Autophagy--A free meal in sickness-associated anorexia

Starvation and infection: The role of sickness-associated anorexia in metabolic adaptation during acute infection

Sickness-associated anorexia, the reduction in appetite seen during infection, is a widely conserved and well-recognized symptom of acute infection, yet there is very little understanding of its functional role in recovery. Anorexic sickness behaviours can be understood as an evolutionary strategy to increase tolerance to pathogen-mediated illness. In this review we explore the evidence for mechanisms and potential metabolic benefits of sickness-associated anorexia. Energy intake can impact on the immune response, control of inflammation and tissue stress, and on pathogen fitness. Fasting mediators including hormone-sensitive lipase, peroxisome proliferator-activated receptor-alpha (PPAR-α) and ketone bodies are potential facilitators of infection recovery through multiple pathways including suppression of inflammation, adaptation to lipid utilising pathways, and resistance to pathogen-induced cellular stress. However, the effect and benefit of calorie restriction is highly heterogeneous depending on both the infection and the metabolic status of the host, which has implications regarding clinical recommendations for feeding during different infections.

Eating in a losing cause: limited benefit of modified macronutrient consumption following infection in the oriental cockroach Blatta orientalis

BACKGROUND

Host-pathogen interactions can lead to dramatic changes in host feeding behaviour. One aspect of this includes self-medication, where infected individuals consume substances such as toxins or alter their macronutrient consumption to enhance immune competence. Another widely adopted animal response to infection is illness-induced anorexia, which is thought to assist host immunity directly or by limiting the nutritional resources available to pathogens. Here, we recorded macronutrient preferences of the global pest cockroach, Blatta orientalis to investigate how shifts in host macronutrient dietary preference and quantity of carbohydrate (C) and protein (P) interact with immunity following bacterial infection.

RESULTS

We find that B. orientalis avoids diets enriched for P under normal conditions, and that high P diets reduce cockroach survival in the long term. However, following bacterial challenge, cockroaches significantly reduced their overall nutrient intake, particularly of carbohydrates, and increased the relative ratio of protein (P:C) consumed. Surprisingly, these behavioural shifts had a limited effect on cockroach immunity and survival, with minor changes to immune protein abundance and antimicrobial activity between individuals placed on different diets, regardless of infection status.

CONCLUSIONS

We show that cockroach feeding behaviour can be modulated by a pathogen, resulting in an illness-induced anorexia-like feeding response and a shift from a C-enriched to a more P:C equal diet. However, our results also indicate that such responses do not provide significant immune protection in B. orientalis, suggesting that the host's dietary shift might also result from random rather than directed behaviour. The lack of an apparent benefit of the shift in feeding behaviour highlights a possible reduced importance of diet in immune regulation in these invasive animals, although further investigations employing pathogens with alternative infection strategies are warranted.

Metabolic regulation in the immune response to cancer

Metabolic reprogramming in tumor‐immune interactions is emerging as a key factor affecting pro‐inflammatory carcinogenic effects and anticancer immune responses. Therefore, dysregulated metabolites and their regulators affect both cancer progression and therapeutic response. Here, we describe the molecular mechanisms through which microenvironmental, systemic, and microbial metabolites potentially influence the host immune response to mediate malignant progression and therapeutic intervention. We summarized the primary interplaying factors that constitute metabolism, immunological reactions, and cancer with a focus on mechanistic aspects. Finally, we discussed the possibility of metabolic interventions at multiple levels to enhance the efficacy of immunotherapeutic and conventional approaches for future anticancer treatments.

