Metabolic clearance rate of biosynthetic growth hormone after endogenous growth hormone suppression with a somatostatin analogue in chronic renal failure patients and control subjects

End-Stage Renal Disease-Related Accelerated Immune Senescence: Is Rejuvenation of the Immune System a Therapeutic Goal?

End-stage renal disease (ESRD) patients exhibit clinical features of premature ageing, including frailty, cardiovascular disease, and muscle wasting. Accelerated ageing also concerns the immune system. Patients with ESRD have both immune senescence and chronic inflammation that are resumed in the so-called inflammaging syndrome. Immune senescence is particularly characterised by premature loss of thymic function that is associated with hyporesponsiveness to vaccines, susceptibility to infections, and death. ESRD-related chronic inflammation has multiple causes and participates to accelerated cardiovascular disease. Although, both characterisation of immune senescence and its consequences are relatively well-known, mechanisms are more uncertain. However, prevention of immune senescence/inflammation or/and rejuvenation of the immune system are major goal to ameliorate clinical outcomes of ESRD patients.

The kidneys play a central role in the clearance of rhGH in rats

The kidneys are thought to play an important role in the clearance of recombinant human growth hormone (rhGH), but the relative importance is not clear. Obtaining knowledge of clearance pathway is an important prerequisite for the development of new long acting growth hormone analogues targeted at treatment of patients with growth hormone disorders. The purpose of this study was to investigate the relative importance of the kidneys in the clearance of rhGH. The study employed a newly validated nephrectomy rat model and a population based pharmacokinetic approach to assess renal clearance of rhGH in non-anesthetized rats, anesthetized rats and in nephrectomized anesthetized rats. Clearance in non-anesthetized rats was 290 ml/h/kg. This was reduced to 185 ml/h/kg by anesthesia and further reduced to 18 ml/h/kg by nephrectomy. As nephrectomy was able to reduce clearance with 90%, we conclude that renal clearance plays a pivotal role in the elimination of rhGH in rats.

Growth hormone, insulin-like growth factor-1, and the kidney: pathophysiological and clinical implications

Besides their growth-promoting properties, GH and IGF-1 regulate a broad spectrum of biological functions in several organs, including the kidney. This review focuses on the renal actions of GH and IGF-1, taking into account major advances in renal physiology and hormone biology made over the last 20 years, allowing us to move our understanding of GH/IGF-1 regulation of renal functions from a cellular to a molecular level. The main purpose of this review was to analyze how GH and IGF-1 regulate renal development, glomerular functions, and tubular handling of sodium, calcium, phosphate, and glucose. Whenever possible, the relative contributions, the nephronic topology, and the underlying molecular mechanisms of GH and IGF-1 actions were addressed. Beyond the physiological aspects of GH/IGF-1 action on the kidney, the review describes the impact of GH excess and deficiency on renal architecture and functions. It reports in particular new insights into the pathophysiological mechanism of body fluid retention and of changes in phospho-calcium metabolism in acromegaly as well as of the reciprocal changes in sodium, calcium, and phosphate homeostasis observed in GH deficiency. The second aim of this review was to analyze how the GH/IGF-1 axis contributes to major renal diseases such as diabetic nephropathy, renal failure, renal carcinoma, and polycystic renal disease. It summarizes the consequences of chronic renal failure and glucocorticoid therapy after renal transplantation on GH secretion and action and questions the interest of GH therapy in these conditions.

Pharmacokinetic predictions for patients with renal impairment: focus on peptides and protein drugs

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Renal impairment may affect the pharmacokinetics of peptide and protein drugs. • Molecular size is a predictor. Small molecules are eliminated by the kidneys, whereas large molecules (>67 kDa) are not. • Urinary recovery of peptide and protein drugs in healthy volunteers is not predictive for pharmacokinetic changes in patients with renal impairment.

