Reduced serum lipoprotein(a) levels in patients with primary biliary cirrhosis

Influence of triglyceride concentration in lipoprotein (a) as a function of dyslipidemia

BACKGROUND

Recently, an inverse relationship between the blood concentration of lipoprotein(a) (Lp(a)) and triglycerides (TG) has been demonstrated. The larger the VLDL particle size, the greater the presence of VLDL rich in apoliprotein E and in subjects with the apoE2/E2 genotype, the lower Lp(a) concentration. The mechanism of this inverse association is unknown. The objective of this analysis was to evaluate the Lp(a)-TG association in patients treated at the lipid units included in the registry of the Spanish Society of Atherosclerosis (SEA) by comparing the different dyslipidemias.

PATIENTS AND METHODS

Five thousand two hundred and seventy-five subjects ≥18 years of age registered in the registry before March 31, 2023, with Lp(a) concentration data and complete lipid profile information without treatment were included.

RESULTS

The mean age was 53.0 ± 14.0 years, with 48% women. The 9.5% of subjects (n = 502) had diabetes and the 22.4% (n = 1184) were obese. The median TG level was 130 mg/dL (IQR 88.0-210) and Lp(a) 55.0 nmol/L (IQR 17.9-156). Lp(a) concentration showed a negative association with TG concentration when TG values exceeded 300 mg/dL. Subjects with TG > 1000 mg/dL showed the lowest level of Lp(a), 17.9 nmol/L, and subjects with TG < 300 mg/dL had a mean Lp(a) concentration of 60.1 nmol/L. In subjects without diabetes or obesity, the inverse association of Lp(a)-TG was especially important (p < 0.001). The median Lp(a) was 58.3 nmol/L in those with TG < 300 mg/dL and 22.0 nmol/L if TG > 1000 mg/dL. No association was found between TG and Lp(a) in subjects with diabetes and obesity, nor in subjects with familial hypercholesterolemia. In subjects with multifactorial combined hyperlipemia with TG < 300 mg/dL, Lp(a) was 64.6 nmol/L; in the range of 300-399 mg/dL of TG, Lp(a) decreased to 38. 8 nmol/L, and up to 22.3 nmol/L when TG > 1000 mg/dL.

CONCLUSIONS

Our results show an inverse Lp(a)-TG relationship in TG concentrations > 300 mg/dL in subjects without diabetes, obesity and without familial hypercholesterolemia. Our results suggest that, in those hypertriglyceridemias due to hepatic overproduction of VLDL, the formation of Lp(a) is reduced, unlike those in which the peripheral catabolism of TG-rich lipoproteins is reduced.

Discordant association of nonalcoholic fatty liver disease with lipoprotein(a) and markers of atherogenic dyslipidemia

Nonalcoholic fatty liver disease (NAFLD) is associated with atherogenic dyslipidemia and an increased risk of cardiovascular events. Previous studies have suggested an inverse relationship between NAFLD severity and lipoprotein(a) [Lp(a)] level, but contemporary data from the U.S. are lacking. Lp(a), lipid profile, apolipoproteins, and nuclear magnetic resonance-based lipoprotein particle concentrations were measured in 151 patients with biopsy-proven NAFLD. Levels were compared between those with nonalcoholic fatty liver (NAFL) on histology and non-alcoholic steatohepatitis (NASH). Median age was 55 [48, 62] years, 67% of patients were women, 83% were White, 43% had NAFL, and 57% had NASH. Triglyceride level was higher and high-density lipoprotein-cholesterol (HDL-C) was lower among those with NASH as compared with NAFL. Circulating apolipoprotein-B (ApoB) and low-density lipoprotein particle concentration (LDL-P) were 9% and 17% higher in the NASH group as compared with NAFL, respectively. Contrastingly, Lp(a) concentration was 50% lower in NASH relative to NAFL group. Hepatocyte ballooning, lobular inflammation, and fibrosis on histology were inversely associated with Lp(a) concentration. NAFLD severity has a discordant association with Lp(a) and other markers of atherogenic dyslipidemia. This relationship may have implications for prognosticating cardiovascular disease risk in patients with NAFLD.

