Purified lipase, injected intracerebrally and intravasculariy in rabbits, gave rise to focal areas of demyelinization in the central nervous system in 10 of 13 animals so treated. In one instance the lesions became manifest within 48 hours and in another they persisted for 6 months; they were not infrequently accompanied by paresis and by tilting or tremor of the head. They were characterized by a focal loss of myelin and moderate gliosis with little or no neuronal destruction or inflammatory reaction, in these respects resembling the plaques of multiple sclerosis. The intracerebral injection of trypsin and chymotrypsin in control animals failed to produce the characteristic demyelinization, but by contrast caused focal areas of necrosis in which all the cerebral tissues were involved. Furthermore, demyelinization did not result when heat-inactivated pancreatic lipase was injected intracerebrally, and similarly negative results were obtained when an incubated mixture comprised of fatty connective tissue that had been acted upon by the pancreatic preparation and then heated to inactivate the lipase, was injected into the brains of rabbits.
In supplementary experiments the pancreatic lipase preparation and fresh rabbit brain, incubated together in vitro, were found to form acid, presumably owing to the breakdown of brain lipids to fatty acids; trypsin and chymotrypsin mixed with brain in control experiments failed to form acid. When incubated with segments of the spinal cord of experimental animals, the lipolytic enzyme brought about a loss of stainable myelin in peripheral areas and in the spinal nerve roots; again trypsin and chymotrypsin had no such effect in control experiments.
The findings as a whole show that an enzyme preparation with lipolytic activity has the ability to destroy myelin in living animals, and in vitro as well, and to produce lesions remarkably similar to those of multiple sclerosis. They have additional interest in light of the demonstration that a lipolytic enzyme is regularly present in the reactive histiocytes of guinea pigs with experimental encephalomyelitis (5).