Long-term correction of type 1 and 2 diabetes by central leptin gene therapy independent of effects on appetite and energy expenditure

Effects of the POMC System on Glucose Homeostasis and Potential Therapeutic Targets for Obesity and Diabetes

The hypothalamus is indispensable in energy regulation and glucose homeostasis. Previous studies have shown that pro-opiomelanocortin neurons receive both central neuronal signals, such as α-melanocyte-stimulating hormone, β-endorphin, and adrenocorticotropic hormone, as well as sense peripheral signals such as leptin, insulin, adiponectin, glucagon-like peptide-1, and glucagon-like peptide-2, affecting glucose metabolism through their corresponding receptors and related signaling pathways. Abnormalities in these processes can lead to obesity, type 2 diabetes, and other metabolic diseases. However, the mechanisms by which these signal molecules fulfill their role remain unclear. Consequently, in this review, we explored the mechanisms of these hormones and signals on obesity and diabetes to suggest potential therapeutic targets for obesity-related metabolic diseases. Multi-drug combination therapy for obesity and diabetes is becoming a trend and requires further research to help patients to better control their blood glucose and improve their prognosis.

Leptin concentrations in type 2 diabetes and non-diabetes Nigerian-Africans

Most studies on leptin in diabetes mellitus (DM) compared to healthy controls were done in Caucasians, with conflicting findings. Paucity of data on this exists in Nigerian-Africans. Therefore, the study determined plasma leptin concentrations in newly diagnosed type-2 diabetes versus controls and its relation to obesity/demographic-metabolic indices. A cross-sectional comparative study on 154 subjects: 67 diabetes and 87 healthy controls at the Ahmadu Bello University Teaching Hospital, Nigeria. Leptin was determined by the sandwich enzyme-linked immunosorbent assay. Mann-Whitney U test, Spearman's Correlation and Step-wise Multiple Logistic Regression analysis of Log-transformed variables determined outcomes. Leptin trended towards lower levels in DM subjects than controls when both sexes were combined, though insignificant (P=0.12). Leptin was significantly (P<0.001) positively correlated with waist circumference (WC) and body mass index (BMI) in DM (WC, r=0.71; BMI, r=0.84) as well as controls (WC, r=0.46, BMI, r=0.51), respectively. Leptin was significantly (P<0.001) higher in females than males, with approximately 2 times Odds of female sex association with log-transformed (Ln₁₀) hyperleptinaemia {Odds Ratio (OR): 1.9, 95% CI, 0.97-3.92, P<0.001}. Age was positively (r=0.21, P=0.05) correlated to leptin in controls, while fasting blood glucose (FBG) negatively correlated to uncontrolled DM (r=-0.26). Leptin showed no significant (P>0.05) correlation to fasting insulin (FI) and HOMA-IR. WC was an independent predictor of Ln₁₀hyperleptinaemia in DM subjects (OR: 1.12, 95% CI, 1.03-1.23, P=0.01). BMI showed significant (P<0.001) association with Ln₁₀hyperleptinaemia in both subjects. Conclusively, leptin trends towards lower levels but are not different in newly diagnosed DM than controls. The association of leptin with obesity is similar but stronger in diabetes than controls, with no relations to FI and HOMA-IR. WC and BMI are independent predictors of hyperleptinaemia.

Gene therapy and type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder characterized by T cell-mediated self-destruction of insulin-secreting islet β cells. Management of T1DM is challenging and complicated especially with conventional medications. Gene therapy has emerged as one of the potential therapeutic alternatives to treat T1DM. This review primarily focuses on the current status and the future perspectives of gene therapy in the management of T1DM. A vast number of the studies which are reported on gene therapy for the management of T1DM are done in animal models and in preclinical studies. In addition, the safety of such therapies is yet to be established in humans. Currently, there are several gene level interventions that are being investigated, notably, overexpression of genes and proteins needed against T1DM, transplantation of cells that express the genes against T1DM, stem-cells mediated gene therapy, genetic vaccination, immunological precursor cell-mediated gene therapy and vectors.

METHODS

We searched the current literature through searchable online databases, journals and other library sources using relevant keywords and search parameters. Only relevant publications in English, between the years 2000 and 2018, with evidences and proper citations, were considered. The publications were then analyzed and segregated into several subtopics based on common words and content. A total of 126 studies were found suitable for this review.

