| Our previous studies showed that dietary supplementation of chromium (Cr) in the form of chromium-silicate nanocomposite (CrNano) could positively alter carcass characteristics in finishing pigs and greatly increase Cr deposit in heart, liver, kidney and longissimus muscle, which indicated that CrNano might have unique absorption mechanism in vivo and high bioavailability. Therefore, the present studies were conducted to investigate the transport and uptake of CrNano, Cr picolinate (CrPic) and Cr chloride (CrCl3) by using Caco-2 cell monolayer model. At the same time, the effects of CrNano, CrPic and CrCl3 on growth performance, carcass traits, serum parameters and tissue Cr deposit in Sprague-Dawley (SD) rats were also evaluated. Our goal was to investigate, compare and probe into the absorption mechanisms of CrNano, CrPic and CrCl3 as well as their in vivo bioeffects. The potential results will provide scientific explanation for positive effects of CrNano on carcass traits and will promote the research and application of nanotechnology in animal nutrition and feed science.The Caco-2 cells were seeded onto the polycarbonate microporal membranes in Snapwell bichambers and cultured on 37?and in an atmosphere of 5% carbon dioxide. After 21 days of culture, the transepithelial electrical resistance was higher than 620?·cm2, the transport rate of mannitol across Caco-2 cell monolayers was less than 0.3%·h-1·cm-2, and the activity of alkaline phosphatase in apical (AP) side was greatly higher than that in basolateral (BL) side. These results indicated that the Caco-2 cells cultured in our laboratory had similarity to intestinal epithelial cells in morphology, produced polarity, formed well tight junctions between cells, and could be used as an in vitro model to investigate absorption mechanisms of substances.The transport and uptake of CrNano, CrPic and CrCl3 in Caco-2 cell monolayers were conducted from AP to BL and BL to AP, respectively. The effects of concentration (0.2-20?mol/L of Cr), time (120 min of incubation) and temperature (37?and 4?on transport and uptake of CrNano, CrPic and CrCl3 were investigated. The results were as follows. Transports of CrNano, CrPic and CrCl3 across Caco-2 monolayers both from AP to BL and BL to AP direction were concentration-and time-dependent. Lowering the incubation temperature from 37?to 4?had no effect on transport amounts of CrNano, CrPic and CrCl3 both from AP to BL and BL to AP direction. The apparent permeability coefficient (Papp) of CrNano was between 5.89×10?cm/s and 7.92×10-6 cm/s. Papp of CrPic was between 3.52×10-6 cm/s and 5.31×10-6 cm/s, and that of CrCl3 was between 0.97×10-6 cm/s and 1.37×10-6 cm/s. Uptakes of CrNano, CrPic and CrCl3 into Caco-2 cells both from AP to BL and BL to AP direction were concentration-and time-dependent. The uptake amount of CrNano into Caco-2 cells in AP side was significantly decreased (P<0.05) when incubation temperature lowered from 37?to 4?, whereas the uptake amounts of CrPic and CrCl3 were unaffected (P>0.05). The transport rate of CrNano, CrPic and CrCl3 was 15.83%±0.76%,9.08%±0.25%, and 2.11%±0.53%, respectively. The uptake rate of CrNano, CrPic and CrCl3 was 10.08%±0.76%, 4.73%±0.60%, and 0.88%±0.08%, respectively. These results indicated that absorption of CrNano in Caco-2 cell monolayers was mainly via transcellular pathway, while absorption of CrPic and CrCl3 were mainly via paracellular pathway. CrNano had higher absorption efficiency than CrPic and CrCl3 in Caco-2 cell monolayers.Transport of 4?mol/L of Cr in the form of CrNano, CrPic and CrCl3 were conducted with 5?mol/L of vitamin C, copper sulfate, ferric chloride, zinc chloride, sucrose, ethylene diaminetetraacetic acid (EDTA), oxalate, or citrate, respectively. Vitamin C, copper, zinc, EDTA, oxalate, citrate and sucrose had no effect on transport of CrNano and CrPic (P>0.05). However, ferric significantly reduced the transport amount of CrNano and CrPic (P<0.05). Vitamin C and oxalate significantly increased the transport amount of CrCl3 (P<0.05). Ferric and sucrose decreased the transport amount of CrCl3 (P<0.05). Copper, zinc, EDTA