Liquid chromatography/mass spectrometry methods for distinguishing N-oxides from hydroxylated compounds

This study describes the application of liquid chromatography/mass spectrometry (LC/MS) methods for distinguishing between aliphatic and aromatic hydroxylations and between hydroxylations and N-oxidations. Hydroxylations and N-oxidations are common biotransformation reactions of drugs. Electrospray (ESI) and atmospheric pressure chemical ionization (APCI) were used to generate ions from liquid chromatographic effluents. ESI-MS, ESI-MS/MS, APCI-MS, and APCI-MS/MS experiments were performed on several metabolites and derivatives of loratadine (a long-acting and nonsedating tricyclic antihistamine) using an ion trap mass spectrometer (LCQ) and a triple-quadrupole mass spectrometer (TSQ). The observations are as follows: (1) LC/ESI-MS produced predominantly [M + H]+ ions with minor fragmentation. (2) LC/ESI-MS/MS data, however, showed a predominant loss of water from metabolites with aliphatic hydroxylation while the loss of water was not favored when hydroxylation was phenolic. N-Oxides (aromatic and aliphatic) showed only a small amount of water loss in the MS/MS spectra. (3) Under LC/APCI-MS conditions, aliphatic hydroxylation could be readily distinguished from aromatic hydroxylation based on the extent of water loss. In addition, N-oxides produced distinct [M + H - O]+ ions. These [M + H - O]+ ions were not produced in the APCI-MS spectra of hydroxylated metabolites. (4) Similar to the ESI-MS/MS spectra, the APCI-MS/MS spectra from the (M + H)+ ions of N-oxides yielded a small amount of water loss but no [M + H - O]+ ions. These results indicate that LC/APCI-MS can be used to distinguish between hydroxylated metabolites and N-oxides.

An LC/MS/MS method for the quantitation of MTIC (5-(3-N-methyltriazen-1-yl)-imidazole-4-carboxamide), a bioconversion product of temozolomide, in rat and dog plasma.

A sensitive and selective HPLC/electrospray ionization tandem mass spectrometric (LC/ESI/MS/MS) method for the quantitative determination of MTIC (5-(3-N-methyltriazen-1-yl)-imidazole-4-carboxamide), a pharmacologically active hydrolysis product of temozolomide, was developed and validated over a linear range from 10 to 400 ng ml(-1) in dog plasma and from 10 to 500 ng ml(-1) in rat plasma. This HPLC method utilized small plasma volumes (70 microl), rapid sample processing, and isocratic elusion conditions to achieve sensitive and selective MS/MS detection. Samples were processed and analyzed one at a time every 4.5 min in order to compensate for the inherent instability of MTIC. Both MTIC and the internal standard DTIC [5-(3,3'-N,N'-dimethyltriazen-1-yl)-imidazole-4-carboxamide] were quantitated in the positive ion, selected reaction monitoring (SRM) mode. The lower limit of quantitation (LLOQ) was 10 ng ml(-1) in the plasma from both species. Inter-assay accuracy and precision of all calibration standards and quality control (QC) samples were within +/- 11 and 12%, respectively, with the exception of the LLOQ in rat plasma (17%). The validated method was used to determine the time dependent plasma concentration of MTIC in rats and dogs following a single oral dose of temozolomide. The standard curve and the quality control data indicate that the method performed acceptably throughout the sample analysis period.

In vitro metabolism of 10-(3-chlorophenyl)-6,8,9,10-tetrahydrobenzo[b][1,8]naphthyridin-5(7H)- one, a topical antipsoriatic agent. Use of precision-cut rat, dog, monkey and human liver slices, and chemical synthesis of metabolites.

The metabolism of SCH 40120, which is the clinically effective antipsoriatic drug 10-(3-chlorophenyl)-6,8,9,10-tetrahydrobenzol[b][1,8]naphthyrid in-5(7H)-one, was determined in vitro. Rat, dog, cynomolgus monkey, and human liver slices hydroxylated the aliphatic, cyclohexenyl ring of the drug and conjugated the resulting carbinol. The identified metabolites comprised the corresponding 6-, 7-, and 9-carbinols, the glucuronide of the 6-carbinol, and the 6-ketone derived from the parent drug. Although the three carbinols appeared in the liver isolates of all species studied, the relative amounts of these metabolites varied across species. With a high, non-physiological ratio of substrate to liver, the 6-carbinol and its glucuronide were the major metabolites in human and monkey, whereas the 6-ketone was a minor metabolite in dog. Containing a stereogenic axis and center, the 6-carbinol existed as diastereomeric atropisomers. Its structure was established by 13C and 1H NMR spectroscopy, mass spectrometry, and comparison to an authentic sample.

Altered collagen in colonic polyps.

By biochemical analysis the molar ratio between hydroxyproline and hydroxylysine as indicator of collagen type were analyzed in normal colons, colonic polyps and carcinomas. Low ratios (type IV) were found in the polyps.

Characterization of collagen hydroxylysyl glycosyltransferases as mainly intramembranous microsomal enzymes.

