CUL5 is required for thalidomide-dependent inhibition of cellular proliferation

Angiogenesis is essential for cancer metastasis, thus the discovery and characterization of molecules that inhibit this process is important. Thalidomide is a teratogenic drug which is known to inhibit angiogenesis and effectively inhibit cancer metastasis, yet the specific cellular targets for its effect are not well known. We discovered that CUL5 (previously identified as VACM-1), a scaffold protein in E3 ligase complexes, is involved in thalidomide-dependent inhibition of endothelial cell growth. Our results show that in human endothelial cells (HUVEC), thalidomide-dependent decrease in cell growth was associated with decreased nuclear localization of CUL5. In HUVEC transfected with anti-VACM-1 siRNA, thalidomide failed to decrease cell growth. Previously it was established that the antiproliferative effect of CUL5 is inhibited in rat endothelial cells (RAMEC) transfected with mutated CUL5 which is constitutively modified by NEDD8, a ubiquitin-like protein. In this study, the antiproliferative response to thalidomide was compromised in RAMEC expressing mutated CUL5. These results suggest that CUL5 protein is involved in the thalidomide-dependent regulation of cellular proliferation in vitro. Consequently, CUL5 may be an important part of the mechanism for thalidomide-dependent inhibition of cellular proliferation, as well as a novel biomarker for predicting a response to thalidomide for the treatment of disorders such as multiple myeloma and HIV infection.

New insights into the mechanism for VACM-1/cul5 expression in vascular tissue in vivo

Vasopressin-activated calcium-mobilizing (VACM-1)/cul5 is the least conserved member of a cullin protein family involved in the formation of E3-specific ligase complexes that are responsible for delivering the ubiquitin protein to their target substrate proteins selected for ubiquitin-dependent degradation. This chapter summarizes work to date that has focused on VACM-1/cul5's tissue-specific expression in vivo and on its potential role in the control of specific cellular signaling pathways in those structures. As mammalian cells may contain hundreds of E3 ligases, identification VACM-1/cul5 as a specific subunit of the system that is expressed in the endothelium and in collecting tubules, structures known for their control of cellular permeability, may have significant implications when designing studies to elucidate the mechanism of water conservation. For example, VACM-1/cul5 expression is affected by water deprivation in some tissues and there is a potential relationship between neddylated VACM-1/cul5 and aquaporins.

VACM-1/cul5 expression in vascular tissue in vivo is induced by water deprivation and its expression in vitro regulates aquaporin-1 concentrations

VACM-1, a cul5 gene product, when overexpressed in vitro, has an antiproliferative effect. In vivo, VACM-1/cul5 is present in tissues involved in the regulation of water balance. Neither proteins targeted for VACM-1/cul5-specific degradation nor factors that may regulate its expression in those tissues have been studied. To identify genes that may be misregulated by VACM-1 cDNA, we performed microarray analysis. Our results indicate that in cos-1 cells transfected with VACM-1 cDNA, mRNA levels for several genes, including AQP1, were decreased when compared to the control group. Our results also indicate that in cos-1 cells transfected with VACM-1 cDNA, endogenous AQP1 protein was decreased about 6-fold when compared to the controls. To test the hypothesis that VACM-1/cul5 may be regulated by conditions that compromise water homeostasis in vivo, we determined if 24 h of water deprivation affects VACM-1/cul5 levels or the effect of VACM-1/cul5 on AQP1. VACM-1 mRNA and protein levels were significantly higher in rat mesenteric arteries, skeletal muscle and the heart ventricle but not in the heart atrium from 24-h water-deprived rats when compared to the controls. Interestingly, 24 h of water deprivation increased modification of VACM-1 by an ubiquitin-like protein, Nedd8, essential for cullin-dependent E3 ligase activity. Although water deprivation did not significantly change AQP1 levels in the mesenteric arteries, AQP1 protein concentrations were inversely correlated with the ratio of the VACM-1 to Nedd8-modified VACM-1. These results suggest that VACM-1/cul5 may regulate endothelial AQP1 concentration both in vivo and in vitro.

