Primary hyperoxaluria: report of an Italian family with clear sex conditioned penetrance

We report the clinical and genetic study of a primary hyperoxaluria type I (PH1) family with two sisters homozygous for p.Gly170Arg who are still asymptomatic at age 29 and 35, and two brothers, also homozygous for the same mutation, who are affected since age 27 and 30. The clear sex difference observed in this family and in others reported in the literature fits well with the prevalence of males over females in the Italian registry. In the KO model of PH1, only male mice develop renal stones, suggesting that the sex difference may affect both oxalate production and stone formation. A likely mechanism is the sex-related expression of glycolate oxidase shown in experimental animals. The stable isotope method recently developed by Huidekoper and van Woerden for in vivo assessment of the endogenous oxalate production could help to clarify the issue in humans.

Protein analysis by capillary zone electrophoresis utilizing a trifunctional diamine for silica coating

A novel method is here reported for the analysis of mixture of proteins with pI ranging from pH 3-9.5 in an ample pH interval (pH 2.5-9.0) without adsorption onto the naked silica wall. It consists of treating the capillary surface at alkaline pH, typically 9.0, with small amounts (2-4 mM) of a quaternarized piperazine derivative: (N-methyl-N-omega-iodobutyl)-N'-methylpiperazine (Q-PzI). It appears that this compound is able to dock onto the wall via trifunctional links: a salt bridge via the quaternary nitrogen, a hydrogen bond via the tertiary nitrogen, and finally, a covalent link via the terminal iodine in the butyl chain and a neighboring ionized silanol. This last reaction seems to be completed in a few minutes of incubation of the capillary at room temperature. Because the compound is permanently affixed to the wall, its presence is not needed during protein/peptide separations. By properly dosing the level of Q-PzI in the preconditioning step, it is possible to strongly reduce the electroendoosmotic flow (EOF), zero it, or reverse it. Unlike dynamic coatings with oligoamines, which are most effective only at acidic pH values and are required as additives during separations, Q-PzI is effective in an ample pH interval (pH 2.5-9.0) and is not needed during the CZE analysis. A broad pI (pH 3-10) protein mix can be separated according to protein mobility in free phase, suggesting a strong modulating capacity of the functionalized wall. The same separation is not obtained in capillaries permanently coated with neutral, hydrophilic polymers (such as polyacrylamide), even if the quality of a single protein/peptide profile in Q-PzI-conditioned capillaries is equivalent to those obtained in capillaries permanently coated. Although there is strong indirect evidence of the ability of Q-PzI to alkylate the silica wall, to which it is then irreversibly bound, such an alkylation event does not occur with proteins on potentially reacting sites, such as the free -SH of Cys or the -OH group of Tyr, as demonstrated by incubating them overnight in a large molar excess at strongly alkaline pH values and analyzing such proteins by MALDI-TOF mass spectrometry.

Omega-iodoalkylammonium salts as permanent capillary silica wall modifiers. Comparative analysis of their structural parameters and substituent effects

Following previous work on the modification and inversion of electroendoosmotic flow (EOF) of naked silica by a cyclic diamine [1-(4-iodobutyl)-1,4-dimethylpiperazin-1-ium iodide] [J. Chromatogr. A 894 (2000) 53], the present report considerably expands previous data by describing additional compounds of the same series of omega-iodoalkylammonium salts. Four of them are able to instantaneously reverse the EOF, thus producing a cationic surface with a highly stable reverse EOF. All these compounds are believed to become covalently attached to the silica surface via alkylation occurring by nucleophilic substitution of ionized silanols on the silica wall by the omega-iodo functionality in the modifier. The unique advantage of such compounds, as compared to adsorbed polymers or oligoamine EOF quenchers, is that they are not needed any longer in the background electrolyte, after the initial conditioning step inducing the covalent bond. It is additionally demonstrated, by running a mixture of cinnamic acid compounds, that some of the omega-iodoalkylammonium salts can act as modulators of analyte migration, thus inducing separations of otherwise identical compounds, such as isomeric species. Such interactions can only occur when the analytes drift close to the silica wall, and must be rapidly reversible, since no peak tailing or broadening is experienced.

Investigating the reaction of a novel silica capillary coating compound with proteins/peptides by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Quaternized piperazine ((N-methyl-N-omega-iodobutyl-N'-methyl)piperazine; QPzl) is a novel compound described as an ideal coating material for the silica capillaries that are commonly used for capillary zone electrophoresis. In the course of such analysis, contact between such coatings and biomolecules may result in certain modifications of the latter. To gain specific information on such potential modifications, solutions at pH 10.0 containing both QPzl and standard proteins/peptides were incubated for various periods and examined by matrix-assisted laser desorption/ionisation mass spectrometry. The reduction of the S-S bridges, denaturation in 8 M urea, the isoelectric point of the protein and the duration of the incubation had a profound influence on the investigated reaction. Analysis in reflectron mode and post source decay identified Cys as the likely site of interaction. The implications of the present measurements for proteome analysis using capillary and gel electrophoresis are discussed.

