Purification and biochemical characterization of xanthopterin from patients with chronic renal failure. II. Biochemical elucidation and structural analysis.

We have identified the primary endogenous fluorescent substance, which has characteristic excitation/emission maxima at 380/440 nm and 400/460 nm, found in the sera of patients with chronic renal failure (Clin Chem 32: 1276, 1988). Preliminary studies, using thin layer chromatography (with cellulose) in conjunction with pteridine standards, indicated that the compound is an unconjugated pteridine. Characterization by gas chromatography-mass spectrometry (electron impact), direct probe-mass spectrometry (electron impact/chemical ionization), and Fourier Transform Infrared analysis showed this compound to be xanthopterin (2-amino 4,6 pteridinedione), an unconjugated pteridine known to be present in man in trace quantities. An authentic sample of this compound had a retention time with high-performance liquid chromatography (HPLC) identical to that of the purified fluorophore. The physiological role of xanthopterin in the pathogenesis of uremia has yet to be elucidated.

Purification and biochemical characterization of xanthopterin from patients with chronic renal failure. I. Isolation, purification and preliminary characterization.

We describe the purification and initial characterization of a hitherto unrecognized fluorescence (excitation/emission maxima at 380/440 nm and 400/460 nm) reported from this laboratory in patients with chronic renal failure (Clin Chem 31: 1988, 1985). Purification was achieved using Sephadex G-10 gel chromatography combined with reverse phase and ion exchange high-performance liquid chromatography (HPLC). Purity of the "blue-green" fluorescent compound was determined to be greater than 99% by HPLC, and two-dimensional thin layer chromatography using an acidic and basic solvent system. The excitation/emission maxima were shown to be 390 nm/456 nm, and ultraviolet scans, at pH 1.0, 7.0, and 13.0, gave absorbance optima at 261 nm/356 nm, 278 nm/390 nm, and 255 nm/394 nm, respectively. The isoelectric point of 4.05 in conjunction with the fluorescent and ultraviolet spectra suggests that the fluorophore belongs to the class of compounds known as pteridines.

Bromate intoxication: hairdressers' anuria.

A 17-year-old hairdresser developed sodium bromate poisoning after drinking a cup of hair neutralizer in a suicide attempt. She presented 1 week later with anuria, required hemodialysis for 5 days, and subsequently recovered. Sensorineural hearing loss, often a characteristic finding, was absent. Early diagnosis of bromate intoxication requires an appreciation that it commonly occurs in hairdressers, may be accompanied by deafness, and may present with insidious anuria.

Focal segmental glomerulosclerosis. A common entity in nephrotic black adults.

We studied 100 renal biopsy specimens from adults with the primary nephrotic syndrome in an inner city hospital serving mostly black patients and found that 47 had focal segmental glomerulosclerosis. Most of the men presented in the third decade of life, a peak distribution not seen in women. Half of the patients were hypertensive at presentation. Two thirds of the patients had not used intravenous drugs. The addicts were younger than nonaddicts (mean +/- SD age, 27 +/- 4 years vs 35 +/- 13 years), had greater proteinuria (10 +/- 5 g/d vs 6.3 +/- 5 g/d), and exhibited more glomerulosclerosis and tubulointerstitial fibrosis on biopsy. Of the 18 patients (8 addicts) remaining under our care, 4 addicts and 4 nonaddicts became uremic within 3 years. We conclude that even in the absence of drug addiction, focal segmental glomerulosclerosis is a common cause of primary glomerular disease in black adults, in whom it may represent a nonspecific glomerular reaction to injury. The prognosis in the nonaddict may not be different from that in the addict, but more patients need to be studied.

Amino acid composition of uremic middle and low molecular weight retention products.

