Deepak Bhatnagar

Serum paraoxonase activity in familial hypercholesterolaemia and insulin-dependent diabetes mellitus

The activity of serum paraoxonase, an enzyme located on high-density lipoprotein, has been investigated in familial hypercholesterolaemia (FH) and insulin dependent diabetes mellitus (IDDM). Increases in total serum cholesterol and apolipoprotein B were present in both FH and IDDM compared to healthy controls and in the patients with IDDM, serum triglycerides were also raised. The serum HDL-cholesterol concentrations in controls and patients with FH and IDDM did not differ significantly. Serum paraoxonase activity was significantly lower in both the FH and IDDM populations than in controls (P less than 0.001 and P less than 0.01, respectively). 72% of the FH population and 67% of the IDDM population were in the lower half of the frequency distribution for serum paraoxonase (activity of less than 112 U/l). It is likely that the common factor related to low paraoxonase activity is hyperlipidaemia. It is possible that paraoxonase has a physiological role in lipid metabolism and that decreases in its activity may accelerate atherogenesis.

Rapid screening for specific mutations in patients with a clinical diagnosis of familial hypercholesterolaemia

We describe a rapid screening procedure to identify known DNA sequence changes in individuals diagnosed as having heterozygous familial hypercholesterolaemia (FH). The screening is made possible by combining a rapid DNA extraction protocol and small scale polymerase chain reaction DNA amplification, followed by oligonucleotide melting or restriction enzyme digestion. We have screened for two different mutations; firstly a mutation in the apolipoprotein B (apo B) gene that results in the substitution of glutamine (Gln) for arginine (Arg) at amino acid residue 3500 (apo B3500 mutation). Apo B is the principal component of the protein moiety of low density lipoprotein (LDL) and the mutation reduces the affinity for the LDL receptor (LDL-R). Secondly we have screened for a point mutation in the LDL-R gene itself that creates a new Pst I restriction enzyme site. This mutation in the LDL-R gene (LDL-R664 mutation) results in the substitution of leucine (Leu) for proline (Pro) at amino acid 664 and is known to slow processing of the LDL-R precursor to the mature form and to reduce the affinity of the receptor on the cell surface for LDL. In 77 unrelated patients with a clinical diagnosis of FH two out of 77 (2.6%) were positive for the apo B3500 mutation. Three (3.9%) were positive for the LDL-R664 mutation. Thus these two mutations might account for 5-6% of patients in the U.K. with a clinical diagnosis of FH (5000-6000 people).(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercholesterolaemia and its management.

Hypercholesterolaemia is one of the major causes of atherosclerosis. Although there are many causes, hypercholesterolaemia is the permissive factor that allows other risk factors to operate.1 The incidence of coronary heart disease is usually low where population plasma cholesterol concentrations are low.2 In Britain coronary heart disease is a major cause of mortality, and a recent Department of Health survey suggested that the average plasma cholesterol concentration in the United Kingdom was 5.9 mmol/l, much higher than the 4 mmol/l seen in rural China and Japan, where heart disease is uncommon.3 Many studies before and after the introduction of statins have indicated that reducing the prevalence of hypercholesterolaemia is an important means of decreasing coronary risk.nnCholesterol plays an important role as the precursor for steroid hormones and bile acids and it is essential for the structural integrity of cell membranes. It is transported in the body in lipoproteins. Figure 1⇓ shows the role of cholesterol in lipoprotein metabolism.nnnnFig 1 The role of cholesterol in the metabolism of lipoprotein. Adapted from Charlton-Menys4nnnnConventionally the upper limit for laboratory reference ranges is based on the 95th or 90th centile for a healthy population. This does not apply to plasma cholesterol, however, as several studies show that the epidemiological relation between plasma cholesterol and risk of coronary heart disease extends to the lower end of the cholesterol distribution. Although the relation becomes progressively steeper, there is no obvious threshold below which it ceases to exist.5 Therefore, it is more rational to base a desirable or healthy concentration of plasma cholesterol on the value at which coronary risk is considered unacceptably high. Most patients developing coronary heart disease have plasma cholesterol concentrations that are likely to be between the 30th and 90th centile for their population …

Outcome of case finding among relatives of patients with known heterozygous familial hypercholesterolaemia

