Limited proteolysis and oxidative modification of proteins in the hepatocytes of patients with resistant forms of tuberculosis

Tuberculosis (TB) continues to be a global problem for humanity (1,2,3). The prevalence of TB comorbidities has grown significantly over recent years. This creates some difficulties with the treatment prescription, requiring an individual approach to the choice of drugs, taking into account the possibility of adverse events and adverse drug interactions. An analysis of available literature sources showed that the digestive system pathology was detected in 62.5% of cases among patients with chemo-resistant TB (4,5). Immune homeostasis disorder, especially in patients with intense symptoms of exacerbation and prolonged relapse, takes an important part in the pathogenesis of the formation of both TB and chronic hepatitis (6,7). TB overlaps the course of chronic hepatitis in the case of comorbidity, which creates certain difficulties in the prescription of full-scale antimycobacterial therapy and reduces the efficacy of etiotropic treatment (8,9). The objective of this study was to investigate the oxidative modification of proteins and limited proteolysis in the hepatocytes of patients with resistant forms of pulmonary TB.

A prospective anatomopathological study was conducted on 60 patients with confirmed pulmonary TB (clinically and anatomopathologically) deaths from various cases. The main group was divided into three subgroups depending on the clinical forms and variants of TB. The first subgroup consisted of 19 cases in which the clinical diagnosis of the newly diagnosed tuberculosis was established, the second subgroup included 21 cases of polydrug-resistant tuberculosis (PDR-TB) and the third subgroup included 20 cases of multidrug-resistant tuberculosis (MDR-TB). The comparison group included 20 corpses without any pathology of the hepatobiliary system and morphological signs of TB infection. The primary medical records were reviewed: in-patient medical records (form No. 003/o) and postmortem examination reports (form No. 103/o). The methodology developed by I. S. Davydenko in 2003, which combines the long-established method of Michel-Calvo staining with bromophenol blue to visualize the ratio of “acid” (with predominance of carbonyl groups) and basic (with dominant amino groups) proteins and computed spectral analysis of the digital copy of the optical image, was used for the evaluation of the intensity of free radical processes in hepatocytes. Histological sections were stained with bromophenol blue using the Michel-Calvo method. The optical images were then digitalised using a digital camera (Target Image File Format, without a compression algorithm), and the latter were analyzed using the GNU Image Manipulation Program (GIMP) computer program (GPL license, 2012, version 2.82) by probe-computed microspectrometry in the RGB (red, green, blue) colour analysis system. The intensity of red and blue in colour staining was evaluated according to the given colour analysis system. The degree of oxidative protein modification (OPM) can be evaluated by detecting the relationship between the intensity of colouration in both colours (spectral regions), since the red colour by the Michel-Calvo method corresponds to the carbonyl groups and the blue colour corresponds to the amino groups of the proteins. Thus, the degree of OPM in histochemical specimens was judged by the magnitude of the red/blue (R/B) ratio, which was determined separately in the hepatocytes of the first, second and third zones (10).

The stoichiometric ninhydrin-Schiff reaction according to A. Yasuma and T. Ichikava, allows evaluating the degree of limited proteolysis, as a result of which the hidden amino groups of proteins are partially “opened”, was used to verify and quantify the free amino groups of proteins. The quantitative measure of limited proteolysis was the value of optical density in relative units of optical density (from 0 – no colour, absolute transparency – up to 1 – maximum colour, absolute opacity), which was measured on digital monochrome copies of the image by computed micro densitometry using a computer GIMP program (GPL license, 2012, version 2.82). Determination of the optical density of a specific colour on the free amino groups of proteins was performed separately in the hepatocytes of the first, second and third zones of the acinus.

Oxidative stress leads to an increase in the production of reactive oxygen species and, as a result, oxidative modification of proteins (11,12,13).

Taking into account the different functional activities of hepatocytes of different zones of the acinus (by Rappoport) according to the literature (7,14) and the results of our own studies, R/B ratio at a specific colouration on the acid and basic proteins by Michel-Calvo and the mean values of the relative units of optical density of a specific colouration on free amino groups of proteins according to A. Yasuma and T. Ichikava were determined separately in the hepatocytes of the first, second and third zones.

When comparing the digital data indicated in our study, it is evident that changes in proteins properties in average tendencies run virtually identically in hepatocytes of different zones of the comparison group. Thus, the difference is unlikely (p > 0.05) when comparing R/B ratio (specific staining of acid and basic proteins by Michel-Calvo) in the hepatocytes of zones I, II and III of the comparison group. A similar trend is observed in the analysis of average values of the optical density of a specific colouration on the free amino group of proteins by A. Yasuma and T. Ichikava (Table 1).

It was established that the results of the study of R/B ratios and the mean values of the optical density of a specific colouration of the free amino group of proteins by A. Yasuma and T. Ichikava in the first subgroup of the main group significantly differ from those in the comparison group (p < 0.01). The average R/B ratio and the optical density of a specific colouration of the free amino group of proteins are reliable in the hepatocytes of the second group of the main group – 1.3 and 1.2 times higher than those in subgroup I, respectively, and the parameters of subgroup I exceed those of subgroup III – 1.7 and 1.3 times, respectively (p < 0.05 in all cases). This tendency indicates an increase in the processes of free radical oxidation of proteins with characteristic effects – the growth of limited proteolysis and oxidation of amino group proteins in the hepatocytes of patients with PDR-TB and MDR-TB (Table 2).

The analysis of the parameters showed a linear increase in the intensity of OPM and limited proteolysis from zone I to zone III (from the periportal to the centrolobular parts of the acinus) in all subgroups of the main group according to the acinus zone (by Rappoport).

Pulmonary TB leads to increased processes of free radical oxidation of proteins with characteristic effects – the growth of limited proteolysis and oxidation of amino groups of proteins in liver hepatocytes. The intensity of the limited proteolysis and oxidation of the amino group of proteins has a linear growth pattern from zone I to zone III of the acinus.

The average R/B ratio for a specific colouration of the acid and basic proteins by Michel-Calvo and the optical density of a specific colouration on the free amino group of proteins by A. Yasuma and T. Ichikava were 1.32 and 1.15 times higher in patients with resistant forms of TB compared with those with susceptible TB, and 1.71 and 1.25 times higher in those with multidrug-resistant pulmonary TB, respectively.

Prospects for further research lie in a more detailed study of changes in oxidative processes in hepatocytes under the influence of long-term chemotherapy of multidrug-resistant and expanded resistant forms of TB.

Inform consent was obtained from the patients in order to participate to the study and write the article.