Periodic Reporting for period 4 - FitteR-CATABOLIC (Survival of the Fittest: On how to enhance recovery from critical illness through learning from evolutionary conserved catabolic pathways)
Periodo di rendicontazione: 2023-04-01 al 2024-03-31
Critically ill patients suffer from life-threatening conditions such as severe trauma, infections, or major/complicated surgeries. Modern intensive care medicine bridges these patients to recovery with use of mechanical devices, vasoactive drugs and powerful anti-microbial agents. By postponing death, a new unnatural condition, intensive-care-dependent prolonged critical illness, has been created. About 25% of ICU patients today require prolonged intensive care, sometimes for weeks or months, and these patients are at high risk of death while consuming 75% of resources. Even when the primary insult has been adequately dealt with, many long-stay ICU patients typically suffer from hypercatabolism, ICU-acquired brain dysfunction and polyneuropathy/myopathy leading to severe muscle weakness, further increasing the risk of late death.
As hypercatabolism was considered the culprit, several anabolic interventions were tested, but these showed harm instead of benefit. We previously showed that fasting early during illness is superior to forceful feeding, pointing to certain benefits of catabolic responses. In healthy humans, fasting activates catabolism to provide substrates essential to protect and maintain brain and muscle function. In addition, we recently found that patients and experimental animals who were overweight or obese prior to becoming critically ill were strikingly protected against muscle wasting and weakness during illness, irrespective of whether they received nutrition or were fasted. Furthermore, this protection coincided with a more effective utilization of stored lipids and with substantially increased ketogenesis, again irrespective of whether being fed or fasted. Such activated lipolysis and ketogenesis even in the fed critically ill state, mimics part of a normal fasting response and may thus play a key role. The general aim of this project was to investigate whether evolutionary conserved catabolic pathways such as lipolysis and ketogenesis can be exploited in the search for prevention of brain dysfunction and muscle weakness in the critically ill patient, with the aim to identify a novel metabolic intervention that can effectively improve recovery from prolonged critical illness.
In obese mice, increased lipolysis with increased ketogenesis was indeed largely explaining the muscle protection. Ketogenic (high lipid content) parenteral nutrition could increase ketosis but at a cost of liver steatosis. Importantly, exogenous administration of the ketone body 3-hydroxybutyrate significantly and safely attenuated the development of muscle weakness in critically ill mice.
We also documented that early reduced caloric intake by withholding parenteral nutrition in critically ill children significantly increased circulating ketones, a direct effect that statistically mediated an important part of its outcome benefit. However, although withholding parenteral nutrition also induced ketosis in critically ill adults, the rise in ketones was much smaller than in children.
Dose-response and toxicity studies performed in our mouse model revealed that ketone esters are superior to ketone salts, with a broader therapeutic window. The efficacy and safety of ketone ester administration in critically ill patients is currently being investigated in a clinical trial.
As hypercatabolism was considered the culprit, several anabolic interventions were tested, but these showed harm instead of benefit. We previously showed that fasting early during illness is superior to forceful feeding, pointing to certain benefits of catabolic responses. In healthy humans, fasting activates catabolism to provide substrates essential to protect and maintain brain and muscle function. In addition, we recently found that patients and experimental animals who were overweight or obese prior to becoming critically ill were strikingly protected against muscle wasting and weakness during illness, irrespective of whether they received nutrition or were fasted. Furthermore, this protection coincided with a more effective utilization of stored lipids and with substantially increased ketogenesis, again irrespective of whether being fed or fasted. Such activated lipolysis and ketogenesis even in the fed critically ill state, mimics part of a normal fasting response and may thus play a key role. The general aim of this project was to investigate whether evolutionary conserved catabolic pathways such as lipolysis and ketogenesis can be exploited in the search for prevention of brain dysfunction and muscle weakness in the critically ill patient, with the aim to identify a novel metabolic intervention that can effectively improve recovery from prolonged critical illness.
In obese mice, increased lipolysis with increased ketogenesis was indeed largely explaining the muscle protection. Ketogenic (high lipid content) parenteral nutrition could increase ketosis but at a cost of liver steatosis. Importantly, exogenous administration of the ketone body 3-hydroxybutyrate significantly and safely attenuated the development of muscle weakness in critically ill mice.
We also documented that early reduced caloric intake by withholding parenteral nutrition in critically ill children significantly increased circulating ketones, a direct effect that statistically mediated an important part of its outcome benefit. However, although withholding parenteral nutrition also induced ketosis in critically ill adults, the rise in ketones was much smaller than in children.
Dose-response and toxicity studies performed in our mouse model revealed that ketone esters are superior to ketone salts, with a broader therapeutic window. The efficacy and safety of ketone ester administration in critically ill patients is currently being investigated in a clinical trial.
In the first objective, we aimed to study the underlying mechanisms through which obese patients are protected during critical illness. Obesity-induced muscle protection during sepsis appeared partly mediated by elevated mobilization and metabolism of endogenous fatty acids. Leptin did not mediate the protective effect of obesity. Instead, obesity—independently of leptin—attenuated inflammation, protein catabolism, and dyslipidaemia, pathways that may play a role in the observed muscle protection. Furthermore, increased availability of ketone bodies, either via activating ketogenesis or via parenteral infusion, protected against sepsis-induced muscle weakness also in lean mice. The impact on brain damage is still under investigation.