Abstract Objectives: To assess the feasibility of detecting new cases of heterozygous familial hypercholesterolaemia by using a nurse led genetic register. Design: Case finding among relatives of patients with familial hypercholesterolaemia. Setting: Two lipid clinics in central and south Manchester. Subjects: 259 (137 men and 122 women) probands and 285 first degree relatives. Results: Of the 200 first degree relatives tested, 121 (60%) had inherited familial hypercholesterolaemia. The newly diagnosed patients were younger than the probands and were generally detected before they had clinically overt atherosclerosis. Concentrations of serum cholesterol were, respectively, 8.4 (1.7 SD) mmol/l and 8.1 (1.9 SD) mmol/l in affected men and women and 5.6 (1.0 SD) mmol/l and 5.6 (1.1 SD) mmol/l in unaffected men and women. Screening for risk factors as recommended in recent guidelines for coronary heart disease prevention would have failed to identify most of the affected relatives in whom hypertension, diabetes mellitus, cigarette smoking, and obesity were uncommon. Conclusions: By performing cholesterol tests on 200 relatives, 121 new patients with familial hypercholesterolaemia were discovered. Because 1 in 500 people in the UK are affected by this condition, to detect a similar number by population screening over 60 000 tests would be required, and only a few of these patients would have been detected had cholesterol testing been restricted to those with other risk factors for coronary heart disease. A case exists for organising a genetic register approach, linking lipid clinics nationally.

The use of statins in people at risk of developing diabetes mellitus: Evidence and guidance for clinical practice

Reducing low-density lipoprotein cholesterol (LDL-C) levels using statins is associated with significant reductions in cardiovascular (CV) events in a wide range of patient populations. Although statins are generally considered to be safe, recent studies suggest they are associated with an increased risk of developing Type 2 diabetes (T2D). This led the US Food and Drug Administration (FDA) to change their labelling requirements for statins to include a warning about the possibility of increased blood sugar and HbA1c levels and the European Medicines Agency (EMA) to issue guidance on a small increased risk of T2D with the statin class. This review examines the evidence leading to these claims and provides practical guidance for primary care physicians on the use of statins in people with or at risk of developing T2D. Overall, evidence suggests that the benefits of statins for the reduction of CV risk far outweigh the risk of developing T2D, especially in individuals with higher CV risk. To reduce the risk of developing T2D, physicians should assess all patients for T2D risk prior to starting statin therapy, educate patients about their risks, and encourage risk-reduction through lifestyle changes. Whether some statins are more diabetogenic than others requires further study. Statin-treated patients at high risk of developing T2D should regularly be monitored for changes in blood glucose or HbA1c levels, and the risk of conversion from pre-diabetes to T2D should be reduced by intensifying lifestyle changes. Should a patient develop T2D during statin treatment, physicians should continue with statin therapy and manage T2D in accordance with relevant national guidelines.

Abnormalities of VLDL, IDL, and LDL characterize insulin-dependent diabetes mellitus.

To identify abnormalities of serum lipoprotein composition and concentration that were specific to insulin-dependent diabetes mellitus (IDDM), the procedure of discontinuous gradient ultracentrifugation was employed to isolate lipoprotein fractions in 44 patients with IDDM, 24 nondiabetic subjects with similar lipid and lipoprotein concentrations, and 19 healthy normocholesterolemic (less than 5.2 mmol/l [less than 200 mg/dl]) subjects. The mass concentration of low density lipoprotein (LDL) was greater in IDDM than in both control groups. The free cholesterol to phospholipid ratio in large very low density lipoprotein (VLDL) was greatest in IDDM in comparison with both of the other groups. The contribution of triglyceride to total large VLDL mass was greater, whereas that of phospholipids was lower, in IDDM than in the dyslipidemic nondiabetic group. Protein concentration was reduced and phospholipid increased in small VLDL in IDDM in comparison with both control groups, and the contribution from protein to lipoprotein mass was least in IDDM. Similarly in intermediate density lipoprotein (IDL), the protein concentration and its contribution to overall mass was also lower in IDDM than in either control group, but by contrast, the phospholipid content was increased. The cholesteryl ester to protein ratio was highest in both small VLDL and IDL in IDDM in comparison with both control groups, whereas the free cholesterol to phospholipid ratio in IDL was least in IDDM. In LDL, total cholesterol and triglyceride concentrations were greatest and the contribution from protein to lipoprotein mass was least in IDDM in comparison with both control groups. The LDL free cholesterol to phospholipid ratio was greater in IDDM than in dyslipidemic control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of immunosuppressive therapy on lipoprotein(a) and other lipoproteins following renal transplantation

