Constitutive sodium permeability in a C. elegans two-pore domain potassium channel.

Two-pore domain potassium (K2P) channels play a central role in modulating cellular excitability and neuronal function. The unique structure of the selectivity filter in K2P and other potassium channels determines their ability to allow the selective passage of potassium ions across cell membranes. The nematode C. elegans has one of the largest K2P families, with 47 subunit-coding genes. This remarkable expansion has been accompanied by the evolution of atypical selectivity filter sequences that diverge from the canonical TxGYG motif. Whether and how this sequence variation may impact the function of K2P channels has not been investigated so far. Here, we show that the UNC-58 K2P channel is constitutively permeable to sodium ions and that a cysteine residue in its selectivity filter is responsible for this atypical behavior. Indeed, by performing in vivo electrophysiological recordings and Ca2+ imaging experiments, we demonstrate that UNC-58 has a depolarizing effect in muscles and sensory neurons. Consistently, unc-58 gain-of-function mutants are hypercontracted, unlike the relaxed phenotype observed in hyperactive mutants of many neuromuscular K2P channels. Finally, by combining molecular dynamics simulations with functional studies in Xenopus laevis oocytes, we show that the atypical cysteine residue plays a key role in the unconventional sodium permeability of UNC-58. As predicting the consequences of selectivity filter sequence variations in silico remains a major challenge, our study illustrates how functional experiments are essential to determine the contribution of such unusual potassium channels to the electrical profile of excitable cells.

Food Systems Interventions for Nutrition: Lessons from 6 Program Evaluations in Africa and South Asia.

Although there is growing global momentum behind food systems strategies to improve planetary and human health-including nutrition-there is limited evidence of what types of food systems interventions work. Evaluating these types of interventions is challenging due to their complex and dynamic nature and lack of fit with standard evaluation methods. In this article, we draw on a portfolio of 6 evaluations of food systems interventions in Africa and South Asia that were intended to improve nutrition. We identify key methodological challenges and formulate recommendations to improve the quality of such studies. We highlight 5 challenges: a lack of evidence base to justify the intervention, the dynamic and multifaceted nature of the interventions, addressing attribution, collecting or accessing accurate and timely data, and defining and measuring appropriate outcomes. In addition to more specific guidance, we identify 6 cross-cutting recommendations, including a need to use multiple and diverse methods and flexible designs. We also note that these evaluation challenges present opportunities to develop new methods and highlight several specific needs in this space.

K+-Driven Cl-/HCO3- Exchange Mediated by Slc4a8 and Slc4a10.

Slc4a genes encode various types of transporters, including Na+-HCO3- cotransporters, Cl-/HCO3- exchangers, or Na+-driven Cl-/HCO3- exchangers. Previous research has revealed that Slc4a9 (Ae4) functions as a Cl-/HCO3- exchanger, which can be driven by either Na+ or K+, prompting investigation into whether other Slc4a members facilitate cation-dependent anion transport. In the present study, we show that either Na+ or K+ drive Cl-/HCO3- exchanger activity in cells overexpressing Slc4a8 or Slc4a10. Further characterization of cation-driven Cl-/HCO3- exchange demonstrated that Slc4a8 and Slc4a10 also mediate Cl- and HCO3--dependent K+ transport. Full-atom molecular dynamics simulation on the recently solved structure of Slc4a8 supports the coordination of K+ at the Na+ binding site in S1. Sequence analysis shows that the critical residues coordinating monovalent cations are conserved among mouse Slc4a8 and Slc4a10 proteins. Together, our results suggest that Slc4a8 and Slc4a10 might transport K+ in the same direction as HCO3- ions in a similar fashion to that described for Na+ transport in the rat Slc4a8 structure.

Edentulism and quality of life in the Salvadoran population: a cross-sectional study.

