Pro-Apoptotic Activity of MCL-1 Inhibitor in Trametinib-Resistant Melanoma Cells Depends on Their Phenotypes and Is Modulated by Reversible Alterations Induced by Trametinib Withdrawal

BACKGROUND

Although BRAFV600/MEK inhibitors improved the treatment of melanoma patients, resistance is acquired almost inevitably.

METHODS

Trametinib withdrawal/rechallenge and MCL-1 inhibition in trametinib-resistance models displaying distinct p-ERK1/2 levels were investigated.

RESULTS

Trametinib withdrawal/rechallenge caused reversible changes in ERK1/2 activity impacting the balance between pro-survival and pro-apoptotic proteins. Reversible alterations were found in MCL-1 levels and MCL-1 inhibitors, BIM and NOXA. Taking advantage of melanoma cell dependency on MCL-1 for survival, we used S63845. While it was designed to inhibit MCL-1 activity, we showed that it also significantly reduced NOXA levels. S63845-induced apoptosis was detected as the enhancement of Annexin V-positivity, caspase-3/7 activation and histone H2AX phosphorylation. Percentages of Annexin V-positive cells were increased most efficiently in trametinib-resistant melanoma cells displaying the p-ERK1/2low/MCL-1low/BIMhigh/NOXAlow phenotype with EC50 values at concentrations as low as 0.1 μM. Higher ERK1/2 activity associated with increased MCL-1 level and reduced BIM level limited pro-apoptotic activity of S63845 further influenced by a NOXA level.

CONCLUSIONS

Our study supports the notion that the efficiency of an agent designed to target a single protein can largely depend on the phenotype of cancer cells. Thus, it is important to define appropriate phenotype determinants to stratify the patients for the novel therapy.

Trametinib-Resistant Melanoma Cells Displaying MITFhigh/NGFRlow/IL-8low Phenotype Are Highly Responsive to Alternating Periods of Drug Withdrawal and Drug Rechallenge

Despite significant advances in targeted therapies against the hyperactivated BRAF^V600/MEK pathway for patients with unresectable metastatic melanoma, acquired resistance remains an unsolved clinical problem. In this study, we focused on melanoma cells resistant to trametinib, an agent broadly used in combination therapies. Molecular and cellular changes were assessed during alternating periods of trametinib withdrawal and rechallenge in trametinib-resistant cell lines displaying either a differentiation phenotype (MITF^high/NGFR^low) or neural crest stem-like dedifferentiation phenotype (NGFR^high/MITF^low). Neither drug withdrawal nor drug rechallenge induced cell death, and instead of loss of fitness, trametinib-resistant melanoma cells adapted to altered conditions by phenotype switching. In resistant cells displaying a differentiation phenotype, trametinib withdrawal markedly decreased MITF level and activity, which was associated with reduced cell proliferation capacity, and induced stemness assessed as NGFR-positive cells and senescence features, including IL-8 expression and secretion. All these changes could be reversed by trametinib re-exposure, which emphasizes melanoma cell plasticity. Trametinib-resistant cells displaying a dedifferentiation phenotype were less responsive presumably due to the already low level of MITF, a master regulator of the melanoma phenotype. Considering new directions of the development of anti-melanoma treatment, our study suggests that the phenotype of melanomas resistant to targeted therapy might be a crucial determinant of the selection of second-line therapy for melanoma patients.

BCL-G: 20 years of research on a non-typical protein from the BCL-2 family

Proteins from the BCL-2 family control cell survival and apoptosis in health and disease, and regulate apoptosis-unrelated cellular processes. BCL-Gonad (BCL-G, also known as BCL2-like 14) is a non-typical protein of the family as its long isoform (BCL-G_L) consists of BH2 and BH3 domains without the BH1 motif. BCL-G is predominantly expressed in normal testes and different organs of the gastrointestinal tract. The complexity of regulatory mechanisms of BCL-G expression and post-translational modifications suggests that BCL-G may play distinct roles in different types of cells and disorders. While several genetic alterations of BCL2L14 have been reported, gene deletions and amplifications prevail, which is also confirmed by the analysis of sequencing data for different types of cancer. Although the studies validating the phenotypic consequences of genetic manipulations of BCL-G are limited, the role of BCL-G in apoptosis has been undermined. Recent studies using gene-perturbation approaches have revealed apoptosis-unrelated functions of BCL-G in intracellular trafficking, immunomodulation, and regulation of the mucin scaffolding network. These studies were, however, limited mainly to the role of BCL-G in the gastrointestinal tract. Therefore, further efforts using state-of-the-art methods and various types of cells are required to find out more about BCL-G activities. Deciphering the isoform-specific functions of BCL-G and the BCL-G interactome may result in the designing of novel therapeutic approaches, in which BCL-G activity will be either imitated using small-molecule BH3 mimetics or inhibited to counteract BCL-G upregulation. This review summarizes two decades of research on BCL-G.

BH3 mimetics potentiate pro-apoptotic activity of encorafenib in BRAFV600E melanoma cells

BRAF^V600- and MEK1/2-targeting therapies rarely produce durable response in melanoma patients. We investigated five BRAF^V600E melanoma cell lines derived from drug-naïve tumor specimens to assess cell death response to encorafenib (Braftovi), a recently FDA-approved BRAF^V600 inhibitor. Drug-naïve cell lines (i) did not harbor damaging alterations in genes encoding core apoptotic machinery, but they differed in (ii) mitochondrial priming as demonstrated by whole-cell BH3 profiling, and (iii) levels of selected anti-apoptotic proteins. Encorafenib modulated the balance between apoptosis-regulating proteins as it upregulated BIM and BMF, and attenuated NOXA, but did not affect the levels of pro-survival proteins except for MCL-1 and BCL-X_L in selected cell lines. Induction of apoptosis could be predicted using Dynamic BH3 profiling. The extent of apoptosis was dependent on both (i) cell-intrinsic proximity to the apoptotic threshold (initial mitochondrial priming) and (ii) the abundance of encorafenib-induced BIM (iBIM; drug-induced change in priming). While co-inhibition of MCL-1 and BCL-X_L/BCL-2 was indispensable for apoptosis in drug-naïve cells, encorafenib altered cell dependence to MCL-1, and reliance on BCL-X_L/BCL-2 was additionally found in cell lines that were highly primed to apoptosis by encorafenib. This translated into robust apoptosis when encorafenib was combined with selective BH3 mimetics. Our study provides a mechanistic insight into the role of proteins from the BCL-2 family in melanoma cell response to targeted therapy, and presents preclinical evidence that (i) MCL-1 is a druggable target to potentiate encorafenib activity, whereas (ii) pharmacological inhibition of BCL-X_L/BCL-2 might be relevant but only for a narrow group of encorafenib-treated patients.

Inhibitors of HSP90 in melanoma

HSP90 (heat shock protein 90) is an ATP-dependent molecular chaperone involved in a proper folding and maturation of hundreds of proteins. HSP90 is abundantly expressed in cancer, including melanoma. HSP90 client proteins are the key oncoproteins of several signaling pathways controlling melanoma development, progression and response to therapy. A number of natural and synthetic compounds of different chemical structures and binding sites within HSP90 have been identified as selective HSP90 inhibitors. The majority of HSP90-targeting agents affect N-terminal ATPase activity of HSP90. In contrast to N-terminal inhibitors, agents interacting with the middle and C-terminal domains of HSP90 do not induce HSP70-dependent cytoprotective response. Several inhibitors of HSP90 were tested against melanoma in pre-clinical studies and clinical trials, providing evidence that these agents can be considered either as single or complementary therapeutic strategy. This review summarizes current knowledge on the role of HSP90 protein in cancer with focus on melanoma, and provides an overview of structurally different HSP90 inhibitors that are considered as potential therapeutics for melanoma treatment.

Abstract A20: 17-Aminogeldanamycin inhibits cytoprotective UPR pathways and cooperates with inhibitors of the MAPK signaling cascade in apoptosis induction

Geldanamycin is an inhibitor of Heat Shock Protein 90 (HSP90). Attenuation of HSP90 activity results in accumulation of unfolded proteins, induction of endoplasmic reticulum (ER) stress, and activation of unfolded protein response (UPR). HSP90 is a chaperone protein participating in appropriate folding of more than 100 proteins, including IRE1α and BRAFV600E. In melanoma cells, BRAFV600E was correlated with chronically induced ER stress and involved in UPR-induced resistance to apoptosis. As geldanamycin is highly hepatotoxic, geldanamycin derivatives exerting similar proapoptotic properties but higher selectivity towards cancer cells are needed. In the present study, 17-aminogeldanamycin exerted higher proapoptotic activity than geldanamycin in patient-derived melanoma cell populations as demonstrated by using fluorescence time-lapse imaging (IncuCyte ZOOM). We have also shown that 17-aminogeldanamycin inhibits ERK1/2 activity and cell proliferation,as well as induces apoptosis transiently, enhancing expression of HSP70 and GRP78. GRP78 regulates activity of the UPR pathway, and we have demonstrated that 17-aminogeldanamycin inhibits IRE1α-dependent pathway of UPR responsible for degradation of unfolded proteins and reduces levels of 36 kDa product of ATF6 cleavage in selected melanoma cell populations. Moreover, we have shown that combination of 17-aminogeldanamycin and trametinib induces apoptosis earlier and more efficiently. Our study suggests that cooperation of 17-aminogeldanamycin and trametinib might result from concurrent inhibition of the MAPK and protective UPR pathways but can be also associated with the basal UPR activity, which is diverse among drug-naïve melanoma cell populations. Further studies are necessary to fully explore antimelanoma capabilities of 17-aminogeldanamycin and its combination with targeted therapy. This work was financially supported by Grant 2014/15/B/NZ7/00947 from National Science Centre (Poland), and 502-03/1-156-01/502-14-318 from Medical University of Lodz.

Citation Format: Aleksandra H. Mielczarek-Lewandowska, Mariusz L. Hartman, Malgorzata M. Sztiller-Sikorska, Marta Osrodek, Anna E. Gajos-Michniewicz, Malgorzata E. Czyz. 17-Aminogeldanamycin inhibits cytoprotective UPR pathways and cooperates with inhibitors of the MAPK signaling cascade in apoptosis induction [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr A20.

