Pre-fixation of virulent Mycobacterium tuberculosis with glutaraldehyde preserves exquisite ultrastructure on transmission electron microscopy through cryofixation and freeze-substitution with osmium-acetone at ultralow temperature

Ultrastructural Examination of Mouse Glomerular Capillary Loop by Sandwich Freezing and Freeze-Substitution

Sandwich freezing is a method of rapid freezing by sandwiching specimens between two metal disks, and has been used for observing exquisite close-to-native ultrastructure of living yeast and bacteria. Recently, this method has been found to be useful for preserving cell images of glutaraldehyde-fixed animal and human tissues. In the present study, this method was applied to observe fine structure of mouse glomerular capillary loops. Morphometry was then performed, and the results were compared with the data obtained by in vivo cryotechnique, which may provide the closest ultrastructure to the native state of living tissue. The results show that the ultrastructure of glomerular capillary loops obtained by sandwich freezing-freeze substitution after glutaraldehyde fixation was close to that of the ultrastructure obtained by in vivo cryotechnique, not only in quality of cell image but also in quantitative morphometry. They indicate that the ultrastructure obtained by sandwich freezing-freeze-substitution after glutaraldehyde fixation may more closely reflect the living state of cells and tissues than conventional chemical fixation and dehydration at room temperature and conventional rapid freezing freeze-substitution of excised tissues without glutaraldehyde fixation. Sandwich freezing-freeze substitution technique should be used routinely as a standard method for observing close-to-native ultrastructure of biological specimens.

Antimycobacterial compound of chitosan and ethambutol: ultrastructural biological evaluation in vitro against Mycobacterium tuberculosis

Chitosan (CS) is a promising biopolymer and has been tested as a complement to the action and compensation of toxicity presented by anti-tuberculosis drugs. The present work studied the adjuvant effect of CS with the drug ethambutol (EMB) as a compound (CS-EMB), to explore its antimicrobial and cytotoxic activity, using transmission electron microscopy (TEM), to examine ultracellular changes that represent possible antimycobacterial action of CS on Mycobacterium tuberculosis (Mtb). Antimycobacterial activities were tested against reference strains Mtb ATCC® H37Rv and multidrug resistant (MDR). In vitro cytotoxicity tests were performed on Raw 264.7. For the studied compounds, morphological, ultrastructural, and physical-chemical analyses were performed. Drug-polymer interactions that occur through the H bridges were confirmed by physical-chemical analyses. The CS-EMB compound is stable at pHs of 6.5-7.5, allowing its release at physiological pH. The antibacterial activity (minimum inhibitory concentration) of the CS-EMB compound was 50% greater than that of the EMB in the H37Rv and MDR strains and the ultrastructural changes in the bacilli observed by TEM proved that the CS-EMB compound has a bactericidal action, allowing it to break down the Mtb cell wall. The cytotoxicity of CS-EMB was higher than that of isolated EMB, IC50 279, and 176 μg/mL, respectively. It is concluded that CS-EMB forms a promising composite against strains Mtb H37Rv and multidrug resistant (MDR-TB).Key points• Our study will be the first to observe ultrastructurally the effects of the CS-EMB compound on Mtb cells.• CS-EMB antimicrobial activity in a multidrug-resistant clinical strain.• The CS-EMB compound has promising potential for the development of a new drug to fight tuberculosis.

A Diverse Range of Hemozoin Inhibiting Scaffolds Act on Plasmodium falciparum as Heme Complexes

A diverse series of hemozoin-inhibiting quinolines, benzamides, triarylimidazoles, quinazolines, benzimidazoles, benzoxazoles, and benzothiazoles have been found to lead to exchangeable heme levels in cultured Plasmodium falciparum (NF54) that ranged over an order of magnitude at the IC₅₀. Surprisingly, less active compounds often exhibited higher levels of exchangeable heme than more active ones. Quantities of intracellular inhibitor measured using the inoculum effect exhibited a linear correlation with exchangeable heme, suggesting formation of heme-inhibitor complexes in the parasite. In an effort to confirm this, the presence of a Br atom in one of the benzimidazole derivatives was exploited to image its distribution in the parasite using electron spectroscopic imaging of Br, an element not naturally abundant in cells. This showed that the compound colocalized with iron, consistent with its presence as a heme complex. Direct evidence for this complex was then obtained using confocal Raman microscopy. Exchangeable heme and inhibitor were found to increase with decreased rate of killing, suggesting that slow-acting compounds have more time to build up exchangeable heme complexes. Lastly, some but not all compounds evidently cause pro-oxidant effects because their activity could be attenuated with N-acetylcysteine and potentiated with t-butyl hydroperoxide. Collectively, these findings suggest that hemozoin inhibitors act as complexes with free heme, each with its own unique activity.

