Short-Chain Fatty Acids in Lypopolysaccharide-Induced Inflammation and Executive Function

Official title

Investigating the Role of Short-Chain Fatty Acids in Endotoxemia-Induced Inflammation and Core Executive Functioning: A Randomized, Triple-Blind, Placebo-Controlled Trial

Overview

Short-chain fatty acids (SCFAs) are substances produced by gut bacteria when they ferment dietary fiber. They can act as signals between the gut and the brain and may help regulate the body's immune and stress responses. Earlier work has shown that delivering SCFAs to the colon can lower the stress hormone response to a mental stress task in healthy people, and laboratory studies suggest SCFAs can reduce inflammation. However, it is not yet known whether SCFAs can reduce inflammation in humans, or whether doing so protects mental performance. This study uses a controlled, acute, and short-lasting challenge. Healthy adults receive a single, low dose of a bacterial substance called lipopolysaccharide (LPS) through a vein. LPS briefly activates the immune system and causes mild, flu-like symptoms (such as fatigue, headache, and feeling unwell) that pass on their own within a few hours. It does not cause a real infection. Participants are randomly assigned to take either SCFA capsules or inactive placebo capsules on the morning of the test day, before the LPS challenge. Neither the participants, the researchers running the visit, nor the researchers analyzing the results know who received which capsules until the study is complete (triple-blind). The main goal of the study is to test whether SCFAs, compared with placebo, reduce the inflammatory response to LPS, measured by markers of inflammation in the blood. The study also examines whether SCFAs reduce the associated sickness symptoms and whether they protect performance on tasks that measure core executive functions: the ability to keep relevant information in mind (working memory), the ability to hold back automatic responses or thoughts (inhibition), and the ability to switch flexibly between tasks or rules (cognitive flexibility). Blood, saliva, and stool samples are collected to measure inflammation markers, SCFA levels, stress hormones, and gut bacteria. Participants attend a screening visit, a test day with monitoring for several hours, and a short follow-up visit the next day.

Detailed description

INFLEX is a single-center, randomized, triple-blind, placebo-controlled, parallel-group interventional trial conducted at UZ Leuven / KU Leuven. Its primary aim is to test whether a single acute dose of colon-delivered SCFAs, relative to placebo, attenuates the systemic inflammatory response induced by experimental endotoxemia in healthy adults. Secondary aims are to test whether SCFAs attenuate LPS-induced sickness behaviour and mitigate endotoxemia-induced changes in core executive functioning, and to characterize associations between systemic SCFA uptake, the inflammatory response, and these outcomes.

Eligible participants are randomized to receive SCFA colon-delivery capsule or placebo capsules, taken on the morning of the test day with a standardized low-fiber breakfast. One hour after capsule intake, participants receive a single intravenous bolus of purified Escherichia coli lipopolysaccharide (0.4 ng/kg body weight), which serves as a fixed inflammatory challenge applied to all participants. The timing is designed so that peak circulating SCFA concentrations (approximately 3-4 hours after colonic delivery) coincide with the peak of LPS-induced cytokines and sickness behaviour (approximately 2-3 hours post-injection).

Participants are monitored for a minimum of 6 hours after the LPS challenge. Vital signs, sickness symptoms, and blood and saliva samples are collected hourly to quantify inflammatory markers (including IL-6 and hs-CRP), serum SCFA, cortisol, and ACTH. Core executive-function tasks are administered before and after the LPS challenge and at a 24-hour follow-up visit. A fecal sample collected at home prior to the test day is used for gut microbiota profiling. To standardize endogenous SCFA production, participants follow a low-fiber diet for three days before the test day and avoid caffeine, alcohol, and strenuous exercise beforehand. The night prior to the test day, participants are instructed to consume a standard dinner that is provided to them.

The study comprises three visits: a screening visit (\~1 hour), the laboratory test day (\~8 hours), and a follow-up visit (\~30 minutes) 24 hours after the LPS challenge.

Interventions

• Dietary supplement Short-Chain Fatty Acid Colon-Delivery Capsules
  Single acute oral dose of pH-dependent colon-delivery capsules delivering a short-chain fatty acid mixture to the colon. The mixture comprises sodium acetate,sodium butyrate, and sodium propionate (54.4%, 21.2%, and 24.4% by weight), providing approximately 186 mmol total SCFA per dose (111 mmol acetate, 32 mmol butyrate, 43 mmol propionate). Capsules are sub-coated with hydroxypropylcellulose and coated with a pH-dependent layer (Eudragit FS 30 D with PlasACRYL T20). Taken on the morning of the
• Dietary supplement Placebo capsules
  Single acute oral dose of placebo capsules containing microcrystalline cellulose and matching excipients, an inert non-fermentable substrate. Matched in appearance and number to the SCFA capsules and taken on the morning of the test day with a standardized low-fiber breakfast.
• Biological Lipopolysaccharide (LPS)
  Single intravenous bolus of purified Escherichia coli-derived lipopolysaccharide (0.4 ng/kg body weight), administered one hour after capsule intake to all participants as a standardized experimental inflammatory challenge common to both study arms.