Non-Apoptotic Cell Death Signaling Pathways in Melanoma

Resisting cell death is a hallmark of cancer. Disturbances in the execution of cell death programs promote carcinogenesis and survival of cancer cells under unfavorable conditions, including exposition to anti-cancer therapies. Specific modalities of regulated cell death (RCD) have been classified based on different criteria, including morphological features, biochemical alterations and immunological consequences. Although melanoma cells are broadly equipped with the anti-apoptotic machinery and recurrent genetic alterations in the components of the RAS/RAF/MEK/ERK signaling markedly contribute to the pro-survival phenotype of melanoma, the roles of autophagy-dependent cell death, necroptosis, ferroptosis, pyroptosis, and parthanatos have recently gained great interest. These signaling cascades are involved in melanoma cell response and resistance to the therapeutics used in the clinic, including inhibitors of BRAFmut and MEK1/2, and immunotherapy. In addition, the relationships between sensitivity to non-apoptotic cell death routes and specific cell phenotypes have been demonstrated, suggesting that plasticity of melanoma cells can be exploited to modulate response of these cells to different cell death stimuli. In this review, the current knowledge on the non-apoptotic cell death signaling pathways in melanoma cell biology and response to anti-cancer drugs has been discussed.

TYRP1 mRNA level is stable and MITF-M-independent in drug-naïve, vemurafenib- and trametinib-resistant BRAFV600E melanoma cells

TYRP1 mRNA is of interest due to its potential non-coding role as a sponge sequestering tumor-suppressive miRs in melanoma. To our knowledge, there is no report on changes in TYRP1 expression in melanomas after development of resistance to targeted therapies. We used patient-derived drug-naïve RAS^Q61R and BRAF^V600E melanoma cell lines. In BRAF^V600E melanoma cells, resistance to vemurafenib and trametinib was developed. A time-lapse fluorescence microscope was used to rate proliferation, qRT-PCR and Western blotting were used to assess TYRP1 expression and MITF-M level and activity. A high TYRP1 protein level in RAS^Q61R cells corresponded with high TYRP1 mRNA level, whereas undetectable TYRP1 protein in BRAF^V600E cells was accompanied by medium mRNA level, also in cells carrying NF1^R135W variant in addition. TYRP1 expression was MITF-M-independent, since similar transcript status was found in MITF-M^high and MITF-M^low cells. For the first time, we showed that TYRP1 expression remained unaltered in melanoma cells that became resistant to vemurafenib or trametinib, including those cells losing MITF-M. Also drug discontinuation in resistant cells did not substantially affect TYRP1 expression. To verify in vitro results, publicly available microarray data were analyzed. TYRP1 transcript levels stay unaltered in the majority of paired melanoma samples from patients before treatment and after relapse caused by resistance to targeted therapies. As TYRP1 mRNA level remains unaltered in melanoma cells during development of resistance to vemurafenib or trametinib, therapies developed to terminate a sponge activity of TYRP1 transcript may be extended to patients that relapse with resistant disease.

Physiologically Relevant Oxygen Concentration (6% O2) as an Important Component of the Microenvironment Impacting Melanoma Phenotype and Melanoma Response to Targeted Therapeutics In Vitro

Cancer cell phenotype largely depends on oxygen availability. The atmospheric oxygen concentration (21%) used in in vitro studies is much higher than in any human tissue. Using well-characterized patient-derived melanoma cell lines, we compared: (i) activities of several signaling pathways, and (ii) the effects of vemurafenib and trametinib in hyperoxia (21% O₂), normoxia (6% O₂) and hypoxia (1% O₂). A high plasticity of melanoma cells in response to changes in oxygen supplementation and drug treatment was observed, and the transcriptional reprograming and phenotypic changes varied between cell lines. Normoxia enhanced the expression of vascular endothelial growth factor (VEGF), glucose metabolism/transport-related genes, and changed percentages of NGFR- and MITF-positive cells in cell line-dependent manner. Increased protein stability might be responsible for high PGC1α level in MITF^low melanoma cells. Vemurafenib and trametinib while targeting the activity of MAPK/ERK pathway irrespective of oxygen concentration, were less effective in normoxia than hyperoxia in reducing levels of VEGF, PGC1α, SLC7A11 and Ki-67-positive cells in cell line-dependent manner. In conclusion, in vitro studies performed in atmospheric oxygen concentration provide different information on melanoma cell phenotype and response to drugs than performed in normoxia, which might partially explain the discrepancies between results obtained in vitro and in clinical settings.

Exogenous growth factors bFGF, EGF and HGF do not influence viability and phenotype of V600EBRAF melanoma cells and their response to vemurafenib and trametinib in vitro

It has been shown that the response of ^V600EBRAF melanoma cells to targeted therapeutics is affected by growth factors. We have investigated the influence of three different growth factors, bFGF, EGF and HGF used either alone or in combination, on the response of ^V600EBRAF melanoma cell populations established from surgical specimens to vemurafenib and trametinib, targeting ^V600EBRAF and MEK1/2, respectively.

We report that proliferation and phenotype of ^V600EBRAF melanoma cell populations were not detectably influenced by exogenous growth factors. Neither cell distribution in cell cycle and CCND1 expression nor activity of signaling pathways crucial for melanoma development and maintenance, including the RAF/MEK/ERK pathway, WNT/β-catenin pathway and NF-κB signaling, were affected by the presence of different growth factors. We furthermore show that vemurafenib and trametinib abrogated the activity of ERK1/2, arrested cells in G₀/G₁ cell cycle phase, triggered apoptosis, induced changes in the expression of CXCL8, CCND1 and CTGF and the frequency of Ki-67^high and CD271^high cells. These effects were, however, similar in the presence of different growth factors. Interestingly, comparable results were also obtained for melanoma cells grown without exogenous growth factors bFGF, EGF and HGF for a period as long as 4 months prior the drug treatment.

We conclude that the composition or lack of exogenous growth factors bFGF, EGF and HGF do not markedly influence viability and phenotype of ^V600EBRAF melanoma cells and their response to vemurafenib and trametinib in vitro. Our results question the necessity of these growth factors in the medium that is used for culturing ^V600EBRAF melanoma cells.

Parthenolide induces MITF-M downregulation and senescence in patient-derived MITF-M(high) melanoma cell populations

The activity of the M isoform of microphthalmia-associated transcription factor (MITF-M) has been attributed to regulation of differentiation, proliferation, survival and senescence of melanoma cells. MITF expression was shown to be antagonized by the activation of transcription factor NF-κB. Parthenolide, an inhibitor of NF-κB, has not been yet reported to affect MITF-M expression. Our results obtained in patient-derived melanoma cell populations indicate that parthenolide efficiently decreases the MITF-M level. This is neither dependent on p65/NF-κB signaling nor RAF/MEK/ERK pathway activity as inhibition of MEK by GSK1120212 (trametinib) and induction of ERK1/2 activity by parthenolide itself do not interfere with parthenolide-triggered depletion of MITF-M in both wild-type BRAF and BRAF^V600E melanoma populations. Parthenolide activity is not prevented by inhibitors of caspases, proteasomal and lysosomal pathways. As parthenolide reduces MITF-M transcript level and HDAC1 protein level, parthenolide-activated depletion of MITF-M protein may be considered as a result of transcriptional regulation, however, the influence of parthenolide on other elements of a dynamic control over MITF-M cannot be ruled out. Parthenolide induces diverse effects in melanoma cells, from death to senescence. The mode of the response to parthenolide is bound to the molecular characteristics of melanoma cells, particularly to the basal MITF-M expression level but other cell-autonomous differences such as NF-κB activity and MCL-1 level might also contribute. Our data suggest that parthenolide can be developed as a drug used in combination therapy against melanoma when simultaneous inhibition of MITF-M, NF-κB and HDAC1 is needed.

Basal insulin peglispro versus insulin glargine in insulin-naïve type 2 diabetes: IMAGINE 2 randomized trial

AIMS

To compare, in a double-blind, randomized, multi-national study, 52- or 78-week treatment with basal insulin peglispro or insulin glargine, added to pre-study oral antihyperglycaemic medications, in insulin-naïve adults with type 2 diabetes.

MATERIAL AND METHODS

The primary outcome was non-inferiority of peglispro to glargine with regard to glycated haemoglobin (HbA1c) reduction (margin = 0.4%). Six gated secondary objectives with statistical multiplicity adjustments focused on other measures of glycaemic control and safety. Liver fat content was measured using MRI, in a subset of patients.

RESULTS

Peglispro was non-inferior to glargine in HbA1c reduction [least-squares (LS) mean difference: -0.29%, 95% confidence interval (CI) -0.40, -0.19], and had a lower nocturnal hypoglycaemia rate [relative rate 0.74 (95% CI 0.60, 0.91); p = .005), more patients achieving HbA1c <7.0% without nocturnal hypoglycaemia [odds ratio (OR) 2.15 (95% CI 1.60, 2.89); p < .001], greater HbA1c reduction (p < .001), and more patients achieving HbA1c<7.0% [OR 1.97 (95% CI 1.57, 2.47); p < .001]. Total hypoglycaemia rate and fasting serum glucose did not achieve statistical superiority. At 52 weeks, peglispro-treated patients had higher triglyceride (1.9 vs 1.7 mmol/L). alanine transaminase (34 vs 27 IU/L), and aspartate transaminase levels (27 vs 24 IU/L). LS mean liver fat content was unchanged with peglispro at 52 weeks but decreased 3.1% with glargine [difference: 2.6% (0.9, 4.2); p = .002]. More peglispro-treated patients experienced adverse injection site reactions (3.5% vs 0.6%, p < .001).

CONCLUSIONS

Compared with glargine at 52 weeks, peglispro resulted in a statistically superior reduction in HbA1c, more patients achieving HbA1c targets, less nocturnal hypoglycaemia, no improvement in total hypoglycaemia, higher triglyceride levels, higher aminotransferase levels, and more injection site reactions.

Randomized, double-blind clinical trial comparing basal insulin peglispro and insulin glargine, in combination with prandial insulin lispro, in patients with type 1 diabetes: IMAGINE 3

AIMS

To compare the efficacy and safety of basal insulin peglispro (BIL), which has a flat pharmacokinetic and pharmacodynamic profile and a long duration of action, with insulin glargine (GL) in patients with type 1 diabetes.