The Effects Of Sucralfate Ingestion On Serum And Specific Tissue Aluminum Concentration In Normal Rats

The effects of sucralfate ingestion on serum and specific tissue aluminum (Al) accumulation were studied in normal rats fed either a control diet or the same diet supplemented with sucralfate. Although serum Al concentrations were not significantly different between the groups, animals fed sucralfate for 8 weeks had significantly higher bone but not brain or liver Al concentrations when compared with controls. This study indicates that 8 weeks exposure to Al in sucralfate leads to an increase in bone Al concentrations, without changes in serum Al concentrations, suggesting that serum Al concentration may be a poor predictor of gastrointestinal absorption and specific tissue retention of Al.

Estrogen-dependent growth and estrogen receptor (ER)-α concentration in T47D breast cancer cells are inhibited by VACM-1, a cul 5 gene

Vasopressin-activated calcium mobilizing receptor (VACM-1)/cullin 5 (cul 5) inhibits growth when expressed in T47D breast cancer cells by a mechanism that involves a decrease in MAPK phosphorylation and a decrease in the early growth response element (egr-1) concentration in the nucleus. Since both MAPK and egr-1 pathways can be regulated by 17beta-estradiol, we next examined the effects of VACM-1 cDNA expression on estrogen-dependent growth in T47D cells and on estrogen receptor (ER) concentrations. Our results demonstrate that in T47D cells, both basal and 17beta-estradiol-dependent increase in cell growth and MAPK phosphorylation were inhibited in cells transfected with VACM-1 cDNA. Further, Western blot and immunocytochemistry data analyses indicate that ER concentrations and its nuclear localization are significantly lower in cells transfected with VACM-1 cDNA when compared to controls. These data indicate that in the T47D cancer cell line VACM-1 inhibits growth by attenuating estrogen-dependent signaling responses. These findings may have implications in the development of cancer treatments.

Truncated form of VACM-1/cul-5 with an extended 3' untranslated region stimulates cell growth via a MAPK-dependent pathway

We have sequenced a 4.9kb clone (KLB22) which shares 99% sequence homology with the rabbit vasopressin-activated calcium mobilizing (VACM-1) protein. The 5' terminus sequence of KLB22 cDNA (nucleotides 1-1961) is continuous and overlapping with nucleotides 1226-3186 of the VACM-1 cDNA sequence. The 3'UTR of KLB22 cDNA extends beyond the 3'UTR of VACM-1 by 2999nt. KLB22 cDNA encodes a 497 amino acid protein, which putatively begins at Met 284 of the 780 amino acid VACM-1 protein. The in vitro translation of KLB22 cDNA yields a 59kDa protein. When expressed in cos-1 cells, the truncated VACM-1 protein localizes to the nucleus. KLB22 cDNA transfected cells show increased growth rates and increased levels of phosphorylated MAPK when compared to the vector or to VACM-1 cDNA transfected cells. Finally, in vivo, KLB22 protein expression is tissue specific and can be detected in kidney and in heart atrium. These results suggest that truncated VACM-1 cDNA (KLB22) increases cell proliferation through a MAPK pathway.

T47D breast cancer cell growth is inhibited by expression of VACM-1, a cul-5 gene

Vasopressin-activated calcium-mobilizing (VACM-1), a cul-5 gene, is localized on chromosome 11q22-23 close to the gene for Ataxia Telangiectasia in a region associated with a loss of heterozygosity in breast cancer tumor samples. To examine the biological role of VACM-1, we studied the effect of VACM-1 expression on cellular growth and gene expression in T47D breast cancer cells. Immunocytochemistry studies demonstrated that VACM-1 was expressed in 0.6-6% of the T47D cells and localized to the nucleus of mitotic cells. Overexpressing VACM-1 significantly attenuated cellular proliferation and MAPK phosphorylation when compared to the control cells. In addition, VACM-1 decreased egr-1 and increased Fas-L mRNA levels. Further, egr-1 protein levels were significantly lower in the nuclear fraction from VACM-1 transfected cells when compared to controls. These data indicate that VACM-1 is involved in the regulation of cellular growth.

