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Research Newsletter-Spring/Summer 2010


Tyler Barker, LPI Graduate Fellow

The anterior cruciate ligament (ACL) is an integral component of knee structure and function. Its role is to limit excessive knee rotation and provide stability to the knee joint. Unfortunately, every year approximately 200,000 Americans injure their ACL. In nearly half the cases, this injury to the ligament requires reconstructive surgery. Immediate and persistent muscle dysfunction commonly follows the injury and surgical repair of a ruptured ACL. Despite advances in orthopedic surgery, physical therapy, and medicine, muscle dysfunction, especially weakness, can continue for years. Although impaired neurological feedback from the surgically repaired knee and reduced physical activity contribute to the muscle dysfunction, the reasons for muscle atrophy and weakness remain a mystery.

We are interested in ACL injury because oxidative stress may play an important role in exacerbating muscle degeneration. Both oxidative stress and pro-inflammatory molecules called cytokines induce muscle dysfunction during aging and in chronic heart failure patients. Therefore, our findings may be applicable to people other than those with ACL injury. Because vitamins E and C are potent dietary antioxidants that modulate diverse inflammatory cytokines, we conducted a randomized, double-blind, placebo-controlled study to investigate the influence of vitamin E and C supplementation on the recovery from ACL reconstructive surgery. We made three major discoveries that we discuss further below.

  1. Vitamin E and C supplementation lowers the increase of an anti-inflammatory cytokine (interleukin-10 or IL-10) and stabilizes the depression of a pro-to-anti-inflammatory cytokine ratio (i.e., IL-6:IL-10) immediately following surgery.
  2. The recovery of leg strength following ACL reconstruction is associated with vitamin C levels in blood prior to surgery and with elevated vitamin C levels post-surgery following vitamin E and C supplementation.
  3. Greater strength gains after ACL surgery are associated with lower oxidative stress and a higher pro-to-anti-inflammatory cytokine ratio but only in the subjects supplemented with vitamins E and C.

Vitamin E and C supplementation improves inflammatory status immediately following ACL surgery

During ACL surgery, a tourniquet is applied to the upper thigh of the leg that is being repaired. This procedure provides a bloodless operating field but also creates an ischemic condition in which blood and oxygen are deprived from the affected area. When the tourniquet is removed and blood begins to circulate again, the tissue is subject to what's known as ischemia-reperfusion injury. The restored flow of blood causes oxidative and inflammatory damage. Ischemia-reperfusion injury is potentiated by oxidative stress, which stimulates pro-inflammatory cytokines that further exacerbate the inflammation. Although it has been documented that there is an increase in local markers of oxidative stress following tourniquet removal, the role of the circulating inflammatory cytokine and oxidative stress marker responses to this ischemia-reperfusion insult has not been well described.

Therefore, we examined oxidative stress and inflammatory cytokines in the circulation after ACL surgery in subjects who received either a placebo or an antioxidant supplement of vitamins E (400 IU) and C (1,000 mg), taken in two equally divided daily doses starting approximately two weeks prior to surgery and continuing for three months after surgery.

As expected, we found that antioxidant supplementation doubled the vitamin E and C plasma concentrations. Nonetheless, within 90 minutes following ACL surgery, we found a significant elevation in oxidative stress in both the supplemented and placebo groups. There were no significant differences in markers of lipid peroxidation—F2-isoprostanes or malondialdehyde—between the groups. These markers decreased to baseline levels a few days following surgery. Additionally, there were increases in markers of muscle damage (creatine kinase) three days after surgery. Inflammation was also increased at three and seven days following surgery, as indicated by an elevation in the proinflammatory cytokine IL-6 and C-reactive protein. However, antioxidant supplementation did not affect biomarkers of muscle damage and inflammation following surgery.

An immune response typically follows surgery, represented by elevated blood levels of the anti-inflammatory cytokine IL-10. At 90 minutes following ACL surgery, IL-10 increased markedly in the placebo but not the antioxidant group. This is remarkable because it suggests that the antioxidant supplementation decreased the body’s need to express an anti-inflammatory cytokine. Vitamins E and C potentially prevented an increase in oxidative stress and/or pro-inflammatory cytokines and provided protection against post-surgery complications. However, further research addressing this question is required.

Another approach to assessing inflammation is to calculate ratios between pro-inflammatory (IL-6) and anti-inflammatory (IL-10) cytokines. Changes in the IL-6:IL-10 ratio, for example, may have prognostic value for poor clinical outcomes, such as infection or death. We observed that the IL-6:IL-10 ratio decreased immediately following ACL surgery. However, this depression was ameliorated in the subjects who received vitamins E and C. Whether the stabilized pro-to-anti-inflammatory cytokine ratio in our antioxidant group translates to improved recovery following surgery is unknown but warrants further investigation.

Greater strength gains after ACL surgery are associated with lower oxidative stress only in subjects supplemented with vitamins E and C

It is unknown if oxidative stress or inflammatory cytokines are associated with leg weakness following ACL surgery and whether supplementation with vitamins E and C would modulate this relationship. We found that the maximum isometric force produced by the injured leg following ACL surgery was inversely correlated with plasma F2-isoprostanes—markers of oxidative stress—within the antioxidant group. That is, the less oxidative stress, the stronger the leg. Furthermore, maximum isometric force of the injured leg also correlated with the IL-6:IL-10 cytokine ratio in the antioxidant group. Therefore, our results indicate that antioxidants decrease oxidative stress, improve the balance of pro- and anti-inflammatory cytokines, and improve the recovery from muscle damage.

Better recovery of leg strength following ACL reconstruction is associated with high plasma vitamin C levels

High levels of vitamins E and C are associated with improved strength and physical performance in the elderly. Whether supplemental vitamins E and C can improve limb strength is unknown. Therefore, we measured plasma vitamin E and C concentrations before and three months after ACL surgery in our two experimental groups described above. Not surprisingly, the injured leg was weaker than the other leg at baseline, and it remained so three months after surgery. However, greater gains in leg strength after surgery were associated with higher plasma vitamin C levels prior to surgery and with elevated vitamin C levels following supplementation, suggesting that vitamin C aids muscle recovery from ACL surgery.

Our data indicate that supplemental vitamins E and C provided protection against undesirable immunological activity after surgery. The reduction of the anti-inflammatory cytokine IL-10 by antioxidant supplementation following surgery may have provided protection against complications, as seen in other conditions. Interestingly, in the subjects supplemented with vitamins E and C, lower oxidative stress and a higher pro-to-anti-inflammatory cytokine ratio were associated with greater leg strength three months after ACL reconstruction. In conclusion, our results suggest that there is a potential therapeutic benefit of vitamin E and C supplementation on both immediate surgically-induced immunological changes and with the short-term recovery of leg strength following ACL reconstruction. Antioxidant supplementation may be of therapeutic benefit to patients suffering from other conditions involving oxidative stress and inflammation.

This work was funded, in part, by USANA Health Sciences, Inc., Salt Lake City, UT, USA.

Last updated June 2010