Protein metabolism and the use of growth hormone and insulin-like growth factor-I in the critically ill patient

Navigating Post-Traumatic Osteoporosis: A Comprehensive Review of Epidemiology, Pathophysiology, Diagnosis, Treatment, and Future Directions

Post-traumatic osteoporosis (PTO) presents a significant challenge in clinical practice, characterized by demineralization and decreased skeletal integrity following severe traumatic injuries. This literature review manuscript addresses the knowledge gaps surrounding PTO, encompassing its epidemiology, pathophysiology, risk factors, diagnosis, treatment, prognosis, and future directions. This review emphasizes the complexity of the etiology of PTO, highlighting the dysregulation of biomineralization processes, inflammatory cytokine involvement, hormonal imbalances, glucocorticoid effects, vitamin D deficiency, and disuse osteoporosis. Moreover, it underscores the importance of multidisciplinary approaches for risk mitigation and advocates for improved diagnostic strategies to differentiate PTO from other musculoskeletal pathologies. This manuscript discusses various treatment modalities, including pharmacotherapy, dietary management, and physical rehabilitation, while also acknowledging the limited evidence on their long-term effectiveness and outcomes in PTO patients. Future directions in research are outlined, emphasizing the need for a deeper understanding of the molecular mechanisms underlying PTO and the evaluation of treatment strategies' efficacy. Overall, this review provides a comprehensive overview of PTO and highlights avenues for future investigation to enhance clinical management and patient outcomes.

Frequent intravenous pulses of growth hormone together with glutamine supplementation in prolonged critical illness after multiple trauma: effects on nitrogen balance, insulin resistance, and substrate oxidation

OBJECTIVES

To estimate the efficacy and metabolic effects of growth hormone substitution as intravenous pulses together with alanyl-glutamine supplementation and tight blood glucose control in prolonged critical illness.

DESIGN

Prospective double-blind, randomized trial with open-label control arm.

SETTING

Intensive care unit of tertiary level hospital.

PATIENTS

Thirty multiple trauma patients (median Injury Severity Score 34).

INTERVENTIONS

Patients were randomized, at day 4 after trauma, to receive intravenous alanyl-glutamine supplementation (0.3 g/kg x day(-1) from day 4 until day 17) and intravenous growth hormone (administered days 7-17, full dose 50 microg/kg x day(-1) from day 10 onward) (group 1, n = 10) or alanyl-glutamine and placebo (group 2, n = 10). Group 3 (n = 10) received isocaloric isonitrogenous nutrition (proteins 1.5 g/kg x day(-1)) without alanyl-glutamine.

MEASUREMENTS AND MAIN RESULTS

Cumulative nitrogen balance for the whole study period was -97 +/- 38 g of nitrogen for group 1, -193 +/- 50 g of nitrogen for group 2, and -198 +/- 77 g of nitrogen for group 3 (p < .001). This represents a daily saving of 300 g of lean body mass in group 1. Insulin-mediated glucose disposal, during euglycemic clamp, as a measure of insulin sensitivity, significantly worsened between days 4 and 17 in group 1 but improved in groups 2 and 3. Group 1 required significantly more insulin to control blood glucose, resulting in higher insulinemia (approximately 70 mIU in group 1 vs. approximately 25 mIU in groups 2 and 3). Despite this, growth hormone treatment caused an increase in plasma nonesterified fatty acid (approximately 0.5-0.6 mM in group 1 in comparison with approximately 0.2-0.3 mM in groups 2 and 3) but did not influence lipid oxidation. There were no differences in morbidity, mortality, or 6-month outcome among the groups.

CONCLUSIONS

Treatment with frequent intravenous pulses of low-dose growth hormone together with alanyl-glutamine supplementation improves nitrogen economy in patients with prolonged critical illness after multiple trauma but worsens insulin sensitivity. Tight blood glucose control is possible but requires higher doses of insulin.

