Previous studies have shown that (E)-8-(3-chlorostyryl)caffeine (CSC) is a specific reversible inhibitor of human monoamine oxidase B (MAO-B) and does not bind to human MAO-A. Since the small molecule isatin is a natural reversible inhibitor of both MAO-B and MAO-A, (E)-5-styrylisatin and (E)-6-styrylisatin analogues were synthesized in an attempt to identify inhibitors with enhanced potencies and specificities for MAO-B. The (E)-styrylisatin analogues were found to exhibit higher binding affinities than isatin with the MAO preparations tested. The (E)-5-styrylisatin analogues bound more tightly than the (E)-6 analogue although the latter exhibits the highest MAO-B selectivity. Molecular docking studies with MAO-B indicate that the increased binding affinity exhibited by the (E)-styrylisatin analogues, in comparison to isatin, is best explained by the ability of the styrylisatins to bridge both the entrance cavity and the substrate cavity of the enzyme. Experimental support for this model is shown by the weaker binding of the analogues to the Ile199Ala mutant of human MAO-B. The lower selectivity of the (E)-styrylisatin analogues between MAO-A and MAO-B, in contrast to CSC, is best explained by the differing relative geometries of the aromatic rings for these two classes of inhibitors. KeywordsMonoamine oxidase A; Monoamine oxidase B; Reversible inhibitor; Isatin; (E)-5-Styrylisatin; (E)-6-StyrylisatinThe oxidative deamination reaction catalyzed by monoamine oxidase B (MAO-B) is one of the major catabolic pathway of dopamine in the brain. Inhibitors of this enzyme lead to enhanced dopaminergic neurotransmission and are currently used in the symptomatic treatment of Parkinson's disease (PD). 1-4 Furthermore, MAO-B inhibitors also may exert a neuroprotective effect by reducing the concentrations of potentially hazardous by-products produced by MAO-B-catalyzed dopamine oxidation. 5 Considering that the human brain exhibits an age-related increase in MAO-B activity, inhibition of this enzyme is especially relevant in the treatment of PD. 6-8 The endogenous small molecule isatin (1) (Fig. 1) has been reported to be a moderately potent inhibitor of human MAO-B with an enzyme-inhibitor *Corresponding author. Tel.: +27 18 2992206; fax: +27 18 2994243. E-mail adress: E-mail: jacques.petzer@nwu.ac.za (J.P. Petzer). Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Another small molecule, caffeine (2), is a weak inhibitor of MAO-B with a K i value of 3.6 mM. The inhibition potency of caffeine is substantially increased by substitution at C-8 of the caffeinyl ring with a styryl...

Mitochondrial disease can be attributed to both mitochondrial and nuclear gene mutations. It has a heterogeneous clinical and biochemical profile, which is compounded by the diversity of the genetic background. Disease-based epidemiological information has expanded significantly in recent decades, but little information is known that clarifies the aetiology in African patients. The aim of this study was to investigate mitochondrial DNA variation and pathogenic mutations in the muscle of diagnosed paediatric patients from South Africa. A cohort of 71 South African paediatric patients was included and a high-throughput nucleotide sequencing approach was used to sequence full-length muscle mtDNA. The average coverage of the mtDNA genome was 81 ± 26 per position. After assigning haplogroups, it was determined that although the nature of non-haplogroup-defining variants was similar in African and non-African haplogroup patients, the number of substitutions were significantly higher in African patients. We describe previously reported disease-associated and novel variants in this cohort. We observed a general lack of commonly reported syndrome-associated mutations, which supports clinical observations and confirms general observations in African patients when using single mutation screening strategies based on (predominantly non-African) mtDNA disease-based information. It is finally concluded that this first extensive report on muscle mtDNA sequences in African paediatric patients highlights the need for a full-length mtDNA sequencing strategy, which applies to all populations where specific mutations is not present. This, in addition to nuclear DNA gene mutation and pathogenicity evaluations, will be required to better unravel the aetiology of these disorders in African patients.