by a high and stable drug clearance until a specific phase in pubertal development (TW2: 800 at age: ±14 years), followed by an important decline in relative dose requirements thereafter. Pharmacogenetic variation demonstrated an age/puberty independent effect. We suggest a critical reappraisal of current paediatric dosing algorithms for tacrolimus and drugs with a similar disposition.

Attenuated expression of episodic growth hormone-induced CYP2C11 in female rats associated with suboptimal activation of the Jak2/Stat5B and other modulating signaling pathways

Inherent sex differences in various parameters of growth, musculoskeletal function, metabolism, and cytochrome P450 (P450)-dependent drug metabolism have been reported in rats and humans administered typical intermittent/episodic growth hormone (GH) replacement therapy. Having infused and monitored the identical physiologic masculine (episodic) growth hormone profile to both hypophysectomized male and female rats, we observed that induction levels of hepatic CYP2C11 were 35 to 40% lower in females. Associated with the reduced expression of the P450 isoform in the episodic GH-treated females were dramatically lower activation levels of Janus kinase (Jak2), signal transducers and activators of transcription (Stat5A and 5B) as well as 50% less binding of Stat5B to the CYP2C11 promoter. Because the Jak2/Stat5B signaling pathway mediates the effects of the masculine GH profile on its target cells, we conclude that the lower induction level of CYP2C11 in females exposed to the masculine GH profile is probably due, at least in part, to the suboptimum activation of the Jak2/Stat5B pathway. In addition to the reduced activation of the Jak2/Stat5B pathway, we observed lower activational levels of mitogen-activated protein kinase (p44/p42) and, indirectly, nuclear factor-kappaB in the episodic GH-treated females that may be involved in attenuating the activity of the Jak2/Stat5B pathway diminishing CYP2C11 expression levels.

Growth hormone does not alter CYP2A6 activity in growth hormone-deficient children

A large number of metabolic alterations are increasingly being treated with growth hormone. Despite the fact that growth hormone is known to be the main regulator of several hepatic drug metabolizing enzymes in rodents, few studies deal with the effect of growth hormone on hepatic enzyme activities in human beings. The aim of this study was to determine the effects of growth hormone replacement therapy for 4 weeks on CYP2A6 activity in children, because changes in this enzyme activity may have important therapeutic and toxic consequences. A total of 31 growth hormone-deficient children (age range 4.1-13.1 years; mean age 9.88 +/- 2.89 years) participated. The genotypes of CYP2A6 gene, CYP2A6*1A, CYP2A6*1B, CYP2A6*4, CYP2A6*1x2 and CYP2A6*9, were determined by polymerase chain reaction. To assess the enzyme activity, we used caffeine as a probe drug at two points in time: before starting growth hormone therapy (Day 0) and after 4 weeks of growth hormone therapy (Day A). Caffeine and metabolite concentrations in urine were assayed by high-pressure liquid chromatography. The metabolite ratio 1,7-dimethilxanthine to 1,7-dimethylurate (17U/17X) served to indicate CYP2A6 activity. Median value and 95% confidence interval at baseline was 1.08 (0.98-1.24). The value after treatment was 1.08 (0.86-1.21). Data comparison between periods showed lack of statistically significant differences (P > 0.05). The relative change, measured by the ratio of medians and 90% confidence interval, was 1.02 (0.84-1.19). There were no significant differences when the ratio between genotype groups were compared. These results indicate that growth hormone replacement therapy of growth hormone-deficient children for 4 weeks does not modify the CYP2A6 activity and hence the efficacy or toxicity of the CYP2A6 substrate compounds.

A molecular basis for the sexually dimorphic response to growth hormone

Once reserved solely for the treatment of short stature, the now readily available recombinant GH has expanded the use of the hormone to include the treatment of cardiovascular, renal, muscular, skeletal, immunological, psychosocial, and metabolic abnormalities associated with GH deficiency. There are also proposals for the widespread use of the hormone to ameliorate or reverse aging. However, this extensive use of GH has revealed intrinsic sexual dimorphisms in which females are considerably less responsive to the therapeutic regimen than are males. Dynamic changes in the Janus kinase-2 (Jak2)/signal transducers and activators of transcription (Stat5B) signaling pathway [as determined by transducer activation, Stat5B binding to the GH-responsive promoter of the CYP2C11 gene, and expression levels of the suppressors of cytokine signaling family (Socs2, Socs3, and Cis)] were examined in male and female rat-derived primary hepatocyte cultures exposed to the masculine-like episodic GH profile. We report that the cellular actions of GH normally mediated by activation of the Jak2/Stat5B pathway are suppressed in female cells possibly due to an inherent overexpression of Cis, a member of the suppressors of cytokine signaling family that normally down-regulates the Jak2/Stat5B pathway.

