A brief review on human mtDNA mutations and NRTI-associated mtDNA toxicity and mutations

Single nucleotide polymorphisms in LCAT may contribute to dyslipidaemia in HIV-infected individuals on HAART in a Ghanaian population

Highly active antiretroviral therapy (HAART) is known to cause lipid abnormalities such as dyslipidaemia in HIV-infected individuals. Yet, dyslipidaemia may not independently occur as it may be worsened by single nucleotide polymorphisms (SNPs) in lecithin cholesterol acyltransferase (LCAT) and lipoprotein lipase (LPL). This case–control study was conducted in three-selected hospitals in the Northern part of Ghana. The study constituted a total of 118 HIV-infected participants aged 19–71 years, who had been on HAART for 6–24 months. Dyslipidaemia was defined based on the NCEP-ATP III criteria. HIV-infected individuals on HAART with dyslipidaemia were classified as cases while those without dyslipidaemia were grouped as controls. Lipid profile was measured using an automatic clinical chemistry analyzer and genomic DNA was extracted for PCR (GeneAmp PCR System 2700). Overall, the prevalence of dyslipidaemia was 39.0% (46/118). High levels of low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), and reduced levels of high-density lipoprotein cholesterol (HDL-C) were observed in all cases. A total of 256 selected PCR amplicons comprising 137 LPL (exons 3, 5 and 6) and 119 LCAT (exons 1, 4, and 6) were sequenced in 46 samples (Inqaba Biotech). Six (6) clinically significant SNPs were identified in exons 1 and 4 for LCAT whereas 25 non-clinically significant SNPs were identified for LPL in exons 5 and 6. At position 97 for LCAT exon 1, there was a deletion of the nucleotide, ‘A’ in 32.5% (13/40) of the sampled population while 67.5% (27/40) of the sample population retained the nucleotide, ‘A’ which was significantly associated with dyslipidaemic outcomes in the study population (p = 0.0004). A total of 25 SNPs were identified in exons 5 and 6 of LPL; 22 were substitutions, and 3 were insertions. However, none of the 25 SNPs identified in LPL exon 5 and 6 were statistically significant. SNPs in LCAT may independently contribute to dyslipidaemia among Ghanaian HIV-infected individuals on HAART, thus, allowing genetic and/or functional differential diagnosis of dyslipidaemia and creating an opportunity for potentially preventive options.

The Novel Roles of Connexin Channels and Tunneling Nanotubes in Cancer Pathogenesis

Neoplastic growth and cellular differentiation are critical hallmarks of tumor development. It is well established that cell-to-cell communication between tumor cells and "normal" surrounding cells regulates tumor differentiation and proliferation, aggressiveness, and resistance to treatment. Nevertheless, the mechanisms that result in tumor growth and spread as well as the adaptation of healthy surrounding cells to the tumor environment are poorly understood. A major component of these communication systems is composed of connexin (Cx)-containing channels including gap junctions (GJs), tunneling nanotubes (TNTs), and hemichannels (HCs). There are hundreds of reports about the role of Cx-containing channels in the pathogenesis of cancer, and most of them demonstrate a downregulation of these proteins. Nonetheless, new data demonstrate that a localized communication via Cx-containing GJs, HCs, and TNTs plays a key role in tumor growth, differentiation, and resistance to therapies. Moreover, the type and downstream effects of signals communicated between the different populations of tumor cells are still unknown. However, new approaches such as artificial intelligence (AI) and machine learning (ML) could provide new insights into these signals communicated between connected cells. We propose that the identification and characterization of these new communication systems and their associated signaling could provide new targets to prevent or reduce the devastating consequences of cancer.

Nucleoside reverse transcriptase inhibitor-induced rat oocyte dysfunction and low fertility mediated by autophagy

Low fertility is one of the most common side effects caused by nucleoside reverse transcriptase inhibitors (NRTIs), whereas the molecular mechanism underlying this process were largely unclear. This study was conducted to investigate whether autophagy plays a role in NRTIs-induced oocyte dysfunction and low fertility in female rat. Both in vivo and in vitro experiments were conducted. For the in vivo experiment, female adult Sprague-Dawley rats were subjected to zidovudine (AZT) and lamivudine (3TC) intragastric treatment for 3, 6, 9, and 12 weeks; a control was also set. Oocytes were collected for maturation evaluation, in vitro fertilization and mitochondrial function assays, and apoptosis and autophagy analysis. For the in vitro experiment, oocytes were collected and assigned to the control, 3-methyladenine (3-MA, an effective autophagy inhibitor), AZT, AZT+3-MA, 3TC, and 3TC+3-MA groups. The oocytes were cultured with the abovementioned drugs for 24, 48, and 72 h and then, subjected to the same assays as in the in vivo study. The results showed a significant time-dependent decrease in oocyte maturation-related maker levels, oocyte cleavage rate, blastocyst formation rate, mitochondrial DNA copy number and adenosine triphosphate level, and apoptosis, and a significant increase in the reactive oxygen species levels (all P-values < 0.05), in both the in vivo and the in vitro experiments. These changes, except for the changes in the oocyte maturation-related markers, were partially attenuated by 3-MA. In conclusion, we demonstrated that NRTIs can cause rat oocyte dysfunction and low fertility, and this damage was, at least partially, mediated by autophagy.

