Cerebrospinal fluid and plasma apolipoproteins in patients with multiple sclerosis

Apolipoprotein (apo) E is synthesized by cells of the central and peripheral nervous systems, and its synthesis and secretion in the peripheral nervous system of animals are greatly stimulated following Wallerian degeneration. It has been suggested that apo E functions in the metabolism of myelin lipids, but its physiologic role in nervous tissue has not been elucidated. To determine if apo E might play a role in demyelinating neuropathy, the concentrations were examined of apos E and A-1 in the cerebrospinal fluid (CSF) and plasma of patients with multiple sclerosis during clinical remission, and in patients with no neurologic disease. Serum and CSF albumin concentrations were measured to account for the possible influences of serum apo E concentration and/or altered blood-brain barrier permeability on the CSF apo E pool. A CSF index for apo E and apo A-1 was calculated in the same manner presently used for calculation of immunoglobulin G (IgG) production in the nervous system of patients with multiple sclerosis (MS). The results showed that the concentrations of apo E, apo A1, and albumin in the CSF of the MS patients were not significantly altered. The concentration of apo E in the serum, however, was significantly (p < 0.001) decreased by 44 percent in the MS patients. The difference was relatively specific for serum apo E because the serum apo A1 and albumin concentrations were unchanged. The calculated CSF apo E index in the MS patients was increased by a factor of four over the control patients; however, the decreased serum apo E concentration, by decreasing the denominator of the equation, accounted for most of the increase in the calculated CSF apo E index in the MS patients. Our data, therefore, do not support the suggestion that the CSF apo E concentration or the calculated index would be useful diagnostically for measuring demyelination or remyelination in MS patients. They do, however, indicate that the serum apo E concentration is altered in certain MS patients. The latter finding is potentially important clinically because serum apo E is a potent suppressor of lymphocyte-mediated immune function and might be related to altered suppressor T lymphocyte function observed in the peripheral blood MS of patients.