Expression cloning of an AVP-activated, calcium-mobilizing receptor from rabbit kidney medulla

Arginine vasopressin (AVP) is a nonapeptide that regulates body fluid and blood pressure homeostasis. We have used expression cloning in the Xenopus laevis oocyte system to identify cDNA clones from a rabbit renal medullary expression library encoding an AVP receptor linked to Ca2+ mobilization. cRNA generated from positive clones conferred upon oocytes the capacity to mobilize intracellular Ca2+ in response to AVP. A cDNA clone encoding a protein of 780 amino acids was isolated, sequenced, and subcloned into an SV40-based expression vector. Expression of the cloned protein [designated the vasopressin-activated, calcium-mobilizing (VACM-1) protein] in COS-1 cells, resulted in increased 125I-labeled AVP binding [dissociation constant (Kd) of approximately 2 nM] and increased AVP-induced mobilization of Ca2+. Importantly, 125I-AVP could be immunoprecipitated both from detergent-solubilized membranes from COS-1 cells expressing VACM-1 protein and from an in vitro translation system, in which VACM-1 protein was synthesized, using antibodies prepared against a synthetic peptide derived from the NH2-terminal sequence of VACM-1. Interestingly, immunohistochemical staining of rabbit kidney sections with this antibody showed specific staining of collecting tubule epithelia. The deduced amino acid sequence is not homologous with any nucleic acid or amino acid sequences reported to date, including those of the V1 and V2 AVP receptors. The VACM-1 protein may represent a novel AVP receptor.

Effects of adenosine on cAMP production and cytosolic Ca2+ in cultured rabbit medullary thick limb cells

The cellular signaling mechanism of adenosine action has been studied in highly purified populations of cultured cells from the rabbit medullary thick ascending limb of Henle's loop (MTAL). The effects of specific adenosine-receptor agonists 5'(N-ethylcarboxamido)adenosine (NECA; A2) and N6-cyclohexyladenosine (CHA; A1) on basal and hormone-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production, cytosolic free calcium concentration ([Ca2+]f), and formation of inositol phosphates were examined. Production of cAMP was stimulated by high doses of NECA and was inhibited by low doses of CHA. The inhibitory effect of CHA was observed in cells in which cAMP production was first stimulated with vasopressin, isoproterenol, prostaglandin E2 (10(-6) M), or calcitonin (100 ng/ml) and was abolished by pretreating the cells with pertussis toxin (PT) for 12-20 h. A highly selective adenosine A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine (CPX), also abolished the inhibitory effect of CHA. Both NECA and CHA induced a rapid (10 s) and transient increase in [Ca2+]f, and this was associated with an increased inositol trisphosphate (IP3) production. Single-cell [Ca2+]f measurements indicated that all MTAL cells responded to CHA. The removal of extracellular Ca2+ failed to inhibit these responses. Pretreatment with PT or administration of CPX abolished both the increase in [Ca2+]f and the formation of IP3 occurring in response to CHA and NECA. Our results suggest that both adenylate cyclase-coupled inhibitory (A1) and stimulatory (A2) adenosine receptors are present in pure populations of cultured MTAL cells. Moreover, activation of an adenosine receptor coupled to a PT substrate results in the increased production of inositol phosphate and elevation of [Ca2+]f.

Vasopressin V1 receptors on the principal cells of the rabbit cortical collecting tubule. Stimulation of cytosolic free calcium and inositol phosphate production via coupling to a pertussis toxin substrate

