Reduced cortisol metabolism during critical illness.

BACKGROUND: Critical illness is often accompanied by hypercortisolemia, which has been attributed to stress-induced activation of the hypothalamic-pituitary-adrenal axis. However, low corticotropin levels have also been reported in critically ill patients, which may be due to reduced cortisol metabolism. METHODS: In a total of 158 patients in the intensive care unit and 64 matched controls, we tested five aspects of cortisol metabolism: daily levels of corticotropin and cortisol; plasma cortisol clearance, metabolism, and production during infusion of deuterium-labeled steroid hormones as tracers; plasma clearance of 100 mg of hydrocortisone; levels of urinary cortisol metabolites; and levels of messenger RNA and protein in liver and adipose tissue, to assess major cortisol-metabolizing enzymes. RESULTS: Total and free circulating cortisol levels were consistently higher in the patients than in controls, whereas corticotropin levels were lower (P<0.001 for both comparisons). Cortisol production was 83% higher in the patients (P=0.02). There was a reduction of more than 50% in cortisol clearance during tracer infusion and after the administration of 100 mg of hydrocortisone in the patients (P≤0.03 for both comparisons). All these factors accounted for an increase by a factor of 3.5 in plasma cortisol levels in the patients, as compared with controls (P<0.001). Impaired cortisol clearance also correlated with a lower cortisol response to corticotropin stimulation. Reduced cortisol metabolism was associated with reduced inactivation of cortisol in the liver and kidney, as suggested by urinary steroid ratios, tracer kinetics, and assessment of liver-biopsy samples (P≤0.004 for all comparisons). CONCLUSIONS: During critical illness, reduced cortisol breakdown, related to suppressed expression and activity of cortisol-metabolizing enzymes, contributed to hypercortisolemia and hence corticotropin suppression. The diagnostic and therapeutic implications for critically ill patients are unknown. (Funded by the Belgian Fund for Scientific Research and others; ClinicalTrials.gov numbers, NCT00512122 and NCT00115479; and Current Controlled Trials numbers, ISRCTN49433936, ISRCTN49306926, and ISRCTN08083905.).

Withholding parenteral nutrition during critical illness increases plasma bilirubin but lowers the incidence of biliary sludge.

UNLABELLED: Cholestatic liver dysfunction (CLD) and biliary sludge often occur during critical illness and are allegedly aggravated by parenteral nutrition (PN). Delaying initiation of PN beyond day 7 in the intensive care unit (ICU) (late PN) accelerated recovery as compared with early initiation of PN (early PN). However, the impact of nutritional strategy on biliary sludge and CLD has not been fully characterized. This was a preplanned subanalysis of a large randomized controlled trial of early PN versus late PN (n = 4,640). In all patients plasma bilirubin (daily) and liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], gamma-glutamyl transpeptidase [GGT], alkaline phosphatase [ALP], twice weekly; n = 3,216) were quantified. In a random predefined subset of patients, plasma bile acids (BAs) were also quantified at baseline and on days 3, 5, and last ICU-day (n = 280). Biliary sludge was ultrasonographically evaluated on ICU-day 5 (n = 776). From day 1 after randomization until the end of the 7-day intervention window, bilirubin was higher in the late PN than in the early PN group (P < 0.001). In the late PN group, as soon as PN was started on day 8 bilirubin fell and the two groups became comparable. Maximum levels of GGT, ALP, and ALT were lower in the late PN group (P < 0.01). Glycine/taurine-conjugated primary BAs increased over time in ICU (P < 0.01), similarly for the two groups. Fewer patients in the late PN than in the early PN group developed biliary sludge on day 5 (37% versus 45%; P = 0.04). CONCLUSION: Tolerating substantial caloric deficit by withholding PN until day 8 of critical illness increased plasma bilirubin but reduced the occurrence of biliary sludge and lowered GGT, ALP, and ALT. These results suggest that hyperbilirubinemia during critical illness does not necessarily reflect cholestasis and instead may be an adaptive response that is suppressed by early PN.

Critical illness evokes elevated circulating bile acids related to altered hepatic transporter and nuclear receptor expression.

UNLABELLED: Hyperbilirubinemia is common during critical illness and is associated with adverse outcome. Whether hyperbilirubinemia reflects intensive care unit (ICU) cholestasis is unclear. Therefore, the aim of this study was to analyze hyperbilirubinemia in conjunction with serum bile acids (BAs) and the key steps in BA synthesis, transport, and regulation by nuclear receptors (NRs). Serum BA and bilirubin levels were determined in 130 ICU and 20 control patients. In liver biopsies messenger RNA (mRNA) expression of BA synthesis enzymes, BA transporters, and NRs was assessed. In a subset (40 ICU / 10 controls) immunohistochemical staining of the transporters and receptors together with a histological evaluation of cholestasis was performed. BA levels were much more elevated than bilirubin in ICU patients. Conjugated cholic acid (CA) and chenodeoxycholic acid (CDCA) were elevated, with an increased CA/CDCA ratio. Unconjugated BA did not differ between controls and patients. Despite elevated serum BA levels, CYP7A1 protein, the rate-limiting enzyme in BA synthesis, was not lowered in ICU patients. Also, protein expression of the apical bile salt export pump (BSEP) was decreased, whereas multidrug resistance-associated protein (MRP) 3 was strongly increased at the basolateral side. This reversal of BA transport toward the sinusoidal blood compartment is in line with the increased serum conjugated BA levels. Immunostaining showed marked down-regulation of nuclear farnesoid X receptor, retinoid X receptor alpha, constitutive androstane receptor, and pregnane X receptor nuclear protein levels. CONCLUSION: Failure to inhibit BA synthesis, up-regulate canalicular BA export, and localize pivotal NR in the hepatocytic nuclei may indicate dysfunctional feedback regulation by increased BA levels. Alternatively, critical illness may result in maintained BA synthesis (CYP7A1), reversal of normal BA transport (BSEP/MRP3), and inhibition of the BA sensor (FXR/RXRα) to increase serum BA levels.

