Antioxidants are key recruits in the body’s battle against aging and degeneration—and new evidence suggests that at least some of these foot soldiers are missing in amyotrophic lateral sclerosis. Scientists at the Tel Aviv Sourasky Medical Center report, in the June 22 Journal of Neurological Science online, that people with ALS have lower serum levels of the antioxidant uric acid than do age-matched controls. In addition, the researchers linked the greatest differences in uric acid to a steeper decline in disease progression. The research suggests that boosting uric acid might help ALS patients. Some support for the benefit of uric acid comes from another paper, published June 24, in the Journal of Neuroscience. Researchers from Harvard Medical School in Boston describe the use of inosine—which the body can convert into uric acid—as a treatment for stroke in rats.

Acid Off Base…
Lowered uric acid levels have been found in people with Parkinson disease (see ARF related news story; Schwarzschild et al., 2008; Weisskopf et al., 2007), and several antioxidants are diminished in Alzheimer disease (Kim et al., 2006). To see if the same was true in ALS, first author Daniel Keizman, senior author Vivian Drory, and colleagues assessed serum uric acid levels in 86 patients and 86 controls matched for gender, age, and body mass index. Control participant serum averaged 5.76 mg/dl uric acid; in people with ALS it averaged less at 4.78 mg/dl.

The authors also looked for a relationship between uric acid levels and the ALS Functional Rating Scale, which scores patients on ability to carry out tasks such as dressing and eating. While they found no direct link between uric acid levels and functional score, they did discover a relationship between two statistics: ΔUA, the difference between a patient’s uric acid level and that of the matched control; and ΔFRS, the rate of change in the functional score between two assessments approximately six months apart (46 patients returned for the second assessment). That is, those patients who had much lower uric acid levels than their control partners lost the most functionality over time.

“Our results could have several implications,” Drory wrote in an e-mail to ARF. For one, people with ALS who also have high uric acid levels from a second condition such as gout might not benefit—and might even suffer—from therapies designed to reduce uric acid. Second, she wrote: “Drugs that raise the level of uric acid might be effective in lowering the rate of disease in ALS.”

There are many ways that uric acid levels could correlate with ALS, wrote Marc Weisskopf of the Harvard School of Public Health, who was not involved in the study, in an e-mail to ARF. The lowered antioxidants could contribute to disease or be a side effect. For example, he suggested, diet is a factor in uric acid levels. “So if diets changed among the cases with ALS, could it be that those dietary changes led to the lower uric acid levels?”

…Purine on Point
If indeed uric acid-directed therapeutics could benefit people with ALS, the purine nucleoside inosine, a uric acid precursor, would be a prime candidate. Inosine has been shown to protect neurons if given to rats before they undergo surgery to cause stroke (Shen et al., 2005) and it activates the protein kinase Mst3b, part of a pathway that releases trophic factors to promote axon outgrowth (Irwin et al., 2006). In the current Journal of Neuroscience study, first author Laila Zai, principal investigator Larry Benowitz, and colleagues show that it also promotes axon growth when given to rats after ischemia and restores fine motor movements.

Zai and colleagues targeted the ischemia to the sensorimotor cortex on one side of the brain. To make a focused lesion, they injected animals with a photosensitive dye, Rose Bengal, then opened the cranium to shine light on one particular spot. The light caused the dye to release free radicals, damaging nearby cells and causing platelets to aggregate, leading to ischemia. Some lesioned rats were then treated with inosine, others received saline solution. Then, the scientists sacrificed some animals and used microscopy to look for new axon growth between the undamaged side of the brain and the ipsilateral side of the body—that is, when the left brain was lesioned, they looked for new connections between the right side of the brain and the right side of the body, or between left brain and left body when the right side was lesioned. Since there are normally very few ipsilateral connections, they could assume that any such networks were new. The researchers counted these ipsilateral axon fibers and found that the inosine-treated animals had triple the new connections of the saline-treated controls. It is possible that other connections also regrew, Benowitz said, but those would not be as obvious.

The researchers monitored fine motor control by training the rats, before surgery, to reach through a slit into a Plexiglas box to retrieve a banana-flavored pellet. Immediately after surgery, all animals showed severely diminished ability to collect the food pellets with the forepaw opposite the damaged hemisphere. After a few weeks, saline-treated animals recovered 35-40 percent of their pre-surgery ability. The inosine-treated animals recovered 80 percent, suggesting that those new connections they were growing translated directly into fine motor functioning.

Inosine had no effect on animals that had not undergone the lesioning treatment, so Benowitz thinks the nucleoside must augment the body’s natural recovery process. In addition to its role in promoting axon outgrowth via Mst3b, inosine has been shown to suppress neurons’ response to toxic glutamate, limit inflammation (Haskó et al., 2000), and protect astrocytes from hypoxia (Jurkowitz et al., 1998). In the case of stroke treatment, it is not clear if inosine itself, or a downstream product—such as uric acid—is the active player.

For stroke, Benowitz thinks inosine treatment is nearly ready for prime time. “We’re hoping that what we’re discovering in animals can move into the clinic,” he said, although he noted that given the heterogeneity of stroke patients, any trial would have to be large-scale, and the effect considerable, to rise above random noise in the data.

For ALS, there is more work to do before uric acid, or inosine, hits the clinic. Drory plans to test drugs that increase uric acid in a mouse model of ALS. “I think the results are very suggestive and definitely worth following up with other studies,” Weisskopf wrote.—Amber Dance.

