Question

Inhibition of 5-lipoxygenase is useful in:

• A. Cardiac failure
• B. Bronchial asthma
• C. Hepatic failure
• D. Arthritis

Hint:

5-lipoxygenase makes leukotrienes, which cause bronchoconstriction. Blocking this enzyme (for example zileuton) helps in asthma.

Answer 1

The Correct Option is B

Step 1: Recall the arachidonic acid pathway.
Arachidonic acid released from cell membranes is metabolised through two main routes: the cyclooxygenase (COX) pathway, which makes prostaglandins and thromboxane, and the lipoxygenase pathway. The 5-lipoxygenase (5-LOX) enzyme specifically converts arachidonic acid into leukotrienes.

Step 2: Recall what leukotrienes do.
Leukotrienes made through 5-LOX, particularly LTC4, LTD4 and LTE4 (together called the cysteinyl leukotrienes, or the old name "slow reacting substance of anaphylaxis"), cause strong and prolonged bronchoconstriction, increase mucus secretion, and raise vascular permeability in the airway. LTB4 additionally attracts and activates neutrophils, adding to airway inflammation.

Step 3: Connect this to bronchial asthma.
In asthma, these leukotrienes are major drivers of bronchospasm and airway inflammation. Blocking 5-LOX with a drug such as zileuton stops leukotriene production at its source, and leukotriene receptor blockers such as montelukast work on the same pathway further downstream. Both approaches reduce bronchoconstriction and are used as add-on therapy in asthma. So inhibition of 5-LOX IS useful here.

Step 4: Check the other options.
Cardiac failure is managed with drugs like diuretics, ACE inhibitors and beta blockers; the leukotriene pathway is not a standard target here. Hepatic failure is managed by treating the underlying cause and supportive care, again not through 5-LOX blockade. Arthritis (osteoarthritis and rheumatoid arthritis) is treated mainly through COX inhibition (NSAIDs) and disease-modifying drugs; 5-LOX inhibitors are not first-line or established therapy for arthritis.

Step 5: Final answer.
5-lipoxygenase inhibition is specifically useful in bronchial asthma, where it blocks the leukotrienes responsible for bronchoconstriction and airway inflammation.
\[ \boxed{\text{Bronchial asthma}} \]