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DETERMINATION OF ELECTROLYTES AND GLYCOSYLATED HAEMOGLOBIN CONCENTRATIONS IN DIABETES MELLITUS PATIENTS IN GWAGWALADA AREA COUNCIL, ABUJA.

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CHAPTER ONE

INTRODUCTION

 

Diabetes Mellitus (DM) is a group of metabolic diseases characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both (Craig et al., 2009). Diabetes has been recognized since antiquity and its symptoms, which include excessive drinking and frequent urination, were noted on Egyptian papyrus in about 1550 BC (later recognized by George Ebers) (MacFarlane et al., 1997). The role of the pancreas in diabetes was described in 1889 by Joseph von Mering and Oscar Minkowski (Von Mering and Minkowski, 1889), eventually leading to the discovery of insulin in 1921 by Sir Frederick Grant Banting and Charles Herbert Best (Banting et al., 1922); this changed the outcome of diabetes dramatically. Before the discovery of insulin, patients with Type 1 diabetes (T1D) became emaciated and usually died within one or two years after diagnosis (Marks, 1965). The first patient was treated in 1922 and the New York Times declared that insulin could cure diabetes (Tuchman, 2009). Mortality rates in patients younger than 20 years declined dramatically a few years later (Patlak, 2002). However, with the introduction of insulin, patients lived longer and complications became more apparent. Renal failure, cardiac arrest, blindness, gangrene and other complications typically shortened life expectancy by 15 years (Patlak, 2002).

Until the 1950s, physicians did not distinguish between T1D and Type 2 diabetes (T2D). Still, they recognized a difference between what they called ―acute, and ―chronic (Tuchman, 2009). Insulin had a more dramatic effect on individuals with the ―acute form, which affected primarily young children. The chronic form tended to affect the middle-age, elderly obese and this form was insensitive to insulin. Currently, the ―acute form represents T1D and the chronic, form represents T2D. The World Health Organization suggested a subdivision of diabetes into four main groups; T1D, T2D, gestational diabetes and other specific types (heterogenic group) (WHO, 1999; Soltesz et al., 2006), the latter includes diabetes caused by genetic defects in beta-cell function, frequently called ―Maturity Onset of the Young (MODY), genetic defects in insulin action, genetic syndromes associated with diabetes and diabetes secondary to other conditions, such as pancreatitis and cystic fibrosis. Despite increased availability of insulin, worldwide mortality is not declining and both prevalence and incidence appears to be increasing. Mortality is an important measure of population health and is often used to assign priorities in health interventions. The International Diabetes Federation (IDF) (2010), estimated that four million deaths in the 20-79 age groups may be attributable to diabetes in 2010, accounting for almost 7% of global mortality, equal to many infectious diseases like Human Immunodeficiency Virus (HIV)/Acquired Immunodeficiency Syndrome (AIDS) (Roglic and Unwin, 2010). Deaths attributable to diabetes in a global perspective have been challenging to estimate because one third of the countries of the world do not have reliable data. Most of these are countries in Sub-Saharan Africa (SSA) (Roglic et al., 2005). Routinely reported statistics based on death certificates can underestimate mortality by threefold because individuals often die of cardiovascular and renal disease and not from a cause directly related to diabetes (Roglic et al., 2000). Diabetes is increasing most rapidly in developing countries, where industrialization and urbanization have led to the adoption of a western lifestyle. According to WHO around 220 million people had diabetes in 2000 and the rate is predicted to double by 2030 (McKee, 2000).

 

1.2       Diabetes Mellitus

The term diabetes mellitus describes a metabolic disorder of multiple aetiology characterized by chronic hyperglycemia with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion, insulin action, or both (Sundaram, 1996). Translated from Greek, diabetes mellitus means ‘honey sweet flow’ and this stemmed from a time in which tasting a patient’s urine was still part of the physician’s diagnostic repertoire. The effects of diabetes mellitus include long-term damage, dysfunction and failure of various organs.

