The I148M PNPLA3 variant mitigates niacin beneficial effects: How the genetic screening in non-alcoholic fatty liver disease patients gains value

Background

The PNPLA3 p.I148M impact on fat accumulation can be modulated by nutrients. Niacin (Vitamin B3) reduced triglycerides synthesis in in vitro and in vivo NAFLD models.

Objectives

In this study, we aimed to investigate the niacin-I148M polymorphism crosstalk in NAFLD patients and examine niacin's beneficial effect in reducing fat by exploiting hepatoma cells with different PNPLA3 genotype.

Design

We enrolled 172 (Discovery cohort) and 358 (Validation cohort) patients with non-invasive and histological diagnosis of NAFLD, respectively. Dietary niacin was collected from food diary, while its serum levels were quantified by ELISA. Hepatic expression of genes related to NAD metabolism was evaluated by RNAseq in bariatric NAFLD patients (n = 183; Transcriptomic cohort). Hep3B (148I/I) and HepG2 (148M/M) cells were silenced (siHep3B) or overexpressed (HepG2^I148+ ) for PNPLA3, respectively.

Results

In the Discovery cohort, dietary niacin was significantly reduced in patients with steatosis ≥ 2 and in I148M carriers. Serum niacin was lower in subjects carrying the G at risk allele and negatively correlated with obesity. The latter result was confirmed in the Validation cohort. At multivariate analysis, the I148M polymorphism was independently associated with serum niacin, supporting that it may be directly involved in the modulation of its availability. siHep3B cells showed an impaired NAD biosynthesis comparable to HepG2 cells which led to lower niacin efficacy in clearing fat, supporting a required functional protein to guarantee its effectiveness. Conversely, the restoration of PNPLA3 Wt protein in HepG2^I148+ cells recovered the NAD pathway and improved niacin efficacy. Finally, niacin inhibited de novo lipogenesis through the ERK1/2/AMPK/SIRT1 pathway, with the consequent SREBP1-driven PNPLA3 reduction only in Hep3B and HepG2^I148M+ cells.

Conclusions

We demonstrated a niacin-PNPLA3 I148M interaction in NAFLD patients which possibly pave the way to vitamin B3 supplementation in those with a predisposing genetic background.

Expanding the phenotypic spectrum of non-alcoholic fatty liver disease and hypertriglyceridemia

Background and aims

Hypertriglyceridemia is a common feature of metabolic syndrome (MetS), as well as of non-alcoholic fatty liver disease (NAFLD), which is considered the hepatic manifestation of MetS. Fat accumulation in hepatocytes may alter mitochondrial homeostasis predisposing to advanced liver disease. Here, we report a case of a 40-year-old woman with early aggressive NAFLD due to severe hypertriglyceridemia that ensued from a combination of genetic variants and additional metabolic risk factors.

Methods

Genetic screening was performed by using whole-exome sequencing (WES), and mitochondrial structures were evaluated by TEM.

Results

At presentation, the patient is reported to have hepatomegaly, hypertriglyceridemia, and raised transaminases. Genetic analysis revealed that the patient beard heritable alterations in genes implicated in lipid handling, among which APOB, APOE, CETP, and HSPG2, accompanied by missense mutations in genes involved in mitochondrial function, i.e., AK2, ALG6, ASPA, NDUFAF1, POLG, and TMEM70. Abdominal ultrasound (US) and transient elastography were suggestive of severe hepatic steatosis and fibrosis. A liver biopsy confirmed the diagnosis of non-alcoholic steatohepatitis (NASH)-related fibrosis. Thus, to better outline whether mutations involved in lipid remodeling and mitochondrial function may also affect organelles’ morphology, we exploited TEM. Along with multifaceted abnormalities of mitochondrial architecture that have been already observed in patients with NAFLD, astonishing ultrastructural defects, such as mitochondrial vacuolization, sub-compartmentalization, and onion-like mitochondria, were identified.

Conclusion

The anomalies reported may expand the phenotypic spectrum of mitochondrial abnormalities observed in patients with NAFLD, which may contribute to the switching toward a progressive disease.

