Optimized protocol for quantification of extracellular nicotinamide adenine dinucleotide: evaluating clinical parameters and pre-analytical factors for translational research

Nicotinamide adenine dinucleotide (NAD+), a coenzyme for more than 500 enzymes, plays a central role in energy production, metabolism, cellular signaling, and DNA repair. Until recently, NAD+ was primarily considered to be an intracellular molecule (iNAD+), however, its extracellular species (eNAD+) has recently been discovered and has since been associated with a multitude of pathological conditions. Therefore, accurate quantification of eNAD+ in bodily fluids such as plasma is paramount to answer important research questions. In order to create a clinically meaningful and reliable quantitation method, we analyzed the relationship of cell lysis, routine clinical laboratory parameters, blood collection techniques, and pre-analytical processing steps with measured plasma eNAD+ concentrations. Initially, NAD+ levels were assessed both intracellularly and extracellularly. Intriguingly, the concentration of eNAD+ in plasma was found to be approximately 500 times lower than iNAD+ in peripheral blood mononuclear cells (0.253 ± 0.02 μM vs. 131.8 ± 27.4 μM, p = 0.007, respectively). This stark contrast suggests that cellular damage or cell lysis could potentially affect the levels of eNAD+ in plasma. However, systemic lactate dehydrogenase in patient plasma, a marker of cell damage, did not significantly correlate with eNAD+ (n = 33; r = -0.397; p = 0.102). Furthermore, eNAD+ was negatively correlated with increasing c-reactive protein (CRP, n = 33; r = -0.451; p = 0.020), while eNAD+ was positively correlated with increasing hemoglobin (n = 33; r = 0.482; p = 0.005). Next, variations in blood drawing, sample handling and pre-analytical processes were examined. Sample storage durations at 4°C (0-120 min), temperature (0° to 25°C), cannula sizes for blood collection and tourniquet times (0 - 120 s) had no statistically significant effect on eNAD+ (p > 0.05). On the other hand, prolonged centrifugation (> 5 min) and a faster braking mode of the centrifuge rotor (< 4 min) resulted in a significant decrease in eNAD+ levels (p < 0.05). Taken together, CRP and hemoglobin appeared to be mildly correlated with eNAD+ levels whereas cell damage was not correlated significantly to eNAD+ levels. The blood drawing trial did not show any influence on eNAD+, in contrast, the preanalytical steps need to be standardized for accurate eNAD+ measurement. This work paves the way towards robust eNAD+ measurements, for use in future clinical and translational research, and provides an optimized hands-on protocol for reliable eNAD+ quantification in plasma.

Sensing Acute Cellular Rejection in Liver Transplant Patients Using Liver-Derived Extracellular Particles: A Prospective, Observational Study

Acute cellular rejection (ACR) after liver transplantation (LT) goes along with allograft dysfunction, which is diagnosed by liver biopsy and concomitant histological analysis, representing the gold standard in clinical practice. Yet, liver biopsies are invasive, costly, time-intensive and require expert knowledge. Herein we present substantial evidence that blood plasma residing peripheral liver-derived extracellular particles (EP) could be employed to diagnose ACR non-invasively. In vitro experiments showed organ-specific EP release from primary human hepatocytes under immunological stress. Secondly, analysis of consecutive LT patients (n=11) revealed significant heightened EP concentrations days before ACR. By conducting a diagnostic accuracy study (n = 69, DRKS00011631), we explored the viability of using EP as a liquid biopsy for diagnosing ACR following LT. Consequently, novel EP populations in samples were identified using visualization of t-distributed stochastic neighbor embedding (viSNE) and self-organizing maps (FlowSOM) algorithms. As a result, the ASGR1⁺CD130⁺Annexin V⁺ EP subpopulation exhibited the highest accuracy for predicting ACR (area under the curve: 0.80, 95% confidence interval [CI], 0.70-0.90), with diagnostic sensitivity and specificity of 100% (95% CI, 81.67-100.0%) and 68.5% (95% CI, 55.3-79.3%), respectively. In summary, this new EP subpopulation presented the highest diagnostic accuracy for detecting ACR in LT patients.