References:
Keizman D, Ish-Shalom M, Berliner S, Maimon N, Vered Y, Artamonov I, Tsehori J, Nefussy B, Drory VE. Low uric acid levels in serum of patients with ALS: Further evidence for oxidative stress? J Neurol Sci. 2009 Jun 22. Abstract

Zai L, Ferrari C, Subbaiah S, Havton LA, Coppola G, Strittmatter S, Irwin N, Geschwind D, Benowitz LI. Inosine alters gene expression and axonal projections in neurons contralateral to a cortical infarct and improves skilled use of the impaired limb. J Neurosci. 2009 Jun 24;29(25):8187-97. Abstract

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Comments on News and Primary Papers

  1. Uric Acid: Not Just for Gout Anymore
    The major flaw of the antioxidant theory of aging is the lack of efficacy of antioxidant supplements against diseases of aging. A patchwork of experimental demonstrations show that oxidative stress is involved in several degenerative diseases, and diet, but not supplements, protects people from those diseases. Dissecting diet from a lifetime of exposure has always raised more questions than it has solved.

    New evidence is establishing a direct link between oxidant balance and disease, demonstrating that increased uric acid, one of the body’s most effective antioxidants, is correlated with reduced risk of amyotrophic lateral sclerosis. Uric acid, a metabolite of purine metabolism, is maintained in the body rather than broken down by uricase, as it is in most animals. Interestingly, save humans, most animals that excrete uric acid do so to reduce water loss through urine. Could it be that human antioxidant needs were the major drive for retention of a uricase mutation in humans that blocks activity and allows high urate levels?

    The contrast of disease reduction caused by urate and diet versus lack of efficacy of supplements should be seen in the context of a strong evolutionary pressure to maintain critical central nervous system functions through strong responses. The metabolic reorganization and stress responses (Martins et al., 1986; Smith et al., 1994) and urate increase may be the best indicators of the primacy of oxidative stress and response in human disease and aging. Seen in this light, gout is not just for big toes anymore.

    View all comments by Xiongwei Zhu

References

News Citations

  1. Antioxidant Levels Mark Progression of PD, Clinical Trial to Follow

Paper Citations

  1. . Serum urate as a predictor of clinical and radiographic progression in Parkinson disease. Arch Neurol. 2008 Jun;65(6):716-23. PubMed.
  2. . Plasma urate and risk of Parkinson's disease. Am J Epidemiol. 2007 Sep 1;166(5):561-7. PubMed.
  3. . Decreased plasma antioxidants in patients with Alzheimer's disease. Int J Geriatr Psychiatry. 2006 Apr;21(4):344-8. PubMed.
  4. . Inosine reduces ischemic brain injury in rats. Stroke. 2005 Mar;36(3):654-9. PubMed.
  5. . Mst3b, a purine-sensitive Ste20-like protein kinase, regulates axon outgrowth. Proc Natl Acad Sci U S A. 2006 Nov 28;103(48):18320-5. PubMed.
  6. . Inosine inhibits inflammatory cytokine production by a posttranscriptional mechanism and protects against endotoxin-induced shock. J Immunol. 2000 Jan 15;164(2):1013-9. PubMed.
  7. . Adenosine, inosine, and guanosine protect glial cells during glucose deprivation and mitochondrial inhibition: correlation between protection and ATP preservation. J Neurochem. 1998 Aug;71(2):535-48. PubMed.
  8. . Low uric acid levels in serum of patients with ALS: further evidence for oxidative stress?. J Neurol Sci. 2009 Oct 15;285(1-2):95-9. PubMed.
  9. . Inosine alters gene expression and axonal projections in neurons contralateral to a cortical infarct and improves skilled use of the impaired limb. J Neurosci. 2009 Jun 24;29(25):8187-97. PubMed.

Further Reading

Papers

  1. . The purine nucleosides adenosine and guanosine delay axonal degeneration in vitro. J Neurochem. 2009 Apr;109(2):595-602. PubMed.
  2. . Plasma urate and progression of mild cognitive impairment. Neurodegener Dis. 2009;6(1-2):23-8. PubMed.
  3. . Low uric acid levels in serum of patients with ALS: further evidence for oxidative stress?. J Neurol Sci. 2009 Oct 15;285(1-2):95-9. PubMed.
  4. . Inosine alters gene expression and axonal projections in neurons contralateral to a cortical infarct and improves skilled use of the impaired limb. J Neurosci. 2009 Jun 24;29(25):8187-97. PubMed.
  5. . Serum uric acid and clinical progression in Parkinson disease: potential biomarker for nigrostriatal failure. Arch Neurol. 2008 Jun;65(6):698-9. PubMed.
  6. . Insulin neuroprotection against oxidative stress in cortical neurons--involvement of uric acid and glutathione antioxidant defenses. Free Radic Biol Med. 2005 Oct 1;39(7):876-89. PubMed.
  7. . Plasma antioxidant status, immunoglobulin g oxidation and lipid peroxidation in demented patients: relevance to Alzheimer disease and vascular dementia. Dement Geriatr Cogn Disord. 2004;18(3-4):265-70. PubMed.
  8. . Diadenosine tetraphosphate protects against injuries induced by ischemia and 6-hydroxydopamine in rat brain. J Neurosci. 2003 Aug 27;23(21):7958-65. PubMed.

Primary Papers

  1. . Low uric acid levels in serum of patients with ALS: further evidence for oxidative stress?. J Neurol Sci. 2009 Oct 15;285(1-2):95-9. PubMed.
  2. . Inosine alters gene expression and axonal projections in neurons contralateral to a cortical infarct and improves skilled use of the impaired limb. J Neurosci. 2009 Jun 24;29(25):8187-97. PubMed.