 

1.2.1    Symptoms of Diabetes Mellitus

Diabetes mellitus may present with symptoms such as thirst, polyuria, blurring of vision and weight loss. In its most severe forms, ketoacidosis or a non-ketosis hyperosmolar state may develop and lead to stupor, coma and, in absence of effective treatment, death. Often, symptoms are not severe, or may be absent, and consequently hyperglycaemia sufficient to cause pathological and functional changes may be present for a long time before the diagnosis is made. The long-term effects of diabetes mellitus include progressive development of the specific complications of retinopathy with potential blindness, nephropathy that may lead to renal failure, and / or neuropathy with risk of foot ulcers, amputation, Charcot joints, and features of autonomic dysfunctions, including sexual dysfunction. People with diabetes are at increased risk of cardiovascular, peripheral vascular and cerebrovascular disease (Bonnefont et al., 2000). Several pathogenetic processes are involved in the development of diabetes. These include processes which destroy the beta cells of the pancreas with consequent insulin deficiency, and others that result in resistance to insulin action. The abnormalities of carbohydrate, fat and protein metabolism are due to deficient action of insulin on target tissues resulting from insensitivity or lack of insulin.

Diabetes has been reported to have significantly higher free radical activity as well as significantly lower concentrations of antioxidants, compared with healthy controls (Sundaram, 1996). In diabetic condition, persistent hyperglycaemia and hyperlipidemia cause increased production of free radicals especially reactive oxygen species, in all tissues from glucose auto-oxidation and protein glycosylation (Aragno et al., 1999; Bonnefont et al., 2000). These changes are of greater magnitude in patients with disease complications than in those without disease complications. It is therefore possible that supplementing with nutrients and herbs that have antioxidant activity would help prevent diabetic gangrene and other organ damage (Sundaram, 1996). These radicals are generated as by-products of normal cellular metabolism. However, certain conditions are known to disturb the balance between ROS production and cellular defense mechanisms. The imbalance can result in cell dysfunction and destruction resulting in tissue injury. The elevated levels of ROS in diabetics might be due to increased production of free radicals and or decreased destruction of free radicals by enzymatic catalase, glutathione peroxidase (GSH- px), and superoxidase dismutase (SOD) antioxidants. The levels of these antioxidant enzymes critically influence the susceptibility of various tissues to oxidative stress and are associated with the development of complications in diabetes. The enzyme superoxide dismutase, glutathione peroxidase and catalase activity contribute to eliminate superoxide anions, hydroxyl radicals and hydrogen peroxide respectively (Soto et al., 2003).

 

1.2.2    Blood Glucose Regulation

Fig. 1 showing the homeostatic mechanism which keeps the blood glucose concentration within a remarkable narrow range is composed of several interacting systems, of which hormonal regulation is the most important. There are two types of mutually antagonistic metabolic hormones that are regulate blood glucose levels as shown in Fig. 1 below. Catabolic hormones such as glucagon, growth hormone e.g. pituitary hormone, glucocorticoid e.g. cortisol, catecholamines e.g. adrenaline, noradrenaline, dopamine which increases blood glucose; while anabolic hormone (insulin) decreases blood glucose. The human blood sugar level should be fairly constant at all times and this is made possible by the action of the two antagonistic hormones, insulin and glucagon. Both insulin and glucagon are secreted by the pancreas, and thus are referred to as pancreatic endocrine hormones. It is the production of insulin and glucagon by the pancreas which determines if a patient has diabetes, hypoglycemia or some other sugar metabolism related problem (John and Henry, 2001).

The inducer of insulin secretion is high blood glucose. Although, there is always low level of insulin secreted by the pancreas, the amount secreted into the blood increases as the blood glucose rises. Similarly, as blood glucose falls, the amount of insulin secreted by the beta cells decreases. Insulin has an effect on number of cells, including muscle cells, red blood cells and fat cells. In response to insulin, these cells absorb glucose out of the blood, having the net effect of reducing the high blood glucose levels to the normal range (John and Henry, 2001). Glucagon is secreted by the alpha cells of the pancreas in the same pattern as insulin, but in opposing biochemical mechanism. If the blood glucose is high, no glucagon will be secreted. When blood glucose has decreased such as during period of fasting, more glucagon will be secreted. The effect of glucagon is to facilitate the release of glucose from the liver cells into the blood stream, with the net effect of increasing blood glucose. Glucagon also facilitates gluconeogenesis.