The effects of arginine vasopressin (AVP) on the cytosolic free calcium concentration ([Ca2+]f) were examined in freshly immunodissected rabbit cortical collecting tubule cells using fluorescent Ca2+ indicators fura-2 and indo-1. The addition of AVP to a cell suspension resulted in a rapid and transient increase in the [Ca2+]f. The 1-deamino-8-D-AVP (dDVP), a V2 receptor agonist of AVP that stimulated adenosine 3',5' cAMP production in these cells, had no effect on [Ca2+]f and did not affect AVP-induced increase in [Ca2+]f. The AVP-induced increase in [Ca2+]f but not cAMP production was blocked by the V1 receptor antagonist, [1-(beta-mercapto-beta-beta-cyclopentamethylene propionic acid), 2-(O-methyl)tyrosine] Arg8-vasopressin. The AVP-stimulated increase in [Ca2+]f appeared to be largely due to Ca2+ release from intracellular stores as reduction of extracellular Ca2+ with EGTA had little if any effect on the AVP-induced increase in [Ca2+]f. This AVP-induced increase in [Ca2+]f was associated with an increase in inositol-1,4,5-trisphosphate production and appeared to involve a guanine nucleotide-binding protein (G), since the pretreatment of cells with pertussis toxin for 4-6 h inhibited this effect. Finally, measurements of [Ca2+]f in single cells suggest that only the principal cells of the collecting tubules respond to AVP with an increase in [Ca2+]f. In summary, these results demonstrate that the principal cells of the cortical collecting tubule possess two distinct receptor systems for vasopressin, the well-known V2 receptor coupled to adenylate cyclase, and a V1 receptor system that leads to the mobilization of cytosolic calcium, coupled through a pertussis toxin substrate (G protein) to a production of inositol phosphates.

Adenosine receptor-mediated calcium mobilization in cortical collecting tubule cells

To investigate the cellular mechanisms underlying the epithelial actions of adenosine, we studied adenosine receptor-effector coupling in cultured rabbit cortical collecting tubule (RCCT) cells. We previously reported, in RCCT cells isolated by immunodissection, that a potent A2 adenosine analogue [5'-N-ethylcarboxamideadenosine (NECA)] stimulates cAMP production [effective concentration 50% (EC50) = 1 microM], and potent A1 analogues [N6-cyclohexyladenosine (CHA) and R-N6-phenylisopropyladenosine (PIA)] inhibit basal and AVP-stimulated cAMP production (EC50 = 5 nM). The present study was undertaken to determine whether adenosine receptors in RCCT cells are also coupled to a signal transduction system leading to the mobilization of intracellular free calcium. RCCT cells were loaded with the fluorescent calcium indicator, fura-2, and were treated with the adenosine analogues NECA, CHA, and PIA. All three adenosine analogues produced dose-dependent (1 nM-0.1 mM), transient increases in intracellular calcium concentration with equal potency (EC50 = 0.5 microM). Chelation of extracellular calcium with ethyleneglycol-bis(beta-aminoethyl ether)N,N,N',N' tetraacetic acid (EGTA) did not abolish the increase in calcium. The adenosine receptor antagonists, 1,3-diethyl-8-propylxanthine and 8-cyclopentyl-1,3-dipropylxanthine, and pretreatment of RCCT cells with pertussis toxin blocked the increase in calcium. These results demonstrate that RCCT cells have, in addition to adenosine receptors associated with the stimulation and inhibition of cAMP, a pertussis-toxin sensitive receptor system that leads to the mobilization of intracellular calcium.

Immunodissection of mitochondria-rich cells from rabbit outer medullary collecting tubule

Two types of mitochondria-rich (MR) cells have been identified in the rabbit collecting tubule based on differences in immuno- and lectin cytochemistry. We have produced a monoclonal antibody, immunoglobulin (Ig) G1 (mr-mct), that reacts specifically with the MR cells (identified by positive histochemical staining for succinate dehydrogenase) found predominantly in the outer medulla (OM) and cells of the proximal tubule. IgG1 (mr-mct) reacted with 18 +/- 2% of the cells of the outer medullary collecting tubule (OMCT) and did not colocalize with peanut lectin-binding MR cells in the cortex. To isolate MR-OMCT cells, collecting tubule cells from collagenase dispersions of the OM were first adsorbed onto plates treated with a monoclonal antibody reactive against all of the OMCT cells. Of the isolated OMCT cells, 17% reacted with IgG1 (mr-mct). Cells were then detached from the plate and transferred to plates coated with IgG1. Greater than 70% of the adsorbed cells were MR as determined by positive staining with IgG1 (mr-mct). This enrichment of MR-OMCT cells was associated with a severalfold increase in adenosine 3',5' cyclic monophosphate (cAMP) production in response to isoproterenol and an attenuated increase in cAMP production to vasopressin. In summary, we report the isolation of highly enriched populations of MR cells from the OM using two-stage solid-phase immunoadsorption. This approach should provide a useful and convenient method for further investigations of the physiological role of these poorly understood tubular cells.

