Aluminum toxicity alters the regulation of calbindin-D28k protein and mRNA expression in chick intestine

Dietary calcium levels regulate calcium transporter gene expression levels in the small intestine of broiler chickens

1. This study investigated the effect of dietary calcium (Ca) levels on growth performance, bone development and Ca transporter gene expression levels in the small intestine of broiler chickens.2. On the day of hatch, 350, Ross 308 male broilers were randomly allotted to one of five treatments with five replicate pens each and 14 birds per pen. Dietary Ca levels in feed were 5.0, 7.0, 9.0, 11.0 and 13.0 g/kg, in which 9.0 g/kg was in the control diet. All diets contained 4.5 g/kg non-phytate phosphorus (NPP).3. The increase in dietary Ca levels from 5.0 to 13.0 g/kg did not affect the growth performance of 1- to 18-day-old broilers (P > 0.05).4. Increasing the Ca levels linearly increased the ash weight and the contents of ash, Ca and phosphorus (P) in the tibia of broilers at 18 days of age (P < 0.05). The contents of ash, Ca and P in broilers fed with 9.0 g/kg Ca were higher than those in birds fed with 5.0 g/kg Ca (P < 0.05).5. Increasing the Ca levels linearly decreased mRNA expression levels of the Ca-binding protein 28-kDa (CaBP-D28k), plasma membrane Ca-transporting ATPase 1b (PMCAlb), sodium (Na)/Ca exchanger 1 (NCX1), nuclear vitamin D receptor (nVDR) and membrane vitamin D receptor (mVDR) in the duodenum of broilers at 18 d of age (P < 0.05). Similar results were seen in the jejunum and ileum. Broilers fed 9.0-13.0 g/kg Ca in feed had lower mRNA expression levels of CaBP-D28k and PMCAlb in the small intestine than birds fed 5.0 g/kg Ca in feed (P < 0.05).6. The data indicated that low levels of dietary Ca stimulated its transporter gene transcription and promoted absorption, but high levels of Ca inhibited transporter gene expression and prevented excessive absorption in the small intestine of broiler chickens.

Aluminium toxicosis: a review of toxic actions and effects

Aluminium (Al) is frequently accessible to animal and human populations to the extent that intoxications may occur. Intake of Al is by inhalation of aerosols or particles, ingestion of food, water and medicaments, skin contact, vaccination, dialysis and infusions. Toxic actions of Al induce oxidative stress, immunologic alterations, genotoxicity, pro-inflammatory effect, peptide denaturation or transformation, enzymatic dysfunction, metabolic derangement, amyloidogenesis, membrane perturbation, iron dyshomeostasis, apoptosis, necrosis and dysplasia. The pathological conditions associated with Al toxicosis are desquamative interstitial pneumonia, pulmonary alveolar proteinosis, granulomas, granulomatosis and fibrosis, toxic myocarditis, thrombosis and ischemic stroke, granulomatous enteritis, Crohn's disease, inflammatory bowel diseases, anemia, Alzheimer's disease, dementia, sclerosis, autism, macrophagic myofasciitis, osteomalacia, oligospermia and infertility, hepatorenal disease, breast cancer and cyst, pancreatitis, pancreatic necrosis and diabetes mellitus. The review provides a broad overview of Al toxicosis as a background for sustained investigations of the toxicology of Al compounds of public health importance.

Effect of early neonatal development and delayed feeding post-hatch on jejunal and ileal calcium and phosphorus transporter genes expression in broiler chickens

Calcium (Ca) and phosphorus (P) are essential minerals involved in many biological processes including bone development and mineralization. Plasma concentration of both minerals is tightly regulated, and Ca and P homeostasis is maintained via intestinal absorption, bone storage and exchange, and renal reabsorption. In the current broiler production systems, chicks are deprived of food and water for up to 72 h due to uneven hatching, hatchery procedures, and transportation time to farms. Post-hatch (PH) feed delay results in lower body and organ weight, higher feed conversion ratio and mortality, and delayed PH growth and GIT development. Little is known about the effects of early neonatal development and delayed or immediate feeding PH on Ca and P transporters. Therefore, the aim of the present study was to characterize expression patterns of Ca and P transporter genes in small intestine during the first 2 wk PH in chickens fed immediately after hatch (FED) or subjected to 48 h delayed feeding (NOTFED). Expression of all Ca and P transporters in jejunum and ileum was significantly (P < 0.05) affected by age. Among Ca transporter genes, only mRNA expression of Calbidin D28k in jejunum and Ca sensing receptor (CaSR) in ileum were significantly (P < 0.05) affected by delay in feed access. For P transporter genes' expression, only P transporter type III (PIT1) mRNA was significantly affected by age, delay in feed access, and their interaction (P < 0.05). In summary, we have shown, for the first time, early developmental changes of Ca and P transporter genes in broiler chickens. Results suggest that an increase in gene expression of some of the transporters corresponds with the switch from yolk to high starch diet. Overall, our results can be helpful in better understanding of Ca and P homeostasis in broilers.

