Bentiromide test for assessing pancreatic dysfunction using analysis of para-aminobenzoic acid in plasma and urine. Studies in cystic fibrosis and Shwachman's syndrome

Repurposing Known Drugs as Covalent and Non-covalent Inhibitors of the SARS-CoV-2 Papain-Like Protease

In the absence of an approved vaccine, developing effective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antivirals is essential to tackle the current pandemic health crisis due to the coronavirus disease 2019 (COVID-19) spread. As any traditional drug discovery program is a time-consuming and costly process requiring more than one decade to be completed, in silico repurposing of existing drugs is the preferred way for rapidly selecting promising clinical candidates. We present a virtual screening campaign to identify covalent and non-covalent inhibitors of the SARS-CoV-2 papain-like protease (PLpro) showing potential multitarget activities (i.e., a desirable polypharmacology profile) for the COVID-19 treatment. A dataset including 688 phase III and 1,702 phase IV clinical trial drugs was downloaded from ChEMBL (version 27.1) and docked to the recently released crystal structure of PLpro in complex with a covalently bound peptide inhibitor. The obtained results were analyzed by combining protein-ligand interaction fingerprint similarities, conventional docking scores, and MM-GBSA-binding free energies and allowed the identification of some interesting candidates for further in vitro testing. To the best of our knowledge, this study represents the first attempt to repurpose drugs for a covalent inhibition of PLpro and could pave the way for new therapeutic strategies against COVID-19.

Glycine conjugation of para-aminobenzoic acid (PABA): a pilot study of a novel prognostic test in acute liver failure in children

BACKGROUND

Fulminant hepatic failure (FHF) is associated with high mortality; few patients survive without liver transplantation. It is important to have a sensitive, specific early predictor of outcome to distinguish potential survivors (S) from nonsurvivors (NS).

OBJECTIVE

Because we had previously shown that glycine conjugation of para-aminobenzoic acid (PABA) quantitatively reflects liver function in children with chronic liver disease, in this pilot study we wanted to determine whether the measurement of the glycine conjugates of PABA could distinguish S from NS in FHF in comparison with standard prognostic indices.

METHODS

Twenty-four patients were studied: acute severe hepatitis (n = 7), subfulminant hepatic failure (n = 7), and FHF (n = 10). Assessment of King's College criteria, measurement of factor V and VII levels, PABA testing, and transjugular liver biopsies were performed in almost all patients within 48 hours of admission. Serum PABA and its glycine conjugates (para-aminohippurate (PAHA) and para-acetamidohippurate (PAAHA)) were measured thirty minutes after oral administration by high-pressure liquid chromatography. Poor prognostic categories as previously established in the literature were defined as factor V < 0.20U/ml, factor VII < 0.08 U/ml, % necrosis >70%, hippurate ratio = 0%, and PAHA = 0M.

RESULTS

The measurement of PAHA was the best predictor of a poor outcome in patients with acute liver failure with a sensitivity of 92%, and negative predictive value (NPV) of 92% compared with a sensitivity of 54% and a NPV of 63% with King's College criteria.

CONCLUSION

Measurement of serum PAHA is the best early prognostic marker of death in children who suffer from FHF.

