Effect of excess dietary manganese on lipid composition of calf blood plasma, heart, and liver

A study on the seasonal transfer of two metals from pasture to animals: health risk assessment

Accretion of heavy metals in forage is a potential risk to grazing animals due to their uptake by plants and its entrance into the food chain. This study aimed to examine the Mn and Cd concentration from different samples. Sampling was done twice after the interval of 6 months during 2018; five different sites from Chakwal (Pidh, Tobar, Ratoccha, Kalar Kahar Road, Choa Saiden Shah and Chakwal Road, Choa Saiden Shah) were selected. Thirty samples of soil, forage (Acacia nilotica, Ziziphus nummularia, and Acacia modesta), and blood were collected. Forage and soil samples were dried, ground very fine, digested by wet digestion method, and analyzed by atomic absorption spectrophotometer. Samples collected from site I and site II had a very high concentration of heavy metals because these sites were very close to the coal mines and receive higher contamination. Manganese concentration in the soil fluctuated from 5.46 to 1.20, in the forage 6.84 to 1.00, and in the blood 5.21 to 1.03 mg/l, and cadmium concentration in the soil fluctuate from 1.85 to 0.03, in the forage 0.57 to 0.16, and in the blood 1.67 to 0.25 mg/l. Manganese concentration was higher as compared to the Cd. Higher concentration of Mn shows that this metal is due to human activities. Pollution load index value of Cd was higher than 1 in some samples, and the value fluctuates from 0.01 to 1.24 mg/kg. The values of a bioconcentration factor for Mn were greater than 1. Daily intake of metal value fluctuates from 0.01 to 1.03 mg/kg. Health risk index value ranges from 0.03 to 1.09 mg/kg. Health risk index of metals showed the risk which is due to the intake of contaminated fodder. From the soil, the metals can enter forage and bioaccumulate in the food chain. The health risk index was highest for Cd. The result obtained from the present research work indicated that there is a biomagnification of both metals in the food chain due to mining activities.

Metabolic effects of manganese in the nematode Caenorhabditis elegans through DAergic pathway and transcription factors activation

Manganese (Mn) is an essential trace element for physiological functions since it acts as an enzymatic co-factor. Nevertheless, overexposure to Mn has been associated with a pathologic condition called manganism. Furthermore, Mn has been reported to affect lipid metabolism by mechanisms which have yet to be established. Herein, we used the nematode Caenorhabditis elegans to examine Mn's effects on the dopaminergic (DAergic) system and determine which transcription factors that regulate with lipid metabolism are affected by it. Worms were exposed to Mn for four hours in the presence of bacteria and in a liquid medium (85 mM NaCl). Mn increased fat storage as evidenced both by Oil Red O accumulation and triglyceride levels. In addition, metabolic activity was reduced as a reflection of decreased oxygen consumption caused by Mn. Mn also affected feeding behavior as evidenced by decreased pharyngeal pumping rate. DAergic neurons viability were not altered by Mn, however the dopamine levels were significantly reduced following Mn exposure. Furthermore, the expression of sbp-1 transcription factor and let-363 protein kinase responsible for lipid accumulation control was increased and decreased, respectively, by Mn. Altogether, our data suggest that Mn increases the fat storage in C. elegans, secondary to DAergic system alterations, under the control of SBP-1 and LET-363 proteins.

The effect of manganese-induced hypercholesterolemia on learning in rats

Since the exact mechanism of manganese (Mn)-induced learning disability is not known, we investigated the role of elevated cholesterol in rats exposed daily to 357 and 714 micrograms Mn/kg for 39 d. Significant Mn accumulation was accompanied by increased cholesterol content in the hippocampal region of Mn-treated rats. The learning, which is based on the time needed to reach food placed at the exit of a T-maze after a 1-d training period, was significantly slower in exposed rats than in unexposed rats. The rats receiving 357 and 714 micrograms Mn/kg reached the food in 104.5 +/- 13.8 and 113.3 +/- 25.7 s, respectively, on d 30, whereas their untreated counterparts reached the food in 28.7 +/- 11.4 s. This delay was completely corrected to 29.3 +/- 7.8 and 30.7 +/- 6.0 s in rats with coadministration of an inhibitor of cholesterol biosynthesis with 357 and 714 micrograms/kg of Mn. The correction of impaired learning was associated with the normalization of hippocampal cholesterol, but the Mn level in this region of the brain was not influenced in rats treated with a drug that inhibits cholesterol biosynthesis. These results suggested that Mn-induced hypercholesterolemia is involved in Mn-dependent learning disability.

Reversibility of manganese-induced learning defect in rats

In this study the mechanism by which manganese (Mn) induces learning defect and its reversibility has been investigated in rats. Female albino rats were dosed orally with 357 micrograms Mn/kg body weight for 15 or 30 days. Attempts were made to correct the Mn-induced learning defect by (1) co-administration of mevinolin and Mn for 30 days; (2) administration of mevinolin for 15 days after 15 days of dosing with Mn, and (3) by withdrawal of Mn treatment (15 days dosing with Mn followed by 15 days without Mn). Mevinolin was given orally at 235.7 micrograms/kg body weight. Significant increases in the Mn and cholesterol levels in the hippocampus were accompanied by an obvious slowness in learning of rats exposed to Mn. After one training period (day 29) the time required to reach the exit of a T-maze was 104.5 +/- 13.8 sec for rats dosed with Mn for 30 days, whereas that of the controls was 28.7 +/- 11.4 sec on day 30. This delay was completely corrected (to 30.7 +/- 6.0 sec) in rats co-administered mevinolin (an inhibitor of cholesterol biosynthesis) with Mn. Withdrawal of Mn, with or without inhibiting the cholesterol biosynthesis, also corrected the Mn-induced learning defect. These results suggest that Mn toxicity produces learning disability by increasing cholesterol biosynthesis and this reversible disability in learning can be corrected by withdrawal of Mn exposure.