Restoring Good Health in Elderly with Diverse Gut Microbiome and Food Intake Restriction to Combat COVID-19

COVID-19 continues to be an ongoing global threat. The elderly with underlying health conditions like cardiovascular and lung diseases, diabetes, obesity, are the most vulnerable to this disease. Curing the pre-existing health conditions will greatly increase a person's resilience to COVID-19 and lower the death rate of the old people. Digestion and immunity form an integrated nutrition acquisition process, especially in obtaining essential amino acids and essential fatty acids from living microbial cells. A mature strong immunity coupled with gut dysbiosis in adults is the main cause of nutritional disorders like morbid obesity, diabetes mellitus, cardiovascular and pulmonary diseases. Nutrition disorders in return worsen dysbiosis. Human microbiome has an intrinsic duality. While a diverse microbiome provides a full spectrum of essential nutrients to our body, nutrition disorders fuel overgrowth of microbiota (dysbiosis) at many sites on or inside our body, and are the main causes of chronic inflammation at these sites. In the case of COVID-19, nutritional disorder impairs the immunity, causes hyperinflammation, and leads to the protracted overload of cytokines by the immune system, i.e., the cytokine storm. Autophagy induced by restrictive eating is an ideal inhibitor of microbiota overgrowth, as autophagy deprives microbiota of excessive nutrition for replication. Autophagy also attenuates inflammation. Therefore, as a precaution, the author suggests restoring good health in the elderly with the support from a diverse gut microbiome and daily regular food intake restriction, so as to lower the risk of developing into severe case even if they are infected by COVID-19.

Association of Diabetes and Admission Blood Glucose Levels with Short-Term Outcomes in Patients with Critical Illnesses

Background

Association of diabetes and admission glucose on the short-term prognosis in patients with critical illnesses are currently ambiguous. We aimed to determine whether diabetes and admission glucose affects short-term prognosis of critically ill patients.

Methods

We performed a retrospective analysis of data on 46,476 critically ill patients from the critical care database. Association of diabetes with 28-day mortality was assessed by inverse probability weighting based on the propensity score. Smoothing splines and threshold effect analysis were applied to explore the relationship between admission glucose and clinical outcomes.

Results

Of the 33,680 patients enrolled in the study, 8,701 (25.83%) had diabetes. In the main analysis, the 28-day mortality was reduced by 29% (hazard ratio (HR)=0.71, 95% confidence interval (CI) 0.67–0.76) in patients with diabetes compared to those without diabetes. The E-value of 2.17 indicated robustness to unmeasured confounders. Significant interactions were observed for glucose at ICU admission, admission type, and insulin use (Interaction P <0.05). A V-shaped relationship was observed between admission glucose and 28-day mortality in non-diabetic patients, with the lowest 28-day mortality corresponding to a glucose level of 101.75 mg/dl (95% CI 94.64–105.80 mg/dl), and admission hypoglycemia or hyperglycemia should be avoided, especially in patients admitted to the surgical intensive care unit (SICU), cardiac surgery recovery unit (CSRU), and coronary care unit (CCU); for diabetic patients, elevated admission glucose does not appear to be associated with a poor prognosis and perhaps may be beneficial except for CCU and CSRU.

Conclusion

The non-detrimental effect of diabetes on the short-term prognosis of critically ill patients was further confirmed, which would reduce 28-day mortality by approximately 29%. For non-diabetic patients, the admission glucose level corresponding to the lowest 28-day mortality was 101.75 mg/dl (95% CI 94.64–105.80 mg/dl); however, for diabetics, the appropriate admission glucose threshold remains unresolved.

The intrinsic and extrinsic elements regulating inflammation

Inflammation is a sophisticated biological tissue response to both extrinsic and intrinsic stimuli. Although the pathological aspects of inflammation are well appreciated, there are still rooms for understanding the physiological functions of the inflammation. Recent studies have focused on mechanisms, context and the role of physiological inflammation. Besides, there have been progress in the comprehension of commensal microbiota, immunometabolism, cancer and intracellular signaling events' roles that impact on the regulation of inflammation. Despite the fact that inflammatory responses are vital through tissue damage, understanding the mechanisms to turn off the finished or unnecessary inflammation is crucial for restoring homeostasis. Inflammation seems to be a smart process that acts like two edges of a sword, meaning that it has both protective and deleterious consequences. Knowing both edges and the regulation processes will help the future understanding and therapy for various diseases.