MATERIALS AND METHODS

In this phase III, 52-week, blinded study, we randomized 1114 adults with type 1 diabetes in a 3 : 2 distribution to receive either BIL (n = 664) or GL (n = 450) at bedtime, with preprandial insulin lispro, using intensive insulin management. The primary objective was to compare glycated haemoglobin (HbA1c) in the groups at 52 weeks, with a non-inferiority margin of 0.4%.

RESULTS

At 52 weeks, mean (standard error) HbA1c was 7.38 (0.03)% with BIL and 7.61 (0.04)% with GL {difference -0.22% [95% confidence interval (CI) -0.32, -0.12]; p < 0.001}. At 52 weeks more BIL-treated patients reached HbA1c <7% (35% vs 26%; p < 0.001), the nocturnal hypoglycaemia rate was 47% lower (p < 0.001) and the total hypoglycaemia rate was 11% higher (p = 0.002) than in GL-treated patients, and there was no difference in severe hypoglycaemia rate. Patients receiving BIL lost weight, while those receiving GL gained weight [difference -1.8 kg (95% CI -2.3, -1.3); p < 0.001]. Treatment with BIL compared with GL at 52 weeks was associated with greater increases from baseline in levels of serum triglyceride [difference 0.19 mmol/l (95% CI 0.11, 0.26); p < 0.001] and alanine aminotransferase (ALT) levels [difference 6.5 IU/l (95% CI 4.1, 8.9), p < 0.001], and more frequent injection site reactions.

CONCLUSIONS

In patients with type 1 diabetes, treatment with BIL compared with GL for 52 weeks resulted in a lower HbA1c, more patients with HbA1c levels <7%, and reduced nocturnal hypoglycaemia, but more total hypoglycaemia and injection site reactions and higher triglyceride and ALT levels.

Basal insulin peglispro: Overview of a novel long-acting insulin with reduced peripheral effect resulting in a hepato-preferential action

Basal insulin peglispro (BIL) is a novel basal insulin with a flat, prolonged activity profile. BIL has been demonstrated in a dog model, in healthy men and in patients with type 1 diabetes (T1D) to have significant hepato-preferential action resulting from reduced peripheral activity. In the IMAGINE-Phase 3 clinical trial program, more than 6000 patients were included, of whom ~3900 received BIL. Of the 7 pivotal IMAGINE trials, 3 studies were double-blinded and 3 were in T1D patients. BIL consistently demonstrated a greater HbA1c reduction, less glycaemic variability and a clinically relevant reduction in the rates of nocturnal hypoglycaemia across comparator [glargine and isophane insulin (NPH)] studies. Trials using basal/bolus regimens had higher rates of total hypoglycaemia with BIL due to higher rates of daytime hypoglycaemia. Severe hypoglycaemia rates were similar to comparator among both patients with T1D or type 2 diabetes (T2D). T1D patients lost weight compared with glargine (GL). Patients with T2D tended to gain less weight with BIL than with glargine. Compared to glargine, BIL was associated with higher liver fat, triglycerides and alanine aminotransferase (ALT) levels, including a higher frequency of elevation of ALT ≥3 times the upper limit of normal, but without severe, acute drug-induced liver injury. Injection site reactions, primarily lipohypertrophy, were more frequent with BIL. In conclusion, BIL demonstrated better glycaemic control with reduced glucose variability and nocturnal hypoglycaemia but higher triglycerides, ALT and liver fat relative to conventional comparator insulin. The hepato-preferential action of BIL with reduced peripheral activity may account for these findings.

Different effects of basal insulin peglispro and insulin glargine on liver enzymes and liver fat content in patients with type 1 and type 2 diabetes

AIMS

To compare effects of basal insulin peglispro (BIL), a hepatopreferential insulin, to insulin glargine (glargine) on aminotransferases and liver fat content (LFC) in patients with type 1 and type 2 diabetes (T1D, T2D).

MATERIALS AND METHODS

Data from two Phase 2 and five Phase 3 randomized trials comparing BIL and glargine in 1709 T1D and 3662 T2D patients were integrated for analysis of liver laboratory tests. LFC, measured by magnetic resonance imaging (MRI) at baseline, 26 and 52 weeks, was analyzed in 182 T1D patients, 176 insulin-naïve T2D patients and 163 T2D patients previously treated with basal insulin.

RESULTS

Alanine aminotransferase (ALT) increased in patients treated with BIL, was higher than in glargine-treated patients at 4-78 weeks (difference at 52 weeks in both T1D and T2D: 7 international units/litre (IU/L), P < .001), and decreased after discontinuation of BIL. More BIL patients had ALT ≥3× upper limit of normal (ULN) than glargine. No patient had ALT ≥3× ULN with bilirubin ≥2× ULN that was considered causally related to BIL. In insulin-naїve T2D patients, LFC decreased with glargine but was unchanged with BIL. In T1D and T2D patients previously treated with basal insulin, LFC was unchanged with glargine but increased with BIL. In all three populations, LFC was higher after treatment with BIL vs glargine (difference at 52 weeks: 2.2% to 5.3%, all P < .01).

CONCLUSIONS

Compared to glargine, patients treated with BIL had higher ALT and LFC at 52-78 weeks. No severe drug-induced liver injury was apparent with BIL treatment for up to 78 weeks.

A randomized clinical trial comparing basal insulin peglispro and insulin glargine, in combination with prandial insulin lispro, in patients with type 1 diabetes: IMAGINE 1

AIMS

The primary objective was to demonstrate that basal insulin peglispro (BIL) was non-inferior compared with insulin glargine (GL) for haemoglobin A1c (HbA1c) at 26 weeks with a non-inferiority margin of 0.4%.

MATERIALS AND METHODS

IMAGINE 1 was a Phase 3, open-label, parallel-arm study conducted in nine countries. Adults with type 1 diabetes (n = 455) were randomized (2:1) to bedtime BIL or GL in combination with prandial insulin lispro for 78 weeks, with a primary endpoint of 26 weeks. An electronic diary facilitated data capture and insulin dosing calculations for intensive insulin management.

RESULTS

At 26 weeks, mean HbA1c was 7.06% ± 0.04% and 7.43% ± 0.06% for patients assigned to BIL (N = 295) and GL (N = 160), respectively (difference -0.37% [95% CI: -0.50 to -0.23], P < .001); more patients on BIL achieved HbA1c <7% (44.9% vs 27.5%, P < .001). Compared with GL, patients using BIL lost weight, with lower fasting serum glucose and between-day fasting blood glucose variability, and 36% less nocturnal hypoglycemia, 29% more total hypoglycemia and more severe hypoglycemia. Total and prandial insulin doses were lower with BIL; basal insulin doses were higher. Alanine aminotransferase increased with BIL, with more patients having elevations ≥3 × ULN. BIL treatment was associated with more frequent injection site reactions and an increase from baseline in serum triglycerides.

CONCLUSIONS

In patients with type 1 diabetes, treatment with BIL compared to GL for 26 weeks was associated with lower HbA1c, less nocturnal hypoglycemia, lower glucose variability and weight loss. Increases in total and severe hypoglycemia, triglycerides, aminotransferases and injection site reactions were also noted.

MCL-1, BCL-XL and MITF Are Diversely Employed in Adaptive Response of Melanoma Cells to Changes in Microenvironment

Melanoma cells can switch their phenotypes in response to microenvironmental insults. Heterogeneous melanoma populations characterized by long-term growth and a high self-renewal capacity can be obtained in vitro in EGF(+)bFGF(+) medium whilst invasive potential of melanoma cells is increased in serum-containing cultures. In the present study, we have shown that originally these patient-derived melanoma populations exhibit variable expression of pro-survival genes from the BCL-2 family and inhibitors of apoptosis (IAPs), and differ in the baseline MCL-1 transcript stability as well. While being transferred to serum-containing medium, melanoma cells are well protected from death. Immediate adaptive response of melanoma cells selectively involves a temporary MCL-1 increase, both at mRNA and protein levels, and BCL-X_L can complement MCL-1, especially in MITF_low populations. Thus, the extent of MCL-1 and BCL-XL contributions seems to be cell context-dependent. An increase in MCL-1 level results from a transiently enhanced stability of its transcript, but not from altered protein turnover. Inhibition of MCL-1 preceding transfer to serum-containing medium caused the induction of cell death in a subset of melanoma cells, which confirms the involvement of MCL-1 in melanoma cell survival during the rapid alteration of growth conditions. Additionally, immediate response to serum involves the transient increase in MITF expression and inhibition of ERK-1/2 activity. Uncovering the mechanisms of adaptive response to rapid changes in microenvironment may extend our knowledge on melanoma biology, especially at the stage of dissemination.

MITF in melanoma: mechanisms behind its expression and activity

MITF (microphthalmia-associated transcription factor) represents a melanocytic lineage-specific transcription factor whose role is profoundly extended in malignant melanoma. Over the last few years, the function of MITF has been tightly connected to plasticity of melanoma cells. MITF participates in executing diverse melanoma phenotypes defined by distinct gene expression profiles. Mutation-dependent alterations in MITF expression and activity have been found in a relatively small subset of melanomas. MITF activity is rather modulated by its upstream activators and suppressors operating on transcriptional, post-transcriptional and post-translational levels. These regulatory mechanisms also include epigenetic and microenvironmental signals. Several transcription factors and signaling pathways involved in the regulation of MITF expression and/or activity such as the Wnt/β-catenin pathway are broadly utilized by various types of tumors, whereas others, e.g., BRAF^V600E/ERK1/2 are more specific for melanoma. Furthermore, the MITF activity can be affected by the availability of transcriptional co-partners that are often redirected by MITF from their own canonical signaling pathways. In this review, we discuss the complexity of a multilevel regulation of MITF expression and activity that underlies distinct context-related phenotypes of melanoma and might explain diverse responses of melanoma patients to currently used therapeutics.

Gene expression profiling identifies microphthalmia-associated transcription factor (MITF) and Dickkopf-1 (DKK1) as regulators of microenvironment-driven alterations in melanoma phenotype

BACKGROUND

The diversity of functional phenotypes observed within a tumor does not exclusively result from intratumoral genetic heterogeneity but also from the response of cancer cells to the microenvironment. We have previously demonstrated that the morphological and functional phenotypes of melanoma can be dynamically altered upon external stimuli.

