The BBB is created by a special system of brain microvascular endothelial cells (BMECs), pericytes (PCs), the capillary basement membrane, and the terminal branches (“end-feet”) of astrocytes (ACs). The key function of the BBB is to protect the central nervous system (CNS) from potentially harmful/toxic substances in the bloodstream by selectively controlling the entry of cells and molecules, including nutrients and components of the immune system. The loss of BBB integrity in response to neuroinflammation, as manifested by an increase in permeability, depends predominantly on the activity of proinflammatory cytokines. However, the pathomechanism of structural and functional changes in the BBB under the influence of individual cytokines is still poorly understood. This review summarizes the current state of knowledge on this topic, which is important from both pathophysiological and therapeutic points of view. The structures and functions of all components of the BBB are reviewed, with emphasis given to differences between this and other locations of the circulatory system. The protein composition of the interendothelial tight junctions in the context of regulating BBB permeability is presented, as is the role of pericyte–BMEC interactions in the exchange of metabolites, ions, and nucleic acids. Finally, the documented actions of proinflammatory cytokines within the BBB are discussed.

The impact of diet on human health is constantly being researched. Nutrition is one of the most powerful tools for influencing gene expression, and dietary habits can promote the expression of genetic predisposition to obesity, diabetes, cardiovascular disease, cancer, and neurodegenerative diseases (NDs). The dietary inflammatory index (DII) is a numerical score that assesses the pro-or anti-inflammatory potential of a given diet. According to high DII scores, a Western diet or a standard American diet (SAD) has proinflammatory properties. By disrupting the gut microbiome, SAD creates an unfavorable environment in the intestine that is associated with a low-grade systemic inflammatory response and oxidative changes that may promote the development of NDs. An increased intestinal permeability and loss of blood–brain barrier (BBB) integrity play key roles in the pathomechanisms of diet-dependent NDs, leading to proinflammatory signaling via the gut–brain axis. The aim of this narrative review is to present in detail the current state of knowledge on the function of the gut–brain axis depending on the pro-/anti-inflammatory potential of the diet, measured by the DII, in the context of the contributions of intestinal and BBB permeability disorders to the development of NDs.

The BBB is created by a special system of brain microvascular endothelial cells (BMECs), pericytes (PCs), the capillary basement membrane and the terminal branches (“end-feet”) of astrocytes. The key function of the BBB is to protect the central nervous system (CNS) from potentially harmful/toxic substances in the bloodstream by selectively controlling the entry of cells and molecules, including nutrients and components of the immune system. The loss of BBB integrity in response to neuroinflammation, as manifested by an increase in permeability (leakage), occurs with the dominant participation of proinflammatory cytokines. However, the pathomechanism of structural and functional changes in the BBB under the influence of individual cytokines is still poorly understood. This review summarizes the current state of knowledge on this topic, which is important from both pathophysiological and clinical–therapeutic points of view. The structures and functions of all components of the BBB are discussed, with particular attention given to the phenotypic differences between BMECs and the vascular endothelium in other locations of the circulatory system. The protein composition of the interendothelial tight junctions in the context of regulating BBB permeability is presented, as is the role of pericyte–BMEC interactions in the exchange of metabolites, ions and nucleic acids. Finally, the documented actions of proinflammatory cytokines within the BBB are summarized.