Cholestatic liver (dys)function during sepsis and other critical illnesses.

OBJECTIVE: In ICU patients, abnormal liver tests are common. Markers of cholestasis are associated with adverse outcome. Research has focused on the possibility that mild hyperbilirubinemia, instead of indicating inadvertent cholestasis, may be adaptive and beneficial. These new insights are reviewed and integrated in the state-of-the-art knowledge on hepatobiliary alterations during sepsis and other critical illnesses. DATA SOURCES: Relevant publications were searched in Medline with search terms bile, bile acids, cholestasis, critical illness, intensive care, sepsis, alone or in combination. DATA SYNTHESIS: Studies have shown that bilirubin, but also bile acids, the main active constitutes of bile, are increased in plasma of patients with critical illnesses. In particular the conjugated fractions of bilirubin and bile acids are high, indicating that during critical illness the liver is capable of converting these molecules to less toxic forms. In human liver biopsies of prolonged critically ill patients, expression of bile acid excretion pumps towards the bile canaliculi was lower, while alternative transporters towards the systemic circulation were upregulated. Remarkably, in the presence of increased circulating bile acids, expression of enzymes controlling synthesis of bile acids was not suppressed. This suggested loss of feedback inhibition of bile acids synthesis, possibly explained by the observed cytoplasmic retention of the nuclear FXR/RXR heterodimer. As macronutrient restriction during acute critical illness, an intervention that improved outcome, was found to further increase plasma bilirubin while reducing other markers of cholestasis, a potentially protective role of hyperbilirubinemia was suggested. CONCLUSION: The increase in circulating levels of conjugated bile acids and bilirubin in response to acute sepsis/critical illnesses may not necessarily point to cholestasis as a pathophysiological entity. Instead it may be the result of an adaptively altered bile acid production and transport back towards the systemic circulation. How these changes could be beneficial for survival should be further investigated.

Impact of parenteral nutrition versus fasting on hepatic bile acid production and transport in a rabbit model of prolonged critical illness.

BACKGROUND: Cholestatic liver dysfunction frequently occurs during critical illness. Administration of parenteral nutrition (PN) is thought to aggravate this. Underlying mechanisms are not clear. METHODS: In a burn model of prolonged critical illness, rabbits were randomized to a nutritional strategy either accepting caloric deficits (fasted, n = 11) or covering caloric needs by PN (fed, n = 10). At baseline and after 7 days of critical illness, markers of hepatotoxicity, circulating bile acids, and the hepatobiliary transport system were studied. RESULTS: Fasted animals had lower circulating alanine aminotransferase/aspartate aminotransferase levels than did the fed animals at day 7. Compared with baseline values, fed animals displayed lower serum unconjugated cholic acid (CA) and deoxycholic acid (DCA) levels. Unconjugated DCA remained unaltered in fasted animals. Unconjugated lithocholic acid was increased comparably in all animals, whereas hyodeoxycholic acid was not altered. In contrast, fasting induced a shift from unconjugated CA and DCA to glyco-CA and glyco-DCA. Total bile acids did not correlate with the bile acid-producing enzyme CYP7A1, but with the basolateral efflux transporter MRP3. Fasting increased protein expression of the basolateral (MRP3) and the canalicular (BSEP) transporter, whereas the canalicular efflux pump MRP2 was suppressed. Gene expression levels of the nuclear receptor farnesoid X receptor were lower with fasting and correlated inversely with MRP3. The heterodimer partner of farnesoid X receptor, retinoid X receptor α, was increased with fasting and correlated positively with MRP3. CONCLUSIONS: During prolonged critical illness, withholding PN improved markers for hepatocyte injury and accentuated bile acid transport toward the blood. This suggests that the latter is an adaptive rather than a dysfunctional feedback to illness.

Contribution of nutritional deficit to the pathogenesis of the nonthyroidal illness syndrome in critical illness: a rabbit model study.

Both starvation and critical illness are hallmarked by changes in circulating thyroid hormone parameters with typically low T(3) concentrations in the absence of elevated TSH. This constellation is labeled nonthyroidal illness (NTI). Because critical illness is often accompanied by anorexia and a failing gastrointestinal tract, the NTI of critical illness may be confounded by nutrient deficiency. In an experimental study performed in a rabbit model, we investigated the impact of nutritional deficit on the NTI of sustained critical illness. Critically ill rabbits were randomly allocated to parenteral nutrition (moderate dose 270 kcal/d) initiated on the day after injury and continued until d 7 of illness or to infusing a similar volume of dextrose 1.4% (14 kcal/d). With early parenteral nutrition during illness, the decrease in serum T(3) observed with fasting was reversed, whereas the fall in T(4) was not significantly affected. The rise in T(3) with parenteral nutrition paralleled an increase of liver and kidney type-1 and a decrease of liver and kidney type-3 deiodinase activity and an increase in circulating and central leptin. Nuclear staining of constitutive androstane receptor and its downstream expression of sulfotransferases were reduced in fasting ill animals. TRH expression in the hypothalamus was not different in fasted and fed ill rabbits, although circulating TSH levels were higher with feeding. In conclusion, in this rabbit model of sustained critical illness, reduced circulating T(3), but not T(4), levels could be prevented by parenteral nutrition, which may be mediated by leptin and its actions on tissue deiodinase activity.