Diurnal uptake of circulating interleukin-1alpha by brain, spinal cord, testis and muscle

Area of Science:

• Immunology
• Chronobiology
• Neuroscience

Background:

• Cytokines are crucial signaling molecules with known diurnal patterns in their effects, synthesis, and release.
• Understanding the temporal dynamics of cytokine interaction with tissues is essential for optimizing therapeutic strategies.

Purpose of the Study:

• To investigate whether the uptake of interleukin-1alpha (IL-1α) by various tissues in mice follows a diurnal rhythm.
• To determine if other cytokines, like tumor necrosis factor-alpha (TNF-α), also exhibit diurnal uptake patterns.

Main Methods:

• Radioactive labeling of recombinant human IL-1α with iodine-125 (¹²⁵I-IL) for tracking uptake.
• Systematic measurement of ¹²⁵I-IL uptake in brain, spinal cord, testis, and muscle tissues every 4 hours in mice.
• Assessment of TNF-α uptake in the same tissues, considering its blood-brain barrier impermeability.

Main Results:

• Statistically significant diurnal variations in ¹²⁵I-IL uptake were observed across all tested tissues.
• Spinal cord showed the largest diurnal variation (nearly 10-fold), while muscle showed the least (less than 2-fold).
• Uptake peaks occurred around 08:00 or 12:00 h, with nadirs at 00:00 or 04:00 h; no significant diurnal variation in blood pharmacokinetics was found.
• TNF-α uptake did not exhibit a diurnal rhythm in any of the examined tissues.

Conclusions:

• Tissue-specific diurnal rhythms in cytokine uptake, exemplified by IL-1α, are present in mice.
• These temporal variations in uptake rates could explain differences in cytokine potency depending on administration time.
• The findings highlight the importance of considering circadian timing in cytokine-based therapies.