 

Fig. 1: The Regulation of Glucose. (Stephanie, 2008)

 

 

 

 

1.3       Classification of Diabetes

 

1.3.1    Type 1 Diabetes Mellitus

This form of diabetes is also called insulin-dependent diabetes, and results from autoimmune mediated destruction of the beta cells of the pancreas (Zimmet et al., 1995). The rate of destruction of beta cells is quite variable, being rapid in some individuals and slow in others (Zimmet et al., 1994). The rapidly progressive form is commonly observed in children, but also may occur in adults (Humphery et al., 1998). The slowly progressive form generally form generally occurs in adults, and is sometimes referred to as latent autoimmune diabetes in adults (LADA). Some patients, particularly children and adolescents, may present with ketoacidosis as the first manifestation of the disease (Japan and Pittsburgh Childhood Diabetes Research Groups, 1985).

Individuals with Type 1 diabetes often become dependent on insulin for survival and are at risk of ketoacidosis (Wallins et al., 1996). At this stage of the disease, there is little or no insulin secretion as manifested by low or undetected levels of plasma C-peptide (Hother-Nielsen et al., 1988). Markers of immune destruction, like islet cell autoantibodies, and/or autoantibodies to insulin, and autoantibodies to glutamic acid decarboxylase (GAD) are present in 85-90% of individuals with Type 1 diabetes mellitus when fasting diabetic hyperglycaemia is initially detected (Verge et al., 1996). The peak incidence of this form of diabetes occurs in childhood to the ninth decade of life (Molbak et al., 1994). There is a genetic predisposition to autoimmune destruction of beta cells. It is also related to environmental factors that are still poorly defined. Although, patients are usually not obese when they present with this type of diabetes, the presence of obesity is not incompatible with the diagnosis. These patients may also have other autoimmune disorders such as Graves’ disease, Hashimoto’s thyroiditis, and Addison’s disease (Betterle et al., 1983).  Epidemiology of Diabetes Interventions and Complication Study (EDIC) reported that cardiovascular benefit was observed ten years after intensive treatment (Nathan et al., 2005); a 42% decrease in the cardiovascular rate and a 15 to 33% reduction in myocardial infarction in T1D subjects (Lillioja et al., 1993).

1.3.2    Type 2 Diabetes Mellitus

Diabetes mellitus of this type is regarded as non-insulin dependent diabetes, or adult-unset diabetes. It is a term used for individuals who have relative (rather than absolute) insulin deficiency (Lillioja et al., 1993). People with this type of diabetes are frequently resistant to the action of insulin (Lillioja et al., 1993; DeFronzo et al., 1997). These individuals do not need insulin treatment to survive. This form of diabetes is frequently undiagnosed for many years because the hyperglycaemia is often not severe enough to provoke noticeable symptoms of diabetes (Harris, 1993; Mooy, et al., 1995). Nevertheless, such patients are at increased risk of developing macrovascular and microvascular complications (Harris, 1993; Mooy et al., 1995). There are probably several different mechanisms which result in this form of diabetes, and it is likely that the number of people in this category will decrease in the future as identification of specific pathogenetic processes and genetic defects permits better differentiation and a more definitive classification with movement into “Other types”.