FINDINGS

In the present study, transcriptome profiles were generated to explore the molecules governing phenotypes of melanospheres grown in the bFGF(+)EGF(+) serum-free cultures and monolayers maintained in the serum-containing medium. Higher expression levels of MITF-dependent genes that are responsible for differentiation, e.g., TYR and MLANA, and stemness-related genes, e.g., ALDH1A1, were detected in melanospheres. These results were supported by the observation that the melanospheres contained more pigmented cells and cells exerting the self-renewal capacity than the monolayers. In addition, the expression of the anti-apoptotic, MITF-dependent genes e.g., BCL2A1 was also higher in the melanospheres. The enhanced activity of MITF in melanospheres, as illustrated by the increased expression of 74 MITF-dependent genes, identified MITF as a central transcriptional regulator in melanospheres. Importantly, several genes including MITF-dependent ones were expressed in melanospheres and original tumors at similar levels. The reduced MITF level in monolayers might be partially explained by suppression of the Wnt/β-catenin pathway, and DKK1, a secreted inhibitor of this pathway, was highly up-regulated in monolayers in comparison to melanospheres and original tumors. Furthermore, the silencing of DKK1 in monolayers increased the percentage of cells with self-renewing capacity.

CONCLUSIONS

Our study indicates that melanospheres can be used to unravel the molecular pathways that sustain intratumoral phenotypic heterogeneity. Melanospheres directly derived from tumor specimens more accurately mirrored the morphology and gene expression profiles of the original tumors compared to monolayers. Therefore, melanospheres represent a relevant preclinical tool to study new anticancer treatment strategies.

Pro-apoptotic activity of BH3-only proteins and BH3 mimetics: from theory to potential cancer therapy

The evasion of cancer cells from the induction of cell death pathways results in the resistance of tumor to current treatment modalities. Therefore, the resistance to cell death, one of the hallmarks of cancer, is a major target in the development of new approaches to selectively affect cancer cells. The complex interplay between individual members of Bcl-2 family regulates both cell survival and the mitochondrial pathway of apoptosis by maintaining mitochondrial membrane integrity (anti-apoptotic Bcl-2 subfamily) and by triggering its disruption in response to stress stimuli (Bax-like subfamily). BH3-only proteins, another Bcl-2 subfamily, act either by direct stimulation of pro-apoptotic proteins of the Bax subfamily or by interfering with anti-apoptotic proteins of the Bcl-2 subfamily. Thus, pro-apoptotic BH3 mimetics, thought to function as BH3-only proteins, are expected to improve the effectiveness of cancer treatment. BH3 mimetics could be either natural or synthetic, peptidic or only based on a helical peptide-like scaffold. Experimental and clinical evidence indicates that BH3 mimetics may not be sufficient to cure cancer patients when used as a single agent. BH3 profiling of cancer cells was introduced to better predict the in vivo responsiveness of tumor to BH3 mimetics combined with conventional therapies. In summary, targeting the Bcl-2 proteins is a promising tool with potential to generate new treatment modalities and to complement existing anti-cancer therapies. This review presents the current knowledge on BH3-only proteins and the spectrum of strategies employing BH3 mimetics in preclinical and clinical studies that aim at tumor targeting.

Parthenolide complements the cell death-inducing activity of doxorubicin in melanoma cells

BACKGROUND

Melanoma is characterized by high resistance to chemotherapy. The aim of this study was to investigate combined effects of doxorubicin and parthenolide on melanoma cells.

MATERIALS AND METHODS

Thiazolyl blue tetrazolium bromide (MTT) assay and flow cytometry were used to evaluate viability. The p53 levels and Poly-ADP ribose polymerase (PARP) cleavage were assessed by western blot. Electrophoretic mobility shift assay (EMSA) and quantitative real-time polymerase chain reaction (qRT-PCR) were used to evaluate changes in nuclear factor-κB (NF-κB) activity and gene expression, respectively.

RESULTS

Both drugs reduced the viability of melanoma cells and induced apoptosis. Expression of the ATP-binding cassette sub-family B member-5 (ABCB5) transporter was enhanced by doxorubicin. Doxorubicin induced activity of p53 and NF-κB. Parthenolide markedly reduced the constitutive and doxorubicin-induced NF-κB activity measured as the nuclear NF-κB, and expression of matrix metalloproteinase-9 (MMP9) and it had no effect on p53.

DISCUSSION

Doxorubicin and parthenolide affected distinct pathways in melanoma, and parthenolide was capable of combating some pro-survival effects of doxorubicin in the combined treatment. This provides a rationale for in vivo investigation of this drug combination.

Anti-apoptotic proteins on guard of melanoma cell survival

Apoptosis plays a pivotal role in sustaining proper tissue development and homeostasis. Evading apoptosis by cancer cells is a part of their adaption to microenvironment and therapies. Cellular integrity is predominantly maintained by pro-survival members of Bcl-2 family and IAPs. Melanoma cells are characterized by a labile and stage-dependent phenotype. Pro-survival molecules can protect melanoma cells from apoptosis and mediate other processes, thus enhancing aggressive phenotype. The essential role of Bcl-2, Mcl-1, Bcl-X(L), livin, survivin and XIAP was implicated for melanoma, often in a tumor stage-dependent fashion. In this review, the current knowledge of pro-survival machinery in melanoma is discussed.

Lipoprotein lipase: a new prognostic factor in chronic lymphocytic leukaemia

The clinical course of patients with chronic lymphocytic leukemia (CLL) is highly heterogeneous. Gene expression analyses have revealed that leukemic cells with unmutated immunoglobulin heavy chain genes (IgV H ) differ from CLL cells with mutated IgV H in the expression level of some genes, i.e. encoding kinase ZAP-70 and antigen CD38. Recently, additional markers in CLL, including the expression level of apoptosis-regulating genes/proteins (Bcl-2, Mcl-1) and microRNAs, have been suggested. In this review, we attempt to provide data concerning the properties of lipoprotein lipase (LPL), as well as to present its prognostic value in CLL. LPL mRNA expression level was able to predict mutational status in a high percentage of CLL cases and high LPL expression was associated with shorter treatment-free survival. Importantly, since LPL activity is low (or absent) in other blood cell types, its expression can be determined by PCR technique in peripheral blood mononuclear cells or in lysed blood samples.

Body composition, physical exercise, growth hormone and obesity

In summary, available literature indicates that GH secretion is blunted profoundly in individuals with relative or absolute obesity. Accumulation of AVF particularly represses GH release. Administration of GH to obese adults decreases total body fat and especially AVF. Furthermore, GH supplementation combined with dietary restriction and/or exercise appears to enhance favorable changes in body composition. Although exercise is a powerful stimulus to GH release, the GH response to exercise is blunted in older and obese individuals. This suggests that higher relative exercise intensities may be necessary for exercise alone to stimulate adequate GH release in obese subjects. In as much as exercise in combination with a second stimulus of GH release (e.g. GHRP-2, L-arginine) drives GH release synergistically, we propose that combining exercise and a GH secretagogue may have utility in restoring GH release in obese adults. Taken as a whole, available data suggest that GH repletion regimens in combination with regular exercise and relevant dietary intervention may provide a tripartite strategy for the management of significant obesity.

Abdominal visceral fat and fasting insulin are important predictors of 24-hour GH release independent of age, gender, and other physiological factors

Numerous physiological factors modulate GH secretion, but these variables are not independent of one another. We studied 40 younger (20-29 yr.; 21 men and 19 women) and 62 older (57-80 yr.; 35 men and 27 women) adults to determine the contributions of several demographic and physiological factors to the variability in integrated 24-h GH concentrations. Serum GH was measured every 10 min for 24 h in an enhanced sensitivity chemiluminescence assay. The predictor variables included: age group (young or old), gender, abdominal visceral fat (by computed tomography), total body fat mass and percentage body fat by dual-energy x-ray absorptiometry, serum IGF-I, fasting serum insulin, 24-h mean estradiol and testosterone, and peak oxygen uptake by graded exercise (treadmill) testing. Multiple ordinary least squares regression analysis was used to quantitatively assess the individual contribution that each predictive measure made to explain the variability among values of integrated 24-h GH concentrations while in the presence of the remaining predictors. The model explained 65% of the variance in integrated 24-h GH concentrations. Abdominal visceral fat (P < 0.002) and fasting insulin (P < 0.008) were consistently important predictors of integrated 24-h GH concentrations independent of age group, gender, and all other predictor variables. Although serum IGF-I was an important overall predictor of integrated 24-h GH concentrations (P = 0.002), this relationship was present only in the young subjects and was modulated by gender. The remaining variables failed to contribute significantly to the model. We conclude that abdominal visceral fat and fasting insulin are important predictors of integrated 24-h GH concentrations in healthy adults, independent of age and gender. Serum IGF-I is an important predictor of integrated 24-h GH concentrations in young but not older subjects. Bidirectional feedback between each of these three factors and GH secretion may account for the strong relationships observed.

Cortisol and growth hormone responses to exercise at different times of day

Exercise of appropriate intensity is a potent stimulus for GH and cortisol secretion. Circadian and diurnal rhythms may modulate the GH and cortisol responses to exercise, but nutrition, sleep, prior exercise patterns, and body composition are potentially confounding factors. To determine the influence of the time of day on the GH and cortisol response to acute exercise, we studied 10 moderately trained young men (24.1 +/- 1.1 yr old; maximal oxygen consumption, 47.9 +/- 1.4 mL/kg.min; percent body fat, 13.2 +/- 0.6%). After a supervised night of sleep and a standard meal 12 h before exercise, subjects exercised at a constant velocity (to elicit an initial blood lactate concentration of approximately 2.5 mmol/L) on a treadmill for 30 min on 3 separate occasions, starting at 0700, 1900, and 2400 h. Blood samples were obtained at 5-min intervals for 1 h before and 5 h after the start of exercise; subjects were not allowed to sleep during this period. Subjects were also studied on 3 control days under identical conditions without exercise. There were no significant differences with time of day in the mean blood lactate and submaximal oxygen consumption values during exercise. The differences over time in serum GH and cortisol concentrations between the exercise day and the control day were determined with 95% confidence limits for each time of day. Exercise stimulated a significant increase in serum GH concentrations over control day values for approximately 105--145 min (P < 0.05) with no significant difference in the magnitude of this response by time of day. The increase in serum GH concentrations with exercise was followed by a transient suppression of GH release (for approximately 55--90 min; P < 0.05) after exercise at 0700 and 1900 h, but not at 2400 h. Although the duration of the increase in serum cortisol concentrations after exercise was similar (approximately 150--155 min; P < 0.05) at 0700, 1900, and 2400 h, the magnitude of this increase over control day levels was greatest at 2400 h. This difference was significant for approximately 130 min and approximately 40 min compared to exercise at 1900 and 0700 h, respectively (P < 0.05). The cortisol response to exercise at 0700 h was significantly greater than that at 1900 h for about 55 min (P < 0.05). A rebound suppression of cortisol release for about 50 min (P < 0.05) was observed after exercise at 2400 h, but not 0700 or 1900 h. Both baseline (before exercise) and peak cortisol concentrations were significantly higher at 0700 h than at 1900 or 2400 h (P < 0.01). We conclude that time of day does not alter the GH response to exercise; however, the exercise-induced cortisol response is modulated by time of day.

