The role of hyperosmotic stress in inflammation and disease

Abstract

Hyperosmotic stress is an often overlooked process that potentially contributes to a number of human diseases. Whereas renal hyperosmolarity is a well-studied phenomenon, recent research provides evidence that many non-renal tissues routinely experience hyperosmotic stress that may contribute significantly to disease initiation and progression. Moreover, a growing body of evidence implicates hyperosmotic stress as a potent inflammatory stimulus by triggering proinflammatory cytokine release and inflammation. Under physiological conditions, the urine concentrating mechanism within the inner medullary region of the mammalian kidney exposes cells to high extracellular osmolarity. As such, renal cells have developed many adaptive strategies to compensate for increased osmolarity. Hyperosmotic stress is linked to many maladies, including acute and chronic, as well as local and systemic, inflammatory disorders. Hyperosmolarity triggers cell shrinkage, oxidative stress, protein carbonylation, mitochondrial depolarization, DNA damage, and cell cycle arrest, thus rendering cells susceptible to apoptosis. However, many adaptive mechanisms exist to counter the deleterious effects of hyperosmotic stress, including cytoskeletal rearrangement and up-regulation of antioxidant enzymes, transporters, and heat shock proteins. Osmolyte synthesis is also up-regulated and many of these compounds have been shown to reduce inflammation. The cytoprotective mechanisms and associated regulatory pathways that accompany the renal response to hyperosmolarity are found in many non-renal tissues, suggesting cells are commonly confronted with hyperosmotic conditions. Osmoadaptation allows cells to survive and function under potentially cytotoxic conditions. This review covers the pathological consequences of hyperosmotic stress in relation to disease and emphasizes the importance of considering hyperosmolarity in inflammation and disease progression.

Figure 1

Hyperosmotic stress and osmoadaptation. Hyperosmotic stress negatively affects many cellular processes. If left unchecked, the cell is primed for, and eventually undergoes, apoptosis. Osmoadaptive mechanisms are in place to counter osmotic stress, and restore water balance and cell homeostasis.

Figure 2

Carbohydrate osmolyte structures. The carbohydrate osmolytes include polyols, such as glycerol, adonitol, xylitol, sorbitol, and mannitol, and cyclitols, such as myoinositol and trehalose.

Figure 3

Methylamine osmolyte structures. The methyamine osmolytes include glycine betaine, triethylamine, and α-glycerophosphocholine. Under certain conditions, methylamines act as excellent molecular chaperones, stabilizing the structure of DNA, RNA, and protein.

Figure 4

Amino acid osmolyte structures. A number of amino acids can function as osmolytes, including glycine, valine, leucine, isoleucine, β-alanine, and proline. The sulfur-containing compounds, taurine and hypotaurine, are also considered amino acid osmolytes.