Although, the specific aetiologies of this form of diabetes are not known, by definition autoimmune destruction of the pancreas does not occur and patients do not have other known specific causes of diabetes. The majority of patients do not have other known specific causes of diabetes. The majority of patients with this form of diabetes are obese; obesity itself causes or aggravates insulin resistance (Campbell and Carlson, 1993; Bogardus et al., 1985). Many of those who are not obese by traditional weight criteria may have an increased percentage of body fat distributed predominantly in the abdominal region (Kissebah et al., 1982). Ketoacidosis is infrequent in this type of diabetes; when seen it usually arises in association with stress of another illness such as infection (Banerji et al., 1994; Umpierrez et al., 1995). Whereas patients with this form of diabetes may have insulin levels that appear normal or elevated, the high blood glucose levels in these diabetic patients would be expected to result in even higher insulin values had their beta-cell function been normal (Polonsky et al., 1996). Thus, insulin secretion is defective and insufficient to compensate for the insulin resistance. On the other hand, some individuals have essentially normal insulin action, but markedly impaired insulin secretion. Insulin sensitivity may be increased by weight reduction, increased physical activity, and/or pharmacological treatment of hyperglycaemia but is not restored to normal (Simonson et al., 1984; Wing et al., 1994). The risk of developing Type 2 diabetes increases with age, obesity, and lack of physical activity (Zimmet, 1992). It occurs more frequently in women with prior gestational diabetes mellitus (GDM) and in individuals with hypertension or dyslipidaemia. Its frequency varies in different racial/ethnic subgroups (Valle et al., 1997). It is often associated with strong familial, likely genetic predisposition. However, the genetics of this form of diabetes are complex and not clearly defined. Some patients who present with a clinical picture consistent with Type 2 diabetes have autoantibodies similar to those found in Type 1 diabetes, and may masquerade as Type 2 diabetes if antibody determinations are not made. Patients who are non-obese or who have relatives with Type 1 diabetes and who are of northern Europe origin may be suspected of having late onset Type 1 diabetes. Individuals with chronic hyperglycaemia insulin resistance, and/or diabetes mellitus Type 2 are of greater risk for hypertension, dyslipidemia, and cardiovascular disease (WHO, 2003). Although genetic factors may play a role in the  etiology of diabetes mellitus Type 2 (McCarthy, 2003), there is now convincing evidence that diabetes mellitus Type 2 is strongly associated with modifiable factors such as diet. Interestingly among the several factors present in diet, “coffee” one of the most widely consumed non-alcoholic beverages in western society (Keijzers et al., 2002), is highlighted as a potent dietary component associated with reduced risk of several chronic diseases, including diabetes mellitus Type 2 and its complications (Paynter et al., 2006). It is evident that early intensive glycemic control seems to reduce the risk of cardiovascular event later in life. In the last two years several trials among T2D patients (Patel, 2008) have investigated if even more intensive glycemic control (HbA1c 6.4-6.9% compared to HbA1c 7.0-8.4%) results in a further reduction in cardiovascular disease and mortality. Intensive control did not seem to influence the outcome in short term (3 to 6 years after) when initiated in those diagnosed many years previously. In one study (Gerstein, 2008), mortality did increase in the intensive treated group and because of the many hypoglycaemic episodes, this study was stopped after 3.5 years due to the rate of hypoglycaemic episodes that was the cause of increased mortality. One suggestion was that less strict HbA1c goals than 7.0% might be indicated for patients who had extensive co-morbid conditions, limited life expectancy, or an increased risk of severe hypoglycemia (Brown et al., 2010).

 

1.3.2.1 Gestational Diabetes

Gestational diabetes is carbohydrate intolerance resulting in hyperglycaemia of variable severity with onset or first recognition during pregnancy (Kissebah et al., 1982). It does not exclude the possibility that the glucose intolerance may antedate pregnancy but has been previously unrecognized. The definition applies irrespective of whether or not insulin is used for treatment or the condition persists after pregnancy (Kissebah et al., 1982). Women who become pregnant and who are known to have diabetes mellitus which antedates pregnancy do not have gestational diabetes but have “diabetes mellitus and pregnancy” and should be treated accordingly before, during, and after the pregnancy. In the early part of pregnancy (e.g. first trimester and first half of second trimester) fasting and postprandial glucose concentrations are normally lower than in normal, non-pregnant women (Polonsky et al., 1996). Elevated fasting or postprandial plasma glucose levels at this time in pregnancy may well reflect the presence of diabetes which has antedated pregnancy, but criteria for designating abnormally high glucose concentration at this time have not yet been established (Polonsky et al., 1996). The occurrence of higher than usual plasma glucose levels at this time of pregnancy mandates careful management and may be an indication for carrying out an OGTT. Nevertheless, normal glucose tolerance in the early part of pregnancy does not itself establish that gestational diabetes may not develop later. Individuals at high risk for gestational diabetes include older women, those with previous history of glucose intolerance, and those with a history of large for gestational babies, women from certain high-risk ethnic groups, and any pregnant woman who has elevated fasting, or casual, blood glucose levels. It may be appropriate to screen pregnant women belonging to high-risk populations during the first trimester of pregnancy in order to detect previously undiagnosed diabetes mellitus. Formal systematic testing for gestational diabetes is usually done between 24 and 28 weeks of gestation (Valle et al., 1997).

 

1.3.2.2 Genetic defects of beta cell function

Several forms of the diabetic state may be associated with monogenic defects in beta-cell function which are frequently characterized by onset of mild hyperglycaemia at an early age (generally before age 25 years). They are usually inherited in an autosomal dominant pattern (Byrne et al., 1960). Abnormalities at three genetic loci on different chromosomes have now been characterized. The most common form is associated with mutations on chromosome 12 in a hepatic nuclear transcription factor referred to as HNF1 alpha (Yamagata et al., 1996). A second form is associated with mutations in the glucokinase gene on chromosome 7p (Vionnet et al., 1992; Froguel et al., 1992).