Structome analysis of virulent Mycobacterium tuberculosis, which survives with only 700 ribosomes per 0.1 fl of cytoplasm

We previously reported the exquisite preservation of the ultrastructures of virulent Mycobacterium tuberculosis cells processed through cryofixation and rapid freeze substitution. Here, we report the “structome” analysis (i.e., the quantitative three-dimensional structural analysis of a whole cell at the electron microscopic level) of virulent M. tuberculosis using serial ultrathin sections prepared after cryofixation and rapid freeze substitution and analyzed by transmission electron microscopy. Five M. tuberculosis cells, which were contained in the serial ultrathin cross sections encompassing from one end to the other, were cut into 24, 36, 69, 55, and 63 serial ultrathin sections, respectively. On average, the cells were 2.71 ± 1.05 μm in length, and the average diameter of the cell was 0.345 ± 0.029 μm. The outer membrane and plasma membrane surface areas were 3.04 ± 1.33 μm² and 2.67 ± 1.19 μm², respectively. The cell, outer membrane, periplasm, plasma membrane, and cytoplasm volumes were 0.293 ± 0.113 fl (= μm³), 0.006 ± 0.003 fl, 0.060 ± 0.021 fl, 0.019 ± 0.008 fl, and 0.210 ± 0.091 fl, respectively. The average total ribosome number was 1,672 ± 568, and the ribosome density was 716.5 ± 171.4/0.1 fl. This is the first report of a structome analysis of M. tuberculosis cells prepared as serial ultrathin sections following cryofixation and rapid freeze substitution and examined by transmission electron microscopy. These data are based on the direct measurement and enumeration of exquisitely preserved single-cell structures in transmission electron microscopy images rather than calculations or assumptions from indirect biochemical or molecular biological data. In addition, these data may explain the slow growth of M. tuberculosis and enhance understanding of the structural properties related to the expression of antigenicity, acid-fastness, and the mechanism of drug resistance, particularly in regard to the ratio of target to drug concentrations.

Genomic mapping of cAMP receptor protein (CRP Mt) in Mycobacterium tuberculosis: relation to transcriptional start sites and the role of CRPMt as a transcription factor

Chromatin immunoprecipitation identified 191 binding sites of Mycobacterium tuberculosis cAMP receptor protein (CRP^Mt) at endogenous expression levels using a specific α-CRP^Mt antibody. Under these native conditions an equal distribution between intragenic and intergenic locations was observed. CRP^Mt binding overlapped a palindromic consensus sequence. Analysis by RNA sequencing revealed widespread changes in transcriptional profile in a mutant strain lacking CRP^Mt during exponential growth, and in response to nutrient starvation. Differential expression of genes with a CRP^Mt-binding site represented only a minor portion of this transcriptional reprogramming with ∼19% of those representing transcriptional regulators potentially controlled by CRP^Mt. The subset of genes that are differentially expressed in the deletion mutant under both culture conditions conformed to a pattern resembling canonical CRP regulation in Escherichia coli, with binding close to the transcriptional start site associated with repression and upstream binding with activation. CRP^Mt can function as a classical transcription factor in M. tuberculosis, though this occurs at only a subset of CRP^Mt-binding sites.

Effects of sub-chronic aluminum chloride exposure on rat ovaries

AIMS

This experiment investigated the effects of sub-chronic aluminum chloride (AlCl3) exposure on rat ovaries.

MAIN METHODS

Eighty female Wistar (5weeks old) rats, weighed 110-120g, were randomly divided into four treatment groups: control group (CG), low-dose group (LG, 64mg/kg BW AlCl3), mid-dose group (MG, 128mg/kg BW AlCl3) and high-dose group (HG, 256mg/kg BW AlCl3). The AlCl3 was administered in drinking water for 120days. The ovarian ultrastructure was observed. The activities of acid phosphatase (ACP), alkaline phosphatase (ALP), succinate dehydrogenase (SDH), Na(+)-K(+)-ATPase, Mg(2+)-ATPase and Ca(2+)-ATPase, the contents of Fe, Cu and Zn, and the protein expression of follicle-stimulating hormone receptor (FSHR) and luteinizing hormone receptor (LHR) in the ovary were determined.

KEY FINDINGS

The results showed that the structure of the ovary was disrupted, the activities of ALP, ACP, SDH, Na(+)-K(+)-ATPase, Mg(2+)-ATPase and Ca(2+)-ATPase, the contents of Zn, Fe and the protein expression of FSHR and LHR were lowered, and the content of Cu was increased in AlCl3-treated rats than those in control.

SIGNIFICANCE

The results indicate that sub-chronic AlCl3 exposure caused the damage of the ovarian structure, the disturbed metabolism of Fe, Zn and Cu and the decreased activities of Na(+)-K(+)-ATPase, Mg(2+)-ATPase and Ca(2+)-ATPase in the ovary, which could result in suppressed energy supply in the ovary. A combination of suppression of energy supply and reduction of expression of FSHR and LHR could inhibit ovulation and corpus luteum development, leading to infertility in female rats.