Co-abuse of ethanol and methamphetamine (METH) is considered as a major public health
concern (Room, Babor et al. 2005, Marshall and Werb 2010). Several studies from our
laboratory and others revealed that glutamatergic, serotoninergic and dopaminergic systems
in the brain are altered with co-exposure to drugs of abuse, including METH and
ethanol (Tata, Raudensky et al. 2007, Halpin, Northrop et al. 2014, Das, Yamamoto et al.
2015, Alshehri, Althobaiti et al. 2016, Althobaiti, Almalki et al. 2016). In this study, we
investigated the effects of sequential exposure to ethanol and METH on these neurotransmitters.
Young adult male Wistar rats were orally gavaged with either ethanol (6 g/kg) or
water for seven days. On Day 8, rats were administered repeated high dose of METH (10
mg/kg, i.p. every 2 h × 4). Ceftriaxone (200 mg/kg), ß-lactam antibiotic known to upregulate
glial glutamate transporter 1 (GLT-1), was injected i.p. for 2 days. Despite evidence of
the high prevalence of ethanol and METH co-abuse, less is known about their sequential
exposure on the tissue content of neurotransmitters in the striatum and hippocampus.
Therefore, we investigated the effect of repeated high-dose METH exposure on the tissue
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content of several neurotransmitters such as glutamate, dopamine and serotonin in the striatum
and the hippocampus in rats exposed to ethanol. Both ethanol and METH exposure,
compared to ethanol alone, increased glutamate tissue content in the striatum but not in the
hippocampus. Interestingly, we showed that sequential exposure of ethanol and METH
caused a reduction of dopamine tissue content in the striatum and in the hippocampus when
compared to the water-meth-cef group with the water-saline group. Also, METH or sequential
ethanol and METH exposure caused depletion of serotonin tissue content in both
the striatum and hippocampus. Ceftriaxone normalized the tissue content of glutamate in
the WMC group as compared to the WS group, but not in the ethanol group. Also, ceftriaxone
did not show any effects on the level of serotonin and dopamine content among all
groups in the striatum and the hippocampus.
To address the issue of co-abuse of ethanol and other drugs of abuse, new therapeutic drugs
for drug dependence are needed. However, designing CNS drugs has been found to be one
of the most challenging areas in the drug discovery field. Because the blood-brain barrier,
which is made up of endothelial cells, separates blood from interstitial fluid, many neurotherapeutic
agents are not delivered to the brain. It has been shown that around 98% of
small molecules and almost all large molecules do not cross the blood-brain barrier
(Pardridge 1998, Pardridge 2005). It was also found that MS-153 is a GLT-1 activator,
hindering the depolarization- and ischemia-induced efflux of glutamate, in the hippocampal
region. Since MS-153 was found to have an impact on glutamate neurotransmission, it
is believed that it modulates the rewarding effects of morphine, methamphetamine, and
cocaine in mice (Nakagawa, Fujio et al. 2005). Sari's lab further studied the effect of MS-
153 on chronic ethanol consumption and the expression of GLT-1 and xCT. Importantly,
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MS-153, 50 mg/kg, i.p. injected in P rats showed a reduction in ethanol consumption over
14 days. Also, it was proved to elevate GLT-1 expression in various brain regions
(Alhaddad, Das et al. 2014, Aal-Aaboda, Alhaddad et al. 2015). These observations led us
to suggest that MS-153 is a lead drug for the syntheses of analogs that might upregulate
GLT-1 expression. Heterocycle pyrazolines were synthesized with varying substituents.
Each substituent has different properties than the original methyl group. The ester and the
amide group can provide hydrogen bonding opportunities while the nitrile and the trifluoromethyl
are lipophilic groups. The scheme used for the synthesis of MS-153 analogs was
selected because it is simple, efficient, and cost-effective compare to other syntheses. Astrocytes,
which are highly variable in their morphology and function, are the main type of
brain neuroglia. These cells regulate more than 90% of extracellular glutamate via a major
the glutamate transporter, GLT-1. Therefore, we hypothesized that modifications of the
MS-153 pharmacophore through substitution of the methyl group with substituents of varying
hydrogen bonding character and hydrophobicity will lead to a potent upregulator of
GLT-1. Subsequently, these analogs may exhibit different activities in primary cell culture
as compared to MS-153. Thus, in vitro assays of MS-153 analogs using primary rat astrocyte
culture were used to measure GLT-1 expression. MS-153 did not upregulate GLT-1
activity at different time points. The only drug that upregulated GLT-1 expression at all
days was analog 20. Also, even though analog 19 was not effective on day 2, it upregulated
GLT-1 expression on day 4 and day 6. GLT-1 expression was upregulated significantly on
day 2 and 4 with analog 25. Additionally, the benzoyl and nicotinoyl groups were found to
be critical for GLT-1 upregulation by these analogs.