Glucokinase converts glucose to glucose-6-phosphate, the metabolism of which in turn stimulates insulin secretion by the beta cell. Thus, glucokinase serves as the “glucose sensor” for the beta cell. Because of defects in the glucokinase gene, increased levels of glucose are necessary to elicit normal levels of insulin secretion. A third form is associated with a mutation in the HNF alpha gene on chromosome 20q (Yamagata et al., 1996). HNF4 alpha is a transcription factor which is involved in the regulation of the expression of HNF alpha. A fourth variant has recently has recently been ascribed to mutations in another transcription factor gene, IPF-1, which in its homozygous form leads to total pancreatic agenesis (Stoffers et al., 1997). Specific genetic defects in other individuals who have a similar clinical presentation are currently being defined. Point mutations in mitochondrial DNA have been found to be associated with diabetes mellitus and deafness (Wagner and Turnbull, 1997). The most common mutation occurs at position 3243 in the tRNAleucine gene, leading to an A to G substitution.

An identical lesion occurs in the MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like syndrome); however, diabetes is not part of this syndrome, suggesting for unknown reasons different phenotypic expressions of these genetic lesions (Johns, 1995). Genetic abnormalities that result in the inability to convert proinsulin to insulin have been identified in a few families. Such traits are usually inherited in an autosomal dominant pattern (Gruppuso et al., 1984; Robbins et al., 1984) and the resultant carbohydrate intolerance is mild. Similarly, mutant insulin molecules with impaired receptor binding have been identified in a few families. These are also associated with autosomal inheritance and either normal or only mildly impaired carbohydrate metabolism (Handa et al., 1984; Sanz et al., 1986).

 

1.4       Prevalence

In the past few decades significant increases have occurred in the pattern of health and diseases in many developing countries including Nigeria. The prevalence of diabetes in African communities is increasing with ageing of the population and life style changes associated with rapid urbanization (Dod, 1989). As malnutrition and communicable disease come under control non communicable diseases like diabetes mellitus and hypertension have begun to emerge as major public health problems. Similar to the experience in many other parts of the world, diabetes mellitus is the most common endocrine metabolic disorder encountered in Nigeria (Frings et al., 1972). Diabetes mellitus is a major global health problem and it has an increasing prevalence due to several factors, such as population, growth, aging, urbanization and increasing prevalence of obesity or lack of physical exercise. The number of people diagnosed with diabetes is increasing at an alarming rate. It is estimated that by the year 2030, 366 million people worldwide will have the disease (Chan et al., 2012).

 

1.5       Complications

Chronic hyperglycemia is associated with damage to small and large vessels, mainly affecting the cardiovascular system, the kidneys, the retina and the peripheral nervous system. The Epidemiology of Diabetes Interventions and Complications Study (EDIC) was a follow up study of the DCCT, eight years after intervention. EDIC (Nathan et al., 2005) confirmed the risk reduction for microvascular complications and provided evidence that intensive diabetes treatment and improved glycemic control lead to a significant risk reduction for macrovascular complications compared to conventional treatment. Clinically evident complications are rare in childhood and adolescence T1D; however, abnormalities may be present a few years after onset of the disease. On the contrary, clinical presentation of T2D is often slow progressing and manifested complications such as dyslipidemia, hypertension.

Albuminuria may be present at diagnosis and should be assessed after blood glucose control has been optimized. In addition, complication testing at diagnosis should include eye examination, liver enzymes and control for obstructive sleep apnea. Risk factors for the development of complications are longer duration of diabetes, older age, puberty, smoking, hypertension and family history of complications (Donaghue et al., 2009). In general, areas with specialized centres report a declining incidence of complications (Bojestig et al., 2011) and areas where health care is not optimal hold a greater risk of complications (Rossing et al., 2002). However, this does not undermine the importance of good glycemic control.

 

1.5.1    Microvascular Complications

Microvascular complications include retinopathy, nephropathy and neuropathy and they are associated with a high degree of morbidity and mortality.