Effects of Aluminum Exposure on the Bone Stimulatory Growth Factors in Rats

Aluminum (Al) is considered to be a potentially toxic metal and inhibits bone formation. Transforming growth factor β1 (TGF-β1) and bone morphogenetic protein 2 (BMP-2) play an important role in regulating the bone formation. Therefore, this study aimed to investigate the effects of Al on the TGF-β1 and BMP-2 in rats. In this study, Wistar rats were randomly divided into Al-treated group and control group. The Al-treated rats were provided with drinking water containing 100 mg/L AlCl3, and the control rats were given distilled water for 30, 60, and 90 days, respectively. Ten rats were sacrificed in each group every 30 days. The Al-treated rats showed lower body weight and higher serum and bone levels of Al compared with the control rats. The expression levels of TGF-β1 and BMP-2 were also significantly decreased in the Al-treated rats. Serum levels of bone gamma-carboxyglutamic acid protein (BGP), carboxy-terminal propeptide of type I procollagen (PICP), and bone alkaline phosphatase (B-ALP) were markedly lower in the Al-treated groups than in the control group. These results indicate that Al inhibits the expression of TGF-β1 and BMP-2 in bone, which inhibits the activity of osteoblasts and reduces the synthesis of BGP, B-ALP, and type I collagen, thereby inhibiting bone formation.

Dietary and pharmacological compounds altering intestinal calcium absorption in humans and animals

The intestine is the only gate for the entry of Ca to the body in humans and mammals. The entrance of Ca occurs via paracellular and intracellular pathways. All steps of the latter pathway are regulated by calcitriol and by other hormones. Dietary and pharmacological compounds also modulate the intestinal Ca absorption process. Among them, dietary Ca and P are known to alter the lipid and protein composition of the brush-border and basolateral membranes and, consequently, Ca transport. Ca intakes are below the requirements recommended by health professionals in most countries, triggering important health problems. Chronic low Ca intake has been related to illness conditions such as osteoporosis, hypertension, renal lithiasis and incidences of human cancer. Carbohydrates, mainly lactose, and prebiotics have been described as positive modulators of intestinal Ca absorption. Apparently, high meat proteins increase intestinal Ca absorption while the effect of dietary lipids remains unclear. Pharmacological compounds such as menadione, dl-butionine-S,R-sulfoximine and ursodeoxycholic acid also modify intestinal Ca absorption as a consequence of altering the redox state of the epithelial cells. The paracellular pathway of intestinal Ca absorption is poorly known and is under present study in some laboratories. Another field that needs to be explored more intensively is the influence of the gene × diet interaction on intestinal Ca absorption. Health professionals should be aware of this knowledge in order to develop nutritional or medical strategies to stimulate the efficiency of intestinal Ca absorption and to prevent diseases.

Aluminum induces osteoblast apoptosis through the oxidative stress-mediated JNK signaling pathway

Aluminum (Al) is considered to be a potentially toxic metal. Al exposure inhibits bone formation. Few studies have investigated the mechanism of inhibitory effects of Al on bone formation. Thus, in this study, osteoblasts were cultured and exposed to different concentrations of Al to investigate the mechanism behind the inhibitory effects of Al on bone formation. Al-treated osteoblasts showed signs of oxidative stress and a high apoptosis rate. The levels of osteoblasts activity markers (bone gamma-carboxyglutamic acid protein and bone alkaline phosphatase) were significantly lower in the Al-treated groups than in the control group. The c-Jun N-terminal kinase (JNK), a major signaling pathway in regulating cell apoptosis, was activated. The phosphorylation state of JNK was significantly increased. The mRNA and protein expression of c-Jun were both significantly upregulated. The pro-apoptotic genes (caspase 3, caspase 9, bax, and factor-related apoptosis ligand) were significantly increased. However, Bcl-2, an anti-apoptotic gene, was significantly decreased. In conclusion, the results of this study indicate that Al induces osteoblast apoptosis by activating the oxidative stress-mediated JNK pathway, which causes cell injuries and reduces the number and function of osteoblasts, thereby inhibiting bone formation.

Link between Aluminum and the Pathogenesis of Alzheimer's Disease: The Integration of the Aluminum and Amyloid Cascade Hypotheses

Whilst being environmentally abundant, aluminum is not essential for life. On the contrary, aluminum is a widely recognized neurotoxin that inhibits more than 200 biologically important functions and causes various adverse effects in plants, animals, and humans. The relationship between aluminum exposure and neurodegenerative diseases, including dialysis encephalopathy, amyotrophic lateral sclerosis and Parkinsonism dementia in the Kii Peninsula and Guam, and Alzheimer's disease (AD) has been suggested. In particular, the link between aluminum and Alzheimer's disease has been the subject of scientific debate for several decades. However, the complex characteristics of aluminum bioavailability make it difficult to evaluate its toxicity and therefore, the relationship remains to be established. Mounting evidence has suggested that significance of oligomerization of β-amyloid protein and neurotoxicity in the molecular mechanism of AD pathogenesis. Aluminum may play crucial roles as a cross-linker in β-amyloid oligomerization. Here, we review the detailed characteristics of aluminum neurotoxicity based on our own studies and the recent literatures. Our aim is to revisit the link between aluminum and AD and to integrate aluminum and amyloid cascade hypotheses in the context of β-amyloid oligomerization and the interactions with other metals.