In order to characterize the spectrum of small peptides retained in chronic renal failure, we carried out high pressure liquid chromatography (HPLC) of serum ultrafiltrates from patients with chronic renal failure (CRF), acute renal failure (ARF), and normal subjects. HPLC patterns in CRF resolved into more than twenty peaks; those in ARF contained fewer peaks and resembled that of normals. We carried out amino acid analysis of HPLC fractions after hydrolysis with 6N HC1 of four patients with CRF, one patient with ARF, and one normal subject. Following hydrolysis each HPLC fraction yielded several amino acids. Glycine, leucine, serine, phosphoserine, glutamic acid, and phenylalanine were found in greatest frequency in the four CRF patients.

Biochemical elucidation and HPLC fractionation of fluorescent peptides in patients with chronic renal failure.

We evaluated the biochemical characteristics of endogenous fluorescent substances, Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm, present in sera of patients with chronic renal failure (Clin. Chem. 31:1988, 1985). Sera from 23 patients with chronic renal failure (CRF) and from 10 normal subjects were filtered through ultrafiltration membranes (cutoff limit of 500 Da). Fluorescence intensity of the aforementioned substances was significantly elevated as compared to normals (p less than 0.001). Fluorescence characteristics of these substances remained unaltered after ultrafiltration and treatment with beta-glucuronidase. Extraction of these fluorescent compounds with organic solvents (dichloromethane, ethyl acetate, chloroform:methanol) could not be achieved after ultrafiltrates were subjected to 6N hydrochloric acid (HC1) hydrolysis. In addition, treatment with 6N HC1 enhanced fluorescence intensity without altering fluorescence excitation/emission maxima. Removal of fluorescence could be accomplished in toto by adsorption onto activated charcoal with subsequent recovery from charcoal by treatment with sodium hydroxide, pH 12 (Ex 380 nm: 51.1%, Ex 400 nm: 91.8%). Analysis of alkali-treated specimens by high performance liquid chromatography demonstrated that peptides associated with these fluorescent substances were denatured, although fluorescence at these previously described excitation/emission maxima persisted. Our studies indicate that the unique fluorescence observed in the sera of patients with CRF is not an intrinsic characteristic of a specific peptide or its amino acids, but rather an inherent property of fluorescent molecules which may bind to these peptides.

Transient and sustained recovery from renal shutdown in accelerated hypertension.

Ten black patients (eight men) with renal shutdown from accelerated hypertension were treated with hemodialysis. Renal function improved, and dialysis was discontinued after 6 +/- 2 months. Five patients (Group I) have maintained good renal function at 25 +/- 3 months of follow-up, whereas the other five (Group II) had deterioration again to advanced azotemia over 16 +/- 6 months. On admission, Group I patients had lower levels of serum creatinine (9 +/- 1.2 mg/dl [mean +/- SE] versus 13.6 +/- 1.7 mg/dl, p = 0.04) and urinary protein (0.98 +/- 0.78 g per day versus 2.17 +/- 1.5 g per day) and were more oliguric (451 +/- 145 ml per day versus 1,122 +/- 494 ml per day) than Group II. In Group I, renal shutdown was faster (8 +/- 4 days versus 38 +/- 28 days), recovery earlier (4 +/- 1.5 months versus 8 +/- 4 months) and greater (lowest serum creatinine level 1.9 +/- 0.3 mg/dl versus 5.7 +/- 1.7 mg/dl, p less than 0.05), and compliance better than in Group II. Two patients in the former group but none in the latter had peripheral schistocytes. It is concluded that the sustained recovery in Group I resulted from the resolution not only of the acute vascular lesions but also of tubular necrosis and microangiopathy, and the postrecovery deterioration in Group II is attributed to the more severe renal damage initially, the progression of the chronic vascular lesions in uncompliant patients, and possibly hyperfiltration damage in the remaining nephrons.

Fluorescent substances in uremic and normal serum.