Changes within the growth hormone/insulin-like growth factor I/IGF binding protein axis during critical illness

Interest in the somatotropic axis,with its complex network of interactions, during critical illness arose only a few decades ago. Te distinguishing neuroendocrine features of prolonged critical illness were not differentiated from those during the acute phase until the early 1990s. This incomplete understanding of the somatotropic axis contributed to some disastrous results, such as the multicenter growth hormone trial. The goal of stimulating the somatotropic axis without a proper preceding neuroendocrine diagnosis should be held obsolete. Moreover, the fascinating link between regulators of carbohydrate metabolism, such as insulin and insulin-like growth factor I, and the somatotropic axis may lead to future therapeutic possibilities.

Risks and benefits of nutritional support during critical illness

Critically ill patients who depend on intensive care for more than a few days reveal profound erosion of lean body mass, which is thought to contribute to high morbidity and mortality. Despite a shortfall of evidence that supplemental feeding actually alters clinical outcome of these life-threatening disease states, this observation evoked an almost universal, albeit often inappropriate, use of nutritional support (NS) in the critically ill, administered via the parenteral or the enteral route. Lack of knowledge and overenthusiasm subsequently resulted in complications associated with both parenteral nutrition (PN) and enteral nutrition (EN), which led to the standing controversy over which should be preferred. With time, however, it became clear that EN and PN are not mutually exclusive and that critically ill patients requiring NS should be fed according to the functional status of the gastrointestinal tract. In addition, tight blood glucose control with insulin is advised in fed critically ill patients because overall metabolic control appears to surpass any outcome benefit attributed to the route of feeding. Recently, various special nutritional formulas have been suggested to prevent or treat multiorgan failure in the critically ill, among other pathways via modulation of immune function. Although special nutritional formulas may be promising in a variety of clinical settings, based on currently available data, these cannot be recommended for routine use in critically ill patients.

The Neuroendocrine Response to Critical Illness is a Dynamic Process

Striking alterations in the hypothalamic-anterior pituitary-peripheral hormone axes hallmark the state of critical illness, their severity being associated with high risk for morbidity and mortality. Early endocrine intervention strategies aimed to correct the hormone balance have been shown ineffective or even harmful because of lack of thorough pathophysiologic understanding of these neuroendocrine changes. Extensive research, however, has provided crucial insights, with the demonstration of the biphasic response of the anterior pituitary to the severe stress of critical illness.

Treatment with GH and IGF-1 in Critical Illness

Trauma, sepsis, and surgery are associated with global hypercatabolism and a negative nitrogen balance. When critical illness is prolonged the relentless loss of lean tissue becomes functionally important. Protein catabolism in the critically ill patient is associated with complex changes in the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis. Many small clinical studies indicate that treatment with recombinant human (rh) GH would be a safe and effective means of limiting the deleterious effects of the catabolic response. Unexpectedly, however, two large prospective randomized controlled trials (PRCTs) demonstrated that administration of rhGH to long-stay critically ill adults increases morbidity and mortality. Some progress has been made in understanding the mechanisms underlying this observation.

Prognostic Value of Thyroid Hormone Levels in Acute Myocardial Infarction: Just an Epiphenomenon?

The purpose of this study was to investigate whether thyroid hormone levels have any predictive value for mortality in patients presenting to the emergency department with acute myocardial infarction (AMI). Three groups of patients admitted to the emergency department within the 11-month study period were considered eligible: 95 patients with chest pain and proven AMI, 26 patients with chest pain and no AMI, and 114 patients who served as controls with no evidence of any major disease. Cardiac enzymes and the following thyroid hormones were analyzed and compared between groups, regarding effects of historical and demographic factors: thyrotrophin, free triiodothyronine (FT3), total triiodothyronine (TT3), free thyroxine (FT4), and total thyroxine (TT4). Sixteen patients with AMI (16.8%) died within the study period. Troponin T and creatine kinase-B with an M-type subunit levels were significantly higher in the nonsurvivors when compared with survivors. Survivors in the AMI group had higher TT3, TT4, and lower FT4 levels, while the nonsurvivors in the AMI group had higher thyrotrophin and lower TT3, FT3 and FT4 levels than controls. In the AMI group, the nonsurvivors had lower TT3 and FT3 levels than the survivors. A history of diabetes mellitus and/or angina, TT3, or FT3 was an independent predictor of mortality. TT3 and FT3 appear to be independent prognostic factors in patients with AMI.