Commentary: Reconciling Hygiene and Cleanliness: A New Perspective from Human Microbiome

Human beings have co-evolved with the microorganisms in our environment for millions of years, and have developed into a symbiosis in a mutually beneficial/defensive way. Human beings have significant multifaceted relationships with the diverse microbial community. Apart from the important protective role of microbial community exposure in development of early immunity, millions of inimitable bacterial genes of the diverse microbial community are the indispensable source of essential nutrients like essential amino acids and essential fatty acids for human body. The essential nutrition from microbiome is harvested through xenophagy. As an immune effector, xenophagy will capture any microorganisms that touch the epithelial cells of our gastrointestinal tract, degrade them and turn them into nutrients for the use of our body.

Nutritional support in sepsis: when less may be more

Despite sound basis to suspect that aggressive and early administration of nutritional support may hold therapeutic benefits during sepsis, recommendations for nutritional support have been somewhat underwhelming. Current guidelines (ESPEN and ASPEN) recognise a lack of clear evidence demonstrating the beneficial effect of nutritional support during sepsis, raising the question: why, given the perceived low efficacy of nutritionals support, are there no high-quality clinical trials on the efficacy of permissive underfeeding in sepsis? Here, we review clinically relevant beneficial effects of permissive underfeeding, motivating the urgent need to investigate the clinical benefits of delaying nutritional support during sepsis.

Insulin as an immunomodulatory hormone

Insulin plays an indispensable role in the management of hyperglycaemia that arises in a variety of settings, including Type I and II diabetes, gestational diabetes, as well as is in hyperglycaemia following a severe inflammatory insult. However, insulin receptors are also expressed on a range of cells that are not canonically implicated in glucose homeostasis. This includes immune cells, where the anti-inflammatory effects of insulin have been repeatedly reported. However, recent findings have also implicated a more involved role for insulin in shaping the immune response during an infection. This includes the ability of insulin to modulate immune cell differentiation and polarisation as well as the modulation of effector functions such as biocidal ROS production. Finally, inflammatory mediators can through both direct and indirect mechanisms also regulate serum insulin levels, suggesting that insulin may be co-opted by the immune system during an infection to direct immunological operations. Collectively, these observations implicate insulin as a bona fide immune-modulating hormone and suggest that a better understanding of insulin's immunological function may aid in optimising insulin therapy in a range of clinical settings.

The good, the bad and the autophagosome: exploring unanswered questions of autophagy-dependent cell death

The recent discovery of autosis as a variant of autophagy-dependent cell death has challenged the conventional understanding of cell death and programmed cell death in cellular decision making. In contrast to previous accounts of distinct cell death modalities, autosis occurs with high autophagic activity, in the absence of apoptotic and necrotic markers and yet is not fully regulated by typical autophagy markers. Given the metabolic importance of autophagic responses and the extensive cross-talk with both apoptosis and necrosis signalling, the classical and morphotype-driven characterization of cell death as pre-determined subroutines is being increasingly called into question. Furthermore, the conflicting evidence with regards to cell death induction through autophagy modulation in various cancer models highlights the lack of consensus over the extent to which autophagy assists in cell death ontrol and whether it is capable of being a bona fide lethal process. This review evaluates the evidence and context of autophagy-dependent cell death and delineates the role of an autophagic flux threshold associated with 'lethal' and 'non-lethal' autophagy and its role in autosis control. In doing so, cancer treatment avenues will be explored with regards to precision modulation of tumour autophagic flux to ascertain whether autosis induction may present a novel therapeutic strategy.

P57-mediated autophagy promotes the efficacy of EGFR inhibitors in hepatocellular carcinoma

BACKGROUND & AIMS

Resistance to EGFR-targeted therapy is a major obstacle in hepatocellular carcinoma (HCC) treatment, but its underlying mechanism remains unclear. Autophagy plays a vital role in antitumour treatment. Our previous study suggested that p57 is associated with autophagy and cisplatin resistance. The present study aimed to investigate whether p57 can enhance the sensitivity of HCC cells to Erlotinib (Er)/Cetuximab(C-225) and further explore the potential mechanisms of Er/C-225 resistance.