 

1.5.1.1 Diabetic Retinopathy

In developed countries diabetic eye disease is among the leading cause of blindness and it is the fifth leading cause of global blindness, affecting an estimated 1.8 billion people (WHO, 2005). Diabetic retinopathy (DR) causes microvascular retinal changes and may lead to visual impairment and blindness. After 20 years of diabetes nearly all patients with T1D have some degree of DR (Skrivarhaug et al., 2006). Adolescents have a higher risk of progression to vision threatening retinopathy compared with adults (Donaghue et al., 2009).

 

1.5.1.2 Diabetic Nephropathy

Diabetic neuropathies are a heterogeneous group of disorders which can affect both the somatic and autonomic nervous system. Diabetic sensorimotoric polyneuropathy is the most common form and is often referred to as – diabetic neuropathy. Neuropathy can cause morbidity with significant impact on the quality of life of the person with diabetes, and can result in early death. The major morbidity is foot ulceration, which can lead to gangrene and ultimately to limb loss. Diabetic neuropathy is the most common form of neuropathy in developed countries and is responsible for 50 to 75% of non-traumatic amputations (Vinik et al., 2006).. A population survey (Harris and Eastman, 1993) reported that 30% of IDDM and 36 to 40% of non-insulin-dependent diabetes mellitus (NIDDM) patients with diabetes experienced neuropathic symptoms. It is expected that diabetic neuropathy is grossly underdiagnosed and undertreated in many countries. Management of the disease is complex and the key to success depends, in part, on discovering the underlying pathological processes in each particular clinical presentation. There has been an increase in the understanding of the pathogenesis of diabetic neuropathies over the last decades and new therapies are emerging that hold promise for the treatment (Vinik et al., 2006).

Diabetic nephropathy (DN) is a major cause of morbidity and mortality among young adults with T1D. DN is characterized by progressive kidney disease caused by angiopathy of capillaries in the kidney glomeruli. It is defined as persistent proteinuria (greater than 500 mg/24 hours) or albuminuria (greater than 300 mg/24 hours) (Donaghue et al., 2009). The first clinical sign of progression to DN is microalbuminuria. Microalbuminuria is defined in one of three ways (Donaghue et al., 2009):

Albumin concentration 30–300 mg/L

Albumin excretion rate (AER) between 20 and 200 μg/min or AER 30–300 mg/24 hours in 24-hours urine collections

Albumin creatinine ratio (ACR) 2.5–25 mg/mmol or 30–300 mg/gm (spot urine)

Persistent microalbuminuria and DN is associated with decreased glomerular filtration rate (GFR) and indicates progression to end stage renal disease (ESRD). ESRD is the prime indication for dialysis and kidney transplantation in many Western countries. DN accounts for 25 to 30% of the patients with ESRD who require dialysis and it has been estimated that 30 to 40% of patients with IDDM will eventually develop ESRD (Selby et al., 1990). The process can be slowed by intensive treatment as shown in EDIC (Steffes et al., 2003). Only 6.8% of the participants in the previous intensive-treatment group developed microalbuminuria and 1.4% developed clinical albuminuria, compared with 15.8% and 9.4% of participants in the previous conventional treated group. The total number of severe kidney events (kidney insufficiency) was more than three times greater in the conventional treated group.

 

1.5.3    Macrovascular Complications

Macrovascular complications include heart disease, stroke and peripheral vascular disease (which can lead to ulcers, gangrene and amputation). Cardiovascular complications constitute the major cause of mortality in patients with T1D and T2D and life expectancy in T2D patients, diagnosed prior to the age of 40 years, is reduced by eight years relative to people without diabetes (Roper et al., 2001). Epidemiological studies have demonstrated that diabetes is an independent risk factor for cardiovascular disease and is associated with a two- to fourfold increased risk of coronary heart disease (Haffner et al., 1998). The metabolic dysregulation associated with diabetes mellitus causes secondary pathological changes in multiple organ systems which imposes a tremendous burden on the individual with diabetes and on the health care system.

 

1.6       What Are Electrolytes?       

Chemically, electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity. Electrolytes are present in the human body, and the balance of the electrolytes in our bodies is essential for normal function of our cells and our organs (Leonard and John, 1989). Common electrolytes that are measured with blood testing include sodium, potassium, chloride, and bicarbonate.

