Mechanism of action tacrolimus is ?
**Core Concept**
Tacrolimus is a calcineurin inhibitor, which means it works by inhibiting the activity of calcineurin, a phosphatase enzyme involved in the activation of T-lymphocytes. This action is crucial in preventing the immune system from attacking the transplanted organ.
**Why the Correct Answer is Right**
Calcineurin is a key regulator of the immune response, responsible for dephosphorylating and activating nuclear factor of activated T-cells (NFAT). When tacrolimus binds to FKBP-12 (a protein), it forms a complex that inhibits calcineurin, thereby preventing the dephosphorylation of NFAT. This leads to a decrease in the transcription of genes involved in the immune response, including interleukin-2 (IL-2), which is essential for T-cell proliferation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as tacrolimus does not act by inhibiting the activity of mTOR (mechanistic target of rapamycin).
**Option B:** This option is incorrect as cyclosporin is another calcineurin inhibitor, but it works by binding to cyclophilin rather than FKBP-12.
**Option C:** This option is incorrect as sirolimus (rapamycin) is an mTOR inhibitor, which has a different mechanism of action compared to tacrolimus.
**Clinical Pearl / High-Yield Fact**
Tacrolimus is known for its nephrotoxicity, which can manifest as acute or chronic kidney injury. Monitoring of serum creatinine levels and urine output is essential to prevent and manage tacrolimus-induced nephrotoxicity.
**Correct Answer: C. Inhibition of calcineurin by binding to FKBP-12**