Coronary heart disease (CHD) is more common in patients with chronic renal failure and is a major cause of death after renal transplantation. Elevated serum levels of lipoprotein(a) (Lp(a)) are a known risk factor for CHD in the general population and levels have been reported to be increased in renal transplant recipients. It has been suggested that cyclosporin may elevate Lp(a) levels. We therefore measured the serum concentration of Lp(a) in 50 renal transplant recipients who were receiving cyclosporin alone as immunosuppressive therapy and 50 who were treated with azathioprine and prednisolone, but not cyclosporin. The patients attended two renal transplant centres, one where cyclosporin alone was used as immunosuppressive treatment when possible and another where many patients commenced on azathioprine and prednisolone remain on this medication rather than cyclosporin. Patients in each group were matched for age and sex, but the time since transplantation was greater in those not receiving cyclosporin. Transplant function, obesity and the underlying cause of renal disease were similar in both groups of patients. Median Lp(a) concentration in the cyclosporin monotherapy group was 32.0 (range <0.8-140.3) mg/dl and was significantly (p < 0.05) greater than that of the azathioprine and prednisolone group which was 18.3 (range <0.8-167.7) mg/dl. The serum high-density lipoprotein (HDL) cholesterol concentration, which was 1.24 +/- 0.39 mmol/l (mean +/- SD) in patients receiving cyclosporin, was significantly (p < 0.05) less than that of those treated with azathioprine and prednisolone in whom it was 1.41 +/- 0.40 mmol/l. The lower level in those on cyclosporin was due to a decrease in the HDL2 subfraction. Serum lipid and lipoprotein concentrations were otherwise similar in the two groups of patients. The serum level of Lp(a) after renal transplantation may be influenced by the choice of immunosuppressive therapy.

Precise measurement of glycated serum albumin by column affinity chromatography and immunoturbidimetry

A precise and easy method for measuring glycated serum albumin using affinity chromatography and immunoturbidimetry on a centrifugal analyser, ensuring complete recovery of serum albumin is described.

Relative Clinical Usefulness of Glycosylated Serum Albumin and Fructosamine During Short-Term Changes In Glycemic Control in IDDM

Serial changes in glycosylated blood proteins and direct measures of glycemia were studied in 100 subjects with insulin-dependent diabetes mellitus (IDDM) over a 6-wk period while attempts were made to improve glycemic control. All measures of glycemic control improved significantly (P < .001). Mean ± SE glycosylated hemoglobin (HbA,) fell from 9.1 ± 0.2 to 8.0 ± 0.1%, glycosylated serum albumin (GSA) from 9.8 ± 0.4 to 7.3 ± 0.3%, and fructosamine from 3.92 ± 0.08 to 3.42 ± 0.07 mM. Fasting blood glucose levels fell from 11.1 ± 0.6 to 8.1 ± 0.7 mM, mean blood glucose levels from 12.5 ± 0.3 to 8.8 ± 0.3 mM, and the M value from 118 ± 7 to 40 ± 3 U. Mean percentage changes in direct measures of glycemia (32–66%) and GSA (29%) were greater than for fructosamine (11%) or HbA, (12%) levels (P < .001). Furthermore, the correlation between the change in GSA and changes in direct measures of glycemia over the initial 2-wk period was significantly different from the corresponding correlations between direct measures of glycemia and fructosamine over this period (P < .05-.01). Changes in GSA also correlated more closely than HbA, or fructosamine did with direct measures of glycemia after 4 and 6 wk. The Spearman rank-correlation coefficient (rs) of absolute changes in GSA, fructosamine, and HbA1 after 2–6 wk ranged from 0.27 to 0.57, confirming that the three measures responded differently to changing glycemic control. Cross-sectional analysis between different measures of glycemia demonstrated considerable variation in the degree of association at different times, with the closest correlations observed after 6 wk when glycemic control was relatively stable. GSA and fructosamine levels correlated with levels of mean blood glucose and M values estimated 2–4 wk earlier. GSA appears to be a more sensitive indicator of short-term improvement in glycemic control and glycemic instability in IDDM than fructosamine or HbA1.

Diagnosis and screening for familial hypercholesterolaemia: finding the patients, finding the genes

Familial hypercholesterolaemia (FH) is a genetic disorder in which the concentration of serum cholesterol is elevated from birth and leads to premature coronary heart disease. FH is commonly caused by a mutation in the LDL receptor, but mutations in other genes can lead to a phenotype similar to FH. FH exhibits marked phenotypic variability due to genetic, metabolic and environmental factors. The presence of tendon xanthomata is the characteristic clinical sign seen in many patients with FH, but they may also have other non-specific signs of lipid disorders such as corneal arcus and xanthelasmata. Premature vascular disease is apparent in many patients. The wide variety of mutations and phenotypic variability have made it difficult to establish definite diagnostic criteria, but three sets of clinical criteria commonly used are the Simon Broome criteria, the Dutch Lipid Clinic criteria and the American criteria. FH screening fits the Wilson and Jungner recommendations for validity of a screening programme. Screening could be carried out on a population basis, in a clinical setting or by application to relatives of probands. This latter approach, termed cascade testing, appears to be the more cost-effective compared with population screening and can be carried out using clinical criteria or genetic testing, or by a combination of both methods. Clinicians need to be made more aware of the clinical features of FH and how to diagnose it in order to increase the index of suspicion and instigate appropriate treatment early, with the aim of preventing premature coronary heart disease.