INTRODUCTION: Edentulism is the partial or total loss of teeth, it is irreversible and disabling due to its sequelae in the masticatory, phonetic and aesthetic function that affect the quality of life. OBJECTIVE: To establish the impact of edentulism and sociodemographic factors on the quality of life of the Salvadoran population. MATERIALS AND METHODS: Secondary cross-sectional analysis of data in 3322 users of the Public Health System of El Salvador, aged 15 to > 60 years. The variables under study were sociodemographic, edentulismo and quality of life. Edentulism was determined by clinical examination using the Oral Impact on Daily Performance scale. The statistical analysis was performed using χ2, OR, multiple regression analysis and set the significance threshold at p < 0.05. RESULTS: Partial edentulism in the upper jaw was present in 68.24% people, partial edentulism in the lower jaw was present in 72.42% people and complete edentulism was observed in 2.02% people. There were significant sex differences and a relationship between sex and quality of life (p < 0.004); the self-perception of severe/very severe impacts was greater in women. People without education or with primary or secondary education only were the most affected (p < 0.05). Tooth loss increases with age, affecting quality of life in a severe/very severe manner. Complete edentulism had greater impacts on quality of life in terms of eating (25.64%), speaking (21.15%), and socializing/enjoying contact with people (10.90%). A severe/very severe impact on quality of life of teeth lost was reported mainly by those over 60 years of age, with an average of 11 missing posterior teeth, 6 missing anterior teeth and 13 missing teeth per patient. Those missing up to 6 anterior teeth were times more likely to perceive severe/very severe impacts on quality of life than those without any missing teeth (OR:5.788). Edentulism affected the quality of life of those examined, especially the loss of upper anterior teeth.

Improving complementary feeding practices, programs and policies for optimal early childhood nutrition in Kenya: What would work?

Complementary feeding practices are greatly influenced by local contexts. Therefore, national home-grown evidence, policies and guidelines are critical to improving infant and young children's diets. This Special Issue has provided a comprehensive, evidence-based analysis of the situation, gaps and context-specific opportunities for improving young children's diets in Kenya. The primary research findings of the Special Issue supported the identification of a set of recommendations articulated across the four systems (food, health, water, sanitation and hygiene [WASH] and social protection) to improve food availability and accessibility in Kenya at the national and subnational levels. It is anticipated that the decentralised government functions seen in Kenya provide a strong opportunity to develop and mainstream context-specific recommendations into action. This Special Issue recommends adopting a multi-sectoral systems approach, including a shared vision, joint planning, implementation and monitoring, towards improving young children's diets with a focus on service delivery as well as scaled-up community social behaviour change interventions. In particular, the approach should entail advocacy for policy revisions for service delivery that support complementary feeding and development of costed implementation strategies in support of the same, across four critical systems-food, health, WASH and social protection, along with, the strengthening of national coordination, monitoring and accountability structures as per the Kenya Nutrition Action Plan. Finally, the development of a legal framework for enhanced accountability from all relevant sectors towards sustainable, nutritious, safe and affordable children's diets. These recommendations provide a clear direction in addressing the complementary feeding challenges, which the primary research of this Special Issue has presented.

Evidence-based complementary feeding recipe book for Kenyan caregivers: A novel approach.

The Kenyan Ministry of Health (MOH) and a consortium of nutritionists, researchers and communication, and design specialists developed a novel approach to create an evidence-based recipe book promoting complementary feeding (CF) in Kenya. The ADAPT approach includes five steps: applied research (A), dialogue with stakeholders (D), adapted behaviour change communication (BCC) theories (A), purpose-driven visual communication (P), and tailoring to priority audiences (T). Through this approach, the recipe book addresses key knowledge gaps using behaviour change theories and visual communication best practice to increase accessibility, acceptability, retention and motivation for behaviour change. The book addresses barriers to CF identified through formative applied research. Dialogue with stakeholders helped ensure cultural appropriateness and the book's alignment with MOH recommendations and key messages. The book uses behaviour change theories to approach the reader in a respectful way that motivates behaviour change. The use of consistent, purpose-driven visuals helps ensure key messages are easily understood and accessible to all caregivers regardless of literacy level. The book's tone and content are tailored to its audiences' attributes, needs and preferences. This five-step process inspired the development of ADAPT, a novel approach that integrates behaviour change and visual communication for greater impact. This paper outlines how the consortium used the ADAPT approach to develop an evidence-based book that thoughtfully and holistically addresses a wide range of barriers, provides practical solutions and increases self-efficacy around CF. It offers a blueprint for public health practitioners from any field who are interested in using visual behaviour change communication to promote healthy behaviour.

3D Data Processing and Entropy Reduction for Reconstruction from Low-Resolution Spatial Coordinate Clouds in a Technical Vision System.

