# Inhibition of CD38 by 78c Enhanced NAD+, Alleviated Inflammation, and Decreased Oxidative Stress in Old Murine Macrophages Induced by Oral Pathogens

## TL;DR

Blocking CD38 with 78c improves NAD+ levels, reduces inflammation, and lowers oxidative stress in old mice macrophages infected with oral pathogens.

## Contribution

Demonstrates that CD38 inhibition with 78c reduces inflammation and oxidative stress in aged macrophages infected by oral pathogens.

## Key findings

- Old macrophages showed increased CD38 and decreased NAD+ after infection with oral pathogens.
- CD38 inhibition by 78c reduced pro-inflammatory cytokines and oxidative stress markers in old macrophages.
- 78c treatment enhanced NAD+ levels and anti-oxidative enzyme expressions in infected old macrophages.

## Abstract

CD38, a nicotinamide adenine dinucleotide (NAD+) glycohydrolase, increases in old murine macrophages after infection compared to young controls. We aimed to determine whether the increase in CD38 in old murine macrophages after infection is directly associated with enhanced inflammation induced by the oral pathogens Aggregatibacter actinomycetemcomitans (Aa) or Porphyromonas gingivalis (Pg) when compared to young controls. Additionally, we determined the effects of a specific CD38 inhibitor (78c) on CD38, NAD+, interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α expressions, and anti-oxidative responses in old murine macrophages induced by oral pathogens. Old and young murine macrophages were either uninfected or infected with the oral pathogens Aa or Pg for 1 to 24 h. Protein levels of CD38 and protein kinases, including nuclear factor kappa-B (NF-κB), phosphoinositide 3-kinase (PI3K), and mitogen-activated protein kinases (MAPKs), NAD+, and inflammatory cytokine (IL-1β, IL-6, TNF-α) levels were evaluated. Additionally, old murine macrophages were treated with a vehicle or a CD38 inhibitor (78c) and cells were either uninfected or infected with Aa or Pg. CD38, NAD+, cytokine (IL-1β, IL-6, TNF-α) levels, reactive oxygen species (ROS), NAPDH oxidase 1 (Nox1), and anti-oxidative enzymes, including superoxide dismutase1 (Sod1), glutathione peroxidase 4 (Gpx4), Peroxiredoxin 1 (Prdx1), thioredoxin reductase 1 (Txnrd1), and catalase (Cat), were evaluated. The results showed that old murine macrophages significantly enhanced CD38 and reduced NAD+ levels 24 h after Aa or Pg infection compared to young controls. This enhanced CD38 in old murine macrophages was not directly correlated with the activation of protein kinases (NF-κB, PI3K, and MAPKs), nor the (IL-1β, IL-6, TNF-α) levels in macrophages. The inhibition of CD38 by 78c reduced CD38, enhanced NAD+ levels, attenuated IL-1β, IL-6 and TNF-α pro-inflammatory cytokine levels, reduced ROS and Nox1 expressions, and enhanced expressions of Sod1, Gpx4, Prdx1, Txnrd1, and Cat in old murine macrophages infected with Aa or Pg. These results suggest that the inhibition of CD38 by 78c is a promising therapeutic strategy to treat aging-associated periodontitis.