A liver secretome gene signature-based approach for determining circulating biomarkers of NAFLD severity

Non-invasive biomarkers of non-alcoholic fatty liver disease (NAFLD) supporting diagnosis and monitoring disease progression are urgently needed. The present study aimed to establish a bioinformatics pipeline capable of defining and validating NAFLD biomarker candidates based on paired hepatic global gene expression and plasma bioanalysis from individuals representing different stages of histologically confirmed NAFLD (no/mild, moderate, more advanced NAFLD). Liver secretome gene signatures were generated in a patient cohort of 26 severely obese individuals with the majority having no or mild fibrosis. To this end, global gene expression changes were compared between individuals with no/mild NAFLD and moderate/advanced NAFLD with subsequent filtering for candidate gene products with liver-selective expression and secretion. Four candidate genes, including LPA (lipoprotein A), IGFBP-1 (insulin-like growth factor-binding protein 1), SERPINF2 (serpin family F member 2) and MAT1A (methionine adenosyltransferase 1A), were differentially expressed in moderate/advanced NAFLD, which was confirmed in three independent RNA sequencing datasets from large, publicly available NAFLD studies. The corresponding gene products were quantified in plasma samples but could not discriminate among different grades of NAFLD based on NAFLD activity score. Conclusion: We demonstrate a novel approach based on the liver transcriptome allowing for identification of secreted hepatic gene products as potential circulating diagnostic biomarkers of NAFLD. Using this approach in larger NAFLD patient cohorts may yield potential circulating biomarkers for NAFLD severity.

Non-genetic influences on lipoprotein(a) concentrations

An elevated level of lipoprotein(a) [Lp(a)] is a genetically regulated, independent, causal risk factor for cardiovascular disease. However, the extensive variability in Lp(a) levels between individuals and population groups cannot be fully explained by genetic factors, emphasizing a potential role for non-genetic factors. In this review, we provide an overview of current evidence on non-genetic factors influencing Lp(a) levels with a particular focus on diet, physical activity, hormones and certain pathological conditions. Findings from randomized controlled clinical trials show that diets lower in saturated fats modestly influence Lp(a) levels and often in the opposing direction to LDL cholesterol. Results from studies on physical activity/exercise have been inconsistent, ranging from no to minimal or moderate change in Lp(a) levels, potentially modulated by age and the type, intensity, and duration of exercise modality. Hormone replacement therapy (HRT) in postmenopausal women lowers Lp(a) levels with oral being more effective than transdermal estradiol; the type of HRT, dose of estrogen and addition of progestogen do not modify the Lp(a)-lowering effect of HRT. Kidney diseases result in marked elevations in Lp(a) levels, albeit dependent on disease stages, dialysis modalities and apolipoprotein(a) phenotypes. In contrast, Lp(a) levels are reduced in liver diseases in parallel with the disease progression, although population studies have yielded conflicting results on the associations between Lp(a) levels and nonalcoholic fatty liver disease. Overall, current evidence supports a role for diet, hormones and related conditions, and liver and kidney diseases in modifying Lp(a) levels.

Low Lipoprotein(a) Levels Predict Hepatic Fibrosis in Patients With Nonalcoholic Fatty Liver Disease

Dyslipidemia and cardiovascular complications are comorbidities of nonalcoholic fatty liver disease (NAFLD), which ranges from simple steatosis to nonalcoholic steatohepatitis, fibrosis, and cirrhosis up to hepatocellular carcinoma. Lipoprotein(a) (Lp(a)) has been associated with cardiovascular risk and metabolic abnormalities, but its impact on the severity of liver damage in patients with NAFLD remains to be clarified. Circulating Lp(a) levels were assessed in 600 patients with biopsy-proven NAFLD. The association of Lp(a) with liver damage was explored by categorizing serum Lp(a) into quartiles. The receiver operating characteristic curve was used to analyze the accuracy of serum Lp(a) in hepatic fibrosis prediction. Hepatic expression of lipoprotein A (LPA) and of genes involved in lipid metabolism and fibrogenic processes were evaluated by RNA sequencing in a subset of patients with NAFLD for whom Lp(a) dosage was available (n = 183). In patients with NAFLD, elevated Lp(a) levels were modestly associated with circulating lipids, carotid plaques, and hypertension (P < 0.05). Conversely, patients with low serum Lp(a) displayed insulin resistance (P < 0.05), transaminase elevation (P < 0.05), and increased risk of developing severe fibrosis (P = 0.007) and cirrhosis (P = 0.002). In addition, the diagnostic accuracy of Lp(a) in predicting fibrosis increased by combining it with transaminases (area under the curve fibrosis stage 4, 0.87; P < 0.0001). Hepatic LPA expression reflected serum Lp(a) levels (P = 0.018), and both were reduced with the progression of NAFLD (P < 0.05). Hepatic LPA messenger RNA levels correlated with those of genes involved in lipoprotein release, lipid synthesis, and fibrogenesis (P < 0.05). Finally, transmembrane 6 superfamily member 2 (TM6SF2) rs58542926, apolipoprotein E (ApoE) rs445925, and proprotein convertase subtilisin/kexin type 9 (PCSK9) rs7552841, known variants that modulate circulating lipids, may influence serum Lp(a) levels (P < 0.05). Conclusion: Circulating Lp(a) combined with transaminases may represent a novel noninvasive biomarker to predict advanced fibrosis in patients with NAFLD.