Control of malabsorption in cystic fibrosis

Intestinal malabsorption is severe and of early onset in virtually all people who have cystic fibrosis. The main cause is deficiency of pancreatic enzymes, but bicarbonate deficiency, abnormalities of bile salts, mucosal transport and motility, and anatomical structural changes are other contributory factors. Appropriate pancreatic replacement therapy will achieve normal or near normal absorption in many patients. It is important to identify both malabsorption and evidence of a pancreatic lesion in all patients who are to receive pancreatic enzymes. All who have evidence of fat malabsorption are deemed pancreatic insufficient and candidates for enzyme replacement therapy. Effective treatment should allow a normal diet to be taken, control symptoms, correct malabsorption and achieve a normal nutritional state and growth. The occurrence of fibrosing colonopathy in some patients receiving very high doses of those enzymes that have the copolymer Eudragit L30 D55 in their covering has resulted in guidelines in the UK to avoid dosages greater than the equivalent of 10,000 IU lipase/kg/day for all patients and also to avoid preparations containing this copolymer in children and adolescents. For patients not responding to 10,000 IU lipase/kg/day, review of adherence to treatment, change of enzyme preparation, variation of the time of administration and reduction in gastric acid may improve absorption. The importance of excluding other gastrointestinal disorders as a cause of the patient's symptoms and the need for early investigations, rather than merely increasing the dosage of enzymes, is stressed. With modern enzymes, adequate control of gastrointestinal symptoms and absorption can be achieved at dosages of 10,000 IU lipase/kg/day or only slightly more, and a normal nutritional state and growth rate maintained in most patients with cystic fibrosis.

Glycine conjugation of para-aminobenzoic acid (PABA): a quantitative test of liver function

OBJECTIVE

To evaluate glycine conjugation of para-aminobenzoic acid (PABA) to the hippurated metabolites, para-aminohippuric acid (PAHA), and para-acetamidohippuric acid (PAAHA) as a quantitative liver function test in patients with liver disease.

DESIGN AND METHODS

Serum concentrations of PABA and metabolites were measured by high pressure liquid chromatography in 24 controls and 50 patients with hepatobiliary disease.

RESULTS

Hippurate formation was significantly decreased in all patient groups with chronic liver disease versus controls. The hippurate ratio (% hippurated metabolites formed) correlated with severity of disease, serum albumin, and factor VII concentrations. PAHA concentration was a better prognostic indicator than factor VII concentrations in patients with acute liver disease; concentrations of zero correctly predicted a poor outcome in patients with fulminant liver failure.

CONCLUSIONS

Glycine conjugation of PABA may be useful as a quantitative liver function test in patients with hepatobiliary disease and as a prognostic index in patients with fulminant liver failure.

Biochemical tests in the diagnosis of chronic pancreatitis and in the evaluation of pancreatic insufficiency

Chronic pancreatitis (adults) and cystic fibrosis (children) are the most common diseases leading to exocrine pancreatic insufficiency that, when reduced to < 5% of normal function, is characterised by steatorrhoea. The pathogenesis of the former condition is outlined, and recent concepts are emphasized. Biochemical tests to detect pancreatic insufficiency and to identify pancreatic disease as the cause of steatorrhoea include: serum enzyme tests (lipase, amylase, trypsin); stool chymotrypsin; isotopic tests based upon the assimilation of [14C] lipids and starch or excretion of the isotope as breath CO2, as well as the dual-labelled Schilling test; oral function tests utilising substrates hydrolysed by pancreatic enzymes such as benzoyl tyrosyl-p-aminobenzoic acid and fluorescein dilaurate; and duodenal intubation studies following meal-induced or hormonal stimulation of the pancreas. The rationale for these tests and the cumulative clinical experience of their utility are reviewed. A recommended diagnostic strategy is briefly presented. The role of various biochemical procedures to evaluate the efficacy of pancreatic enzyme replacement therapy is also described.

Improvement of fecal fat excretion after addition of omeprazole to pancrease in cystic fibrosis is related to residual exocrine function of the pancreas

Pancreatic function tests were performed in 11 adult cystic fibrosis (CF) patients with a fecal fat excretion of more than 10% during treatment with pancrease 2 capsules three times a day. These tests included urinary p-aminobenzoic acid (PABA) excretion, fasting serum trypsin and pancreatic polypeptide (PP), and glucose and insulin in fasting and postprandial serum. Subsequently, the patients entered a double-blind placebo-controlled crossover study to assess the effect of gastric acid inhibition by 20 mg omeprazole on fecal fat excretion. Adjunct therapy with omeprazole resulted in a reduction of fecal fat excretion in patients with residual pancreatic function. This improvement showed significant positive correlations with urinary PABA excretion and the increase in serum PP after the meal (P < 0.02 and P < 0.05), but not with the other parameters studied. Therefore, the addition of omeprazole to pancrease is most successful in CF patients with residual pancreatic function, determined by urinary PABA excretion or incremental PP.