This paper proposes an advancement in the application of a Technical Vision System (TVS), which integrates a laser scanning mechanism with a single light sensor to measure 3D spatial coordinates. In this application, the system is used to scan and digitalize objects using a rotating table to explore the potential of the system for 3D scanning at reduced resolutions. The experiments undertaken searched for optimal scanning windows and used statistical data filtering techniques and regression models to find a method to generate a 3D scan that was still recognizable with the least amount of 3D points, balancing the number of points scanned and time, while at the same time reducing effects caused by the particularities of the TVS, such as noise and entropy in the form of natural distortion in the resulting scans. The evaluation of the experimentation results uses 3D point registration methods, joining multiple faces from the original volume scanned by the TVS and aligning it to the ground truth model point clouds, which are based on a commercial 3D camera to verify that the reconstructed 3D model retains substantial detail from the original object. This research finds it is possible to reconstruct sufficiently detailed 3D models obtained from the TVS, which contain coarsely scanned data or scans that initially lack high definition or are too noisy.

Attributes of parenting identities and food practices among parents in Nairobi, Kenya.

Dramatic changes in daily life are leading to increased rates of obesity and non-communicable diseases (NCD) in Kenya, including among children. Parenting plays a vital role in helping children establish healthy eating habits to prevent obesity and NCDs. The objective of this study was to describe parenting identity and how attributes of parenting influence food parenting practices in an urban Kenyan context. A qualitative study design was employed with 18 participants recruited using quota sampling to include parents who were born in (n = 8) or migrated to Nairobi in the last five years (n = 10). In-depth qualitative interviews were conducted by an experienced ethnographic interviewer that inquired about parenting identity and food parenting practices. Transcripts were analyzed using thematic coding in a multi-step and emergent process. Parents described their parenting identities as an integration of tradition and personal experiences during their upbringing with the modern realities of daily life. Their own experiences with discipline, modern urban lifestyles, and social pressures were dominant influences on their identities. Parenting identities included four distinct but related attributes: good disciplinarian, trustworthy, protective, and balanced provider and nurturer. Food parenting practices were described as expressions of parenting identity and included the goals: children becoming better eaters; nourishing through food; impart joy; and bonding. The study findings illustrate the influence of modern urban lifestyles on food parenting identities and practices. Understanding emerging identities and practices in rapidly changing low- and middle-income countries (LMIC) contexts is essential for health promoting policies and programs.

Intracellular Helix-Loop-Helix Domain Modulates Inactivation Kinetics of Mammalian TRPV5 and TRPV6 Channels.

TRPV5 and TRPV6 are calcium-selective ion channels expressed at the apical membrane of epithelial cells. Important for systemic calcium (Ca2+) homeostasis, these channels are considered gatekeepers of this cation transcellular transport. Intracellular Ca2+ exerts a negative control over the activity of these channels by promoting inactivation. TRPV5 and TRPV6 inactivation has been divided into fast and slow phases based on their kinetics. While slow inactivation is common to both channels, fast inactivation is characteristic of TRPV6. It has been proposed that the fast phase depends on Ca2+ binding and that the slow phase depends on the binding of the Ca2+/Calmodulin complex to the internal gate of the channels. Here, by means of structural analyses, site-directed mutagenesis, electrophysiology, and molecular dynamic simulations, we identified a specific set of amino acids and interactions that determine the inactivation kinetics of mammalian TRPV5 and TRPV6 channels. We propose that the association between the intracellular helix-loop-helix (HLH) domain and the TRP domain helix (TDh) favors the faster inactivation kinetics observed in mammalian TRPV6 channels.

Human Bone Marrow Mesenchymal Stem Cells Promote the M2 Phenotype in Macrophages Derived from STEMI Patients.

Acute ST-elevation myocardial infarction (STEMI) leads to myocardial injury or necrosis, and M1 macrophages play an important role in the inflammatory response. Bone marrow mesenchymal stem/stromal cells (BM-MSCs) are capable of modulating macrophage plasticity, principally due to their immunoregulatory capacity. In the present study, we analyzed the capacity of MSCs to modulate macrophages derived from monocytes from patients with STEMI. We analyzed the circulating levels of cytokines associated with M1 and M2 macrophages in patients with STEMI, and the levels of cytokines associated with M1 macrophages were significantly higher in patients with STEMI than in controls. BM-MSCs facilitate the generation of M1 and M2 macrophages. M1 macrophages cocultured with MSCs did not have decreased M1 marker expression, but these macrophages had an increased expression of markers of the M2 macrophage phenotype (CD14, CD163 and CD206) and IL-10 and IL-1Ra signaling-induced regulatory T cells (Tregs). M2 macrophages from patients with STEMI had an increased expression of M2 phenotypic markers in coculture with BM-MSCs, as well as an increased secretion of anti-inflammatory cytokines and an increased generation of Tregs. The findings in this study indicate that BM-MSCs have the ability to modulate the M1 macrophage response, which could improve cardiac tissue damage in patients with STEMI.

