Interaction of Herbal Compounds with Biological Targets: A Case Study with Berberine

Berberine is one of the main alkaloids found in the Chinese herb Huang lian (Rhizoma Coptidis), which has been reported to have multiple pharmacological activities. This study aimed to analyze the molecular targets of berberine based on literature data followed by a pathway analysis using the PANTHER program. PANTHER analysis of berberine targets showed that the most classes of molecular functions include receptor binding, kinase activity, protein binding, transcription activity, DNA binding, and kinase regulator activity. Based on the biological process classification of in vitro berberine targets, those targets related to signal transduction, intracellular signalling cascade, cell surface receptor-linked signal transduction, cell motion, cell cycle control, immunity system process, and protein metabolic process are most frequently involved. In addition, berberine was found to interact with a mixture of biological pathways, such as Alzheimer's disease-presenilin and -secretase pathways, angiogenesis, apoptosis signalling pathway, FAS signalling pathway, Hungtington disease, inflammation mediated by chemokine and cytokine signalling pathways, interleukin signalling pathway, and p53 pathways. We also explored the possible mechanism of action for the anti-diabetic effect of berberine. Further studies are warranted to elucidate the mechanisms of action of berberine using systems biology approach.


Introduction
The majority of clinical drugs achieve their effect by binding to a cavity and regulating the cavity, of its protein targets [1]. In general, drugs act on four main types of regulatory proteins that mediate the actions of hormones, neurotransmitters, and autacoids. These four types of regulatory proteins are carriers, proteins, ion channels, and receptors [2]. Certain characteristics are expected for therapeutic targets [3]. A potential target needs only not to be druggable but also linked to disease, most preferably playing critical and inimitable roles in disease state. Binding sites are to have certain structural and physiochemical properties to accommodate high-affinity site-specific binding and subsequent regulation of protein activity by drugs. They are not significantly involved in other important biological processes to avoid potential side effects. Useful information about these targets may be investigated by analysing their sequence properties, protein families, structural folds, biochemical classes, similarity proteins, gene location in the human genome, and associated pathways [4]. This information can be potentially useful in derivation of rule and developing predictive tools in the search for druggable and potential targets [4].
The number of molecular targets acted on by current drug therapy is still in dispute. In 1996, Drews and Ryser identified a total of 483 drug targets addressed by drug therapy [5,6]. Approximately 45% are cell membrane receptors, 28% are enzymes, and the remaining classes comprise 2 The Scientific World Journal hormones (11%), ion channels (5%), nuclear receptors (2%), and DNA (2%). About 7% of the targets are not known biochemically. Later, Hopkins and Groom challenged this figure and suggested that "rule-of-five" compliant drugs acted primarily through only 120 underlying molecular targets [3,7]. However, the statistical analysis of disease genes and related proteins suggested that the total number of the estimated potential targets in the human genome ranges from 600 to 1,500 [3]. In the meantime, another report showed the estimated total number of distinct targets is in the range of 1,700-3,000 [8]. Chen et al. reported targets collected in the Therapeutic Target Database [9] is 997 distinct proteins, 1,494 distinct protein subtypes, and 41 nucleic acids, which are only targeted by at least one marketed drug and 1,267 research targets, which are only targeted by investigational agents that are not approved for clinical use at present [4]. Targets for neoplasm diseases, circulatory system diseases, infectious diseases, and nervous system and sense organs disorders constitute the largest number of targets [1]. An increase in target numbers is made possible by advances in genomics, proteomics, better molecular understanding of diseases, and increased effort in the exploration of new therapeutic targets as well as increased knowledge of unknown or unreported targets of previous existing drugs. An improvement in technology for target identification and validation also contributes greatly.
Chinese herbal medicine (CHM) has always been an integral part of traditional Chinese medicine (TCM), which has been practiced in the east for thousands of years. Chinese herbs are usually in the forms of dried whole plants or parts of the plants (roots, leaves, body, etc.); sometimes shells and even minerals are used. Chinese herbs are often used in a compound formula, consisting of several different herbs hosting different roles according to the principle of Jun-Chen-Zuo-Shi described by the ancient Chinese. Each of Jun, Chen, Zuo, and Shi function together to harmonise the body, with Shi (courier) herbs are included in many formulae to ensure that all components in the prescription are well absorbed and to help to deliver or guide them to the target organs [10]. On some level, the guiding function of Shi herbs relates to modern drug delivery techniques, guiding the drug compound to target tissues. In the modern world, complementary medicine has gained vast popularity in the West. There has been increased use of herbal medicine to manage chronic diseases and promote wellbeing, in countries such as Australia, New Zealand, USA, and Europe [11]. Reports show that 18.9% of the American population used natural products in the precedent year [12]. This increase in popularity is closely related to its proven effectiveness in clinical practice over the past centuries. To date, more than 11,000 species of plants are used medicinally and about 300 are commonly used [13].