WHAT THIS STUDY ADDS

• An apparently continuous non-linear relationship between molecular weight and pharmacokinetic alterations as observed in patients with severe renal impairment or end-stage renal disease is described. • Potentially relevant pharmacokinetic changes were found for drugs with a molecular weight below 50 kDa. • Analysis of observed pharmacokinetics in patients with severe renal impairment may be a useful approach, especially when urinary recovery in healthy volunteers is not predictive.

AIM

Drug dosage adjustments in renal impairment are usually based on estimated individual pharmacokinetics. The extent of pharmacokinetic changes in patients with renal impairment must be known for this estimation. If measured data are not available, an estimate based on drug elimination in urine of healthy subjects or patients with normal renal function is commonly made. This is not reliable, however, if renal drug metabolism is involved, as is presumably the case for many peptide and protein drugs. In the present study a new method to predict pharmacokinetic changes for such drugs based on molecular weight was derived.

METHODS

Articles reporting measured pharmacokinetics of peptide and protein drugs in patients with severe renal impairment or end-stage renal disease were identified from the scientific literature, the pharmacokinetic parameter values were extracted and a statistical data synthesis was performed. A sigmoid E(max) model was applied and fitted to the data and the prediction error was analyzed.

RESULTS

Overall, 98 peptide and protein drugs were identified. Relevant pharmacokinetic data in patients with renal impairment were found for 21 of these drugs. The average drug clearance was 30% and the average prolongation in half-life was 3.1-fold for low molecular weight peptides or proteins. The median root squared percentage of the prediction error was 18% (drug clearance) and 12% (half-life).

CONCLUSION

An apparently continuous non-linear relationship between molecular weight and pharmacokinetic alterations in patients with severe renal impairment was found. The derived equations could be used as a rough guide for decisions on drug dosage adjustments in such patients.

Growth hormone doping in sports: a critical review of use and detection strategies

GH is believed to be widely employed in sports as a performance-enhancing substance. Its use in athletic competition is banned by the World Anti-Doping Agency, and athletes are required to submit to testing for GH exposure. Detection of GH doping is challenging for several reasons including identity/similarity of exogenous to endogenous GH, short half-life, complex and fluctuating secretory dynamics of GH, and a very low urinary excretion rate. The detection test currently in use (GH isoform test) exploits the difference between recombinant GH (pure 22K-GH) and the heterogeneous nature of endogenous GH (several isoforms). Its main limitation is the short window of opportunity for detection (~12-24 h after the last GH dose). A second test to be implemented soon (the biomarker test) is based on stimulation of IGF-I and collagen III synthesis by GH. It has a longer window of opportunity (1-2 wk) but is less specific and presents a variety of technical challenges. GH doping in a larger sense also includes doping with GH secretagogues and IGF-I and its analogs. The scientific evidence for the ergogenicity of GH is weak, a fact that is not widely appreciated in athletic circles or by the general public. Also insufficiently appreciated is the risk of serious health consequences associated with high-dose, prolonged GH use. This review discusses the GH biology relevant to GH doping; the virtues and limitations of detection tests in blood, urine, and saliva; secretagogue efficacy; IGF-I doping; and information about the effectiveness of GH as a performance-enhancing agent.

A review of the effects of growth hormone changes on symptoms of frailty in the elderly with chronic kidney disease

The incidence and prevalence of chronic kidney disease (CKD) is increasing worldwide, especially in the elderly. Recently, functional impairment and frailty have been recognized as factors affecting the quality of life, and outcomes in elderly patients with CKD and therapeutic interventions to improve function and reduce frailty are therefore being considered. Growth hormone (GH) levels decrease with age and GH actions are impaired in CKD patients. GH stimulates protein synthesis, bone, and glucose metabolism, and affects body composition by reducing body fat and increasing lean body mass. An increase in lean body mass may reduce frailty and thus avoid functional impairment. Thus, providing GH to elderly CKD patients could potentially improve outcomes and quality of life by lowering the risk of frailty and associated functional impairment. There are few studies assessing the long-term effects of GH administration on symptoms of frailty in elderly patients with CKD. In this review we will try to shed some light on the trials assessing the administration of GH to elderly subjects and to patients with CKD and focus on the possible role GH administration may play to improve frailty and quality of life in those patients.

