Circulating human C-reactive protein binds very low density lipoproteins.

Area of Science:

• Biochemistry
• Immunology
• Clinical Chemistry

Background:

• C-reactive protein (CRP) is an acute-phase protein involved in innate immunity.
• Hyperlipoproteinaemia encompasses various disorders characterized by abnormal lipoprotein levels.
• The interaction between CRP and lipoproteins is not fully understood, particularly in specific hyperlipoproteinaemia subtypes.

Purpose of the Study:

• To investigate the binding interactions between native human CRP and specific lipoproteins.
• To determine the influence of different hyperlipoproteinaemia types on CRP-lipoprotein complex formation.
• To elucidate the characteristics of CRP-lipoprotein binding, including calcium dependence and inhibition.

Main Methods:

• Analysis of CRP complex formation in patient sera with various hyperlipoproteinaemia types (III, IV, V, IIa).
• In vitro experiments involving the addition of isolated lipoproteins (beta-VLDL, LDL, normal VLDL) to acute phase serum or purified CRP.
• Assessment of binding specificity using human and rabbit CRP with homologous and heterologous lipoproteins.

Main Results:

• Human CRP formed soluble complexes with abnormal beta-VLDL in sera from patients with type III, IV, and V hyperlipoproteinaemia.
• Complex formation was calcium-dependent and inhibited by free phosphorylcholine, but not observed with high LDL levels (type IIa).
• Isolated beta-VLDL induced CRP-lipoprotein complex formation in normolipoproteinaemic serum, while normal VLDL caused agglutination.

Conclusions:

• Human CRP specifically binds to abnormal beta-VLDL in certain hyperlipoproteinaemia conditions.
• The binding is calcium-dependent and sensitive to phosphorylcholine, suggesting a specific molecular interaction.
• These findings highlight a potential role for CRP-lipoprotein interactions in the pathophysiology of specific dyslipidaemias.