Primary outcome measures

• Serum interleukin-6 (IL-6) response to the LPS challenge [Time frame: 2 hours before LPS injection, and at 0, 1, 2, 3, 4, 5, and 6 hours after LPS injection]

Secondary outcome measures (12)

• Serum pro- and anti-inflammatory cytokine response to the LPS challenge [Time frame: 2 hours before LPS injection, and at 0, 1, 2, 3, 4, 5, and 6 hours after LPS injection]
• High-sensitivity C-reactive protein (hs-CRP) response to the LPS challenge [Time frame: 2 hours before LPS injection, and at 2, 6, and 24 hours after LPS injection]
• LPS-induced sickness behaviour (SicknessQ) [Time frame: 2 hours before LPS injection, and at 0, 1, 2, 3, 4, 5, and 6 hours after LPS injection]
• Body temperature response to the LPS challenge [Time frame: 2 hours before LPS injection, and at 0, 1, 2, 3, 4, 5, and 6 hours after LPS injection]
• Heart rate response to LPS challenge [Time frame: 2 hours before LPS injection, and at 0, 1, 2, 3, 4, 5, and 6 hours after LPS injection]
• Blood pressure response to the LPS challenge [Time frame: 2 hours before LPS injection, and at 0, 1, 2, 3, 4, 5, and 6 hours after LPS injection]
• Salivary cortisol response to the LPS challenge [Time frame: At 0, 1, 2, 3, 4, and 6 hours after LPS injection]
• Plasma ACTH [Time frame: At 0, 1, 2, 3, 4, and 6 hours after LPS injection]
• Working memory performance (3-back task) [Time frame: 2 hours before LPS injection, 2.25 hours after LPS injection, and 24 hours after LPS injection]
• Response inhibition (Stop Signal Task) [Time frame: 2 hours before LPS injection, 2.25 hours after LPS injection, and 24 hours after LPS injection]
• Cognitive flexibility - task switching (Number-Letter task) [Time frame: 2 hours before LPS injection, 2.25 hours after LPS injection, and 24 hours after LPS injection]
• Cognitive inhibition (Stroop task) [Time frame: 2 hours before LPS injection, 2.25 hours after LPS injection, and 24 hours after LPS injection]

Eligibility criteria

Inclusion criteria

• Voluntary written informed consent obtained prior to any study procedure
• Healthy, with no gastrointestinal or psychological complaints
• Age 18-45 years
• BMI 18.5-27 kg/m2
• Proficiency in English and/or Dutch

Exclusion criteria

• History of previous or current neurological disorder (e.g., epilepsy, multiple sclerosis, migraine with aura)
• History of previous or current psychiatric disorder (e.g., depression, anxiety disorders, bipolar disorder, schizophrenia)
• History of previous or current gastrointestinal disorder (e.g., Crohn's disease, ulcerative colitis, irritable bowel syndrome)
• History of previous or current endocrine disorder (e.g., diabetes, thyroid disorders, polycystic ovary syndrome)
• History of immune system disorder, including inflammatory, autoimmune, or severe allergic conditions (e.g., rheumatoid arthritis, lupus, celiac disease, or severe allergies such as anaphylaxis)
• History of neuropsychiatric disorder (e.g., ADHD, autism spectrum disorder, learning disorder, Tourette's syndrome)
• History of major head trauma (e.g., concussion with loss of consciousness or long-term symptoms)
• History of severe infection (e.g., sepsis, pneumonia requiring hospitalization, meningitis, endocarditis, or other systemic infection requiring hospitalization, intravenous antibiotics, or intensive care)
• One or more diagnoses based on the Mini International Neuropsychiatric Interview (MINI)
• One or more diagnoses based on ROME-IV criteria for gastrointestinal disorders
• Any disorder that, in the investigator's opinion, might jeopardise the participant's safety or compliance with the protocol
• Any prior or concomitant treatment that might jeopardise the participant's safety or compromise the integrity of the study
• Participation in an interventional trial with an investigational medicinal product (IMP) or device
• Current or recent (past month) prescribed medication use, with particular attention to cardiovascular drugs, steroids, NSAIDs, and centrally-acting drugs (excluding isolated over-the-counter use such as ibuprofen or paracetamol, and hormonal contraceptives in women)
• Use of psychotropic medication within the past year (e.g., antidepressants, anxiolytics, antipsychotics)
• Use of antibiotics within three months preceding the study
• Use of pre- or probiotics within one month preceding the study
• Current or recent (past month) infection (e.g., common cold, influenza, COVID-19)
• Recent (past month) vaccination
• Pregnant or lactating women
• Previous or current substance or alcohol dependence or abuse (>2 units/day or >14 units/week)
• Smoking
• Night-shift work
• Adherence to special diets (e.g., vegan, vegetarian, weight-loss, lactose-free, gluten-free)
• Previous experience with or knowledge of any of the cognitive tasks used in the study (questionnaires excluded)
• C-reactive protein higher than 0.5mg/dL on the day of the injection.
• Colour vision deficiency or colour-blindness

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Quadruple blind

Primary purpose

Basic science

Study locations

Belgium · 1 center

• University Hospital Leuven (UZ Leuven) — Leuven

Identifiers

NCT: NCT07713641 · S69844

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