Pathophysiology of hyperlipidemia in diabetes mellitus

Many lipoprotein abnormalities are seen in the untreated, hyperglycemic diabetic patient. The non-insulin-dependent diabetic (NIDDM) patient with mild fasting hyperglycemia commonly has mild hypertriglyceridemia due to overproduction of TG-rich lipoproteins in the liver, associated with decreased high-density lipoprotein (HDL) cholesterol levels. The more hyperglycemic untreated NIDDM and insulin-dependent diabetic (IDDM) patient have mild to moderate hypertriglyceridemia due to decreased adipose tissue and muscle lipoprotein lipase, (LPL) activity. These patients also have decreased HDL cholesterol levels associated with defective LPL catabolism of TG-rich lipoproteins. Treatment of diabetes with oral sulfonylureas or insulin corrects most of the hypertriglyceridemia and some of the decrease in HDL cholesterol. The abnormality in adipose tissue LPL activity corrects slowly over several months of therapy. The treated IDDM patient often has normal lipoprotein levels. The treated NIDDM patient may continue to have mild hypertriglyceridemia, increased intermediate-density lipoprotein levels, small dense low-density lipoproteins (LDL) with increased apoprotein B, and decreased HDL cholesterol levels. The central, abdominal distribution of adipose tissue in IDDM is associated with insulin resistance, hypertension, and the above lipoprotein abnormalities. Improvement in glucose control, in the absence of weight gain, leads to lower triglyceride and higher HDL cholesterol levels. In addition, the diabetic patient is prone to develop other defects that, in themselves, lead to hyperlipidemia, such as proteinuria, hypothyroidism, and hypertension, treated with thiazide diuretics and beta-adrenergic-blocking agents. When a diabetic patient independently inherits a common familial form of hypertriglyceridemia, he might develop the severe hypertriglyceridemia of the chylomicronemia syndrome.