Endocrine evaluation of patients with critical illness

Prolonged critical illness has a high morbidity and mortality. The acute and chronic phases of critical illness are associated with distinct endocrine alterations. The acute neuroendocrine response to critical illness involves an activated anterior pituitary function. In prolonged critical illness, however, a reduced pulsatile secretion of anterior pituitary hormones and the so-called "wasting syndrome" occur. The impaired pulsatile secretion of GH, thyrotropin and gonadotropin can be re-amplified by relevant combinations of releasing factors, which also substantially increase circulating levels of IGF-1, GH-dependent IGFBPs, thyroxin, tri-iodothyronine and testosterone. Anabolism is clearly re-initiated at the time GH secretagogues, thyrotropin-releasing hormone and gonadotropin-releasing hormone are coadministered but the effect on survival remains unknown. A lethal outcome of critical illness is predicted by a high serum concentration of IGFBP-1, pointing to impaired insulin effect rather than pituitary function, and survival was recently shown to be dramatically improved by strict normalization of glycemia with exogenous insulin. In addition to the illness-induced endocrine alterations, patients may have pre-existing central or peripheral endocrine diseases, either previously diagnosed or unknown. Hence, endocrine function testing in a critically ill patient represents a major challenge and the issue of treatment remains controversial. The recent progress in knowledge of the neuroendocrine response to critical illness and its interrelation with peripheral hormonal and metabolic alterations during stress, allows for potential new therapeutic perspectives to safely reverse the wasting syndrome and improve survival.

Hypothalamic growth hormone-releasing hormone (GHRH) cell number is increased in human illness, but is not reduced in Prader-Willi syndrome or obesity

BACKGROUND

Acute illness leads to increased GH, but reduced IGF-I secretion, while both are reduced in chronic illness. Prader-Willi syndrome (PWS) is a genetic obesity syndrome, with GH deficiency a feature independent of obesity. Reduced GH secretion may result from decreased hypothalamic release of GH-releasing hormone (GHRH).

OBJECTIVE

To quantify hypothalamic GHRH neurone cell number in control subjects with various lengths of premorbid illness duration, PWS and non-PWS obese subjects.

DESIGN

We examined GHRH neurones in the infundibular nucleus/median eminence complex of control subjects (n = 26, including four children), PWS (n = 6) and non-PWS (n = 4) obese adults and PWS children (n = 2), by quantitative immunocytochemistry, using postmortem material.

RESULTS

We found: (i) higher GHRH cell number during prolonged illness prior to death in both control adults (r = +0.62, P = 0.002, cell number vs. premorbid illness duration) and PWS adults (r = +0.90, P = 0.02); (ii) higher GHRH cell number in female than male adults [by 53% (95% confidence interval 28-83%) in controls, P = 0.005, correcting for premorbid illness duration]; (iii) no difference in GHRH cell number between PWS adults and control or non-PWS obese adults (P = 0.7 and P = 0.4, adjusting for sex and illness duration); and (iv) low GHRH cell number in only one PWS child (who had been receiving exogenous GH therapy).

CONCLUSIONS

These findings suggest continued activation of GHRH neurones during prolonged illness. There is no evidence that the GH deficiency in PWS results from reduced GHRH cell number, and GHRH neuronal responses to illness and exogenous GH treatment appear normal in PWS.