Population pharmacokinetic model for human growth hormone in adult patients in chronic dialysis compared with healthy subjects

OBJECTIVE

To develop a population pharmacokinetic (PK) model of recombinant human growth hormone (rhGH) treatment in patients with end-stage renal disease (ESRD) and healthy volunteers (HVs), to support future study design.

DESIGN

This was an open, non-randomized, single-centre parallel-group study lasting 8-9 days. Various compartment models with first-order and Michaëlis-Menten absorption and elimination were explored. Eleven adult ESRD patients and 10 matched HVs received 50 microg/kg/day rhGH (subcutaneous (s.c.) injection) for 8 or 7 days, respectively. Blood samples were drawn every 30 min for 24h following dosing on Days 0, 7 and 8 (ESRD patients). Influence of the covariates subject group (ESRD/HV), gender, weight, and dialysis flow-rate on model parameters was examined.

RESULTS

The final model was one-compartmental with Michaëlis-Menten absorption and elimination. The following estimates were obtained: maximum absorption rate (VMA) - 11.3 microg/kg/h (both groups); amount of drug corresponding to half-maximum absorption rate (KMA) - 1.06 and 18.8 microg/kg (ESRD patients and HVs, respectively; P<0.001); maximum elimination rate (VM) - 9.37 and 13.0 microg/kg/h (ESRD patients and HVs, respectively; P<0.001); amount of drug corresponding to half-maximum elimination rate - 18.9 microg/kg (both groups). Significant differences in KMA and VM between HVs and ESRD patients corresponded to higher absorption and lower elimination rates in ESRD, but all GH profiles were back to baseline by 20-22h and no overall accumulation occurred. Simplified posterior predictive checks indicated that the model satisfactorily captured PK. All non-compartmental estimates for AUC(0-24h) and C(max) lay within 95% confidence limits of the simulated distributions.

CONCLUSIONS

A population PK model was established, which showed acceptable performance for trial-simulation purposes.

Pharmacokinetics and pharmacodynamics of growth hormone in patients on chronic haemodialysis compared with matched healthy subjects: an open, nonrandomized, parallel-group trial

BACKGROUND

GH may be beneficial in treating patients with end-stage renal disease (ESRD). However, the efficacy and safety of GH could be compromised by the potential for accumulation in the circulation.

OBJECTIVE

The objective was to investigate the pharmacokinetics and safety of GH treatment in ESRD patients.

DESIGN

This was an open, nonrandomized, single-centre parallel-group study lasting 8-9 days.

SUBJECTS

Eleven adult ESRD patients and 10 matched healthy individuals received recombinant human GH (50 microg/kg/day for 7 days) by subcutaneous injection; there were two dose reductions (25%) from Day 5/7. ESRD patients underwent dialysis four times.

MEASUREMENTS

Serum concentrations of GH, insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-I (IGFBP-I), IGFBP-III and GHBP were measured. The primary end-point was GH exposure [area-under-the-curve (AUC) calculated from the 24-h profile] on Days 7-8.

RESULTS

GH AUC(0-24 h) was greater for patients (387.91 +/- 134.13 microg h/l) than healthy subjects (225.35 +/- 59.63 microg h/l) and the 90% confidence interval (CI) for the estimated patient : healthy subject ratio (1.40-2.07) was not within the acceptance interval (0.67-1.50). GH AUC(18-24 h) for patients and healthy subjects (3.03 +/- 2.71 microg h/l and 6.37 +/- 4.21 microg h/l) returned approximately to baseline (2.86 +/- 3.91 microg h/l and 1.09 +/- 1.43 microg h/l); terminal half-life (t(1/2,z)) was shorter for patients (2.28 +/- 00.43 h vs. 3.23 +/- 00.75 h). No major safety issues were identified.

CONCLUSIONS

Results demonstrate a difference between patients and healthy subjects regarding GH AUC(0-24 h). However, GH concentrations for both groups were comparable to baseline by 20-22 h, thus GH was not retained in the circulation of ESRD patients.

