Development of a turbidimetric assay to study the effect of urinary components on calcium oxalate precipitation

The pharmacological treatment of calcium urinary stones, most of which are made of calcium oxalate (CaOx), is only prophylactic. The causes of nephrolithiasis are often unclear, and a number of patients were found to be deficient in physiological inhibitors, e.g. citrate, pyrophosphate, magnesium, and specific proteins. The identification and characterization of these inhibitors can be performed in vitro by a number of methods, most of which are complex and time-consuming. Thus, we developed a simple turbidimetric method based on the precipitation of CaOx from a supersaturated solution. Using this approach, we determined that ionic strengths > 0.2 and pH < 5 inhibited the precipitation of CaOx. The first observation is of interest if one considers that the osmolarity of urine varies in the range of 50-1,400 mmol/kg, while the effect of pH is not usually seen in vivo because of the influence of other phenomena, such as the precipitation of uric acid. The activity of sodium chloride, magnesium and citrate was displayed at concentrations not far from their normal urinary level. Among several mono-, di- and tricarboxylic acids, like acetic, ascorbic, citric, isocitric, formic, fumaric, gluconic, glutaric, alpha-ketoglutaric, maleic, malic, malonic, propionic, pyruvic, succinic, and tartaric acid, only isocitric acid was more potent than citric acid. Pyrophosphate was a potent inhibitor in vitro, but its urinary level may not be sufficient for a significant effect in vivo. Amino acids like Ala, Arg, Asp, Glu, Gly, and Ser which are known to bind calcium, showed little activity. Work is in progress to search for new compounds potentially useful in the treatment of nephrolithiasis.

Stabilization of rat serum proteins following oral administration of fish oil

The mechanism of action of fish oil (FO), currently used in different chronic inflammatory conditions such as rheumatoid arthritis (RA), is not completely understood, although it is thought that it could alter the metabolism of endogenous autacoids. In addition, we hypothesized that the known capability of fatty acids (FA) of stabilizing serum albumin and perhaps other proteins, may be of pharmacological relevance considering that it is shared by other anti-rheumatic agents (e.g. nonsteroidal antiinflammatory drugs). Thus, we studied the effect of oral administration of FO and corn oil (CO), a vegetable oil with a different composition, on the stability of rat serum proteins, evaluated by a classical in vitro method based on heat-induced protein denaturation. FO, and, to a lower extent, CO inhibited heat-induced denaturation of rat serum (RS): based on the inhibitory activity (EC50) of the major fatty acids against heat-induced denaturation of RS in vitro, it was possible to speculate that in vivo effects of palmitic acid (C16:0) and eicosapentaenoic acid (EPA, C20:5, n-3) may be more relevant than that of linolenic acid (C18:2). To better investigate this phenomenon, we extracted albumin from the serum of animals treated or not with FO with a one-step affinity chromatography technique, obtaining high purity rat serum albumin preparations (RSA-CTRL and RSA-FO), as judged by SDS-PAGE with Coomassie blue staining. When these RSA preparations were heated at 70 degrees C for 30 min, it was noted that RSA-FO was much more stable than RSA-CTRL, presumably due to higher number of long chain fatty acids (FA) such as palmitic acid or EPA. In conclusion, we provided evidences that oral administration of FO in the rat stabilizes serum albumin, due to an increase in the number of protein bound long chain fatty acids (e.g. palmitic acid and EPA). We speculate that the stabilization of serum albumin and perhaps other proteins could prevent changes of antigenicity due to protein denaturation and glycosylation, which may trigger pathological autoimmune responses, suggesting that this action may be involved in the mode of action of FO in RA and other chronic inflammatory diseases.

Inhibition of protein denaturation by fatty acids, bile salts and other natural substances: a new hypothesis for the mechanism of action of fish oil in rheumatic diseases

Natural hydrophobic substances like bile salts (cholate, deoxycholate, chenodeoxycholate, lithocholate and their conjugates with glycine and taurine), fatty acids (caprylic, capric, lauric, myristic, palmitic, stearic, oleic, linoleic, arachidonic, eicosapentaenoic and docosahexaenoic acid) were much more active (EC50 approximately 10(-4)-10(-5) M) than selected amino acids (EC50 > 10(-2) M) and inorganic salts (EC50 approximately 10(-1) M) in inhibiting heat-induced denaturation of human serum albumin in vitro. Fish oil, rich in n-3-polyunsaturated acids such as eicosapentaenoic acid and docosahexaenoic acid, administered p.o. (1 ml/kg) in the rat, protected ex vivo (after 2 hr) serum against heat-induced denaturation more than bendazac, a known antidenaturant drug. Thus, we speculated that the antidenaturant activity of fish oil may be partly (in addition to the known effect on endogenous eicosanoid composition) responsible for its beneficial effects in rheumatoid arthritis and other rheumatic conditions. In this connection, it is of note that the in vitro antidenaturant activity of fish oil fatty acids was higher than that of known antidenaturant drugs such as bendazac and bindarit and nonsteroidal anti-inflammatory drugs like phenylbutazone and indomethacin which could exert beneficial effects in chronic inflammatory conditions by stabilizing endogenous proteins.

