Leptin: a pleitropic factor in physiology

Abstract

Leptin, a 16 kDa protein and a product of the ob/ob gene, has a tertiary structure similar to that of a cytokine. It is primarily secreted by white adipose tissue and its levels in the blood correlate positively with percentage body fat. Leptin was first identified in 1994 as a major factor that regulated food intake and energy balance. Leptin in the circulation exists either as a free monomeric hormone or bound to its soluble receptor. Its serum levels usually range from 0.5 to 37.7 ng/ml in males and 2.0 to 45.2 ng/ml in females. The half-life of leptin is between 20 - 30 minutes and it is eliminated mainly by the kidneys. However, research over the last 25 years has revealed numerous other physiological roles for leptin, including roles in inflammation, immune function, neuro-endocrine function, bone metabolism, blood pressure regulation and sexual maturation. Most of these roles have been identified from studies on leptin deficient rodents. Apart from energy balance and sexual maturation, where its role is direct and obvious, its actions on the rest of the other systems are permissive. Actions of leptin are both centrally and peripherally mediated involving receptors that are widely distributed in the body. Six leptin receptor isoforms, belonging to the class 1 cytokine receptor family, have been identified. These receptors are products of the OBR gene. The cellular actions of leptin are mediated through any one of five different signalling pathways that include the JAK-STAT, PI3K, MAPK, AMPK, and the mTOR signalling pathways.

A Cross-Sectional Study on the Combined Effect of Body Weight and Coffee Consumption on Serum Levels of Leptin, Vitamin B12, and Folic Acid in Healthy Young Adult Males

“…14 Leptin levels in our study are positively related to BMI and this is consistent with results obtained from a study performed on Greek men where the levels of leptin in men with a BMI > 30 kg/m 2 were 170% higher than in men with a BMI < 27 kg/m 2.11 Our results support that leptin is an important marker of obesity 27,46 where its expression in obese subjects is, on average, 2-fold higher than that in lean individuals. 26,49 Moreover, our results comply with a previous cross-sectional study conducted on Jordanian youth males that revealed obese and overweight subjects had high leptin levels and these levels were positively associated with parental history of T2DM. 50 The levels of serum leptin in NW and OW groups were not affected by CCR; moderate coffee consumers had similar levels to those who are heavy coffee consumers.…”

“…20 Besides that, it was suggested there is a J-shaped relationship between CCR and health outcomes in which moderate consumption is beneficial, whereas heavy consumption is detrimental. 21,22 Leptin, an adipokine hormone, 25,26 plays an important role in the regulation of appetite, energy expenditure by inhibiting hunger and reducing food intake, which in turn diminishes the body weight (BW) and fat storage in adipocytes. 25,27 Moreover, leptin is involved in the regulation of sexual maturity and reproduction, cardiovascular functions, metabolisms, and stress response.…”

“…Leptin, an adipokine hormone, 25 , 26 plays an important role in the regulation of appetite, energy expenditure by inhibiting hunger and reducing food intake, which in turn diminishes the body weight (BW) and fat storage in adipocytes. 25 , 27 Moreover, leptin is involved in the regulation of sexual maturity and reproduction, cardiovascular functions, metabolisms, and stress response.…”

“… 25 , 27 Moreover, leptin is involved in the regulation of sexual maturity and reproduction, cardiovascular functions, metabolisms, and stress response. 26 , 28 , 29 Circulating leptin levels are directly proportional to the amount of body fat and weight, 25 and the levels increase with age and decrease during fasting and starvation. 30 Obesity is associated with high levels of leptin, which is considered as an important obesity marker.…”

“…Excess leptin has been associated with many obesity-related diseases, such as hypertension, cardiovascular diseases, and infertility. 26 Some studies claimed that caffeine, a major constituent in coffee, has anti-obesity properties through stimulation of sympathetic nervous which leads to increased thermogenesis and fat oxidation and possibly down-regulation of leptin release. 32 However, studies on the effect of CCR on leptin are rare and conflicting, and more investigation is required.…”