Hyperlipidaemia in primary biliary cholangitis: treatment, safety and efficacy

Primary biliary cholangitis (PBC) is an autoimmune liver disease associated with altered lipoprotein metabolism, mainly cholesterol. Hypercholesterolaemia, a major modifiable risk factor for cardiovascular disease in the general population, occurs in 75%-95% of individuals with PBC. The impact of hypercholesterolaemia on cardiovascular risk in PBC, however, is controversial. Previous data have shown that hypercholesterolaemia in PBC is not always associated with an increase in cardiovascular events. However, patients with PBC with cardiovascular risk factors may still warrant cholesterol-lowering therapy. Treatment of hypercholesterolaemia in PBC poses unique challenges among primary care providers due to concerns of hepatotoxicity associated with cholesterol-lowering medications. This review summarises the current understanding of the pathophysiology of hypercholesterolaemia in PBC and its pertinent cardiovascular risk. We will also discuss indications for treatment and the efficacy and safety of available agents for hypercholesterolaemia in PBC.

Risk of Cardiovascular Events in Patients with Primary Biliary Cholangitis - Systematic Review

Background and Aims: Hypercholesterolemia is a common finding in patients with primary biliary cholangitis (PBC) and is a well-defined risk factor for cardiovascular disease. However, studies have been mixed on whether PBC patients do, in fact, have higher cardiovascular risk. The aim of this study is to review the current literature and provide an evidence-based assessment of cardiovascular risk in PBC patients. Methods: We performed a systematic literature search on PubMed regarding patients with PBC and cardiovascular events from the database inception to July 1, 2017. A total of 33 articles fulfilling our inclusion criteria were found. Results: The majority of the studies evaluated yielded no statistically significant difference in cardiovascular disease in the PBC population compared to the general public. However, some reports found a statistically significantly increase in coronary artery disease. Several studies have looked at the specific lipid profile of patients with PBC with hypocholesteremia. While these lipid abnormalities differ by stage of disease, there is evidence to suggest that the specific lipid profile in PBC may have lower atherogenicity than in patients with hypercholesterolemia without PBC. Studies looking at patients with PBC with other risk factors for cardiovascular disease, such as hypertension and metabolic syndrome, have consistently found a higher risk for cardiovascular disease in these patients. Statin treatment is effective in reducing lipid levels and possibly improving endothelial inflammation in patients with PBC with hypercholesterolemia. Conclusions: There is not enough evidence to suggest an increased risk of cardiovascular disease in patients with PBC with hypercholesterolemia, except for those individuals with concomitant features of metabolic syndrome. In patients with PBC with no additional cardiovascular risk factors, individual risk/benefit discussion on lipid-lowering treatment should be considered.

Lipoprotein (a): impact by ethnicity and environmental and medical conditions

Levels of lipoprotein (a) [Lp(a)], a complex between an LDL-like lipid moiety containing one copy of apoB, and apo(a), a plasminogen-derived carbohydrate-rich hydrophilic protein, are primarily genetically regulated. Although stable intra-individually, Lp(a) levels have a skewed distribution inter-individually and are strongly impacted by a size polymorphism of the LPA gene, resulting in a variable number of kringle IV (KIV) units, a key motif of apo(a). The variation in KIV units is a strong predictor of plasma Lp(a) levels resulting in stable plasma levels across the lifespan. Studies have demonstrated pronounced differences across ethnicities with regard to Lp(a) levels and some of this difference, but not all of it, can be explained by genetic variations across ethnic groups. Increasing evidence suggests that age, sex, and hormonal impact may have a modest modulatory influence on Lp(a) levels. Among clinical conditions, Lp(a) levels are reported to be affected by kidney and liver diseases.