Development of an HPLC assay to study the effect of endogenous and exogenous substances on heat-induced aggregation of human serum albumin

The mechanism of action of non-steroidal anti-inflammatory drugs which are used in high doses in chronic inflammatory conditions is not clearly understood. Their known protein-stabilizing properties could play a significant role. The inhibition of cyclooxygenase may not be essential for their anti-rheumatic activity, since compounds with strong anti-denaturant properties and devoid of anti-inflammatory activity were shown to be effective in an experimental model of rheumatoid arthritis. Hence, to develop new anti-rheumatic drugs it is essential that a simple in vitro method to evaluate the anti-denaturant activity of endogenous and exogenous compounds is available. We developed a new assay, using gel permeation high performance liquid chromatography, to study the effect of endogenous and exogenous compounds on heat-induced aggregation of human serum albumin in conditions in which protein precipitation does not occur. Non-steroidal anti-inflammatory drugs like diclofenac, ibuprofen and naproxen inhibited the aggregation of albumin at low concentrations (EC50 10(-4)-10(-5) mol/l) comparable to those active in a classical turbidimetric method, whereas the effect of weak stabilizers, like sodium cloride and formic, fumaric, maleic, malonic, and succinic acid (EC50 10(-1)-10(-2) mol/l in the Mizushima test) was not detectable. Furthermore, the HPLC assay allowed the examination of a number of coloured substances, including bilirubin, which appeared to be a strong stabilizer of its physiological carrier, albumin. These data could be clinically relevant, since the drugs examined are used at very high doses in rheumatoid arthritis and related conditions, with plasma levels that could cause significant stabilization of serum albumin and perhaps other proteins.

An increase in the carbohydrate moiety of alpha 2-macroglobulin is associated with systemic lupus erythematosus (SLE)

Using lectin blots in conjunction with peptide mapping, alpha 2-macroglobulin micropurified from systemic lupus erythematosus (SLE) patients was shown to become abnormally glycosylated suggesting the occurrence of complex glycosylation in this pathological condition. To confirm there is indeed a quantitative increase in specific monosaccharides in this protein; alpha 2-macroglobulin was micropurified from a battery of 37 serum samples which included 6 normal donors (3 male and 3 female), 23 SLE patients, 6 rheumatoid arthritis patients, 1 mixed connective tissue disease patient, and 1 Sjogren's syndrome patient; for carbohydrate analysis. It was noted that the concentration of total monosaccharides in alpha 2-macroglobulin micropurified from serum samples of SLE patients is significantly higher than normal donors with a mean +/- SD of 188 +/- 410 micrograms/mg protein (SLE, n = 23) versus 14.5 +/- 4 micrograms/mg protein (normal, n = 6) even though there was a high variation in the level of monosaccharides among the SLE patients. An increase in oligosaccharides in alpha 2-macroglobulin from SLE patients compared to normal subjects was confirmed by concanavalin A (Con A) blots using peptide fragments derived from the micropurified protein. Since the interaction of peptide fragments derived from alpha 2-macroglobulin with Con A requires the presence of mannose and/or glucose residues, we have also examined if there are any correlations between the levels of mannose and glucose in alpha 2-macroglobulin and SLE. The concentration of mannose (38 +/- 60 micrograms/mg protein) in alpha 2-macroglobulin derived from SLE patients was significantly higher than normal donors (mannose, 4.8 +/- 1 micrograms/mg protein) however, the concentration of glucose in alpha 2-macroglobulin derived from SLE patients when compared to normal donors was not statistically significant, 18 +/- 20 micrograms/mg protein in SLE versus 2 +/- 0.5 micrograms/mg protein in normal donors due to high variation between samples. Also, the concentration of galactose in alpha 2-macroglobulin from SLE patients was significantly higher than normal donors (45.7 +/- 173 micrograms/mg protein versus 0.13 +/- 0.03 microgram/mg protein). These results illustrate quantification of carbohydrate in selected glycoproteins such as alpha 2-macroglobulin may be a novel and alternative clinical marker for SLE.

Rat testicular testibumin is identical to sulfated glycoprotein-1 (SGP-1) whose mRNA expression in the testis is age- but not germ cell-dependent

Using sequential HPLC and capillary electrophoresis (CE), testibumin (CMB-1) has been purified to apparent homogeneity from Sertoli cell-enriched culture medium prepared from 20-day-old rat testes. N-Terminal amino acid sequence analysis of the purified testibumin revealed a partial sequence of NH2-XPVQDPKI. When this partial sequence was compared to existing protein database, it was shown that it is identical to a previously isolated Sertoli cell secretory protein, sulfated glycoprotein I (SGP-1). The fact that testibumin is equivalent to SGP-1 was further confirmed when its full-length cDNA was isolated and sequenced. Studies using quantitative PCR to examine the changes of steady-state mRNA level of testibumin (SGP-1) in the rat testes between 3 and 60 days of age indicated that its mRNA increased rapidly after birth, peaked at 10-20 days, and declined rapidly where the adult testibumin mRNA level was similar to the neonatal rat at 3 days of age. Depletion of germ cells by a single dose of lonidamine, an antispermatogenic drug, did not induce an increase in testibumin (SGP-1) mRNA level indicating its mRNA expression is not dependent on germ cells.