Despite its widespread use, CHM is associated with high levels of uncertainty. This is mainly due to lack of evidence, base of efficacy, targets, and safety data. During the process of therapeutic drug development, owing to the preselection of targets, researchers have a basic if not full understanding of which molecular structures the drug will react with or which biological pathway in the body it might alter. Knowledge on molecular interactions and modulations of the drug is anticipated and researched on. However, this is not the case for CHM. There is no preselection of molecular targets in the body but CHM has been used for thousands of years and is proven to be effective. The exact mechanism of the herbs actions is yet to be elucidated.
The proven clinical efficacy of some herbal medicines is considered to be due to the interaction of pharmacologically active components from the herbs with molecular targets in the body. Similar to synthetic drugs, active compounds of herbal medicine may bind to and undergo interactions with molecular structures or herbal targets to produce therapeutic or adverse effects. However, there is a lack of understanding of how CHMs exert their biological and clinical effects at a molecular level, which impedes development of CHMs and the incorporation of CHMs into mainstream medicine in the West.
Berberine (Figure 1, molecular formula C 20 H 19 NO 5 and a molecular weight of 353.36) is an isoquinoline alkaloid found in many medicinal plants [14]. It is a major constituent of many medicinal plants of families Papaveraceae, Berberidaceae, Fumariaceae, Menispermaceae, Ranunculaceae, Rutaceae, and Annonaceae [15]. It is present in Hydrastis canadensis (goldenseal), Coptis chinensis (Coptis or goldenthread), Berberis aquifolium (Oregon grape), Berberis vulgaris (barberry), and Berberis aristata (tree turmeric). The berberine alkaloid can be found in the roots, rhizomes, and stem bark of the plants. Berberine is one of the main alkaloids found in the Chinese herb Huang Lian (Rhizoma coptidis) [16]. Huang Lian has traditionally been used to treat diarrhoea and diabetes. In China, berberine has been manufactured into the over-the-counter drug Huang Lian Su Pian, also known as Coptis Extract Tablets for the treatment of traveler's diarrhoea [14,17]. In recent years, there has been a growing interest in the pharmacological activities of berberine and many studies have been carried out to elucidate the mechanisms of action of berberine. This study aims to review molecular targets of berberine based on in vitro studies. Berberine has shown to have good hypoglycaemic effects, so we also reviewed the effects of berberine in animal and human studies, with a focus on diabetes mellitus.

Data
Retrieval from the Literature. In vitro studies related to berberine and its targets were searched using Pubmed (from inception to April 2012). Search terms used were a combination of "berberine," "in vitro," "human cell," and "mechanism." Only studies using human cell lines were used to extract current berberine targets. Studies using animal cell lines or berberine derivatives or in a language other than English were excluded. Information extracted from these studies includes molecular targets of berberine (name and gene symbols), cell type, effects of berberine, and possible clinical applications.

PANTHER Analysis.
Using the PANTHER Classification System, in vitro berberine targets were analysed using three approaches: molecular function, biological process, and pathway involvement Table 2. PANTHER is a publicly available database that relates protein sequence evolution to evolution of protein functions and biological roles (http://www.pantherdb.org/).

Targets of Berberine.
A total of 90 berberine targets were identified in our literature search, as shown in Table 1.
Extensive research has been carried out to study the effects of berberine on cancer cells in vitro. This may be related to recent discovery of anti-cancer drugs with natural compound origin, for example, paclitaxel and topotecan.
Berberine treatment increased the expression of apoptotic cell death proteins, promotes cell cycle arrest, and induces cell death in human cancer cell lines. For instance, in human prostate epithelial cells (PWR-1E), berberineincreased expression of BCL2-associated X protein (Bax) was observed after berberine treatment, inducing cell death and demonstrating pro-apoptotic properties [29]. Similar effects of berberine were observed in prostate carcinoma cells (DU145, PC-3, and LNCaP) [21,30]. Berberine also increased levels of Bax in promyelocytic leukemia cells [31], gastric carcinoma cells [24], and lung cancer cells [20].