[Effect of biliary obstruction on lipoprotein(a) concentration]

OBJECTIVES

This study was appointed to determine the correlation between the concentration of lipoprotein(a) [Lp(a)], apolipoproteins and lipids with biochemical parameters of liver function in a group of patients with reversible cholestasis. We have also determined the concentration of these parameters once solved the biliary obstruction process.

MATERIAL AND METHODS

Eighteen adults over 17 years with extrahepatic cholestasis were included in the study on a prospective basis, and we determined in them biochemical liver function parameters and lipoprotein metabolism parameters, particularly Lp(a) before and after unblocking.

RESULTS

The concentration of Lp(a) prior to desobstruction was inverse and statistically significantly correlated with the concentration of gamma glutamyl transpeptidase (correlation coefficient [r] = -0.757, P = .018). The concentration of Lp(a) (median = 2.66 mg/dL, interquartile range = 5,62) showed a statistically significant increase (median = 9.72 mg/dL, interquartile range = 28.76, P < .001), once the unblocking was performed. Concentrations of total cholesterol and triglycerides had a statistically significant decrease, and HDL cholesterol and apolipoprotein A-1 showed a statistically significant increase once the unblocking was carried out.

CONCLUSIONS

The concentration of Lp(a) is decreased during cholestasis, although there is a significant simultaneous hypercholesterolemia. Cholestasis has a causal role in lowering Lp(a), because the unblocking of bile duct recovers Lp(a) concentration. Our study supports the concept that bile acids exert a controlling effect on the synthesis of Lp(a) and open a mechanism for the treatment of hyper Lp(a).

Impact of viral hepatitis on apo- and lipoprotein status in blood

OBJECTIVES

To investigate the effect of viral hepatitis on serum levels of apo- and lipoproteins in different forms of liver diseases.

MATERIALS AND METHODS

One hundred and thirty adult patients and 100 healthy age- and gender-matched control individuals participated in this study. Patients were grouped according to four types of liver disease: acute viral hepatitis, chronic active hepatitis (CAH), cirrhosis of the liver and fulminant hepatic failure.

RESULTS

Hepatitis B virus, C virus and E virus (HEV) infections were recorded in different combinations in these patients, but viral infections of hepatitis A and D were not seen in any of the patient groups. The results of lipo- and apoprotein analysis showed different patterns. The low-density lipoprotein value was high in the CAH group. In the other three groups, low-density lipoprotein level was comparable to the control value. The high-density lipoprotein level (p = 0.02) was significantly low in all groups except in the cirrhosis group. Apo-A was significantly reduced in the acute viral hepatitis and fulminant hepatic failure groups, whereas Apo-B level was low in the CAH and cirrhosis groups. The lipoprotein (a) level in these groups was low, compared to control.

CONCLUSION

No apparent relationship was observed between etiological viruses and ensuing changes in lipid/lipoprotein profile..

Primary biliary cirrhosis

Primary biliary cirrhosis is a chronic cholestatic liver disease of adults. This disorder is characterised histologically by chronic non-suppurative destruction of interlobular bile ducts leading to advanced fibrosis, cirrhosis, and liver failure. The precise aetiopathogenesis of primary biliary cirrhosis remains unknown, although dysregulation of the immune system and genetic susceptibility both seem to be important. Affected patients are typically middle-aged women with abnormal serum concentrations of alkaline phosphatase. Presence of antimitochondrial antibody in serum is almost diagnostic of the disorder. Identification of primary biliary cirrhosis is important, because effective treatment with ursodeoxycholic acid has been shown to halt disease progression and improve survival without need for liver transplantation. However, therapeutic options for disease-related complications-including fatigue and metabolic bone disease-remain unavailable. Mathematical models have been developed that accurately predict the natural history of primary biliary cirrhosis in individuals. Despite advances in understanding of the disease, it remains one of the major indications for liver transplantation worldwide.

Basal and post-methionine serum homocysteine and lipoprotein abnormalities in patients with chronic liver disease

BACKGROUND

Lipoprotein abnormalities are commonly found in chronic liver diseases (CLDs), particularly hypercholesterolemia in primary biliary cirrhosis (PBC). However, affected patients may not be at increased risk of coronary heart disease. Cirrhotic patients display impaired methionine clearance, and an increased level of homocysteine, a methionine metabolite, is an independent risk factor for coronary heart disease. Thus, we hypothesized that the low risk of coronary heart disease in patients with CLD may be related to low serum levels of homocysteine. The aim of this study was to test this hypothesis after methionine load and to describe the serum lipoprotein profile in patients with PBC and in patients with hepatocellular liver disease.