METHODS

HCC cells were transfected with pIRES2-EGFP-p57 and pIRES2-EGFP-nc, accompanied by Er/C-225 treatment. Cell viability was detected by an Annexin apoptosis kit and MTT assay. Xenograft experiments were performed to study the function of p57 in the treatment of Er/C-225 in vivo. The level of autophagy was determined by analysis of the appearance of autophagic vacuoles. Western blotting was used to investigate the potential pathways involved.

RESULTS

Up-regulation of p57 decreased the level of Er/C-225-induced autophagy and enhanced the decrease in Er/C-225-induced cell viability. P57 overexpression combined with CQ treatment further enhanced the therapeutic efficiency of Er/C-225. The xenograft experiment verified that p57 up-regulation sensitizes HCC cells to Er/C-225. Moreover, a mechanistic investigation demonstrated that the up-regulation of p57 resulted in a decrease of LC3B-II and beclin-1, and an increase in p-PI3K, p-AKT and p-mTOR protein expressions.

CONCLUSIONS

Through activating the PI3K/AKT/mTOR signalling pathway, p57 can reverse Er/C-225-induced autophagy, and thereby increase the therapeutic efficiency of Er/C-225 treatment. Given these results, p57 up-regulation may be applicable as a therapeutic strategy to improve EGFR-targeted therapy in HCC.

Bone resorption: supporting immunometabolism

Activation of the immune system is associated with an increase in the breakdown of various peripheral tissues, including bone. Despite the widely appreciated role of inflammatory mediators in promoting bone resorption, the functional value behind this process is not completely understood. Recent advances in the field of immunometabolism have highlighted the metabolic reprogramming that takes place in activated immune cells. It is now believed that the breakdown of peripheral tissue provides metabolic substrates to fuel metabolic anabolism in activated immune cells. We argue that phosphate, liberated by bone resorption, plays an indispensable role in sustaining immune cell metabolism. The liberated phosphate is then incorporated into macromolecules such as nucleotides and phospholipids, and is also used for the phosphorylation of metabolites (e.g. glycolytic intermediates). In addition, magnesium, also liberated during the breakdown of bone, is an essential cofactor required by various metabolic enzymes which are upregulated in activated immune cells. Finally, calcium activates various additional molecules involved in immune cell migration. Taken together, these factors suggest a key role for bone resorption during infection.

Nutrient excess and autophagic deficiency: explaining metabolic diseases in obesity

Over-nutrition and a sedentary lifestyle are the driving forces behind the development of metabolic diseases. Conversely, caloric restriction and exercise have proven to be the most effective strategies in combating metabolic diseases. Interestingly, exercise and caloric restriction share a common feature: both represent a potent mechanism for upregulating autophagy. Autophagy is rapidly induced by nutrient deprivation, and conversely, inactivated by amino acids as well as growth factors (e.g. insulin). Here, we review evidence demonstrating that autophagy may indeed be attenuated in metabolic tissue such as liver, muscle, and adipose, in the context of obesity. We also highlight the mechanistic basis by which defective autophagy may contribute to the manifestation of metabolic diseases. This includes a compromised ability of the cell to perform quality control on the mitochondrial matrix, since autophagy plays a pivotal role in the degradation of defective mitochondria. Similarly, autophagy also plays an indispensable role in the clearance of protein aggregates and redundant large protein platforms such as inflammasomes. Autophagy might also play a key role in the metabolism of endotoxins, implicating the importance of autophagy in the pathogenesis of metabolic endotoxemia. These observations underpin an unprecedented role of autophagy in the manifestation of obesity-induced metabolic derangement.

