Autophagy-inducing nutritional interventions in experimental and clinical oncology

Dietary intake of polyamines in a Spanish adult population: Age-dependent correlation with Healthy Eating Index and Dietary Inflammatory Index scores

OBJECTIVES

A healthy and balanced diet is crucial to maintaining optimal health. Understanding the benefits of different food components is essential. The polyamine spermidine is linked to age-related disease protection, but daily intakes and whether these vary with age are unknown. This study aimed to determine polyamine intake in a Mediterranean diet population and its association with participants' age and Healthy Eating Index (HEI) and Dietary Inflammatory Index (DII) scores.

METHODS

A database was created with references concerning polyamine content in foods to determine the daily intake of foods frequently consumed by 203 participants (84 males and 119 females), ages 18 to 90 y, using a nutritional survey (VioScreen) that includes HEI and DII scores.

RESULTS

The participants' characteristics were as reported in the corresponding 2020 Spanish nutritional survey. Two-thirds demonstrated moderate to high adherence to the Mediterranean diet. The mean HEI score was 74.45 (out of 100), and the mean DII was -1.94 (anti-inflammatory). The median intake of polyamines was 45.59 mg/d/person (mean, 46.89 mg/d/person, 410.57 µmol/d/person), without sex differences. After normalizing the intake per kilocalorie, the Kruskal-Wallis test showed significant differences among age groups for total polyamines ingested, putrescine, and spermidine. The intake of putrescine and spermidine was significantly higher in the 60 to 69 age group compared with the 24 to 59 and 18 to 23 age groups, respectively. HEI scores were positively correlated with polyamine intake, whereas DII scores were negatively correlated.

CONCLUSIONS

Polyamine intake was higher than reported in other populations, did not decrease based on age, and was associated with healthy eating and anti-inflammatory foods.

Molecular determinants of immunogenic cell death elicited by radiation therapy

Cancer cells undergoing immunogenic cell death (ICD) can initiate adaptive immune responses against dead cell-associated antigens, provided that (1) said antigens are not perfectly covered by central tolerance (antigenicity), (2) cell death occurs along with the emission of immunostimulatory cytokines and damage-associated molecular patterns (DAMPs) that actively engage immune effector mechanisms (adjuvanticity), and (3) the microenvironment of dying cells is permissive for the initiation of adaptive immunity. Finally, ICD-driven immune responses can only operate and exert cytotoxic effector functions if the microenvironment of target cancer cells enables immune cell infiltration and activity. Multiple forms of radiation, including non-ionizing (ultraviolet) and ionizing radiation, elicit bona fide ICD as they increase both the antigenicity and adjuvanticity of dying cancer cells. Here, we review the molecular determinants of ICD as elicited by radiation as we critically discuss strategies to reinforce the immunogenicity of cancer cells succumbing to clinically available radiation strategies.

Harnessing Autophagy to Overcome Antigen-Specific T-Cell Dysfunction: Implication for People Living with HIV-1

Like other chronic viral infections, HIV-1 persistence inhibits the development of antigen-specific memory T-cells, resulting in the exhaustion of the immune response and chronic inflammation. Autophagy is a major lysosome-dependent mechanism of intracellular large-target degradation such as lipid and protein aggregates, damaged organelles, and intracellular pathogens. Although it is known that autophagy may target HIV-1 for elimination, knowledge of its function as a metabolic contributor in such viral infection is only in its infancy. Recent data show that elite controllers (EC), who are HIV-1-infected subjects with natural and long-term antigen (Ag)-specific T-cell protection against the virus, are characterized by distinct metabolic autophagy-dependent features in their T-cells compared to other people living with HIV-1 (PLWH). Despite durable viral control with antiretroviral therapy (ART), HIV-1-specific immune dysfunction does not normalize in non-controller PLWH. Therefore, the hypothesis of inducing autophagy to strengthen their Ag-specific T-cell immunity against HIV-1 starts to be an enticing concept. The aim of this review is to critically analyze promises and potential limitations of pharmacological and dietary interventions to activate autophagy in an attempt to rescue Ag-specific T-cell protection among PLWH.

Molecular targets of spermidine: implications for cancer suppression

Spermidine is a ubiquitous, natural polyamine with geroprotective features. Supplementation of spermidine extends the lifespan of yeast, worms, flies, and mice, and dietary spermidine intake correlates with reduced human mortality. However, the crucial role of polyamines in cell proliferation has also implicated polyamine metabolism in neoplastic diseases, such as cancer. While depleting intracellular polyamine biosynthesis halts tumor growth in mouse models, lifelong external spermidine administration in mice does not increase cancer incidence. In contrast, a series of recent findings points to anti-neoplastic properties of spermidine administration in the context of immunotherapy. Various molecular mechanisms for the anti-aging and anti-cancer properties have been proposed, including the promotion of autophagy, enhanced translational control, and augmented mitochondrial function. For instance, spermidine allosterically activates mitochondrial trifunctional protein (MTP), a bipartite protein complex that mediates three of the four steps of mitochondrial fatty acid (β-oxidation. Through this action, spermidine supplementation is able to restore MTP-mediated mitochondrial respiratory capacity in naïve CD8⁺ T cells to juvenile levels and thereby improves T cell activation in aged mice. Here, we put this finding into the context of the previously described molecular target space of spermidine.

Immunogenic cell death in cancer: concept and therapeutic implications

Mammalian cells responding to specific perturbations of homeostasis can undergo a regulated variant of cell death that elicits adaptive immune responses. As immunogenic cell death (ICD) can only occur in a precise cellular and organismal context, it should be conceptually differentiated from instances of immunostimulation or inflammatory responses that do not mechanistically depend on cellular demise. Here, we critically discuss key conceptual and mechanistic aspects of ICD and its implications for cancer (immuno)therapy.