Social and economic factors influencing intrahousehold food allocation and egg consumption of children in Kaduna State, Nigeria.

Adequate intake of high-quality nutritious foods during infancy and early childhood is critical to achieving optimal growth, cognitive and behavioural development, and economic productivity later in life. Integrating high-quality and nutrient-dense animal source foods (ASFs), a major source of protein and micronutrients, into children's diets is increasingly considered essential to reducing the global burden of malnutrition in low- and middle-income countries. While eggs are an ASF that shows promise for mitigating child undernutrition, interventions promoting egg consumption among children have had mixed results in improving egg intake and child growth outcomes. As part of an evaluation of a demand creation campaign promoting egg consumption, qualitative research was carried out in September 2019 to assess sociocultural and household factors affecting egg intake among young children living in Kaduna State, Nigeria, where a thriving egg industry and childhood stunting rates of 50% exist. Methods included freelisting exercises (11), key informant interviews (11), in-depth interviews (25) and FGDs (4). Results illuminated cultural rules that restrict egg consumption among children living in low-income households. These rules and norms reflect social and economic valuations that foster male dominance in household decision-making and guide food purchasing and intrahousehold food allocation that allow men to consume eggs more regularly. Study results highlight sociocultural considerations when selecting food interventions to address child malnutrition in low-income contexts. Interventions encouraging increased consumption of ASFs, and specifically eggs in young children, should be informed by formative research to understand sociocultural norms and beliefs guiding egg consumption.

Effectiveness of the Eggs Make Kids demand-creation campaign at improving household availability of eggs and egg consumption by young children in Nigeria: A quasi-experimental study.

Using a quasi-experimental design, our study aimed to determine the effectiveness of the 'Eggs Make Kids Sharp & Bright and Strong & Active' demand-creation campaign in Nigeria. The intervention arm received emotionally compelling radio and television advertisements about eggs, and was exposed to promotional activities and advertising about eggs at points of purchase, schools and health facilities; the comparison arm received no intervention. Children 6-59 months of age (intervention: n = 1359; comparison: n = 1485) were assessed 14 months apart. Intent-to-treat analyses with analysis of covariance method assessed the impact of the intervention on caregivers' behaviour towards eggs, caregivers' willingness to pay for eggs, availability of eggs in households, and consumption of eggs by children 6-59 months of age. Analyses were adjusted for possible confounders and perceived effects of COVID-19 on finances and food consumption. Compared to the comparison arm, the intervention arm showed a greater prevalence of household egg acquisition (odds ratio = 1.34, p < 0.0001), and larger improvements in caregiver self-efficacy (ß = 0.242, p = 0.004) and intent to feed eggs to children (ß = 0.080, p = 0.021). No effects were found on children's egg consumption or caregivers' reported willingness to pay for eggs. The lack of impact on child egg consumption despite increased acquisition of eggs and caregiver self-efficacy suggests that other barriers to child consumption may exist. Additional research should further investigate factors that may influence intrahousehold distribution of eggs and whether these may also influence other nutritious foods.

Shannon Entropy Used for Feature Extractions of Optical Patterns in the Context of Structural Health Monitoring.

A novelty signal processing method is proposed for a technical vision system (TVS). During data acquisition of an optoelectrical signal, part of this is random electrical fluctuation of voltages. Information theory (IT) is a well-known field that deals with random processes. A method based on using of the Shannon Entropy for feature extractions of optical patterns is presented. IT is implemented in structural health monitoring (SHM) to augment the accuracy of optoelectronic signal classifiers for a metrology subsystem of the TVS. To enhance the TVS spatial coordinate measurement performance at real operation conditions with electrical and optical noisy environments to estimate structural displacement better and evaluate its health for a better estimation of structural displacement and the evaluation of its health. Five different machine learning (ML) techniques are used in this work to classify optical patterns captured with the TVS. Linear predictive coding (LPC) and Autocorrelation function (ACC) are for extraction of optical patterns. The Shannon entropy segmentation (SH) method extracts relevant information from optical patterns, and the model's performance can be improved. The results reveal that segmentation with Shannon's entropy can achieve over 95.33%. Without Shannon's entropy, the worst accuracy was 33.33%.

Determinants of egg consumption by infants and young children in Ethiopia.