Novel, trifunctional diamine for silica coating in capillary zone electrophoresis

A novel compound ¿quaternarized piperazine [(N-methyl,N-4-iodobutyl)-N'-methylpiperazine] (QPzI)¿ for the coating of a silica capillary able to reduce or invert the electroosmotic flow (EOF) in capillary zone electrophoresis is reported. Unlike standard oligoamines (like spermine and tetraethylene pentamine) which are very efficient in quenching macromolecule interaction with the silica wall, but only in acidic pH ranges, QPzI acts all along the pH scale, including alkaline pH ranges. It is believed that QPzI behaves like a trifunctional derivative: it forms ionic bonds with dissociated silanols via its quaternary nitrogen, hydrogen bonds via its tertiary nitrogen and, most importantly, a covalent bond via alkylation of ionized silanols through the terminal iodine atom in the butyl chain. Excellent separations are obtained with a variety of organic compounds, such as aromatic carboxylic acids, tryptophan metabolites and arylalkanoic acids. Such separations could not be obtained in naked capillaries in the presence of oligoamines and on some occasions not even with capillaries coated with a covalent layer of neutral polymers. In separations taking place in alkaline media, QPzI is not added to the background electrolyte, but is used simply in the capillary pre-conditioning step, a unique feature strongly supporting the hypothesis of its covalent binding to the silica surface. In difficult separations, such as in the case of o-/p-OMe-phenylacetic acids or nicotinic/picolinic acid, which would not normally occur under standard conditions, it is believed that QPzI acts as a discriminator, thus playing an active role in the separation process, rather than simply modulating the EOF.

Quantitation of protein binding to the capillary wall in acidic, isoelectric buffers and means for minimizing the phenomenon

Notwithstanding the use of acidic, amphoteric, isoelectric buffers with isoelectric points (pI) in the pH 2-3 range, adsorption of proteins to the naked silica wall can be non-negligible. Two such buffers have been tested: iminodiacetic acid (IDA; pI 2.23, apparent pH 3.2 in 7 M urea) and aspartic acid (pI 2.77, apparent pH 3.7 in 7 M urea). Three potential quenchers of such interactions have been tested: hydroxyethylcellulose (HEC; number average molecular mass, Mr 27,000), TEPA (tetraethylenepentamine) and a novel, quatemarized piperazine [N(methyl-N-omega-iodobutyl)-N'-methylpiperazine] (Q-Pip), either alone or in binary and ternary mixtures. Human alpha- and beta-globin chains have been used as test proteins in capillary electrophoresis separations. It has been found that mixtures of these compounds are the worst possible remedy. E.g., a ternary mixture comprising 0.5% HEC, 0.5 mM TEPA and 1 mM Q-Pip still leaves behind 4.5% adsorbed protein onto the silica surface in runs in IDA buffer and 7 M urea (pH 3.2). Conversely, 0.5 mM TEPA or 1 mM Q-Pip, when used alone, minimize adsorption down to only 1.8% and 0.5%, respectively. When the same globin chain separations are performed in Asp and 7 M urea (pH 3.7), the situation is much worse: 44% protein is adsorbed in a ternary mixture of 0.5% HEC, 1 mM Q-Pip and 0.5 mM TEPA. However, when used alone, 0.5 mM TEPA and 1 mM Q-Pip reduce globin adsorption to levels of 8% and 5%, respectively. TEPA and Q-Pip are found to be in all cases the best quenchers of protein interaction to naked fused-silica; in addition they exhibit the unique property of smoothing the base-line and giving reproducible runs. The best method for desorbing bound protein was found to be an electrophoretic step consisting in driving sodium dodecylsulphate micelles from the cathodic reservoir.

Surface modification based on Si-O and Si-C sublayers and a series of N-substituted acrylamide top-layers for capillary electrophoresis

