Regulation of ketone body flux in septic patients

Metabolism as Disease Tolerance: Implications for Sepsis-Associated Acute Kidney Injury

Sepsis is a significant cause for mortality among critically ill patients. Metabolic derangements that develop in sepsis are often considered to be pathologic, contributing to sepsis morbidity and mortality. However, alterations in metabolism during sepsis are multifaceted and are incompletely understood. Acute anorexia during infection is an evolutionarily conserved response, suggesting a potential protective role of anorexia in the host response to infection. In animal models of bacterial inflammation, fasting metabolic programs associated with acute anorexia such as those regulated by fibroblast growth factor 21 and ketogenesis are associated with improved survival. Other fasting metabolic pathways such as fatty acid oxidation and autophagy are also implicated in preventing acute kidney injury (AKI). Global metabolic changes during sepsis and current clinical interventions can potentially affect disease tolerance mechanisms and modify the risk of AKI.

Impact of tight glucose control on circulating 3-hydroxybutyrate in critically ill patients

BACKGROUND

Recent evidence suggests a potentially protective effect of increasing ketone body availability via accepting low macronutrient intake early after onset of critical illness. The impact of blood glucose control with insulin on circulating ketones is unclear. Whereas lowering blood glucose may activate ketogenesis, high insulin concentrations may have the opposite effect. We hypothesized that the previously reported protective effects of tight glucose control in critically ill patients receiving early parenteral nutrition may have been mediated in part by activation of ketogenesis.

METHODS

This is a secondary analysis of 3 randomized controlled trials on tight versus liberal blood glucose control in the intensive care unit, including 700 critically ill children and 2748 critically ill adults. All patients received early parenteral nutrition as part of the contemporary standard of care. Before studying a potential mediator role of circulating ketones in improving outcome, we performed a time course analysis to investigate whether tight glucose control significantly affected ketogenesis and to identify a day of maximal effect, if any. We quantified plasma/serum 3-hydroxybutyrate concentrations from intensive care unit admission until day 3 in 2 matched subsets of 100 critically ill children and 100 critically ill adults. Univariable differences between groups were investigated by Kruskal-Wallis test. Differences in 3-hydroxybutyrate concentrations between study days were investigated by Wilcoxon signed-rank test.

RESULTS

In critically ill children and adults receiving early parenteral nutrition, tight glucose control, as compared with liberal glucose control, lowered mean morning blood glucose on days 1-3 (P < 0.0001) via infusing insulin at a higher dose (P < 0.0001). Throughout the study period, caloric intake was not different between groups. In both children and adults, tight glucose control did not affect 3-hydroxybutyrate concentrations, which were suppressed on ICU days 1-3 and significantly lower than the ICU admission values for both groups (P < 0.0001).

CONCLUSION

Tight versus liberal glucose control in the context of early parenteral nutrition did not affect 3-hydroxybutyrate concentrations in critically ill patients. Hence, the protective effects of tight glucose control in this context cannot be attributed to increased ketone body availability.

Effect of withholding early parenteral nutrition in PICU on ketogenesis as potential mediator of its outcome benefit

Background

In critically ill children, omitting early use of parenteral nutrition (late-PN versus early-PN) reduced infections, accelerated weaning from mechanical ventilation, and shortened PICU stay. We hypothesized that fasting-induced ketogenesis mediates these benefits.

Methods

In a secondary analysis of the PEPaNIC RCT (N = 1440), the impact of late-PN versus early-PN on plasma 3-hydroxybutyrate (3HB), and on blood glucose, plasma insulin, and glucagon as key ketogenesis regulators, was determined for 96 matched patients staying ≥ 5 days in PICU, and the day of maximal 3HB-effect, if any, was identified. Subsequently, in the total study population, plasma 3HB and late-PN-affected ketogenesis regulators were measured on that average day of maximal 3HB effect. Multivariable Cox proportional hazard and logistic regression analyses were performed adjusting for randomization and baseline risk factors. Whether any potential mediator role for 3HB was direct or indirect was assessed by further adjusting for ketogenesis regulators.

Results

In the matched cohort (n = 96), late-PN versus early-PN increased plasma 3HB throughout PICU days 1–5 (P < 0.0001), maximally on PICU day 2. Also, blood glucose (P < 0.001) and plasma insulin (P < 0.0001), but not glucagon, were affected. In the total cohort (n = 1142 with available plasma), late-PN increased plasma 3HB on PICU day 2 (day 1 for shorter stayers) from (median [IQR]) 0.04 [0.04–0.04] mmol/L to 0.75 [0.04–2.03] mmol/L (P < 0.0001). The 3HB effect of late-PN statistically explained its impact on weaning from mechanical ventilation (P = 0.0002) and on time to live PICU discharge (P = 0.004). Further adjustment for regulators of ketogenesis did not alter these findings.

Conclusion

Withholding early-PN in critically ill children significantly increased plasma 3HB, a direct effect that statistically mediated an important part of its outcome benefit.

Lipid testing in infectious diseases: possible role in diagnosis and prognosis

INTRODUCTION

Acute infections lead to significant alterations in metabolic regulation including lipids and lipoproteins, which play a central role in the host immune response. In this regard, several studies have investigated the role of lipid levels as a marker of infection severity and prognosis.

