Guidance for the diagnosis and treatment of hypolipidemia disorders.

The Abetalipoproteinemia and Related Disorders Foundation was established in 2019 to provide guidance and support for the life-long management of inherited hypocholesterolemia disorders. Our mission is "to improve the lives of individuals and families affected by abetalipoproteinemia and related disorders". This review explains the molecular mechanisms behind the monogenic hypobetalipoproteinemia disorders and details their specific pathophysiology, clinical presentation and management throughout the lifespan. In this review, we focus on abetalipoproteinemia, homozygous hypobetalipoproteinemia and chylomicron retention disease; rare genetic conditions that manifest early in life and cause severe complications without appropriate treatment. Absent to low plasma lipid levels, in particular cholesterol and triglyceride, along with malabsorption of fat and fat-soluble vitamins are characteristic features of these diseases. We summarize the genetic basis of these disorders, provide guidance in their diagnosis and suggest treatment regimens including high dose fat-soluble vitamins as therapeutics. A section on preconception counseling and other special considerations pertaining to pregnancy is included. This information may be useful for patients, caregivers, physicians and insurance agencies involved in the management and support of affected individuals.

Leptin sensitizing effect of 1,3-butanediol and its potential mechanism.

Leptin is an adipocyte-derived hormone that regulates appetite and energy expenditure via the hypothalamus. Since the majority of obese subjects are leptin resistant, leptin sensitizers, rather than leptin itself, are expected to be anti-obesity drugs. Endoplasmic reticulum (ER) stress in the hypothalamus plays a key role in the pathogenesis of leptin resistance. ATP-deficient cells are vulnerable to ER stress and ATP treatment protects cells against ER stress. Thus, we investigated the therapeutic effects of oral 1,3-butanediol (BD) administration, which increases plasma ß-hydroxybutyrate and hypothalamic ATP concentrations, in diet induced obese (DIO) mice with leptin resistance. BD treatment effectively decreased food intake and body weight in DIO mice. In contrast, BD treatment had no effect in leptin deficient ob/ob mice. Co-administration experiment demonstrated that BD treatment sensitizes leptin action in both DIO and ob/ob mice. We also demonstrated that BD treatment attenuates ER stress and leptin resistance at the hypothalamus level. This is the first report to confirm the leptin sensitizing effect of BD treatment in leptin resistant DIO mice. The present study provides collateral evidence suggesting that the effect of BD treatment is mediated by the elevation of hypothalamic ATP concentration. Ketone bodies and hypothalamic ATP are the potential target for the treatment of obesity and its complications.

Current Diagnosis and Management of Abetalipoproteinemia.

Abetalipoproteinemia (ABL) is a rare autosomal recessive disorder caused by biallelic pathogenic mutations in the MTTP gene. Deficiency of microsomal triglyceride transfer protein (MTTP) abrogates the assembly of apolipoprotein (apo) B-containing lipoprotein in the intestine and liver, resulting in malabsorption of fat and fat-soluble vitamins and severe hypolipidemia. Patients with ABL typically manifest steatorrhea, vomiting, and failure to thrive in infancy. The deficiency of fat-soluble vitamins progressively develops into a variety of symptoms later in life, including hematological (acanthocytosis, anemia, bleeding tendency, etc.), neuromuscular (spinocerebellar ataxia, peripheral neuropathy, myopathy, etc.), and ophthalmological symptoms (e.g., retinitis pigmentosa). If left untreated, the disease can be debilitating and even lethal by the third decade of life due to the development of severe complications, such as blindness, neuromyopathy, and respiratory failure. High dose vitamin supplementation is the mainstay for treatment and may prevent, delay, or alleviate the complications and improve the prognosis, enabling some patients to live to the eighth decade of life. However, it cannot fully prevent or restore impaired function. Novel therapeutic modalities that improve quality of life and prognosis are awaited. The aim of this review is to 1) summarize the pathogenesis, clinical signs and symptoms, diagnosis, and management of ABL, and 2) propose diagnostic criteria that define eligibility to receive financial support from the Japanese government for patients with ABL as a rare and intractable disease. In addition, our diagnostic criteria and the entry criterion of low-density lipoprotein cholesterol (LDL-C) ＜15 mg/dL and apoB ＜15 mg/dL can be useful in universal or opportunistic screening for the disease. Registry research on ABL is currently ongoing to better understand the disease burden and unmet needs of this life-threatening disease with few therapeutic options.