METHODS

Fifteen female patients (mean age, 58.2 +/- 11.7 years) with PBC, 15 female patients (mean age, 54.5 +/- 9.6 years) with other causes of CLD, and 15 healthy sex- and age-matched controls were given L-methionine (50 mg/kg of ideal body weight). Basal fasting serum homocysteine level and 2, 4, and 6 hours of post-methionine load were determined using high-performance liquid chromatography with a fluorometric detector. Levels of fasting serum cholesterol, triglycerides, high-density lipoprotein (HDL), low-density lipoprotein (LDL), lipoprotein (a) (Lp(a)), and apoprotein B were also determined.

RESULTS

Results showed that mean basal and post-methionine load (6 hours) serum homocysteine levels were statistically significantly higher in the patients with PBC and with CLD than in the control group (P=0.04) and that levels of serum cholesterol, LDL, HDL, and apoprotein B were significantly higher in the PBC patients than in the other two groups (P < or = 0.05). There was no correlation between any of these parameters and the severity of liver disease. Serum HDL was significantly lower in the CLD group (P < or = 0.05) and correlated with severity of liver disease. There was no significant difference in serum cholesterol, LDL, or apoprotein B between the CLD group and the controls. Serum triglyceride and Lp(a) levels were similar for all three groups.

CONCLUSIONS

In contrast to previous reports, the site of the methionine metabolic impairment was found to be below the homocysteine synthesis level. For most patients with CLD, factors other than serum homocysteine or Lp(a) are responsible for the reduction in the risk of coronary heart disease. Further studies with larger samples are needed.

Serum apolipoprotein(a) concentrations and Apo(a) phenotypes in patients with liver cirrhosis

OBJECTIVE

The liver is the major site of apolipoprotein(a) synthesis, and an inverse correlation between the size of apolipoprotein(a) isoforms and its serum levels have been described. We evaluated the Apo(a) serum levels and its isoforms in patients with liver cirrhosis at different stages of the disease (Childe Turcotte classification), and during the characteristic phase of liver synthesis decline.

METHODS

We studied 84 patients with liver cirrhosis and 185 control subjects with normal liver function.

RESULTS

Apo(a) serum levels were significantly lower (p < 0.01) in cirrhotic patients and, after 24 months, six patients showing a change from class A to class B had a statistically significant decrease in Apo(a) concentrations (p = 0.0313). Moreover, our data showed an inversion of the small/large isoforms ratio in patient with cirrhosis in spite of the reduction in plasma concentration.

CONCLUSION

We showed a reduction of Apo(a) serum concentrations in a large number of patients with cirrhosis and, for the first time, during the characteristic phase of liver synthesis decline, confirming the liver as the major site of Apolipoprotein(a) synthesis. Moreover we showed in the cirrhotic patients that the normal correlation between Apo(a) isoforms and Apo(a) concentrations is not conserved and the low levels are not dependent upon a high prevalence of large isoforms.

Primary biliary cirrhosis: clinical and associated autoimmune features and natural history

Primary biliary cirrhosis, a chronic liver disease, predominately affects middle-aged women. The diagnosis is established by the presence of disease-specific autoantibodies and compatible liver histology showing focal immune-mediated damage to the intrahepatic bile ducts. Patients now are detected prior to the onset of symptoms typical of cholestasis with abnormal liver function tests, or even prior to the onset of abnormal liver function tests, with positive antimitochondrial antibodies. Earlier diagnosis is changing not only our appreciation of the prevalence of this condition, but also of the natural history. The disease appears to be heterogeneous with some patients having a slow progression and a normal life-expectancy, although other patients have a more aggressive course developing symptoms and end-stage disease that leads to death or liver transplantation.

