Peripheral Nerves with Higher Long-Chain Omega-3s Better Protected from Injury
Peripheral nerves—those in the trunk and limbs—connect the brain and spinal cord to all other parts of the body. They allow us to sense temperature, pressure, touch and so on. If disease or injury damages the peripheral nerves, communication between the affected area and the brain is disrupted and sensory information may not be appropriately relayed. Such circumstances make an individual more susceptible to injury, burns and falls. Damage to the peripheral nerves is called peripheral neuropathy and can be sensed by tingling, numbness, pricking sensations or muscle weakness (Illustration). Conditions that may result in peripheral neuropathy include diabetes mellitus, alcohol abuse, tumors, repetitive strain injuries, autoimmune diseases, infections and traumatic injury. Peripheral neuropathies can often be treated, sometimes cured and usually managed to prevent new damage. As long as the nerve cells have not been destroyed, peripheral nerves can regenerate.
One strategy for improving the neural sensitivity of patients with peripheral neuropathy is to promote nerve regeneration. A promising approach for this is to increase the availability of long-chain omega-3 fatty acids (omega-3s), found mainly in fish and shellfish. Research attention has focused particularly on DHA, one of the two major seafood omega-3s. Several studies in animals have shown that dietary restriction of omega-3s leads to lower levels of DHA in the brain and retina. Animals fed supplemental DHA exhibit improved visual acuity, nerve growth and resistance to damage from injury or disease. Nerves require DHA to grow and concentrate this fatty acid in their endings where growth occurs. A clear demonstration of the effect of DHA on nerve regeneration is described in a study on corneal nerves in this issue.
Other research has reported improved recovery and reduced damage after spinal cord injury in animals given DHA or omega-3s. In this article, investigators in London, UK, evaluated the effect of peripheral nerve injury and recovery in animals with higher levels of omega-3s and lower amounts of omega-6 fatty acids. They used mice specially bred to have more omega-3s and less omega-6s in their tissues and compared them with control animals.
First, the researchers analyzed the fatty acids in spinal cord neurons (Figure) and confirmed that the specially bred animals had significantly more DHA. These neurons also had higher levels of another long-chain omega-3 (DPA). Next, they stretched isolated nerve cells from these animals and assessed their ability to withstand strain. This mechanical injury resulted in a 2½-fold loss of cells compared with uninjured cells. However, cells from the high-omega-3 animals lost only 13% of their cells.
The researchers also explored the ability of the nerve cells to withstand an atmosphere of reduced oxygen. Those conditions were designed to mimic what happens when blood flow is reduced, which reduces the supply of oxygen. When the cells from control animals were kept in a low-oxygen atmosphere for a time, 8% to 21% of the cells perished. In contrast, cells from the high omega-3 animals resisted damage from the low oxygen environment and were comparable to cells not exposed to low oxygen.
Working with the whole animal, the investigators examined peripheral nerve recovery in the control and high omega-3 animals. As early as one day after sciatic nerve injury, the high omega-3 animals were more responsive to touch than the control animals. This difference was observed with the amount of force needed to provoke the injured limb to withdraw. After 4 and 7 days, both groups had improved, but the high omega-3 animals were significantly more sensitive than the control animals by day 7. In a separate evaluation, the investigators observed significantly improved recovery in the high omega-3 animals compared with the controls, although recovery was not complete.
In summary, these studies showed that peripheral nerve fibers and cells enriched in long-chain omega-3s are more resistant to injurious conditions, regenerate better and lose less functional ability compared with conventional nerve fibers. These observations suggest that higher levels of omega-3s in peripheral nerves may have protective effects and may confer greater resistance to adverse conditions. In these demonstration studies, nerve enrichment was accomplished using animals specially bred to have higher tissue levels of omega-3s. A big question is whether increasing the consumption of omega-3s would have the same effect. These findings may spark more studies aimed at improving nerve regeneration with omega-3s in individuals with peripheral neuropathy or nerve injury.