The neurotoxic effect of gold sodium thiomalate on the peripheral nerves of the rat. Insights into the antiinflammatory actions of gold therapy

Gut microbiome: An intermediary to neurotoxicity

There is growing recognition that the gut microbiome is an important regulator for neurological functions. This review provides a summary on the role of gut microbiota in various neurological disorders including neurotoxicity induced by environmental stressors such as drugs, environmental contaminants, and dietary factors. We propose that the gut microbiome remotely senses and regulates CNS signaling through the following mechanisms: 1) intestinal bacteria-mediated biotransformation of neurotoxicants that alters the neuro-reactivity of the parent compounds; 2) altered production of neuro-reactive microbial metabolites following exposure to certain environmental stressors; 3) bi-directional communication within the gut-brain axis to alter the intestinal barrier integrity; and 4) regulation of mucosal immune function. Distinct microbial metabolites may enter systemic circulation and epigenetically reprogram the expression of host genes in the CNS, regulating neuroinflammation, cell survival, or cell death. We will also review the current tools for the study of the gut-brain axis and provide some suggestions to move this field forward in the future.

Neurogenic Aspects of Inflammation

The relationship between the inflammatory process and the nervous system is twofold. The nervous system is activated by inflammation which causes inflammatory pain and impaired motor function. Conversely, the nervous system acts back on the peripheral process. This is achieved by output systems at different levels, including primary afferent fibers (neurogenic inflammation), spinal cord (reflexes), and the brain (eg, neuroendocrine functions). This article first addresses the activation of the nociceptive system by inflammation; the second part describes the effects of the nervous system on inflamed tissue.

Pain in childhood rheumatic arthritis

Pain is a major symptom in chronic inflammatory arthropathies such as rheumatoid arthritis and affects the health status of arthritis patients negatively. There has been much debate about the role of pain in juvenile chronic arthritis and this review deals with the controversies about this subject. Pain in children is best understood as a multifactorial concept in which pain is the result of somatosensory, behavioural and environmental factors. The role of the different factors contributing to pain will be assessed with special reference to mechanisms relevant to children with chronic pain, the various instruments to measure pain, such as visual analogue scales and algometry, and the treatment of chronic pain in juvenile chronic arthritis. For a true understanding of chronic pain in children, these multidimensional assessments should be integrated into a biobehavioral model, by means of which a better understanding should lead to new therapeutic interventions for one of the most common symptoms of rheumatic diseases in childhood: pain.

The effect of gold salts on substance P levels in rheumatoid arthritis

The effect of gold salt therapy on substance P immunoreactivity levels in plasma and synovial fluid was studied in 42 patients with rheumatoid arthritis. Decreased levels of synovial fluid substance P, although not statistically significant, were found in rheumatoid patients who were currently receiving gold therapy when compared to either those patients previously treated or to those who never received this therapy. In addition, we found that patients who received more than 1000 mg of gold salts had significantly lower levels of substance P in synovial fluid than those treated with lower doses. Our results, therefore, seem to support the hypothesis that gold salts appear to be slow-acting neurotoxic drugs that significantly decrease the intrasynovial concentrations of substance P, a well-known inflammatory neuropeptide, in arthritis patients.

Gold ion induces contraction in frog skeletal muscle fibers

In Ringer solution, gold ions (Au3+) at concentrations more than 50 microM produced a phasic and subsequent tonic contraction spontaneously in single toe muscle fiber of frog. When 1.8 mM Ca2+ in Ringer solution was replaced by 3 mM Mg2+, tonic contraction was no longer provoked in response to Au3+. Only phasic contraction was potentiated by 10 mM perchlorate (an L-type Ca2+ channel activator) irrespective of external Ca2+, and both phasic and tonic contractions were blocked by 10 microM nifedipine (an L-type Ca2+ channel blocker). Upon application of 5 mM dithiothreitol to the contracting fiber, the Au(3+)-induced tension disappeared rapidly. The fiber pretreated with 0.05% H2O2 for 10 min did not respond to Au3+ with visible contraction. Treatment of H2O2-paralyzed fibers with dithiothreitol (to reduce oxidized sulfhydryl groups) fully restored the Au(3+)-induced contraction. These results suggest that the phasic contraction induced by Au3+ probably is mediated through sulfhydryl groups in the L-type Ca2+ channel (dihydropyridine receptor) on the transverse tubular membrane. Sustained contraction was produced by Ca2+ application to Au(3+)-treated fibers in Mg(2+)-Ringer solution, and Au3+ caused membrane depolarization in a dose-dependent manner. These effects of Au3+ may explain tonic contraction development.

Autometallographic detection of gold in dorsal root ganglia of rats treated with sodium aurothiomalate

Ultraviolet light autometallography, a very sensitive method for gold detection, was applied to sections of dorsal root ganglia from adult male Wistar rats treated with intraperitoneal injections of sodium aurothiomalate. Silver-amplified traces of gold were detected within the cytoplasm of ganglion cells, satellite cells, Schwann cells, macrophages, endothelial cells, and fibroblasts throughout the ganglia. Gold was never detected in axons nor myelin sheaths. In the electron microscope, gold deposits were restricted to the lysosomes irrespective of cell type or dosage.

The effect of gold, an antirheumatic therapy, on substance P levels in rat peripheral nerve

Intramuscular injections of gold sodium thiomalate in the rat produce a significant depletion of the proinflammatory neuropeptide substance P (SP) from the sciatic nerve. The greatest reduction in SP content occurred during the first two months of treatment. The level of SP in the nerve, however, remained low, throughout an eight month administration of gold. These results, coupled with previous findings that gold produces a selective decrease in the number of unmyelinated axons in peripheral nerve, are consistent with the hypothesis that the anti-inflammatory action of gold involves a neurotoxic effect on peptidergic afferents.

The sensory-efferent function of capsaicin-sensitive sensory neurons

Capsaicin-sensitive sensory neurons convey to the central nervous system signals (chemical and physical) arising from viscera and the skin which activate a variety of visceromotor and neuroendocrine reflexes integrated at various levels (intramurally in peripheral organs, at level of prevertebral ganglia, spinal and supraspinal level). Much evidence is now available that peripheral terminals of certain sensory neurons, widely distributed in skin and viscera have the ability to release, upon adequate stimulation, their transmitter content. In addition to the well-known "axon reflex" arrangement, the capsaicin-sensitive sensory neurons have the ability to release the stored transmitter also from the same terminal which is excited by the environmental stimulus. The efferent function of these sensory neurons is realized through the direct and indirect (i.e. mediated by activation of other cells) effects of released mediators. The action of released transmitters on postjunctional elements covers a wide range of effects which may have a physiological or pathological relevance. Development of drugs capable of controlling the sensory-efferent functions of the capsaicin-sensitive sensory neurons represent a new and very promising area of research for pharmacological treatment of various human diseases.

Mechanisms of persistent synovitis

Rheumatoid arthritis is characterised by persistent and symmetrical synovitis. In this article we propose two linked hypotheses to explain these observations. A mechanism to explain symmetry of synovitis is described whereby fine afferent nerve fibres from joints become bilaterally sensitized to movement with resultant release of neuropeptides promoting an inflammatory response. Clinical and experimental evidence is reviewed and shows that movement and resulting hypoxic reperfusion injury leads to a persistent synovitis.