Lipids and lipid-activated vitamins in chronic cholestatic diseases

Primary biliary cirrhosis, primary sclerosing cholangitis and autoimmune cholangiopathy are cholestatic liver diseases of unknown cause. Destruction of small to medium bile ducts (in primary biliary cirrhosis and autoimmune cholangiopathy) and large bile ducts (in primary sclerosing cholangitis) leads to progressive cholestasis, liver failure and end-stage liver disease. A variety of abnormalities in lipid metabolism have been described in primary biliary cirrhosis, and range from alterations in serum lipid levels and lipoprotein subsets to deranged metabolism of cholesterol. Progressive cholestasis and, consequently, decreased small intestinal bile acid concentrations in these cholestatic liver disease can also lead to impaired absorption of fats and fat-soluble vitamins, resulting in steatorrhea and deficiencies in vitamins A, D, E, and K. This article focuses on abnormalities in lipid metabolism in primary biliary cirrhosis and primary sclerosing cholangitis, and on lipid-activated vitamin deficiencies in these disorders.

Elevated levels of lipoprotein(a) in women with preeclampsia

OBJECTIVE

We examined the hypothesis that lipoprotein(a) levels are elevated in preeclampsia and associated with severity of the disease.

STUDY DESIGN

Plasma lipoprotein(a) levels were measured in 24 normal pregnant women, 18 mild, and 8 severe preeclamptic women using an enzyme-linked immunosorbent assay method. Kruskall-Wallis one-way analysis of variance was used to evaluate the difference in plasma lipoprotein(a) among different groups. The Mann-Whitney U test was used to compare the differences between two groups.

RESULTS

The plasma lipoprotein(a) levels were increased in pregnant women with both severe preeclampsia (median 826.9 mg/L [interquartile range 590.7, 986.9 mg/L], n = 8, p < 0.0001) and mild preeclampsia (median 357.7 mg/L [interquartile range 208.0, 477.1 mg/L], n = 18, p < 0.0001) compared with normal pregnancy (median 78.5 mg/L [interquartile range 45.2, 127.9 mg/L], n = 24). The lipoprotein(a) level was significantly higher in severe than in mild preeclampsia (p < 0.001).

CONCLUSION

This study has demonstrated that lipoprotein(a) levels are elevated in preeclampsia and associated with severity of the disease. It may serve as a marker of the pathogenic process.

Lipoprotein (a) serum levels in patients with hepatocarcinoma

Lipoprotein (a) [Lp(a)] is synthesised by liver cells, and patients with liver cirrhosis (LC) show low serum levels of Lp(a) associated with the degree of liver failure. On the contrary, increased serum levels of Lp(a) have been reported in patients with cancer. In this report, the behaviour of Lp(a) serum levels in patients with hepatocarcinoma (HC), a complication of LC, has been evaluated with the aim to study whether HC cells were able to cause an increase of serum concentrations of this lipoprotein when impaired liver protein synthesis is present. We selected eighteen patients affected by LC + HC, eighteen patients matched for sex, age and degree of liver failure with LC only, and eighteen patients with other cancer types. A significant increase of serum levels of Lp(a) was observed in patients affected by LC + HC or other cancer types compared with healthy subjects. Forty-four percent of LC + HC patients showed Lp(a) values more than 70.4 Units/dl, i.e., the upper limit of values observed in patients with LC only. Lp(a) serum concentrations were significantly associated with serum albumin both in LC and in LC + HC but not in other cancer-type patients. Thus, comparing patients with similar serum albumin concentrations, Lp(a) serum levels were significantly higher in patients with LC + HC than in patients with only LC and quite similar to those observed in patients with other cancer types. In conclusion, HC cells, in vivo, seem able to produce a greater amount of Lp(a) despite the reduced liver protein synthesis typical of LC.

Abnormalities of serum apo A1 containing lipoprotein particles in patients with primary biliary cirrhosis