Genetics Is of the Essence to Face NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the commonest cause of chronic liver disease worldwide. It is closely related to obesity, insulin resistance (IR) and dyslipidemia so much so it is considered the hepatic manifestation of the Metabolic Syndrome. The NAFLD spectrum extends from simple steatosis to nonalcoholic steatohepatitis (NASH), a clinical condition which may progress up to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). NAFLD is a complex disease whose pathogenesis is shaped by both environmental and genetic factors. In the last two decades, several heritable modifications in genes influencing hepatic lipid remodeling, and mitochondrial oxidative status have been emerged as predictors of progressive hepatic damage. Among them, the patatin-like phospholipase domain-containing 3 (PNPLA3) p.I148M, the Transmembrane 6 superfamily member 2 (TM6SF2) p.E167K and the rs641738 membrane bound-o-acyltransferase domain-containing 7 (MBOAT7) polymorphisms are considered the most robust modifiers of NAFLD. However, a forefront frontier in the study of NAFLD heritability is to postulate score-based strategy, building polygenic risk scores (PRS), which aggregate the most relevant genetic determinants of NAFLD and biochemical parameters, with the purpose to foresee patients with greater risk of severe NAFLD, guaranteeing the most highly predictive value, the best diagnostic accuracy and the more precise individualized therapy.

[Hemo-lymphopoietic tumors in agriculture. Case-control study in an epidemiologic area of southern Bari]

In order to evaluate the association between hemolymphoietic tumors and agriculture, we are carrying out a case-control study in the southern province of Bari (Italy). In the period 1st July 1987-30 June 1989, seventy-one incident cases of limphomes, leukemias and multiple myeloma and three fold higher number of controls (other tumors) aged more than fourteen years old were selected. A structured questionnaire was carried out to collect informations, focusing attention to the use of pesticides. For the evaluation of the exposure to specific substances a crop exposure matrix with "multiple circumstantial determinants" (crops and/or type of breeding, phytopatologies, areas and time windows) will be used. In this update a specific pesticides analysis was not conducted. Therefore, we classified as exposed farmers, farm laboures, breeders and whoever affirmed the regular use of pesticides. Up to 1st July 1995, one hundred and seventy-three subjects were contacted. Twenty-three (13%) of them refused to participate to the study, one hundred and fifteen (87%) of them, thirty-one (21%) case and one hundred and nineteen (79%) controls, were interviewed. Nineteen (61%) of cases were males, twelve (39%) of cases were exposed; seventy-two (60.5%) of controls were males, fourty-five (38%) of controls were exposed. The risk of hemolymphoietic tumors associated with exposure was null (O.R. = 1.04; I.C. 95% = 0.42-2.50); no job category (farmer, farm labourer, breeder) was statistically significant associate with cases. An association with farmer (O.R. = 4.87; I.C. 95% - 1.12-20.52) and breeder (O.R. = 4.83; I.C. = 1.19-18.11) was statistically significant if those fourteen subjects with leukemia were considered as cases. Using a logistic model (which independent variables were age, sex, information gathered directly from the subject of from relatives and smoking habit) O.R. for leukemia and farmer resulted statistically significant (O.R. = 5.38; I.C. 95% = 1.31-21.99); instead a considerable decreased O.R. was observed for leukemia and breeder (O.R. = 1.20; I.C. 95% = 0.73-2.00). These results could be subject to variation after the next data input.

[Tumors of the hemolymphopoietic tract and employment in agriculture: a case-control study carried out in an epidemiologic area in southern Italy]

To evaluate the role of agricultural exposures in the development of lymphatic and haemopoietic tumors a population-based case-referent study has been carried out in three health districts of Southern Italy. All incident cases of leukemia, lymphoma and myeloma from 1 July 1987 to 30 June 1989, aged 14 years or more, have been identified (71 subjects). The control group is formed by subjects with other neoplasms. A Job Exposure Matrix, specific to 10 areas, to 6 major crops and to 4 calendar periods, was built for assessing pesticide exposure. To date 100 interviews (to the index subject or to proxies) have been carried out (26 cases and 74 referents). The odds ratio (OR) of hematologic malignancies for agricultural workers was 1.63 [95% Confidence Intervals (95% CI): 0.69-4.34] in the whole sample and 6.00 (95% CI: 1.21-25.52) in the female group. Significative increased risks have been observed for exposure to DDT and creolin (OR = 4.11; 95% CI: 1.16-14.55) and, for leukemia, for cattle breeders (OR = 6.38; 95% CI: 1.46-27.83).