Lipid metabolism in lipoatrophic diabetes

Apolipoprotein CIII and Angiopoietin-like Protein 8 are Elevated in Lipodystrophy and Decrease after Metreleptin

Context

Lipodystrophy syndromes cause hypertriglyceridemia that improves with leptin treatment using metreleptin. Mechanisms causing hypertriglyceridemia and improvements after metreleptin are incompletely understood.

Objective

Determine relationship of circulating lipoprotein lipase (LPL) modulators with hypertriglyceridemia in healthy controls and in patients with lipodystrophy before and after metreleptin.

Methods

Cross-sectional comparison of patients with lipodystrophy (generalized lipodystrophy n = 3; partial lipodystrophy n = 11) vs age/sex-matched healthy controls (n = 28), and longitudinal analyses in patients before and after 2 weeks and 6 months of metreleptin. The study was carried out at the National Institutes of Health, Bethesda, Maryland. Outcomes were LPL stimulators apolipoprotein (apo) C-II and apoA-V and inhibitors apoC-III and angiopoietin-like proteins (ANGPTLs) 3, 4, and 8; ex vivo activation of LPL by plasma.

Results

Patients with lipodystrophy were hypertriglyceridemic and had higher levels of all LPL stimulators and inhibitors vs controls except for ANGPTL4, with >300-fold higher ANGPTL8, 4-fold higher apoC-III, 3.5-fold higher apoC-II, 1.9-fold higher apoA-V, 1.6-fold higher ANGPTL3 (P < .05 for all). At baseline, all LPL modulators except ANGPLT4 positively correlated with triglycerides. Metreleptin decreased apoC-II and apoC-III after 2 weeks and 6 months, and decreased ANGPTL8 after 6 months (P < 0.05 for all). Plasma from patients with lipodystrophy caused higher ex vivo LPL activation vs hypertriglyceridemic control plasma (P < .0001), which did not change after metreleptin.

Conclusion

Elevations in LPL inhibitors apoC-III and ANGPTL8 may contribute to hypertriglyceridemia in lipodystrophy, and may mediate reductions in circulating and hepatic triglycerides after metreleptin. These therefore are strong candidates for therapies to lower triglycerides in these patients.

Metreleptin therapy lowers plasma angiopoietin-like protein 3 in patients with generalized lipodystrophy

BACKGROUND

Reduced triglyceride clearance due to impaired lipoprotein lipase-mediated lipolysis contributes to severe hypertriglyceridemia in lipodystrophy. Angiopoietin-like protein 3 (ANGPTL3) and 4 (ANGPTL4) impair clearance of triglycerides by inhibiting lipoprotein lipase. Whether circulating ANGPTL3/4 levels are altered in lipodystrophy and the effects of leptin replacement on these ANGPTLs are unknown.

OBJECTIVE

To examine if ANGPTL3/4 levels are elevated in patients with generalized lipodystrophy and assess the effects of leptin replacement on these ANGPTLs.

METHODS

Preleptin treatment plasma levels of ANGPTLs in patients with generalized lipodystrophy (n = 22) were compared with healthy controls (n = 39) using a post hoc case-control study design. In a prospective open-label study, we studied the effects of metreleptin therapy (16-32 weeks) on plasma ANGPTL3/4 in patients with generalized lipodystrophy.

RESULTS

Plasma ANGPTL3 (geometric mean [95% confidence interval]; 223 [182-275] vs 174 ng/mL [160-189], P = .02) but not ANGPTL4 levels (55 [37-81] vs 44 ng/mL [37-52], P = .26) were higher in patients with lipodystrophy compared with healthy controls. There was a significant decrease in total cholesterol, triglycerides, and glycosylated hemoglobin (A1C) levels following metreleptin therapy. After metreleptin, ANGPTL3 concentrations decreased significantly (223 [182-275] vs 175 ng/mL [144-214], P = .01) with no change in ANGPTL4 (55 [37-81] vs 48 ng/mL [32-73], P = .11).

CONCLUSIONS

These findings suggest that elevated plasma levels of ANGPTL3 in leptin-deficient states is attenuated with leptin therapy.

Congenital lipodystrophies and dyslipidemias

Lipodystrophies are rare acquired and genetic disorders characterized by the selective loss of adipose tissue. One key metabolic feature of patients with congenital inherited lipodystrophy is hypertriglyceridemia. The precise mechanisms by which the lack of adipose tissue causes dyslipidemia remain largely unknown. In recent years, new insights have arisen from data obtained in vitro in adipocytes, yeast, drosophila, and very recently in several genetically modified mouse models of generalized lipodystrophy. A common metabolic pathway involving accelerated lipolysis and defective energy storage seems to contribute to the dyslipidemia associated with congenital generalized lipodystrophy syndromes, although the pathophysiological changes may vary with the nature of the mutation involved. Therapeutic management of dyslipidemia in patients with lipodystrophy is primarily based on specific approaches using recombinant leptin therapy. Preclinical studies suggest a potential efficacy of thiazolidinediones that remains to be assessed in dedicated clinical trials.