Berberine can also promote cell death by the regulation of antiapoptotic proteins. Decreased expression of antiapoptotic Bcl-2 protein was observed in human oral squamous cell carcinoma after berberine treatment [23]. Studies done in other cancer cell lines such as lung cancer, gastric cancer, and prostate cancer also showed reduced levels of Bcl-2 after berberine treatment [20,21,24,30]. Cell cycle arrest at different phases has also been observed in human cancer cell lines after treatment with berberine. In giant cell carcinoma and prostate carcinoma cells, berberine also decreased G 0 /G 1 phase-associated cyclins (D 1 , D 2 , E, Cdk2, Cdk4, and Cdk6), inducing G 0 /G 1 arrest and suppressing cell proliferation [21,25,30,32]. Further, in HepG2 cells, berberine acted on Bcell CLL/lymphoma 2 (BCL2), procaspase-3 and -9, and poly (ADP-ribose) polymerase (PARP), induced cell cycle arrest at G 2 /M phase and inhibited cell proliferation [22].
In addition to its effects on cancer cells, berberine also acts on molecular targets related to insulin resistance. In freefatty-acid-induced insulin resistance muscle cells, berberine improves insulin resistance and improves glucose uptake by decreasing PPARγ and FAT/CD36 protein expression [37]. Another study reported increased insulin receptor (InsR) mRNA and protein expression increases insulin sensitivity in liver cells after berberine treatment [38]. In Caco-2 cells, berberine inhibited alpha-glucosidase and disaccharidases activities, leading to reduced glucose levels [39]. In Hep G 2 4 The Scientific World Journal The Scientific World Journal 5 The Scientific World Journal Cell apoptosis, anticancer [21,25,30,83,90] The Scientific World Journal 7  Inhibitor of NF-κB kinase subunit alpha (IκB kinase)

Top1
Recombinant human topoisomerase I

Top1 inhibition
Anticancer [121] Transcription factor AP-1        The Scientific World Journal   The Scientific World Journal 21 cells, berberine also improved insulin signal transduction through various mechanisms such as decreased phosphorylation of PERK and eLF2-α, increased phosphorylation of IRS-1 tyrosine and AKT serine [40]. In intestinal NCI-H716 cells, berberine enhanced glucagon-like peptide 1 (GLP-1) release and promotes proglucagon mRNA expression [41]. These results demonstrate that berberine has great potential for insulin resistance treatment and should be explored further in animal and human studies.

PANTHER Analysis of Berberine Targets.
Distribution of berberine therapeutic targets in vitro varied in each of these functional classifications. Tables 3, 4, and 5 show various distributions of the most frequent occurring berberine targets in vitro based on molecular functions, biological processes, and pathways, respectively. As shown in Table 3, berberine acts on a diverse range of molecular targets in vitro. The most common classes of molecular functions include receptor binding, kinase activity, protein binding, transcription activity, DNA binding, and kinase regulator activity. Known berberine targets in vitro from the receptor binding class include epidermal growth factor receptor (EGFR), vascular endothelial growth factor A (VEGFA), interleukin-1β (IL1B) and interleukin-6 (IL6), growth/differentiation factor 15 (NAG-1), and glucagon-like peptide (GLP1).
According to the PANTHER Classification System, in vitro berberine targets correlate with a mixture of biological pathways, such as Alzheimer disease-presenilin and secretase pathways, angiogenesis, apoptosis signalling pathway, FAS signalling pathway, Huntington disease, inflammation mediated by chemokine and cytokine signalling pathways, interleukin signalling pathway, and p53 pathways ( Table 5).