Lack of effect of growth hormone replacement therapy on CYP1A2 and xanthine oxidase activities in growth hormone–deficient children

BACKGROUND AND OBJECTIVES

The recombinant human growth hormone (rhGH) is being increasingly used for a number of metabolic alterations. GH is the main regulator of several hepatic drug metabolizing enzymes in rodents. In addition, GH could play a major role in defining the interface between pharmacogenetics and development. However, little is known about the effect of GH on the activity of hepatic enzymes in children. The aim of this study was to determine the effect of rhGH replacement therapy for 4 weeks on CYP1A2 and xanthine oxidase (XO) activities in children.

METHODS

We used caffeine as a probe drug to assess the enzyme activities at two points in time: before starting GH treatment (day 0) and after 4 weeks on rhGH therapy (day A). A total of 31 GH-deficient children (age range: 4.1-13.1 years, mean age: 9.88+/-2.89 years) participated. Urinary concentrations of caffeine and metabolites were determined by high-performance liquid chromatography (HPLC) to calculate the metabolite ratios: (AFMU+1X+1U)/17U for CYP1A2 and 1U/(1X+1U) for XO.

RESULTS

Four weeks of GH substitution did not importantly alter the markers of the enzyme activities measured in this study. Median values and 95% confidence intervals (CI) at baseline were 5.17 (3.87-5.59) for the CYP1A2 ratio and 0.62 (0.56-0.65) for the XO ratio. These values, after treatment, were 4.57 (3.90-5.97) for the CYP1A2 marker and 0.62 (0.59-0.67) for the XO ratio. Data comparison between periods showed lack of statistically significant differences (P>0.05). The relative changes measured by the ratios of medians and 90% CI were 1.14 (0.90-1.31) and 0.99 (0.94-1.06) for CYP1A2 and XO, respectively.

CONCLUSIONS

The absence of significant changes in the markers of enzyme activities CYP1A2 and XO suggests that rhGH replacement therapy of GH-deficient children for 4 weeks could not noticeably modify the efficacy or toxicity of substrates of these metabolic enzymes.

Effects of growth hormone deficiency and rhGH replacement therapy on the 6beta-hydroxycortisol/free cortisol ratio, a marker of CYP3A activity, in growth hormone-deficient children

OBJECTIVE

To determine the effect of both growth hormone deficiency (GHD) and rhGH replacement therapy on CYP3A activity as well as the potential influence of gender.

METHODS

The sample consisted of 35 GHD children (16 males and 19 females), aged 2.9-13.1 years, and a control group of 35 healthy children matched for age and sex. The urinary ratio 6beta-hydroxycortisol/free cortisol was used as a marker of CYP3A activity. In patients, urine samples were collected at two times, prior to starting rhGH replacement treatment and 30 days after beginning therapy.

RESULTS

A significantly higher metabolic activity in GHD children was observed in relation to controls ( P=0.0001) without sex differences. Paired comparisons demonstrated a sexually dimorphic effect of rhGH therapy on the CYP3A activity. While boys displayed a significant decrease ( P=0.003), girls showed no significantly different values of CYP3A marker ( P>0.05). Unpaired comparison between controls and GHD children after therapy demonstrated absence of significant differences in boys ( P>0.05) and a strikingly higher activity in girls ( P=0.0001).

CONCLUSIONS

The data suggests that: (a) GHD in children increases CYP3A activity in a non-sex-dependent manner, (b) rhGH treatment for 30 days to GHD children results in a sexually dimorphic effect on CYP3A activity, with a significant decrease in males toward normalization in relation to controls and non-significant changes in females. The results of this study may have important clinical implications for GHD children, since changes in CYP3A activity importantly affect the metabolism of both steroid hormones and CYP3A substrate drugs.