Disease tolerance: concept and mechanisms

Two distinct defense strategies provide a host with survival to infectious diseases: resistance and tolerance. Resistance is dependent on the ability of the host to kill pathogens. Tolerance promotes host health while having a neutral to positive impact of pathogen fitness. Immune responses are almost inevitably defined in terms of pathogen resistance. Recent evidence has shown, however, that several effects attributed to activation of innate and adaptive immune mechanisms, cannot be readily explained with the paradigm of immunity as effectors of microbial destruction. This review focuses on integrating the concept of disease tolerance into recent studies of immune system function related to the regulation and resolution of tissue damage, T cell exhaustion, and tolerance to innocuous antigen.

Nutrition, inflammation and cancer

Quantitative and qualitative aspects of nutrition have a profound effect on leukocytes and thereby affect proinflammatory carcinogenic effects or anticancer immune responses. As a result, nutrition affects the incidence, natural progression and therapeutic response of malignant diseases, both in humans and in preclinical animal models. Here we discuss the molecular mechanisms through which alimentary cues modulate metabolic, microbial and neuroendocrine circuitries and thus affect the probability of developing premalignant lesions that progress to clinically manifested disease and the response to therapeutic intervention. We examine each of the connections that compose the triangle of nutrition, immunological and inflammatory reactions and cancer while focusing on the mechanistic aspects of these relationships.

Assessing pathophysiology of cancer anorexia

PURPOSE OF REVIEW

Cancer anorexia is a negative prognostic factor and is broadly defined as the loss of the interest in food. However, multiple clinical domains contribute to the phenotype of cancer anorexia. The characterization of the clinical and molecular pathophysiology of cancer anorexia may enhance the efficacy of preventive and therapeutic strategies.

RECENT FINDINGS

Clinical trials showed that cancer anorexia should be considered as an umbrella encompassing different signs and symptoms contributing to appetite disruption in cancer patients. Loss of appetite, early satiety, changes in taste and smell are determinants of cancer anorexia, whose presence should be assessed in cancer patients. Interestingly, neuronal correlates of cancer anorexia-related symptoms have been revealed by brain imaging techniques.

SUMMARY

The pathophysiology of cancer anorexia is complex and involves different domains influencing eating behavior. Limiting the assessment of cancer anorexia to questions investigating changes in appetite may impede correct identification of the targets to address.

Hyperglycaemia in critically ill patients: the immune system's sweet tooth

There is an ongoing debate regarding the efficacy of glycaemic control in critically ill patients. Here we briefly highlight the key function of elevated glucose in critically ill patients, namely, to enable elevation of aerobic glycolysis in rapidly dividing cells. In particular, aerobic glycolysis provides metabolic intermediates necessary for expansion of biomass in immune cells and promotion of tissue repair. Furthermore, we emphasise that insulin may inhibit autophagy, a cell survival process used in the bulk degradation of cellular debris and damaged organelles. These observations provide a rational basis for tolerating elevated glucose levels in certain critically ill patients.

Sickness-Associated Anorexia: Mother Nature's Idea of Immunonutrition?

During an infection, expansion of immune cells, assembly of antibodies, and the induction of a febrile response collectively place continual metabolic strain on the host. These considerations also provide a rationale for nutritional support in critically ill patients. Yet, results from clinical and preclinical studies indicate that aggressive nutritional support does not always benefit patients and may occasionally be detrimental. Moreover, both vertebrates and invertebrates exhibit a decrease in appetite during an infection, indicating that such sickness-associated anorexia (SAA) is evolutionarily conserved. It also suggests that SAA performs a vital function during an infection. We review evidence signifying that SAA may present a mechanism by which autophagic flux is upregulated systemically. A decrease in serum amino acids during an infection promotes autophagy not only in immune cells, but also in nonimmune cells. Similarly, bile acids reabsorbed postprandially inhibit hepatic autophagy by binding to farnesoid X receptors, indicating that SAA may be an attempt to conserve autophagy. In addition, augmented autophagic responses may play a critical role in clearing pathogens (xenophagy), in the presentation of epitopes in nonprovisional antigen presenting cells and the removal of damaged proteins and organelles. Collectively, these observations suggest that some patients might benefit from permissive underfeeding.