Biological activity of synthetic human insulin

Bioactive Agent Discovery from the Natural Compounds for the Treatment of Type 2 Diabetes Rat Model

Diabetes mellitus is a well-known chronic metabolic disease that poses a long-term threat to human health and is characterized by a relative or absolute lack of insulin, resulting in hyperglycemia. Type 2 diabetes mellitus (T2DM) typically affects many metabolic pathways, resulting in β-cell dysfunction, insulin resistance, abnormal blood glucose levels, inflammatory processes, excessive oxidative reactions, and impaired lipid metabolism. It also leads to diabetes-related complications in many organ systems. Antidiabetic drugs have been approved for the treatment of hyperglycemia in T2DM; these are beneficial for glucose metabolism and promote weight loss, but have the risk of side effects, such as nausea or an upset stomach. A wide range of active components, derived from medicinal plants, such as alkaloids, flavonoids, polyphenol, quinones, and terpenoids may act as alternative sources of antidiabetic agents. They are usually attributed to improvements in pancreatic function by increasing insulin secretions or by reducing the intestinal absorption of glucose. Ease of availability, low cost, least undesirable side effects, and powerful pharmacological actions make plant-based preparations the key player of all available treatments. Based on the study of therapeutic reagents in the pathogenesis of humans, we use the appropriate animal models of T2DM to evaluate medicinal plant treatments. Many of the rat models have characteristics similar to those in humans and have the advantages of ease of genetic manipulation, a short breeding span, and access to physiological and invasive testing. In this review, we summarize the pathophysiological status of T2DM rat models and focus on several bioactive compounds from herbal medicine with different functional groups that exhibit therapeutic potential in the T2DM rat models, in turn, may guide future approach in treating diabetes with natural drugs.

The evolution of insulin glargine and its continuing contribution to diabetes care

The epoch-making discovery of insulin heralded a new dawn in the management of diabetes. However, the earliest, unmodified soluble insulin preparations were limited by their short duration of action, necessitating multiple daily injections. Initial attempts to protract the duration of action of insulin involved the use of various additives, including vasoconstrictor substances, which met with limited success. The subsequent elucidation of the chemical and three-dimensional structure of insulin and its chemical synthesis and biosynthesis allowed modification of the insulin molecule itself, resulting in insulin analogs that are designed to mimic normal endogenous insulin secretion during both fasting and prandial conditions. Insulin glargine was the first once-daily, long-acting insulin analog to be introduced into clinical practice more than 10 years ago and is specifically designed to provide basal insulin requirements. It has a prolonged duration of action and no distinct insulin peak, making it suitable for once-daily administration and reducing the risk of nocturnal hypoglycemia that is seen with intermediate-acting insulins. Insulin glargine can be used in combination with prandial insulin preparations and non-insulin anti-diabetic agents according to individual requirements.

Oral glutamine is superior than oral glucose to promote glycemia recovery in mice submitted to insulin-induced hypoglycemia

The effect of the oral administration of blood glucose precursors on glycemia recovery and liver glucose production in fasted mice subjected to insulin-induced hypoglycemia (IIH) was investigated. IIH was obtained with increasing doses (from 0.5 to 2.0 U·kg(-1)) of intraperitoneal regular insulin where glycemia was evaluated from 0 to 300 min after insulin injection. The dose of 1.0 U·kg(-1) showed the best results, that is, a clear glycemia recovery phase without convulsions or deaths. Thus, this dose was used in all experiments. Afterwards, mice submitted to IIH received orally by gavage: saline (control group), glucose (100 mg·kg(-1)), glycerol (100 mg·kg(-1)), lactate (100 mg·kg(-1)), alanine (100 mg·kg(-1)), or glutamine (100 mg·kg(-1)). It was observed that glutamine was more effective in promoting glycemia recovery if compared with glucose, lactate, glycerol, or alanine. In agreement with these results, the best performance in terms of liver glucose production was obtained when glutamine was used as glucose precursors. These results open perspectives for clinical studies to investigate the impact of oral administration of gluconeogenic amino acids to promote glycemia recovery during hypoglycemia.

The new insulins. Their characteristics and clinical indications

In the past 10 years the techniques of gel filtration and ion exchange chromatography have made available insulins of markedly enhanced purity. These highly purified insulins have made immunological insulin resistance a rarity, and result in absent or clinically insignificant levels of insulin antibodies in insulin-treated diabetics. Insulin allergy has not been reported with highly purified insulins alone, and is rare even when the patient has previously received recrystallised insulin. Generalised allergic reactions to insulin and insulin resistance are associated with the enhanced immunological reaction to intermittent insulin therapy. The use of highly purified insulins for short courses of treatment is therefore mandatory, particularly in patients with infections. Injection-site lipoatrophy, a relatively common occurrence with the older insulins, disappears on changing to highly purified preparations. Following a change to highly purified insulins, insulin dose requirements will fall gradually with insulin antibody levels. When switching from conventional beef to highly purified pork insulins, a more immediate change in dose requirements may occur so that prospective reductions in insulin dose are indicated. It is still uncertain whether moderate levels of insulin antibodies are associated with any difference in metabolic control. This is partly a reflection of difficulties in measuring diabetic control, and partly a lack of properly designed studies. Current insulins of both older and newer types give plasma insulin profiles that are far from physiological. Insulin antibodies cross the placenta and may contribute to increased fetal insulin secretion and neonatal hypoglycaemia. Pre-pregnant patients should be changed to the newer preparations. Highly purified insulins cost little more than conventional insulins in the free market, and should be used in all newly diagnosed insulin-requiring diabetics. More recently, human insulin has become available through both DNA recombinant technology and amino acid substitution techniques. It has proved to have identical characteristics to pork insulin both in vitro and in normal subjects. Clinical trials with human insulin are at present in progress.