 

1.6.1    Sodium

Sodium is the major positive ion (cation) in fluid outside of cells. The chemical notation for sodium is Na+. When combined with chloride, the resulting substance is table salt. Excess sodium (such as that obtained from dietary sources) is excreted in the urine. Sodium regulates the total amount of water in the body and the transmission of sodium into and out of individual cells also plays a role in critical body functions (Rao, 1992). Many processes in the body, especially in the brain, nervous system, and muscles, require electrical signals for communication. The movement of sodium is critical in generation of these electrical signals. Therefore, too much or too little sodium can cause cells to malfunction, and extremes in the blood sodium levels (too much or too little) can be fatal. Increased sodium (hypernatremia) in the blood occurs whenever there is excess sodium in relation to water. There are numerous causes of hypernatremia; these may include kidney disease, too little water intake, and loss of water due to diarrhea and vomiting. A decreased concentration of sodium (hyponatremia) occurs whenever there is a relative increase in the amount of body water relative to sodium. This happens with some diseases of the liver and kidney, in patients with congestive heart failure, in burn victims, and in numerous other conditions.

A Normal blood sodium level is 135 – 145 milliEquivalents/liter (mEq/L), or in international units, 135 – 145 millimoles/liter (mmol/L).

 

1.6.2    Potassium

Potassium is the major positive ion (cation) found inside of cells. The chemical notation for potassium is K+. The proper level of potassium is essential for normal cell function. Among the many functions of potassium in the body are regulation of the heartbeat and the function of the muscles (Van, 1928). A seriously abnormal increase in potassium (hyperkalemia) or decrease in potassium (hypokalemia) can profoundly affect the nervous system and increases the chance of irregular heartbeats (arrhythmias), which, when extreme, can be fatal. Increased potassium is known as hyperkalemia.

Potassium is normally excreted by the kidneys, so disorders that decrease the function of the kidneys can result in hyperkalemia. Certain medications may also predispose an individual to hyperkalemia. Hypokalemia, or decreased potassium, can arise due to kidney diseases; excessive loss due to heavy sweating, vomiting, or diarrhea, eating disorders, certain medications, or other causes. The normal blood potassium level is 3.5 – 5.0 milliEquivalents/liter (mEq/L), or in international units, 3.5 – 5.0 millimoles/liter (mmol/L).

 

1.6.3    Chloride

Chloride is the major anion (negatively charged ion) found in the fluid outside of cells and in the blood. An anion is the negatively charged part of certain substances such as table salt (sodium chloride or NaCl) when dissolved in liquid. Sea water has almost the same concentration of chloride ion as human body fluids. Chloride also plays a role in helping the body maintain a normal balance of fluids (Rao, 1992).

The balance of chloride ion (Cl) is closely regulated by the body. Significant increases or decreases in chloride can have deleterious or even fatal consequences: Increased chloride (hyperchloremia): Elevations in chloride may be seen in diarrhea, certain kidney diseases, and sometimes in over activity of the parathyroid gland. Decreased chloride (hypochloremia): Chloride is normally lost in the urine, sweat, and stomach secretions. Excessive loss can occur from heavy sweating, vomiting, and adrenal gland and kidney disease. The normal serum range for chloride is 98 – 108 mmol/L.

 

1.6.4    Bicarbonate

The bicarbonate ion acts as a buffer to maintain the normal levels of acidity (pH) in blood and other fluids in the body. Bicarbonate levels are measured to monitor the acidity of the blood and body fluids (Leonard and John, 1989). The acidity is affected by foods or medications that we ingest and the function of the kidneys and lungs. The chemical notation for bicarbonate on most lab reports is HCO3 or represented as the concentration of carbon dioxide (CO2). The normal serum range for bicarbonate is 22-30 mmol/L. The bicarbonate test is usually performed along with tests for other blood electrolytes. Disruptions in the normal bicarbonate level may be due to diseases that interfere with respiratory function, kidney diseases, metabolic conditions, or other causes.

