Use of azathioprine as an alternative has shown to reduce the incidence of gouty arthritis.Ciclosporin is listed as an IARC Group 1 carcinogen (i.e. there is sufficient evidence of carcinogenicity in humans), specifically leading to squamous cell skin cancer and non-Hodgkin lymphoma. Pharmacology
Mechanism of action
Ciclosporins main effect is to lower the activity of T-cells; it does so by inhibiting calcineurin in the calcineurin–phosphatase pathway and preventing the mitochondrial permeability transition pore from opening. Ciclosporin binds to the cytosolic protein cyclophilin (immunophilin) of lymphocytes, especially of T cells. This cyclosporin—cyclophilin complex inhibits calcineurin, which is normally responsible for activating the transcription of interleukin 2. In T-cells, activation of the T-cell receptor normally increases intracellular calcium, which acts via calmodulin to activate calcineurin. Calcineurin then dephosphorylates the transcription factor NF-AT (nuclear factor of activated T-cells), which moves to the T-cell nucleus and increases the transcription of genes for IL-2 and related cytokines. Ciclosporin, by preventing the dephosphorylation of NF-AT, leads to reduced effector T-cell function; it does not affect cytostatic activity.Ciclosporin also binds to the cyclophilin D protein that constitutes part of the mitochondrial permeability transition pore (MPTP), thus preventing MPTP opening. The MPTP is found in the mitochondrial membrane of cardiac muscle cells. MPTP opening signifies a sudden change in the inner mitochondrial membrane permeability, allowing protons and other ions and solutes of a size up to ~1.5 kDa to go through the inner membrane. This change of permeability is considered a cellular catastrophe, leading to cell death.
In Japan, neonatal screening was previously performed on infants within one month of birth; infants demonstrating a blood histidine level of 6 mg/dl or more underwent careful testing as suspected histidinemia cases. A typical characteristic of histidinemia is an increase in the blood histidine levels from normal levels (70–120 μM) to an elevated level (290–1420 μM). Further testing includes: observing histidine as well as imidazolepyruvic acid metabolites in the urine. However, neonatal urine testing has been discontinued in most places, with the exception of Quebec. Treatment
It has been suggested that a possible method of treatment for histidinemia is through the adoption of a diet that is low in histidine intake. However, the requirement for such dietary restrictions is typically unnecessary for 99% of all cases of histidinemia. Prevalence
Histidinemia is a rare autosomal recessive disorder. However, histidinemia is considered the most prevalent inborn error of metabolism with a reported incidence of 1:8600 (Quebec); 1:180,000 (New York) and 1:9600 (Japan); and an average of 1:12,000 observed in the neonatal screening of over 20 million newborns. See also
Prolinemia
Sarcosinemia
Tyrosinemia

References


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