Insulin-like growth factor I levels during growth hormone (GH) replacement in GH-deficient adults: a gender difference

Adult Stature and Protein Intake During Childhood and Adolescence From 3 Years Onward

CONTEXT

Varying protein intake is known to influence human height growth. However, whether a habitually higher protein intake consistently above dietary recommendations during childhood and adolescence affects adult stature is not known.

OBJECTIVE

To examine whether protein intake in excess of recommendations from childhood onward may exert an anabolic effect on adult stature.

METHODS

We examined habitual protein intake based on 3-day weighed dietary records and 24-hour urinary biomarker excretions in a longitudinal cohort of 189 healthy individuals aged between 3 and 17 years (analyzing 11 diet recordings and 11 24-urine samples per child on average). Urinary urea nitrogen (uN) excretion was used as a biomarker for protein intake. Multilinear regressions were applied to examine the prospective associations of average total and average animal protein intake during growth with the outcome adult height (AH) after adjusting for parental heights, energy intake, dietary potential renal acid load (PRAL), and pubertal, early-life, and socioeconomic factors.

RESULTS

Mean SD scores of total (P = .001) and animal (P < .0001) protein intake as well as uN (P = .01) were prospectively and independently related to adult height in girls, but not in boys. Also for girls only, the fully adjusted regression for renal biomarkers (R2total = 0.79) indicated an inverse relationship between AH and the urinary biomarker for dietary acidity PRAL (P = .06).

CONCLUSION

Our prospective, biomarker-confirmed findings on habitual protein intake during the pediatric period provide evidence that protein ingestion above dietary recommendation contributes to an enhanced AH in girls. This enhancement, in turn, may be weakened by an insufficient alkalizing potential through PRAL-raising fruit- and vegetable-poor nutrition.

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

Irreversible perinatal imprinting of adult expression of the principal sex-dependent drug-metabolizing enzyme CYP2C11

We proposed to determine whether, like other sexual dimorphisms, drug metabolism is permanently imprinted by perinatal hormones, resulting in its irreversible sex-dependent expression. We treated newborn male rats with monosodium glutamate (MSG), a total growth hormone (GH) blocker, and, using cultured hepatocytes, examined expression of adult CYP2C11, the predominant cytochrome-P450 expressed only in males, as well as the signal transduction pathway by which episodic GH solely regulates the isoform's expression. In addition, adolescent hypophysectomized (hypox) male rats served as controls in which GH was eliminated after the critical imprinting period. Whereas renaturalization of the masculine episodic GH profile restored normal male-like levels of CYP2C11, as well as CYP2C12, in hepatocytes from hypox rats, the cells derived from the MSG-treated rats were completely unresponsive. Moreover, GH exposure of hepatocytes from hypox rats resulted in normal induction, activation, nuclear translocation, and binding to the CYP2C11 promoter of the signal transducers mediating GH regulation of CYP2C11 expression, which dramatically contrasted with the complete unresponsiveness of the MSG-derived hepatocytes, also associated with hypermethylation of GH-response elements in the CYP2C11 promoter. Lastly, neonatal MSG treatment had no adverse effect on postnatal and adult testosterone levels. The results demonstrate that the sexually dimorphic expression of CYP2C11 is irreversibly imprinted shortly after birth by a hormone other than the customary testosterone, but likely by GH.

Inherent sex-dependent regulation of human hepatic CYP3A5

BACKGROUND AND PURPOSE

Expression of hepatic cytochromes P450 (CYP) in all species examined, including humans, is generally sexually dimorphic. We examined the sex-dependent expression of CYP3A5 and the hormone-regulated molecular mechanism(s) responsible for any dimorphism.

EXPERIMENTAL APPROACH

CYP3A5 levels as well as nuclear translocation and promoter binding of transcription factors regulating CYP3A5 expression were measured in primary hepatocyte cultures derived from men and women exposed to physiological-like levels of growth hormone alone, dexamethasone alone and the combined regimen.

KEY RESULTS

We observed a dramatic inherent CYP3A5 sexual dimorphism (women > men) with all treatments as a result of a ~2-fold greater level of hormone-induced activation and nuclear accumulation of hepatocyte nuclear factor-4α (HNF-4α), pregnane X receptor (PXR) and retinoic X receptorα (RXRα) in female hepatocytes. Furthermore, PXR : RXRα exhibited significantly higher DNA binding levels to its specific binding motif on the CYP3A5 promoter in female hepatocytes, inferring a possible explanation for the elevated expression of the isoform in women. Results from experiments using HepG2 cells treated with siRNA-induced knockdown of HNF-4α and/or transfected with luciferase reporter constructs containing the CYP3A5 promoter were in agreement with the basic mechanism observed in primary hepatocytes of both sexes.

CONCLUSIONS AND IMPLICATIONS

Female-predominant expression of human CYP3A5 is due to an inherent, sex-dependent suboptimal activation of the transcription networks responsible for hormone-induced expression of the isoform in men. Accordingly, in conjunction with previous studies of other human CYPs, men and women are intrinsically unlikely to handle many drugs in the same way; thus, sex should be a requisite component factored into the design of personalized drug therapies.

