Diabetes mellitus is a chronic metabolic disease, characterized by hyperglycemia with disturbances of carbohydrate, protein and fat metabolism due to an absolute or relative deficiency of insulin (^{Barcelo and Rajpathak 2001}). Type II diabetes mellitus results from a combination of defective insulin secretion and insulin resistance, almost certainly involving the insulin receptor. Diabetic nephropathy is a syndrome occurring in people with diabetes mellitus, characterized by albuminuria, hypertension, and progressive renal insufficiency (^{Stedmans 2005}).

Diabetes mellitus is one of the most prevalent diseases in the developing world and the urgency for its management is increasing as the number of cases in these countries grows each year. In 2006, according to the World Health Organization (WHO), at least 171 million people worldwide suffered from diabetes and this figure is expected to double by the year 2030 (^{WHO 2007}). Globally type II diabetes mellitus is the 3rd and 10th leading cause of loss of years of potential life among women and men respectively (^{Boyne et al 2006}). A study done in 2001 among people 35?64 years old found that in Trinidad and Tobago, over 10% of the population had diabetes (^{Barcelo and Rajpathak 2001}).

The red cell membrane contains approximately equal amounts of lipids and proteins. Membrane lipids are either phospholipids or neutral lipids, mostly unesterified cholesterol. Membrane phospholipids are asymmetrically arranged into a lipid bilayer two molecules thick. Choline phospholipids are more abundant in the extracellular surface whereas amino phospholipids are more concentrated on the inner leaflet of the bilayer. Cholesterol is intercalated between the phospholipid molecules. The relative amounts of cholesterol and phospholipids are responsible for the fluid properties of the erythrocyte membrane (^{Ballas and Krasnow 1980}; ^{Nagle and Tristram-Nagle 2000}). Alterations in the membrane cholesterol-phospholipid ratio result in morphologically abnormal erythrocytes with decreased life span. Alterations in blood rheological properties have been reported in poorly controlled diabetes mellitus (^{Bryszewska et al 1986}; ^{Miossec et al 1999}). Changes in lipid composition of RBC membranes resulting in an impairment of RBC deformability may play a role in an altered blood rheological pattern (^{Bakan et al 2006}). There are few reports on the relationship between serum and RBC membrane lipid composition in other populations. ^{Lee and colleagues (2004)} showed that diet and general health status has close relation to the flow behavior of blood, which influences the circulation of the blood in the body. In their study they demonstrated that the high level of cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in vivo alter the morphology and flow behavior of blood cells that can subsequently increase the risk of impairing physical function and microcirculation (^{Lee et al 2004}). The present study has sought to determine and examine the relationship of the RBC membrane and serum lipid composition in Trinidadian type II diabetes with or without nephropathy (between the ages of 18?65 yrs). In addition, it has sought to determine the relationship between the RBC membrane and serum lipid composition in noninsulin-dependent diabetes mellitus (NIDDM) patients in the multiethnic population of Trinidad, a third world country in the Americas.

This study has aimed to establish a link between the lipid composition of the RBC membrane and serum to aid in the early diagnosis and treatment of patients with type II diabetes mellitus, thus preventing the development of further complications including the impaired RBC deformability.

Table 1 and bar diagrams show the anthropometric and biochemical values for the three groups of subjects. The body mass index and the systolic blood pressure of the diabetics (28.17 ? 4.98 kg/m², 153.21 ? 22.10 mmHg) and nephropathic diabetics (25.87 ? 4.68 kg/m², 158.60 ? 22.49 mmHg) were higher compared with controls (24.67 ? 5.18 kg/m², 119.15 ? 13.03 mmHg). The diabetic (175.89 ? 102.73 ?g/mg/protein) and diabetic nephropathy (358.80 ? 262.66 ?g/mg/protein) subjects showed significantly higher levels of RBC membrane cholesterol compared with controls (132.27 ? 66.47 ?g/mgprotein) (Figure 1). The membrane phospholipids, protein and Na⁺/K⁺ATPase concentrations for controls were: (9.17 ? 9.23 ?g/mgprotein, 0.94 ? 0.47 mg/mL, 0.021 ? 0.021 ?moles/ml) for diabetics: (5.31 ? 4.51 ?g/mg protein, 0.65 ? 0.38 mg/mL, 0.026 ? 0.039 ?moles/ml), nephropathic diabetics: (19.67 ? 14.83 ?g/mg protein, 1.19 ? 0.79 mg/mL, 0.023 ? 0.020 ?moles/ml), respectively (Figure 2). The trend of increased serum cholesterol and decreased HDL in diabetics (206.85 ? 47.34 mg/dL, 43.45 ? 9.45 mg/dL) and those with nephropathy (209.90 ? 66.13 mg/dL, 41.60 ? 9.23 mg/dL) were compared with controls (184.50 ? 35.69 mg/dL, 48.05 ? 12.42) but were not significant as expected. The LDL cholesterol was significantly higher in diabetics (131.00 ? 35.63 mg/dL) when compared with those with nephropathy (116.40 ? 54.03 mg/dL) and the control subjects (118.70 ? 37.75 mg/dL).

