Increased hypothalamic hydrogen sulphide contributes to endotoxin tolerance by down-modulating PGE₂ production

Area of Science:

• Neuroimmunology
• Physiology
• Biochemistry

Background:

• Systemic inflammation can cause altered body core temperature (Tb), with some individuals experiencing immune paralysis and normal Tb.
• Endotoxin tolerance, induced by repeated lipopolysaccharide (LPS) administration, is a model for immune paralysis, but its neuroimmune mechanisms are unclear.
• Hydrogen sulfide (H2S), a gaseous neuromodulator produced by cystathionine β-synthase (CBS) in the brain, is implicated in various physiological processes.

Purpose of the Study:

• To investigate the role of hypothalamic hydrogen sulfide (H2S) in the neuroimmune mechanisms of endotoxin tolerance.
• To determine if modulating hypothalamic H2S affects fever responses and immune signaling during endotoxin tolerance.

Main Methods:

• Rats were subjected to daily low-dose LPS administration for four days to induce endotoxin tolerance.
• Hypothalamic CBS expression and H2S production rates were measured.
• An inhibitor of H2S synthesis (AOA) was administered intracerebroventricularly to tolerant rats to assess its effect on fever and immune responses.

Main Results:

• Endotoxin tolerance was associated with increased H2S production and CBS expression in the anteroventral preoptic area (AVPO) of the hypothalamus.
• Inhibition of hypothalamic H2S synthesis reversed endotoxin tolerance, restoring fever and increasing AVPO and plasma PGE2 levels.
• Plasma cytokine surges remained suppressed despite H2S inhibition, indicating a dissociation between fever and peripheral cytokine responses.

Conclusions:

• Endotoxin tolerance involves complex neuroimmune mechanisms beyond peripheral cytokine reduction.
• Hypothalamic H2S production is a critical modulator of endotoxin tolerance and fever regulation.
• Targeting hypothalamic H2S may offer therapeutic strategies for modulating inflammatory responses and fever.