1. INTRODUCTION:

Leptin, a cytokine product of the ob gene, is secreted into the blood from adipocytes¹ once released into the circulation; leptin lowers body weight by decreasing appetite and altering metabolic processes². Doesn’t only leptin influences appetite, energy expenditure, and neuroendocrine axes via a high affinity receptor expressed mainly in hypothalamus, but also in other tissues³. Leptin deficiency or defective leptin signaling, due to mutation in the genes encoding leptin (ob) and the leptin receptor (obR), causes severe obesity in rodents. In human obesity, however; ob mRNA abundance, leptin secretion from adipose tissue, and circulating leptin concentrations are increased, and are positively correlated with the degree of obesity⁴.This suggests that resistance to leptin, rather than leptin deficiency, is common in obese patients⁵ .The secretion of leptin seems to be modulated by several factors including sex, age ,insulin, glucocorticoids, catecholamines, cytokines (TNF, interleukin1) and smoking⁶.

Type 2 diabetes mellitus (T2DM) is approaching epidemic proportions, mostly due to a sharp increase in the prevalence of obesity , and associated insulin resistance⁷. Being overweight or obese has become highly prevalent, and is rapidly reaching epidemic proportions in developing world⁸. Insulin resistance is common soil between obesity and T2DM and modifies leptin response to several stimuli⁹.

We did our study in type 2 diabetics who are really uncompensated insulin resistant Syrian population and compared the findings with that of non-diabetic controls. Thereby we tried to explore the association of obesity and leptin with actual insulin.

2. MATERIALS AND METHODS:

2.1. Subjects: 126 (68 men and 62 women ) were recruited from several medical centers in Damascus.

Samples were collected during 8 months from 4 April 2011 to 24 January 2012. Mean (X)and Standard Deviation (SD) for ages in males (X± SD: 49±2.12)years and in females (X ±SD : 46±6.36 ) years.

Each participant was interviewed by a physician, who obtained a detailed medical history and elicited dietary habits and lifestyle characteristics (including smoking status, exercise status, and alcohol consumption).All subjects don’t use any drugs which affect the studied parameters. Subjects with any other chronic illness like tuberculosis, malignancy, hepatitis, hypertension, renal diseases, hormonal derangements other than diabetes like Cushing’s syndrome, hypothyroidism etc, pregnancy, alcoholism, and any other acute or chronic illness related or unrelated to diabetes were excluded from the study

2.2. Biochemistry: For all kinds of measurements, fasting venous blood was collected and the serum used immediately after separation. Serum glucose was measured using a Hitachi 747 autoanalyser (Hitachi, Tokyo) with dedicated reagents, Serum insulin was measured by Electro Chemiluminiscence Assay( ECLIA ) using Elecsys 2010 Roche Kite, leptin levels were measured by Leptin (Sandwich) ELISA using DRG kit.

HOMA-IR was defined using the following formula:( Fasting Insulin μU/mL x Fasting Glucose mg/dl) / 405

2.3. Anthropometry: Height and weight were measured using standard techniques while the subject was wearing light clothes and bare-footed. Height was measured to the nearest 0.1 cm and weight to the nearest 0.1 kg. The body mass index was calculated as weight in kilograms divided by the square of height in meters. The waist circumference was measured midway between the lower rib and the iliac crest, and the hip circumference at the level of the great trochanters, the waist to hip ratio (WHR) was calculated as the ratio between the waist and the hip circumferences.

2.4. Statistical analyses: All statistical analyses were performed using the SPSS-PC program (version 7.5, Chicago, IL, USA). Adopted t-Test for the Significance of the Difference between the Means. Also, Pearson correlation coefficient was used to study the correlation between the studied parameters. and P < 0.05 was considered statistically significant.

3. RESULTS AND DISCUSSION:

Compared to the values of the variables studied between the patient group and the control group was seen in table 1.