The targets of berberine distributed across a large number of PANTHER classifications of molecular functions, biological processes, and pathways. This can be an advantage in terms of drug discovery using berberine. Seen that berberine targets are involved in a wide range of molecular  1  Transmembrane transporter activity  2  Transcription factor  2  Transcription factor activity  9  Transmembrane receptor protein kinase activity  3  Transmembrane receptor protein tyrosine kinase  activity  3 Tumor necrosis factor family member 1 Voltage-gated potassium channel activity 1 activities, in turn, can alter many pathological states of the body. Thus, berberine can be explored for the treatment 22 The Scientific World Journal

Data from In Vivo Studies with a Focus on Diabetes
Mellitus. In China, Huang Lian (Rhizoma coptidis) has been used to treat diabetes for more than 1,400 years [16]. Berberine is one of the main active alkaloids present in Rhizoma Coptidis and has shown to have good hypoglycaemic effects in vitro [37][38][39]42]. Further, the chemical structure of berberine is different from the commonly used other hypoglycaemic agents such as sulphonylureas, biguanides, thiazolidinediones, or acarbose [14]. Thus, it is meaningful to investigate the efficacy and safety of berberine treatments for diabetes mellitus to confirm the possibility of berberine serving as a new class of antidiabetic medications. Extensive research has been done to investigate the hypoglycaemic effects of berberine in animal models. This section will highlight the effects of berberine in diabetic animal studies, focusing on different mechanisms of actions of berberine. Hyperglycemia is a hallmark metabolic abnormality associated with metabolic diseases such as type 2 diabetes. Berberine has shown to significantly decrease fasting blood glucose levels in diabetic rats (diet or drug induced), this has been observed in a number of studies [43][44][45][46]. Berberine can reduce fasting blood glucose level via different mechanisms. For example, Liu et al. [43] reported that berberine reduced fasting blood glucose (FBG) levels by inhibiting intestinal disaccharidases in a concentration-dependent manner. Xia et al. [46] reported berberine reduced fasting glucose level via the inhibition of gluconeogenesis, via decreased PEPCK and G6Pase genes in the liver, reduced hepatic steatosis, and inhibition of FAS expression.
Current diabetes therapies do not address the key driver of this condition, β-cell dysfunction [47,48], and do not alter the progressive nature of insulin secretory deficit [49]. Berberine increased pancreatic β-cell numbers and β-cell mass in streptozotocin-induced diabetic rats [41,50]. It also reversed pathological changes of pancreatic β-cells in diabetic rats induced by streptozotocin and diet [51]. Further, The Scientific World Journal in berberine treated diabetic rats, the pancreatic and plasma insulin levels increased after glucose load, reducing blood glucose levels [41,50]. These observations are significant as berberine may be explored further as an additional therapy to existing antidiabetic drugs to effectively preserve β-cell functions, reverse β-cell damage, and promote insulin secretion in diabetes patients.
Further to β-cell dysfunction and insulin secretory deficit in diabetes, defects in insulin receptor (InsR) expression or function can cause insulin resistance and diabetes mellitus [52]. Thus, regulation of InsR expression may improve insulin resistance in diabetes mellitus. Berberine increases InsR mRNA and protein expression in human liver cells and in animal model in a dose-and time-dependent manner [38]. Berberine upregulates InsR and leads to enhanced insulin signalling pathway, confirming berberine as an insulin sensitiser.
Glucagon-like peptide 1 (GLP-1) is an intestinal peptide hormone released in response to food ingestion [53]. GLP-1 enhances meal-related insulin secretion and promotes glucose tolerance. In streptozotocin-induced rats, berberine enhanced GLP-1 release and promotes proglucagon mRNA expression, increased beta cell mass and pancreas insulin levels after glucose load [41]. This observation was in line with the groups, previous experiments in vitro. Lu et al. [50] also reported that berberine increased proglucagon mRNA expression and plasma insulin levels in streptozotocininduced diabetic rats. The glucagon gene encodes GLP-1 and the increased expression of proglucagon mRNA assists in controlling the blood glucose homeostasis.
Berberine also reduced body weight and caused a significant improvement in glucose tolerance without altering food intake in db/db mice [54]. Oral glucose tolerance improvement in diabetic rats after berberine treatment has also been observed in other studies [55,56].