and citrate did not affect the transport of CrCl3 (P>0.05). These results indicated that dietary factors played different roles in affecting diverse sources of Cr. CrCl3 was easily affected by dietary factors relative to CrNano and CrPic.A total of forty male SD rats were randomly assigned to four dietary treatment groups. Rats in the first group were fed basal diet as a control. Rats in the second, third and fourth group were fed basal diet supplemented with 300?g/kg Cr in the form of CrCl3, CrPic and CrNano, respectively. Feeding trial was conducted for six weeks. During the period of trial, body weight of rats was weighed and feed consumption was recorded. At the end of trial, body composition, serum parameters and tissue Cr content were determined. In comparison to the control, supplemental Cr from CrNano increased average daily gain and feed efficiency by 12.68%(P<0.05) and 25.59%(P<0.05), respectively. Addition of Cr from CrPic and CrCl3 had no effect on growing performance of rats (P>0.05). Supplementation of CrNano increased lean body mass by 15.57%(P<0.05) and decreased percent body fat by 24.42%(P<0.05). Addition of CrPic increased lean body mass by 14.82%(P<0.05) while had no effect on percent body fat (P>0.05). Addition of CrCl3 had no effect on body composition of rats (P>0.05). Supplemental Cr from CrNano increased serum contents of insulin-like growth factor I, total protein and high-density lipoprotein by 78.57%(P<0.05), 25.05%(P<0.05) and 23.07%(P<0.05), respectively, and decreased serum contents of insulin, glucose, triglyceride, and urea nitrogen by 45.38%(P<0.05),31.84%(P<0.05), 46.67%(P<0.05), and 48.75%(P<0.05), respectively. Addition of Cr from CrPic increased serum contents of insulin-like growth factor I and high-density lipoprotein by 38.46%(P<0.05) and 26.15%(P<0.05), respectively, and decreased serum contents of glucose, triglyceride, urea nitrogen by 15.05%(P<0.05),36.00%(P<0.05), and 57.62%(P<0.05), respectively. However, supplementation of Cr from CrCl3 had no effect on serum parameters in the rats. In addition, Cr content in blood, liver, kidney, jejunum and hind leg muscle of rats fed supplemental Cr was higher than that in the corresponding tissues of rats fed basal diet and diet supplemented with CrCl3 and CrPic. These results suggested that CrNano had higher absorption efficiency than CrPic and CrCl3 in SD rats. In addition, CrNano had significantly higher bioavailability than CrCl3 and tended to be more bioavailable than CrPic in rats.A total of seventy male SD rats were randomly allotted to seven dietary treatment groups. Rats in the first group were fed basal diet as control. Rats in the second, third, fourth, fifth, sixth and seventh group were fed basal diet supplemented with 75,150,300,450,600, and 1200?g Cr/kg diet in the form of CrNano, respectively. The feeding trial was conducted for six weeks. The body weight of rats was weighed and feed consumption was recorded during the trial. At the end of the trial, body composition of rats was assessed by dual energy X-ray absorptionmetry. Samples of organs were collected for analysis. Supplementation of 75,150 and 300?g/kg Cr in the form of CrNano significantly increased average daily gain (P<0.05). Feed efficiency was increased by addition of 75,150,300 and 450?g/kg Cr from CrNano (P<0.05). Lean body mass was increased by 300 and 450?g/kg Cr as CrNano (P<0.05). Addition of 150,300,450 and 600?g/kg Cr from CrNano decreased percent body fat of rats significantly (P<0.05). Addition of from 75?g/kg to 1200?g/kg Cr from CrNano significantly increased Cr content in blood (P<0.05). The Cr concentration in liver and kidney was greatly enhanced by supplementation of from 150?g/kg to 1200?g/kg Cr (P<0.05). In addition, Cr content in hind leg muscle of rats was significantly increased by addition of 300,450 and 600?g/kg Cr from CrNano. These results suggested that supplementation of CrNano to the diet of rats could promote growth, positively alter body composition, increase Cr deposit in tissues. However, no restrict dose dependent effect was detected. |
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