Half a hundred white lab rats have seemingly proved a point: Grievous injury to the human spinal cord need not mean the rest of life wheelchair-bound. Each year, approximately 10,000 Americans sustain crippling trauma to their spinal cords.
“Although there have been encouraging reports of deficit reduction and axonal regrowth in efforts to correct spinal cord injury [SCI],” observed Harvard neuroscientist Evan Snyder, “as yet there is no practical treatment for SCI.” With the help of his 50 laboratory rats, he aims to reverse that situation. Synder is senior author of a paper in the Proceedings of the National Academy of Sciences (PNAS), dated March 5, 2002. Its title: “Functional recovery following traumatic spinal cord injury mediated by a unique polymer scaffold seeded with neural stem cells.”
“These findings imply a possible regeneration component,” Snyder told BioWorld Today. “They may suggest a new approach to SCI, and serve as a prototype for multidisciplinary strategies against complex neurological problems.
“We sought a conceptually new approach that simulated the architecture of the healthy spinal cord,” Snyder observed. “The implant we designed consisted of a polymer seeded with neural stem cells, modeled after the gray and white matter of the intact cord. The scaffold is designed to fit into a variety of cavities. In this PNAS study, it contours into the cavity created by a midline lateral hemisection in the spinal cord of an adult rat. We hypothesized that this degradable, synthetic fixture might mitigate secondary injury, impede glial scarring, direct cell replacement, facilitate regeneration and guide repair to create a more physiologically relevant structure. The scaffolds,” he went on, “were fabricated from a blend of 50:50 poly(lactic-co-glycolic acid) chosen to achieve a degradation rate of 30 to 60 days.
“To better direct repair following spinal cord injury,” Snyder continued, “we designed an implant modeled after the intact spinal cord. It consisted of a multicomponent polymer scaffold seeded with neural stem cells. Implantation of that unit into an adult rat hemisection model of SCI promoted long-term improvement in function persisting for one year in some animals. At 70 days post-injury,” he recounted, “animals implanted with scaffold plus cells exhibited coordinated, weight-bearing hindlimb stepping. Histology suggested that this recovery might be attributable partly to diminished glial scarring.” (See BioWorld Today, Jan. 31, 2002, p.1.)
Spinal Microsurgery Crippled Rats Reversibly
Snyder described the surgical spinal cord injury inflicted on his 50 adult female rats: “Under anesthesia, using a dissecting microscope, we made a laminectomy at the ninth to 10th thoracic spinal vertebrae, following by a lateral hemisection. For this, with a surgical blade, we created a 4-millimeter-long longitudinal incision along the midline of the cord, followed by lateral cuts at the rostral and caudal ends.” He characterized the four cohorts into which the 50 animals were divided each reflecting a different permutation of the construct: “Either the full treatment, consisting of inserting the NSC-seeded scaffold scaffold plus cells’ 13 rats, or one of three control treatments (polymer implant without NSCs scaffold alone’ (11 rats); NSCs suspended in medium cells alone’ (12 rats); or hemisection alone lesion control’(12 rats).
“One day post-injury, and weekly thereafter,” Snyder reported, “behavioral analyses fielded a battery of three physical performance tests to rate open-field locomotion the ability to maintain body position on an inclined plane; contact-righting reflex; and spinal-cord-mediated hindlimb withdrawal in response to pain.
“For the inclined-plane test,” he recounted, “the highest degree of inclination was defined to see if the animal could maintain its position for five seconds on two separate trial runs.
“Open-field locomotion on both the ipsilateral and contralateral sides in the scaffold-plus-cells group,” the PNAS paper summed up, “was significantly enhanced in the subchronic phase (up to 28 days post injury) with respect to both rate and absolute level of improvement achieved. This enhanced performance was maintained into the chronic phase of recovery (70 days post-injury). Performance of the unlesioned side mirrored the lesioned side, both in absolute mean values achieved and statistical significance.
“Both hindlimbs were affected, and recovery of both was improved by the scaffold-plus-cells intervention. In the late chronic stage (56 days p.i. and later) they scored frequent-to-consistent, weight-supported plantar stepping, and occasional forelimb-hindlimb coordination. In contrast, the cells-alone and lesion-control cohorts scored very low.
“Encouragingly,” the paper noted, “the scaffold-alone group scored in the 9 performance range, indicating the onset of weight-supported locomotion. This suggested that even the scaffold-alone contingent was capable of leading to improvement in functional recovery. Defining the onset of significant walking behavior as achieving a score of 10 or more at 70 days p.i., 69 percent of the scaffold-plus-cells groups, 54 percent of scaffold alone, but only 17 percent of cells-alone and 33 percent of lesion-control cohorts attained scores of at least 10.
“For inclined-plane performance, animals were tested facing both upward and downward. Upward-facing performance reflected forelimb strength which should be unaffected by this spinal cord injury in healthy animals; downward measures hindlimb motor function. Overall, the inclined-plane results suggest that the scaffold-plus-cells intervention is associated with significantly long-term improvement of motor function.
“A controlled brief pinch of the toes induced a normal pain withdrawal reflex. At 70 days p.i., approximately 50 percent of the rats regained a normal pain reflex on the lesioned side.
“We hypothesize,” Snyder observed, “that the scaffold may impede scarring and subsequent cyst formation. The absence of scar formation is correlated with a higher degree of tissue preservation at the injury epicenter.”
Splints As Resorbable As Surgical Sutures
“Although the mechanism by which the scaffold may augment recovery is not known, in vitro evidence suggests that the outer scaffold inhibits ingrowth of a variety of cell types. Because the scaffold is completely degradable like surgical sutures this inhibition is temporary. The mechanism by which the scaffold and neural stem cells augment functional recovery need to be explored further,” Snyder allowed.
Summing up, he concluded, “Implantation of the scaffold with NSCs significantly improves functional recovery compared with cells alone and lesion controls. Indeed, eight scaffold-plus-cell animals maintained for one year p.i. continue to show enduring recovery with respect to performance scoring.”