Lipodystrophy: lessons in lipid and energy metabolism

PURPOSE OF REVIEW

Lipodystrophies are rare inherited and acquired disorders characterized by the selective loss of adipose tissue. Despite marked phenotypic and genotypic heterogeneity, most lipodystrophic syndromes predispose to similar metabolic complications seen in patients with obesity, such as insulin resistance, diabetes mellitus, hepatic steatosis and dyslipidemia. The purpose of this review is to highlight the current understanding of the mechanisms underlying dyslipidemia in patients with lipodystrophies.

RECENT FINDINGS

Marked hypertriglyceridemia and reduced levels of high-density lipoprotein cholesterol are commonly seen, and the severity of these metabolic abnormalities seems to be related to the extent of fat loss. The precise mechanisms by which the lack of adipose tissue causes hypertriglyceridemia remain unknown. Anecdotal kinetic studies in hyperglycemic patients with lipodystrophies have revealed accelerated lipolysis and increased free fatty acid turnover, which drives hepatic triglyceride and very low-density lipoprotein synthesis. Other mechanisms may also be involved in causing dyslipidemia and ectopic triglyceride accumulation in the liver and skeletal muscles that remain to be identified.

SUMMARY

Understanding the pathophysiology of dyslipidemia in these rare disorders of lipodystrophies may offer insights into the normal role of adipocytes in maintaining metabolic homeostasis, and its disturbances in common forms of obesity.

Lipid Evaluation in HIV-1-Positive Patients Treated with Protease Inhibitors

There is accumulating evidence that human immunodeficiency virus type 1 (HIV-1) protease inhibitors (PIs) can induce hyperlipidaemia. To evaluate the frequency and type of hyperlipidaemia in PI-treated patients, 98 outpatients were prospectively analysed for their lipoprotein characteristics at the Medizinische Hochschule in Hannover, Germany. Fifty-seven percent of the patients studied presented with hyperlipidaemia. Both hypertrigylceridaemia (type IV and V hyperlipoproteinaemia, 33%) and hypercholesterolaemia (type IIa hyperlipoproteinaemia, 6%) were detectable. The remaining 18% had a type IIb hyperlipoproteinaemia. Increased lipid levels were highly statistically significant compared to a control group of PI-naive HIV-1-infected patients [low-density lipoprotein (LDL) 146 mg/dl (range, 53–274 mg/dl) versus 105 mg/dl (range, 22–188 mg/dl; P=0.0006); very-low-density lipoprotein (VLDL) 35.5 mg/dl (5–253 mg/dl) versus 18 mg/dl (range, 3–94 mg/dl; P=0.0002)]. All PIs used (saquinavir, indinavir, nelfinavir and ritonavir) were associated with this variable form of hyperlipidaemia according to the Fredrickson classification. There was no significant correlation of any determined lipid value with the duration of treatment. A higher frequency of the apolipoprotein E2 allele and E4 allele was observed in the hyperlipidaemic subjects. Patients with excessive hypertriglyceridaemia showed a reduced lipoprotein lipase activity. Lipodystrophy was observed especially in hyperlipidaemic patients and to a lesser extent in normolipidaemic subjects. The frequency of hyperlipidaemic risk factors was surprisingly high in the group studied, which in turn may explain the proposed increased risk of atherogenesis in HIV-1 PI-treated patients. Therefore, PI-treated subjects should also be evaluated for their lipoprotein pattern, which may require antihyperlipidaemic interventions.

Generalized lipodystrophy, congenital and acquired (lipoatrophy)

This review is based on longitudinal studies on our seven patients with congenital generalized lipodystrophy, our patient with acquired generalized lipodystrophy, and published papers on these subjects. An inability to store energy in adipose tissue is of pathogenetic importance. In congenital lipodystrophy, insulin resistance is present from birth, resulting in hyperinsulinaemia, dyslipidaemia. and insulin-resistant diabetes with an anabolic syndrome worsened by a voracious appetite. Clinically, we observed increased height velocity in pre-school age children, and organomegaly with hypertrophic cardiomyopathy, which seems to be lethal in early adulthood: three of our patients died at the ages of 24, 32 and 37 years. The oldest alive, 39 years, suffers from stenocardia. Regarding treatment, it is most important to reduce energy consumption. The congenital form is recessively inherited. The aetiology may be related to insulin receptor or postreceptor mechanisms. Acquired generalized lipodystrophy seems to be an autoimmune disorder with secondary destruction of the adipose organ: the anabolic syndrome with insulin-resistant diabetes is secondary. Our patient died when 24 years old from pneumonia.