The localization of collagen hydroxylysine galactosyl- and galactosyl-hydroxylysine glucosyltransferases in purified chick embryo bone microsomes was studied by differential solubilization with nonionic detergents. Brij-35 (polyoxyethylene 25-lauryl ether) which selectively releases intracisternal proteins, and Triton X-100, whose specificity varies with its concentration, were used in the presence or absence of high ionic strength NaCl. These methods were used previously to characterize prolyl hydroxylase as intracisternal and lysyl hydroxylase as mainly intramembranous. The distribution of both glycosyltransferases within microsomes was similar to that of lysyl hydroxylase; approximately 70-80% of their activities are intramembranous with the remainder intracisternal. Collagen hydroxylysine glucosyltransferase differed from prolyl and lysyl hydroxylase and the galactosyltransferase in that its activity in vitro was apparently inhibited by membrane vesicles, even in the presence of detergents at concentrations which permeabilize the membrane. Accurate measurement of its activity could be achieved only by its separation from vesicles after detergent treatment. The common location of the major portion of lysyl hydroxylase and the glycosyltransferase activities suggests that they may act as a multienzyme complex to preferentially modify certain lysyl residues in nascent procollagen chains as they traverse the membrane of the endoplasmic reticulum. Since these enzymes do not act on helical collagen, their physical separation from prolyl hydroxylase may ensure that modifications of lysine residues occur prior to formation of hydroxyproline, which stabilizes the helical form.

Characterization of an amyloid fibril protein from localized amyloidosis of the skin as lambda immunoglobulin light chains of variable subgroup I (A lambda I).

Amyloid fibrils obtained from a case (Hud) of localized, tumorous amyloidosis of the skin were investigated by immunological and biochemical methods including amino acid sequence studies. Evidence was obtained that a lambda immunoglobulin light chain protein, A lambda I, and differently sized N terminal fragments (mol. wt 14,000 and 10,000) of the same protein comprised a major component of the fibrils. The chemical nature of this protein suggested that this case of cutaneous amyloidosis belonged to the idiopathic form of amyloidosis, probably as a special type of systemic, idiopathic amyloid disease.

Automated triple assay for proline, hydroxyproline and hydroxylysine on one single sample.

1. A new, quick, sensitive and specific assay for the quantitative determination of proline is presented together with its automatization. The use of glacial acetic acid-formaldehyde as the solvent for ninhydrin lends a series of advantages to the reaction. 2. A serial automated procedure for the simultaneous detection of proline, hydroxyproline and hydroxylysine in one single sample is pesented. The advantage of the triple assay lies in the use of one single sample instead of three previously aliquoted fractions in three individual automated assays. The triple assay is as specific, reproducible and sensitive as the individual assays. 3. A quick, manual assay for hydroxylysine is presented. This method represents a further simplifiction of previous ones by the same author and adds the advantage of rapidity to their sensitivity and specificity.

Three automated quantitative assays for serum proteins.

Three quantitative assays for detection of proteins are reported. One is an adaptation to the Auto-Analyzer of the widely used method of Lowry et al. In another procedure, the product of the reaction of proteins with a modified biuret reacts with the phosphomolybdic--phosphotungstic reagent of Folin and Ciocalteu. The third method, performed on hydrolyzed sample, is based on the measurement of proline (Pro) and the conversion of the Pro content into protein. The universal presence of proline in serum proteins suggested this assay. The values for total serum proteins as assayed by the three procedures are similar. The second and the third assay for proteins, described in this paper, can also be performed manually. Studies on interfering substances and their elimination as well as on the sensitivity of the assays are reported.

Variation of urinary acid glycosaminoglycan and collagen metabolite excretion with disease activity in generalized scleroderma.

Follow-up of patients with generalized scleroderma improving during treatment with collagen biosynthesis inhibitors showed a decrease towards normalization of the elevated urinary values for acid glycosaminoglycans and collagen catabolites. The determinations supply objective evidence of the disease activity as well as of the efficacy of treatment. In the control group, relatively high urinary values for the two macromolecules were found in the second decade of life in comparison with older age groups.

Biochemical analysis of dermis and urine in generalized scleroderma.

The urinary excretion of uronic acid and the hydroxyproline of a urinary fraction of high molecular weight collagen peptides (% of total Hyp) indicate disease activity in generalized scleroderma. A significant decrease in the content of Hyp and Hyl in the skin of sclerodermal patients is not related to activity, but rather to the duration of the disease. Parallel analyses of skin and urine of the same patients are reported.

Studies on the effect of (+)catechin on connective tissue in the guinea pig and in organ culture.

Decreased biosynthesis of (14C) hydroxyproline in skin collagen was observed after injection of the flavonoid (+)catechin into guinea pigs. No alteration in already synthesized collagens was noted, as measured by the content of hydroxyproline and hydroxylysine. No alteration in the content of skin acid glycosaminoglycans was observed. The variable binding of (+)catechin to different tissues was demonstrated. No special sensitivity to the drug of any collagen type was found.

Effect of hydralazine and dihydralazine on connective tissue and binding to serum protein.

