2. Experimental animal model of PPA-induced neurotoxicity

Administration of PPA to rodents, results in CNS lesions that selectively target right lateral ventricle associated within striatum, cortex, cerebellum, hippocampus, amygdala recapitulating the regional and neuronal specificity of pathologic events especially in autism [37]. The mitochondrial toxin PPA interferes with the conversion of succinate to fumarate in TCA cycle, responsible for the generation of FADH2 utilized in the complex-II in mitochondrial electron transport chain (ETC) by which it direct inhibits the activity of the mitochondrial metabolic enzyme succinate dehydrogenase and reduced the definite amount of NADH where it consumed in complex-I with the help of an enzyme complex-I (NADPH oxidase) as well as involve in the dysregulation of complex-IV (cytochrome c oxidase), is the final protein complex in the ETC helping to establish a transmembrane difference of proton electrochemical potential that the complex-V (ATP synthase) then uses to synthesize ATP [38].PPA has now become an experimental tool to study neuronal susceptibility and motor phenotypes that are characteristic of autism (Figure 1) [39].

In rats, PPA-induced lesions in brain region that are associated with elevated lactate levels resulted in increased NMDA-receptor binding. PPA toxicity arises from secondary excitotoxic mechanisms, whereby energy depletion within vulnerable neurons facilitates abnormal activation of NMDA receptors and subsequent Ca2+ influx [40]. Stimulating energy generation by administering creatine markedly attenuates PPA toxicity and ameliorates lesion volume, lactate production and ATP depletion in PPA-treated rats [41]. Numerous reports assert that PPA toxicity is associated with increased oxidative damage within the CNS. The involvement of impairments in intrinsic anti-oxidant protection pathways after PPA administration is further supported by observations of reduced glutathione (GSH) levels in autistic brain [42].

function, lipid metabolism, immune functions, gap junctional gating, and modulation of gene expression through DNA methylation and histone acetylation [47]. Initial studies using this rodent model revealed that repeated brief infusions of PPA into the lateral cerebral ventricles (i.e., AP 1.3 mm, ML 1.8 mm, and DV 3.0 mm) of adult rats produced behavioral, biochemical, electrophysiological and neuropathological effects consistent with those seen in autism [43]. PPA through oxidative mechanisms inhibits Na+/K+ ATPase and increases glutamate receptor sensitivity which can enhance neural depolarization leading to neural hyper excitability in brain

Neuroprotective Strategies of Blood-Brain Barrier Penetrant "Forskolin" (AC/cAMP/PKA/CREB Activator)…

http://dx.doi.org/10.5772/intechopen.80046

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Mitochondrial dysfunction has been well established to occur and play an important role in the pathogenesis of autism [48]. Preliminary magnetic resonance spectroscopy studies showed decreased synthesis of ATP and a disturbance of energy metabolism in the brain of individuals with autism. PPA is also capable of altering dopamine, serotonin, GABA and glutamate

3. List of proposed parameters can be evaluated on the basis of behavioral and biochemical alterations in neurotoxic experimental animal models of

Proposed experimental design of propionic acid-induced behavioral and biochemical estima-

Spatial navigation task in Morris water maze, spontaneous locomotor activity, string test for grip strength, elevated plus maze test, beam crossing task, force swim test, rota rod apparatus

Preparation of homogenate, estimation of biochemical parameters in serum and tissue homogenate such as protein estimation, lactate dehydrogenase (LDH) assay, estimation of malondialdehyde (MDA) levels, glutathione levels, superoxide dismutase (SOD) activity, catalase activity, acetyl

Estimation of total urea, estimation of uric acid, estimation of biochemical parameters in tissue

Complex-1 activity (NADPH dehydrogenase), complex-II activity (succinate dehydrogenase/

cholinesterase (AChE) levels, determination of protein carbonyl (PC), nitrite levels

6. Preparation of crude mitochondrial fraction from rat whole brain homogenate

SDH), complex IV activity (cytochrome oxidase), complex-V activity (ATP synthase)

5. Estimation of biochemical parameters in serum and urine

homogenate for mitochondrial complex activity

7. Estimation of biochemical parameters in serum

regions linked to locomotor activity (Figure 2).

autism

tions (Figure 3)

1. Measurement of body weight 2. Measurement of brain weight

4. Estimation of biochemical parameters

3. Behavioral parameters

systems in a manner similar to that observed in autism [49].

Figure 1. PPA-induced neurotoxicity; selective mitochondrial inhibition.

#### 2.1. Propionic acid and autism

Propionic acid (PPA) is a short chain fatty acid formed endogenously in the human body as an intermediate of fatty acid metabolism and a metabolic end product of enteric gut micro biota such as clostridia and propionic bacteria [43–46]. MacFabe et al. and Shultz et al. have demonstrated that PPA intraventricularly infused to rats provides a suitable animal model to study autism. Being a weak organic acid, PPA exists in ionized and nonionized forms at physiological pH allowing it to readily cross lipid membranes, including the gut-blood and blood-brain barriers. PPA and other short-chain fatty acids (i.e., butyrate and acetate), affect diverse physiological processes such as cell signaling, neurotransmitter synthesis and release, mitochondrial

Figure 2. Intraventricular injection of PPA-inducing neurotoxic effect in mitochondrial respiratory chain (ETC).

function, lipid metabolism, immune functions, gap junctional gating, and modulation of gene expression through DNA methylation and histone acetylation [47]. Initial studies using this rodent model revealed that repeated brief infusions of PPA into the lateral cerebral ventricles (i.e., AP 1.3 mm, ML 1.8 mm, and DV 3.0 mm) of adult rats produced behavioral, biochemical, electrophysiological and neuropathological effects consistent with those seen in autism [43]. PPA through oxidative mechanisms inhibits Na+/K+ ATPase and increases glutamate receptor sensitivity which can enhance neural depolarization leading to neural hyper excitability in brain regions linked to locomotor activity (Figure 2).

Mitochondrial dysfunction has been well established to occur and play an important role in the pathogenesis of autism [48]. Preliminary magnetic resonance spectroscopy studies showed decreased synthesis of ATP and a disturbance of energy metabolism in the brain of individuals with autism. PPA is also capable of altering dopamine, serotonin, GABA and glutamate systems in a manner similar to that observed in autism [49].