Long-term hyperglycaemia can lead to increased risk of cardiovascular complications. In hyperglycemia and hypercholesterolemia rats with injured cardiac functions, berberine (15, 30 mg/kg/day, i.g for 6 weeks) increased cardiac output, left ventricular systolic pressure, and +dp/dt max by 64, 16, and 79%, but decreased left ventricular end diastolic pressure and −d p/dt max by 121 and 61% in the rats receiving HSFD/streptozotocin, respectively, when compared with the untreated rats of hyperglycemia and hypercholesterolemia [57]. Berberine caused significant increase in cardiac fatty acid transport protein-1 (159%), fatty acid transport proteins (56%), fatty acid beta-oxidase (52%), and glucose transporter-4. These results demonstrate the cardioprotective functions of berberine in hyperglycemia/hypercholesterolemia through alleviating cardiac lipid accumulation and promoting glucose transport 4 [57]. Another study also showed improved vasorelaxation in impaired aorta in diabetic rats after berberine treatment (100 mg/kg/day, 8 weeks) [45]. Thus, in addition to its hypoglycaemic effects, berberine can also be investigated for cardiomyopathy in diabetes.
Berberine also regulates lipid metabolism which is closely related to diabetes. In rats with induced diabetic hyperlipidemia, berberine (75,150, 300 mg/kg/day for 16 weeks) effectively reduced liver weight and liver/body weight ratio, levels of total cholesterol, triglycerides, and lowdensity lipoprotein-cholesterol [58]. In rats with a high fat diet, berberine significantly reduced body weight, alleviated liver steatosis, and improved insulin resistance [59]. This observation indicates that berberine can be an effective treatment for diabetes with obesity.
Clinically, preeminent factors for monitoring glycaemia and evaluating the risks of complications of diabetes include FBG, haemoglobin A 1c (HbA 1c ) [60]. Triglyceride synthesis is closely associated with glucose metabolism so serum triglyceride levels are determined. Clinical studies often measure FBG, HbA 1c , and triglyceride levels, along with other factors to study the hypoglycaemic effects of berberine. The efficacies of berberine in type 2 diabetes patients have been reported. Through literature search, key clinical studies on berberine effects on type 2 diabetes patients are summarised.
Zhang et al. [61] conducted a randomized, double-blind, placebo-controlled multicenter trial (n = 116). The authors found that when berberine (1.0 g daily) was administered for 3 months in type 2 diabetes patients with dyslipidemia, the fasting and postload plasma glucose levels decreased from 7.0 ± 0.8 to 5.6 ± 0.9 and from 12.0 ± 2.7 to 8.9 ± 2.8 mM/L, HbA 1c from 7.5 ± 1.0% to 6.6 ± 0.7%. Further, in the treatment group, triglyceride levels were reduced from 2.51 ± 2.04 to 1.61 ± 1.0 mM/L, total cholesterol from 5.31 ± 0.98 to 4.35 ± 0.96 mM/L, and LDL-cholesterol from 3.23 ± 0.81 to 2.55 ± 0.77 mM/L. Results from the treatment group was significant compared to the control group. In the treatment group, patient's body weight was also significantly reduced. Mild-to-moderate constipation was reported in 5 patients from the treatment group and 1 patient from the control group; however, this finding was not statistically significant. No other adverse events were reported. At 3 months, berberine was found to be effective in lowering blood glucose, lipids, body weight, and blood pressure with a good safety profile.
Yin et al. reported a 3-month study comparing berberine to antidiabetic drug metformin (0.5 g t.i.d) [14]. In this study, berberine exhibited identical effect as metformin in the regulation of glucose metabolism, significant decreases in HbA 1c (by 2%, P < 0.01), FBG (by 3.8 mmol/L; P < 0.01), and postprandial blood glucose (PBG) (by 8.8 mmol/L; P < 0.01). Further, the regulation of lipid metabolism was The Scientific World Journal 25 better in the berberine group than the metformin group. Triglycerides and total cholesterol levels were significantly lower than in the metformin group (P < 0.05). At the same time, the same group of researchers used berberine as a combination therapy to evaluate its additive or synergistic effects on the commonly used hypoglycemic agents, such as sulphonylureas, biguanides, thiazolidinediones, and acarbose. Patients were given 500 mg berberine three times daily for 3 months in addition to their previous treatment. At week 5, berberine significantly (P < 0.01) reduced HbA 1c (from 8.1% to 7.3%), FBG, PBG, and fasting insulin levels. Blood lipids including triglyceride, total cholesterol, and LDL-C decreased significantly lowered compared to baseline. In both studies, incidences of gastrointestinal adverse events were observed, including diarrhea, constipation, flatulence, and abdominal pain. Interestingly, patients did not suffer from severe gastrointestinal adverse events when berberine was used alone and in combination therapy; adverse effects disappeared after berberine dosage was reduced. No pronounced elevation in liver enzymes or creatinine was observed, suggesting that berberine did not cause damage to the liver or kidneys.
