[Molecular mechanisms of the alternative lipogenic function of insulin]

The proposed hypothesis suggests that major function of insulin is stimulation of triglyceride accumulation in adipose tissue and glycogen synthesis in liver and muscles. The impairment of insulin functioning diminishes triglyceride storage in adipose tissue, elevates the level of its metabolite in periphery and suppresses glucose intake by cells. Leptin disturbs direct insulin action on adipocytes, and prevents fat accumulation. Leptin deficiency or impairment of its functioning facilitate lipogenic effect of insulin, and induce obesity. Lipodystrophy decreases leptin secretion and enhances triglyceride production activated by insulin. Triglycerides are not accumulated in adipose tissue because of its deficiency, and overwhelm peripheral tissues. Lipid metabolites decrease glucose consumption and induce lipoatrophic diabetes. The hypothesis on the lipogenic insulin functioning is confirmed by specific knockout of Insr gene in only tissue: muscles, adipose tissue and other, and by the restoration of its expression in transgenic mice.

Severe localized lipoatrophy related to therapy with insulin analogs in type 1a diabetes mellitus

Insulin analog-related lipoatrophy is a rare complication of this type of treatment. We report a case of severe localized lipoatrophy in different locations in a patient with type 1a diabetes mellitus associated with other autoimmune disease.

[Insulin-induced lipoatrophy in children]

Insulin-induced lipoatrophy is a rare but serious complication of insulin treatment. Its incidence decreased during 1970' and 1980's, but several reports of this phenomenon have again recently been published. Traditional treatment options have included injecting insulin or pump cannula to the area surrounding the lipoatrophy or changing the insulin type or preparation. In this report we present 4 children who developed severe lipoatrophy during insulin pump treatment. Changing injection sites did not help but lipoatrophy disappeared in one patient after changing the insulin preparation. In the three other patients no new atrophy sites have appeared after change in insulin preparation or simultaneous treatment with local pimecrolimus or sodium cromoglicate.

Peroxisomal proliferator activated receptor-gamma deficiency in a Canadian kindred with familial partial lipodystrophy type 3 (FPLD3)

BACKGROUND

Familial partial lipodystrophy (Dunnigan) type 3 (FPLD3, Mendelian Inheritance in Man [MIM] 604367) results from heterozygous mutations in PPARG encoding peroxisomal proliferator-activated receptor-gamma. Both dominant-negative and haploinsufficiency mechanisms have been suggested for this condition.

METHODS

We present a Canadian FPLD3 kindred with an affected mother who had loss of fat on arms and legs, but no increase in facial, neck, suprascapular or abdominal fat. She had profound insulin resistance, diabetes, severe hypertriglyceridemia and relapsing pancreatitis, while her pre-pubescent daughter had normal fat distribution but elevated plasma triglycerides and C-peptide and depressed high-density lipoprotein cholesterol.

RESULTS

The mother and daughter were each heterozygous for PPARG nonsense mutation Y355X, whose protein product in vitro was transcriptionally inactive with no dominant-negative activity against the wild-type receptor. In addition the mutant protein appeared to be markedly unstable.

CONCLUSION

Taken together with previous studies of human PPARG mutations, these findings suggest that PPAR-gamma deficiency due either to haploinsufficiency or to substantial activity loss due to dominant negative interference of the normal allele product's function can each contribute to the FPLD3 phenotype.

Resistin levels in human immunodeficiency virus-infected patients with lipoatrophy decrease in response to rosiglitazone

Resistin is a recently recognized adipocytokine thought to contribute to insulin resistance. We determined resistin levels and metabolic parameters in 24 HIV-infected men and women with lipoatrophy and hyperinsulinemia and studied the effect of 12 wk of the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone (4-8 mg/d) on resistin in these subjects. Participants completed metabolic testing before and after rosiglitazone including fasting determination of resistin, adiponectin, and leptin levels, serum inflammatory markers, and hyperinsulinemic euglycemic clamp testing. Resistin concentration decreased significantly after rosiglitazone (12.17 +/- 1.15 ng/ml to 10.23 +/- 1.05 ng/ml; P = 0.02), in conjunction with significant increases in adiponectin- (P < 0.001) and insulin- stimulated glucose disposal (P = 0.004). Leptin levels, as well as TNF-alpha, did not change with rosiglitazone. In summary, among HIV-infected subjects with insulin resistance and lipoatrophy, resistin levels decreased significantly after rosiglitazone. Further investigation into the physiological role of this peroxisome proliferator-activated receptor-gamma-responsive adipocytokine in the metabolic abnormalities associated with HIV is warranted.