SCOPE OF REVIEW

We review here the role of lipids in immune response and the potential mechanisms underneath. Moreover, we summarize studies on lipid and lipoprotein alterations in acute bacterial, viral and parasitic infections as well as their diagnostic and prognostic significance. Chronic infections (HIV, HBV, HCV) are also considered.

RESULTS

All lipid parameters have been found to be significantly dearranged during acute infection. Common lipid alterations in this setting include a decrease of total cholesterol levels and an increase in the concentration of triglyceride-rich lipoproteins, mainly very low-density lipoproteins. Also, low-density lipoprotein cholesterol, apolipoprotein A1, low-density lipoprotein cholesterol and apolipoprotein-B levels decrease. These lipid alterations may have prognostic and diagnostic role in certain infections.

CONCLUSION

Lipid testing may be of help to assess response to treatment in septic patients and those with various acute infections (such as pneumonia, leptospirosis and others). Diagnostically, new onset of altered lipid levels should prompt the clinician to test for underlying infection (such as leishmaniasis).

Influence of Glycemic Control on Endogenous Circulating Ketone Concentrations in Adults Following Traumatic Brain Injury

BACKGROUND

The objective was to investigate the impact of targeting tight glycemic control (4.4-6.1 mM) on endogenous ketogenesis in severely head-injured adults.

METHODS

The data were prospectively collected during a randomized, within-patient crossover study comparing tight to loose glycemic control, defined as 6.7-8.3 mM. Blood was collected periodically during both tight and loose glycemic control epochs. Post hoc analysis of insulin dose and total nutritional provision was performed.

RESULTS

Fifteen patients completed the crossover study. Total ketones were increased 81 μM ([38 135], p < 0.001) when blood glucose was targeted to tight (4.4-6.1 mM) compared with loose glycemic control (6.7-8.3 mM), corresponding to a 60 % increase. There was a significant decrease in total nutritional provisions (p = 0.006) and a significant increase in insulin dose (p = 0.008).

CONCLUSIONS

Permissive underfeeding was tolerated when targeting tight glycemic control, but total nutritional support is an important factor when treating hyperglycemia.

N-3 Polyunsaturated Fatty Acids Improve Liver Lipid Oxidation-Related Enzyme Levels and Increased the Peroxisome Proliferator-Activated Receptor α Expression Level in Mice Subjected to Hemorrhagic Shock/Resuscitation

Appropriate metabolic interventions after hemorrhagic shock/resuscitation injury have not yet been identified. We aimed to examine the effects of fish oil on lipid metabolic intervention after hemorrhagic shock/resuscitation. Firstly, 48 C57BL/6 mice were assigned to six groups (n = 8 per group). The sham group did not undergo surgery, while mice in the remaining groups were sacrificed 1–5 days after hemorrhagic shock/resuscitation. In the second part, mice were treated with saline or fish oil (n = 8 per group) five days after injury. We determined serum triglyceride levels and liver tissues were collected and prepared for qRT-PCR or Western blot analysis. We found that triglyceride levels were increased five days after hemorrhagic shock/resuscitation, but decreased after addition of fish oil. After injury, the protein and gene expression of carnitine palmitoyltransferase 1A, fatty acid transport protein 1, and peroxisome proliferator-activated receptor-α decreased significantly in liver tissue. In contrast, after treatment with fish oil, the expression levels of these targets increased compared with those in the saline group. The present results suggest n-3 polyunsaturated fatty acids could improve lipid oxidation-related enzymes in liver subjected to hemorrhagic shock/resuscitation. This function is possibly accomplished through activating the peroxisome proliferator-activated receptor-α pathway.

LPS decreases fatty acid oxidation and nuclear hormone receptors in the kidney

Inflammation produces marked changes in lipid metabolism, including increased serum fatty acids (FAs) and triglycerides (TGs), increased hepatic TG production and VLDL secretion, increased adipose tissue lipolysis, and decreased FA oxidation in liver and heart. Lipopolysaccharide (LPS) also increases TG and cholesteryl ester levels in kidneys. Here we confirm these findings and define potential mechanisms. LPS decreases renal FA oxidation by 40% and the expression of key proteins required for oxidation of FAs, including FA transport protein-2, fatty acyl-CoA synthase, carnitine palmitoyltransferase-1, medium-chain acyl-CoA dehydrogenase, and acyl-CoA oxidase. Similar decreases were observed in peroxisome proliferator-activated receptor alpha (PPARalpha)-deficient mice. LPS also caused a reduction in renal mRNA levels of PPARalpha (75% decrease), thyroid hormone receptor alpha (TRalpha) (92% decrease), and TRbeta (84% decrease), whereas PPARbeta/delta and gamma were not altered. Expression of PGC1 alpha and beta, coactivators required for PPARs and TR, was also decreased in kidneys of LPS-treated mice, as were mitochondrial genes regulated by PGC1 (Atp5g1, COX5a, Idh3a, and Ndufs8). Decreased renal FA oxidation could be a by-product of the systemic coordinated host response to increase FAs and TGs available for host defense and/or tissue repair. However, the kidney requires energy to support its transport functions, and the inability to generate energy via FA oxidation might contribute to the renal failure seen in severe sepsis.