Hydralazine and dihydralazine, chelators of Fe2+, Fe3+ and Mn2+ ions, inhibited collagen biosynthesis in organ culture of chicken embryo tibiae. Both substances inhibited the in vitro hydroxylation of [14C]Pro-labelled protocollagen by protocollagen proline hydroxylase. A decreased incorporation of [14C]-D-glucosamine into glyco- and/or muco-proteins was found under the effect of the two drugs. Dihydralazine, a cationic compound, was bound to DNA and acid mucopolysaccharides (glycosaminoglycans), forming an insoluble complex. Both substances were bound to serum alpha 2-globulin. Subcutaneous injections of dihydralazine in rats produced a local as well as a general toxic effect.

Lack of dermal changes in uninvolved skin after photochemotherapy of psoriasis: biochemical studies.

Low Hyp and Hyl values were found in psoriatic lesions. Treatment with PUVA achieved a return to normal values. No effect of PUVA on the collagen of uninvolved skin of psoriatic patients could be demonstrated after 4 months. There were no age-related differences in the content of Hyp and Hyl between samples of uninvolved skin of psoriatics.

Urinary proline to hydroxyproline ratio varies with age.

Urinary excretion of proline and hydroxyproline was studied in five groups of subjects, viz. controls, pituitary dwarfs, familial dwarfs, patients with fibrodysplasia ossificans progressive and patients with generalized scleroderma. The ratio Pro/Hyp in the urinary fraction precipitated with 5 parts of acetone (1 + 5 fraction) was close to one in children and youngsters in all the groups, while in adults it was higher than two. Total Pro/Hyp does not give an accurate index of age.

Fibrodysplasia ossificans progressiva. Biochemical changes in blood serum, urine, skin, bone, and ectopic ossification.

Increased urinary output of total hydroxyproline, hydroxylysine and uronic acid was found in two patients suffering from fibrodysplasia ossificans progressiva. Before treatment of one of the patients, the high molecular weight peptide fraction deriving from newly synthesised collagen was particularly increased. Treatment with disodium etidronate (diphosphonate) reduced the values. The urinary values of sodium, potassium and calcium were also depressed during treatment, and, in both patients, serum phosphate was high, while serum calcium was normal. The hydroxyproline and hydroxylysine contents in skin and bone of FOP patients did not differ from controls, while ectopic ossifications showed a considerable increase in hydroxylysine in relation to normal bone.

Abnormal skin collagen in scleroderma.

A significant decrease in the content of hydroxyproline and hydroxylysine was found in the skin of patients with generalized scleroderma (acrosclerosis), the lowering of Hyp being more marked than that of Hyl. The production of an abnormal collagen or a change from one collagen type to another is suggested to take place.

Hydroxyproline to hydroxylysine molar ratio indicates collagen type.

By using the molar ratio Hyp to Hyl, types I and II of collagen can be differentiated in 0.5 to 10 mg of dried, defatted tissue. Analyses on human skin, tendon, bone, aorta, cartilage, as well as nucleus pulposus, and annulus fibrosus of intervertebral discs are reported. Analyses of collagen of mesenchymal tissues of other vertebrates are also reported. From amino acid analysis of purified collagen samples published in the literature, the molar ratio Hyp/Hyl was calculated. Type I and type III collagen were differentiated from type II, and the latter was differentiated from type IV collagen. The molar ratios obtained with our analyses followed closely the values from previously reported amino acid analyses on purified collagen.

Subhydroxylated collagen in scleroderma.

In sclerodermal skin, the values for proline (Pro), hydroxyproline (Hyp) and hydroxylsine (Hyl) are lower than in normal skin. The molar ratio Hyp to Hyl is lowered. The molar ratio Pro to Hyp was found to be elevated, while that of Pro to Hyl was like that of normal skin. It was concluded that in slceroderma the hydroxylation of Pro to Hyp is incomplete, resulting in an abnormal collagen.

Effects of some connective-tissue active drugs on protocollagen proline hydroxylase activity.

The effect on protocollagen proline hydroxylase of drugs reported to be capable of inducing the lupus erythematosus syndrome and in some way acting on connective tissue and inflammation was studied in an in vitro system for the hydroxylation of 14C-Pro-labelled protocollagen. Some derivatives were also studied. It was found that benzoic acid and phenothiazine derivatives, hydroxyphenols, (+)catechin, beta-amino propionitrile, certain B vitamins, dihydrazinophthalazine, cysteine and dimethylcysteine were inhibitors of PPH. The chelation of Fe2+ions by the compounds mentioned is suggested to be essential.

Effect of (+)catechin on connective tissue.

The effect of (+)catechin on connective tissue was studied in organ cultures of chick embryo tibiae and after in vivo injection in rats and mice. Collagen biosynthesis and hydroxylation of 14C-Pro-labelled protocollagen in vitro by protocollagen proline hydroxylase (PPH) were inhibited. In vivo, a slight decrease in the biosynthesis of collagen and in the PPH activity in skin of rats and mice was noticed as an effect of (+)catechin. No effect of the drug was observed on the incorporation of 14C-D-glucosamine by chick embryo tibiae. Increased urinary excretion of acid mucopolysaccharide metabolites by the mice injected with (+)catechin was observed.