Dynamic neuroendocrine responses to critical illness

Prolonged critical illness has high morbidity and mortality. The acute neuroendocrine response to critical illness involves an activated anterior pituitary function. In prolonged critical illness, however, a reduced pulsatile secretion of anterior pituitary hormones and the so-called 'wasting syndrome' occur. The impaired pulsatile secretion of growth hormone (GH), thyrotropin and gonadotropin can be re-amplified by relevant combinations of releasing factors, which also substantially increase circulating levels of insulin-like growth factor (IGF)-I, GH-dependent IGF-binding proteins, thyroxine, tri-iodothyronine, and testosterone. Anabolism is clearly re-initiated when GH secretagogues, thyrotropin-releasing and gonadotropin-releasing hormones are co-administered but the effect on survival remains unknown. A lethal outcome of critical illness is predicted by a high serum concentration of IGF-binding protein 1, pointing to impaired insulin effect rather than pituitary function, and survival was recently shown to be dramatically improved by strict normalization of glycemia with exogenous insulin. The recent progress in the knowledge of the neuroendocrine response to critical illness and its interrelation with peripheral hormonal and metabolic alterations during stress allows for potential new therapeutic perspectives to safely reverse the wasting syndrome and improve survival. These novel insights will be reviewed herein.

Neuroendocrine pathobiology of chronic critical illness

The neuroendocrine stress response is a dynamic process involving multiple hormonal alterations with distinct features in the acute and chronic phase of critical illness. In the initial response to an acute stress event, the anterior pituitary actively releases its hormones into the circulation while in the periphery, anabolic target organ hormones are inactivated. This response is thought to be beneficial and adaptive. When critical illness becomes prolonged, pulsatile secretion of anterior pituitary hormones becomes uniformly reduced due to reduced (hypothalamic) stimulation, and this underlies reduced activity of the respective target tissues and impaired anabolism. This difference in the acute and chronic stress response may not be trivial. It was the (inappropriate) assumption that acute stress responses, such as GH resistance, persist throughout the course of critical illness, which had formed the (inappropriate) justification to administer high doses of GH to long-stay intensive care patients to induce anabolism [102]. The concomitant endocrine changes in chronic critical illness may have predisposed to severe side effects of high doses of GH. In view of the significant benefits of strict glycemic control using exogenous insulin recently demonstrated in ICU patients [101], GH-induced insulin resistance and hyperglycemia may have played a role. It remains to be studied whether endocrine intervention with releasing factors such as TRH and GHRP in prolonged critical illness will accelerate recovery of patients who have entered the vicious circle of prolonged intensive care dependency.

The neuroendocrine response to stress is a dynamic process

The initial neuroendocrine response to critical illness illness consists primarily of activated anterior pituitary function, the peripheral anabolic pathways being inactivated. This response presumably provides metabolic substrates, establishes the host's defences and is thus considered to be adaptive and beneficial. It was previously assumed that the acute stress response persisted throughout the course of critical illness, but this assumption has now been disproved. Indeed, a uniformly reduced pulsatile secretion of growth hormone, thyroid-stimulating hormone, prolactin and luteinizing hormone has been observed in protracted critical illness, impairing the function of target organs. A reduced availability of thyrotropin-releasing hormone, gonadotropin-releasing hormone, the endogenous ligand of the growth hormone-releasing peptide receptor (possibly ghrelin) and, in very long-stay critically ill men, also growth hormone-releasing hormone seems to be involved. The pulsatile secretion of growth hormone, thyroid-stimulating hormone, prolactin and luteinizing hormone can be re-established by relevant combinations of releasing factors, which also substantially increase the circulating levels of insulin-like growth factor-1, growth hormone dependent binding proteins, thyroxine, tri-iodothyronine and testosterone. Active feedback inhibition loops prevent the target organs being overstimulated. The metabolism is altered in a beneficial way when growth hormone-secretagogues, thyrotropin-releasing hormone and gonadotropin-releasing hormone are administered together, whereas the effect of single-hormone treatment is minor and accompanied by side-effects. This new concept of a selectively reduced stimulation of pituitary function in the chronic phase of critical illness unveils new therapeutic perspectives to reverse the paradoxical wasting syndrome' and intensive care dependency.