OBJECTIVE: To identify determinants of egg consumption in infants and young children aged 6-23·9 months in Ethiopia. DESIGN AND SETTING: Data used were from the cross-sectional baseline survey of an egg campaign in Ethiopia implemented by the Global Alliance for Improved Nutrition. PARTICIPANTS: Children aged 6-23·9 months (n 453) were sampled. Data on socio-demographic characteristics, economic resources, caregiver's behaviour, child health and feeding practices, and egg consumption in the last 7 d were collected using interviewer-administered questionnaires. Multivariable ordinal logistic regression was used to examine the association between explanatory variables and egg consumption in the last 7 d. RESULTS: About half of children (53·4 %) did not consume eggs in the last 7 d. The odds of children consuming eggs were 4·33 (P < 0·002) times higher when their caregivers had some college education compared with no education. Wealth was positively (OR, 1·13, P = 0·029) and household food insecurity was negatively (OR, 0·96, P = 0·117) associated with child egg consumption. Purchasing eggs (OR, 9·73, P < 0·001) and caregiver's positive behavioural determinants (OR, 1·37, P = 0·005) were associated with child egg consumption. The associations of socio-demographic characteristics and economic resources with egg consumption provide evidence of partial mediation through caregiver behaviour and child health. CONCLUSIONS: About half of children aged 6-23·9 months consumed eggs. Availability of eggs in households, mainly through purchase, was strongly associated with egg consumption. Education of caregivers and household heads and economic resources were associated with egg consumption and may operate through caregiver behaviour.

Oral health profile status and treatment needs in the Salvadoran elderly population: a cross-sectional study.

INTRODUCTION: Older adults are a highly vulnerable group in their general health condition, including oral health that can be influenced by different factors, among them, changes in oral tissues inherent to the physiological processes of aging and by systemic condition. In El Salvador, it is a group that has received little attention at the public health level. OBJECTIVE: To determine the profile of the oral health status and treatment needs of the elderly population in El Salvador. MATERIALS AND METHODS: Secondary cross-sectional analysis of data from the last oral health survey in 471 Salvadorans aged 60 years and older. The variables under study were: sociodemographics, brushing frequency, oral hygiene according to simplified oral hygiene index (OHI-S), caries experience according to decayed, missing, and filled teeth index (DMFT) modified with international caries detection and assessment system (ICDAS) criteria, periodontal status through the community periodontal index of treatment needs (CPITN), edentulism and treatment needs. Statistical analysis was conducted using chi-square test, ANOVA, z-test and linear regression (p < 0.05). RESULTS: The older adults presented poor oral hygiene, low brushing frequency, high tooth loss with an average of 16 missing teeth while one third presented total edentulism. Most of the older adults were categorized as having "poor or very Poor" oral hygiene. Almost all respondents presented some degree of periodontal disease and required restorative intervention. CONCLUSION: The oral health status of elderly Salvadoran is poor. Furthermore, the development of public policies and specific oral health strategies aimed at this population is urgent.

Functions of social networks in maternal food choice for children in Mexico.

Food choice for children has important implications in establishing early-life dietary habits and preferences. Food choice for children has been studied as parent-child dyad dynamics, but little is known about the extended system of relationships in maternal food choice for children. The objective of this study was to understand the functions of mothers' social networks in the food choices that mothers make for their children ages 1 to 5 years old in rural Mexico. In-depth interviews were conducted with 46 participants in three rural communities. The interviews inquired about participants' child-feeding practices, personal and local beliefs about child feeding and the individuals with whom they had conversations about food and child feeding. All interviews were conducted in Spanish, audio-recorded, transcribed verbatim, verified for quality and analysed using the constant comparative method. Five interconnected networks emerged, consisting of household family, non-household family, community, children's initial school and health and nutritional programme personnel. Each network had functions in food choice that ranged from shared food decision-making in the household family network to imparting formal dietary guidance in the health and nutritional programme personnel network. Across the networks, professionals, participants' mothers and mothers-in-law, community senior women and other women with children emerged as prominent figures whom participants would turn to for child-feeding advice. These findings provide empirical evidence that social networks, as an organized system of interconnected relationships, have vital functions in establishing social norms for food choices made for children that can be leveraged to promote healthy food choices.

Diversity of functional alterations of the ClC-5 exchanger in the region of the proton glutamate in patients with Dent disease 1.