Inhibitory effect of aluminium on calcium absorption in small intestine of rats with different thyroid hormone status

To analyse the influence of thyroid status on the effect of aluminium (Al) upon intestinal calcium (Ca) absorption, adult male Wistar rats with experimentally altered thyroid hormones circulating levels, were orally treated (o.g.) with 0 (control), or 50 mg elemental Al (as chloride)/kg body weight (b.w.) per day, for a 14 d period. Hyper- and hypo-thyroid conditions were respectively achieved by means of administration of either sodium levothyroxine (50 microg/kg b.w. per day, o.g.) or methimazole, a thyroxine synthesis inhibitor (1mg/kg b.w. per day, o.g.). In duodenum-jejunum segments, in vitro mucosa-to-serosa (45)Ca flux (JCa(ms)) and kinetics of (45)Ca uptake in isolated enterocytes, were determined. In serum, concentrations of thyroxine (T4) and triiodothyronine (T3) were measured by chemiluminescent enzyme immunoassay. Unlike non-Al-treated rats, JCa(ms) of Al-exposed rats decreased as serum levels of T4 and T3 increased, showing a significant inverse correlation in both cases (T4: r(2)=0.414, P=0.024; T3: r(2)=0.443, P=0.018). Enterocytes isolated from rats treated with Al plus thyroxine showed a reduction of both maximum Ca uptake (4.86+/-0.44 vs. 6.85+/-1.04 nmol Ca/mg protein, P<0.05) and K(m) (0.84+/-0.18 vs. 1.05+/-0.36 mM, P<0.05) when compared to control. The observed variability in the Al effect on Ca transport with thyroid status of rats could be reflecting a negative interaction of Al with thyroid hormone action mechanisms on intestinal Ca absorption, which would take place mainly at Ca entry into enterocyte from lumen.

Effect of aluminium on duodenal calcium transport in pregnant and lactating rats treated with bromocriptine

The aim of present work was to study the effect of oral aluminium (Al) overload on intestinal calcium (Ca) absorption in the critical stages of pregnancy and lactation of rats and to find out possible relationships with prolactin (PRL) and 17beta-estradiol (E2) circulating levels. Adult female Wistar rats were orally treated from day 1 of pregnancy with 0 (control), or 50 mg elemental Al (as chloride)/kg body weight per day. Ca transport was determined by everted duodenal sacs technique using 2 microCi of (45)CaCl(2) as flux marker (JCa(ms)). Al treatment reduced JCa(ms) either in late pregnancy (day 19) or in middle lactation (day 9 postpartum). Oral administration of bromocriptine (BrC), an inhibitor of PRL secretion, at dose of 10 mg/kg body weight given 18 h before JCa(ms) measurements were done, produced a significant decrease in the inhibitory effect of Al on JCa(ms), expressed as percent of control, at day 9 of nursing (vehicle: 51+/-7%, BrC: 28+/-4%, P <0.05). A positive correlation between Al effects on JCa(ms) and the physiological variations of E2 serum levels along pregnancy and lactation in BrC-treated rats was also found (r(2)=0.277, P =0.001). We conclude Al could reduce transcellular Ca absorption in the duodenum by interfering with physiological mechanisms of Ca transport partially mediated by serum level increments of E2 and PRL, observed in late pregnancy and mainly during middle lactation of rats.

Aluminium-induced impairment of transcellular calcium absorption in the small intestine: calcium uptake and glutathione influence

Aluminium (Al) has been recognised as a cause of bone tissue disorders. The aims of this work were to investigate: (i) whether Al affects calcium (Ca) entry into enterocyte, and (ii) the possibility that the Al effect upon calbindin-D-related Ca transport would be influenced by intestinal glutathione (GSH) levels. In isolated chicken duodenal enterocytes, 100 microM Al lactate produced a decrease in both, the maximum uptake rate and the affinity constant of 45Ca uptake (CaUPT). This effect of Al on CaUPT was concentration-dependent in the micromolar range, showing an inhibitory saturation type phenomenon which appeared to be higher at pH 6.5 than at pH 7.4, and was not modified by the Ca channel activators A23187 and capsaicin. The simultaneous administration of Al (50 mg elemental Al/kg body weight, as AlCl3) and GSH (10 mmol/kg body weight) to rats during 7 days, prevented the inhibitory effects of Al on Ca transport. The protective effect of GSH was accompanied by an increased duodenal calbindin-D9k expression. Experimental depletion of intestinal GSH by means of D,L-buthionin-[S,R] sulfoximine, a gamma-glutamylcystein-synthase inhibitor, given as a single i.p. dose of 2 mmol/kg body weight, enhanced the degree of reduction of Ca absorption ascribed to Al. Our results suggest that Al might interfere Ca uptake by enterocytes through a general effect on cell membrane, and that an oxidative stress state induced by Al would reduce intestine GSH level affecting calbindin-D function and/or synthesis, thus leading to a reduced transcellular Ca absorption in the small intestine.