Growth hormone distribution kinetics are markedly reduced in adults with growth hormone deficiency

OBJECTIVE

Growth hormone (GH) circulating levels are highly dependent not only on GH secretion rate from the pituitary, but also on the hormone distribution in the compartments of the body and elimination phenomena. In adult GH-deficient patients these factors become critical nowadays, especially when recombinant human GH (rhGH) is available for replacement therapy. In the present study, we assess the influence of both distribution and elimination phenomena on GH pharmacokinetics in adult GH-deficient patients.

METHODS

We used a four-step methodology following a compartmental approach after an intravenous bolus of recombinant GH in adult GH-deficient patients.

RESULTS

We found that GH kinetics are clearly explained by a bi-exponential, two-compartmental model in GH-deficient patients, similarly than in normal or diabetic subjects, as previously shown. We have also observed a marked delay in the whole GH elimination process in GH-deficient patients compared to normal adult subjects, as revealed by metabolic clearance ratio (MCR), elimination constant from central compartment (k(10)), and mean resident time in the body (MRT). Interestingly, such a delay appear to be caused by deep changes in the distribution phase (Mtt(1)- mean transit time-1; T(1/2alpha)- GH half-life at distribution phase), while the elimination phenomenon remains unaltered.

CONCLUSION

Our results emphasize the relevance of distribution phenomena in GH pharmacokinetics, and indicates that studies avoiding data from the GH distribution phase, such as those carried out in steady-state conditions, or those using noncompartmental models, could easily miss relevant information. Our data should be taken into consideration when establishing the appropriate dosage for GH replacement treatments in GH-deficient patients, and calculations should include GH distribution kinetics.

Growth hormone, IGF-I and its binding proteins (IGFBP-1 and -3) in adult uraemic patients undergoing peritoneal dialysis and haemodialysis

OBJECTIVE

The GH/IGF axis is altered in chronic renal failure (CRF). CRF patients usually show normal or high serum concentrations of GH and IGF-I, whereas all IGF binding proteins (IGFBP-1 to -6), except IGFBP-5, considerably increase with declining renal function. The aims of the present study were to quantify serum concentrations of GH, IGF-I, IGFBP-1 and IGFBP-3 in a group of patients with CRF, and determine whether there were differences according to the type of dialysis, that is, peritoneal dialysis (PD) and haemodialysis (HD).

DESIGN

A cross-sectional study in the setting of a dialysis unit of a general hospital.

PATIENTS AND MEASUREMENTS

We studied 108 dialysis patients treated by PD (n = 54, 32 males and 22 females, mean age 61.0 +/- 1.4 years) or HD (n = 54, 31 males and 23 females, age 62.6 +/- 1.5 years). A group of 42 healthy subjects of similar age, sex and body mass index (BMI) served as the control group. Baseline serum concentrations of GH, insulin, IGF-I, IGFBP-1 and IGFBP-3 were measured in all patients and control subjects.

RESULTS

Fasting serum concentrations of IGF-I and its binding proteins (IGFBP-1 and IGFBP-3) were significantly higher in dialysis patients than in subjects with normal renal function. IGF-I (248.9 +/- 23.4 vs. 205.5 +/- 15.5 micro g/l, NS), IGFBP-3 (5.6 +/- 0.4 vs. 5.5 +/- 0.2 mg/l, NS) and IGFBP-1 (36.1 +/- 5.9 vs. 44.1 +/- 6.5 micro g/l, NS) concentrations were similar in both groups of dialysis (PD vs. HD) patients. However, GH (2.3 +/- 0.3 vs. 1.1 +/- 0.1 micro g/l, P < 0.001) and insulin (40.4 +/- 4.5 vs. 30.1 +/- 3.1 micro U/ml, P < 0.05) levels were significantly higher in the PD group than in the HD group. Both groups of dialysis patients showed significantly higher levels of insulin than healthy subjects (14.7 +/- 1.9 micro U/ml, P < 0.0001 and P < 0.01 for PD and HD, respectively). In both groups of dialysis patients, IGF-I correlated inversely with IGFBP-1 (PD group r = -0.46, P = 0.0006; HD group r = -0.57, P = 0.0001) and directly with IGFBP-3 (PD group r = 0.44, P = 0.001; HD group r = 0.73, P = 0.001). No correlation between insulin and IGFBP-1 was found in any of the groups studied.