 

 

 

1.7       Inter Relationship of Diabetes with Sodium- Potassium and ATPase

The Na+, K+-ATPase (NKA) is an ubiquitous enzyme consisting of α, β and γ subunits, and is responsible for the creation and maintenance of the Na+ and K+ gradients across the cell membrane by transporting 3 Na+ out and 2 K+ into the cell (Suhail and Rizvi, 1990). Sodium pump regulation is tissue as well as isoform specific. Intracellular messengers differentially regulate the activity of the individual NKA isozymes. Regulation of specific NKA isozymes gives cells the ability to precisely coordinate NKA activity to their physiological requirements (Reed et al., 2006). It is the only known receptor for the cardiac glycosides used to treat congestive heart failure and cardiac arrhythmias. Endogenous ligands structurally similar to cardiac glycosides may act as natural regulators of the sodium pump in heart and other tissues. Identification of naturally occurring regulators of  NKA could initiate the discovery of new hormone-like control systems involved in the etiology of selected disease processes, hence the importance of understanding the relation of the sodium pump and its ligands to disease. Diabetes has a marked effect on the metabolism of a variety of tissues and because the NKA is critical for the membrane potential and many transports, a change in its activity in diabetes would have profound consequence in these tissues (Kimelberg, 1975).

This is in contrast to the outside of the cell, where there is a high concentration of extracellular Na+ and a low concentration of extracellular K+. Thus, a concentration gradient exists for the loss and gain of intracellular K+ and Na+, respectively. This gradient is maintained through the activity of various ionic channels and transporters, but predominantly the activity of the NKA. A typical cell keeps a resting membrane potential of -70 mV. Potassium ions will tend to flow out of the cell, since their equilibrium potential (-91 mV) is more negative than the trans membrane potential. Sodium ions have a very strong force driving them into the cell, since both the chemical and electrical gradients (equilibrium potential of +64 mV) favor Na+ uptake. The enzymatic manifestation of the sodium pump is the NKA. This enzyme, found in all mammalian cell membranes, is necessary for proper cellular function since it helps to preserve the ionic gradients across the cell membrane and thus the membrane potential and osmotic equilibrium of the cell (Cox et al., 2005). This function is crucial for cell survival and body homeostasis since the Na+ gradient is used as an energy source to transport ions or solutes, and is at the origin of the vectorial Na+ reabsorption in the kidney and of action potentials in excitable tissues. It is putative component of a biological membrane that affects the transfer of these ions from one side of the membrane to the other. It is active transport which is responsible for the well-established observation that cells contain relatively high concentrations of potassium ions but low concentrations of sodium ions. The mechanism responsible for this is the sodium-potassium pump which moves these two ions in opposite directions across the plasma membrane (Raccah et al., 1996). This was investigated by following the passage of radioactively labeled ions across the plasma membrane of certain cells. It was found that the concentrations of sodium and potassium ions on the two other sides of the membrane are interdependent, suggesting that the same carrier transports both ions. It is now known that the carrier is an ATPase and that it pumps three sodium ions out of the cell for every two potassium ions pumped in. It catalyzes the transfer of 2 K+ from the extracellular space into the cell and the extrusion of 3 Na+, while hydrolyzing adenosine triphosphate (ATP) to adenosine diphosphate (ADP) and inorganic phosphate (Pi). The transport of 3 Na+ for 2 K+ across the membrane, through the means of the sodium pump, maintains trans membrane gradients for the ions and produces a convenient driving force for the secondary transport of metabolic substrates such as amino acids and glucose (Suhail and Rizvi, 1990). In addition, the nonequivalent transport is electrogenic and leads to the generation of a trans membrane electrical potential allowing cells to become excitable. The “pump” couples the energy released in the intracellular hydrolysis of adenosine triphosphate (ATP) to the transport of cellular ions, a major pathway for the controlled translocation of sodium and potassium ions across the cell membrane. NKA therefore controls directly or indirectly many essential cellular functions, e.g. cell volume, free calcium concentration, and membrane potential. Regulation of this enzyme (transporter) and its individual isoforms is thought to play a key role in the etiology of some pathological processes (Cox et al., 2005)

1.7.1    Relevance in Diabetes Mellitus

Diabetes has a marked effect on the metabolism of a variety of tissues and because the NKA is critical for the membrane potential and many transports, a change in its activity in diabetes would have profound consequence in these tissues (Leonard and John, 1989). We have observed significant effect of diabetes in the metabolism of diabetic erythrocytes and significant decrease in the activity of NKA in alloxan induced diabetic rats. Erythrocytes of diabetic patients have reduced life span, altered membrane dynamic properties and increased membrane thermo-stability (Knip et al., 2005). It has also been reported that diabetic patients with poor metabolic control have lower erythrocyte membrane enzymes activity as compared to healthy control subjects. The modified proteins have altered functions such as modified enzymatic activities, lower affinities for their receptors.

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