The Effect of Nicotinamide Riboside on LDL-Cholesterol Induced T-Cell Dysfunction
Date
2022-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Aging is associated with chronic low-grade inflammation (“inflammaging”)
and is a significant risk factor for multiple chronic diseases, including cardiovascular
disease, Alzheimer’s disease, and cancer. Inflammaging is caused by the deterioration
of the innate and adaptive immune systems, often accompanied by
immunosenescence. T-lymphocytes (T-cells), primarily known for their role in the
adaptive immune system responding to foreign antigens, are increasingly recognized
as contributors to inflammaging via immunosenescence and impaired mitochondrial
function. Age-related declines of cellular nicotinamide adenine dinucleotide (NAD+)
levels may be the trigger of immunosenescence and mitochondrial dysfunction.
However, the mechanisms leading to T-cell mediated inflammaging and mitochondrial
dysfunction are not fully known. One mechanism which might contribute to age related T-cell dysfunction is an increase in endogenous low-density lipoprotein
cholesterol (LDL-C) in blood plasma. Increased endogenous LDL-C occurs with aging
and has been linked, cross-sectionally, to mitochondrial damage and dysfunction,
reduction of ATP synthesis, and increased reactive oxygen species. Subsequently, this
damage can lead to various cellular consequences, rapid aging, and disease onset.
Supplementation with nicotinamide riboside (NR), a precursor to nicotinamide
adenine dinucleotide (NAD+), might be a novel therapeutic to protect T-cells from the
deleterious effects of high LDL-C. In addition to its role as a regulator of cellular
reoxidation-reduction reactions, NAD+ is a critical co-substrate for several energy-sensing and stress-resistance enzymes. These enzymes are referred to as “NAD+-
consuming enzymes” and include the silent mating type information regulation of two
homologs (sirtuins; SIRTs), poly adenosine diphosphate (ADP) ribose polymerases
(PARPs), cyclic ADP (cADP)-ribose synthases, and CD38/156 ectoenzymes. These
enzymes contribute to a multitude of homeostatic processes including the maintenance
of biological stress resistance, DNA damage repair, and the regulation of immune cell
function. Supplementation with NR has been shown to increase NAD+ bioavailability.
NAD+ has emerged as a vital and intriguing cofactor for maintaining mitochondrial
fitness by up-regulating enzymes that repair mitochondrial DNA. However, whether
NAD+ can protect T-cell mitochondria from immunosenescence is unknown. This
study aimed to investigate the efficacy of exogenous NAD+ supplementation in
protecting young T-cells from the effects of hypercholesterolemic conditions
associated with aging. I hypothesized that treatment with LDL-C would impair T-cell
mitochondrial respiration and induce T-cell inflammation and that NR would exert a
protective effect on T-cells, preserving mitochondrial respiration and reducing the
inflammatory response.
Seven adults (6 female/ 1 male) between the ages of 22 and 26 participated in
this study. Blood samples were collected in EDTA coated vacutainer tubes from all 7
participants. Peripheral Blood Mononuclear Cells (PBMCs), isolated from whole
blood, were further isolated into a pan T-cell sample. The isolated T-cells were later
treated and used for the Seahorse XF Analyzer. The supernatant was isolated and
frozen to use for the quantification of cytokines. Pan T-cells were treated with high (4.9 mMol/L) physiologic concentrations of LDL-C and co-incubated with high LDL C and NR compared to control (Serum-free media, 0 mMol/L). T-cell mitochondrial
function and inflammatory cytokine production were assessed by measuring
mitochondrial respiration using an extracellular flux analyzer (Seahorse XFe96
Analyzer) and multi-plex protein quantification (Luminex Magpix), respectively.
Concentrations of pro-and anti-inflammatory cytokines, specifically interleukin-6 (IL 6) and interleukin-10 (IL-10), were measured across the three treatment groups of the
pan T-cell samples. Proinflammatory cytokines up-regulate the production of radical
oxygen species (ROS) and anti-inflammatory cytokines reduce the production of ROS.
Contrary to our hypothesis, LDL-C non-significantly augmented T-cell
mitochondrial respiration during maximal oxygen consumption rate (OCR), while it
non-significantly decreased basal OCR and ATP-linked OCR. Further, the addition of
NR to LDL-C treated samples exacerbated mitochondrial respiration in all accounts.
Anti-inflammatory cytokine production showed a non-significant decrease with the
LDL-C and LDL-C+NR treatments. Proinflammatory cytokine production displayed a
non-significant increase within the LDL-C and LDL-C+NR treatment groups.
The additional NR treatment to LDL-C treated T-cells significantly decreased
the basal, maximum, and ATP-linked OCR, but it is unclear if LDL-C treatment alone
had a significant effect on T-cell mitochondrial dysfunction. Cytokine production was
not significantly affected with either treatment at the current sample size and may
require more samples to clarify a relationship.
Description
Keywords
Aging, Nicotinamide riboside, T-cells, Lipoprotein cholesterol