Herbal Medicine: Back to the Future

Allicin and carvacrol have been appreciated as broad-spectrum antimicrobial agents since the early 20th century and used in both Ayurvedic and traditional Chinese medicines for at least five thousand years. Although research since the 1980s identified several important mechanisms of action for allicin and carvacrol, neither has become part of a classical pharmaceutical regimen. Allicin and carvacrol, like other natural phytochemicals, have been hard to purify and stabilize, which has been a major barrier in their entry into a drug discovery process. During the past two decades, two distinct strategies have changed this position. Bioengineering has allowed allicin and carvacrol to be bound to nanoparticles and immobilized onto coated surfaces or into gels; all these methods maximize the retention of activity coupled with a more targeted release. The fields of synthetic and computational chemistry have long been used to create semi-synthetic and synthetic variants of natural molecules or predict binding strengths of molecules that have improved activity and or bioavailability when compared with the parent compounds. Stabilization using one, or both, of these strategies, has been successful for both allicin (garlic) and carvacrol (oregano). This chapter will review the antimicrobial spectrum of these agents and document the methods that have currently been used to stabilize or generate semi-synthetic forms of each of them. Finally, potential and currently available delivery systems will be explored.

The use and search for new medicines and dietary supplements derived from plants have enhanced in the modern era. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. Polyphenols are natural compounds characterized by a high structural variety, and their existence in plants makes them essential components. Increasingly, resistant bacteria require the continuous need for new and effective antibiotics. This class of natural products is becoming the target of anti-infective research, and many groups have identified that phenolic compounds are possessing broad-spectrum antibacterial and antiviral activity. Owing to interest in their biological activities, both the chemical structure of the phenolic moiety and any attached chemical groups define whether the polyphenol is bioactive or not. Compared to other phenolics, flavonoids class have been abundantly used in anti-infective research.

This chapter summarizes the application of polyphenol tested by various groups against infectious diseases caused by bacteria and viruses as pathogens. The reported MIC values are presented in a concise table, which is conflicting among different groups, possibly due to assay parameters and strain variation. However, it is shown that phenolic compounds have great potentials, which requires future research for the development of novel antimicrobial or antiviral agents or aid as a synergistic agent in combination with conventional anti-infective drugs.

The pandemic of COVID-19 is a grim reminder of the fact that viruses can be very contagious and that devising a vaccine and treatments against a viral disease is difficult and time-consuming. Our ancestors grappled with this problem for some infectious diseases until the late 19th century—and for others into the late 20th century. The chief weapons against infectious diseases were soap, disinfectants, isolation and quarantine, destruction of tainted items, and application of botanicals for symptoms of the viral diseases. This chapter describes Russians’ multi-millennia experiences in treating infectious diseases with botanicals—from their earliest recorded history down to the present. The chapter is based on Russian-language sources—for the early period on information from chronicles and herbals recorded by Russian medical historians and for the modern period based on my personal research into pharmaceutical books and journal articles, interviews, and case records of practicing phytotherapists and healers.

The 21st century is witnessing a war between mankind and microorganisms. The worldwide outbreak of infectious diseases is responsible for morbidity and mortality. The pharmaceutical industry has limited drugs in the pipeline against infectious diseases. Resistance of microorganisms against already available drugs is another concern. An initiative from researchers to search for new ways to prevent or treat infectious diseases is necessary. Many herbal drugs are known to be effective against pathogenic organisms from ancient times. Repurposing of herbal medicines for infectious diseases is a prodigious initiative. Azadirachta indica, commonly known as neem, is known to be effective against infectious diseases from ancient times. It is a member of the Meliaceae family. Leaves, seeds, fruits, and roots of this plant are reported to be effective according to Chinese, Ayurvedic, and Unani medicine. The plant has antiviral, antibacterial, and antifungal properties. The principal component of neem is azadirachtin. Other constituents, namely nimbolinin, nimbin, nimbidin, nimbidol, are also known to be having medicinal properties. Antibacterial and antifungal properties can be attributed to azadirachtin, quercetin, ß-sitosterol, gedunin, and polyphenolic flavonoids. Many pharmacological studies report antimicrobial efficacy of Azadirachta indica. The present chapter will explain the link between phytochemical constituents of neem to antimicrobial activity along with possible underlying mechanisms and pathways. Clinical studies on neem are also discussed in great detail to highlight the emergence of this traditional medicine into modern medicine in the battle against infectious diseases.

Background: Since ancient times, herbal medicine has been widely used worldwide. The advancement of pharmaceutical technology and pharmacotherapy has allowed the great expansion in the development of novel drug delivery systems.

Purpose: The use of these novel delivery systems has remarkable advantages over conventional ones including: improved drug solubility, bioavailability, biological effect, and stability, in addition to improved toxicological profile and decreased side effects. Most natural products suffer from low solubility, low bioavailability, instability, difficult administration, and unpleasant odor and taste leading to low compliance, which limits its use.

Methods: The exploration of novel drug carriers to incorporate plant actives and extracts can improve their use and administration producing a revolution in the pharmaceutical and cosmeceutical fields for the prevention as well as treatment of several diseases including infectious diseases. Different types of nanometric and micrometric delivery systems can be used; these comprise lipid-based, polymer-based, polysaccharide-based, surfactant-based, and cholesterol-based systems and nanoemulsions in addition to hybrid nanoparticles.

Conclusion: The present article focuses on the role of the novel carriers in the development and revival of herbal medicine. The types, composition, efficacy, and challenges of different new carriers are discussed.