Long-term dietary potential renal acid load during adolescence is prospectively associated with indices of nonalcoholic fatty liver disease in young women

Nonalcoholic fatty liver disease (NAFLD), frequently already present in young subjects, has been linked to reduced growth hormone levels and signaling. Similar hormonal changes occur during metabolic acidosis (MA), which may thus contribute to an increased NAFLD risk. Because subclinical MA can be diet induced, we aimed to examine whether a higher diet-dependent acid load during adolescence is prospectively associated with several currently used NAFLD surrogates in young adulthood. Dietary acidity during adolescence (boys:10-15 y, girls: 9-14 y) was calculated as potential renal acid load (PRAL) from at least three 3-d weighed dietary records according to a published algorithm considering dietary protein and minerals in 145 healthy participants. Routine measurements derived from blood analysis and anthropometric data in participants' young adulthood (18-25 y) were used to determine the NAFLD surrogates alanine-aminotransferase (ALT), hepatic steatosis index (HSI), and fatty liver index (FLI). Sex-stratified linear regression models, adjusted for dietary fiber, saturated fat, protein, and adolescent BMI SD scores, were run with PRAL as the independent variable. Dietary PRAL during puberty was positively associated with ALT (P = 0.02), HSI (P = 0.002), and FLI (P = 0.005) in adult females but not males. Females with an adolescent dietary acid load in the highest tertile had 3.5, 4.4, and 4.5 higher values of ALT, HSI, and FLI as adults, respectively, compared to females with the lowest PRAL. The present findings suggest that higher dietary acidity in adolescence may be prospectively associated with hepatic lipid accumulation in females. Whether this relationship is due to the higher proton load or rather represents an unhealthy dietary pattern requires further investigation.

Intrinsic sexually dimorphic expression of the principal human CYP3A4 correlated with suboptimal activation of GH/glucocorticoid-dependent transcriptional pathways in men

Cytochrome P450 (CYP)3A4 is the principal and most abundant human isoform of CYP responsible for the metabolism of more than 50% of all consumed drugs and innumerable endogenous compounds. Expression of CYP3A4 is sexually dimorphic and regulated by the combined actions of GH and glucocorticoids. In the case of the rat, nearly all of the CYPs are "intrinsically" or "inherently" sexually dimorphic, meaning that the expressed sex differences are permanent and irreversible. Using primary hepatocyte cultures derived from men and women exposed to physiologic-like levels of continuous GH (the feminine circulating profile) alone, dexamethasone alone, and the combined regimen, we observed a dramatic inherent CYP3A4 sexual dimorphism (women more than men) with all treatments. The molecular basis for this intrinsic sexually dimorphic expression of CYP3A4 appears to be due, at least in part, to a greater level of hormone-dependent activation and nuclear translocation of both hepatocyte nuclear factor-4α (HNF-4α) and pregnane X receptor in female hepatocytes. Furthermore, these transcription factors exhibited significantly higher DNA binding levels to their specific motifs on the CYP3A4 promoter in female hepatocytes, inferring a possible explanation for the elevated expression of CYP3A4 in women. Accordingly, experiments using HepG2 cells treated with small inhibitory RNA-induced knockdown of HNF-4α and/or transfected with luciferase reporter constructs containing a CYP3A4 promoter lacking HNF-4α-binding motifs demonstrated that GH, to a greater extent dexamethasone, and to the greatest extent the combine hormone regimen, stimulated HNF-4α and pregnane X receptor promoter transactivation, signifying enhanced transcription of CYP3A4 and, thus, identifying a molecular mechanism contributing to the intrinsic sexual dimorphic expression of human CYP3A4.

[Clinical, laboratory and therapeutics aspects of Sheehan's syndrome]

Sheehan's syndrome is characterized by hypopituitarism that occurs as a result of ischemic pituitary necrosis due to severe postpartum hemorrhage. Nowadays it is not usually seen in developed countries because of the improvements in obstetric care. However, in developing countries it is still frequent and probably one of the most common causes of hypopituitarism. Most patients usually present it months to years later, with a history of failure of postpartum lactation, failure to resume menses and other signs of panhypopituitarism. In mild forms of the disease, patients may remain undetected and do not receive treatment for many years. Early diagnosis and appropriate treatment are important to reduce the morbimortality of the patients with Sheehan's syndrome. The aim of this review is to describe clinical, laboratory and therapeutic aspects of Sheehan's syndrome, including our experience in the replacement of recombinant GH in these patients.

Growth hormone action in puberty: effects by gender

OBJECTIVE

Adult females receiving GH may be less sensitive to the metabolic effects of GH than males, however these differences are less well studied in adolescence. We aimed to investigate if metabolic effects of GH vary by gender during puberty.