Extended liver resection in mice: state of the art and pitfalls-a systematic review

Background

Rodent models of liver resection have been used to investigate and evaluate the liver’s complex physiology and pathology since 1931. First documented by Higgins and Anderson, such models were created to understand liver regeneration mechanisms to improve outcomes in patients undergoing extensive liver resection for liver cancer or other underlying liver diseases.

Methods

A systematic search was conducted using Pubmed, gathering publications up to January 2019, which engaged with the mouse model of extended liver resection as a method itself. The results of this search were filtered according to their language, novelty, and relevancy.

Results

The Boolean search found 3741 articles on Pubmed, with 3130 publications remaining when filtered by language and the presence of a full text. In total, 21 of these publications examined the key themes of the animal model described. The mortality varied from 0 to 50% depending on the surgeon's experience and the resection method. The liver resection was mainly performed with classic sutures (14 out of 21 publications) and isoflurane was used for anaesthesia (10 out of 21 publications) in combination with analgesics (buprenorphine or ketamine/xylazine). The most used mouse strain was C57BL/6 (7 of 21 publications) which was on average 11 weeks old with a weight of 23 g.

Conclusion

Through the overview, laid out in the selected publications, this paper reviews the shift of the extended liver resection model from rat to the mouse, describes the state of the art in the experimental setting, and discusses the possible limitations and pitfalls. Clearly, the extended liver resection in mice is a reproducible, practical and easy to learn method.

Increased Cell-Free DNA Plasma Concentration Following Liver Transplantation Is Linked to Portal Hepatitis and Inferior Survival

Donor organ quality is crucial for transplant survival and long-term survival of patients after liver transplantation. Besides bacterial and viral infections, endogenous damage-associated molecular patterns (DAMPs) can stimulate immune responses. Cell-free DNA (cfDNA) is one such DAMP that exhibits highly proinflammatory effects via DNA sensors. Herein, we measured cfDNA after liver transplantation and found elevated levels when organs from resuscitated donors were transplanted. High levels of cfDNA were associated with high C-reactive protein, leukocytosis as well as granulocytosis in the recipient. In addition to increased systemic immune responses, portal hepatitis was observed, which was associated with increased interface activity and a higher numbers of infiltrating neutrophils and eosinophils in the graft. In fact, the cfDNA was an independent significant factor in multivariate analysis and increased concentration of cfDNA was associated with inferior 1-year survival. Moreover, cfDNA levels were found to be decreased significantly during the postoperative course when patients underwent continuous veno-venous haemofiltration. In conclusion, patients receiving livers from resuscitated donors were characterised by high postoperative cfDNA levels. Those patients showed pronounced portal hepatitis and systemic inflammatory responses in the short term leading to a high mortality. Further studies are needed to evaluate the clinical relevance of cfDNA clearance by haemoadsorption and haemofiltration in vitro and in vivo.

The nanomolar sensing of nicotinamide adenine dinucleotide in human plasma using a cycling assay in albumin modified simulated body fluids

Nicotinamide adenine dinucleotide (NAD), a prominent member of the pyridine nucleotide family, plays a pivotal role in cell-oxidation protection, DNA repair, cell signalling and central metabolic pathways, such as beta oxidation, glycolysis and the citric acid cycle. In particular, extracellular NAD⁺ has recently been demonstrated to moderate pathogenesis of multiple systemic diseases as well as aging. Herein we present an assaying method, that serves to quantify extracellular NAD⁺ in human heparinised plasma and exhibits a sensitivity ranging from the low micromolar into the low nanomolar domain. The assay achieves the quantification of extracellular NAD⁺ by means of a two-step enzymatic cycling reaction, based on alcohol dehydrogenase. An albumin modified revised simulated body fluid was employed as standard matrix in order to optimise enzymatic activity and enhance the linear behaviour and sensitivity of the method. In addition, we evaluated assay linearity, reproducibility and confirmed long-term storage stability of extracellular NAD⁺ in frozen human heparinised plasma. In summary, our findings pose a novel standardised method suitable for high throughput screenings of extracellular NAD⁺ levels in human heparinised plasma, paving the way for new clinical discovery studies.