More than 400 traditional plant treatments for diabetes mellitus have been recorded, but only a small number of these have received scientific and medical evaluation to assess their efficacy. Traditional treatments have mostly disappeared in occidental societies, but some are prescribed by practitioners of alternative medicine or taken by patients as supplements to conventional therapy. However, plant remedies are the mainstay of treatment in underdeveloped regions. A hypoglycemic action from some treatments has been confirmed in animal models and non-insulin-dependent diabetic patients, and various hypoglycemic compounds have been identified. A botanical substitute for insulin seems unlikely, but traditional treatments may provide valuable clues for the development of new oral hypoglycemic agents and simple dietary adjuncts.

Thiazolidinediones (TZDs) are a new class of oral antidiabetic agents. They selectively enhance or partially mimic certain actions of insulin, causing a slowly generated antihyperglycaemic effect in Type 2 (noninsulin dependent) diabetic patients. This is often accompanied by a reduction in circulating concentrations of insulin, triglycerides and nonesterified fatty acids. TZDs act additively with other types of oral antidiabetic agents (suphonylureas, metformin and acarbose) and reduce the insulin dosage required in insulin-treated patients. The glucose-lowering effect of TZDs is attributed to increased peripheral glucose disposal and decreased hepatic glucose output. This is achieved substantively by the activation of a specific nuclear receptor - the peroxisome proliferator-activated receptor-gamma (PPARgamma), which increases transcription of certain insulin-sensitive genes. To date one TZD, troglitazone, has been introduced into clinical use (in Japan, USA and UK in 1997). This was suspended after 2 months in the UK pending further investigation of adverse effects on liver function. TZDs have been shown to improve insulin sensitivity in a range of insulin-resistant states including obesity, impaired glucose tolerance (IGT) and polycystic ovary syndrome (PCOS). In Type 2 diabetes, the TZDs offer a new type of oral therapy to reduce insulin resistance and assist glycaemic control.

The effects on glucose homeostasis of eleven plants used as traditional treatments for diabetes mellitus were evaluated in normal and streptozotocin diabetic mice. Dried leaves of agrimony (Agrimonia eupatoria), alfalfa (Medicago sativa), blackberry (Rubus fructicosus), celandine (Chelidonium majus), eucalyptus (Eucalyptus globulus), lady's mantle (Alchemilla vulgaris), and lily of the valley (Convallaria majalis); seeds of coriander (Coriandrum sativum); dried berries of juniper (Juniperus communis); bulbs of garlic (Allium sativum) and roots of liquorice (Glycyrhizza glabra) were studied. Each plant material was supplied in the diet (6.25% by weight) and some plants were additionally supplied as decoctions or infusions (1 g/400 ml) in place of drinking water to coincide with the traditional method of preparation. Food and fluid intake, body weight gain, plasma glucose and insulin concentrations in normal mice were not altered by 12 days of treatment with any of the plants. After administration of streptozotocin (200 mg/kg i.p.) on day 12 the development of hyperphagia, polydipsia, body weight loss, hyperglycaemia and hypoinsulinaemia were not affected by blackberry, celandine, lady's mantle or lily of the valley. Garlic and liquorice reduced the hyperphagia and polydipsia but did not significantly alter the hyperglycaemia or hypoinsulinaemia. Treatment with agrimony, alfalfa, coriander, eucalyptus and juniper reduced the level of hyperglycaemia during the development of streptozotocin diabetes. This was associated with reduced polydipsia (except coriander) and a reduced rate of body weight loss (except agrimony). Alfalfa initially countered the hypoinsulinaemic effect of streptozotocin, but the other treatments did not affect the fall in plasma insulin. The results suggest that certain traditional plant treatments for diabetes, namely agrimony, alfalfa, coriander, eucalyptus and juniper, can retard the development of streptozotocin diabetes in mice.

The metabolic syndrome is a clustering of risk factors which predispose an individual to cardiovascular morbidity and mortality. There is general consensus regarding the main components of the syndrome (glucose intolerance, obesity, raised blood pressure and dyslipidaemia [elevated triglycerides, low levels of high-density lipoprotein cholesterol]) but different definitions require different cut points and have different mandatory inclusion criteria. Although insulin resistance is considered a major pathological influence, only the World Health Organization (WHO) and European Group for the study of Insulin Resistance (EGIR) definitions include it amongst the diagnostic criteria and only the International Diabetes Federation (IDF) definition has waist circumference as a mandatory component. The prevalence of metabolic syndrome within individual cohorts varies with the definition used. Within each definition, the prevalence of metabolic syndrome increases with age and varies with gender and ethnicity. There is a lack of diagnostic concordance between different definitions. Only about 30% of people could be given the diagnosis of metabolic syndrome using most definitions, and about 3540% of people diagnosed with metabolic syndrome are only classified as such using one definition. There is currently debate regarding the validity of the term metabolic syndrome, but the presence of one cardiovascular risk factor should raise suspicion that additional risk factors may also be present and encourage investigation. Individual risk factors should be treated.

This article traces the roots of the antihyperglycaemic biguanide metformin from the use of Galega officinalis (goat's rue or French lilac) as a herbal treatment for the symptoms of diabetes. G. officinalis was found to be rich in guanidine, a substance with blood glucose-lowering activity that formed the chemical basis of metformin. This insulin sensitising drug was introduced in 1957. Copyright Many biguanides and related guanidine derivatives have been examined as potential antidiabetic agents, 11,29 although much of this work pre-dates the availability of present models of insulin resistance. However, the multiple mechanisms of action and unique pharmacokinetic and pharmacodynamic properties of metformin confer a favourable risk-benefit ratio that has established metformin as a leading treatment for patients with type 2 diabetes. 30,31 Postscript of ironiesThere are several ironies about metformin. In our high-tech era of drug discovery and development this firstline treatment for type 2 diabetes is little removed from a herbal remedy of the middle ages. Despite its chemical simplicity and detailed investigation, metformin continues to evade a complete exposé of its cellular activity. While endless pharmacovigilance has monitored the safety profile of metformin, its natural ancestor, G. officinalis (known as Professor Weed in the USA) is a Class A Federal Noxious Weed in 35 states of America, and appears on the database of poisonous plants. 32 SHORT REPORTMetformin: its botanical background