Development of conjugated linoleic acid (CLA)-mediated lipoatrophic syndrome in the mouse

Conjugated linoleic acids (CLA) are positional and geometric dienoic isomers of linoleic acid. Dietary CLA supplementation leads to a drop in fat mass in various species, including in humans. The t10,c12-CLA isomer is responsible for this anti-obesity effect. The reduction of fat mass is especially dramatic in the mouse, in which it is associated with severe hyperinsulinemia, insulin resistance and massive liver steatosis. The origin of these adverse side effects and putative chronology of events leading to CLA-mediated lipoatrophic syndrome are presented and discussed in this review.

Lipoatrophic diabetes in Irs1(-/-)/Irs3(-/-) double knockout mice

Based on the phenotypes of knockout mice and cell lines, as well as pathway-specific analysis, the insulin receptor substrates IRS-1, IRS-2, IRS-3, and IRS-4 have been shown to play unique roles in insulin signal transduction. To investigate possible functional complementarity within the IRS family, we generated mice with double knockout of the genes for IRS-1/IRS-3 and IRS-1/IRS-4. Mice with a combined deficiency of IRS-1 and IRS-4 showed no differences from Irs1(-/-) mice with respect to growth and glucose homeostasis. In contrast, mice with a combined deficiency of IRS-1 and IRS-3 developed early-onset severe lipoatrophy associated with marked hyperglycemia, hyperinsulinemia, and insulin resistance. However, in contrast to other models of lipoatrophic diabetes, there was no accumulation of fat in liver or muscle. Furthermore, plasma leptin levels were markedly decreased, and adenovirus-mediated expression of leptin in liver reversed the hyperglycemia and hyperinsulinemia. The results indicate that IRS-1 and IRS-3 play important complementary roles in adipogenesis and establish the Irs1(-/-)/Irs3(-/-) double knockout mouse as a novel model of lipoatrophic diabetes.

Lipoatrophic diabetes and end-stage liver disease secondary to nonalcoholic steatohepatitis with recurrence after liver transplantation

BACKGROUND

Lipoatrophic diabetes is an insulin resistance syndrome characterized by the complete or partial lack of adipose tissue and disturbances in lipid and glucose metabolism. Nonalcoholic steatohepatitis (NASH) is a well-described change in liver pathology consisting of steatosis, hepatitis, and fibrosis that can be associated with lipoatrophic diabetes.

RESULTS

This article describes the first reported case of lipoatrophic diabetes with NASH leading to liver failure and liver transplantation. Before transplantation, the patient required 600-700 U of insulin/day. After transplantation, a dramatic decline in her insulin requirements was observed, despite corticosteroids. Eighteen months after transplantation, her glycemic control worsened, and she developed recurrent NASH on serial liver biopsies.

CONCLUSIONS

NASH associated with lipoatrophic diabetes can recur after liver transplantation, and in this case, was accompanied by increased insulin requirements. These results suggest that the development of NASH itself may contribute to the insulin resistance observed in lipoatrophic diabetes.

A-ZIP/F-1 mice lacking white fat: a model for understanding lipoatrophic diabetes

The A-ZIP/F-1 mouse is lacking virtually all white adipose tissue. Like humans with extensive deficiencies of adipose tissue, the A-ZIP/F-1 mice develop a severe form of insulin resistant diabetes. We have studied the physiology of the A-ZIP/F-1 mice. Their adaptation to fasting is notable for its rapidity and the use of torpor, a hibernation-like state, to minimize energy needs. Transplantation of adipose tissue reversed the metabolic manifestations in the mice, demonstrating that the lack of adipose tissue is the cause of the insulin resistance. Leptin replacement is not very effective in reversing the diabetes of the A-ZIP/F-1 mice, which contrasts with its efficacy in the aP2-SREBP-lc mouse.

Improved glucose tolerance after effective lipid-lowering therapy with bezafibrate in a patient with lipoatrophic diabetes mellitus: a putative role for Randle's cycle in its pathogenesis?

This report describes a patient with lipoatrophic diabetes mellitus (LDM), which is a rare clinical syndrome characterized by lipoatrophy and severe insulin resistance. Although a genetic abnormality is suspected in the development of LDM, no functional mutations in key domains of the insulin receptor gene were detected. Therapy was directed primarily at decreasing the availability of non-esterified fatty acids (NEFA), and thereby improving glucose tolerance (Randle's cycle), by the administration of a lipid-lowering drug, bezafibrate. Serial changes in fasting levels of the hormones of glucose homeostasis and lipids were measured, as well as glucose and insulin responses to a 75-g oral glucose challenge at onset and following 3 and 6 months of fibrate therapy. Progressive reductions in the patient's levels of triglycerides and NEFA were paralleled by an improvement in beta-cell function, a decrease in insulin resistance, and the attainment of normal glucose homeostasis. We conclude that the pathogenesis of LDM may be related primarily to abnormal regulation of lipid, rather than glucose, metabolism.