Comparison of tryptophan metabolism in vivo and in isolated hepatocytes from vitamin B6 deficient mice

Plasma kynurenine and related measures in tic disorder patients

OBJECTIVE

Increased plasma kynurenine has been reported in tic disorder patients, and this observation has been suggested to be indicative of immune dysregulation. In the present study, we examined plasma levels of kynurenine and related molecules in a group of tic disorder patients.

METHODS

Plasma concentrations of tryptophan, kynurenine, cortisol, and neopterin were determined in Dutch tic disorder patients (N = 59), and healthy volunteers (N = 32). Group means were compared and age-controlled intra-individual correlations between tic severity and plasma levels of these molecules were examined.

RESULTS

No significant differences were found between patient and control groups in plasma levels of tryptophan, kynurenine, and cortisol concentrations, nor in the kynurenine/tryptophan ratio. However, neopterin was significantly (p = 0.035) higher in patients (mean = 5.13 nmol/l) than in controls (mean = 3.30 nmol/l). Plasma levels of these molecules did not correlate with tic severity, with the exception of tryptophan (r = -0.289, p = 0.049). In patients, plasma neopterin correlated with kynurenine (r = 0.438, p = 0.002); in healthy subjects, tryptophan correlated with kynurenine (r = 0.670, p < 0.001).

CONCLUSION

While the observed elevation in plasma neopterin is consistent with immune activation in a subset of tic disorder patients, metabolism of tryptophan through the kynurenine pathway appears to be unaltered in tic disorder patients.

The central role of magnesium deficiency in Tourette's syndrome: causal relationships between magnesium deficiency, altered biochemical pathways and symptoms relating to Tourette's syndrome and several reported comorbid conditions

Prior studies have suggested a common etiology involved in Tourette's syndrome and several comorbid conditions and symptomatology. Reportedly, current medications used in Tourette's syndrome have intolerable side-effects or are ineffective for many patients. After thoroughly researching the literature, I hypothesize that magnesium deficiency may be the central precipitating event and common pathway for the subsequent biochemical effects on substance P, kynurenine, NMDA receptors, and vitamin B6 that may result in the symptomatology of Tourette's syndrome and several reported comorbid conditions. These comorbid conditions and symptomatology include allergy, asthma, autism, attention deficit hyperactivity disorder, obsessive compulsive disorder, coprolalia, copropraxia, anxiety, depression, restless leg syndrome, migraine, self-injurious behavior, autoimmunity, rage, bruxism, seizure, heart arrhythmia, heightened sensitivity to sensory stimuli, and an exaggerated startle response. Common possible environmental and genetic factors are discussed, as well as biochemical mechanisms. Clinical studies to determine the medical efficacy for a comprehensive magnesium treatment option for Tourette's syndrome need to be conducted to make this relatively safe, low side-effect treatment option available to doctors and their patients.

Increased plasma kynurenine and its relationship to neopterin and tryptophan in Tourette's syndrome

Fasting plasma levels of tryptophan, kynurenine and the pteridines, neopterin and tetrahydrobiopterin were measured in seven patients with Gilles de la Tourette syndrome (GTS) and 10 healthy controls. Plasma kynurenine was significantly elevated in the GTS patients. The lowest patient value was higher than the highest control value. Values for tryptophan, neopterin and tetrahydrobiopterin were similar in TS patients and controls. However, in TS patients only, there was a significant negative correlation between tryptophan and neopterin and a significant positive correlation between kynurenine and neopterin when controlling for tryptophan. This finding indicates that activation of cellular immune processes is a possible explanation for the rise in plasma kynurenine.

Elevated plasma kynurenine in Tourette syndrome

Fasting plasma kynurenine concentrations were significantly elevated in a group of 7 patients (4 female) conforming to DSM-III-R of the American Psychiatric Association (1987) criteria for Tourette syndrome, in comparison with 10 healthy controls (7 female). Simultaneous normal plasma biopterin and neopterin concentrations indicated that this rise was probably not a consequence of peripheral cellular immune mechanisms.