The purpose of this study is to determine whether Urinary Kallikrein has an additional effect on enhancing collateral circulation in symptomatic intracranial atherosclerotic patients under clopidogrel and aspirin dual antiplatelet therapy.

Inclusion Criteria:

1. Acute ischemic stroke or TIA within 72 hours;
2. Intracranial ICA, MCA M1 segment stenosis (>70%)

Exclusion Criteria:

1. >70% Stenosis in an intracranial artery other than the culprit artery.
2. >50% Stenosis of an extracranial carotid or vertebral artery on the ipsilateral side.
3. Perforator strokes based on MRI.
4. Non-atherosclerotic lesion, for example, moyamoya disease, vascular inflammatory disease due to infection, autoimmunity diseases, developmental or genetic abnormalities, for example, fibromuscular dysplasia, sickle-cell anaemia, suspected vasospasm.
5. Potential cardiac embolism as cause.
6. Intracranial haemorrhage within 6 weeks.
7. Concomitant intracranial tumour, aneurysm or arteriovenous malformation.
8. Known contraindications for heparin, aspirin, clopidogrel or contrast.
9. Haemoglobin <10 g/dL, blood platelet count <100 000, international normalisation ratio >1.5, or other uncorrectable coagulopathies.Impaired liver function (alanine aminotransferase or glutamic oxalacetic transaminase ≥ 3×upper limit of normal) or renal function (serum creatinie ≥ 1.5mg/dl);
10. A baseline modified Rankin Score of ≥3.
11. Life expectancy of <1 year due to the concomitant illness.
12. Pregnant or lactating women.
13. long-term statins users.
14. History of mental instability or dementia.