Intensity of acute exercise does not affect serum leptin concentrations in young men

PURPOSE

We examined the effects of exercise intensity on serum leptin levels.

METHODS

Seven men (age = 27.0 yr; height = 178.3 cm; weight = 82.2 kg) were tested on a control (C) day and on 5 exercise days (EX). Subjects exercised (30 min) at the following intensities: 25% and 75% of the difference between the lactate threshold (LT) and rest (0.25 LT, 0.75 LT), at LT, and at 25% and 75% of the difference between LT and VO2peak (1.25 LT, 1.75 LT).

RESULTS

Kcal expended during the exercise bouts ranged from 150 +/- 11 kcal (0.25 LT) to 529 +/- 45 kcal (1.75 LT), whereas exercise + 3.5 h recovery kcal ranged from 310 +/- 14 kcal (0.25 LT) to 722 +/- 51 kcal (1.75 LT). Leptin area under the curve (AUC) (Q 10-min samples) for all six conditions (C + 5 Ex) was calculated for baseline (0700-0900 h) and for exercise + recovery (0900-1300 h). Leptin AUC for baseline ranged from 243 +/- 33 to 291 +/- 56 ng x mL(-1) x min; for exercise + recovery results ranged from 424 +/- 56 to 542 +/- 99 ng x mL(-1) x min. No differences were observed among conditions within either the baseline or exercise + recovery time frames. Regression analysis confirmed positive relationships between serum leptin concentrations and percentage body fat (r = 0.94) and fat mass (r = 0.93, P < 0.01).

CONCLUSION

We conclude that 30 min of acute exercise, at varying intensity of exercise and caloric expenditure, does not affect serum leptin concentrations during exercise or for the first 3.5 hours of recovery in healthy young men.

Exercise-dependent growth hormone release is linked to markers of heightened central adrenergic outflow

To test the hypothesis that heightened sympathetic outflow precedes and predicts the magnitude of the growth hormone (GH) response to acute exercise (Ex), we studied 10 men [age 26.1 +/- 1.7 (SE) yr] six times in randomly assigned order (control and 5 Ex intensities). During exercise, subjects exercised for 30 min (0900-0930) on each occasion at a single intensity: 25 and 75% of the difference between lactate threshold (LT) and rest (0.25LT, 0.75LT), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT, 1.75LT). Mean values for peak plasma epinephrine (Epi), plasma norepinephrine (NE), and serum GH concentrations were determined [Epi: 328 +/- 93 (SE), 513 +/- 76, 584 +/- 109, 660 +/- 72, and 2,614 +/- 579 pmol/l; NE: 2. 3 +/- 0.2, 3.9 +/- 0.4, 6.9 +/- 1.0, 10.7 +/- 1.6, and 23.9 +/- 3.9 nmol/l; GH: 3.6 +/- 1.5, 6.6 +/- 2.0, 7.0 +/- 2.0, 10.7 +/- 2.4, and 13.7 +/- 2.2 microg/l for 0.25, 0.75, 1.0, 1.25, and 1.75LT, respectively]. In all instances, the time of peak plasma Epi and NE preceded peak GH release. Plasma concentrations of Epi and NE always peaked at 20 min after the onset of Ex, whereas times to peak for GH were 54 +/- 6 (SE), 44 +/- 5, 38 +/- 4, 38 +/- 4, and 37 +/- 2 min after the onset of Ex for 0.25-1.75LT, respectively. ANOVA revealed that intensity of exercise did not affect the foregoing time delay between peak NE or Epi and peak GH (range 17-24 min), with the exception of 0.25LT (P < 0.05). Within-subject linear regression analysis disclosed that, with increasing exercise intensity, change in (Delta) GH was proportionate to both DeltaNE (P = 0.002) and DeltaEpi (P = 0.014). Furthermore, within-subject multiple-regression analysis indicated that the significant GH increment associated with an antecedent rise in NE (P = 0.02) could not be explained by changes in Epi alone (P = 0.77). Our results suggest that exercise intensity and GH release in the human may be coupled mechanistically by central adrenergic activation.

Hormone pulsatility discrimination via coarse and short time sampling

Pulsatile hormonal secretion is a ubiquitous finding in endocrinology. However, typical protocols employed to generate data sets suitable for "pulsatility analysis" have required 60-300 samples, rendering such studies largely research methodologies, due primarily to considerable assay expense. One successful mathematical strategy in calibrating changes in pulsatility modalities is approximate entropy (ApEn), a quantification of sequential irregularity. Given the degree of differences between ApEn values in pathophysiological subjects vs. healthy controls reported in several recent studies, we queried to what extent coarser (less frequent) and shorter duration time sampling would still retain significant ApEn differences between clinically distinct cohorts. Accordingly, we reanalyzed data from two studies of 24-h profiles of healthy vs. tumoral hormone secretion: 1) growth hormone comparisons of normal subjects vs. acromegalics, originally sampled every 5 min; and 2) ACTH and cortisol comparisons of normal subjects vs. Cushing's disease patients, originally sampled every 10 min. By multiple statistical analyses, we consistently and highly significantly (P < 0.0001) established that serum concentration patterns in tumor patients are more irregular than those of controls, with high sensitivity and specificity, even at very coarse (e.g., 60 min) sampling regimens and over relatively short (2-4 h) time intervals. The consistency of these findings suggests a broadly based utility of such shorter and/or coarser sampling methodologies. Substantial reduction in sampling requirements holds the potential to move analysis of pulsatile hormone release from a primarily research tool to a clinically applicable protocol, in appropriate diagnostic and therapeutic contexts.

Obesity attenuates the growth hormone response to exercise

Resting serum GH concentrations are decreased in obesity. In nonobese (NonOb) individuals, acute exercise of sufficient intensity increases GH levels; however, conflicting data exist concerning the GH response to exercise in obese individuals. To examine the exercise-induced GH response in obese individuals, we studied 8 NonOb, 11 lower body obese (LBO), and 12 upper body obese (UBO) women before, during, and after 30 min (0800-0830 h) of treadmill exercise at 70% oxygen consumption peak. Blood samples were taken every 5 min (0700-1300 h) and were analyzed for GH concentrations with a sensitive (0.002 microg/L) chemiluminescence assay. The impact of 16 weeks of aerobic exercise training on the GH response to exercise was also examined in the obese women. In response to exercise, the 6-h integrated GH concentration was significantly greater (P < 0.05) in the NonOb women (1006 +/- 220 min/microg x L) than in either of the obese groups (LBO, 435 +/- 136; UBO, 189 +/- 26 min/microg x L). No differences were found between the LBO and UBO women. The increased integrated GH concentrations could be accounted for by a greater 6-h GH production rate [micrograms per L distribution volume (Lv)] in the NonOb women than in either of the obese groups (NonOb, 45.6 +/- 12.3; LBO, 16.9 +/- 1.2; UBO, 8.7 +/- 0.64 microg/Lv; P < 0.05). This increase was attributed to a greater mass of GH secreted per pulse in the NonOb women (NonOb, 10.8 +/- 2.5; LBO, 4.9 +/- 0.8; UBO, 4.0 +/- 0.5 microg/Lv; P < 0.05, NonOb vs. both obese groups). After 16 weeks of aerobic training, maximal oxygen consumption increased from 44.7 +/- 2.2 to 48.5 +/- 1.9 mL/kg fat-free mass x min; P < 0.05), but no significant change in body composition occurred in the 10 obese women who completed the training. No change was observed in the GH response to exercise after training (n = 10; pre, 379 +/- 144; post, 350 +/- 55 min/microg x L). In conclusion, the GH response to exercise was attenuated in the obese women compared to NonOb women. Short term aerobic training improved fitness, but did not increase the GH response to exercise.

Impact of acute exercise intensity on pulsatile growth hormone release in men

To investigate the effects of exercise intensity on growth hormone (GH) release, 10 male subjects were tested on 6 randomly ordered occasions [1 control condition (C), 5 exercise conditions (Ex)]. Serum GH concentrations were measured in samples obtained at 10-min intervals between 0700 and 0900 (baseline) and 0900 and 1300 (exercise+ recovery). Integrated GH concentrations (IGHC) were calculated by trapezoidal reconstruction. During Ex subjects exercised for 30 min (0900-0930) at one of the following intensities [normalized to the lactate threshold (LT)]: 25 and 75% of the difference between LT and rest (0.25LT and 0.75LT, respectively), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT and 1.75LT, respectively). No differences were observed among conditions for baseline IGHC. Exercise+recovery IGHC (mean +/- SE: C = 250 +/- 60; 0.25LT = 203 +/- 69; 0.75LT = 448 +/- 125; LT = 452 +/- 119; 1.25LT = 512 +/- 121; 1.75LT = 713 +/- 115 microg x l(-1) x min(-1)) increased linearly with increasing exercise intensity (P < 0.05). Deconvolution analysis revealed that increasing exercise intensity resulted in a linear increase in the mass of GH secreted per pulse and GH production rate [production rate increased from 16. 5 +/- 4.5 (C) to 32.1 +/- 5.2 microg x distribution volume(-1) x min(-1) (1.75LT), P < 0.05], with no changes in GH pulse frequency or half-life of elimination. We conclude that the GH secretory response to exercise is related to exercise intensity in a linear dose-response pattern in young men.