Mutations in the CLCN5 gene encoding the 2Cl- /1H+ exchanger ClC-5 are associated with Dent disease 1, an inherited renal disorder characterized by low-molecular-weight (LMW) proteinuria and hypercalciuria. In the kidney, ClC-5 is mostly localized in proximal tubule cells, where it is thought to play a key role in the endocytosis of LMW proteins. Here, we investigated the consequences of eight previously reported pathogenic missense mutations of ClC-5 surrounding the "proton glutamate" that serves as a crucial H+ -binding site for the exchanger. A complete loss of function was observed for a group of mutants that were either retained in the endoplasmic reticulum of HEK293T cells or unstainable at plasma membrane due to proteasomal degradation. In contrast, the currents measured for the second group of mutations in Xenopus laevis oocytes were reduced. Molecular dynamics simulations performed on a ClC-5 homology model demonstrated that such mutations might alter ClC-5 protonation by interfering with the water pathway. Analysis of clinical data from patients harboring these mutations demonstrated no phenotype/genotype correlation. This study reveals that mutations clustered in a crucial region of ClC-5 have diverse molecular consequences in patients with Dent disease 1, ranging from altered expression to defects in transport.

Molecular Pharmacology of K2P Potassium Channels.

Potassium channels of the tandem of two-pore-domain (K2P) family were among the last potassium channels cloned. However, recent progress in understanding their physiological relevance and molecular pharmacology revealed their therapeutic potential and thus these channels evolved as major drug targets against a large variety of diseases. However, after the initial cloning of the fifteen family members there was a lack of potent and/or selective modulators. By now a large variety of K2P channel modulators (activators and blockers) have been described, especially for TASK-1, TASK-3, TREK-1, TREK2, TRAAK and TRESK channels. Recently obtained crystal structures of K2P channels, alanine scanning approaches to map drug binding sites, in silico experiments with molecular dynamics simulations (MDs) combined with electrophysiological studies to reveal the mechanism of channel inhibition/activation, yielded a good understanding of the molecular pharmacology of these channels. Besides summarizing drugs that were identified to modulate K2P channels, the main focus of this article is on describing the differential binding sites and mechanisms of channel modulation that are utilized by the different K2P channel blockers and activators.

KCTD5, a novel TRPM4-regulatory protein required for cell migration as a new predictor for breast cancer prognosis.

Transient receptor potential melastatin 4 (TRPM4) is a Ca2+ -activated nonselective cationic channel that regulates cell migration and contractility. Increased TRPM4 expression has been related to pathologies, in which cytoskeletal rearrangement and cell migration are altered, such as metastatic cancer. Here, we identify the K+ channel tetramerization domain 5 (KCTD5) protein, a putative adaptor of cullin3 E3 ubiquitin ligase, as a novel TRPM4-interacting protein. We demonstrate that KCTD5 is a positive regulator of TRPM4 activity by enhancing its Ca2+ sensitivity. We show that through its effects on TRPM4 that KCTD5 promotes cell migration and contractility. Finally, we observed that both TRPM4 and KCTD5 expression are increased in distinct patterns in different classes of breast cancer tumor samples. Together, these data support that TRPM4 activity can be regulated through expression levels of either TRPM4 or KCTD5, not only contributing to increased understanding of the molecular mechanisms involved on the regulation of these important ion channels, but also providing information that could inform treatments based on targeting these distinct molecules that define TRPM4 activity.

Implementation of a regulatory food policy to reduce availability of energy-dense foods in Costa Rican high schools.

OBJECTIVE: To assess the extent to which mandatory Guidelines to improve the school food environment were being implemented in Costa Rican high schools and to explore the perspectives of key policy actors towards the Guidelines. DESIGN: Semi-structured interviews and site observations. Interviews were recorded, transcribed verbatim and imported to NVivo 12 for analysis. Inductive and deductive themes were identified, and elements of the RE-AIM framework and the social process framework were used when classifying these themes. SETTING: Sixteen public high schools in San José, Costa Rica. PARTICIPANTS: High school principal and kiosk concessionaires. RESULTS: Products that did not adhere to the Guidelines were still widely available in schools, and amongst the most prevalent challenges to implementation that emerged from our interviews, were a lack of understanding of the policy content, a lack of monitoring and accountability, and competing values amongst actors which affected their views on the role that the school must have in offering a healthy food environment. CONCLUSION: Most products offered in high schools did not meet the criteria required by the mandatory Guidelines, and several contextual factors were found to influence implementation. Strengthening the implementation of the Costa Rican Guidelines will require further actions at the governmental and school levels.