Regional Changes in Brain Histamine Levels Following Dietary-Induced Thiamine Deficiency in Rats

Profiling plasma levels of thiamine and histamine in Jordanian children with autism spectrum disorder (ASD): potential biomarkers for evaluation of ASD therapies and diet

BACKGROUND

The current work involved monitoring two biomarkers in the plasma of children with ASD: the cofactor thiamine that is involved in neurotransmitters modulation for acetylcholine, and the compound histamine, which acts as a neuromodulator by regulating the release of other neurotransmitters. This is the first report to highlight the potential utilization of plasma levels of the selected two brain-related biomarkers in children with ASD.

METHODS

A total of 43 children with ASD of both genders (age 4-12 years) were involved in this study and compared to age and gender-matched control children (n = 42). The diagnosis of ASD was based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM5), followed by an additional assessment using the Childhood Autism Rating Scale (CARS). All participants were Jordanian children on Mediterranean diet, and had no history of chronic illness or medications. Measurement of thiamine and histamine in plasma was performed using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The outcomes revealed that average histamine levels (31.7 ± 18.5 ng/ml) of ASD group were 5.3× higher (p < .001) compared to their control (0.013 ± 0.011 ng/ml; 6.03 ± 4.25 ng/ml), while thiamine (10.78 ± 7.49 ng/ml) levels of ASD group were significantly lower (p < .001) than the control (37.92 ± 26.87 ng/ml; 0.209 ± 0.054 ng/ml).

CONCLUSIONS

The study is proposing that monitoring of the plasma levels of thiamine and histamine as biomarkers for future evaluation and development of ASD therapies and nutritious diets.

Enantioselective Pharmacokinetics of α-Fluoromethylhistidine in Rats and Its Comparison with Histidine

The enantiomer-specific pharmacokinetics of histidine and its analogue, α-fluoromethylhistidine (FMH), were investigated in rats. After bolus intravenous administration of each enantiomer of histidine or FMH at a dose of 40·3 mg kg−1 as free base equivalents, the plasma concentrations of l-histidine, d-histidine, (S)-FMH and (R)-FMH decreased biexponentially with half-lives of 39·2, 20·8, 32·8 and 25·0 min, respectively, in the elimination phase. Although the concentration of l-histidine in the plasma was lower than that of d-histidine, there was no large difference in plasma concentration-time curves of the enantiomers of FMH. The apparent total clearance of l-histidine from rat plasma was about 4 times that of d-histidine or the enantiomers of FMH. l-Histidine was quickly transferred to the peripheral tissues where the concentrations also decrease biphasically. l-Histidine penetrated more rapidly into the brain than either its d-enantiomer or a compound closely related in structure such as FMH. However, the disappearance of l-histidine from the various brain regions was very rapid. In contrast, brain/plasma ratios of d-histidine and (S)-FMH increased continuously after injection of these compounds, indicating that d-histidine or (S)-FMH partitioned into the brain and was very slowly removed from the brain; (R)-FMH was not distributed to the brain. These results suggested stereoselectivity in disposition of histidine and FMH enantiomers in rats.

The disposition of thioperamide, a histamine H3-receptor antagonist, in rats

An HPLC method using an ovomucoid-conjugated column has been developed for measurement of thioperamide, a histamine H3 antagonist, with a minimum quantitation limit of 0.05 micrograms mL-1. The assay was used to study the disposition of thioperamide in rats. After bolus intravenous administration of thioperamide (10 mg kg-1), the plasma concentration decreased monoexponentially with a half-life of 26.9 min. The apparent total body clearance of thioperamide from rat plasma was 74.6 mL min-1 kg-1. Although thioperamide was quickly transferred to various tissues, its concentrations in peripheral tissues were higher than that in the brain. However, the brain regional tissue/plasma ratios of thioperamide increased continuously after its injection.