Validity of methods of body composition assessment in young and older men and women

We examined the validity of percent body fat (%Fat) estimation by two-compartment (2-Comp) hydrostatic weighing (Siri 2-Comp), 3-Comp dual-energy X-ray absorptiometry (DEXA 3-Comp), 3-Comp hydrostatic weighing corrected for the total body water (Siri 3-Comp), and anthropometric methods in young and older individuals (n = 78). A 4-Comp model of body composition served as the criterion measure of %Fat (Heymsfield 4-Comp; S. B. Heymsfield, S. Lichtman, R. N. Baumgartner, J. Wang, Y. Kamen, A. Aliprantis, and R. N. Pierson Jr., Am. J. Clin. Nutr. 52: 52-58, 1990.). Comparison of the Siri 3-Comp with the Heymsfield 4-Comp model revealed mean differences of </=0.4 %Fat, r values >/= r = 0.997, total error values </= 0.85 %Fat, and 95% confidence intervals (Bland-Altman analysis) of </=1.7 %Fat. Comparison of Siri 2-Comp, DEXA, and anthropometric models with the Heymsfield 4-Comp revealed that total error scores ranged from +/-4. 0 to +/-10.7 %Fat, and 95% confidence intervals associated with the Bland-Altman analysis ranged from +/-5.1 to +/-15.0 %Fat. We conclude that the Siri 3-Comp model provides valid and accurate body composition data when compared with a 4-Comp criterion model. However, the individual variability associated with the Siri 2-Comp, DEXA 3-Comp, and anthropometric models may limit their use in research settings. The use of anthropometric estimation methods resulted in large mean differences and a considerable amount of interindividual variability. These data suggest that the use of these techniques should be viewed with caution.

The use of anthropometric and dual-energy X-ray absorptiometry (DXA) measures to estimate total abdominal and abdominal visceral fat in men and women

OBJECTIVE

A single-slice computed tomography (CT) scan provides a criterion measure of total abdominal fat (TAF) and abdominal visceral fat (AVF), but this procedure is often prohibitive due to radiation exposure, cost, and accessibility. In the present study, the utility of anthropometric measures and estimates of trunk and abdominal fat mass by dual-energy X-ray absorptiometry (DXA) to predict CT measures of TAF and AVF (cross-sectional area, cm2) was assessed.

RESEARCH METHODS AND PROCEDURES

CT measures of abdominal fat (at the level of the L4-L5 inter-vertebral space), DXA scans, and anthropometric measures were obtained in 76 Caucasian adults ages 20-80 years.

RESULTS

Results demonstrated that abdominal sagittal diameter measured by anthropometry is an excellent predictor of sagittal diameter measured from a CT image (r=0.88 and 0.94; Total Error [TE]=4.1 and 3.1 cm, for men and women, respectively). In both men and women, waist circumference and abdominal sagittal diameter were the anthropometric measures most strongly associated with TAF (r=0.87 to 0.93; Standard Error of Estimate (SEE)=60.7 to 75.4 cm2) and AVF (r=0.84 to 0.93; SEE=0.7 to 30.0 cm2). The least predictive anthropometric measure of TAF or AVF was the commonly used waist-to-hip ratio (WHR). DXA estimates of trunk and abdominal fat mass were strongly associated with TAF (r=.94 to 0.97; SEE=36.9 to 50.9 cm2) and AVF (r=0.86 to 0.90; SEE=4.9 to 27.7 cm2).

DISCUSSION

The present results suggest that waist circumference and/or abdominal sagittal diameter are better predictors of TAF and AVF than the more commonly used WHR. DXA trunk fat and abdominal fat appear to be slightly better predictors of TAF but not AVF compared to these anthropometric measures. Thus DXA does not offer a significant advantage over anthropometry for estimation of AVF.

Recovery of growth hormone release from suppression by exogenous insulin-like growth factor I (IGF-I): evidence for a suppressive action of free rather than bound IGF-I

To determine the time course of recovery of GH release from insulin-like growth factor I (IGF-I) suppression, 11 healthy adults (18-29 yr) received, in randomized order, 4-h i.v. infusions of recombinant human IGF-I (rhIGF-I; 3 microg/kg-h) or saline (control) from 25.5-29.5 h of a 47.5-h fast. Serum GH was maximally suppressed within 2 h and remained suppressed for 2 h after the rhIGF-I infusion; during this 4-h period, GH concentrations were approximately 25% of control day levels [median (interquartile range), 1.2 (0.4-4.0) vs. 4.8 (2.8-7.9) microg/L; P < 0.05]. A rebound increase in GH concentrations occurred 5-7 h after the end of rhIGF-I infusion [7.6 (4.6 -11.7) vs. 4.3 (2.5-6.0) microg/L; P < 0.05]. Thereafter, serum GH concentrations were similar on both days. Total IGF-I concentrations peaked at the end of the rhIGF-I infusion (432 +/- 43 vs. 263 +/- 44 microg/L; P < 0.0001) and remained elevated 18 h after the rhIGF-I infusion (360 +/- 36 vs. 202 +/- 23 microg/L; P = 0.001). Free IGF-I concentrations were approximately 140% above control day values at the end of the infusion (2.1 +/- 0.4 vs. 0.88 +/- 0.3 microg/L; P = 0.001), but declined to baseline within 2 h after the infusion. The close temporal association between the resolution of GH suppression and the fall of free IGF-I concentrations, and the lack of any association with total IGF-I concentrations suggest that unbound (free), not protein-bound, IGF-I is the major IGF-I component responsible for this suppression. The rebound increase in GH concentrations after the end of rhIGF-I infusion is consistent with cessation of an inhibitory effect of free IGF-I on GH release.

The Growth Hormone Research Society consensus guidelines for the diagnosis and treatment of adult GH deficiency

The Growth Hormone Research Society (GRS) convened a workshop in Port Stephens, Australia in April 1997 to establish consensus guidelines for the diagnosis and treatment of adults with GH deficiency (GHD). Scientists with expertise in the field, representatives from industry involved in the manufacture of GH and representatives from health authorities from a number of countries participated in the workshop. The workshop considered the following questions: (1) How should adult GHD be defined? (2) Who should be tested for adult GHD? (3) How should the diagnosis of adult GHD be established? (4) How should GH and insulin-like growth factor-I (IGF-I) assays be standardized? (5) Who should be treated for adult GHD? (6) What dose of GH should be used for treatment of adult GHD? (7) How should treatment of adult GHD be monitored? (8) What are the contraindications to treatment of adult GHD? (9) What safety issues need to be considered? (10) How long should treatment of adult GHD be continued? The consensus guidelines developed at this workshop and the rationale for some of these recommendations will be reviewed in this paper.

Human growth hormone response to repeated bouts of aerobic exercise

We examined whether repeated bouts of exercise could override growth hormone (GH) auto-negative feedback. Seven moderately trained men were studied on three occasions: a control day (C), a sequential exercise day (SEB; at 1000, 1130, and 1300), and a delayed exercise day (DEB; at 1000, 1400, and 1800). The duration of each exercise bout was 30 min at 70% maximal O2 consumption (VO2max) on a cycle ergometer. Standard meals were provided at 0600 and 2200. GH was measured every 5-10 min for 24 h (0800-0800). Daytime (0800-2200) integrated GH concentrations were approximately 150-160% greater during SEB and DEB than during C: 1,282 +/- 345, 3,192 +/- 669, and 3,389 +/- 991 min.microgram.l-1 for C, SEB, and DEB, respectively [SEB > C (P < 0.06), DEB > C (P < 0.03)]. There were no differences in GH release during sleep (2300-0700). Deconvolution analysis revealed that the increase in 14-h integrated GH concentration on DEB was accounted for by an increase in the mass of GH secreted per pulse (per liter of distribution volume, lv): 7.0 +/- 2.9 and 15.9 +/- 2.6 micrograms/lv for C and DEB, respectively (P < 0.01). Comparison of 1.5-h integrated GH concentrations on the SEB and DEB days (30 min exercise + 60 min recovery) revealed that, with each subsequent exercise bout, GH release apparently increased progressively, with a slightly greater increase on the DEB day [SEB vs. DEB: 497 +/- 162 vs. 407 +/- 166 (bout 1), 566 +/- 152 vs. 854 +/- 184 (bout 2), and 633 +/- 149 vs. 1,030 +/- 352 min.microgram.l-1 (bout 3), P < 0.05]. We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise.

The influence of anatomical boundaries, age, and sex on the assessment of abdominal visceral fat

Single-slice abdominal computed tomography (CT) scanning has been used extensively for the measurement of abdominal visceral fat (AVF). Optimal anatomical scan location and pixel density ranges have been proposed and are specifically reported to allow for the replication and standardization of AVF measurements. Standardization of the anatomical boundaries for CT measurement of AVF and the influence of age and gender on results obtained with different boundary locations have received much less attention. To determine the influence of three boundary analysis methods (AVF-1, AVF-2, and AVF-3) on the measurement of AVF by CT, 54 older (60 years to 79 years) and 37 younger (20 years to 29 years) healthy men and women were examined. The measurement boundary for AVF-1 was the internal most aspect of the abdominal and oblique muscle walls, and the posterior aspect of the vertebral body. AVF-2 used fat measurements enclosed in a boundary formed by the midpoint of the abdominal and oblique muscle walls, and the most posterior aspect of the spinous process. AVF-3 used fat measurements enclosed in a boundary formed by the external border of the abdominal and oblique muscle walls, and the external border of the erector spinae. Greater AVF measures were obtained with AVF-2 and AVF-3 compared with AVF-1 (p < 0.0001). These differences were greater in older compared with younger subjects (p < 0.0001) and greater in women compared with men (p < 0.02). The significantly greater AVF measurements obtained with AVF-2 and AVF-3 resulted from the inclusion of larger amounts of fat that are not drained by the portal circulation. This included retroperitoneal, intermuscular, and intramuscular lipid droplets, which increase with aging. On the basis of these results, we recommend the AVF-1 anatomical boundaries for the measurement of AVF in clinical investigations, particularly with older subjects. These data demonstrate the importance of precise and reproducible anatomical boundaries for the measurement of AVF, particularly in longitudinal studies.