Another clinical study [62] randomly divided 97 type 2 diabetes mellitus patients into berberine treatment (1 g/day) for 2 months, using metformin therapy (1.5 g/day) and rosiglitazone group (4 mg/b.i.d) as reference groups. Blood samples were taking before and after treatments to measure FBG, HbA 1c , triglyceride, and serum insulin levels. Compared to values prior to treatment, berberine significantly lowered FBG by 25.9% (P < 0.001), HbA 1c by 18.1% (P < 0.00), and triglycerides by 17.6% (P < 0.01). The hypoglycaemic effects of berberine were comparable to metformin and rosiglitazone. Serum insulin level was declined significantly (P < 0.01) by 28.2%; this indicates increased insulin sensitivity in peripheral tissues by berberine treatment. Peripheral blood lymphocytes from berberine treated patients were isolated to examine the InsR expression. The surface expression of InsR significantly elevated by 3.6-fold after berberine treatment.
Metformin and rosiglitazone are not recommended for use in diabetic patients with liver function damage [54,63]. So the effect of berberine was tested in hyperglycaemic patients with hepatitis. Hepatitis B and C patients with hyperglycaemia received berberine at 1 g/day for 2 months. In both diabetic hepatitis B and C patients, berberine significantly reduced FBG and triglyceride levels. Berberine treatment also reduced the elevated alanine transaminase and aspartate aminotransferase levels in these patients. Overall, berberine is safe and effective in hyperglycaemic patients with liver function damage. Table 6 compares clinical studies of berberine in diabetes patients. Across the studies, berberine has shown to significantly reduce FBG, PBG, and HbA 1c levels. Berberine also demonstrated ability to reduce triglyceride and cholesterol levels. Minimal gastrointestinal side effects were shown but no liver or kidney damage was observed. These observations in diabetes patients demonstrate that berberine is a safe and effective antidiabetic agent.

Discussion
The "rule-of-five" analysis by Lipinski et al. [7] shows that poor absorption or permeation of a compound is more likely when there are more than five hydrogen-bond donors; the molecular mass is more than 500 Da; the lipophilicity is high (expressed as cLog P > 5); the sum of nitrogen and oxygen is more than 10. Specific structural and physiochemical properties, such as "rule-of-five," are required for clinical drugs to have sufficient levels of efficacy, bioavailability, and safety, which define target sites to which drug-like molecules can bind [4].
Plant compounds exhibit enormous structural diversity and only a small portion of the diversity has been explored for its pharmacological potential [64]. In recent years, herbal compounds have been source of new drugs [64]. Approximately 28% of new molecular entities (NMEs) between 1981 and 2002 were natural products or natural product derived; further to this, 20% of these NMEs were natural product mimics [65]. There are a number of successful plantderived drugs, especially in anti-cancer treatment. Medicinal herbal compounds have become an important source for the discovery of new drugs. Further, drugs derived from medicinal plants can also be used as drug leads suitable for optimization by medicinal and synthetic chemists [65].
As Chinese herbal medicine becomes increasingly popular in the west, researchers are spending more time looking into mechanisms of actions of crude extracts and herbal compounds such as berberine. In recent years, extensive research has been done to explore the effects of berberine on various cell lines in vitro. In cell-based studies, berberine has shown effects on multiple molecular targets and alters various biological pathways. Berberine associates with a range of conditions, particularly diabetes, hyperlipidemia, and cancer. Many in vitro studies showed potent anticancer properties of berberine against various cancer cells. This observation is valuable in the search for new anti-cancer therapeutics with potent anti-cancer effects but reduced side effect. So berberine may potentially be developed into an anticancer agent, like other natural compounds (taxol, camptothecin) that have been developed and used as anticancer agents.