Leptin inhibits and ghrelin augments hypothalamic noradrenaline release after stress.

Metabolic conditions affect hypothalamo-pituitary-adrenal responses to stressful stimuli. Here we examined effects of food deprivation, leptin and ghrelin upon noradrenaline release in the hypothalamic paraventricular nucleus (PVN) and plasma adrenocorticotropic hormone (ACTH) concentrations after stressful stimuli. Food deprivation augmented both noradrenaline release in the PVN and the increase in plasma ACTH concentration following electrical footshocks (FSs). An intracerebroventricular injection of leptin attenuated the increases in hypothalamic noradrenaline release and plasma ACTH concentrations after FSs, while ghrelin augmented these responses. These data suggest that leptin inhibits and ghrelin facilitates neuroendocrine stress responses via noradrenaline release and indicate that a decrease in leptin and an increase in ghrelin release after food deprivation might contribute to augmentation of stress-induced ACTH release in a fasting state.

Absence of hormone-sensitive lipase inhibits obesity and adipogenesis in Lep ob/ob mice.

Hormone-sensitive lipase (HSL) plays a crucial role in the hydrolysis of triacylglycerol and cholesteryl ester in various tissues including adipose tissues. To explore the role of HSL in the metabolism of fat and carbohydrate, we have generated mice lacking both leptin and HSL (Lep(ob/ob)/HSL(-/-)) by cross-breeding HSL(-/-) mice with genetically obese Lep(ob/ob) mice. Unexpectedly, Lep(ob/ob)/HSL(-/-) mice ate less food, gained less weight, and had lower adiposity than Lep(ob/ob)/HSL(+/+) mice. Lep(ob/ob)/HSL(-/-) mice had massive accumulation of preadipocytes in white adipose tissues with increased expression of preadipocyte-specific genes (CAAT/enhancer-binding protein beta and adipose differentiation-related protein) and decreased expression of genes characteristic of mature adipocytes (CCAAT/enhancer-binding protein alpha, peroxisome proliferator activator receptor gamma, and adipocyte determination and differentiation factor 1/sterol regulatory element-binding protein-1). Consistent with the reduced food intake, hypothalamic expression of neuropeptide Y and agouti-related peptide was decreased. Since HSL is expressed in hypothalamus, we speculate that defective generation of free fatty acids in the hypothalamus due to the absence of HSL mediates the altered expression of these orexigenic neuropeptides. Thus, deficiency of both leptin and HSL has unmasked novel roles of HSL in adipogenesis as well as in feeding behavior.

Cross-talk between peroxisome proliferator-activated receptor (PPAR) alpha and liver X receptor (LXR) in nutritional regulation of fatty acid metabolism. I. PPARs suppress sterol regulatory element binding protein-1c promoter through inhibition of LXR signaling.

Liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs) are members of nuclear receptors that form obligate heterodimers with retinoid X receptors (RXRs). These nuclear receptors play crucial roles in the regulation of fatty acid metabolism: LXRs activate expression of sterol regulatory element-binding protein 1c (SREBP-1c), a dominant lipogenic gene regulator, whereas PPARalpha promotes fatty acid beta-oxidation genes. In the current study, effects of PPARs on the LXR-SREBP-1c pathway were investigated. Luciferase assays in human embryonic kidney 293 cells showed that overexpression of PPARalpha and gamma dose-dependently inhibited SREBP-1c promoter activity induced by LXR. Deletion and mutation studies demonstrated that the two LXR response elements (LXREs) in the SREBP-1c promoter region are responsible for this inhibitory effect of PPARs. Gel shift assays indicated that PPARs reduce binding of LXR/RXR to LXRE. PPARalpha-selective agonist enhanced these inhibitory effects. Supplementation with RXR attenuated these inhibitions by PPARs in luciferase and gel shift assays, implicating receptor interaction among LXR, PPAR, and RXR as a plausible mechanism. Competition of PPARalpha ligand with LXR ligand was observed in LXR/RXR binding to LXRE in gel shift assay, in LXR/RXR formation in nuclear extracts by coimmunoprecipitation, and in gene expression of SREBP-1c by Northern blot analysis of rat primary hepatocytes and mouse liver RNA. These data suggest that PPARalpha activation can suppress LXR-SREBP-1c pathway through reduction of LXR/RXR formation, proposing a novel transcription factor cross-talk between LXR and PPARalpha in hepatic lipid homeostasis.