Vasopressin increases cytosolic free calcium in LLC-PK1 cells through a V1-receptor

We examined the effects of arginine vasopressin (AVP), parathyroid hormone (PTH), and bradykinin (BK) on the cytosolic free calcium concentration ([Ca]i) in cultured LLC-PK1 and MDCK kidney cell lines by use of the fluorescent Ca chelator fura-2. In LLC-PK1 cells, the addition of AVP but not [1-desamino-8-D-arginine]vasopressin (dDAVP, V2 agonist), PTH, or BK (10(-6) M) caused a significant increase in [Ca]i. The AVP-induced increase in [Ca]i from 61 +/- 6 to 225 +/- 44 nM (n = 7, P less than 0.01) was rapid and transient, returning to base line in 2 to 3 min. The effect of AVP was dose dependent and was present at 1 (61% increase) but not 5 min after extracellular Ca was removed. The effect of 10(-6) M AVP could be blocked with the pressor (V1) antagonist, d(CH2)5Tyr(Me)AVP, but not dDAVP. In MDCK cells, BK, but not AVP and PTH, increased [Ca]i from 146 +/- 11 to 281 +/- 31 nM (n = 9, P less than 0.001). The removal of extracellular Ca (5 min), reduced but did not abolish this effect. These results indicate that [Ca]i mobilized by activation of V1-receptors may mediate AVP-regulated function in some transporting epithelia.

1,25-Dihydroxyvitamin D3 increases serum and tissue accumulation of aluminum in rats

We examined the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in both hypercalcemic and hypocalcemic rat models and the effect of exogenous 25-hydroxyvitamin D3 (25(OH)D3) on serum and tissue aluminum (Al) burdens. Rats fed a 0.2% Al diet received daily subcutaneous injections of either 1,25(OH)2D3 (80.9 ng/kg, n = 5 and 809 ng/kg, n = 8), 25 (OH)D3 (809 ng/kg, n = 4, and 8090 ng/kg, n = 8) or propylene glycol vehicle for 18 days. Rats given 809 ng/kg of 1,25(OH)2D3 were hypercalcemic and when compared with pair-fed controls had higher serum (33.1 vs. 14.3 micrograms/L, P less than 0.01), bone (21.2 vs. 13.2 micrograms/gm, P less than 0.01), and kidney (6.5 vs. 2.0 micrograms/gm, P less than 0.01) but not brain (1.2 vs. 1.5 micrograms/gm) or liver (0.9 vs. 0.8 micrograms/gm dry tissue) Al concentration. The lower dose of 1,25(OH)2D3 had no effect on serum or tissue Al. Treatment with 25(OH)D3 did not increase serum Ca and Al or tissue Al concentration. To dissociate a specific effect of exogenous 1,25(OH)2D3 from the concurrent hypercalcemia, endogenous production of 1,25(OH)2D3 was stimulated. Animals were fed a low Ca diet until hypocalcemia developed and were then divided into four groups: one given low Ca (n = 7) for 21 days, one given low Ca plus 0.2% Al (n = 7) for 21 days, one returned to a normal Ca diet (n = 4) for 30 days, and one returned to a normal Ca diet for 9 days and continued with a normal diet plus 0.2% Al (n = 5) for 21 days. Hypocalcemic rats fed the Al diet, when compared with hypocalcemic controls, had higher serum (143.6 vs. 31.8 micrograms/L, P less than 0.01), bone (16.0 vs. 2.9 micrograms/gm, P less than 0.01), and kidney (8.2 vs. 2.8 micrograms/gm, P less than 0.005) but not brain (3.4 vs. 2.3 micrograms/gm) or liver (3.8 vs. 2.3 micrograms/gm) Al concentrations. Serum, bone, and kidney Al concentration was also significantly higher than that in normocalcemic rats fed the Al diet. These results indicate that pharmacologic doses of 1,25(OH)2D3 and dietary hypocalcemia enhance gastrointestinal Al absorption and serum, kidney, and bone Al concentration.

