What is CYP3A5?
CYP3A5 is one of the cytochrome P450 monooxygenases (CYPs). These are enzymes that eliminate most of the drugs and toxins from the human body .
This enzyme is very similar in structure and function to CYP3A4 . However, unlike CYP3A4, it’s activity varies greatly between people, and many actually don’t have a functional version of this enzyme.
The enzyme is functional in most Africans, but in few Whites .
In people who do have this enzyme, it can represent over 50% of the total liver CYP3A activity , contributing greatly to CYP3A metabolism.
This enzyme metabolizes:
- Antihypertensive drugs: felodipine  and nifedipine .
- Immune suppressants: sirolimus , tacrolimus [7, 8] and cyclosporine A .
- Antiemetics: granisetron .
- Anticancer drugs: lapatinib  and vincristine .
- TNF inhibitor etanercept .
- Cholesterol-lowering drugs: simvastatin and atorvastatin 
- Sedatives midazolam and alprazolam (Xanax) .
- Antibiotic erythromycin .
- Antiretroviral drugs: saquinavir .
It plays an important function in the kidneys and may be related to blood pressure .
This enzyme can act as a tumor suppressor.
CYP3A5 combats hepatocellular carcinoma (liver cancer). Lower enzyme levels were associated with more aggressive disease, shorter time to disease recurrence after treatment, and worse overall patient survival .
A nonfunctional enzyme variant increased the risk of developing acute and chronic leukemia, emphasizing the significance of effective Phase I detoxification in fighting cancer (144 patients and 241 controls) .
This enzyme promotes prostate cancer cell growth .
Japanese women with the functional enzyme had a higher risk of breast cancer (873 subjects) .
There are over 25 variants of this enzyme . Many of them are nonfunctional.
The fully functional variant is known as the CYP3A5*1 .
The frequency of the functional variant is substantially different across ethnic groups. The functional enzyme is found in 45–94% of subjects of African descent, 8–15% of Whites and 23–40% of Asians [15, 2].
People with the functional variant may be more susceptible to salt-sensitive hypertension (elevated blood pressure) (373 and683 subjects) [19, 20]. CYP3A5*1 carriers tend to reabsorb more sodium in the kidneys as they get older .
Enhanced kidney sodium re-absorption could have an advantage in equatorial populations experiencing water shortage by increasing sodium retention. This may explain why this variation is correlated with the geographical distance from the equator .
Japanese women with the functional enzyme have a higher risk of breast cancer (873 subjects) .
Having this variant increases the risk of acute leukemia (ALL), chronic leukemia (CML), and colorectal cancer, especially among Asian and Caucasian populations (meta-analysis, 17 studies, 7,458 cancer patients, and 7,166 controls) .
Children with this variant that use inhaled beclomethasone have improved asthma control (64 subjects) .
Increasing or Decreasing CYP3A5
It is very likely that many of the compounds that increase or decrease CYP3A4 also increase or decrease the CYP3A5 enzyme. However, compared to CYP3A4, a lot less research has been carried out testing CYP3A5. Studies that include this enzyme are listed below.