Insufficient autophagy contributes to mitochondrial dysfunction, organ failure, and adverse outcome in an animal model of critical illness.

OBJECTIVE: Increasing evidence implicates mitochondrial dysfunction as an early, important event in the pathogenesis of critical illness-induced multiple organ failure. We previously demonstrated that prevention of hyperglycemia limits damage to mitochondria in vital organs, thereby reducing morbidity and mortality. We now hypothesize that inadequate activation of mitochondrial repair processes (clearance of damaged mitochondria by autophagy, mitochondrial fusion/fission, and biogenesis) may contribute to accumulation of mitochondrial damage, persistence of organ failure, and adverse outcome of critical illness. DESIGN: Prospective, randomized studies in a critically ill rabbit model. SETTING: University laboratory. SUBJECTS: Three-month-old male rabbits. INTERVENTIONS: We studied whether vital organ mitochondrial repair pathways are differentially affected in surviving and nonsurviving hyperglycemic critically ill animals in relation to mitochondrial and organ damage. Next, we investigated the impact of preventing hyperglycemia over time and of administering rapamycin as an autophagy activator. MEASUREMENTS AND MAIN RESULTS: In both liver and kidney of hyperglycemic critically ill rabbits, we observed signs of insufficient autophagy, including accumulation of p62 and a concomitant decrease in the microtubule-associated protein light-chain-3-II/microtubule-associated protein light-chain-3-I ratio. The phenotype of insufficient autophagy was more pronounced in nonsurviving than in surviving animals. Molecular markers of insufficient autophagy correlated with impaired mitochondrial function and more severe organ damage. In contrast, key players in mitochondrial fusion/fission or biogenesis were not significantly different regarding survival status. Therefore, we focused on autophagy to study the impact of preventing hyperglycemia. Both after 3 and 7 days of illness, autophagy was better preserved in normoglycemic than in hyperglycemic rabbits, which correlated with improved mitochondrial function and less organ damage. Stimulation of autophagy in kidney with rapamycin correlated with protection of renal function. CONCLUSIONS: Our findings put forward insufficient autophagy as a potentially important contributor to mitochondrial and organ damage in critical illness and open perspectives for therapies that activate autophagy during critical illness.

Increasing intravenous glucose load in the presence of normoglycemia: effect on outcome and metabolism in critically ill rabbits.

OBJECTIVES: Endocrine disturbances and a feeding-resistant wasting syndrome, characterized by a negative protein balance, promote delayed recovery and poor outcome of critical illness. Parenteral nutrition alone cannot counteract the hypercatabolic state, possibly in part as a result of aggravation of the hyperglycemic response to illness. In critically ill rabbits, we investigated the impact of varying amounts of intravenous glucose while maintaining normoglycemia on mortality, organ damage, and markers of catabolism/anabolism. DESIGN: Prospective, randomized laboratory investigation. SETTING: University animal and molecular laboratory. SUBJECTS: Three-month-old male rabbits. INTERVENTIONS: Critically ill rabbits were randomized into a fasting group, a standard parenteral nutrition group, and two groups receiving either intermediate or high additional physiological amounts of intravenous glucose while maintained normoglycemic with insulin. These groups were compared with a hyperglycemic group and healthy rabbits. Protein and lipid load was equal for all fed groups. MEASUREMENTS AND MAIN RESULTS: Varying intravenous glucose load did not affect mortality or organ damage provided hyperglycemia was prevented. Fasted critically ill rabbits lost weight, which was attenuated by increasing intravenous glucose load. As compared with healthy rabbits, mRNA expression and/or activity of several ubiquitin-proteasome pathway components, cathepsin-L and calpain-1, was elevated in skeletal muscle of fasted critically ill rabbits. Intravenous feeding was able to counteract this response. Excessive glucose load and/or hyperglycemia, however, reduced the protective effect of feeding. Genes investigated in the diaphragm and myocardium revealed roughly a similar response. Except in the normoglycemic group with intermediate glucose load, circulating thyroid hormone and insulin-like growth factor-1 levels decreased, most pronounced in hyperglycemic rabbits. CONCLUSIONS: Increasing intravenous glucose infusion within the physiological range, while maintaining normoglycemia, was safe for organ function and survival of critically ill rabbits. Concomitantly, it reduced the catabolic responses as compared with fasting. Whether this has a beneficial effect on muscle function and mass remains to be investigated.

