Neuroprotective effect of carnosine in the olfactory bulb after vanadium inhalation in a mouse model

Abstract

Carnosine (β-alanyl-L-histidine) is synthesized in the olfactory system, has antioxidant activity as a scavenger of free radicals and has been reported to have neuroprotective action in diseases which have been attributed to oxidative damage. In neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases, impairment of olfactory function has been described. Vanadium derivatives are environmental pollutants, and its toxicity has been associated with oxidative stress. Vanadium toxicity on the olfactory bulb was reported previously. This study investigates the neuroprotective effect of carnosine on the olfactory bulb in a mice model of vanadium inhalation. Male mice were divided into four groups: vanadium pentoxide (V₂ O₅ ) [0.02 mol/L] inhalation for one hour twice a week; V₂ O₅ inhalation plus 1 mg/kg of carnosine administered daily; carnosine only, and the control group that inhaled saline. The olfactory function was evaluated using the odorant test. Animals were sacrificed four weeks after exposure. The olfactory bulbs were dissected and processed using the rapid Golgi method; cytological and ultrastructural analysis was performed and malondialdehyde (MDA) concentrations were measured. The results showed evidence of olfactory dysfunction caused by vanadium exposure and also an increase in MDA levels, loss of dendritic spines and necrotic neuronal death in the granule cells. But, in contrast, vanadium-exposed mice treated with carnosine showed an increase in dendritic spines and a decrease in neuronal death and in MDA levels when compared with the group exposed to vanadium without carnosine. These results suggest that dendritic spine loss and ultrastructural alterations in the granule cells induced by vanadium are mediated by oxidative stress and that carnosine may modulate the neurotoxic vanadium action, improving the olfactory function.

Keywords: carnosine; granule cells; neuroprotection; olfactory bulb; oxidative stress; vanadium.

Figure 1

The effect of vanadium and carnosine treatment in the olfactory function. Data are expressed as means ± SEM. *P < 0.05 vs control

Figure 2

Quantitative analysis of the size of granule cells of the olfactory bulb comparing controls and vanadium‐exposed groups (abbreviated as V) with or without carnosine treatment (abbreviated as car). Data are expressed in major axis and minor axis (means ± SEM). *P < 0.05 vs control, +P < 0.05 vs vanadium

Figure 3

Golgi silver impregnation of the olfactory bulb granule cells of mice in the four experimental groups. (A) Control group with the presence of dendritic spines, (B) group exposed to vanadium that observe the prominent dendritic spine loss in secondary dendrites, (C) group exposed to vanadium and treated with carnosine and (D) group treated with carnosine; the spine density is similar to controls. Scale bar = 10 μm

Figure 4

Quantitative analysis of dendritic spine number of the granule cells in olfactory bulb comparing control and experimental groups. The bars show a decrease in dendritic spine density during the exposure. Carnosine‐treated animals had a significantly improved spine density compared to controls. Mean values ± SEM (n = 5). *P < 0.005 vs control, one‐way ANOVA [Colour figure can be viewed at http://wileyonlinelibrary.com]

Figure 5

Electron micrograph of granule cell layer from the olfactory bulb. (A) Control, three granule neurons with prominent nuclei and sparse cytoplasm with some mitochondria (m) are shown. (B) Apoptotic granule cell (arrow) with condensation and margination of chromatin, next to a normal cell from a mouse exposed to vanadium. (C) An unaltered granule neuron after V‐exposure and treated with carnosine [mitochondria (m), axon (a)]. (D) Carnosine‐treated neuron, a granule neuron with undamaged mitochondria (m), is shown. Scale bar = 1 μm

Figure 6

Ultrastructural alterations in the olfactory bulb of vanadium‐exposed groups, including necrosis, apoptosis and mitochondrion oedema. Data are represented as percentage (mean ± SEM). *P < 0.005 vs control, +P < 0.05 vs vanadium, one‐way ANOVA

Figure 7

Effect of vanadium and carnosine treatments in the olfactory bulb malondialdehyde (MDA) concentration. Data are represented as mean ± SEM of nmol MDA/mg protein. *P < 0.005 vs control, +P < 0.05 vs vanadium, one‐way ANOVA