| Worldwide epidemiological studies have reported significant inverse associations between drinking water hardness and mortality from coronary heart disease and other cardiovascular disease. A strong claim has been made for magnesium as the key water factor. Purified water, as a kind of soft water, hardly has any mineral elements, such as calcium (Ca2+), magnesium (Mg2+) and so on. It is intensively indicated by the references in home and abroad that drinking of soft water for a long time decreased the concentration of Mg2+ in blood and increased the blood lipid and the incidence of cardiovascular diseases, especially arteriosclerosis (AS). In Our previous studies with Wistar rats drinking of purified-water for 20 weeks have higher blood lipids (TG,CH,LDL) and lower Mg2+ concentration in blood. Some investigations have indicated a relationship between soft water or low magnesium concentrations in drinking water and cardiovascular disease. However, there is few report to explore the molecular mechanisms of blood lipid disorder induced by soft water.Lipoprotein metabolism is a complex dynamic process, among which apolipoprotein, lipoprotein receptor of cell membrane and some enzymes of lipoprotein metabolism play determined roles. The role of factors mentioned above in higher blood lipids induced by purified water is seldom reported. The present study was designed to assess whether the factors of lipid metabolism were related to alterations of blood lipid, which induced by drinking of purified water in rats.Methods: A total of 180 male and female Wistar rats weighing 68±17 g were equally randomized into 3 groups: Tap-water group (TW), purified water group (PW) and purified water+MgSO4 group (PW+Mg, 0.5g/L MgSO4). Rats were supplied free with water and food. The changes of body weight and diet of rats were observed every week and per month, respectively. After 3 and 6 months' treatment, the rats were killed and their livers were rapidly removed and immediately plunged into liquid nitrogen. The samples were stored for determination of apoAI, apoB and LDLR mRNA levels. The aortic arch, heart (frontal wall of left ventricle) and liver (lateral middle part of left lobe) were taken and fixed in 4% formaldehyde followed by embedding in paraffin 72 h later. The main organ weight (heart, liver, spleen, lung, kidney) was measured. Blood was collected for determination of serum LCAT and LPL and HL levels, and the concentrations of apoAⅠand apoB were measured.Results and Discussion: 1. The heart and kidney weight were significantly increased in females of PW group after 6 months treatment (P<0.05). 2. Compared with the TW, the serum apoB concentration was significantly increased (P<0.05) and apoAⅠ/ apoB was decreased in PW, although not statistically significant. Drinking of purified water may affect transportation and metabolism of LDL-C via alteration serum apoB concentration, leading to blood lipid disorder. This is supposed one of important reasons, which increase cardiovascular disease morbidity and mortality caused by drinking of soft water. 3. The serum HL activity was significantly decreased (P<0.05) and LPL, HL levels were also reduced in PW. The results suggest that drinking of purified water can disturb the key enzymes of lipid metabolism to some extent and result in dysfunction of reverse cholesterol transport and metabolism of LDL. 4.The present study demonstrated an increase in apoB and decreases in apoAI and LDLR of gene expression in the liver in PW, but no differences were seen. Drinking of purified water might delay the clearing of lipoprotein, which contain apoB through down-regulating hepatic LDLR mRNA expression, thus leading to a significant increase of serum apoB concentration. There was a discrepancy between significant increasing of serum apoB concentration and no significant up-regulation of apoB mRNA, down-regulation of LDLR mRNA .It suggested that effect of LDLR on decomposition and metabolism of apoB might exist in post-transcriptional control. 5. Supplementation of Mg2+ to purified wat...
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