In the second objective, we aimed to investigate whether ketone bodies could act as superior energy substrates or whether ketone bodies play a role as signaling molecules during critical illness. Neither the supplementation of parenteral nutrition with 3-hydroxybutyrate nor the infusion of high lipid doses in lean septic mice could replicate the observed obesity-induced protection against muscle wasting. This suggests that the preservation of muscle mass in the overweight/obese is likely related to other pathways. Supplemented ketones appeared to function as signaling molecules rather than energy substrates and increased markers of muscle regeneration. Furthermore, tracer technology revealed that 3-hydroxybutyrate was preferentially taken up by muscle and metabolized into the cholesterol precursor mevalonate, rather than TCA metabolites. Exogenous 3-hydroxybutyrate increased plasma cholesterol and altered cholesterol homeostasis resulting in increased myofiber cholesterol content. Furthermore, circulating cholesterol levels were lower in weak than in non-weak critically ill patients, and in multivariable analysis adjusting for baseline risk factors, circulating cholesterol was inversely correlated with weakness.
In the third objective, we aimed to investigate to what extent ketogenesis can be increased during human critical illness by macronutrient restriction (accepting virtual fasting) when blood glucose is also lowered to normal fasting ranges and to what extent ketogenesis explains the beneficial effects of these interventions. We could demonstrate that macronutrient restriction during the first week of critical illness, indeed moderately increased ketogenesis, more so in critically ill children than in adults, and that this increase in circulating ketone levels partly explained the outcome benefit of macronutrient restriction in children, but not in adults. In contrast, in the fully fed state, lowering blood glucose levels into healthy fasting ranges in critically ill adults and children did not affect ketone levels. In a virtually fasted state brought about by not using parenteral nutrition for up to one week in the ICU, lowering blood glucose levels did not affect mortality, but reduced kidney and liver dysfunction. Whether ketones play a role in this morbidity benefit is currently still under investigation.
In the fourth objective, we aimed to test the therapeutic potential of increased ketone body availability for human critical illness. In the mouse model, exogenous administration of 3-hydroxybutyrate, administered as a sodium salt or as a ketone ester, significantly attenuated the development of muscle weakness. Subsequent dose-response and toxicity studies revealed that ketone esters are superior to ketone salts, with a broader therapeutic window. The efficacy and safety of ketone ester administration in critically ill patients is currently being investigated in an ongoing clinical trial.
In the second objective, we aimed to investigate whether ketone bodies could act as superior energy substrates or whether ketone bodies play a role as signaling molecules during critical illness. Neither the supplementation of parenteral nutrition with 3-hydroxybutyrate nor the infusion of high lipid doses in lean septic mice could replicate the observed obesity-induced protection against muscle wasting. This suggests that the preservation of muscle mass in the overweight/obese is likely related to other pathways. Supplemented ketones appeared to function as signaling molecules rather than energy substrates and increased markers of muscle regeneration. Furthermore, tracer technology revealed that 3-hydroxybutyrate was preferentially taken up by muscle and metabolized into the cholesterol precursor mevalonate, rather than TCA metabolites. Exogenous 3-hydroxybutyrate increased plasma cholesterol and altered cholesterol homeostasis resulting in increased myofiber cholesterol content. Furthermore, circulating cholesterol levels were lower in weak than in non-weak critically ill patients, and in multivariable analysis adjusting for baseline risk factors, circulating cholesterol was inversely correlated with weakness.
In the third objective, we aimed to investigate to what extent ketogenesis can be increased during human critical illness by macronutrient restriction (accepting virtual fasting) when blood glucose is also lowered to normal fasting ranges and to what extent ketogenesis explains the beneficial effects of these interventions. We could demonstrate that macronutrient restriction during the first week of critical illness, indeed moderately increased ketogenesis, more so in critically ill children than in adults, and that this increase in circulating ketone levels partly explained the outcome benefit of macronutrient restriction in children, but not in adults. In contrast, in the fully fed state, lowering blood glucose levels into healthy fasting ranges in critically ill adults and children did not affect ketone levels. In a virtually fasted state brought about by not using parenteral nutrition for up to one week in the ICU, lowering blood glucose levels did not affect mortality, but reduced kidney and liver dysfunction. Whether ketones play a role in this morbidity benefit is currently still under investigation.
In the fourth objective, we aimed to test the therapeutic potential of increased ketone body availability for human critical illness. In the mouse model, exogenous administration of 3-hydroxybutyrate, administered as a sodium salt or as a ketone ester, significantly attenuated the development of muscle weakness. Subsequent dose-response and toxicity studies revealed that ketone esters are superior to ketone salts, with a broader therapeutic window. The efficacy and safety of ketone ester administration in critically ill patients is currently being investigated in an ongoing clinical trial.
The project was able to fully close the “translational loop”, starting from a controversial idea, over testing the “why” and the “how” in a clinically relevant in vivo animal model, all the way to a randomized controlled clinical trial that is testing a newly identified metabolic intervention for efficacy and safety in the real-life clinical ICU setting, with the ambition to change practice.