Temporal pattern of humoral immune response in mild cases of COVID-19.

BACKGROUND: Understanding the humoral response pattern of coronavirus disease 2019 (COVID-19) is one of the essential factors to better characterize the immune memory of patients, which allows understanding the temporality of reinfection, provides answers about the efficacy and durability of protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and consequently helps in global public health and vaccination strategy. Among the patients who became infected with SARS-CoV-2, the majority who did not progress to death were those who developed the mild COVID-19, so understanding the pattern and temporality of the antibody response of these patients is certainly relevant. AIM: To investigate the temporal pattern of humoral response of specific immunoglobulin G (IgG) in mild cases of COVID-19. METHODS: Blood samples from 191 COVID-19 real-time reverse transcriptase-polymerase chain reaction (RT-qPCR)-positive volunteers from the municipality of Toledo/ Paraná/Brazil, underwent two distinct serological tests, enzyme-linked immunosorbent assay, and detection of anti-nucleocapsid IgG. Blood samples and clinicoepidemiological data of the volunteers were collected between November 2020 and February 2021. All assays were performed in duplicate and the manufacturers' recommendations were strictly followed. The data were statistically analyzed using multiple logistic regression; the variables were selected by applying the P < 0.05 criterion. RESULTS: Serological tests to detect specific IgG were performed on serum samples from volunteers who were diagnosed as being positive by RT-qPCR for COVID-19 or had disease onset in the time interval from less than 1 mo to 7 mo. The time periods when the highest number of participants with detectable IgG was observed were 1, 2 and 3 mo. It was observed that 9.42% of participants no longer had detectable IgG antibodies 1 mo only after being infected with SARS-CoV-2 and 1.57% were also IgG negative at less than 1 mo. At 5 mo, 3.14% of volunteers were IgG negative, and at 6 or 7 mo, 1 volunteer (0.52%) had no detectable IgG. During the period between diagnosis by RT-qPCR/symptoms onset and the date of collection for the study, no statistical significance was observed for any association analyzed. Moreover, considering the age category between 31 and 59 years as the exposed group, the P value was 0.11 for the category 31 to 59 years and 0.32 for the category 60 years or older, showing that in both age categories there was no association between the pair of variables analyzed. Regarding chronic disease, the exposure group consisted of the participants without any comorbidity, so the P value of 0.07 for the category of those with at least one chronic disease showed no association between the two variables. CONCLUSION: A temporal pattern of IgG response was not observed, but it is suggested that immunological memory is weak and there is no association between IgG production and age or chronic disease in mild COVID-19.

Validation of a liquid chromatographic/tandem mass spectrometric method for the determination of scopolamine butylbromide in human plasma: application of the method to a bioequivalence study.

A sensitive and specific LC/MS/MS method was developed and validated for the determination of scopolamine butylbromide in human plasma. Scopolamine butylbromide and propanolol (internal standard) were extracted from the plasma by liquid-liquid extraction with dichloromethane as the extraction solvent and separated on a C18 analytical column (50 x 4.6 mm id) maintained at 40 degrees C. The analytes were eluted at a constant flow rate of 0.45 mL/min; the mobile phase consisted of acetonitrile and a buffer of 5 mM ammonium acetate and 0.1% formic acid (60 + 40, v/v). The mass spectrometer, equipped with an electrospray source in the positive ionization mode, was set up in the multiple-reaction monitoring mode to monitor the transitions m/z 360.6 > 102.5 (scopolamine butylbromide) and m/z 259.7 > 115.6 (propanolol). The chromatographic separation was obtained within 2.0 min, and the responses were linear over the concentration range of 0.10-40.00 ng/mL. The mean extraction recoveries of scopolamine butylbromide and propanolol from plasma were 69.00 and 80.76%, respectively. Method validation parameters, such as specificity, linearity, precision, accuracy, and stability, were within the acceptable range. Moreover, when the proposed method was successfully applied to a pharmacokinetic study of healthy human volunteers, the results showed that the two scopolamine butylbromide formulations tested are not bioequivalent in rate and extent of absorption.

Development and validation of a liquid chromatographic/tandem mass spectrometric method for determination of tetracycline in human plasma: application to bioequivalence study.

A fast, sensitive, and specific liquid chromatographic/tandem mass spectrometric method was developed and validated for determination of tetracycline in human plasma. Tetracycline and oxytetracycline [internal standard (IS)] were extracted from the plasma by protein precipitation. The mobile phase consisted of acetonitrile-formic acid 0.1% (48 + 52, v/v), run at a flow rate of 1 ml/min (split 1:5). Detection was performed by positive electrospray ionization in multiple reaction monitoring mode, monitoring the transitions 444.8 > 410.0 and 461.0 > 426.0 for tetracycline and IS, respectively. The analysis was performed in 3.5 min and the method was linear in the plasma concentration range of 50-6000 ng/mL. The mean extraction recoveries for tetracycline and IS from plasma were 92.14 and 94.04%, respectively. Method validation investigated parameters such as the linearity, precision, accuracy, specificity, and stability, giving results within the acceptable range. The proposed method was successfully applied for determination of tetracycline in human plasma samples to support bioequivalence studies.