Bentiromide test using liquid-chromatographic measurement of p-aminobenzoic acid and its metabolites for diagnosing pancreatic insufficiency in childhood

We assessed the diagnostic capability of the bentiromide test using a high-pressure liquid-chromatography method to analyze p-aminobenzoic acid and its metabolites in plasma as an indirect measure of exocrine pancreatic function. Mean total amine concentration in pancreatic-insufficient subjects was significantly lower than in control subjects. There were 3 of 15 false-negative results and no false-positive results. We conclude that this chromatographic method is an effective means of analyzing p-aminobenzoic acid and its metabolites after ingestion of bentiromide.

The bentiromide test using plasma p-aminobenzoic acid for diagnosing pancreatic insufficiency in young children. The effect of two different doses and a liquid meal

The bentiromide test was evaluated using plasma p-aminobenzoic acid as an indirect test of pancreatic insufficiency in young children between 2 months and 4 years of age. To determine the optimal test method, the following were examined: (a) the best dose of bentiromide (15 mg/kg or 30 mg/kg); (b) the optimal sampling time for plasma p-aminobenzoic acid; and (c) the effect of coadministration of a liquid meal. Sixty-nine children 91.6 +/- 1.0 years) were studied, including 34 controls with normal fat absorption and 35 patients (34 with cystic fibrosis) with fat maldigestion due to pancreatic insufficiency. Control and pancreatic insufficient subjects were studied in three age-matched groups: (a) low-dose bentiromide (15 mg/kg) with clear fluids; (b) high-dose bentiromide (30 mg/kg) with clear fluids; and (c) high-dose bentiromide with a liquid meal. Plasma p-aminobenzoic acid was determined at 0, 30, 60, and 90 minutes then hourly for 6 hours. The dose effect of bentiromide with clear liquids was evaluated. High-dose bentiromide best discriminated control and pancreatic insufficient subjects, due to a higher peak plasma p-aminobenzoic acid level in controls, but poor sensitivity and specificity remained. High-dose bentiromide with a liquid meal produced a delayed increase in plasma p-aminobenzoic acid in the control subjects probably caused by retarded gastric emptying. However, in the pancreatic insufficient subjects, use of a liquid meal resulted in significantly lower plasma p-aminobenzoic acid levels at all time points; plasma p-aminobenzoic acid at 2 and 3 hours completely discriminated between control and pancreatic insufficient patients. Evaluation of the data by area under the time-concentration curve failed to improve test results. In conclusion, the bentiromide test is a simple, clinically useful means of detecting pancreatic insufficiency in young children, but a higher dose administered with a liquid meal is recommended.

Basic studies on ursodeoxycholyl-para-aminobenzoic acid for evaluation of intestinal microflora