Table1. Characteristic and Profiles of the study population

Variable	Patients	Controls	p-value
Leptin -males	19.21 ng / mL	5.45 ng / mL	p=0.002
Leptin-females	30.16 ng / mL	9.34 ng / mL	p=0.001
Glucose	145.23 mg / dl	88.39 mg / dl	P<0.001
BMI-males	36.13 kg / m²	26.10 kg/m²	P=0.007
BMI-females	34.89 kg / m²	24.82 kg/m²	P=0.001
insulin	33.18 µIU/mL	10.55 µIU/mL	P<0.001
HOMA-IR	10.12	2.28	P<0.001
Waist circumference - males	114.11 cm	93.67 cm	P=0.022
Waist circumference -female	107.33 cm	80.81 cm	P=0.035
WHR- males	1.05	0.91	P=0.004
WHR- females	0.92	0.82	P=0.006

The serum leptin levels were clearly higher and statistically significant in patients groups, males and females, compared with the control group of the same sexes (figure 1). And Serum leptin levels of females were significantly higher than those of males.

In males:

Serum leptin levels were positively correlated with body mass index (R=0.19 ,P=0.001), HOMA-IR (R=0.25, P<0.001), insulin (R=0.26,P=0.001), waist circumference (R=0.41 ,P= 0.008) , and waist to hip ratio (R= 0.45 , P<0.001).

In females:

Serum leptin levels were positively correlated with body mass index (R=0.33, P<0.001), HOMA-IR(R=0.26, P<0.001), insulin (R=0.16 ,P= 0.011), waist circumference (R=0.42 ,P= 0.001) ,and waist to hip ratio (R= 0.32, P=0.005).

There was not statistically significant correlation between Serum leptin levels and Glucose in both sexes.

Figure1: the leptin levels in diabetic and healthy subjects in males (M) and females (F)

We found in our study that the levels of serum leptin were statistically significant higher in patient groups compared with the control group in both sexes. Serum leptin Levels were higher in males compared with females groups and this could explain the existence of a direct effect of estrogen in increasing the production of leptin, and the proportion of body fat in females than males who have the same BMI, and males generally have higher metabolic activity This leads to increased hormonal response and lower resistance to leptin¹⁰.

The significant positive correlation between serum leptin levels and WHR suggests the role of leptin in regulating central obesity, also WHR is considered important biomarker between central obesity and many related diseases ¹¹.The visceral adipose tissue (VAT) obesity is the key role that could explain the high levels of serum leptin in obesity. Many studies demonstrated that leptin levels increase with BMI in males and females ¹² .It is now established that leptin is an anorexigenic peptide which fails to break food intake in case of resistance to its by the hypothalamic centers ¹³.The positive correlation between total body fat mass and serum leptin is probably explained primarily by the increased release of leptin from large fat cells compared with small fat cells . On average, leptin release per gram of adipose tissue is two times greater in obese than in lean subjects. Since fat cell size is usually enlarged 2–4 times in the obese, when expressed per fat cell, leptin secretion is up to 7 times higher in obese than in lean subjects. In addition, an increased number of fat cells, particularly in extreme obesity, undoubtedly contributes to an increases in serum leptin ¹⁴. This finding is corroborative with some previous studies that also found direct correlation between central obesity, insulin resistance and cardiovascular risk factors ^15,16. Regarding the adverse effects of obesity, in particular, the visceral obesity on glucose metabolism many probable mechanisms have been suggested which include, excessive lipid “supply” by a mechanism currently referred to as “lipotoxicity.” When FFA (Free Fatty Acids) are elevated for a prolonged period, they have a direct effect on insulin action in skeletal muscle tissue and liver, reducing the normal responses to insulin to promote glucose uptake and to suppress hepatic glucose output, respectively. In both tissues, FFA increase cellular levels of acyl-CoA derivatives, which lead to an increase in the activity of cellular signaling molecules, termed serine kinases that oppose the normal tyrosine phosphorylation cascade of the insulin receptor. The increased intracellular lipid accumulation that occurs in obese subjects as “ectopic fat”, that is, triglyceride stored in the target organs themselves rather than in a benign adipose depot is an important source of intracellular acyl-CoA molecules that can affect normal insulin signal transduction¹⁷.leptin also directly affects insulin sensitivity by regulating the efficiency of insulin mediated glucose metabolism by the skeletal muscle¹⁸ .

The positive correlation between leptin and insulin may explain the role of leptin in insulin resistance¹⁹.

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Received on 08.09.2013 Modified on 12.09.2013

Research J. Pharm. and Tech. 6(10): October 2013; Page 1149-1151