The correlation between waist/hip ratio and blood pressure in diabetics and diabetics with nephropathy was not significant (Figure 3). There was an increase in the means of serum cholesterol in diabetics and diabetics with nephropathy, however there were no significant relationship when diabetics and diabetics with nephropathy were compared to controls (p = 0.611 and p = 0.415, respectively) (Figure 4).

The mean values of RBC membrane cholesterol showed the same increase as serum cholesterol; however the relationship for this variable between controls and diabetics is not significant (p = 0.514) whereas, the relationship for this variable between diabetics and diabetics with nephropathy is significant (p = 0.023) (Figure 5). The RBC membrane protein mean values was lower in diabetics (0.65 ? 0.38) compared with controls and a larger value in diabetics with nephropathy (1.19 ? 0.79) compared with controls (0.94 ? 0.47). The mean reading of Na⁺/K⁺ATPase activity was higher in diabetics with nephropathy (0.023 ? 0.020) and much higher in diabetics (0.031 ? 0.039) when compared with controls (0.021 ? 0.021). The mean readings of RBC membrane phospholipids showed a decrease in diabetics (5.31 ? 4.51) but an increase in diabetics with nephropathy (19.67 ? 14.83) when compared with controls (9.17 ? 8.23).

The means of LDL showed an increase in diabetics (131.00 ? 35.63) and a decrease in diabetics with nephropathy (116.40 ? 54.03) when compared with controls (118.70 ? 37.75) (Figure 6). The mean HDL readings decreased in diabetics (43.45 ? 9.45) and more in diabetics with nephropathy (41.60 ? 9.23) when compared with controls (48.05 ? 12.42) (Figure 6).

The increase in body mass index and waist/hip ratio was expected since obesity is a known risk factor of diabetes. Blood pressure was also elevated in the diabetic group as compared to controls since increased blood pressure, in diabetics, is correlated with increased waist circumference. Blood pressure was elevated in diabetics with nephropathy because angiopathy of renal glomeruli is an associated pathology.

Higher serum cholesterol in diabetics than controls could be attributed to the metabolism of acetate, a precursor to cholesterol, produced in increased amounts from the catabolism of fatty acids, carbohydrates and amino acids in the diet of this group (^{Talwar and Srivastava 2003}). Serum cholesterol level was further elevated in diabetics with nephropathy since hypercholesterolemia is a constant feature of nephrotic syndrome (^{Kumar et al 2003}). LDL-cholesterol increased in diabetics when compared to the control subjects from less than ideal management of diabetes, including poor diet control such as high intake of saturated fats and carbohydrates without the use of statins. In the diabetics with nephropathy the lower LDL-cholesterol was thought to be due to better disease management in these patients who attend a renal clinic and receive specialist attention. Decreased HDL levels in diabetics and an even further decrease in diabetics with nephropathy can be explained by reduced action of insulin at the tissue level and therefore insulin resistance (^{Valabhji and Elkeles 2003}).

The increased RBC membrane cholesterol and altered phospholipid concentration in diabetics and diabetic nephropathy subjects when compared with controls may explain poor metabolic control. The increase in RBC membrane cholesterol in diabetics with and without nephropathy appears to reflect serum cholesterol.

^{Prisco and colleagues (1989)} observed altered levels of RBC membrane phosholipid ratio in diabetics which could account for the impaired RBC deformability frequently reported in diabetes mellitus (^{Prisco et al 1989}). Researchers also showed the relationship of altered RBC lipid composition and rheological impairment of the RBC (^{Garnier et al 1990}). RBC membrane protein was decreased in diabetics when compared with controls and this could be due to damage of membrane proteins by nonenzymatic glycation (^{Sampietro et al 1986}; ^{Watala et al 2005}). In vitro studies of researchers demonstrated the decreased lipid fluidity in diabetics caused by nonenzymatic glycation of RBC membrane proteins (^{Watala 1988}). RBC membrane protein was higher in the cases of diabetics with nephropathy, possibly due to the altered, healthier diets that diabetics with nephropathy are strictly advised to adhere to. Such diets would ensure that glucose levels were maintained within limits, thereby reducing RBC deformability. The decrease in membrane phospholipids in diabetics could have occurred from damage induced by nonenzymatic glycosylation of the cell membrane and subsequent loss of phospholipids from the RBC membrane (^{Ellenberg and Rifkin 1983}). The management of diet and better disease control could have resulted in increased membrane phospholipids in the diabetics with nephropathy. ^{Miossec and colleagues (1999)} investigated the relationship between erythrocyte deformability, plasma lipids, lipid membrane composition, and cytosolic cations in poorly controlled type 2 diabetic patients and they concluded that in poorly controlled type 2 diabetic patients there is a link between the chemical composition and the rheological properties of erythrocytes.

Our data suggest that there is a relationship between RBC membrane and serum lipid composition in subjects with type II diabetes with and without nephropathy. This relationship shows that diet and lifestyle plays a significant role in the alterations of the lipids both in serum and RBC membrane. Diet and management of diabetes plays a significant role not only in altering the lipid profile but also preventing rheological impairment of the RBC.

The study was funded by a Campus Research Fund, the University of West Indies. Authors extend their thanks to Miss Kezia Willie, and Dr. Celia Poon King, House officers, nursing staff and laboratory persons for their assistance during the study. Authors sincerely thank Prof. Lexley Pinto Pereira for editing the manuscript.