Changes in the central component of the hypothalamus-pituitary-thyroid axis in a rabbit model of prolonged critical illness.

INTRODUCTION: Prolonged critically ill patients reveal low circulating thyroid hormone levels without a rise in thyroid stimulating hormone (TSH). This condition is labeled "low 3,5,3'-tri-iodothyronine (T3) syndrome" or "nonthyroidal illness syndrome (NTI)" or "euthyroid sick syndrome". Despite the low circulating and peripheral tissue thyroid hormone levels, thyrotropin releasing hormone (TRH) expression in the hypothalamus is reduced and it remains unclear which mechanism is responsible. We set out to study whether increased hypothalamic T3 availability could reflect local thyrotoxicosis and explain feedback inhibition-induced suppression of the TRH gene in the context of the low T3 syndrome in prolonged critical illness. METHODS: Healthy rabbits were compared with prolonged critically ill, parenterally fed animals. We visualized TRH mRNA in the hypothalamus by in situ-hybridization and measured mRNA levels for the type II iodothyronine diodinase (D2), the thyroid hormone transporters monocarboxylate transporter (MCT) 8, MCT10 and organic anion co-transporting polypeptide 1C1 (OATP1C1) and the thyroid hormone receptors alpha (TRalpha) and beta (TRbeta) in the hypothalamus. We also measured the activity of the D2 and type III iodothyronine deiodinase (D3) enzymes. RESULTS: In the hypothalamus of prolonged critically ill rabbits with low circulating T3 and TSH, we observed decreased TRH mRNA, increased D2 mRNA and increased MCT10 and OATP1C1 mRNA while MCT8 gene expression was unaltered as compared with healthy controls. This coincided with low hypothalamic thyroxine (T4) and low-normal T3 concentrations, without a change at the thyroid hormone receptor level. CONCLUSIONS: Although expression of D2 and of the thyroid hormone transporters MCT10 and OATP1C1 were increased in the hypothalamus of prolonged critical ill animals, hypothalamic T4 and T3 content or thyroid hormone receptor expression were not elevated. Hence, decreased TRH gene expression, and hereby low TSH and T3 during prolonged critical illness, is not exclusively brought about by hypothalamic thyrotoxicosis, and infer other TRH suppressing factors to play a role.

Early parenteral nutrition evokes a phenotype of autophagy deficiency in liver and skeletal muscle of critically ill rabbits.

Muscular and hepatic abnormalities observed in artificially fed critically ill patients strikingly resemble the phenotype of autophagy-deficient mice. Autophagy is the only pathway to clear damaged organelles and large ubiquitinated proteins and aggregates. Fasting is its strongest physiological trigger. Severity of autophagy deficiency in critically ill patients correlated with the amount of infused amino acids. We hypothesized that impaired autophagy in critically ill patients could partly be evoked by early provision of parenteral nutrition enriched with amino acids in clinically used amounts. In a randomized laboratory investigation, we compared the effect of isocaloric moderate-dose iv feeding with fasting during illness on the previously studied markers of autophagy deficiency in skeletal muscle and liver. Critically ill rabbits were allocated to fasting or to iv nutrition (220 kcal/d, 921 kJ/d) supplemented with 50 kcal/d (209 kJ/d) of either glucose, amino acids, or lipids, while maintaining normoglycemia, and were compared with healthy controls. Fasted critically ill rabbits revealed weight loss and activation of autophagy. Feeding abolished these responses, with most impact of amino acid-enriched nutrition. Accumulation of p62 and ubiquitinated proteins in muscle and liver, indicative of insufficient autophagy, occurred with parenteral feeding enriched with amino acids and lipids. In liver, this was accompanied by fewer autophagosomes, fewer intact mitochondria, suppressed respiratory chain activity, and an increase in markers of liver damage. In muscle, early parenteral nutrition enriched with amino acids or lipids aggravated vacuolization of myofibers. In conclusion, early parenteral nutrition during critical illness evoked a phenotype of autophagy deficiency in liver and skeletal muscle.