CONCLUSIONS

These findings demonstrate that adult dialysis patients have elevated IGF-I, IGFBP-1 and IGFBP-3 serum concentrations compared with subjects with normal renal function. Only GH and insulin show statistically significant differences in relation to type of dialysis. Finally, the negative correlation between IGF-I and IGFBP-1 and the positive correlation between IGF-I and IGFBP-3 are maintained in both groups of adult dialysis patients.

End-stage renal disease: endocrine aspects of treatment

End-stage renal disease (ESRD) is a deadly disease unless supportive treatment is administered in the form of haemodialysis, peritoneal dialysis or kidney transplantation. Although marked improvements have occurred in the efficiency of dialysis and in overall care, patients with ESRD still have poor long-term survival. The outcome is largely dependent on age, nutritional status, efficiency of dialysis and underlying reason for renal failure. As a consequence of renal failure, these patients experience a number of endocrine and metabolic disorders that may affect their well being and overall outcome. Disturbances in the somatotropic axis have been documented at several different levels, including an end-organ resistance to both growth hormone (GH) and insulin-like growth factor-I (IGF-I). A consequence seen in childhood is reduced growth velocity and short final height that may be overcome by long-term GH treatment, and it is possible that metabolism and nutritional status in adults with ESRD may be influenced by these abnormalities. Although a few small trials of GH treatment in adults with ESRD suggest that nutritional status may improve, long-term trials are needed to demonstrate other benefit of such treatment. This review will give a brief description of endocrine problems in adult patients with ESRD with a focus on the somatotropic axis, and it will review the experience reported in published trials of GH treatment in this patient group.

Altered GH elimination kinetics in type 1 diabetes mellitus can explain the elevation in circulating levels: bicompartmental approach

Type 1 diabetes mellitus (DM 1) is associated with elevated circulating GH concentrations. Because these high GH levels could be explained either by an augmented pituitary secretion and/or delayed elimination clearance or distribution, we sought to evaluate GH pharmacokinetics to propose a model that better explains the elimination kinetics in patients with DM 1 and assess possible differences with normal volunteers that could justify elevation in GH circulating levels in these patients. A multicompartmental analysis was applied to serum GH concentrations measured at different times for 150 min in six patients with DM 1 and six age-, sex-, and body mass index-matched normal subjects after the administration of an iv bolus of recombinant human GH (200 microg), previous suppression of endogenous GH release with octreotide. The best fitting to the GH disappearance profiles was obtained with the biexponential equation in both groups. From it, we propose a bicompartmental model to explain GH kinetics in normal and diabetic patients. The mean transit time in both compartments and the mean residence time in patients with DM 1 were more than twice the values from control group. So in DM 1 elevated circulating GH concentrations are, at least partially, caused by a delayed GH plasmatic clearance. The DM 1 patients included in this study had a normal renal function; thus, our results agree with the hypothesis that DM 1 constitutes a GH-insensitivity state because a reduced GH clearance by its receptor-mediated mechanism might explain the delayed GH elimination kinetics shown in patients with DM 1. However, the possibility of additional factors contributing to the slowed GH removal from circulation is not completely excluded.

