Hormonal responses to fasting and refeeding in chronic renal failure patients

Recognition of Nonneoplastic Hypercortisolism in the Evaluation of Patients With Cushing Syndrome

The evaluation of suspected hypercortisolism is one of the most challenging problems in medicine. The signs and symptoms described by Dr Harvey Cushing are common and often create diagnostic confusion to even experienced endocrinologists. Cushing syndrome is classically defined as neoplastic hypercortisolism resulting from an ACTH-secreting tumor or from autonomous secretion of excess cortisol associated with benign or malignant adrenal neoplasia. The increasing recognition of the negative cardiometabolic effects of mild cortisol excess without overt physical signs of Cushing syndrome has led to more screening for endogenous hypercortisolism in patients with adrenal nodular disease, osteoporosis, and the metabolic syndrome. However, sustained or intermittent activation of the dynamic hypothalamic-pituitary-adrenal axis caused by chemical (alcohol), inflammatory (chronic kidney disease), psychologic (major depression), and physical (starvation/chronic intense exercise) stimuli can result in clinical and/or biochemical features indistinguishable from neoplastic hypercortisolism. Nonneoplastic hypercortisolism (formerly known as pseudo-Cushing syndrome) has been recognized for more than 50 years and often causes diagnostic uncertainty. This expert consultation describes two patients with features of Cushing syndrome who were referred for inferior petrosal sinus sampling for the differential diagnosis of ACTH-dependent hypercortisolism. Both patients were discovered to have nonneoplastic hypercortisolism: one from a covert alcohol use disorder and the other to chronic kidney disease. This consultation emphasizes the value of a good history and physical examination, appropriate laboratory testing, and the desmopressin acetate stimulation test to aid in distinguishing neoplastic from nonneoplastic hypercortisolism.

Cortisol excess in chronic kidney disease - A review of changes and impact on mortality

Chronic kidney disease (CKD) describes the long-term condition of impaired kidney function from any cause. CKD is common and associated with a wide array of complications including higher mortality, cardiovascular disease, hypertension, insulin resistance, dyslipidemia, sarcopenia, osteoporosis, aberrant immune function, cognitive impairment, mood disturbances and poor sleep quality. Glucocorticoids are endogenous pleiotropic steroid hormones and their excess produces a pattern of morbidity that possesses considerable overlap with CKD. Circulating levels of cortisol, the major active glucocorticoid in humans, are determined by a complex interplay between several processes. The hypothalamic-pituitary-adrenal axis (HPA) regulates cortisol synthesis and release, 11β-hydroxysteroid dehydrogenase enzymes mediate metabolic interconversion between active and inactive forms, and clearance from the circulation depends on irreversible metabolic inactivation in the liver followed by urinary excretion. Chronic stress, inflammatory states and other aspects of CKD can disturb these processes, enhancing cortisol secretion via the HPA axis and inducing tissue-resident amplification of glucocorticoid signals. Progressive renal impairment can further impact on cortisol metabolism and urinary clearance of cortisol metabolites. Consequently, significant interest exists to precisely understand the dysregulation of cortisol in CKD and its significance for adverse clinical outcomes. In this review, we summarize the latest literature on alterations in endogenous glucocorticoid regulation in adults with CKD and evaluate the available evidence on cortisol as a mechanistic driver of excess mortality and morbidity. The emerging picture is one of subclinical hypercortisolism with blunted diurnal decline of cortisol levels, impaired negative feedback regulation and reduced cortisol clearance. An association between cortisol and adjusted all-cause mortality has been reported in observational studies for patients with end-stage renal failure, but further research is required to assess links between cortisol and clinical outcomes in CKD. We propose recommendations for future research, including therapeutic strategies that aim to reduce complications of CKD by correcting or reversing dysregulation of cortisol.

Immune Dysfunction in Uremia 2020

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Abnormalities in Glucose Metabolism, Appetite-Related Peptide Release, and Pro-nflammatory Cytokines Play a Central Role in Appetite Disorders in Peritoneal Dialysis

Background: Appetite disorders are frequent and scantly studied in peritoneal dialysis (PD) patients and are associated with malnutrition and cardiovascular complications. Objective: We investigated the relationship between uremic insulin resistance, pro-inflammatory cytokines, and appetite-related peptides release (ARPr) with eating-behavior disorders in PD patients. Methods: We included 42 PD patients (12 suffering anorexia, 12 obese with high food-intake, and 18 asymptomatic) and 10 controls. We measured blood levels of ARPr including orexigens [neuropeptide-Y (NPY), ghrelin, and nitric-oxide], anorexigens [cholecystokinin, insulin, corticotropin-releasing factor, leptin, and adiponectin (Ad)], and cytokines (TNF-α, sTNFα-R2, and IL-6) both at baseline and after administering a standard-food stimulus (SFS). We also measured the expression of TNF-α, leptin and Ad-encoding mRNAs in abdominal adipose tissue. We compared these markers with eating motivation measured by a Visual Analog Scale (VAS). Results: Anorexics showed both little appetite, measured by a VAS, and low levels of orexigens that remained constant after SFS, coupled with high levels of anorexigens at baseline and after SFS. Obeses showed higher appetite, increased baseline levels of orexigens, lower baseline levels of anorexigens and cytokines and two peaks of NPY after SFS. The different patterns of ARPr and cytokines pointed to a close relationship with uremic insulin resistance. In fact, the euglycemic-hyperglycemic clamp reproduced these disorders. In anorexics, TNF-α fat expression was increased. In obese patients, leptin expression in fat tissue was down-regulated and showed correlation with the appetite. Conclusion: In PD, appetite is governed by substances that are altered at baseline and abnormally released. Such modulators are controlled by insulin metabolism and cytokines and, while anorexics display inflammatory predominance, obese patients predominantly display insulin resistance.