Patients with primary biliary cirrhosis (PBC) do not appear to have an increased risk of cardiovascular disease despite elevations in serum cholesterol. Recent evidence has pointed to LpA1 (an apo A1 containing particle which contains apo A1 but not apo A2) in protecting against atherosclerosis. The aim of this study was to investigate apo Al containing particles in the serum of patients with PBC. Lipids and apolipoproteins were measured in 31 patients with PBC (30 females) and 27 control subjects (26 females). Patients were divided into 3 groups: group 1 with bilirubin < 18 micromol/l (n = 17); group 2 with bilirubin > 18 micromol/l (n = 11); and group 3 with end stage liver disease (ESLD, n = 3). As expected group 1 and 2 patients had higher total cholesterol, HDL cholesterol and phospholipids than control subjects. Apo B and apo A1 concentrations were similar to control subjects. However, LpA1 was greatly increased: 0.96 g/l (0.60-1.50), median (range) in group 1 and 1.09 g/l (0.75-1.33) in group 2 versus 0.62 g/l (0.45-0.93) for controls both P < 0.005 and the percentage of total apo A1 in the LpA1 fraction was increased: 54.8% (37.9-63.4) in group 1 and 55.7% (47.8-73.7) in group 2 versus 36.8% (25.1-49.1) for controls, both P < 0.005. Apo A2 concentration was reduced in group 1 0.38 g/l (0.30-0.51) and group 2 0.31 g/l (0.14-0.58) versus controls 0.43 g/l (0.36-0.57), P < 0.05 and P < 0.005 respectively. Patients with ESLD had reduced HDL cholesterol, apo A1, LpA1 and apo A2 compared to controls. These results suggest that PBC is associated with an altered distribution of apo A1 favouring an increased concentration of the protective LpA-I particles. Increased LpA1 concentration may be one of the factors contributing to the paradoxically low incidence of atherosclerosis in PBC patients.

Primary biliary cirrhosis in The Netherlands. An analysis of associated diseases, cardiovascular risk, and malignancies on the basis of mortality figures

BACKGROUND/METHODS

In 1979 death rate registration for primary biliary cirrhosis (PBC) became available in The Netherlands. In the 14-year period 1979-92, 417 persons died of and 179 with PBC. We investigated secondary causes of death using standardized mortality ratios (SMR) (1.0 as reference, P < 0.001 regarded as significant).

RESULTS

Median age was 70-74 (35 to > 85) years. Secondary causes of death originated from the circulatory, digestive, and respiratory tracts and malignancies. Younger persons (< 60 years), dying of PBC, more often died with "toxicity related to immunosuppression' than older persons (P < 0.01). Younger persons (< 60) dying with PBC, more often died of hepatocellular carcinoma (HCC) than older ones (P < 0.05). In patients with PBC the frequency of HCC (SMR, 25.5; P < 0.0001) and diseases of the musculoskeletal system/connective tissue (SMR, 5.1; P < 0.0001) was higher than in the general population. Malignancies in general (SMR, 0.7), pancreatic carcinoma (SMR, 2.5), breast cancer (SMR, 0.1) and diseases of the circulatory system (SMR, 0.8) differed but not significantly (P < 0.05 - < 0.01). No difference existed in the localization of malignancies in patients dying of as compared with those dying with PBC.

CONCLUSIONS

Deaths occurred predominantly in the older age classes, with an age-related difference in some associated disorders. Patients with PBC showed an increased risk of HCC and diseases of the musculoskeletal system. Similar studies from different countries are needed.

Lipoprotein(a) concentration and phenotypes in primary biliary cirrhosis

We studied a selected group of 39 female patients suffering from primary biliary cirrhosis (PBC). This disease is characterized by typical lipoprotein alterations and elevated concentrations of serum cholesterol. Despite the increased concentration of atherogenic lipoproteins, enhanced atherogenesis is not characteristic of PBC. Serum total cholesterol, triglycerides, HDL2 and HDL3-cholesterol concentrations were measured by enzymatic methods or in combination with precipitation procedures. Apolipoproteins were determined by using immunonephelometric methods. ELISA sandwich method was used for lipoprotein(a) determinations. Apoprotein(a) phenotyping (isoforms) was performed by Western blotting with specific antibodies. The concentrations of serum lipids, lipoproteins and apoproteins (AI, AII and B) were found in the range of earlier investigations. The serum lipoprotein(a) concentration did not differ between the PBC patients and control subjects (10.0/0.1-54/, median 2.55 vs. 11.5/0-75/, median 5.2 mg/dl). In the advanced stages of PBC we found a higher number of patients with low lipoprotein concentration (lower than 1 mg/dl). In patients with shorter durations and milder histological alterations high HDL2 cholesterol subfractions has been detected (stage I = 0.42 +/- 0.18, stage II = 0.53 +/- 0.29 and stage III = 0.62 +/- 0.41 vs. stage IV = 0.26 +/- 0.15 mmol/l, P < 0.05). Despite the elevation of atherogenic lipoproteins, high HDL2-cholesterol and normal lipoprotein(a) concentrations may be one of the reasons why patients with advanced PBC are not placed at increased risk for atherosclerosis.

