Amyotrophic lateral sclerosis (ALS), or motor neuron disease (MND), is a rapidly progressive,
fatal neurodegenerative condition characterized by loss of upper and lower motor neurons in
the brain and spinal cord. The terms ALS and MND are often used inter-changeably to cover the
different clinical syndromes, which include upper and lower motor neuron disorder,
progressive bulbar palsy, and pseudo-polyneuritic form.
Degeneration of lower motor neurons (LMN) in the anterior horns of spinal cord and brainstem
leads to progressive muscular atrophy and eventually to death within a few years due to
respiratory insufficiency. During the course of the disease, the involvement of tongue and
pharynx muscles causes swallowing impairment with marked drooling, need of parenteral or
enteral feeding, and finally gastrostomy. Denervation of laryngeal muscles causes loss of
speech. Cramps and fasciculation typically occur from the early phases of the disease.
Degeneration of upper motor neurons (UMN) in the brain cortex causes pyramidal tract
dysfunctions including clonus, Babinski sign, hypertonia, and loss of dexterity that further
limit patients' daily activities.
The incidence of ALS varies from 0.2 to 2.5 cases per 100,000 per year, although estimates
vary between countries, likely reflecting a combination of availability of medical services,
diagnostic accuracy, and demo-graphic characteristics of the area. Increasing life expectancy
and improvements in standards of treatment and care will also result in an increased
incidence of ALS. Globally, the overall rate is approximately 2 per 100,000. Its prevalence
is approximately of 7 per 100,000. In Italy, the reported incidence of ALS is 2.2
cases/100,000/year.
There is currently no cure for ALS. Despite initial positive results in preclinical and early
clinical studies, large-scale clinical trials with all agents except riluzole failed to
demonstrate a clinically meaningful therapeutic effect in patients with ALS. Riluzole at the
dose of 100 mg/day showed a significant difference on survival (6.4%; gain of 3 months) and
slowed deterioration in muscle strength.
Primary involvement of apoptotic mechanisms has important implications in selecting drug
candidates for therapy in ALS. Recent preclinical studies have demonstrated that TUCA is
endowed with antioxidant, antiapoptotic and neuroprotective activities. In particular, TUDCA
can cross the blood-brain-barrier and has been shown to exert a significant therapeutic
effect in a model of HD mice.
Tauroursodeoxycholic acid (TUDCA) is a hydrophilic bile acid that is normally produced
endogenously in humans at very low levels. TUDCA is synthesized in the liver by conjugation
of taurine to ursodeoxycholic acid (UDCA), which is commonly used as a bile acid replacement
therapy for the treatment of certain cholestatic syndromes.
The main pharmacological activity of TUDCA consists in its ability in increasing the
cholesterol solubilising activity of bile, thus transforming "lithogenic" bile in
"non-lithogenic" or "litholytic" bile.
TUDCA inhibits mitochondrial-associated apoptosis via many pathways: 1) it inhibits the
mitochondrial permeability transition (MPT) and cytochrome C release, 2) it inhibits
mitochondrial membrane depolarization, and 3) it antagonizes Bax translocation from the
mitochondria and caspase activation in hepatocytes and brain. TUDCA may also ease oxidative
stress.Study relevant TUDCA pharmacology consists in its antioxidant, antiapoptotic and
neuroprotective activities evidenced in preclinical studies.
Recent reports have shown that hydrophilic bile acids, such as UDCA and TUDCA, can prevent
hepatic cytotoxicity through several mechanisms. For example, TUDCA prevents the production
of reactive oxygen species and thus acts as an antioxidant. Additionally, TUDCA mitigates
mitochondrial insufficiency and toxicity, and prevents apoptosis, in part, by inhibiting Bax
translocation from cytosol to the mitochondria. In hepatocytes, this inhibition results in
reduced mitochondrial membrane perturbation, release of cytochrome c, and activation of
downstream caspases. TUDCA reduced cytotoxicity in neurons through similar mechanisms, as
well as mitochondrial pathways that are independent of the permeability transition. TUDCA
prevented striatal degeneration and ameliorated locomotor and cognitive deficits in the in
vivo 3-nitropropionic acid (3-NP) rat model of HD. Intracellular inclusions were
significantly reduced, and the TUDCA-treated mice showed improved locomotor and sensorimotor
abilities.
In addition, the antiapoptotic and cytoprotective effects of TUDCA have been tested in models
of acute stroke. The possibility that TUDCA exerts an antiapoptotic action by ameliorating
mitochondrial function raises the issue whether other neurological disorders, including
Friedreich's ataxia, amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's
disease, can benefit by the administration of TUDCA. This drug is a candidate neuroprotective
agent for a variety of chronic neurodegenerative conditions.