FINDINGS

Generally, the pros and cons of each of the gene-based therapies have been discussed based on the results collected from the literature. However, there are certain interventions that require further detailed studies to ensure their effectiveness. We have also highlighted the future direction and perspectives in gene therapy, which, researchers could benefit from.

Benefits of healthy adipose tissue in the treatment of diabetes

The major malfunction in diabetes mellitus is severe perturbation of glucose homeostasis caused by deficiency of insulin. Insulin deficiency is either absolute due to destruction or failure of pancreatic β cells, or relative due to decreased sensitivity of peripheral tissues to insulin. The primary lesion being related to insulin, treatments for diabetes focus on insulin replacement and/or increasing sensitivity to insulin. These therapies have their own limitations and complications, some of which can be life-threatening. For example, exogenous insulin administration can lead to fatal hypoglycemic episodes; islet/pancreas transplantation requires life-long immunosuppressive therapy; and anti-diabetic drugs have dangerous side effects including edema, heart failure and lactic acidosis. Thus the need remains for better safer long term treatments for diabetes. The ultimate goal in treating diabetes is to re-establish glucose homeostasis, preferably through endogenously generated hormones. Recent studies increasingly show that extra-pancreatic hormones, particularly those arising from adipose tissue, can compensate for insulin, or entirely replace the function of insulin under appropriate circumstances. Adipose tissue is a versatile endocrine organ that secretes a variety of hormones with far-reaching effects on overall metabolism. While unhealthy adipose tissue can exacerbate diabetes through limiting circulation and secreting of pro-inflammatory cytokines, healthy uninflamed adipose tissue secretes beneficial adipokines with hypoglycemic and anti-inflammatory properties, which can complement and/or compensate for the function of insulin. Administration of specific adipokines is known to alleviate both type 1 and 2 diabetes, and leptin mono-therapy is reported to reverse type 1 diabetes independent of insulin. Although specific adipokines may correct diabetes, administration of individual adipokines still carries risks similar to those of insulin monotherapy. Thus a better approach is to achieve glucose homeostasis with endogenously-generated adipokines through transplantation or regeneration of healthy adipose tissue. Our recent studies on mouse models show that type 1 diabetes can be reversed without insulin through subcutaneous transplantation of embryonic brown adipose tissue, which leads to replenishment of recipients’ white adipose tissue; increase of a number of beneficial adipokines; and fast and long-lasting euglycemia. Insulin-independent glucose homeostasis is established through a combination of endogenously generated hormones arising from the transplant and/or newly-replenished white adipose tissue. Transplantation of healthy white adipose tissue is reported to alleviate type 2 diabetes in rodent models on several occasions, and increasing the content of endogenous brown adipose tissue is known to combat obesity and type 2 diabetes in both humans and animal models. While the underlying mechanisms are not fully documented, the beneficial effects of healthy adipose tissue in improving metabolism are increasingly reported, and are worthy of attention as a powerful tool in combating metabolic disease.

Recombinant human leptin does not alter gut hormone levels after gastric bypass but may attenuate sweet cravings

Bariatric surgery improves glucose homeostasis and alters gut hormones partly independent of weight loss. Leptin plays a role in these processes; levels are decreased following bariatric surgery, creating a relative leptin insufficiency. We previously showed that leptin administration in a weight-reduced state after Roux-en-Y gastric bypass (RYGB) caused no further weight loss. Here, we discuss the impact of leptin administration on gut hormones, glucostasis, and appetite. Weight stable women after RYGB were randomized to receive placebo or recombinant human metreleptin (0.05 mg/kg twice daily). At weeks 0 and 16, a liquid meal challenge was performed. Glucose, insulin, C-peptide, GLP-1, PYY, glucagon, and ghrelin (total, acyl, and desacyl) were measured fasting and postprandially. Appetite was assessed using a visual analog scale. Mean post-op period was 53 ± 2.3 months; mean BMI was 34.6 ± 0.2 kg/m(2). At 16 weeks, there was no significant change in weight within or between groups. Fasting PYY was significantly different between groups and the leptin group had lower sweets craving at week 16 than the placebo group (P < 0.05). No other differences were observed. Leptin replacement does not alter gut hormones or glucostasis but may diminish sweet cravings compared to placebo in this population of post-RYGB women.