Nucleoside/nucleotide reverse transcriptase inhibitors attenuate angiogenesis and lymphangiogenesis by impairing receptor tyrosine kinases signalling in endothelial cells

BACKGROUND AND PURPOSE

Cardiovascular disease associated with antiretroviral therapy (ART) has become a major clinical challenge for HIV-positive patients. However, the role of ART in blood vessel growth is largely unknown. Here, we examined an integral component of ART, nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) and investigated their effects on key microvascular functions, including angiogenesis and lymphangiogenesis.

EXPERIMENTAL APPROACH

The angiogenesis/lymphangiogenesis capability of endothelial cells (ECs) was evaluated using migration, proliferation and tube formation assays in vitro, and mouse ear and Matrigel plug assays in vivo. Expressions of signalling molecules and mitochondrial antioxidant catalases were determined using Western blotting. Receptor tyrosine kinase (RTK) internalization and endocytosis were examined using flow cytometry and confocal immunofluorescence microscopy respectively. Mitochondrial DNA copy number and ROS were determined using quantitative real-time PCR and MitoSOX staining respectively.

KEY RESULTS

Pharmaceutical doses of NRTIs [azidothymidine (AZT), tenofovir disoproxil fumarate (TDF) and lamivudine (3TC)] inhibited angiogenesis and lymphangiogenesis both in vivo and in vitro by affecting the proliferation and migration of ECs. Correspondingly, NRTIs selectively attenuated the activation and transduction of endothelial RTK signals, VEGFR2 and FGFR1 pathways, in vascular ECs and the VEGFR3 pathway in lymphatic ECs. Both TDF and 3TC restrained RTKs' endocytosis into early endosomes but not internalization, while AZT blocked the protein maturation of RTKs. Excessive ROS levels were detected in NRTI-treated ECs, and the MnSOD mimic MnTMPyP alleviated the angiogenic/lymphangiogenic defects induced by NRTIs.

CONCLUSIONS AND IMPLICATIONS

NRTIs negatively regulate angiogenesis and lymphangiogenesis by inducing mitochondrial oxidative stress and subsequently impairing RTK signalling in ECs.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

The Δ133p53 Isoform Reduces Wtp53-induced Stimulation of DNA Pol γ Activity in the Presence and Absence of D4T

The mitochondrial toxicity of nucleoside reverse transcriptase inhibitors (NRTIs) is due to the inhibition of mitochondrial DNA (mtDNA) polymerase γ (pol γ). Previous studies have shown that wild type p53 (wtp53) can interact with pol γ and mtDNA to enhance mitochondrial DNA base excision repair (mtBER) activity and increase the accuracy of DNA synthesis. The N-terminal transactivation domain and central specific DNA-binding domain of p53 play critical roles in the stimulation of BER. In this study, we identified the possible roles of wtp53, Δ40p53 and Δ133p53 in regulating mtDNA pol γ activity in cells with d4T treatment. The results show that Δ40p53 and Δ133p53 can exist in mitochondrial fragments and form polymers with themselves or wtp53. Unlike wtP53, Δ133p53 alone cannot increase DNA pol γ activity. More importantly, we found that Δ133p53 played a negative role in p53 stimulation of DNA pol γ activity when studied in d4T-treated and d4T-untreated mitochondrial extracts. Gel shift data also indicate that Δ40p53 and Δ133p53 cannot interact with APE. Wtp53 and Δ40p53 can act antagonize the effect of d4T inhibition of DNA pol γ activity. However, when wtp53 interacted with Δ133p53, DNA pol γ activity was significantly decreased. Conclusion: Δ133p53 negatively regulates p53’s stimulation of pol γ in the presence and absence of d4T.

Investigational reverse transcriptase inhibitors for the treatment of HIV

INTRODUCTION

While considerable advances have been made in the development of antiretroviral agents, there is still work to be done. Reverse transcriptase inhibitors are important drugs for the treatment of HIV, and considerable research is currently ongoing to develop new agents and to modify currently existing agents.

AREAS COVERED

Herein, the authors discuss both investigational nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs), including agents that are in various stages of development. They also discuss novel formulations that are being investigated for currently available drugs, and discuss the advantages that these new formulations may provide.

EXPERT OPINION

New formulations and co-formulations of currently existing antiretrovirals will represent an important area of development, as a means to improve adherence for HIV-positive individuals. New formulations will continue to be developed, with a focus on allowing for less-frequent administration, as well increasing drug concentrations at local sites such as vaginal tissue, rectal tissue and sites in the immune system.