Two approaches were used to prepare a series of surface-modified capillaries. In the first, a sublayer was formed by coupling gamma-methacryloxypropyltrimethoxysilane to the surface silanol groups forming an SI-O bond; a top layer was then formed by polymerizing acrylamide in the capillary, which reacted with the sublayer. In the second approach, a sublayer was formed by silanol chlorination, followed by Grignard coupling of vinylmagnesium bromide to form an Si-C bond at the surface; a top layer was formed by polymerizing either acrylamide (AA), dimethylacrylamide (DMA), N-acryloylaminoethoxyethanol (AAEE), or N-acryloylaminopropanol (AAP) onto the sublayer. The Si-Cpoly(AA) capillaries were more stable and produced an approximately 10-fold lower electroosmotic flow compared to the Si-O-poly(AA) capillaries. The Si-C sublayer was used to compare the performance of all four top layers. Electroosmotic flow decreased in the order: Si-O-poly(AA), Si-C-poly(AA), Si-Cpoly(AAEE), Si-C-poly(DMA), and Si-C-poly(AAP). Si-C-poly(AA) showed evidence of irreversible degradation at pH 9 already after 40-50 runs. Si-C-polyAAP-coated capillaries demonstrated superior efficiency and migration time reproducibility for a number of alkaline proteins and for fluorescently labeled ovalbumin. Excellent performance was maintained, in the case of poly(AAP), for a least 300 runs (of 30 min duration) at pH 9.0.

Novel acrylamido monomers with higher hydrophilicity and improved hydrolytic stability: I. Synthetic route and product characterization

The novel acrylamido monomer reported by our group (N-acryloylaminoethoxyethanol, AAEE; Chiari et al., Electrophoresis 1994, 15, 177-186), found to combine high hydrophilicity with extraordinary resistance to alkaline hydrolysis, has come under closer scrutiny due to unexpected and random autopolymerization while stored as a 1/1 v/v water solution at 4 degrees C (possibly due to a greater oxidability of the ether group). We have additionally found a unique degradation pathway of the monomer, called "1-6 H-transfer", by which the C1 (on the double bond site), by constantly ramming against the C6, next to the ether oxygen (O7, which in fact favors the transfer of the hydrogen atom by C1), produces radicals which more efficiently add to the monomer favoring autopolymerization and cross-linking. A number of novel monomers is proposed while maintaining the other unique characteristics of AAEE. One of them, N-acryloylaminopropanol, offers all the unique, special qualities of AAEE, without the noxious aspects of autopolymerization. Additionally, a synthetic route was optimized, yielding an essentially pure product in a single reaction step, with a yield > 99% and an equivalent purity (> 99%). The synthesis consists in reacting acryloyl chloride at -40 degrees C in presence of a twofold molar excess of aminopropanol and in ethanol (instead of methanol) as solvent. Other solvents, as well as the use of triethylamine for neutralizing the HCl produced, were found to give a variety of undesired byproducts.

Novel acrylamido monomers with higher hydrophilicity and improved hydrolytic stability: III. DNA separations by capillary electrophoresis in poly (N-acryloylaminopropanol)

Separation of DNA fragments in a novel polymer network, consisting of N-acryloylaminopropanol (AAP) is reported. The performance of this novel monomer, as a sieving liquid polymer in capillary zone electrophoresis, was evaluated. In 50 microns ID capillaries, an 8% solution of poly (AAP) can afford apex-resolution of the 123/124 bp adjacent pair of DNA fragments in marker V, typically unresolved in any poly (acrylamide) formulation. It is proposed that the distal-OH group in the AAP molecule can form transient H-bonds with the DNA double helix. Molecular modeling shows a meandering structure for poly (AAP), lacing the walls of half a cylinder, with kinks protruding at regular intervals, potentially able to fit into the major groove of DNA. Contrary to previously held beliefs, there seems to be a minimum length of the polymer for proper sieving of DNAs. For poly (acrylamides), a weight average molecular mass Mw 30 000 polymer offers no resolution, whereas a polymer of 250 000 to 400 000 Da exhibits optimum resolving power. For poly (AAP), the optimal length is in excess of 450 000 Da in Mw. Thus, it is shown that both the chemical composition of the monomer and the length of the polymer play a subtle, cooperative role in DNA separation.

Novel acrylamido monomers with higher hydrophilicity and improved hydrolytic stability: II. Properties of N-acryloylaminopropanol

The physico-chemical properties and the electrophoretic behavior of the novel set of monomers reported by (Simò-Alfonso et al., Electrophoresis 1996, 17, 723-731) have been evaluated. Of utmost importance was the combination of high hydrophilicity and extreme hydrolytic stability, most desired properties for, any electrophoretic matrix, especially for protein fractionation. One of these monomers (N-acryloylaminopropanol, AAP) was found indeed to be extremely hydrophilic (with a partition coefficient P of only 0.10, vs. P = 0.13 for N-acryloylaminoethoxyethanol and P = 0.20 for acrylamide) and to possess excellent stability to alkaline hydrolysis. Its hydrolysis constant (0.008 L mol-1 min-1), as a free monomer, in an alkaline milieu, was found to be about one order of magnitude lower than conventional acrylamide (0.05 L mol-1 min-1). In the polymer state, the resistance to hydrolysis of poly(AAP) was assessed as 500 times greater than a conventional poly(acrylamide) matrix.