This is a single center, open label, 12-week study of inosine treatment. Inosine treatment leads to an increase in the levels of urate (uric acid) in the blood.

The primary objective of the study is to determine the tolerability of oral administration of inosine.

Secondary study objectives include the measurement of biomarkers of oxidative stress and damage in response to inosine treatment.

Amyotrophic lateral sclerosis (ALS) is a fatal, neurodegenerative disease for which there is no cure. Multiple lines of evidence have implicated oxidative stress in the pathophysiology of ALS. Urate (uric acid) is an endogenous antioxidant system, and urate may serve as a major defense against oxidative stress. Urate has emerged as a promising neuro-protectant and therapeutic target based on convergent epidemiological, laboratory, and clinical data in multiple neurodegenerative diseases, most notably Parkinson's disease (PD). In PD, urate elevation has been pursued as a potential therapy by administration of inosine, a urate precursor that is available as an over-the-counter supplement. Administration of inosine results in a predictable elevation of urate levels and has been shown to be safe and well tolerated in PD.

Analysis of ALS databases revealed that higher urate levels are an independent predictor of slower progression and prolonged survival in ALS. However, whether elevating urate in people with ALS would result in better outcomes is unknown. As a first step towards development of inosine as a potential treatment for ALS, in this study we will test whether inosine administration in ALS is safe and correlates with changes in the levels of biomarkers of oxidative stress and damage (as biomarkers of the intended biological effect).

The primary outcome measures will be safety, as measured by adverse events and clinically meaningful changes in vital signs, physical examination, and standard clinical laboratory tests, and tolerability, defined as the ability of subjects to complete the entire 12-week study.

The secondary objective of the study is to quantify the effect of the treatment on biomarkers of oxidative damage and stress.

An exploratory objective of the study is to measure whether changes in these biomarkers are different in people with bulbar-onset ALS compared to people with limb-onset ALS.

This study will be conducted in people who meet the El Escorial criteria of possible, laboratory-supported probable, probable, or definite criteria for a diagnosis of ALS. At screening, eligible individuals must be at least 18 years old and must provide written informed consent prior to screening. Subjects on a stable dose of riluzole and those not taking riluzole, and women of child-bearing age at screening are eligible for inclusion as long as they meet specific protocol requirements.

Study participants will be administered oral inosine daily. The dose of inosine will be titrated to obtain serum urate levels of 7 - 8 mg/dL.

Study participants will remain on treatment until the Week 12 visit. Each participant will also have a Week 16 Follow-up Telephone Interview to assess for adverse events (AEs), changes in concomitant medications and to administer the ALSFRS-R.

Inclusion Criteria:

1. Age 18 years or older.
2. Sporadic or familial ALS diagnosed as possible, laboratory-supported probable, probable, or definite as defined by revised El Escorial criteria (Appendix 1).
3. Capable of providing informed consent and following trial procedures.
4. Serum urate < 5.5 mg/dl at screening (i.e. below the population median serum urate levels).
5. Willingness to undergo magnetic resonance spectroscopy (MRS) at Baseline and at Week 12 of the study.
6. Women must not be able to become pregnant (e.g. post menopausal, surgically sterile, or using adequate birth control methods) for the duration of the study and 3 months after study completion. Adequate contraception includes: abstinence, hormonal contraception (oral contraception, implanted contraception, injected contraception or other hormonal (patch or contraceptive ring, for example) contraception), intrauterine device (IUD) in place for ≥ 3 months, barrier method in conjunction with spermicide, or another adequate method.

Exclusion Criteria:

1. History of urolithiasis.
2. Urine pH < 5.5 at screening (as acidic urine is a major determinant of uric acid urolithiasis).
3. Urate crystalluria at Screening.
4. History of gout.
5. History of stroke or myocardial infarction.
6. History of symptomatic coronary artery disease (e.g. angina pectoris) or symptomatic peripheral arterial disease within 1 year prior to Screening.
7. Symptomatic congestive heart failure with a documented ejection fraction below 45%.
8. Poorly controlled arterial hypertension (SBP>160mmHg or DBP>100mmHg at Screening).
9. Contraindications to undergo magnetic resonance spectroscopy (MRS) at Baseline and at Week 12 of the study such as history of claustrophobia, inability to lie flat for approximately one hour, or metal implants (metal pins or plates, extensive non-removable dental work, cerebral aneurysm clips, pacemaker).
10. Women who are pregnant or lactating.
11. The presence of unstable psychiatric disease, cognitive impairment, or dementia that would impair ability of the subject to provide informed consent, according to PI judgment, or a history of active substance abuse within the prior year.
12. Anything that, in the opinion of the investigator, would place the subject at increased risk or preclude the subject's full compliance with or completion of the study.
13. Use of the following within 30 days prior to Screening: inosine, allopurinol, probenecid, more than 300mg vitamin C daily (note that a subject may take a standard multivitamin up to one tablet or capsule daily). Use of thiazides is permissible as long as the subject is on a stable dose from 1 week prior to Screening.
14. Known hypersensitivity or intolerability to inosine.

32 subjects were consented, however, 25 patients were randomized/treated to received the study drug.

Adverse events were collected from the time the subject signed consent until 28 days after a subject's last dose of study drug.