Evaluation of bidirectional aluminum transfer across hollow fiber dialyzers

The ultrafiltrable fraction of plasma aluminum (UFAl) determined utilizing the hollow fiber dialyzer is variable and ranges from 10% to 50%. This extreme variability in UFAl led us to examine the possibility of Al binding to the hollow fiber dialyzer. Ultrafiltrate of aqueous Al solutions was obtained by applying a negative pressure of 250 mm Hg to a hollow fiber dialyzer (TriEx-1). In the first of three experimental protocols, Al was measured before and after recirculation of solutions containing 344 to 9244 micrograms/L Al through a hollow fiber dialyzer until the entire volume was collected as ultrafiltrate. UFAl ranged from 0.9% to 37.6% and did not correlate with the initial Al concentration. Total Al binding ranged from 42 micrograms to 1.3 mg. In the second, 16 L of aqueous AlCl3 solution (n = 3), containing from 205 to 411 micrograms/L Al were passed through the blood compartment of a hollow fiber dialyzer. The percentage of UFAl ranged from 4.1% to 17.3% during the first 20 minutes and 79.3% to 81.8% at 120 minutes. Finally, to investigate Al transfer from dialysate, 16 L of deionized distilled water were passed through the blood compartment while 16 L of AlCl3 solutions of 330 micrograms/L and 398 micrograms/L AI passed through the dialysate compartment. Samples were collected from blood and dialysate outflow ports every 20 minutes for 120 minutes. The transfer of Al from dialysate to blood compartment increased with time. However the concentration of Al at the blood outflow port never reached that at the dialysate outflow port.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal handling of aluminum in the rat: clearance and micropuncture studies

Previous uncertainty regarding glomerular ultrafilterability (UF) of aluminum has limited the definition of renal Al handling. Glomerular micropuncture was therefore performed in hydropenic Munich-Wistar rats infused with AlCl3 to achieve plasma (P) Al levels between 2 and 10 mg/liter. Glomerular fluid, P, and urine Al concentrations were measured by flameless atomic-absorption spectrophotometry. UFA1 was inversely correlated with PA1 [%UFA1 = 10.3 - 8.4 (log PA1), r = -0.90, P less than 0.01]. When this equation was used to calculate the filtered load (FLA1), A1 excretion (UA1V, ng/min) in simultaneously collected samples was found to be a direct function of FLA1 [UA1V = 5.7 + 0.37 (FLA1), r = 0.93, P less than 0.01]. Fractional excretion (FE) of A1 was 39.4 +/- 4.2% in these hydropenic experiments (FENa = 0.3 +/- 0.1%). We next evaluated the tubular handling of A1 (using these UF data) during step-wise extracellular fluid volume expansion with isotonic saline (2.5, 5.0, 7.0, and 7.0% body wt) and during the infusion of increasing doses (2.7, 5.3, 8.0, and 8.0 mg X kg-1 X h-1) of furosemide as urinary losses were quantitatively replaced. The natriuresis produced by volume expansion (FENa = 1.0, 3.0, 8.4, and 7.9%) and furosemide (FENa = 4.2, 6.0, 6.6, and 6.7%) were comparable. At similar FLA1, 7% volume expansion but not furosemide (at any dose) increased UA1V (240 and 95 ng/min, respectively, vs. 116 ng/min in hydropenia) and FEA1 (84.5 and 29.4 vs. 37.4%, respectively). These data indicate that at pharmacological PA1 levels, less than 8.4% of PA1 is ultrafilterable, suggesting extensive plasma protein binding.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of aluminum loading on selected tissue calcium and magnesium concentrations in rats