DESIGN

Sixteen adolescents (8 M/8 F, mean age (SE): 13.1+/-0.2 yr) with significant short stature due to either GH insufficiency or idiopathic short stature were studied before and after 8 w of daily GH therapy. Differences in rates of protein and glycerol turnover ((13)C leucine and d5-glycerol infusions), substrate oxidation rates (indirect calorimetry), hormones, growth factors, lipid concentrations, body composition (DEXA) and 1 yr growth velocity were measured.

RESULTS

Protein synthesis rates per kg FFM were similar in boys and girls before and after GH and increased similarly on treatment in both genders. Rates of whole body lipolysis were similar at baseline and increased after GH in both genders comparably. Plasma lipids were similar between boys and girls before and after GH, and triglycerides increased post-GH in both. Insulin increased after GH comparably in both genders, yet no significant difference in glucose or adiponectin concentrations during treatment or between genders was observed. IGF-I concentrations were similar between boys and girls at baseline, but with a more robust increase in males after 8 w of GH (boys: +629+/-65 ng/ml, girls: +331+/-67, p=0.007). Body composition changes and bone mineral density were similar between genders after GH. HT SDS increased comparably after 1 yr (boys -2.2+/-0.09 to -1.77+/-0.11, p=0.0002; girls -2.49+/-0.24 to -2.02+/-0.25, p=0.04). There were no gender differences on the linear growth responses after 12 mo.

CONCLUSIONS

As compared to girls, boys had: (1) similar sensitivity to GH for protein synthesis, lipolysis, lipid concentrations and body composition changes as well as comparable glucose and adiponectin concentrations; (2) higher IGF-I responses to 8 w of GH. Differences in IGF-I during GH treatment may account in part for the gender differences in physique and strength that develop during human puberty; however, using conventional doses of GH, these differences do not translate into differences in linear growth after 12 mo. Contrary to adults, these data do not support the need for different GH dosing depending on gender during puberty.

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.

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.

Two years of growth hormone replacement therapy in a group of patients with Sheehan's syndrome

To investigate the effects of GH replacement on lipid profile, carotid artery intima-media thickness (IMT), glucose metabolism and visceral fat in patients with Sheehan's syndrome, ten patients, mean age 44.8+/-9.5 yr, compared with 10 controls matched for age and body mass index were studied. Total cholesterol, Triglycerides (TG), HDL-c, LDL-c, Apolipoprotein A and B (apoA and apoB) and Lipoprotein (a), serum IGF-1, ultrasonography of the carotid arteries, oral glucose tolerance test (OGTT), HOMA insulin resistance index, insulin sensitivity index (ISI)-composite and abdominal CT scan were performed. When compared to a control group, patients presented lower HDL concentrations (p=0.05) and 2-h OGTT insulin levels (p<0.04) and increased TG levels (p<0.04). After 24 months of GH replacement a reduction in the relation ApoB/ApoA (p=0.04) was observed, as well as an increase in HDL (p<0.004). A decrease in carotid artery IMT and in visceral fat over time was found, p<0.03 and p<0.04 respectively, though without any significant differences during post hoc comparisons of means, which may be explained by the small number of cases studied, but there was a tendency, p=0.08 and p=0.09 respectively. The 2-h OGTT insulin levels increased (p<0.02) as well as the prevalence of glucose intolerance (prevalence = 42.8%, p<0.05). GH replacement therapy promoted favorable effects on carotid artery IMT, lipid profile and visceral fat in patients with Sheehan's syndrome. On the other hand, patients developed abnormal glucose tolerance probably due to an increase in insulin resistance, demonstrated by higher insulin levels, despite favorable changes in body composition.

Influence of estrogen administration on the growth response to growth hormone (GH) in GH-deficient mice

In women who are growth hormone (GH) deficient, exogenous estrogens increase the dosage of GH that is needed to normalize circulating levels of insulin-like growth factor (IGF-1). Serum IGF-1 derives mostly from the liver, and it is unknown whether the peripheral effects of GH are also impaired by estrogens. Because the ultimate effect of GH is longitudinal growth, we have investigated the influence of estrogen administration on the growth response to recombinant mouse GH therapy in prepubertal GH-deficient (GHD) GHRH knockout (GHRHKO) female mice. Twenty-four GHRHKO female mice (4 animals/group) were treated for 4 weeks (from the second to sixth week of age) with the following schedules: Group I, GH only (25 microg/day); Group II, subcutaneous (sc) ethynil estradiol (EE) (0.035 ES01247g/day); Group III, GH + scEE; Group IV, oral (po) EE (0.035 microg/day); Group V, GH + poEE; Group VI, placebo. At the end of the treatment period, we measured uterine weight, total body weight (TBW), body length (nose-anus, N-A), and femur length. In addition, serum IGF-1 levels were measured. Uteri of mice treated with oral or scEE showed similar increases in weight. There was no difference in the increase in longitudinal growth parameters between mice treated with GH alone or with GH in association with oral or scEE. Serum IGF-1 decreased in animals treated with GH + scEE, compared with GH group, but no group was significantly different from placebo. These results show that subcutaneous or oral EE does not reduce the growth response to GH in female GHD mice.