We measured the fluorescence, at various excitation (Ex) and emission (Em) wavelengths, of serum ultrafiltrates and fractions of serum resolved by chromatography on Sephadex G15, studying both normal subjects and patients in chronic renal failure requiring hemodialysis. We found hitherto undescribed fluorescence at Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm, the intensity being greatly increased in patients with chronic renal failure in comparison with normal subjects (p less than 0.005). This fluorescence persisted unaltered when serum was filtered through membranes having cutoffs ranging from 10 000 to 500 Da. Each serum fraction resolved by gel chromatography demonstrated a characteristic fluorescence, which was generally much more intense in uremics. The most intense fluorescence (Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm) was emitted in the higher-Mr fractions.

Metabolic utilization and renal handling of D-lactate in men.

This study was carried out to investigate the renal handling of d- and l-lactate and the extent of their metabolism in men. Ten healthy male subjects were given an intravenous (IV) infusion of a racemic mixture of d- and l-lactate. At an infusion rate of 1.0 to 1.3 meq/kg body weight of each isomer, d-lactate achieved a concentration in plasma of 1.7 to 3.0 meq/L, and l-lactate 2.8 to 4.2 meq/L. At these levels, fractional excretion of d-lactate ranged from 40% to 65%, while fractional excretion of l-lactate was always less than 5%. At a higher infusion rate, 1.8 to 2.0 meq/kg/h, plasma concentrations of d- and l-lactate reached 4.5 to 6.0 meq/L, and 4.0 to 6.7 meq/L, respectively. Fractional excretion of d-lactate then ranged from 61% to 100%, while that of l-lactate ranged from 9% to 30%. At plasma concentrations of d-lactate less than 3.0 meq/L, reabsorption of l-lactate was nearly complete, but when plasma d-lactate exceeded 3.0 meq/L, reabsorption of l-lactate was considerably impaired. Similarly, for a given concentration of plasma d-lactate, its reabsorption was more efficient when the plasma l-lactate concentration and fractional excretion of l-lactate were low than when they were high. At an infusion rate of d-lactate of 1.0 to 1.3 meq/L, about 90% of the infused lactate was metabolized, and at a higher infusion rate, still more than 75% of the infused lactate was metabolized.(ABSTRACT TRUNCATED AT 250 WORDS)

Minoxidil in a once-a-day step-3 antihypertensive program.

Convenience of medicine-taking and lack of side effects are two major factors that favor compliance. Using a simple and convenient once-a-day regimen of minoxidil, nadolol, and chlorthalidone, we treated successfully 30 patients with moderate to severe hypertension. All patients were previously taking at least three medications, usually three to four times a day. Treatment was started with nadolol (160 mg) and chlorthalidone (50 mg) once daily. If diastolic blood pressure remained above 90 mmHg, minoxidil was added at a starting dose of 2.5 mg/day and increased weekly until blood pressure was controlled or the maximum dose of 100 mg/day was reached. The average blood pressure decreased from 170.9/107.0 mmHg (sitting) and 174.1/110.8 mmHg (standing), before the addition of minoxidil, to 138.8/86.7 mmHg (sitting) and 140.0/89.5 mmHg (standing), at the third month of minoxidil therapy. At the sixth month of minoxidil therapy, the figures were 140.9/86.3 and 141.9/89.8 mmHg. With this single-dose program, smooth blood pressure control throughout 24 hours was documented by 24-hour ambulatory blood-pressure monitoring. Hypertrichosis was common but was bothersome only to women patients. Pericardial effusions occurred in five patients, but they were all small and asymptomatic. Subjective side effects of the regimen were usually so mild that all patients who completed the study decided to remain on the same regimen.

Inhibition of platelet function by uremic middle molecules.

To further define the platelet abnormality responsible for uremic bleeding, we studied platelet aggregation with adenosine diphosphate, ristocetin, and collagen in serum fractions obtained by Sephadex G-15 chromatography. We found that uremic patients had considerable inhibition in several peaks of middle molecular range, but the findings were inconsistent and not clearly related to the degree of uremia.