Abstract Introduction

Aromatic (ar-) turmerone is a major bioactive compound of the herb Curcuma longa. It has been suggested that ar-turmerone inhibits microglia activation, a property that may be useful in treating neurodegenerative disease. Furthermore, the effects of ar-turmerone on neural stem cells (NSCs) remain to be investigated.

We exposed primary fetal rat NSCs to various concentrations of ar-turmerone. Thereafter, cell proliferation and differentiation potential were assessed. In vivo, nave rats were treated with a single intracerebroventricular (i.c.v.) injection of ar-turmerone. Proliferative activity of endogenous NSCs was assessed in vivo, by using noninvasive positron emission tomography (PET) imaging and the tracer [18F]-fluoro-L-thymidine ([18F]FLT), as well as ex vivo.

In vitro, ar-turmerone increased dose-dependently the number of cultured NSCs, because of an increase in NSC proliferation (P<0.01). Proliferation data were supported by qPCR-data for Ki-67 mRNA. In vitro as well as in vivo, ar-turmerone promoted neuronal differentiation of NSCs. In vivo, after i.c.v. injection of ar-turmerone, proliferating NSCs were mobilized from the subventricular zone (SVZ) and the hippocampus of adult rats, as demonstrated by both [18F]FLT-PET and histology (P<0.05).

Both in vitro and in vivo data suggest that ar-turmerone induces NSC proliferation. Ar-turmerone thus constitutes a promising candidate to support regeneration in neurologic disease.

Curcumin and ar-turmerone are the major bioactive compounds of the herb Curcuma longa. Although many studies have demonstrated curcumin to possess antiinflammatory and neuroprotective properties (reviewed by [1]), to date, the effects of ar-turmerone remain to be elucidated. For example, antitumor properties, exerted via the induction of apoptosis [2] and inhibition of tumor cell invasion [3], have been attributed to ar-turmerone. Park et al. [4,5] recently suggested that ar-turmerone also possesses antiinflammatory properties resulting from the blockade of key signaling pathways in microglia. Because microglia activation is a hallmark of neuroinflammation and is associated with various neurologic disorders, including neurodegenerative diseases [6,7] and stroke [8,9], ar-turmerone constitutes a promising therapeutic agent for various neurologic disorders.

The regenerative potential of endogenous neural stem cells (NSCs) plays an important role in neurodegenerative disease and stroke. Endogenous NSCs are mobilized by cerebral ischemia [10] as well as by various neurodegenerative diseases [11,12], although their intrinsic regenerative response is insufficient to enable functional recovery. The targeted (that is, pharmacologic) activation of endogenous NSCs has been shown to enhance self-repair and recovery of function in the adult brain in both stroke [13,14] and neurodegeneration [15]. Importantly, NSCs and microglia relevantly interact with each other, thereby affecting their respective functions [16,17].

Thus, with the perspective of ar-turmerone as a therapeutic option in mind, we investigated the effects of ar-turmerone on NSCs in vitro and in vivo.

NSCs were cultured from fetal rat cortex at embryonic day 14.5, as described previously [18]. Cells were expanded as monolayer cultures in serum-free DMEM/F12 medium (Life Technologies, Darmstadt, Germany) with N2 supplement (Gibco, Karlsruhe, Germany) and fibroblast growth factor (FGF2; 10ng/ml; Invitrogen, Karlsruhe, Germany) for 5days and were replated in a 24-well plate at 10,000 cells per cm2. FGF2 was included throughout the experiments.

Ar-turmerone (Fluka, Munich, Germany) was added to cultures at replating at concentrations of 0, 1.56, 3.125, 6.25, 12.5, and 25g/ml. All experiments were performed in triplicate. After 72hours, representative pictures were taken by using an inverted fluorescence phase-contrast microscope (Keyence BZ-9000E). Three images were taken per well, and cells were counted by using the software ImageJ with a threshold of 20 px (National Institutes of Health, Bethesda, MD, USA, Version 1.47k).

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