Double-blind, placebo-controlled study of growth hormone treatment in elderly patients undergoing chronic hemodialysis: anabolic effect and functional improvement

Elderly patients with end-stage renal disease often have protein and/or caloric malnutrition that severely affects general well-being and mortality. Uremia is associated with resistance to the action of growth hormone (GH). This resistance could be of clinical importance in elderly dialysis patients. In the present study, the effects of GH treatment were assessed in elderly patients receiving chronic hemodialysis. Twenty hemodialysis patients with a mean age of 71.7 years (range, 53 to 92 years) were included on a 6-month, randomized, double-blind, placebo-controlled trial of GH treatment. The dose of GH was 66.7 microgram/kg, administered subcutaneously three times weekly immediately after each dialysis session. Body composition was measured using total-body potassium levels, computed tomography of the lower leg, and bioelectrical impedance analysis. Serum albumin concentrations and handgrip strength were also measured. GH treatment increased the serum concentration of insulin-like growth factor-I (IGF-I), IGF-I/IGF-binding protein-3 ratio, fat-free mass, and the serum concentration of albumin compared with placebo. The number of patients with serum albumin levels less than 40 g/L was reduced by a factor of three in the GH-treated group. Handgrip strength increased in response to GH treatment compared with placebo. Six months of GH treatment in elderly hemodialysis patients produced anabolic effects, with improved muscle performance. Also, the number of patients with low albumin levels was markedly reduced, indicating improved nutritional status and/or attenuated catabolism. These are all important beneficial effects for individual patient outcomes.

Acquired growth hormone resistance in adults

Acquired growth hormone resistance (AGHR) may be defined as the combination of a raised serum growth hormone (GH) concentration, low serum insulin-like growth factor-1 (IGF-1) concentration and a reduced anabolic response to exogenous GH. A wide range of conditions exhibit the syndrome to a variable degree, including sepsis, trauma, burns, AIDS, cancer, and renal or liver failure. The primary defect seems to be a reduction in IGF-1 concentration which then leads to increased GH concentration by a loss of negative feedback. It is not clear whether IGF-1 concentration falls because of decreased production or increased clearance from the circulation, or both. Treatment to reverse the biochemical defect by restoring IGF-1 levels, either by the administration of GH or IGF-1, has resulted in improvements in a wide range of metabolic parameters and, more recently, to definite clinical benefit in well-defined groups, such as patients with AIDS. These results cannot be extrapolated to other groups with AGHR as a recent unpublished report suggested increased mortality in critically ill patients treated with GH. Research needs to focus on the molecular basis of AGHR if we are to develop therapies for catabolism.

Impaired secretion of growth hormone in experimental uremia: relevance of caloric deficiency

To evaluate the impact of uremia and associated caloric restriction on physiologically pulsatile growth hormone (GH) release, we used deconvolution analysis of spontaneous plasma GH profiles in 5/6-nephrectomized male rats (NX, N = 9). Three different normal renal function sham-operated groups were used: rats fed a normal diet ad libitum (SAL, N = 9); NX pair-fed rats (SPF, N = 6); NX rats pair-fed for protein ingestion but calorically supplemented up to the energy intake of SAL (SPF+, N = 8). Severe renal failure was confirmed by much higher (P < 0.001) BUN in NX than sham groups. NX rats were growth retarded as shown by reduced (P < 0.01) weight and length gains as compared with sham animals. Deconvolution analysis (mean +/- SEM) of plasma samples obtained every 10 minutes over 6 hours, and 14 to 16 days after second stage nephrectomy showed that NX rats had a longer GH t(1/2) (17.0 +/- 1.8 vs. 11.6 +/- 0.8 min), less GH mass secreted per burst (48 +/- 15 vs. 95 +/- 16 ng/ml/pulse), lower secretory pulse amplitude (1.9 +/- 0.5 vs. 5.8 +/- 0.9 ng/ml/min), and a reduced total GH secretion (240 +/- 69 vs. 400 +/- 56 ng/ml/6 hr) than SAL rats. Corresponding data were not significantly different between NX and SPF, or between SAL and SPF+ groups. In summary, stunted rats with chronic renal failure exhibit a prolonged GH t(1/2) and suppression of GH secretory pattern burst mass. Control data from rats with normal renal function suggest that the amplitude-specific depression of GH secretion may be attributed, at least in part, to chronic renal failure-associated calorie deficiency.