Human dietary selenium deficiency as a risk factor in the pathogenesis of endemic burkitt's lymphoma in Nyanza

Abstract

Endemic Burkitt lymphoma (eBL) has been associated with Epstein-Barr virus (EBY) and holoendemic Plasmodium falciparum malaria. However, recent eBL incidence maps showing more refined spatial clustering within malaria holoendemic areas, suggest that other risk factors may be involved in the etiology of eBL. Therefore, we hypothesized that the selenoprotein glutathione peroxidase (GPx), a surrogate of nutritional status known to regulate homornal, enzymatic pathways, viral mutations and virulence, is an important biomarker for eBL risk.

The study measured plasma GPx, anthropometric markers of malnutrition, EBY viral loads and malaria parasitemia in children aged 1-9 years (n=258) from two Locations in Nyanza Province, Kenya with higher than expected and lower than expected incidence of eBL. The study participants were malaria asymptomatic children from the community. The level of GPX selenium was determined using BIOXYTECH® Plasma (pGPX) Enzyme ImmunoassaysTM. USA. Q-PCR was used to determine EBY loads after extracting the DNA from EDTA preserved blood. Malaria parasite densities were determined from smears stained in 4% Giemsa by counting parasites against 200 wbc and multiplying results by 40 for values per microliter of blood. The distribution range of pGPx selenium in the study area was 0.55 - 7.lmcgldL mean 2.88mcgldL (n=167). Children residing in eBL low risk clusters had higher mean GPx Se 3.767, SD1.570.

The min-max (0.910 -7.1 OmcgldL) (n=66) and those living in eBL high risk areas had 2.308; SO 0.670; min-max GPx Se 0.589 - 3.330 mcgldL (n= 101), differences were significant at p<O.05 (P < 0.0001). The EBY loads by Q-PCR indicated that 43.9% (n=116) of 264 children tested, had non-detectable levels (NOL) EBY. Children (n=70) had 2.5 - 599 EBY copies and (n=78) had greater than 6OOcopies/mL of blood. The EBY (Q-PCR (+)) who were also tested for GPx selenium showed70% of 74 children from eBL low risk areas had detectable EBY copies, mean [2.57; SO 0.80] compared to'47% detects in 68 children from eBL high risk areas [3.38; SO 1.53] copies/mL of blood. EBY load were lower in the eBL low risk areas as compared to eBL high risk areas (P < 0.0001). The EBY loads were significantly higher in children with positive smears for malaria parasites [3.41±1.47] compared to those without malaria [2.65±1.0], p=O.OOl. Additionally, GPx levels were significantly lower in children with the highest EBY viral load and those with P. falciparum infections (p==O.035 and p==O.OO4, respectively).

There was also a significant negative correlation between Selenium levels and EBY viral loads (r=O.157, P = 0.041). Comprehensive stepwise multiple regression model with EBY viral load as the dependent variable, age as a covariate, and pGPX Selenium levels, sex, malaria status and area of residence as predictor variables was performed. The selection was based on statistical significance when variables were correlated with GPX Selenium levels (P < 0.05). However, this particular analysis did not show any significant association between selenium levels and EBY viral loads (P = 0.843).

The results suggest that selenium deficiency may be an important risk factor for eBL pathogenesis, in part, through the modulation of EBV viral loads as high viral loads have been shown to deplete GPX-selenium and its precursor cysteine which can affect liver detoxification, lymphocyte activation, viral transactivation and mitochondrial functions. Taken together, these results suggest that selenium deficiency may be an additional risk factor that needs to be considered in the etiology of endemic Burkitt lymphoma. The outcomes from the study are important public health surveillance tools. Increased EBV viral load suggests activation of EBVinfection in children and may be considered a putative risk factor for EBV tumerigenesis.