Lipoprotein(a) in renal disease

Lipoprotein(a) [Lp(a)] is a genetically determined risk factor for atherosclerotic vascular disease. Several studies have described a correlation between high Lp(a) plasma levels and coronary heart disease, stroke, and peripheral atherosclerosis. In healthy individuals Lp(a) plasma concentrations are almost exclusively controlled by the apolipoprotein(a) [apo(a)] gene locus on chromosome 6q2.6-q2.7. More than 30 alleles at this highly polymorphic gene locus determine a size polymorphism of apo(a). There exists an inverse correlation between the size (molecular weight) of apo(a) isoforms and Lp(a) plasma concentrations. Average Lp(a) levels are high in individuals with low molecular weight isoforms and low in those with high molecular weight isoforms. Mean Lp(a) plasma levels are elevated over controls in patients with renal disease. Patients with nephrotic syndrome exhibit excessively high Lp(a) plasma concentrations, which can be reduced with antiproteinuric treatment. The mechanism underlying this elevation is unclear, but the general increase in protein synthesis caused by the liver due to high urinary protein loss is a likely explanation. Patients with end-stage renal disease (ESRD) also have elevated Lp(a) levels. These are even higher in patients treated by continuous ambulatory peritoneal dialysis than in those receiving hemodialysis. Lipoprotein(a) concentrations decrease to values observed in controls matched for apo(a) type following renal transplantation. This clearly demonstrates the nongenetic origin of Lp(a) elevation in ESRD. Both the increase in ESRD and the decrease following renal transplantation are apo(a) phenotype dependent. Only patients with high molecular weight phenotypes show the described changes in Lp(a) levels. In patients with low molecular weight types the Lp(a) concentrations remain unchanged during both phases of renal disease. As in the general population, Lp(a) is a risk factor for cardiovascular events in ESRD patients. In this patient group the apo(a) phenotype seems to be equally or better predictive of the degree of atherosclerosis than is Lp(a) concentration. Further prospective studies will be necessary to confirm these observations. Whether Lp(a) also plays a key role in the pathogenesis and progression of renal diseases needs further study. Controversial data on the role of the kidney in Lp(a) metabolism result from insufficient sample sizes of several studies. Due to the broad range and skewed distribution of Lp(a) plasma concentrations, large study groups must be investigated to obtain reliable results.

Lipoprotein(a) in health and disease

Lipoprotein(a) [Lp(a)] represents an LDL-like particle to which the Lp(a)-specific apolipoprotein(a) is linked via a disulfide bridge. It has gained considerable interest as a genetically determined risk factor for atherosclerotic vascular disease. Several studies have described a correlation between elevated Lp(a) plasma levels and coronary heart disease, stroke, and peripheral atherosclerosis. In healthy individuals, Lp(a) plasma concentrations are almost exclusively controlled by the apo(a) gene locus on chromosome 6q2.6-q2.7. More than 30 alleles at this highly polymorphic gene locus determine a size polymorphism of apo(a). There exists an inverse correlation between the size (molecular weight) of apo(a) isoforms and Lp(a) plasma concentrations. The standardization of Lp(a) quantification is still an unresolved task due to the large particle size of Lp(a), the presence of two different apoproteins [apoB and apo(a)], and the large size polymorphism of apo(a) and its homology with plasminogen. A working group sponsored by the IFCC is currently establishing a stable reference standard for Lp(a) as well as a reference method for quantitative analysis. Aside from genetic reasons, abnormal Lp(a) plasma concentrations are observed as secondary to various diseases. Lp(a) plasma levels are elevated over controls in patients with nephrotic syndrome and patients with end-stage renal disease. Following renal transplantation, Lp(a) concentrations decrease to values observed in controls matched for apo(a) type. Controversial data on Lp(a) in diabetes mellitus result mainly from insufficient sample sizes of numerous studies. Large studies and those including apo(a) phenotype analysis came to the conclusion that Lp(a) levels are not or only moderately elevated in insulin-dependent patients. In noninsulin-dependent diabetics, Lp(a) is not elevated. Conflicting data also exist from studies in patients with familial hypercholesterolemia. Several case-control studies reported elevated Lp(a) levels in those patients, suggesting a role of the LDL-receptor pathway for degradation of Lp(a). However, recent turnover studies rejected that concept. Moreover, family studies also revealed data arguing against an influence of the LDL receptor for Lp(a) concentrations. Several rare diseases or disorders, such as LCAT- and LPL-deficiency as well as liver diseases, are associated with low plasma levels or lack of Lp(a).