Changes in membrane enzymes and glycosphingolipids in lymphocytes from HIV-1--infected and noninfected intravenous drug users

Addiction habits in a rural cohort of injection drug users and effects on serum lipid profile: Analysis of a repeated measures study from an eastern state of India

Background Injecting drug use (IDU) is associated with several cardiometabolic risks. We aimed to measure the independent effects of IDU behaviour and related factors on serum lipid profile among people who inject drugs (PWIDs). Methods We did a longitudinal study with six follow-up measurements at an interval of 2 months among 104 PWIDs from 11 selected hotspots under two blocks in West Bengal, India. Generalized estimating equations with robust standard errors analysed the effect of addiction habits on lipid profile parameters. Results The mean (SD) age of the participants was 27.6 (5.24) years, 36.5% married and 44.3% were unemployed at the time of recruitment. At the baseline, the mean (SD) body mass index (BMI) and fasting blood sugar (FBS) were 20.0 (1.82) kg/m2 and 112.0 (15.90) mg/dl, respectively. The mean duration of drug use was 2.5 (1.20) years. While 62.5% had normal triglyceride (TG), 14.4% had high total cholesterol (TC) and 69.2% had dyslipidaemia at the baseline. Adjusted for age, BMI, FBS and other addiction-related variables, models showed that longer duration of drug use (>3 years) resulted in higher levels of TG, higher TC-to-high-density lipoprotein ratio and dyslipidaemia. Tobacco use and high FBS level were also risk factors for dyslipidaemia. Conclusions Higher duration of IDU, tobacco use and higher FBS were associated with deranged lipid profile among PWIDs.

Neprilysin expression and functions in development, ageing and disease

Neprilysin (NEP) is an integral membrane-bound metallopeptidase with a wide spectrum of substrates and physiological functions. It plays an important role in proteolytic processes in the kidney, cardiovascular regulation, immune response, cell proliferation, foetal development etc. It is an important neuropeptidase and amyloid-degrading enzyme which makes NEP a therapeutic target in Alzheimer's disease (AD). Moreover, it plays a preventive role in development of cancer, obesity and type-2 diabetes. Recently a role of NEP in COVID-19 pathogenesis has also been suggested. Despite intensive research into NEP structure and functions in different organisms, changes in its expression and regulation during brain development and ageing, especially in age-related pathologies, is still not fully understood. This prevents development of pharmacological treatments from various diseases in which NEP is implicated although recently a dual-acting drug sacubitril-valsartan (LCZ696) combining a NEP inhibitor and angiotensin receptor blocker has been approved for treatment of heart failure. Also, various natural compounds capable of upregulating NEP expression, including green tea (EGCG), have been proposed as a preventive medicine in prostate cancer and AD. This review summarizes the existing literature and our own research on the expression and activity of NEP in normal brain development, ageing and under pathological conditions.

HIV-1 reduces Abeta-degrading enzymatic activities in primary human mononuclear phagocytes

The advent and wide introduction of antiretroviral therapy has greatly improved the survival and longevity of HIV-infected patients. Unfortunately, despite antiretroviral therapy treatment, these patients are still afflicted with many complications including cognitive dysfunction. There is a growing body of reports indicating accelerated deposition of amyloid plaques, which are composed of amyloid-β peptide (Aβ), in HIV-infected brains, though how HIV viral infection precipitates Aβ accumulation is poorly understood. It is suggested that viral infection leads to increased production and impaired degradation of Aβ. Mononuclear phagocytes (macrophages and microglia) that are productively infected by HIV in brains play a pivotal role in Aβ degradation through the expression and execution of two endopeptidases, neprilysin (NEP) and insulin-degrading enzyme. In this study, we report that NEP has the dominant endopeptidase activity toward Aβ in macrophages. Further, we demonstrate that monomeric Aβ degradation by primary cultured macrophages and microglia was significantly impaired by HIV infection. This was accompanied with great reduction of NEP endopeptidase activity, which might be due to the diminished transport of NEP to the cell surface and intracellular accumulation at the endoplasmic reticulum and lysosomes. Therefore, these data suggest that malfunction of NEP in infected macrophages may contribute to acceleration of β amyloidosis in HIV-inflicted brains, and modulation of macrophages may be a potential preventative target of Aβ-related cognitive disorders in HIV-affected patients.

The increased CD38 expressed by lymphocytes infected with HIV-1 is a fully active NADase

The NADase activity of the ectoenzyme CD38 on intact cells has been measured by a fluorometric assay using epsilon-NAD as a substrate. The enzyme activity was tested in the Daudi cell line, PHA-activated blasts and peripheral blood and tonsil lymphocytes from HIV-1-negative and -positive individuals. There was a direct correlation in all cells tested between the number of cell surface CD38 molecules added in the assay and the NADase activity of the same cells expressed as fluorescent units. This indicates that CD38 is expressed in its fully active form when up-regulated on T cells from HIV-1-infected patients. One of the suggested roles of the CD38 ectoenzyme is to degrade extra cellular NAD and thus recycle its permeable metabolites. This finding is consistent with the hypothesis that the increase in CD38 expression on lymphocytes during the chronic phase of HIV-1 infection is a mechanism to compensate for impaired capacity of these cells to synthesize ribonucleotides de novo.

HIV-1-induced perturbations of glycosphingolipid metabolism are cell-specific and can be detected at early stages of HIV-1 infection

The metabolism of glycosphingolipids (GSL) has been investigated in peripheral blood mononuclear cells (PBMC) from 8 patients at an early stage of HIV-1 infection. Following metabolic labeling of these cells with [14C]galactose, the GSL were purified and the radioactivity incorporated into each individual GSL quantitated by phosphoimaging. Compared with PBMC from seronegative donors, the GSL metabolism in PBMC from HIV-1-infected individuals was characterized by an increased synthesis of two GSL: the B-lymphocyte differentiation antigen globotriaosylceramide (Gb3, also referred to as CD77), and the monosialoganglioside GM3, a marker of T-lymphocytes and macrophages. The accumulation of Gb3 and GM3 in PBMC from HIV-1-infected patients was associated with the appearance of anti-Gb3 and anti-GM3 antibodies. Because these GSL are involved in the control of cell proliferation and signal transduction, such anti-GSL autoantibodies may contribute to the immune suppression during the course of HIV-1 infection. Studies on purified cell populations showed that GM3 accumulation occurred preferentially in HIV-1-infected monocytes/macrophages, whereas the synthesis glucosylceramide, the common precursor of complex GSL, was enhanced in both macrophages and CD4+ lymphocytes. Taken together, our data suggest that the dysregulation of GSL metabolism is an early event of HIV-1 pathogenesis that can induce important effects on immune cells homeostasis.