Diabetes mellitus is a major health problem around the world and its prevalence is on the rise. Diabetes mellitus drug therapy is limited by availability of effective medications, as existing oral hypoglycaemic agents often have side effects and fails in long-term administration [14]. Berberine has shown significant results in fasting blood glucose levels reduction, increase in insulin sensitivity, and improvement in insulin resistance in vitro, in diabetic animal models and in diabetic patients. Further, berberine shows mechanism that current antidiabetic drugs do not have. For instance, berberine has shown effects on pancreatic β-cell number and mass improvement [41,50,51]. In addition, berberine has a good safety profile and does not show side effects such as hypoglycaemia, weight gain, or liver and kidney damage. Metformin and rosiglitazone are not recommended for use in diabetic patients with liver function damage [54,63]. Berberine has shown to be effective in the reduction of blood glucose level and is safe in diabetic patients with 26 The Scientific World Journal viral hepatitis [62]. Berberine can therefore be investigated as an effective diabetes therapy with patients with liver function damage. In addition to its hypoglycemic effects in diabetic patients, berberine also reduced triglyceride and cholesterol levels. Abnormalities in lipid metabolism often deteriorate diabetes and cause complications. The regulation of lipid metabolism in diabetes patients by berberine may have clinical significance in managing diabetic patients with hyperlipidemia. Although there are only a small number of clinical studies and evidence is limited, current reports still show a promising future for berberine being developed into a new antidiabetic agent. In China, berberine has been manufactured into the over-the-counter drug Huang Lian Su Pian, also known as Coptis Extract Tablets for the treatment of traveler's diarrhea [14,17]. However, in vitro and in vivo studies have shown that berberine has potent anti-cancer, antidiabetic, antilipidemic, and anti-inflammatory effects. Therefore, further clinical studies are warranted to investigate the potential of berberine in the application of cancer and diabetes treatments in the future.
Pharmacological activity of CHMs begins with the binding of the active components to their molecular targets. CHMs are considered as typical multitherapeutics that can interact simultaneously with multiple targets. The origins and the progression of diseases are multifactorial. Complex disorders such as cancer, cardiovascular disease, and depression tend to result from multiple molecular abnormalities, not from a single defect [66]. Biochemical and genetic studies revealed the molecular mechanism that underlie common illnesses [66]. Reports show that targets for neoplasm diseases, circulatory system diseases, infectious diseases, and nervous system and sense organs disorders constitute the largest number of targets [1]. Because drug targets are presented at the molecular level, increased knowledge of herbal targets can facilitate deeper understanding of complex diseases at its fundamental level. In turn, it is likely to determine the optimal molecular targets for therapeutic intervention [6].
Further to assisting the molecular dissection of the mechanism of action of CHMs, knowledge on herbal targets makes it possible to use disease specific targets and design more desirable herbal drugs/formulas with increased specificity and efficacy. Target-oriented synthesis in drug discovery involves in preselected protein targets [67]. Binding of drugs to preselected protein target/s is dependent on which biological pathway the drug is aimed to modulate the target or the diseased pathway(s) [67]. Target and disease specific drug design results in improved efficacy and reduced side effects, especially in high impact diseases that require more effective and more treatment options. However, due to the fact that diseases often involve in multiple molecular abnormalities, diversity-oriented syntheses are used in efforts to identify simultaneously therapeutic protein targets and their small-molecule regulators [67]. Target-oriented drug design allows more focused drug design, which in turn costs less time and money for pharmaceutical companies.
Protein structure of well-validated old and new targets should be able to guide the chemical effort directed at new drugs [68]. Study of various aspects of known targets including molecular mechanism of their binding agents and related adverse effects is useful for finding clues to new target identification [9]. Based on the knowledge of molecular targets and molecular understanding of disease state and using this knowledge will allow some direction in identifying potential targets. Potential herbal targets may come from the same class as confirmed therapeutic targets and have similar physiological functions, or maybe a structure along a biological pathway. Additionally, with increased number of potential targets from ∼500 to >5,000, the nature of pharmaceutical research has changed. This increase in numbers has given researchers more opportunities to discover and design new and improved drugs.
Target selection may be one of the most important determinants of attrition and the overall R&D productivity. There are few ways to overcome this challenge and improve the target selection process, in turn, improving R&D productivity. First of all, researchers can discover new target classes. Targets of herbal medicine are becoming a popular resource to find new target classes. In addition, increased understanding of genetic variations/polymorphisms of drug targets or drug metabolising enzymes can assist in target selection and drug metabolism. Further, the use of new technology can help to speed up the early exploratory discovery phase of drug discovery.
In summary, updated knowledge of herbal targets is valuable contribution to complex disease understanding and clinical responses. Further, drug discovery and development from herbal medicines can be supported by new target discovery and target-focused drug design. This will speed up the exploratory phase of drug R&D and benefit the pharmaceutical industry in terms of cost and time.