A newly synthesized conjugate of ursodeoxycholic acid with para-aminobenzoic acid (PABA) was investigated to determine its suitability for evaluation of enteric bacteria. This compound, PABA-UDCA, was deconjugated by cholylglycine hydrolase to release free PABA, whereas it was completely resistant to deconjugation by pancreatic and intestinal mucosal enzymes. In bacteriologic experiments almost all the microorganisms that split glycocholic acid deconjugated PABA-UDCA. In rat experiments urinary excretions of PABA were measured during 6 h after oral administration of 10 mg PABA-UDCA (PABA-UDCA administration test). Ten control rats excreted 338.5 +/- 13.8 micrograms (mean +/- SE) of PABA; 10 rats with intestinal stagnant loop excreted more (673.6 +/- 70.2 micrograms; P less than 0.01); whereas 10 rats in each of 7 groups pretreated with oral administration of various antibiotics excreted less (P less than 0.001; polymixin B + tinidazole, 14.0 +/- 2.5 micrograms; polymixin B, 224.9 +/- 23.5 micrograms; tinidazole, 42.7 +/- 8.6 micrograms; kanamycin, 50.3 +/- 5.8 micrograms; clindamycin, 57.4 +/- 7.4 micrograms; vancomycin, 70.4 +/- 8.5 micrograms; and paromomycin, 160.4 +/- 16.4 micrograms). This result was reflected by the bacterial mean count of feces. In the PABA-UDCA administration test, after 2 months of feeding with different diets, rats with high-fiber diet (n = 10) excreted less PABA in urine (70.9 +/- 15.9 micrograms; P less than 0.001) than rats on a control diet (n = 10) and a high-protein-high-fat diet (n = 10) (288.9 +/- 34.5 micrograms and 386.7 +/- 61.2 micrograms, respectively). Fecal bacteriologic status was consistently altered. In human volunteers 250 mg PABA-UDCA was tested. Amounts of PABA excreted in urine during 6 h after dosing were 21.11 +/- 2.02 mg in controls (n = 5) and 12.20 +/- 1.01 mg in the group treated with polymixin B plus tinidazole (n = 5; P less than 0.01). No adverse effect was observed. These basic studies indicate that this compound is likely to offer a simple and rapid method for evaluation of the intestinal microorganisms without use of radioisotopes or expensive, special equipment.

Comparison of BT-PABA test and fecal chymotrypsin measurements in normal subjects and diabetic patients

A N-benzoil-L-tyrosil-PABA test on 6h urine collection, a plasma PABA assay 2 h after administration and a fecal chymotrypsin assay were performed on 66 patients (36 controls and 30 type 2 diabetic patients on insulin therapy). All patients were hospitalized and without gastrointestinal and renal disease. The mean values of plasmatic PABA and fecal chymotrypsin were significantly lower in the diabetic group than in the controls (p less than 0.025 and p less than 0.01, respectively), although they remained within normal range. But this was not the case for PABA urinary excretion values. This may indicate a slower but more protracted PABA absorption during the third or fourth hour with the result that urinary excretion over 6h is not greatly affected. There was good correlation between fecal chymotrypsin values and both PABA urinary excretion values and serum PABA values, a trend observed both in diabetics (p less than 0.005 and p less than 0.001, respectively) and in controls (p less than 0.001 and p less than 0.005, respectively). This could indicate that even at lower mean levels, the diabetic patients show the same behavior pattern and therefore maintain the same indexes of correlation as the control population. Our results suggest that these indirect, but simple, economical and well-tolerated tests could be considered a valid alternative for investigating pancreatic function especially in those patients that cannot be tested by a Secretin-Cerulein test.

Simplified oral pancreatic function test

The standard Bentiromide test and a new modified test using p-aminosalicylic acid (PAS) as a pharmacokinetic marker for p-aminobenzoic acid (PABA) have been evaluated in the detection of pancreatic exocrine insufficiency in children. The conventional two day test using a colorimetric assay for urinary PABA discriminated poorly between five children with pancreatic insufficiency and 13 others with normal pancreatic function. Two further groups of patients, comprising 28 with pancreatic exocrine insufficiency and 20 with normal pancreatic function underwent the modified test, and urine samples were analysed by high performance liquid chromatography. The results showed a complete separation between groups. The use of PAS eliminates a number of sources of error inherent in a two day Bentiromide test and provides a simplified and accurate diagnostic test for pancreatic insufficiency. The PABA-PAS modified test enables collection of the urine to be done during a single six hour period.

The development of the chymotryptic activity during postnatal life using the bentiromide test

The chymotryptic activity was assessed in 40 newborns and infants age 3-180 days using the NBT-PABA test. Nine newborns were studied serially at different age periods. A group of 18 cystic fibrosis patients and a group of 17 healthy children served as pancreatic insufficient and pancreatic sufficient controls, respectively. The results demonstrate a gradual increase with age of chymotryptic activity, approaching the levels of older children at about 180 days. The newborns who were studied serially demonstrated an individual pattern of increase in their chymotryptic activity. In the first days of life, newborns show low chymotryptic activity similar to that found in cystic fibrosis patients.