ISSLS prize winner: repeated disc injury causes persistent inflammation.
METHODS
An in vivo rat model of disc degeneration with emphasis on characterizing acute and chronic cytokine production.


OBJECTIVE
To compare the morphologic and proinflammatory response between a single and triple-stab injury in attempts to establish mechanisms of chronic disc inflammation.


BACKGROUND
The features that distinguish physiologic (asymptomatic) from pathologic (symptomatic) degeneration are unclear. Epidemiologic evidence suggests that cumulative damage and elevated disc cytokine levels may be linked to increased low back pain rates. Although acute injury stimulates a healing response that includes transient cytokine production, repetitive damage may be necessary to trigger the persistent inflammation suspected to underlie chronic pain.


METHODS
Tail discs were exposed surgically and stabbed with a number 11 blade. During the subsequent acute healing phase, triple-stab discs were percutaneously injured with a 23-gauge needle at day 3 and then again at day 6 after the initial blade incision. Cytokine (IL-1 beta, IL-6, IL-8, and TNF-alpha) production was quantified using enzyme linked immunosorbent assay, and, in addition to MAPK signaling pathways (phosphorylated forms of ERK, JNK, and p38), was localized by immunohistochemistry. Disc architecture was evaluated using histology.


RESULTS
Both single-stab and triple-stab discs degenerated with time, yet degeneration was more severe with repeated injury where nuclear proteoglycan was replaced by disorganized collagen. Four days after single-stab, there was a transient peak in IL-1 beta and IL-8 production that was localized to the wound track and associated granulation tissue. By contrast, triple-stab induced an activated annular fibroblast phenotype (p38 positive) that caused a prolonged, diffuse inflammatory response with elevated levels of TNF-alpha, IL-1 beta, and IL-8 up to 28 days after injury. Disc inflammation was accompanied by reactive changes in the adjacent vertebral marrow spaces that was initially lytic at day 4, becoming sclerotic by day 56.


CONCLUSIONS
Our results demonstrate that repeated injury during active healing leads to persistent inflammation and enhanced disc degeneration. These data support the premise that damage accumulation and its associated inflammation may distinguish pathologic from physiologic disc degeneration. In the future, this triple-stab model may be useful to evaluate the efficacy of anti-inflammatory low back pain treatments.
Ulrich
Jill A
JA
Orthopaedic Bioengineering Laboratory, Department of Orthopaedic Surgery, University of California at San Francisco, San Francisco, CA 94143-0514, USA.
Liebenberg
Ellen C
EC
Thuillier
Daniel U
DU
Lotz
Jeffrey C
JC
D000208:Acute Disease; D000818:Animals; D001363:Awards and Prizes; D002908:Chronic Disease; D016207:Cytokines / Q000378:metabolism*; D015299:Discitis / Q000150:complications / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D007403:Intervertebral Disc / Q000201:enzymology / Q000293:injuries* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D017116:Low Back Pain / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D008233:Lymphotoxin-alpha / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013122:Spinal Diseases / Q000150:complications* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors; D014945:Wound Healing; D014951:Wounds, Stab / Q000150:complications* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D016207:Cytokines; D053583:Interleukin-1beta; D015850:Interleukin-6; D016209:Interleukin-8; D008233:Lymphotoxin-alpha; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases