Multifaceted pathogenesis of liver steatosis in inflammatory bowel disease: a systematic review

OBJECTIVE

Non-Alcoholic Fatty Liver Disease (NAFLD), as a hepatic manifestation of metabolic syndrome (MET)-related obesity, insulin resistance, dyslipidemia, and hypertension, is the main cause of chronic liver disease. Inflammatory Bowel Diseases (IBD), (Crohn's Disease (CD) and Ulcerative Colitis (UC)), are often associated with extraintestinal manifestations. Of these, NAFLD is one of the most frequently reported. To highlight the etiopathogenesis of NAFLD in IBD, we performed a systematic review emphasizing the relationship between NAFLD genetic alterations, metabolic syndrome, and drugs.

MATERIALS AND METHODS

According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement (PRISMA) criteria, we performed a systematic literature search on PubMed, Google Scholar, and Web of Science for literature updated from 2010 to 1 March 2021. Inclusion criteria for studies were observational design and Randomized Controlled Trials (RCTs); written in English; primary research only; based on adult patients, and human research only.

RESULTS

We identified nine studies on the link between NAFLD and IBD. Among these, two described the genetic predisposition to NAFLD of patients with IBD. Four reported an association between MetS and NAFLD in IBD patients. Regarding medications, none of four studies included, detected a relationship between NAFLD onset and IBD treatment (corticosteroids, immunomodulators, methotrexate, or biologics).  However, a retrospective study showed a protective effect of anti-TNF alpha therapies against altered liver enzymes.

CONCLUSIONS

In this interplay between genetic, metabolic, drug, and inflammatory factors, the underlying pathogenic mechanisms behind NAFLD in IBD are still far from clear. Further studies are needed to better clarify the role of individual components influencing the development of NAFLD in IBD.

ANGPTL4 gene E40K variation protects against obesity-associated dyslipidemia in participants with obesity

OBJECTIVE

ANGPTL4 inhibits lipoprotein lipase in adipose tissue, regulating plasma triglycerides levels. In persons with obesity plasma ANGPTL4 levels have been positively correlated with body fat mass, TG levels and low HDL. A loss-of-function E40K mutation in ANGPTL4 prevents LPL inhibition, resulting in lower TGs and higher HDLc in the general population. Since obesity determines metabolic alterations and consequently is a major risk factor for cardiovascular disease, the aim was to explore if obesity-related metabolic abnormalities are modified by the ANGPTL4-E40K mutation.

METHODS

ANGPTL4-E40K was screened in 1206 Italian participants, of which 863 (71.5%) with obesity. All subjects without diabetes underwent OGTT with calculation of indices of insulin-sensitivity.

RESULTS

Participants with obesity carrying the E40K variant had significantly lower TG (p = 0.001) and higher HDLc levels (p = 0.024). Also in the whole population low TGs and high HDLc were confirmed in E40K carriers. In the obese subpopulation it was observed that almost all E40K carriers were within the lowest quartile of TGs (p = 1.1 × 10-9). E40K had no substantial effect of on glucose metabolism. Finally, none of the obese E40K carriers had T2D, and together with the favourable lipid profile, they resemble a metabolically healthy obese (MHO) phenotype, compared to 38% of E40E wild-type obese that had diabetes and/or dyslipidaemia (p = 0.0106).

CONCLUSIONS

In participants with obesity the ANGPTL4-E40K variant protects against dyslipidemia. The phenotype of obese E40K carriers is that of a patient with obesity without metabolic alterations, similar to the phenotype described as metabolic healthy obesity.

Causal relationship of hepatic fat with liver damage and insulin resistance in nonalcoholic fatty liver

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease is epidemiologically associated with hepatic and metabolic disorders. The aim of this study was to examine whether hepatic fat accumulation has a causal role in determining liver damage and insulin resistance.

METHODS

We performed a Mendelian randomization analysis using risk alleles in PNPLA3, TM6SF2, GCKR and MBOAT7, and a polygenic risk score for hepatic fat, as instruments. We evaluated complementary cohorts of at-risk individuals and individuals from the general population: 1515 from the liver biopsy cohort (LBC), 3329 from the Swedish Obese Subjects Study (SOS) and 4570 from the population-based Dallas Heart Study (DHS).

RESULTS

Hepatic fat was epidemiologically associated with liver damage, insulin resistance, dyslipidemia and hypertension. The impact of genetic variants on liver damage was proportional to their effect on hepatic fat accumulation. Genetically determined hepatic fat was associated with aminotransferases, and with inflammation, ballooning and fibrosis in the LBC. Furthermore, in the LBC, the causal association between hepatic fat and fibrosis was independent of disease activity, suggesting that a causal effect of long-term liver fat accumulation on liver disease is independent of inflammation. Genetically determined hepatic steatosis was associated with insulin resistance in the LBC and SOS. However, this association was dependent on liver damage severity. Genetically determined hepatic steatosis was associated with liver fibrosis/cirrhosis and with a small increase in risk of type 2 diabetes in publicly available databases.

CONCLUSION

These data suggest that long-term hepatic fat accumulation plays a causal role in the development of chronic liver disease.

Molecular analysis of three known and one novel LPL variants in patients with type I hyperlipoproteinemia

BACKGROUND AND AIMS

Type I hyperlipoproteinemia, also known as familial chylomicronemia syndrome (FCS), is a rare autosomal recessive disorder caused by variants in LPL, APOC2, APOA5, LMF1 or GPIHBP1 genes. The aim of this study was to identify novel variants in the LPL gene causing lipoprotein lipase deficiency and to understand the molecular mechanisms.

METHODS AND RESULTS

A total of 3 individuals with severe hypertriglyceridemia and recurrent pancreatitis were selected from the Lipid Clinic at Sahlgrenska University Hospital and LPL was sequenced. In vitro experiments were performed in human embryonic kidney 293T/17 (HEK293T/17) cells transiently transfected with wild type or mutant LPL plasmids. Cell lysates and media were used to analyze LPL synthesis and secretion. Media were used to measure LPL activity. Patient 1 was compound heterozygous for three known variants: c.337T > C (W113R), c.644G > A (G215E) and c.1211T > G (M404R); patient 2 was heterozygous for the known variant c.658A > C (S220R) while patient 3 was homozygous for a novel variant in the exon 5 c.679G > T (V227F). All the LPL variants identified were loss-of-function variants and resulted in a substantial reduction in the secretion of LPL protein.

CONCLUSION

We characterized at the molecular level three known and one novel LPL variants causing type I hyperlipoproteinemia showing that all these variants are pathogenic.

Adverse effects of fructose on cardiometabolic risk factors and hepatic lipid metabolism in subjects with abdominal obesity

BACKGROUND

Overconsumption of dietary sugars, fructose in particular, is linked to cardiovascular risk factors such as type 2 diabetes, obesity, dyslipidemia and nonalcoholic fatty liver disease. However, clinical studies have to date not clarified whether these adverse cardiometabolic effects are induced directly by dietary sugars, or whether they are secondary to weight gain.

OBJECTIVES

To assess the effects of fructose (75 g day^-1 ), served with their habitual diet over 12 weeks, on liver fat content and other cardiometabolic risk factors in a large cohort (n = 71) of abdominally obese men.

METHODS

We analysed changes in body composition, dietary intake, an extensive panel of cardiometabolic risk markers, hepatic de novo lipogenesis (DNL), liver fat content and postprandial lipid responses after a standardized oral fat tolerance test (OFTT).

RESULTS

Fructose consumption had modest adverse effects on cardiometabolic risk factors. However, fructose consumption significantly increased liver fat content and hepatic DNL and decreased β-hydroxybutyrate (a measure of β-oxidation). The individual changes in liver fat were highly variable in subjects matched for the same level of weight change. The increase in liver fat content was significantly more pronounced than the weight gain. The increase in DNL correlated positively with triglyceride area under the curve responses after an OFTT.

CONCLUSION

Our data demonstrated adverse effects of moderate fructose consumption for 12 weeks on multiple cardiometabolic risk factors in particular on liver fat content despite only relative low increases in weight and waist circumference. Our study also indicates that there are remarkable individual differences in susceptibility to visceral adiposity/liver fat after real-world daily consumption of fructose-sweetened beverages over 12 weeks.

Beta-glucan, inositol and digestive enzymes improve quality of life of patients with inflammatory bowel disease and irritable bowel syndrome

OBJECTIVE

To evaluate the efficacy of a mixture of beta-glucan, inositol and digestive enzymes in improving gastrointestinal symptoms in patients affected by inflammatory bowel disease (IBD)-irritable bowel syndrome (IBS).

PATIENTS AND METHODS

The study was conducted at the IBD Unit of the University of Catanzaro. Forty-three IBD patients with IBS symptoms were included in the study. IBD diagnosis was performed by clinical, endoscopic, histological and radiological criteria. Patients were in clinical remission and in treatment only with systemical and topical mesalamine. All study participants fulfilled the Rome III criteria for the diagnosis of IBS. The study participants were randomized into 2 groups: group A (n=23) received conventional treatment (systemical and topical mesalamine) plus a mixture of beta-glucan, inositol and digestive enzymes (one tablet after lunch and dinner) for four consecutive weeks; group B (n=20) received only conventional treatment. The prevalence and intensity of gastrointestinal (GI) symptoms were evaluated both at the enrollment (T0) and after four weeks of treatment (T1).

RESULTS

Patients who received mesalamine plus the mixture of beta-glucan, inositol and digestive enzymes (group A) reported a reduction in abdominal pain together with reduction in bloating and flatulence after four weeks of treatment. Importantly, an overall improvement in the general well-being has been recorded. Patients who underwent only mesalamine treatment (group B) reported a mild reduction in the evacuative urgency without any other improvements.

CONCLUSIONS

We have shown that supplementation with a mixture of beta-glucan, inositol and digestive enzymes reduces bloating, flatulence and abdominal pain, improving the overall clinical condition of IBD-IBS patients.

Genetic diagnosis of familial hypercholesterolaemia by targeted next-generation sequencing

OBJECTIVES

The aim of this study was to combine clinical criteria and next-generation sequencing (pyrosequencing) to establish a diagnosis of familial hypercholesterolaemia (FH).

DESIGN, SETTING AND SUBJECTS

A total of 77 subjects with a Dutch Lipid Clinic Network score of ≥ 3 (possible, probable or definite FH clinical diagnosis) were recruited from the Lipid Clinic at Sahlgrenska Hospital, Gothenburg, Sweden. Next-generation sequencing was performed in all subjects using SEQPRO LIPO RS, a kit that detects mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9) and LDLR adapter protein 1 (LDLRAP1) genes; copy-number variations in the LDLR gene were also examined.

RESULTS

A total of 26 mutations were detected in 50 subjects (65% success rate). Amongst these, 23 mutations were in the LDLR gene, two in the APOB gene and one in the PCSK9 gene. Four mutations with unknown pathogenicity were detected in LDLR. Of these, three mutations (Gly505Asp, Ile585Thr and Gln660Arg) have been previously reported in subjects with FH, but their pathogenicity has not been proved. The fourth, a mutation in LDLR affecting a splicing site (exon 6-intron 6) has not previously been reported; it was found to segregate with high cholesterol levels in the family of the proband.

CONCLUSIONS

Using a combination of clinical criteria and targeted next-generation sequencing, we have achieved FH diagnosis with a high success rate. Furthermore, we identified a new splicing-site mutation in the LDLR gene.