Imagine you suddenly suffer from intravascular hemolysis! Do you know what that is?

You have been told that the cause can be a scary sounding disease like subarachnoidal bleeding, autoimmune transfusion reactions, preeclampsia, intraventricular hemohorrhage or a probably more familiar sounding one like malaria (Andersen et al., 2012; Nantasenamat, Prachayasittikul and Bulow, 2013).

What is going to happen to you? What is going to help you?

You don't know? Then you have found the perfect website!

During intravascular hemolysis, which is the breakdown of erythrocytes in the blood vessels, the erythrocytes release haemoglobin (Hb) into the blood plasma. Haemoglobin is the carrier molecule of diatomic gases such as carbon monoxide, nitric oxide and dioxygen. In humans it is normally found in tetrameric form. However, when being released into the plasma it dissociates as two dimers and its highly reactive haem groups can cause oxidative damage to the tissue by formation of free radicals (Nantasenamat, Prachayasittikul and Bulow, 2013).

So, how can that be prevented? The answer is the glycoprotein haptoglobin (Hp).

It binds to haemoglobin dimers in the blood plasma with very high affinity (K_D = 10^-14) forming the haptoglobin-haemoglobin complex (Figure 1) (Nantasenamat, Prachayasittikul and Bulow, 2013).

Figure 1: Haptoglobin-Haemoglobin complex. The haemoglobin chains are shown in blue and haptoglobin chains in red/purple

The protein complex shows high affinity to the macrophage scavenger receptor CD163 that allows engulfment and degradation in macrophages. It is very important to look at the interactions between Hb and Hp in the complex to understand how binding prevents toxicity of Hb. This might have clinical relevance in allowing deactivation and removal of free Hb during surgical operations (Alayash et at., 2013).

Have a look around on our website to find out more and remember that you can click on pictures to enlarge them!