Effect of aging on the sensitivity of growth hormone secretion to insulin-like growth factor-I negative feedback

To determine the effect of aging on the suppression of GH secretion by insulin-like growth factor (IGF)-I, we studied 11 healthy young adults (6 men, 5 women, mean +/- SD: 25.2 +/- 4.6 yr old; body mass index 23.7 +/- 1.8 kg/m2) and 11 older adults (6 men, 5 women, 69.5 +/- 5.8 yr old; body mass index 24.2 +/- 2.5 kg/m2). Saline (control) or recombinant human IGF-I (rhIGF-I) (2 h baseline then, in sequence, 2.5 h each of 1, 3, and 10 micrograms/kg.h) was infused iv during the last 9.5 h of a 40.5-h fast; serum glucose was clamped within 15% of baseline. Baseline serum GH concentrations (mean +/- SE: 3.3 +/- 0.7 vs. 1.9 +/- 0.5 micrograms/L, P = 0.02) and total IGF-I concentrations (219 +/- 15 vs. 103 +/- 19 micrograms/L, P < 0.01) were higher in the younger subjects. In both age groups, GH concentrations were significantly decreased by 3 and 10 micrograms/kg.h, but not by 1 microgram/kg.h rhIGF-I. The absolute decrease in GH concentrations was greater in young than in older subjects during the 3 and 10 micrograms/kg.h rhIGF-I infusion periods, but both young and older subjects suppressed to a similar GH level during the last hour of the rhIGF-I infusion (0.78 +/- 0.24 microgram/L and 0.61 +/- 0.16 microgram/L, respectively). The older subjects had a greater increase above baseline in serum concentrations of both total (306 +/- 24 vs. 244 +/- 14 micrograms/L, P = 0.04) and free IGF-I (8.5 +/- 1.4 vs. 4.2 +/- 0.6 micrograms/L, P = 0.01) than the young subjects during rhIGF-I infusion, and their GH suppression expressed in relation to increases in both total and free serum IGF-I concentrations was significantly less than in the young subjects. We conclude that the ability of exogenous rhIGF-I to suppress serum GH concentrations declines with increasing age. This suggests that increased sensitivity to endogenous IGF-I negative feedback is not a cause of the decline in GH secretion that occurs with aging.

Exercise training decreases the growth hormone (GH) response to acute constant-load exercise

To assess the influence of exercise training on the growth hormone (GH) response to acute exercise, six untrained males completed a 20-min, high-intensity, constant-load exercise test prior to and after 3 and 6 wk of training (the absolute power output (PO) during each test remained constant x PO = 182.5 +/- 29.5 W). Training increased (pre- vs post-training) oxygen uptake (VO2) at lactate threshold (1.57 +/- 0.33 L.min-1 vs 1.97 +/- 0.24 L.min-1 P < or = 0.05). VO2 at 2.5 mM blood lactate concentration ([HLa]) (1.83 +/- 0.38 L.min-1 vs 2.33 +/- 0.38 L.min-1, P < or = 0.05), and VO2peak (3.15 +/- 0.54 L.min-1 vs 3.41 +/- 0.47 L.min-1, P < or = 0.05). Power output at the lactate threshold (PO-LT) increased with training from 103 +/- 28 to 132 +/- 23W (P < or = 0.05). Integrated GH concentration (20 min exercise + 45 min recovery) (microgram.L-1 x min) after 3 wk (138 +/- 106) and 6 wk (130 +/- 145) were significantly lower (P < or = 0.05) than pre-training (238 +/- 145). Plasma epinephrine and norepinephrine responses to training were similar to the GH response (EPI-pre-training = 2447 +/- 1110; week 3 = 1046 +/- 144; week 6 = 955 +/- 322 pmol.L-1; P < or = 0.05; NE pre-training = 23.0 +/- 5.2; week 3 = 13.4 +/- 4.8; week 6 = 12.1 +/- 6.8 nmol.L-1; P < or = 0.05). These data indicate that the GH and catecholamine response to a constant-load exercise stimulus are reduced within the first 3 wk of exercise training and support the hypothesis that a critical threshold of exercise intensity must be reached to stimulate GH release.

Body composition by DEXA in older adults: accuracy and influence of scan mode

Dual energy x-ray absorptiometry (DEXA) measures bone mineral content (BMC), bone mineral density (BMD), fat-free mass (FFM), and provides estimates of percent body fat. Changes in scan mode geometry (pencil beam vs array) may impact these measures and body composition estimates using multi-compartment models. Forty-one adults, ages 59-79 yr, were scanned in each mode and also underwent hydrostatic weighing and measurement of total body water (tritiated water dilution). The effect of scan mode on measurement of DEXA BMC, BMD, FFM, and percent body fat (DEXA %Fat) was examined. The effect of scan mode on percentage body fat determined by a 4-compartment body composition model (4 Comp %Fat) and comparison of DEXA %Fat and 4 Comp %Fat were also examined. BMC and DEXA %Fat were greater (1.3% and 3.9%, respectively, P < 0.01), and BMD and FFM were lower (1.1% and 1.9%, respectively, P < 0.01) with the array scan mode. The 4 Comp %Fat was significantly greater (0.2%) when the array scan mode measurements of total body bone mineral were used; however, these differences were physiologically inconsequential. Comparison between DEXA %Fat and 4 Comp %Fat measures revealed a total error of +/-5.0% in the older adults examined. These results indicate significant scan mode differences in total body BMC, BMD, FFM, and DEXA %Fat measurements and demonstrate the importance of using a single DEXA scan mode for clinical investigation, particularly with longitudinal studies. For all investigations with DEXA, the scan mode should be reported. Furthermore, the error associated with using DEXA alone to estimate percent fat in an older population suggests that this technique is unacceptable in a research setting.

Effect of obesity and feeding on the growth hormone (GH) response to the GH secretagogue L-692,429 in young men

GH secretion and the response to GH secretagogues are significantly diminished in obese individuals. Previous studies have shown that L-692,429 (L), a nonpeptide mimetic of GH-releasing peptide, selectively stimulates GH release in normal young men and in the elderly, who also have diminished GH secretion. A paired, two-site study examined the effects of L on GH release in 12 healthy obese (part A; mean +/- SD: age, 26.1 +/- 3.3 yr; body mass index, 35.0 +/- 3.1 kg/m2) and 10 nonobese (part B; age, 22.2 +/- 2.3 yr; body mass index, < or = 27.0) young men. In part A, placebo, low dose L (0.2 mg/kg), or high dose L (0.75 mg/kg) was administered iv over 15 min on 3 separate occasions after an overnight fast. Samples for GH, PRL, and cortisol determinations were obtained every 15 min. GH release (mean +/- SE) was significantly increased by both doses of L compared to the effect of placebo: 12.6 +/- 1.8 micrograms/L (low dose), 18.5 +/- 2.7 micrograms/L (high dose), and 0.84 +/- 0.1 microgram/L (placebo), respectively (P < 0.05). In a subset of 6 obese men, in samples collected every 5 min, the GH response to both doses of L was significantly greater than that to 1 microgram/kg GHRH. To compare the response to low dose L in the obese and to determine the effects of feeding on this response, 0.2 mg/kg L was administered as described in part A to nonobese young men after an overnight fast (fasted) or a standardized breakfast (fed; part B). Low dose L was an effective GH secretagogue in nonobese young men; however, this effect was attenuated with feeding [43.6 +/- 7.9 (fasted) vs. 17.7 +/- 4.8 (fed) micrograms/L]. Of note, the response to low dose L in fasted obese individuals was similar to that in fed nonobese individuals. The administration of L was well tolerated in both groups. We conclude that L is an effective GH secretagogue in obese and nonobese young men and may have therapeutic benefits when administered to relative (obese or elderly) or absolute GH-deficient individuals.

A kindred with a variant of multiple endocrine neoplasia type 1 demonstrating frequent expression of pituitary tumors but not linked to the multiple endocrine neoplasia type 1 locus at chromosome region 11q13

Acromegaly is uncommon in kindreds with multiple endocrine neoplasia type 1 (MEN1), whereas primary hyperparathyroidism (PHP) has the highest penetrance of any endocrinopathy. We report an unusual MEN1 kindred with frequent expression of pituitary tumors and a low penetrance of PHP. Four members were found to have disease: PHP in generation I, acromegaly (2 cases) in generation II, and hyperprolactinemia associated with a pituitary tumor in generation III. There was no evidence for PHP in 1 patient with acromegaly (age 60 yr), the patient with hyperprolactinemia and the pituitary tumor (age 22 yr), and 1 asymptomatic obligate carrier (age 50 yr). Screening of 26 members revealed the possible diagnosis of PHP in 1 family member in generation II and possible early acromegaly in 2 members of generation III with elevated serum concentrations of insulin-like growth factor I and insulin-like growth factor-binding protein-3 but normal patterns of pulsatile GH release. Although the predisposing genetic defect in typical MEN1 families has previously been mapped to chromosome location 11q13 without evidence of heterogeneity among the 87 families analyzed, linkage of disease in this family to the MEN1 region is unlikely based on haplotype analysis. Localization of the gene(s) responsible for disease in such atypical families may aid in the understanding of the pathogenesis of MEN1. In addition, further study of the earliest changes in patterns of pulsatile GH release in familial acromegaly may allow more insight into the pathogenesis and natural history of this disease.

Growth hormone-releasing hormone and growth hormone-releasing peptide as therapeutic agents to enhance growth hormone secretion in disease and aging

Growth hormone (GH) secretion is pulsatile and is tightly regulated. In this chapter the effects of aging, nutrition, the feedback effects of IGF-I, and the role of body composition in the decline of GH secretion will be discussed. In GH-deficient adults there is an increase in the amount of intra-abdominal (visceral) fat. Similarly, with increasing age, there is an increase in visceral fat and there is a tight correlation between 24-hour GH release and visceral fat in the elderly. This may have serious metabolic consequences, including insulin resistance and increased cardiovascular risk. There are at least four potential mechanisms for the age-related decline in GH secretion: 1) decreased release of growth hormone releasing-hormone (GHRH); 2) increased release of somatostatin; 3) enhanced sensitivity to IGF-I feedback; and 4) decreased somatotroph mass. The latter two potential mechanisms are discussed. There is little evidence that there is any change in sensitivity to IGF-I feedback with aging and the somatotroph cell mass appears to be preserved in older subjects. The GH axis may be stimulated by either GHRH or by growth hormone-releasing peptide (GHRP) and related compounds. Chronic therapy with GHRH in GH-deficient children restores GH secretion and accelerates linear growth. Mutations of the GHRH receptor lead to GH deficiency and short stature. This indicates the essential role of GHRH in regulation of GH secretion. Growth hormone releasing peptide was discovered in 1981. Recently, the GHRP/GH secretagogue receptor has been cloned and orally active GHRP mimetics have been developed. One such compound, MK-677, stimulates pulsatile GH secretion and its effects persist for 24 hours. Oral administration of MK-677 for a month in the elderly demonstrates that this route stimulates a physiologic pattern of GH secretion. The amplitude of the GH pulses was increased but the number of GH pulses was unchanged. Thus, in older individuals, the amount of GH secreted in 24 hours is restored toward that seen in young adults. This compound also enhances GH secretion in GH-deficient adults who had been GH-deficient during childhood. The development of stable, orally active molecules to stimulate the GHRP/GH secretagogue receptor is a practical reality. These GH secretagogues may have a therapeutic role in short stature and adult GH deficiency. In addition, the use of GH secretagogues in normal aging merits investigation, as growth hormone may regulate body composition in older adults.

Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects

Aging is associated with declining activity of the GH axis, possibly contributing to adverse body composition changes and increased incidence of cardiovascular disease. The stimulatory effects on the GH-insulin-like growth factor I (IGF-I) axis of orally administered MK-677, a GH-releasing peptide mimetic, were investigated. Thirty-two healthy subjects (15 women and 17 men, aged 64-81 yr) were enrolled in a randomized, double blind, placebo-controlled trial. They received placebo or 2, 10, or 25 mg MK-677, orally, once daily for 2 separate study periods of 14 and 28 days. At baseline and on day 14 of each study period, blood was collected every 20 min for 24 h to measure GH, PRL, and cortisol. Attributes of pulsatile GH release were assessed by 3 independent algorithms. MK-677 administration for 2 weeks increased GH concentrations in a dose-dependent manner, with 25 mg/day increasing mean 24-h GH concentration 97 +/- 23% (mean +/- SE; P < 0.05 vs. baseline). This increase was due to an enhancement of preexisting pulsatile GH secretion. GH pulse height and interpulse nadir concentrations increased significantly without significant changes in the number of pulses. With 25 mg/day MK-677 treatment, mean serum IGF-I concentrations increased into the normal range for young adults (141 +/- 21 microgram/L at baseline, 219 +/- 21 micrograms/L at 2 weeks, and 265 +/- 29 micrograms/L at 4 weeks; P < 0.05). MK-677 produced significant increases in fasting glucose (5.4 +/- 0.3 to 6.8 +/- 0.4 mmol/L at 4 weeks; P < 0.01 vs. baseline) and IGF-binding protein-3. Circulating cortisol concentrations did not change, and PRL concentrations increased 23%, but remained within the normal range. Once daily treatment of older people with oral MK-677 for up to 4 weeks enhanced pulsatile GH release, significantly increased serum GH and IGF-I concentrations, and, at a dose of 25 mg/day, restored serum IGF-I concentrations to those of young adults.

Enhancement of pulsatile growth hormone secretion by continuous infusion of a growth hormone-releasing peptide mimetic, L-692,429, in older adults--a clinical research center study

L-692,429 ([L]) is a GH-releasing peptide mimetic that stimulates GH secretion when administered acutely. To determine the effect of its continuous administration, six older adults (four men and two women, aged 64-82 yr) received i.v. transfusions of 1) saline for 24 h (control), 2) [L] (0.05 mg/kg.h) for 24 h (low dose), and 3) [L] (0.1 mg/kg.h) for 12 h, then saline for 12 h (high dose), followed on all admissions by saline for 2.5 h. GHRH (1 microgram/kg, i.v.) was given 30 min before the end of each 24-h treatment. Blood was collected every 10 min for GH measurement, and GH secretion was assessed by deconvolution analysis. Pulsatile GH secretion continued throughout both [L] infusions. During the first 12 h (when comparison of both doses was possible), [L] exerted a dose-dependent stimulatory effect on mean GH concentrations, from 0.6 +/- 0.1 (control, mean +/- SE), to 1.2 +/- 0.2 (low dose [L]) and 2.3 +/- 0.5 microgram/L (high dose [L]; P < 0.05, high dose vs. control), and on calculated GH secretory rates [1.6 +/- 0.3 (control), 2.5 +/- 0.3 (low dose [L]), and 5.8 +/- 0.7 microgram/L distribution vol.h (high dose [L]); P < 0.05, high dose vs. control]. GH secretory pulse height and area increased significantly in a dose-responsive manner, without significant changes in GH secretory pulse number, half-duration of pulses, or GH half-life. GH concentrations remained elevated during the second 11.5 h of low dose [L] infusion. Over the 23.5-h period before GHRH administration, mean GH concentrations and secretion rates were significantly higher than control values with high dose, but not low dose, [L]. Low dose [L] enhanced the peak GH response to GHRH (17.4 +/- 3.5 micrograms/L) compared to the control value (8.4 +/- 2.8 micrograms/L; P < 0.05). We conclude that the administration of [L] to healthy older adults by continuous i.v. infusion enhances pulsatile GH secretion by increasing the mass of GH secreted per pulse, but not the number of secretion pulses, and increases the GH response to GHRH.

Pulsatile growth hormone secretion in older persons is enhanced by fasting without relationship to sleep stages

Spontaneous secretion of GH decreases with aging. To investigate whether fasting increases pulsatile GH secretion in older as it does in younger subjects, we studied six subjects (four postmenopausal women and two men, aged 55-81 yr; body mass indexes, 22-24 kg/ m2). Blood was obtained every 5 min for 24 h on a control (fed) day and on the second day of a fast. Serum GH concentrations, measured by an immunoradiometric assay, were analyzed with a multiple parameter deconvolution method to stimultaneously resolve endogenous GH secretory and clearance rates. Two days of fasting induced a 4-fold increase in the 24-h GH production rate (38 +/- 25 vs. 166 +/- 42 micrograms/L distribution volume; P = 0.003) and a 2-fold increase in the amount of GH secreted per pulse (2.4 +/- 1.4 vs. 5.5 +/- 1.2 micrograms/L distribution volume; P = 0.02). The latter was a result of increased secretory burst amplitudes with unchanged secretory burst durations. The number of detectable GH secretory bursts per 24 h was also increased by fasting (13 +/- 1.4 vs. 30 +/- 1.1; P = 0.0004); the GH pulse frequency may have been underestimated in the fed state, as 33 +/- 4.9% of the samples had undetectable ( < 0.2 microgram/L) serum GH concentrations compared to 5.2 +/- 2.6% of the samples on the fasting day (P = 0.004). The t1/2 of endogenous GH was not significantly altered by fasting. The fold increase in GH secretion with fasting was similar to that previously observed in young men, although absolute levels of GH secretion were approximately 50% lower in both fed and fasted conditions. Fasting decreased the proportion of sleep time spent in rapid eye movement sleep (4.7 +/- 1.3 vs. 15 +/- 2.1%; P = 0.005), but did not significantly increase slow wave (stages 3 and 4) sleep. In both fed and fasted conditions, mean GH secretion rates were similar during daytime wakefulness, nocturnal wakefulness, rapid eye movement sleep, and stages 1, 2, and 3 of sleep. We conclude that hyposomatotropism associated with aging is partially reversed by fasting, and the enhancement of GH secretion by fasting is not related to changes in slow wave sleep. These data indicate that GH secretion in older persons can be enhanced by physiological interventions.

Both oral and transdermal estrogen increase growth hormone release in postmenopausal women--a clinical research center study

To determine if the mode of 17 beta-estradiol (E2) administration affects growth hormone (GH) concentrations, eight postmenopausal women were studied under the following conditions: (1) control (no E2), (2) oral E2 (Estrace, 1 mg every 12 h for 2 weeks) and (3) transdermal E2 (Estraderm patch, 0.1 mg, two patches changed daily for 2 weeks). Blood was collected every 5 min for 24 h and assayed for serum GH concentrations using a sensitive chemiluminescence assay. Serum E2 levels were comparable during both E2 treatment regimens when measured with a specific chemiluminescence assay. The 24-h integrated GH concentrations (IGHC, min . micrograms/L) increased in all eight subjects from (mean +/- SE) 494 +/- 102 during control to 860 +/- 111 (P < 0.05) and 832 +/- 149 (P < 0.05) during oral and transdermal E2, respectively. Both E2 treatments significantly increased GH pulse height, individual pulse area, incremental pulse amplitude, interpeak valley concentration, and interpeak valley nadir (as measured by Cluster algorithm) when compared with control. No significant differences were observed in the number of GH pulses per 24 h. Insulin-like growth factor-I (IGF-I, micrograms/L) concentrations decreased from 165 +/- 19 (control) to 109 +/- 11 (oral E2, P < 0.05) and 122 +/- 15 (transdermal E2, P < 0.05). No statistically significant differences in attributes of pulsatile GH release or IGF-I concentrations were observed between the oral and transdermal E2 treatments. We conclude that both oral and transdermal E2 treatment increase serum GH concentrations in postmenopausal women. This increase is manifested by larger GH pulses and higher basal (interpulse) GH levels, not by changes in pulse frequency. Both routes of E2 administration decrease serum IGF-I concentrations, which may attenuate IGF-I negative feedback on pituitary somatotrophs and hypothalamic somatostatin secretion, resulting in enhanced pulsatile GH release.

Females secrete growth hormone with more process irregularity than males in both humans and rats

In humans, serum growth hormone (GH) concentrations are significantly higher in women than in men, but the neuroendocrine mechanisms that underlie such gender differences are not known. We compared normal episodic GH secretion in males and females in three distinct settings: two human studies employing quite different assay techniques (immunoradiometric assay and a high-sensitivity immunofluorimetric method) and a rat study. To quantify the amount of regularity in data, we utilized approximate entropy (ApEn), a scale- and model-independent statistic. In each study, females exhibited significantly greater statistical irregularity in GH concentration series than their male counterparts (P < 10(-3) for each human study, P < 10(-6) for the rat study), implying that mass and mode of GH secretion are regulated differently in males and females. The regularity comparisons indicated complete gender separation (100% specificity and sensitivity) for the rat study and nearly complete separation for the immunofluorimetric assay study. The consistency and statistical significance of these findings suggest that this gender difference may be broadly based within higher animals and that this may be readily evaluated objectively by analysis of ApEn.