Haptoglobin And Cerebral Vasospasm After Subarachnoid Hemorrhage

BACKGROUNDCerebral vasospasm (CVS) is a leading cause of poor outcome after subarachnoid hemorrhage (SAH). Identifying patients at risk of CVS would allow for selective and targeted care. It could also lead to novel therapeutics aimed at reducing the incidence and severity of CVS. It is generally agreed that hemoglobin (Hb) released from decayed red blood cells triggers cerebral arterial constriction. Haptoglobin (Hp) is a plasma protein that binds extracellular hemoglobin to inhibit Hb's oxidative cytotoxicity. It also facilitates the uptake and degradation of hemoglobin by hepatocytes and monocytes/macrophages. Hp is composed of two polypeptide chains: theα-chain and theβ-chain. A genetic polymorphism has been described that leads to the generation of two distinct alleles, Hp1 and Hp2, which define three major haptoglobin genotypes and phenotypes:Hp1-1, Hp1-2 and Hp2-2. In humans, levels of plasma Hp varies considerably ranging from 30 to 300 mg/dl.METHODSInclusion criteria1, Older than 18 years of age.2, SAH onset was known.3, SAH resulted from aneurysm.4, SAH had a Fisher Grade of 3(i.e. greater than 1-mm-thick blood layers or clots) as detected by CT scan within 48 hours after ictus.5, SAH had a Hunt-Hess score of 2-3.6, extension of the hemorrhage into the brain parenchyma or ventricular system was acceptable if other CT criteria and Hunt-Hess score were met.Determination of symptomatic cerebral vasospasm (SCVS)Symptomatic cerebral vasospasm, which was defined by meeting one or more of three indexes and other potential etiologies being excluded as the cause. First, patients had a deteriorated conscious state that was determined by decrease in at least 2 points on Glasgow Coma Scale score. Second, patients developed new neurologic symptoms. Third, patients had ischemic injury on repeated computerized tomography(CT) scans that was not detected on the admission or immediate postoperative CT scans. Determination of Iconographic CVS (ICVS)Transcranial Doppler (TCD) was used as the secondary measure of delayed-vasospasm. Bilateral TCD measurements of blood flow velocities in nine cerebral arteries were performed between 7-14 days after ictus adapted from a report by Sloan et al. A flow velocity above the threshold of "possible" but under the "presumed definite" vasospasm was further analyzed by Lindegaard ratio. If a flow velocity ratio of the middle cerebral artery to extracranial internal carotid artery was greater than 3, vasospasm was diagnosed.Plasma HaptoglobinA plasma haptoglobin was measured by a commercial enzyme linked immunosorbent assay(ELISA) Kit according to the manufacturer's instructions. A standard curve was generated on CurveExpert 1.3 and used to determine Hp concentrations in blood samples.Haptoglobin genotypingTwo methods were used to accurately genotype Hp:polyacrylamide gel electrophoresis and a TaqMan-based real-time polymerase chain reaction (PCR).RESULTSThe mean level of peripheral blood Hp was 50.56±30.35 mg/dl for SCVS positive patients, significantly lower than 68.45±36.69mg/dl for SCVS negative patients (p=0.037). It was 57.83±33.38mg/dl and 63.16±39.47mg/dl for ICVS positive and negative patients(p=0.563). SCVS was found of 28.57%(2/7),56.52% (13/23) and 47.06% (16/34) in Hp1-1, Hp1-2 and Hp2-2 genotypes(p=0.420). ICVS was found of 57.14%(4/7),52.17%(12/23)and 47.06%(16/34)in Hp1-1, Hp1-2 and Hp2-2 genotypes(p=0.859). However, there is a disparity between clinically determined and TCD-determined CVS in patients with Hp1-1 genotype (28.57% vs. 57.14%, p=0.592).Conclusions:These findings suggest that Hp concentration in peripheral blood associates with delayed SCVS after aneurysmal SAH. Patients with Hp1-1 genotype show a tendency toward to a lower incidence of SCVS.