Considerable evidence implicates elevated brain aluminum (Al) concentration in the pathogenesis of several forms of central nervous system dysfunction seen particularly among dialysis patients. In animals Al intoxication also leads to cerebral dysfunction. Since increased brain calcium (Ca) concentration has been associated with similar disturbances of cerebral function, this study was initiated to examine the effects of increased Al concentration on Ca and magnesium (Mg) concentrations in brain and other selected tissues. Daily intraperitoneal injection of Al (2.7 mg) for 10 d resulted in a significant increase in brain, liver, spleen, bone, and heart Al concentrations when compared to controls receiving saline injection. In brain, liver, and spleen, but not heart, Ca concentration was significantly higher in Al-treated rats than controls. In brain there was a significant correlation between Ca and Al concentration. Total plasma Ca concentration was not significantly different between the groups. Al loading had no significant effect on tissue Mg concentration. These results indicate that Al affects selected tissue Ca concentrations which ultimately may be involved in Al organ toxicity.

Microcytic anemia secondary to intraperitoneal aluminum in normal and uremic rats

Dialysis patients exposed to high aluminum (Al) dialysate develop a microcytic anemia which is reversed by deionization (DI) of the dialysate. Because DI removes substances in addition to Al which are known to cause anemia, these experiments were undertaken to determine if Al causes anemia and if the anemia of uremia can be enhanced by Al. Four groups of rats were studied: sham control (A) N = 6; uremic control (B) N = 6; Al-loaded non-uremic (C) N = 7; and Al-loaded uremic (D) N = 5. Aluminum treatment was 1 mg Al intraperitoneally daily for 6 weeks. Uremic rats (B+D) were 1 5/6 nephrectomized; non-uremic (A+C) were sham-operated. Blood samples (200 microliter) were obtained prior to (C1) and weekly during treatment (T1 to T6) and analyzed by Coulter Counter. No significant difference in hemoglobin (Hb), hematocrit (Hct), or mean cell volume (MCV) was noted at C1 X At T3, MCV of Al-treated rats (C+D) was significantly less than sham control (A) (55.1 +/- 0.5 and 53.0 +/- 0.8 vs. 60.8 +/- 1.5 mu3, P less than 0.05). At T6, MCV, Hb, and Hct of Al-loaded uremic rats (D) (49 +/- 0.5 mu3; 11.8 +/- 0.5 g/dl; 25.1 +/- 2%) were significantly less than both A (58.6 +/- 1.3 mu3; 16.1 +/- 0.4 g/dl; 44.8 +/- 0.3%) and B (58.7 +/- 1.4 mu3; 13.8 +/- 0.4 g/dl; 33.6 +/- 0.5%) (P less than 0.05) and MCV, Hb, and Hct of Al-loaded non-uremic rats (C) (51.7 +/- 1.7 mu3; 12.6 +/- 0.3 g/dl; 29.4 +/- 1.5%) was significantly less than A (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired renal function and aluminum metabolism

The consequences of renal functional impairment on aluminum (Al) excretion are not clear inasmuch as little is known about its glomerular filtration, tubular reabsorption, or secretion. The association of Al and the etiology of the dialysis encephalopathy syndrome and osteomalacia among patients with uremia suggests that renal functional impairment is a prerequisite for increased body Al stores. However, considerable evidence argues against the concept that tissue Al accumulation occurs as a simple consequence of renal failure. Many dialysis patients have high parathyroid hormone (PTH) concentrations that have been associated with neurologic abnormalities, bone disease, and anemia. The toxicity of PTH could be either direct or indirect by influencing the metabolism of potentially toxic substances such as Al. Our studies in normal rats suggest that gastrointestinal Al absorption and specific tissue burdens are enhanced by PTH, but not irreversibly, because the withdrawal of PTH resulted in Al egress. Dialysis patients are often treated with vitamin D analogs to prevent or control consequences of hyperparathyroidism and impaired 1,25-dihydroxycholecalciferol synthesis. Although some reports suggest that high bone Al in osteomalacia may be responsible for vitamin D resistance, our studies with normal rats suggest that its metabolites may also increase tissue Al burdens independent of PTH action. Thus, several factors operative in uremia other than impaired renal function may contribute to altered Al metabolism and, consequently, to its toxicity.