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

The peptidic middle molecules: is molecular weight doing the trick?

Chronic kidney disease (CKD) is characterized by a gradual endogenous intoxication caused by the progressive accumulation of bioactive compounds that in normal conditions would be excreted and/or metabolized by the kidney. Uremic toxicity now is understood as one of the potential causes for the excess of cardiovascular disease and mortality observed in CKD. An important family of uremic toxins is that of the peptidic middle molecules, with a molecular weight ranging between 500 and 60,000 Da, which makes them, as a consequence, difficult to remove in the process of dialysis unless the dialyzer pore size is large enough. This review provides an overview of the main and best-characterized peptidic middle molecules and their role as potential culprits of the cardiometabolic complications inherent to CKD patients.

Hormonal regulation of energy-protein homeostasis in hemodialysis patients: an anorexigenic profile that may predispose to adverse cardiovascular outcomes

To assess whether endocrine dysfunction may cause derangement in energy homeostasis in patients undergoing hemodialysis (HD), we profiled hormones, during a 3-day period, from the adipose tissue and the gut and the nervous system around the circadian clock in 10 otherwise healthy HD patients and 8 normal controls. The protocol included a 40-h fast. We also measured energy-protein intake and output and assessed appetite and body composition. We found many hormonal abnormalities in HD patients: 1) leptin levels were elevated, due, in part, to increased production, and nocturnal surge in response to daytime feeding, exaggerated. 2) Peptide YY (PYY), an anorexigenic gut hormone, was markedly elevated and displayed an augmented response to feeding. 3) Acylated ghrelin, an orexigenic gut hormone, was lower and did not exhibit the premeal spike as observed in the controls. 4) neuropeptide Y (NPY), a potent orexigenic peptide, was markedly elevated and did not display any circadian variation. 5) Norepinephrine, marginally elevated, did not exhibit the normal nocturnal dip. By contrast, α-melanocyte-stimulating hormone and glucagon-like peptide-1 were not different between the two groups. Despite these hormonal abnormalities, HD patients maintained a good appetite and had normal body lean and fat mass, and there was no evidence of increased energy expenditure or protein catabolism. We explain the hormonal abnormalities as well as the absence of anorexia on suppression of parasympathetic activity (vagus nerve dysfunction), a phenomenon well documented in dialysis patients. Unexpectedly, we noted that the combination of high leptin, PYY, and NPY with suppressed ghrelin may increase arterial blood pressure, impair vasodilatation, and induce cardiac hypertrophy, and thus could predispose to adverse cardiovascular events that are the major causes of morbidity and mortality in the HD population. This is the first report attempting to link hormonal abnormalities associated with energy homeostasis to adverse cardiovascular outcome in the HD patients.

Up-regulation of NPY gene expression in hypothalamus of rats with experimental chronic renal failure

Anorexia is possibly one of the most important causes of malnutrition in uremic patients. The cause of this abnormality is still unknown. Considering that: (a) NPY is one of the most important stimulants of food intake; (b) eating is a central nervous system regulated process and (c) NPY is expressed in hypothalamus, we hypothesized that the decrease of NPY gene expression in the hypothalamus could be an important factor contributing to anorexia associated with uremic state. In contrast to the prediction, the results presented in this paper indicate that the NPY gene expression in the hypothalamus of chronic renal failure (CRF) rats was significantly higher than in the hypothalamus of control (pair-fed) rats. Moreover, we found that serum NPY concentration in CRF rats was higher than in control (pair-fed) animals. The increase of plasma NPY concentration in CRF rats may be due to the greater synthesis of the neuropeptide in liver, since higher level of NPY mRNA was found in liver of CRF rats. The results obtained revealed that experimental chronic renal failure is associated with the increase of NPY gene expression in hypothalamus and liver of rats.

Does Hemodialysis Increase Protein Breakdown? Dissociation between Whole-Body Amino Acid Turnover and Regional Muscle Kinetics

Hemodialysis (HD) is a protein catabolic procedure. Whole-body amino acid turnover studies identify dialysate amino acid loss and reduced protein synthesis as the catabolic events; proteolysis is not increased. Regional amino acid kinetics, however, document enhanced muscle protein breakdown as the cause of the catabolism; muscle protein synthesis also increased but to a lesser magnitude than the increment in protein breakdown. This discordance between whole-body and regional kinetics is best explained by the contrasting physiology between the muscle and the liver. During HD, muscle releases amino acids, which then are taken up by the liver for de novo protein synthesis. There seems to be a somatic to visceral recycling of amino acids. Evidence supporting this concept includes the increased fractional synthesis of albumin and fibrinogen during HD. It should be emphasized that region- or organ-specific kinetics vary, and whole-body turnover is a composite of all of the visceral and somatic compartments taken together. Reduced whole-body protein synthesis may be a compensatory adaptation to dialysate amino acid loss with a consequent reduction in plasma amino acid concentration. Notwithstanding the protein catabolic nature of HD, evidence is accumulating that intradialytic nutritional supplementation may blunt its catabolic effect.